Project Work

1 CHAPTER 1

CLASSIFICATION OF GANTRY CRANES This section addresses the types of overhead cranes used in nuclear power plants, their applications, and the variations in their usage and demand requirements.

1.1. Principal Crane Service Types 1.1.1. Type I Crane A Type I crane is one that is used to handle a critical load. It is designed and constructed so that it remains in place and supports the critical load during and after a seismic occurrence, but it does not have to be operational after this occurrence. “In place” means remaining on the runway and retaining all components on the crane. Single-failure-proof features are included so that failure of a single component does not result in the loss of capability to stop and hold the critical load. The containment building polar crane is typically a Type I crane. 1.1.2.Type II Crane A Type II crane is not used to handle a critical load, but it is designed and constructed so that it remains in place with or without a load during a seismic occurrence. However, the crane need not support the load and need not be operational during and after such an occurrence. Single failure-proof features are not required. The new-fuel crane or spent-fuel cask crane is typically a Type II crane.

1.1.3. Type III Crane :

2 A Type III crane is one that is not used to handle a critical load and for which seismic considerations and single-failure-proof features are not required. A Type III crane would typically be designed in accordance with CMAA specification. 1.2. Crane Service Classifications 1.2.1. Class A (Standby and Infrequent Service) – This service class covers cranes used in installations such as power houses, public utilities, turbine rooms, nuclear reactor buildings, motor rooms, and nuclear fuel handling and transfer stations, where precise handling of valuable machinery at slow speeds with long idle periods between lifts is required. Rated loads may be handled for the initial installation of machinery and for infrequent maintenance. These types of cranes are also used in installations such as small maintenance shops, pump rooms, testing laboratories, and similar operations, where the loads are relatively light, the speeds are slow, and a low degree of control accuracy is required. The loads may vary anywhere from no load to full rated load with a frequency of a few lifts per day or month. 1.2.2.Class B (Light Service) - This classification covers cranes such as those used in repair shops, light assembly operations, service buildings, and light warehousing, where the service requirements are light and the speed is slow. Loads may vary from no load to full rated load with an average load of 50% of rated load with two to five lifts per hour, averaging 15 feet (4.6 m), not over 50% of the lifts at rated load.

1.2.3.Class C (Moderate Service) - This class covers cranes such as those used in machine shops and paper mill machine rooms, where the service requirements are medium. In this type of service the crane will handle loads that average 50% of the rated load with 5–10 lifts per hour averaging 15 feet (4.6 m), not over 50% of the lifts at rated load.

3 1.2.4.Class D (Heavy Duty) - This classification covers cranes, usually cab operated, such as those used in heavy machine shops, foundries, fabricating plants, steel warehouses, and lumber mills, and standard duty bucket and magnet operation cranes, where heavy duty production is required but with no specific cycle of operation. Loads approaching 50% of the rated load are handled constantly during the working period. High speeds are desirable for this type of service with 10–20 lifts per hour averaging 15 feet (4.6 m), not over 65% of the lifts at rated load. 1.2.5.Class E (Severe Duty Cycle Service) - This type of service requires a heavy-duty crane capable of handling the rated load continuously, at high speed, in repetition throughout a stated period per day, in a predetermined cycle of operation. Applications include magnet, bucket, magnet bucket combination cranes for scrap yards, cement mills, lumber mills, and fertilizer plants with 20 or more lifts per hour at rated load. 1.2.6. Class F (Continuous Severe Service) – Cranes in this type of service should be capable of handling loads near its rated capacity continuously under severe service conditions for its operational life. These cranes are required to have high reliability and design features that facilitate maintenance efforts. Class F cranes may be used in specialty applications that support a production facility or other specialized tasks.

1.3. Service Use Classifications In addition to the design service classes established by CMAA, the American Society of Mechanical Engineers B30 series (an American National Standard) has established a group of three service-use classifications for use in inspection of lifting equipment, as follows:

4 Normal Service – That service which involves operating at less than 85% rated load and not more that 10 lift cycles per hour, except for isolated instances Heavy Service – That service which involves operating at 85–100% of rated load or in excess of 10 lift cycles per hour as a regular specified procedure Severe Service – That service which involves normal or heavy service with abnormal operating conditions. 2.1. INTRODUCTION: For a crane to operate properly and reliably, crane components must be in proper alignment. Structural connections associated with the following components generally use bolts to accommodate field installation and shipping limitations: •

Girders and end trucks

•

Girders and end ties

•

Τ trolley frame members

These connections should utilize close-tolerance body structural bolts, in close fitting drilled or reamed holes, to fulfill the need for alignment integrity of these connections.

2.2. Frame : The frame basically consists of the two trucks and the one or two load girt. Where shipping limitations do not govern, the frame is welded into a one-piece unit of plates and structural

2 shapes. If the size of the finished trolley necessitates dismantling for shipment, the load girt are secured to the trucks with tolerance-body bolts in reamed holes. The load girt support makes up a large percentage of the overhead bridge crane live load because it contains the upper block and the running and equalizer sheaves. The trolley trucks support the load-girt reactions and, in most cases, the hoist-gear units and the drumsupporting bearings. They also contain the wheel assemblies. 2.3. Girders : Girders provide the main structural support for a crane. Girders support the trolley and the end trucks that provide crane lateral movement. There are three types of girders typically found in crane construction: single-web, box, and latticed. Single web or wide-flange beams are used for bridge girders with comparatively short spans. This girder resembles a typical I-beam except that the upper and lower flanges are considerably wider than a typical I-beam. The allowable stress for a wide-flange beam decreases as the span increases. The capability of a single web can be improved by welding flat plate across the beam span from flange to flange. This procedure will tend to stiffen the beam. Also, a capping plate can be welded to top flange to increase the useful span of the beam and its load rating. The box girder is the most widely used girder for overhead traveling cranes. This girder is just an adaptation of the single-web with welded plate. The key difference is that there are quite a few plates welded in the web portion of the beam.

3 These welded plates are then covered by a full-length cover plate along the beam. The weld plate and the cover plate give the girder excellent rigidity. The latticed girder is typically used when there is a long span on outdoor cranes. This girder has several design factors that make it especially useful for particular applications. Making the beam a lattice reduces the dead load of the crane and lowers the surface area (wind impact). This girder design allows the weight of the girder to be more evenly distributed over the entire crane. The primary drawback to latticed girders is that they are labor intensive to manufacture.

Solid model of girder of 30T EOT crane

2

2.4. Girder End Connections (End Tie) : End connectors or end ties are typically provided between crane girders to provide a more rigid and stable crane . The girder end connections also assist in providing frame squareness and assist with load transfer to the girders. Girder loads enter the truck structure as direct bearing loads through the end diaphragm plates and shelf angles. An additional means of holding the girder square with the truck is provided by the large gusset plate welded to the bottom of the truck and attached to the girders with tolerance body bolts in reamed holes. A substantial end tie must be provided to give horizontal fixed-end rigidity to the girders. This end tie may be a separate member or may be part of the truck itself. 2.5. Trucks : Crane trucks (often referred to as end trucks) are assemblies that contain wheels, bearings, axles, Structural members, and other components that support crane locomotion. There are typically Two sets of trucks on a crane: bridge trucks and trolley trucks. 2.5.1 Bridge Trucks : The bridge trucks are designed to move a crane along the runway. The crane runway is a Horizontal beam that is attached to building columns or walls and supports a runway rail on Which the crane travels. The design of structural members, bearings, and axles of the bridge trucks is primarily Determined by the maximum wheel load. This load can be computed by adding the fixed(Dead) load and the rated load.

2.6 Wheel Assemblies :

3 Wheels are designed to carry the maximum wheel load under normal conditions without excessive wear. Larger wheels on the same rail have a greater load carrying ability than smaller wheels. The constants used for various classes of service have been established to give reasonable wheel life for each class. Rolled steel or forged steel is recommended for crane wheels. These materials have good strength and good ductility to withstand the concentrated loading that occurs at the line contact between the railhead and the tread of the wheel. Untreated wheels having tread hardness of approximately 262 BHN are recommended for service classes A, B, and C. Rim-toughened wheels having a tread hardness of approximately 600 BHN can be used under special circumstances of severe service, but such extreme hardness results in a loss of tread ductility and can increase rail wear.

Bridge wheels may be designed with tapered or straight treads. Tapered tread of 3°40′ is recommended for bridge wheels. Tapered tread wheels have the advantage of keeping a crane square with the runway. Should one end of a crane with tapered tread wheels tend to skew or advance ahead of the opposite end, the leading wheel would tend to rotate on its large diameter. This action causes the leading wheel to slow down and the trailing wheel to speed up, bringing the crane square with the runway. The large diameter of the taper must be toward the center of the span. In order to minimize rail wear, the driver and the idler wheels are usually tapered.

4

Girders with wheel assembly 2.7. Crane Stops : Stops are devices that are attached to the crane runway and bridge rails to physically limit the bridge and trolley travel. Early design stops were designed to come in contact with the actual drive wheel and stop bridge or trolley motion. This method is not recommended due to the possibility of bridge or trolley impacting these stops and causing the bridge or trolley to derail. Cranes are typically supplied with bumpers or buffers that are designed to impact a stop, absorb the force of the impact, and limit the bridge or trolley travel. Wheel stops are located at the allowable bridge or trolley travel limits. These devices are intended to prevent the movement of the bridge or trolley beyond a designated place of travel. In most cases, the bridge stops are designed to contact a device that is mounted on the bridge truck. The stop is typically welded to the support girder. Bridge stops are typically designed to withstand the force equivalent to about 40% of rated bridge speed.

5 These values are allowable because typically at or near the end of the operating limits of the bridge or trolley, a crane is operated at slow speeds. Some applications require a crane to operate at normal operating speeds at or near its operating limits of its runway. Under these conditions, it may be advisable to design a stop that is capable of withstanding the impact of the crane at full speed. 2.8. Sheaves : Sheave grooves should be smooth and free from surface defects that could cause wire rope damage. The cross-sectional radius at the bottom of the groove should form a close-fitting saddle for the size of wire rope used, and the sides of the groove should taper outward to facilitate entrance of the rope into the groove. Flange corners should be rounded, and the rims run true about the axis of rotation. 2.9. Hooks : Hooks should meet the manufacturer’s recommendations, and should not be overloaded. Swiveling type hooks should be able to rotate freely, Hooks should be equipped with latches unless the application makes the use of a latch impractical. When required, a latch should be provided to bridge the throat opening of the hook so that slings, chains, and similar devices are retained under slack conditions All hooks are made from ductile material so that the hook gives visible evidence of overloading by slowly opening at the throat. Hooks with deformation or cracks should never be used. When used, crane hooks should have visual inspections daily and monthly inspections with signed reports. Hooks with cracks or that have more than 15% in excess of normal throat opening or more than a 10° twist from the plane of the unbent hook should be replaced.

6

Crane hook 2.10. Auxiliary Hoist : The usefulness of many cranes is increased by providing the trolley with one or more auxiliary hoists in addition to the main hoist. There are occasions when loads of considerably less weight than the rated load of the crane must be lifted frequently. Because the load rating of an auxiliary hoist is normally about 10–25% of the main hoist, hoisting speeds can be much faster and stilluse an equal or smaller auxiliary hoist motor. Because the difference between main and auxiliary hoists is a quantitative one, the previous discussions regarding load blocks, wire rope, drums, and gear units apply equally well to auxiliary hoists. In general, an auxiliary hoist may have a more severe service class rating than the main hoist.

2.11. Hoist Wire Rope :

7 Replacement rope should be the same size, grade, and construction as the original rope furnished by the crane manufacturer unless otherwise recommended by a wire rope or crane manufacturer due to actual working condition requirement. Wire rope used for overhead and gantry cranes is usually of the six strand, 36 wires per strand, classification. The six strand, 19 wire classification can be used where abrasive problems are severe. Because it has a greater number of smaller diameter wires, the six strand, 36wire class of rope is a more flexible construction so it is more often considered for general crane service. Although crane rope is classified as 6 x 36 construction, the actual number of wires per strandcan vary from 27 to 49, depending on the nominal diameter of the rope, the manufacturer, and the grade of steel used. The greater the number of wires per strand, the greater the flexibility of the rope, but with reduced resistance to abrasion. The number of wires per strand does not affect the nominal breaking strength. Wire crane ropes can be obtained with either fiber or wire core. Fiber core has been the usual choice in the past because of its alleged lubricant-holding property. With the increased trend toward higher strength ropes, however, wire core is becoming much more common because it provides greater support to the six outer strands. 2.11.1. Wire Rope Splicing and Socketing : Eye splices in wire rope should be made as recommended. Rope thimbles should be used in the eye. Rope clips attached with U-bolts should have the U-bolts on the dead or short end of the rope. Spacing and number of all types of clips should be in accordance with the clip manufacturer’s recommendations. Nuts on clip bolts should be tightened evenly to the manufacturer’s recommended torque.

8 After the initial load is applied to newly installed rope and the rope is under tension, the nuts of the clip bolt should be tightened again to the required torque in order to compensate for any decrease in rope diameter caused by the load. Swaged or compressed fittings should be applied as recommended by the rope or crane manufacturer. Socketing should be done in the manner specified by the manufacturer of the assembly or the rope manufacturer. Rope should be secured to the drum.

2.11.2. Wire Rope Reeving : As can be seen from the reeving diagrams, a crane uses the principal of the block and tackle in that the drum pull is multiplied by the reeving reduction to obtain the pull at the hook and is divided by the reeving reduction to obtain the hook speed. Doubling the number of parts of rope occurs in the two lead lines from the drum during hoisting and in the two lines from the equalizer sheaves when lowering. The actual load in one of these lines can be found by use of the lead line factor, a function of the reeving efficiency, taken from and multiplied by the sum of the rated load and the weight of the block.

9 This value is always somewhat greater than that obtained by dividing the sum of the rated load and the weight of the block by the number of parts of reeving. Again, referring to the various reeving diagrams, the two lines attached to the drum are called lead lines, and the two lines going to the equalizer sheaves are called tow lines. Each lead and tow line has an additional load beyond that supported by the other lines, due to the friction of the sheaves. The actual maximum load in the various parts of rope occurs in the two lead lines during hoisting and in the two tow lines when lowering. The lead angle, or fleet angle, of the ropes relative to the drum and to the various sheaves does not affect the strength of the reeiving system, but it should be considered in relation to wear of the rope and resultant useful life. In general, satisfactory rope life can be obtained in Class A, B, or C service if the lead angle does not exceed a ratio of 1:12 or 4.75°. For Class E service, the lead angle should probably not exceed approximately 3° for good rope life, and Class D service should be somewhere between the two. The lead angle between the ropes and the drum approaches its maximum value only near the upper and lower extremes of hook travel. The lead angle passes through zero degrees and reverses direction somewhere between the extremes. The lead angle between the ropes and the upper sheaves reaches its maximum value at the upper extreme of hook travel and is essentially zero degrees at the lower extreme. 2.12. Bumpers (Buffers) Bridge bumpers, also known as buffers, are used to protect the crane from damage due to hitting the stops at the end of the runway or due to contacting other cranes on the same runway. Their secondary function is to minimize swinging of the load. Since the adoption of

10 the OSHA requirement for bumpers on practically all trolleys, wheel stops are seldom used. A solid stop, welded to the girder, is provided to contact a bumper mounted on the trolley Bumpers can be of the compression-coil, torsion, coned-disc or flat spring type and can be made of steel, bronze, rubber, polyurethane, or similar resilient material. Buffers can be hydraulic or

pneumatic shock absorbers. A crane is provided with bumpers or other

automatic means to provide an equivalent effect. Bumpers are not required if: The crane travels at a slow rate of speed and has a faster deceleration rate due to the use of sleeve bearings. The crane is not operated near the ends of the bridge. The crane is restricted to a limited distance by the nature of the crane operation, and there is no hazard of striking any object in this limited distance.

11 End buffer : Bumpers can be used for rated bridge speeds up to 350 feet (91 m) per minute (FPM). Above that speed, bumpers are recommended. Bumpers are designed in accordance with ASME guidance and OSHA requirements. A bumper is selected, usually from a standard table, that has a spring rate soft enough to meet the deflection requirement and strong enough to meet the energy requirement. Note that the weight of the load is not considered in determining the bumper force. The load is free to swing. Therefore, the energy of the moving load is absorbed over a longer and different time period than the energy of the moving crane. The forces are relatively small because of the longer time and greater stopping distance. The maximum force occurs later and usually acts to retard the bounce-back of the crane. Bumpers are mounted so that there is no direct shear on the bolts. Bumpers are designed and installed to minimize parts falling from the crane in case of breakage. In general, this means that bumpers should have restraining cables. In addition to the above requirements, polyurethane bumpers and hydraulic or pneumatic buffers are designed to cushion the impact at 100% of rated full load speed, but at higher decelerating values. The comments regarding bridge bumpers also apply to trolley bumpers except that OSHA specifies different criteria for trolley bumper design. A trolley is provided with bumpers or other automatic means to achieve an equivalent effect unless the trolley: •

Travels at a slow rate of speed

•

Is not operated near the ends of the bridge

1 •

Is restricted to a limited distance and there is no hazard of striking any object in this limited distance

•

Is used in similar operating conditions

Trolley bumpers and buffers are designed in accordance with the following OSHA requirements, Section 1910.179 [3]: The bumpers shall be capable of stopping the trolley (not including the lifted load) at an average rate of deceleration not to exceed traveling in either direction at one-third of the rated speed. When more than one trolley is operated on the same bridge, each shall be equipped with bumpers or equivalent on their adjacent ends. 2.13. Footwalks and Handrailing : A foot walk with handrail and toe boards is required along the drive girder on all cabcontrolled Cranes. Such a foot walk is recommended for floor-controlled cranes, per OSHA regulations. The footwalk should have a walking surface of raised-tread floor plate or other slip-resistant walking surface. Expanded metal or subway grating is sometimes used for crane footwalks. In addition to the footwalk along the drive girder, a footwalk approximately twice the length of the trolley is provided along the idler girder to give access to the opposite side of the trolley, the bridge conductors, or other equipment on the side of the crane. If the crane is not equipped with Such a walk, then an equivalent footwalk or platform should be provided on the end of the Building. Where a footwalk is provided on the driver and idler girders of a crane, a crosswalk with standard handrailing should be included across one or both end trucks. The inner edge of the footwalk must extend at least to the line of the outside edge of the lower cover plate or flange of the girder.

2 The 1978 National Electrical Code recommends that 2.5 feet (76 cm) clearance be provided between the live parts of any control panels (mounted along the footwalk) and the nearest handrail or other member. 2.14. Cabs : The general arrangement of the cab and the location of the control and protective equipment is such that all operating devices such as levers and buttons are within convenient reach of the operator when facing the area to be served by the load block or when facing the direction of travel of the cab. The arrangement of the cab should allow the operator a full view of the load block in all positions. This is an important condition, but it is recognized that there are physical arrangements that can make this impossible. When the load block is in these positions, such as behind a large fabricated member or lowered into a hatchway, the operator should be aided by other means of communication, such as a signal person, telephone, or two-way radio. The standard location of the operator’s cab is at one end of the crane bridge on the drive girder side with the operator facing the opposite end of the bridge. However, operating conditions usually determine the best location of the cab. In selecting the desired cab location, consider that the operator can best position the load when lowering when the operator has a good side view of the load. Side views are not possible with the cab on the trolley, overhanging the idler girder, or with a trailer cab traveling with the trolley. It is also not possible with a center cab for loads handled near the center of the span. With these cab locations, the operator is looking down on itsposition accurately. When a large load is being handled, the load itself will block the operator’s view of the area beneath the load. Crane cabs can be either the open type for indoor service or the enclosed type for outdoor

3 service or where indoor conditions make an enclosed cab desirable for operator comfort. Open cabs imply cabs that require no enclosure beyond that required for structural and protective purposes. The pulpit-type cab is popular because of the high angle of visibility furnished an operator when seated. A complete handrail or equivalent enclosure with protected opening for access must be supplied, as well as a ladder or other means of access to the crane footwalk. The ladder must meet OSHA requirements. An enclosed cab should be provided with shatter-resistant glass or an equivalent, similar to ANSIStandard 7.26.1 [8]. Provision should be made for cab ventilation by opening of windows or by a mechanical ventilating system. If an integral outside platform is provided, the door must be of a sliding type or open outward. In the absence of an outside platform, the door must be of the sliding type or open inward and in either case shall be self closing. The cab construction should offer protection from falling objects, if this possibility exists. The protection should be of sufficient strength to support a 50 lb per square foot (2.3 kPa) static load. All cabs must be equipped with a warning device such as a mechanical gong or electrical bell. The cab should also be equipped with a light and/or heater for operator comfort where conditions necessitate 2.15.Rails : Crane bridge runway and trolley runway rail sizes will be governed by the wheel diameter and crane design load.

2.15.1.Rail Dimension Outline :

4 The bridge rails support the trolley wheels, while the runway rails support the bridge. As stated Rails should be arranged so that joints on opposite runway girders are staggered with respect to each other and the wheelbase of the crane. Rail joints should not coincide with runway girder splices. Rails are furnished with standard drilling for commercial rail splices. Rails purchased for crane runways should be specified “for crane service” to obtain proper hardness. Rails should be held firmly in all directions. Improperly secured rails can cause rapid wheel wear and overheating of Crane drive motors. Do not paint the railhead (top of rail) because this can cause the wheels to slip, resulting in Skewing of the bridge and possible damage to the drive gearing. Paint on the railhead can also Interfere with the proper electrical grounding of the crane. Rails should be fastened securely to the runway with adjustable bolted clips. Several patented types are available or standard clips with slotted holes can be used. Floating clamps should not be used because they do not maintain proper rail alignment. Hook bolts are also not recommended because the bolts stretch and the nuts loosen under the lateral forces produced by the crane. Where used, they must be frequently inspected and adjusted to maintain rail alignment. Bridge rails are attached to the bridge girders by means of alternately spaced rail clips that are welded to the girder or attached with welded studs. The welding of clips is preferred. There should be no need for future realignment of bridge rails, which is in contrast to the occasional realignment needs of runway rails.

5

Rail design

2.15.2.Bridge Rail Attachments : On cranes over 30 tons (27 metric tons) rated load, it is recommended that the bridge rails be Supported on bars welded on top of the top cover plate and positioned above each girder Diaphragm, so that the bending stress produced in the rail by the trolley wheel loads is not transmitted into the top cover plate. 2.15.3. Rail Sweeps : Rail sweeps are provided in front of each leading wheel to brush away any objects that might fall on the runway rail. Rail sweeps are not provided in situations where such brushing would cause the object to fall to the floor and possibly injure people below the runway. 2.16. Axles : Wheel assemblies are generally supported and centered by either the fixed-type axle (pin-and keeper) or rotating-type axle. The fixed-type axle is rarely used and is now considered obsolete due to problems of properly lubricating and enclosing the gearing and due to problems in uniformly hardening the axle for use with antifriction bearings. The rotating-type axle is mounted on antifriction bearings in a fixed housing and is more commonly seen. In

2 this design, the axle is driven directly from the cross shaft through a flange coupling. The rotating-type axle can also be driven by a gear, mounted on and keyed to the axle. 2.17. Couplings : Flexible couplings of the elastomer, disc, or gear type are used for connecting the motor to the Gear drive when the two are directly coupled. A flexible coupling is used because it facilitates Motor alignment with the crane during initial installation and simplifies realignment of the motor When it is removed the specific type of flexible coupling to be used depends on the Specific service condition, such as service class, motor horsepower, and environment. Solid couplings of the flange type with halves connected by bolts in machined holes are recommended for connecting sections of the cross shaft and for connecting the cross shaft to the bridge drive and to the axles. Couplings having shrouded bolts are preferred. Coupling bolts should be in shear to minimize stretching of the bolts and loosening of the nuts. 2.18. Bearings : Antifriction bearings have replaced bronze bearings in most of the crane applications. Longer service life, reduced maintenance and inspection, less frequent lubrication, accurate and permanent alignment of vital parts, and smaller horsepower motors are some of the advantages made possible by the use of ball and roller bearings. Antifriction bearings are selected to give a minimum life expectancy based on full load rated speed as follows:

3

Coupling Anti-Friction Bearing Life : Class A

2500 hours

Class B

2500 hours

Class C

5000 hours

Class D

10000 hours

Class E

20000 hours

Class F

40000 hours

The loading on antifriction bearings varies greatly, depending on the actual load on the crane hook. For typical applications, bearing loads for life-computation purposes may be assumed

2 equal to 75% of maximum for bridge bearings and 65% of maximum for trolley and hoist bearings. The basic load rating “C” for a ball bearing is that loading the ball bearing can endure for a base of one million revolutions. For example, a bearing with a given load rating of 28,000 lb. C90 means that the bearing can endure a 28,000-lb load for 90 million revolutions. Short-term load capability for the bearing may be a multiple of 28,000 lb. Bronze sleeve bearings have a maximum allowable unit bearing pressure of 1,000 psi (6,900 kPa) of projected area. Lifetime lubricated bearings with a long life grease are normally recommended and used. Bearing enclosures are designed as far as practical to exclude dirt and minimize grease leakage. 2.19.Pillow Block Bearings : Pillow block bearings found on overhead bridge cranes are self-aligning and are equipped with either roller or ball bearings. The housings for ball bearings are one-piece cast iron constructionPillow blocks equipped with roller bearings are held in a split-type cast iron housing both types are lubricated with grease through grease fittings mounted on the housing. Ball bearings are secured to the shaft by the use of set screws through the extended inner race. The roller bearings are attached to the shaft through use of a tapered split adapter sleeve and nut. Installation of the ball type bearing involves sliding the entire pillow block assembly over the shaft.

2.20.Trolley :

3 The trolley travel is accomplished through gearing and cross shaft to a driving wheel at each sideof the trolley in a manner similar to a bridge drive. Because the gauge of a trolley is short Compared to the span of a bridge, it is not necessary that the trolley drive be symmetrically Mounted to proportion (twist) angular deflection twist of the cross shaft, as is done on a bridge.In fact, many small trolleys have the drive unit mounted outboard of one bridge rail due to space Limitations. For the same reason, the diameter of the trolley cross shaft is determined on a torqueBasis, not on the angle of twist. The slower the speeds selected that will perform the given job, the less horsepower is required. This in turn permits the use of smaller gear drives, which all tend toward a lighter-weight trolley with the subsequent savings in bridge and runway initial cost plus the operating savings due to lower power consumption for all motions of the crane.

Trolley truck CHAPTER 3

2 DESIGN MEMORANDUM OF 30/7.5 TONNES EOT CRANE

Description of the component Serial No

Parameters of the EOT crane in design synthesis

1

General classification

IS : 3177 - 1999

2

Type of EOT crane

Double-girder EOT crane

3

Type of service

Indoor

4

Runway conductors

DSL Festoon cable

5

Design ambient temperature

50o C

6

Capacity / main hoist

7

Main hoist – Rated SWC

30 ton

8

Test load -

37.5 tonnes

9

Capacity / auxiliary hoist

10

Rated SWC

7.5 tonnes

11

Test load

9.375 tonnes

12

Type of hooks Ramshorn type swiveling hook with locking

13

Main hoist

14

Auxiliary hoist

15

Number of trolleys

16

Number of hoists on trolley

17

Crane span

As per requirement

18

Carne runway length

As per requirement

device as per IS 5749 Standard type swiveling hook with locking device as per IS 3815 One(1) Two (2) 1 main 1 auxiliary hoist

Highest point of main hook from Preferably in line with top of runway rail but not 19 20

top of gantry rail Power supply

exceeding 1000mm 415 V +/- 10 % 3 phase, 4 wire, 50 Hz, +/- 5%

3 AC Totally enclosed, fan cooled, class B/F Insulation, Slipping induction motor. For creep speed – 21

Motors

planetary gear and point brake arrangement will be provided on hoisting drive to achieve 10 % speed of main speed. 110/ 240 +/- 10% 1 phase 50 hz +/- 5% AC as per

22

Control voltage manufacturer`s standard. Brakes

23

Hoist (Main/ auxiliary)

2 No’s DC electromagnetic shoe brakes

24

Bridge travel

2 No’s DC electromagnetic shoe brakes

25

Crab travel

2 No’s DC electromagnetic shoe brakes

26

Emergency brake

Parking brake opera table from operator’s cabin

27

Operating speeds

28

Main hoist

3 meters/min

29

Auxiliary hoist

6 meters/min

30

Trolley travel

10 meters/min

31

Longitudinal bridge travel

10 meters/min

Creep speeds

Required for all motions and rated for 10% of full

32

speed of all motions

33

DSL (Runway)

34

Operator`s cabin

MS angle Fixed open type of size (2.5 x 2 x 2 meters) –

35

steel fabricated open type for indoor service with Type 4 to 6 mm shatter proof glass above 1m height of cabin on 3 sides.

36

Location

On one side of the bridge 6 x 36 / 6 x 37 with factor of safety as per IS :

37

Rope

3177

4 Rope drums shall be spur / helical gear type and Rope drum 38

should be fabricated from MS as per IS : 2062 and should be stress relieved. Forged steel double flanged with minimum

39

Cross travel & long travel wheels

40

Bearings for the wheels

41

Lifting beams

42

Lubricant

grease

43

Arrangement of lubrication

Through grease nipple

44

End stops

Fabricated (4)

45

Material

MS

wheels hardness 300 – 350 BHN Anti friction bearings Fabricated from MS to IS: 2062, weight not

46 47 48 49 50 51

exceeding 25 tonnes.

Crane rails IS 3443 deflection of main girders with maximum 1 / 1000 of span load at the centre shafts and axles carbon steel runway conductors : DSL cross travel conductors flexible trailing cable power conductors minimum 6 mm² aluminum

5

CHAPTER 4

DESIGN calculations of 30/7.5 T EOT Crane Hoist motion : Auxiliary Hoist motion

Main hoist hoist

Load Q Load Q1

30 T

7.5 T

(Bottom Block) Velocity V

1T

0.2 T

(m/min)

3

6

6

Coefficient Of 1.5

1.5

975 rpm

700 rpm

Reserve (S) Speed (N)

Torque required = 975×Q+Q1×V×S×10006120×N

For main hoist

= ( 975×(30+1)×3×1.5×1000)/(6120×975) =

22.794Kg-m

For auxiliary hoist = (975×(7.5+0.2)×6×1.5×1000)/(6120×700) =

15.978 Kg-m

7

For Travel Motion : Main Hoist

Travel motion(main hoist)

cross travel

Longitudinal travel

Safe Working Load ( Q )

30 T

30 T

Weight of Trolley ( G )

8T

15 T

Rated Speed ( V )

10 m/min

10 m/min

Coefficient of Reserve ( S )

1.25

1.25

Average acceleration ( a )

7cm/sec2

8 cm/sec2

Static Resistance

8

8

Torque Factor ( T )

1.7

1.7

Motor Speed ( N )

930 rpm

930 rpm

( Wst` ` ) in Kg/t

2 Number of Motors ( n )

2

2

Torque Required = 975×Q+G×V×S6120×T×N×n×1100×a981+Wst

For cross travel = (975×(30+8)×10×1.25)/(6120×930×1.7× 2)×(((1100×7))/981+8) =

0.379 Kg-m

For Longitudinal Travel =975×30+15×10×1.256120×930×1.7×2×1100×8981+8 =0.480

Kg-m

3

For Travel Motion : Auxiliary Hoist

Travel motion

cross travel

Longitudinal travel

Safe Working Load ( Q )

7.5 T

7.5 T

Weight of Trolley ( G )

0.2 T

0.5 T

(auxiliary hoist)

10 m/min Rated Speed ( V )

10 m/min

Coefficient of Reserve ( S )

Average acceleration ( a ) Static Resistance

( Wst )

1.25

1.25

7 cm/sec2

8 cm/sec2

8

8

1.7

1.7

700 rpm

700 rpm

2

2

in Kg/t Torque Factor ( Tvf ) Motor Speed (N) Number of Motors

2

Torque Required = 975×Q+G×V×S6120×Tvf×N×n×1100×a981+Wst

For cross travel = 975×7.5+0.2×10×1.256120×700×1.7×2×1100×7981+8 =

For

Longitudinal

0.102 Kg-m

Travel

=

1.7×2)×(((1100×8))/981+8) =

0.113

Kg-m

(975×(7.5+0.2)×10×1.25)/(6120×700×

1

For Hoist Motion at Micro Speed : Hoist motion

Auxiliary Main hoist

(micro speed)

hoist

Safe Working Load Q

30 T

7.5 T

1T

0.2 T

31 T

7.7 T

0.25

0.5

Cv

0.67

0.67

Cdf

1.5

1.5

0.918

0.918

0.95

0.95

Weight of bottom block(Q1) Q+Q1 V

Overall efficiency (E) Camb

Power Required (kW)

= (M×V×Cv×Cdf)/(6.12×E×Camb)

For Main Hoist

= (31×0.25×0.67×1.5)/(6.120.918×0.95) =

For Auxiliary Hoist

1.45 kW

= (7.7×0.5×0.67×1.5)/( 6.12×0.918×0.95) = 0.724 kW

Wheel load calculations :

2 LT Wheel load (without Impact) is given by (SWL+Hoistweight / 2 X [ Span – Hook approach / span ] + (crane weight – hoist weight / 4 ) = 30+42×18-0.7518

=

20 T

LT Rail size=105Lbs/yd LT wheel diameter

= (1.5×Wheel load)/( Top width of Rail) =

(1.5×20000)/132 = 250 mm

Selected wheel diameter = 250mm

Wire rope : Selection of wire rope for MH:Load/fall = (SWL+BBWT+Rope weight)/(number of falls)×Factor of safety =

(30+1+0.20)/4×6

= 46.8 T/fall Selected rope= 26mm diameter, 6×36 construction, Fiber core, R.H lay with Ultimate Tensile Strength =320 Kg/mm2

Rope Drum and Pulleys : Main Hoist

3 Pulley diameter at root = 17×26= 442 mm Selected pulley diameter is 450 mm Selection of wire rope for AH : Load/fall

= (SWL+BBWT+Rope weight)/(number of falls)×Factor of safety =

(7.5+0.13+0.07)/4×6

= 11.5Ton/fall Selected rope= 14mm diameter, 6×36 construction, Fiber core, R.H lay with Ultimate Tensile Strength =180 Kg/mm2 Auxiliary hoist : Pulley diameter at root = 17×14=238mm Selected pulley diameter is 250mm

Ropes drum selection : Selected rope drum dia. 320 mm with LH & RH Grooves. Rope drum length= [((lift × no. of falls)/(2×3.14×pcd of rope drum)) + 3]× 2 pitch of rope + 420 =

=

2142.96 Selected drum 320 dia & 2200 mm long.

4

Sheave : Material: cast steel / forged steel / rolled steel. (D d) = 12 x d x C df x C re x C rr d- Calculated diameter of the rope , in mm. C df - Duty factor for hoisting. C re – Factor dependent for hoisting for the appropriate mechanism class as per IS. C rr – Factor dependent upon the type of receiving system. For main hoist: Diameter of sheave = 12 x 26 x 1.2 x 1 x 1.12 = 419. 328 mm For auxiliary hoist: Diameter of sheave = 12 x 14 x 1.2 x 1 x 1.12 = 225.792 mm

Bearing : Static load is the most important criteria for the design of bearing. F sb = P x C df

2 P = Maximum static load on the bearing under any load condition. C df = Duty factor. Hoist weight = 4000 kg Fsb

= 4000 x 1.4 = 5600 kg.

Permissible Stress : Fp = F ult/ (C df x C bf x C sf) Fp = permissible stress, N/mm2 F ult = ultimate tensile stress N/mm2 C df = duty factor of the mechanism C bf = basic stress factor of the loading C sf = safety factor of the material used Fp = 180/ (2.5 x 1.12 x 1.06)

(Horizontal)

= 60.64 N/ mm2. Fp = 180/ (2.5 x 1.12 x 1.25) = 51. 428 N / mm2 (Vertical)

3

Load on Girder The load is assumed to be a central load and acts uniformly at the centre of the span. Pd = Maximum vertical uniform load.

4 Md = maximum Bending moment = Pd L / 8. L = span of girder. MI = (L – C/2)2 x PI / 4L C = Wheel base of the trolley = 2meters. P I = Vertically concentrated load , PI M V = Md + Mi Md = BM max = Pd L / 8 = 30 x 10^3 x 18 / 8 = 67500 kg – meters. Mi = (L – C / 2)2 P I / 4L = (18-2/2)2 x 30 x 10^ 3 / 4 x 18 = 3333.33 kg – meters. MT = M d + M I = 70833.33 kg-meters.

5

CHAPTER 5

WEAR PARTICLE ANALYSIS 5.1. Ferrography : Ferrography is a means of microscopic examination used to analyze particles separated from fluids. A ferrographic analysis of wear particles starts with magnetic separation of machine wear debris from the lubricating or hydraulic media in which it becomes suspended. It was developed in 1971, the success of this technique in monitoring the condition of military aircraft engines lead to further developments for practical uses. Today in many industries, ferrography is valuable in maintenance of machinery. The Wear particle Analysis is a Pro-active Predictive maintenance system. Wear Metals Particles are extracted from an oil sample, then magnified up to 1000X for wear identification.

Many industrial plants feature varieties of gearboxes and hydraulic systems that are amenable to lube analysis monitoring. Typical basic packages, however, don't always provide a window to fully assess machinery condition. One reason is because medium to slow speed rotating units often do not generate very small [<5microns] wear particles proportionate to large. If the large particles are not monitored, failure may occur without prior warning, if only basic lube analysis is in use. Wear particle analysis, on the other hand, addresses these larger particles. In the case of ferrography or patch analysis, microscopic analysis is available to

6 observe particles directly. Pictures can be taken, as well, as visual support of the Evaluator’s conclusions. Wear particle analysis is a technique of microscopic examination used to analyze particles separated from fluids, developed in 1971,it was initially used to precipitate wear particles from lubricating oils. The success of this technique in monitoring the condition of military air craft engines led to further developments for other practical uses. One such development was a modification to precipitate nonmagnetic particles from lubricants and other fluids. Today in a wide range of industries, WPA can valuable in helping to determine the maintenance needs for machinery by identifying the specific conditions of machine wear.

5.2. What is W P A? WEAR PARTICLE ANALYSIS is a predictive maintenance tool. IT is a technique for analyzing the particles present in fluids that indicate mechanical wear. It uses microscopic examination and was developed in the 1970’s for predictive maintenance, initially analyzing ferrous particles in lubricating oils Predictive and reliability-centered maintenance programs are far more apparent today than even five years ago. At the heart of these progressive trends are technologies such as ferrography. Ferrography, or wear-particle analysis, is the identification of all particles suspended in the lubricating fluids of any oil-wetted machinery. This technology was developed by the U.S. Navy in the 1970s. Today, it is available worldwide through commercial laboratories.

7 Ferrography provides a non-invasive look at historic, current and future conditions of a machine's lubricated components. This is all accomplished without the time and expense of physical examination. Analytical methods identifying the size, shape, composition and concentration of particles is the core of ferrography. Once a trained analyst determines these factors, an association between the wear particles and the specific component of origin can be determined. This is done through direct examination of the particles. Glass substrate, or ferrogram analysis, is one common method of particle identification. Predict/DLI of Cleveland developed a method of particle distribution that uses a magnetic gradient field. A combination of incline, sample preparation and a magnetic field ensure all particles present in the lubricant sample are deposited on the substrate for examination. Particles ranging in size from less than 1 micron to greater than 2,000 microns are released on the substrate. To further aid particle categorization, this method establishes consistent ferrogram patterns or maps. Ferrous wear particles are deposited in strings between the poles of the magnetic assembly positioned below the substrate, perpendicular to the flow of the sample. They are released in a general order of size, with the largest ferrous particles being collected at the entry end of the substrate. Non-ferrous wear particles are released in a random manner throughout the length of the substrate, often appearing between the strings of ferrous particles. Contaminants, such as sand and dirt, fibers and friction polymers also are distributed in an irregular fashion throughout the length of the substrate.

8 Chemicals fix the particles to the slide and aid dispersal of the lubricant. Reduction of sample surface tension through the use of diluents, increased sample temperatures and mechanical means further aids in the release of particles from the sample. This method of ferrographic examination provides a complete picture of the internal components of a piece of machinery. An analyst can identify all particles-from ferrous wear particles to contaminants such as insect parts-and evaluate the effect of their presence. Cumulatively, the particles present in a sample carry with them the story, or fingerprint of the internal workings of an individual piece of equipment. Identifying these particles and the wear mechanisms that generated them can effectively demonstrate the equipment's operating history and current state of performance, as well as generate alarms to future wear conditions. Normal rubbing wear produces platelet particles typically ranging in size up to a major dimension of 15 microns . They are generated by two sliding surfaces and are usually of a benign nature, unless concentrations are substantial enough to affect lubricant quality. Bearing platelet wear has a flaked appearance and is easily misidentified as normal rubbing wear. Bearing wear typically occurs in larger formations than normal rubbing wear. The morphology of these particles may be of greater significance than their size. The difference between a case-hardened bearing platelet and a low-alloy steel bearing platelet is indicative of the severity of bearing wear. The concentration of bearing platelets from abnormal wear is significantly lower than the number of particles generated by other wear mechanisms, making the verification of their composition a crucial alarm in noting abnormal wear patterns.

9 Gear wear is a combination of rolling and sliding wear. The rolling action produces an irregular shaped particle with a generally smooth surface .The sliding motion produces striations very similar to those produced by severe sliding wear. Gear wear particles are typically very large compared with other particles. Their composition may often be of greater significance than their size. The progression from high-carbon alloy steels to low-carbon alloy steels indicates wear severity. Cutting wear is created by one surface penetrating another .It is perhaps the easiest particle to identify and indicates the most devastating types of wear. There are two classifications of this wear: two- and three-body. Two-body cutting wear results when the softer of two surfaces is gouged by the harder surface, leaving relatively long, wire-like cutting wear. Three-body cutting wear occurs when the softer surface becomes imbedded by very hard particles, such as sand or dirt, and cuts the adjacent hard surface, creating short curly particles. Severe sliding wear is identified by parallel striations on the particle surface and sharp fractured edges. These become more prominent with wear severity . Excessive load or speed are common root causes of these particles. Spheres are associated with rolling bearing fatigue . The magnified surface of these particles appears dimpled like a golf ball. Their presence, depending on quantity and size, can indicate impending abnormal bearing wear long before any actual spalling occurs. However, it is possible that in higher-than-normal loads and in clean lubricating systems, these spheres may not be produced in significant quantities to alarm on their own.

10 Sand and dirt are some of the most common contaminants found in lubricating fluids and can also be the most damaging. The very fluid designed to protect component surfaces can carry with it the most devastating contaminants. These particles often cause cutting wear. Other commonly noted particles include red oxides, which are associated with water contamination. They are a form of iron oxide and can be used to identify a current moisture problem and historic difficulties. Black oxides indicate periods of marginal lubrication. These particles are heavily oxidized in appearance, which proves an obstacle in identifying their original composition. Corrosive debris is most often found in heavily concentrated amounts at the exit end of the ferrogram. It is generally smaller than 1 micron. These particles may be used to monitor a change in overall lubricant quality. Corrosive debris in large enough quantities can be associated with a rise in lubricant acidity. Quantifying ferrous wear In any machine, one of the two surfaces in contact must be ferrous. Plain bearings are always in contact with a ferrous shaft, and brass bevel gears have steel worm gears as meshed contact. Although the non-ferrous surface may wear first, corresponding ferrous wear is always seen. There are statistical databases for virtually every type of equipment in use today that can be used to cross reference the amount of ferrous wear in a particular component against that of similar, if not identical components. Through these information systems, industry averages (normal wear rates) have been established. Various methods of quantifying ferrous wear are used by different laboratories. One method uses optical density. A powerful magnetic field causes particle deposition into a glass

11 precipitator tube. The tube is then subjected to two channels of the optical density emission source . Particles larger than 5 microns, up to a maximum of approximately 2,000 microns, are deposited at the beginning of the magnetic field, directly under the first optical emission source. Particles smaller than 5 microns are released several millimeters down the tube under the second light source. As the particles are distributed throughout the length of the tube, the change in light density is measured and reported in two categories: DL-density of particles larger than 5 microns; and DS-density of particles smaller than 5 microns. From these totals, a wear particle concentration (WPC) is calculated: DL + DS = WPC. The WPC, indicative of the rate of wear, is compared to industry >averages for the specific type of equipment being tested. Abnormal wear usually manifests in the appearance of particles larger than 10 microns. The percentage of large particles (PLP) can be calculated: PLP = ((DL-DS) / WPC) The PLP is often used to indicate the onset of abnormal wear conditions. The whole picture assembling all the elements of the analysis allows an evaluation of equipment condition to apply a rating of critical, marginal or normal. Often, laboratories provide graphic images of significant particles.

12 Physical recognition of wear patterns is the primary key to this technology, however, in many instances, the particle morphology is as, if not more, important. Various composition verification methods are used. Subjecting a ferrogram to a controlled heat source at different temperatures for a specified length of time is a common procedure. Oxidation of the particles determines composition. Applying the heat source in stages makes the effects of oxidation readily apparent. Introduction of acids and bases can be particularly useful identifying non-ferrous particles. Support tools such as viscosity measurements are routinely taken and can further aid the analyst in rating existing conditions. This measurement, when compared to the lubricant manufacturer's specifications, can also be an indicator of lubricant condition. Contamination testing for the presence of water, glycol or fuel (dependent upon the equipment being tested) is also commonly performed. Trending the rate (WPC) and severity (PLP) of wear indicates significant changes. In conjunction with the subjective analytical overview of all the particles present in a sample, an analyst is able to assess equipment condition, pinpoint current and potential problems, and make recommendations for corrective measures. Having the ability to identify and monitor component deterioration provides the time and opportunity to cost effectively schedule necessary maintenance. Expensive and unexpected failures can be virtually eliminated. Usedoil analysis or ferrography. Used-oil analysis (spectrographic analysis) has been around for decades and is a common maintenance tool. Spectrographic analysis generally identifies the presence of predetermined elements in a lubricant and reports this information in parts per million. Through other routine testing, it can also demonstrate the current physical properties of lubricating oil.

14 A typical used-oil analysis includes: Viscosity measurement by vibrating cylinder or oil bath; Elemental analysis; Spectrometer; Total acid number; Total base number; Presence of water (crackle); Quantity of water in parts per million; and Particle count. Combining these tests provides an invaluable tool for determining lubricant condition. They afford the opportunity to extend drain intervals and monitor the remaining serviceable life of a lubricant. In the case of a lube system containing several thousand gallons, this can be a substantial saving. Routine testing for contaminants such as glycol, water and fuel may alarm to, and prevent a catastrophic event. Monitoring lubricant condition also can ensure that component surfaces are not subjected to insufficient lubrication protection for extended periods of time. In effect, deterring the overuse of a lubricating fluid can reduce the rate and severity of wear. Unfortunately, oil analysis cannot detect particles indicative of impending component failure. Abnormal wear is generally indicated by particles larger than 10 microns. Knowing the composition of the normal wear particles (smaller than 10 microns) present in a lubricant is of no value when equipment condition is a concern.

5.3. Ferrographic Instruments and Techniques :

16 Advances in ferrographic instrumentation have paved the way for broader study and for classifying wear particles produced by many different metals and substances, both magnetic and nonmagnetic. To establish accurate baselines for the running condition of a machine , samples are taken at regular intervals from carefully selected locations within the machine system preferably during normal operation. Two basic types of ferrographs are: Direct reading ferrograph Analytical ferrograph The direct reading ferrograph is used to obtain numerical baseline values for normal wear. When sudden increase in direct readings occurs, the analytical ferrograph allows us to visually analyze the wear particles to identify the site and nature of wear in time to prevent catastrophic damage. 5.3.1. Direct reading ferrograph The direct reading ferrograph measures the concentration of wear particles in a lubrication oil or hydraulic fluid. The particles are subjected to a powerful magnetic gradient field and are separated by order of decreasing size. Particle concentrations are sensed at two locations- at the entry deposit and at a point approximately 4mm further down the tube. A value based on the amount of light measured at the two locations is then determined. Based on the measurements of the density of large particles and the density of small particles we can derive the values for wear particle concentrations and percentage of large particles. With these measurements machine wear base lines can be established and trends in wear condition can be monitored.

2

5.3.2. Analytical ferrographic system When direct ferrograph readings indicate abnormal wear, analytical ferrographic techniques can be used to study the wear pattern. The purpose is to pinpoint the difficulty and identify the nature of potential machine problems. The ferrographic system includes: A ferroscope for measurement and analysis The FM3 ferrograph, which accurately prepares ferrograms or slides on which wear particles have been deposited. The FAST Systems for data management and reporting 5.4. Ferroscope The ferroscope is a 3power bichromatic microscope with instant and 35mm cameras. Under magnification of 100X, 500X and 800X, the ferroscope utilizes both the transmitted and reflected light sources with red, green and polarizing filters to distinguish the size, composition, shape and texture of both metallic and nonmetallic wear particles.

3 5.5. The Ferrogram Maker The FM3 ferrogram maker is designed with two independent stations to permit two samples to be prepared at the same time. Each station includes a holder that accurately positions a slide at slight incline over the machine assembly .Ferrogram as depicted can be prepared automatically, semi-automatically or manually.

In automatic mode the oil sample is

deposited on the glass slide at a carefully controlled rate. At the end of sample deposition cycle the wash cycle is automatically initiated and an audio and visual signal indicate when the ferrogram is complete. A sample of used fluid, which can be a lubricant preparation, and hydraulic fluid, or an aqueous solution, is prepared by diluting with tetrachloroethylene as a fixer to improve particle precipitation and adhesion.

The prepared sample is allowed to flow down the

inclined slide, passing across the magnetic field. Wear particles arrange themselves along the slide, with the largest particles deposited first. Ferrous particles line up in strings that follow the magnetic field lines of the instrument,

nonferrous particles and contaminants travel

down in a random distribution pattern not oriented by the magnetic field.

This long

deposition pattern spreads the wear particles out, providing good resolution of large and small particles. Good resolution is important in diagnosing wear problem.

When the sample has been run, a wash cycle automatically washed away the lubricant. When the slide is dry, the wear particles remain tightly adhered to the ferrogram and are ready for ferrographic examination. The FAST system. The automated mode features the FAST analytical system for enhanced date management, comparative analysis and reporting.

4 The system features a video camera that projects the image through a personal computer to a high-resolution video monitor. The system also incorporates an optical disk drive for data storage and retrieval 5.6. Modes of wear in Gear Boxes The modes of gear wear considered in a gear system are; Pitch line fatigue Scuffing or scoring Severe sliding wear Overload wear Wear from abrasive contaminants 5.6.1 Pitch Line Fatigue Fatigue particles from a gear pitch line have much in common with rolling element bearing fatigue particles. They generally have smooth and frequently irregularly shaped. Depending on the gear design the particles may have a ratio of major dimension to thickness between 4:1 and 10:1. A high ratio of large particles to small particle is also found as in rolling element bearing fatigue. This ratio is indicated by direct reading ferrograph.

5.6.2. Scuffing or Scoring Scuffing of gears is caused by too high a load or a too high a speed. Excessive head breaks down the lubricant film and causes adhesion of the mating gear teeth. Roughening of the wear surfaces ensures with the subsequent increase in wear rate. The regions of gear teeth

5 affected are between the pitch line and both gear root and tip. Once initiated, scuffing usually affects each tooth on gear resulting in a considerable volume of wear debris. The ratio of large to small particles in a scuffing situation is small all particles have a rough surface and a jagged circumference. Because of the thermal nature of scuffing, quantities of oxides are usually present W and some of the particles may show evidence of partial oxidation. The degree of oxidation depends the lubricant and the severity of scuffing. 5.6.3. Sliding wear and overload wear Severe sliding wear begins when the wear surface stresses become excessive from high loads or speeds. The shear mixed layer becomes unstable, and large particles break away, causing an increase in wear rate. If the stresses applies to surface are increased even more, a second transition point is reached at which the complete surface breaks down and a catastrophic wear rate ensues ratio of large to small particle depends on how far the surface stress is exceeded. The higher the stress the higher the ratio becomes. Severe sliding wear particles are 15 or greater in diameter. Some of these particles have surface striations as a result of sliding. They frequently have straight edges and the ratio of major dimension to thickness is approximately 10:1. As the wear becomes more severe within wear mode, the striations and straight edges on particles become more prominent. 5.7. Gear wear mode in relation to load and operating Wear occurs where heavy loads are carried at low speeds because the oil film is broken. At higher speeds the allowable load increases because the oil film survives for this shorter time of contact. 5.8. Case Study of Gear wear modes

6 These cases are: Combining severe sliding and overload arising from ineffective lubrication. Water in the oil Abrasive wear 5.8.1. Severe Sliding and overload from lubricant Shows the entry view in dichromatic light at low magnification of a ferrogram made from an oil sample obtained from a reduction gearbox. A cursory examination of the ferrogram at low magnification using dichromatic light makes the large number of large metal particles immediately obvious this condition indicates that abnormal wear is taking place. What is often done in manufacture of gears, particularly for industrial users, is that a gear will be case hardened.

That is it will be made of steel and then heated in a carbon

atmosphere so that carbon will diffuse into outer layers of the gear. Subsequent quenching and tempering of the gears makes the outer case with the high carbon content hard, but it leaves the steel core soft. The result hard, where resistant surface with a core resistant to tough shocks to prevent teeth from breaking. In heat treated ferrogram from such a gear, the particles will range blue to straw colored depending on the carbon content. The problem was solved by using a gear box oil with EP additive. This oil arrested the excessive wear.

7

5.8.2. Wear in Oil The samples are taken from the vertical gear box of rope drum of EOT crane. The sample taken after one month of operation however reflected a wear situation that had deteriorated. The photo shows the entry of the ferrogram in polarized reflected light. This figure shows the many red oxides and tortured morphology of the metal particles, many of which were oxide coated. Not only does water in the lubricant cause an oxidative attack, but it also compromises the ability of the lubricant to carry a load. The consequence is large abnormal wear particles. In the oil were many red oxides, which are characteristic of water attack. Practically no free metal wear particles were found in this sample, which could because of the oxidative attack caused by the water during the two week storage time before the ferrogram was prepared. The sample resulted in direct reading ferrograph values of DL=40.6 and DS=2.6, which gives an usually high ratio of large to small particles. Water in oil, at least in concentrations above a few tenths of a percent, may be easily detected by placing a drop of oil on a hot plate heated to about 200-250 C. If there is water in it the water will boil causing the oil drop to sputter. In this case oil sample was cloudy because the water has formed an emulsion. It sputtered vigorously when a drop was put on hot plate.

9

5.8.3. Abrasive Wear A base line was established by taking one sample from each of several machines the following ferrogram shows heavy strings of ferrous wear particles and many non metallic crystalline particles. Compared with the base line sample this ferrogram deposit it extremely heavy.

A closer examination showed that large cutting wear particles dominate the

ferrogram. The recommendation was to change the oil and oil filter and to examine the machine for possible base in which contaminants could be getting into it.

5.8.3.1. Procedure Samples of lubricant collected every month from the coupling. These samples were sent to the lab for ferrography wear particle analysis. Machine condition analysts at the lab studied the particles of the wear in these samples and reported their findings. 5.8.3.2. Analysis

2 Abnormally high concentrations of large size copper alloy particles were indicating severe bearing cage damage. A severity rating of 9 on10 was assigned to this wear. An increase in the concentration of significant size bearing wear particles was observed in the DEC sample. This indicated initiation of damage of bearing parts like rolling elements and raceways, caused by the deteriorated condition of the bearing cage.

Both these wear patterns

contributed to the wear particle concentration trend increasing over time. 5.8.3.3. Recommendation The equipment was rated CRITICAL and the inspection of the bearing cage was recommended. THE EQUIPMENT WEAR CONDITION DISCUSSION-RECOMMENDATION The WPC 450 is high, equipment wear rate is critical. As the ferrogram shows the large quantities of cast iron cutting wear particles, Babbitt bearing wear particles, friction polymers and fibers.

The other particles found on the ferrogram are normal rubbing wear, severe

sliding copper alloy, case hardened steel and sand, these are not immediate concern. Recommended inspection of the cylinder liners, the Babbitt bearings, and crankshaft and copper alloy components. Clean the lubricant to remove the existing contaminants, consider change of filters. Continue the normal operation only after the above maintenance action. 5.8.3.4. Conclusion Ferrography today has advanced as one of the predictive maintenance tools. This technique of particle analysis is becoming prominent in the pulp and paper industry, especially for new plants with automated operations.

With minor financial outlay, ferrography offers a

3 diagnostic tool that enables plant and maintenance managers to make decision more effectively. Ferrography was designed to monitor equipment condition. It can be used to monitor component deterioration in order to maximize service life without the risk and associated costs of secondary damage. It may be implemented to monitor a critical piece of manufacturing or processing equipment to prevent downtime and subsequent loss of production. Wear-particle analysis can warn of potential failures well in advance of physical manifestation, allowing timely, cost-effective scheduling of needed repairs. In addition, ferrography may eliminate the need for routine overhauls or component replacement, reducing parts inventory and maximizing repair personnel's productive time. Ferrography's greatest liability is also its greatest attribute. It relies on a person, not a machine, to examine wear particles and interpret information. Industry averages have been established to suggest acceptable wear rates, but the crucial determination of the severity and implications of the wear is left largely to the subjective interpretation of the analyst.

CHAPTER 6 FINITE ELEMENT METHOD IN DESIGN ANALYSIS 6.1 Introduction The finite element method has been a powerful tool for the numerical solution of a wide range of engineering problems. Applications range from deformation and stress analysis of automotive, aircraft, building, defense, missile and structures to the field analysis of

4 dynamics, stability, fracture mechanics, heat flux, fluid flow, magnetic flux, seepage and other flow problems. With the advances in computer technology and CAD systems, complex problems can be modeled with relative ease. Several alternate configurations can be tried out on a computer before a first prototype is built. The basics in engineering field are must to idealize the given structure for the required behavior. The proven knowledge in the typical problem area, modeling techniques, data transfer and integration, computational aspects of the finite element method is essential. Most often it Is not possible to ascertain the behavior of complex continuous systems without some sort of approximations. For simple members like uniform beams, plates etc. , classical solutions can be sort by forming differential and integral equations through structures like machine tool frames, pressure vessels, automobile bodies, ships, aircraft structures, domes etc., need some approximate treatment to arrive at their behavior, be its static deformation, dynamic properties or heat conducting properties. Indeed these are continuous systems with their mass and elasticity beam continuously distributed. The classical differential equation solution approach leads to intractability. To overcome this, engineers and mathematicians have from time to time proposed complex structure is defined using a finite number of well defined components. Such systems are then regarded as discrete systems. The discretisation method could be finite difference approximation, various residual procedures. Finite element method comes under this category of discretisation method R.W. Clough appears to be the first to use this term of finite element since early 1960’s there has been

5 much progress in the method. The method requires a large number of computations requiring a fast computer. Infact digital computer advances have been responsible for the expanding usage of the finite element method. The finite element was initially developed to solve the structural problems. Its use of late has been rapidly extended to various fields, like Soil& Rock Mechanics, Thermal and Fluid mechanics, Hydro elasticity and Noise problems etc. 6.2 Broad steps of Finite Element Methods The method is based on stiffness analysis. Stiffness is defined as the force required per unit displacement and reciprocal of flexibility. In this method the structure is assumed to be built of numerous connected tiny elements. From this comes the name “Finite Element Method”. Extremely complex structures can also be simulated by proper arrangement of these elements. Finite element method allows accurate modeling through t he use of variety of beam, plate and solid elements simultaneously. The method being essentially convergent I n nature, solutions of engineering accuracy can be easily expected. The broad step in the finite element method when it is applied to structural mechanics is as follows: Divide the continuum into a finite number of regions of simple geometry triangles, quadrilaterals, tetrahedron etc. Select key points on the elements to serve as nodes where condition of equilibrium and compatibility are to be enforced. Assume displacement functions within each element so that the displacements at each generic point are depend upon nodal values.

6 Satisfy strain displacement and strain-strain relationships with a typical element. Determine stiffness and equivalent nodal loads for a typical element using work or energy principles. Develop equilibrium equations for the nodes of the discretized continuum in terms of the element contributions. Solve the equilibrium equations for the nodal displacement. Calculate support reactions at restrained nodes if displaced. Determined stresses at selected points with in the elements. 6.3 Geometric Definitions: There are four different geometric entries in pre-processor namely key point, lines, areas and volumes. These entities can be used to obtain the geometric representation of the structure. All these entities are independent of each other and have unique identification labels. 6.3.1.Key points A key point is a point in 3-D space. It is basic entity and usually the first entity to be created. They can be generated by many methods by individual definitions, by transporting existing key points and from each other entities; e.g. intersection of two lines, key points at corners etc. 6.3.2. Line A general line in 3-D can be defined by a parametric cubic equation. Areas can be generated from a number of grids. Sweeping a specified grid about a given axis through a desired included angle can generate a circular arc.

7 6.3.3. Area An area is a 3-D surface defined using a parametric cubic equation. Area can be generated by using four key points or four line method, depending on the geometry. Some inbuilt areas like circles, rectangles and polygon can be directly created to the required size. 6.3.4.Volume Volume is a general 3-D solid region defined by using a parametric equation. Similar to areas, volumes also have parametric directions. Using 2 or 4 areas can generate these. Spinning an area about an axis can also generate volume (swept volume). Volumes of cylinder, prism and sphere can be directly created to the required dimensions. 6.4 General description of FEM: In the finite element method, the actual continuum of body of matter like solid, liquid or gas is represented as an assemblage of sub-divisions called finite elements. These elements are considered to be inter-connected at specified points known as nodes or nodal points. The nodes usually lie on the element boundaries where an adjacent element is considered to be connected. Since the actual variation of the field variable like (displacement, stress, temperature, pressure and velocity) inside the continuum is not known, we assume that the variation of field variable inside a finite element can be approximated function (also called interpolation models) are defined in the terms of the value at nodes. When the field equations (like equilibrium equations) for the whole continuum are written, the new unknown will be the nodal value of the field variable. By solving, the field variables will be known. Once these are known, the approximating functions define field variables through the assemblage of elements.

8 The element analysis is given in the following pages. This description provides general outlook of FEM. General Explanation for each step-by-step procedure involved is also given. 6.4.1. Descritisation of domain: The discretisation of the domain or solution into sub-regions (finite elements) is the first step in the finite element method. This is equivalent to replacing the domain having an infinite number of degrees of freedom by a system having finite number of degrees of freedom. 6.4.2. Basic element shape: For any given physical body we have to use engineering judgment in selecting appropriate elements for discretisation. The geometry of the body and the number of independent spatial coordinates necessary to discretize the system dictate mostly the choice of the type of element. Some of the popularly used one, two or three dimensional elements are given.

6.4.3. Types of elements : Often the type of element to be used is evident from the problem itself. For example, if the problem involves the analysis of a truss structure under a given set of load conditions, the type of element to be used idealization is obviously the “bar of line elements”. However, in some case the type of the element to be used for idealization may not be appropriate and in such cases one has to choose the type of elements judicially. 6.4.4. Number of elements The number of elements to be chosen for idealization is related to accuracy desired, size, shape of elements and number of degrees of freedom involved. Although an increase in

9 number of elements generally means more accurate results for a given problem, there will be certain number of elements reaching the point, where no significant improvement will be found. Moreover, since the use of large number of elements, involve large number of degrees of freedom, we may not be able to store the resulting matrices in the available computer memory. 6.4.5. Size of elements : The size of element influences the convergence of the solution directly and hence it should be chosen with care. If the size of element is small, the final solution is expected to be more accurate. Sometimes, we may have to use elements of different size in the same body. The size of elements has to be very small near the region where stresses concentration is expected to be at far away places.

6.4.6. Location of nodes Details of the problem can be described in terms of two independent spatial coordinates, if the body has no abrupt changes in the geometry, material properties and external conditions (like load, temperature, etc.) it can be divided into equal sub-divisions and hence the spacing of the nodes can be uniform. On the other hand, if there are any discontinuities in the problem, nodes have to be introduced, obviously, at these discontinuities. 6.5 Nodal degrees of freedom: The basic idea of FEM is to consider a body as composed of several elements, which are connected at specific node points. The unknown solution or the field variable (like displacements, pressures or temperatures) inside any finite element is assumed to be given by

10 a simple function in terms of nodal values of the elements nodal displacement, rotations necessary to specify completely the deformation of the finite element is the degree of the element. The nodal values of the solution, also known as nodal degrees of freedom, are treated as unknown in formulating the system of overall equations, the solutions of the system equation (like force equilibrium equations) gives the value of the unknown nodal degree of freedom. Once, the nodal degrees of freedom are known, the solution within any elements will also be known to us. For having the results in terms of nodal degrees of freedom the interpolation function must be derived in terms of nodal degrees of freedom. 6.6 Convergence requirement Since the finite element method is numerical technique, we obtain a sequence of approximate solutions as the element size is reduced successively. This sequence will converge to the exact solution if the interpolation polynomial satisfies the following requirements. (a) The displacement function must be continuous within the element. This can be easily satisfied, by choosing polynomials for the displacement model. (b)

The displacement function must be capable of representing rigid body displacements

corresponding to the rigid body motion. The element should not experience any strain and hence leads to nodal forces. The constant terms in the polynomials used for the displacement models would usually ensure these conditions. (c) The displacement function must be capable of representing strain states within the element. The reason for this can be understood if we imagine the condition when the body or structure is divided into smaller and smaller elements. As this elements approach infinitesimal size, the strains in elements also approach constant values.

11

Physical problem

Change of physical problem

Mathematical Model Improve the mathematical model Governed by different equations, assumption Geometry Kinematics Finite Element Solution Choice of Finite Element Design analysis through FEM

Assessment of accuracy of finite Design Interpolation Improvements of results element

Define Mesh

Define Analysis

12

6.7 Assembly of element equations Once the element characteristics, namely, the element matrices and element vectors are found in a global co-ordinate system, namely, the element matrices and element vectors are found in a global co-ordinate system, the next step is to construct the overall or system equations. The procedure of assembling the element matrices and vectors is based on the requirement of “compatibility” at the element nodes. This means that at the nodes where elements are connected, the values of unknown degrees of freedom of the variables are same for all the elements at the nodes. 6.8 Incorporation of the boundary conditions: After assembling the characteristic matrices [K(e)] and element characteristic vectors P(e) the overall system equation of the entire domain or the body can be written (for and equilibrium problems) as [K]{Ø} = {p} These equations cannot be solved for {Ø} since the matrix [K] will be singular and hence its inverse does not exist. The physical significance of this , in case of solid mechanics problem is that the loaded body or structure if free to undergo unlimited rigid body motion unless some support constraints are imposed to keep the body or structure under equilibrium under the loads. Hence some boundary conditions have to be applied before solving for {Ø}. In non-structural problems, we have to specify one or more than one degrees of freedom. The number of degrees of freedom is dictated by the physics of the problem.

13 6.9 Types of Meshing 6.9.1 Manual meshing In manual meshing the elements are smaller at joint. This is known as mesh refinement, and it enables the stress to be captured at the geometric discontinuity. Manual meshing is long and tedious process for models with any degree of geometric complication, but with useful tool emerging in pre-processors, the task is becoming easier. Meshing controls The default meshing controls that the program uses may produce a mesh that is adequate for the model we are analyzing. In this case, we need not specify any meshing controls. However, if we do use meshing controls, we must set them before meshing the solid model. Meshing controls allow us to establish the element shape, mid side node placement, and element size to be use din meshing the model. This step is one of the most important of the entire analysis for the decisions we make at this stage in the model development will profoundly affect the accuracy and economy of the analysis. 6.9.3. Smart sizing of elements Smart element sizing (smart sizing) is a meshing feature that creates initial element sizes for the free meshing operations. Smart sizing gives the mesher a better chance of creating reasonably shaped elements during automatic meshing generation. 6.9.4. Free or mapped mesh

2 A free mesh is a one that has no restrictions in terms of element shapes, and no specific pattern applied to it. Compared to a free mesh, a mapped mesh is restricted in terms of the element shape it contains and the pattern of the mesh. A mapped mesh contains only quadrilateral (area) or only hexahedron (volume) elements. If this type of mesh is desired, the user must build the geometry as series of fairly regular volumes and/or areas that can accept a mapped mesh. 6.10. Types of analysis There are two types of analysis that are use din industry: 2-D modeling and 3-D modeling. While 2-D modeling conserves simplicity and allows the analysis to run on a relatively normal computer, it tends to yield much accurate results. 3-D modeling produces more accurate results while sacrificing the ability to run on all but fastest computers effectively. There are different types of analysis that are used. They are; Structural, Modal, Harmonic, Transient & Spectrum. Structural analysis consists of linear and non-linear models. Linear models use simple parameters and assume that material is not plastically deformed. Non-linear models consist of stressing the material past its elastic capabilities. The stresses in the material then vary with the amount of deformation. Vibration analysis is used to test the material against random vibrations. Each of these incidents may act on the natural vibration frequency of the material, which, in turn, may cause resonance and subsequent failure. So, analysis is done on the material to predict the life of the material.

3 Heat transfer analysis models the thermal conductivity or thermal fluid dynamics of the material or structure. This may consist of a steady or transient transfer. Steady-state transfer refers to constant thermo-properties in material that yield linear heat diffusion. 6.11. Finite element analysis process The structure to be analyzed is sub-divided into mesh of finite sized elements of simple shape. Within each element, the variation displacement is assumed to be determined by simple polynomial shape functions and nodal displacement. Equations for strain and stress are developed in terms of unknown nodal displacement. From this, the equations of equilibrium are assembled in a matrix form, which can be easily programmed and solved on a computer. After applying appropriate boundary conditions, the nodal displacements are found by solving the matrix stiffness equation. Once the nodal displacements are known, element stresses and strains can be calculated. 6.12. Results of Finite element analysis process Analysis helps designer to predict the life of material or structure by showing the effects of cyclic loading on specimen. Such analysis can show the areas where crack propagation is most likely to occur. Failure due to fatigue may also show the damage tolerance of the material. This method of product design and testing is far superior to the manufacturing costs, which would accrue if each sample is built and tested. 6.13. Advantages of FEM •

Its ability to use various sizes and shapes and to model a structure of arbitrary geometry.

1 •

Its ability to accommodate arbitrary boundary conditions and loading including thermal loading.

•

Its ability to model composite structures involving different structural components such as stiffening member on a shell and combinations of plates, bars and solids etc.

•

The finite element structures closely resembles the actual structure instead of being quite obstruction that is hard to visualize.

•

The FEM is proven successfully in representing various types of complicated material properties and material behavior (non-linear, an-isotropic, time dependent or temperature dependent material behavior).

•

It readily accounts for non-homogeneity of the material by assigning different properties to different elements or even it is possible to vary the properties within an element according to a pre determined polynomial pattern.

6.14. Disadvantages of FEM •

Specific numerical result is obtained for a specific problem.

•

Experience and judgment are required in order to construct a good finite element model.

•

A big computer and a reliable computer program (software) are essential.

•

Input and output data are tedious to prepare and interpret.

2

CHAPTER 7

ANSYS 7.1 Introduction The ANSYS program is self contained general purpose finite element program developed and maintained by Swason Analysis Systems Inc. The program contain many routines, all inter related, and all for main purpose of achieving a solution to an engineering problem by finite element method. ANSYS finite element analysis software enables engineers to perform the following tasks: •

Build computer models or transfer CAD models of structures, products, components, or systems.

•

Apply operating loads or other design performance conditions.

1 •

Study physical responses, such as stress levels, temperature distributions, or electromagnetic fields.

•

Optimize a design early in the development process to reduce production costs.

•

Do prototype testing in environments where it otherwise would be undesirable or impossible (for example, biomedical applications).

The ANSYS program has a comprehensive graphical user interface (GUI) that gives users easy, interactive access to program functions, commands, documentation, and reference material. An intuitive menu system helps users navigate through the ANSYS program. Users can input data using a mouse, a keyboard, or a combination of both. A graphical user interface is available throughout the program, to guide new users through the learning process and provide more experienced users with multiple windows, pulldown menus, dialog boxes, tool bar, and online documentation.

7.2 Organization of the ANSYS Program The ANSYS program is organized into two basic levels: Begin level Processor (or Routine) level The Begin level acts as a gateway into and out of the ANSYS program. It is also used for certain global program controls such as changing the job name, clearing (zeroing out) the database, and copying binary files. When you first enter the program, you are at the Begin level. At the Processor level, several processors are available. Each processor is a set of functions that perform a specific analysis task. For example, the general preprocessor (PREP7) is where you build the model, the solution processor (SOLUTION) is where you apply loads and obtain the solution, and the general postprocessor (POST1) is where you

2 evaluate the results of a solution. An additional postprocessor, POST26, enables you to evaluate solution results at specific points in the model as a function of time.

7.3. Performing a Typical ANSYS Analysis The ANSYS program has many finite element analysis capabilities, ranging from a simple, linear, static analysis to a complex, nonlinear, transient dynamic analysis. The analysis guide manuals in the ANSYS documentation set describe specific procedures for performing analyses for different engineering disciplines. The next few sections of this chapter cover general steps that are common to most analyses. A typical ANSYS analysis has three distinct steps: •

Build the model.

•

Apply loads and obtain the solution.

•

Review the results.

The following table 4.1 shows the brief description of steps followed in each phase. Pre-Processor

Solution Processor

Post- Processor

Assigning element type

Analysis definition(type)

Read results

Geometry definition

Constraint definition

Plot results on graphs

Assigning real constants

Load definition

View animated results

Material definition

Solve

Mesh generation Model display

7.4. Pre-Processor

2 The input data for an ANSYS analysis are prepared using a preprocessor. The general preprocessor ( PREP7 ) contains powerful solid modeling and mesh generation capabilities, and is also used to define all other analysis data (geometric properties (real constants), material properties, constraints, loads, etc.), with the benefit of database definition and manipulation of analysis data. Parametric input, user files, macros and extensive online documentation are also available, providing more tools and flexibility for the analyst to define the problem. Extensive graphics capability is available throughout the ANSYS program, including isometric, perspective, section, edge, and hidden-line displays of three-dimensional structures, x-y graphs of input quantities and results, and contour displays of solution results. The pre-processor stage involves the following: 1. Specify the title, which is the name of the problem. This is optional but very useful, especially if a number of design iterations are to be completed on the same base mode. 2. Setting the type of analysis to be used, e.g., Structural, Thermal, Fluid, or electromagnetic, etc. 3. Creating the model. The model may be created in pre-processor, or it can be imported

from

another

CAD

drafting

package

format(IGES,STEP,ACIS,PARASOLID etc.,) 4. Defining element type, these chosen from element library.

via

a

neutral

file

1 5. Assigning real constants (thickness, etc) and material properties like Young’s modulus, Poisson’s ratio, density, thermal conductivity, damping effect, specific heat, etc. 6. Applying mesh. Mesh generation is the process of dividing the analysis continuum into number of discrete parts of finite elements. 7.5. Solution processor Here we create the environment to the model, i.e. applying constraints & loads. This is the main phase of the analysis, where the problem can be solved by using different solution techniques. Here three major steps involved : Solution type required, i.e. static, modal, or transient etc., is selected. Defining loads. The loads may be point loads, surface loads; thermal loads like temperature, or fluid pressure, velocity are applied. Solve. FE solver can be logically divided into three main parts, the pre-solver, the mathematical-engine and post-solver. The pre-solver reads the model created by preprocessor and formulates the mathematical representation of the model and calls the mathematical-engine, which calculates the result. The result return to the solver and the post solver is used to calculate strains, stresses, etc., for each node within the component or continuum.

1

7.6. Post-Processor Post processing means reviewing the results of an analysis. It is probably the most important step in the analysis, because we are trying to understand how the applied loads affect the design, how good your finite element mesh is, and so on. The analysis results are reviewed using postprocessors, which have the ability to display distorted geometries, stress and strain contours, flow fields, safety factor contours, contours of potential field results (thermal, electric, magnetic), vector field displays mode shapes and time history graphs. The postprocessors can also be used for algebraic operations, database manipulations, differentiation, and integration of calculated results. Root-sum-square operations may be performed on seismic modal results. Response spectra may be generated from dynamic analysis results. Results from various loading modes may be combined for harmonically loaded axisymmetric structures. Review the Results. Once the solution has been calculated, you can use the ANSYS postprocessors to review the results. Two postprocessors are available: POST1 and POST26. We use POST1, the general postprocessor, to review results at one sub step (time step) over the entire model or selected portion of the model.. We can obtain contour displays, deformed shapes, and tabular listings to review and interpret the results of the analysis. POST1 offers many other capabilities, including error estimation, load case combinations, calculations among results data, and path operations. We use POST26, the time history postprocessor, to review results at specific points in the model over all time steps. We can obtain graph plots of results data vs. time (or frequency) and tabular listings. Other POST26 capabilities include arithmetic calculations

2 and complex algebra. Details of POST1 and POST26 capabilities and how to use them are described in chapters later in this document. In the solution phase of the analysis, the computer takes over and solves the simultaneous set of equations that the finite element method generates. The results of the solution are: Nodal degree-of-freedom values, which form the primary solution Derived values, which form the element solution. 7.7. Meshing Before meshing the model, and even before building the model, it is important to think about whether a free mesh or a mapped mesh is appropriate for the analysis. A free mesh has no restrictions in terms of element shapes, and has no specified pattern applied to it. Compared to a free mesh, a mapped mesh is restricted in terms of the element shape it contains and the pattern of the mesh. A mapped area mesh contains either only quadrilateral or only triangular elements, while a mapped volume mesh contains only hexahedron elements. In addition, a mapped mesh typically has a regular pattern, with obvious rows of elements. If we want this type of mesh, we must build the geometry as a series of fairly regular volumes and/or areas that can accept a mapped mesh 7.7.1. Free Meshing In free meshing operations, no special requirements restrict the solid model. Any model geometry, even if it is irregular, can be meshed. The element shapes used will depend on whether you are meshing areas or volumes. For area meshing, a free mesh can consist of only quadrilateral elements, only triangular elements, or a mixture of the two. For volume meshing, a free mesh is usually restricted

3 to tetrahedral elements. Pyramid-shaped elements may also be introduced into the tetrahedral mesh for transitioning purposes. If our chosen element type is strictly triangular or tetrahedral (for example, PLANE2 and SOLID92), the program will use only that shape during meshing. However, if the chosen element type allows more than one shape (for example, PLANE82 or SOLID95), you can specify which shape (or shapes) to use by one of the following methods:

7.7.2. Mapped Meshing We can specify that the program use all quadrilateral area elements, all triangle area elements, or all hexahedral (brick) volume elements to generate a mapped mesh. Mapped meshing requires that an area or volume be "regular;" that is, it must meet certain criteria. Mapped meshing is not supported when hard points are used. An area mapped mesh consists of either all quadrilateral elements or all triangular elements. For an area to accept a mapped mesh, the following conditions must be satisfied: •

The area must be bounded by either three or four lines (with or without concatenation).

•

The area must have equal numbers of element divisions specified on opposite sides, or have divisions matching one of the transition mesh patterns (see Transition Patterns).

•

If the area is bounded by three lines, the number of element divisions must be even and equal on all sides.

•

The meshing key must be set to mapped. These setting results in a mapped mesh of either all quadrilateral elements or all triangle elements, depending on the current element type and/or the setting of the element shape key .If our goal is a

2 mapped triangle mesh, you can also specify the pattern ANSYS uses to create the mesh of triangular elements. •

Area Mapped Meshes shows a basic area mapped mesh of all quadrilateral elements, and a basic area mapped mesh of all triangular elements.

7.8. Structural Static Analysis A static analysis calculates the effects of steady loading conditions on a structure, while ignoring inertia and damping effects, such as those caused by time-varying loads. A static analysis can, however, include steady inertia loads (such as gravity and rotational velocity), and time-varying loads that can be approximated as static equivalent loads (such as the static equivalent wind and seismic loads commonly defined in many building codes). Static analysis is used to determine the displacements, stresses, strains, and forces in structures or components caused by loads that do not induce significant inertia and damping effects. Steady loading and response conditions are assumed; that is, the loads and the structure's response are assumed to vary slowly with respect to time. The kinds of loading that can be applied in a static analysis include: Externally applied forces and pressures Steady-state inertial forces (such as gravity or rotational velocity) Imposed (nonzero) displacements Temperatures (for thermal strain) Fluences (for nuclear swelling)

7.9. Modal Analysis You use modal analysis to determine the vibration characteristics (natural frequencies and mode shapes) of a structure or a machine component while it is being designed. It

2 also can be a starting point for another, more detailed, dynamic analysis, such as a transient dynamic analysis, a harmonic response analysis, or a spectrum analysis. We use modal analysis to determine the natural frequencies and mode shapes of a structure. The natural frequencies and mode shapes are important parameters in the design of a structure for dynamic loading conditions. They are also required if you want to do a spectrum analysis or a mode superposition harmonic or transient analysis. We can do modal analysis on a prestressed structure, such as a spinning turbine blade. Another useful feature is modal cyclic symmetry, which allows you to review the mode shapes of a cyclically symmetric structure by modeling just a sector of it. Modal analysis in the ANSYS family of products is a linear analysis. Any nonlinearity, such as plasticity and contact (gap) elements, are ignored even if they are defined. You can choose from several mode extraction methods: Block Lanczos (default), subspace, Power Dynamics, reduced, unsymmetrical, damped, and QR damped. The damped and QR damped methods allow you to include damping in the structure. Details about mode extraction methods are covered later in this section The procedure for a modal analysis consists of four main steps: 1. Build the model. 2. Apply loads and obtain the solution. 3. Expand the modes. 4. Review the results

2

CHAPTER 8 ANALYSIS OF THE EOT CRANE GIRDER USING ANSYS 8.1 Description Perform static analysis on the Crane girder to identify the displacement and stress against safe working load. The model had been scaled and analysis performed in MKS units. Due to the complexity involved the rail and wheel assemblies were not involved in the calculations. The girder is considered to be in direct contact with guide beam. Structural analysis has been performed by considering the guide beam fixed at bottom in all direction and operating load of 30 tonnes is applied at the center of span. In heavy-duty material handling equipment, major concern is optimum utilization of material for equipment construction without sacrificing the design parameters. To understand this aspect and also to validate the design, as this kind of equipment is a vital part of any

3 manufacturing industry, finite element analysis is one of the best method that can be used extensively. The major advantage is that the equipment need not be manufactured and tested physically to find out the drawbacks. Instead one can simulate the conditions through finite element analysis to obtain an optimum design. The finite element analysis was carried out for the rated load condition with some impact factor and also for the overload condition. Maximum stress and displacement locations were obtained for each of the components to check the validity of design values. All these values obtained through detailed finite element analysis were found to be within the design limit. The complete analysis work gave a very good insight on various component design of crane and also a high degree of confidence, with cost saving. Heavy material handling equipments have been traditionally designed using some standards with factor of safety included into the design. This can lead to over design of the component. This paper presents a case study required for a design that is optimum and safe with respect to the available standards as well as easy to manufacture This analysis for each of the above three components has been carried out for the loads as specified by relevant crane standards. The analysis also involved redesign of the structure wherever needed to meet requirements of stresses and displacements. Online change in design is an advantage not available to this particular industry. Another significant aspect of this analysis was that the results were accepted as equivalent to carrying out field load test as prescribed by the Crane standards. Only a limited load field load test was carried out to ascertain the accuracy of the results.

4 8.2. Types of element used Solid-45 It is a 8-node hexa 3-d element. The element is defined by 8 nodes with 3 degrees of freedom each node: translation in x, y, z directions. The element has plasticity, creep, swelling, stress stiffening, large deflection and large strain capabilities. 8.3. Material properties Material is structural steel. Young’s modulus EX = 2e5 MPa Density ρ = 2900 Kg/ m3 Poisson’s ratio = 0.3. 8.4. Building the model The solid model is imported from CATIA using IGES file. The geometric model, which is imported, is mapped meshed in order to generate finite element model. There by 19661 number of elements and 23891 number of nodes are obtained.

6

Geometric model of EOT Crane

Load diagram

7

Meshed model of girder considered for analysis.

8

Guide beam fixed in all directions at the bottom face.

9

30 tonnes load applied at the center of the span

10

Deformation plot (5.225 mm)

VALUES OF MAX. AND MIN. MIN.

MAX.

DISPLACEMENT FOR THE LOAD DISPLACEMENT

DISPLACEMENT

CASES HALF LOAD RATED LOAD

1.8 5.225

0.6506 0.58

11

von Mises stress plot (284 MPa) von Mises stress values LOAD ON HOOK

HALF LOAD

Bending stress (kg/mm2)

15 T

MIN

MAX

0.0001

95

12 FULL LOAD

30T

0.009

284

Conclusions

The following conclusions are drawn from the present work The design of 30/7.5T EOT crane has been done as per IS: 3177-1999. All the calculations pertaining to the design have been calculated and results are tabulated The failure analysis i.e. vibration, Bearing, WPA has been done. Design validation of girder has been performed using ANSYS finite element software indicates that the calculated deformation is 5 mm which is less than the allowable deformation of 18 mm as per IS standards. The calculated von Misees stress is 284 Mpa which is less than the allowable stress of 520 Mpa with a safety factor 1.83.

Therefore, the crane girder will perform safely during its operating conditions

Future scope At present, the market size for EOT cranes and hoists is approximately Rs 3000 crores . The Indian infrastructure, construction and civil construction industries lead to a huge requirement generation for the material handling industry. Primarily, there is a direct requirement for equipment at various project sites like gantry cranes for precast segment

13 yards, gantry cranes for bridge constructions, specialized hoisting equipment for bridge launching girders etc. Typically, the capacities for such cranes can range from 10 ton to 150 ton. A lot of multinational crane manufacturing companies are now entering into the Indian market and we expect some sort of consolidation to take place over the next three-four years. The demand for cranes merely reflects the growth across all sectors of the industry. More importantly, the demand for world-class cranes over the traditional Indian design cranes is increasing drastically due to the advent of almost every global company worth its salt setting up manufacturing facilities in India. We estimate a growth rate of around 20 to 30 per cent annualized in this industry.

.

s