Wire Rope Excavator

Wire rope excavator

 

Project Title: Wire Rope Excavator Created by: V.Bhanu Chander, Tirupati (city), AP (state). India (country). [email protected]

Problem Statement: This is a practical problem, the main objective of which is to replace the present day Hydraulic operated JCB or excavators with WIRE ROPE operation in order to minimize the hydraulic network. This system may also prove to be simple rather than a complex and cumbersome design which is usually observed in the Hydraulic operated machines.

Introduction: The operation of an excavator or JCB Machine involves hydraulic systems by means of which only it performs the desired work. The hydraulic system incorporates complex arrangements for pressurizing the hydraulic fluid, and hence to move the arms along with the jaws (buckets). A number of cylinders, rams, valves e.t.c was also involved.

Wire rope excavator

 

In fact the fluid is pressurized by means of a heavy diesel engine (generally 6 or 12 cylinder type) which consumes a lot of fuel, the engine structure being complex and so the arrangement proves to be uneconomical. The present day engines need also to be eco friendly and so these facts make us to think for some other options if possible. This section presents a new idea which may be adopted if this sounds good.

Description: The proposed unit uses ropes which reduces the hydraulic arrangements. The idea was in fact to move and operate the arms with the above said unit. Although this seems to be not practical, yet we may make it by care full design and investigations. Two or three of the hydraulic mechanism may be removed. The hydraulic system consists of cylinders, inside of which a piston is able to reciprocate and to which a ram is connected. This motion is obtained by using hydraulic fluids which are supplied to the cylinders at very high pressures.

Wire rope excavator

 

The present machine (Excavator) is designed such that the rams and the cylinder above one of the arms and the one attached to the body of the excavator are removed and are replaced by an arrangement which comprises of cone pulleys mounted above the arms as shown in the figure. Wire ropes move above the pulley and are fixed to the arm end by means of a pin. The other side of the rope is wound over a rope drum just as we observe in a hoist machine (cranes). The rope drum is supposed to be arranged inside the body of the machine, particularly in front of the cabin where the driver or the operator sits. The bucket movement may be obtained by the regular arrangement, i.e by the hydraulic means. This is necessary because the rope arrangement cannot handle the work in such location, the reason will be understood in the coming discussions.

Feasibility: First of all let us check the feasibility. That is we precede the topic by checking whether the wire ropes are capable of carrying and handling the large loads. For this reason consider the case of a big dam which are usually provided with gates weighing several tones. In such situations, to open the gate a wire rope hoist is used which pulls the gate

Wire rope excavator

 

upwards. This is shown in the figure. In this figure the black lines represents ropes which is wound over rope drum (shown in Rose color). Similarly in the case of cranes the ropes are capable of handling large tons of weight. So from the above facts what we can interpret is that the wire ropes can handle large loads and sudden pressures which normally arise during digging or other similar work. So we may use wire ropes comfortably without any fear of breakage. Secondly the ropes should act such that they should give desired motion to the arms, including the bucket without any miss function. This is achieved by selecting suitable mechanism which functions as per the operator does. For the present case a double side acting wire rope mechanism is proposed to meet the above said requirement.

Mechanism for the first arm: As shown in the figure the rope should be fixed to the arm at two points, one being at the extreme end where a pin is fixed in between the recess provided in the arm. The other should be tied, may be nearly at the centre (appro.). The ropes should not get interference with the other members in any manner when in operation. The ropes are then made to pass over

Wire rope excavator

 

cone pulleys placed above and downside the arm such that the rope make two or more complete turnaround it (probably a multi groove pulley may be helpful). The other ends of the ropes are then wound on rope drums. Actually the drums are powered by means of diesel engine, but we may also install a D.C.Motor if sufficient power supply is available. If the system is capable of operating by motor then the advantage lies there in.

Mechanism for the second arm: The second arm which is connected to the main body is moved by a similar fashion but in this case it doesn’t require pulleys to be mounted on the arm. The pulleys are arranged to the main body itself. In this case it is required that the rope should act on both sides, the reason of which will be understood in the coming discussion. Difficulties: The major difficulties that may arise during the operation of the rope type machine on single side (single acting) is: ¾ When the arm attached to the main body is raised by using rope (only on one side) and if the second arm is to be raised then the problem may occur since the arm attached to the body turns about its pivot due to increase in turning moment. This can be understood in the figure1. ¾ If the arm carrying the bucket is arranged with only one side action of rope then it is very difficult to perform the operation of digging. It means that the whole mechanism of excavator becomes useless.

Wire rope excavator

 

Figures showing possible deviations from the usual operation when ropes are operated one side only. ¾ When the bucket is moved by means of rope arrangement, instead of hydraulic means then also the digging operation becomes difficult. In order to eliminate the difficulties as above (that may arise during the proposed machine operation), the mechanism should be such that the rope acts on both side. This is what required for getting the desired motion. Operation: The operation of this type of machine consists of moving the arms and the bucket properly. To raise the arm connected to the body, the rope attached above the arm is pulled by using rope drum powered by the engine or motor. On the other side of the arm the rope should be loosen by the same amount. To lower the arm, reverse operation is done that is the rope attached above the arm loosens and that attached to the other side tightens such that both of them will be of same amount and after the operation the arm will be in perfect position without any miss motion. The reason is explained below.

Wire rope excavator

 

To raise the arm to which the bucket is attached, the rope tied to the pin arranged at the end of the arm should be pulled (wound over the drum) and on the other part where one more rope is tied to the same arm the rope should be loosen such that the amount of tightening and loosening in both the respective sides are same. Then the arm moves to the desired position without any miss functioning. Essential Requirements: The main requirement for this system to be effective is that the rope mechanism should not undergo any miss function. This necessitates the rope (double side acting) to act in such a manner that whatever the amount of rope wound on one side, the same amount of rope should be released on the other side. It means the length of the rope on both sides (while in operation) should undergo equal and opposite changes (one extending and the other winding). This condition is must because when the rope on one side is pulled much than that on the other side then stresses may develop in the latter and this may cause the rope to fail. Some unwanted motion may also be encountered during such conditions. So the selected mechanism should be such that increase

Wire rope excavator

 

in length on one side should be made equal to the decrease in length on the other side. This is a must and should condition to be noted while designing. Bucket motion: It is clear that the bucket attached to the arm is necessary to be operated with hydraulic arrangement, in order to make the system and the work to be handled effective. The arrangement is somewhat difficult to incorporate rope for the excavator to do the expected job. But we may also arrange a rope mechanism for the bucket if the size of the excavator is small or in other words the work handling capacity is to be small. In case of such an assumption and arrangement also the mechanism seems to be cumbersome with adjacent ropes overlapping. Thus this is not at all considerable. The arrangement as shown in the figure with opposite bucket arrangement may be possible. Design Considerations: 9 One of the important members in the excavator that should be designed properly is the Pins (and their joints) or short sized shafts that are used to connect ropes. These pins are subjected to stresses and the design should be such that the pin so selected should be able to carry the maximum load without any wearing effects. 9 The rope should have the capacity to carry the maximum load that should be handled by the machine.

Wire rope excavator

 

9 The pulleys that are required to be mounted on the arm and also the body are supposed to offer less friction. 9 The overall proposed mechanism should use less power to handle a given task (either from Diesel engine or D.C.Motor) than the power consumed by a similar sized hyd. Operated machine. Use of motors: It can be easily verified that a diesel engine consumes more input to develop a rated power than that consumed by an electrically operated motor. Also the cost involved to develop some output from a given engine for a specific time is more than that involved by using electricity. Factors like difficulty in the availability of diesel, gases that are released during combustion makes us to look for a better fuel (alternate fuel) or if possible a motor. Test to be conducted: The load carrying ability of an excavator determines the number of cylinders in case of diesel engine and the size and number of motors in case of motor arrangement. For a given load the mass rate of diesel consumed should be evaluated for a specific time. Then the cost of diesel incurred for that mass flow rate is evaluated. For the motor, the units of power consumed for the same load should be noted for the same period of time and then the cost incurred is to be evaluated. Both the results are to be compared and the one which is economical can thus be found. This test should also include the possible losses.

Wire rope excavator

 

Advantages: • The system eliminates much of the hydraulic circuit. • The losses incurred in this case may be reduced since the hydraulic system which offers viscous resistances are minimized and only few moving parts may be encountered. The advantages of the above system can be experienced only when the model is studied well and put into real working model. Some drawbacks: ™ The proposed unit may not handle the work effectively as that done by a hydraulic unit. ™ The system is not recommended for heavy duty applications. ™ The bucket is required to be run using hydraulic system and hence separate arrangement in addition to the wire rope mechanism is required to drive the machine. This may seems to be complicated. ™ The difficulty in supplying large units of electric current to the machine whenever required is the main draw back in case if the excavator is operated by motor arrangement. This is because the machine cannot store electric energy which is required for operation. Conclusions: Although the development of wire rope excavator seems to be difficult, it may be confirmed about the usage by making a prototype (model) of the above said mechanism, evaluating all the constraints and the possible limitations. For this purpose a thorough investigation is necessary.

 

Wire rope excavator

Also the performance of both the diesel engine and a wire rope D.C.Rope

(in

terms of cost and its effective operation) helps us to decide the installation of the suitable type of power input. All we need is to develop a suitable system which is capable of storing large amount of electric energy and discharging it whenever required. Results of any idea will be found only when the proposal is put into practical model and hence the above model may be prepared, as there is no harm in trying.

The End