1
CERTIFICATE
This is to certify that Mr./miss…...........................................bearing pin… ………… has completed his/her project work on “LIFE IMPROVEMENT OF BULL HEAD HAMMERS” as a student of final year mechanical in year 2007-2008 for partial fulfillment of requirement for award of engineering in mechanical engineering department under the guidance of Mr.T.V.Rama Gopal,Sinter plant RINL VSP. INTERNAL GUIDE: Mr. kodanda Rama Rao, Asst professor, Dept. of mechanical engineering, Gudlavalleru engineering college. EXTERNAL GUIDE:
Mr.T.V.Rama Gopal DCM (sinter plant) RINL-VSP
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LIFE IMPROVEMENT OF DOLOMITE CRUSHING BULL HEAD HAMMERS The project report is submitted in partial fulfillment of requirements for the award of BACHELOR OF TECHNOLOGY IN MECHANICAL ENGINEERING
By 1. Sk Rahaman Basha 2. K Stephen small 3. K. Pavan Kumar 4. Sampath Anne. Under the Esteemed guidance of Mr. T.V.J.Rama Gopal DCM (Sinter plant) RINL-VSP
3 PROJECT WORK GOAL . OBJECTIVES: VISITING ONE MAJOR INDUSTRY. STUDY OF MECHANICAL CONCEPT. DOING PROJECT WORK RELATED TO MECHANICAL CONCEPT. INTERACTING WITH TECHNICAL EXPERTS, HEAD OF DEPARTMENTS AND WORK FORCE. WE HAVE SELECTED DOLOMITE CRUSHING HAMMERS AS STUDY TOPIC AND LIFE IMPROVEMENT OF BULL HEAD HAMMERS AS LIVE PROJECT. PERIOD OF STUDY: THE PROJECT WORK HAS BEEN CARRIED OUT FROM 2-12-2007 TO 22-12-2007. INDUSTRY
: VISAKHAPATNAM STEEL PLANT.
AREA
: SINTER PLANT & QATD.
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CERTIFICATE
Mr.A.Sampath Mr.k.Stephen Small Mr.k.Pavan Kumar Has satisfactorily completed the project work entitled “LIFE IMPROVEMENT OF DOLOMITE CRUSHNING HAMMERS” in partial fulfillment of the requirement for the degree of Bachelor of technical in mechanical engineering during the academic year 2007-2008. Place: Visakhapatnam Date: 22-12-2007
T.VJ.RAMA GOPAL D.C.M (SP) PROJECT GUIDE
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ABSTRACT: The project “LIFE IMPROVEMENT OF DOLOMITE CRUSHING HAMMERS” is carried out in engineering shops and foundry. In sinter plant, crushing of dolomite is carried out by crushing machine in which hammers are the main components. But these hammers are not giving expected life. In order to overcome this failure we concentrate on two parameters. The main aim of our project is to improve the life of bull head hammer by forging the head as well as shank portion. After forging heat treatment process takes place in which the hammer is quenched in circulating water system.
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Introduction: Visakhapatnam Steel Plant, the first coastal based steel plant of India is located, 16km south west of Visakhapatnam. Bestowed with modern technologies, VSP has an installed capacity of 3 Million tones per annum if liquid steel and 2.656 Million tones of saleable steel. VSP Products meet exalting International Quality Standards such as JIS, DIN, BIS, BS etc... VSP has the distinction to be the first integrated steel plant in India to become an ISO-9001, EMS-14001&OHSAS-18001 certified company. These certificates cover quality systems of all operational, maintainance, services units besides purchase system, environmental management systems and occupational healthy safety measures. VSP by successfully installing and operating efficiently Rs 460 crores worth of pollution control systems and converting the barren landscapes by planting more than 3Million plants has made the steel plant, steel township and surrounding areas into a heaven of lush greenery. Having a total manpower of about 17250 VSP has envisaged a labor productivity of not less than 270 tones per man-year of liquid steel, which is the best in the country when compared with international levels. VSP exports quality pig iron and steel products to srilanka, Myanmar, Nepal, Middle East, USA& South East Asia(pig iron).RINL-VSP was awarded “Star Trading House” status during 1997-2000. It is also awarded with “Energy Conservation Award” at national level successively for three consecutive year’s viz., 2002, 2003, and 2004.
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MAJOR FACILITIES: Coke ovens
: 3 Batteries each of 67 ovens having7.0 meter height. Useful Volume 41.6cum.
Sinter Plant
: 2 Sinter Machines of Dwight Lloyd type having 312sq meter area.
Blast Furnace
: 2 Blast furnaces having 3200cu.meter useful each.
Steel Melting Shop
: 3LD converters having 133 cu.meter volumes each and 6 no’s of 4 strand continuous bloom casters.
LMMM
: 7, 10,000tons per annum capacity a9rateda0.
WRM
: 8, 50,000 tons per year capacity (rated).
MMSM
: 8, 50,000 tons per year capacity (rated).
Besides these a captive power plant with a capacity of 284MW Oxygen Plant, Acetylene Plant, Compressed Air Plant, extensive repair and maintenance units are available at VSP. It has sufficient infrastructure to expand the plant to 10Millon tones per annum of liquid steel capacity.
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PLANT LAYOUT:
RAW MATERIAL
COKE OVENS
SINTER PLANT
BLAST FURNACE
STEEL MELTING SHOP
CONTINUOUS CASTING SHOP P R O D U C T
LMMM MMSM
MILLS
WRM
LMMM: Light & Medium Merchant Mill. MMSM: Medium Merchant & Structure Mill. WRM : Wire Rod Mill.
Sinter Plant: WHAT IS SINTER? Sinter is agglomeration of fine particles of iron ore, limestone, dolomite, coke fines and metallurgical wastes obtained by the application of heat which results in conventional of these fines in to large, hard and porous lumps.
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The formation of lumps is caused by: An incipient fusion of these particles at contact surface which binds them together. The formations of diffusion bond through crystallization and crystal growth of hematite and magnetize which keeps these particles together. WHY IS SINTERING NEEDED?
Sintering increases the productivity of Blast Furnace. Improves the quality of pig iron. Thermal load to blast furnace decreases. Improves in size grading. Blast furnace movement is smoother. Elimination of 80-90% sulphur and minimum quantity of volatile matter si charged in to blast furnace.
SINTER PLANT LAY OUT RMHP BLAST FURNACE
RMB
SCREENING
BASE MIX YARD
BELT CONVERYS
SINTER MACHINE
STRAIGHT LINE COOLER
CRUSHERS
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SINTER PLANT - An over view The process of sintering involves agglomeration of fine ore particles along with necessary additions of flux and carbonaceous materials. Sintering accommodates variety of metallurgical wastes that are generated in integrated steel plants and thus takes care of waste disposal problems. Sinter plant of VSP has the capacity to produce 5.256 MT of sinter per annum, which will cater for 80 % of Iron bearing feed to Blast furnace. Two Sintering machines of Dwight Lloyd type having 312 M2 total grate area are provided for this purpose. Sinter machine is designed to operate at the rate of 1.2 T/hr/M2 for 330 days in a year. Sinter plant is having flux crushing plant in addition to other units for making sinter. Salient features of plant 1.
Independent, closed circuit crushing and screening of flux materials(lime stone and dolomite).
2.
Two-stage proportioning of raw mix.
3.
Blending facility for base mix.
4.
Separate mixing and nodulising palletizing drums.
5.
Three-stage screening of sinter.
6.
Electrostatic precipitators for cleaning dust laden gas and air.
7.
sinter machine exhausters of big capacity’
8.
Dirty water re-circulation and slime recovery.
9.
Complete recycling of different wastes generated in sinter plant.
10.
Open sinter storage of capacity of 60,000 T.
VARIOUS STAGES IN SINTERING •
Receiving and preparation and storage of raw materials.
•
Primary proportioning of raw materials to make ‘base mix’.
•
Base mix pile stacking and reclaiming to get sufficient blending.
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Secondary proportioning of blended base mix, sinter returns/ screenings trimming addition of flux and coke in order to make sinter mix.
•
Granulation of sinter mix in pellitizing(nodulising) drum with optimum water addition.
•
Loading of sinter mix on sinter m/c pallets, ignition of sinter mix bed surface to commence sintering operation, sintering of whole bed with application of suction from bottom of pallet gate.
•
Crushing of sinter to separate different size fractions and sinter dispatch to BF/storage yard.
Flux Crushing Plant: Flux crushing plant consists of four reversible Hammer crushers to crush Limestone and Dolomite to – 3 mm. Limestone of 6 to 80 mm size and Dolomite of 6 to 80 mm size are received from raw material handling plant. Crushers are fed with the help of vibro feeders. The crushed material is conveyed to screening plant by a conveyor.
COMPONENTS OF CRUSHING EQUIPMENT: Armour plates Grate bars Impact plates Bore beams Rotor Hammers etc. are the some of the main components of crushing equipment. Among the above mentioned, Bull head hammers are the critical components which are subjected to high impact loads and are prone to greater wear. So these hammers play a key role in assessing the performance of crushing plant.
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HAMMER CRUSHER HAMMERS
COUPLING
BEARING BEARING
FIVE ROWS OF NINE HAMMERS EACH ARE THERE. TOTAL 45 NOS. OF HAMMERS ARE THERE IN ONE CRUSHER.
SCHEMATIC REPRESENTATION OF HAMMER CRUSHER AT VSP
SECTIONAL VIEW OF ARRANGEMENT OF HAMMERS 1
2
3
X X
X
X
6
7
X X
X X
X
5
X
X
X
4
X
X
Hammer
10
11
X
13
X
15
X
17
X X
X X
X
16
X X
X X
14
X X
X X
12
X X
X X
9
X
X
X
8
X X
X X
X
X X
X
X
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DETAILS OF BULL HEAD HAMMER PURPOSE OF BULL HEAD HAMMER: Out of the spares supplying by ES&F, Bull head hammer is one of the important spares, which is used in Hammer crusher of Sinter Plant for crushing of
NECK AREA
120 mm
100 mm
100 mm
SCHEMATIC DIAGRAM OF BULL HEAD HAMMER
Dolomite and Limestone. These hammers are made in Forge shop and Central machine shop. In Forge shop, raw materials is forged to the required shape, stress relieved/annealed and send to CMS for further operations like drilling and heat treatment .The raw material for bull head hammer is being procured from M/s VSNL, BHADRAWATI, and the material specification is 50CrMO4. Average life of Bull-head hammer is 60 hrs Technical specifications OF BULL HEAD HAMMERS as per drawing:
14 1. Hammer is to made by stamping. 2. Hammer should be weighed and weights. Punched on bullhead hammers. 3. Surface defects like laps and cracks are not allowed. 4. The compensation hole is to be drilled if the weight exceeds 17.6 kg 5. Hammers are to be heat treated up to 380- 500 BHN.
MATERIAL COMPOSITION OF 50CRM04: C : 0.46-0.54, Cr : 0 .9-0.12, Mo: 0.25-0.3, Hotrolled, spherodoisedannealed Si : 0.15-0.4, Mn : 0.5-.8, P : 0.03 max, S : 0.03 max,
Qualities required by BHH are 1. Hardness 2. Toughness 3. Wear resistance 4. Ultimate tensile strength HARDNESS- It is a fundamental property which is closely related to strength. It is defined as resistance to abrasion / penetration. It also includes resistance to cutting & scratching. Its unit is N/mm2 .hardness of bull head hammer should be 380 to 500 BHN range. it should not be less it should be increased. TOUGHNESS – It is defined as amount of energy required for fracture. The toughness of a material is its ability to withstand both plastic & elastic deformation. So it is a desirable quality of bull head hammer.
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WEAR RESISTANCE - Bull head hammer should have sufficiently wear resistance. if it is not there then it will be worn out faster ,leading to the low life of BULL HEAD hammer. UTS (ULTIMATE TENSILE STREGTH) - The strength of material is its capacity to withstand destruction under the action of external load. The stronger the material the greater the load it can withstand. it therefore determines the ability of a material to withstand stress without failure. The maximum stress that any material will withstand before destruction is called its ultimate strength. This is the desired quality of BHH as it is under continuous stress while crushing of limestone and dolomites in hammer crusher. THE ABOVE QUALITIES CAN BE ACHIEVED BY THE HEAT TREATMENT PROCESSES.
FOLLOWING
HEAT TREATMENT - It is defined as an operation or combination of operations involving the heating and cooling of metal or alloys in the solid state to produce certain desired properties. All heat treatment processes may be considered to consist of three main stages. 1. The heating of the metal to to predetermined temp. 2. The soaking of metal at that temp until the structure becomes uniform throughout the mass. 3. The cooling of the metal at some predetermined rate to cause the formation of desired structure within metal/alloy for desired purpose. 4. ANNEALING - The purpose of annealing is to soften the steel so that it may be more easily machined and to relieve the internal stresses which may have been caused by working the metals or by unequal contraction in casting .The process of annealing involves heating the metals slowly to the required temp , then holding at that temp for long enough to enable the internal changes to take place and finally cooling slowly . Annealing reduces the hardness, increases ductility and usually reduces its strength.
16 HARDENING- Hardening is a heat treatment process .It is made to develop high hardness to resist wear as well as to improve strength, elasticity, ductility and toughness to the material. Hardening process consists of heating the steel to a temperature above critical point, holding at this temp for considerable period and finally quenching in water, oil or molten salt bath. TEMPERING - When a steel specimen has been fully hardened, it is very hard and brittle and has high residual stresses. The steel is unstable and tends to contract on aging. The internal stress can be relieved by an additional heating process. This heating process is called tempering. After specimen has been fully
hardened by
quenching from above critical temp, it is reheated to some temp below the critical temp for a certain period of time and then allowed to cool in still air. The temp to which it is reheated depends upon the composition and the degree of hardness or toughness desired. Tempering reduces the elastic limit and ultimate strength lightly but they are still higher than they were before drawing.
Hardening with subsequent
tempering serves the following purposes for bullhead hammer. It develops high hardness to resist wear and to enable it to cut another metals. It also improves strength, elasticity, and ductility. Tempering is a term historically associated with the heat treatment of martensite in steels. It describes how the microstructure and mechanical properties change as the metastable sample is held isothermally at a temperature where austenite cannot form. The changes during the tempering of martensite can be categorized in to stages. During the first stage, excess carbon in solid solution segregates to defects or forms clusters within the solid solution. It then precipitates, either as cementite in low-carbon steels, or as transition iron-carbides in high-carbon alloys. The carbon concentration that remains in solid solution may be quite large if the precipitate is transition carbide. Further annealing leads to stage 2, in which almost all of the excess carbon is precipitated, and the carbides all convert into more stable cementite. Any retained austenite may decompose during this stage. Continued tempering then leads to the coarsening of carbides, extensive recovery of the dislocation structure, and finally to the recrystallisation of the ferrite plates into equiaxed grains.
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HARDNESS PROFILES IN HEAT TREATED CARBON STEELS Carbon steels have low hardenability. Historically this was beneficial in that forged blades could be water quenched giving a 1-4mm “hard skin” (martensite) with “softer” core (pearlite). Such blades (digging tools, chisels) were attractive as when the “hard skin” wore off they could be reheated (extended life). Hence on water quenching the surface hardness greatly exceeds the axial hardness. As carbon content increases so does the gradient. Carbon
Water quench
hard skin
softer core
Which functionality is associated with each of these hardness profiles? •
Hard skin/ Softer core
Wear resistance without
fracture. •
Hard skin/ hard core
wear resistance but fracture on
shock load. •
Soft skin/soft core
wear without fracture.
BASIS FOR SELECTING 50 CR MO4 AS RAW MATERIAL FOR BULL HEAD HAMMER COMPOSITION OF 50CRM04: C : 0.46-0.54, Cr : 0 .9-0.12, Mo: 0.25-0.3,
Hot rolled, spherodoised annealed Si : 0.15-0.4, Mn : 0.5-.8, P : 0.03 max,
18 S
: 0.03 max,
CHROMIUM(Cr) – The addition of chromium results in the formation of various carbides of chromium which are very hard , yet the resulting steel is more ductile that a steel of same hardness produced by a small increase in carbon content. Chromium also refines the grain structure so that these two combine effect results in both increased toughness and hardness. The addition of Cr increases the critical range of temperature and raises strength at the high temperature. Alloy of chromium resists abrasion and wear. MOLIBDENUM ( Mo) – It acts very much like Cr but is more powerful in action. It also increases depth of hardness after heat treatment. Mo finds its greatest use when combined with the alloying element Like Cr, Ni, or both. Mo increases critical range of temp. Except for carbon it has the greatest hardening effect and results in the retention of a great deal of toughness. SILICON- It is added to all steels as deoxidizing agent. When added to very low carbon steels it produces a brittle and a high magnetic permeability. The principal use of silicon is with other alloying element, such as manganese, chromium, and vanadium to stabilize carbides. MANGANESE- It is added to all low and the manganese content is high over one percent, then it is classified as a manganese alloy. It lowers the critical range of temperature. SPHERODOISED ANNEALING – The mach inability of high carbon tool steel is at its best condition when the structure is composed of grained or globular pearlite. An alloy steels, including those of the carbide class, as well as ball bearing steels should have a structure of globular pearlite in the deliverable state. The process of producing a structure of globular pearlite is known as spheredoising or spherodoised annealing.
Effects on properties due to Annealing: Since full annealing restores the material to a strain-free lattice structure, it is essentially a softening process. Property changes produced by plastic deformation are removed, and the material returns very nearly to its original properties. Therefore,
19 during annealing, the hardness and strength decreases, whereas the ductility increases. some useful graphs are
20
Martensite transformation is first defected at Ms and is virtually completed at Mf .Between Ms& Mf austenite is retained as a result of induced stress.
MANUFACTURING PROCESS OF BHH Raw material is procured from VISL. Material is 50CRMO4.Raw material size is 6000x100x 100mm.
Process involved in forge shop1. Length is reduced to 3 m by gas cutting. 2. Heat treatment is done in bogie type hearth furnace in order to reduce hardness from range of (236 to 246) to 170 BHN. 3. Shearing of billet. Size of the billet is reduced to 100x100x217mm.
21 4. Heating is done in fixed hearth type furnace for forging operation. Heating is done up to 1250.c. for 5 hrs. At the rate of 200.c / hr heating is done then half an hour soaking is done. 5. With the help of manipulator and open die hammer, manual forging is done. Only 90 mm size is forged. Shank portion width is made to 36 mm. And total length is made to 360 mm. shank portion length is kept as per drawing equal to 193.5 mm. for checking the size during the process template is used. After this process the BHN of BHH is approx 350BHN. 6. Annealing is done after forging in order to reduce hardness from 350 to 220 .so that drilling may take place successfully. Room temp loading is done for annealing, it is heated up to 500.c at the rate of 150.c /hr then half an hr soaking again heating at the same rate up to 850 .c then one hr soaking. Then furnace cooling is done for 38 hrs. Due to this annealing hardness come down to 210-220 BHN. 7. Inspection is done with respect to shape and size of BHH. 8. BHH is sent to Central Machine shop after inspection. They are sent in batch as Batch size is 400 jobs per batch.
PROCESS INVOLVED IN CENTRAL MACHINE SHOP(a) A hole of 50 mm dia. is made in shank portion of BHH as per drawing. If required another hole is also drilled in order to control the weight of BHH. (b)Hardening - heat treatment is done in CO gas fired fixed hearth type furnace. it is twin chamber type. Heat treatment cycle for BHH is-
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(1) Heating the hammers up to 600 +0+25 at a constant rate of 150.c /hr. (2) Soaking at 600.c for 30 minute. (3) Raising the temp from 600.c to 875.c at 100.c/hr. (4) Soaking at 875+0+25 for 2 hrs. (5) Quenching in recirculating water up to 100 mm.
c)TEMPERING500 400
Soaking
300
Heating
(1hr) Air Cooling
100 OC / Hr
200 100
time TEMPERING CYCLE FOR BHH
Tempering is done in carburising furnace. (1) Heating the job up to 350 +0+25at a const rate of 100.c / hr
23 (2) Soaking of the hardened hammer at that temp for one hr (3) Hammers are allowed to cool to room temp in air. Inspection is done by CPS for the purpose of hardness checking.
Inspection procedure: After completion of tempering BHH is offered for inspection for checking the hardness in addition to dimensional checking. Inspection is carried out by CPS. Inspection of BH Hammers is done by sampling as it is of mass productive nature. In case of sampling inspection lot size is chosen to keep the number of jobs between 50 to 70 and about 20% of jobs are inspected (next higher integer if 20% of fraction (Lot is accepted only if the rejection rate is less than or equal to 2% of the lot size (next lower integer incase of if 2% is fraction). 100% inspection is done if sampling inspection rejects the lot. On each job work order number and date of inspection are marked to indicate that inspection is done. Accepted hammers whose hardness in between 380 to 550 BHN are marked ‘OK’. Hammers which are of low hardness, consisting of cracks, dimensional inaccuracy like drill hole position, are coming under Rejected jobs which are marked ‘REJ’ and jobs for rework are marked R/W.
1 PROCESS FLOW DIAGRAM FOR BHH 2 1. TRANSPORTATION 2. SHEARING OF BILLETS 3 3. HEATING FOR FORGING UPTO 1250.C 4. FORGING 5. ANNEALING FOR SOFTENING 6. INSPECTION FOR DIMENTIONAL CHECKING
7. TRANSPORTATION TO CMS
4
5 6
7
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8. DRILLING OF 50 MM HOLE
8
9. HARDENING
9
10. TEMPERING
1 0
11. SAMPLING 12. INSPECTION FOR HARDNESS CHECKING
1 1 12
13. TRANSPORTION TO CUSTOMER 13
Problems are being faced by Sinter Plant wrt BHH.
LOW LIFE
FRACTURE
INCREASE IN DOWN TIME OF CRUSHERS DUE TO FREQUENT HAMMER CHAGING
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POOR CRUSHING
LOW PRODUCTION
HIGH PRODUCTION COST
HIGH MAINTENANCE COST
INDUSTRIAL RELATION PROBLEMS
INTER DEPARTMENTAL RELATIONS
CUSTOMER SATISFACTION Lowlife and High WEAROUT of the hammers is identified as the root cause for all above problems initiating alternatives for making a better Bhh.
26 The wearing of bull head hammer in sinter plant May be due to high temp generated and strong impact between hammer and dolomite. We can cool it by circulating cool air the spark (heat) generated will be given less time to propagate through the material and change the grain size and deformation. Another idea is pre-crushing of the dolomite ore installing one more raw material handling plant. if we want to enhance the life of hammer without any changes in the current process we can focus on two areas. 1. heat treatment 2. chemical composition and its behavior and at high temp Heat treatment as we have already discussed what heat treatment is, we concentrate on whether the treatment is good or not. We are quenching after the heat treatment and sending them to sinter plant if we temper (reheating) the brittleness can be reduced. Another thing is the hammer is made of 50crmo4 while the shield is made of 40cr4. The hammer which is rotating at 1000rpm is wearing quickly than the shield which is stationary the idea is to make the hammer with the same material as that of shield. Another idea is to change the shape of the hammer without changing the composition is a risky one because the people working there are facing difficulty in lifting them every time.
Considering the heat treatment process The bottom surface of the hammer is in contact with the floor of the furnace. If we keep the bottom portion of the hammer open to air by means of a shaft as shown in fig.
27 The heat treatment should be done at a proper temp. The best temp suitable foe heat treatment is 723c. The current system heat treatment is done at 816c. Since martensite is formed from the austenite by diffusion less, two step shear transformation it has the same composition as austenite. Martensite is appreciably harder than the equilibrium combination of ferrite +carbide. During quenching martensite is formed. The formation will be more if the time given for quenching is less by means of relatively cool water than we are using now. The outer surface will be harder. We should also take care about the brittleness if we cool fast it will be more brittle. So tempering should be done to reduce the brittleness. So our point out interest is to maximize the amount of martensite in the quenched hammer.
BULL HEAD HAMMER ANALYSIS – Three bull head hammers have been studied for analysis to identify the reasons to improve the life of bull head hammers in crushers of Sinter Plant. This hammer was broken at neck portion while crushing, was sent for study in QATD (Quality assurance and technology department) for its micro structure. The following are the pictures of broken Bull head hammer.
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REASONS AND SUGGESTIONS (a) As per technical specification given in drawing, hammers may be tried by stamping (b) Heat treatment as per proposed cycle is difficult to achieve due to poor functioning valves, actuators. (c) Heat transfer rate is difficult to achieve in furnaces since there is no facility of considering time factor during heat treatment. to control the heat treatment , pyrometer may be used for checking temp of different bullhead hammer at different areas of furnace. According to this measured temp , different burners of heat treatment furnace may be kept on or off so that uniform temp of each bull head hammer may be achieved as per proposed heat treatment cycle. (d) Tempering
furnace also has no facility to control the heat transfer rate. Air-
cooling is not being done. (e) Temperature control of hammers inside furnace is difficult to achieve uniformly. Procurement of a heat treatment furnace, which can be controlled automatically, will reduce the problems related to heat treatment of bull head hammers. (f) Magnetic testing is not done Quench cracks also come during quenching of bull head hammer... Magnetic testing may be done in order to avoid any quench cracks. (g) Toughness testing is also not being done Toughness is important property in consideration of bull head hammer failure. If it is less it is more prone to failure. Right now there is no provision for checking
29 of toughness of bull head hammer. Izod impact test / charpy test may be done on sample basis. (f) Improper quenching due to formation of water bubble. While doing quenching, it is proposed that quenching should be in up to max 100 mm in head area, but due to boiled water bubble formation length may goes up to high. So proper checking of stand dimension, proper height should also be maintained carefully.
(g) Proper care during heat treatment can be done; pyrometer may be used for checking temp of different bullhead hammer at different position. According to this measured temp different burners of heat treatment furnace may be kept on or off so that uniform temp of each bull head hammer may be achieved as per proposed heat treatment cycle. (h)While doing quenching, it is proposed that quenching should be in up to max 100 mm in head area, but due to boiled water bubble formation length may goes up to high. So proper checking of stand dimension, proper height should also be maintained carefully. (i) Due to not proper recirculation of water, in quench area steam layer forms, which resists further cooling and contact of water. So it is desired that proper recirculation of water may take place to perform proper quenching. (j)Range of hardness as per drawing is 380 to 500 BHN. This large range may lead to variation of properties of each and every bull head hammer. This range should be minimized in order to get uniform properties of each and every bull head hammer.
30 CONCLUSIONS AND RECOMMENDATIONS: 1. Forging is done for the handle portion only. If the head can be forged it will give better mechanical properties for the hammer. Chances of better hammer life will be more. 2. The existing recommended range of hammer hardness is 150 BHN i.e. from (380BHN-530BHN) which is very broad band. This may be reduced to a narrow band of 60BHN i.e. from 470BHNto 530BHN. 3. If the heat treated cycle of sangham hammer is known it is possible to increase to life of the hammer up to 110-120 hrs. 4. Manufacturing of hammers by stamp forging instead of open die forging may also result in improvement of life time due to the formation of uniform grain structure throughout its length. 5. Productivity may also be increased by crushing the raw material in two stages.
BIBLIOGRAPHY:
1. Workshop technology by HAZRA CHOUDARY. 2. Machine design by Dr P.C. SHARMA & Dr D.K.AGARWAL. 3. Alloy steel plant product profile & manual By SAIL. 4. Physical metallurgy by Abnur 5. Material science BY RAGHWAN 6. Introduction to physical metallurgy by AVNER 7. Mechanical metallurgy by GEORGE E.DIETER
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