“A CASE STUDY ON FAILURE OF

BULL HEAD HAMMER FOR LAST THREE MONTH” PRESENTED BY – SONIA PRIYADARSHINIMT (T),CPSEngg Shops&Foundry

GUIDED BY-

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ACKNOWLEDGEMENTS

Project completion fetches any individual, a fair amount of happiness,

which cannot be expressed in words. I feel in the same way after the successful

completion of my project. It happened only because of some esteemed co-

operation from some people.

With a great sense of pleasure & previlage i m happy to express my deep sense of

gratitude to my project guide Mr. V. CHITTI BABU, DCM (CPS) ES&F, whose

support and encouragemant have been a constant push up to undertake this

project.

In this regard I am deeply indebted to Sri .P .Subba Rao D.G.M. Engineering

shops &Foundry , Visakhapatnam Steel Plant, who has given valuable information

and suggestions in completing my project work.

I would also like to express my sincere thanks to all who helped

directly and indirectly for successful completion of this project.

Sonia Priyadarshini

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CERTIFICATE

This is to certify that this project report entitled “A case study on

failure of BULL HEAD HAMMER at Sinter Plant” is a bonafied work

done by Mrs. SONIA PRIYADARSHINI an MT(T) ,CPS ES&F , under my

guidance and supervision .

V.CHITTIBABU Dy.Chief Manager

(Engg Shops&Foundry)VisakhapatnamSteel plant

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A Case study on“Failure of Bull head hammers for the last three months”.

INTRODUCTION Engineering Shops and Foundry Department caters to the needs of ferrous

and nonferrous spares of different departments. ES&F manufactures as well as

repairs the job as required by Customer departments. ES&F has various sections

like CENTRAL MACHINE SHOP, STRUCTURAL SHOP, FORGE SHOP, FOUNDRY

SHOP, and UTILITY EQUIPEMENT REPAIR SHOP. Central planning section is the

main planning section of Engg shops and foundry and it works as a bridge

between Customer departments and shops of ES&F. Central Machine Shop(CMS)

is having facilities for turning boring, milling, thread cutting and various

machining operations. Heat treatment furnaces, equipments for assembly &

dismantling are also available in CMS. Forge shop as name indicates, forging is

the main function of this shop. It produces shafts couplings, flanges, Drill rods for

BF, bull head hammers for SP, V-hooks for SMS etc. In Structural shop,

fabrication and repair of structural jobs are done. UERS is responsible for repair

and manufacturing of small spares, impellers, valves etc. In Foundry, casting of

cast iron, cast steel and non-ferrous materials of different shape and size as

required by the customer.

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

Dolomite and Limestone. These hammers are made in Forge shop and Central

machine shop. In forge shop, raw material 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, but for the last three months its average life has

drastically come down to 30hrs. I am going to study on failure of bull-head

hammers and the reasons for decrease of life. In my project, I am also trying to

suggest what modifications may be possible regarding raw material, processes

so that life of the Bull head hammer may be enhanced as well as breaking/fracture

can be minimized which will ultimately effect saving of raw material , production

cost and equipment availability.

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Engineering shops & foundry

Engineering shops & Foundry is set up to meet the requirements of Ferrous &

non-ferrous spares of different departments. Engineering shops & Foundry is

divided into Central Machine Shop, Steel Structural Shop, Forge shop, Foundry

and Utility equipment repair shop.

DESCRIPTION OF SHOP FACILITIES

CENTRAL MACHINE SHOP

INPUTS:- Iron & Steel castings, forgings, rolled sections, repair and rectification

parts, non ferrous castings,fabrication structure.

Products and Services:- Shafts, Pinions, Gears, Crane Wheels, Rollers,

Machining of various fabrication jobs done in SSS, Repair & reconditioning

of various assembly jobs like L&T Column, TK stands, pulleys, revisioning

of gear boxes.. For preparing them for machining, metal cutting saws,

facing and centering machines, hacksaws, and gas cutting facilities are

provided. The machining section has over 100 major machine including

lathes, milling, boring, and planning slotting shaping, grinding and other

machines. The assembly section undertakes medium repair and general

overhauling of mechanical equipment. Horizontal and vertical presses,

washing tanks, oil berths etc. are provided. The tool room has facilities for

manufacture of special tools, jigs and fixtures, re-grinding of tools and

cutter and brazing of tipped tools. The heat treatment section is provided

with annealing, normalizing, heat tempering furnaces, carbonizing furnaces,

heat treatment furnace with protective gas atmospheres, high frequency

hardening machine, quenching tanks oil cooling arrangements, welding

generator and transformers for normal welding, sub-merged arc welding

machine etc. Facilities for surface grinding, pipe bending and threading are

provided.

FORGE SHOP

Inputs: Ingots from foundry, blooms from SMS, billets, rods from mills etc.

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Products: Raw material for shafts, couplings, gears, pinions, flanges bull head

hammers for sinter plant hammer crusher, drill rods for blast furnace, v-hooks for

SMS, straightening of pallet middle frames of sinter plant.

The shop is designed for production of shafts, coupling:- flanges etc.

and also of forged shapes such as crusher hammer heads, special bolts, nuts,

etc.The repair and testing of chains are also carried out. The annual production

from the shop is about 2,400 tons based On 300 working days per year and two

shifts per day. These inputs consisting of ingots, billets, blooms and flats of

various sizes.

In heavy forging section, open die forgings of long shafts, gear blanks,

couplings etc. is made with the help of 2-ton bridge type pneumatic hammers.

Each hammer will be provided with twin chamber heating furnaces. Floor type

manipulator and Jib Crane are provided for handling heavy jobs. In general

forging section, 1 ton, 500 Kg, and 200 Kg hammers with separate heating

furnaces are provided. A 2 ton drop stamp hammer with a heating furnace

trimming press etc. is provided for stamping. For cutting them to size, a cold saw,

a billet shear and gas cutting facilities are provided. For stress relieving, a bogie

type-annealing furnace is provided.

STRUSTURAL SHOP

Inputs:- Sheets of various sizes, plates, angles, channels, beams for fabrication

of jobs.

Production & services: All types of fabrication jobs, repair of slag pots of

SMS, Mfg. And repair of tundishes for SMS, Mfg. Of scrap boxes for SMS, for

sinter plant, hot metal ladle for SMS, 500 metres launder for SMS, mfg. Of KAMAG

body for FMD, repairing of buckets for LMMM, WRM.The annual production of

fabricated structures are about 4,500 tones and the input consisting of sheets,

plates, channels, angles, beams etc. are, about 5,100 T .

For marking, cutting to size, forming and bending, guillotine shear,

circular saw plate bender, gas cutting unit etc. are provided. For welding

transformer, automatic and semi-automatic machines and submerged arc welding

machines are provided. Painting is carried out partly with help pf spray guns and

partly by hand. Wire brush, spray guns etc. are provided. A maintenance section

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equipped with lathe, shaper, drill etc. are provided for running repair of shop

equipment.

FOUNDRY

Inputs: Pings, MS scrap, ferro alloys, graphite electrodes, sodium silicate, silica

sand CO2 gas, moulding additives etc.

Products: Steel, cast iron & non ferrous castings, Emergency containers,

tundish covers, bull gear for SMS, hot metal runners, ladle paw for blast furnace,

coke roll liners, sprockets, pallets for sinter plant, raw supports, bowl for RMHP,

guide troughs for WRM, face of scrap bucket for MMSM, slag pot segments for

SSS repair, ingots for forge shop, non ferrous castings like bushes (below 20 kg)

etc.

Iron castings up to a weight of 5 tons will be produced. A main frequency

coreless induced furnace with two 2-ton capacity crucibles and a 5T capacity

main frequency coreless induction furnace for melting iron are provided. There is

a centralized sand preparation unit. A drier and a bin is be provided for green

sand. Belt conveyors transport green sand, prepared mix and burnt sand.

Moulds and cores are drier in 3 ovens lip pour ladles with capacity between 50 kg

and 10 tons is provided for handling hot metal. Two swing frame grinders and two

pedestal grinders are provided for finishing of iron castings.

Steel castings up to maximum piece weight of 10 T and Steel Ingots up

to 1.3 tons for forging are produced. An 8 Ton direct arc furnace and a two-ton

medium frequency electric induction furnace is installed for melting of steel scrap

and pig iron. Each of the two sand mixers is having 1.5-ton batch. A bogie hearth

furnace for annealing/ normalizing of plain carbon steel castings and fixed hearth

furnace for heat treatment of manganese steel castings with quenching facility is

provided. The woodwork shop manufactures patterns for foundries. The principal

equipment for pattern making will be band saws, disc grinding, wood working

lather, adequate facilities are provided for saw grinding, painting, timber and

pattern storage etc.

UTILITY EQUIPMENT REPAIR SHOP

Inputs: sheets, plates, channels, angles, beams, billets, rounds for forge shop for

mfg. Shafts, steel and iron castings.

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Products & services:- Mfg. Of impellers to various departments, repair of GCP

Id fan, repair of steam exhausters for SMS, supply of cones & ducts of various

sizes, in house manufacturing of MBC impeller for CCCD, buildup & machining of

various components, reclamation jobs like valve repairs, conveyor idlers, PCM

rollers etc.

Repair of ventilation, air conditioning and water supply equipment is

also carried out here. There is a machining section having 15 major machines like

lathes, milling, slotting, shaping and grinding machines, Sheet bending machines,

Guillotine shear & semi-folding machine are provided in fabrication section. 250

kg pneumatic hammer with necessary facilities and a welding section for semi

automatic, automatic and shielded are welding machines are provided in

plumbing section. There is a separate equipment repair section.

CENTRAL PLANNING SECTION (CPS):

Central planning section of Engineering Shops & Foundry plays an

important role in coordinating various departments and the shops of ESF for

supply of spares, castings, fabricated structures and repaired .

Scrutiny of annual jobs, monthly jobs projected by customer

dept.Preparation of monthly plan based on annual, monthly and MBC

projection

Preparation of material procurement plan based on the annual requirement

Issue of B/D, MBC and Normal work orders to section based on Work

Requisitions from Customer Depts.

Inspection of semi/ finished jobs of 5 sections

Daily monitoring of jobs progress and preparation of daily production

report

Weekly reviewing B/D jobs

Monthly monitoring of MBC jobs

Preparation of monthly progress

Preparation of feed back report and sending to customers every month

Computerization of details of inter-shop and dispatch to depts.

Drawings control as per the ISO guidelines

Looking after Excise formalities of ESF

Attending MOU meetings of customer depts.

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FLOW CHART OF WORK ORDERand

JOB PROCESSING

CMS - CENTRAL MACHINE SHOP

SSS - STEEL STRUCTURAL SHOP

FS - FORGE SHOP

FDY - FOUNDRY

UERS- UTILITY EQUIPMENT REPAIR SHOP

CPS - CENTRAL PLANNING SECTION

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CUSTOMER

CUSTOMER

C

P

S

C

M

S

S S S

FDY

F S

UERS

SINTER PLANT - An over view

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.

Flux Crushing Plant:

Flux crushing plant consists of four reversible Hammer crushers to crush

Limestone and Dolomite to 0 – 3 mm. Limestone of 6 to 40 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.

HAMMER CRUSHER

DETAILS OF BULL HEAD HAMMER

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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 Dolomite and

Limestone. These hammers are made in Forge shop and Central machine shop.

In Forge shop, raw material 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:

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.

Qualities required by BHH are 1. Hardness

2. Toughness

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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 its ability to withstand both plastic & elastic

deformation. So it is a desiarable quality of bull head hammer.

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

dolamite in hammer crusher.

THE ABOVE QUALITIES CAN BE ACHIEVED BY THE FOLLOWING HEAT TREATMENT PROCESSES.

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 s of three main stages.

1. The heating of the metal to to predetermined temp.

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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.

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.

HARDENING- Hardening is a heat treatment process .It is made to devlop 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 categorised in to stages. During the first stage, excess carbon in solid solution

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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 a 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.

BASIS FOR SELECTING 50 CR MO4 AS RAW MATERIAL FOR BULL HEAD HAMMER

COMPOSITION OF 50CRM04:

C: 0.46-0.54, Si: 0.15-0.4, Mn :0.5-.8, P: 0.03 max, S: 0.03 max, Cr :0 .9-0.12, Mo 0.25-0.3, hot rolled, spherodoised annealed

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.

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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 machinability 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.

MANUFACTURING PROCESS OF BHH Raw material is procured from VISL. material is 50 CR MO 4.Raw material size is

6000x100x 100mm.

Process involved in forge shop-

1. 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.

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 350 bhn.

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.

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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-

(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.

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©TEMPERING-

Tempering is done in carburising furnace.

(1) Heating the job up to 350 +0+25at a const rate of 100.c / hr

(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 are 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.

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500

400 Soaking (1hr)

300 Air CoolingHeating 100 OC / Hr

200

100

TEMPERING CYCLE FOR BHH

time

PROCESS FLOW DIAGRAM FOR BHH

1.TRANSPORTATION

2.SHEARING OF BILLETS

3. HEATING FOR FORGING UPTO 1250.C

4. FORGING

5. ANNEALING FOR SOFTENING

6.INSPECTION FOR DIMENTIONAL CHECKING

7.TRANSPORTATION TO CMS

8.DRILLING OF 50 MM HOLE

9.HARDENING

10. TEMPERING

11. SAMPLING

12.INSPECTION FOR HARDNESS CHECKING

13. TRANSPORTION TO CUSTOMER

Problems are being faced by Sinter Plant wrt BHH.

LOW LIFE

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1

8

4

11

10

9

2

3

5

6

12

13

7

FRACTURE

INCREASE IN DOWN TIME OF CRUSHERS

LOW PRODUCTION

HIGH RAW MATERIAL COST

HIGH PRODUCTION COST

HIGH MAINTENANCE COST

INDUSTRIAL RELATION PROBLEMS

INTER DEPARTMENTAL RELATIONS

CUSTOMER SATISFACTION

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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.

FIRST BULL HEAD HAMMER: 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.

PICTURE 1

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PICTURE2

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Picture 1, 2 shows radial marks point to the failure origin

PICTURE-3

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Picture 3 shows quench cracks at the neck portion

PICTURE-4

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PICTURE-4 shows tempered martensitic structure at neck portion, hardness at this area is 50-53 RC

SECOND BULL HEAD HAMMER :- This hammer has given less life. The following

are the figures of Bull Head hammer whose life was <20 hrs .

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The above figure shows the absence of tempered martensite structure due to

improper heat treatment. When this BHH is checked for hardness, it’s hardness is

low, which shows softness of material resulting in low life.

Third BULL HEAD HAMMER - After implementing some suggestions like usage of

Fixture rod without bend for quenching, proper heat treatment and quenching, In

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the first week of march, one set of bull head hammers(45 nos.) has given life of

55 to 60 hrs .Two pieces in the size of 100x100x15 mm were cut from the head

portion of that bull head hammer and sent to QATD for detail analysis regarding

micro structure and hardness .

Micro structure at four points has been studied and it matches with our

requirement ,i.e existence of tempered martensite with hardness 380- 550 range

for BHH. The following are micro structure figures . Its hardness is in the range

450-525 BHN .

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the above figure consisting of tempered martensite which is obtained by

decomposition of austenite due to very rapid cooling and then quenching. It is

observed that needle like crystals in angular arrangements indicates the

existence of tempered martensite.

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The following figure shows the hardness indicating at different sections, at

different points which is the result of hardness test conducted in QATD.

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Hardness at different points has been done .From the figure it is very clear that

hardness at the side position ,which is directly exposed to water quenching is

more. As going at inside dimentions it is in the decreasing nature. Hardness at the

center of BHH head at three different thickness may also be compared .It is 573

BHN at surface, 451 at the next 15mm thickness and after 30mm it is 388 mm. This

trend shows heat treatment effectiveness slows down for inside positions.But it is

within our requirement.

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.

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Procurement of a heat treatment furnace, which can be controlled

automatically, will reduce the problems related to heattreatment 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 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

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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.

BABLIOGRAPHY

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.

31

4. Physical metallurgy by Abnur

5. Material science BY RAGHWAN

32