Heat Treatment Processes in Gear Design

8/20/2019 Heat Treatment Processes in Gear Design

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HEAT TREATMENTPROCESSES

IN GEAR DESIGN

Prepared By:- Kartik Thakkar

Website:- http://steps2learning.blogspot.com


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Heat TreatmentProcesses

It is a process of heating cycles here the

metal is s!b"ected to controlled temperat!re

changes in solid state. #eating process can

change the si$e and shape of grain str!ct!re

and can also change the constit!ents and

hence the properties of steel.


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%e-& e'!ilibri!m diagram shoing temperat!re ranges for (ario!s heattreatment processes.


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Types of Heat Treatment

).Annealing

2. Normalizing

*. Quenching or Hardening

+. Tempering

,. Surface Hardening

. Case Hardening

. Austempering. Marquenching

0. Ausforming


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Hardening Processes for Gears

There are mainly folloing * processes hich

are !sed for hardening the gears

1) Thro!gh #ardening

12 &ase #ardening:1a &arb!ri$ing3

1b 4itriding3

1c &arbo-4itriding.

1* 5!rface #ardening:

1a Ind!ction #ardening3

1b %lame #ardening.


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Thro!gh #ardening

This includes heating of the whole material to form austenite and


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CASE HARDENING

Case Hardening produces a hard, wear resistancecase or surface layer on the top of a d!ctile3 shock

resistance interior or core.

The idea ehind the case hardening is to !eep thecore of the gear tooth at a le"el around #$ to %$ H&C

to a"oid tooth rea!age while hardening the outer

surface to increase the pitting resistance

&ase hardening consists of three processes:1a &arb!ri$ing6

1b4itriding6

1c &arbo-4itriding.


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CARBURIZING

&arb!ri$ing is a heat treatment process in hich iron or steel

is heated in the presence of another material hich liberates

carbon as it decomposes3 at temperature etween '($ and

)($*C, at which austenite, with its high soluilit+ for caron,

is the stale crystal str!ct!re. #ardening is accomplished henthe high-carbon s!rface layer is '!enched to form 7artensite so

that a high-carbon martensitic case ith good ear and fatig!e

resistance is s!perimposed on a to!gh3 lo-carbon steel core.

ears are almost alwa+s oil quenched ecausedistortion must e held to the lowest possile le"el.

After case hardening, the hardness otained lies in the

range H&C (' to - ut in hea"il+ loaded gears a minimum

of H&C -$ is required.


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NITRIDING 4itriding is a s!rface-hardening heat treatment thatintrod!ces nitrogen into the s!rface of steel at a

temperature range of ($$ to (($*C, while it is in the

ferrite condition.

/ecause nitriding does not in"ol"e heating into the

a!stenite phase field and a s!bse'!ent '!ench to form

martensite3 nitriding can be accomplished ith a minim!m

of distortion and ith e8cellent dimensional control.

4itriding is done to to obtain high s!rface hardness3

increase ear resistance3 impro(e fatig!e life3 impro(e

corrosion resistance 1e8cept for stainless steels3 obtain a

s!rface that is resistant to the softening effect of heat attemperat!res !p to the nitriding temperat!re.


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Carbo-Nitriding &arbonitriding is one of most common type of case hardening

processes for gears &arbonitriding is essentially a modified (ersion of gas carb!ri$ing.

The modification consists of bringing in ammonia into the gas

carb!ri$ing atmosphere. This adds nitrogen to the carb!ri$ed case.

The nitrogen gets diff!sed sim!ltaneo!sly into the steel along ithcarbon.

9enerally a carbonitriding process is done at a loer temperat!re

and for a '!icker span of time than that of gas carb!ri$ing.

It has been fo!nd that after Caro0Nitriding of ears there has

een considerale impro"ement in useful life for man+ of thegears. Ad"antages for gears include temper resistance,

heightened luricit+ during cold start, etter strength of the

ase metal in terms of tensile, +ield and fatigue, an increase in

throughput, also elimination of prolems li!e quench

crac!ing.


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Surfac Hardning

This is a special hardening process in

hich a partic!lar s!rface of steel is

made hard itho!t altering the hardness

of any other portion. There are to types of s!rface

hardening processes

). Ind!ction #ardening2. %lame #ardening


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Induction Hardning

Ind!ction hardening is a heat treating techni'!e that can be !sed to

selecti(ely harden portions of a gear3 s!ch as the flanks3 roots and

tips of teeth3 pro(iding impro(ed hardness3 ear resistance3 and

contact fatig!e strength itho!t affecting the metall!rgy of the core

and other parts of the component that dont re'!ire change. 1nduction hardening does not require heating the whole gear.

2ith induction, heating can e localized to onl+ those areas in

which metallurgical changes are required. 3or e4ample, the

flan!s, roots and tips of gear teeth can e selecti"el+ hardened.

; ma"or goal of ind!ction gear hardening is to pro(ide a finegrain

martensitic layer on specific areas of the part.

54ternal spur and helical gears, worm gears and internal gears,

e"el gears, rac!s and sproc!ets are among the parts that are

t+picall+ induction hardened.


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Induction Hardening OfGears


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Flame Hardening The flame hardening of gear teeth is a so!nd in(estment since it

increases the life of the gear by abo!t , times. Flame hardening decreases both rolling friction and

deformation.9enerally there are to methods of flame

hardening gear teeth - spin hardening or progressive hardening .

With spin hardening all the teeth are heated < then '!enched.With progressive hardening indi(id!al tooth flanks are heated <

'!enched.

Flame hardening applies to most gear types - sp!r3 helical3 be(el3

spiral be(el3 herringbone and racks.

; ide (ariety of materials may be flame hardened incl!ding carbon

and alloy steels3 martensitic stainless steels and 59 cast irons.

9enerally steels ith appro8imately =.*,-=.,, percent carbon are

s!itable for flame hardening . &ast irons3 higher carbon and higher

alloy steels are s!sceptible to cracking < e8tra care sho!ld be taken

to red!ce this risk.


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Flame Hardening In Gears

%lame hardening process in


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y :- Kartik Thakkar ebsite:- http://steps2learning blogspot com

Heat Treatment Processes in Gear Design

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