Process Induction hardening

1 process

1.1 definition
1.2 history
1.3 principal methods

1.3.1 single shot hardening
1.3.2 traverse hardening


1.4 equipment

1.4.1 power required
1.4.2 frequency


1.5 advantages
1.6 applications

process

induction heating non contact heating process uses principle of electromagnetic induction produce heat inside surface layer of work-piece. placing conductive material strong alternating magnetic field, electric current can made flow in material thereby creating heat due ir losses in material. in magnetic materials, further heat generated below curie point due hysteresis losses. current generated flows predominantly in surface layer, depth of layer being dictated frequency of alternating field, surface power density, permeability of material, heat time , diameter of bar or material thickness. quenching heated layer in water, oil, or polymer based quench, surface layer altered form martensitic structure harder base metal.

definition

a used process surface hardening of steel. components heated means of alternating magnetic field temperature within or above transformation range followed immediate quenching. core of component remains unaffected treatment , physical properties of bar machined, whilst hardness of case can within range 37/58 hrc. carbon , alloy steels equivalent carbon content in range 0.40/0.45% suitable process.

a source of high frequency electricity used drive large alternating current through coil. passage of current through coil generates intense , rapidly changing magnetic field in space within work coil. workpiece heated placed within intense alternating magnetic field eddy currents generated within workpiece , resistance leads joule heating of metal.

this operation commonly used in steel alloys. many mechanical parts, such shafts, gears, , springs, subjected surface treatments, before delivering, in order improve wear behavior. effectiveness of these treatments depends both on surface materials properties modification , on introduction of residual stress. among these treatments, induction hardening 1 of employed improve component durability. determines in work-piece tough core tensile residual stresses , hard surface layer compressive stress, have proved effective in extending component fatigue life , wear resistance.

induction surface hardened low alloyed medium carbon steels used critical automotive , machine applications require high wear resistance. wear resistance behavior of induction hardened parts depends on hardening depth , magnitude , distribution of residual compressive stress in surface layer.

history

the basis of induction heating systems discovered in 1831 michael faraday. faraday proved winding 2 coils of wire around common magnetic core possible create momentary electromotive force in second winding switching electric current in first winding on , off. further observed if current kept constant, no emf induced in second winding , current flowed in opposite directions subject whether current increasing or decreasing in circuit.

faraday concluded electric current can produced changing magnetic field. there no physical connection between primary , secondary windings, emf in secondary coil said induced , faraday s law of induction born. once discovered, these principles employed on next century or in design of dynamos (electrical generators , electric motors, variants of same thing) , in forms of electrical transformers. in these applications, heat generated in either electrical or magnetic circuits felt undesirable. engineers went great lengths , used laminated cores , other methods minimise effects.

early last century principles explored means melt steel, , motor generator developed provide power required induction furnace. after general acceptance of methodology melting steel, engineers began explore other possibilities use of process. understood depth of current penetration in steel function of magnetic permeability, resistivity , frequency of applied field. engineers @ midvale steel , ohio crankshaft company drew on knowledge develop first surface hardening induction heating systems using motor generators.

the need rapid automated systems led massive advances in understanding , use of induction hardening process , late 1950s many systems using motor generators , thermionic emission triode oscillators in regular use in vast array of industries. modern day induction heating units use latest in semiconductor technology , digital control systems develop range of powers 1 kw many megawatts.

principal methods
single shot hardening

in single shot systems component held statically or rotated in coil , whole area treated heated simultaneously pre-set time followed either flood quench or drop quench system. single shot used in cases no other method achieve desired result example flat face hardening of hammers, edge hardening complex shaped tools or production of small gears.

in case of shaft hardening further advantage of single shot methodology production time compared progressive traverse hardening methods. in addition ability use coils can create longitudinal current flow in component rather diametric flow can advantage complex geometry.

there disadvantages single shot approach. coil design can extremely complex , involved process. use of ferrite or laminated loading materials required influence magnetic field concentrations in given areas thereby refine heat pattern produced. drawback more power required due increased surface area being heated compared traverse approach.

traverse hardening

in traverse hardening systems work piece passed through induction coil progressively , following quench spray or ring used. traverse hardening used extensively in production of shaft type components such axle shafts, excavator bucket pins, steering components, power tool shafts , drive shafts. component fed through ring type inductor features single turn. width of turn dictated traverse speed, available power , frequency of generator. creates moving band of heat when quenched creates hardened surface layer. quench ring can either integral following arrangement or combination of both subject requirements of application. varying speed , power possible create shaft hardened along whole length or in specific areas , harden shafts steps in diameter or splines. normal when hardening round shafts rotate part during process ensure variations due concentricity of coil , component removed.

traverse methods feature in production of edge components, such paper knives, leather knives, lawnmower bottom blades, , hacksaw blades. these types of application use hairpin coil or transverse flux coil sits on edge of component. component progressed through coil , following spray quench consisting of nozzles or drilled blocks.

many methods used provide progressive movement through coil , both vertical , horizontal systems used. these employ digital encoder , programmable logic controller positional control, switching, monitoring, , setting. in cases speed of traverse needs closely controlled , consistent variation in speed have effect on depth of hardness , hardness value achieved.

equipment
power required

power supplies induction hardening vary in power few kilowatts hundreds of kilowatts depending on size of component heated , production method employed i.e. single shot hardening, traverse hardening or submerged hardening.

in order select correct power supply first necessary calculate surface area of component heated. once has been established variety of methods can used calculate power density required, heat time , generator operating frequency. traditionally done using series of graphs, complex empirical calculations , experience. modern techniques typically use finite element analysis , computer-aided manufacturing techniques, such methods thorough working knowledge of induction heating process still required.

for single shot applications total area heated needs calculated. in case of traverse hardening circumference of component multiplied face width of coil. care must exercised when selecting coil face width practical construct coil of chosen width , live @ power required application.

frequency

induction heating systems hardening available in variety of different operating frequencies typically 1 khz 400 khz. higher , lower frequencies available typically these used specialist applications. relationship between operating frequency , current penetration depth , therefore hardness depth inversely proportional. i.e. lower frequency deeper case.

the above table purely illustrative, results can obtained outside these ranges balancing power densities, frequency , other practical considerations including cost may influence final selection, heat time , coil width. power density , frequency, time material heated influence depth heat flow conduction. time in coil can influenced traverse speed , coil width, have effect on overall power requirement or equipment throughput.

it can seen above table selection of correct equipment application can extremely complex more 1 combination of power, frequency , speed can used given result. in practice many selections obvious based on previous experience , practicality.

advantages

applications

the process applicable electrically conductive magnetic materials such steel.

long work pieces such axles can processed.