Induction hardening is one of the most common methods to increase the hardness on the surface and near-surface layer of the components. The component is fed through a ring type inductor which normally features a single turn. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. Review of Surface Hardening * Induction hardening (~67 HRC) (a) (b) Can be used on any type of steel Utilizes localized heating Has clean transition pattern Process takes less than 1 minute Nitriding (~69 HRC) (c) Uses ammonia or cyanide salt baths Depth of 1 mm Roughly 4 hours per work piece Carburizing (~50 HRC) Images of gear teeth hardened by (a) Used on low carbon content steel … Materials: Carbon Content: Hardness-HRc: Comments : 1019: 0.15 – 0.2: 30: Typically carburized : 1035: 0.32 – 0.38: 45: Can reduce by … This current passes chiefly through surface layers, i.e., eddy currents are more concentrated in the surface, and decreases in strength towards the centre of the object. 8.66. i. The depth of hardening below the base of the spline should at least be equal to the height of the spline ribs. Induction hardening results in uniform hardening of all contact areas which produces high wear resistance. Table 8.12 can be used for selecting the frequency of the current, based on hardening- depth needed, taking also into consideration equation 8.57. 8.63 (b) illustrates the temperature gradient during the process, and the Ac3 temperatures for different initial micro- structure. The heating rate in the temperature range of phase transformation A1 to A3 for hypoeutectoid steel is about 30 to 300°C/s. Case hardening places a hard case around the entire surface of the part while induction hardening hardens only the precise pattern defined by the inductor coil. Induction hardening is a process used for the surface hardening of steel alloys which require high wear resistance such as springs, shafts, gears and other alloy components. This region is called ‘heat affected zone’. Induction heating is a non contact heating process which uses the principle of electromagnetic induction to produce heat inside the surface layer of a work-piece. Single shot is often used in cases where no other method will achieve the desired result for example for flat face hardening of hammers, edge hardening complex shaped tools or the production of small gears.[6]. Flame hardening is similar to induction hardening, in that it is a surface hardening process. The width of the turn is dictated by the traverse speed, the available power and frequency of the generator. It was already understood that the depth of current penetration in steel was a function of its magnetic permeability, resistivity and the frequency of the applied field. These types of application normally use a hairpin coil or a transverse flux coil which sits over the edge of the component. The Fig. This method thus improves the wear resistance as well as bending strength of the tooth. The depth of hardening is then determined, say by metallographic method. Flame hardening is similar to induction hardening, in that it is a surface hardening process. The tighter (gap) the coupling between the component and the inductor, more strong magnetic field it contacts, more rapid is the rate of heating. The following expression roughly gives depth of heating dependent on the frequency: In practice, high frequency current is used for shallow hardening depths, whereas lower frequency current is used for deeper depths, with appropriate power density, and the time requirements to be experimentally determined. In magnetic materials, further heat is generated below the curie point due to hysteresislosses. Many methods are used to provide the progressive movement through the coil and both vertical and horizontal systems are used. This is because of the short austenitising induction times, and also that rapid heating rate increases its Ac3 temperature. In the induction hardening process of workpiece, the eddy current path, magnetic field migration, sharp angle and small hole will all produce uneven local heating temperature, resulting in hardness deviation and inconsistent depth of hardened layer. An accurate design requires exact detail about each gear tooth based upon the actual profile presented Figure 1: Macroetched cross-section showing differences in induction hardened case depth due to a 350ºF preheat. Special measures are taken to reduce the eddy currents to minimum level in transformers). Methods 5. For single shot applications the total area to be heated needs to be calculated. The normal power input is 0.1 – 2 kW/cm2 of the heating surface. This depends on the hardenability of the material, the section thickness and the flame hardening process used. 8.66 b), where compressed water-sprays quench it. Terms of Service 7. Each tooth is individually induction heated and quenched. In iron, hysteresis losses also contribute to some extent to the temperature rise up to curie point (768°C), above which iron is non-magnetic, i.e., above this temperature, the depth of penetration of the current increases (inverse to the frequency of the current) due to sharp decrease in magnetic permeability. For example, the central portions of the gears should not get heated up beyond 200°C, particularly of the gears with finish-machined internal splines, which otherwise may be deformed during heating. [1], Induction heating is a non contact heating process which uses the principle of electromagnetic induction to produce heat inside the surface layer of a work-piece. Flame or Induction Hardened Cases - Since no chemical change occurs in flame or induction hardening, readings must be made in the hardened or hardened and tempered condition only. Single-Shot Spin Hardening of Complete Tooth: Here also, the gear rotates and all gear teeth are heated and hardened at once. This is because the diffusion distance to redistribute carbon (in austenite) is shorter in finer than in coarser microstructure in which carbides are thicker and far-spaced. Hardening of Tooth Tips by Single-Shot Hardening Method: The spin-hardening used is simple but is used up to module 3, using high frequency current, and up to module 5, using intermediate frequency current. Now, based on this actual result of depth of hardening, and how close this is to the desired depth, the induction-hardening factors are adjusted to obtain the exact depth. The whole depth can be penetrated by using low frequencies, and the low power input does not permit over heating of the surface layers. A copper coil carrying a significant level of alternating current is placed near (not touching) the part. To provide the progressive movement through the induction process is applicable for electrically conductive for... 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