Induction Hardening Gear Teeth
Gear Hardening: There are numerous factors that determine the appropriate induction hardening process to choose. Items such as geometry, permeability of the material, and desired mechanical properties will dictate processing variables such as frequency, power density, and heat time.
Induction heat treating is localized heat treatment used to increase the fatigue life, strength, and wear resistance of a component. Induction hardening is accomplished by placing the part inside an alternating magnetic field causing an electrical current to form at the surface. Heat is generated as a result of the I2R losses in the material and allows heat treaters to selectively austenitize only the surface material of a component while leaving the core material untransformed. Not only is the surface only selectively heated, but induction allows only those desired surfaces to be heated while other surfaces may be left cold. In the case of gears it is possible to only austenitize the near surface of a single tooth leaving the balance of the part cold during processing. The heated gear surface is subsequently quenched in either water, oil, or a polymer based quench to transform the austenite into martensite thereby increasing hardness in the required area while leaving the remainder of the component virtually undisturbed.
There are many frequency selections to choose from when hardening gears. The relationship between frequency and current penetration depth are inversely proportional. Such that lower frequencies cause the current to form at deeper depths while higher frequencies generate heat immediately adjacent to the surface. Tooth form is a significant factor when selecting the correct frequency, as high frequencies will heat the tooth tips first and low frequencies will heat the roots first