Talk about the requirements for heating time when using high frequency induction heating equipment for rotary quenching

Rotary hardening is the most common method of gear induction hardening, and is often applicable to gears with small and medium-sized modules. The gear rotates during the heating process to ensure uniform energy distribution (heating stage) and cooling. Single or multi turn coil inductors can be used around the entire gear.

 

When using a circular coil, five parameters play an important role in obtaining the required hardened layer: frequency, power density, period, coil shape, and cooling conditions. Various forms of induction hardening layer can be obtained with different heating time, frequency and power. The three hardness distributions of gears show the changes of different tooth top quenching methods and various hardening layer depths. The geometric shape of the teeth significantly affects the distribution of heat generated. At the same time, industry has accumulated Rule of thumb for rough estimation of gear quenching process parameters, such as how to only need tooth top hardening, high-frequency induction heating equipment and high power density should correspond to short heating time, etc.

 

It must be kept in mind that the simple use of Rule of thumb to determine the optimal combination of process parameters may cause deviations. Because each induction hardened gear has its own characteristics in terms of material type, original structure, geometric shape, function, etc. When using high-frequency induction heating equipment, the current penetration depth is relatively small, and the generated eddy currents flow along the contour of the tooth top, resulting in an increase in the power induced at the tooth top (compared to the tooth root). In addition, compared to the tooth root, the metal mass for heat storage at the tooth top is less. Therefore, when compared to the top of the tooth, there is a large heat absorbing body below the tooth root. Due to these two factors, the tooth top will experience the fastest temperature rise during the heating cycle, resulting in the tooth top easily reaching the austenitizing temperature. In order to harden the tooth root, we use a lower frequency. The combination of a sufficiently low frequency and an increase in current penetration depth may lead to the cancellation of eddy currents at the tooth tip or even reaching the indexing circle. This makes it easier for the induced current to pass through a shorter path, passing through the tooth base circle or tooth root circle, rather than flowing with the tooth profile. The result is that the heating density of the tooth root area is higher than that of the tooth tip area, and then the Martensite is obtained by quenching in this area. A high power density produces a shallow hardness layer, while a low power density will produce a deeper hardness layer accompanied by a wide transition zone.