Application of high-frequency induction heating equipment in gear surface quenching

The surface quenching principle of high-frequency induction heating equipment is based on the principle of electromagnetic induction. The workpiece is placed in an induction coil with a certain frequency of alternating current. Under the action of the alternating magnetic field, a large induced current is formed on the surface of the workpiece, thereby rapidly quenching the workpiece surface. The surface quenching process operates by heating to austenitizing and then rapidly cooling.

The basic principles of quenching using high-frequency induction heating equipment:

1. Electromagnetic induction and skin effect. The workpiece is placed into an inductor coil surrounded by a hollow copper tube. AC current of a certain frequency is passed into the inductor to generate an alternating magnetic field. Due to electromagnetic induction, an induced current of the same frequency and opposite direction will be generated in the workpiece. The induced current will produce eddy current and hysteresis loss to heat the workpiece, and they are unevenly distributed, mainly on the surface layer. The current intensity decays exponentially from the surface to the center. This phenomenon becomes a skin effect.

2. Proximity effect. When current passes through two adjacent conductors, the current distribution changes due to the interaction of the alternating magnetic fields they generate. When the current directions of two adjacent conductors are opposite, the current flows from the inside of the two conductors. When the current directions of the two adjacent conductors are the same, the current passes from the outside of the two adjacent conductors. This phenomenon is called the proximity effect.

3. The phenomenon that the current passing through the induction coil is concentrated on the inside of the workpiece and appears on the surface of the workpiece is called the ring effect.

4. Sharp corner effect. When the protruding parts with sharp corners, edges and small curvature radius are placed in the inductor for heating, the induced current density of the sharp corners or protrusions of the workpiece is too large and the heating speed is increased, which is called the sharp corner effect.

Methods to avoid the sharp corner effect of high-frequency induction heating equipment quenching are: the design is to appropriately increase the gap between the inductor and the sharp corners or protruding parts of the workpiece to reduce the number of magnetic lines there. In the shape of an arc, the radius of curvature is appropriately increased at the protrusion of the workpiece to maintain uniformity of temperature across the entire heating surface.

The depth of the quenching hardened layer of gear high-frequency induction heating equipment. The distribution and density of the high-frequency quenching hardened layer have a great impact on the gear life. It is ideal for the hardened layer to be distributed along the tooth profile. Whole-tooth quenching will seriously affect the fatigue strength of the gear and damage the toughness of the material. Restricted by the power of the equipment, it is difficult to achieve a reasonable distribution of the hardened layer for gears with large modules. Using single-tooth quenching and rationally designing the sensor can greatly improve the distribution of the hardened layer. If the hardened layer is too shallow, it will be easily pressed through and peeled off; if the hardened layer is too deep, it will easily cause deformation and cracking. Therefore, choosing the appropriate quenching hardness layer according to the modulus is the best effect for gear quenching.