Excavator sprocket quenching by medium frequency induction heating power supply

The excavator needs to use a medium frequency induction heating power supply for quenching according to its own quenching requirements. The sprocket material of the excavator is generally SCSIMN2H steel. The heat treatment requirements are: the surface hardness of the gear is 40-47HRC, the depth of the tooth top hardened layer is 18mm, and the tooth root is hardened. The layer depth is greater than or equal to 3mm.

The gear processing process is casting embryo - normalizing - mechanical processing - medium frequency induction heating surface quenching + low temperature tempering + fine machining - finished product.

①Normalize the fire. The heating temperature is 840-860 degrees Celsius, the holding time is 2H, and then it is air-cooled out of the oven.

②Medium frequency induction heating power supply surface quenching. The overall medium-frequency induction heating and buried spray quenching cooling methods are adopted. The quenching liquid uses 4%-6% AQ251 quenching medium.

③Self-tempering. That is, the cooling time of induction heating surface quenching is controlled so that the surface of the workpiece is quenched but not quenched through. The preheat inside the quenching zone is quickly transmitted to the quenching surface of the workpiece and reaches a certain temperature to temper the surface quenching layer. The self-tempering temperature can be measured with a thermometer pen to maintain the surface temperature of the workpiece at about 350 degrees celsius.

Analysis of heat treatment process

①Normalize the fire. Eliminate the gradual residual stress, uniformize the structure, refine the particles, improve the cutting process performance, and prepare the structure for the final heat treatment - medium frequency induction heating equipment surface quenching.

②Medium frequency induction heating power supply surface quenching. Due to the large size of the workpiece and the relatively deep depth of the hardened layer, a medium frequency induction heating power supply is used for surface quenching.

The current frequency should be selected according to the depth of the hardened layer required by the workpiece. The required thermal penetration depth of induction heating > the depth of the hardened layer. When selecting the induction frequency, the diameter and shape of the workpiece should also be properly considered. For workpieces with smaller diameters, a higher current frequency should be used to obtain better electrical efficiency. The selection should be based on the depth of the hardened layer and the diameter of the workpiece.

Key points for implementation of heat treatment process technology

① The normalizing process should strictly control its heating temperature and holding time. In production practice, it was found that due to insufficient normalizing and holding time, the workpiece structure failed to be refined, resulting in the coarse grains existing in the casting being retained, thus making the workpiece quenched after medium-frequency induction heating. A coarse martensite structure is generated.

② The quenching coolant used in medium frequency induction heating surface quenching is 4%-6% (mass fraction) AQ251 quenching medium. AQ251 water-soluble quenching medium is a patented product of the American Houghton Company.