How to deal with the deformation defects caused by heat treatment of hollow rollers using medium frequency induction heating power supply

The large hollow rollers of the semi-continuous rolling hot output roller table are made of 45 steel seamless steel pipes, with shaft heads hot-assembled at both ends. The technical requirements are: roller surface hardness ≥ 40HRC, roller surface deformation ≤ 1.00mm, and central shrinkage ≤ 0.70mm. The heat treatment uses medium frequency induction heating surface quenching. The equipment is a medium frequency heating power supply with a frequency of 1-8KHz. The single-turn inductor is continuously quenched and heated by water spray cooling. The effect is not good, causing many workpieces to be scrapped due to excessive deformation, seriously affecting product quality. and normal production, the economic losses will be relatively large. Today, Zhengzhou Gou's technical staff will analyze the causes of deformation defects in hollow rollers.

Tests and production have found that after the roll surface is quenched, the roll surface diameter shrinks and the roll body elongates; when the hollow roll surface is quenched, the roll surface bending deformation also occurs. Analysis suggests that the deformation that occurs during heat treatment of hollow rollers is the result of uneven plastic deformation of the workpiece caused by thermal stress and structural stress generated during induction heating. In heat treatment production, the actual stress state of the workpiece is the result of the combined action of thermal stress and tissue stress. The test found that this composite effect is closely related to the central shrinkage and bending deformation of the workpiece and the quenching heating temperature. Through experiments, it was concluded that the induction quenching heating temperature of 860-870°C is the best for hollow rollers with minimal deformation. Therefore, the following process improvement measures are proposed:

(1) The workpiece is quenched and heat treated using a medium frequency induction heating power supply, and the induction quenching heating temperature is 860-870°C.

(2) The workpiece must not shake when rotating, and the tailstock spring must not be pressed too tightly; the workpiece and the sensor sprinkler should be placed concentrically, and the sensor sprinkler should be placed horizontally and not skewed.

(3) The linear speed of the spindle speed should be greater than the rising speed of the inductor, so that the workpiece can be cooled evenly and better, and the hardness of the workpiece can be more uniform after surface hardening. The spray holes of the water spray ring should be evenly distributed, and there should be no less than 3 water inlets to ensure a stable and uniform amount of water spray.

(4) During tempering, the convex side of the workpiece should be upward and both ends should be padded to reduce bending deformation.

After many manufacturers adopt the above improvement measures, the shrinkage deformation of the middle part of the hollow roller produced has been reduced from 1.10mm to 0.24mm, and the bending deformation has been reduced from 1.30mm to about 0.30mm, which meets the technical requirements. The product performance is excellent and good technical and economic results have been achieved benefit.