Analysis of deformation defects and process improvement of hollow rollers during medium frequency induction quenching

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, central shrinkage ≤0.70mm. The heat treatment adopts medium frequency induction annealing and quenching. The equipment is medium frequency induction annealing equipment and vertical quenching machine tool. The frequency is 1-8KHZ. The single-turn inductor is continuously quenched, heated and sprayed with water for cooling. During production, it was found that the hollow rollers were greatly deformed after quenching, and the correction of large roll workpieces was very difficult and ineffective, resulting in many workpieces being scrapped due to excessive deformation. It seriously affects product quality and normal production, and causes huge economic losses.

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.

Based on the hollow roller deformation test, the following process improvement measures are proposed:

(1) The heating temperature for induction quenching of the workpiece is 860-870°C, and the equipment used is medium frequency induction heating equipment.

(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 concentrically aligned, 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. After surface hardening, the hardness of the workpiece becomes more uniform and consistent. 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 adopting the above process improvement measures in production, the effect is obvious. The shrinkage deformation in the middle part of the hollow roller dropped from 1.10 to 0.24. The bending deformation dropped from 1.30 to about 0.30, which meets the technical requirements. The product has excellent performance and has achieved good technical and economic benefits.