Countermeasures for soft belt defects when quenching machine tool spindles using small high-frequency induction quenching equipment

When the machine tool spindle uses small high-frequency induction quenching equipment for quenching heat treatment, during the operation, affected by various factors, the spindle may have low hardness, deformation, cracks and quenching soft zone defects. These defects may at least affect the service life of the spindle, or at worst may cause the workpiece to be scrapped. Therefore, understanding the causes of defects and corresponding countermeasures is of very important practical significance. Today, we will take a look at the countermeasures for defects in quenched soft belts.

The material of the machine tool spindle is 45 steel. After using the high-frequency induction quenching process, the surface hardened layer of the inner taper hole of the spindle is in the shape of a spiral band, resulting in a spiral soft band defect, which cannot meet the technical requirements. To this end, we propose the following countermeasures:

1) The taper hole sensor inside the spindle is double-tube U-shaped. The inner layer is an induction conductor and is cooled by water. The outer layer is a water spray pipe, which is used to spray water to cool the surface of the inner taper hole of the spindle. The diameter of the outer water spray hole is φ1.5mm, and the water spray pressure is 0.15-0.20MPa. Install a magnet or conductive powder (use epoxy resin or 502 glue) on the outside of the induction conductor, with a thickness of about 3-4mm. The gap between the sensor and the surface of the cone hole should be 2-3mm.

2) When the inner taper hole of the spindle is heated by a small high-frequency induction quenching equipment, position the lower center of the spindle of the quenching machine tool and the quenching center fixing frame of the spindle to be processed, and use a self-centering chuck to fix the sleeve so that the spindle can be positioned on the quenching machine tool. The slide rail slides up and down and can also rotate. Then put the sensor into the inner cone hole, adjust the gap size and fix it, and cool it with water. When the taper hole in the spindle is heated to the quenching temperature, it is immediately cooled by spraying water.

After adopting the improved high-frequency induction quenching process, the quenching temperature of the tapered hole in the spindle is uniform. The depth of the hardened layer is uniform, about 2-3mm. The hardness of the inner taper hole of the spindle is uniform, with a hardness of 52-54HRC, eliminating quenching soft spots and soft zones. The metallographic structure is fine tempered martensite structure (level 6).