Medium frequency induction heating furnace has many advantages, such as fast heating, less oxidation, accurate temperature control, better production conditions, stable and reliable operation and so on. It has been widely used in mass production of automobile forgings. Our company is a professional production partner of automobile hub and axle pipe, most of which are mainly hot extrusion parts of hydraulic press. Figure 1 shows the semi axle bushing used in the front and back drive bridge of the world advanced level in our company. Its material is: 45Mn2, using thlO2mm x 13.5mm high quality alloy steel tube, 3 local heating and 3 hot piers extrusion forming. After every local heating and pier extrusion, process tests are carried out to prevent defects from hot extrusion. In the process inspection, it is often found that there is a folding phenomenon of the inner hole, which not only reduces the qualified rate of the product, but also can cause a great loss if it is misjudged or the magnetic flaw detection is missing and processed into the finished product. For this reason, the reasons for the folding of the inner hole part of the hot extrusion part were carefully analyzed, and corresponding measures were taken to achieve good results.

1. Problems Analysis 

500kW / 1KHz medium frequency power is used for medium frequency heating. The diameter of the inductor's inner lining is 180mm, and the bottom of the reheating furnace is made of 1Crl8Ni9Ti austenitic heat-resistant steel tube (diameter 14mm). When the 102mm * 13.5mm tube is heated locally, the inner hole of the inductor can not coincide with the inner hole center of the tube material, the upper part of the pipe is far away from the coil, and the electric efficiency is low relative to the lower part of the tube, resulting in the inconsistency of the upper and lower temperatures. The deformation resistance of the high temperature side decreases relative to the low temperature side. When the hot extrusion is applied, the inner hole part is easy to form folds. Before, when the forging was heated by artificial timing, the pipe material was rotated by 180 degrees. The labor intensity of the workers was large, and the human factors were many, and the waste loss accounted for 5%, which made the enterprise a great loss.

2．Solutions

In order to reduce the loss of waste, we designed the automatic rotation device, which is installed in the MF furnace, and solved the problem of the temperature disagreement between the top and the bottom of the material well. The device is mainly composed of armrest, mobile car, base bracket and positioner. The two rolling rod 5 with a large gear 8 is connected with the bottom plate of the moving car 10 through the bearing seat 4; the straight line gear 3 on the output shaft of the wD10o - 60 one reducer is meshed with the large gear 8 on the rolling rod. The motor drives the reducer and passes the power to the two rolling rod through the small gear wheel on the output shaft of the reducer, so that the heating pipe between the two rolling rods is automatically and evenly rotated. Turn. The heating length can be determined by the sliding scale on the speed locator 10 and the position of the front dead point of the mobile car. In the local medium frequency heating, the operator only needs to pull the mobile car out through the armrest 1, put the billet in the two rolling rod and close the outer end of the billet to the sliding scale of the positioner, and then push the moving car to the position of the front dead point, and the suspension part of the billet can rotate automatically in the medium frequency heating furnace, and the heat can be evenly heated. Obviously, the successful application of the device largely reduced the labor intensity of workers, and solved the problem of uneven heating of local heating materials.

The rotary device has the following advantages:

(1) Due to the use of motor slewing mode, the heating temperature is even, which reduces the influence of human factors.

(2) Compared with previous manual rotating billets, the labor intensity of workers is reduced, and the labor motivation of workers is improved.

(3) Through inspection and verification, the loss rate of waste products caused by folding of inner orifice is reduced to 0.3 per thousand.

3. Conclusion

In the forging industry, some enterprises rotate 180 of the billet with manipulator. To solve such problems, the rotary device has the advantages of simple structure, easy operation and low failure rate. It is an effective way to solve such problems. After more than one year's practice, the device has solved the problem of uneven heat of the billet during the medium frequency induction heating, which can guarantee the quality of the axle tube and greatly improve the qualified rate of the product.