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Problems arising in the bearing forging process

Jime

In the forging process of bearing ring, cracks, overburning, depression, forging folding and wet cracking of the ring caused by defects of bearing steel material, forging processing technology, processing equipment and human factors can cause bearing damage and affect bearing life, resulting in early bearing damage. The following share several common defects in the forging process of bearing rings, hoping to help you do a good job of prevention in advance.

1. Bearing forging cracks caused by raw material defects

(1) The penetrating crack in the outer diameter of bearing forgings is shown in Figure 1, which is caused by an obvious rolling crack on the surface of the bearing steel rod. In forging, bearing steel rods containing surface cracks will be further expanded after being pressed.

(2) Bearing forgings heart crack, the inner ring forgings heart crack is more obvious. The length of the crack is 30mm, accounting for about 3/4 of the diameter length of the ring, the largest part of the width is 5mm, and the depth is about 10mm. This defect is mainly caused by cracks in the core of the bearing steel rod. As shown in FIG. 4, after hot pickling, there are deep cracks in the core of the bearing steel rod cutting sample with a length of 10mm and width of 1mm, and the cracks are penetrable.

(3) After the raw materials of bearing steel are imported into the factory, strict inspection shall be conducted according to the entry inspection standards of bearing steel to ensure that qualified bearing steel is put into production and use.

2.Forging overburning

Small holes are distributed on the surface of bearing ring forgings after turning. The metallographic microstructure has been oxidized and overburned. The main reason for this defect is that when the bearing ring is forged, if the heating temperature exceeds the upper limit specified in the process and the heat preservation time at this temperature is too long, the material will overheat or overburn in serious cases, resulting in the oxidation cracking of the metal grain boundary and the formation of angular caves. The surface shape of the forged overburned ring is like orange peel, which is distributed with fine cracks and thick oxide peel. Because the surface of the ring is covered by oxide skin after forging, it is not easy to find, and the burning characteristics can be fully exposed after grinding.

Measures were taken: The bearing steel heating device is equipped with a three-way sorting mechanism, which can automatically separate underheated and overheated products. The workpiece under heat (less than 1050℃) can be separated by a three-way sorting device, which can be reheated to the allowable initial forging temperature before normal forging processing; Overheated and overburned (temperature over 1150℃) workpiece, can not be reheated and put into use, should be placed in a special covered red box for isolation, and before the shift cleaning scrap, to ensure that the heating temperature within the required range.

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