Several common defects in the forging process of bearing rings

Bearing rings in the forging process, due to bearing steel material defects, forging processing technology, processing equipment and human factors such as cracks, overburning, dents, forging folding and wet cracking and other defects, these defects can cause bearing damage, but also to the bearing life of the impact, resulting in early bearing breakage.

1, raw material defects caused by the bearing forging cracks

(1) bearing forgings outside diameter through the crack, the cause of the crack is a more obvious rolling crack on the surface of the bearing steel bar stock. In forging, containing surface cracks in the bearing steel bar stock by pressing, the crack is further expanded.

(2) bearing forging heart cracks, forging nesting, the inner ring forging heart has more obvious cracks. Crack length of 30mm, about 3/4 of the length of the diameter of the ring, the width of the part of 5mm, depth of about 10mm. The main reason for this defect is because there is a crack in the heart of the bearing steel bar stock, bearing steel bar stock cutting specimens after hot pickling heart position 10mm in length and 1mm in width of the depth of the crack, and the crack is penetrating. This with cracked material into production, cracked material after forging further expansion.

(3) measures bearing steel raw materials into the plant, according to the bearing steel into the plant inspection standard strict inspection to ensure that qualified bearing steel into production use.

2, forging overburning

Bearing ring forgings by turning the surface distribution of small holes. Metallographic microstructure of the product boundary has been oxidation overburned. The main reason for this defect is bearing rings in the forging if the heating temperature exceeds the upper limit of the process, the insulation time at this temperature is very long, resulting in material overheating, serious overburning, resulting in metal grain boundaries are oxidation cracking, the formation of sharp-angled caves. Forging over-burned collar surface form such as orange peel, the distribution of small cracks and very thick oxide skin. Because the surface of the ring after forging is covered with oxide, generally not easy to find, in order to fully expose the overburning characteristics after the grinding process.

Measures: The bearing steel heating device is equipped with a three-way sorting mechanism, which can automatically sort out underheated and overheated products. Through the three-way sorting device to sort out underheated (less than 1050 ℃) workpiece, can be reheated to the allowable starting forging temperature after normal forging processing; overheated overburned (temperature more than 1150 ℃) workpiece, can not be reheated and put into use, should be placed in a special covered red box for isolation, and clean up before the shift scrap, to ensure that the heating temperature in the required range.

3、Forging folding

Collar forgings in the expansion of the hole rolling plane concave heart is too deep, more than the amount of grinding left, then to the finished product when the plane left a long circular crack, this defect is called forging folding, as shown in Figure 7, Figure 8. Causes in the collar in the forging process can be formed by the convergence of two (or more) metal convection; can also be formed by a rapid and massive flow of metal will be adjacent to part of the surface metal with the flow, the two convergence; can also be formed by the deformation of metal bending, reflux; can also be part of the metal local deformation, was pressed into another part of the metal and formed. Folding is related to raw materials and billet shape, die design, forming process arrangement, lubrication situation and forging actual operation.

4、Forging depression

Bearing ring forging inside diameter part of the depression, the cause of the ring in the forging expansion process in the die surface due to wear burrs, resulting in contact with the die inside diameter of the ring by the expansion of the groove. The defect is not completely eliminated after turning individual deep depressions.

Measures: Strictly control the life of the die, the specified service life in time to change the arch in the tool to prevent the die wear caused by defects.

5, forging wet crack

Bearing ring outer diameter, end face, chamfering with obvious linear, diagonal, dendritic cracks. Cracks around the obvious decarburization and crack tail bald, known as forging wet crack. The reason is that after the completion of the forging and reaming of the collar, the individual collar has a certain temperature when it touches the water on the ground, resulting in wet cracking.

Measures: Before working every day, clean up the cooling water drainage ditch at the reaming equipment to ensure that there is no water on the ground. Eliminate the wet crack caused by the collar falling in the water after reaming.