1. Bearing forging cracks caused by raw material defects
(1) Cracking of the outer diameter of the bearing forgings is caused by obvious rolling cracks on the surface of the bearing steel rods. When forging, the bearing steel rod with a crack on the surface is pressed, and the crack is further extended.
(2) There is a crack in the center of the bearing forging. After the forging is nested, there is obvious crack in the center of the inner ring forging. The crack length is 30mm, about 3/4 of the ring diameter. The maximum width is 5mm, and the depth is 10mm. The main reason for this defect is the crack in the center of the load-bearing steel bar. After hot pickling, there is a deep crack of 10mm long and 1mm wide in the center of the bearing steel bar cutting sample, and the crack is permeable. The cracked material was put into production and then further expanded after forging.
(3) Take measures. Bearing steel raw materials shall be inspected in strict accordance with bearing steel entry standards after entering the factory to ensure that qualified bearing steel is put into production and use.
2. Overburning of forging
The bearing forging manufacturer indicates the fine holes distributed on the surface of the bearing ring forgings after turning. The metallographic structure has been oxidized and charred. The main reason for this defect is that when forging bearing rings, if the heating temperature exceeds the upper limit specified by the process and the holding time is very long at this temperature, the material will be overheated, and in serious cases, it will overburn, leading to oxidation cracking of metal grain boundaries and the formation of sharp holes. The surface of the forged overburned ring is like orange peel, which is distributed with fine cracks and thick oxide skin. Because the forged ring surface is covered with oxide skin, it is generally difficult to find, after turning, grinding can fully expose the characteristics of over-burning.
Measures taken: The bearing steel heating device is equipped with a three-way sorting mechanism, which can automatically sort underheated and overheated products. The underheated (below 1050℃) workpiece is sorted by a three-way sorting device, and then heated to the allowable initial forging temperature. Overheated (temperature over 1150℃) workpiece can not be reheated into use. They should be isolated in a special red box with a lid, cleaned and scrapped before the shift to ensure that the heating temperature is within the required range.
3. Forging and folding
The bearing forging manufacturer indicated that the concave core of the forging ring was too deep when it was reamed and rolled, exceeding the turning allowance, and there were long arc cracks on the plane when the finished product was processed. This defect is called forging folding. The reason is that the ring can be formed by the convection and convergence of two (or more) strands of metal during forging. It can also be the rapid flow of a large amount of metal, carrying away adjacent parts of the surface metal, the two meet and form; It can also be formed by bending and refluxing deformed metal; It can also be formed by the partial deformation of one part of the metal and being pressed into another. It is related to the shape of folding raw materials and billets, die design, forming process arrangement, lubrication and actual forging operation.
4. Forge depression
The bearing forging manufacturer indicated that the forging inner diameter of the bearing ring was depressed, and burrs appeared on the surface of the die due to wear during the forging and reaming process, resulting in grooves after reaming at the contact point between the inner diameter of the ring and the die. After turning, the defect has some deep depressions and has not been completely eliminated.
Take measures: strictly control the service life of the mold, make clear the service life, timely update the tool, prevent mold damage caused by defects.
5. Forging wet crack
The bearing forging manufacturer indicated that there were obvious linear, oblique and dendritic cracks in the outer diameter, end face and chamfer of the bearing ring. There is obvious decarbonization around the crack, crack tail bald, known as forging wet crack. The reason is that after the completion of ring forging and reaming, some rings still have a certain temperature when they touch the ground, resulting in wet cracking.
Measures: Before work every day, clean the cooling water drain at the reaming equipment to ensure that there is no water on the ground. Eliminate the wet crack caused by the ring falling into the water after reaming.