1、 Failure form

Whether the working performance of rolling mill bearings can be effectively utilized depends to a considerable extent on the lubrication situation. Lubricants are known as the "fifth largest component of bearings". More than 40% of the causes of damage to rolling mill bearings are due to poor lubrication. Therefore, in order to reduce the consumption of rolling mill bearings, it is necessary to select lubrication methods and excellent lubricants that are suitable for use conditions, and to design and install reliable sealing devices that prevent the intrusion of foreign matters such as water and oxide skin. Under normal installation, lubrication, and maintenance conditions, during the operation of bearings, fatigue peeling caused by alternating loads on the surfaces of the inner and outer raceways and rolling bodies is the main form of failure of bearings, followed by wear, pitting, plastic deformation, and cracking.

2、 Cause of failure

(1) Assembly Impact

When the axial clearance of the rolling mill bearing is too small or a certain preload is generated due to excessive tightening of the pressing end cap screws, the outer ring of the centripetal ball bearing moves axially, eliminating some of its own clearance and clearance. When the preload exceeds a certain range, the axial movement of the bearing outer ring has completely eliminated its own clearance and clearance, and the centripetal ball bearing ball moves in the runway. At this time, the axial displacement of the roller is zero. In this state, when the roller operates under high speed and heavy load, the bearing will quickly generate heat. After the shaft is subjected to heat, the body expands and deforms, and the ball is damaged. The lubricating oil film between the roller and the bearing pair causes thousands of friction. The temperature further increases, causing other components to expand linearly after being heated, further increasing the preload, damaging the lubrication effect, and causing the radial ball bearing to burn out and fail.

(2) Effect of lubrication conditions

In practical work, bearing burning due to poor lubrication often occurs. The main reasons are as follows: such as oil circuit design issues; Quality problems of lubricating grease; Oil quantity problem; Fatliquoring method issues. When filling grease for the first time, it is sufficient to fill the internal space of the bearing. For vertical or oblique rollers, the upper and lower covers of each bearing seat should be filled with sufficient grease. After each roll change, check whether the lubricating grease has hardened and turned black, whether it has been contaminated by impurities, and whether it has been oxidized and emulsified. In case of any of the above situations, the lubricating grease should be completely replaced and the seals and sealing structures should be inspected for timely replacement or improvement; If the condition is still good, it can be supplemented with new grease before continuing to use.

(3) Foreign matter influence

There are several main sources of foreign matter, including ash or other impurities brought by lubricating grease; Metal chips remaining after processing of parts and components; Environmental foreign matters enter the bearing during removal; Local damage caused by mechanical impact during assembly; Dust in the working environment, etc. When the diameter of foreign particles exceeds the thickness of the oil film, it will damage the oil film, causing strain, causing bearing damage or early failure. When the diameter of the foreign matter is smaller than the minimum working clearance of the bearing, the foreign matter can be stirred with the grease through the clearance.

This causes friction on the working surface of the rolling element. When the diameter of the foreign matter is greater than the working clearance of the bearing, the foreign matter is crushed or ground into thin dust that adheres to or embeds in the bearing surface. If crushed foreign debris is not embedded in the working surface and enters the lubricating grease, it will further aggravate bearing wear. This causes fatigue peeling off of the bearing and increases the temperature of the working surface. The lubricating oil then loses its function, making the bearing ineffective. After foreign matters are crushed or embedded in the rolling body, the oil film is quickly damaged, resulting in damage to the shaft during operation under dry friction.

(4) Overload effects

Rolling bearings operating under overload conditions generally produce abnormal wear and fatigue damage. In steel rolling machinery and equipment, roller bearings often suffer from unidirectional overload or cyclic load overload. These overload effects often cause fatigue cracks to initiate locally on the rolling element, resulting in bearing fatigue failure.

(5) External temperature influence

When the roller is working, its cooling water should take away the heat generated by rolling in a timely manner. However, due to various reasons, the cooling water is small or does not play a good role in this cooling, which increases the temperature of the roller bearing and quickly turns the lubricating grease into a liquid state. A large amount of grease leaks outward through the seals. The rapid decline in lubrication conditions leads to further increases in the bearing ambient temperature and bearing failure.