Although rolling bearings for rolling mills turn very reliably, improper installation, use or manufacture can also cause early failure. The study of early failure in the expected life of bearings can prevent frequent early failure of bearings in use.

In order to reduce the early failure of the rolling bearing, in order to determine the failure causes of the early failure of the rolling bearing, it is necessary to understand the steel alloy composition of the manufacturing of the bearing, the processing process of the bearing from feeding to the finished product and the bearing accuracy level according to the working conditions. According to its application, the rolling force, linear speed, rolling product variety, lubrication method and effect, bearing sealing effect, raw material shape of rolled plate and quality of finished product after rolling are properly collected and used. Bearing failure analysis is carried out according to the collected rolling mill data and all bearing data.

When the bearing cannot operate according to the expected requirements, it can be considered that the bearing has failed. Usually, the early failure is far earlier than the time when the bearing completely loses its function, so the research and analysis of the early failure of the bearing is very necessary. See the picture below:

Early understanding of mill bearings before delivery. For bearings, a new rolling environment designer needs to know the use of the bearings before, if possible, early investigation should include observation of the bearing before and during disassembly and disassembly of the basic characteristics of the bearing mating parts, these characteristics should be recorded in the form of text and photos. In order to design more practical rolling mill bearings according to working conditions, the improper place in the installation and disassembly process should be pointed out and corrected. The damage characteristics of previously used bearings should be fully understood, and early bearing failure should be avoided as far as possible through early understanding of the data.

The installation and disassembly methods of bearings vary according to different types and are not explained here. No matter what method is used, care must be taken to avoid damaging the bearing, and violent means (such as hammer smashing, iron bar prying, etc.) are not allowed; Even minor scratches can cause deviations in use or subsequent failure analysis. The bearing seat and roll size tolerances at the time of installation can be referred to the relevant national standards. After the bearing is damaged, the first site should be saved for bearing failure analysis. If it is urgent to disassemble the damaged bearings and accessories, take photos and obtain evidence, and remove the waste bearings should be placed in the warehouse and kept in the original state.

Failure mechanism

Mechanical damage: Rolling mill bearing parts have good machining accuracy and surface roughness, poor operation during installation, when the rolling contact surface is scratched, the surface stress state will change, which will affect the bearing life, especially when these scratches and indentation are produced on the rolling surface, it is more harmful. When the metal particles produced by scratches and scrapes are moved and embedded in the raceway, the bearing will be affected again.

The permanent indentation produced when the rolling element is overloaded is called Brinell indentation, which will lead to bearing failure, for example; Bearing drop or improper installation, etc. Abnormal noise emitted during bearing operation is the initial signal of Brinell indentation.

When the bearing is subjected to vibration and the rolling body does not rotate, the raceway will also be damaged, which is called false Brinell indentation, which mainly occurs before and after the bearing installation. Pseudo-brinell indentation damage can be observed in bearings on equipment subjected to vibration during transportation and idle for long periods of time.

In the grinding process of the bearing raceway, due to the vibration of the machine tool, the grinding wheel dressing is not sharp, the unreasonable configuration of the workpiece and the grinding wheel linear speed ratio and the micro-vibration of the raceway surface and the improper treatment of rough peaks and troughs are the causes of early failure, which will be shown in the detection of the finished bearing.

Wear damage

Wear usually causes gradual damage to rolling mill bearing parts, and eventually leads to the loss of dimensional accuracy of bearing parts and other related problems, wear caused by failure does not mean that just replace the bearing. As the clearance and fit change, other states caused by wear may become the main failure mechanism, and wear may produce a source of stress concentration that causes cracks.

Under appropriate lubrication conditions, the bearing pair surface micro-convex may have plastic deformation and cold pressing and become flat, in this state, the bearing can reach the expected service life. However, when the lubrication conditions deteriorate, the metal to metal contact formed on the rolling surface inside the bearing resulting in increased friction force, resulting in local deformation and friction welding inside the bearing, in this alternating force can tear the local friction solder from the body and increase the plastic deformation, so that the surface pitting will be formed, and the other part will have transfer materials on the surface. Whether this condition worsens or not depends on the state of operation; minor adhesion injuries are called abrasions, and severe adhesion is called biting.

When hard particles are included between the contact surfaces of bearing parts and move relative to the contact surface, the abrasive particles will be worn, and sharp abrasive particles can produce obvious furrows, which is also the root cause of early failure. The abrasive particles mainly come from inside the bearing or from inside the machine system, such as: the purity of lubrication, the cleanliness of the bearing installation, and the cleanliness of the bearing cleaning before the factory.

Crack failure

Cracks in bearing parts are caused by overload or cyclic load stress, smelting process and processing process can also cause manufacturing cracks, in addition to the cracks caused by inclusions and oxides, cracks caused by smelting and processing process, it is impossible to enter the subsequent processing process.

The cracks generated in the subsequent processing of bearings are usually related to heat treatment and grinding processes, and if there are cracks in a manufacturing process into the next process, the cracks will be promoted to expand rapidly in the subsequent processing. However, there is an exception, the final grinding stage of the crack if not checked out, will be carried to the operating equipment. Excluding the above situation, the cracks usually encountered are mostly related to the installation and operation process, and are caused by installation scratches, scrapes and cyclic loads. The static stress caused by the installation of the residual stress of the part and the stress caused by the external load interact with each other to make the stress state, because the crack expansion direction is perpendicular to the direction of the acting stress, so certain information can be obtained due to the crack expansion direction.

In the maintenance of rolling mill bearings, the early failure source of bearings can be found according to these crack failure information, so that rolling mill bearings can get longer life.

There are many reasons for the failure of rolling mill bearings, not to solve or explain one or two reasons can improve the service life of rolling mill bearings, if you want to improve the life of rolling mill bearings, should be integrated every factor link, must be strengthened from the selection of materials, processing technology manufacturing, transportation process, installed operation state and so on.