Discussion on Failure Analysis Process of Rolling Mill Bearings

Early understanding of rolling mill bearings before delivery. For bearings, a new steel rolling environment designer needs to know the conditions before the bearing. If possible, the early investigation should include observing the basic characteristics of the bearing and the bearing parts before and after the disassembly and after disassembly. These features record the characteristics of each component in the form of text and photos, so that the designer can design more practical rolling mill bearings according to working conditions, and should point out and correct the improper parts in the installation and disassembly process. The damage characteristics of the previously used bearings should be fully understood, and the early failure of the bearing should be avoided by using the data as early as possible.

The method of mounting and dismounting the bearing varies depending on the type and will not be described here. No matter what method is used, care must be taken to avoid damage to the bearings. Violent means (such as hammers, iron bars, etc.) are not allowed; minor scratch marks can cause use or deviations from subsequent failure analysis. Housing tolerances and roll dimensional tolerances during installation can be found in 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 camera and take care of the damaged bearings and accessories, the waste bearing should be placed in the warehouse and stored in the original state without damage.

Failure mechanism

Mechanical damage: The rolling mill bearing parts have good machining accuracy and surface roughness. When the installation is bad, when the rolling contact surface is scratched, the surface stress state will change, which will affect the bearing life, especially when these scratches And the indentation is more harmful when rolling the surface, and the metal particles generated by the scratches and scratches will move again and become embedded in the raceway.

Permanent indentations that occur when the rolling elements are overloaded are referred to as Brinell indentations, which can cause bearing failures, such as bearing drops or improper installation. The abnormal noise emitted during the operation of the bearing is the initial signal of Brinell indentation.

When the bearing is subjected to vibration and the rolling element does not rotate, the raceway will also be damaged. This damage is called pseudo-Brinell indentation, which occurs mainly before and after the bearing is installed. Pseudo-Brinell indentation damage can be observed in bearings that are subject to vibration during transport and for long periods of idle equipment.

During the grinding process of the bearing raceway, due to the vibration of the machine tool, the grinding wheel is not sharply trimmed, the micro-vibration of the raceway surface caused by the unreasonable configuration of the workpiece and the grinding wheel, and the rough wave crest are improperly handled. The root cause of failure, this phenomenon will be manifested when the finished bearing is tested.

Wear and tear

Wear often causes gradual damage to the rolling mill bearing components and ultimately leads to loss of dimensional accuracy of the bearing components and other related problems. Failure caused by wear does not mean just replacing the bearings. Because of changes in play and fit, other states caused by wear may become the primary failure mechanism, and wear may create a source of stress concentration that causes cracks.

Under proper lubrication conditions, the micro-protrusions on the surface of the bearing counterpart may be plastically deformed and flattened by cold pressing. In this state, the bearing can achieve the expected service life. However, when the lubrication condition deteriorates, the internal rolling surface of the bearing forms a metal-to-metal contact, which causes an increase in frictional force, causing local deformation and friction welding inside the bearing. Under this alternating force, the local friction welding joint can be removed from the body. The upper tear increases the plastic deformation, which causes surface pitting, and the surface of the other part has a transfer material. Whether this state deteriorates depends on the operating state, a slight adhesion damage is called a scratch, and a severe adhesion is called a bite.

Wear particles between the contact surfaces of the bearing parts and the relative contact surfaces will cause abrasive wear, and sharp abrasive grains can produce obvious furrows, which is the root cause of early failure. The abrasive particles are mainly from the inside of the bearing or from the inside of the machine system, such as the purity of the lubrication, the cleanliness of the bearing installation, and the cleanliness of the bearing before leaving the factory.

Crack damage

Cracks in bearing parts are caused by overload or cyclic load stress. Smelting processes and processing techniques can also cause manufacturing cracks. In addition to cracks caused by inclusions and oxides, cracks caused by smelting and processing processes are unlikely to enter the follow-up. In the processing process.

The cracks generated by the subsequent processing of the bearing are usually related to the heat treatment and the grinding process. If a crack flows into the next process in a certain manufacturing process, the crack will be rapidly expanded in the subsequent processing. With one exception, cracks from the final grinding stage are brought to the operating equipment if they are not checked. Excluding the above, the crack problems usually encountered are mostly related to the installation and operation process, caused by installation scratches, scratches and cyclic loads. The static stress caused by the residual stress installation of the part and the stress caused by the applied load interact to make the stress state. Since the crack propagation direction is perpendicular to the action stress direction, certain information can be obtained due to the crack propagation direction.

When the rolling mill bearing is under machine maintenance, the crack failure information can be used to find the early failure source of the bearing, so that the rolling mill bearing can obtain a longer life.

There are many reasons for the failure of rolling mill bearings. It is not necessary to solve or explain one or two reasons to improve the service life of rolling mill bearings. If the bearing life of rolling mill bearings is to be improved, each factor should be integrated. It must be selected from materials, processing technology, transportation process, Strengthen the control of the installed operation status and other links.