Summary of analysis:

The rolling element material of backup roll bearing is carburized steel, which is suitable to be used in the manufacture of super large bearing with high speed and heavy load (such as backup roll bearing of rolling mill). This steel is characterized by surface hardened steel, surface Rockwell hardness of hrc60-63, core hardness of hrc33-48, hard outside and soft inside, which can both wear resistance and impact resistance, and its own characteristics determine its general damage characteristics The fatigue shedding of local surface layer and subsurface layer is mostly in the form of fine particles or fish scales.

According to the analysis of material characteristics, the main causes of the rolling element damage are as follows:

① Surface crack

On the premise of eliminating the grinding burn of rolling element in the process of rough grinding and fine grinding (which can be eliminated by grinding process control and inspection and flaw detection), the surface cracks caused by rolling element wear are mainly as follows:

a. In the process of operation, the rolling element rotates 360 degrees, the outer ring and each retaining ring are stationary. When the rolling element enters and leaves the bearing load area, it is in the process of mutual transformation between the stressed and non stressed states. When the rolling element enters and leaves the bearing load area, the sliding friction between the end face and the end face of each retaining ring is serious, which is a major factor causing surface cracks.

b. For the wear between the surface of the cage strut and the central hole wall of the rolling element, the running sequence of the bearing is as follows: the inner ring drives the rolling element to rotate, and the rolling element pushes the cage to rotate. During the process, the cage operates passively, and the pillar of the cage and the central hole wall of the rolling element are sliding friction, especially the sliding friction and collision between the support of the cage and the central hole wall of the rolling element when the rotation speed changes The serious impact is one of the main factors causing the hole wall crack in rolling body.

Improvement measures:

a. On site: during the installation, the axial clearance of the main bearing of the support roll must be well controlled to ensure that the main gland and the bearing end face are in a fit state after the bearing is installed, and the clearance is less than 0.05mm. The clearance between the gland and the bearing side retaining ring should be measured each time when installing and changing the load area, so as to avoid the actual use caused by the elastic failure of the adjusting gasket and the different width tolerance of the bearing The larger axial clearance aggravates the wear of the rolling element end face and the end face of each retaining ring, and also aggravates the wear of the cage support surface and the roller center hole wall.

b. In terms of bearing, the friction hidden danger between the rolling element and each retaining ring ring shall be reduced to a great extent, and the clearance between the outer ring raceway and the rolling element shall be greatly reduced, and the rolling element swing tendency caused by the excessive clearance between the rolling element and the rib shall be eliminated; the hidden danger of friction between the cage support surface and the central hole wall of the rolling element shall be strictly controlled, and the surface roughness and hardness of the support shall be strictly controlled Fit clearance H.

② Material nonmetallic inclusion

The non-metallic inclusions in raw materials exceed the standard and the content of harmful substance s (sulfur) P (phosphorus) O (oxygen) is high, which leads to poor material stability and defects in heat treatment, which is another factor leading to the overall cracking of rolling element.

In view of this, when domestic materials are selected for bearing manufacturing, Grade-A products, namely g20cr2ni4a, should be selected at a lower level, and non-a-grade g20cr2ni4 is not recommended.

DMD is particularly strict in material selection. In order to ensure the internal quality of bearings, meet the needs of important parts of the rolling mill, and fundamentally solve the problems of reliability and life of bearings, the carburized bearings of domestic famous steel plants (northeast special steel, Hubei Daye, Xining Special Steel, etc.) or grade a carburized bearings of Timken 3311 standard are adopted for bearing carburizing of large and extra large rolling mill Steel to make rings and rollers.

Timken3311 material is superior to domestic high-quality carburizing steel in quality, mainly in the content of harmful substances such as oxygen, phosphorus and sulfur, which is far better than the current national standards and the actual domestic carburizing steel. See the element content comparison in the figure below.

DMD has accumulated more than ten years' experience in bearing application and intelligent manufacturing of oversize rolling mill. Relying on years of experience in repairing oversize imported bearings, through the analysis of bearing product data of fag, Timken, Koyo and other foreign manufacturers, combined with the field application, the unique method of bearing parts common error matching is summarized. According to the field working conditions of each customer, the data is optimized and customized“ "More durable rolling mill bearings" brand strategy, continue to create more durable "DMD" brand rolling mill bearings!