The four-row cylindrical rolling bearing FC5068170 is widely used in 430 and 370 rolling mills for bar and high-speed wire rod production. Through the statistics of the bearing damages in the last 2 years, the following summary is made.
1. Bearing fault classification table
| Damaged position | Cage | Seals | Inner ring | Outer ring | Rollers |
| Fault type | teeth broken | damaged | crack | damaged | damaged |
| Proportion | 35% | 20% | 25% | 10% | 10% |
2. Bearing fault analysis and preventive measures
2.1 broken teeth of the cage
Cage in a four-row cylindrical roller bearing, the main role is to divide the rolling element and guide the roller to run normally on the inner ring and outer ring raceway. The cage does not bear the axial and radial load produced by rolling and belongs to the passive operation part, which is driven by the rolling element. However, there are many faults on the site, which are caused by cage fracture and bearing burning. The most important 2 reasons as below:
2.1.1. The long service life of the cage leads to a larger gap between the cage pocket and rolling element diameter. The larger clearance will cause the bearing to incline beyond the range when it is running at high speed. When the tilted rolling element passes through the bearing bearing bearing area, harmful friction will occur between the inclined rolling element and the outer ring rib, resulting in abnormal torque load and vibration load being transmitted to the cage, eventually leading to cage deformation, tooth breakage, and other faults.
2.1.2 the invasion of foreign matters, especially the cage corresponding to the first row of rolling elements (close to the roll body side) is the first to invade. The invasion of hard particles leads to abnormal wear and stress between the cage and rolling element diameter, even causes the rolling element unable to rotate, resulting in pure sliding friction, and finally leading to tooth fracture and bearing locking failure.
2.1.3 measures to prevent cage fracture
(1) Check the clearance between the rolling element and the pocket, and replace the bearing which has been used for a long time regularly.
(2) Optimize the coordination of cage and rolling element to ensure the strength of rolling element and cage.
(3) Increase the crown value of the rolling element to prevent the stress concentration at the edge of the rolling element and outer ring bearing area.
(4) Strengthen the packing and transportation of bearing to facilitate on-site handling.
(5) To prevent foreign matters and impurities from invading the bearing, the main means at this stage is to check whether the sealing ring lip is hardened or damaged.
2.2. The seal ring is damaged and invalid
2.2.1. Optimize the coordination between the sealing ring lip and the moving labyrinth ring, and replace the movable labyrinth ring with obvious damage and wear.
The outer diameter of the labyrinth ring is directly matched with the sealing lip, and its surface condition is directly related to the service life and sealing effect of the sealing ring. The surface damage in Figure 1 directly leads to the basically ineffective sealing effect, and the sealing ring is damaged in almost a few hours. Secondly, replace the damaged and hardened sealing ring, as shown in Fig. 2.
2.2.2 during disassembly and assembly, the quality spot inspection of the bearing body, inner sleeve, and sealing ring shall be strengthened to prevent hidden danger bearing from being used on-line. The outer diameter surface roughness of the assembled labyrinth ring is not greater than ra0.35, and the surface hardness is not lower than HRC35.
2.3. Inner ring cracking
2.3.1 the cause of inner ring cracking is overload fracture and thermal fracture.
(1) Overload fracture
When the stress acting on the bearing is greater than the tensile strength of the material, the inner ring cracks. Usually, due to improper installation, such as the inclination and cross of the frame during rolling, the bearing partial load is caused and the bearing is fractured due to local overload. In addition, when the bearing is installed with interference, excessive interference will also lead to the cracking of the bearing ring. Especially for the inner ring with thin section thickness (section thickness < 12mm), too large interference often leads to axial cracking of the inner ring.
Fig. 3 is a typical example of the inner ring fracture caused by the inclination and cross of the stands during rolling, resulting in bearing partial load and bearing local overload. The control and inspection of rolling mill installation accuracy should be strengthened. The clearance between the mill housing and the bearing housing should be checked to ensure that the clearance is within the required range.
(2) Thermal fracture
The thermal fracture is mainly caused by the sliding friction between the parts matched with the bearing end face. There are an inner ring end face and moving labyrinth, inner diameter, and roller neck friction. Under the action of axial force, the friction of the end face produces high heat, which causes the end face to burn and discolor. The friction and high heat cause cracks on the bearing end face. The characteristic of the crack is perpendicular to the direction of friction operation and has a great influence on the inner ring with thin section thickness (section thickness < 12mm), especially for heavy load high speed or medium speed rolling mill.
(3) Measures to prevent thermal fracture of the inner ring
A. The matching of bearing inner diameter and roller adopts a base hole system. If the inner diameter of the bearing is the standard size, the tolerance zone should be selected for the roll neck. For fc4054170 recommended shaft limit deviation Ф 200 (+ 0.79 + 0.05) P6, take the upper deviation.
B. The labyrinth ring is matched with the roll neck to take R6.
2.4 other preventive measures
2.4.1 the manufacturer is required to supply rolling mill bearings with stable quality.
2.4.2 the preparation workshop is required to strengthen the bearing inspection during disassembly and assembly, so as to ensure that the qualified rolling mill bearing can be used online.
2.4.3 the production workshop is required to strengthen the on-site monitoring and timely stop the machine from handling abnormal situations such as taking over and current.
2.4.4 regularly check and replace the thrust bearing of the rolling mill.
2.4.5 implement online refueling in strict accordance with the system.
Please check the Product Guide to select suitable bearings for your machinery.
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