ITS Technology Knowledge: Analysis and Control of Abnormal Failure of Four Row Cylindrical Roller Bearings for Cold Rolling Mill

Long life design, manufacturing and environmental constraint control.

 

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Abstract: in view of the abnormal failure of a cold rolling mill in use, the failure form of its key component four row cylindrical roller bearing is analyzed, and suggestions on bearing design, manufacturing and application environment control are given.

 

Key words: rolling bearing; cold rolling mill bearings; failure analysis; control

 

Improving the service life of rolling mill bearings has always been the goal of rolling mill bearing design. Both the improvement of bearing structure and the improvement of host equipment have made great progress in recent years. However, rolling mill bearings still often encounter some problems in use. Through practical cases, this paper summarizes the aspects of design, manufacturing, environmental control and maintenance, hoping to be helpful to the design and use of rolling mill bearings.

 

1. Abnormal failure forms and analysis of four row cylindrical roller bearings

Figures 1 to 3 show several typical cases of damage to four row cylindrical roller bearings used in cold rolling mills taken at the production and use site of a rolling main engine factory: Figure 1 shows the inner ring of four row cylindrical roller bearings used in backup rolls. The entire inner ring is broken along the axial direction and runs through the inner diameter, and the inner hole surface is severely burned; Figure 2 shows the inner race surface of the four row cylindrical roller bearing used by the work roll. The color has shown a red color, with serious burns, and the race surface is full of pits and pits; Figure 3 shows the roller and outer ring components of the four row cylindrical roller bearing used by the backup roller. The surface material of the roller is peeled off, and the surface of the roller is reddish brown, which is severely burned.

 

The main machine is a 1450 cold rolling mill, and the boundary dimension of the four row cylindrical roller bearings used for the backup roll is 520mm × 735mm × 535mm, the maximum rolling speed is 900m / min; The maximum rolling force is 10000kN.

 

According to the introduction, due to the output task, the rolling mill often works at full load, and the lubrication is not timely. At the same time, the warning system of the rolling mill is damaged and not repaired in time, and the abnormal bearing is not found in time, resulting in the fire of the backup roll. From the analysis of bearing damage, Figure 1 shows that the ferrule is axially broken, and the crack is axially broken along the ferrule, which is caused by overload load or improper (too tight) selection of bearing installation coordination; Figure 2. The fatigue peeling off of the raceway has obvious wear marks on the surface, and the metal has flake peeling off, which is also caused by overload load and lubricant failure; Figure 3 the edges of both ends of the roller are seriously worn, and the roller is broken and broken. It is mainly caused by overload and lubrication failure.

 

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Fig. 1 Axial fracture of inner ring

 

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Fig. 2 Inner race surface damage

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Fig. 3 Roller failure form

 

2. Long life design and manufacturing

2.1 Improve the design life of bearings

In the design of rolling mill bearings, combined with the research of bearings at home and abroad, the main parameters are limited to ensure the maximum rated load and the longest calculated service life (the theoretical service life of rolling mill bearings is 40000~50000h under normal service conditions). When selecting materials, generally select high-quality vacuum degassed steel or electroslag remelted high-carbon chromium bearing steel to ensure that the oxygen content of bearing steel material is less than 15 × 10 ~%, short-time carburizing or nitriding treatment can also be added during quenching and heating, so that there is a large residual compressive stress on the surface, which is helpful to improve the fatigue resistance; For large impact load, carburizing material should be selected to keep 1~3mm thick carburizing layer on the working surface of the ferrule, so that the working surface of the bearing has high hardness and the heart has good impact toughness.

 

2.2 Lubrication structure design

The rolling mill bearing is used in a bad environment, and the re lubrication structure of the bearing is very important for the rolling mill bearing. The lubrication structure designed in this case is: four row cylindrical roller bearings are designed with lubricating oil grooves and oil holes on the bearing end face and outer diameter surface, as shown in Figure 4.

 

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Fig. 4 lubrication structure diagram of four row cylindrical roller bearings

 

2.3 Bearing processing and manufacturing

The roller and ferrule are usually in line contact, so the line contact elastohydrodynamic lubrication theory can be used to analyze the bearing lubrication state. According to the minimum oil film thickness calculated in the literature, the typical film thickness is o.1-1um, and the film thickness ratio is usually 3-10 (3<a<10).

 

The roller and ferrule are usually in line contact, so the line contact elastohydrodynamic lubrication theory can be used to analyze the bearing lubrication state. According to the minimum oil film thickness calculated in the literature, the typical film thickness is 0.1~1um, and the film thickness ratio is usually 3~10 (3<a<10). In the manufacturing process of bearings, this factor is considered in the selection of roughness when machining raceways. According to foreign research, under the condition of selecting the appropriate lubricant viscosity, when the roughness processing is suitable and meets the corresponding oil film thickness, the bearing reliability life coefficient can be increased to more than 1 for roller bearings, which is very beneficial to the life of bearings.

 

According to the actual use of cold rolling mill bearings, improve the bearing accuracy reserve, reduce the discreteness of bearing related equivalence, and reduce the bearing

The roughness of the joint surface is the following points: in the manufacturing process, the following points are mainly considered:

 

(1) Eliminate bearing processing stress. The internal stress caused by the processing of bearing parts has a great impact on the dispersion of bearing fit size and raceway size, and the stability of raceway oil groove size. In the use of bearings, due to the transmission of load by rollers, the raceway oil groove and inner ring of the bearing are under great stress when subjected to impact load. The existing internal stress is the cause of peeling off at the end of the roller and cracking of the inner ring of the bearing, which can-not be ignored. Add heat treatment and tempering stabilization process after ferrule grinding between manufacturing processes to eliminate stress to minimize the harm. If conditions permit, the time for stress relief should be extended as much as possible, such as natural aging, to fully release the stress.

 

(2) Control the discreteness of bearing fit size. The discreteness of the inner and outer diameter dimensions should be small to ensure that the gap between the two sides of the rolling mixer is uniform and the stress is stable when the host is installed. Under the condition of ensuring the inner diameter of the bearing roller group, the internal raceway size and roller size of the bearing need to be selected and determined to ensure the bearing clearance. Because the processing of the two rows of raceways is not completed synchronously in the processing, it is necessary to strictly ensure the dispersion of the two rows of raceways and roller size, so as to avoid the premature loss of accuracy and damage caused by the force deflection and uneven lubrication of the bearing during operation.

 

(3) Improve the roughness requirements of bearing mating surface. In the process of machining, select the appropriate grinding wheel granularity, reasonably adjust the grinding wheel dressing times, and use the appropriate coolant to make the machining accuracy and roughness of the bearing mating surface have a high level.

 

3. Environmental constraint control

3.1 Environmental requirements and installation of bearings

The system vibration produced by the shaft and bearing pedestal matched with the bearing and other mechanical components will affect the service performance of the bearing itself. The common methods to ensure the reasonable use of bearings are to reasonably control the flatness of the steel housing on the tapping side of the mill, the wall thickness difference of the bearing housing seat hole and the deflection of the roll shaft. At the same time, the assembly clearance between the bearing seat and the bearing outer ring should be reasonably selected and controlled. When the bearing seat is matched with the bearing outer ring, the interference is too large or the original clearance is too small, which often leads to the fracture or sintering of the bearing ring. The loose fit between the roll neck and the bearing will cause the sliding and abrasion of the bearing.

 

The data shows that more than 30% of the failure of rolling mill bearings is caused by improper installation of bearings. When installing the bearing, pay attention to the concentricity of the bearing and the mating surface of the roll neck and seat hole, so as to avoid eccentric load when using the bearing. In order to eliminate the manufacturing deviation of rollers, at present, the inner ring of four row cylindrical roller bearings mostly adopts the method of pre assembly and grinding of rollers and bearing inner ring, which is simple and practical. The internal clearance of bearings after assembly and grinding must match the service environment and temperature rise of bearings.

 

3.2 Use and maintenance of bearings

Two points should be paid attention to in the use of bearings: one is that they cannot be overloaded, and the other is that the lubrication is reasonable. After the installation of the bearing, regularly check the smoothness of the lubricating oil circuit, listen and measure its working temperature; Check or analyze the lubricating grease in the static state of the bearing; Avoid premature bearing failure caused by overload of equipment; Thoroughly inspect the bearings every 3-12 months; Carefully check the wear of the raceway of the disassembled bearing and build a history card; Bearings that are not used temporarily should be lubricated with oil, packed and stored in a proper place; During the operation of the bearing, the monitoring facilities of the bearing shall be increased to prevent the problem first, find the problem as soon as possible, and avoid greater losses.

 

4. Conclusion

According to the form of abnormal failure of cold rolling mill bearings, the causes are analyzed. It is not only necessary to improve the design and manufacturing: improve the design life, select excellent materials, reasonably design the lubrication structure, improve the accuracy reserve of bearings and the roughness requirements of their mating surfaces, and reduce the dispersion of bearing technical indicators. It is also necessary to reduce the manufacturing error of the roll journal and bearing seat, install and use correctly, maintain reasonably, and diagnose in time in combination with the factors such as the installation and use environment of the bearing. Only in this way can we really improve the service life of bearings, fundamentally reduce bearing consumption, save energy and increase efficiency.

 

More about ITS Cylindrical Roller Bearing

ITS cylindrical roller bearing top quality brand has guaranteed production and highly active management.

 

The cylindrical roller bearings have a high radial load capacity and are suitable for high speeds. They are in linear contact with the raceways. They are designed to be reliable and a good fit for the environment. The bearing is highly versatile and can be used for many applications.

 

Cylindrical roller bearings are also available in sealed or split designs. In sealed bearings, the rollers are protected from contaminants, water and dust, while providing lubricant retention and contaminant exclusion. This provides lower friction and longer service life.

 

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2022-07-25

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