（1） High speed wire rolling mill bearings and their applications

In order to meet the increasing demand for construction steel in China's metallurgical industry, dozens of high-speed wire rod production lines have been introduced from abroad in recent years, with discharge speeds ranging from 63 to 100m/s and annual production mostly reaching 60% × 104~100 × Between 104t. Due to the special nature of high-speed wire rolling mill operation, stricter requirements have been put forward for the matched bearings. This article briefly introduces the working characteristics, structural form, design points, and manufacturing keys of high-speed wire rolling mill bearings (hereinafter referred to as high-speed wire rolling mill bearings).

1. Performance requirements

1.1 High reliability

The most significant feature of high-speed wire rod production lines is the high reliability of continuous operation of rolling mills. Due to the high unit output of high-speed wire rod production lines, it is required that bearings, as key components on the rolling mill, have higher reliability than ordinary rolling mill bearings within the specified inspection cycle. If the bearing malfunctions, it will cause the entire production line to stop production, which the manufacturer cannot tolerate. Therefore, when designing and manufacturing high-speed rolling mill bearings, it is necessary to ensure their reliability in continuous operation under high-speed operating conditions.

1.2 Wear resistance

High speed rolling mill bearings should have strong wear resistance and be able to adapt to high-speed rotating work environments. Example: For a high-speed wire rod production line, if the outlet line speed is 63m/s and the working diameter of the outlet rolling mill roll is 330mm, the working speed of the bearing is 3650r/min. Long term operation under high speed and heavy load will be a severe test for the wear resistance of the bearing. This requires that the supplied bearings must have wear resistance requirements.  

1.3 Long fatigue life

The fatigue life of bearings in high-speed wire rolling mills is longer. Under normal circumstances, the bearings of high-speed wire rolling mills provided by foreign countries are used for three years (as half of the time the roller components need to be unloaded for maintenance and refurbishment, the actual working time is one and a half years), so users require domestic bearings to be used for at least two years. 

1.4 Better impact toughness

The impact toughness of bearings in high-speed rolling mills is good, especially for bearings used in rough rolling mills. During the process of rolling continuous casting billets into bars, the impact load is very high. Therefore, the bearing of high-speed wire rolling mill should not rupture when working at high speed and high impact conditions. In summary, the working characteristics of high-speed wire rolling mill bearings are the ability to work continuously, stably and reliably under high speed and high impact conditions, and have a long fatigue life.

2. Bearing structure form

There are two types of bearings for high-speed wire rolling mills: four row tapered roller bearings and double row cylindrical roller bearings. In general, four row tapered roller bearings are used for rough and medium rolling mills, double row cylindrical roller bearings are used for finishing mills, and bearings of the same model are used for horizontal and plumb mills. Whether it is a four row tapered roller bearing or a double row cylindrical roller bearing, its basic structure is similar to traditional rolling mill bearings, but the design of each component fully considers lubrication and heat dissipation issues, that is, there are many grooves, holes, etc. in the inner ring, outer ring, spacer ring (for four row tapered roller bearings), cage, roller (for double row cylindrical roller bearings). In this way, the lubrication and heat dissipation channels formed by grooves and holes, as well as the channels on the bearing seat and roller, form a reliable lubrication and heat dissipation system. Coupled with good sealing devices, the bearings can operate stably under high-speed and high-pressure conditions. Although the design styles of high-speed rolling mill bearings provided by various manufacturers are different, they all have one common feature: the inner ring wall thickness is thicker compared to ordinary bearings of the same specification, and the outer ring is relatively thinner. 

3. Bearing design method

Firstly, adjust the main parameters appropriately based on the operation, service life, failure status, and user requirements of the bearings on each line to achieve a satisfactory design effect. Secondly, reasonably determine the technical conditions, based on the measured results of similar products, and considering the specific working state of bearings, propose reasonable technical requirements.

4. Manufacturing of bearings for high-speed wire rolling mills

Due to the unique nature of high-speed wire rolling mill work, two main aspects of work were carried out during the manufacturing process. The first is the selection of materials and heat treatment processes, and the second is the control of rolling surface roughness. Due to the thicker inner ring wall and thinner outer ring wall, some manufacturers specify in their technical documents that the inner ring is made of carburized steel and the outer ring is made of high carbon chromium steel. Accordingly, the inner ring adopts carburizing process, and the outer ring adopts isothermal quenching and tempering process as far as possible, so that the obtained metallographic structure is lower Bainite. After this treatment, the strength, wear resistance, impact toughness, fatigue life and other performance indicators of the bearing are taken into account, so that the bearing can meet the above working requirements. In addition, the hardness of heat treatment also varies depending on the different conditions of rough, medium, and finish rolling mills. For rough rolling mills, the speed is relatively low and the impact load is relatively large, so the hardness of bearing parts is relatively low; For finishing mills, the speed is relatively high and the impact load is relatively small, so the hardness of bearing parts is high; The hardness of bearings used in rolling mills is in the middle. Through observation and testing analysis, it has been found that the surface roughness values of the inner and outer rings of the high-speed rolling mill bearings, such as the raceway surface, retaining edge surface, and the rolling surface reference end face of the rollers, are smaller than those of ordinary rolling mill bearings. Therefore, measures should be taken in the process to ensure that the surface roughness mentioned above reaches or approaches the level of foreign products.

5. Trial use of bearings

Since May 1997, 9 models of high-speed wire mill bearings have been trial-produced or mass-produced for 3 high-speed wire rod production lines in China. The vast majority of bearings have been in good use and there have been no operational failures that caused the entire line to shut down. Among them, in May 1997, it was the first batch of trial produced rolling mill bearings (four row tapered roller bearings) installed on a plumb hammer mill in a certain high-speed line in Southwest China (the working condition of the plumb hammer mill is worse than that of the horizontal plane mill). Except for one set of bearings that had been running for a period of time and were found to have cracks in the outer ring during normal unloading inspection, the remaining three sets did not show any wear, fatigue, or failure until June 2000.

6. Suggestions

Further development and application of high-speed rolling mill bearings to stabilize their performance at a higher level should be carried out from the following aspects.

(1) According to literature, a new type of rolling mill bearing steel with excellent performance has been melted based on experiments and research, including carburized bearing steel and high carbon chromium bearing steel.

(2) Based on the analysis, research, and comparison of similar products, the main parameters are determined based on the usage of bearings, and product design is done well. In addition, structural changes to the parts, such as the arrangement of slot holes and the shape of spacers, cannot be ignored.

(3) Carry out process research to make up for the reality of relatively poor material performance and relatively backward equipment capabilities. The focus is on heat treatment and grinding to ensure the effective depth and hardness uniformity of the carburized layer. The impact toughness of high carbon chromium steel parts, as well as the geometric tolerance and surface roughness of the parts, are within a certain accuracy range.

(4) Develop standardized and detailed installation, debugging, maintenance, and inspection instructions; Send technical personnel to the users to explain the precautions for bearing use to on-site technical personnel and workers, answer the questions raised by on-site personnel, and do a good job in after-sales service. Users need to collaborate well with bearing manufacturers.

（2） Use and fit of bearings

1. Use of bearings

Rolling bearings are precision parts, so it is necessary to adopt a cautious attitude when using them. Even if high-performance bearings are used improperly, the expected performance effect cannot be achieved. Therefore, when using bearings, the following precautions should be taken:

① Keep the bearings and their surrounding environment clean. Even if invisible smile dust enters the bearing, it will increase the wear, vibration, and noise of the bearing.

②When using and installing, it is necessary to be careful and careful. It is not allowed to forcefully punch, directly hit the bearing with a hammer, or transmit pressure through rolling elements.

③ Use appropriate and accurate installation tools, try to use specialized tools as much as possible, and avoid using fabrics and short fibers as much as possible.

④To prevent rusting of bearings, when directly taking them by hand, it is necessary to thoroughly wash off the sweat on the hands and apply high-quality mineral oil before proceeding with the operation. Special attention should be paid to rust prevention during the rainy season and summer.

⑤ The selection of fit: The inner and outer diameter dimensions of rolling bearings are manufactured according to standard tolerances. The tightness of the fit between the inner ring of the bearing and the shaft, as well as the fit between the outer ring and the seat hole, can only be achieved by controlling the tolerances of the journal and the seat hole. The fit between the inner ring of the bearing and the shaft adopts a base hole system, while the fit between the outer ring of the bearing and the seat hole adopts a machine shaft system. To choose a correct fit, it is necessary to know the actual load conditions, operating temperature, and other requirements of the bearing, which is actually very difficult. Therefore, in most cases, the selection of coordination is based on the use of precision grinding.

⑥The magnitude of the load between the collar and the shaft or casing depends on the magnitude of the load. For heavier loads, a larger overload is used, while for lighter loads, a smaller overload is used.

（3） New Applications of Lubricating Bearings

1. SF-2 boundary lubrication bearing:

Acidic polymethylglyoxal has high wear resistance. When assembling with oil storage pits on the bearing surface with regular arrangement, it must be coated with lubricating grease. It is particularly suitable for rotating and swinging movements under high loads and low speeds, as well as parts that are often opened and closed under load and are not easily lubricated by fluid. Under boundary lubrication conditions, it can be used for a long time without refueling and maintenance, and refueling during the process can prolong the service life of the bearing, Currently suitable for metallurgical machinery, mining machinery, water conservancy machinery, automotive parts, construction machinery, agricultural machinery, etc.

2. Oil free self-lubricating bearings:

This product is made of steel plate as the substrate, sintered spherical bronze powder in the middle layer, and a mixture of polytetrafluoroethylene and lead rolled on the surface. It has the characteristics of low friction coefficient, wear and corrosion resistance, oil-free self-lubrication, and long service life. Using it can reduce costs, reduce noise, and prevent sticking and slipping. It is widely used in the sliding parts of various machines, such as printing machines, textile machines, hydraulic Cart, tobacco machines, medical machinery, fitness machines, micro motors, cars, motorcycles, etc.

3. Metal based embedded solid self-lubricating bearings:

It is a novel lubricating bearing that combines the characteristics of metal bearings and self-lubricating bearings. It is loaded by a metal matrix and lubricated by a specially formulated solid lubricating material. It has characteristics such as high load-bearing capacity, impact resistance, high temperature resistance, and strong self-lubricating ability.

4. Traditional oil bearing:

Due to its low noise and self-lubricating advantages, oil bearing has become a new favorite for computer CPU fan bearings, with a high market demand; In addition, with people's increasing demand for noise, the application of oil bearing in daily household appliances is also expanding.