High-speed wire rod rolling mill bearings and their applications

In order to meet the increasing demand for construction steel, China's metallurgical industry has introduced dozens of high-speed wire rod production lines from abroad in recent years. The discharge port speed ranges from 63 to 100m/s, and the annual output is mostly 60×104-100× Between 104t. Due to the special nature of the high-speed wire mill, more stringent requirements are put forward for the matching bearings. This article briefly introduces the working characteristics, structure, design points and manufacturing key of high-speed wire rod rolling mill bearings (hereinafter referred to as high-speed wire rolling mill bearings).
1 Performance requirements
1.1 High reliability
The most remarkable feature of the high-speed wire rod production line is the high reliability of the continuous operation of the rolling mill. Due to the high unit output of the high-speed wire rod production line, it is required that the bearings, which are the key components of the rolling mill, have higher reliability than the ordinary rolling mill bearings within the specified inspection cycle. If a bearing failure will cause the entire production line to stop, this is something that the manufacturer cannot tolerate. Therefore, in the design and manufacture of high-speed wire rolling mill bearings, the reliability of continuous operation under high-speed operating conditions should be ensured.
1.2 Wear resistance
High-speed wire rolling mill bearings have strong wear resistance and can adapt to high-speed rotating work occasions. Example: For a high-speed wire rod production line, the export line speed is 63m/s, and the working diameter of the export rolling mill roll is 330mm, then the working speed of the bearing is 3650r/min. Long-term operation under high speed and heavy load will reduce the wear resistance of the bearing. It is a severe test. This requires that the supplied bearings must have wear resistance requirements.
1.3 Long fatigue life
High-speed wire mill bearings have a long fatigue life. Under normal circumstances, high-speed wire rolling mill bearings provided abroad are used for three years (because the roll components have to be unloaded for maintenance and repair half of the time, 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 Impact toughness is better
High-speed wire rolling mill bearings have better impact toughness, especially bearings used in rough rolling mills. In the process of rolling continuous cast billets into bars, the impact load is very large. Therefore, the bearing of high-speed wire rolling mill should not be broken when working under high speed and high impact.
To sum up, the working characteristics of high-speed wire rolling mill bearings are that they can work continuously, stably and reliably under high speed and high impact conditions, and have a long fatigue life.
2 Bearing structure
High-speed wire rolling mill bearings have four-row tapered roller bearings and double-row cylindrical roller bearings. In general, four-row tapered roller bearings are used for rough and intermediate rolling mills, double-row cylindrical roller bearings are used for finishing rolling mills, and bearings of the same type are used for horizontal rolling mills and plumb mills.
Whether four-row tapered roller bearings or double-row cylindrical roller bearings, their basic structure is similar to traditional rolling mill bearings, but the design of each part fully considers the problems of lubrication and heat dissipation, that is, the inner ring, outer ring, and spacer Rings (for four-row tapered roller bearings), cages, and rollers (for double-row cylindrical roller bearings) have many grooves and holes. In this way, the lubrication and heat dissipation channels formed by the grooves and holes and the channels on the bearing seat and the roll form a reliable lubrication and heat dissipation system. Coupled with a good sealing device, the bearing can run stably in high-speed and high-pressure conditions.
Although the design styles of high-speed wire rolling mill bearings provided by various manufacturers are different, they all have one thing in common, that is, the wall thickness of the inner ring is relatively thicker than that of ordinary bearings of the same specification, and the outer ring is relatively thinner.
3 Bearing design method
First, according to the operating conditions, service life, failure status and user requirements of the bearings on each line, the main parameters are appropriately adjusted to achieve a relatively satisfactory design effect.
Secondly, reasonably determine the technical conditions, put forward reasonable technical requirements based on the actual measurement results of similar products, and consider the specific working status of the bearing.
4 High-speed wire rolling mill bearing manufacturing
In view of the particularity of the work of the high-speed wire mill, two main tasks have been done in the manufacturing process. *** is the choice of material and heat treatment process, and the second is the roughness control of the rolling surface. Because the inner ring wall is thicker and the outer ring wall is thinner, some manufacturers specify in technical documents that the inner ring is made of carburized steel and the outer ring is made of high-carbon chromium steel. Correspondingly, the inner ring adopts the carburizing process, and the outer ring adopts the austempering and tempering process as much as possible, so that the obtained metallographic structure is lower bainite, so that the bearing's strength, wear resistance, impact toughness and Performance indicators such as fatigue life enable the bearing to meet the aforementioned work requirements. In addition, the hardness of the heat treatment also differs according to the different conditions of the roughing, medium and finishing mills. For the roughing mill, the speed is relatively low, and the impact load is relatively large, so the hardness of the bearing parts is low; for the finishing mill, the speed Relatively high, and the impact load is relatively small, so the hardness of the bearing parts is high; the hardness of the bearing for the middle rolling mill is in the middle.
Through observation and test analysis, the surface roughness values ​​of the raceway surface, rib surface, and the reference end surface of the roller rolling surface of the inner and outer ring of the high-speed wire rolling mill bearing are smaller than those of ordinary rolling mill bearings. For this reason, measures are taken in the process to make the above-mentioned surface roughness reach or close to the level of foreign products.
　　5 Bearing trial status
　　Since May 1997, 9 models of high-speed wire rolling mill bearings have been trial-produced or mass-produced for 3 high-speed wire rod production lines in my country, and most of them are in good condition, and there has been no operation failure that caused the entire line to stop. Among them, in May 1997, it was the first batch of medium-rolling mill bearings (four-row tapered roller bearings) that were installed on a plumb mill (plumb mills are worse than horizontal rolling mills), which were trial-produced for a high-speed wire in Southwest China, except for one set After the bearing was in operation for a period of time, the outer ring was found to be broken during the normal unloading inspection, and the other three sets had no failures such as wear, fatigue, and rupture until June 2000.
　　6 Suggestions
　　 Further development and application of high-speed wire rolling mill bearings to stabilize their performance at a higher level should be carried out from the following aspects.
　　(1) According to the introduction of literature, on the basis of experiments and research, new-type rolling mill bearing steels with excellent performance have been smelted, including carburized bearing steel and high-carbon chromium bearing steel.
　　(2) On the basis of analysis, research and comparison of similar products, the main parameters are determined according to the use of the bearing, and the product design is done. In addition, the structural changes to the parts, such as the arrangement of the slots and the shape of the spacer, cannot be ignored.
　　(3) Carry out technological research to make up for the relatively poor material performance and relatively backward equipment capabilities. The emphasis is on heat treatment and grinding to ensure the effective carburized layer depth and hardness uniformity, the impact toughness of high-carbon chromium steel parts, and the shape and position tolerances and surface roughness of the parts are within a certain accuracy range.
(4) Develop standardized and detailed installation, commissioning, maintenance and inspection instructions; send technicians to users to explain the precautions of bearing use for on-site technicians and workers, answer questions raised by on-site personnel, and do a good job in after-sales service . Users need to cooperate well with bearing manufacturers.