Abstract: The double and four-row tapered roller bearings with double-sided seal used in hot plate rolling mill adopt sealing ring and double lip structure to prevent the foreign matter such as oxidized iron sheet and cooling water from leaking into the bearing and lubricating oil, so as to improve the service life of the bearing, protect the environment, save energy and reduce consumption.

Key words: hot sheet mill; Sealed bearing; Energy saving and consumption reduction

1 Overview

The double and four row tapered roller bearings are used in the rolling mill of each rolling mill, and the bearings work in the impact, high temperature, high speed, heavy load, poor lubrication, high pressure water erosion and other harsh working conditions. The end of the bearing box is designed with seals, mainly to prevent foreign bodies from entering the bearing, such as impurities, cooling water, oxide sheet and so on. When the new seal is just used, the sealing effect is good, but after a period of time, the sealing effect becomes worse, at this time, if the seal is not replaced in time, the sealing effect is very poor, coupled with the bearing assembly and disassembly frequently affect the seal and other reasons, the foreign matter such as the oxide sheet and cooling water generated during the rolling process will enter the bearing, and the lubricating oil will leak out. This will cause non-fatigue damage to the bearing, reduce the service life of the bearing, but also increase the workload of workers often add grease, and the use and emissions of oil, resulting in environmental pollution. For these reasons, there is an urgent need to develop a bearing with its own seal.

2 Seal structure and characteristics

Considering the above reasons, the double and four row tapered roller bearings with double sealing for hot rolling plate mill are designed and produced, as shown in FIG. 1 and FIG. 2.

As can be seen from Figure 1 and Figure 2, the double-sided sealed bearing adopts a sealing structure with sealing rings on both sides, a contact lip seal with a skeleton and a compression spring inside the inner spacer. The lip seal is a double lip structure, divided into primary and secondary lips. The main lip (see A in the figure) is equipped with a helical spring, which acts on the working surface of the outer diameter of the inner ring and the lip seal with a certain adhesive force. The diameter of the lip and the outer diameter of the inner ring adopt interference fit. The interference amount takes different values according to the bearing inner diameter d, the general value range is 300mm < d < 400mm, GYL (interference amount, the same below) =2.4~4.0mm; 400mm < d < 600mm, GYL=2.8~4.4mm; 600mm < d < 800mm, GYL=3.1~4.9mm. The outer diameter of the inner ring matched with the lip should be grind-in to prevent the small abrasion marks left by reciprocating grinding from damaging the sealing lip and affecting the sealing effect. The main lip is mainly to prevent the oxide sheet, cooling water, foreign matter generated in the rolling process from entering the bearing, causing wear to the bearing or making the roller and raceway easy to produce indentation, resulting in abnormal fatigue damage, that is, affecting the fatigue life of the bearing. The diameter of the secondary lip (see B in the figure) is loosely matched with the diameter of the mating surface of the inner ring, which is generally about 0.5 to 1.0mm according to the difference of the bearing inner diameter d. The secondary lip is mainly to prevent the leakage of lubricating oil in the bearing. The outer diameter of the lip seal is matched with the inner diameter of the bearing seal ring, which is generally a transition fit, and the seal ring adopts H8 fit. The outer diameter surface of the sealing ring is provided with a slot, and the O-type sealing ring is installed to prevent the cooling water from entering the bearing inside from the gap between the bearing box aperture and the bearing outer diameter. On the sealing ring end face in the direction of the bearing box end cover, according to the size of the inner and outer diameter of the bearing, the car is a wide × deep groove, generally about (1.5~3) mm~ (3~5) mm, when the lip seal is loaded into the sealing ring, chisel 6~8 points on the end groove to press the lip seal end face and prevent the phenomenon of the lip seal falling off the sealing ring due to internal pressure. The seal at the inner spacer adopts an internal compression spring, and the lip is in contact with the mating surface of the inner ring. The interference fit is adopted, and the interference amount is generally 0.5~1mm.

For double and four-row tapered roller bearings with double-sided sealing, due to the sealing ring structure on both sides, the effective height of the whole set of bearings is reduced under the condition that the bearing assembly height is unchanged, that is, the length of the roller is reduced under the condition that the wall thickness of the ring is unchanged. According to the radial basic rated dynamic load Cr formula and basic rated life L10 formula of rolling bearing:

Formula:

Cr -- Radial basic dynamic load rating (N)

bm - the rating factor of contemporary commonly used materials and machining quality, which varies with bearing type and design;

fc - Coefficients related to the geometry, manufacturing accuracy and material of bearing parts;

i -- the number of roller rows in the bearing;

Lwe - Roller length (mm) used in load rating calculation;

α - nominal contact Angle of the bearing (°);

Z -- the number of rollers per row in multiple rows of bearings with the same number of rollers per row;

Dwe - Roller diameter (mm) for load rating calculation;

L10 -- basic rated life (×106r/min);

Pr -- radial equivalent dynamic load (N);

It can be seen from formula (1) that when the effective length Lwe of rollers is reduced, the Cr value will decrease when other parameters remain unchanged. According to formula (2), the Cr value will decrease, and the L10 calculated theoretically will also decrease for the same radial equivalent dynamic load. Generally, the Cr value of the four-row tapered roller bearing with double-sided seal is 6%~13% lower than that of the four-row tapered roller bearing without seal. Double row tapered roller bearings because there are only two rows of rollers, with sealing on both sides, the length size reflected in the roller is reduced more, so the Cr value is reduced more, generally 15% to 30%. Considering that the double-row bearing is only subject to axial load when it is paired with the four-row bearing, the bearing contact Angle can be appropriately increased according to the specific operating conditions of the rolling mill when designing the double-row bearing with seal, so as to improve its axial bearing capacity. In the actual use of the bearing, due to the double-sided sealing structure of the bearing, the working environment of the bearing is greatly improved, and the foreign matter such as the oxide sheet, cooling water, and impurities generated during the rolling process cannot enter the bearing, and the lubricating oil does not leak, which makes the bearing parts always in a good oil film lubrication state during the operation. Therefore, the actual service life is better than the service life of unsealed double and four-row tapered roller bearings.

3 Application of sealed bearings

Designed for the work rolls of a seven-stand tropical steel continuous rolling mill in a steel plant with double-sided sealing double and four-row tapered roller bearings, models 3806/488.95-2RS (for F1-F3 racks), 3806/482.6-2RS and thrust bearings 3706866-2rs (for F4-F7 racks) respectively. After more than a year of operation, with 89.7% of bearings still in normal use, the average rolled steel volume is 1.604 million tons, which exceeds the average rolled steel volume of sealed bearings imported from Japan by 1.4 million tons (see the following table), and the oil gradually transitions from the original refueling per shift to refueling every 1 month, every 3 months, every 6 months. A total of 106.79 tons of grease is saved a year, and the emissions of waste fat are reduced, the environment is improved, the labor intensity of workers is reduced, and the purpose of energy saving and consumption reduction is achieved.

The three kinds of sealed bearings passed the new product identification conducted by the Sichuan Economic and Trade Commission entrusted by the State Economic and Trade Commission in August 2002.

4 Quality of seals

At present, most of the domestic manufacturers of seals, due to materials, technology, processing equipment and other reasons, the production of seals can not fully meet the design requirements, such as the shape of the seal is unstable, large and small, the size of the same batch of seals produced is larger, harder, shorter service life, and can not reach more than one year. Some can only be used for a month, etc. These problems still need to be further proposed by the seal manufacturer.

5 Closing remarks

Since the successful development of double and four row tapered roller bearings with double-sided seals, they have been successively used in other hot rolled plate mills, through one or two years of operation, have achieved good results, to achieve the purpose of energy saving and consumption reduction. We are ready to continue to promote the use of sealed bearings in the entire metallurgical industry, saving a lot of manpower, financial and material resources for the country.

【 Reference 】

[1] WANG Zhenhua "Practical Bearing Manual" [M]. Shanghai Scientific and Technical Literature Press,1996.

[2]GB/T 6391-1995, rolling bearings. Rated dynamic load and rated life [S].