Abstract: This paper introduces the technical measures adopted in the selection, assembly and use of roll bearings for high-line rolling mill in Anyang Iron and Steel Group Company to extend the service life. The production line has not occurred a burning bearing accident for 29 consecutive months, reaching a higher level in the same industry.

Key words: roll bearing; Life span; Assemble; Use

1 Introduction

Anyang Iron and Steel Group's high-speed wire rod production line has a total of 30 rolling mills [1], of which the roughing and middle rolling zone is 1 # ~ 14 # rolling mill, flat vertical arrangement [2], and the equipment is manufactured in China. In order to reduce the accidental damage of roll bearings, technicians have accumulated a lot of experience in the production.

2  Selection of roll bearings and accessories

2.1 Bearing Selection

The selection of roll bearing in rough rolling is mainly to calculate the rated dynamic load and rated static load according to the rolling mill parameters, select the configuration mode, bearing type and radial clearance.

2.1.1 Configuration Mode

According to the main rolling parameters of 1 # ~ 14 # frame, see Table 1, the configuration method of four rows and single and double rows is selected. Double-row angular contact bearings with strong axial fixing ability are used at the adjusting end of the rolling mill, and single-row deep groove ball bearings are used at the non-adjusting end.

2.1.2 Bearing model

The products of Germany FAG Company and Beijing People's Bearing Factory (hereinafter referred to as human shaft) are selected, as shown in Table 2.

2.1.3 Radial clearance

According to bearing load, speed, lubrication, temperature rise, mating surface roughness, bearing inner diameter matching interference and other conditions, the radial clearance group is selected as C4. Detailed parameters are shown in Table 3.

2.1.4 Matching of rolling bearings

The matching between the bearing inner ring and the roll neck adopts the interference matching with the base hole, as shown in Table 4.

The matching between bearing outer diameter and bearing seat adopts base shaft clearance matching, as shown in Table 5.

2.2 Bearing Seal

The ideal bearing seal can effectively prolong the service life of the rolling mill bearing, reduce the accidental damage of the bearing, and improve the operation rate. According to the field conditions, the labyrinth seal is selected on the outside of the bearing, and the double skeleton rubber seal is used on the shaft, as shown in Figure 1. The rubber material is made of imported NBR special skeleton oil seal, the gum hardness is HSD70 ~ 75; The spring material is 1Cr18Ni9Ti; The skeleton material is made of 45 steel cold rolled sheet. The dimensional processing accuracy of the bearing seal should be controlled between +0.10 and +0.20mm, and the seal shape should not have coarse grain, pattern or crack.

This form of sealing can make the disassembly of the roll very convenient, and when the grease is added to the bearing seat in the work, the old grease can overflow from the lip of the sealing ring, and the external water, oxide and other impurities are prevented by the lip. When the roll speed is high, the centrifugal force will reduce the working pressure on the base surface and reduce the wear of the sealing ring.

2.3 Bearing lubrication

According to the dynamic lubrication theory of elastic fluid and the technical parameters of high line rough rolling, the grade of grease is determined by EHI calculation, as shown in Table 6.

3 Bearing assembly

3.1 Cleaning

After the roll is replaced, the removed bearing needs to be cleaned. The cleaning fluid is generally kerosene or diesel, and the cleaning time should be determined according to the temperature, as shown in Table 7. Because kerosene and other cleaning fluid will destroy the viscosity of the lubricating oil, so after the end of cleaning, the remaining cleaning oil inside and outside the bearing must be wiped clean.

3.2 Assembly

Before bearing assembly, all accessories should be carefully checked, including size, shape and fit tolerances and surface quality. The following 6 points should be noted during assembly:

(1) When assembling bearing bushings and sealing rings, matching heaters should be used according to different models. Bushing heating temperature ≤100℃; Labyrinth heating temperature ≤120℃.

(2) During assembly, it is not possible to use hard assembly such as impact. The fit of labyrinth ring and roll diameter is generally a tight dynamic fit, and the two ends of the labyrinth ring must be parallel and closely fit with the shaft shoulder and bearing inner ring [3].

(3) The top rod of the roll balance hydraulic rod must be flexible during assembly, and oil leakage is not allowed.

(4) The lateral pressure clearance between the double-row bearing end cover and the four-row bearing is generally controlled in that the clearance of the washer after compression is within 0∙1 mm, and the total momentum of the bearing seat after installation should be controlled within 1.0mm.

(5) A rubber seal is installed between the bearing seat and the roll diameter to prevent water and iron oxide from leaking to the bearing seat.

(6) In order to ensure that the bearing seat does not move after the assembly line, the special wrench is used to lock the bolt according to the technical parameters (see Table 8).

4 Bearing use and maintenance

During production, roll bearings are also affected by many actual conditions, such as: the vertical frame has different degrees of bearing seat leakage, leakage of iron sheet and other problems, some of the frame lubrication effect is not good, rapid temperature rise. Therefore, in use, attention should also be paid to:

(1) During operation, regularly observe the bearing and measure its working temperature with a thermometer. When the cooling water is used normally, the general bearing temperature is controlled below 65 ° C.

(2) Regular injection of grease, four columns of cylindrical roller bearing grease should account for 1/3 of the bearing chamber.

(3) Check seals and roll bushings regularly and replace them in time.

5 Conclusion

After adopting the above technology, Angang High Line unit has been put into operation since July 2001, the process is stable, the rolling is smooth, and 850,000 tons of steel has been produced. There has been no burning of bearings for 29 consecutive months, reaching a higher level in the same industry in the country.

【 Reference 】

[1] Xie Jifeng, LI Zilin, ZHAO Ziyi. Brief Introduction to the Design of High-speed Wire Rod Production Line of Angang [J]. Steel Rolling, 2002,19 (1) : 44-46

[2] Fang Shixing, et al. High Speed Wire Mill Equipment Technology [M] ∙ Beijing: Metallurgical Industry Press, 1997∙

[3] Zhou Lishen. Hot Roll Assembly [Z] · Technical Theory Training Materials for Metallurgical Workers (Intermediate Edition), Beijing: Ministry of Metallurgical Industry, 1985