Common accident analysis and solutions for high-speed rolling mill finishing mills, rolling mill technology

The finishing roll mill unit of a high-speed wire factory adopts a 45° top-crossing cantilever rolling mill designed by Italian DANIELI company, which was put into use in 2015, and its main production wire specifications are Ф5.5 to Ф16mm. The unit is composed of eight rolling mills, and the maximum designed speed of the mill is 116m/s. In the initial period of production, the unit frequently had a problem of roll box water ingress, TC ring crack, and jamming of the locking device during operation, which seriously affected normal production. To this end, the high-speed wire plant set up a research team to tackle such frequent accidents.

• Common accident analysis and solutions

1.1 Principle of mill roll shaft sealing

The inner and outer oil throw rings are installed at the shoulder of the roll shaft, and the double lip seal is installed on the figure eight panel. The seal is in contact with the inner surfaces of the inner and outer oil throw rings, and a certain pretension pressure is given. The seal and figure eight panel remain static, and the inner and outer oil throw rings rotate synchronously with the roll shaft at high speed. The sealing lip shrinks inward to generate pressure, forming a sealed area, and at the same time, the seal throws out the lubricating oil accumulated in the periphery and driven by the high-speed rotation of the roller shaft to return it to the oil tank. The sealing structure is shown in Figure 1.

1.2  Analysis of the reason for the water leakage in the roll box

• The gap between the outer oil thrower ring and  the “八” type panel is too large, and the high-pressure cooling water enters the oil thrower ring and the seal from the gap, thereby brought impurities make the sealing lip damaged; or the inner and outer oil thrower rings  match with the seal improperly, above matters make water enter the roll box.

• Due to installation or accidents, the “八” type panel deforms, destroying the sealing conditions of the roll box and “八” type panel; improper installation of seal rings, eccentric sleeves and other components, resulting in a fitting gap, making water in the roll box.

• The material of the double lip seal has insufficient oil resistance, which causes the seal lip to form dry friction with the roller shaft at high temperature, which accelerates the aging of the seal and causes the sealing effect fail.

• The pressure of compressed air is insufficient, and it didn’t reach the setted value, and the cooling effect of the cooling water purge and the sealing lip is not achieved.

1.3  Solution

• Standard installation requirements, including the flatness of the roller box panel, the “八” type panel, the joint surface of the roll box and the cone box into the installation operation regulations; for the “八” type panel retainer, the “八” type panel and roll box panel joint surface Wait for grinding treatment and flatness test; carefully check whether there is local deformation or residue before installing the oil throwing ring. It is strictly forbidden to use metal tools during assembly; when installing double lip seals, pay attention to the holder and double Whether the skeleton of the lip seal is loose, and then pressurize at the same time until it is installed in place; it is strictly prohibited to knock the lip of the double lip seal.

• Improve the material and optimization of double lip seals, mkae structure and size strict, control the lip interference of double lip seals, and ensure the service life.

• Strengthen the control of compressed air pressure to ensure that the pressure is within the specified range, and regularly unclog the air pipe to ensure the smoothness of the pipeline.

• Formulate roll box assembly process standards, assembly cleaning requirements, and regular replacement of spare parts, and strengthen the quality control and measurement of spare parts.

• Roll ring fragmentation

2.1  Accident analysis

• The roll ring locking device is not locked in right place, the roll ring is loose, causing the roll ring and the roll shaft to rotate relatively. High-speed rotating friction generates a large amount of heat, causing the roll ring to crack.

• The pressure of the roll ring cooling water is insufficient, the flow rate is not enough, the roll ring temperature is always in a high temperature state, which accelerates the aging of the rolling groove, thereby generating cracks.

• Due to the high temperature baking the roll ring, the roll ring is put into production without cooling. The high-temperature roll ring is suddenly sprayed with cooling water, and uneven heating inside and outside causes the roller ring crack.

• Roll rings have internal defects during manufacture, which is also one of the reasons for the cracking.

2.2  Roll box solution

• Standardize the installation operation of the roll ring, clean the cone sleeve and the roll shaft, and avoid oil stains and impurities on the interface between them; the tapered sleeve and the roll shaft of the lower line must measure the taper; the unqualified cone sleeve and the roller shaft are prohibited from being used on the line,

• Regularly clear the nozzles of the cooling water block to avoid blockage; ensure that the water supply pressure cannot be lower than the set value, and add sound and light alarm devices, pay attention to water pressure and flow.

• Due to the accident, the roll ring should naturally cool down after being baked at high temperature, and it is forbidden to turn on the cooling water to cool down. If it is urgently needed for production, a new roll ring can be replaced to reduce the downtime of the production line.