Abstract: Based on a brief overview of the technical requirements of mechanical seals, taking a Zagang enterprise as an example, the installation and maintenance strategy of rolling mill bearing mechanical seals in this enterprise was analyzed and studied in detail from the aspects of preparation, installation steps, daily maintenance and troubleshooting, etc., in order to promote the good application effect of rolling mill bearing mechanical seals.

Key words: rolling mill bearing; Stable operation; Mechanical seal; Installation and maintenance

Rolling mill bearings often run for a long time in a series of harsh environments such as high temperature and heavy load and frequent impact load. In the rolling process, the cooling water required is usually ubiquitous, which is easy to affect the actual lubrication effect of bearings. In order to improve the sealing effect of bearing, it is necessary to deeply discuss the installation and maintenance of mechanical seal, so as to improve the sealing quality of rolling mill bearing and ensure the stable and efficient operation of rolling mill.

1 Mechanical seal overview

The mechanical seal mainly refers to a device that can prevent fluid leakage by at least a pair of effective perpendicular to the corresponding rotating axis end face, while maintaining long-term adhesion under the continuous action of fluid pressure and the compensating mechanism elasticity, as well as the close cooperation of the auxiliary seal. In 1885, the mechanical seal technology was born in the United Kingdom, China's development in the field is relatively late, at this stage, the mechanical seal can withstand the pressure can reach 42MPa or more, the actual temperature can withstand about 190 ~ 450℃, the speed is close to 50000r/min, the PV value can reach 1000MPa·m/s. In essence, it belongs to a special shaft seal device for rotating machinery, such as centrifuges or compressors and other equipment, because the drive shaft generally runs through the inside and outside of the equipment, there is often a circular gap between the shaft and the equipment, and the media in these equipment can continue to leak outward with the help of the gap, therefore, it is necessary to install a high-quality oil seal device that can prevent leakage. At present, there are many types of oil seals, and mechanical seals have become a widely used shaft sealing method for all kinds of equipment with many advantages such as less leakage and long service life [1]. Mechanical seals have certain technical requirements in the actual installation process, as shown in Table 1.

2 Analysis of mechanical seal design of rolling mill bearing

A domestic steel rolling company was established in 1999, the business scope is more extensive, such as ferrous metal smelting and related rolling processing products and by-product manufacturing, ferroalloy, automotive steel plate processing and metallurgical raw materials processing. The company's revenue in 2021 reached 21.68 billion yuan, an increase of nearly 31% compared to 2020, and a variety of rolling mills are used in the actual production and processing process, such as: In order to improve the sealing effect of all kinds of rolling mill bearings, the company uses mechanical seals, and the related seals are reformed and designed, and good sealing effect has been achieved.

As shown in Figure 1, the working principle of the mechanical seal is mainly to change the geometry of the seal, and then carry out scientific use of the effect of gravity and centrifugal force, so that the flowing (can be changed to cooling) water can be smoothly discharged along the bearing box. In the bearing mechanical seal design, the seal cover near the roll side is designed as a labyrinth seal cover, and an O-type seal ring is added to the contact surface of the seal cover and the inner hole of the bearing seat on both sides, so as to effectively prevent the cooling water from flowing into the bearing seat. The positioning sleeve on the left and right sides of the bearing is in close contact with the lip seal, and relative movement occurs during the high-speed rotation of the roll, so the positioning sleeve material is 42CrMo, and the surface is heat treated to improve its wear resistance life. A groove is designed on the surface of the positioning sleeve near the roll side to throw the cooling water through the labyrinth seal cover along the radial direction, reduce the pressure on the lip seal, and effectively reduce the probability of cooling water penetrating into the bearing seat.

3 Analysis of mechanical seal installation strategy of rolling mill bearing

The mechanical seal device belongs to a very high precision component, as shown in Figure 2 on the following page. In the actual installation process, it should not be hit hard, and at the same time, it should be handled gently to ensure stable operation of the seal device and achieve the ideal sealing effect [2].

3.1 Making preparations Before Installation

Before the actual installation of the bearing mechanical seal of the rolling mill, it is necessary to do a good job of the preparatory work before installation, mainly including the following aspects:

1) The staff will carefully check the specifications and models of the mechanical seals to be installed to ensure that all the contents are accurate, and strictly check whether there is a lack of relevant parts.

2) Check in detail whether there is damage to the mechanical seal components, especially the static ring, the corresponding seal end face of the dynamic ring, the need to strictly check whether there is a collision problem, if there is a damage problem, the damaged parts must be repaired, or directly replaced. In addition, a series of sealing elements should be cleaned with kerosene or gasoline, ensuring that the cleaning process is clean enough until there is no foreign matter or dust on the surface of the element.

3) Carry out a comprehensive inspection on the surface of the shaft or shaft sleeve, the inner wall of the sealing cavity and the inner surface of the corresponding sealing end cover to ensure that there are no grooves or burrs and other problems. Once the above problems exist, it must be repaired and polished in time. After completion, it must be cleaned with kerosene or gasoline to ensure that all parts are clean enough until there is no debris and dust on the surface of each part [3].

4) When scrubbing the surface of the moving ring and the static ring, it is strictly forbidden to use unclean cotton or cloth, and it is necessary to scrub with absorbent cotton and clean and soft gauze to ensure thorough and clean cleaning.

5) In the actual assembly process, all links are clean and clean, and at the same time, it is necessary to ensure that the sealing end of the static ring and the moving ring will not be scratched or broken during the actual installation. In order to enhance the convenience of installation and further reduce the difficulty of installation, an appropriate amount of oil should also be applied on the surface of the shaft or sleeve, and the end face of the moving ring and the static ring should also be applied appropriately to avoid dry friction during the actual starting process, so as to effectively protect the mechanical properties.

3.2 Installation steps of mill bearing mechanical seal

In order to improve the installation efficiency and quality of mechanical seals, installation operations are carried out according to the relevant steps as follows:

1) The corresponding geometric size of the parts and the actual processing accuracy should meet the requirements of the drawings, especially the size of the formation of the waterway must meet the requirements. According to the requirements of the assembly drawing, the actual installation position of the rotating parts should be specified, and reasonable adjustment should be made [4].

2) Before the actual assembly work, the mechanical lubricating oil should also be applied to the roll, and the parts should be scrubbed at the same time to avoid debris or dust, which will adversely affect the actual quality and effect of the mechanical seal.

3) In the actual parts installation operation, it is necessary to ensure the corresponding installation position of each part, and make appropriate and reasonable adjustments to avoid changes in the installation position due to the size error of the parts processing.

4) The installation of mechanical seals shall be carried out in the specified order, and the assembly shall be carried out in accordance with the relevant regulations, and it is strictly forbidden to vigorously knock and bump during the process. In addition, the sealing fastening screws of the bearing box should be tightened evenly to prevent leakage problems caused by inconsistent screw tightness or deflection of the end cap.

5) After the installation is completed, it should be carefully checked whether the auxiliary device is in normal condition to avoid dry friction, and pay attention to whether there are abnormal phenomena when turning the car. It can be delivered after running for a period of time.

4 Analysis of daily maintenance work of bearing mechanical seal of rolling mill

In order to ensure the safe and reliable operation of the rolling mill bearing mechanical seal, scientific and reasonable maintenance and maintenance of the sealing parts should be carried out in daily work, the specific practices are as follows:

1) Before the actual driving, the specific installation sequence of the mechanical seal and the configuration of all parts are comprehensively and carefully checked [5].

2) Gently rotate the roll with your fingers, under normal circumstances, you can feel the rotation is very light, there will be no resistance, to prove that the mechanical seal parts are installed normally and run reliably.

3) In the actual rotation process, carefully check whether the bearing is sufficiently lubricated, whether there is abnormal sound, etc.

5 Do a good job of handling common mechanical seal failures

1) Overheating and smoking occurred in the actual rotation process. The causes of such failure problems generally include: the size and shape accuracy of the machined parts are relatively low; Parts have deformation problems during actual transportation or maintenance; During the actual installation process, the parts were knocked and deformed. The parts themselves are installed in an incorrect sequence [6].

The specific treatment methods are: before the actual installation, carry out strict inspection work for all parts combined with drawings, especially with the size, the geometric shape accuracy of the parts themselves, etc., need to focus on inspection; Carry out special management and storage of sealed parts to avoid parts deformation due to unreasonable storage; Avoid collision with heavy objects as much as possible during transportation; During the installation process, it is strictly prohibited to use a sledgehammer to knock the seal. Generally, it can be heated in advance by hot loading method, and then hit with a small hammer until it is finally in place.

2) After completing the sealing operation, there is still a small amount of water into the bearing box. The causes of such problems are: after the completion of the installation operation, the seal tilt or parts geometric accuracy problems; There is a problem that the fit surface of the roll and the corresponding seal is not suitable in geometric size, which can not form a good interference fit. The corresponding seals on the bearing box have quality problems or have been damaged.

The specific treatment methods are: strict inspection of parts according to the requirements of drawings; Do a good job of cleaning during the actual assembly of parts; Carefully check the bearing box gasket, once there is a quality problem or has been damaged, timely replacement.

6 Conclusion

The bearing mechanical seal of rolling mill is a key measure to ensure the stable and efficient operation of rolling mill and extend its service life. The installation and maintenance of the bearing mechanical seal of rolling mill can improve the installation level of the mechanical seal and reduce the occurrence of safety accidents.

【 Reference 】

[1] Lin Haibo, Yang Jianxi. Design and Test of Lubrication and Sealing Structure Improvement of High Speed Ball Bearing [J]. Journal of Mechanical Transmission, 2022,46 (5) : 139-143.

[2] Jia Qian, Ruan Qi, Liu Chaofeng, et al. Calculation and Experimental Study on Tribological Performance of Mechanical Seal of Turbopump [J]. Fluid Machinery, 202, 50 (2) : 1-7.

[3] Xu Jie, Yu Shurong, Yan Ruqi, et al. Flow Field Analysis and Sealing Characteristics of Flexible end-face gas Film Seals [J]. China Mechanical Engineering, 2022,33 (6) : 656-663.

[4] Zhang Fuying, Gao Yongxin, He She-yan, et al. Research on Influencing Factors of Reliability of Rotary shaft lip seal based on Orthogonal Test [J]. Lubrication & Seals, 202, 47 (5) : 112-120.

[5] Zhang Fuying, Zhang Yuanhao, Gao Yongxin. Research on Life prediction of Rotary shaft lip seal Ring [J]. Lubrication & Seals, 2022, 47 (2) : 96-101.

[6] Miao Shufeng, Wang Qingfa, Guo Qianli, et al. Research status of shaft sealing technology [J]. Southern Agricultural Machinery, 2022,53 (4) : 38-43.