The sealing ring and double humiliation structure are used to prevent foreign matter such as iron oxide scale and cooling water from entering the bearing and the leakage of lubricating grease, so as to extend the service life of the bearing, protect the environment, save energy and reduce consumption.
Keywords: rolling mill bearings; sealed bearings; tapered roller bearing
The 3200 rolling mill in the plate factory of a steel company is a second-hand equipment imported from abroad in 1998, transformed and put into production. The roughing mill has a four-roller reversible structure. The back-up rollers use four-row tapered roller bearings with an overall size of φ780mm × φ1220mm × φ840mm. The work rolls use sliding bearings. The bearing works under harsh conditions such as impact, heavy load, wear, and 20MPa high-pressure water erosion, and the rolling force is 3000t. The working speed is 0~32.786~65.571r/min. The main engine design requires the service life of the bearing to be rolled 3×104t steel.
Design and development of four-row tapered roller bearings
Since the outer dimensions of the bearing are non-standard and the size series is indefinite, the model is designated as 3806/780. According to the working conditions of the rough rolling mill in the medium and heavy plate plant, the rolling bearing limit design method is adopted in the design. First determine the strength boundary value of the ferrule, and then derive a set of formulas to make the designed rolling element size infinitely approach the strength boundary values of the ferrule, that is, the designed rolling element has the largest diameter and the longest length.
The rated dynamic load Cr of the 3806/780 bearing design is 28.4MN, which meets the design requirements of the host. In terms of materials, the inner and outer rings and rolling elements are all made of high-quality electroslag remelting carburized steel G20Cr2Ni4A. In addition, corresponding measures are also taken in terms of technology, tooling, inspection, assembly, etc. to ensure that the 3806/780 produced can meet various design requirements.
The 3806/780 bearings have been installed and used to meet the performance requirements of the main engine. However, during use, there are also the following problems. When the 3200 medium and heavy plate rolling mill was purchased, the seals on the bearing seats were damaged. Therefore, during the rolling process, iron oxide scale, foreign matter, etc. often enter the bearing due to the erosion of high-pressure water, causing indentations on the raceway, causing non-fatigue damage to the bearing and reducing the actual service life of the bearing. In addition, the leakage of lubricating grease in the bearings due to the action of high-pressure water is also serious, and oil needs to be added every 8 hours. This not only increases the usage and emissions of grease, but also increases the labor intensity of workers. Taking into account factors such as cost saving, consumption reduction, and environmental protection, a self-sealed four-row tapered roller bearing was designed and developed based on the 3806/780 bearing.
Development and use of single-sided sealed four-row tapered roller bearings
Single-sided sealing is chosen because the dimensions of the bearing box and the bearing have not changed, and the sealing ring takes up a certain amount of space. Therefore, the effective length of the rolling elements of the bearing is shortened to a certain extent compared with unsealed bearings. According to the calculation formula of the basic radial dynamic load rating Cr of the rolling bearing, the rolling element length Lwe decreases, and the Cr value decreases. Considering that the Cr value of the bearing’s load-bearing capacity cannot be reduced too much, a single-sided seal is used, that is, a seal is added close to the roll body. The model of the single-sided sealed four-row tapered roller bearing is 3806/780-RS, and its design still adopts the rolling bearing limit design method. Its rated dynamic load value is Cr=27.1MN, which is only 4.6% lower than the Cr value of 3806/780 without seal. The design load can still meet the performance requirements of the host. In addition, the same measures as 3806/780 have been adopted in terms of materials, processes, tooling, inspection, and assembly.
As can be seen from Figure 1, there are three seals in single-sided sealed bearings. Its main seal is a double lip seal with a skeleton. The frame is made of low carbon steel and mainly supports the entire lip seal. The lip seal is made of rubber material and is divided into main lip, auxiliary lip and main lip (I in Figure 1). It is mainly to prevent the iron oxide scale, cooling water, foreign matter, etc. generated during the rolling process from entering the bearing and causing the bearing to wear or This causes indentations on the rollers and raceways, causing abnormal fatigue damage and affecting the fatigue life of the bearing. The main lip and the inner ring mating surface adopt an interference fit, and the interference amount is 4±0.9mm. A spring is used to generate a certain adhesion force at the contact point between the main lip and the inner ring mating surface. To ensure that the sealing force remains within the appropriate range during use. The auxiliary lip (II in Figure 1) is mainly to prevent the grease in the bearing from leaking. The mating surface of the auxiliary lip and the inner ring adopts a transition fit, and the transition amount is 1±0.9mm. The outer diameter of the inner ring that matches the lip should be ground by the cutting method to prevent the tiny wear marks left by reciprocating grinding from damaging the sealing lip and affecting the sealing effect. The outer diameter of the lip seal matches the inner diameter of the bearing seal ring, usually a transition fit, and the seal ring adopts H8 fit. O-rings are installed on the outer diameter surface of the sealing ring and the inner spacer ring to prevent cooling water from entering the inside of the bearing from the outer diameter of the sealing ring and the inner diameter of the bearing. A 3mm x 5mm groove is processed on the end face of the sealing ring in the direction of the bearing box end cover. After the lip seal is installed in the sealing ring, 8 points are chiseled on the end face groove to press the lip seal end face. Prevent the lip seal from falling off the sealing ring due to internal pressure.
According to statistics on the service life of 3806/780-RS bearings, the average steel rolling volume has reached 62.44×104t. Compared with unsealed bearings, its service life has been greatly improved, reaching twice the original design level, and it is a long-life bearing. .
When sealed bearings are not used, the bearings are refueled every 8 hours. After using single-sided sealed bearings, the refueling time is changed to every 2 days. The consumption of lubricating grease in that year is 28.74t less than the average consumption of grease in the first three years. . Afterwards, based on experience, the refueling interval was adjusted to once every 3 days, saving 41.94% of grease.
When sealed bearings are not used, the discharged and lost grease, iron oxide scale, cooling water, etc. enter the sedimentation tank of the circulation system together to form sludge and sink to the bottom of the tank. During the equipment maintenance every year, the sedimentation tank needs to be completely cleaned. After changing to sealed bearings, this part of the cost has also been greatly saved. 3806/780-RS bearings significantly improve the lubrication effect, realize the localization of extra-large sealed bearings, and bring considerable economic benefits to the users.