Abstract: Large scale steel rolling machinery equipment has the characteristics of high load capacity, low operating speed, and high impact load. Therefore, the working environment of the bearing is often harsh. In this working environment, how to ensure the safe and stable operation of the bearing can not only extend the service life of the bearing, but also enhance the service cycle of the entire steel rolling equipment. This is also an important problem faced by current technical personnel.
Keywords: steel rolling; Mechanical equipment; overhaul
1. Common problems during bushing maintenance process
(1) Performance and characteristics of bushing
1.In large-scale steel rolling machinery equipment, bushing have high wear resistance, as well as good wear reduction ability and strong running in performance.
2.When working at room temperature, the bearing can ensure that the working strength is not affected, and it also has high compressive and impact resistance capabilities.
3. Has strong adaptability in resisting friction.
4. The processing technology is excellent, with good thermal conductivity and strong corrosion resistance.
Under the conditions with the above characteristics, the most common failure problem of bushing is the generation of wear. Due to various frictions or fatigue damage, the surface of the bushing is damaged or the bearing wear reducing layer is damaged, resulting in the damage of the bushing.
(2) Problems and preventive measures that are prone to occur during the pouring process of bushing
1. The surface of the bearing alloy has defects. If there are slag inclusions, air holes, and other phenomena on the surface of the bearing, it will cause the bearing to malfunction during operation, and the main reason may be the influence of the alloy's chemical composition, the temperature of pouring, or the filling conditions of the mold. As for the tile shaft of large-scale steel rolling equipment, the casting and process are often relatively simple, so the main influencing factor is the control of pouring temperature. If the pouring temperature is high, the alloy can have good fluidity, and its filling effect will also be higher when pouring the bearing, which can prevent cold insulation and slag inclusion caused by low temperature. However, it should be noted that the pouring temperature should not be too high. If the temperature is too high, it will cause the shrinkage of the core to continuously increase, and its suction volume will also increase, making the oxidation of the bearing more severe, which is prone to the formation of pores and shrinkage holes. Therefore, when pouring the bushing, strict control should be exercised over their pouring temperature, ensuring that the filling capacity of the liquid alloy is not affected while controlling the pouring temperature. Under normal circumstances, it is advisable to pour liquid alloys at a temperature of around 230 ℃ to 250 ℃. When pouring, the bearings and shaft core should be fully preheated first, and the temperature should be controlled at 150 ℃. At this time, the heat dissipation speed of the alloy can be well controlled, thereby improving the filling ability of the liquid alloy and playing a good drying role in the mold. When pouring, the starting speed should be slow. As the pouring time increases, the pouring speed gradually accelerates uniformly. When the pouring is about to be completed, the pouring speed should be slowed down again. Throughout the pouring process, attention should be paid to whether the liquid alloy fully combines with the iron sheet. Furthermore, it should be noted that a certain degree of continuity should be maintained throughout the entire pouring process, and there should be no interruptions in between. After pouring is completed, a layer of preservation material should be covered on the surface of the bearing, allowing it to slowly cool and form naturally under natural conditions.
If the babbitt alloy and bearing liner are not firm after pouring the bushing, the main reason is that there is no complete preparation work. Therefore, before pouring, sufficient preparations should be made to thoroughly clean the bearing liner and use alkaline water to thoroughly clean it, especially without leaving any oil stains. After drying, thoroughly clean with ZnCl2 saturated solution to make it easier for the bearing liner to hang tin during pouring. At the same time, ensure that the pouring is carried out at a uniform speed and balance as much as possible, so that the bearing can hang tin evenly without leaving any gaps.
(3) Problems that are prone to occur during the scraping and grinding process of bushing and preventive measures
1.During the scraping process of bushing, it is easy to encounter phenomena such as uneven distribution of contact points or uneven stress on the bushing. In addition, scratches on the contact surface of the bushing are also a common problem.
The reason for the above problems is, on the one hand, due to the stress on the bushing. Due to the strong toughness of the raw materials used in the bushing, they are prone to deformation under the action of the journal force. When the bushing deform, their mouth will shrink inward, resulting in a profit, and the contact angle between the shafts will gradually increase. At this point, the force area of the bearing shell is also affected and increases, resulting in uneven contact surfaces between the shaft and the bearing shell. If the equipment is running, the areas with higher force will start to heat up first, while the areas with lower force will heat up slower, resulting in uneven temperature at different contact points. This temperature difference will continue to increase with the operation of the equipment, causing damage to the bearing shell.
Improvement of scraping and grinding the bushing. Good is the key to ensuring the normal operation of the bearing and extending its service life. The correct and reasonable scraping and grinding of the bearing pads should ensure uniform bearing capacity, appropriate stress area, smooth oil wedge insertion, and easy formation of a good oil film. After multiple practices, the following scraping method has been determined. The contact angle for scraping and grinding in the bearing area of the bearing is around 80 °. Within this range, the hard grinding points are evenly distributed from the middle to both sides and gradually become invisible. The number of bearing pad grinding points should be controlled at 4 or more (25mm x 25mm). The oil wedge of the bearing is wedged into the side, and the grinding point in the middle is faint. The two sides of the bearing are hard and solid, gradually transitioning to form a wedge shape. During the scraping process, the direction of the scraper blade intersects with the previous direction each time. And, after each scraping, the edges and burrs of the knife marks should be gently smoothed out.
2. Adjustment of clearance between bushing
After replacing the new bearing, the tightening force of the bearing should be fixed according to the specified data, so that the back of the bearing can tightly adhere to the bearing seat, and ensure that the outer diameter of the bearing should not be less than the inner diameter of the bearing seat hole. This can effectively prevent the bearing from loosening during operation. If the fit clearance of the bearing is not properly adjusted, it is easy to loosen and deform during the operation of the bearing. Therefore, the fit clearance of the bearing should be adjusted appropriately, not too large or too small, otherwise it is easy to cause operational defects in the bearing.
3. An effective method to extend the service life of bushing
3.1 Regular cleaning and inspection of the bearing system should be carried out to ensure the normal operation of the working system.
3.2 The oil should be replaced regularly to ensure that the oil used is clean and effective, and to prevent oxidation or deterioration of the oil.
3.3 Ensure the use of correct operating techniques. Before starting the equipment, if it is in the north and the winter temperature is low, the engine should be rotated to allow the oil inside the machine to flow into the bushing before starting the equipment. After starting the equipment, first idle for a few minutes, and then start when the water temperature reaches 40 ℃ or above; Only when the water temperature reaches 60 ℃ or above can load operations be carried out. It should be noted that the engine should not operate under load for too long and should be controlled.
When maintaining and repairing the bushing, it should be ensured that the dimensions of their inner and outer circles meet the requirements of mechanical equipment assembly. Finally, it should be noted that the occurrence of bearing accidents should be avoided in order to effectively extend the service life of the bearing.
In recent years, with the increasing use of bushing, their maintenance methods have also been continuously improved and perfected. In order to gradually expand the application scope of bushing and simplify and facilitate their troubleshooting during use, this article provides a simple analysis of the detection and maintenance methods of bushing, enabling them to be continuously applied in various fields and promoting the rapid development of related industries.
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