This paper main writes Causes and Analysis of Rolling Table Failures
Rolling table failure analysis, steel rolling technology
rolling table, bearing seat, steel billet
The conveying roller table is the equipment with the largest number in the rolling production line, and it is also the equipment with the most failures. Due to the continuity of rolling production, any roller table in the rolling production line does not turn, which will cause production interruption. The bevel gear drive roller table supported by the traditional bearing seat is a commonly used structure for medium and larger steel rolling production lines, but the loss of rolling stoppage caused by it is very alarming. For a medium profile production line with an annual output of 300,000 tons of bevel gear drive roller table, the average daily downtime caused by the roller table is more than two hours. For such a production line, one hour of downtime during the production process will cost 5,000 yuan. The above coal consumption and labor cost losses will cause economic losses of more than three million a year. Therefore, reducing the failure rate of the roller table and reducing the time for emergency repair of the roller table failure is one of the main ways to improve the benefits of the steel rolling enterprise.
- Analysis of the causes of the failure of the rolling table
The working characteristics of the steel rolling table are that the temperature of the conveyed billet is high and the conveying load is relatively large. The roller table supported by the traditional bearing seat has two structures, one is the chain drive structure and the other is the bevel gear drive structure. for bevel gear drives).
1. Analysis of the causes of roller bearing damage
① The bearing seat changes the design oil clearance of the bearing
One of the working characteristics of the steel rolling table is that the temperature of the steel billet being conveyed is high. When the high temperature steel billet is transported by the roller table, the heat will be directly transferred to the bearing ring through the roller table shaft, and the bearing must expand from the ring to the axial and radial directions respectively. .The bearing in the traditional bearing seat is in the axial direction, because the width of the bearing chamber is often more than 10% larger than the width of the bearing, the bearing may expand in the axial direction, and the bearing will not cause “burning damage”. However, the bearing is in the radial direction, because The bearing seat is a structure fixed by upper and lower bolts, and the diameter of the bearing chamber cannot be changed. When the bearing ring continues to expand with the continuous increase of temperature, the outer ring of the bearing is fastened by the bearing seat and cannot expand. Therefore, the original design of the bearing The oil gap between the outer rings will be reduced, and the bearing will generate heat because the oil gap between the outer rings is too small, which will quickly increase the bearing temperature until it “locks up”.
In order to reduce the temperature and improve the bearing life, some companies design the roller bearing seat as a water-penetrating structure. This measure has both advantages and disadvantages for the bearing. The advantage is that the temperature of the outer ring of the bearing is lowered, so that the lubricating oil in the bearing chamber will not be “baked dry”, which reduces the damage of the bearing due to lack of oil. factor. The downside is that after reducing the temperature of the bearing outer ring (the expansion of the bearing ring still exists), the oil gap between the bearing outer ring will become smaller, which will accelerate the heating and damage of the bearing.
② The bearing seat causes the bearing to run in a non-concentric manner
High temperature, large load and large impact, this is the unchangeable working environment of the rolling table. No matter how flat the roller table is made, it will be deformed during the production process. The two bearing seats fixed on the roller table will be concentric, and the two bearings installed on the same roller table will run under the condition that they are not concentric. The “separation force” caused by this non-concentric operation acts on the bearing, and the service life of the bearing is bound to be greatly reduced.
③ The bearing seat makes it inconvenient to check and refuel.
The characteristics of steel rolling production require that the roller bearing seat must be checked frequently and refueled frequently, while the upper cover of the traditional bearing seat is fixed with bolts. To check or refuel, the upper cover of the bearing seat must be opened, and the continuity of steel rolling production does not allow frequent Shutdown, so the bearing will often lack oil, which will accelerate the damage of the bearing.
④ The bearing seat is not tightly sealed, water and dust will seriously affect the bearing life
The dust produced in the steel rolling production process is not only a lot, but also a hard metal compound. The hard dust entering the bearing will seriously damage the bearing and reduce the bearing life. In addition, due to process or equipment requirements, there are many places where water needs to be sprayed (splashed water) on the roller table. The water enters the bearing chamber with dust, which will damage the bearing more seriously. The upper and lower openings of the traditional bearing seat are all flat contact seals. Most of the input and output shaft holes are not sealed, and a small number of them are just ordinary blanket seals. Most of the time, even if there is a seal, it will not work at all. The roller bearing is running in the mixture of oil, water and dust, which seriously affects the life of the bearing.
2. Failure analysis of bevel gear drive roller table
The bevel gear drive roller table has the advantages of smooth transmission and low noise. However, it has the disadvantages of high failure rate and long replacement time. The failure of the bevel gear drive roller table is mainly due to bearing damage and bevel gear wear. Due to the limited installation space of the roller table driven by the bevel gear, the selected bearings are light and narrow series bearings with low life, plus the axial force caused by the bevel gear, the high failure rate of the bearing is inevitable. In addition to the fast wear and tear of the bevel gear of the drive roller table, the bearing has a slight axial clearance, and the bevel gear will change the meshing state and soon the “bald tip” cannot run. Therefore, the failure of the bevel gear drive roller table is often more than twice that of the other way of driving the roller table.
3. Comparison of emergency repair time for steel rolling table failure
In the steel rolling production process, once the bearing or bevel gear of the roller table fails, it must be repaired to reduce downtime. For the chain drive roller table, in addition to the preparation and hoisting time, the main time required for emergency repair is the disassembly and assembly of the upper cover of the bearing seat, which generally takes about 30 minutes. For the bevel gear drive roller table, in addition to the preparation and hoisting time, the time necessary for emergency repair is mainly used in the disassembly and assembly of the bearing housing cover, the disassembly and assembly of the bevel gear box, the disassembly and assembly of the bevel gear and the bearing. . It usually takes more than two hours.