As we all know, roll fractures in hot-rolled steel bars will seriously affect work efficiency and production safety.
The rolling temperature of 4751 superalloys was about 1140 ℃. In order to make a good feed for rolling. Usually, when steel bite into the water before, steel bite immediately after boiling water cooling. When the steel rolled to more than ten rolls, the roll broke.
According to our analysis, there are generally two types of roll fracture
- Brittle fracture, the fracture shape of this kind of roller is relatively flat, and the surface of the roll body around the fracture is relatively neat;
- The fracture shape of this kind of roller is mushroom head, and the roller body near the fracture is in the form of comminution.
By comparing the two, it is found that the roll breaking accident is a brittle fracture. Both brittle fracture and ductile fracture are caused by the roller stress exceeding the core strength.
The reason is related to the residual stress of the roll itself, the mechanical stress during rolling, and the thermal stress of the roll, especially when the temperature difference between the surface of the roll body and the core is large. This temperature difference may be caused by poor roll cooling, interruption of cooling, or overheating of the roll surface at the beginning of a new rolling cycle. The large temperature difference between the surface and the core of the roll causes large thermal stress. When the large thermal stress, mechanical stress, and residual stress of the roll exceed the core strength of the roll, the roll will be broken.
For example, when the temperature difference between the roller surface and the core is 70 ℃, the roll will increase the longitudinal thermal stress of 100MPa. The greater the temperature difference is, the greater the increased thermal stress will be. Compared with the roll with brittle fracture, the core material with ductile fracture has better toughness and less fracture.
To prevent accidents:
- Roll break usually occurs at the end of the roll life cycle. It is the early stage when the roller wear is about to be scrapped. But it can be rolled for about three months. At this time, the outer diameter of the roller is small, and the compressive strength is small. Easy to break. It is very important to select a high-quality hot mill roller supplier.
- Cooling should be uniform. The temperature difference between the roller center temperature and the roller outer surface temperature should be avoided.
- Don’t roll cold steel. Easy to break roll.
UKO in the production of hot rolling mill roll this piece of very professional, stable quality, is a trustworthy long-term partner.