In metalworking, rolling is a metal forming process. The metal billet is passed through one or more pairs of rolls to reduce the thickness, make the thickness uniform and impart the required mechanical properties.
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The rolls are hot rolls and cold rolls. Hot rolls usually work in a high temperature environment of 700-800°C, and the surface needs to withstand strong friction and repeated heating of the rolled material, as well as thermal fatigue due to large changes in cooling water cooling temperature. It has thermal fatigue crack resistance, and no cracks are allowed on the surface.
Today let’s take a look at the 4 forms of hot roll surface damage.
1. Roll surface crack
Cracks are divided into normal cracks and abnormal cracks. Normal cracks are also called thermal cracks, which are the gradual cracking of the roll surface caused by the thermal stress generated by multiple temperature cycles, and are a micro-surface phenomenon that occurs on the roll surface.
Abnormal cracks are thermal shock cracks caused by accidents such as slipping, sticking steel, jamming steel, stacking steel, and tail flicking during the rolling process, and locally form cracks with a certain depth and elongation on the surface of the roll surface.
2. Indentation
It mainly refers to the intrusion of foreign matter such as iron scale due to cleaning reasons during the production process, resulting in a continuous or discontinuous distribution of irregularly shaped pits on the roller surface.
3. The oxide film falls off
At the beginning of rolling, after a period of hot rolling, a layer of silver-gray or light blue thinner oxide film will be formed on the surface of the roll.
It is very important to protect the roll surface and improve the surface quality of the rolled piece.
Due to the repeated action of the rolling force, the oxide film will produce microcracks along the carbide. When the cooling capacity of the roll is insufficient, it is difficult to form a dense oxide film on the roll surface, and even if the oxide film is formed, it will deteriorate quickly.
If the rolling is unreasonable, the oxide film will be destroyed rapidly during the formation process, which will cause the oxide film to fall off, leaving defects such as meteor spots on the roller surface, resulting in increased roller surface roughness and increased wear.
4. Sticking to steel, abnormal wear
Due to abnormal rolling, the adhesion between the roll surface and the rolled piece is caused, and steel sticking occurs. The unreasonable process parameters during rolling cause excessive consumption of the same-width kilometer roll, resulting in uneven wear of the roll surface.
In production, we should start with standardized operations and equipment maintenance to avoid damage to the roll surface of cast iron rolls.
