What Are the Surface Damages of Hot Mill Rolls?
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What Are the Surface Damages of Hot Mill Rolls?
- Roll surface cracks: The pattern is divided into normal cracks and abnormal cracks. Normal cracks are also called thermal cracks, which are caused by the gradual cracking of the roller surface caused by the thermal stress generated by multiple temperature cycles. It is a micro-surface layer phenomenon that occurs on the roller surface; Normal cracks are thermal shock cracks caused by slipping, sticking steel, stuck steel, piled steel, tail-flicking and other accidents during the rolling process, and locally formed cracks with a certain depth and ductility on the surface of the roll.
- Indentation: It mainly refers to the pressing of foreign matter such as iron oxide scale due to cleaning reasons during the production process, and the continuous or discontinuous distribution of irregularly shaped pits on the roller surface.
- The oxide film falls off: At the beginning of rolling, after a period of time, a thin silver-gray or light blue oxide film is formed on the surface of the roll, which 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 , Causing the oxide film to produce micro-cracks around the carbide; when the cooling capacity of the roll is insufficient, it is difficult to form a dense oxide film on the roll surface, even if the oxide film is formed, it will quickly deteriorate. When the rolling is unreasonable, the oxide film is quickly destroyed 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.
- Sticky steel, abnormal wear: Due to the abnormal rolling, the adhesion between the roll surface and the rolled piece occurs, and the steel is stuck; the unreasonable process parameters during rolling cause excessive consumption of the roll with the same width of kilometers, resulting in uneven roll surface wear.
In production, we should start with standardized operations and equipment maintenance to avoid damage to the hot rolling mill rolls surface in the above aspects.
How to choose the material of the hot roll?
In order to improve the surface wear resistance of the hot roll, the material of the hot roll is continuously improved. Its basic development process: chilled cast iron → high chromium cast iron → semi-high speed steel → high speed steel → cemented carbide roll.
Since the middle of the last century, cemented carbide cantilever beam rolls have been applied to twist-free wire rod mills. Practice has proved that cemented carbide is very suitable for manufacturing hot rolls. Its life span is 20 times that of ordinary cast iron rolls and more than twice that of high-speed steel. Many Chinese cemented carbide hot roll manufacturers have developed many hot mill rolls grades under different working conditions to meet customer requirements.
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