In the rolling industry, the selection of appropriate mill rolls is a critical technical and economic decision. Rolls are not only costly to purchase but also to maintain. More importantly, their performance directly determines the efficiency of the production line, the quality of the final product, and overall operational costs. However, the performance requirements for rolls are often contradictory—demanding both high hardness and superior toughness, or excellent wear resistance and outstanding thermal crack resistance.
There are many types of rolls; commonly used roll types are cast steel rolls, cast iron rolls, and forged rolls. There are also a small number of carbide rolls in the profile mill.
Molding method: casting rolls refers to the smelting steel or molten iron directly poured molding manufacturing rolls. According to the material, cast rolls can be divided into cast steel rolls and cast iron rolls two categories; According to process technology, rolls can be divided into integral rolls and composite casting rolls two categories
What are the performance requirements of the mill rolls?
1. Anti-heat cracking: Usually rough rolls are the main roll, supplemented by hot cracking; the work roll of a small 20-inch rolling mill is only 100 grams, while the support roll of a wide and thick plate mill weighs more than 200 tons. When using rolls, select the safety carrier material (various grades of cast iron, cast steel or forged steel, etc.) based on the basic strength of the roll.
2. Hardness: The speed of the finishing roll is high, and the final rolled product must have a certain surface quality, which mainly requires hardness, wear resistance, etc. Then, its wear resistance should be considered when using the roller. The mechanism of roller wear is complex, and the main influencing factors include:
- Mechanical stress.
- Thermal effect and cooling.
- The chemical effect of the cooling lubricating medium.
Due to the lack of a comprehensive assessment method for wear resistance, and because hardness is easy to measure and can indirectly reflect the wear resistance, the industry typically uses the radial hardness curve as an indicator of the wear resistance of the rolls.
3. Impact resistance: In addition, there are some special requirements for the rolls, such as the size of the pressure, which requires the rolls to have strong bite ability and stronger impact resistance.
Smoothness: When rolling thin-gauge products, there are strict requirements for the rigidity of the roll, uniformity of structural properties, processing accuracy and surface finish.
4. Cutting performance: When rolling complex sections, the cutting performance of the roll working layer must be considered.
The key factors determining the quality of the rolls
When selecting a roll, some of the performance requirements for the roll are often opposite. Rolls are expensive to purchase and maintain, so the technical and economic pros and cons must be fully weighed to decide whether to use casting or forging, alloy or non-alloy, single material or composite materials.
The performance and quality of the rolls are determined by their chemical composition and manufacturing process. Specific considerations can be made in the following aspects: microstructure, physical and mechanical properties, as well as the type of residual stress within the roll body.
The use effect of mill rolls in the mill is not only dependent on the material of the roll and its metallurgical quality, and it is also related to the conditions, roll design, and operation maintenance.
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