1. Classification of Rolls
There are several ways to classify rolls, the main methods being:
By Product Type: Steel strip rolls, section steel rolls, wire rod rolls, etc.
By Position in the Rolling Mill: Billet rolls, roughing rolls, finishing rolls, etc.
By Function: Scale-breaking rolls, piercing rolls, leveling rolls, etc.
By Material: Steel rolls, cast iron rolls, carbide rolls, ceramic rolls, etc.
By Manufacturing Method: Cast rolls, forged rolls, hardfacing rolls, sleeve rolls, etc.
By State of the Material Rolled: Hot-rolled rolls, cold-rolled rolls.
These classifications can be combined to give more specific definitions, such as a centrifugal cast high-chromium cast iron work roll for hot rolling steel strip.
2. Selection of Rolls
The commonly used roll materials and their applications are shown in the table. The performance and quality of rolls depend mainly on their chemical composition and manufacturing methods, and can be evaluated based on their microstructure, physical and mechanical properties, as well as the type of residual stresses within the roll (see Roll Inspection). The effectiveness of a roll in a mill depends not only on the material and metallurgical quality but also on operating conditions, roll design, and maintenance.
The rolling conditions in different types of mills vary greatly. The factors contributing to these differences include:
Mill Conditions: Type of mill, roll and mill design, roll gap design, water cooling conditions, bearing types, etc.
Rolling Conditions: Type and specification of the rolled material, deformation resistance, reduction regime, temperature regime, production requirements, and operational factors.
Product Quality and Surface Finish Requirements: The level of quality required for the final product and its surface finish.
Different types of mills, or mills of the same type with varying operating conditions, have different performance requirements for the rolls used. For example, rolls in the roughing stands for billet and slab mills need to have good torsional and bending strength, toughness, bite resistance, hot cracking resistance, thermal shock resistance, and wear resistance. On the other hand, hot strip mill finishing stands require rolls with high hardness at the surface, resistance to compression marks, wear, spalling, and hot cracking.
Understanding the operating conditions of the rolls and the failure modes of rolls used in similar types of mills is crucial. Additionally, knowledge of the performance and manufacturing processes of current roll materials allows for the correct formulation of technical specifications and the selection of suitable, economical roll materials for a particular mill.
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