Roll Application
The purpose of the roll determines the material and design selection for the roll. In a rolling mill, the rolls are required to deform the incoming material to reduce its cross section and obtain the desired shape, size and surface finish. Rolls are made from a variety of materials with characteristics to suit the application. The material selected for a given roll manufacturing application depends on the detailed nature of the task to be undertaken.
Rolls are available in cast iron, steel, and stainless steel, with the preferred roll material depending on the application. For hot rolling stages, cast iron is typically used due to its high thermal conductivity and good wear resistance. In intermediate stands steel is common, while for finishing and roughing stands stainless steel is common due to its increased corrosion and wear resistance. Cast iron rolls are often used in powder compaction and are sometimes coated with a hard material to increase their wear resistance.
Rolls tend to wear out over time and require removal so they can be remade or reground. Hot mill stands have thermally bowed rolls that need to be regularly straightened to such a tolerance that regrinding is not feasible. Hairline cracks will occur in the roller material as it wears, which has to be monitored for possible complete failure of the roll. The material and design of a roll must also take into account the operational environment. Some applications require rolls to resist erosion and abrasion from particles, which is especially common when processing hard abrasive materials.
Rolls can also be treated in different ways to control their surface properties. Grade and end use are the dominant factors in material selection since the properties of the roll must be matched to the stresses induced by its particular application. Some rolls are fully hardened and others may be selectively hardened at the parts of the roll that are critical to its performance. To reduce wear and tear, some rolls can be sprayed with ceramic material to increase their resistance to abrasion.
Another consideration that must be taken into account is the thermal loading of the rolls. To reduce thermal stresses in the rollers, they need to be properly cooled while in use. The cooling can be done by using either oil or water cooling systems, depending on the type of rollers and the application.
To ensure the longevity and satisfaction of the user, the rolls must be inspected for any potential defects and non-conformances before delivery. The inspection protocols for rolling mills must take into account the standards established for the rolling technology and application. Purchasing agents must choose a manufacturer that is both ISO 900 certified and familiar with the required standards for their particular rolling application. Proper quality control and stringent inspection protocols should be adhered to in order to ensure a consistently high quality product.
Rolls are a critical component of the rolling mill and the material selection for these components are of utmost importance. The material and design of the roll must take into account the type of applications it is intended for, the amount of wear it will experience, the environment it will be used in, and the desired surface properties. Manufacturers must adhere to stringent quality control and inspection standards to ensure the highest possible quality rolls are being delivered to the customer. With careful consideration to the design and material selection parameters, a high quality and reliable roll can be produced that meets the needs of the rolling operation.
