Roll Materials and Roll Life
Rolls are usually made from tool steel, the grade being dependent on the expected production and finish of the piece part. For general duty applications where a smooth finish strip is to be formed or when shapes are formed from hot rolled, unpickled steel, a High Chrome-High Carbon tool steel (AISI D-2) with about 1.5% carbon and 12% chrome is to be suggested. This generally heat treats to 60-63 Rockwell “C” and represents about 2 to 2½ times the life of the previously used oil hardening tool steel. This tool steel has good wear quality and for the average run of light gauge cold formed sections could be expected to roll several, on the order of 3 to 5 million feet or more before regrinding. Generally speaking, 4 to 5 regrinds can be made before the rolls are scrapped.
For specific industry and product applications, other materials may be used. For light gauge, pre-painted or galvanized wide products, such as building panels or metal roofing, chromed coated alloy steel may be used, due to the liberal tolerances of the application and the light forming duties involved. Additionally, if there is a non-magnetic or temperature sensitive environment for the roll tooling, such as inline welding or heat treating, other materials may be required, specifically aluminum bronze (non-magnetic) or AISI H13 tool steel (heat resistance compared to D2). Finally, for extremely high speed, high wear applications, most commonly tube mills, tungsten carbide tooling may be used. Carbide tooling may offer an order of magnitude improvement in tooling wear, but it is substantially more brittle than toolset, so case must be taken in the handling of the tooling pieces.