The mechanical rolling conditions in hot strip mills are precisely defined by various variables, which are taken directly forth the rolling schedule (separation force, torque, speed, strip thickness) or calculated from figures of the rolling schedule and dimensions of the mil (strip reduction, roll diameter, etc.). These variable allow describing the mechanical rolling conditions of all passes be supplemented by the metallurgical rolling conditions. They then give basic information on the conditions which determine wear and fine crazing.
There is a good chance to use the experience of other mills with various roll grades by analog comparison - as long as the rolling conditions are similar. This method is limited by “abnormal rolling conditions”, which require totally different roll grades, although if it would be much better to eliminate the abnormal conditions.
In hot strips mills, slabs of 150 to 250mm thick are rolled to strip 1.5 to 12mm thick. Conventional hot strip mills consist of roughing and finishing stands. The configuration of the roughing mills varies widely. A mill with one reversing stand is called a semi-continuous mill. A mill with one reversing stand and one or two continuous roughing stands is called a % continuous mill and a mill with 4 to 6 continuous roughing stands is called a continuous mill.
In 3/4 continuous and continuous mills, the first stands are usually two high stands while the remainder is 4 high rolling mill stands. In addition to these horizontal stands, several edgers are also used. The finishing mills have a minimum of stands but normally have 6 or 7 stands.
Rolling conditions vary from mill to mill, stand to stand and pass to pass. Mill configuration is designed for a desired total strip (thickness) reduction, however, each stand is limited in trip reduction by the maximum separation force, maximum torque, risk of slippage, etc.