According to the number of rolls, there are five types of rolling mills, namely two-roller, three-roller, four-roller, multi-roller, and universal rolling mill, which are described below:
(1) Two-roll rolling mill (also called double rolling mill) can be divided into reversible and irreversible. The direction of rotation of the rolls of the two-roller irreversible rolling mill is constant during the rolling process, and the rolling piece passes in only one direction between the rolls. For the two-roll reversing mill, the rolls can be reversed and the rolled piece can be rolled back and forth. This mill is driven by a DC motor. The blooming mill for rolling ingots is in this form.
(2) Three-roll mill (also called triple-roll mill), the direction of rotation of the rolls is fixed, the rolled piece is rolled from the middle and lower rolls, and rolled from the middle and upper rolls, so-called reciprocating rolling, also known as shuttle rolling. In this type of rolling mill, there are three section rolling mills with the same roll diameter; and three-roller type steel plate mill with the same upper and lower roll diameter and thin middle roll. In addition, there is a three-roll mill which has three rolls, but the rolled piece is only rolled between two rolls, that is, upper roll and middle roll or middle roll and lower middle roll. In the roughing mill of the horizontal small or wire workshop, the rolling piece alternately passes between the middle rolls, lower rolls and the upper roll, middle rolls of the adjacent stands, and the roll that does not bear the rolling in each stand is only used for transmission. When the rolling piece passes through the middle and lower rolls, it is called lower rolling line rolling, and when it passes between the upper and middle rolls, it is called upper rolling line rolling. In order to distinguish it from a general three-roll mill, this type of mill is usually called a two-roll alternate rolling mill. In order to distinguish it from the general three-roll mill, this type of mill is usually called two-roll alternate rolling mill.
(3) Four-roll mill (also called quadruple mill), in which two middle rolls are work rolls, and the upper and lower rolls are support rolls, and the work roll diameter is smaller than that of support roll. The four-roll mill has two transmission modes: one is the transmission work roller, the support roller is driven by friction; the other is the transmission support roller, and the work roller is driven by friction. The former is mostly used for the production of hot-rolled steel sheets and thick cold-rolled steel sheets.
(4) Multi-roll mills, which are used for rolling ultra-thin strip steels, such as six-roll, eight-roll, twelve-roll, fourteen-roll, sixteen-roll, and twenty-roll mills. There is also a planetary rolling mill for strip and steel sheet production.
(5) The universal rolling mill, which is characterized by a vertical roll. During rolling, the rolled piece can be processed simultaneously or sequentially in the directions of the upper and lower sides. The universal mill can be divided into two-roller, three-roller, and four-roller. The vertical rolls are mounted on the front or the back of the rolling mill.