Rough rolling compresses or stretches the billet, producing workpieces with the required section shape, accurate dimensions, and good surface quality. Typically, the section size of the rolled pieces after rough rolling is greater than or equal to 50 mm.
The rough rolling process varies due to differences in raw materials. In single-line wire mills, flat and vertical stands are used alternately for rolling without twist. In contrast, other types of mills employ twist rolling using two-high horizontal stands. In practice, except for high-alloy steels, most steel bars and wires can be produced using the twist rolling method.
After rough rolling, it is necessary to cut off the head and tail ends of the rolled pieces. This is because the deformation and heat dissipation at both ends differ significantly from the middle section, resulting in poor plasticity and irregular shapes. Such defects may cause the rolled piece to block the entry guide or lead to biting failures during continuous rolling.
Horizontal two-high rolling mills are the most commonly used and are particularly suitable for rolling carbon structural steel and low-alloy steels. The rolling line may employ close mills, prestressed mills, or short-stress-line mills. Close mills typically use a trolley to replace the roll set, while prestressed and short-stress mills perform roll or housing replacement offline. It is common to use an individual drive for each stand, which facilitates mill adjustment and eliminates the complexity of roll matching in group drives.
Flat/vertical tandem rolling mills are especially suitable for producing high-grade alloy steel wire rods. Due to the high torsional deformation resistance and low plasticity of alloy steels, twist rolling often causes cracks and defects. Therefore, twist-free rolling is essential. Flat/vertical alternating tandem mills, driven individually, are commonly used in multi-grade, single-line, high-speed wire rod mills. Except for two-high close stand mills and short-stress mills—which adopt an upward drive—the vertical rolling mills usually employ a downward drive configuration.
Short center-distance compact rolling mills apply large deformation to the rolled pieces, with a bite angle ranging from 38° to 42°. Due to the large pass deformation and rolling force, the rolls in compact mills wear quickly. Additionally, the narrow spacing between mill stands makes it difficult to resolve failures promptly, negatively impacting production continuity. For this reason, such mills are rarely used in modern rolling lines.
