A two-roll cold rolling mill is a type of rolling mill used to reduce the thickness of metal strips or sheets at room temperature. It's a fundamental process in metallurgy and manufacturing, crucial for producing materials with precise dimensions and enhanced mechanical properties.
1. Applications of Two-Roll Cold Rolling Mill
The two-roll cold rolling mill serves as experimental equipment for cold rolling low-carbon steel, copper, silver, lead, aluminum, non-ferrous metal sheets, and alloy powder strips.
Automotive: Body panels, structural components.
Appliances: Refrigerator panels, washing machine parts.
Packaging: Food and beverage cans (often followed by further processing).
Construction: Roofing, siding, structural elements.
Electronics: Components for electrical devices.
Aerospace: High-strength, thin sheets.
2. Working Principle of the Two-Roll Cold Rolling Mill
Two-roll cold rolling mills are categorized into reversible and non-reversible types, with reversible models being predominantly used today. The mill primarily employs two rotating rolls to grip the workpiece, achieving dimensional changes in the material to complete the rolling process. When rolling plates, the working surfaces of the rolls are flat. The thickness of the plate is adjusted by regulating the roll gap via a reduction device. For wire rolling, the rolls are grooved with a die profile. The material undergoes changes in cross-sectional shape and dimensions within this die profile. The cross-sectional dimensions can also be adjusted by regulating the roll gap through the reduction device.
3. Primary Functions of the Two-Roll Cold Rolling Mill
This equipment serves as an experimental cold rolling facility for low-carbon steel and non-ferrous metal sheets. It features an advanced computerized data acquisition system for rolling process parameters, enabling measurement of rolling pressure, torque, motor power, rotational speed, and other critical metrics. Consequently, this equipment facilitates research into material rolling processes and the development of cold-rolled components.
4. Composition and Structural Features of the Two-Roll Cold Rolling Mill
The machine comprises a main motor, reducer, bevel gear housing, universal joint shaft, working frame, and electrical control cabinet. The roll system utilizes specialized rolling mill bearings, with roll material specified as 9Cr2Mo.
Two Rolls: These are the heart of the mill. They are typically made of hardened steel or cast iron and are precisely ground.
Work Rolls: These are the rolls that directly contact and deform the metal.
Backup Rolls (in some configurations): While a "two-roll" mill strictly means two work rolls, some systems might incorporate larger backup rolls to support the work rolls and prevent them from bending under the immense forces. However, in its simplest form, it's just two work rolls.
Mill Housing/Frame: A robust structure that holds the rolls, bearings, and screw-down mechanisms in place, designed to withstand the high rolling forces.
Screw-Down Mechanism: This system adjusts the gap between the rolls, which directly controls the final thickness of the rolled material. It can be manual or hydraulic.
Drive System: A motor and gearbox that provide the rotational power to the rolls.
Coil Holders/Uncoilers and Recoilers: Equipment at the entry and exit sides to feed the metal strip into the mill and re-spool it after rolling.
Cooling and Lubrication System: Essential for dissipating heat generated during deformation and reducing friction between the rolls and the workpiece.
5. Process Steps:
Preparation: The metal strip is cleaned and sometimes annealed (heat-treated to soften it) if it's too hard for initial cold rolling.
Feeding: The strip is fed from an uncoiler into the gap between the two work rolls.
Rolling: As the rolls rotate, they pull the strip through, compressing it and reducing its thickness. The amount of reduction per pass depends on the material, roll diameter, and mill capabilities.
Work Hardening: The plastic deformation at room temperature increases the hardness, strength, and yield stress of the metal, while decreasing its ductility. This is known as work hardening or strain hardening.
Coiling: The thinned strip is then recoiled at the exit side of the mill.
Multiple Passes & Annealing: Achieving significant thickness reductions often requires multiple passes through the mill. To prevent the metal from becoming too brittle due to excessive work hardening, intermediate annealing steps might be performed between passes to restore ductility.
