The emergence of the chrome plated roller technology is due to the fact that the current chrome plated rollers generally suffer from poor precision and lack of wear resistance which often leads to downtime for roll changes and affects normal production. The application of the chrome plated roll technology has achieved good economic benefits.
The chrome plated rolls are hairy, which increases the friction coefficient and makes them fit more closely to the strip during operation. In addition, the chrome plated rollers form a protective gas film between the strip and the chrome plated rolls due to the storage of gas in the chrome plated roller micro-pits, which prevents the chrome plated rollers from scuffing the strip. This has a very important influence on the continuity of the chrome plated rollers.
The chrome plated rollers are treated with the following technologies: shot blasting, EDM, laser, and so on. The most advanced of these technologies is the laser haircut, but its maturity in use is lower than that of the traditional shot blasting technology. The hardness and fatigue strength of the chrome plated roller surface is improved after shot blasting, and the chance of slippage between the strip and the chrome plated roller is effectively reduced to avoid strip abrasion.
The idler rolls in the cold rolling line are generally covered with rubber rolls and ordinary steel rolls, which have poor precision and insufficient wear resistance, often leading to downtime for roll changes and affecting normal production. At present, some steel mills have started to apply chrome plated rollers, and have achieved good economic benefits.
1. The surface of the roll body is inductively quenched to a depth of 3-5mm so that the surface hardness reaches HRC45-55, and then the surface of the roll body is ground to the roughness of Ra≤0.8μm, and no spiral roll marks or grinding vibrations are present. For rolls with high surface quality requirements, grinding and polishing to Ra＜0.2μm is required, while the rolls are subjected to dynamic balance testing. Using the de-weighting method, small blind holes are drilled in the roll end to ensure the balance quality grade is higher than G16.
2. The roll face is then grossed up to increase its coefficient of friction so that it fits more closely to the strip during operation. In addition, due to the role of the roll surface micro-pit storage gas, the strip and the roll surface are between the formation of a layer of protective gas film, to avoid the roll surface strip abrasion.
3. Finally, the roll surface is treated with hard chrome plating. The thickness of the plating layer is 0.05-0.15mm (should not be greater than 0.20mm), and the hardness can reach HV900-1000. the roll body should be degreased and cleaned before plating, and the quality of the roll surface should be strictly inspected, no defects such as porosity, cracks, rust, and scratches are allowed. After plating, the surface of the roll should be bright and flat, without color difference, and be processed by grinding and peaking.
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