Problems of Cold Rolling Sheet Lines and Guide to Fixing Them
Problems in cold rolling sheet lines may occur for various reasons in the production line. The cold rolling sheet process involves machinery and equipment; therefore, the occurrence of issues in these lines is not unexpected. Sometimes, after a period of operation, some equipment may develop problems. Sometimes, using unsuitable equipment may lead to defects. Sometimes, issues in some of the processes performed during cold rolling can cause defects in the produced sheet.
In this article from Mazs Group Industrial Company Magazine, along with a brief explanation about cold rolling sheet, we will discuss the problems of cold rolling sheet lines. Finally, we will also present solutions for troubleshooting cold rolling sheet lines. If you work with cold rolling sheet production lines in your industry, this content can provide you with useful information.
This article examines the following topics:
What Is Cold Rolling Sheet?
Before discussing the problems of cold rolling sheet lines, it is better to briefly understand what cold rolling sheet is. If you need more information about cold rolling, refer to the article “What is Cold Rolling?”. Cold rolling is a process used to reshape metals. In cold rolling, the thickness of steel sheets is reduced so they become suitable for producing various industrial products. This process is performed in such a way that the reduction of metal thickness occurs at a temperature lower than its recrystallization temperature.
The difference between hot rolling and cold rolling is precisely this processing temperature. In hot rolling, metals are heated to temperatures above their recrystallization point. This leads to differences in the characteristics of sheets produced by hot rolling and cold rolling.
A set of equipment is used in cold rolling lines. In the cold rolling process, several processes are applied to the steel sheet—steps such as pickling, passing through rollers, annealing, cooling, skin-pass rolling, and finally sheet production. Problems may occur in cold rolling that require troubleshooting of cold rolling sheet lines.
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What Are the Problems of Cold Rolling Sheet Lines?
As mentioned, various problems may arise in the cold rolling sheet production line. In this section, we discuss these problems in a listed form.
- In the cold rolling process, there are rollers that become worn and abraded after some time. Damage to the roller surface causes defects on the appearance of the produced sheet. Maintenance and replacement of these rollers also increases costs.
- Scrap of steel sheets is another problem in cold rolling sheet lines. The head and tail of the steel coil, which cannot be rolled or turned into a high-quality product and is known as “aspireh,” is considered waste material in the cold rolling production line and is costly.
- The time required to change coils and rollers in the cold rolling line reduces production efficiency. Stopping the production line also affects the health of the equipment.
- During the cold rolling sheet process, sheet tearing may occur. This problem increases costs and reduces production rate.
- Non-metallic impurities produced during casting may separate from the metal during cold rolling and create scratches and lines on the sheet surface.
- During cold rolling, the sheet edges may become serrated.
- The rolling emulsion may cause stains or dark spots on the sheet surface.
- Formation of center waves on the sheet surface and lack of flatness.
Troubleshooting Solutions
The previous section described the problems of cold rolling sheet lines. In the following, we intend to troubleshoot each of the mentioned issues.
• During the cold rolling sheet process, rollers become worn and damaged over time. Roller problems can damage the sheet surface and reduce its quality. One method to repair damaged roller surfaces in cold rolling production lines is roller grinding.
• As noted, steel sheet scrap is one of the problems in cold rolling lines. To reduce it, high-weight raw coils can be used.
• To minimize the problem caused by coil and roller replacement and reduce downtime in the production line, using high-weight coils is also useful and increases efficiency and equipment lifespan.
• To prevent sheet tearing, the incoming coil, control systems, and mechanical equipment of the cold rolling lines must be checked. To reduce the likelihood of sheet tearing, the non-uniformity of the incoming sheet in the cold rolling line should be controlled and reduced. Also, timely replacement of rollers and proper lubrication helps reduce friction and therefore lowers the chance of tearing.
• To troubleshoot surface scratching caused by non-metallic impurities, impurity tape can be used. When impurity tape is applied to the surface and removed, the impurity detaches and becomes noticeable.
• The cause of serrated edges during cold rolling may be due to issues in the pickling process. This occurs when edge trimming is performed without sheet tension, or when the blades are not compatible with sheet thickness or have become dull. These factors prevent uniform cutting of the sheet edges.
• When droplets of emulsion remain on the sheet and air-blowing or drying is not done properly, and the lubricant penetrates the layers of the coiled sheet, over time emulsion stains appear on the sheet surface.
• Emulsion is responsible for controlling sheet surface flatness. If a nozzle becomes clogged and parts of the roller are not cooled properly, the sheet surface becomes defective. Center waves occur due to thermal expansion on the sheet surface caused by improper cooling and incomplete lubricant spraying.
Conclusion
In this article from Mazs Group Industrial Company Magazine, we examined the problems of cold rolling sheet lines. Along with a brief explanation of the cold rolling sheet process and possible issues in these lines, troubleshooting solutions for cold rolling sheet lines were also presented.
FAQ
Cold rolling lines include equipment for pickling, rolling mills, annealing furnaces, cooling systems, skin-pass rolling units, and final sheet production machinery.
Rollers wear out due to continuous friction and pressure during the rolling process. This wear leads to surface defects on the final sheet and increases maintenance costs.
Using heavier raw coils helps reduce scrap, especially the unusable head and tail portions of the coil.
