Detection of Surface Defects as a Turnkey Solution
The production of metal rolls, frequently used for treatment of web material, is subject to stringent requirements concerning surface quality and concentricity. A rolling process carried out with even only slightly defective elements seriously affects the quality of the final product. For this reason, in order to limit roughness of the roll surface, their production is often complemented by a final treatment performed by grinding machines. This special treatment is useful to ensure a high-gloss finish.
Defects to be examined in this application are very small, their size is often lower than 0.5 mm – hard to discover by human eye. Rework in the course of the production of the final product however, proves to be complicated and expensive. Large rolls with a diameter of 2 m and a length of 10 m are very difficult to remove and to reinstall. In order to avoid corresponding inconveniencies, it is essential to support the manufacturing process of the rolls themselves by a reliable quality control in the form of an automated final inspection.
In this case, an already existing cylindrical grinding machine was intended to be upgraded by a powerful inspection system in a Turnkey Solution. The inspection process for a large roll had to be limited to a duration of 60 minutes, and was still expected to be able to offer a stable and complete detection of defects. In order to prepare targeted repair, a further challenge consisted in the determination of the position of the individual detected defects by means of a simple procedure. The theoretical alternative of coupling the system to the proprietary machine control -in order to obtain required position information- was too complex from a technical point of view and could not be implemented.
QuellTech Complete Solution
As the Quelltech Q6 laser scanner features an extremely precise resolution of 4096 Pixels/Profile at a high scan rate, this model proved to be able to meet the requirements and was mounted onto the positioning stage of the grinding machine. Furthermore, an industrial measurement computer was added, used for the analysis software of the point cloud. On the basis of this configuration, the entire roll surface could be recorded on a helical path.
The data volume for evaluation of these large rolls would be excessive and had to be reduced, as a quantity of 4.2 billion points would be involved. For this reason, a special software was developed, intended to detect and to visualize the defects already during the recording procedure. A defect marking system with colored ink was connected to the measuring PC. In the end of the inspection, defects on the roll are clearly marked and can be identified at once. This enables a targeted repair procedure to be launched in no time.
The user software for this Turnkey Solution developed by QuellTech includes an analysis for the concentricity of the rolls as well. This way, height fluctuations caused by worn machine bearings can be determined, and a corresponding trend does not remain hidden.
Benefits for the client
Continuous and reliable supervision of the roll surface is essential to ensure the quality of the final product. By means of the presented method, defects become obvious already during final inspection, before the rolls are delivered to the client. The inspection procedure represents a user friendly Turnkey Solution, convenient also for mobile applications on different grinding machines. Expensive sampling in a separate test station is no more required, and routines for preventive maintenance of machine bearings on the basis of a trend analysis can be established as well. This system increases customer satisfaction, and saves time and money.
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