Tag Archives: technology

Defect Mapping A Useful Troubleshooting Tool

 Defect mapping is a very simple useful technique that can be used to characterize a web coated defect and determine possible causes for the defect. In this technique, a map is created which shows the exact location of all observed defects in both the machine (Md) and the transverse direction (Td). The map can be created in two different methods. The on-line Surface Inspection Systems can create a roll defect map shows the defect distribution in the entire coated roll. Figure I is an example of typical roll map generated by such a system. The ability to easily generate a map for defective rolls has increased the usefulness  of this technique. The second method, is to obtain a long full width, roll sample and then visually mark the defect type, since there can be more then on defect. The data is processed to determine the defect frequency and location, using a spreadsheet or data analysis program to generate the map and statistics.

The map can provide an insight to observed defects and provide information on defect cause and suggest cure. If roll repeating spots, that are caused by contamination on a roll, are observed, then the Md spacing between the spots is a direct function of the roll circumference that is causing the spots. If there is a table in the coater that shows the roll circumference, diameter and location in the coater all rolls with that diameter can be checked to determine which ones are the cause. The Td location will indicate the exact location of the instigating spot.  There are many spot type defects, which lend themselves to this analysis. Figure 2 is an example of a Roll Repeat spot Defect Map
When chatter bars are detected then the spacing between the bars can be used to determine the chatter frequency and help to locate source. When streaks are observed   the Td location can be used to check for coater hardware defects at that location or roll contaminated by dried coating,
In many coated rolls there may be more then one defect, since the map shows the type of defect, then the major one can be identified and troubleshooting focused on only that one.
The coating weight profiles generated by the on-line coating weight systems are also  defect maps, which are used to determine non-uniform coating weight.      \