The overall goal of the action plan is to determine what has changed in the current process that is causing the defect and eliminate it. Specific steps 5-8 to accomplish this are described in the next sections of this post.
5. Use external defect-data sources
The fundamental mechanism for coating defects formation is not affected by the end use of the product being coated. Therefore, defect information from different products can help reduce current observed defects. As a result, there are defect references that can be used to provide information on current defect being studied [1-3]. A modification of the format can also be adapted to your local database. Reference 3 also contains a glossary, which can be very useful in naming defect(s).
6. Analyze data and develop defect-cause hypothesis
This step uses the developed process data, analytical measurements, and observations to determine defect causes. All participating personnel should present their data and tentative conclusions to the group, for discussion and solution development. Copies of data should be available to all because they help assimilate data. At the end of the meeting, there should be potential mechanisms for defect correction and modifying the action plan, if needed. This meeting should be conducted daily to rapidly act on potential defect causes.
For example, a defect map shows that the spot defect is located 14 in. from the web edge with the distance between the spots of 12.57 in. This suggests a 4-in.-dia. roll is contaminated and thus causing the defect.
7. Plan tests to verify hypothesis
Next, testing to verify the defect mechanism from the previous step needs to be done. For the repeating spot, all 4-in.-dia. rolls should be checked and cleaned, if necessary. Then, coatings should be conducted to verify if the mechanism is correct and normal production can be resumed. More complicated causes may require pilot-plant statistical experiments and in-plant experiments to verify defect cause(s).
8. Document results
The action plan is not complete until all the data, observations and test results have been documented, distributed and stored for further use. The documents should also contain recommendations for process upgrades, if required.
1. Cohen, E.D., Gutoff E.B. Coating and Drying Defects Troubleshooting Operating Problems, second edition, John Wiley and Sons, New York, 2006.
2. Smith, R.D, et al. Roll and Web Defect Terminology, second edition, TAPPI Press, Norcross, GA. 2007.
3. Smith, R.D. The Ultimate Roll and Web Defect Troubleshooting Guide with Glossary, TAPPI Press, 2013.