- To verify that variables are within the required operating range
- To determine their long- and short-term reproducibility
- To correlate the individual variables with product performance & defects
- To provide data for statistical analysis to optimize process conditions
- To troubleshoot problems when they are identified by customers
The basis for determining which variables to measure is that it is more efficient to measure too many variables than too few. There are several reasons for this:
- It will ensure that all of the needed data is available for future analysis, problem-solving and troubleshooting of defects.
- By measuring a minimal number of variables, there is a high probability that important information is not obtained. Therefore, problem-solving will be longer and more expensive.
- It will also result in an increased knowledge of process behavior and may help identify previously unknown interactions.
- It is now feasible because of the availability of low-cost reproducible sensors, data acquisition hardware, analysis software and and computers will result in cost-effective systems.
- It will generate cost savings and improved product quality.
It is worthwhile to analyze current and new coating lines to determine that the important process variables are being measured and to determine if new measurements are needed. Coating lines have a long lifetime, and the specified measure in the original designed may not be adequate in view of information gathered since startup. Often the importance of variables that were not known when the coating line was being designed were not included. In addition, new systems have been developed which result in measuring variables that were not possible when the coater was originally designed. Also different products may not have the same response to process variables.
The analysis of measurement requirements should focus on parameters that are missing. The precision and accuracy of current measurements need to be analyzed to verify that they are adequate for current products. This analysis and determining if upgrades are needed can be conducted by representatives of all functions. The variables that need to be measured for the coating solution during a production campaign are:
- Flow rates of solution to the coating applicator *
- Temperature *
- Percent solids *
- Viscosity *
- Density *
- Bubble level *
- Surface tension *
* On-line measurement systems available