Choosing the Right Cleaning Tests
The successful manufacturer doesn’t only avoid costs, but also values knowing as much as possible about the benefits and limitations of a cleanliness test, and of staying on top of process trends.
Manufacturers want to produce quality products that are competitive and profitable. Achieving and monitoring acceptable surface cleanliness can be the hardest challenge in this pursuit. There are a number of different options for affordable, low-cost cleaning tests, yet, low-cost tests are not the only way to take a wealthy person’s approach to quality on a pauper’s budget.
Being frugal is not looking for the lowest cost—it’s looking for the smartest cost. The successful manufacturer doesn’t only avoid costs; he or she values knowing as much as possible about the benefits and limitations of something like a cleanliness test, and of staying on top of process trends. A test that fails to detect a contaminant, either because it is the wrong test or not sensitive enough, wastes time and costs. The wrong test gives a false sense of security, and this security will be shattered if the process drifts out of control and yields plummet. A more-costly analytical lab test can save money overall if it helps avert a problem.
Analytical testing should be used frugally. Manufacturers typically know their processes, likely contaminants, and current customer and performance requirements better than a lab. They know, or can determine, the acceptable levels for contamination at specific points in the manufacturing process. By working with the lab and advisors to choose the right test, manufacturers can save money. Is contaminant identification or characterization needed? For some applications, the number and size of particles, not what they are made of, is what counts. In other instances, non-specific testing for organic residue may be enough. On some surfaces that need to be coated, limited inorganic residue may be acceptable, but oils or greases would compromise coating quality.
Contaminants come in many shapes, sizes and composition. Characterization of dirt should be an early step in designing successful cleaning programs, including verification tests. The dirt found might be a residue from a previous manufacturing step, including upstream supply chain processes, or it may be finger oil or skin flakes from assemblers.
Perceived odors also can be a useful warning sign of contamination, and they also can be analyzed by another low-cost test. An airborne contaminant can waft in on air drafts from a nearby agricultural facility or from the company cafeteria. A molecular-level airborne contaminant may not be blocked by a particle air filter, even by HEPA filters.
Not only knowing exactly which tests to perform, but knowing when to test is crucial. Testing only at the completion of a manufacturing process may not be sufficient to avoid problems. A volatile contaminant can be present at the time of the coating process, but it may be gone by the time coating failure is detected and tests are run.
It can be frugal to use an expensive test that clearly identifies the contaminant. Knowing the molecular composition of a contaminant may pinpoint its source, and then steps could be instituted to prevent the contamination from occurring. This can involve adding the appropriate air or fluid filter, or changing the supplier of the subassembly. If contamination can’t be avoided, you could adapt the cleaning process to focus on the contaminant that has been identified. In this way, the specificity of a test can easily be worth the higher price tag.
A more realistic way to perform salt spray tests.
The German Association of the Automotive Industry’s VDA Volume 19 is the first comprehensive standardization document for characterizing the cleanliness of products within the automotive industry’s quality chain.
Specific questions about zinc phosphate and pretreatment are answered in one article...