Many customers come to Craftech with a need for fasteners made from high performance plastics that can stay strong even when exposed to multiple stress factors. These stress factors include high and low temperatures, large torque or loads, and exposure to acidic or basic vapors, to name a few. While Craftech is always ready to provide guidance and support to engineers looking for the right high performance plastic, I cannot emphasize enough the importance of testing plastic parts in your application and environment. Repeat testing is the only way to guarantee that your high performance plastics are going to work in your application over the long term.
There is one major reason why engineers must absolutely do their own testing. Most, if not all, of the large corporations that manufacture raw high performance plastics do a surprisingly small amount of their own testing. When they do test, they do not necessarily test every grade of plastic. For example, it can be quite difficult to track down a detailed chemical resistance chart for a specific high performance plastic. Even if available, the information will often be quite generalized, with categories like “Alkalis” or “Alcohols.”
High performance plastic manufacturers also tend to test for only one quality, such as heat resistance or acid resistance. Due to the time and expense of testing multiple, overlapping characteristics, this sort of testing is rarely carried out. So what if you need a high performance plastic that can stand a heavy torque and is resistant to salt water? Or a plastic component that resists both mineral acids and chlorinated hydrocarbons? Official testing done by suppliers is also almost always restricted to relatively short time periods. For example, very rarely do companies test a high performance plastic’s chemical resistance for more than a month, a very short time relative to the life span of most applications. This kind of specific information is not publicly available and can only be discovered through individual testing.
Another problem with corporate testing of high performance plastics is the lack of any standardized system for displaying results. Say one looks up the data developed by a company for its hypothetical new high performance plastic, ‘X’. If one looks up X’s rating for a 30 day exposure to methyl ethyl ketone (MEK), for example, and finds that it earned a B+ rating, what does that mean? One company’s B+ might be another’s A- or even D. Does B+ mean that X would continue to survive with minor surface crazing? What would happen in another two months? The rating does not tell the would-be user any of that. Nor does it tell him/her what would happen if the testing temperature had been 20 degrees higher or lower. Suppose a load was also applied or another chemical was mixed in with the MEK. As you can see, there are a myriad of different possible factors to take into consideration which fall outside the scope of corporate testing.
Another important fact to remember when comparing mechanical properties and chemical resistance presented by different companies is that each company formulates ‘standard’ high performance plastics in its own way. The engineer should not assume that one manufacturer’s PVDF, for example, is the same as another’s. A look at the ingredients will often show that various alternative solvents and precursors may be substituted when others are too expensive or not available. For this reason, and others, the suitability of a given high performance plastic must have a wide margin of acceptability.
It is hard to say exactly why companies spend so little time testing their high performance plastics. One could postulate that the lack of testing results from a desire to save money or that testing is limited due to a desire to avoid putting into print less than desirable results. Whatever the reason, the truth remains that every application functions in a unique environment. No company would be able to test for every possible permutation of tolerances over time. Therefore there is only one alternative: one must test, test, and test some more.
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