Metal finishing Q&As since 1989

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Standards and Test procedures for checking and acceptance of PTFE coating

We use metal mandrels (core) for getting the required port shape in solid propellant (used in rockets) motors. These cores called mandrels shall be coated with PTFE. The mandrels are made of carbon steel material. As the metal comes in contact with chemicals (Initially in the form of slurry and then it gets solidified), PTFE serves as an anti corrosive coating and mainly as a mandrel releasing agent. Right now we depend on water drop test, tape test( in this we bond the tape on coated surface and will be peeled off) to ensure proper bonding. I feel, these test don;t have any value to compare and say that a particular coated surface is good. In this context, I would like to know, what are all the tests we should conduct to qualify the PTFE coating? Any standards are available for PTFE testing? Lastly, what should be the recommended thickness? We generally specify 30-40 microns.

Mandava Prasad
Project Engineer - Sullurpeta, Andhra Pradesh, India
2004

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The most important things to control are:

- thickness (non destructive) with a gauge.
- adhesion (destructive) with cross test.
- curing ( to check if the coating I fully cured) curing temperature profile - also the kind of fluoropolymer applied is very important in your application, you are talking about PTFE, but you must to consider to use FEP or PFA.

The best system to know if your coating is still in good conditioned is to insert a dynamometer between the solid fuel and the system to take it out from the mold, you'll see that the kilos you need to de-mold the part will increase with the time (PTFE degradation). You just need to know at how many kilos are you going to re-coat again.

Jordi Pujol
Teflon coater - Barcelona, SPAIN
2004

Teflon coating is carried out with precision and the coater has to ensure that the final product when coated is as per the standard.

Tapan Thanavala
- Mumbai, Maharashtra, India
January 18, 2012