Thermal spray and furnace charts

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That the biggest customer for thermal spray coatings is the aerospace industry is very well known. Of course thermal spray coatings are used in other industries too such as ground based gas turbines, paper and printing, pump and valve and other commercial industrial applications. But the aerospace industry accounts for a major portion of thermal spray coatings sales. And the aerospace industry is very strict when it comes to quality control expectations of its thermal spray coatings applicators. Conversely stated, if you are a thermal spray coatings vendor and are either performing work currently for the aerospace industry or are envisioning getting into the aerospace thermal spray coatings applications, quality control has to be high on your mind.

This is where I find a one thing lacking in SOME thermal spray coatings contractors that deal with the aerospace industry and even SOME quality auditors from customers whose task it is to ensure that the flame spray coatings vendor is adhering to and potentially going beyond the requirements of the specification. After all, that is what separates a good thermal spray coatings vendor from a so-so contractor. And so, in this post, we will discuss the quality aspect that I have been alluding to above. And that has to do with furnace charts.

Now, for the most part, thermal spray coatings engineers claim they never deal with furnaces and therefore furnace charts are foreign to them. Not so, I say. Every time you send a coated part for diffusion heat treatment, such as an aluminized part, you need a furnace chart. Well, we don’t do any aluminizing one may claim. Fair enough. Now, every time you put a set of bond slugs into an oven to cure, you are dealing with a furnace and therefore you DO need a furnace chart and you should keep the furnace chart as part of the quality documentation and if you are an auditor, you should ask to see a couple of these charts to ensure that the bond slugs were in fact cured at the correct temperature and for the correct duration of time specified in the procedures.

Tensile bond slugs used for testing purposes are very important from a quality stand point and great care needs to be exerted to ensure the correct epoxy is used, the correct temperature of curing is used and the correct time is followed. And yet, some vendors do NOT keep the furnace charts with these slugs in their records.

There is another aspect dealing with the curing of tensile bond slugs in curing ovens and that is performing a uniformity survey of the furnace at periodically scheduled frequencies. Uniformity survey of the furnace is extremely important to ensure that the slugs are not being placed where the temperature of the oven is NOT what it is supposed to be.

So the next time you walk by the met lab in your company or the next time you receive bond strength results, ask for the furnace chart, ask for the uniformity survey and ensure thus that the bond slugs have been through a proper curing procedure; for if the test coupon is suspect, so are the test results!

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