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Making for Electrostatic Powder Coated parts.

Making for Electrostatic Powder Coated parts.

Making for Electrostatic Powder Coated parts.

(OP)
We are currently having problems with masking Electrostatic Powder Coated parts.  

Hand masking with teflon tape is too expensive.  

We made plastic masks of a material recommended by the Coater but they melted in the 400 deg F bake.  

Then we made Stainless Steel masks but where the coating bridged between the part and the mask left an unacceptable serrated break line leaving exposed metal when the parts were assembled.  

The coating vendor then told us to put a .010 in. gap between the edges of the part and the mask because the coating would not bridge this gap.  This resuted in a build-up of coating in the gap and the need to scrape the excess off the area that is not supposed to be coated.  This is very time consuming and expensive also.

Does anyone know of a better means of masking parts for mass production or a better coating alternative for Ductile Iron which must be both durable and okay for food applications?

Thank you,

Bob

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RE: Making for Electrostatic Powder Coated parts.

Check with a masking supply company - not knowing what your part actually looks like, I can't provide you with what I think the best solution might be.  Your description was not too vivid, and it sounded like you tried a couple of different options.

That being said, don't use Teflon tape (WAY to expensive for that purpose).  If your curing temps are no higher than 400F, use the widely available green polyester powder coating tape.  If higher temps than that, a Kapton or glass cloth would be needed (typically good to 500F).  

If a custom molded or die cut part may work better, sheet silicone (easily die cut with relatively inexpensive dies) or molded silicone (the most expensive method, but sometimes cuts the most labor time for you, saving $$$) are other options.

Most masking companies can die cut to any shape, slit tape to any width or design a custom molded part depending on what you are trying to do.  Again, not knowing what your part looks like makes it difficult to provide a better assessment.  Hope that helps.

RE: Making for Electrostatic Powder Coated parts.

(OP)
magic612,

Thanks for the advice on different masking materials, I'll look into it.

They are round parts of gearheads which are exposed to the shop environment when mounted in the machine.  Therefore the outer portion of the unit must be powder coated but the interface surfaces and seal bores cannot for dimensional requirements.  We cannot power coat after assembly because of the 400 degree bake to cure the coating.  We have to coat the OD, some vertical surfaces, counterbored clearance holes and chamfers.  We are coating stacks of the same part, 15-20, sandwiched between SST masks which cause the vendor to bring the bake to 500 degrees to ensure the entire stack was brought to temp.

The chamfers seem to be the biggest problem.  None of our masking attempts have produced a clean edge and we invariably have to scrape the parts by hand after coating due to a build-up where the mask meets the part.

RE: Making for Electrostatic Powder Coated parts.

Thanks for the parts description - that helps give me a better idea of what your up against. Two thoughts:

1) you could get a molded silicone part made that is a "negative" of the gear teeth and wrap it around the gear(s) - silicone handles up to 600F, though this could be pricey if your quantities are low.

2) There are liquid "spray-on" masks available. This would be a two-part process - you'd have to mask the rest of the part first (say with an inexpensive crepe tape circle die cut), spray the part where you need it masked for powder coating (on the gear teeth), then remove the tape mask. More labor intensive than the first method, so I'm not sure which is your best solution (and I DON'T know if liquid mask will handle 500F).

Not sure if I've helped, but either one of those could be viable directions to pursue. Good luck - any other thoughts let me know.

RE: Making for Electrostatic Powder Coated parts.

(OP)
magic612

We are really trying to avoid hand taping, it is more expensive than scraping.  Our gear teeth are well inside the part and are not an issue.

We did use a laser marking machine to remove the powder coat on external surfaces.  It worked pretty well but the bores were not so easy to clean.  Now we are trying to control the build-up on the edges of the mask to make it easier to scrape post-coating.  The laser will not take this off without a lot of burning, smoke and fumes.  The powder coat comes of relatively easy if there is a transition from standard coating on the chamfer to a thick berm on the surface to be cleaned.

Any input is good input and you have given me some new avenues to pursue.  I appreciate it.

Thanks again,

Bob



RE: Making for Electrostatic Powder Coated parts.

Have you considered using silicone plugs for the bored surfaces (I'm assuming they're round)?  There are a number of different styles of plugs available which may be useful - regular tapered plugs, pull plugs, flangeless plugs, etc.  Even silicone caps (which are usually used to cap studs or tubes) can be pushed into a hole to plug it, provided the OD of the cap is the right size.  I would think those might help you mask the bores to avoid having to burn the coating off.

Wish I could give you better advice on how to avoid getting excessive buildup (requiring the scraping); unfortunately, that subject is not my area of expertise.  I know more about preventing coating by using masking.

Good luck!

Dave

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