Painting Valves
Painting Valves
(OP)
Hey Guys!
I'm new to this forum and I've got a perplexing dilemma regarding paint adhesion to our valves. First off-our valves are Standard Low temp Carbon Steel Bodies and our valve types are:Ball valves and high pressure globe style valves.
We have been having a problem with our two-part epoxy paint "peeling" on the flanges (which are machined).We have introduced a parts washer to our paint process with a phosphate base to see if this will help with adhesion.
Any help would be greatly appreciated in resolving this issue!
I'm new to this forum and I've got a perplexing dilemma regarding paint adhesion to our valves. First off-our valves are Standard Low temp Carbon Steel Bodies and our valve types are:Ball valves and high pressure globe style valves.
We have been having a problem with our two-part epoxy paint "peeling" on the flanges (which are machined).We have introduced a parts washer to our paint process with a phosphate base to see if this will help with adhesion.
Any help would be greatly appreciated in resolving this issue!





RE: Painting Valves
RE: Painting Valves
Can you recommend a better paint for our valves? We apply our paint with a hvlp gravity feed Sata-Jet and I'm just not sure that our 2 part epoxy is the way to go!?
RE: Painting Valves
The product bulletin for the paint should give specific cleaning & pretreatment instructions. Two-part epoxy is very broad category; some will need a compatible primer, some will need phosphating + primer, and some are suitable for bare metal (self-priming).
The initial peeling was perhaps due to inadequate cleaning of cutting lubricant from the machined flanges, but it would take a little bit of testing to confirm. Do the cleaned surfaces produce a water break-free surface when rinsed in high purity water? A smooth sheet of water, without beading or breaks, is a good indicator of freedom from oils.
"We have introduced a parts washer...with a phosphate base..."
Sounds like an alkaline phosphate cleaner, trisodium phosphate or similar. Best used warm (~70 oC) or per instructions & rinsed in very clean (low TDS) hot water to avoid residues & aid in drying prior to painting. The alkaline processes are much better than the acidic ones in not causing the flash rusting warned about by FinishingTalkdotcom.
RE: Painting Valves
Thank you for your post. Yes,it's an alkaline phosphate cleaner! This washer has recently been introduced in our process,so we're hoping that this is indeed the answer to our peeling issue.
I was of the impression that the peeling was due to the fact that we are coating over a machined surface. We decided that shot blasting may be an option-something for the primer to bind to...any thoughts?
RE: Painting Valves
Anyway, if blasting, necessary to preclean to avoid embedding contamination.
But, you still need the proper chemistry -- a primer or self-primer for bare metal. It's true that phosphating is often used as a pretreatment for mass production (good adhesion for primer), but it is a messy process (produces sludge in bottom of phophating tank) & requires a lot of energy for heating. Also, is phosphating permitted inside the valves?
If your paint's bulletin says OK for bare metal, the improved cleaning may suffice.
RE: Painting Valves
I will def. put your suggestions to use. Yes,we are using a primer (epoxy)and,no-phosphate is not permitted in the valves- so we use magnet covers on the flanges during the shot blasting process.
Cheers!
RE: Painting Valves
The best coating for valve body is fusion bobded epoxy coating and for the ball is better to protected with rubber lining.
Regards
Kamal