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E-Coat Paint

E-Coat Paint

(OP)
My company makes link rods for the automotive industry and we're having problems with our ecoat painting on these link rods.  We used to have problems with the paint "blistering" but that has diminished and now we're having a problem with the paint looking as though it builds up on the side of the part, making it have the pattern of tiger stripes.  But its not down the entire part and its only on one side of the part.  You can feel the defection with your finger and can only see it with good lighting.  It also does not seem to be consistent with the direction and angle that the rods are placed on the racks before they're dipped.  

Has anyone else ever come across this problem and what would be a good direction towards solving it?  

RE: E-Coat Paint

Call the mfg.  Is this spray painting or powder coat??

RE: E-Coat Paint

Might want to re-post this in the Paint/Coatings forum.

RE: E-Coat Paint

Guys, it's neither spray nor powder, more like plating.
Brief overview here:
http://www.clearclad.com/clearclad_resources/ecoat.htm

As a consumer, I think I've seen tiger stripes, on link rods, before, so maybe it's an old problem.  As noted, your coating supplier may have expertise.

My guesses:
Electric field nonuniform, possibly due to masking by other parts or the racks.
Deposited film being disturbed before baking, e.g. rough motion during, er, un-dipping.
Bath contamination, e.g. a film of oil floating on the bath surface, adhering to the part on the way into the bath.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: E-Coat Paint

It's not entirely clear to me whether or not this is an in-house electrocoat line, but if it is, then you definitely should be discussing this with your pretreatment and paint supplier(s).  There are only a few vendors for this type of coating, and companies like PPG and BASF have a great deal of technical expertise.  The following links are for some general troubleshooting advice for electrocoat lines:

http://www.pfonline.com/articles/troubleshooting-for-electrocoating


http://www.electrocoat.org/troubleshoot/index.html


With regards to surface defects, if there is a "tiger stripe" appearance, this is likely related to the grinding operation.  Grinding can leave a surface that is difficult to clean and obtain good paint adhesion.  I would investigate whether or not the parts are taking on a good phosphate coating, specifically in the areas where the stripes appear.
 

RE: E-Coat Paint

Quote:

An unfinished product is immersed in a bath containing the electrophoretic paint emulsion, and then an electric current is passed through both the product and the emulsion. The paint particles that are in contact with the product adhere to the surface, as described in the above mechanism, and build up an electrically insulating layer. This layer prevents any further electrical current passing through, resulting in a perfectly level coating even in the recessed parts of complex-shaped goods. The product is then removed from the paint bath and baked in an oven.
Evidently not ;)

If their description of the process is correct, then it's self-leveling... a non-uniform electric field would do it, but how on Earth would you create one?  Once each bit becomes insulated, it's effect on the field should be zero.

Blistering would scream contamination to me, but you said that problem has disappeared... do you know why it disappeared?  Maybe they're contaminating it in another way.

Do you have a pic of how these are laid on the racks?  That may lead us to better suggestions.

Dan - Owner
http://www.Hi-TecDesigns.com

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