Posts by DustinGebhardt

I second the recommendation for the porous pot.  When run correctly, they greatly extend the life of a chrome bath by filtering out contaminants and converting trichrome back to hexchrome.  

As far as reducing the buildup of the contaminants in the first place, I would check your rinsing practices.  Poor rinsing, especially with blind parts or parts that can trap solution, is a major contributor to contamination.

I had a similar problem that was traced back to trace amounts of water trapped in the base coating that came out during cure and ruined the final part.  We fixed this by pre-baking the parts with a normal cycle, minus powder of course.

It's a little hard to tell from the photos, but it looks like your problem is either orange peel or due to surface imperfections from the blasting.  Try running a panel with only solvent cleaning (non-abraded) with the orange powder.  If the problem goes away, it was due to your media blasting.  If the problem is still there, it is probably due to "orange peel".  There are many causes of this problem: cure time, cure temp, powder thickness, the powder itself (poor quality, lots of filler), or powder application technique to name a few. 

What are the cure specs for that specific powder?  Time?  Temp?  Thickness?  Your parts look fairly thin, so actual part temperature should be pretty close to oven temp throughout the cure cycle.  

I'm out of the plant this week (11-3 to 11-7).  I'll be back on Monday the 10th. 

It sounds like you are having some fun cutting your proverbial teeth.  :-) 

I wish I could get back to my hometown, but I can't.  Stay classy, San Diego!

If you are seeing nickel delamination, most likely the parts are losing their connection while in the nickel bath.  If it is the whole barrel, I would check the barrel contacts.  If it is only a few parts within the barrel, I would either add more load weight, investigate new danglers, or slow down the barrel rotation. 

If you want to make your deposit more uniform, you can reduce the amount of nickel metal in the bath.  The higher the nickel metal, the more efficient the bath is a high current densities, and the easier it is for the bath to build up larger thicknesses.  Increasing load weight and/or rotation speed can also help increase uniformity.  You can also try adding some brighteners, which on the small scale, can help reduce the buildup of metal in the high current density areas and preferentially deposit in the low current density areas.  Although brighteners can also make the deposit more deposed toward passivation, wh …

While I don't have the actual spec, doing a Google search came up with this spec:

GMNA GM4350M - Painted Part Performance Requirements

I would assume that this spec would cover your question.  If the bumper is plastic, this line may apply:

"For painted plastic parts only, the combinations of substrate, surface
preparation and applied paints shall use that which are shown in GM
Approved Paint on Parts Systems (APOPS) database. When APOPS testing is
performed each test must be completed on a minimum of three (3)
samples, each obtained from separate parts."

So you may be able to go to the guy that did the touch up and ask to see his proof that his paint, equipment, and pretreatment are all APOPS certified.

I'm assuming that the heat spots you are referring to are due to the heat generated during the extrusion process?

Do you have a picture of the problem?

Have you tried annealing the part after extrusion?

What alloy is this?

What is your anodizing process?

I did a quick Google search and I keep seeing recommendations to increase the cooling on the runout table.

For the utmost in paint adhesion, you typically want 2 things:

1) A clean surface.  Usually a solvent degreaser or auqueous cleaner is used to remove any dirt and oils.

2) A micro/macroscopically rough surface for maximum paint adhesion.  Many painters use media blasting to get this surface.  There are also some other means to get this, but they typically don't apply to nickel substrates.

With nickel (and most other metals) you also have to deal with oxidation.  Media blasting can remove the majority of the oxidation.  You can also try acid dip the part.  There are additives that you can use with the acid to help remove oxides.  In a best case scenario, you can also try running reverse current through the acid bath, which drastically eliminates the oxide.

Most likely, this is due to unequal current density on the parts.  I would expect that the darker parts are closer to the cathodes?  I suspect that the portion of the part that is closest to the cathode is getting more current, which is building up a thicker anodize film (oxide layer). 

Are you dying the parts after anodizing them?  Dying the oxide film can be tricky, but usually you can increase the time in the anodize bath to help smooth out any inconsistencies.  

If you are not dying the parts, I would greatly suggest that you try to make the part equal-distant from the cathodes or use auxiliary cathodes.

More info might help us.  What type of anodizing is this?  Type I, II, or III?  What is your process?  Seal type?

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