POWDER COAT EXPERTS: Quick question

911 tweaks · 12-20-2007, 03:11 PM

Can the experts comment on the point made to me recently:

I was told that DO NOT get any pcoat on any metal area(s) that will come in contact with other metal!! Over a short amount of time, the typical shake-rattle-roll that a car goes through, will loosen up these joined areas causing parts to break and damage to such pcoated parts and associated joined pieces.

HELP!! I hope this is not true as I am concerned that if this is true, does it also mean that areas under the washers, areas under bolt heads, ect...IF these have pcoat there, these bolts will loosen up with obvious catastrophic potential results!!

I will sit and sweat bullets for the expert to tell me my fait!
Bob

SoCal70RSR · 12-20-2007, 03:42 PM

Hmmm... I'm curious now. What parts did you powdercoat that have you concern?

My valve covers are powdercoated, and others have done this to before and I've never heard of the issues you're referring to.

However, I did remove any remnat powdercoat and smoothed out the back portion of the valve covers that touch the heads. I did the same to the bottom of the intake runners for my 3.2

gshiwota · 12-20-2007, 03:52 PM

I was a powder coater in a former life and based upon my experience the answer depends on which parts were coated. I believe the information you heard is true in theory, powder coating could come off on high stress metal/metal contact areas. However it would take quite a bit of shearing forces to remove powder coating especially between two highly torqued parts. Properly pre-treated and coated parts have excellent adhesion properties and would not come off easily under these conditions.

For instance, wheels are typically coated in their entirety so lug nuts would be in direct contact with powder coating. Wheels are a great example since they probably experience the most shake/rattle/and roll of any part on the vehicle. In my experience I have never seen a lug nut back off or even powder coating damaged by the sheering effect of a fastener. If the coating did fail its usually because it was chipped or during the removal process of a fasteners or subject to extreame heat. BTW.. I use powder coated lug nuts on my 911SC.

If you're a DIY powder coater with a home set, I would definately NOT apply powder coating to mating surfaces. The adhesion strength of powder coatings is not in the powder coating itself, but rather in the pretreatment of the metal surface. DIY powder coaters rarely have access to professional pretreatment chemicals or processes - 3 or 5-stage iron-phosphate pretreatment enables powder coatings to have exceptional adhesion to metal.

Any other powder coating question??? Shoot em my way.

Thanks.

Gabe
--------
82 SC targa
61 356 karmann notchback

Buckterrier · 12-20-2007, 05:54 PM

Quote:

Originally Posted by gshiwota

I was a powder coater in a former life and based upon my experience the answer depends on which parts were coated. I believe the information you heard is true in theory, powder coating could come off on high stress metal/metal contact areas. However it would take quite a bit of shearing forces to remove powder coating especially between two highly torqued parts. Properly pre-treated and coated parts have excellent adhesion properties and would not come off easily under these conditions.

For instance, wheels are typically coated in their entirety so lug nuts would be in direct contact with powder coating. Wheels are a great example since they probably experience the most shake/rattle/and roll of any part on the vehicle. In my experience I have never seen a lug nut back off or even powder coating damaged by the sheering effect of a fastener. If the coating did fail its usually because it was chipped or during the removal process of a fasteners or subject to extreame heat. BTW.. I use powder coated lug nuts on my 911SC.

If you're a DIY powder coater with a home set, I would definately NOT apply powder coating to mating surfaces. The adhesion strength of powder coatings is not in the powder coating itself, but rather in the pretreatment of the metal surface. DIY powder coaters rarely have access to professional pretreatment chemicals or processes - 3 or 5-stage iron-phosphate pretreatment enables powder coatings to have exceptional adhesion to metal.

Any other powder coating question??? Shoot em my way.

Thanks.

Gabe
--------
82 SC targa
61 356 karmann notchback

+1 , well said... as we say in the paint business... we dont' paint metal we paint pre-treatment

Axiom · 12-20-2007, 06:09 PM

I also agree, I don't know why prep work is taking for granted so often.

911 tweaks · 12-20-2007, 06:41 PM

great answers guys...especially as I review this I need to give you more/the complete story..

I removed all (98%) of the suspension pcs from a 82' SC and had all the metal pcs cleaned properly at the platers (or medialblasted if needed) then they were the 3 step plated...I think it goes: clean - chromate - plate.

NOW, I want to clear pcoat to preserve the yellow zinc parts to keep the "new" part look as long as possible and I was told the above.
I am not concerned about the engine surround tin as this is not high stress or strength; I am concerned about the mating surfaces of the engine mount bar to the u-shaped metal pc that covers the engine timing pully as this IS a high stress & weight area.
I am also concerned about any place where a bolt passes through a sway bar shakel into the body; front struts where the steering arm bolt/connect to them... you catch my drift.

Now what? I plan to use the hi temp teflon tape (500 degree) rated stuff to mask off areas I dont want the pcoat...the threaded areas will get silicone plugs to prevent the threads from getting all gunked up...I am freaking about the thru bolt contact areas even with your gled to hear pcoat lug nuts and such. Any other re assuring bits you can pass my way??

Thanks alot guys...this is my, I THINK, last hurdle to starting re-assembly of the project that has been sitting in my garage for the past 5 yrs!!!!!
Bob

911 tweaks · 12-21-2007, 02:31 PM

hopeing for some other comments before I tape off what I think needs to be before I go to the pcoater...I have been thinking about the area under the bolt head and maybe the fastener being tightened down will "dig" through the pcoat and this be a mute point? I am obviousley not very familiar with pcoat other than handeling treated parts and they are shinney, smooth and seem to have an indestructable outer surface.
help!!
Bob

Axiom · 12-21-2007, 03:02 PM

When they do powder coat they sandblast the items, you may lose the cad plating finish.

We can start with that.

Now back to the Xmas party.