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Old 07-01-2004, 11:24 AM
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powdercoating

has anyone ever tried powder coating body panels. I mean, it seams like a really durable means of covering something like wheels, it seems like a great way to help with those obnoxious scratches that come with owning a black car. Seems like you can get it really shiny too...I've never actually worked with powder coating so I dont know...is it just finding an oven big enough for everything, or are there far worse reasons why I never hear of people coating their cars?

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Old 07-01-2004, 11:41 AM
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It can be done! I was somewhere in northwest Alabama a few years ago and this place had just done a model A body.
It just looked perfect on that model car.
It was neat, the said they charged $2000.
There is or was a powder coating chemist on here once in a while hopefully he will see this and can advise.
One thing for sure, there is nothing stronger.
They also said the body must be dipped.
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Old 07-01-2004, 11:43 AM
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well lets be logical about this:
finding an oven big enough yep that will be a problem.
then lets think about the heat needed to cure the powdercoat, thats what 400F??
have you any idea what will hapen to panels heated that high?
and then there are some details like windows, wiring, rubber bushings, seam sealer etc those parts sure will LOVE that kinda heat.
and thats just for starters I bet there are plenty more reasons why nobody has done it
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Old 07-01-2004, 12:03 PM
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If you dip the body, than none of that stuff is on.
so don't matter.
How hot do you think the factory bakes?
Freightliner is 475 degrees with Duramix seam sealers.

They do car frames all the time. If oven will do frame it will do a body.

Last edited by BarryK; 07-01-2004 at 04:01 PM.
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Old 07-01-2004, 12:10 PM
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Sure you can coat anything that can stand 400F. Bodies are a problem 'cause of the lead or Bondo fillers that don't like those temps. Here are a couple shots of some of the stuff I had powder coated for my '53 Chevy pickup. In addition I coated the engine and head white and tranny clear and all suspension parts gloss black.

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Old 07-01-2004, 12:19 PM
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Did you do these parts yourself?
If so what kit did you buy?
I have heard pros and cons about the do-it yourself kits???
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Old 07-01-2004, 01:14 PM
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No I only use commercial services. For one thing, that much sand blasting would be a royal mess, the powders have a definite shell life, and it is so cheap that it is worth it even if all they did was sand blast the parts. If the cost goes sky high like chrome has then I will consider DIY. I am doing a lot of my own chrome with a Caswell kit 'cause commercial chrome is astronomically expensive.
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Old 07-01-2004, 07:24 PM
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Powder coating of automotive body panels is feasible, and has been done commercially. For example, many Chevy S-10 bodys have been produced with powder primer-surfacer. There are also two powder clear topcoat installations that I'm aware of, one for BMW, and the other for Mercedes (although one of these is a powder slurry as opposed to a conventional powder).

Some of the easiest and most feasible type of parts are detachable assembles such as front fenders, from a standpoint of both the absence of temperature-sensitive components and from the size of the oven required.

For an entire car body to be done in one assembly obviously requires a fairly large oven. It will also be necessary to remove any components which will melt or distort at the bake temperature that is used. The bake temperature that is required depends on the particular powder formulation used. A typical high bake formula would require a bake schedule of around 10 minutes at 400 F (metal temperature) or 20 minutes at 375 F. A more reactive product formulated for lower bakes can cure at bake schedules of 20 minutes to 30 minutes at 300-325 F. This is where the product selection process starts to get tricky. Unless the powder is properly formulated for low temperature cure and non-blooming, cure temperatures below 350F can result in an objectionable phenomenon called "blooming" (which I can cover in a separate discussion if anyone is interested).

Another factor to be considered in product selection is the exterior durability (gloss retention) characteristics of the product. Most standard polyester powder resins are based on terephthalic acid, and will begin to lose gloss in 18-24 months of Florida exterior exposure. For an automotive topcoat application, one of the so-called "superdurable" polyesters (which is basically a polyester resin based primarily on isophthalic acid) would be best. Properly formulated, these can go 4-5 years of Florida exposure before they lose much gloss. There are also available acrylic powders which are suitable for such applications, although they are less commonly used in industrial applications, hence probably harder for the average rodder to find.

I would personally be very leery of trying to bake an entire body with a home-rigged bank of infra-red elements or schemes of that sort, as the consequences of not fully curing some parts of the body are (in my opinion) too traumatic to warrant the risk.

So bottom line- it is indeed feasible and possible, but not particularly easy. Finding a job shop with adequate facilities and finding the right powder coating product to use for the job would represent the major obstacles.

If I can help answer any specifics or further explain, please feel free to ask.
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Old 07-01-2004, 08:15 PM
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thanks powderbill! yes. I am interested in learning about "blooming". what if you only did the parts that get the most trauma...bumpers, door skins, nose, etc... and then still put a clear coat over it? Because, my GN's front end is getting torn up from rocks...it didn't really start happening until this most recent highway trip > and my bumper is cracking and the paint is starting to flake off on one side...you know, the aggravation of getting a used car and then DRIVING it.
oh..also, couldnt you just re-clear coat it when it dulled?
thanks,
wesley
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Old 07-02-2004, 07:32 AM
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[QUOTE]Originally posted by madhat
[B]thanks powderbill! yes. I am interested in learning about "blooming". what if you only did the parts that get the most trauma...bumpers, door skins, nose, etc... and then still put
************************************************** *
Ditto here Powderbill, also I had thought about when building the new plant to have a room about the size of single car garage for baking powder coat. Just for frames and hobby stuff and friends stuff.
Where do I start to see how this room should be built.
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Old 07-02-2004, 08:49 PM
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Madhat, sorry not to get back to you sooner- I about had a reply written last night after bedtime, but then the phone rang before I got it posted, it kicked me offline, and I lost it all!

re: blooming- If a typical standard durability polyester powder formulation is cured at a lower temperature and longer time than it was designed for (typically below about 350F), a white haze can form on the surface of the finish. (Even though, given a long enough bake time, the powder film may be fully cured.) This haze can create an objectionable appearance (particularly noticeable in dark colors) and can also cause intercoat adhesion problems with liquid topcoats. (The haze consists of a low molecular weight cyclic ester comprised of two moles of terephthalic acid and two moles of neopentyl glycol, the typical main resin components of most standard durability powder resins.) At higher bake temperatures, the blooming is not observed on the film surface, as it simply volatilizes off the film.

The two ways to eliminate blooming are to raise the part temperature over about 350F, or to use a blooming resistant powder formula in the first place. All of the true so-called superdurable powder formulations will not bloom, because they are formulated with alternative (better weathering) diacids instead of with terephthalic acid. Also, it is possible to design resins with standard durability, but with resistance to blooming, by incorporating alternative glycols into the resin structure.

So, the moral of the story is, it pays to know as much as you can about the powder formulation that you're using, and it also pays not to stray too far from the cure schedules that the manufacturer recommends (at least unless you're willing to conduct your own experiments).

I'll respond to the other comments posted in a separate post. Don't want to get burned by getting kicked offline two nights in a row.

Madhat inquired about the feasibility of powder coating certain body components that receive the roughest treatment.

I think this should be feasible. A possible scenario follows: First, remove the existing coating from the parts in question, preferrably down to bare metal. Second, optional but highly preferred, apply a high quality metal pretreatment, with a good zinc phosphate treatment being the most preferred. ( A well maintained iron phosphate treatment can also be used as an alternative, if your job shop isn't set up for zinc phosphate). Third, apply the powder as a high build (2-4 mil) prime coat. Fourth, apply a liquid two-component urethane topcoat. This is where it pays to be cautious. The vast majority of urethane topcoats give good adhesion over a polyester powder- but you don't want your application to be the rare exception. TEST the adhesion of your proposed powder-topcoat combination before you apply it to your parts! From this step on, finish as you normally would, ie clear coat (if so inclined), color-sand, etc.

The practical reason for using a urethane topcoat over the powder is to be able to get a color and appearance match with the rest of the car that is not powder coated. Don't plan on french-fitting powder topcoats and liquid topcoat parts together and expecting them to match. It's hard as heck to do on an application like a John Deere tractor, where many, many man-hours are devoted to researching how to make the appearance match. If you try to do it yourself in your garage, you will either be extraordinarily lucky or highly disappointed. That's the reason I'm suggesting using the powder as a primer only (unless you have decided to powder coat the entire body).

I'm not certain if I understood madhat's question about clear coating correctly. I think the question could be stated thus: Is it feasible to apply a standard durability polyester powder as a topcoat, then when it begins to chalk or fade, apply a clear coat at a later date? If I've stated the intended question correctly, it's an approach I'd avoid. My concern is that if the powder surface is exposed to sufficient UV to begin to chalk, it may cause intercoat delamination of the clear coat. Much better to use the very best durability powder you possibly can, and clear coat it initially, making sure the clear coat is designed for use with base/clear systems, as such clears will generally have UV absorbers that will help protect the base-clear interface from failure.

Perhaps one of the foremost problems in using powder coatings for hot rod applications is that it's generally hard for the average guy to know if the powder he's managed to get ahold of is suitable for the application or not. Most powder coatings are designed for non-automotive industrial applications, and unless you're privy to the formulation details, it's somewhat hard to know what you've got. This is in contrast to liquid auto refinish applications which are highly refined formulations designed for clearly stated purposes.

Barry, in it's simplest form, a batch oven is a well-insulated box with ventilation, air make-up, a heat source, and controls. There are occasionally used batch ovens for sale in trade publications. I don't know if there are ever suitable ovens on ebay or not. (I have seen decent powder spray guns on ebay though, some at good prices.)

The thing I'd be especially careful about if contemplating a self-built oven is making sure you don't inadvertantly create a fire hazard from the operating temperatures of the oven. The ones I'm familiar with are double wall construction, typically with ventilation between the walls. Oven design is really out of my area of expertise, so I'd better not say much more for fear of adding to problems rather than helping avoid them.

Hope this helps! Let me know if I can clarify any of the above. Time for me to get back out to the garage and see if my gel coat is ready to work with!

Last edited by powderbill; 07-02-2004 at 08:49 PM.
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Old 07-02-2004, 09:58 PM
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(Posted later) Barry, on further reflection, I want to make sure my reply to your question about home built ovens didn't sound flip. I know from your previous posts that you are a professional who would know better than to design an oven that would be hazardous. Perhaps a helpful step would be to view a suitable batch oven first hand, with an eye toward designing a similar version yourself. Is there a coating job shop that might have such an oven nearby you? Also, I'll try to look around the web and see if any of the batch oven manufacturers that I'm familiar with (ie Despatch) have enough info on their websites to be of any value. I don't know if you travel around much or not, but if you ever get the chance to be in the vicinity of a Powder Coating Institute trade show, there will likely be some ovens on display there, too. By the way, two well-known powder spray gun manufacturers are located in Cleveland and Indianapolis, and both have well-equipped application labs with batch ovens just the size you'd want. If you let them know that you're interested in buying a hand spray gun, I bet they'd let you have a quick tour their of their application labs. Regards, Bill
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Old 07-03-2004, 06:15 AM
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PowderBill,
That was an education! Can't thank you enough!

One question, I assume after reading all you wrote that powder coat sticks the same way as paint resin??

Its estimated that paint sticks by 45-55% +/- charge and rest mechanical adhesion (sanding).
It it fair to assume the powder coat sticks by charge more than mechanical?

Thanks again, Bill!
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Old 07-03-2004, 06:45 AM
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Barry, Interestingly, when powder is applied in dry form to a non-preheated substrate, there is only very weak adhesion to the part, almost surely entirely electrostatic attraction. At this stage, the powder adheres to the part well enough to make it to the cure oven, but it can be very easily wiped off (or blown off with an air hose, for that matter).

Powder that is under-cured typically exhibits relatively poor adhesion to metal substrates. That is one reason why it pays to always make sure that powder coatings are fully cured.

After fully curing on the substrate, the adhesion of powder is typically very good. I don't know how to quantify the portion due to mechanical adhesion, but I think it's fair to say that at least for the most popular powder cure chemistries, there are certainly enough polar groups formed during curing (secondary hydroxyls formed from the reaction between carboxyl groups and epoxide rings) that much of the adhesion is likely due to polar interactions between the cured resin and the substrate. (The ester linkages in polyesters probably also contribute to adhesion in similar fashion.)

Regards, Bill
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Old 07-03-2004, 08:05 AM
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[enough polar groups formed during curing (secondary hydroxyls formed from the reaction between carboxyl groups and epoxide rings) that much of the adhesion is likely due to polar interactions between the cured resin and the substrate. (The ester linkages in polyesters probably also contribute to adhesion in similar fashion.)

Regards, Bill [/B][/QUOTE]

I had no idea how the power was formulated never really looked at it, but looking at the above I bet its 80-90% charge and rest pure strength!?
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