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Powdercoating Can Give Your Muscle Car Parts a Durable and Good Looking Finish

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If you’re building a car, you have three choices for refinishing the various metal bits involved: painting, plating, or powdercoating (also known as electrostatic painting). Powdercoating may seem new and high-tech, but it’s actually been around for over 40 years. Once used primarily for industrial applications, today it’s become a very popular option for getting a durable and good-looking finish on parts for our classic Chevys.

As the name implies, powdercoating is a coating initially applied as a powder, as opposed to traditional paint, which is a pigment suspended in a solvent or water solution. These powders are comprised of epoxy, polyester, and acrylic resins combined with various crosslinking compounds. It can get pretty technical, but in short, colored dust is stuck to metal and melted to form a coating.

As the colored dust passes through a specialized application gun, it’s given a low-voltage electrostatic charge. The parts are given a negative charge so the positively-charged colored dust particles are attracted to the metal surface where they cling much like the magnets on your fridge.

How thick the powder coats the surface of the metal depends on the voltage used on the system. At some point the powder thickness inhibits more particles from sticking, which is why it’s self-leveling. Complex surfaces sometimes create a Faraday Cage effect (look it up) where the powder has a hard time clinging. Specialized guns, gun output, spray angle, and voltage changes are used by professional shops to get around this uncommon issue. One common cause of the Faraday Cage effect is dirty metal hangers, which interferes with the charge in the part compounding the effect.

Once the powder is on the part, it’s cured in an oven (typically between 350 and 400 degrees F) where the thermoset powder coating chemically reacts to produce long molecular chains, resulting in a high cross-link density, which is very resistant to breakdown. All that fancy talk equates to a finish that’s much harder and chemical resistant than traditional paint. However, powdercoated finishes aren’t immune from damage. They stand up well to brake fluid and gasoline, but will discolor and can fail if exposed long enough. And powdercoated finishes can scratch and chip if you try hard enough. Also, nothing will kill powdercoat faster than acetone. Once the heat-curing process is done, the parts are allowed to cool slowly and are then ready for installation.

For automotive use, there are basically three types of powder: standard polyester, enhanced polyester, and super polyester. For your patio furniture it doesn’t matter, but for your pride and joy, we would recommend going with at least enhanced—and preferably super-polyester powder. All three types can be had in low-cure (flow out around 400-degrees F), which is perfect for temperature-sensitive car parts.

Recently, the powder industry has adopted a standard numbering system called a “RAL.” This number relates to a specific color. For example, RAL 5005 is Signal Blue, while RAL 3000 is Flame Red. This makes it easy to see if your local powdercoater has the specific color you’re looking for. Powdercoating prices range anywhere from $20 for a bracket to $500 for a chassis. Parts that require a lot of taping off will cost more as well, and going with common colors will generally be cheaper.

If you’re adventurous, there are do-it-yourself kits on the market. Just don’t let your spouse catch you using the kitchen oven to cure parts!

To check out the process firsthand, we dropped by Eddie Motorsports in Rancho Cucamonga, California, to follow along as they powdercoat some parts for a Camaro project we’re working on.

2 Powdercoat Parts Prep 2/14

01. The first step in the process is cleaning and prepping the parts to be coated. There’s a ton of ways to skin this cat, some of them pretty exotic, but for most hot rod applications the parts are mediablasted. Just like painting a part, preparation is key since any contaminants on the surface will compromise the finish. Also, any bits (rubber, tape, plastic, bushings, etc.) that can’t handle high temps have to be removed from the part to be coated. Panels that might be damaged by mediablasting can be chemical-dipped followed by a phosphate bath. Rust under the powdercoating will eventually bubble the coating just like with paint.

3 Powdercoat Tape Threads 3/14

02. Since the powder will attach to every metal surface of the part, care must be taken to keep it off areas where it’s not wanted. These include bearing surfaces, threads, etc. Here, a specialized tape (one designed to survive the oven curing process) was used to protect the threads.

4 Powdercoat Aluminum Foil Hole Plug 4/14

03. Good old aluminum foil is handy as well. So long as it covers the area and will survive the oven, it’s good to go. Keep in mind that powdercoating adds thickness to parts (about 1 to 3 mils), so take that into account on parts that interface with other parts.

5 Powdercoat Silicone Stoppers 5/14

04. For this Chassisworks rearend housing, the third member studs were wrapped in tape and the main hole was blocked off with a piece of cardboard, which surprisingly does fine in the oven. All small holes were plugged with silicone plugs. Most powdercoating operations have a huge assortment of these plugs in every conceivable size.

6 Powdercoat Pre Bake Parts 6/14

05. While not technically necessary, pre-baking the parts prior to application of the powder is a good idea. This greatly reduces outgassing common in many types of metal and will help remove any remaining contaminants in the metal. Care should be taken not to overheat the part since this can cause the powder to start flowing during application, which can cause runs if the powder is laid on heavily.

7 Powdercoat Colors Eddie Motorsports 7/14

06. Powder colors are available in just about any hue you can imagine, including clear and metallic. Because it’s applied dry (unlike a traditional paint where the pigment is suspended in some type of solvent) powdercoats are typically much thicker than paint. You can also get cool effects by mixing the powders or by stacking colors (a solid base with a translucent top coat, for example).

8 Powdercoat Powder Hopper 8/14

07. The powder is poured into a hopper, which feeds the electrostatic application gun. To prevent contamination, each pigment typically has its own hopper. There are two basic types of powder: thermosets and thermoplastics. Under heat, thermoset coatings undergo a chemical reaction, which offers superior chemical and heat resistance. This type is commonly used in automotive applications. Thermoplastics don’t undergo any type of chemical change during the heating process. They simply melt and flow and aren’t seen much in our hobby.

9 Powdercoat Electrostatic Coating 9/14

08. Powdercoating is also referred to as electrostatic coating since the spay guns utilized impart a positive electric charge to the powder, which causes it to be attracted to and stick to the negatively charged part to be coated. Most of the powder propelled out of the gun goes onto the part, and any overspray is pulled into the specialized application booth. Since there are no VOCs involved, powdercoating is very environmentally friendly.

10 Powdercoat Pre Cured Parts 10/14

09. OK, here’s a physics lesson. The thicker metal of the rearend housing held more heat from the pre-bake, and as such, the powder applied there started to flow and get shiny. The thin metal of the inner fenderwell didn’t hold much heat and still has a matte finish to the powder.

11 Powdercoat Curing Oven 11/14

10. The rack of parts was then rolled into the large oven where they cured (baked) for around 10 minutes at 390 degrees Fahrenheit. This time and temperature will vary based on the type and brand of powder being used.

12 Powder Coat Matt Black Parts 12/14

11. Once the timer went off, the parts rack was removed from the oven. The parts now have the same uniform satin black appearance. Once out of the oven, the parts were left alone to slowly cool down to room temperature.

013 Powdercoat Threaded Hole 13/14

12. Once cooled down a bit, the tape and various plugs used to protect certain surfaces were removed from the parts.

14 Powdercoat Bracket 14/14

13. OK, here’s a helpful life hack. Even though powercoating is many times thicker than paint, it doesn’t really hide flaws in the surface of the item being coated. If the item has bumps, gouges, pits, or other flaws, they will still most likely be there after coating. Using a powder with a bumpy finish (such as hammertone) will help hide some of these flaws. This rust-pock-marked leaf spring pocket still looked pockmarked even after application.

Sources

Eddie Motorsports
Rancho Cucamonga, CA 91730
888-813-1293
www.eddiemotorsports.com

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