Powder Coating Questions & Answers | Super Coupe Club of America

Answers about Powder Coating

Ok since we have two questions about the Eastwood powder coating system, I will combine them in one answer.

The first question is about "starter sets for powder coating"...The only company that I am aware of that makes complete kits for hobbyist (homeowner) powder coating is Eastwood. I had a hand in helping them select the ovens for their program and a few other technical issues over the years. They started out buying a "powder coating gun" from a China supplier that is pretty low-tech, but gets the job done. Sears and Summitt both have homeowner guns as well, but no ovens, etc. This gun uses a TV "fly-back" transformer to charge the powder during application, a far cry from industrial grade equipment. But it does not have the $4k price tag as the industrial equipment either. Once they had a gun, they needed all the other stuff to execute the powder process. They came up with a line of cleaning chemcials, cure ovens, booths, etc. to support the hobbyist and haven't looked back. Their real money maker is the powder they sell. Average powder coatings cost between $2.50 to $5.00 per pound (except the real sexy stuff) but come in one pound to 300 pound containers (automotive and appliance manufacturers buy their powder in pound totes!). Since the average homeowner does not need that much powder, Eastwood buys regular powder in 50 pound quantities and re-packages it into small containers. The price ends up at around $50.00 per pound. Nice business model!

To perform powder coating safely you need a spray gun, powder spray booth (designed for powder), cleaning method, and cure oven. The most expensive piece is the cure oven. You need the gun to charge and atomize the powder to get it to coat and stick to the part before placing it into the oven. You need the spray booth to contain the overspray and collect it for disposal (industrial users often re-use the overspray). Without a booth, you could have an explosion. You need a cleaning system to clean the parts before your apply the powder, because any paint job is only as good as the surface you apply it to. You need the cure oven to heat the part above 250 degrees F to melt and cure the powder. Do not use your wife's cooking oven, as the next meal may not taste like you expect! Check the Eastwood website for current prices of these equipment components.

As for the question about clear coating over the silver (chrome) powder...Silver (chrome look-a-like) powders look great but have insufficient mechanical properties. They will scratch and mar easily. This is why they reccomend applying the clear over the top of the chrome powder. The clear can get cloudy, as seen in your picture, due to several issues. First, the quality of the clear powder may not be that great. Second, the thickness of the clear can affect the clarity of the coating (too much clear will get cloudy). Third, the clear can cloud up if it is under or over cured (under baked or over baked). Fourth the clear can cloud up if the oven does not have sufficient exhaust (oven contaminants).

Clears and chromes are "high risk" powder coatings, as they are very finicky to apply and still look good. Start out by buying a good clear powder. Apply it at less than 3 mils (0.003 inches) thick. Check cure by dipping a q-tip in MEK and rubbing it on the surface. The clear coating should not become sticky or tacky after 25 double rubs (one double rub is one single back & forth motion). If it does get soft, it is under cured. Finially increase your oven exhaust, if you have one, to improve the quality of the cured clear coating.

Sorry for the lengthy reply. It is just the Engineer in me comming out! Sorry folks, but since the weather got so nice in the Northeast the last couple of days I was out in the garage working on my 89 SC and did not check the posts for this thread lately. I check my emails frequently, but did not see anything from the SCCoA forum letting me know there were a few more posts!

Following are the next group of answers to the recently posted questions:

"I'm just using a kitchen oven (not the one we cook food in) I guess doesn't have much exhaust. A fan does kick on on it sometimes. Maybe I should figure a manual override for the fan?"

A kitchen oven does not have much exhaust at all, as it is designed to keep heat in and smoke out of your kitchen! Paint curing ovens on the otherhand have a heat source (gas burner or electric element), a circulation fan (convection heat type oven), and an exhaust fan. The heat source provides the heat energy, the circulation fan delivers the heat energy to the part, and the exhaust fan removes the by-product of combustion (natural gas only) and the by-products of powder cure. Having an oven with an inadequate heat source, no circulation fan, and inadequate exhaust will combine to cause numerous problems.

I recently answered a similar question for my Powder Coating magazine column last week:

Question: " i have been trying to powder coat a set of 350 chevy heads and when i shoot the heads with wet black powder and then cook them the powder is not flowing out it comes out as if it was never cooked. how can i get the parts to flow out. is it that the heads are soaking up the powder. please help me with this. i am baking at 500 degrees thank you for your help chris"

Answer: "Chris:

The 350 C.I.D. Chevy motor is very reliable. I had one in several vehicles over the year. However, I prefer the horsepower or the higher revving 327 C.I.D.

The description of the problem you are having tell me that you are not heating the cylinder heads to a point where the powder coating even melts, yet alone cures. If the powder on the part looks the same when you take it from the oven as when you put it in the oven (still a powder and not a coating), then it is time to evaluate what you are using to heat your part.

This problem has to do with the weight (mass) of the cylinder heads and the energy capacity of your heat source. I have lifted my share of Chevy heads over the years and from my recollection they weigh about 100 pounds. Considering that the cylinder head is made from steel and has a specific heat of 0.125 BTU per pound it will take 4,375 BTUs to head one cylinder head to 350 degrees F (the average cure temperature for powder coating). If you put this cylinder head into an oven whose heat source has an energy capacity of 1,000 BTUs per hour, it will take 4.375 hours to get the cylinder head up to temperature and an additional 25 minutes to fully cure the powder coating. That is almost five hours of “baking time”! However, if you use an oven with a heat source that has an energy capacity of 10,000 BTUs per hour it will take less than an hour. This relationship between the energy capacity of heat sources and cure time can easily be related to horsepower and speed; “The more you have the faster you will go!”.

I frequently tell my clients that the size of their oven burners determines how fast their products will achieve the desired powder cure temperature. I often tell them that you can cure a 10,000 pound part using a cigarette lighter, it will just take a couple of hundred years. The same goes for you. If you are trying to cure your cylinder heads in a toaster oven, then I hope you are very patient, as it will take quite a while to melt, flow, and cure the powder. Remember the old racer’s adage: “Go big or go home”. Of course, they were talking about engines (horsepower), but you get the point." Powder Coating Safety

Makes sense.
Oh yeah, and whats gonna blow up if you don't have a booth?

Powder coatings are "organic" in nature and, as susch, will combust if mixed with the right amount of air. The same thing applies to any organic dust, such as baking flour, sugar, etc. I am sure you have heard of tragic cases where a sugar mill or flour mill had an explosion. Well powder coating materials are just as dangerous! Believe me, as I have investgated numerous powder coating lines that had fires and explosions, some of which had fatalities!

The risk with powder coating is dramitically lower than using solvent type liquid paints (i.e. laquers, etc.). However, that does not mean that they are not dangerous in their own right.

Powder coatings will not combust (burn) in the container as there is too much powder (fuel) and not enough air. Same goes for the opposite condition, where a small amount of powder is mixed with a lot of air, the powder will not combust either. The problem occurs when powder coatings are atomized with just the right amount of air. This "just-right" mixture is between the "lower explosion limit" (LEL) and the "maximum explosion limit" (MEL) and is often the exact mixture of powder and air at the gun applicator tip. If a source of ignition is present with this "perfect mixture" the powder cloud will ignite! The result is a fireball that releases a tremendous amount of energy. If this energy is expended in a small area (what is called containment) the result is an explosion.

It is just like your SC engine works: gasoline is mixed with air and ignited in a contained area (the combustion chamber) and the resultant explosion sends the piston in the opposite direction. Ignite the same gasoline/air mixture in an open cup, and a fireball will happen, but no explosion since there is insufficient containment .

Most explosions happen when powder coating ungrounded (or improperly grounded) parts. The part will absorb some of the electrostatic energy used to charge the powder (so that it sticks to the part before curing). If the part is improperly grounded (more than one megohm = one million ohms resistance), the part will eventually become saturated with electrostatic energy and discharge to the closest ground (typically the gun tip). This results in an arc (ignition source) much like when you discharge static electricity in the wintertime after shuffleing your feet on a carpet and touch the light switch. The ignition source and the powder/air cloud cause a fireball at the end of the gun, the person spraying the powder usually screams and drops the gun, and the fire goes out harmlessly as the gun trigger is released stopping the power/air from fueling the fire. This event usually requires a change of clothes for the powder sprayer, at least their pants anyways!!!

However, if the person has been spraying a lot of powder in an enclosed garage, without ventilation, and there is a large cloud of power, then the next sound they hear is St. Peter asking them what they did back on earth to get into Heaven! The large powder cloud provides a significant energy source or fuel and air and the garage provides the containment...a very bad combination. The energy released from such an explosion is awesome. I have seen 40 feet of cinderblock wall moved 20 feet in a powder explosion!

Now that I scared the Sh-t out of you, it is time to bring you back to reality. Powder coating is the safest method of painting, except for using laytex paint and a brush. Follow these important rules for safe powder coating:

1. Spray powder coatings in a powder coating booth that is designed with proper airflow. This ensures that there is not enough powder and too much air to have a combustion fireball (except right at the gun tip).

2. Always coat parts that are properly grounded. Use a ground wire attached to an electrical ground or cold water pipe at one end and attached to the part at the other end.

3. Eliminate all sources of ignition during spray operations. No smoking, no welding, no grinding, etc.

4. Cover all electrical devices within five feet of the spray area with air tight bags. Actually code requirements call for "dust tight explosion proof" electrical devices in this area, but they are very expensive.

5. Always wear a dust mask and safety glasses to protect your health when powder coating. Powder Coating Wheels

If the center caps are the aluminum ones you can powder them. The earlier wheels have metal centers, right?

Yeah you will want to strip the wheels to bare metal.

Here are my recommendations for having your Aluminum wheels powder coated:

1. Remove the existing coating by either chemical stripping or media blasting. Do not use thermal stripping methods (burn-off oven) as the + degree heat will anneal (soften) the aluminum. NEVER USE THERMAL STRIPPING METHODS ON MAGNESIUM WHEELS, AS A FIRE WILL OCCUR THAT THE FIRE DEPARTMENT WILL HAVE GREAT DIFFICULTY EXTINGUISHING (AS WATER APPLIED TO BURNING MAGNESIUM WILL EXPLODE)! Acceptable blast media is Aluminum Oxide, CO2, or Plastic. Do not use steel based media, as it will start corrosion sites under the coating (galvanic reaction with the aluminum). Sand as a blast media has all but been outlawed (silicosis health problems).

2. Ask your powder coater if they can apply a chromate conversion coating to the aluminum wheels before powder coating. Sometimes reffered to as Alodine, this conversion coating will increase the service life of the coating by a factor of 5, or more.

3. Select either a TGIC polyester or Acrylic powder for your color, as these are the formulations that the original manufacturer used and are best suited for this application.

4. Consider using a clear coating over the color, for a better "depth of finish" and better wear life.

5. Instruct your powder coater to cure the coatings on the wheels at a temperature below 325 degrees F. This will ensure that you do not anneal the temper (hardness) of the aluminum. They will have to cure the wheels longer at this lower temperature, but it is the safe way to go!

This recipe will provide wheels that look great, will last a long time, and will not change the metalurgical charateristics of the wheel.

Let’s Start Powder Coating!

Powder coating is a fun and creative niche market for everyone. There are many powder coating operations all around the world from garages to multimillion-dollar facilities. If you want to start powder coating and be one of the successful ones you’ll need assistance from  suppliers in the industry to help you avoid many of the pitfalls that affect beginning companies.

If you want to learn more, please visit our website.

Be sure to ask questions and make good use of all the advice and help available from the industry equipment and product suppliers.

The rest of this article lists a few essential items and equipment that are required to help entrepreneurs and businesses set up a brand new powder coating operation. All of these must be considered whether you’re going with all batch equipment, a fully automated (conveyor) system, or something in between.

Pretreatment (Chemical or Mechanical)

Pretreatment is a very crucial step in the powder coating application process. The type of pretreatment will vary significantly depending on what is being powder coated.

Abrasive blasting and/or chemical cleaning (etching) are the most common practices of preparing the substrate (typically iron phosphate or zinc phosphate). These methods remove soils and create a profile on the substate, which gives the powder a surface to adhere to.

The Abrasive Cleaning/Blast Media/Blasting Equipment category on PCO can be a great source of information. See also Stripping Chemicals & Equipment and  Pretreatment Chemicals categories.

Powder Coatings

Depending on the project you’re working on and on what substrate, you’ll quickly learn there are many different powder coating chemistries, characteristics  and colors to consider. Work closely with your powder supplier to figure out what kind of powder works best for your application.

Check this chart of the different powder types and the characteristics of each.

***Here is PCO’s Powder Coating Suppliers category.

Powder Coating Gun

To apply powder coating you will need a powder coating gun and system. There are multiple powder coating systems from hobby guns to multi-gun automatic systems.

One can use including cup guns , box feeders, hopper units and large automatic units. Here is where you talk to the powder gun suppliers to figure out what kind of gun works best for you.

***Check PCO’s Powder Coating Spray Gun Suppliers category for a list of gun suppliers to contact.

Powder Booth

You’ll need some kind of area (Powder Booth) in which to spray your powder. The two primary forms of powder coating booths are recovery and non-recovery booths, i.e ones that recover the over-spray powder and ones that do not (“spray to waste”). It is essential to have a booth that has a great ventilation and filter systems to properly filter out the powder. Lighting is also important with 100 kindle from ceiling to floor as the industry standard.

If you are looking for more details, kindly visit YD Powder Coating.

***Link to PCO’s category of Suppliers of Powder Booths

Cure Oven

Powder coating ovens come in all sizes and can be custom-built for operations. The two common choices of ovens used are infrared and convection ovens. It is important to keep in mind when installing an oven that will fit the largest parts. Great air circulation is also critical to ensure the heat is evenly distributed on the substrate.

***Find the oven you need here on PCO:  Cure Oven Suppliers

Hooks & Racks

You’ll also need hooks and some kind of rack(s) on which to hang your item as it passes through your cure oven. Racking systems can be very simple or complicated, but the goal is always to be able to hang your item to spray and cure efficiently.

Many companies that have fabrication capabilities tend to design their own racks. Sturdy racks to hang the powder coated parts from without being unbalanced are key for proper grounding. The importance of proper grounding can not be overemphasized. Read this great article about grounding: Proper Grounding Techniques for Powder Coating

If you need help with your racking, a company who specializes in supplying just hooks and racks is your best choice to call for help.    ***Hooks & Racking Suppliers  

***Most masking product suppliers also sell hooks and racks: Masking Suppliers

Protective Gear/PPE/Safety Considerations

Gloves, face mask, goggles, respirator and body suit are recommended for protection.
Read this article: Powder Coating Safety Considerations

***Safety Equipment & PPE suppliers

There is no question the powder coating process can seem daunting at first. However, with the correct tools and assistance you will be able to start a new hobby or business with the items listed above, keeping in mind, of course, this is a very basic guide. For more detailed how-to-powder-coat information – literature, training classes, podcasts, resources, etc. – visit  PCO’s Powder Coaters Corner.

There are also many Training Classes and Webinars available to you.
Take advantage of these when you can.

Also, Powder Coating Consultants are available to call when/if you need more in-depth, more technical or difficult answers,

***Click  How to Powder Coat/The Powder Coaters Corner for more information, links and resources.

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Contact us to discuss your requirements of powder coating factory. Our experienced sales team can help you identify the options that best suit your needs.