Powder Coating Questions & Answers

[nliberto@powder]

Powder Coating Consulants (PCC) is an internationally recognized technical services company specializing in Powder Coating. We will provide free help to any member of SCCoA, as I am a member myself. Go to our website for more information www.powdercc.com.

Nick

 

[nliberto@powder]

Free help with powder coating advice!

I thought I would "bump" my own thread to see if anyone needs powder coating advice.

Our firm charges $125 per hour for our expert help, and I am offering it for free to any SCCoA member. My Accountant and Wife frown when I give away free advice, but what the heck.

Ask away and play stump the Consultant! PM me or send an email directly to nliberto@powdercc.com. Our website is www.powdercc.com. You can even call on our toll free hotline (800) 97 POWDE(R). Operators (me that is) are standing by!

 

[qc89SC]

kk

whats would be a starter set to make our own powder coating at home on small parts like spindle??? and where to buy equipment?

 

[BLOWN38]

I would like to know the secret on how to keep eastwoods reflective chrome looking like chrome during the clearcoat stage?

I apply the chrome and bake it at 375 for 20 mins and it looks great. Then I apply the super gloss clear and set oven for 375 to bake the part and it turns alittle grey. First pic is before clear 2nd is after clear.

 

[nliberto@powder]

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 1500 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!

 

[XxSlowpokexX]

Makes sence. Clears are always an issue but i can def see that happening when doing it over a chrome looking surface.

 

[BLOWN38]

Makes sense. On the exhaust and the thickness of the coat. 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?

I have thought that its been the thickness of the clear, but when I've tried to change it some spots have come out dry and rough. I did an intake manifold and a part of it came out good where the clear didn't cloud and have tried to replicate it without success yet. I'll keep pluggin away at it.

Thanks for the reply. The worst part of powder coating is prepping the parts.

I am using the craftsman electric gun. It works well for me and what I use it for. I am getting better.

Here's a water outlet that came out great. This was before the clear.

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

 

[Regul8r]

My question is on stock 90 wheels.

Looking to do them like the Annie cars but change the black to White AND make the center caps MATCH! Make the outer ring polished looking like the Annie's have.

How do I do that?
Can you do it? How much?

 

[nliberto@powder]

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."

 

[nliberto@powder]

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.

 

[nliberto@powder]

Powder Coating Q&A

My question is on stock 90 wheels.

Looking to do them like the Annie cars but change the black to White AND make the center caps MATCH! Make the outer ring polished looking like the Annie's have.

How do I do that?
Can you do it? How much?

Who is Annie???

Doing multiple colors (or no color) on the same part with powder coating can be very tricky. Each color has to applied separately and the other areas masked. The part needs to be partially cured between coats. This means that the masking materials must survive the cure oven (around 350 to 400 degrees F). There are numerous masking devices (tapes, plugs, etc) that can do this, but they are expensive and not available at Home Depot or the autopart store.

The easiest way to do what you want is to coat the wheel and caps separately using the colors you want. Cure both parts (cap and wheel). Remove the powder on the outer ring using a mild abrasive and polish it to a bright finish.

I have no idea what this would cost, but it sounds expensive!

 

[Regul8r]

Nick,
any guidance on doing the Stock 90 rims up in white like the Black ones on a 35th?

Can you powder coat the center caps as well?

Would the rims need to be sand blasted to clear off the factory coatings?

 

[BLOWN38]

Nick,
any guidance on doing the Stock 90 rims up in white like the Black ones on a 35th?

Can you powder coat the center caps as well?

Would the rims need to be sand blasted to clear off the factory coatings?

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.

 

[nliberto@powder]

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 1000+ 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.

 

[nliberto@powder]

Just a friendly Bump.

 

[BLOWN38]

Is there a ratio for how much longer to cure when you cure at a lower temp? And whats the lowest cure temp?

When you are doing the multiple coats. What lenght of time should you partial cure? Like say you want to put a translucent color over a bright base like chrome? And then maybe clear the whole thing?

 

[nliberto@powder]

Powder Coating Cure Time & Temperture

Is there a ratio for how much longer to cure when you cure at a lower temp? And whats the lowest cure temp?

When you are doing the multiple coats. What lenght of time should you partial cure? Like say you want to put a translucent color over a bright base like chrome? And then maybe clear the whole thing?

Every powder coating is formulated to a time temperature curve. This curve shows the higher the cure temperatures the lower the cure times. However, each powder formula is unique in its curve. But rest assured that there are some basics that apply to all powder cure temperature/time relationships.

1. All temperatures quoted here and in any powder coating literature are "metal temperature" not oven temperature. That means that the temperature of the metal must be at the described tempearture, regardless of the oven setpoint.

2. Oven Dwell Time = Powder Cure Time + Part Bring-up Time. Therefore, the time you must cure a part in your oven is equal to the time it takes to heat your part to the desired temperature plus the cure time provided by the powder formulator.

3. All powder coatings must be heated to a 250 degree F metal temperature to begin melting on the part. But that does not mean that you can cure most powders at this temperature.

4. Some "low-cure" powder formulations can be cured at 250 degrees F metal termperture. However, the coating must be rated as "low temperature cure".

5. All powder cure curves have the same relationship: higher cure temperatures = shorter cure times and conversely lower cure temperatures = longer cure times.

6. Always follow the guidlines of the powder formulator for proper cure temperatures and cure times. Typical cure times are as follows: 400 degrees F metal tempearture for 10 minutes; 375 degrees F metal temperature for 15 minutes; 350 degrees F metal tempearture for 20 minutes; 325 degrees F metal temperature for 25 minutes; 300 degrees F for 30 minutes; 250 degrees F for 60 minutes.

7. Powder coatings typically have 100% overbake resistance built into the formula (except for clears, tinted clears, some metalics which have 50% overbake resistance, or less). This means that you can keep your part at the desired metal temperature for twice as long as the specified powder cure time without any detriment. This does not mean twice the oven dwell time!!! Therefore, if your powder has a cure time of 20 minutes at 350 degrees F and it takes 20 minutes for your part to reach 350 degrees F, you can leave your part in the oven for 40 minutes (minimum) and 60 minutes (maximum).

Now you know the whole story about cure!

 

[nliberto@powder]

Update to cure time/temps for powder coatings.

By the way, did you know you can cure some powder coatings in 30 seconds. It just requires the part to be at 600 degrees F metal temperature.

Normally, this is accomplished using high intensity infrared light to heat the surface of the part to 600 degrees F very quickly. This is how powder coatings are cured on a coil coating line at speeds up to 150 feet per minute. Of course, liquid coil coating lines run much faster, up to 300 feet per minute.

 

[nliberto@powder]

Just a friendly Bump, for those who have yet to play "stump the consultant"!

 

[XxSlowpokexX]

ok..Powdercoating magnesium :O)