Boston Biker visits a local Custom Powder Coating Shop

We have been hearing about powder coated frames, engines, and other components on motorcycles for a while now.  What is powder coating?  Is it better than paint?  How is it done?  We went to a local powdercoating shop to find out.  The owner took the time out of a busy day to describe the product, explain the process, and answer all of our questions.  

Quick Summary:
Powder coating is a process where finely ground particles of color pigment and resin are electrostatically charged and sprayed onto the item to be coated. The item goes into an oven where the particles melt and form a durable, high-quality finish. We are already familiar with electrostatic charges.  When you walk across a carpeted room and touch the door knob and when a child rubs a balloon over their hair.  Those are electrostatics at work.  In our example, the balloon picks up a static charge and the child's hair stands on end as it is attracted to the charged balloon.  In powder coating, the dry pigment and resin particles are charged and are attracted to the item we want to coat.

Additionally, the powdercoating process is more environmentally friendly than painting.  There are more color choices in powdercoating than in paint, including metallics, metalflake, and holographic colors. 

 

  

Before:
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After:
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Powder coated items may look like they were painted but there are some differences.  Traditional painting involves the use of solvents that are needed to suspend the pigments and transport them to the part being painted.  These solvents then evaporate (the paint drying or curing process) leaving the pigment bonded to the surface of the item. 

In powder coating, the pigments are ground up into very fine particles and then dry sprayed onto the item.  No solvents.  This is important for a few reasons.  The solvents aren't good for the person doing the spraying or for the environment.  Also, the paint sits on top of the metal.  Yes, it is bonded to the metal but it sits on top of it.  In powder coated applications, when the item is heated in the oven the metal's pores open just a bit and the now liquid resin flows into the pores.  

Now to describe the process.  

Parts arrive in every conceivable condition.  Some are painted, some are raw metal, others are rusted and pitted.  The first thing to do is to remove any grease or oils from the parts.  There isn't anything special about this part of the process.  If you'd like to save a few dollars on your powdercoating process you can do this yourself but it isn't suggested.  They should be pressure washed or degreased as much as possible.  If you don't have the resources most powdercoating shops can take care of it for you.

Next the parts get media blasted (I've always called it sand blasting but sand really isn't used much any longer).  It is suggested that you don't do this yourself.  People use the wrong media and frequently miss the really important sections of the piece.  It is important to use the correct media, have experience in the blasting process, and leave the piece with the correct texture.

Parts ready for blasting... This cabinet uses 
P2040012.jpg (24748 bytes)

Glass bead media is used 
for smaller and more delicate parts.

 

P2040013.jpg (34793 bytes)
Almost any size part can fit in 
the cabinet.  Truely HUGE parts 
(like auto/truck frames) will be blasted outside.
P2040014.jpg (35811 bytes)
Aluminum oxide media is used for the 
larger, more aggressive cleaning

It is necessary to create the correct "profile" on the surface for the powder to adhere to.  For aluminum, a surface that feels like 400 sandpaper is optimal while for steel the ideal surface feels like 180 grit paper.  If any paint or grease is left on the item you will not be happy with the powdercoated finish.  Any paint that remains in cracks or pits will burn during the curing process and will ruin the powdercoat finish. All machined surfaces are protected during the blasting process to maintain the surface tolerances.

If you see rust, that means there is most likely moisture in the metal.  Most shops will pre-bake the part to drive out any moisture so that it doesn't ruin the part shortly after you have taken it home.  Most painters won't take the time to pre-bake a part to ensure that it is fully dried before applying the primer.  Later on, this trapped moisture will start to lift the primer and cause the paint to fail prematurely.

Now that the part is down to bare metal, it is time for any repairs by welding, brazing, or soldering as needed.  The part will then ground smooth.  No plastic fillers should ever be used here, only metal on metal.

 

P2040015.jpg (40096 bytes) The part now goes over to the prep area.  It is here that all areas are masked wherever you don't want powdercoating when you are finished.  The temperatures in the powdercoating oven isn't very high so a variety of materials can be used for the masking process.  The shops will have a large variety of plugs and caps for inside and outside threaded surfaces.  High temperature tape can be used for flat surfaces and even tin foil can be used for very large surfaces.  

 

P2040017.jpg (37342 bytes) Experience comes into play with the how the parts are hung in the coating booth.  If the wrong type hanger is used the coating won't be uniform and uncoated portions will be noticeable near the hanger location.  

 

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P2040018.jpg (37449 bytes) The spray equipment looks simple but proper usage takes years to master.  The powder is loaded into the fluidizing bucket and depending on the density of the various powders it needs to sit in the bucket under pressure and "fluidize".

State of the art guns can be controlled up to 12 ways.  The control panel allows adjusting flow rate and electrostatic charge among other things for the particular job at hand.  Deep cavities, recoating, touchups, adjusting for the differing powder specific gravities, and the desired coating thickness are only some of the variables.  

 

P2040028.jpg (34487 bytes)

 

P2040026.jpg (45085 bytes) Once the power has fluidized we are ready to start coating.  When the trigger is pulled the tip of the gun gets energized and charges the powder as it exits the gun.  The charged particles are attracted to the grounded metal part.  Any overspray gets picked up in the filters at the back of the booth.

One "coat" of powder (around 3 mil) is equivalent to around 6-8 coats of paint. This provides a more durable and integrated finish.

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An average motorcycle frame will cost around $175 for the masking, powder, and baking.  Depending on the condition of the frame when it arrives the cost for media blasting can vary from $40 to $100.  If any repairs or molding is needed then the costs go up.  Overall, you are looking at around $300 or so for a motorcycle frame to be powdercoated compared to $600 to $800 for it to be painted. 

P2040025.jpg (42364 bytes) The shop we visited has one of the largest powdercoating ovens in New England (7' wide, 6' tall, and up to 22' long) to handle the largest parts.  Other shops use heat lamps for large parts but you run the risk of inconsistent heating and non-uniform surfaces.  Carefully check out the equipment of a shop when you are looking for a custom powdercoater.

The oven temperature is usually around 400 degrees.  This will vary depending on the particular powder used and the base material being coated.  Again, experience comes into play.  The oven temperatures are constantly monitored to ensure that the curing environment is ideal.

When the coated part is heated the pores in the meal open up, the powder turns to a gel and flows into the pores, and it becomes physically attached to the metal (like a tattoo).  Paint on the other hand sits on the surface, powdercoat penetrates the metal. 

Once the required oven time has been achieved, the parts are rolled out of the oven and allowed to cool.

That's it!   Powder coating in a nutshell. 

 

frame.jpg (38519 bytes)
This race car frame was powdercoated for durability and corrosion resistance
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A base for an expensive vibration table.
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Inside and outside ceramic coating improves looks and performance of headers.  This coating can handle temperatures up to 2250 degrees Fahrenheit for exhaust. Additional colors are black.  These typically won't discolor as normal temperatures for the first few inches doesn't exceed 1100 degrees. The coating inside keeps carbon and rust from forming on the inside.  

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This agricultural spray equipment (pumps, boom, etc.) was coated to protect against the corrosive agents in the sprays.
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It isn't recommended to powdercoating all engine surfaces.  Here you see the jugs and valve covers are coated with the heads left bare.  Powdercoating the fins will reduce their ability to cool the engine
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These 1970's black wrinkle valve covers look better than new and are much more durable!
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A powdercoated primary cover was hanging on the wall.
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Polished parts can be clearcoated so they don't need to be polished again.

   


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