Joe, being the Powder king, can probably best answer this but I'll put it out there for all to consider.

What are the limitations (if any) of surfaces that can be powder coated?

Stainless steel for example....does powder take to it well? Is there a special prep needed for stainless, or same prep as for say Au or sheet metal?

What about fiberglass or poly carbonate surfaces?

 

You can't powder coat polycarb or GRP...oven temps would distort the parts

 

Well that just goes to show how deep my knowledge is on the subject, hence the question. I am more knowledgable already

Reason I ask is I want to explore powder coating different parts for the bike and don't wanna waste time and $$ getting something powdered that wont take the coating well and end up having to be redone/replaced.

TIA!

 

I'm sure Joe will chime in, but here's a few thoughts on the topic.

There are some plastic powders, but they are very specialized. Saturn body panels were powdercoated for example.

There are also different pre-treatment processes and coatings in use, some better suited to certain materials than others. Iron Phosphate coating after washing was very prevalent, but Zinc Phosphate is becoming more common; and there are microceramic coatings coming into play as well. Think of it this way, the powdercoat doesn't "stick" to the part, it "sticks" to the coating.

Different pretreatment processes also have a wide range of effectivity on problem areas that parts present. Manufacturing technologies are varied, and some examples of areas of concern are "oxide scale" around holes created at laser cutting, weld **** (contamination) from weldment assembly. There are many more, but you get the idea. These areas must be taken into consideration and addressed to assure optimal powdercoating performance.

A big factor is getting the parts to run thru the process and achieve the correct "Cure" within the manufacturers "Cure Curve". Undercure results in things like poor adhesion, and poor solvent resistance. Overcure has detrimental effects on many of the properties of the finished coating, and can cause yellowing/color shifting as well as brittleness.

This can cause issues with running parts made of different materials without doing test runs using an instrument called a "datapaq" which measures the "time at temperature" that parts actually reach during a cycle.

This comes into play when determining the line speed, and oven settings for powdercoating a specific part.

A powdercoat line that is optimized for sheet metal for example, will not be optimal for running extruded Aluminum. Aluminum does not "take on" heat as rapidly as steel, and will not achieve the same "time at temperature" as the steel would, and may not achieve full cure. Stainless will have similar issues.

Another thing that needs to be considered is the design of the part. Sheet metal parts/weldments with 90 degree bends create "Faraday Cage" effects. The powdercoat is deposited electrostaticly, and areas where 2 planes meet reduce the electrostatic charge. This means that powder will not build up to the desired thickness easily in these areas, and as such, corrosion resistance is lost without appropriate counter measures, such as e-coating prior to powdercoating. Tubing is also problematic as powder will not do a very good job getting inside.

Weldments with components of differing mass are also problematic. Imagine a .100" thick sheet of steel 12"x12", with a 4"x4"x4" block of steel welded to it. The sheet metal will absorb heat at a much faster rate that the block will, so the end result is that either the sheet metal will be properly cured while the block is undercured, or the block is properly cured and the sheet is overcured. Many times there is an attempt at compromise between the two, and depending on the overcure latitude of the powder, there may be success; but it is a factor to be considered.

 

My guy not only did a chem treatment but also blasted the parts before coating - some cut out a step to save time and $.

 

I have powder coated glass before!

If it can take 300-350 degrees without distorting it can be powder coated. Pre heat to about 250 then apply the powder. Set the powder on plastic, wood etc at around 300-350. IF there is any flex in the plastic after the powder is applied, it will not stay on long.

BUT, I would stick to paint on plastic.....

 

90% of what James covered is only relevant in a production coating environment. His info assumes no blasting, which removes the majority of the pre treatment information mentioned. Scale around holes, etc. Line setups and heat curves and so forth, none of that is relevant to a custom coating question. It's simple enough to just watch your PMT with an IR gun like we do when doing customs.

If you had to choose between blasting or chemical pre treatment for prep, blasting is the far superior choice. Combining the two with steel parts is even better since James is correct in that using a phosphate on bare steel will enhance adhesion. However blasting steel then coating with a zinc rich epoxy based primer prior to color like we do is probably the most ideal situation for strength and corrosion resistance.

Here's the rule. Any substrate that can handle the curing temps without harm, can be coated technically. However that doesn't mean it's going to come out good. Fiberglass for example will take the temps, but the resins will never stop outgassing and bubbling the powder no matter how many outgas cycles you try. Other materials such as carbon fiber may not be wise since there's no solid data out there that dictates how heat effects the strength of that substrate. You just need to be smart and use logic, research, and then experiment with the material in question.

To answer the question, from a custom coating standpoint, no concern to us what type of metal we are coating. We have proven methods and materials to properly handle all types properly.

* we aslo chemical strip then blast parts, if nessassary also have a degrease tank as well