FINISHING ANSWERS: Ask Joe Powder
September 1, 2007
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"How can I match an auto manufacturer’s paint code to a RAL number for powder coating?"
Dear Joe,
How can I match an auto manufacturer’s paint code to a RAL number for powder coating?
--Rich’s Powder Coating
Hello RPC,
Simply put - you can’t. These are two independent color systems. The only possibility is to obtain a physical representation of the automaker’s color and compare to an RAL color collection. You may find something close, but you won’t find an exact match. Of course, acceptability will be predicated on how close you need to be.
*************
Dear Joe,
I am currently restoring a WWII tank. The inside of the tank and just about all of the components are pure white. Obviously the original coating was painted on, and as much as I would strive for originality, paint just does not hold up for very long. The trouble with paint inside a tank is that it gets beat up pretty fast, even when it is restored as a historic object. The other main problem is condensation. All that steel takes a while to warm up with the ambient temperature outside, and all that recurrent dampness leads to peeling paint and rust. My thought was to powder coat the inside. Sandblasting and applying the powder seems pretty benign, but how could it be cured? It would be impossible to make an oven around the tank. Do any other practical methods exist that would allow me to achieve the appropriate cure? Would radiant heat lamps give an uneven temperature if they were moved around inside? Any thoughts would be greatly appreciated.
--Dave
Hi Dave,
Powder does offer one of the most durable coatings for metal substrates. One of the characteristics of powder technology is the need to bake the coating at a minimum temperature for a certain period of time. Time and temperature are relative; low temps require long dwell times, whereas high temps cure powder in shorter periods of time. State-of-the-art technology bottoms out around 240°F. At this temperature, you can get some specially formulated polyesters and epoxies to cure within about 30 minutes. However, this is the metal temperature, not just the oven or ambient temperature.
An emerging powder technology uses ultraviolet (UV) cure chemistry to chemically react or harden the coating. With this technique, the powder is melted at temperatures ranging from 200 to 240°F. The molten powder is then exposed to a high dose of UV energy, which enables the binder components to chemically react. This technique requires high intensity UV lamps that are relatively cumbersome to handle. They are usually fixed at a prescribed distance from the part surface, and the coated part traverses the path of the focused UV energy. Seems a little too expensive and complicated for your project.
With radiant heat lamps, you would need to get the surface up to a minimum of 240°F and hold it for about 30 minutes. Heavy-gauge substrates only add to this challenge. It appears that this approach may be insurmountably impractical.
Here’s what I propose: Powder coat any parts that can be removed and will fit into an oven. You may have powder coating capability, so you’ll recognize what will fit in your oven. If you use a jobcoater, check with the coater for oven dimensions. The parts that can’t be removed and baked should be coated with a high-quality, dare I say, air-dry liquid primer (I suggest an epoxy specifically formulated for steel) then topcoated with a high quality two-component liquid urethane. Believe it or not, this system performs as well as or better than a single coat of a typical powder.
One more thing - be absolutely certain to rigorously clean and prepare the substrates prior to the application of any coating system. Applying a high-quality finish is never enough to achieve excellent performance. The quality of the preparation of the substrate is just as instrumental in performance as is the coating technology. This means removing all existing coatings, dirt and oil. Abrasive blasting followed by a thorough solvent cleaning is a good starting point.
I hope this helps. I love to recommend using powders, but this is one application where liquid technology may be your best option.
Ask Joe Powder is a regular feature of Finishing Today magazine. Please send your questions to askjoepowder@yahoo.com.
Dear Joe,
How can I match an auto manufacturer’s paint code to a RAL number for powder coating?
--Rich’s Powder Coating
Hello RPC,
Simply put - you can’t. These are two independent color systems. The only possibility is to obtain a physical representation of the automaker’s color and compare to an RAL color collection. You may find something close, but you won’t find an exact match. Of course, acceptability will be predicated on how close you need to be.
*************
Dear Joe,
I am currently restoring a WWII tank. The inside of the tank and just about all of the components are pure white. Obviously the original coating was painted on, and as much as I would strive for originality, paint just does not hold up for very long. The trouble with paint inside a tank is that it gets beat up pretty fast, even when it is restored as a historic object. The other main problem is condensation. All that steel takes a while to warm up with the ambient temperature outside, and all that recurrent dampness leads to peeling paint and rust. My thought was to powder coat the inside. Sandblasting and applying the powder seems pretty benign, but how could it be cured? It would be impossible to make an oven around the tank. Do any other practical methods exist that would allow me to achieve the appropriate cure? Would radiant heat lamps give an uneven temperature if they were moved around inside? Any thoughts would be greatly appreciated.
--Dave
Hi Dave,
Powder does offer one of the most durable coatings for metal substrates. One of the characteristics of powder technology is the need to bake the coating at a minimum temperature for a certain period of time. Time and temperature are relative; low temps require long dwell times, whereas high temps cure powder in shorter periods of time. State-of-the-art technology bottoms out around 240°F. At this temperature, you can get some specially formulated polyesters and epoxies to cure within about 30 minutes. However, this is the metal temperature, not just the oven or ambient temperature.
An emerging powder technology uses ultraviolet (UV) cure chemistry to chemically react or harden the coating. With this technique, the powder is melted at temperatures ranging from 200 to 240°F. The molten powder is then exposed to a high dose of UV energy, which enables the binder components to chemically react. This technique requires high intensity UV lamps that are relatively cumbersome to handle. They are usually fixed at a prescribed distance from the part surface, and the coated part traverses the path of the focused UV energy. Seems a little too expensive and complicated for your project.
With radiant heat lamps, you would need to get the surface up to a minimum of 240°F and hold it for about 30 minutes. Heavy-gauge substrates only add to this challenge. It appears that this approach may be insurmountably impractical.
Here’s what I propose: Powder coat any parts that can be removed and will fit into an oven. You may have powder coating capability, so you’ll recognize what will fit in your oven. If you use a jobcoater, check with the coater for oven dimensions. The parts that can’t be removed and baked should be coated with a high-quality, dare I say, air-dry liquid primer (I suggest an epoxy specifically formulated for steel) then topcoated with a high quality two-component liquid urethane. Believe it or not, this system performs as well as or better than a single coat of a typical powder.
One more thing - be absolutely certain to rigorously clean and prepare the substrates prior to the application of any coating system. Applying a high-quality finish is never enough to achieve excellent performance. The quality of the preparation of the substrate is just as instrumental in performance as is the coating technology. This means removing all existing coatings, dirt and oil. Abrasive blasting followed by a thorough solvent cleaning is a good starting point.
I hope this helps. I love to recommend using powders, but this is one application where liquid technology may be your best option.
Ask Joe Powder is a regular feature of Finishing Today magazine. Please send your questions to askjoepowder@yahoo.com.
