plating, anodizing, & finishing Q&As since 1989
Chrome-look powder coating becomes greyish after applying clear powder
September 17, 2010
Hi I am trying to start a powder coating business but I'm battling with the chrome powder when I apply clear powder and clear it it becomes greyishJp kruger
partner - Newcastle, RSA
September 27, 2010
I think that the description Chrome Powder is very misleading in that the resultant finish even at twenty paces does not resemble a hard chrome finish. Probably calling it "Super Aluminium" would be more realistic. Chrome powder consists of a highly polished leafing aluminium (it floats on water) dispersed in a pigmented grey powder (normally a polyester). However, a chrome powder can be mf from other shades of polyester--it has been observed that slow moving or off spec colours have been used as the aluminium flake covers this up (have you ever noticed a red, blue etc hue to a batch of chrome you recently sprayed out)?
So why does the chrome finish turn a greyish colour when over-coated with a transparent powder. Unlike a liquid bright aluminium finish, not all the flakes during deposition and cure end up in a flat plane. Over-coating this cured film alters the angle light leaving the coated item and it appear to turn slightly grey. Some applicators express another reason that poor cure of the aluminium coat is also a factor.
What are the alternatives: Applying a 5 micron film of waterbourne aluminium over an epoxy primer, followed by a top coat of transparent powder. The aluminium used in this case is very expensive (ɣ400/kilo) as it is the result of vacuum deposition of aluminium. The deposited super bright aluminium can only be collected from the vacuum chamber in very small quantities. Because the aluminium film is being deposited from a liquid phase nearly 100% of the flake ends up in a flat plane.
The nearest to chrome plated finish that can be achieved is the utilisation of vacuum deposition technology--the alloy wheel is loaded into a vacuum deposition chamber and coated in a micro film of vaporised aluminium after which an acrylic powder is applied and baked to complete the process.
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Birmingham, United Kingdom