Sep 01 2016

The Dangers of Using Anodized Surfaces for Cosmetics

Anodized Sheet Metal

This week we have been battling with our plater to improve the cosmetic quality of the anodized sheet metal parts that he is supplying us. The problem is that it is a losing battle – for both of us.  I first heard of anodizing aluminum parts as a low cost coating for corrosion protection in the electronic sheet metal chassis.  It costs less than powder-coating and provides much of the same protection.  It doesn’t peel or chip.  It can even come in a variety of colors.  For protecting surfaces, it does a good job; the problem is when people start to use it for cosmetics.  They want cheap paint, but there are a number of challenges:

1. Anodizing does come in a variety of colors, but the number is limited and the color can vary from lot to lot.

The important thing to remember is that your anodized parts are dyed the color you want. Just like your kids’ Easter eggs, the color saturation depends on the amount of die as well as the duration your parts stay in the tank.  Small variations in die or duration lead to color variability.  To compound this, the residue that comes off the anodized part into the die tank can slowly change the color.  Deep colors hide some of this better than light colors, but if you are looking for color consistency, powder-coating is a better option.  This variation issue is compounded if you want lot to lot consistency since die tank composition and timing might vary slightly from shift to shift.


2. Anodizing reflects the base material and its defects.

Because the anodizing process actually etches the base material and creates a film or coating on that surface, the final coating surface reflects the quality and consistency of the base material. In most cases, our platers use a cleaning process so any shop oil or residue is removed, which provides a good anodized cosmetic.  Sometimes the cleaning isn’t 100% and the final part cosmetics are affected.  Other times hardware is installed on the opposite side (or tack welding is performed).  In these cases a shadow will be visible on the cosmetic side.  Bear in mind that the coating is 100% functional, however, it may not meet the cosmetic needs required.

Surface Defect

3. While anodized surfaces do not peel or flake, they do scratch.

Anodizing provides a thin layer of protection, so anodized parts can get scratched easily. We send all of our parts out with extra protection and they are returned protected, but if these parts are around things like screws and screwdrivers, scratching can happen.  We’ve even had issues with the divider paper between parts abrading the parts during transportation (like light sandpaper) and had to reject an entire lot.  The same thing is true for cardboard boxes and anodized parts that fit too snuggly into them.

Scratched part

So what happens when your industrial designer really, really wants that anodized look, but you are really worried about all the product claims due to scratched sheet metal parts? One option is to clear coat the anodized part.  The texture is not the same, but you have much better scratch resistance.  Other times, we’ve had customers switch to powder-coating and they found a color/texture solution that gave them that special look without the headaches of dealing with lots of scratched rejects.  Bottom line – when you are choosing anodized surfaces in a cosmetic sheet metal application, remember that extra handling and extra parts are also part of the costs.

If you want to see more examples or learn more about reducing the risk, please contact us at 978-486-9050.

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