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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Will press fit into plastic rub anodizing off?

Q. I'm designing an aluminum tube that I want to anodize for corrosion resistance + food safety. My objective is to press fit it into a larger tube of clear acrylic, so the aluminum is able to show through a transparent outer layer of plastic. Press fit would probably aim for +0.002 in of interference, taking into account that the anodization adds slight width to the aluminum. However, I'm a little worried/unsure about whether the anodization layer will scratch or rub off during the press fit. Has anyone done something similar or could speculate on the best strategy here?

Pierce Broderick
Student - San Francisco, California
November 7, 2016

A. Hi Pierce. I can't picture the anodizing being rubbed off; rather, I think it will scratch .002" deep into the clear acrylic, perhaps spoiling its clarity.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2016

Q. Hi Ted, thanks for your reply! Is there any finish I can put on to the acrylic to mediate this issue, or perhaps a type of clear plastic where this is less of an issue?

Pierce Freeman [returning]
- San Francisco, California
November 7, 2016

A. Hi again. I may be imagining a problem which won't develop at all, and even if it does I have no idea how severe the problem would be. I think you need to press fit an anodized aluminum tube into the acrylic and learn what issues arise ... it's just that I don't feel that the anodizing wearing or chipping off will be one of them :-)

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 2016

A. Maybe you're attacking the problem the wrong way - acrylic has coefficient of expansion 3 times that of aluminum, meaning it expands quite a bit if warmed up, I'm not sure about the sizes of your acrylic and aluminum parts, but if machined to proper press fit dimensions and warming the acrylic up to 100-120 °C (acrylic usually will still be quite rigid at this temperature) may be enough to fit the aluminum part into the acrylic by hand or gentle tapping - so there would be no rubbing and risk of any sort of cosmetic damage to the clear acrylic surface.

Janis Ziemelis
private - Riga, Latvia
November 12, 2016

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