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Thermal Expansion Characteristics of a Chrome Plated Component

Gentlemen,
As a working engineer I have a question concerning the characteristics of thermal expansion when dealing with a chrome-plated component. The mass of the part is steel (6.3E-10/°F) with a 002" Cr (3.3E-06/°F) plate. This component interfaces with an aluminum (1.35E-05/°F)part with a slight interference fit at an elevated temp. The parts do not seem to behave as expected. So, I am wondering if perhaps the steel substrate is being constricted by the chrome plating. The results seem to indicate that the latter is true. However, I find this counterintuitive since the mass of the part (Ø20") is steel. Does anyone have any insight on this?

MD Siferd
product design engineer - Findlay, Ohio, USA
April 1, 2009

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Hi, MD. I'm not sure that your dimensions withstood the automatic translations that email and mail servers and web servers and browsers impose, but this part is 20" in diameter? There is no way that a .002" thick plating of chrome is constraining this object from thermally expanding.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 2, 2009

You have to focus on total stresses at the final operating temperature. Nominal thermal parameters have no meaning until multiplied times the other variables. As Ted said, the cross section of a 0.002" thick chrome times its modulus of elasticity is far from that of the heavy steel times its own. You didn't say much about the aluminum part but I'd bet your problem is there. G. Marrufo-Mexico

Guillermo Marrufo
Monterrey, NL, Mexico
April 4, 2009