One must take care to separate fact from opinions. "Mixing metals" as you mention is NOT necessarily a sure way to promote corrosion. Yes, steel against aluminum us not good practice since they are far enough apart on the electromotive series that they will act as a local battery (in the presence of an electrolyte such as salt water), and the aluminum will corrode. Another bad pair is aluminum against copper alloys.
But in a dry environment, no problem can occur since no moisture is present. Galvanic corrosion without the presence of an electrolyte is impossible. Other metal combinations are also problematic such as aluminum against zinc plated or galvanized steel (or zinc plated anything). Cadmium plated steel against aluminum is generally considered an acceptable combination, as is 300-series stainless steel against most metals. 300-series stainless (especially type 316) is considered relatively "passive". One must simply choose the metal pairs carefully, taking into account the environment, and if necessary making sure they are sufficiently "close" in voltage potential to each other on the electromotive scale. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: Wan Juang Foo [mailto:f...@np.edu.sg] Sent: February 28, 2002 11:12 PM To: emc-p...@majordomo.ieee.org Subject: RE: Pencil erasers for pre-EMI cleaning? (cleaning mating surfaces, chassis, ) David, You mention that you have a Steel and Aluminium to content with. My opinion about mixing metal parts in an assembly (chassis) is a sure way of promoting corrosion, especially if the installation is in a humid environment. If you want the chassis to be a reliable electrostatic shield do not have panels that are made with different metal bolted to the 'frame' or chassis. Under some codes this is a 'No Go' area. BTW, I assume that you must be working with a small box, otherwise you would need much more than a 'rubber eraser' to clean the mating surfaces. All equipment metalwork should be electrically bonded in a manner which does not rely on 'hopeful' electrical conduction through anti-corrosive treatment like anodised aluminium and paint. Careful attention to the assembly process will weed out things like ball-bearings races, nylon runners and coasters, or other insulating materials. Conduction through painted panels should not be dependent on the gripping action of star washers. The design should be such that no currents flows in any part of the metal work. The objective is to ensure that any part of the metalwork can be relied upon as an effective electrostatic screen and not the reverse, a radiator. Tim Foo ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
