[Amps] Anodize versus alodine/chromate conversion

[Bill Fuqua]

Actually, using lock washers to dig thru surface is a good idea unless you 
have gold plated chassis. Almost all surfaces, particularly aluminum become 
oxidized. Using a "star" external tooth lock washer breaks thru surface 
oxidation and forms a air tight electrical connection with the aluminum 
underneath the oxidation ( even thinly anodized surfaces).  The points of 
the washers press thru the surface and the fresh aluminum cold flows around 
them to make a very good contact that is also air tight.

73
Bill wa4lav


At 10:55 AM 1/15/2003 -0700, John T. M. Lyles wrote:
>Its true that anodize is a non conductive hard coating on aluminum while 
>the alodine/iridite/etc are chromate conversion coatings which are quite 
>conductive. They stabilize the aluminum from the long term effects of 
>oxidation which increases surface resistance and besides, it looks ugly.
>
>Phil C. says that Henry anodizes their PA chassis and uses lockwashers to 
>'dig' through the coating to the bare metal underneath.
>
>In high power RF work, we stay away from anodizing; also many drawers in 
>the lab are full of brass hardware, or good nonmagnetic stainless. 
>Chromate Conversion coatings are, on the other hand, welcomed and actually 
>required for many RF systems under mil specs. No serrated lockwashers are 
>required, and you mount a component to the chassis, it makes reasonable 
>contact for RF current.
>
>Anodizing looks really nice, forever. You can get nice colors like green, 
>red, black, whatever the stylists say the 'in' color is this year to sell 
>gadgets. I recommend that the home constructor stay away from it for 
>things where you have surface RF connections or current in the skin. Use 
>it for front panels if you must.
>
>73
>John
>K5PRO
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