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
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
|