Rick:
I would assume that the main concern is damage to the protective paint layer
which gets ripped open and may give access to moisture with potential for
corrosion. That is, if you paint the bare steel without any protective coating.
If you used zinc plating (or similar) in the first place, no question should
arise, although damage to the plating due to the bite of the washers and
possible damage to the plating due to slippage of the washer may keep the debate
going.. You are right in assuming that the toothed washer provides gas-tight
contact (specify a minimum torque requirement before this can gets opened!) but
in my opinion, damage to the paint would negate this over time.
The way I see it, the question boils down to money (as usual): are you willing
to engage in a protracted argument "my expert vs. your expert", or would it be
cheaper to not paint the areas of concern and provide some selective plating?
Another cheap way would be to put some spray paint on the screws after
everything has been tightened down, which may lead again to arguments as above.
Please let me know how this ends.
Bogdan M. Matoga
bogdan.mat...@fibre.com
______________________________ Reply Separator _________________________________
Subject: Bonding of structures
Author: Rick Busche <rbus...@es.com> at Internet
List-Post: emc-pstc@listserv.ieee.org
Date: 6/2/97 16:43
I have a projector assembly which is essentially a large metal
structure (frame) with a metal projector platform which swivels for
purposes of maintenance. The structure is painted steel, with pressed
in bronze bushings at all motion points each of which have been
measured at significantly less than 0.10 ohms. Arguably, there is no
guarantee that these structures will remain bonded at these levels
over time and bonding wires (braid, with crimped ring lugs) have been
added across the pivot points. These wires are secured to the
structure using a toothed washer and screw. The intent of the toothed
washer is to bight through the paint to ensure conductivity.
My customer's safety officer (in Europe) is now insisting that the
paint must be ground off to bare metal and coated with Zinc paint
prior to affixing the lug to the structure. I am concerned that this
is an excessive requirement. It has been my understanding that the
toothed washer (and the screw for that matter) creates a gas tight
connection which is acceptable for all bonding requirements.
I would be interested in hearing from the group regarding this bonding
issue. I can find no standard or specification which disallows this
biting washer or requires Zinc paint.
Any comments would be appreciated.
Rick Busche
rbus...@es.com
