Re: Enclosure advice please - glueing metal

From: Dave Marsh (me_at_privacy.net)
Date: 06/09/04 

Date: Wed, 9 Jun 2004 14:02:26 +0100

"John Popelish" <jpopelish@rica.net> wrote in message
news:40C7062C.15ECEF54@rica.net...
> Dave Marsh wrote:
> >
> > Hi,
> >
> > I have a small front panel made of anodized aluminum (0.06 inches
thick). I
> > need to space off the PCB (buttons, LEDs etc.) behind it by approx 0.25
> > inches.
> >
> > The PCB has 4 drilled holes for M3 machine screws. My problem is that I
> > can't put holes through the front panel. My idea at the moment is to
glue 4
> > hex spacers to the back of the front panel and then bolt the PCB to it.
> >
> > So far, I've tried nickel-plated brass spacers attached with epoxy
("plastic
> > steel" by Draper) on to the sanded aluminum. This came apart after some
> > pretty gentle leverage testing.
> >
> > Just wondering (a) if I'd be better using nylon spacers - would these
glue
> > better to the aluminum? And (b) what type of glue should I use for metal
> > spacers (or nylon spacers) on to anodized aluminum?
> >
> > Many thanks,
> >
> > Dave
>
> Nylon is almost impossible to attach to anything with glue of any kind
> I have ever tried. Epoxy has exceptional adhesion to anodized
> aluminum, better than to plated or unplated brass, I think. It also
> has good stick to thermally oxidized aluminum. You can make good
> clean thermal oxide by baking aluminum parts in a 450 degree oven for
> an hour or so. But any clean aluminum has a thin film of oxide on it.
>
> Most epoxies don't develop their full strength for a long time, or
> until after they are thermally post cured. Can your control panel
> tolerate a bake at 120 to 150 degrees F?
>
> Another rule of thumb is that the slower the cure , the higher the
> strength, so quick cure epoxies are useless for high strength
> applications.
>
> Filled epoxy is no stronger in adhesion that plain epoxy. That said,
> some of the highest strength epoxies I have used (especially if
> properly post cured) are Hysol filled epoxies like 9430 (white) or
> 9460 gray). These both contain silica, so they cannot be machined by
> steel tools, but this doesn't sound like it would be a problem in your
> application.
>
> --
> John Popelish

Many thanks John for passing on your experiences. Yes, the front panel could
tolerate a bake of 150degF AFAIK. The two epoxises you mention sound very
good and I'll try to give them a go.

Dave

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