Epoxy stiffness?

[Esther & Fester Bestertester]

I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.

What property am I looking for in data sheets? Am I looking for a high Shore
Hardness value? That's what Devcon uses in its data sheets to specify
hardness.

Is this something that I can achieve by adding a hardener? If so, do I lose
something if I add this?

Any personal experiences with epoxies that you found to be stiffer than
others?

Thanks.
FBt

[Esther & Fester Bestertester]

x-posting to sci.polymers...

I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.

What property am I looking for in data sheets? Am I looking for a high Shore
Hardness value? That's what Devcon uses in its data sheets to specify
hardness.

Is this something that I can achieve by adding a hardener? If so, do I lose
something if I add this?

Any personal experiences with epoxies that you found to be stiffer than
others?

Thanks.
FBt

[Mark Thorson]

Post by Esther & Fester Bestertester
I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.
What property am I looking for in data sheets? Am I looking for a
high Shore Hardness value? That's what Devcon uses in its data sheets
to specify hardness.

Actually, what you want is flexural modulus, but
most data sheets won't have that. Shore hardness
is not a bad substitute.

Post by Esther & Fester Bestertester
Is this something that I can achieve by adding a hardener?
If so, do I lose something if I add this?

No, you want a high loading with a mineral filler.

Since you don't mention cost as a constraint,
I'd recommend an epoxy formulated for use as
a microelectronics encapsulant. Some of those
have silica filler loadings above 90%. That's
difficult to achieve, so you're better off buying
it than trying to make it yourself. I believe
Sumitomo Bakelite offers these materials.

[j***@aspenresearch.com]

Post by Esther & Fester Bestertester
x-posting to sci.polymers...
I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.
What property am I looking for in data sheets? Am I looking for a high Shore
Hardness value? That's what Devcon uses in its data sheets to specify
hardness.
Is this something that I can achieve by adding a hardener? If so, do I lose
something if I add this?
Any personal experiences with epoxies that you found to be stiffer than
others?
Thanks.
FBt

What frequencies are you exposing the material to? The higher the
frequency, the stiffer the epxoy will be, as you will be exceeding the
relaxation times of larger portions of the polymer.

John
Aspen Research, - www.aspenresearch.com
"Turning Questions into Answers"

Opinions expressed herein are my own and may not represent those of my
employer.

[Brian Whatcott]

On Fri, 21 Mar 2008 08:21:19 GMT, Esther & Fester Bestertester

Post by Esther & Fester Bestertester
I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.
What property am I looking for in data sheets? Am I looking for a high Shore
Hardness value? That's what Devcon uses in its data sheets to specify
hardness.
Is this something that I can achieve by adding a hardener? If so, do I lose
something if I add this?
Any personal experiences with epoxies that you found to be stiffer than
others?
Thanks.
FBt

Off the top, and untested, but I imagine that regular epoxy
well-loaded with either metal powder, or fine sand might well be stiff
and hence brittle.

Brian W

[dvt]

Post by Esther & Fester Bestertester
I need an epoxy that is stiff to the point of brittle. I want no flex; it has
to transmit vibration as close to 100% as possible. It's not carrying any
weight, so strength isn't important. I'm just tired of finding only epoxies
that seem to keep their resin-y qualities after curing.
What property am I looking for in data sheets? Am I looking for a high Shore
Hardness value? That's what Devcon uses in its data sheets to specify
hardness.
Is this something that I can achieve by adding a hardener? If so, do I lose
something if I add this?
Any personal experiences with epoxies that you found to be stiffer than
others?

In my experience, stiffness (and vibration transmission) are optimized
by making the epoxy layer thinner. Thickness is often more important
than the epoxy's modulus. Epoxies using a filler often make a thicker
layer than those without, so I try to avoid fillers for jobs like
mounting accelerometers.

I've used Shell's EPON 828 resin mixed with 3140 hardener at ratios
100:33 to make a thin, stiff joint. Based on Shell's extreme
unwillingness to provide tech support, I wouldn't recommend their
product unless you already have experience with it. Since that
experience with their tech support, I've tried Loctite Hysol M-121HP,
and early indications are that it has pretty similar properties. But I
have far less experience with that epoxy and no recent experience with
their tech support.

How about a non-epoxy? Cyanoacrylates (superglues) can make a pretty
thin joint.

Of course, your application may constrain the thickness of the epoxy
layer. If that's the case, then ignore everything I've said.

[Esther & Fester Bestertester]

Post by dvt
How about a non-epoxy? Cyanoacrylates (superglues) can make a pretty
thin joint.

I think of CA as a not-serious adhesive (the TV ad of the guy hanging from
his hard hat comes to mind). China mending, etc.

I suspect that I'm not giving it its due. How does it stack up to epoxy for
adhesion and strength?

I stopped by the local hobby store which has a quite sizable range of
different CAs, mostly differing by their set speed. There is also a spray-on
accelerator.

[dvt]

Post by Esther & Fester Bestertester

Post by dvt
How about a non-epoxy? Cyanoacrylates (superglues) can make a pretty
thin joint.

I think of CA as a not-serious adhesive (the TV ad of the guy hanging from
his hard hat comes to mind). China mending, etc.
I suspect that I'm not giving it its due. How does it stack up to epoxy for
adhesion and strength?
I stopped by the local hobby store which has a quite sizable range of
different CAs, mostly differing by their set speed. There is also a spray-on
accelerator.

I have only done a very small amount of testing (shear lap strength)
that compared a few epoxies to one CA. So my experience is based on a
very small sample size. In those experiments, the CA had similar shear
lap strength to epoxies.

You want maximal vibration transmission, and that suggests that you may
be mounting accelerometers or a similar application. I think it's quite
telling that a set of accelerometers that I bought a few years back each
included a tube of Loctite CA (I can't remember which one... 411,
maybe?). And CA is often recommended by accelerometer manufacturers.

So if you can live with the limitations of CA (short work life,
inability to fill large gaps, susceptibility to solvents, etc), you
might like to try it. If you can't live with those limitations, I'd
recommend an epoxy without fillers to produce the thinnest joint possible.