See no n.g. for adhesives & epoxies, so if there's a better forum for this,
just point me to it.
I need an epoxy that is strong to the point of brittle. I want no flex; it
has to transmit vibration as close to 100% as possible.
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 changing the mix of the 2 parts? If
so, what do I lose if I use more hardener?
Any personal experiences with epoxies that you found to be harder than
For spacecraft vibration testing we use Dental cement. It's extremely
non-compliant so it is good for transmitting vibration from a
structure to an accelerometer. It is brittle so we remove them by
just taping them with a hammer and breaking them off the surface. We
first put a layer of thin tape on the surface to protect the surface.
the tape does not affect the vibration response.
Sounds to me as if you're actually looking for stiffness, not
I think you'd want to look for (or make) a filled epoxy. A
high-strength epoxy which is loaded up with (e.g.) chopped or milled
fiberglass would be very stiff.
Filled epoxies (loaded with various mineral and glass bits)
are much more rigid than plain epoxy. But if you start with
a slow cure epoxy (30 minute versus 5 minute) the epoxy,
itself will also be a lot harder. Glass micro spheres are a
good filler if you want to lower the density, and glass
micro beads or aluminum oxide if you want to raise it. Even
adding talcum powder adds to the rigidity, but the gas
bubbles it entrains lowers it (foams are less rigid than
solids of the same material), so vacuum degassing increases
A very rigid mineral filled epoxy is Hysol 1C:
A slighter harder aluminum filled formula is Hysol 9434:
I cannot suggest a harder epoxy but you pressed a sensitive button on
so here I go.
Many years ago (1991, to be precise) I opted to epoxy-fill my first
coils I did for my then employer in Cologne, Germany. I used no
straight flyback @ 5kV; about 1000 windings on an RM8 core, winding
and insulation layers being an art of their own. I located some very
epoxy meant for that purpose, then the whole module went filled, using
vacuum to make sure there were no cavities. Everything worked fine,
was perfect - I got asked how come the space between the *windinds*
not filled (0.05 wire, mylar foil between each layer) by my then
Some years later I had founded TGI in Bulgaria and did the first HV
making the coil more or less the same. However, I used off-the-shelf
it did not get as hard (although it was by far not as liquid before
and after some warmup it began to conduct just enough to make the
noisy... I wasted more than one coil (wound with a lot of work) until
got what was going on, I spent days if not weeks on that nightmare...
Eventually I learned I needed no filling at all, just a few drops of
silicon at the right spots did the job (still does) quite well.
And on another occasion I had a guy from a detector repairshop in
use the same effect trying to cheat on me... The HPGe gamma detectors
are very sensitive things, the front FET is cooled to -90C or so for
noise. The bias is a few kV (3.5 in that case), and the HV input is
through a 1Gohm/0.47uF group. Well, he had had the detector in his
to "check it" for me and had put a stripe of such epoxid along the
between its pins... (The resistor is a rectangle, say 20x5mm, 1mm
After some warmup - the preamp consumes not so little, they have not
changed its design for >20 years - the detector begins to behave like
when it needs repair. Well he did not get it for repair because I
and discovered what he had done and cleaned the mess up -and the
worked fine. A few years later he got the same detector in his hands
directly from customers and did the same, this time he had added a
across the capacitor, though, and had scratched the paint of the
resistor between the pins. Mind you, I had told him I knew what he had
done the first time and he had done it again. I guess the epoxy must
had braindamaging effect as well.... (and I had refused to believe
people telling me he was sabotaging detectors before I got burned, the
epoxy must have worked on my brain as well - perhaps while dealing
with my coils... :-).
Dimiter Popoff Transgalactic Instruments
With the way you worded this, it would seem that a technical response
would go right over your head.
Epoxy mix ratios are NEVER meant to be altered. You need to find an
epoxy that matches your needs. The only time I ever saw mix ratio ranges
to alter behavior, it was with an epoxy branded as "stycast". Which,
would oddly meat your needs.
It will not likely be cheap, however.
Dunno if it's tough enough but I use GR epoxy glue from Industrial
24 hour cure. (Sometimes a pita.)
Here in BC.
"We have an epoxy system for almost any project".
All I know is that GR epoxy has less flex than Lepage 2 page epoxy
(dual syringe) I got from the hardware store.
D from BC
sci.polymers or sci.materials might be a better bet. There are two
general ways you can make a given epoxy harder: bake it (an hour at 100C
does wonders) or put filler in it.
If you're bonding hard materials, you might want to use a glass bead
filler. When you squeeze the bondline down, the spheres contact the
surface, and as the epoxy shrinks (1% or so), it applies a preload to
the glass/substrate interfaces. That's a pretty stiff joint.
If you're trying to do something in shear, e.g. attach a strain gauge,
glue is not your friend at all. You might be better off using solder or
indium bonding or something like that.
I have been waiting a few minutes until the epoxy is no longer runny. I turn
the oven on to 200, but turn it off before it reaches temperature. Have also
used a heat gun on something that was part of a large stationary object
(toilet). I haven't bothered, but this information should be available from