Epoxy

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 others?
Thanks. FBt
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wrote:

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. bob
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On Thu, 20 Mar 2008 21:09:14 GMT, in sci.electronics.design Esther &

try searching for sci.engr.chem or sci.engr.*
martin
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Esther & Fester Bestertester wrote:

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 the rigidity.
A very rigid mineral filled epoxy is Hysol 1C: http://www.gluguru.com/Hysol%20Data%20Sheets/1C.htm
A slighter harder aluminum filled formula is Hysol 9434: http://www.gluguru.com/Hysol%20Data%20Sheets/9434.htm
But they make lots of variations: http://www.gluguru.com/HyEpSelecGuide.htm
--
Regards,

John Popelish
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I cannot suggest a harder epoxy but you pressed a sensitive button on me so here I go.
Many years ago (1991, to be precise) I opted to epoxy-fill my first 5kV coils I did for my then employer in Cologne, Germany. I used no multiplier, straight flyback @ 5kV; about 1000 windings on an RM8 core, winding and insulation layers being an art of their own. I located some very liquid epoxy meant for that purpose, then the whole module went filled, using vacuum to make sure there were no cavities. Everything worked fine, the filling was perfect - I got asked how come the space between the *windinds* was not filled (0.05 wire, mylar foil between each layer) by my then employer... Some years later I had founded TGI in Bulgaria and did the first HV source making the coil more or less the same. However, I used off-the-shelf epoxy; it did not get as hard (although it was by far not as liquid before hardening), and after some warmup it began to conduct just enough to make the thing noisy... I wasted more than one coil (wound with a lot of work) until I 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 melted 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 Sofia 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 lowest noise. The bias is a few kV (3.5 in that case), and the HV input is filtered through a 1Gohm/0.47uF group. Well, he had had the detector in his hands to "check it" for me and had put a stripe of such epoxid along the resistor between its pins... (The resistor is a rectangle, say 20x5mm, 1mm thick). 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 looked and discovered what he had done and cleaned the mess up -and the detector 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 stripe 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 have had braindamaging effect as well.... (and I had refused to believe other 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
------------------------------------------------------ Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com ------------------------------------------------------ http://www.flickr.com/photos/didi_tgi/sets/72157600228621276 /
Esther & Fester Bestertester wrote:

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Sounds to me as if you're actually looking for stiffness, not necessarily strength?
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.
--
Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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If you can afford it, Araldite 2014. 4-6 hrs grab, 24hr set.It's a grey paste two part.-
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I like Araldite 10, fast cure, 10 minutes to set, 1hr cure. The last time I ordered it it came as Huntsman 10. You should be able to find a spec. sheet online. Huntsman Advanced Materials Americas Inc. 4917 Dawn Ave. East Lansing Mi. 48823-5691 517-351-5900 Mike
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On Thu, 20 Mar 2008 21:09:14 GMT, Esther & Fester Bestertester

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.
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Don't let your meat loaf ;-)
Tim
-- Deep Fryer: A very philosophical monk. Website @ http://webpages.charter.net/dawill/tmoranwms
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There are some epoxies that give different characteristics with a different mix ratio, but not many, and NONE of those that do not should be manipulated in such a way.
The "stycast" I mentioned has about four different hardening schedules, and uses about three different hardening medias. All yield differing results for heat resistance, high temp softening after cure, etc.
When it is several grams of base media, and a few drops of "hardener", I call it barely qualified to be called epoxy.
When the mix is closer to 50 50, one will find it is more stringently adhered to as both constituents are critical to the finished medium.
Some mixes have to be accurate to within 0.1 grams or 0.1%.
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On Mon, 24 Mar 2008 19:27:09 -0700, The Last Mimsy

Curious, I have been using epoxies for more than 40 years and have read many articles on epoxies in for instance Adhesives and Sealants magazine, and I have never once seen or heard of any epoxy whose properties do not depend on mix ratio; although in many cases exact mix ratio is not critical.

"Epoxy" is not an adhesive, it is a family of adhesives that includes many different specific chemistries. All high strength epoxies are multi-functional, that is, they are a blend of two or more of the basic epoxy chemistries. In any critical application it is foolish not to discuss your specific requirements with one or more epoxy formulators to obtain a blend closely optimized to your needs, and then to qualify the materials and application process with testing. Master Bond is one supplier of specialty epoxies with good tech support.
On the other hand, for hobby applications, you can get good variation in hardness with mix ratio with any nominally 5:1 ratio marine epoxy. These epoxies are normally available with slow or fast hardeners in order to allow reasonable working time in cool (use fast hardener) to hot (use slow hardener) conditions. More hardener results in more flexibility with lower strength and hardness. I mostly use "The West System" with pump dispensers for easy measurement - one stroke of each is 5:1, for small amounts I count drops. With the addition of fumed silica (available from the same marine suppliers as the epoxy) it can be thickened into a non-running paste very easily, or with the addition of fine wood dust as a filler you can make epoxy foam.
BTW, by far the most common reason for lower than normal strength epoxy is inadequate mixing, especially in the filled, pasty formulations. It is best to consider the point where the epoxy appears to be completely mixed to be the half way point in mixing. If you actually measure the strength or hardness of the cured epoxy the additional mixing will almost always result in better and more consistent properties.
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Two. Epoxy, by definition is a two part mix.
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wrote:

You're talking about different things. Epoxy is a two part mix when you buy it, but that doesn't mean that each part is not made of multiple compounds mixed inmanufacture.
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On Thu, 20 Mar 2008 21:09:14 +0000, Esther & Fester Bestertester wrote:

sci.materials is good.
Al
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If you have been letting it cure at room temperature, try about 15 minutes at 160 F or so. It will get a lot harder.
Tam
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Does it matter when the heat is applied? Right away? Or after it seems to have cured as much as it is going to at room temp?
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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 the manufacturer.
Tam
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hand held hair dryers work fine
let epxy cure to near solid, then heat
else it will reliquify and run with gravity, messy!!
my work once required magnets to be epoxied to core pieces in meter movements, they went thru ovens after primary cure for abt 15 minutes at 200 deg F
that was before engneering started using cryanoacrylite type adhesives, they seemed much better and harder with less work time, never had a release either.
preparation is key to good results
cryo is avail in gel or near gooy form
Loctite corporation has tons of alternatives available

to
turn
also
from
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wrote:

Wrong. There are plenty of epoxies that stay right where they are put.
Not only that, but capillary attraction will hold most in place.
Also, the extremely high temp a hair dryer or heat gun puts out is too much. It needs to be in an oven at a known temperature to cure correctly.
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