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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 7th Oct 2015, 9:20 am   #1
Goldieoldie
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Default Epoxy resin

Hi,
What's the best epoxy resin or other material ?
I used to use araldite but now find it soft when cured
I want to form a small amount glued to brass and then file it to shape
Any ideas please ?
Cheers Pete
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Old 7th Oct 2015, 9:32 am   #2
vidjoman
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Default Re: Epoxy resin

The quick setting type always seems to stay slightly soft. The original is much harder, but takes a day to harden. Don't use it in cold temperatures as it takes even longer.
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Old 7th Oct 2015, 9:50 am   #3
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Default Re: Epoxy resin

JB weld is without question the best you can buy.
Mick
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Old 7th Oct 2015, 10:08 am   #4
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Default Re: Epoxy resin

There are several glues sold as Araldite. You want the one which takes days to cure. It used to be sold as 'Araldite Precision' but it may be called something else now.
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Old 7th Oct 2015, 10:11 am   #5
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Default Re: Epoxy resin

If you need to build up any amount of depth or bulk then get a small tub of fibre-glass repair resin from the car accessory shop.

It dries harder than any epoxy I've ever used and can be filed to shape in any thickness.
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Old 7th Oct 2015, 11:39 am   #6
David G4EBT
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Default Re: Epoxy resin

I've tried all sorts and without a doubt, Plastic Padding 'Super Steel Epoxy Weld' is way out in front of anything else. (It's widely avaiable from the likes of Halfords and on e-bay for about £6.00). It's a nonsense to use the term 'weld' of course, because the process of welding involved melting the parent metal of two items being welded, and adding more molten metal into the motlen pool via a welding rod - most often via either electric arc, MIG or oxy acetylene.

But setting that bit of marketing hype to one side, the product itself is a two-part epoxy which sets really hard in a couple of minutes or so. Though it's claimed that it contains particles of steel, it doesn't conduct electricity. I've tested a short length of it applied to a strip of glass, using an insulation tester at 1000V - infinite resistance. Hence, I've used it in such applications as sealing the ends of electrolytic caps that I've re-stuffed. Ive also used it for repairing Bakelite cabinets prior to spraying them, and for filling unwanted holes in die-cast aluminium boxes to re-use them. The appearance when set is gloss black, but when filed or sanded, is darkish grey.

It files and sands excellently.

I don't often find much use for Araldite - too soft and no better than the stuff sold in Pound shops.

Hope that's of interest.
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Old 7th Oct 2015, 12:04 pm   #7
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Default Re: Epoxy resin

That's interesting, I thought it was the way I mixed it. I also have experienced Araldite to set with a small amount of pliancy compared to how I remembered it. My earliest memory was in the 60's when it was, I think, still a fairly high tech adhesive. I remember my dad "curing" the repairs in the oven.
Good tip about the automotive stuff, i never thought about it and I have a stock in the garage. is it any good for "potting" circuits that I sometimes build for use in vibration sensitive applications?
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Old 7th Oct 2015, 12:13 pm   #8
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Default Re: Epoxy resin

Quote:
Originally Posted by bikerhifinut View Post
Is it any good for "potting" circuits that I sometimes build for use in vibration sensitive applications?
It might be, unless the formulation has changed in the last 50 years or so. There was a part of a circuit in early Vox guitar amplifiers which was similarly potted. In this case, it was because the designer of the amps (Dick Denney) had "borrowed" the circuit and wanted to hide the evidence. In this case, the hardened araldite made trying to investigate the circuit nigh-on impossible, except to the dedicated and patient.
If I were you, I would look at proper potting-compound; I would think it is still available. Don't use silicone bath-sealant, because this releases acetic acid as it cures (vinegary smell) and this will attack any components embedded in it.
Colin.
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Old 7th Oct 2015, 12:34 pm   #9
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Default Re: Epoxy resin

Thanks.
Yes I am aware of the acetic acid issue in normal domestic silicone compounds. I imagine the first thing that would do is attack the solder and fairly rapidly too.
Normal potting compound is available, I have used it, but its a very expensive commodity.
At least in the quantities I would use.

A.
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Old 7th Oct 2015, 12:40 pm   #10
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Default Re: Epoxy resin

Araldite Precision - yes, the slow-setting stuff - sets hard but it has to be well mixed in the correct ratio. And curing at 50°C helps too. Once set, subsequent heating does not make it any harder.

For potting circuits, generally something slightly flexible is needed, to cope with thermal expansion of the potted circuitry getting warm. There is also the fact that when epoxy sets, it shrinks - the molecules pull closer together - and if its sets hard, there is a permanent stress on the embedded components.

Adding a filler might well help! A filler reduces the shrinkage, makes it harder, and tougher so less liable to crack (the minute particles of filler act to deflect any crack as it starts so it doesn't propagate). Aluminium oxide is great, as is silica - but for domestic use you might well try powdered talc from the bathroom. Just be sure it is well dried first, by baking for a few hours and stirring.
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Old 7th Oct 2015, 1:23 pm   #11
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Default Re: Epoxy resin

Hot melt glue makes a good cheap'n'cheerful potting compound.

I've never had problems with Araldite Precision and use it for all demanding applications. I agree that Araldite Rapid (?) is little better than the generic Poundland stuff.
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Old 7th Oct 2015, 1:35 pm   #12
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Default Re: Epoxy resin

ISTR that Araldite was the stuff that English Electric used to glue the wings on Lightning aircraft. I think they may have used it in a controlled environment.
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Old 7th Oct 2015, 1:40 pm   #13
paulsherwin
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Default Re: Epoxy resin

It was also used on Concorde.
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Old 7th Oct 2015, 2:03 pm   #14
John Caswell
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Default Re: Epoxy resin

Heat, not excessive heat, always speeds up the curing time. I think standard epoxy (Araldite) is best.

John
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Old 7th Oct 2015, 2:25 pm   #15
reelguy
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Default Re: Epoxy resin

You could try "Milliput " standard.
I bought some to try and make a knob for a reel recorder , left it to harden over night and it's solid. I'm pleased with it...
It bonds to metals ,wood,plastics, glass brick etc.
Costs about £ 2.0 from a hardware shop.
You could google it for more info.
Peter W ..Reelguy.....
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Old 7th Oct 2015, 2:27 pm   #16
julie_m
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Default Re: Epoxy resin

Whenever I've used pound store epoxy (which seems to set whenever the heck it feels like it), I have mixed it on a beermat with a matchstick; and observed the setting of the excess adhesive on the beermat as a guide.
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Old 7th Oct 2015, 3:01 pm   #17
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Default Re: Epoxy resin

Quote:
Yes I am aware of the acetic acid issue in normal domestic silicone compounds.
There are two different kinds of silicone sealant on the market. One kind stinks of acetic acid and the other has a milder organic smell. I have used the latter kind for potting EHT multipliers with good effect.
The snag is that they often don't write on the tube what kind it is. I think the "exterior" kind was the OK one. There are other kinds of specialist silicone rubber too.

Don't pot circuits with anything with added "steel". Just because it doesn't conduct doesn't mean it won't cause trouble - the obvious problem (could be a feature in some situations) would be a significant magnetic permeability.

Going back on topic: I have noticed that Araldite is not as good as it was. There are several setting speeds available and I always found the intermediate one the best compromise - setting in about half an hour. The latest ones seem to set in a few minutes - often too fast.

Although they didn't like to mention it, the hardness/rubberiness of the final result could be varied by the ratio of the two components.

I notice that the Araldite brand is no-longer used for just epoxy resins - so be careful what you are buying!
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Old 7th Oct 2015, 6:14 pm   #18
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Default Re: Epoxy resin

True Araldite is hard, strong and very rigid. I cast a racing seat back for my cammy Velo 50+ years ago, and my goodness that was hard. I still have a green tube of traditional araldite from the '60s, and recently acquired some more 20+ year old tubes of both rapid and traditional. So far I have never seen any softness if mixed correctly. "Plastic Padding" was (probably still is) a polyester resin, generally regarded as cheaper and inferior to epoxy resins.
I regularly use non-acidic silicone sealant (available from CPC), but also I get tubes of Loctite 5920, an orange coloured sealant which I use for all sorts of stuff. I would certainly consider using that for small scale potting jobs.
Les.
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Old 7th Oct 2015, 6:31 pm   #19
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Thumbs up Re: Epoxy resin

Quote:
Originally Posted by John Caswell View Post
Heat, not excessive heat, always speeds up the curing time. I think standard epoxy (Araldite) is best.
"Not excessive heat": a very valid point. From personal experience, I know that moderate heat does indeed reduce setting time, but excessive heat seems to produce a chemical change and the adhesive then never sets.

Al.
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Old 7th Oct 2015, 6:36 pm   #20
Skywave
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Question Re: Epoxy resin

Quote:
Originally Posted by David G4EBT View Post
Plastic Padding 'Super Steel Epoxy Weld' . . . . I've used it in such applications as filling unwanted holes in die-cast aluminium boxes to re-use them.
That's a useful tip - but one Q., please. How do you stop the set adhesive - which, presumably, is then flush with each side of the box - from simply falling out of the now-filled holes?

Al.
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