Solvent for araldite

Charles,

Heating the Araldite/casting will make the Araldite more runny. I'm not sure what the upper limits of the heat applied should be, but I used to use heat sources like the top of a radiator, or under an Anglepoise lamp shade on a desk. The application of heat does shorten the setting time on the 24 hour Araldite (the reason I usually heated mine).

Jim.

Problem with solvent is that it will leave the Araldite porous when it evaporates.

Why not use a polyester (fibreglass) resin. Some of them are as thin as winkle pee - especially if warmed to around 35 degC.

The commercial way of doing this and Rolls has all their aero engine castings done from new, is to us a resin, dip applied under pressure.

Sorry can't help with the type of resin only that using a simple pressure container may help.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

Charles As Jim Guthrie has said heating will make the stuff runny and this may be sufficient for your purpose. If not, I have several different types of some extremely runny specialist resins which are used, amongst other things, to penetrate the matrixes let by woodworm damage in the timbers of old buildings. It's viscosity is rather like that of, say, SAE 20 grade motor oil (I guess you're old enough to remember that!) I haven't used this stuff for several years so I would need to check to see what I have - and if it's still useable! How much heat, if any, will the treated casting be subjected to, how critical is the application? I have also got Trich but you really don't want to go there if you can avoid it...it's a known carcinogen which is why it was withdrawn from general use in the first place. It would also be a problem to get it to you - the mail is a definite no no although I'm sure the UKRME collective could find a solution if challenged.

Tell us a bit more about what you're doing. If I can't help with resin, I know a man who can........ --

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

I often heat Araldite to decrease its viscosity - I usually play a Bunsen flame over it. Tends to form a crust if I overdo it, but leaves the underlying glue at about the viscosity of gear oil.

It's necessary to warm to job too - if you apply heated Araldite to a cold surface it'll just thicken up and won't go anywhere.

I tend to use two glues for a job like this; In the first instance I'll 'wash' the job with a superglue, which has superb penetration, then finish up with heated Araldite for its filling properties.

Araldite make many varieties of epoxy adhesives - might be worth checking out a commercial supplier to see if they'll sell you a small batch of one of the more fluid epoxies.

Regards,

Thanks for all the advice. The original idea is copied from the Coventry Climax Toolroom - they sealed porosity in the 1.5litre V8 engines by using Araldite and solvent - and they won the Formula 1 world championship with it so it must work.

What I think that I'll do is test the "warm araldite" route first on warm scrap and see how it goes. Since it's an unpressurised water system it doesn't need to be Rolls Royce standards!

Thanks

Charles

There are several commercial companies making a living out of sealing porosity in castings by using impregnation with resins - practically every casting in a modern vehicle has been impregnated, by a vacuum-pressure cycle. The oldest technology was to use silicates (water glass) but all modern impregnants are cross-linked acrylic resins, put in by vacuum impregnation and cured by heating in hot water. Epoxies would be very good because they have very low polymerisation shrinkage but no-one has ever found a way of keeping them under control on a commercial scale.

Ultraseal

are the experts in the UK. IMP in Germany are also a big player.

The nearest thing you could get to a commercial sealant would be one of the Loctite anaerobic sealants. Run it into the pores then cover the surface with aluminium foil to exclude air.

Don't use superglue - it has rather poor hydrolytic stabilty and will break down over time if exposed to hot water.

Warming Araldite is fine - will thin it but accelerate hardening. If there is any way to get some "suck" on the porosity that will improve things greatly.

You can thin it with practically any organic solvent. I've used dichloromethane to make sprayable lacquer from it but only in a proper fume hood in a chemistry lab. Acetone will do fine and is a lot safer (and still fairly easy to get).

Acetone and/or isopropyl alcohol will work, but the final resin will be a bit weaker - as a rule of thumb a 10% dilution leaves the resin 10% weaker - and may leave it slightly porous, depending on resin and solvent.

It can also for some reason make the resin take longer to set - don't worry, if it was going to set normally it will eventually set after dilution. It could take a day or two though - warmth helps.

I have had good results using a slow setting resin with a 10-15% isopropyl alcohol dilution and a post-set cure (an hour in a 85C or so lowest-setting oven _after_ it has cured enough not to be dentable-with-a-fingernail).

Heating can make resin runnier, but it also speeds up the setting process, and the resin may have begun to set (=thicken) before it gets a chance to wet the part thoroughly. A slow-setting resin helps here.

You probably don't really want to use shop araldite though - a laminating epoxy resin will be much thinner and runnier than typical araldite. I can let you know of some brand names if you tell me how much you will need (and how much you want to spend!).

Are some online suppliers.

The other half of the story is to prepare the surface first - aluminium can be cleaned with detergent and then etched by a quick immersion in a 1% solution of caustic soda (use goggles and rubber gloves and a nylon scrubbing brush) (beware, this will eat the aluminium if left in contact too long) or better 2% copper sulphate and 10% common salt (which is gentler, but will still eat Al if left too long).

A 3% solution of washing soda will do in a pinch, and will cost about 50p.

Rinse _thoroughly_ in clean water immediately after etching. If at all practicable boil the part for ten minutes (in deionised water, yet) and apply the epoxy as soon as it has air-dried (which it will do quickly after removal, from the heat).

Best bet for thinning epoxy resin is methanol, you can also use acetone but the advice I got from FibreTech GB is that acetone is a bit hard on the resin. You only need about 10% methanol to get the resin to a very runny state so be careful not to overdo it. I have had no problems with porosity when skinning toy aeroplane wings with glasscloth and epoxy resin using this technique.

Hth,

Interesting point, might be worth trying to suck some of the air from inside the pump casting after applying the resin ?

That's handy. My brother in law has a methanol powered Jap in his Cooper. A cup full will be no problem...

Charles

Not quite what you're after, but might help: I've tried various techniques for removing bubbles from slow set/professional Araldite prior to use. You'd think vacuum degassing would be ideal, but the resin just expands into a foam ball and stays that way until set! I'm not sure if this is a solvent they use boiling off under vacuum or caused by tiny mixed in air bubbles expanding. I suspect it's both. The best method I've found is to mix the Araldite on a bit of paper and then use a hot air blower (like a hair drier, but hotter and with a very slow blow) to gently heat the mix from below and above. This massively reduces the viscosity. As you pass the heater over from above the bubbles that have made it to the surface burst, making space for the next batch... Works really well as long as you don't heat it too much and cause it to set too soon. I think you'll find there is a potential danger in using halogenated solvents like Trichloroethylene with aluminium. It can react violently. The problem is worse with freshly machined material. Here we go:

Scrim

Make sure there's no oil in it first though ;-)

These folk will also do small quantities of runny epoxy by post.

cheers, David

I was under the impression that trichlorethylene was withdrawn because it's an ozone depleting substance; bad news if it is a carcinogen as I used to use it to deflux PCBs in a repair workshop for many years. Carbon tetrachloride, used before trich was introduced, is a carcinogen however. Martin

See

sadly, both carbon tetrachloride *and* trichloroethylene are both recognised carcinogens ...." if the left hand don't getcha then the right hand will ....... : {

--

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

Any yacht chandlers should be able to sell you a runny epoxy resin as used for fibreglass repairs on boats. Both slow and fast hardeners are available, if you use the slow one you can heat the resin for better penetration.

One of the more popular brands is West System and their website

gives lots of technical info.

Russell.

If you are heating to get better penetration the workpiece temperature is more important rather than the bulk resin. This is because, in small voids, the resin almost instantly heats or cools to workpiece temperature.

Jim

-- Posted via NewsDemon.com - Premium Uncensored Newsgroup Service ------->>>>>>

In article , Norman Billingham writes

It's very inflammable though. Had a couple of very exciting fires* when pumping acetone and the tubing came off and sprayed it on the pump motor

- and the acetone was even chilled to -45 degrees or so.

*Ah, the days of our lives! Why is it we remember the disasters so much more vividly than the successes? Because they get the adrenaline going, I guess.

David