I would like to make aradite "more runny" to help eliminate some
porosity in a water pump casting.Anybody have experience of using a
solvent to help make aradite run better? I've heard of
Trichloroethylene being used. Also I'll need to be able to buy the
solvent of course.
Other suggestions for eliminating porosity in an aluminium casting
appreciated.
Charles
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can avoid it...it's a known carcinogen which is why it was withdrawn from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
formatting link
are the experts in the UK. IMP in
Germany
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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!).
formatting link
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,
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:
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
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
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
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