Epoxy meltdown problem

[Andre]

Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

I found that thin layers poured at about 20 minute intervals seem to
work , but is there a better method ?

Thanks

-A

"Windows isn't a virus . Viruses DO something !"

(unknown)

 

[Boris Mohar]

On 30 Jul 2003 12:11:15 -0700, testing_h@yahoo.com (Andre) wrote:

Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

I found that thin layers poured at about 20 minute intervals seem to
work , but is there a better method ?

The rate of exothermal reaction is partially governed by the rate of the
heat loss. If you mix in a bucket the surface area is minimal so the heat
buildup at the "core" is high. Pour in a shallow container after mixing.
If your potting volume is high maybe you have to keep it in the fridge
while curing.

--

Regards,

Boris Mohar
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Aurora, Ontario

 

[Ian Stirling]

Andre <testing_h@yahoo.com> wrote:

Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

I found that thin layers poured at about 20 minute intervals seem to
work , but is there a better method ?

Find a slower curing epoxy.

Ass filler to improve thermal conductivity, thermal mass and reduce total
heat generation due to less epoxy. (maybe cheaper too)

See if you can mix it in different ratios, and get a slower cure while
not doing bad things.

Cure in fridge.

--
http://inquisitor.i.am/ | mailto:inquisitor@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
Get off a shot FAST, this upsets him long enough to let you make your
second shot perfect. -- Robert A Heinlein.

 

[Don Klipstein]

In <bg99ll$nk7$3$8302bc10@news.demon.co.uk>, Ian Stirling wrote in part:

See if you can mix it in different ratios, and get a slower cure while
not doing bad things.

The other (snipped) suggestions make sense, especially adding a filler.

I would not deviate from the specified mixing ratio until your epoxy is
proven to behave well if you do this. Deviating from the specified mixing
ratio can result in an incomplete cure.

If the epoxy cures slowly at first and then suddenly with a nasty
temperature rise at room temperature, it may take ages to cure if chilled.

Another idea: If the layer is barely thick enough to get a nasty
temperature rise, you may be able to head off the temperature rise by
blowing a fan at it. But this will not work for potting something in a
bucket.

- Don Klipstein (don@misty.com)

 

[Andre]

don@manx.misty.com (Don Klipstein) wrote in message news:<slrnbigj07.d1d.don@manx.misty.com>...

In <bg99ll$nk7$3$8302bc10@news.demon.co.uk>, Ian Stirling wrote in part:

See if you can mix it in different ratios, and get a slower cure while
not doing bad things.

The other (snipped) suggestions make sense, especially adding a filler.

I would not deviate from the specified mixing ratio until your epoxy is
proven to behave well if you do this. Deviating from the specified mixing
ratio can result in an incomplete cure.

Yes, I found that .

Most of the epoxy worked except for two containers that partially
melted .

So much for using wax moulds . Works OK for small amounts though

Idea - make an epoxy reflector by attaching a bowl to a motor, pouring
in epoxy mixed with metal powder, and spinning to get the required
curvature .

If the epoxy cures slowly at first and then suddenly with a nasty
temperature rise at room temperature, it may take ages to cure if chilled.

Another idea: If the layer is barely thick enough to get a nasty
temperature rise, you may be able to head off the temperature rise by
blowing a fan at it. But this will not work for potting something in a
bucket.

- Don Klipstein (don@misty.com)

 

[CWatters]

"Andre" <testing_h@yahoo.com> wrote in message
news:2c2cf14c.0307301111.664489e4@posting.google.com...

Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

I found that thin layers poured at about 20 minute intervals seem to
work , but is there a better method ?

That's the normal trick but Epoxy doesn't always stick to itself very well
so doing it in layers might not always work.

If you are "potting" something in a container you might be able to stand the
container in a bucket of water to extract the heat?

Try cooling the epoxy in a fridge before you mix it? That will make mixing
harder but should buy some time.

 

[Zak]

Andre wrote:

Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

You need a slower curing hardener. Varing mixing rations is risky - the
ingredients are quite reactive and you do not want too many of the
reactive bits to remain.

Slower curing hardeners exist especially because of this problem.

Also, above some thickness it will be very difficult to achieve
sufficient cooling.

"epoxy retarder" shows some google hits in the direction I'd search.

Note that for polyester resin this is more easily available in the form
of 'clear cast' resins.


Thomas

 

[Andre]

Zak <Zak@spam.invalid> wrote in message news:<bY9Wa.20479$KF1.308542@amstwist00>...

Andre wrote:
Hi group .

Anyone found a way to solve the epoxy "meltdown if you mix it in bulk"
syndrome

You need a slower curing hardener. Varing mixing rations is risky - the
ingredients are quite reactive and you do not want too many of the
reactive bits to remain.

Slower curing hardeners exist especially because of this problem.

Also, above some thickness it will be very difficult to achieve
sufficient cooling.

"epoxy retarder" shows some google hits in the direction I'd search.

Note that for polyester resin this is more easily available in the form
of 'clear cast' resins.

Well I think I fixed it

Here is the preparation procedure .
1) Obtain one or more (depending on the size of your casting base) CPU
heatsinks and fans .
2) Obtain some heatsink grease
3) Affix fans to some hard surface (wooden grid maybe) so all the
heatsink plates are aligned .
4) Coat heatsink plates with heatsink grease
5) Sit the mould on the heatsink plates . Be sure that the two are
pressed together properly .
6) Attach fans to 12V (or 5V) power supply.

Put the object to be casted in the mould, and then pour in a maximum
of 1.5cm of epoxy . (I haven't tested it with anything larger than
this yet) .
Put the completed assembly outside in fairly bright sunlight , so the
epoxy gets a chance to set .

The advantages of this method are that it ensures a reasonably clear
cast as all the bubbles rise to the top, with no "bubbling" caused by
overheated epoxy (plus you can re-use the mould) .

Have fun

-A

Thomas