Epoxy meltdown problem

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)

Reply to
Andre
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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.

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Regards,

Boris Mohar
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Reply to
Boris Mohar

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.

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http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
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Reply to
Ian Stirling

In , Ian Stirling wrote in part:

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 ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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 .

Reply to
Andre

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.

Reply to
CWatters

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

Reply to
Zak

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

Reply to
Andre

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