Normal epoxy or polyester resins for potting?

Epoxys are more usually used with carbon fibre they are several multiples of cost above polyester resins which are commonly used with glassfibre.

Think potting compounds are generally epoxy to keep exothermic effects down, heat when curing, and shrinkage.

Polyesters get hot whilst curing and in castings are built up to save the thing cracking or in extreme cases self igniting, er ,guess who put too much catalyst in ;-) Polys are not, without additives , very flexible and also shrink by up to 3 or 4 % .

Heat also finds every dry joint in your board ...

Adam

Having said all above have potted a few things with poly resins, dont make a

3" deep block of the stuff in one pour, if it needs to be deep do it in a few stages.

Use a filler, it helps extend, bulk out the resin , and mitigate shrinkage and heat, aluminium powder or `micro balloons`, both commonly available from glass fibre suppliers. look for boat building suppliers rather athn a DIY store, the differnce in cost is fairly dramatic.

HTH Adam

much

also

I think that using less catalyst will help avoid the heat problem. It will take longer to cure, but end result will be the same. Atleast that is my limited experience from messing up the resin/catalyst ratio when making fiberglass parts with polyester.

I'm concerned about effects from the resin being hard as most potting compounds are flexible. Will this be a problem?

I was also concerned about chemical compatibility, ie. the resin disolving plastics used in IC packages or other components, but I guess this can not be a problem since you have used polyester.

Any long term problems?

Anyone else who has tried polyester resin for potting?

-- Emil Johnsen

the

Should have siad hardner, strictly speaking catalyst is a differnt coponent that is pre added.Adding less hardner will lower exotherm and slow hardening.But in large pours thing still gets hot.

Think its only a problem if compnents are likely to get hot and try and expand, power transistors,voltage regulators etc.

My experince is it hasn`t been a problem, your mileage may vary.

Polyesters are actually organic and some actually degrade under water over time.

HTH Adam

"Emil Johnsen" wrote in news:cjqtaf$2ds6$ snipped-for-privacy@toralf.uib.no:

I have used Devcon 5 minute to pot connectors and several small modules. It doesn't seem to degrade plastics. The stuff is clear and doesn't contain any fillers.