On 06/17/2016 11:18 PM, axolotyl wrote:
Its only half metalwork but I'm pretty sure some of you guys will know a
bit about this!


In point form:


1) Casting epoxy into a CNC machined mould.

2) Having problems with getting a consistent surface finish.

3) We are spraying the PVA release agent using a small touch up spray gun.

4) Sometimes we get small runs.

5) Sometimes part finish is matte due to the PVA drying too quickly.




Being a novice I think these problems are pretty much down to
application technique.

Any tips on what we can try to make the process of applying the PVA more
forgiving?



Alternatively would making the next mould from Teflon be worth trying?

I don't know if the machining finish would be smooth enough but my guess
is it could be used without a release agent.



Any ideas or experience?

I've not used PVA mold release but I have used aerosol spray-on silicone
mold release from www.smoothon.com in aluminum molds to cast their
polyurethane, usually shore 70A rubber (part PMC780). They recommend
spraying the mold, then brushing with a small paint brush to get a uniform
film, then letting it sit for 30 minutes or more to flow out and dry. I was
casting small stuff, 1-3" max dimension, so used those disposable "battery"
brushes, 1/4" or 3/8" wide. If I did all of that the surface finish was
usually very good, as good as the mold. On prototype parts that I didn't
care so much about I would spray, wait a minute, then start mixing the
polyurethane. Those usually had a light fish scale look, with the
occasional run still visible :-). Anyway, maybe the same technique would
work with your PVA mold release?

-----
Regards,
Carl Ijames