Pressure casting question

[AdamG]

Hi Guys,

I'm playing around with my vacuum set up and i think my mould making is not quite there yet as I still get the odd air bubble. Im working on more feeds in the new moulds.

I've also thought about degassing then moving over to my pressure pot to let cure under 70psi.

This of course will impact on the number of moulds I can turn around as my pressure pot will be tied up for 50 - 60 mins at a time.

So im experimenting with keeping the moulds under pressure for 20mins or so until the left over resin has visibly cured and feels solid. The models at this stage are still pretty soft and flexible so I wouldn't de mould but would remove from pressure.

Initial experiments seem to show this works but wondered if anyone else had tried this or had thoughts on it?

Cheers

Adam

[Drop Bear]

Thats what I do with mine

Its a good balance i find between turnover and quality

[rattrap]

Yep, I do much the same too.

70 PSi sounds a bit excessive though, is your pot rated this high? I do mine at 50 PSi with no problems.

I use Smooth Cast 305, so I pull mine from the pot at around 15 mins, or when the resin starts to harden in the leftover resin in the pouring cup.

Would depend what curing time your resin is though.

[AdamG]

Cool thanks for the replies,

The pressure pot is rated to 80, so I click off at around 70 just to give me a buffer zone.

Casts are coming out crisp, which is always nice. I've been using 305 but have been having a bit of a nightmare with temp. If it gets cold, it really isn't happy.

Going to crack on today and see how I get on at 50PSI

Cheers

Adam

[Drop Bear]

I havent noticed much difference between 50-70 psi pressure really, i usually go to 60 as its easy to read on the gauge

your temp problem is interesting, I find that during hot days where i am i need to put the resin in dry ice to give me more work time, tho too much cold will thicken the parts. maybe that is your problem?

[rattrap]

I always give the mould a spray of release then open it up in front of my electric fire for a few seconds, then get it ready for the resin. Maybe that would help you?

[mangozac]

The increased benefit due to an increase in pressure drops as the pressure is increased. Does that make sense? Above 60 PSI there's really not that great an effect. I have heard of people casting at over 100 PSI, but that requires very special pressure chambers and IMO for the kind of stuff we're casting is completely unnecessary.

But if you're set up for 70 it certainly doesn't hurt either

Applying pressure after vacuuming is what most of us doing volume production are doing. We have the vacuum pump and compressor both hooked up to the pressure pot though, so you don't have to screw around moving the moulds from one chamber to another. You don't need to watch the vacuuming process of the resin. I've explained in a few posts on here the different effects the two techniques provide, so combining them into the same process gives the best of both worlds.

Note that if you pull the moulds out of the pressure pot too soon (while the resin is still soft) some bubbles near the surface may still be able to expand back out and cause a "pimple" on the outer surface.