Thread: casting under pressure

Under pressure resin takes a lot longer to set, and the opposite for vacuum, it takes less time to set. Temperature certainly helps and your idea of an electric blanket would be good although sometimes I like it to take longer so it has more time for the resin to penetrate. Here in Qld there are not as many cold days so I can just pick my times. I try to cast under pressure when it is ~30 C and then in the pot it is equivalent to ~25 C (not a conversion, merely a guess, but you get my drift). I also tend to leave my casting overnight and recommend 24 hrs anywhere where it is less than 30 C.

Over 30 C is fine for most applications, except as mentioned previously, I want to penetrate the timber as much as possible. In these circumstances I release pressure, top up resin, then re-pressurise sometimes a few times to enable any bubbles to rise and release. If too hot, the resin just sets too fast and releasing the pressure can cause debonding.

thanks for the input Neil

for the next 6 months we probably wont get a day over 25C and the evenings soon will down around the 10C mark

i am not doing the WW casts so penetration is not an issue, i am using the pressure to compress any small bubbles that might occur when casting on uneven surfaces

as an added question what pressure do you all think is needed just to compress bubbles, i have been using 50psi it seems to compress the molds a little, i think i will dial it back to around the 35psi mark as an experiment next time

MIK

I always take the pressure the pot can withstand, in my case, 45psi. Whilst at George's place at Mt Compass I got to use his pot he takes to 100psi (I stood around corner ). It was a modified pot and he has had it tested to 150psi, but it still has a thin top with bolt marks on the rim (where they fail), so I wasn't confident of the safety at only FoS 1.5.

On my next trip to Melb I am picking up a huge pot under my mum's house I didn't know was there. Heavy duty steel reinforced tank ~600 deep that I am hoping once cleaned up can take a higher pressure. At 100psi the resin even penetrates rotten timber and has less chance of debonding and bubbles.

When I cast under pressure I go up to 45 psi, I always leave under pressure overnight. I try to keep heat down to a minimum as I prefer a slower cure so as to reduce the chances of cracking or debonding.

i tried out my new idea on tube in casting today, i just have to let the resin go off completely before i can demold them..... tomorrow night.... if it works i will be able to do 30 - 40 tubes in one go of the pressure pot

here's hoping

where does everyone in OZ buy their silicon stoppers, i found only one place on ebay and they don't have a very big range, i will try the local bearing shops sometime this week, but they don't tend to go out of their way for the hobbyist which is a pity

all the best

MIK

I got some stoppers from the local home brew shop.
They werent real cheap at $2.50 each, but they do the job.

You could try lab suppliers. They would probaby stock a range of sizes.

I got mine from Ebay, but I do NOT use this type of mold under pressure. I know you can, I believe 20psi max is recommended, but normally things cast with the tubes in don't need pressure.

I used to cast under pressure. When casting SWMBO applied constant pressure on me to mow the lawn instead