Printable View
Some of you may be aware that I have succombed to the need of a pressure pot. Bought one at the last Supercheap sale and have converted it as per Big shed's guidance.That PDF file is a great help as following that the pot stayed at 50 psi for 5 days while testing. :2tsup:
So I did my first casting using the pot and my question is how long do I leave it under pressure before it is set. The casts are pure resin with a translucent dye for mylighthouses. No fancy timber concoctions as yet.
Peter.
Peter, in a word........it depends.
Firstly on how much catalyst you have used, secondly on ambient temperature and thirdly on what type and how much pigment/dye you have added. Also how big the cast is.
I normally use 1.5% w/w MEKP and in the current weather that would normally result in the resin setting in about 2-4 hours for a pen blank size cast (150x20x20).
The bigger the cast the quicker the resin sets as it can get quite warm (hot) in bigger cross sections. So if you did a cast for, say, bottle stoppers you would cut back the catalyst to about half of the above.
I normally leave my casts in the pot overnight and take them out in the morning. If the surface is still a bit sticky I put them outside in the sun, or in cooler months put them in a small oven I have in the shed for this purpose. About 15-20 mins at about 100C, if still sticky - repeat.
Thanks Fred,
I used small take away type coffee cups as moulds. 150 ml per cup and 1 ml MEKP and enough liqued dye to give colour, about 3 or 4 drops of the dye from Barnes.
I want to finish up with a coloured translucent tube about 50 mm by 50 mm diameter suitable for an led light to go inside and mounted on turned lighthouses.
Quite warm today, but the temp in my workshop was only 19 %.
I can leave it for a couple of days, but an wondering of the minimum time under pressure.
Peter.
Peter, that sounds like about the right amoun of MEKP for that cross section.
As the object of the exercise is to eliminate, or at least minmise, bubbles you only have to leave it under pressure until sets, after that pressure is not going to add anything to the process. I would guess you can take it out after 2-4 hours.
If the cast gets really hot (it is an exothermic reaction) then you may have to reduce the MEKP as it can start to crack if it gets too hot.
The other thing to watch is that you don't want to stir too vigorously to avoid introducing bubbles. Once you add the resin to the cup let it sit to allow bubbles to come to the surface before you add dye and MEKP, then stir gently.
Peter, just sank in what you are using as moulds. If these take away coffee cups are the waxed cardboard type then they can substantially delay the surface cure of the resin.
Something to be aware of.
I use the clear polystyrene cups for mixing and PVC, HDPE or (mainly) silicone for moulds.
They are the waxed cardboard cups, as these were the ones Fly used last year when he made some for me, so I'll leave them in the pot under pressure for a few days. I'll be too busy for the next few days anyway to do any turning.
Peter.
I was able to spend some time in the workshop today so I took the castings out of the pressure pot.
They were still a bit sticky on the outside so I got myself a little oven from Kmart for the workshop. After warming in that for a while they were perfect. Nice and clear with lovely green, blue and red tints.
Previously I used the dyes from Solid Solutions but on my small quantities of resin the colours were too dark. The new dyes are so much better and now I can start making some lighthouses.:2tsup:
Thanks for the help Fred.
Peter.