Trouble

[MBUMIK]

howdy doody

felt really good this arvo, finally got all the bits to get the vacuum pump connected to the pressure pot, everything connected so easily it wasn't funny, made a great little stand to put the tubes in, that even went together without a hitch, i just knew something had to go wrong and sure enough i wasn't let down at all

i got some of those little round pine cone type things - we called them noggin' nuts as kids - dropped them in to some conduit, poured some resin over the top, waiting for the buubles to subside then topped them up some more

i thought i would just do 3 to see how it went - glad i did

poped them into the specialy made rack, wacked on the lid, hooked all the hoses up and started up the vacuum pump, for 25 minutes, damn i wish the pot was glass so i could see what was happening, man it was hard not to run over and open it all up to have a look, well i lasted 25 minutes anyway.

i turned off the vacuum pump and slowly opened the air valve just a little bit, didn't want the air rushing in toooooo fast (maybe this was the wrong bit)

i thought before i hook up the pressure i will have a sneak peek at how it all looked, man was i shocked, most of the resin was all over my nice spiffy rack and the pine cones were scattered all over the inside of the pot, well not realy just around the tubes they came out of.

i now have a very nice puddle of blue/pink/yellow resin in the bottom of the presure pot as well on the groovy stand that i made, not to mention a number of lightly resined noggin' nuts

should i have put something over the top of the tubes to stop the noggin' nuts from coming out, or is there something else i didn't do right

i call upon the gods of resin casting to help this poor creature to work out what the bloody hell he did wrong

thanks for reading about my delightful afternoon

MIK

[gawdelpus]

Bugger ! not gone this way as yet , I suspect that your "nuts" may have contained more air than you anticipated ,so when evacuating the chamber they would try to rise ,some sort of stopper to keep them in place sounds like the go ,as long as you leave some room for air to escape during the process :) I am still not sure why when sucking out the air you don't suck out all the resin as well hehe . No doubt some more experienced and technical persons will have the answers you seek :) John

[dj_pnevans]

your stand looks good. try and use pressure.
david

[BoomerangInfo]

I've never tried vacuum myself, but I think if you go search on IAP you might find stories from others with similar experiences. If you had enough vacuum, it would lower the boiling point enough for the resin to boil at room temperature.If a nut was jammed in, and an air pocket stuck below it, possibly it could act like a rocket too and shoot out, but I think that's probably unlikely as it would have to be jammed tight, and leak-proof for that to occur. More likely that it boiled.

Russell.

[MBUMIK]

thanks guys, the stand was groovy until it got covered in goooop, thems the breaks

i am guessing from the research i have done that i must have pulled tooo big a vacuum, 28" of vacuum will boil resin, which is where Russell was pointing

thats the problem with no gauge, anyone know where i can buy a vacuum gauge from??

MIK

[gawdelpus]

Try E-Bay , I got a good oil filled one a while back , don't get a car vacuum gauge though hehe. Neil got one recently from a local supplier so plenty around I would think ,

[dai sensei]

Yep, what ever you cast must be either held down, or wedged down.

Too much vacuum can make it boil or even separate, so keep it below 26" Hg. Depends on your vacuum pump, most of the cheaper ones can't get much higher for a paint pot.

I only use the vacuum to remove air trapped in the item, but then swap to pressure before the resin goes off. Beware, resin goes off a lot faster under vacuum, so don't leave for too long- 3mins at 25 C max. With a vertical mould like yours you probably don't need vacuum, provided you slowly place the items into the resin letting the resin fill the voids, but I would still use pressure.

Pressure does help forcing air out and hold it all together. Be warned though, under pressure, those casts will want to stay in the tubes. I used to use split conduits for casting under pressure

[MBUMIK]

thanks Neil

my vacuum pump came from a refrigeration mechanic, it didn't pull enough vacuum for him anymore but he said it will still pull 29 - 30"

i think it gets there real quick which might be one of the probs

i tried some WW today, made a new groovy stand, without the holes for the flat moulds that i have made

i thought about the vacuum pump and decided to try a little different, i ran the pump for 60 secs, let it rest for 2 minutes, ran it again for 30 secs, let it rest again for 2 minutes, ran it again for 30 secs, left the vacuum sit for 5 minutes, then pumped the pressure up to 45 psi for 5 hours, i have pulled them out of the pot now but i probably should have left them in overnight, i was amazed that one of the moulds had very little resin left in it, i am guessing that the vacuum and pressure sucked or pushed it into the wood, i have since made some more and poured in on top of the original resin

the reason i say that i should have left the moulds in for longer is because there were bubbles coming out of the resin when i pulled the moulds out, be interesting to see what they are like on the inside later in the week when i turn them down

my new groovy stand has some resin on it as well, i think from the bubbles coming out of the resin when the vacuum was starting up, oh well things are only new until they are used

i didn't take any early pickies, didn't think about it to document totally what i have done, thems the breaks

MIK

[NewLondon88]

BTW.. I love that stand! :2tsup:

I think a few people have hit on the problem .. resin can boil under vacuum, so you
need to be careful of that. Your idea if pulling a vacuum in stages is a good one, but
might take some experimentation on your part to find out what works for you. Note that
if you change your pipe size, you might also need to change your routine. Every change
affects something else.. and this is all new to lots of us. The 'rules' aren't
understood well enough to write the book, yet.

Another thing to note is that air bubbles expand under vacuum. That is one of the reasons
for using vacuum to clear air bubbles .. they get very large, so they rise to the surface
faster and easier. A large air bubble on the bottom will rise and push out the resin that
is above it.

Warming the resin can help with this, as the warmed resin is thinner and more easily
able to move around the rising air bubble. If your supplier carries styrene thinner, this
may also help. Just imagine the difference in an air bubble rising through water and
that same air bubble rising through molasses and you get the picture.

One more thing to note (as if there weren't enough!) those 'noggin nuts' can hold
moisture, and that can just ruin all of your plans. If I were going to try this, I'd put
them on a cookie sheet and pop them in a warm oven for a few hours. (Warm can
mean simply leaving the light bulb on, not the oven itself) That will usually remove
any residual moisture and eliminate one more variable. Resin + water = Foam!

Did I mention that I love that stand? :2tsup:


ps .. if your pot will fit in a freezer, the metal can contract and possibly
release the resin in the bottom. You might be able to just 'pop it off'.

[MBUMIK]

i didn't think about the bubbles expanding under vacuum, of course they will when they contract under pressure

the nuts were pretty dry, i threw them in the microwave for a bit

my freezer isn't big enough to put the pot in but i was planning on leaving it there just to remind me of the mistakes

thanks for your input

the WW looks to have worked pretty good, so heres hoping

MIK

[MBUMIK]

thinking about it further i am guessing that the bubbles expanding under vacuum wood have acted like a parachute in reverse and pushed the noggin nuts and resin up out of the tube

[NewLondon88]

thinking about it further i am guessing that the bubbles expanding under vacuum wood have acted like a parachute in reverse and pushed the noggin nuts and resin up out of the tube

That makes sense in my brain .. that's a good way to picture it.

[MBUMIK]

gotta have an imagination:U:doh:

[gawdelpus]

And I thought only the "Irish" would think of reverse parachutes !! stand on the ground, pull the rip-cord , and up up and awaaaay ! :doh: hehe ,cheers ~ John

[dai sensei]

Did a banksia cast last night and got side tracked whilst the vacuum was on, only for 5 mins, but enough to achieve a similar result to yours :doh: 13 half cast blanks and resin all over the pot :-

[MBUMIK]

man i know how you feel

[MBUMIK]

i have been thinking about these noggin nuts since i had the trouble, there was a solidish piece in the bottom of one tube so i turned it to see what it looked like, pretty damn good in my opinion

so now i have been racking my little brain to come up with an answer, and brain storm

i am going to try connecting all the nuts together with fuse wire, which i will attach to the bottom of a tube with the tape that seals the bottom anyway

this should stop the nuts from rising to the top along with the bubbles

this works in my mind in theory but i guess not neccessarily in practice, i will try tomorrow or tonight if i get a chance (gotta mow the lawns - well i should call them jungles)

interested in your thoughts

MIK

[dj_pnevans]

Good luck mate.
David

[MBUMIK]

Failed again

i will be putting this on hold for a little while until i can find a glass container to use so that i can see what is happening with the vacuum

MIK

[NewLondon88]

I was thinking about this, too.
I think the first thing I would do is use longer tubes. That gives the expanding resin
someplace to go while still staying within the tube. See if you can leave enough room
for the resin's volume to at least double, possibly triple. Vacuum can do that.

If you stuff the tube with noggin nuts and then pour your resin, you already understand
that the nuts are full of air.. so you're going to want to fill the tubes beyond the level of
the nuts. But .. if you go too far, the vacuum will make it overflow.

Taking your idea about vacuuming in stages, I think I would try doing the vacuum and
then release it after a minute. When you release the vacuum, any spaces that WERE
full of air, but are NOW under liquid will quickly fill with resin. (nature abhors a vacuum
and all of that..) So .. if you do this in stages .. vacuum, rest, release the vacuum and
then top off with more resin repeat, repeat, repeat etc. then eventually there won't be
much (if any) air left in the nuts.

The problem at this point would be that the density of the nuts may still be lighter
than the resin. This could cause them to float. You might be able to put a small
piece of screen over the nuts and weight it down somehow.. keeping the nuts under
the level of the resin surface.

Of course, this will mean that the screen will be locked into your blank.. so plan your
size accordingly so that you can cut away the screen (parting tool?) and still have the
length you need for the blank.

It works in my mind, but that doesn't mean much.
Up there, I'm also a handsome hero.

[MBUMIK]

i should say that the failure was not complete

the wire worked well to hold all the nuts together, i still had some bubbles in the mix

i do like your ideas in the post above

i found a big jar that i can use, only problem is i have to wait until it is empty, full of olives, now why couldn't it be full of something i like to eat

thanks for the input

MIK