Pressure or Vacuum - choose one

[Gizmo3k]

If you only had the budget for either a vacuum chamber or a pressure pot, and didn't have any sort of pump, which would you go for? (Obviously I need to get a pump too).

I am looking to make pen blanks (Polyester Resin for now, probably epoxy in the future) and resin/wood hybrid jewelry, plus anything else that fits. I am limited to shopping from Amazon, as i have a gift voucher for there.

I have about £100 to play with - is it possible?

 

[Phil Dart]

There are others out there that know far more about this than me - but my understanding is that polyester doesn't require either, polyurethane and epoxy require pressure, and stabilizing, hybrid and mould silcone require vacuum. I've been going through this research process too Alan, so maybe someone will come along and either confirm that or put us both right.

 

[Graham_C]

Awaiting responses with interest!

 

[Bammer]

You can cast with PR without either a pressure pot or a vacuum chamber.

A Vacuum chamber will be needed to stabalise wood blanks properly, but on your budget I don't think you'll get far, plus the stabalising stuff is around £112 a gallon
A Vacumm chamber will de-gas any molds if you make your own, and remove bubbles from your chosen resin

A pressure pot is only required if you want to go into it big time, and start using other casting resins. I have been doing it for ages and only just treated myself to a pot .... plus you'll need a compressor ...

If I was you, I would buy your wife something she wants and cast without either.

A vacuum chamber and pump somewhere around £160 - £200
A pressure pot around £200
and then you still need a compressor.



This is only my opinion of course

 

[Sawes]

Think Brad covered most of the cost implications of both options and uses of each.
If only looking to use polyester resin at minute, as Phil said, you can get away without anything special. One tip would be to make sure the resin is quite warm though so that any bubbles caused by mixing can rise easier.
I already had a compressor for other air tools so paying out for pressure pot want such a big expense as such. The vacuum chamber was different story and since buying first one with pump I have now expanded to 3 of varying sizes.


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[fingwe]

It really depends what you intend to do in the future, but I'll give you my, somewhat limited, experiences - I'm sure others out there have far more experience than me.

I have both vacuum and pressure equipment. However, to date, I have not used the pressure pot, for a number of reasons - mainly that the air compressor was bought second hand and I'm not sure how well it has been maintained - although it looks new, I'm not sure I trust it not to have rusted spots or whatever in the tank (me being over cautious).

Anyway, I have cast polyester, polyurethane and epoxy, as well as stabilised wood.

Polyester doesn't require a pressure pot, or vacuuming. Just mix, pour and wait.

Polyurethane almost always needs something. I tend to vacuum the resin after I have mixed it, but before I've poured it. This generally gets rid of 99% of bubbles. I occasionally come across tiny bubbles remaining, but nothing major. If I'm mixing something like mica powder, which contains lots of air, then I'll generally mix that with one part of the resin, vacuum that, then mix the two parts of the resin together, and vacuum again. Some resins do have a very short open time, but I've found that I can vacuum a resin with a 2.5 minute open time, as long as I'm only doing a single colour pour (both colours can go into the vacuum chamber together so that isn't an issue, I just don't have the extra time available to mix a second colour). Some resins are thicker, and will require longer in the vacuum chamber, but I've found that these tend to have a slower setting time, so it hasn't been a problem.

Epoxy isn't generally supposed to need pressure or vacuum, as it generally sets slowly enough that bubbles will be released naturally. However, I have used a quicker setting epoxy (something like 15 minutes work time, rather than the usual several hours) which was full of bubbles. I treated that the same as I do polyurethane, and that got rid of almost all bubbles.

So, I get on fine just using vacuum....but I daresay it would be quicker and easier to just use a pressure pot. I guess my ideal would be to use a vacuum to get rid of any bubbles in the resins before they're mixed, when time isn't an issue - especially if I've mixed with any kind of mica powders. Then to use pressure one everything is mixed and poured. I would think that that would virtually guarantee castings free from even the tiniest bubbles.

Of course, if you intend to stabilise wood, then vacuum is the way to go. But then if you wanted to cast with wood, or anything else, you'd probably find that they introduced bubbles into your mix....so you'd want pressure.

As for price...I honestly can't see that you'd get anything suitable for either for £100. You're looking at several hundred pounds for either set up.

 

[Gizmo3k]

Thanks for all the responses!

I have done a bit of PR casting, it seems to work ok without pressure or vacuum, but the most recent thing I have tried is to make some wood and resin jewelry, in some PVC piping. I am going to get it out tonight, and see if it breaks apart too easily - if it does I may need to change to epoxy instead, but I thought you needed vacuum for epoxy, hence the questions.

I assume something like Mini Vacuum Pump, GOCHANGE DC12V Negative Pressure Suction Pump with Bracket 5L/min 120kpa: Amazon.co.uk: DIY & Tools would be completely useless (coupled with something like 710Vacs Acrylic 1 Gallon 4.8 Litre Vacuum Chamber Modelling Purge Degassing Vac: Amazon.co.uk: Garden & Outdoors )?

 

[fingwe]

Provided you get a slow setting epoxy (most take at least a day to set), you should be fine without any equipment.

If you do still get bubbles and you're wanting to incorporate wood, pressure would be the way to go, as the vacuum won't get rid of the air bubbles that the wood will introduce in the mould. You generally vacuum the resin before it goes into the mould, not whilst it's in there. Whilst vacuuming it in the mould is possible, it would be very messy!

 

[fingwe]

Forgot to mention - if you do get bubbles introduced by the wood, it would be far cheaper to do a 2 step process. Just coat the wood in clear epoxy and let that set, so it is sealed, and then put that into your moulds and cast as normal.

 

[Gizmo3k]

Thanks Melanie,

My thinking was if vacuum is used while everything is in the mould, there would be a physical join between what gets sucked into the wood, and what is left outside, so it would be stronger. I may of course be wrong! Of course you would need additional resin in the mould to account for some 'disappearing'.

My current 'mould' is PVC piping held vertically, so there is plenty room for bubbling!

 

[Bill Mooney]

You can use an ultra sonic cleaner. The vibration migrates the bubbles. I paid £16 from Aldi for mine so you should be able to buy one through Amazon without breaking the bank.

 

[fingwe]

Thanks Melanie,

My thinking was if vacuum is used while everything is in the mould, there would be a physical join between what gets sucked into the wood, and what is left outside, so it would be stronger. I may of course be wrong! Of course you would need additional resin in the mould to account for some 'disappearing'.

My current 'mould' is PVC piping held vertically, so there is plenty room for bubbling!

Yes, I understand your thinking. It could work, but you could also say the same about pressure - it will force the resin into the wood. I honestly couldn't say which would work best, all I know is that most people who cast Alumilite (polyurethane) and wood blanks use pressure - but that may be as much to do with the relatively short working time of Alumilite.

 

[Bammer]

Gizmo, just warm your resin before you add the catalyst. Imagine how slow the bubbles rise in honey then think of a beer. So reducing the thickness (not using that other word again) and therefore allowing the bubbles to rise more easily. if you have a scroll saw, sit your mold on that, the vibrations will help it them rise as well

Woody had some great results without any special equipment

This was made without either as well



Melanie you compressor should be fine, it isn't that you got to worry about ...

Now if your pressure pot was rusty .... it could go BANG !!

 

[Penpal]

All things considered this subject has been discussed well, I would hold firing off your 100 and weigh up the benefits, Pauls recent pours and vids have simplified my visions of casting.

Peter.

 

[Graham_C]

What an informative thread , and what a great bunch of folks on here! Might find myself having a go at something

 

[wm460]

Imagine how slow the bubbles rise in honey then think of a beer.

Ok I just thought of a Beer, so I better go and have one.:pint:

 

[Sawes]

Ok I just thought of a Beer, so I better go and have one.:pint:

I blame Brad for the 6 or 7 I had last night and got nothing done in workshop.



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[Phil Dart]

Imagine how slow the bubbles rise in honey then think of a beer.

Ok I just thought of a Beer, so I better go and have one.:pint:

I blame Brad for the 6 or 7 I had last night and got nothing done in workshop.

Yep, I found that part easy too. A bit like the film Icecold in Alex, but with less effort beforehand.

 

[Gizmo3k]

Thanks for all the comments, turned into a really interesting thread!

Of the 3 test pieces I cast, 2 survived the de-moulding process (insert rod into pipe, hit rod with hammer until everything comes out the other end ). The one that failed was a flat edge (endgrain), cut at an angle. Of the other two, one was kind of L-shaped (more surface area to bond to), and the other had a hold drilled into the wooden part to act as a tenon - I will hit them a bit more tonight to see if they hold up to rough treatment!

Oh, and I will try to remember a release agent next time

I will try to post some pictures if they don't explode all over the place :)

 

[Goggomobile]

Hi all from Australia
Great thread. Very helpful. I do a lot of polyester resin casting for Decals in silicon moulds. I use all of the tips mentioned in the thread. I sometimes get a small bubble stuck to the Decal. I use CA to fill the bubble hole and finish off ...

A friend of mine had a job for a wedding where we glued crushed oyster shell onto the barrels before casting in polyester resin. As you would expect there was a lot more small bubbles clinging to the small shells. The small holes we filled with CA - perfect result.

All without pressure or vacuum. I will try pressure cast this year .. time to experiment.

Another piece of info that might help is I use clear casting polyester resin. There are many blends and mixtures of polyester resin available depending on what you are doing ... not all the same. I learnt the hard way with the catalyst. Too much and the mix goes off hot and maybe more brittle. Quality, humidity, temperature, and age of catalyst can affect the cure time. I try for a longer cure time to enable the bubbles to come out. I thought about temperature. I live in a subtropical part of Australia. Mostly warm here even in winter ... in the U.K. I guess it can be freezing for a warm blooded person like me...

A trick I found with polyester resin ... I used to shake the tin before I opened it and vigorously stir the resin in ... all created lots of bubbles and esp. microbubbles. ... so now I don't shake and dont turn the can over before using. I pour very slowly and gently ... when mixing the calalyst I mix slowly with a flat stick (ice cream stick) and without creating too many bubbles. Remember it's usually 30-35c in my shed so it's already heated. When I pour into the mould I pour in such a way so that it slowly wets the barrel or whatever I'm casting .. mostly from the bottom up .. I pour so that the resin pushes any bubbles out which might be trapped from underneath. I cover the mould with a container just in case dust or junk doesn't settle in the resin before curing. I get a lot of gum leaves and dust blowing around ( you may not have this problem)

Randal