Pressure pot

[Graham Warner]

Hi folks, I want to get into resin turning & will soon be in the market for a decent pressure pot.

What I want to know is should I pay out for a pot specifically made for resin casting or convert a paint pressure pot, I'm more than a little concerned about a diy one with the psi involved, obviously don't want the thing exploding because i have over pressurised it but i have to say i'm very tempted because of the huge difference in price.

What are peoples views on diy or made for the job

 

[sometimewoodworker]

Hi folks, I want to get into resin turning & will soon be in the market for a decent pressure pot.

What I want to know is should I pay out for a pot specifically made for resin casting or convert a paint pressure pot, I'm more than a little concerned about a diy one with the psi involved, obviously don't want the thing exploding because i have over pressurised it but i have to say i'm very tempted because of the huge difference in price.

What are peoples views on diy or made for the job

With the pressures involved and having a painting pressure pot & seeing how it’s constructed there is no way I’d be doing a DIY job. The energy involved is significant and if you get a catastrophic failure there are seriously dangerous bits of metal going to be travelling around.

this is just 1 hold down of 4

It is substantial

Most diy involves pressure cookers that are designed for short term pressure holding, resin and painting needs long term pressure holding, so quite different stress.

 

[Dominik Pierog]

Bigger = better I have cheap 10L pot inside dia 24cm x 20cm ... but fast found its too small.
https://www.ukworkshop.co.uk/threads/bubbles.128389/post-1440152

 

[clogs]

I always thought it would be better with a vacuum than pressure...
my thinking was if little or no air was pressant then the resin would take it's place.....
am I so wrong....?
I know you would have to buy another pump.....as most already have a compressor....
how would it affect air bubbles in the resin.....?
I'm just asking cos I've no idea...
might want to use resin in the future.....

 

[Dominik Pierog]

I first de-gass resin using vacuum pump. For full remove bubbles its take hours and resin open/working time depend of type 10min to 60min.
So its too slow. Also wood is full of air so during resin curing proses it will give away bubbles, when resin soaks inside wood.

 

[sometimewoodworker]

I always thought it would be better with a vacuum than pressure...
my thinking was if little or no air was pressant then the resin would take it's place.....
am I so wrong....?
I know you would have to buy another pump.....as most already have a compressor....
how would it affect air bubbles in the resin.....?
I'm just asking cos I've no idea...
might want to use resin in the future.....

It’s different processes involved. The pressure version makes the bubbles smaller, often small enough to be virtually invisible. The vacuum version enlarges the bubbles enough so they can migrate out of the resin.

Pressure tanks and compressors are far more common than vacuum pumps and vacuum rated vessels.

 

[sometimewoodworker]

What I want to know is should I pay out for a pot specifically made for resin casting or convert a paint pressure pot,

There is no conversation needed all you need to do is to restrict the pressure you add to around 60psi

 

[Sandyn]

I have seen the results of a pressure cooked exploding in a kitchen, pretty devastating. The pot went downwards bending the top of the cooker. Not just the pot supports, but the burner plate. The lid went up and embedded itself in the ceiling, one of the clamps embedded itself in the wall near where someone was sitting The contents of the pot went everywhere. Really lucky the person wasn't killed. It would have been much more than 60psi though.

 

[julianf]

It’s different processes involved. The pressure version makes the bubbles smaller, often small enough to be virtually invisible. .

This i don't understand -

I mean, if i put the bubbles in a balloon, and put them in a pressure chamber, sure, the diameter of the balloon reduces... whilst its in the pressure chamber.

As soon as it comes out, it goes back to the same diameter.


I'm not saying it doesn't work, just that i cant understand that its just a case of making them smaller, and id like to understand better!

 

[Dominik Pierog]

Pressure pot change small(that wasn't escape) bubbles to dust particle in clear cast.
But big ones will only shrink to small bubble. So if you don't prepare resin and cast properly you end with bubbles even if you use pressure pot.

 

[Inspector]

When the resin is under pressure the air in the resin stays dissolved. When it cures and is hard the air is part of the solid. If you put the resin under vacuum the dissolved air forms bubbles which may or may not float to the top. Think divers getting the bends surfacing too fast. If the resin is a slow setting type prolonged vacuum may cause some of the chemicals to "boil" off messing with the chemistry of the product. Slow setting resins are not desired with coloured casting as the suspended micas or other sparkly dust and colours have time to settle out. So pressure is used to keep bubbles from forming and vacuum is used briefly to remove bubbles under some circumstances and for stabilizing wood. The stabilizing resin, usually heat setting, replaces the air in the wood while under vacuum and when the vacuum is released the atmospheric pressure forces more resin into the wood. Then the wood is heated to cure the stabilizing resin.

The use of paint pots as pressure vessels is safe as long as the pressures used are within the pot's limits. Many advertise 60psi or 80psi max but that is the point where the safety valve lets the air out and is not the working pressure which may only be 30psi or 40 psi. Lots of people use them with those working pressures and are successful with them. Others feel they must have higher pressures and take the risk running at high pressures by replacing the safety valve with higher rated ones. Or they look for high quality domestically made pressure pots that are designed and rated to run high pressures but those come at a much higher cost. Pots sold as casting pots are presumably safe to use at the rated working pressure but are for all intents and purposes a converted for you paint pot. You will see youtube and read people advocating removal of the regulators from paint pots and just relying on the one on the compressor. I don't think you should because if by any chance you adjust the pressure between casting sessions (like use an air tool) and forget to reduce it again you will over pressurize the pot putting yourself at risk. With a dedicated regulator for the pot that is less likely to happen.

If anyone is converting a pot the first time they put air to it they should fill the pot to the very top with water. That way there is very little air to expand if something lets go and the energy released is minimal. It is also advised to do it at some distance from yourself, preferably in or behind something substantial.

I feel that if Graham does not have the mechanical background to know and understand how to safely change over a paint pot to a casting pot he should buy a ready made one.

sometimewoowdworker there is a lot of white space between "this is just 1 hold down of 4" and "It is substantial". There is no picture or whatever should be there.

Pete

 

[J-G]

sometimewoowdworker there is a lot of white space between "this is just 1 hold down of 4" and "It is substantial". There is no picture or whatever should be there.

There is on my screen.

 

[Inspector]

Now there is a picture of a pressure pot lid hold down.

Pete

 

[sometimewoodworker]

sometimewoowdworker there is a lot of white space between "this is just 1 hold down of 4" and "It is substantial". There is no picture or whatever should be there.

You have confused me. There is a picture showing the hold down. If you are not seeing it then your connection, computer or patience is at fault
Here is a screen shot

showing the picture and text under is a thumbnail

but I usually never use thumbnails due to buggy forum software,

 

[sometimewoodworker]

Now there is a picture of a pressure pot lid hold down.

Pete

It was always there

 

[Inspector]

Beats me why the picture wasn’t there for me but I did look at the thread multiple times after your initial post and even after I posted and it was clean as a whistle. It’s been there since J-G posted though.
Pete

 

[sometimewoodworker]

Beats me why the picture wasn’t there for me but I did look at the thread multiple times after your initial post and even after I posted and it was clean as a whistle. It’s been there since J-G posted though.
Pete

It is almost certainly the bugs that exist in the forum software, the picture was in the post, not added later.

 

[sometimewoodworker]

This i don't understand -

I mean, if i put the bubbles in a balloon, and put them in a pressure chamber, sure, the diameter of the balloon reduces... whilst its in the pressure chamber.

As soon as it comes out, it goes back to the same diameter.


I'm not saying it doesn't work, just that i cant understand that its just a case of making them smaller, and id like to understand better!

your balloon is not encased in a resin that cures, is it?

1) add resin to mould Mixing in as few bubbles as is possible.
2) put mould in pressure pot, add air to 60psi, this reduces the size of bubbles.
3) wait for up to 24 hours while maintaining the pressure, this allows the resin to cure completely

when the pressure is released, which must be after the resin is totally cured, the resin has ample strength to maintain pressure on the tiny bubbles.

 

[julianf]

your balloon is not encased in a resin that cures, is it?

1) add resin to mould Mixing in as few bubbles as is possible.
2) put mould in pressure pot, add air to 60psi, this reduces the size of bubbles.
3) wait for up to 24 hours while maintaining the pressure, this allows the resin to cure completely

when the pressure is released, which must be after the resin is totally cured, the resin has ample strength to maintain pressure on the tiny bubbles.

Thank you - I fully understand that now.

I did not realise that the whole part was being cured under pressure.

The YouTube that I've watched has mostly been resin tables and they often put the resin (not the table) in some sort of pressure / vacuum device, hence my confusion.

I'm guessing they are applying vacuum to the resin only.

Thank you for clearing it up for me.


As a side comment, I use slow setting resin on parts too large to get under pressure. But I think the vast majority of my air is not from mixing the resin at all, but gradual release from the wood.

I see YouTubers pre painting surface, I guess to stop this, however that's not really applicable to pippy oak etc.

 

[Graham Warner]

When the resin is under pressure the air in the resin stays dissolved. When it cures and is hard the air is part of the solid. If you put the resin under vacuum the dissolved air forms bubbles which may or may not float to the top. Think divers getting the bends surfacing too fast. If the resin is a slow setting type prolonged vacuum may cause some of the chemicals to "boil" off messing with the chemistry of the product. Slow setting resins are not desired with coloured casting as the suspended micas or other sparkly dust and colours have time to settle out. So pressure is used to keep bubbles from forming and vacuum is used briefly to remove bubbles under some circumstances and for stabilizing wood. The stabilizing resin, usually heat setting, replaces the air in the wood while under vacuum and when the vacuum is released the atmospheric pressure forces more resin into the wood. Then the wood is heated to cure the stabilizing resin.

The use of paint pots as pressure vessels is safe as long as the pressures used are within the pot's limits. Many advertise 60psi or 80psi max but that is the point where the safety valve lets the air out and is not the working pressure which may only be 30psi or 40 psi. Lots of people use them with those working pressures and are successful with them. Others feel they must have higher pressures and take the risk running at high pressures by replacing the safety valve with higher rated ones. Or they look for high quality domestically made pressure pots that are designed and rated to run high pressures but those come at a much higher cost. Pots sold as casting pots are presumably safe to use at the rated working pressure but are for all intents and purposes a converted for you paint pot. You will see youtube and read people advocating removal of the regulators from paint pots and just relying on the one on the compressor. I don't think you should because if by any chance you adjust the pressure between casting sessions (like use an air tool) and forget to reduce it again you will over pressurize the pot putting yourself at risk. With a dedicated regulator for the pot that is less likely to happen.

If anyone is converting a pot the first time they put air to it they should fill the pot to the very top with water. That way there is very little air to expand if something lets go and the energy released is minimal. It is also advised to do it at some distance from yourself, preferably in or behind something substantial.

I feel that if Graham does not have the mechanical background to know and understand how to safely change over a paint pot to a casting pot he should buy a ready made one.

sometimewoowdworker there is a lot of white space between "this is just 1 hold down of 4" and "It is substantial". There is no picture or whatever should be there.

Pete

Thanks for that info Pete, I think i'll shell out the extra & get one made for the job