Casting and Mold Making Question

[Calvin]

Mufizal, there are a lot of urban legends about pressure casting. What you need is a compressor able to pull at least at 1/1.5 CFM with a 2/3 gallons tank and a minimum operating pressure of 60/70 PSI.

Best compressors on heart are the SIL-AIR but they are expensive as hell:
http://www.silentaire.com/silentaire/sil_air.asp

I have one like this:
http://www.steelmodels.com/SOFT-AIR-...16.-1.uw.aspx#
and it works like a charm since 5 years. It's not cheap but take a look out there sure you will find it cheaper.

Now about pressure pots the best option are the dental pots because the ultra fast closing system which allows you to use fast (<2 min) resins, but dental pots are small and expensive so depending on your requirements you can use a regular pressure cooker and modify it AT YOUR OWN RISK. On eBay a 23 quarts Presto pressure cooker sells for less than 80, so do your math. I also use a Presto 16 quarts pulling up to 20 PSI and it works fine.

Dental pots usually stand up to 2/2.5 bar (30/35 PSI) while cooking pots only stand 1/1.5 bars (15/20 PSI) but the magic about using pressure is just that, you will never need more than 1.5 bars (20 PSI) because it's all about molding desing and pouring technique. Over 2 bar you start getting nasty things like shrinkage, deformation, etc. Pressure per-se, as vacuum, doesn't get rid of nothing, the only air bubbles/pinholes I ever get were because a bad mold design.

A fellow told me think as an air bubble and when I got it I got almost perfect casting, it's all about physics of liquids and air, the more the better with pressure and vacuum simply doesn't work, keep in mind that air must be forced to flow, not compressed nor sucked.

Good luck.

[mrclean08]

Originally Posted by Jesse321

Check the Clubhouse, there are lots of tutorials there as well.

$800? How big of a pressure pot are you looking for 10 gallon? I picked up a GREAT 5 gallon set up for 1/2 of that, and a 5 gallon will usually only run you about 200.00 or less if you catch it on a good sale.

Also, no you need something a little more powerful than an airbrush compressor, funny thing, airbrush compressors are WAY more expensive then a regular shop compressor which can be had for less than 100 dollars.

I can't seem to register for the Clubhouse forums. Is that forum still active or is the site down? I tried registering almost a month ago and tried again this evening and still no luck.

[kenkaj]

Originally Posted by mrclean08

I can't seem to register for the Clubhouse forums. Is that forum still active or is the site down? I tried registering almost a month ago and tried again this evening and still no luck.

I have had the same problem.

[mufizal]

Originally Posted by Calvin

Mufizal, there are a lot of urban legends about pressure casting. What you need is a compressor able to pull at least at 1/1.5 CFM with a 2/3 gallons tank and a minimum operating pressure of 60/70 PSI.

Best compressors on heart are the SIL-AIR but they are expensive as hell:
http://www.silentaire.com/silentaire/sil_air.asp

I have one like this:
http://www.steelmodels.com/SOFT-AIR-...16.-1.uw.aspx#
and it works like a charm since 5 years. It's not cheap but take a look out there sure you will find it cheaper.

Now about pressure pots the best option are the dental pots because the ultra fast closing system which allows you to use fast (<2 min) resins, but dental pots are small and expensive so depending on your requirements you can use a regular pressure cooker and modify it AT YOUR OWN RISK. On eBay a 23 quarts Presto pressure cooker sells for less than 80, so do your math. I also use a Presto 16 quarts pulling up to 20 PSI and it works fine.

Dental pots usually stand up to 2/2.5 bar (30/35 PSI) while cooking pots only stand 1/1.5 bars (15/20 PSI) but the magic about using pressure is just that, you will never need more than 1.5 bars (20 PSI) because it's all about molding desing and pouring technique. Over 2 bar you start getting nasty things like shrinkage, deformation, etc. Pressure per-se, as vacuum, doesn't get rid of nothing, the only air bubbles/pinholes I ever get were because a bad mold design.

A fellow told me think as an air bubble and when I got it I got almost perfect casting, it's all about physics of liquids and air, the more the better with pressure and vacuum simply doesn't work, keep in mind that air must be forced to flow, not compressed nor sucked.

Good luck.

Thanks calvin!

I now understand the concept of pressure casting better, it means that you can get away from making your mold design good with plenty of air channels. ill look into the SIL-AIR and the dental pots. but ill think twice about the cooking pots , id rather pay money to live than save money and die ina freak pressure pot accident

Ill let you know how it goes!


Thank you

Mufizal

[Jesse321]

Originally Posted by mrclean08

I can't seem to register for the Clubhouse forums. Is that forum still active or is the site down? I tried registering almost a month ago and tried again this evening and still no luck.

Originally Posted by kenkaj

I have had the same problem.

If you're trying to register with a freebie email account like hotmail, yahoo or gmail, you won't be approved. They, and a lot of other forums (including my own), have had problems with spammers, so you have to register using a valid traceable ISP address.

You also might want to Google your email, and see if it might register on any online spammer list, and if it does, get it off that list.

[Kdawg59]

I don't know if I am too late to the party or not... but let me tell you... I LOVE LOVE LOVE my pressure pot... When I die I want to be ground up into dust and buried in there at 40psi...

I pressure cast everything I can now and even wax castings from transfer mold. and I pressure cast the waste mold.

I still use the same old silicone in a box/dixie cup/party cup to make the molds... then using my garage compressor I pump my pressure pot (5 gallon) up to 40psi... let it all cure...

I do the same with castings whether they be wax or resin... maybe less pressure in the tank... like 30-35psi. Pressure cast wax is a lot more dense than if you pour in and leave it set without pressure...

I can't believe that old tutorial is still around I don't think I can tell you where the hell the pics went for it, but hopefully you can glean some good info from it still anyway.

A pressure pot just takes everything to the next level as far as "worry free" molding and casting... it was my very first purchase after my first actual gig...

[Calvin]

Originally Posted by mufizal

but ill think twice about the cooking pots , id rather pay money to live than save money and die ina freak pressure pot accident

Right, anyway keep in mind that dental pots are nothing but modified cooking pots. For this kind of items there are three components which cannot fail, the release valve, the pressure gauge and the air intake. Most of troubles happen because a release valve failure or the pot not plugged properly, placing an additional control valve/gauge on the compressor out solves the first issue.

[JetFire76]

Hey all,

*sigh*... so I'm thinking about biting the bullet on the purchasing a pressure pot after purchasing my last kit and comparing it to my castings... there was absolutely no comparison... the pressure casted one looked so much better.

So after doing some research, here are some of the questions I had:

1) I was looking to purchase the pressure pot at Smooth-on (5 gallons) with a max of 80 PSI but it does not come with an air compressor. Can I just purchase one at a Home Depot or Sears? And what's the price range on these? I'm assuming I should get one that can exert 160PSI (according to Pop sculpture book.. you should get double the PSI of what the Pot can hold?)

2) When placing silicone into the pressure pot, since I use foamboards to create a box for the mold, should I be concerned about overflow of silicone? And if I use recycled chopped up silicone that had not been in the pressure pot in my new silicone mold, and it has air bubbles, should I be concerned about it imploding or exploding thus having a bad effect on my new mold?

3) Sorry about my lack of knowledge, but is there some kind of guage either on the air compressor or the pressure pot where if I wanted to set it at 30 PSI, that it will stop there? And once it reaches 30 PSI, and I have the Silicone in the pressure pot, do I leave the air compressor on all night while the silicone is curing?

Any help would be greatly appreciated. I'm still in my discovery mode so these are the questions that I came up with while doing research on this.

Thank you all.

[TGping]

Originally Posted by JetFire76

Hey all,

*sigh*... so I'm thinking about biting the bullet on the purchasing a pressure pot after purchasing my last kit and comparing it to my castings... there was absolutely no comparison... the pressure casted one looked so much better.

So after doing some research, here are some of the questions I had:

1) I was looking to purchase the pressure pot at Smooth-on (5 gallons) with a max of 80 PSI but it does not come with an air compressor. Can I just purchase one at a Home Depot or Sears? And what's the price range on these? I'm assuming I should get one that can exert 160PSI (according to Pop sculpture book.. you should get double the PSI of what the Pot can hold?)

2) When placing silicone into the pressure pot, since I use foamboards to create a box for the mold, should I be concerned about overflow of silicone? And if I use recycled chopped up silicone that had not been in the pressure pot in my new silicone mold, and it has air bubbles, should I be concerned about it imploding or exploding thus having a bad effect on my new mold?

3) Sorry about my lack of knowledge, but is there some kind of guage either on the air compressor or the pressure pot where if I wanted to set it at 30 PSI, that it will stop there? And once it reaches 30 PSI, and I have the Silicone in the pressure pot, do I leave the air compressor on all night while the silicone is curing?

Any help would be greatly appreciated. I'm still in my discovery mode so these are the questions that I came up with while doing research on this.

Thank you all.

As someone who just bought that exact model, I can tell you its awesome!

To answer some of your questions:

Pot pressure, 80 PSI is fine, as you'll only work in the 30-40 PSI range, so there's your double the pressure I also just got the cheapest compressor from lowes for 100$... and it came with a nail gun... whut?! I WILL get one of those silent compressors I see online though, that thing is a loud -----, use earplugs. If the pressure is not enough with the small one, you can return it for an exchange within 30 days. Lowes is cool like that. At least mine is.

My process for molding/casting:
-turn on air compressor, let it fill up, and it should stop automatically once at full capacity.
-while air compressor is filling up, prep molds by spraying with mold release/then filling with resin/rubber depending on if you are mold making or casting.
-place mold in pressure pot(instructions should be included for having pot lie on its side for ease of placement)
-bolt on lid, tighten so you avoid leaks
-make sure release valves are closed and intake valve is open(the thing the compressor hooks up to)
-turn on compressor, let guage fill to 30(or desired PSI) do not go above 40
- as soon as the guage reaches desired PSI you turn the intake valve to off. Takes a matter of minutes. Usually less than 2
- then switch off the power to the compressor. Once the PSI in the pot is reached it stays that way, no reason to leave compressor on after the pot is pressurized.
-let mold/cast cure. Do not open pot early, let parts fully cure.
-to open pot, open release valves. Make sure pressure is zero before you open pot.

You do have to watch the pot for a little bit until it reaches the pressure you want, but you dont have to watch it after you get it where you want it. So the compressor is on for a total of 5 minutes.

I believe Smooth-on has videos on how to do this... they have a bunch of resources on their website. I'm just lucky I live close to one of their vendors. Which I'd be happy to ask questions if you have any. Just post em and I'll bring em up next time I'm over there CALL smooth-on, I did this and they actually found the vendor close to me, they are super helpful and will answer questions to.

Wear earplugs, goggles, and mask. smooth-on has a good mask to.

[JetFire76]

Hey TGPing! Wow! Thank you so much! That was very informative and very very helpful!

I called smoothon about their pressure pot but the guy that I spoke to wasn't too well informed about it. But I saw their instruction PDF and that was somewhat helpful.

I found a pressure pot specifically for casting and molding on the bay for $410 and the pot looks exactly like the one on Smooth on but uses Black teflon steel or something.

I'm trying to figure out if it would be worth it to do it myself or to have a pro do it for me. I create waste molds for stuff I want to transfer to wax and I want to learn how to cast and mold properly as well. I think the only thing that was setting me back was the cost and not knowing the process. It was the same with learning wax... but now I love it... so maybe I'll experience the same with pressure casting?

Really... thanks again TGPing!!