[Archive] Pressure Casting

JMR:

Very cool sculpts Zonk. What I am most impressed about is how you manage to have such perfect casts. I see next to zero air bubbles. I was wondering if you use a pressure or vacuum chamber to get rid of the air?

Could you explain how you cast your models?

Keep up the good work :slight_smile:

Zonk:

I was wondering if you use a pressure or vacuum chamber to get rid of the air?
Could you explain how you cast your models?

Keep up the good work :)

JMR
I use pressure. In the self-made chamber. I use tight metal ware. With thick walls - the Pressure cooker. I have altered it. Also I do casting in it, at pressure in 200 kPa.
Pressure is forced by the manual bicycle pump through the automobile valve. All is very simple )))) This photo from my workshop


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JMR:

Hmmm… very interesting. Thanks for sharing. I’m afraid such equipment is going to be a bit too expensive for me though. Maybe if I can find a pressure cooker second hand or something.

I’ll have to give this some more thought. Thanks again!

Borador:

So what you are basically doing while casting with a pressure cooker is:

1. Pour resin into the moulds
2. Put them into the pressure cooker
3. Add the valve (where do you put this thing?)
4. Apply pressure which you run through a meter to monitor the amount of pressure

Is this correct?

My other questions are:

�?� where do you mount the valve?
�?� how long do you leave the moulds in the pressure cooker at 200 pKa?

Thanks in advance (:

G.2:

I too was fasinated with Zonk’s setup, so I googled “pressure casting” and found this informative youtube video (there appear to a few others on the topic), but this one explains how it works. It is slightly different setup and more professional but I think it explains the concept of pressure casting quite well. And it does explain how Zonk’s system works.

Have a looks here

Pressure casting resin with Cindy http://www.youtube.com/watch?v=XMdicfz5Ouk

Also a professional Pressure casting unit (which looks similar to the one on Youtube video costs about $600 dollars, and that doesn’t cover the cost of the air compressor.



Also here is a PDF about Using a ‘Pressure Chamber To Create Bubble-Free Castings’

http://www.smooth-on.com/pdf/Pressure_Chamber_TB_SO.pdf

I am certainly now interested in this process. But I need to get some money from somewhere.

Zonk:

....... costs about $600 dollars, and that doesn't cover the cost of the air compressor.

G.2
?????
This very expensive and unnecessary equipment. If you do on 1000-2000 models in day - such equipment am necessary . If you do on 200-300 models in day enough cheap equipment which I use.

Сompressor? Pressure in 2 atmospheres (200 кРа) can be pumped up in the manual way. If the capacity is tight - pressure remains to constants. What for to search for expensive and difficult equipment if it is possible to manage simple and cheap?

Personally I don't see necessity for expensive equipment.I have spent 35 dollars and have received the wished.

The special pressure cooker is necessary. The cover is inserted from within and has the oval form. I have bought it in shop for 600 roubles that approximately equally 19 American dollars. It is possible to find the necessary pressure cooker at our auctions or in shops. The price of a new pressure cooker of 1700 roubles = 54 American dollars, second-hand 800-600 roubles = 25-19 American dollars.

http://www.avito.ru/items/samara_posuda_i_tovary_dlya_kuhni_skorovarka_rabochaya_48565647
http://www.avito.ru/items/bryansk_posuda_i_tovary_dlya_kuhni_skorovarka_6l_24811849
http://www.avito.ru/items/volgograd_posuda_i_tovary_dlya_kuhni_skorovarka_novaya_48455504

I use pressure at molding, but some prefer vacuum - an example of manufacturing of the vacuum chamber.
http://forum.rcdesign.ru/f41/thread139894.html
So what you are basically doing while casting with a pressure cooker is:

1. Pour resin into the moulds
2. Put them into the pressure cooker
3. Add the valve (where do you put this thing?)
4. Apply pressure which you run through a meter to monitor the amount of pressure

Is this correct?

Borador
Yes
My other questions are:

�?� where do you mount the valve?
�?� how long do you leave the moulds in the pressure cooker at 200 pKa?

Thanks in advance
*In a pressure cooker cover there are two apertures in which I established a manometer and the valve from an automobile tire.
*Pressure remains in a pressure cooker before full hardening of weight. Rubber - 24 hours. Plastic of 30-40 minutes.

P|S ...  It seems to me, we discuss it not in that theme. It is necessary to ask to allocate moderators discussion about technology of molding under pressure in a separate branch and to transfer here here. http://www.chaos-dwarfs.com/forum/forumdisplay.php?fid=13

... I am sorry for my language

zobo1942:

Interesting!

This message was automatically appended because it was too short.

JMR:

I just wanted to add that I think it’s important to note that if anyone intends to try this stuff out, you should realise that you are applying quite a bit of force on an object when pressurising. You do not want it to go wrong. If you use the wrong materials, you basically have a grenade in your hobby-room that can cause serious harm.

I’ve checked some pressure cookers and found that not all of them are able to cope with 200 kPa.

I’ll have to give this some more thought myself, but figured it was good to give people a fair warning about the risks involved.

Also, while surfing the web on this subject, I’ve seen people suggest to use talc powder in your molds in order to deal with bubbles. Apparently the talc “sucks” the resin into hard to reach details that would otherwise be filled with air. Some claim it works wonders. I’m sceptical, but will have to give it a try.

Finally, I agree it might be worthwhile to cut this thread up and place it in the Ideas and Advice section.

Zonk:

........serious harm.



JMR
At any work safety precautions both qualitative materials and tools for work are important.

At talc addition in pitch - its fluidity decreases. On the experience I was convinced that addition in talc pitch not effectively. Casting turn out poor-quality.

Only Russian pressure cookers are capable to sustain pressure in 2 and more а�,м.(200кРа) .они are made of a high-strength material. The pressure cooker in a photo is capable to sustain pressure in 5 atmospheres (500кРа) - but such pressure is excessive and dangerous. For molding of pitch there is enough pressure in 200 кРа.

Grimbold Blackhammer:

Pressure casting is one option but certainly not the only one. I and several locals are having excellent success using standard castings. I suppose my only question is - why go through the extra expense of pressure casting? Are the models more durable? Is it faster process? I haven’t had any durability issues so far and I can cast a model every 15 minutes or so if I needed to. Is there any difference?

Zonk:

Everyone works as to it more conveniently. I like quality of models at moulding under pressure.

JMR:

Pressure casting is one option but certainly not the only one.  I and several locals are having excellent success using standard castings.  I suppose my only question is - why go through the extra expense of pressure casting?  Are the models more durable?  Is it faster process?  I haven't had any durability issues so far and I can cast a model every 15 minutes or so if I needed to.  Is there any difference?

Grimbold Blackhammer
The reason I'm looking at pressure casting is because I'm having quite some issues with trapped air. I didn't expect to have these issues. Maybe it's just the way I've sculpted things, but seeing Zonk here pull of perfect casts of one-piece, fairly complex miniatures, I can't imagine why my sculpts wouldn't work.

Here's an old picture of the sculpts I'm talking about:


I'm talking about the legs here. The issues I have is that I get air-bubbles at the end of the scales in the scale mail. I really think it should be easy enough for the air to escape out of these details, but maybe I was wrong. Either way, the end result is that I have to manually sculpt/repair a lot of the scales on every cast. Kinda defeats the purpose of casting in the first place :P

If anyone has any thoughts on this matter, they're most welcome.

I realise I'm derailing this thread even more now, so maybe a mod can move the last page or so to a separate thread if deemed necessary.

snowblizz:

I really think it should be easy enough for the air to escape out of these details, but maybe I was wrong.

JMR
What can I say, it does seems like the air likes to stick to your models. Another thing I know people have talked about is agitating, ie vibrating, the mould to break some of the tension and encourage airbubbles to float out.

Presumably it shouldn't be impossible to reverse the process and make a low pressure in the pressure cooker. Theoretically speaking at least. I don't think you need a very low one either, say total vacuum, just enough that the air trapped in the casting material will want to surface.

Zonk:

Time of polymerization of plastic isn’t enough, therefore vibration won’t help to get rid of air vials in weight. It is necessary either pressure, or vacuum. Talc addition in plastic too won’t help will get rid of air vials. It is necessary to project correctly a casting mold, and correctly to put ingates on which plastic is filled in. Forgive for my language

Grimbold Blackhammer:

I think I know what’s happening and I had the same issue. If you turn your mini upside-down and imagine it as your mold, air is getting trapped in the tips of the scale armour because, as the air rises, it gets to those tips and has no escape route. If you were to fill the model from the top (out into the hat instead of into the feet), the air would escape out the hat freely and I would bet you wouldn’t have that issue.

Making molds is an art. I’m still learning.

JMR:

If you turn your mini upside-down and imagine it as your mold, air is getting trapped in the tips of the scale armour because, as the air rises, it gets to those tips and has no escape route.  If you were to fill the model from the top (out into the hat instead of into the feet), the air would escape out the hat freely and I would bet you wouldn't have that issue.

Grimbold Blackhammer
The legs are separate from the body(bodies). I'm only casting the legs at the moment. I've made my molds like you suggested, so the resin enters the feet first and then exits towards the belt.

I'm honestly surprised about getting bubbles in so many scales. I guess I'll try tapping the mold more when the resin is curing and give the talc a try to see what happens. Like I said before though, I don't have a lot of faith in the talc :)

If anyone else has had similar issues, please share your thoughts. Surely I'm not the first to cast models with scale-mail armor :P

Grimbold Blackhammer:

Oh definitely tap the mold!  I drum my fingers on it for 5 full minutes while it dries to get the air bubbles out!

Just in case I wasn’t clear (or I’m misunderstanding you which is entirely possible) I assumed you were pouring the resin into the feet so the mini is essentially upside down.  If you were to instead pour it into the head with the mini standing on its feet, the air bubbles would flow the opposite direction and be able to escape.  Yes, I know you’ve already made your molds so that won’t happen but still…

Grimbold Blackhammer

Bolg:

Also, while surfing the web on this subject, I've seen people suggest to use talc powder in your molds in order to deal with bubbles. Apparently the talc "sucks" the resin into hard to reach details that would otherwise be filled with air. Some claim it works wonders. I'm sceptical, but will have to give it a try.

JMR
I heard this tip before and I gave it a try last night.
Well actually I didnt have any Talk powder so I used powdered sugar, but still I got a lot better result on my squig molds than before, more little toes and a bit more detail.

So yes this tip works, and I can only imagine using real talc powder will work even better....

JMR:

So yes this tip works, and I can only imagine using real talc powder will work even better....

Bolg
That's great to hear, Bolg. I'm not sure when I'm gonna try casting again, but I'll let you know how talc works out for me. Have to get everything set up again. Oh the effooooort! :s

Sugar-coated squigs huh? I see a business opportunity...

Zonk:

If you have decided to mix talc replace with its powder се�?еб�?янной is better with pitch. It will execute two functions, will paint casting and will force out a part of bubbles. Silver powder is on sale in building shops and costs not much. Usually it mix with a building varnish and the silver paint turns out. But without pressure or vacuum use all the same will be ос�,ава�,ся bubbles in casting.