Basic questions

[r1237h]

I've never done casting, but plan to start. I've gone thru the library, but haven't seen what I am looking for, so maybe someone can explain a few basics for me:

I understand that one can use pressure, vacuum, or neither. Is it personal preference, such as "I just happen to have a spare vacuum pump laying around" or is it dependent on what is being cast, such as stamps, feathers, carbon sleeves, etc?

Also, it seems that I am about to receive an air compressor, which seems to be good for pressure. I have seen how to make the pressure pot, but am a bit unclear as to what next, i.e. how much pressure, and does one keep the compressor going all the time, or does the pressure maintain itself once I get it to an acceptable level (perhaps this depends on how good I made the pot...?)? And for how long does it need to stay pressurized? Does it depend on the material, or is it a general thing?

Thanks.

 

[seamus7227]

I will attempt to give you simple answers to your questions. Keep in mind that these are only MY opinion and may not be the opinion of others.

Your casting method is a personal preference(silicone molds, pvc pipe, clear tubes), however, I must say that since i went to pressure casting, my success rate has now gone into the high 90 percentile with minimal failures.

I would not recommend building your own pressure pot, but rather buying one. Set up is critical to achieve excellent results. If set up properly, once you pressurize the pot, it will maintain that pressure until it is released.

I use 65lbs of pressure to cast. Some mathmeticians may say that is overkill, but it makes me feel better so i do it!:biggrin:

I usually leave the blanks under pressure for 24 hrs, however, here lately i have been using less heat (slows down the curing process) so i have been leaving them in the pot for 48hrs now. End result, they still come out flawless!

Results of failures are 99% of the time (for me) a direct result of too much heat. mold too warm, resin too warm, blank to be cast too warm, mix all of that together with catalyst, creates catastrophic shrinking of the resin, therefore withdrawing from the tube creating a silvery sheen across the entire surface of the blank.

Hope this helps to get you started. Dont be discouraged with your failures, you WILL have them, but its part of the learning curve.!

 

[Draconias]

If you are thinking of getting into casting, you might want to see if you can find a michaels close to you. The are having a 50% off one item sale:
Arts & Crafts | Michaels.com
That will drop the price from $33 for a quart of PR (Castin'Craft Clear Polyester Casting Resin) down to $17.50. You will also need to buy the catalyst, but it is a nice saving to get into casting.

Ron

 

[healeydays]

I agree with Seamus7227 Pressure is what is used, not vacuum for casting if either is used. Vacuum is used more for stabilization.

And like he said, don't make your own pressure vehicle, buy one designed for holding pressure at least 10 psi higher than what you are using it for. Remember, if something breaks in vacuum, it implodes, under pressure it's a bomb.

As for failure rate, it also goes the other way, If your resins are too cold, they also have issues and then again failures. (I guess it's advice difference from the hots of TX and the colds of NH)

 

[r1237h]

So I should get the famous harbor fright paint pot.....?

 

[seamus7227]

So I should get the famous harbor fright paint pot.....?

there are those that will strongly oppose the HF pot. I own two of them and have no problems. A little common sense goes a long way when using one.

healeydays: in the summertime i really dont have to worry about pre-heating my resin since it is so hot outside. Our winter this year has been cooler than normal but i have found that preventing the resin from getting too hot, sure makes all the difference in the world! In the summer, i also keep my resin inside the house so it lasts longer.

 

[TerryDowning]

Difference between pressure and vacuum.

Either can be used successfully for casting. It has to do with removing air from the resin.

Pressure either squeezes the air bubbles out of the resin or crushes them down to imperceptible size.

Vacuum removes the air bubbles by drawing it out of the resin completely.

That being said, it is possible/permissible to create casting with out either. You just have to be careful about the introduction of air into the casting material.

Dealer's choice on which method you choose.

But please do be careful. These are harmful chemicals and pressure vessels are dangerous.

 

[Ed Kerns]

Thanks very much for this question - and answers! I've turned a few dozen pens, but have never made a casting. Like you, I've read the library, but sometimes it's hard to get a foothold on the really basic stuff. The question in my mind is whether to begin trying to cast (embedding really interests me) without the pressure pot, or to make the investment right off the bat.
By the way thanks also to all of those who have contributed to the library. What a resource!!

 

[HamTurns]

does one keep the compressor going all the time, or does the pressure maintain itself once I get it to an acceptable level (perhaps this depends on how good I made the pot...?)? And for how long does it need to stay pressurized? Does it depend on the material, or is it a general thing? Thanks.

You shouldn't need to keep the compressor going, the pressure pot should be tight enough to not leak for the time period you need your casting under pressure. Connect your compressor to the pressure pot, open the shut off valve and bring it up the pressure you're using and shut the valve. Then remove the air line from the pressure pot. I use a portable air tank for my pressurizing because my compressor is to far away from where I cast.

I have used Alumilite and the de-mold time (how long after you pour can you take your new casting out of the mold) is pretty short, 20 minutes to an hour. But it's different for each different material your casting. So for me when using Alumilite I leave my castings under pressure for about an hour. That has been long enough for me.


Yes, the time it stays under pressure depends on the material you're casting and many more variables like; tempurature, humidity, mold tempurature, casting material tempurature, how well you've mixed your resins, and how well you've mixed your colors into your resins, what the ratio of one resin with color mixed into it compared to another resin with color mixed into it and how they'll "mix" in the mold.


I've decided to stay with one kind of resin until I get more proficient casting it. Get consistant results and be happy with my outcomes. After I have confidence that I can cast with one material I may venture out into other materials, but I want to get my feet on the ground with one resin first.

I hope this helps.
Tom

 

[jbswearingen]

Difference between pressure and vacuum.

Either can be used successfully for casting. It has to do with removing air from the resin.

Pressure either squeezes the air bubbles out of the resin or crushes them down to imperceptible size.

Vacuum removes the air bubbles by drawing it out of the resin completely.

That being said, it is possible/permissible to create casting with out either. You just have to be careful about the introduction of air into the casting material.

Dealer's choice on which method you choose.

But please do be careful. These are harmful chemicals and pressure vessels are dangerous.

A couple of errors here:

Pressure doesn't remove bubbles by squeezing them out of the mixture. It just compresses them such that you can't see them.

A vacuum doesn't remove bubbles by drawing them out completely. A vacuum allows them to expand, which will decrease their density, causing them to rise more quickly to the surface and "break".

The rest is good.

 

[Jim Burr]

Until I bought a pot, I did casting using vibration and common sense for a couple years. 0% failure rate by; warming the resin, avoid excessive mixing, shake the crap outa the sucker!!! I have an old HF drill press that's really clunky. Set the mold on the platform, pour, stir gently and flip the switch!

 

[mikespenturningz]

So I should get the famous harbor fright paint pot.....?

there are those that will strongly oppose the HF pot. I own two of them and have no problems. A little common sense goes a long way when using one.

healeydays: in the summertime i really dont have to worry about pre-heating my resin since it is so hot outside. Our winter this year has been cooler than normal but i have found that preventing the resin from getting too hot, sure makes all the difference in the world! In the summer, i also keep my resin inside the house so it lasts longer.

I also use a HF pressure pot. I checked my manual and is says it is good for 85lbs. I also pressurize to about 60-65 for at least 2 hours. I use alumilite for my casting. I have not been able to cast much this winter but as soon as summer gets here I will be back at it.