vacuum pump

[saltwein]

In using a vacuum pump to draw air bubbles from casting resin, what is the minimum requirements for a pump. Can a vacuum pump be used to eliminate the air in the resin before casting instead of pressure?

Regards, Steve

 

[its_virgil]

Steve,
Not sure I understand the minimum requirement question. I use a rotary vacuum pump(2.5CFM) because I have one. I'm sure it is overkill for doing this on a small scale. Several here use the venturi pump from Harbor Freight which uses an air compressor and costs somewhere around $20. I don't know how those work but there are several posts about them.

To answer your other question, I mix the catalyst in the resin, apply vacuum for 12 minutes, release the vacuum and pour the resin into the molds them place the casting under 30 psi pressure.

I use the Harbor Freight pressure paint tank for both a vacuum chamber and pressure vessel.

Do a good turn daily!
Don

Originally posted by saltwein
<br />In using a vacuum pump to draw air bubbles from casting resin, what is the minimum requirements for a pump. Can a vacuum pump be used to eliminate the air in the resin before casting instead of pressure?

Regards, Steve

 

[Fred]

I know that a vacuum applied after the casting material is mixed (degassing)will immediately remove any air bubbles.

Also, a vacuum applied after the initial pouring will remove any air that gets trapped on the tubes. Also, it will pull any air from under anything around the tubes, i.e., snake skins for example.

Just my .02 cents worth...

Fred

 

[Fred]

I usually mix all the casting materials and then pour down the side of the mold SLOWLY to try and avoid any intrapment of bubbles. Even then I will always pull a minimum vacuum of around -15 psi on the material for a minute or so to ensure all air/gases are removed. Depending on the temperature of your "mix" and the amount of catylist added setup will begin after this negative pull is done. It just takes a bit of practice to get the timing right. However you do the procedure you will need to move fast and be prepared to finish with all the vacuuming and other stuff WITHOUT any hinderances at all.

One BIG suggestion I would like to offer you/everyone is to make use of very good quality disposable gloves as the chemicals are messy and hard to get off of human flesh ... and impossible to get our of your cloths. Harbor Freight has a selection of nitrile gloves that are good for this purpose ... and even come in handy with finishes and glue too ... especially Gorilla Glue which will turn your fingers black as coal. Then you will need lots of sandpaper to get that black tissue off.

I use a Ghast laboratory vacuum pump that I got from a recent drug raid. The pump is capable of pulling up -28 psi and holding this level indefinitely. I have added two levels of cut-off valves thus adding another way of holding and adjusting the vacuum that I allow to be pulled by the pump.

Hope this makes sense and if you have more questions ASK. We are all here to hopefully help each other in our hobby endeavors.

Fred

 

[Alumilite]

We typically recommend a 5 or 6 cfm pump. The cheapest one we have found is a Robinair from www.tooltopia.com. Here is a direct link to the site (you might have to cut and paste it in): http://www.tooltopia.com/index.asp?PageAction=VIEWPROD&ProdID=9012

The part # is ROB15600. I believe that the $252 is a delivered price. We recommend them for our Water Clear Urethane and Flex 80 urethane rubber but mostly for our silicone rubber mold making materials.

We sell a pretty decent size Vacuum Chamber that is approx 10" in diameter and 12" tall (probably overkill for the amount of materials you typically mix up). The Robinair is able to pull 29" of Hg in about 1 minute. We've found that 29" of Hg is the magic number to make rubber and resin degas very quickly. 28" of Hg works but may take too long. For whatever reason, when you hit 29" of Hg the material starts dancin'. The lower the cfm, typically the longer it takes to reach the sufficient vacuum needed to effectively remove the air. Also the smaller the vacuum chamber, the less volume is in the chamber, and the less time it will take a pump to pull down the same amount of vacuum.

I am not a pen turner but am very intrigued with the process ever since a couple on this board starting teaching me. They started by asking me a few simple questions about our Water Clear and now I think I've asked them 5 times the questions they've asked me. But from my perspective, I believe that yes you can simply mix the resin, degas it and slowly pour a perfectly clear blank that is ready to turn without any pressure. I say that because this is the exact process most people use when casting Water Clear parts with our resin. Since most mold makers already have vacuum and may not have pressure, they simply remove the air from the system before pouring. The only thing you have to be careful about that the pressure takes care of for you is the air bubbles formed when you pour. That is why as Fred_erick mentioned, tip your mold on an angle and pour it slowly down the side to avoid the waterfall affect of introducing air while pouring just as you would a tall cold one.

Mike
Alumilite
800 447-9344

 

[Tanner]

Thanks Mike, I have some Alumilite and some of the dye's you guys sell. I'll be giving it a try soon.