vaccum caster pump.

[owen bush]

I would like to make a vaccum caster , in the uk these are quite expensive as finished units (nearly 2000 dollars) . and they seem to be quite simple as machines go.....

I am after information on the spec of pumps in these machines so that I can go about finding a suitable donor pump.

Thanks for any info in advance.

all the best Owen

[J.Arthur Loose]

Hey Owen, I've been looking for an old fridge pump to do the same thing, as I've heard that will do the trick, though I want it for the investing side of the process. I have a centrifugal caster but my little vibratey investment thingy doesn't get rid of bubbles nearly as well as a vacuum pump. I have an old compressor and thought to simply hook up the reverse end of things but I think it would be hard to control the pressure and the bell jar might implode. I hear it's bad news when this happens.

 

I don't know if the fridge pump would be enough for the actual casting part of the process though. I'd imagine the compressor would... Maybe that's helpful and maybe it isn't.

[Howard Clark]

Vacuum pumps are always wet in an oil bath when they run. Refrigeration service pumps will work, but you need a reservoir plumbed into the system, which is not a big deal. I don't know if an air compressor would pull enough vacuum. A piston type refrigeration compressor certainly will though.

 

I have all the components but have yet to set up a working system. I think I am going to have the table mounted on springs, and use both vacuum and a vibrator to get the bubbles out.

 

I think you'll be able to get a system together, Owen. You have good scrounging skills.

[Patrick Hastings]

There is another way at least for investment...

Drawing a vacuum on it makes tiny bubbles grow large enough that they can't help but to float to the top well that is how its supposed to work. As we all know they tend to need a little help sometimes by tapping and drawing again or using vibration during the draw... However This causes the dreaded boil over of the your flasks and its really messy...it also does not deal effectively with any bubble traps that are underneath the model "trapped in the umbrellas". it can also damage your delicate parts if there are bubbles in your wax model...

Another approach is to reverse the strategy... By putting the bubbles under pressure and making them disappear entirely. Using a pressure vessel and the compressor you already own, you bring your flasks up to about 80-90 psi. Allow them to cure to green hard while under pressure. The gas bubbles do not just shrink they go into solution and are no longer bubbles even in the umbrella zones. Once the investment sets the pressure can be released without the bubbles reforming...

I built my own pressure vessel out of a portable air tank. it took about a day to fabricate the lid and lock downs. Buying the tanks new and the hardware came out to less than $40 I think...

Patrick

Edited October 11, 2011 by Patrick Hastings

[Howard Clark]

Thanks Patrick ! I had not thought of that. Many advantages there.

[owen bush]

I am looking at casting under vaccum....... I guess that would work under positive pressure as well ?

or would it?

[owen bush]

thinkoing about it more I am sure that removing the gasses in the mold as well as sucking the bronze/silver/whatever in is more important than the pressure aspect.

[Sean McGrath]

Owen, I don't know about England, but the best way to get a good quality refrigeration pump here is to talk to a large HVAC shop. Before I retired, that's what I did for a living, and most of the companies that I worked for had at least a couple of high quality, but well used pumps setting around in their shops. Sometimes they use them for spare parts, sometimes they will eventually get around to rebuilding them, but most just end up setting around collecting dust, or taken home by an employee to do service work on the side. If you know a service man, or anybody else in the HVAC trade, ask him/her if their company has any used units that they would sell.

 

In the US, if it is a name-brand unit, there are generally factory re-build kits for them. That may be a way for you to get a high quality pump considerably cheaper than new. I've never rebuilt one myself, but from what I understand it's not hard. I've got a few friends keeping an eye out for one myself. I intend on using it with an aluminum paint-pot (looks kind of like a pressure cooker), to stabilize my own wood.

 

Edit:

I don't know if the fridge pump would be enough for the actual casting part of the process though.

If you're talking about speed, I would think you could adapt a portable air tank. Instead of filling it with compressed air, you could draw a vacuum on the tank instead, then use a ball valve to control how fast it sucks the air out of your mold.

Edited October 11, 2011 by Sean McGrath

[Greg Thomas Obach]

Hi Owen

 

i built one with a fridge compressor for stabilizing wood... even did a tutorial on it

http://primalfires.yuku.com/topic/1027/Stabilizer?page=1

 

it worked ok ...not a heck of strong vacuum but worked with linseed oil n turps

 

myself, i'd fear that it wouldn't pull enough .... fast enough ... to get the effect you need in time (before the metal solidified )

 

Howard has a solid plan...with the bigger compressor.. or even a scientific vacuum pump which tend to come up in the local bargan hunter for 100 to 300bucks

 

or heres an idea... what about a large pvc pipe and a sorta rubber plunger/seal on the inside... sorta like a giant syringe ... the idea is that you pull it quickly and get a fast vacuum within your vessel ( how much mercury you can pull, i haven't a clue

-- errr.. and it'll be cheap aswell

-- but so is a free fridge compressor

 

oh... and becareful... the bottom of my fridge compressor was filled with alot of oil... just keep your pipes aimed upward to keep the oil in the bottom of the apparatus

 

 

Greg

[Patrick Hastings]

I am looking at casting under vaccum....... I guess that would work under positive pressure as well ?

or would it?

 

I was speaking specifically of investment. There such a thing as pressure casting metal, but it is not a do it your yourself operation IMO...

In Vacuum casting you have to keep in mind that your never really going to draw a high vacuum of any kind. The investment is porous and the air gets sucked into and through it to no end. Its more about moving a volume of air. So there is no need to get a pump that can pull high vacuum (they are more expensive anyway). I would look for middle of the road vacuum wise and go more for volume.

The idea of a vacuum storage tank is something I have considered, but never tried. I think if the tank was large enough it might work great. It would enable you to use just about any pump as you could take as much time as you need to draw it in advance. You could take advantage of the instant strong draw on the flask and take advantage of larger diameter plumbing if needed.

patrick

[cdent]

....Another approach is to reverse the strategy... By putting the bubbles under pressure and making them disappear entirely....

 

 

Very interesting idea, good to know there're viable options that are easily doable. I always assumed (I know) that the density of the investment needed vacuum. Maybe more flash or surface finishing without vacuum, but I never thought to try any other way.

 

If someone prefers vacuum, the bay has occasional great deals on vacuum investment mixers, try 'whipmix'. They usually come with the mixing bowl and have a vibration 'arm' built in. Doesn't help with the casting part, but the vacuum tank concept is another great idea.

 

Take care, Craig