Mark's First investment casting

[aarggh]

How strong a vacuum can one get with a venturi vacuum setup?

With a good quality venturi the best I could pull was around 25-26 on a good day. With the rotary vane pump I could pull a fraction over 29 from memory.

 

[ajoeiam]

With a good quality venturi the best I could pull was around 25-26 on a good day. With the rotary vane pump I could pull a fraction over 29 from memory.

I'm thinking its not the level of vacuum that's going to be my issue - - - - its the cfm capable.

Any info on that?

Have toyed with using a roots blower and using the suction side.
Just that's a bunch of $$$$$$ and I'd like some idea that the project would be successful before I spend the beans!!!!!!!!

 

[stanstocker]

Hi Folks,

Would a low cost HVAC vacuum pump do the job? Might want to fill up empty space in a large vacuum pot with "stuff" to reduce the pump down time. The one from amazon was around $100 and pulls down a line set and inside unit in a few minutes. The lowest cost units are around 2.5 to 3.5 CFM, they are readily available from makers like Robinaire in up to 8 CFM. Maybe not fast enough for vacuum casting, but might be fine for degassing. I don't have a vacuum pot, so can't do the boil a cup of water test to check this. Here's a video on making and showing a home made vacuum pot using one of these pumps to degas silicone.



Now there's another project on my "It would be neat to do" list!

Cheers,
Stan

 

[dnalot]

Update

I have determined that my old vacuum pump has about 1.5 CFM of flow and I think twice that is needed. The vacuum chamber I ordered finally arrived but the way they mounted the manifold to the pot is crappy. It allows the manifold to wiggle around and it does not seal. So before I can move on I need to get another pump and fix the vacuum chamber. I have an old portable compressor that has a pump that looks just like my vacuum pump but is twice the size. Something is wrong with it as at about 60 PSI the motor bogs way down. If I can get it to run properly I will replumb it to be a vacuum pump. I also have a V-2 compressor pump with a 3 HP motor. Way bigger that I want or probably need.

Mark T

 

[ajoeiam]

Update

I have determined that my old vacuum pump has about 1.5 CFM of flow and I think twice that is needed. The vacuum chamber I ordered finally arrived but the way they mounted the manifold to the pot is crappy. It allows the manifold to wiggle around and it does not seal. So before I can move on I need to get another pump and fix the vacuum chamber. I have an old portable compressor that has a pump that looks just like my vacuum pump but is twice the size. Something is wrong with it as at about 60 PSI the motor bogs way down. If I can get it to run properly I will replumb it to be a vacuum pump. I also have a V-2 compressor pump with a 3 HP motor. Way bigger that I want or probably need.

Mark T

Where did you find that V-2 vacuum pump - - - - that's a size I'm looking for!

 

[dnalot]

Where did you find that V-2 vacuum pump

In my shops attic. I have a lot of old stuff up there. It is a compressor now but could be used as a vacuum pump.

Mark T

 

[dnalot]

Well that sucks. But in a good way. 20 years ago I bought a portable compressor at an auction for $20. I never really needed it and it had a problem in that it pumped slowly after getting to about 60 PSI. So now I need a vacuum pump for the lost resin casting project. This morning I bundled up and went up into the attic of my shop and found the old compressor and brought in down to the shop. A little squirt of oil into the inlet port fixed the slow pumping problem. I hooked the vacuum side of the pump to the 3 gallon vacuum chamber and let her fly. 55 seconds and I had about 26.5 HG. (I am at 1500 feet elevation) I don't know how many CFM it is. No nameplate, just a sticker that says 1HP 15 Amps, made in USA. I think I'm in business.

Mark T

Update: I found this compressor on E-bay and at Grainger. Price $1,385 (WOW) Thomas compressor/vacuum pump model 2807CE72 ~ 6.6 CFM. E-Bay had a used one for $750

 

[dnalot]

Update:

Good Bad and Ugly

I have been keeping busy working out what size element works best in my homemade kiln. And getting a proper size vacuum pump and vacuum chamber setup. During this time the patterns I had printed with castable resin sat on a shelf and warped. So lesson learned, print and cast right away. I used the patterns anyway.

My second attempt was not as good as my first. Two problems, first my plaster was probably to soupy. And that caused problems that resulted in cracks forming in the plaster during burnout. The cracks fill with metal and leave flashing on the parts. I had lowered the first stage of the burnout from 300 degrees F to 230 degrees F and should have lengthened the hold time by and hour. The second problem was pouring my brass at too low a temperature. I could tell I had a problem as soon as I poured. You can see the difference in the surfaces of the spurs. Could also be problems with the flask temperature. My first go the flask was cooler by 100 degrees.

I need to keep better records of what I have done, what worked and what did not.

Still there was a bright spot. The little wheel turned out OK and demonstrated how thin a part can be and still cast completely. The spokes are .060” wide and .040” thick. The little speed handle cast OK as well but I bent it cleaning the plaster off ( and then broke it off). This part needs to be cast in Bronze, the pokes are to soft and bend easily. After a light sand blasting it looked like a usable part.

Burnout was complete and that is good to see. Perhaps I can shorten the final high temp hold time a bit. And I had far fewer and smaller little metal balls on the parts. Most all of them would pop off with a little pressure with a pocket knife. I was much better organized this time and I think my problems are entirely operator error.

 

[Richard Hed]

Update:

Good Bad and Ugly

I have been keeping busy working out what size element works best in my homemade kiln. And getting a proper size vacuum pump and vacuum chamber setup. During this time the patterns I had printed with castable resin sat on a shelf and warped. So lesson learned, print and cast right away. I used the patterns anyway.

My second attempt was not as good as my first. Two problems, first my plaster was probably to soupy. And that caused problems that resulted in cracks forming in the plaster during burnout. The cracks fill with metal and leave flashing on the parts. I had lowered the first stage of the burnout from 300 degrees F to 230 degrees F and should have lengthened the hold time by and hour. The second problem was pouring my brass at too low a temperature. I could tell I had a problem as soon as I poured. You can see the difference in the surfaces of the spurs. Could also be problems with the flask temperature. My first go the flask was cooler by 100 degrees.

I need to keep better records of what I have done, what worked and what did not.

Still there was a bright spot. The little wheel turned out OK and demonstrated how thin a part can be and still cast completely. The spokes are .060” wide and .040” thick. The little speed handle cast OK as well but I bent it cleaning the plaster off ( and then broke it off). This part needs to be cast in Bronze, the pokes are to soft and bend easily. After a light sand blasting it looked like a usable part.

Burnout was complete and that is good to see. Perhaps I can shorten the final high temp hold time a bit. And I had far fewer and smaller little metal balls on the parts. Most all of them would pop off with a little pressure with a pocket knife. I was much better organized this time and I think my problems are entirely operator error.

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That's very VERY nice

 

[propclock]

Very Nice indeed!