Thought I'd start a new thread on this, rather than adding it to my "I'm back" thread. The vibrating base for the vacuum chamber is set to go. Roughly speaking, I started with the design that this guy described on YouTube: His is a lot bigger than I needed, and is used for vibrating concrete molds. But the basic design worked: Build a steel base, use valve springs (I used some off an old Kawasaki motorcycle) to connect it to a "table", attach a vibrating motor, and Bob's your uncle. I used of 1.5" mild steel square tube for most of the fabrication. I used a little bit of 1" square tube for the two little pieces that actually hold the motor. That was needed to create some clearance between the bottom of the vacuum chamber for the motor bolt heads. I didn't have any sort of motor lying around. Called a few appliance repair places, and they'd sell me one out of a washing machine for $25 ish. But by the time I factored in all the various bibs and bobs it would take (pulleys, bearings, shafts, belts, etc, etc, etc) to make it work, not to mention additional fabrication time, I realized that buying a purpose built vibrator from Grainger was the better option. I ended up with this: The motor mounts underneath: I built the vacuum chamber itself out of 1" Lexan. Spent quite a bit of time trying to work out how to attach it to the table. Ended up deciding to bolt it down solid, which meant drilling holes through the bottom. I was worried that the bolts would end up wearing on the Lexan and maybe creating cracks, so I made a couple of strips out of 2" x 1/8" steel to hopefully spread out the stress a bit. Time will tell how this holds up. The whole setup looks like this (without the lid, natch): At the moment, it's all just dry fit together to make sure it was all going to line up. Next step is to take it back apart, torque and Locktite the nuts, and figure out a way to seal up the holes in the bottom of the chamber so it holds vacuum. God willing, everything will come together such that I can do a pour by the end of the week and see if all this solves my air bubble problem.
Locktite and Lexan are not a good match - chemical stress cracking. Find some silicone that is specifically formulated for use with Lexan. 3M says their 4000 is compatible with Lexan, but there are others. Also, keep an eye on the spring welds for fatigue cracking. I was not aware of the existence of the little vibrating motors you chose. Learned something today that I will probably put to use next spring in the garden.
Looks good. Looking forward to seeing how the vibrator does. I was eyeing a much smaller knockoff thinking it'd be good enough.
That looks very nicely done Omaha. You'll have to let us know how the vibrator performs. I was tempted to buy one or several of the import equivalents for my lost foam rig but I think they may be a little bit underpowered for me..........I'm trying to shake/pack 300-500lbs in a barrel suspended on dies spring. I do it now with pneumatic turbine vibrators but they are power pigs. Best, Kelly
We have those vibrators (but larger) on our sodium bicarb silos at work. I can feel them when they run up in the control room. That's about 100 feet away, and on the second floor... so I'm guessing they could do what you need....
I'm betting those are much larger. The one in the OP's post are probably fine for agitating smaller masses like the OPs, but I never bothered with them because even if they were 100% efficient, at .07kw, they're a very small fraction of the pneumatic energy being expended on my rig and I'm still underpowered on my big rig. They'd also be a small fraction of the power applied per pound to the commercial vibed flasks. Lost foam mold vibration takes a lot of power. That G25 turbine vibrator is about right for a 5 gallon bucket of silica sand which weighs about 65lbs. It G25 uses about 16 scfm at 90 psi. My %HP compressor can barely manage one continuously. You'd have to make an educated guess about efficiency of each device but no matter what, that's a lot of power compared to .07kw. When it comes to vibratory packing, there is frequency and there is amplitude, and both matter. Multiples of the smaller vibrators will not do what a single higher power/amplitude unit will do for larger masses. I initially opted for a G25 and four smaller G8s because I thought there was no way I could pull 5 G25s but I have since replaced two of the smaller units with G25s. I can charge the 80 gallon tank to 150 psig, run them (at diminishing power) for a short time say a minute or so, then recharge and repeat if needed. A minute or two with that very high power does a far better job than all day with the smaller vibrators. The rig also sits on die springs to make as unstable and easy to excite as possible. I might even replace the last two smaller vibrators but I think I'm starting to bump into the pressure drop limits of my 1/2" ID hose from the compressor tank. What I have seems to do fine for 30gal/400lb+ flask. It gets another 10gal/70lbs with the flask extender. I vibe as I'm filling because the pattern is in the lower part of the flask and the mass is lower. The top of the mold is just sprue and cup which is much less critical. I thought about making my own vibrator with double shafted 3ph or dc motors so frequency could be varied.......but think what I have is good enough for most of what I do. But......I need more power (and coffee) Scotty! For the OP, you have a spring table so just keep the mass as low as possible. You might experiment with the position of the vibrator.......it can make a noticeable performance difference. What do you figure the whole thing weighs with a load of investment? Best, Kelly
I didn't weight the chamber itself, but it's fairly heavy. Probably about 20 to 30 pounds. The frame it attaches to (the part above the springs) probably adds another ten. A fully loaded flask comes in at 45lbs. So all in, probably looking at something like 90 to 100 pounds. The motor I got has a rated "Bin Weight Capacity" of 704 lbs, but I really don't know what that means. I did do a test where I filled a flask with water and set it in the chamber. Just judging by the action on the top of the water, it's getting a lot of vibration, but no telling if that means anything. I've got a few more molds to make, then I'll do an investment probably on Friday. I'll shoot a video and post it.
First test pour is complete. Sorry, I didn't get a video of the vibrating vacuum chamber in action. From the looks of it, I have to say this was a complete success. I haven't media blasted the piece yet, but so far I can't see any air bubbles anywhere.
