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  1. #41
    Registered drcrash's Avatar
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    (doubled/mangled post deleted... sorry... see next one)

    Last edited by drcrash; 05-31-2007 at 11:55 AM. Reason: double post


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    The VE2100 is 10 CFM of free air flow on 220/50, the 2TW-1E was 2 CFM on 220/50. Yes, both will pull a tank to 30"hg. How long it will take from 20"hg to 30"hg verses the size of tank that would match the job well, is where the trouble can start. I could not find a chart that shows either pumps performance curve in that regard.

    The problems I have seen with this style of pump is that the oil traps contaminates which if not changed regularly can kill the pump. That includes tank rust, moisture and wood particles. I've tried filters, but when they get clogged, the vacuum flow is restricted. Too much trouble compared to the oiless pumps in my experience.

    The larger oiless rotary vane pump itself without a motor would cost about as much as these oil filled pumps that come with a motor. Spare motors may not be as easy to come by in your area?

    Your circumstance may direct you to buy what is available without the addition work of coupling the motor to the pump. Either way, get the largest free air flow as price and availability you can afford and see how it performs for your immediate needs.

    DC



  3. #43
    Registered drcrash's Avatar
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    Quote Originally Posted by tomoohoi View Post
    I don't understand , why vacuum pump (with 12 CFM , 0.3 pa ultimate vacuum ) create not strong vacuum in tank, (only 20" ???)

    as i understand , if ultimate vacuum is 0.3 pa , 30 in.hg - 0.3 pa = 98067 pa - 0.3 pa , ie, allmost 30 in.hg strong vacuum it tank , is it that ?

    0.3 pa ultimate vacuum = 30" - 0.3 pa pressure vacuum in tank .
    ie , vacuum gauge which connected to tank will show 30" ???
    That should be fine. (Much better than you need, actually.)

    You don't really need to pull the tank down very close to a perfect vacuum---once you've gotten 80 percent or so of the air out of the tank, there is not much improvement to be gained by getting the last little bit of air out.

    A pump that only pulls 24 inches of mercury can be very good for vacuum forming. 20 inches actually isn't bad for relatively thin plastic.

    A more important is whether you can evacuate your tank quickly enough. A "12 CFM" pump only pumps 12 cubic feet per minute at the very beginning. As the air in the tank gets rarefied, each pumping action removes less actual air, so it takes a lot longer to approach the maximum vacuum than the CFM rating would suggest.

    (It is often not worth it. If 20 inches of mercury gets you good detail for your material and thickness, it is not worth waiting twice as long for your pump to pump most of the remaining air out, and wearing out your pump that much faster.)

    How fast a pump you need will depend on your tank size and your vacuum forming cycle time requirements. If you need to maximize production, and not wait on a slow pump, you need a fast pump. If you are not producing a large number of parts, that may not be an issue.

    Since you are making molds, and they may be used many times before you need to vacuum form new ones, cycle time and speed of pumping may not be an issue for you.

    It sounds to me like your pump is not your problem right now. If it is getting most of the air out of your big tank quickly enough for your needs, do not worry about it.

    You need to make sure that your plumbing is working correctly and that you are heating the plastic well.

    I suspect that you have a leak or a bottleneck (flow restriction) somewhere. Either your plumbing is pulling too much air in from outside, and not enough from under the plastic, or it's not pulling the air out fast enough (before the plastic cools too much).

    It is hard to tell where the leak or bottleneck could be without details about your platen, valves, etc.

    If your plastic is not hot enough around the edges, it may not make a good seal to the edge of the platen. If the platen edge is not very smooth, that could be the problem.

    If your valves' throats are too small, or any fitting between the tank and the platen is too small, you could lose most of your air flow at that point.

    (Some tanks have small connections for pipes, because they are not meant to be filled or emptied very quickly. Attaching a larger pipe doesn't do much good if that hole is too small.)

    If your molds sit too closely over the vacuum hole(s) in the platen, they can restrict the air flow. You need enough space under the molds for air to flow around and under them to the hole(s).

    Can you take photographs and post them?

    Can you explain your plumbing diagram? Please say what each valve is supposed to do, and how you operate it. I don't understand your design.

    I got the impression that you were trying to operate it in two stages, using the pump alone for the first stage, i.e., the initial pull-down. Unless you have an extremely fast pump, that will not work. That would explain why your plastic would cool before being pulled down enough.

    I am not sure you understand the logic of two-stage plumbing. The first stage should get most of the air out as quickly as possible, and the second stage should pull the plastic down hard. Normally a vacuum pump can't pull air fast enough for the first stage, by itself, so you must uses a lower vacuum but higher volume pump (such as a vacuum cleaner), or a vacuum tank with big enough pipe into it.

    (The first-stage tank doesn't have to be very big, but the piping into it must be big enough that it can suck the air out from under the plastic very quickly. You should be able to switch to second-stage operation within a second or so.)

    For now, I'd suggest simplifying your plumbing into a one-stage system. That should work fine. If you want two stages, you'll need another tank for the first stage. It does not need to be very big---about twice the volume of the air under your plastic.



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    If you're interested in two-stage plumbing, you might want to read this three-posting series I just posted:

    http://www.cnczone.com/forums/showthread.php?t=38493

    It may explain one- and two-stage plumbing ideas more clearly than I've done before. (Let me know if it helps.)

    But for now, I'd work on getting one-stage plumbing to work. I think your pump and tank are probably fine for that.

    (Two-tank, two-stage operation would probably save wear on your pump, but that's not your pressing problem right now.)



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    Default Re: building a vacuum /thermoforming machine

    i saw vacuum pump: 1/3HP, 220V, 50Hz, 120l/min, 8,5kg, ultimate vacuum 0,5bar... my question is. Will this vacuum pump make up only 0.5 bar in my 160liter tank?or i need buy pump at least 1bar ultimate vacum? sorry for my language...



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    Default Re: building a vacuum /thermoforming machine

    In the packaging industry, pressure forming is one of the ways that blister cards are formed. We use pressure, just shop air, the top pressure plate just has a 1/8 o ring around the od, the forms we use are aluminum (you'll need to drill a lot of small air bleed holes) for a standard single ought capsule I use two .o3 holes to release the air as the pvc comes into the form. I don't think the temperature gets over 250 deg f. But you'll have to heat it pretty much evenly. Our blister machines just use an aluminum plate with cartridge heaters in it, but it's only about 12" x 8", so getting a 60 x 60 plate hot all over might be a challenge. On our blister machines the heat plate comes down while the pvc isn't being pulled and is raised by air cylinders about 2" when the material is being pulled or the machine is stopped. I don't think vacuum forming will work anywhere as well as pressure forming. And no, it isn't a bomb. The air will leak out of the pressure plate because you'll never get a perfect seal.



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building a vacuum /thermoforming machine

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