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  • lakeside53
    replied
    Originally posted by Paul Alciatore View Post
    It seems to me that the biggest problem with epoxy dispensers is one or both of the components tend to harden somewhat when exposed to air, even small amounts of air. This tends to say that you really want a new, fresh dispenser after a period of time, perhaps a year or so. In any case, it would be a very good idea to keep any air out of the reservoirs.

    That is my experience with the available dispensers. Use them often and no problem - go back to them after a few months and one or the other is gooped up and almost impossible to clean.

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  • lakeside53
    replied
    Originally posted by Paul Alciatore View Post
    And, I have never had any real problems with matching the amounts of equal part epoxies. The modern epoxies seem to be tolerant to small mistakes in the proportions. I wonder if you are seeking a solution to a problem that does not really exist.
    It's "tolerant", but... if strength or adhesion is an issue, you really need exact proportions or the excess parts just stays as a liquid trapped in a lattice of hardened material.

    Very small quantities are the most difficult to get right.

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  • lakeside53
    replied
    Those work for the quick set junk, but are almost impossible to press with the real (thicker) stuff.

    Postage scale is the easiest for small quantities.

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  • J Tiers
    replied
    The pump would be easier than these?



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  • Glug
    replied
    I also like the idea of a peristaltic pump. Partially because it would be a fun project to make. But I think it should be manual. The diameter of the drive/pump ring will determine the volume for each degree of turn. I think the metering could be very exact once you get it primed. The thickness should maintain the prime.

    Maybe you could use some little metal flip caps, like on olive oil bottles, to isolate the epoxy from air and dust (I'd make those)? Or enclose the whole thing in a nice little wall mounted box, under a cabinet.

    I wonder if silicone tubing could be used, as purchased at hobby shops for fuel? Or would the residual silicone impact the performance of the epoxy? I like the way the silicone responds to squeezing by the pump roller, as compared to less flexible tubes.

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  • boslab
    replied
    How about a couple of small pistol type grease guns, the grease delivery tube is usually rigid but a shorter flex cut in two would suffice those things can squeze viscous stuff?
    Mark

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  • superUnknown
    replied
    Move fluid safely from here to there with this very nice little pump. Unlike most liquid pumps, this is a peristaltic type - the pump squishes the silicone tubing that contains the liquid ...


    $25 peristaltic pump. Use them for accurate reagent dosing, they'll pump up to 14 PSI when run on 12VDC. Considering a Cole Parmer peristaltic pump is $1200, these are amazing little geegaws.

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  • Paul Alciatore
    replied
    It seems to me that the biggest problem with epoxy dispensers is one or both of the components tend to harden somewhat when exposed to air, even small amounts of air. This tends to say that you really want a new, fresh dispenser after a period of time, perhaps a year or so. In any case, it would be a very good idea to keep any air out of the reservoirs.

    And, I have never had any real problems with matching the amounts of equal part epoxies. The modern epoxies seem to be tolerant to small mistakes in the proportions. I wonder if you are seeking a solution to a problem that does not really exist.

    Leave a comment:


  • darryl
    replied
    Waste in this case would be what's left in the pump and lines at the time I'd be throwing the whole thing out. Otherwise as I refill the 'tanks', the old gets used up before the new comes in. I would have to make sure I always put the supply in the proper tanks

    I don't have a production environment, but there are often times that I'd mix up a dozen or more small batches in an evening- probably do this on average about once every week or so. Mixing is easy as I just poop it out onto a non-absorbent surface and stir it around with a toothpick- usually the same tool that I'm applying it with. That's not likely to change. I just want easier metering of small volumes and not have to mess with caps. Must be related to OCD

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  • J Tiers
    replied
    If you are not doing this on a production basis, why go to the trouble?

    Most types are available in dual piston dispensers, and there is no real requirement to use the mixer tubes if you are not using really fast cure stuff, and are careful about mixing by hand. Even the box stores have dual piston dispensers for some varieties.

    You wanna talk about waste.... all the stuff between the peristaltic pump and the nozzle that sticks to the walls and won't pump back.... For non-production-volumes, the whole approach seems like an unbelievable mess and hassle.

    Suit yourself, though.

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  • lwalker
    replied
    One of the standard ways to do this is with replaceable syringes in controlled slides. Each slide moves a measured distance to dispense the desired amount of fluid. This allows you to create infinitely variable mix volumes. Imagine a holder for the epoxy syringe that has a leadscrew and a stepper motor to drive the syringe piston the distance needed.

    The machines I work on (I write the control software) will normally use a single piston or syringe pump with solenoid valves to allow aspirating fluid from multiple locations. Since I'm an electrical/software guy, this is easier for me to visualize than a purely mechanical method.

    We also use peristaltic pumps, but they aren't as precise.

    Now the question: after you have a precise fluid dispense, how do you mix it?

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  • GadgetBuilder
    replied
    You can purchase pumps and epoxy from West:


    The pumps aren't expensive but the ratio of epoxy to hardener may not match the epoxy you're using. You could get two epoxy pumps and work out the ratio for your epoxy.

    The West epoxy works well, commonly available at boat yards where it is used for fiberglass repairs.

    John

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  • firbikrhd1
    replied
    Not a very exotic answer, but 50 cc syringes are available as are 100 cc units. A couple of those, one with each part of the epoxy and you can accurately meter out what you need regardless of the ratio. Clean 'em up with alcohol and use 'em over.

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  • darryl
    replied
    I've also considered something like a peristaltic pump- what I had in mind was a flexible chamber that would be alternately squeezed and then released. One way valves would direct the flow of fluid. You would have valves but no seals and pistons. During the release phase, the chamber would have to return to shape via its own power of elasticity. Having that 'softness' as it were, it would likely be more subject to detrimental effect by the fluid it's handling.

    You could use a diaphram, and then of course you'd have to make sure it could 'inhale' and expel a fixed volume of fluid for each activation. Could be done I suppose.

    In either of these methods, I've thought to use a hydraulic fluid on one side of the device- that would be controlled with a piston and cylinder. The difference would be that the piston would be working in the hydraulic fluid and not the fluid being pumped. Still though it seems like a less precise method- maybe I can think about this more.

    A long time ago I considered how I could use surgical tubing as part of a vacuum pump- again the idea was to remove the need to have seals and pistons involved in the actual pumping. The idea was to contain and pressurize a short length of surgical tubing inside a cylinder. Ideally, the shape inside the cylinder would be exactly the shape the tubing would take when inflated. Then when you let the pressure out, the tubing would collapse and draw a vacuum behind it. As a pressure pump it would be inflated to force the volume between the tubing and the cylinder to evacuate through a one-way valve. Releasing the pressure would cause the tubing to shrink, drawing in a fresh charge of whatever is being pumped.

    My experiments along these lines used typical 1/4 inch surgical tubing and lengths of about six inches. I found it would inflate up to about one inch in diameter before reaching a point where it 'got tight'. From this I determined that I could have it expand to about 3/4 inch (inside some 3/4 inch ID tubing perhaps) and it would remain undamaged over many cycles and a reasonable length of lifetime. My last experiment with the tubing was to continue to inflate it as hard as I could until something let go- and it did. It blew very loudly and disappeared. All I had left was two ends and a ringing in my ears.

    In a very conservative constraint of operating parameters though, this could make a good pump. Likely the tubing would be more affected by the fluid when it's inflated, and in any event it would have to be tested.
    Last edited by darryl; 03-22-2014, 11:14 PM.

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  • garyhlucas
    replied
    A twin tube peristaltic pump will work very well if you make it reversible. Pump out what you need, reverse to push it all back in the bottle. I happen to sell industrial ones and many of the them don't even have rollers. They just have sliding shoes, lobes on a shaft and they lube everything up with silicone grease. A rotor with three lobes would work great as a manual pump. The big pumps adjust the occlusion (squeeze) of the tube with shims under the lobes. Once it is set no need to adjust again.

    You could also look for stackable peristaltic pump heads on Ebay and just make a manual drive handle you hand crank.

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