Sticky Stuff Dispenser – Care and Feeding

I’ve got a Sticky Stuff Model A Dispenser made by Michael Engineering that I use to dispense my resin.  It’s got a static mixer mainfold, which means I can dispense fully mixed resin from the pump using a disposable static mixer.  Lately, it’s been giving me problems.  I wil freely admit, these problems have been self inflicted.  It all started when the resin seemed to be dispensing at a much slower rate, and instead of thinking “hey, maybe there’s a partial clog in the mixer manifold” I thought “hey let’s just lift up hard on the handle.”  Well, shortly after that, I noticed that the seal on the bottom of the resin piston was leaking a tiny bit.  Then one day, I felt something catch when pushing the handle down, and that was the end of that seal – it just started spilling resin out the bottom.  Whoops.  I promptly ordered a new o-ring seal, and set about tearing the machine down once it arrived.  I figured while I was at it, it would be a good time to do a few upgrades and checks to the machine.

First, replacing the failed o-ring.  You start by getting the pump block off the machine.  The check valve at the bottom of the reservoir must be removed.  Disconnect the springs from the handle.  Then the hard line leading to the manifold must be removed.  Remove the two bolts securing the pump block to the frame and the pivot bolt at the end of the handle.  After that, the block can be freed from the frame.  After cleaning the block with acetone, I pulled the old o-ring out of the block using a pick awl.  I wasn’t able to get it out without breaking it, but hey it’s already broken:

The inner surface of the o-ring seemed to be quite flat but didn’t seem to have any real big visible nicks.  It occurs to me that my practice of using a heat gun to get the block nice and toasty might have backfired by making the o-ring soft and allowing it to deform.  That could have been where the problem started, but I noticed that there was a decent amount of hardened resin (just air dried) on the bottom of the pump piston.  That hardened resin could have cut a small groove in the o-ring, making it fail.  Like I said, I’m sure my problems with the unit have been self inflicted.  Anyway, once I got the new o-ring in, and thoroughly cleaned and inspected the pump piston, all that was left was re-assembly.  The piston was lubricated with some lube that was provided by Michael Engineering.  The piston should be mirror-like and free of any scratches or resin.

The piston was far harder to get back in the block with the new o-ring installed, which I took to be a good thing, but once in it slid easily with very little friction.  After putting everything back together, and putting some resin and hardener back in the reservoirs, all that was left was to test the new seal.  I tightened down all the fittings going to the manifold, and noticed that one had indeed become a little loose.  Any air that leaks into your lines can cause metering problems and introduce air into your resin, so you really want to check these things every once in a while.  Anyhow, when you prime the pump, you don’t want to waste all the resin that you’re pumping through just to get it primed.  So, I insert some 1/4″ plastic line I get at my local hardware store into the holes in the mixer manifold, and pump into separate small cups. 

This way I can keep the resin and hardener separate and then dump them back into the reservoirs.  Since it can sometimes take 10 pumps to get it fully primed, this would otherwise be a lot of wasted material.  The new seal works perfectly, nothing spilling out the bottom.  This was a good opportunity to do a ratio check, since I hadn’t done that for more than a year.  The particular resin I’m using – PTM&W PT 2520 A/B is a nice high temp laminating epoxy.   I like it very much – you get a very high service temp with a room temp setting resin that is relatively easy to use.  It takes quite a while to cure to the point where it can be de-molded, but I’ve found that with electric blankets it can be taken off the mold in 10-12 hours.  The ratio for this resin is 100:16 by weight.  To check the ratio, all you have to do is tare out the weight of the cup you’re using to measure with, and then weigh the resin and hardener separately and divide the hardener weight by the resin weight.  The first check looked like this:

Hardener: 11.7 grams

Resin: 75.8 grams

Ratio: (11.7/75.8)*100=15.4:100

I’d like it to be a bit closer than that, and changing the ratio is fairly easy.  The bracket that attaches the hardener piston to the lever arm has a bolt which can be loosened, and then the bracket can be slid along the lever arm to change the ratio.  In this case, I wanted more hardener, so I slid the bracket a bit to the right, and then re-checked.  A few times back and forth, and the bracket ended up about 3/32″ to the right of its’ original position.  The ratio now looks like:

Hardener: 11.6g

Resin: 72.7 g

Ratio:15.95:100

Okay, that’s better.

The last thing to do is to check that the static mixer is adequately mixing the resin.  The key here, beyond the proper ratio, is that the TIMING of the resin and hardener must match.  This means that when the resin starts to dispense, the hardener starts at the same time, and that they also stop at the same time.  If they are significantly off, even if the ratio is correct, you could end up with some parts of your resin not being properly mixed, since a small portion of it may be under of over catalyzed.  If the timing is off, the likely culprit is the exhaust check valves on the front of the pump blocks.  Just take the fittings off and clean everything down with acetone and then re-assemble.  I had this happen once, and it took all of five minutes to fix.  Ralph at Michael Engineering says that often times the contaminant is so small you won’t even see it when cleaning the check valves.  Since the timing looked perfect, I put on a static mixer and got it cleared of air with just a few pumps.  Then I dispensed three full pumps into a cup, and without any secondary mixing or swirling, set it aside to cure.

The resin cured fully within 18 hours and had absolutely no sticky spots or areas that appeared to be uncured.  If you look carefully at the pic above, you’ll see there’s something in the resin and hardener reservoirs – I bought some aquarium heaters at Petco to try to raise the temp of my resin and hardener a bit.  I also got some aquarium temperature gauges, which proved to be useless and were later removed.  The resin is indeed a bit warmer – now coming out around 80 F, but I would ideally like it to be even hotter – around 90 or so.  That way it will flow down into the fabric quickly and easily.  I don’t worry about this stuff exotherming or kicking off too soon – it’s pretty “cold” stuff and as soon as it gets spread out on the fabric on the table at room temp, the resin temp comes right back down.

I certainly learned through this to have a bit more respect for this unit – I’d rather not have to tear it down in the future, but at least I know it’s easy to do and I always feel like I learn something whenever I tear something apart and put it back together.  I’ve also found a way of preventing most of this in the first place – remember that this all went back to there being a partial clog in the mixer manifold, in the resin port.  Over time, the resin will air dry and become hard.  I’ve found that the best way to prevent this from happening is to leave those 1/4″ plastic tubes in when not using the machine.  This keeps any air dried bits contained in the disposable tubes, which can be thrown away when they clog.  Since I started leaving the tubes in, I haven’t had any problems with blockage in the mixer manifold.  Michael Engineering supplies a nut which covers the manifold when not in use, but I find that even with that in place, there is some mixing on the resin and hardener in the nut and that it’s just easier to use my tube method.

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