Sealing it

With the melt tank installed and the pump body assembled, I can now start fitting the injection cylinder to the tank. The large (50mm!) air cylinder moves a piston in the pump body to draw in molten plastic, and then force it into the mold cavity. The piston seals to the pump body with a cup seal. The original mold-a-rama actually has no seal on the piston itself, it seals around the shaft of the injection cylinder, the seal can be seen here:

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This is the injection ram of the mold-a-rama. The seal is in the center of the picture on the aluminum plate, the fiberglass insulation is covering the tank.

Installing the seal was a real bear. The cup seal is sized for a 3″ cylinder, it flares out to ~3.25″ OD to press against the cylinder walls. I needed to compress is to fit it into the cylinder. Softening the seal really had no impact on it’s flexibility, what I really needed was a piston ring compressor. Lacking that I used several daisy chained cable ties. That still didn’t work well so I used some plastic tools to push the seal in.

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I wasn’t sure what to use to insulate the melt tank until a fateful trip to Lowes. In the pipe insulation section I found this self-adhesive aluminum foil backed foam tape. The adhesive holds up to the tank temperatures, and the heat radiating off the tank is noticeable reduced (as measured using the calibrated portion of the back of my hand).

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I looked long and hard for a plastic water tank that was compact, but had a large enough opening to fit the water pump through. The water pump is supposed to be submerged in the water tank, this  will extend the pump life by keeping it cooler. I gave up on finding a plastic tank and made a metal one myself. The body is made from 6″x6″x.120″ wall aluminum tubing with a water jet aluminum flange and lid. A cable gland seals around the power cable. The gold cylinders sticking out from the flange are rivnuts, those along with thumb screws will allow tool-less removal of the water tank  lid for refills. I plan to add a sight glass later on so I can check the water level with out removing the lid.

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The mount for the mold delivery cylinder (the one that pushes the finished plastic part into the retrieval bin) is made from a small piece of 1″x3″ aluminum tubing welded to the top frame and a shaft collar.

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The lower half of the aluminum shaft collar is welded to the back of the rectangular tubing, the upper half is free  and is what clamps onto the cylinder.

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The molder is pretty awkward to move around as it doesn’t sit on a wheeled base. I added handles to each side to make moving it a little easier. The first set of handles I got from McMaster were plastic, thinking the machine couldn’t weight more than 100-150lbs, it turns out I forgot to take into account two very heavy items: the water chiller and the compressor. After putting those in, the machine weights closer to 200lbs. The plastic handles were quickly swapped out for some beefy aluminum ones. I’ll still probably move the machine with the compressor and chiller removed, but now I have a lot move confidence in the handles while moving the machine.

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And finally, before I go, a sneak peak of the new molds!

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