I do a lot of work on antiques and custom projects, so a lot of times I need to either produce or reproduce parts made of plastic. My go to technique has always been casting resins, but many times they don’t have the ‘feel’ of plastic parts even if they look the part. Sometimes there just is nothing like an injected plastic part.
I started work on a David Gingery style home made plastic injector a couple years ago, but I was never happy with the way the ram was designed. I purchased a nice electronic PID temp controller for the project, and temp control was never an issue, but there were enough other issues with it that I never put it into use.
Last week I saw this pop up on ebay…..
Hmmmm, a $2500-3000 injection unit that had been torn open and no one knew if it was working. The seller was asking a price that would put it on my doorstep for around $200. After looking at the pics, I figured that the ram and chamber were were professional made, the lever linkages would have proper geometry, there was a neat little filler for the plastic feed, and as a bonus there was a mold hold down clamp. Those were all things missing in my home made unit. If the only thing wrong with it is the temp control, then this would be a good purchase so I bought it.
It showed up on my doorstep a couple days ago and I didn’t waste any time tearing it down to see what I had received for my money.
I stripped the heat guards off of it to see what was left under the covers. Turns out that nothing in the heater and injection parts had been touched, things are looking positive!
Here is all the temp wiring as I received it. Everything looks good, I couldn’t see anything obvious wrong with it. I did notice that it is an older type mechanical temp control which are prone to temperature fluctuations, I decided to replace it with my digital PID controller. The data plate on the back said it’s a 220V unit, I will rebuild it as 110v since I will be rewiring everything anyway.
During the tear down to get to the heating cartridges I noticed a few things that the professional unit had that the home brew didn’t, like this bevel on the ram to make feeding pellets easier.
Another lucky bit were the heating cartridges used in the machine. They wired two 110v heaters in series to make a 220v unit. I could just rewire them parallel to make the 110v unit if they were still working. I decided to test them since I had them out of the machine. I put them on a large steel plate as a heat sink, wired them to my digital controller, and tested the system I wanted to install on the bench.
Everything worked. The heaters got hot, and the controller turned them on and off. The next thing to do was modify the heating chamber to install the temp sensor that feed information back to the temp controller.
In the upper center of the picture is the heating chamber and heat cartridges, in the middle is the temp sensor I need to install. I chose to drill out and tap the small hole towards the bottom of the heating chamber where the original heat probe was located.
Hole drilled and tapped. Temp sensor installed. Time to reassemble.
Reassembled with the new parts in it. I hadn’t put the heat shroud back on yet since I wanted to do a test of everything. The test went well, I brought it up to 131’C which is a good temp to begin melting polypropylene plastic for injection.
Since the digital sensor will let me regulate all the way down to room temperature I can melt several different materials for injection molding, so another use for this machine will be injection of casting wax into molds. This will let me make precise investment molds for metal casting.
