Hi Guys! Like many on here I've read all 36 pages of this thread and I'm totally impressing with collective problem solving going on. I'm not really a slingshot guy myself, I'm just interested in the plastic processing and you all seem to be on the cutting edge. I'm interested in a lot of applications but mostly turning it on my wood lathe.
Anyway, I did 10 or so runs in a plywood mould with clamps and just took a swing at the long bake & slow cool method tonight. I'm having the typical issues with the wood mould but I think they will be ok. I haven't turned all my blocks to see what's inside but a couple of them turned nice.
The long bake on the other hand was mostly a fail. I did a batch with an old clear-ish 5 gallon bucket (really dingy but I did wipe it down pretty good), a small batch of junk (all the detergent bottle labels, some LDPE, a ziplock, and a few random off cuts), and a batch of US Gov issue canteen bottles.
I put them in for 90 min. at 400 F then dropped the temp 25 every 10 min.
Results: 5 gallon bucket was pretty scorched and had visible bubbles top and bottom. My junk turned out ok but would have had a lot of voids if it weren't for the LDPE that runs a lot more and filled in. The labels look pretty cool and seem to have fused with all the other plastic (obviously only used plastic labels no paper). The canteen bottles barely melted together. They are labeled #2 but they sure don't seem to melt at the same temps as everything else.
What do you guys think? Did the bucket scorch and still have bubbles because it was weathered and dirty or did I do something wrong? Why do you suppose my junk batch didn't "run" very well except for the LDPE? I didn't put any weight or anything on it but I wasn't worried about warping so I figured it would be ok and it seems like that might trap any bubbles at the surface.
I have a ton of ideas and questions but I'll finish with this for now. Do you all have any suggestions for moulding HDPE in a cylinder shape and still getting rid of the air pockets? I just did a couple on a cookie sheet at 350F until malleable, rolled them to shape, pressed them into a pipe by hand, laid the pipe horizontal and heated for another 10-15 min at 370, then clamped a wood plunger in each end. I haven't cut into them yet but I would imagine I still have air pockets. With the mould being heated a little the surface came out a lot smoother than with the wood mould.