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An idea for recycling HDPE and the mysteries of steam!

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AdeV:
There's another option - mix it with candle wax (in a 4 parts wax, 1 part HDPE) and heat to around 175-200C. Mix thoroughly. Allow to set (it will shrink massively). Tada - machinable wax!

I used LDPE for my machinable wax, but HDPE should do just fine - it'll probably make it a little harder, which isn't a bad thing.

If you can find scrap candle wax for cheap, that'd be ideal; but failing that, the cheapest candles you can find in bulk will work just as well.

vtsteam:
Welcome back John!  :beer:

I've seen polyethylene scrap from plastic bottles melted in (I think) an open top bread loaf pan and I believe the air bubbles just slowly rose to the surface, and were then popped with a wire. If I remember correctly it was in a video about a guy who made slingshots.

vtsteam:
Here it is:

John Hill:
Thanks, that is good but not want I want!  He is making flat pieces  but I want to make rounds  for playing in my lathe!

His method of heating in the oven pan is pretty much what I do but I have to use something like a silicone oven mat under the plastic otherwise it is almost impossible to get out when hot, which is what I must do if putting it in my cylindrical moulds.

With this method by the time I have got the hot plastic off the silicone mat and tried to roll it to go in the mould the surfaces have chilled so I get air inclusions weakness where layers fail to bond.

vtsteam:
Well John a couple of (possibly worthless) suggestions, not having tried them on plastic.

1. Split the tube mold and braze on a cabinet hinge so it can be opened and closed to release the part. Tack on some rod handles so it is easier to open and close. Use a clip over the handles to hold them closed. The rods will apply spring tension.

2.Try soot on the inside of the tube mold as a release agent. (I use a candle held close to the surface for this as a release for casting aluminum over a releasable steel mandrel.)

3.Heat the tube itself to melt the plastic

There still might be bubbles that don't make it to the top in time to open them up with picks, it depends on how deep your mold is and how long you give it. Air is the main cause of scorching (besides heat and time). If you can exclude it somewhat you can heat for longer. I guess a deep mold should scorch only at the top. Maybe add a piece of wood to float on top?

Vibrator to help move the bubbles?

BTW what are the dimensions of the finished ingot?

(photos from long gone but not forgotten, brilliant "Build Your Idea" website.

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