Matt_NZ wrote:The same stuff milk jugs are made of.
I wonder if anyone has tried molding a milk jug to make a block of HDPE?
I tried it and it didn't work very well. Milk jugs have some kind of mold release contaminate on the surface, so even though it melts, the resulting rubbery goo does not flow into a solid mass, but instead is full of cracks holes and such.
If you look at the plastic planking made from used shopping bags and recycled plastic, you get about the same result. It does not turn into a nice solid chunk of plastic.
Look up "Recycled Plastic Lumber" to see what the stuff will be like. It's OK for a park bench or decking, but lousy for building pistons.http://www.theparkcatalog.com/itemdesc.asp?ic=133-1024&source=Froogle
Molten HDPE can best be described as having the consistancy of a cross of melted cheeze and gummy bears. It feels like rubber much like gummy bears. You need to get it up to about 375-425 degrees F do do this. You won't want to touch it with your bare hands. The stuff is hot when melted.
They will squish together with lots of pressure, but they won't become a solid mass simply by putting a bunch in a jar. I used clamps to laminate the piston. Simply stacking the melted faces toghther does not work. Melting a bunch of cut up milk cartons provides the same poor results.