Can you melt and cast polyethylene

I wanted to make some "outrigger pads", which are square pads something like 24x24x3" thick. I have some scrap polyethylene cutoffs
and I was wondering, if I just melt and cast them, do I lose any possible assurance of strength?
i
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Just melting and casting scraps, void free, without starting a huge sticky fire will be quite the project by itself.
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Heat breaks down molecules so keep the heat low enough to melt and merge all together and then pour (maybe trowel) the result into a form. Nice thing, it is in the 300 some odd temp. Color might change the melting temp.
Martin
On 11/12/2015 8:15 PM, Ignoramus885 wrote:

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Well, with ordinary polyethylene, there isn't much assurance of strength - it's polyethylene.
One can certainly melt ordinary low-density polyethylene, it's a bit like sticky wax. But do it outside.
The higher the molecular weight, the harder to handle.
What is the purpose of these slabs?
Joe Gwinn
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"Ignoramus885" wrote in message
I wanted to make some "outrigger pads", which are square pads something like 24x24x3" thick. I have some scrap polyethylene cutoffs and I was wondering, if I just melt and cast them, do I lose any possible assurance of strength?
i =============================================================== I've played a bit trying to melt very small pieces of PE, and I usually got charring and smoke long before I got any kind of fluid state that I could pour. I think there is a reason they use injection molding with PE and not simple pouring - get it hot, pump it in so it doesn't need to have a very low viscosity, and get it cooled before it can decompose. Guessing that you only want two or four pads, I'd weld up a pan to use as the mold from mild steel, maybe 1/4" thick or more on the bottom for decent temperature uniformity and 1/8" or whatever on the sides with some angle for easy release, and put it on a stove top with two or all four burners going. Put in your chunks of PE and try to melt them in place, stirring as you go as much as you can. Even if you don't get it all truly molten you might get enough mixing to get a fairly cohesive mass. Then just turn off the burners, cover it and let it cool slowly, and hope it doesn't crack too badly. Do your pads have to be solid, or would high density foam work? You can get some pretty thick foam from ULine for not that much $$.
----- Regards, Carl Ijames
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Outrigger ground pads - sounds like you want some tough stuff lifting up the crane with them. I would think you might squish them out from under the feet. 1/2" steel plate would be nice, I see a lot of large lam blocks or log cabin cutoffs.
I saw the guys here in town - they have some neat cranes! - They use counter balance weights. They move them with the crane while setting up - boom not extended... light enough to use tires...
I would think plate weights would be in the scrap line of yours.
Martin
On 11/12/2015 10:30 PM, Carl Ijames wrote:

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On Thu, 12 Nov 2015 20:15:27 -0600, Ignoramus885

I think polyethylene would difficult to melt and fuse successfully. It'd probably be heavier and less stiff than the traditional wood as well. If you got it done, it'd certainly take a beating. I'd go for bolted live oak or whatever you have of similar toughness up there. I've had to drill a pilot hole to drive a nail in live oak.
Good luck.
Pete Keillor
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On Fri, 13 Nov 2015 06:20:23 -0600, Pete Keillor

I have success with HDPE welding with a 200 watt iron and the lock strip from HDPE bucket lids. Flows well and very controllable. I am not sure how a casting would work.
You might consider several yard sale/trash pile cutting boards interlaced and bolted.
--
Mr.E

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On 11/13/2015 9:50 AM, Mr.E wrote: ...

Several? If a cutting board is 12 x 16 x 1/2 (WAG), it would take 18 of them to make 24 x 24 x 3.
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On Thu, 12 Nov 2015 20:15:27 -0600, Ignoramus885

POlyethylene comes in different densities and six or seven different types. Also, consumber products often are made of hybrids and mixtures (sometimes "alloys") and I've heard that they don't mix well. When the scrap is re-melted, it's usually to make lower-grade products.
I don't know if you can just melt it and cast it. When they make products from recycled poly, it's usually pelletized and then injection-molded. You'd have to see if you can get it to flow with just gravity alone.
--
Ed Huntress

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On Fri, 13 Nov 2015 11:03:02 -0500, Ed Huntress
Nope, will not work.

Or granulated, which is a crude approximated pellet. Many products have a percentage regrind added back. Sprues, risers (injection) tops, tails (blow molding) and reject parts are ground and added back to the virgin pellets. Even baby bottles! Of which I had my grubby fingers in hundreds of thousands of back when I was a blow molding operator. (Someone had to give the inspectors / packers breaks and lunches) Almost identical with injection molding and similar with roto molding other than the regrind has to be turned to powder first and is sometimes 100% recycled which was never the case when I worked with blow or injection molding. (Shift supervisor and then maintenance there)

Nope, will not work.
--
William

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Agree, I managed a lancet injection line for a time. The temperatures NEVER got high enough to liquify PE at atmospheric pressure. The screws were delivering it at about 150 atmospheres.
Lloyd
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On Sat, 14 Nov 2015 20:23:46 -0600, "Lloyd E. Sponenburgh"

Powdered PE will melt / fuse at atmospheric or very slightly above if the vent tubes are partially plugged. But hollow pads are not what Iggy needs.
When I started there (roto) ten years ago they were running mostly low density PE but had a second silo of high density for the few customers who wanted it. After a powder mill was added to save the ten cent per pound difference (~three million pounds per year, it adds up!) we switched to medium density PE for every one. One silo for pellets and one for powder.
Been gone four years now and miss that place like a stubbed toe!
--
William

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Is there a material and method suitable for amateurs with some machining capability?
I've molded rubber in a simple brass mold compressed in a bench vise and heated with a propane torch until a drop of solder on it melted.
-jsw
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On Sun, 15 Nov 2015 07:03:25 -0500, "Jim Wilkins"

What are you trying to make? After thermoforming roto molding is probably the easiest for an amateur to try. Lots of videos on Youtube showing DIY rotomolding 'contraptions'. Most using compounds which do not require heat. So if you want to melt powdered plastic use metal where they use wood.
Finished part must be hollow, very simple shapes do not always require draft though it helps. Complex shapes must have ample draft or you will never get the part out. 1 to 1 ratio will only work for very simple shapes, 4 to 1 is better for complex parts. 4 to 1 and the faster 8 to 2 were about all we used when I worked there.
If you want to build a mold and have it run by a commercial shop this page may be of help. http://www.mysecondbathouse.com/firstmold.html Place I worked at was always slow around the holidays even during busy years. Much more receptive to small runs when things are slow.
--
William

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Maybe "more receptive", but what would be the cost of a custom mold?
Don't kid me! I was IN that business. I know what (domestically-made) molds cost! <G>
Lloyd
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On Sun, 15 Nov 2015 19:21:02 -0600, "Lloyd E. Sponenburgh"

Yes, injection (and blow) molds are very expensive. When I worked at Evenflo was told one of my two cavity bottle molds was probably the least expensive mold in the plant at $20,000! Multi (24 - 36) cavity injection mold that could mold threads and 'unscrew' before ejecting might be a quarter million. Pretty sure this included the thermolator which could send coolant at different temperatures to various places in the mold. In some cases the mold cost twice what the machine it ran on cost.
Rotomolding tooling is an order of magnitude cheaper since there is little or no pressure involved. Cast aluminum and weldments, steel or aluminum are the norm. Only seen one machined from solid rotomold and it was extremely small. Out of time...
--
William

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On Sat, 14 Nov 2015 21:15:54 -0500, William Bagwell

That's what I thought. We needed the voice of experience in there. Thanks for contributing it.
--
Ed Huntress

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On Thu, 12 Nov 2015 20:15:27 -0600, Ignoramus885

The PE will probably be prone to cracking if you do this. Eric
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On Thursday, November 12, 2015 at 6:15:30 PM UTC-8, Ignoramus885 wrote:

Yeah, melting polyethylene was the basis of toy-soldier home kits some years ago. It's do-able. The problem is, you need low-density polyethylene or the temperature/pressure requirements will be a nuisance. Some (very cheap) hotmelt glues, and P-tex candles (for ski repairs) are melt-friendly (more 'soften', really) polyethylene.
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