# Degassing HD-PE with vacuum-pot ?



## Peter Hendriks (Mar 9, 2015)

Hi all,

Im new to this forum and are actually a wood turner.

Now that i am interested in turning HDPE and have seen allot of videos on youtube on melting hdpe, ive not seen a video of someone using a vacuum pot to "de-gas" the hot HDPE so that there a absolutely no air bubbles in the plastic.

Is there someone who can tell me if this is going to work?

Otherwise im willing to make the needed equipment and right a report on this.

kind regards,

Peter.


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## you'llshootyereyeout (Apr 5, 2014)

Hey Peter,

I haven't seen anything about vacuum pots in regards to HDPE. The person to ask is CanOpener. He is a talented ornamental turner and is very experienced in dealing with HDPE. I find it hard to imagine you could find someone with more combined knowledge of both topics.

What kind of turning do you plan to do with the HDPE? If you were gonna turn vessels or other large items I think fusing segments with a heat gun would be a possibility.

Would love to see some of your work plus whatever you end up making in HDPE.


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## Susi (Mar 3, 2013)

Your question involves a lengthy answer on two points...fusing pieces and turning.

I infer from the statements you are a wood turner and you propose to turn HDPE in presumably a wood lathe. On that premise here are some ideas. And know that HDPE does not react to tooling like wood, it's a whole nutha medium. It's about as easy to work as wood with hand tools but lathe work, it's gonna be different to some degree.

I used a vacuum chamber to debubble silicone mold RTV compound in the jewelry mfg biz..mandatory it was, else the mold cavity would have 'zits;' where bubbles were on the item's surface to be molded, and for debubblizing gypsum/silica mold compoiund (like plaster of Paris sort of) for lost wax casting...a must, else countless 'zits' appear on the castings, lengthening clean up time. I unfortunately sold my vacuum machine with the rest of my stuff when I left USA. I longed for it when one of my HDPE projects, the camo one, turned out pretty bubbly. I think a vacuum machine/chamber would work excellently with an HDPE melt provided it was done fast so the melt doesn't thicken and harden more than it is already. For bubbles to expand under vacuum and therefore rise theoretically to the surface, the medium must be liquid enough to permit bubble rise, else the bubbles just form and don't rise, rather contract when the vacuum is released, having zero effect. It's worth a try if you know a manufacturing jeweler with a vacuum device well enough to have a toaster oven in his shop, melt the HDPE, then remove it form the oven and put it in the vacuum chamber and vacuum away. It would not vaporize so there's no worry of fumes, just froth. MAKE SURE your mold or container in which you melt the HDPE is at least twice the volume of the HDPE melt so your melt doesn't run over and mess up his/her vacuum chamber's intake or whatever. HDPE froth all over the place wouldn't be a nice thank you for a willing jeweler and YET another sixpack of his/her choice or bottle of vino de jour might cost you more.

Regarding turning and large HDPE items above, definitely welding pieces together by melting both sides to be fused is whatcha gotta do to ensure a good bond. Melted plastic should ooze from the joint and the two pieces should be stabilized or clamped to ensure a real voidless bond. I did this several times on the super ergo models in my gallery to make the index finger hole/module and pinkey rests..worked fine...got the idea from Matt (*you'llshootyoureyeout"). He uses a heat gun, I don't have one, so used carefully a propane torch played over the surface with care not to burn or ignite the plastic, just melt it good. I advise a heat gun and care to not over heat the plastic, it may produce a brittleness you don't want.

In working with two HDPE melts and four sling shots made from them, and being also pretty adept at wood shop, I would not hesitate to turn HDPE...at least give it a shot. Since it's not exactly the rigidity of wood, the tail stock may cut and the plastic piece break lose and the piece fly all around the shop or in yo' face...just don't hog much material with the lathe chisel so as to lessen tail stock stress and lessen the likelihood of the work breaking lose and hopping all around the shop. Also, I pound the tail stock into the wood, but with HDPE, I doubt you'll be able to pound a tail stock into it, so the problem exists of how to get the tail stock's four blades and center spike into the HDPE to give it enough purchase to turn it. Caveat on turning HDPE in a wood lathe. Possibly without destroying the temper of the tail stock, you could heat the tail stock to about 360deg F or 169ish C using an infrared temperature instrument to "see" on the digital screen the temp, then place it in the center of the HDPE billet to turn, then using pressure on the tail stock, with gloves of course, melting its way into the plastic for a firm grip. These suggestions are only ideas I have not tried...no guarantees.

If the piece starts to slow down or wobble in rotation, stop...it means the tail stock is cutting through it's grip and it's about to make a flight tour of the shop. It's the same principle as turning a very soft wood. HDPE may not be of risk but I thought I'd mention it in case it is. I never turned HDPE, only machine grade PVC and machjine grade nylon in my metal lathe...with no prob but a metal lathe grips the piece, i.e. round stock, and rod or round stock is not a big chunk like you're talking about, with three powerful jaws, not a tail stock. The larger diameter the rotating work the more stress by leverage is applied to the tail stock grip. Physics.

If you are careful when you melt your HDPE chips, and don't melt pieces which are not flat, that is, prone to capture air, your bubbles won't be as prolific. If you make sure the plastic chips you added are thoroughly melted before adding more, likewise you lessen the likelihood of voids or captured air. Bottle caps and other cup shapes will capture air if inverted on top of the melt when adding plastic to the melt.

Also in the bubble subject of this thread, not all stuff that's marked HDPE is the same HDPE. One of my melts was rock solid, no voids/bubbles, the other was littered with bubbles. The problem arose from some of the plastic being (I think) already recycled and likely contained low density poly (LDPE) which likely has a lower melting point and therefore likely a lower vaporizing point...or had other plastics other than polyethylene in the mix...resulting in gas bubbles from SOMETHING vaporizing. . The melt temp was the same for both batches. I've heard of other HDPE makers with the same problem, which is why some use new poly but cheap items bought at stores. It doesn't take much HDPE to make a nice SS...so a few bucks spent on, say, buckets or the like isn't much of a consideration.

By the way if you become a sling shot making addict as many of us are, a vacuum machjine is good for impregnating wood with plastic or epoxy resins to plasticize them making for waterproof durable frames...by immersing a wood item in a tub of resin, vacuuming the wood item to extract as much air from the wood cells as possible, releasing the vacuum to let ambient 14.7lbs/sq.inch air pressure to force the resin into voids previously occupied by air, plasticizing the item inside and out.

This may be better served in the tutorial section after the poster has read his thread.

Chuck


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## Susi (Mar 3, 2013)

I just added to the above post and put the result with more info than I posted above in the tutorial section where such lengthy advisories belong. I would appreciate a critique so I can make it better still. PM me please or offer comment on the tutorial article section. Thanx, Chuck


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## hainfelder (Oct 19, 2014)

well - a vacuum treatment of heated HDPE would be nice ---

but I guess you would need a *heated vacuum chamber* ?

the blank do harden pretty fast from the outside - a bubble would then be enclosed


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