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Melting PVC

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Melting PVC

Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 3:10 pm

I have been contemplating the use of PVC for coating or casting applications, like reinforcing the outer walls of a shell made of flour, water and ground up cellulose (paper/fiber). After checking Wikipedia for thermoplastics, it seems that short of ordering Shapelock or other similar materials, PVC has the lowest melting point of any thermoplastics that are widely available to even the most restricted spudfiles user.

After further research, Polyethylene, the stuff shopping bags are made of, seems to be a close alternative, but would be slightly more difficult to handle, because it's melting point is slightly higher than the boiling point of water.

So. Before I run off and grab a pot and light a fire, I decided to start a thread to discuss the proper way to melt PVC. After limited experience with something called a plastic welding kit (nothing more than a heat gun with plastic sticks included), I found that if too rapidly introduced to heat, PVC will burn, and easily. So, any ideas?


If anyone wants to try it out first and develop a working procedure from scratch, here's a sample starting point. THIS WILL MOST LIKELY NOT WORK. Please keep in mind we want this process to be able to be used by even the most restricted spudder, so the use of a grill or stove or campfire would probably be good, and detailed instructions would be greatly appreciated. Granted, epoxy might solve all of these applications, but sometimes, PVC would just be better.

Get either PVC bar stock or just regular pipe, and cut it into little pieces and shred as much as possible.

Put these into a double boiler, or if this is unavailable, place the scraps into a pot and place that pot over a pot of boiling water, and slowly apply heat bringing the temperature over 90C.

Stir the PVC often, especially if melting a large amount. If you can do it, you might consider making a slow-turning radial mixer that you place over the container, or you might even make a container with a mixer built in. Keep ringing the temperature up very slowly until melting occurs.

If casting, slowly pour the PVC into your mold. Put a cap on the outlet, and shake violently to rid bubbles from the mold. If coating, bring the temperature slowly up until a runny constancy is achieved, slowly lower the object to be coated into the PVC, and while slowly spinning it axially to ensure an even coat, pull it up.
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Last edited by SEAKING9006 on Thu Aug 21, 2008 7:14 pm, edited 3 times in total.
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Unread postAuthor: jonnyboy » Thu Aug 21, 2008 3:34 pm

You could get really fine pvc dust with a sander. I would think it would melt faster and less prone to burning when in a sand like form. I think an oven would be best, there's no flame. When I made a hot glue piston 250 degrees Fahrenheit was enough melt/deform the pvc fairly quickly. You might find some information looking in the how to section on making pvc sheet out of tubing.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 3:40 pm

I know how to form PVC, I used to do it for my High School's robotics team. They had me use a toaster oven and a heat gun. I have neither. And I mean melting PVC, not softening. Sanding the PVC will yield fine dust, but fine dust may be undesirable. The best form to have something in for melting is in small chips, or shavings.
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Last edited by SEAKING9006 on Thu Aug 21, 2008 3:42 pm, edited 1 time in total.
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Unread postAuthor: explsvcookie257 » Thu Aug 21, 2008 3:41 pm

That sounds like something I will try when i go to my dads house. Jonnyboy I wanted to make a piston out of hot glue and was wondering how good of a material is hot glue for a piston like does it hold up well does it deform under pressure and how much pressure are you using with it. Thanks. Oh and SEAKING9006 that is a good idea you have thought of thanks.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 3:44 pm

Thanks, cookie. And no, hot glue is not a good material AT ALL. It deforms far too easily, having the consistency of rubber that doesn't like to bounce back after you push into it. Feel the hot glue gun sticks, that's what It'll be like.
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Unread postAuthor: jonnyboy » Thu Aug 21, 2008 3:50 pm

I wouldn't recommend it. Mine was sticky and getting the perfect fit was a *****., plus it gunked up the sander basically ruining the belt.The glue seemed to expand in the mold so I had to cut the pvc lengthwise to pop it out. I decided to scrap it and remelt the glue as a filler for a cardboard tube that i had. It also broke when i dropped it. I've read of hot glue pistons deforming melting in hot weather. There's a nice tutorial on epoxy piston making by jsr [url]http://www.spudfiles.com/forums/making-epoxy-pistons-t8919.html]here[/url].

P.S. anyone know how to make the link just a work?


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Last edited by jonnyboy on Thu Aug 21, 2008 4:09 pm, edited 2 times in total.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 3:52 pm

To make the link one word, type [ url = (insert URL here)]
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Unread postAuthor: Eddbot » Thu Aug 21, 2008 5:44 pm

if you have trouble melting it without burning it, try putting the pvc shavings in a separate bowl, then put that bowl on top of your pot, fill your pot with water, and use the steam to melt the pvc, that's the way to melt chocolate without burning it...(i never thought cooking skills would come into spudgunning)
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 7:09 pm

Actually, I'm surprised that I hadn't remembered double boilers. That's actually a good idea, I'll refine the instructions on first post, I'll use them as a kind of development log.
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Unread postAuthor: Fnord » Thu Aug 21, 2008 7:18 pm

Actually, I'm surprised that I hadn't remembered double boilers. That's actually a good idea, I'll refine the instructions on first post, I'll use them as a kind of development log


Er... if pvc melted at 212 degrees, it wouldn't be used for hot water systems.

Cooking oil might work, but isn't as safe. I'd just try melting it in a zero oxygen environment.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 7:20 pm

The water will be at a boil underneath the pot with the PVC. The water is simply a way of transferring heat to the PVC without burning it.
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Unread postAuthor: CasinoVanart » Thu Aug 21, 2008 7:34 pm

http://en.wikipedia.org/wiki/Polyvinyl_chloride

It says here that it melts at 80c. ? Not much.
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Unread postAuthor: SEAKING9006 » Thu Aug 21, 2008 7:39 pm

CasinoVanart wrote:http://en.wikipedia.org/wiki/Polyvinyl_chloride

It says here that it melts at 80c. ? Not much.


That melting point is actually not a good representation of what you and I would take to mean actually 'melting'. Its real melting point is actually higher, something above 85C, depending on a number of factors. All in all, melting should be easily achieved with an improvised double boiler over a campfire.
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Unread postAuthor: explsvcookie257 » Thu Aug 21, 2008 8:52 pm

Well SEAKING9006 thanks for the info I was just wondering would if it would work even though I am going to make an epoxy piston I guess I should have said that earlier. And to go along with what others are saying the pvc doesnt actualy melt at 80c. I boiled the pvc for just a litlle to make a pvc piston which I kinda messed up but I will have to redo but the pvc was just all bendy not like mushy melty. I think the pvc would have to be melted in an oven though.
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Unread postAuthor: jimmy101 » Fri Aug 22, 2008 12:39 pm

_Fnord wrote:Er... if pvc melted at 212 degrees, it wouldn't be used for hot water systems.

PVC isn't code approved for hot water systems. That's what CPVC is for. At 212F pressure rated PVC would have to be temperature derated by a huge amount. According to Harvel, at a temp of just 140F the temperature derating is 0.22. The derating factor goes down by about 0.1 per 10F so at 212F PVC won't hold any pressure at all.

PVC really doesn't have a "melting temperature". Amorphous solids, like PVC, have "softening temperatures" or "softening ranges". The difference is the width of the temperature range and other technical aspects of the process (like whether it is possible to have a stable mixture of both solid and liquid at the melting point). Something with a true melting point will generally go from solid to liquid over a slow temperature rise of ~1C. Amorphous solids won't do that. The material softens, then deforms, then sags and eventually will start to flow, all happening over a range of anything from several degrees to a hundred degrees or more.

I've never seen 212F (boiling water) melt PVC. In my experience it gets soft but never really gets hot enough to flow. So I don't think boiling water (or a double boiler) will work. It works great for converting a piece of PVC pipe into a flat sheet but it won't work for casting.

The 80C "melting point" for PVC that appears in Wiki (and many other places on the web) is just plain wrong, or it refers to something other than Type 1 Grade 1 PVC. At 80C the PVC we use won't melt, at least not in the normal sense of "melt". One problem is that "PVC" really isn't sufficient to describe the material. All the name PVC (polyvinyl chloride) really describes is the monomer that the polymer is made from. It doesn't describe what or how much plasticizer was used. The plasticizer makes a huge difference in the physical properties of the final PVC. Those soft flexible "gummi type" worms you can buy for fishing lures are often made out of PVC.

The true flow temperature for "PVC Type 1 Class 1" certainly should be out there somewhere. The only one I could find was for GELFLEX at 130 to 160 C. It is possible that our type of PVC can not be used as a thermoplastic without significant risk of poisoning.
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