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Teflon lined wire reinforced drywall mud extruder.

Posted by jgilmore 
Teflon lined wire reinforced drywall mud extruder.
August 30, 2008 05:59PM
I read about the concrete extruder awhile back, and haven't really heard anything about it lately. Seems like it'd be a good idea, strong, cheap, and readily available. I've seen comments that say it doesn't work, but nothing to say why. I also haven't seen an official "Eureka! Use this instead of slippery, expanding, expensive, and unreliable PTFE!"

So, in the absense of any hard experimental data about it, I came up with a design to fix the only potental problems I could see with it.

First, the plastic may melt up inside the concrete, cool there, and make the extruder impossible to restart.

Secondus, the concrete has relatively poor tensile strength and may crack under pressure.

To solve the first problem I'll get a short length of teflon tubing with a 1/8" (3mm) inner diameter. Then we drill the top section of the extruder tube a little wider to fit the outside diameter of the teflon tube. Now, when it's completely assembled, we'll have a teflon lined section that will prevent the plastic from seeping into the concrete.

To solve the second problem I'll solder some bailing wire to the bottom of the nut, running it up into the side of the concrete and looping back down under the nut. Since it's tensile strength we're concerned about, the solder joint won't be stressed, and looping the wire through the concrete will lock the block of concrete together. I'll probably do three loops.

I'm actually planing on using some leftover drywall mud in place of the concrete. The mechanical properties are similar but weaker. Much less tensile strength, for instance. Still, I think it should work. I will definately need reinforcement for it! You probably wouldn't need the reinforcement if you where doing just concrete. I'd have to buy the concrete, and I have the drywall mud on hand. It's reusable, washes away with water. So if it cracks I'll just go buy some concrete and replace the drywall mud.

I though I'd ask your opinions. And I made a pretty picture to illustrate it. OH! and yes, this is planned for extruding plastic (I plan on ABS, actually) not extruding drywall mud!

I'm building it with Baling Wire
open | download - extruder with Teflon lining and wire reinforcement.JPG (6.9 KB)
Re: Teflon lined wire reinforced drywall mud extruder.
September 02, 2008 04:19PM
Hm are you going to heat up the concrete? Thought it might be a little resistant to heat compared to metal?

Or is the scetch incomplete on the lower side?

If you are using metal for the heater, how do you connect it to the mud/concrete?
Re: Teflon lined wire reinforced drywall mud extruder.
September 02, 2008 06:59PM
The heater barrel is built as normal, threads on the top, a small hole in the bottom, and nichrom wire and a thermistor between.

The insulator is the differance. And that's made of reinforced mud in the following fashion:

First, get a nut that will fit the top of the extruder barrel. Solder the wire onto this (or not, doesn't make much difference, but it makes holding things in place later easier)

Then assemble the whole thing, sans the mud, inside a plastic cup. This includes the teflon tube lining that extends up to the top of the cup, with the wires sticking up all around it. The barrel extends below the cup through a hole in the bottom. The wire should be placed so that it runs UNDER the nut, between the nut and the bottom of the cup, and extends in loops around the teflon tube in the middle, but it musn't touch the cup, the tube, or come all the way of to the top of the cup.

Then fill the cup with drywall mud or concrete. Insert a couple of bolts for attaching the polymer pump into the top layer of mud.

Wait for it to dry/set, take off the plastic cup, and you're done. The teflon reduces the friction and prevents the molten plastic from embedding itself into the porous dried mud. And the wire prevents the weaker drywall mud from coming apart under the ~8lbs of force exerted by the pump.

I'll avoid the melting/deforming problems I'd get from a PTFE insulator, it'll be lower friction that any of the other suggestions I've seen, and it'll be cheaper.

I'm building it with Baling Wire
Re: Teflon lined wire reinforced drywall mud extruder.
September 02, 2008 07:13PM
Make sure you use rusty wire.
Concrete is somewhat ironophobic so it won't stick to the wire if the wire isn't rusty winking smiley
That's why the reinforcement steel is always rusty at building constructions.

Re: Teflon lined wire reinforced drywall mud extruder.
September 02, 2008 07:58PM
I don't care if it sticks, though it would help. It's bound into a channel mechanically. It's a loop and can't be "pulled out". The texture on the outside of re-bar is for the same thing. There's a formal name for the little bumps, but I forget what it is. The welded wire is welded at all joints for the same reason - the wire is smooth, but it's bound at the joints and can't move even if it was zero friction.

And conscruction guys often go to great lenghts to keep the enamel coating on the iron from getting scratches, to avoid rust. Because once it's rusty, it will continue to rust, and rust takes up more space than iron, which means the concrete will be busted up from the inside, cracking. It has low tensile strength so this happens easily. It's the main failure mode for steel-reinforced concrete structures.

I've did a lot of reading about thus subject a month or so back - I've been looking at using fiberglass reinforcment for a concrete house, specifically because of the rust issue. There's even people selling FRP (fiberglass reinforced plastic) rebar for use in highly rusty environments like overpasses (in regions where they salt the roads in the winter) and seashore applications. The added durability apparently more than offsets the slightly higher price. More info can be found at [www.fiberglassrebar.com] but I still haven't found a supplier I like. No hurry though, I have yet to finallize the design for the house, and won't start the foundation for at least another year. Thank God I have land in an area that doesn't insist on the UBC crap!!

Now, you may be right for indoor applications. But I still wouldn't use rusty wire for anything I wanted to last.

The insulator block is going to be indoors only. So it won't get wet. And mine is going to be drywall mud (at least the first time) so it's no nearly as caustic (alkaline) as concrete. And it doesn't need to last more than a couple years at most. So I wouldn't mind rusty wire for that. So even though my bailing wire isn't rusty, I wouldn't care if it was for this application.

I'm building it with Baling Wire
Re: Teflon lined wire reinforced drywall mud extruder.
September 02, 2008 09:04PM
Well, but reinforcement of concrete should prevent cracks,
otherwise its pretty useless.

If you're going to use steel, you need to have it attached firmly to the concrete, that is rust or bust winking smiley
A certain amount of rust is needed, another allowed above that the steel bar is useless, true... still rust is a must *gg*

And Nope, "construction guys" LOVE rust on the concrete reinforcement. it's there for a reason (as I mentioned)
And NOPE it wont rust any further as soon as it is fully embedded in the concrete, then there's not enough moisture to let the rust go any further.
and you'll never find enamel on such reinforcement bars. NOT EVER.

Don't mess reinforcement with T-bar rests.

reinforcement should look like this:

Nevermind, it's just an extruder barrel, but do yourself a favour and never build a concrete building, not for yourself nor family winking smiley


[edit] oh btw:
what do you think those fibreglass rebars have that rough surface for?

Edited 1 time(s). Last edit at 09/02/2008 09:05PM by sid.
Re: Teflon lined wire reinforced drywall mud extruder.
September 03, 2008 04:10AM
... as mentioned in the other PTFE-thread, i made moulds with a high-temp 2K-silikone.

With a shortcut to another discussion about virtual stone (made from sand and epoxy) i would say that a perfect replacement for concrete (because of the brittleness) and/or PTFE (because of poor thermal stability) would be a compound of sand and this 2K-silikone.

This silikone is good for 350
Re: Teflon lined wire reinforced drywall mud extruder.
September 03, 2008 03:54PM

you'll never find enamel on such reinforcement bars. NOT EVER.

etc, etc, etc. [www.google.com] "epoxy coated rebar" gets 136K hits.
and [www.google.com] is the offical ASTM standards for epoxy-coated rebar. It's widely used.

OK, so it's epoxy and not "enamel" - same diff, isn't it?

The outside of the rebar is bumpy, and that's sufficient. Any lost chemical bonding is more than offset by increased corrosion resistance. I never see highway workers around here with non-coated rebar, or anything even slightly rusty. If you lived in arizona, (dry, and they don't salt the roads) you may see rusty rebar going into new overpasses, but not around here! Rusting rebar is a major cause of deterioration in ageing reinforced concrete structures: [findarticles.com] Interestingly, this book review cites worldwide maintenance problems particularly in the UK and US.

I've concluded building with rusty rebar in anything that you want to last more than 10-20 years is an uninformed descsion at best. And imho, building with any sort of steel rebar (epoxy coated or not) in anything you want to have last more than 50 years is less than wise.

I'm building it with Baling Wire
Re: Teflon lined wire reinforced drywall mud extruder.
September 03, 2008 05:42PM
epoxy is not enamel winking smiley
and yes what do I know about reinforcemnt of buildings...
just spend six years at the university with architecture...
go ahead, I'm bored

Re: Teflon lined wire reinforced drywall mud extruder.
September 04, 2008 12:12PM
OK, I suppose I have some time too.

I see people selling FRP rebar, why don't I see people selling just the FR part? As in fiberglass cord/cable for embeding in concrete? I have seen concrete board, which is essentially a fiberglass net folded in half and with concrete poured in in, but apparently you can't but just the net?

Maybe the fiberglass & resin people is where I should be looking. But reinforcing concrete w/ fiberglass required alkali-stable fiberglass... *shrug*

I figure it'd take a darn thick fiberglass cable to do the required reinforcement for a concrete floor beam, but I haven't run the numbers on it yet. Partly because I've not found a supplier, but mostly because I haven't cared enough yet.

But if you've just spent six years studying architecture, then you should have the calculations easyily at hand for that sort of thing. Assume the beam is 16' long, and 3' high, spaced 4' appart, and supports a 6" concrete floor. How thick is it, and what is the required reinforcement? How thick would the steel have to be vs. using fiberglass? Should beam be taller?

Wait, are you in the UK? maybe you'd prefer a word problem with metric measurements... smiling smiley

I'm building it with Baling Wire

"Results show that up to 2% of rust increases the bond strength regardless of concrete strength and diameter of reinforcing bar like the existing data. It might result from the roughness due to rust. As expected, the bond strength increases as compressive strength of concrete increases and the diameter of bar decreases."

This doesn't mention if it is a good thing or not - it just notes that it increases bond strength between re-bar and the concrete.
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