vacuum impregnating tubes

[MadMat]

While trying to roll extra paper on one of my thin walled tubes, I encountered some problems; getting a tight roll, preventing "telescoping" all while trying to glue at the same time. I realized without the glue, these problems would be easily corrected. It was then I came up with the idea of vacuum impregnating the rolled tube with glue after it was rolled. I started a post about a vacuum drying chamber http://www.amateurpyro.com/forums/topic/11050-vacuum-drying-chamber/, and decided this chamber could accomplish that. So I rolled up a tube and secured it with a little tape, placed it in the vacuum chamber with a few inches of water thinned PVA glue and applied the vacuum. It appears to have worked well and am waiting for it to dry. I will report on the results. This technique could lead to stronger, lighter, thin walled tubes that could be made at home fairly easy. Hmm... fiberglass or even carbon fiber cloth vacuum impregnated with a high temperature epoxy??

Edited September 27, 2015 by MadMat

[mikeee]

The only concern would be the ability of the "glue compounds" to migrate through the paper layers.

Interesting concept if you can get a "glue" to impregnate all the layers and bond them together.

Another possibility would be to coat the paper with a "glue", let it dry and then roll the paper into

a tube and then put it in your vacuum chamber. This would allow the "glue compounds" to evenly

coat each layer of paper and be reactivated during the vacuum saturation process. The paper layers

may act as a filter media to filter the "glue compounds" from reaching the inner layers evenly.

 

They use the same process for carbon fiber and fiberglass cloth which allows all air to be pulled from

the cloth and the liquid resin to fully saturate the layers. This would be a viable option for high powered

rocketry but might not be cost effective for less demanding motors that would use cardboard or PVC tubes.

[Mortartube]

An interesting method for getting good strong tubes (I haven't tried to thicken an existing tube with this but it might work), is to dry roll a paper tube with a sheet of plastic (thick plastic bag).

 

Put the paper on the bench as usual, with the sheet of plastic on top. Roll around the former and hold with wire (or cooking foil wrapped around it, to stop it unrolling) and bake in a medium oven for about 20 mins. Use oven gloves when you remove it from the former. I can't recall where I read this method (possibly on these forums), but I have tried it and it produces a remarkably strong tube when it's cooled. The plastic needs to be fairly thick, I find the sort of plastic used for fertiliser bags or decorative shingle to be the right sort.

[FloridaCracker]

I've never heard of using a separate sheet of plastic which seems like it might be hard to roll 2 sheets of different material tight and evenly. But plenty of people have used a plastic backed paper similar to freezer paper and done the same thing. Roll it up tight and bake in the oven to melt the plastic and hold everything together.

 

As to the original method, I agree that paper with glue already applied and dried might give more even results. And instead of using glue in the vacuum process use plain water to activate the glue. You could use gummed paper tape to see how well it works. A glue that is easily activated with just a little solvent like acetone or alcohol might dry quicker and more evenly so there is less chance of warping? Not sure if there is a good glue that would work and be easy to pre-apply.

[MadMat]

I think there are a number of possibilities with a vacuum impregnation process. As for the cost effectiveness, the heart of my system is a compressor from a scrap air conditioner or refrigerator. This makes it rather inexpensive and puts a technique into the hands of a amateur for very little cost. As for the tube I made this morning, I giving it some air time in the sun and then back into the vacuum chamber where I will draw a hard vacuum on it to remove any remaining water. But for now, it looks like I got very good penetration with the glue. I weighed the tube before and will weigh it after I'm convinced it is completely dry and see what the difference is. I actually came up with the idea because I worked in the materials lab some years ago at a company that produced electronic circuit assemblies. Circuit boards that were subject to harsh environmental conditions were coated with a porous phenolic resin. then vacuum impregnated with wax. This produced a very durable and moisture resistant conformal coating.

Edited September 26, 2015 by MadMat

[Col]

I`d use a bit of sandpaper to loosen the fibres so the glue has a key.If the original glue is dextrin based, which is likely, just wetting the surface will be enough. If you cant get glue to penetrate the surface, a vacuum wont help much.

Apply a film of glue to the paper and let it sit for a minute or two so it tacks up before rolling it on, sounds like you`ve got too much glue on the paper

Edited September 26, 2015 by Col

[schroedinger]

I know that the method with plastic/paper works quite good and isn't very hard since you use dry materials. First time i read sbout it was on the wouter visser site.

 

There is also an other method for producing nice tubes at home. I read about it in one of the best of AFN books (i think it was 3). Thats steamed tubes. Basicall what you do is roll up your tubes using dry gummed tape. This way it is easy to tighten them really strong. After this you take a pressure coocker add some water and a fake bottom out of wire or punched sheet metal. Now stand your tubes into it and cook for 20 min under pressure. This gives really nice tubes, all that has to be checked after cooking is that the inside flap is glued down good. If not take a dowl and fix it.

[Col]

I wouldnt trust gummed tape for anything critical 1lb rocket tubes would fit upright in a pressure cooker but finding 7.5" wide rolls of gummed tape could be a problem To make seriously strong tubes, glue up multiple sheets of virgin kraft and roll them as a single sheet.

[Mortartube]

The method I mentioned above made rock hard tubes. I stood on a tube made of newspaper and plastic and it hardly deformed. It was about 25mm ID and had a wall thickness of about 8mm. I am not a small guy. I was astounded by the strength. Possibly the molten plastic soaked into the fibres of newspaper where it might not do that with kraft!

[Col]

If the tube is 25 id x 41mm od (area is 1.285 in2) and you weigh 25 stone (350 lb), standing on top of the tube will exert a force of 272 psi

According to Ned`s tube strength testing on skylighter, his plastic laminated tube failed at 4100 psi vs 6800 psi for a good quality tube. Taking into account the grief you may get from the missus about the oven smelling of burning plastic, i`d use kraft

Edited September 27, 2015 by Col

[MadMat]

Well my vacuum impregnated tube worked quite well. I got successful flight. The dimensions of the rocket were 7/8" I.D. x 6 3/4" long (22.22mm x 171.45mm). I filled it with approx. 97g Rcandy (I made a 100g batch and had a little bit left over). The original wall thickness was 3/32" (2.38mm) I added kraft paper up to a wall thickness of .111" (2.82mm). that was only 3 additional turns of paper @.006" thick. I had a nozzle dia of .203" (5.16mm). I cut open the tube after flight and the pva glue had penetrated through all the added paper and Very close to all of the original tube. The only short coming was pva glue doesn't hold up well to heat. The hot tube felt somewhat pliable. With a better resin I think I'm on to something. The rocket had a full core with no RIO added. I'm thinking I might try high temperature enamel paint as an impregnating resin. It has a low viscosity, so it will penetrate well. I just have to see how much strength it will add. My next test will be what I call a short core (the core runs only 15% of the length of the grain) and add RIO. I will drop the nozzle dia. down to 3/16" (4.76mm)

 

I have to add that I was only able to make these original thin walled tubes work with a nozzle dia. of .25" (6.35mm). Any smaller and the tubes blew out.

Edited September 27, 2015 by MadMat

[mikeee]

You could also try testing the wall strength with your different "glues" by pressing a motor without a tube support.

Record the pressure reading when the tube fails and you should be able figure out which "glue" is providing a

better saturation and bonding of the layers of paper.

[Col]

wheat starch handles heat better than pva, the bond will be plenty good enough with a keyed surface. The fresh paper will shrink and tighten up on the old tube as it dries. You could use silicate, which is even better for heat. but as it`ll only be on the 3 outer turns it may be of limiited benefit. Downside of silicate is it adds quite a bit of weight to the tube, i only use it for handrolled tubes as its a nightmare to clean off the glue machine rollers once it dries..

[MadMat]

I thought about wheat paste, but it is a large molecule colloidal dispersion (starches are essentially long chains of sugar molecules). This would cause problems with penetration. I am thinking that synthetic resins, dissolved in a solvent, are the path to follow

Edited September 27, 2015 by MadMat

[Col]

Depends what glue the original tube used, i`d soak one in warm water and see if you can unroll it. If you can you`ll know its water based and reversable.

[Mumbles]

As a point of reference, do you happen to know the average molecular weight of PVA in Elmer's glue?

 

Wood hardener, or components therein, might also be something to look into. It was common to soak some rocket tubes in it to strengthen things up. To the best of my knowledge, they utilize urethane polymers most of the time, and were quite effective.

[MadMat]

Don't know the molecular weight of pva. Urethanes might well be a good choice. I was also thinking epoxies. I know some of them, before curing, have reasonably small molecules and with a small amount of a solvent carrier can have fairly low viscosity. Back in the days I worked at Mepco/Centralab (the electronic circuit assembly company mentioned earlier). I was involved in R&D for a new epoxy conformal coating for a military contract. The various physical characteristics of all the available epoxy resins was rather amazing.

Edited September 27, 2015 by MadMat

[Col]

The issue with high tech adhesives is they are more expensive and not as biodegradable as the natural alternatives. Kraft paper is cheap enough that you could probably double or triple the wall thickness for less than the cost of the glue. The bulk of the tube strength comes from the type of paper used

[MadMat]

Yeah. I get OCD'ish sometimes about things like this. But then again, if something as simple as high-temp enamel paint does the trick (something I'm actually going to try), then... who knows? I guess this is more geared for high-powered rocketry than fireworks

Edited September 27, 2015 by MadMat

[Col]

I doubt anyone is more ocd than me when it comes to paper tubes

I make my tube rolling glue in exactly the same way everytime and destructively test tubes rolled from each and every batch to be sure they are consistant. I have a machine to apply the glue quickly and evenly, it can also calender multiple sheets of kraft into a single thick sheet which is/was the method NEPT employed. The rolling machine is a bit of a beast but it can roll any tube between 8mm ID and 60mm OD.

 

Top: Glue machine (heavy duty, chain driven) ,

Middle: rolling machine,

Bottom: closer shot of the sectional glue pick-up roller (adjustable length)

 

 

[stix]

I doubt anyone is more ocd than me when it comes to paper tubes

 

+1. But you left out your obsession with Glue!!

 

That's a very nice looking machine Col - any chance of seeing it in action?

[Col]

I`m over that one now, i just "stick" with a select few glue recipes these days

I`ll get a vid of the roiller in action but its pretty basic and not that entertaining.

The preglued paper goes in under the mandrel. The 3 coloured rollers are raised (via a motorised scissor jack and 4 linear bearings on supported rails) which clamp and wrap the paper around both sides of the mandrel. The open end of the sheet is directed into the nip point created between the mandrel and the paper thats then running over the top of the blue roller (glue side up). When the mandrel spins, the paper is towed in. After the rolling is done, the coloured rollers are lowered and the tube is shoved off the end of the mandrel. Nothing to it really.

 

Here`s a bit more detail on the spring loaded mounts i came up with for the bottom roller. They serve to keep the bottom roller (and paper) pinned to the underside of the mandrel as the blue/green rollers continue to travel upwards.

 

 

 

 

 

 

Edited September 28, 2015 by Col

[Col]

Here`s a quick vid to show how i deal with getting the tricky1st turn onto the mandrel. The paper (2ft wide) was dry for the vid but it works the same way for glued paper.

https://youtu.be/lRjyrx_N1vo

[MadMat]

Hmm... interesting. I guess "temporary extra rollers" do wonders.

[Col]

Aye, in practice i just throw them onto the mandrel once the rollers have been raised, the paper is towed in automatically when the mandrel starts spinning. Its not much use for handrolling unless you`re part octopus