How to roll pyro-tubes

[Col]

The premixed paste should be thicker (gelified) than diluted pva. so logically the water shouldnt penetrate into the paper as fast. I dont think there will be a big difference in solids content between the two, the 66/33 pva/water mix will be around 33% solids if the pva starts at 50% solids. Starch based glues are typically 30% or less. Adding yellow dex (5-10%) to bump the solids/reduce the water content may be an option, assuming the two are compatible

The local wickes has a couple of tubs of the ready mix in stock so i`ll pick one up in the week.

[dagabu]

The documentation says 38% solids, I am going to try it plain first, stay tuned!

[Mixer]

Pretty close - the one i`m using has 40% solids.

Edited December 4, 2018 by Mixer

[Col]

38 or 40 isnt bad for a starch paste Will be picking up a tub tomorrow with a bit of luck, wickes is just out of town off the beaten path.

Planning a 4 way side by side test with different glues: (evostick resin w, waterproof, blue bottle) 66/33 pva/water mix, straight wickes ready mix, straight wallrock power adhesive and the gravy. With the kraft paper coming off the same roll, the only difference should be down to the glue.

Edited December 4, 2018 by Col

[Mixer]

It will be interesting to see your results Col. I`m assuming you are rolling your tubes on a machine?

I think the Wallrock may have the edge over the Wickes adhesive ( tube strength wise) - it was my preferred glue initially, but when used up I couldn`t find a local shop for more - so I started using the Wickes stuff.

 

With all the glues I tried - initially i put a dab of each on a slide and when the solvent/water was evaporated off I tested the hardness and grip of each of them - the ready mixed came out best, being nice and hard but not brittle - the worst was the neat PVA which was far too flexible - the boiled Dextrin was hard and glass like, made incredibly strong tubes, but was a pig to work with when rolling by hand.

Edited December 5, 2018 by Mixer

[Col]

I`ll do them by hand as it`ll be quicker than cleaning the glue roller and pump tubing 4 times. I test the solids content of glue and burst strength of tubes but thats about it. Disposable plastic cup, write the empty cup weight on the side and add 10g of glue. Chuck it in the drying box, checking and recording the weight until it stops getting lighter. The neat evostick pva is 50%, gravy 58%, i thought i`d marked the wallrock solids on the tub but obviously didnt. I`ll have to test that again when i do the wickes stuff.

Edited December 5, 2018 by Col

[dagabu]

It's funny that my PVA tubes (white glue) don't seem to flex at all! I wonder if in fact it has the same adhesive as yours?

[Col]

Pour a puddle of the pva onto paper, let it dry out completely and see if it will bend before it breaks

[dagabu]

Hmmm, I guess my definition of flexible is a little more "flexible" than yours? I am looking at the flexibility of the motor casing in relation to failure or burst strength vs its plastic characteristics.

 

In the case of White Dextrin, the initial tack was fantastic, open time was fine and workability was great but upon drying, the Dextrin was fragile and because it was not plastic at all, it shattered and the casing became pliable. I choose white glue over dex any day.

 

I have yet to drag my press into my wood shop to test these tubes, I am guessing that the crush damage using an adhesive which is not flexible will result in lower burst pressures?

[Col]

The failure point of the less flexible will be abrupt, the flexible will be more gradual.

[dagabu]

Agreed but there is no correlation in your comment to burst strength. If by gradual, you mean that the white glue will take seconds to become plastic, I think that would be OK for tubes? If by abrupt, you mean the tube will shatter, I am not so sure that is a good thing?

[Col]

The inflexible glue tube will just hang on until the very end. The needle on the press will climb steadily to the failure pressure and then drop straight down..kind of all or nothing. The tube will usually split full length and all the way through the wall, no shattering The flexible glued tube is harder to judge because the peak failure pressure is more of a flat topped plateau which gradual falls away after its failed. It happens in slow motion compared to the inflexible glued tube. The tube will usually bulge and then split but not the full length of the tube.

The burst pressure will depend on the weakest link, poor quality paper and the best glue wont be as strong as good quality paper and mediocre glue

Edited December 5, 2018 by Col

[dagabu]

You really have me motivated to get that press set up so I can test the burst. I have a PTF gauge at hand so I should be able to keep an eye on the max pressure. I looked for a cheap hydraulic gauge with the second indicator that records the high pressure reached but they all look to be water gauges, not enough pressure.

[dagabu]

Well... I stumbled across a great way to make 'slime' for my grand daughter, just add some white Dextrin to your white glue.

 

It lost all its 'tack' and is much like commercial slime now.

 

Edited December 6, 2018 by dagabu

[Col]

She`ll have hours of fun with that You can add pva to thicken wheat paste and increase tack but not to dex.

When burst testing its a good idea to video the pressure gauge, then you can review it afterwards frame by frame.

[Mixer]

The failure point of the less flexible will be abrupt, the flexible will be more gradual.

Yup,

 

when pressure testing my boiled dextrin wound tubes, they

failed abruptly with an almighty BANG splitting the 2" section end to end

The thinned PVA ones failed steadily at a lower pressure.

 

In fact I found the Dextrin bound tubes too strong as they needed more pressure than i like to use to enable each charge to very slightly concave the inner tube walls for a good `lock in`

 

My test of a good tube is using both hands I squeeze the end as hard as possible and if there isn`t any deformation i`m happy.

 

Of course at the end of the day it`s all dependent on your desired loading pressures as to what quality of tube you want.

Edited December 6, 2018 by Mixer

[Mixer]

Occasionally I get a tube that has the odd outer wrinkle in it due to my pasting timings being a bit off.

This bugs me, so now I speed the whole process up by using the oven.

My pre pasted lengths go in at 50c for a few minutes to completely dry, and when a tube is rolled that goes in the oven stood on end with the former still attached for 10 minutes or so - to get the bulk of the water out fast - which completely eliminates any tube wrinkling. The tubes come out great

Edited December 6, 2018 by Mixer

[Mixer]

In my early days many years ago I regularly had CATO`s and for ages couldn`t figure out why until I started doing post mortem`s on the duff tubes.

 

Although I thought I had decent tubes - on close inspection I found a small (black) perforation where the tube/s had a tiny split and the flame front had whipped along it and over pressurized the motor.

 

This is what started me on my quest for good tubes, and thankfully I haven`t had a CATO from that day to this.

Edited December 6, 2018 by Mixer

[Mixer]

If anyone needs proof of why it`s so important to have the least possible amount of adhesive on the paper - just spread a blob on a single piece of Kraft and let it evaporate out. The surface tension will put more wrinkles in it than my Grandma`s

Edited December 6, 2018 by Mixer

[Col]

I dont think there will be much between these three

 

Testing the wallrock, its lost 44% of its start weight so far but still has a way to go.

 

Edited December 6, 2018 by Col

[Mixer]

Col,

out of interest what temp do you dry your tubes at?

Edited December 6, 2018 by Mixer

[Col]

room temp

Here`s the difference in paper curl between the 3 glues, front and the back views.

 

[Mixer]

Oh I wasn`t meaning paper curl as such in my last post. I just meant that (as a demo) how excess glue or prolonged wetness can (multi directional) wrinkle the paper.

 

When I was testing the glue for solids content I applied a thick blob, and when dried the Kraft was seriously wrinkled in the centre.

 

Regarding the drying - I tried a couple this morning at 200c in two stages. It worked well - nice and quick too.

[Col]

The water in the glue causes the paper fibres to swell, they dont go back to their original state or position on drying I`m wary of using high temperatures to force dry tubes because the exposed surfaces (outside and in the bore) heat up faster than the interior of the wall. A fast evaporation rate increases the risk of voids and wrinkles. If the external surfaces form a barrier to moisture once dry, the water inside the wall cant escape as easily I tend to find the inside of the tube is the last part to dry, i guess the RH% may be higher vs the outer surface which leads to lower evaporation rate.

[Mixer]

Yes, this is why I leave the former in the tube as that heats up as well. Sometimes the theory doesn`t always match what happens in practice. It`s just a trial - i`ll cut one open in a few days to inspect it.

Edited December 6, 2018 by Mixer