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#1 Sparky

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Posted 02 August 2015 - 10:57 PM

Hi all

 

I seem to be single handedly dominating all new posts at the moment, apologies lol.

 

Anyway...your wisdom is needed yet again!

 

I have 3/4" gerb tooling which I've been using with great success for a while. I can't remember the nozzle diameter but I remember it being within the usual range recommended for the ID of the gerb. It is closed enough to build up enough pressure to eject the effect a nice height.

I use thick walled spiral wound paper tubes that in their 7 inch form are strong enough for core burning rockets (well usually but I think that's me...see other post) but for gerbs I are 3 1/2" long. This length is perfect for a gerb and the paper does not burn through even with some hotter burning compositions.

 

My problem is that I want the gerbs to last longer but if I use a longer tube I get burn through occurring. Slower burning composition are not what I want and I've been trying to use 7" tubes with basic BP titanium gerb compositions but I get burnthrough.

 

Is there anything you can recommend to help make them more durable? I've seen some articles about using wood hardeners but they seem to be aimed at improving strength for rockets and not durability against burning through. I wondered if there were some fire retarding chemicals I could dip them in etc but that wouldn't influence the firework effect?

Any suggestions? I'm not really up for rolling my own tubes as yet before you make that suggestion  :D



#2 Sparky

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Posted 02 August 2015 - 11:01 PM

p.s. Is there anything to stop me or any value in actually augmenting commercially bought tubes by wrapping extra layers around them?



#3 JamesB

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Posted 03 August 2015 - 05:47 AM

I'm sure I remember reading somewhere about using water glass (Sodium silicate) to coat the nozzles of hummers and perhaps stinger style rockets to limit expansion of the nozzle hole (by burn-through). Might be worth seeing if you could do the same coating the inside of the tube with this? 


Edited by JamesB, 03 August 2015 - 07:41 AM.


#4 Sam Miller

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Posted 03 August 2015 - 09:58 AM

I remember reading the same James.

I also recall reading that coating with PVA also helps but i might be completely wrong with that!


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#5 cooperman435

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Posted 03 August 2015 - 10:11 AM

Pva will aid strength and I imagine a small help in flame/heat proofing but sodium sillicate watered down to allow it to soak into the tubes interior surface will do the most.

There was a thread a while back also discussing the back face of the nozzle helping greatly. Flat faced rears caused a swirl of burning gasses to erode the tube whereas angled or even curved rears funnelled them away from the wall towards the nozzle and stopped the issue

#6 Sparky

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Posted 03 August 2015 - 03:47 PM

I'm going to attack this from all angles...

 

  • Sodium Silicate solution bath for the tubes, I presume a saturated solution would be a starting point or would this be too much?
  • I'll need to check my tooling but I am fairly sure the nozzle interior is a flat wall so I it sounds like I need to modify a wood dowel to ram the nozzle with some curvature on it.
  • I may also try and extra layer of hand wrapped kraft paper to add thickness to the tubes at the crucial weak point.

 

Thanks for the advice as always!



#7 Pyro-centric

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Posted 04 August 2015 - 09:12 AM

Thanks for the questions Sparky, Although I don't make, I learn from the answers too.



#8 BlackCat

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Posted 04 August 2015 - 03:13 PM

Extra wrapping around a preformed cardboard tube is certainly possible and quite straightforward. I use a fairly strong wallpaper paste made up at 4.5g of paste to 100ml of water, weaker solutions often have problems with adhesion. For a 3/4" internal diameter tube with a wall thickness of 2.5mm, a 750mm strip of 90g/m2 Kraft paper will add about 1.5mm to the wall thickness and, of, course you can add as many layers as you need to achieve whatever wall thickness you like but, bear in mind that each subsequent layer will increase the diameter slightly less due to the increased circumference. I like to cut a width of paper that's about 40mm wider than the tube is long giving about 20mm extra at each end of the tube and allows plenty for trimming. I like to trim when the tube is dry enough, about 3 days for a 3mm extra wrapping using a plumbers plastic pipe cutter. A good allowance for trimming is necessary, if you go this way, as the tube needs to be supported on both sides of the blade and it is almost impossible to role the tubes without a degree of the wrappings running offline. I usually allow 7 days at room temperature to ensure they're dry and they should be stood on end whilst drying rather than laid on their side. 

 

As for sodium silicate, it is used as a passive fireproofing material in building and construction so might work in pyro tubes. It's solubility is 22g per 100ml of water at 25 deg C so this is a guide to the maximum. However, solutions in water are commonly known as water glass and they're quite viscous, rather like Golden Syrup so you'll have to dilute it down to a more reasonable concentration to allow it to impregnate the cardboard. It's so viscous because the silicate anion is polymeric and, like all polymer solutions it's molecular weight produces significant viscosity. I have no experience of using it in the way you suggest and bow to the other posters who may have more experience, however, I do have one concern; its fire retardant properties come from the fact that it's an intumescent material. In a fire, the heat causes the silicate to release water of crystallisation as steam and the steam blows the coating up into a foam, the polymeric nature of the silicate anion stabilises the foam and prevents it breaking and the fact that it's a mineral means that it doesn't burn. Imagine something like a bath sponge made out of glass and you'll get the picture. All foams are great insulators so it prevents the heat of the fire reaching the substrate and thereby prevents further decomposition of the substrate with the release of flammable gasses so preventing combustion of the substrate. Intumescent materials can swell up by many times their original thickness, 50 - 100 times is not unusual so there is a slight risk of the silicate foam causing a blockage of the tube with unpleasant consequences. I'm not saying "don't" but be aware of the possibility and, first time out take suitable precautions.

 

Another way of fire proofing the inside of the tube that you might like to consider is using Parlon. Chlorinated hydrocarbons like Parlon were originally developed as fire retardants in the plastics industry and are still widely used  as such. There's a certain irony, I think, about using a fire retardant as an important pyro ingredient but, that's the way of chemistry. Parlon has the advantage of being soluble in acetone so such a solution used to impregnate a tube would not suffer from the extended drying times that would be necessary for any water based treatment. I would make as concentrated solution as is possible from a practical point of view and apply several coats to the inside of the tube with a short drying time in between. Perhaps a longer drying time or drying somewhere warm would be advisable after the last coat.

 

Hope the above helps and I'd be interested to hear of any results.



#9 Sparky

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Posted 04 August 2015 - 11:16 PM

Cheers BlackCat, nice detailed response there.

 

I actually have a fair amount of Sodium Silicate simply because of the "fun" chemistry aspects of it lol.

 

I'll try a fairly dilute solution, it will need to impregnate a good few layers of paper to be effective. I'm well used to using paper paste with kraft paper as I have pasted a lot of shells over the years. Good tip about the cutter though. I need to invest in one of those.



#10 BlackCat

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Posted 06 August 2015 - 02:03 PM

No problem Sparky, the tubing cutter is also excellent for cutting cardboard tubes to whatever length you want.






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