Author Topic: Gerbs (Fountains)  (Read 457 times)

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Offline Astroboy

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Gerbs (Fountains)
« on: September 28, 2012, 07:38:56 PM »
Gerbs (Fountains)

A gerb is a type of firework which produces a jet of sparks, usually lasting between 15 and 60 seconds. It is a thick-walled tube filled with pyrotechnic composition and possessing a choke, which is a narrowing in the tube. Gerbs are often referred to as 'fountains'.
Sometimes a small charge of black powder is added to the bottom of a gerb to make it finish with a bang: this charge is known as the 'bounce'. These are commonly used at sporting events.
Gerbs intended for use indoors near a proximate audience, such as at a rock concert, typically have shorter duration's (from 1/8 to 30 seconds) and heights (4 to 50 feet).
Commercial Gerbs are usually measured in terms of time and height. For example a 4 x 4 burns for 4 seconds at a height of 4 feet.
« Last Edit: February 24, 2014, 07:28:49 PM by Astroboy »
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Offline Bismuth

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Re: Fountains/Gerbs
« Reply #1 on: December 12, 2012, 01:15:22 AM »
Pre-testing:

It has been one of my goals since I was first exposed to some commercial fireworks back when Canberra was still in action, to replicate a classic golden fountain. Not exactly hard to get one working, but I really want to get it close as possible to the ones I used to remember. More or less, the criteria for these would probably be:

  • Long burn duration
  • Thick length of sparks
  • Good golden colour
  • Low Sulfur content

My memory isn't great, but I believe the commercial ones were nozzleless. I'm sure anyone who has played around with Fe fountains would also know, if you use a nozzle, it quickly gets blocked by the build of molten slag and affects the output of sparks a lot more than other fountains. An easy remedy to the problem is press some fast meal incrementally throughout the fountain to shoot out this slag, but it's just more reason in my opinion to try one without a nozzle.



Alright, after two rather disappointing test trials I have opened my eyes that I've goofed a bit. I've began by using:

'Basic Fountain Mix'

Potassium Nitrate    66         
Charcoal Airfloat    24         
Sulfur                    10
by Tom Perigrin that I took from Passfire's database:

which states that you can add up to about 10% of any addictive(metal) to it. I started off in the wrong path I reckon by using willow charcoal, but I felt it may just screw up my burn time more than anything. I want a long trail of sparks expelling from the fountain, not so much just orange everywhere so it's probably not that critical. For these tests, I have been using iron granules purchased at diversehobbies and 100mesh iron powder. Will change to hardwood charcoal for upcoming tests.

First trial (~10% iron granules and hand pressed)
- Duration sucked as expected.
- Sparks were rather condense in a nice long trickle effect. Not perfect, but not bad.
- Colour needed improvement -- needed more sparks
- Sulfur content is low, so the fountain wasn't unpleasing for audience.

No video for this one, sorry.

Second trial (more iron granules, maybe 15% and then added some 100mesh iron powder)

Video:
<a href="http://youtu.be/kHYcZbZtJoU" target="_blank" class="aeva_link bbc_link new_win">http://youtu.be/kHYcZbZtJoU</a>


Definitely peaked the amount of iron in there that even without a nozzle, it was clogging up. Kicking myself I wasn't smart enough to write down how much I added, but even with the first one I know I need to maximize what iron I put in there so it doesn't get wasted and the solution isn't to just keep adding more iron. Maybe incremental shifts of meal in there?

If you look at maybe like the first 1/2 second of the fountain in the video, the sparks there aren't looking too bad before it gets choked like a bitch. But otherwise, it was a piece of crap. Back to the shop.

Advice, criticism and feedback all appreciated. Will continue to almost blog my progress with this project.

Offline grauling

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Re: Fountains/Gerbs
« Reply #2 on: December 12, 2012, 09:46:23 AM »
You could try more consistent pressing/ramming, in my fountains it made all the difference as far as burn duration and spark plume is concerned. If slagging is a problem and you don't want to widen the nozzle, ramming a half increment of hot bp every now and then will clean things up. Interestingly enough I've found nasty BBQ charcoal to be the best for fountains.

Offline Bismuth

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Re: Fountains/Gerbs
« Reply #3 on: December 12, 2012, 10:09:34 AM »
You could try more consistent pressing/ramming, in my fountains it made all the difference as far as burn duration and spark plume is concerned. If slagging is a problem and you don't want to widen the nozzle, ramming a half increment of hot bp every now and then will clean things up. Interestingly enough I've found nasty BBQ charcoal to be the best for fountains.

Yeah, I agree I need to find a better way to press these fountains. I need to modify my arbor press in order for that to occur though, but I think I've worked out a way to do that easy.

Normally I use BBQ charcoal too, and it works quite well.


Offline mango

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Re: Gerbs (Fountains)
« Reply #4 on: March 01, 2014, 10:29:16 AM »
hi there pyros,i make fountains that burn real good,i use my normal ratio bp, with pine charcoal, i mix magnesium chips,aluminium powder 200  mesh,some aluminium turnings from engine reconditioners and a sprinkle of cast iron powder or very fine chips also from the engine reconditioners, i put a few teespoons of each with my bp in a chinese food container and mix it well, i put a couple of spoons of bp in my tube and ram it with a wooden dowel and wooden mallet,igive it around 10 even hits,then i put a couple of spoons of mix and ram it again,repeat this until the tube is nearly full then i use bp for the last bit..ignition is with a couple of sparklers and a bit of loose bp....i dont choke mine..  i make these fountains in dried bamboo and they take a half kilo of mix i put a couple of radiator hose clips around the bamboo in case they split and i put the fountain in a can of sand to give it stability... they go real good...bye for now and go out and light something

Offline Lemonjelly

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Re: Gerbs (Fountains)
« Reply #5 on: March 04, 2014, 02:36:29 PM »
My favourite plain gold gerb has no iron, but using a mix of course charcoal from the BBQ shop maybe 60# with air float. Hard to make a failure!
And of course, always a winner, the Westech Silver recipe.
When incorporating fine metals in gerb mixes, instead of just mixing everything in an ice cream container, wet,granulate and dry the mix. You will get a much more harmonious visual effect with little or no spluttering.

Offline Lemonjelly

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Re: Gerbs (Fountains)
« Reply #6 on: March 04, 2014, 03:12:04 PM »
WATER GERBS
Has anyone tried to make a water gerb?
"A what??"
Forget teacup candles in the spa for that next cozie night together! (or alone :) Try a few of these!!
It's a gerb which has a collar of balsa or cork secured about two thirds from the base so that when you throw it into water the collar acts as a buoyancy device to keep the gerb upright. You seal them with some waterproof capping and use a waterproof fuse.
Haven't made one yet but I imagine several of these on the water would look amazing

Offline Bismuth

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Re: Gerbs (Fountains)
« Reply #7 on: March 04, 2014, 09:07:41 PM »
I need to get back on these fountains. Very poor effort. I have made some good fountains, but I'm not after the roaring or tall burning ones. They're easy. I'm trying to re-create a slow burning, majestic iron flame with a parabolic curve that disappears as it touches the ground.

Three lessons learned:

1. Screw Perigrin's forumlas. Not to say that one was particularly bad, but he wasn't very good at all.

2. Need to press it. Body weight has poor results and ramming iron containing powder in my opinion is a bad idea. I need to coat my iron too since I think it was rather oxidised.

3. Much wider nozzle.

Lemonjelly:

I have made floating starmines. I used a 19mm? tube and threw it into the river. Used microstars. It worked VERY well. I will get the video.

Hardt has a great section on aquatic fireworks. I haven't tried a fountain.



Offline Astroboy

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Re: Gerbs (Fountains)
« Reply #8 on: March 09, 2014, 08:45:58 PM »
My latest efforts with fountains have been using 1.15"x 4" tubes, the tooling by J1R has an 8mm nozzle that is hollow and allows you to press a fuse in after the nozzle.


Im going to half fill this one with my latest Ti fountain comp, may look to slow it down a little as it burns pretty fast and the nozzle is less than 1/3 of the tube dia.


Im predicting this will run at about 12' to 15' and burn pretty consistent based on earlier tests, Ill light it once it gets dark and post the vid

<a href="http://youtu.be/XhOh0OuVroI" target="_blank" class="aeva_link bbc_link new_win">http://youtu.be/XhOh0OuVroI</a>

As yo can see from the vid it actually cracked about 18' to 20'
« Last Edit: March 09, 2014, 08:48:38 PM by Astroboy »
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Offline stinger

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Re: Gerbs (Fountains)
« Reply #9 on: March 09, 2014, 09:50:30 PM »
Nice. What ti you got in there? wouldn't mind writing that one down for later.

Offline Astroboy

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Re: Gerbs (Fountains)
« Reply #10 on: March 10, 2014, 11:37:41 AM »
Don't really have a formula for this one but I can tell you how I made it.

First I made up 6.25 kg of a base mix (what can I say, I was bored)

BASE MIX

Potassium Nitrate 3.0 kg
Charcoal 1.0 kg
Sulfur 1.0 kg

I milled this together for about 2-3 hours

I then added 1.25 kg of milled Potassium Nitrate, I put this in a large bucket and shook it to integrate for a couple of minutes

Broken down to parts for a smaller batch

Potassium Nitrate 50 pts
Charcoal 20 pts
Sulfur 20 pts

+ 25 pts milled Potassium Nitrate

My thinking for this base mix was to use it for a variety of fountain types including a Glitter hence the high sulfur content

To the base mix I then add one of a variety of metals depending on the effect I want.

Titanium for a Silver White 10%-15% (60m to 100m mix is what i used in the vid)

Cast Iron Granules for Gold 15%

Aluminium for a Silver & Gold  8%-12%(100m to 200m mix) If using 10% or more Al try adding 5%-10% Charcoal Powder as well, this helps with gas production and promotes a cleaner burn and will reduce any issues with the Al slagging the nozzle

For the fountain in the vid I used a further dulled down version, as I was using a large ID tube with a relatively narrow nozzle

Base mix with 15% Ti  5 pts by volume
Tiger Tail made with Willow well milled 1 pts

The base mix with 15% Ti makes an excellent fuel for my 12 mm core burners, nice 6' or 8' tail and good performance
« Last Edit: March 10, 2014, 11:40:43 AM by Astroboy »
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