Gerb/Fountain Issues

[Photon_Junkie]

Hello all,

While I do not consider myself a beginner to pyro, I am new to making gerbs. As most of you know, the Skylighter newsletter has been running articles on gerbs and set-pieces for the past couple of issues. Personally, I have never had an interest in making these things until just recently I had a chance to create a beautiful waterfall arrangement.

Therefore, I thought I would start at the beginning before trying to make the waterfall type gerbs.

 

I made these 4 gerbs using a very straight forward Lancaster mixture:

 

Potassium nitrate - 40

Meal powder - 16

Charcoal, 150 mesh - 8

Sulfur - 8

Iron, 20 mesh - 24

Aluminum, flitter, 10-30 mesh - 4

 

I have the Skylighter fountain set tooling and the proper tube to match that tubing. I cut the original tubes in half so I could make test fires and not waste an entire 12" length.

 

I hand-rammed using a rawhide mallet and followed every instruction I could find on forming nozzle mixtures. I used a mixture of bentonite clay and kyanite with 4% paraffin wax.

 

The link below shows my results. My question is: Why do my fountains loose sparks temporarily then spew forth a large gob of sparks at once? I did place "bumps" at the end of the gerb, so at the very end you should see a burst of sparks. But in the middle of the burn, you see no sparks only a small jet of flame. Then all of a sudden you get an eruption that almost looks like molten lava. I am sure its the iron or dross forming, but why and how do I stop it.

 

As always, any help is appreciated.

 

The guest password is 'rocket' (without quotes)

http://s510.photobucket.com/albums/s347/sc...MyFountains.flv

[Mumbles]

It's formula not technique. It is a very pretty formula, but seems to burn kind of "slaggy". This means there is excess residue building up inside the body of the tube. You can see earlier you will occasionally get big globs flying out and a little puff. Over time it gets more and more aggresive and apparant to the point it completely blocks out the comp until the interior pressure builds and sprays it out. Classic example of an age old proble,

 

I don't know how the skylighter tooling is setup, but is the interior of the nozzle angled at all? A flat interior makes this problem much worse. To make it better you could possibly increase the amound of meal powder or back off the KNO3 a bit perhaps.

[FrKoNaLeaSh1010]

I agree with mumbles that it appears that you are getting too much slag build up. I had this problem when using glitter formulas in fountains. Using a nozzle as mumbles described that is a cone shaped helps or if all else fails use a larger nozzle. Also the comp calls for rather large flitters and idk what size nozzle you were using but i hope you made sure that the particles were small enough to actually come out of the nozzle. I used some very large aluminum flitter that i think i got from mumbles back in the day for a bp based fountain and had a similar problem because it was getting clogged in the nozzle and was sputtering like that. Edited September 4, 2008 by FrKoNaLeaSh1010

[Photon_Junkie]

The Skylighter tooling does have an "eased" or rounded slope on the interior of the nozzle. I have yet to do an autopsy on the spent tubes, once I do that I will post some pictures. I want to take a look on the inside and see how my nozzle mix performed.

 

I agree with both of you, I think the next step is to increase the amount of meal powder and/or decrease the iron.

 

Oh...also...I didn't have flitters per se, I used spherical aluminum in the 10 to 20 micron size. There is only a pinch in this formula but I thought I would mention it. My microstars (#3 and #4 in the video) were very small size...less than 1/2 the diameter of the exit hole.

 

Thanks for your replies!