71 replies to this topic

[Brakkie]

Although I don't have much experience with making bombettes I can tell you that 2-3 grams of photoflash really isn't that much. Photoflash is powerful but it seems to give a pretty soft break nonetheless. I've done some photoflash salutes past new year and they were a lot "softer" than with regular 7/3 flash. I've done 2" shells with 5 grams of photoflash and they still broke relatively soft concidering the ammount of flash that went in there. I think 2-3 grams of flash definetly won't be too much, not even for 30mm bombettes.

I think you could actually go with 3FA BP. From the little experience in disecting inserts I've noticed just like you that they use relatively large grains in their inserts. It would definetly save some on the BP.

[AdmiralDonSnider]

First I wanna say thanks for the kind cooperation in this place!

Secondly... I´m currently trying to acquire the right clay for the job. I want something that will "bite" into the tube when compressed and that does not easily blow out. So plain bentonite is bad as long as it isn´t treated with wax or slt; moreover it won´t bite.

My commercial samples all seemed to use a kind of granulated red fireclay, and the granules - due to the friction - cohered quite well when pressed. So I assume actually using granules is a much better idea than using plain powdered clay, right?
Sources like passfire suggest including "grog" in your treated clay, such as broken pieces of glazed tiles and so on.

I don´t really have a lot of experience using clay, so I wonder if there is an all-round clay mix you can use for rocket nozzles, fountain chokes and clay end plugs and that sustains a lot of force before blowing out?

[Brakkie]

Personally I go for kitty litter and I don't bother milling it. As long as it's rammed (or pressed) hard it'll turn out a hard nozzle that will bite easily into your tubes. Some guys I've heard talking about 50/50. Grinding some and adding course kitty litter to use as the bite.

I'll try to see if I got some time for trying out some bombettes. Gonna see how a 19mm bombette with 2 grams of 60/40 MgAl-flash breaks.



Edit: Kitty litter is the same as bentonite granules. Kitty litter is used as a filler for the boxes where cats do their business

Edited by Brakkie, 23 January 2009 - 11:08 PM.

[cooperman435]

I use plain bentonite clay powder and I guarantee you would never get a clay plug to come out of a tube without destroying it

[AdmiralDonSnider]

I see; however isn´t the question if you manage to press it sufficienly hard to perform as you said. Especially using non-kraft paper the tubes deformed easily and the clay remained scratchable with your nails.

Do you treat your bentonite, isn´t there a moisture issue with tails, prime and air humidity over storage?

Concerning "kitty litter" - I´m not sure what that is (I live in the center of Europe) cause this stuff isn´t available here. Is this bentonite in granules?

[cooperman435]

well you have to press it sufficiently yes but you will need to do so with an additive such as grog in the mix or it wont be forced into the tubes walls to bite in anyway.

Kitty litter is a name we use for cat tray powder? the stuff used to absorb cat waste in trays in you house. I'm a little short of other ways to describe it so hopes that makes sense (which now I read it back the thought of a tray intended to contain cat waste in someone house doesn't seem to make sense to start with!)

Edited by cooperman435, 23 January 2009 - 11:09 PM.

[AdmiralDonSnider]

I understand....

...assuming I´ll have to use it before the cat does.

Nice idea anyway. No wax treatment in your bentonite?

[digger]

I understand....

...assuming I´ll have to use it before the cat does.

Nice idea anyway. No wax treatment in your bentonite?

Yes I agree that you can press bentonite so hard that it ends up looking like glass (3 - 4 tonnes per square inch). However a case former is required for this.

Yes you are right that moisture will affect a straight bentonite plug in storage with the constant swelling shrinking cycles which can cause a cato in a rocket due to reduced nozzle size or simply blowing the nozzle out due to the tube / clay interface being weakened.

I have tried many mixes to overcome this, I would like to use fireclay but this for several reasons is difficult to source in the UK.

One of the better mixes I have tried is:-

50% bentonite oven dried and treated with 10% paraffin wax whilst still hot
25% Molochite 40 mesh
25% Molochite 80 mesh to dust

This mix performs in a more predicable way than straight bentonite which is brittle by itself when pressed very hard. In the case of rocket nozzles under severe stress the nozzle erodes slightly during the burn (with Ti in the fuel) whereas a straight bentonite nozzle may have chunks broken away around the nozzle opening.

[pyrotrev]

Anyone tried a bentonite/sodium silicate mix??? ought to set seriously hard.

[seymour]

Anyone tried a bentonite/sodium silicate mix??? ought to set seriously hard.

I have, but due to expanding/contracting as it dried it's not as strong as desired.

I'm with Brakkie. I never mill my cat litter, and it always makes solid plugs that due to the angular grains bite into the tube.

AdmiralDonSnider, why is it important that the plugs are hard to scratch? is is purely aesthetic? I admit, pressed bentonite plugs are very pretty.

[AdmiralDonSnider]

I just thought something that is still pretty easily affected by a simple fingernail scratch will not be that hard. But you´re right, not really the deal. I personally prefer ugly but working devices over failing ones however.

Just to make sure I got that right: You only pour kitty litter in grains into the tube and compact it? There is no powder at all, right?

Edited by AdmiralDonSnider, 24 January 2009 - 09:43 AM.

[Mortartube]

I powder my cat litter for rocket and gerb chokes as I think it is stronger where there is a prolonged thrust on the choke, but for a bombette I would imagine that if granules were pressed hard enough they would do the job.

If I need to powder cat litter, I use a coffee mill. Incidentally a small handful of cat litter in a coffee mill, is a quick and easy way of cleaning it out in many cases. Just throw the stuff away that you have used for cleaning.

[leosedf]

I tried ceramic clay (dust) some time a go, allmost no corrosion at all on the nozzle but the whole thing was not grabbing on to the tube. I may retry this stuff with some grog or kitty litter.= to see what happens.

Edited by cooperman435, 27 January 2009 - 09:01 PM.

[starseeker]

I remember reading on this forum somewhere that some people smear PVA glue inside the nozzle end of the tube,dip the tube in course sand,allow to dry and then ram your plug.

But i must say i have no problems just using rammed bentonite.

[Pretty green flames]

Alright guys, here are two rammed chinese plug taken from commercial cakes, this stuff literally looks like it was dug up from the backyard and rammed into the tubes as is





It reminds me of crushed clay flowerpots (the orange stuff) bit I have no clue as to what the white stuff may be. It's not bentonite i'll tell you that. And what's amazing is that this stuff adheres to the paper wall REALLY well (glue? Sodium silicate solution?) you can't remove tha paper from the clay plug.

And this type of "clay" is VERY VERY hard, I tried to scratch it with my finger nail, no go. And even with a hardened steel tip I had to put it under considerable pressure to scratch it. Amazing stuff.

DonSnider, have you tried asking your chinese contact for any info on the clay they use? He seems cooperative.