durhams rock hard water puddy

[hondo]

I got some durhams rock hard water puddy and made some rocket nozzels with it and it works great, you have to dampen the mixture just a little and then press it once it dries its hard as a rock like it says, NO nozzle erosion at all, you could probably add some grog or kitty litter in if you wanted

[Miech]

I guess that is something like a mixture of chamotte clay and sodium silicate? That indeed produces exellent nozzles, but I always have a hard time trying not to ruin the tube it has to be put in. From my mind I would say it is heat resistant to about 1300 degrees Celsius, but I'm not absolutely sure.

[psyco_1322]

Always wondered what that stuff was, never really looked into it though. You could probably press/ram it dry into a tube. Ill have to try that next time I make something with a nozzle.

[Mumbles]

Is it hygroscopic normally? I had always figured it worked something like plaster where a suspension of the anhydrous particles was made, and upon drying it forms a solid mass. If it is hygroscopic normally, it will need to be wet in order to maintain dimensions and not swell from absorbtion of water.

[s1xfiv3tw0]

Always wondered what that stuff was, never really looked into it though. You could probably press/ram it dry into a tube. Ill have to try that next time I make something with a nozzle.

 

 

 

I have never used Durham's Rock Hard water puddy, but if you can't find it at your store, a good (but possibly) messier alternative is to use the paste/glue used for fireplaces or furnaces. I found one at my local hardware store and since it needs to withstand the temperature of fire, I am sure it should be able to withstand it for a rocket. Also, nice post count psyco_1322.

[Arqwat]

Thanks for the idea - I've never tried to ram it damp or dry.

 

I've made several nozzles by casting & drilling, but they didn't seem to hold up for multiple firings as well as rammed bentonite.

These were all with 18mm paper case reloads (KNSU/RIO).

With rammed bentonite, I can get up to 4 or 5 firings from an 18mm nozzle in a paper casing.

Care must be taken not to damage the nozzle throat during cleaning.

 

KNSU is a very low temp fuel & hardly burns the inside layer of the case on an efficient firing.

 

Durhams is more simply determined (by me) to be an extra tough plaster of paris.

It seems to be no more hydroscopic than P of P.

It does set & dry much harder than plaster though.

Cast Durham nozzles can be reinforced with a steel washer.

(not sure if this is legal for pyro motors, but seems to be accepted by TRA Research guidelines).

 

In short - every workshop needs a can of Durhams . . it's great all-around stuff . . .

 

Cheers

[psyco_1322]

I dont think its really hygroscopic, not like dextrin where you get it on your hands it quicky makes them sticky feeling, its just dry.

 

How does plaster of paris and things like it work anyways? Got an insight Mumbles?

 

Thanks, 652, Ive been around.

[Mumbles]

The water of hydration converts the plaster back into gypsum which solidifies and hardens as it dries. Physically I'm not sure what happens, but possibly some crosslinking between water or sulfate molecules. Calcium really likes oxygen, so neither would suprise me. I don't think it'd make a great nozzle though. What makes it heat resistant is the evaporation of the waters of hydration which absorb heat and energy. This would likely also cause the nozzle to weaken and possibly rupture. This probably isn't an issue in pyro sized things though.

[s1xfiv3tw0]

Furnace cement takes a heat-cure to bring it to the strength needed to not immediately erode if used as a nozzle.

 

There might be a use for it, if you have a particularly high temp or long-burning grain, or one that has a high metal content.

 

Be aware that cured furnace cement expands a LOT (much more than Durham's Water Putty, for instance)!

 

Don't heat cure this material if assembled in a rocket that has fuel already in it, obviously.

 

Interesting. The last time I used this stuff was a few months ago (it got replaced when I got a rammer + bentonite clay) and I don't remember it expanding at all. I just remember it looking like hard, wet sand.

 

Cast Durham nozzles can be reinforced with a steel washer.

(not sure if this is legal for pyro motors, but seems to be accepted by TRA Research guidelines).

Cheers

That doesn't sound too safe, what happens if the nozzle or whole rocket blows up or anything else?

Edited September 17, 2008 by s1xfiv3tw0

[Arqwat]

That doesn't sound too safe, what happens if the nozzle or whole rocket blows up or anything else?

My Take :

Using a small washer weighing a few grains (or mg) (we're not talking a 1 oz washer here) ;

 

Assuming A. You're at the recommended safe distance for launch.

. . . . . . . . B. The rocket (launch rod) is angled upward within guidelines.

 

If the entire rocket explodes, the washer would be an integrated component of one of many pieces of flying debris.

Probably the hardest piece would be the nozzle end of the motor.

The washer would have little if any bearing on force & velocity of the flying motor or nozzle.

The most hazardous debris would probably be burning propellant. (refer to "safe distance")

 

In the event the nozzle was ejected from the motor.

The rocket motor should be pointed at the ground when fired.

This would eject the nozzle into the ground.

In the case of the nozzle impacting a blast deflector, the nozzle would most likely be "spattered".

This would use up most of the transferred energy from the flying nozzle leaving the washer with minimal force & velocity.

I don't think it would be any more hazardous than the ejected nozzle itself. (refer to "safe distance")

As well - many reusable motors use steel closure hardware that would fall under the same consideration.

 

Repeating - this seems to be acceptable within TRA Research guidelines :

 

9.4.3.1 Cases, front and rear closures, and nozzles shall not be fabricated of steel.

9.4.3.2 Screws, washers, compression rings and related closures, and sealing devices shall be exempt from requirement

In summary, any additional risk from using a reinforcement washer would be negligable.

 

Any Inputs Welcome . . (especially from any active TRA Research flyers).

 

Cheers

Edited September 17, 2008 by Arqwat

[Arqwat]

No confusion here. That's what we do on here - discuss ideas.

Agreed on clay being the best/easiest nozzle material I've found.

But I'm also an experimenter, so when I hear of a new or different idea I'm tempted to try it out.

I'm hard headed, so I just gotta try ideas out to be convinced.

 

I've gone to great lengths experimenting & tooling with nozzles for some (non-pyro) aluminum motors I've made.

Some ideas were failures but some also worked well.

 

-------Extra Feature--------

 

From a friends motor experimentation gone awry (the agony of defeat):

Jimmy is a friend and a mentor - you may have already seen this.

Jimmy : Tried the silly thing again, the drag queen drag race but made a silly mistake.

Used a hardware-store washer for the nozzle support ring. BAD IDEA.

See the results @ . . . http://www.payloadbay.com/video-7924.html

 

Ouch - Better luck next time . . . .

 

Cheers

Edited September 17, 2008 by Arqwat

[EEguy]

Here is a cast

for your viewing pleasure.

[TheSidewinder]

Let's see if we can embed that....

 

 

http://www.youtube.com/watch?v=KIWRJAPyBfk

 

 

EDIT: Yup. The full link is a larger picture size, but this isn't bad.

[morbidlust]

The Durhams Rock Hard Water Putty is the nozzle recommended in "The Incredible 5 Cent Sugar Rocket" pamphlet from years back. These are obviously very small sugar rockets but it stood up to those quite well. I've had some tubes with the nozzles formed and drilled that have sat in a non insulated garage for about 2 years with very moist winters and they don't seem to have come loose and worked perfectly fine when using one of them recently. Edited July 27, 2010 by morbidlust

[EEguy]

Durham's Rock Hard Water Putty is gypsum based according to their website. Thus, it is mainly hemihydrate CaSO4+1/2H20 (aka-Plaster of Paris). They won't publish on the MSDS, but I'm sure there is some type of glue additive/s. After it is cast, the CaSO4 is attached to two H2O molecules (CaSO4+2H2O), and you have the dihydrite gypsum (a crystal form). The thing to see is that the hardened gypsum has absorbed all the H2O it can, and is not so much hygroscopic anymore, where as before it was. That is why the nozzle will not burn very well; like dry-wall. Interestingly, CaSO4, when baked to form the anhydrous form, is actually a common desiccant, and if used at high enough temperatures, is also a strong oxidizer. Edited February 16, 2011 by EEguy