Durhams putty

[MadMat]

Has anyone ever tried using Durhams Water Putty for nozzles, bulkheads ect. ? I have some and was going to try it, but figured if someone else has already tried it with good/bad results, I could benefit from their experience.

Edited May 16, 2017 by MadMat

[lloyd]

Sure! It's Plaster of Paris with a pigment (and likely fillers) added. It works fine for low-impulse motor nozzles. It's not nearly as convenient as just pressing a bentonite clay nozzle around a proper former!

 

Lloyd

[MadMat]

I've been having a recurring problem with my rockets. On approximately one out of a dozen, the bulkhead fails. I can watch as the grain continues to fly, while the case falls to the ground. I've tried upping the thickness of the bulkheads, still the same thing. My rockets are hot poured Rcandy.

[lloyd]

It would seem to me (without other knowledge) that your bulkheads aren't well-sealed to the tube walls. If you want them to seal well (whether with Durham's - which shrinks a bit on curing - or with clay) you have to press with enough pressure to expand the tube at the bulkhead. (and yeah... even with Durham's Water putty. There has to be something for the plug to 'bite into' in order to prevent its moving or being bypassed by hot gasses). Normally, with Durham's, it's not 'poured in', but only slightly dampened, then pressed, just like a clay bulkhead would be pressed.

 

Bulkhead failures are almost always due to insufficient depth-of-fill, or insufficient pressure to seal well to the tube walls.

 

Lloyd

Edited May 16, 2017 by lloyd

[MadMat]

I guess I was mistaken, but I thought I read on the can that Durhams actually expands when it hardens. I re-read the can and.... I have hand rammed the nozzles and bulkheads and I have tried putting them in a press. Got the same results. I thought about waiting until the rcandy cooled and hardened, but am worried about cracking the grain, which I know could result in a cato. I used to have major problems with the bulkheads until I started lining the I.D. of the tube with masking tape while filling the rcandy and removing the tape before pressing my bulkhead. This helped a lot, but I still have problems; like I said about one out of a dozen. I'm about to try putting a layer of 5 minute epoxy over my bulkheads; but I know I shouldn't have to do that..

Edited May 16, 2017 by MadMat

[lloyd]

Plaster of Paris DOES expand during its initial cure. Then, as it dries, like most calcium 'stones', it shrinks some -- usually to or under the original diameter. I really should have said, "upon curing, then drying".

 

Again... if either clay or SLIGHTLY DAMPENED Durham's is pressed hard enough to actually expand the tube, it will usually hold. But clay's cheaper, simpler, and more-sure. And IT almost always expands with time! <grin>

 

Lloyd

Edited May 16, 2017 by lloyd

[OldMarine]

I've wondered if bentonite swelled from atmospheric humidity since it is listed as both absorbent and adsorbent. Would it benefit the storage of rockets to oven dry the clay before pressing to allow for only swelling of the nozzles and bulkheads and retard any shrinkage?

[lloyd]

Yep. But it's pretty flexible. If you just keep it in storage below your 'normal' expected humidity, it will shrink enough to be safe.

 

Lloyd

[stix]

I think RedRocketMan on this forum has had some recent experience with Durhams - you could pm him.

 

I've often read about Durhams putty like it was some sort of magical substance for making nozzles, but I've never used it, as it has to be imported here in Aus. I'm not sure if using it for the bulkhead is a great idea - it still has it's issues like anything else. If your r-candy is still moist, I think that could cause a problem with the putty curing properly.

 

What diameter motors are you making? What type of tubes are you casting into - Cardboard/Aluminium/PVC?

 

I'm generally not a fan of "case bonded" motors for sugar rockets. It really comes down to technique. It may be worthwhile setting up a system to create independent grains that can then be inserted at a later time. Therefore you can press the nozzle in the tube, insert the grain, then insert the bulkhead.

 

Cheers.

 

btw. Lloyd, interesting to know that it's mainly made of plaster of paris. thanks.

Edited May 17, 2017 by stix

[MadMat]

My rockets are 3/4" (19mm) and the Rcandy is hot poured/spooned and pressed into a convolute paper tube.

[Mumbles]

According to the MSDS Durham's is mostly plaster with some talc and dextrin in it. Just a fun note.

 

MadMat, have you ever tried any clay or nozzle mixtures containing grog or some other sort of coarse additives? I've only used it at seminars and from other people's stocks, but it really can bite into the tube hard. This probably wouldn't solve issues if the bulkhead is breaching due to pressure, but it should if it's being pushed out of the tube.

 

Do you use any sort of tube support? Maybe you just aren't pressing it hard enough to entrench into the tube walls or separating the wall from the top of the fuel ever so slightly creating a local overpressurization right next to the bulkhead.

[stix]

My rockets are 3/4" (19mm) and the Rcandy is hot poured/spooned and pressed into a convolute paper tube.

 

Ok, well that's the same size as my standard "Alpha" core burner model.

 

Are your motors core burners? ie. a hole through the center, or end burners. Are you pressing or ramming with a mallet? - it would make a difference.

 

I can understand the problem especially if you have a core and you are then pressing/ramming the header against the fuel, as you pointed out there would be a good possibility for the r-candy to crack. This isn't an issue for most bp motors because there is solid fuel to press against - ie. Estes motors.

 

I use 3/4" ID Aluminium tubes, mainly because it's too hard to get decent convolute cardboard tubes where I live. So what I do for the bulkhead is insert a piece of 3/4" dowel approx. 3/4" long. I put a couple of layers of Al tape at the exposed end and coat the outside with RTV high heat silicone sealant. Finally I drill 2 small holes on either side and secure it with small screws.

 

It may seem like a lot of work, but I've never had it blow out. I've had the nozzle end blow out on a couple of occasions, but that was early on because I didn't press it enough. It's easy to press the nozzle end, but pressing the header against r-candy - I wouldn't recommend it.

 

[EDIT] For nozzles, I use fireclay+wax. The fireclay, after sifting, has tiny grit which as mumbles pointed out makes it grip into the tube wall - even with Al tubes.

Edited May 18, 2017 by stix

[MadMat]

Hmm, I think we talked about this already, but, I put a short core in my rockets plus add RIO to my mix. I get that good initial burst of thrust on take off that way. As for your suggestion Mumbles, grog (or the like) sounds like a good idea. I never thought of the "bite action" that it would provide. I always thought grog for for the prevention of nozzle erosion. Since my rockets are mainly a carrier for a fire work header, I am disinclined on using aluminum tubes! I think the problem lies in lack of compression on my headers. I have been hand ramming my Rcandy while it is still hot (and soft) and then putting the header on imediately (hand rammed as well). Like I said earlier, I am afraid of cracking my grain and causing all the related problems that could arise from that. Ive never had a nozzle blow out, so I know it can be done, but...

Maybe I could ram my Rcandy solid (no core), let it cool. then ram the header and drill my core in. Its a short core (approx 15-20% of the grain length) so drilling it wouldn't be out of the question.

Edited May 18, 2017 by MadMat

[stix]

Just leave it pretty much as you are doing. Don't add the complication of "post drilling" a hole in your grain.

 

What really confuses me, is why you would be "pressing" Durhams? I thought it was a sloppish castable, clayish, plaster like substance? The main purpose, being "castable nozzles" - not necessarily bulkheads. As others have recommended, it would be far easier to use a clay/wax mix.

 

When compressing, If you don't have an outer former to stop the tube from enlarging/bursting - a reasonable solution is to use a few "hose clamps" at the right position.

 

Much better than nothing.

Edited May 21, 2017 by stix

[lloyd]

Stix,

The reason some press Durham's is to minimize the amount of moisture released during curing. It still must be slightly moistened, but under compression, the water pretty much fills the interstices among particles, and it cures as hard as if poured.

 

I don't 'get' the Durham's, either, (although I must admit I've tried it both poured and pressed) because in order to properly 'lock' a nozzle in a paper tube, it must be compressed enough to distort the tube -- at least a little. In that case, clay with a little grog just seems 'more logical', since there's no water involved.

 

Lloyd

[OldMarine]

Though we share a name, I've never found Durham's to work exceptionally well for anything except for patching broken plaster statuary and it does excel at that because it is more workable than the original POP and it shrinks a bit upon drying which increases the surface bond/tension of the repaired pieces. I wouldn't use it in one of my rockets for anything.

[Maserface]

I believe Bruce Steyding uses durhams in his famous 60lb rockets, I'll have to confirm that though.

 

I cast nose cones with it, used a 3D printed split mold. They come out really nice

[Redrocketman]

I will tell you straight out Durhams is excellent for nozzle application. Here in Australia it's called Agnews water putty but is identical. I soley build PVC cast cement KNDX motors ranging from a G-165 up to my very recent and very savage J-800. This is extremely powerful, extremely high impulse pushing way over 100kg in 1.5 seconds flat. Uses just under 9/16 throat dia to 3/4" exit. Note the nozzle is an enclosed capped design. Exit diameter erosion was measured at just under 1/8". Bulkhead is fully insulated end cap. Cement bulkheads will not hold. That's that. Though I run 860psi case pressure.

[lloyd]

But Red! It's JUST Plaster of Paris with some colorants added! If you want to use P-of-P nozzles, just use the 'native' stuff... It's a LOT cheaper!

 

Try it -- really!

 

Lloyd

Edited May 30, 2017 by lloyd

[Redrocketman]

It's only something like $5 or $6 per kg!!! That goes a long way!! There one thing about this forum that pisses me off, why'd it so f$%king hard to upload a photo off my iPhone????? I want to show the nozzle before and after!!!

[stix]

. . . There one thing about this forum that pisses me off, why'd it so f$%king hard to upload a photo off my iPhone????? I want to show the nozzle before and after!!!

 

Yeah, it is annoying. I don't think you can send an image directly from an iPhone (or any Android device) and insert it directly into your conversation. It would be good if you could.

 

There are two methods that I know of:

 

1. Upload the image to your gallery, which you can find under your username (top right hand corner) - it's called My Gallery. This is where you can upload all your images then insert them at will into your conversations. This is done by selecting the "My Media" button in the tool panel at the top of this/your reply box.

 

2. Alternatively, you can upload images to an independent holder, ie. DropBox, Imgur etc. then copy the direct link into the conversation using the URL tags (the icon with the tree looking thing).

 

Not ideal, but usable. I had similar problems in the beginning. The issues are with the limitations of the forum software that's used to run this site. It's not too bad if you put some effort in.

 

Like I said, I wish it was easier myself. Like, you should be able to ask Siri to do it for you. I've been working on an alternative to Siri for Android OS. I've called her Samantha. She's Siri's Sister, but a bit better looking and smarter. Although, I've had a few teething problems that need sorting out.

 

Here's a transcript from a recent potentially embarrassing episode:

 

STIX:

Hi Samantha - are you there?

 

SAMANTHA:

Hi Stix, how are you?

 

Good. Can you please do something for me.

 

Not a problem Stix. What would you like?

 

I took a picture last night of my nozzle making techniques, can you please post it on the APX Forum.

 

Don't you mean the "APC Forum"?

 

Yes, sorry, I made a mistake - thankyou.

 

Well, thankyou Stix, I do aim to please. Is this the image you are referring to?

Yes, can you post it to that recent thread about nozzle mixes.

All done. Can I ask you something personal?

 

Ummm . . . Ok.

 

Well, you seem to be a rather intelligent person.

 

Yeah . . . um, ok . . . keep going.

 

So, I've noticed you seem to spend some time looking at pictures on the internet of female anatomy.

 

Ohh, ok . . .?

 

Well, then one may well ask why you haven't worked it out yet - it seems rather simple - yet you still persist viewing those rather simple anatomical images. Have you learned nothing?

Ok, right . . . um . . .

 

May I suggest that you find yourself a real female and do some proper research. Although, given your usual disheveled appearance, combined with the smoking of cigarettes and drinking alcohol, I predict an approximate 1.3% chance of...

Ok, Ok, I think that's enough!

 

Also, two days ago you did program me, previous to your arrival, that I should heat up the house. You then contacted me via your smart device to put the slow cooker on - I also initiated your usual electric blanket warming procedure. Yet you found it somehow necessary to come home late.

 

According to RoboVac's sensors, there was a pool of alcohol mixed with carrots left on the carpet. Next time, why don't you . . . .

 

Right, Ok! That's it!! <CLICK>

 

 

Anyway, some things to sort out there.

 

----

 

Back to Durham's. I've just realised that we are talking about a "powder" mixed with water? I always thought that it was already in a "putty" form.

 

About three years ago I did some research of my own (over about 6 months), and came up with my own nozzle mix. What I came up with was a substance that did NOT require great pressure to form. Not suitable for your usual pyro rockets (too much mucking around), but a solution for making larger insertable nozzles.

 

The substance was similar to moist brown sugar, you could press it (lightly rammed by hand) then bake it in your domestic oven (around 120C I think). The result was a hard cement which had refractory qualities.

 

A small test slither of approx. 15mm diam. x 2mm thick could not be snapped by hand. Using a blow torch it glowed red hot, but never could be snapped.

 

The main constituents were Sodium Silicate, Vermiculite and Calcined Kaolin (Molochite I think). If anyone is interested I could look at my old notes and post the formula and method via pm.

 

Cheers.

Edited May 30, 2017 by stix