Durable nozzles, rocket tooling vs. grog

[mabuse00]

With my BP Coreburners I settled on pure betonite/graphite/oil.

This is very tool friendly, even aluminium tools do not suffer.

 

However, there is always notable erosion, wich I accepted (it also seems to lead to a constant thrust, overlayed with the coreburner's progressive behaviour).

 

However, when trying my first Endburners I felt it affects performance to much.

Also I'd like to do some experimentation with perchlorate composite fuel based on Epoxy.

This burns much hotter than BP and puts additional strain on the nozzles.

 

I feel the need for something more durable!

 

Now I'm loocking for some experience:

Most people seem to use fireclay/grog in their nozzle mixes.

->On typical steel spindle/aluminium rammer combination, how much does it hurt the tooling?

->How much more durable are such nozzles? Does it make a big difference? Especially when using higher temperature fuels, like whistle-hybrid stuff.

[nater]

I use hawthorn bond clay / graphite / paraffin and have not noticed any significant erosion on core burners, including whistle and hybrid motors. I use the same mix for fountains without any noticeable erosion, but I have not made end burners with it. I quit using grog because it was marring my tooling.

 

For AP composite fuels, don't they typically use a machined nozzle of some sort and a metal casing? I only have some notes about composite / epoxy stars and I'm not really set up to experiment with them right now.

[Mumbles]

Nater, what sort of tooling do you have? I've been looking into getting some tooling. I was just curious if steel spindles, or Nituff coated things might be more resistant to more aggresive nozzle mixes.

[nater]

I have a Nituff coated spindle from Wolter that is scratched a little from nozzle mix, but far from damaged enough to cause problems. Most of my tooling is from Firesmith and turned from bronze, I have never tried a nozzle mix with grog in it. I also have some basic aluminum tooling that took the biggest damage from pieces of grog. This is still very usable, but I don't want to cause any more wear or I might start to have issues with the motor sticking to the spindle.

 

I do press my motors to 7500, the nozzle mixtures are loaded in a complete increment, but need to be pressed part way, then released and pressed again to the full pressure. The nozzle mix can flow around the outside of the rammer causing big problems if it is brought to the high pressure quickly.

 

I am experimenting with a nozzle mix suggested to me by Steve Majdali which uses linseed oil with the clay and graphite. His method is outlined in the Anthology under the SBR articles. He suggested to me that this eliminates erosion with high performance motors. I am HOPING that granulating the fine clay with the oil and solvent. Help prevent it from flowing around the rammed, but I will have to wait for the linseed oil to dry to know.

 

Edited April 5, 2013 by nater

[dagabu]

Mum, I believe that Nituff has to be applied only to aluminum, not steel. When I got my quote from Pioneer Metals last year I was told that only aluminum would take the Nituff coating.

 

Nozzle mixes are like rocket sticks, everybody has an opinion and most are just fine but may not be optimized for use. Nozzle clay can be a combination of a lot of different things but like Nater says, he has some problem with reflow around the rammer that binds it so he has to do small increments to control that. Using wax, boiled linseed oil, virtually any phlegmatizer will help keep the reflow down but using too much causes an even worse problem.

 

The Hybrid fuels like the BP and Whistle mix often used to boost pressures don't seem to erode nozzles like longer burning motors, they even have some tendency to clog at times. Grog helps a lot in keeping nozzles in the tube but pressing any nozzle to 7500 LPI will keep it in the tube way past the tubes failure point, just make sure that the junction where the nozzle top and tube meet does not become the weak point. Even adding a small scoop on top of a hard pressed nozzle and halving the pressure can act as a buffer allowing the tube to not fail right at that spot.

 

I am using Bentonite, Hawthorne fire clay and Kaolin with 1% wax melted in as well as 1% (or less) graphite powder (seed lubricator) to help with compaction and heat reflection. Plus, the nozzles are pretty.

[mabuse00]

hawthorn bond clay / graphite / paraffin and have not noticed any significant erosion on core burners, including whistle and hybrid motors

That sounds good.

 

This hawthorn fireclay stuff (like this here? http://www.sheffield-pottery.com/HAWTHORN-BOND-35M-Fire-Clay-50lb-BAG-p/rmhawbon50.htm)

is originally intended to be used in ovens, fireplaces ect. and is supposed to be mixed with water to make some kind of putty - is that right?

 

Because here in middle europe there are other designations for such stuff, american brand names dont help much

Do we talk about the same stuff?

 

Such oven-putty is usually much finer, I expect it to be more tooling friendly - is that assumption correct?

How many percent do you normally put in there?

[dagabu]

That sounds good.

 

This hawthorn fireclay stuff (like this here? http://www.sheffield.../rmhawbon50.htm)

is originally intended to be used in ovens, fireplaces ect. and is supposed to be mixed with water to make some kind of putty - is that right?

 

Because here in middle europe there are other designations for such stuff, american brand names dont help much

Do we talk about the same stuff?

 

Such oven-putty is usually much finer, I expect it to be more tooling friendly - is that assumption correct?

How many percent do you normally put in there?

 

As far as I know, each clay has one English name each, you should be able to have a pottery shop close to you help with the names if they are written in your native language. The point being that you want a refractory clay like Hawthorne that will not melt and does not heat up very fast to act as the "teeth" to your other finer clays. That said, get the Hawthorne as fine as they make it, don't worry, there is plenty of bite to it.

 

Kaolin and Bentonite both have properties that work well but need a binder, wax works well as that binder, it lubes the flow and allows the grains to slip a bit allowing them to compact better. The Graphite acts as a heat shield and allows the raw clay to be slippery and flow down the tube better.

[mabuse00]

OK. I thik I'll just get some of that oven fireclay and compare the erosion.

 

How many percent do you usually use in your mix?

Edited April 11, 2013 by mabuse00

[Oinikis]

i use bentnite/paraffin wax. i coffemill it, but half of it i mill very finely, half of it only a bit, so it consists of like 1 and less mm grains in diameter, then heat it up and add 10% parrafin wax. when ramming the particles break appart, and doesn't hurt my spindle (it's steel) but before breaking, these particles still dig in the tube. plug and the nozzle are same tall as the ID, it works without recesing the nozzle and the plug, but i do reccease it, just in case, and for better centering. my tooling is homemade BTW. the nozzles doesn't erode. fuel is Sugar/KNO3, ballmilled. Edited April 12, 2013 by Oinikis

[leedrill]

might seem a silly question but i use just straight bentonite is very very fine and compresses beautifully with my static tests ive done even on my end burners i get basically no erosion but have decided to to add 1 or 2% graphite to the clay but

 

i am still at a loss to the correct loading pressure to consolidate bentonite i try to press it to the same pressures recommended for whistle i get no noticeable wear on my nituff coated spindles but am i pointlessly putting too much pressure on it

i.e. will i get more swelling storing my motors putting too much pressure on it

[gregkdc1]

 

I am experimenting with a nozzle mix suggested to me by Steve Majdali which uses linseed oil with the clay and graphite. His method is outlined in the Anthology under the SBR articles. He suggested to me that this eliminates erosion with high performance motors. I am HOPING that granulating the fine clay with the oil and solvent. Help prevent it from flowing around the rammed, but I will have to wait for the linseed oil to dry to know.

 

Do you have more information about this nozzle mix like the ratio of ingredients? I am assuming that the linseed oil eventually cures and bonds the nozzle to the paper casing? How long does it take for them to set up and does it help to add additional catalyst to the mix like Japan dryer?

Last how much punishment can these nozzles take; do you think they could handle APCP? I am going to make some 38 mm single use sugar motors with paper tubes for the next TRA research launch. It would be cool if you could do the same thing with APCP but I don't think paper tubes can operate at a high enough pressure to get a stable burn. It would still be fun to try.

I am actually getting away from reloadable motors. After you figure the expense of the case, I just lost one the other day, the cost of liners, O-rings, nozzles etc. they are still expensive compared to a single use paper tube. Not to mention you don't have to fiddle with assembly at the field.

[nater]

I apologize, my nozzle experiments were set aside for a little bit. What little hobby pyro time was left after things at work was taken up planning a show that we shot this past weekend.

 

To answer your questions, the base percentages are printed in a copyrighted work which I don't have permission to share. I had been using Hawthorn Bond clay with 10% graphite added. Using linseed oil is the new technique for me, and yes Japan Drier helps speed up the curing process. Like I said, I'm hoping the granulated and cured clay / graphite mixture will solve my problem with the nozzle mix flowing outside the rammers.

 

I am under the impression that APCP motors need stronger tubes than paper, so I don't think this would work. I will be more forthcoming with more information after I am positive it works.

[gregkdc1]

 

 

To answer your questions, the base percentages are printed in a copyrighted work which I don't have permission to share.

 

Don't worry about it I understand. Anyway you have given me the info that I need to start experimenting, it was the general theory on how they work that I needed validating.

 

.

 

I am under the impression that APCP motors need stronger tubes than paper, so I don't think this would work. I will be more forthcoming with more information after I am positive it works.

Exactly I thought APCP needs a relatively high pressure to maintain a stable burn; they tend to chuff if the pressure is too low. Anyway I am going to use a large grain of catalyzed KNO3/dextrose propellant epoxied into the head of the tube for the delay/igniter grain. I want to see if having such a large burning grain of KN/DX would help stabilize the burn at a lower pressure?

Does anybody know off hand about how much pressure a basic 48 oz. rocket motor tube is rated for? If this doesn't work it will work with sugar propellant as I have already made similar motors out of PVC, but as we all know those aren't allowed at research launches. Thanks Greg

Edited May 28, 2013 by gregkdc1

[AirCowPeacock]

Creagan.net has a page on tube strengths somewhere.