Neutral and progressive burn from nozzleless motors

[dagabu]

Does that help you find your answer then? I gotta say that after a decade of chasing my tail trying to find better inhibitors for grains in HP rockets, I gave up and just did the dunk-n-drip like most others I knew.

 

I cant think of how a layer of the exact same thickness can be applied to only a portion of the grain except by brushing. You probably will have several mills difference from section to section doing that.

[NeighborJ]

I was thinking of using a q-tip for an applicator, at least that's what I used before. Has to be done fast otherwise it'll get stuck to the grain.

[NeighborJ]

Well I've got most of my ducks in a row for my experimental motor. Tooling from Caleb, several versions of whistle mix but not much time. In the little time I do have available I did manage to press the first motor but also ran into my first road bump.

I had decided to use up an old batch of vanilla whistle in the first motor so as not to waste my high quality whistle if any problems arise. The first thing I had issues with was an extremely sticky spindle, I damn near needed a pipe wrench to remove the spindle. The second issue I found was a cracked fuel grain. I'm not surprised to find this because I believe I know what I did wrong. The vanilla used had a flegmatizer content of 2%, normally on larger motors 3-4% is needed to get those solid grains. The problem on this motor is exacerbated by the huge cone shaped spindle, as the fuel is pressed down it is also squeezed out by the cone, the end result was a network of hairline cracks running the length of the bottom cone.

I will take my fuel and add more flegmatizer To Help it flow better under pressure. I may also try wax instead of mineral oil, yeah DavidF I'm going to try wax. I'm still expecting more issues with the construction of this motor but I will address them as they arise, for now I haven't the time to do much experimenting.

[DavidF]

I'd wax the spindle too! Also, when I had that problem with whistle with universal tooling, I added a 'base' of waxed BP for the whistle to press on, and the cracks went away. The BP has more elasticity than whistle, I think. Another consideration is the length of empty tube at the bottom. If that area is not nice and tight in the tube support, it compresses and re-expands, causing cracks. Steve Laduke calls that 'relaxing'. I also found that twisting off the motors works much better than using a puller, if cracks are an issue. Hopefully something I said is helpful.

[dagabu]

There have been claims of whistle Motors lighting up when being Twisted off spindles. Personally I use my auto eject for pulling spindles out of hot motors now because of that.

[NeighborJ]

Base? As in a first increment of BP? Or a small percentage of BP mixed into the whistle? Please elaborate.

[dagabu]

I have done that too, the first increment of black powder so that I could fuse the Rocket motors differently than straight whistle. I haven't had issues with cracking but it can't be a bad idea to help absorb some of those stresses.

[NeighborJ]

Dag, you gave me an idea. I hate to modify Caleb's new base plate but I may be able to drill and tap two or three holes around it to push on an appropriately sized washer. The washer can be set around the spindle and the push bolts can be left out until after the motor is pressed, then incrementally tightened round robin style.

[DavidF]

Yes, I meant an increment of black powder under the whistle propellant to give it something to press against. In a nozzled 'regular' BP motor, the nozzle performs the same function of containing the crumbly grain.

 

Dag, I don't know what you mean by auto eject, but your Acme screw thread design for rocket spindles is unique and intriguing. The way it splits up the frictional forces to make spindle removal easier is what impressed me most. I would think that any whistle rocket motor ignition that occurred while removing the spindle would be front page news in the pyro community and talked about for years afterward?

[NeighborJ]

OK another attempt at pressing this motor has ended in failure. Another cracked grain.

I made a few modifications to my process and wanted to see what if anything those mods have improved. The first thing is an improved tube support. I split a sch160-2" nipple and used cut off fitting threads as the belly bands, they also serve as the spindle removal tool. By unwinding the thread against the spindle base, it pushes the spindle out of the motor quite easily.

The second thing I did was use a tiny amount of BP against the spindle base.

Neither of these things made any difference, the grain cracked within a minute of removing the spindle again. I don't care about the chipped bottom lip, it's the long length cracks that propagate the entire length of the spindle.

I still have to add more phlegmetizer to the fuel, I just didn't want to change too many things and not know what caused the next issue.

[dagabu]

Typical sign of the relaxation theory SLD has mentioned over the years. This means that the fuel grain still has a lot of stored energy in it and once you remove the support, it moves to equalize that energy, burst casings and cracked grains are typical.

 

You may wish to experiment by trying to increases the pressure on the increment or reduce the pressure but make sure to pay special attention to the size of the increment. I have found (along with hundreds of others) that an increment of less than 1/2 the ID will make the increment solid and add some dwell time (I use the gauge to tell me when it's done) where the ram is holding pressure for a predetermined time on the increment. This helps me a lot in not expanding the grain or cracking after pressing.

 

One final bit of advice, if you are willing. Stay away from split pipe for supports, I have had fantastic luck using David's brass shim stock to make my motors and if I use a tube 1" taller than the support, no tools are needed to tighten or release the tube.

 

Good luck and keep us posted.

[NeighborJ]

I agree with everything you've said Dave although I've had issues with the shim stock. I've streched out the brass on several types of stock causing a bulged bottom so I abandoned the idea. I used very small measured increments, never exceeding 1/8", must have taken 50 presses.

Another limitation I am dealing with is a press capacity of 8000#. This is the reason for such small increments with long dwell times. The whistle fuel doesn't seem to have much comppressability but I do believe the tube walls are absorbing the compression.

The only place the grain is relaxing is on the lower part of the spindle so it may be beneficial to decrease the pressure on the bottom half of the motor in proportion to the pressing surface area of each rammer.

The next goal is to press a motor with increased phlegmatizers, at the current 2% it is just too dry to make a solid grain without extreme hi pressures.

[OldMarine]

What are you using as a phlegmatizer? Oil or wax?

[NeighborJ]

Mineral oil for now, the next batch will be wax.

[DavidF]

Dag, in post #34 I asked about your auto-eject or Acme screw-type spindle release method(s). Did you miss that or is it not something you want to elaborate on? Also, now that I have used my supports for a long time, I can recommend using finger-tightening instead of any kind of tool. I stick the appropriate finger inside the tube. A medical glove adds friction if needed. It works for waxed tubes just as well. I always make sure to insert the end of the tube in the support before dampening it.

 

NeighborJ, I have to wonder how you damaged the brass shim stock support. The plastic washer underneath is important to keep the bottom edge from deforming during pressing. Also, I do NOT recommend Ned's approach of hacking the piece of brass up to make 2 supports out of one piece! I use the 120" length it comes in, always. I've pressed rockets to pretty high forces and never deformed one-? My stock is .005" thick.

[OldMarine]

Dave, I found Dag's picture of his acme thread spindle remover in his gallery:

http://www.amateurpyro.com/forums/gallery/image/2701-img-0285/

[NeighborJ]

Ahh the only stock I could find local was 36". It was not enough.

Why is split pipe not preferred? I was about to remake this one with a SS nipple and fittings if it worked well enough.

[OldMarine]

Check here Neighbor

https://www.mcmaster.com/#shim-stock/=16q41f9

[DavidF]

Thanks OldMarine. That method seems the most suited to this application. NeighborJ, see how he withdraws just the tapered portion while the grain is held in place? That could be quite helpful with the cracking issue. I was wondering though, if Dag's auto eject is different from the Acme design, or just another word for it. Either way, I like it!

[NeighborJ]

My 1# adjustable length spindle works the same way, it draws the spindle out thru the divergent former cone by turning a nut on the base.

I felt that the split pipe would work better because it loosens the support as the spindle is pulled out. The theory is that it will have an even pressure release from both inside and outside simultaneously.

[Maserface]

DaveF,

 

Dave G has two different spindle removal designs, one uses the ACME thread, and one uses a transforming base that pushes the rocket off the spindle-

 

http://www.amateurpyro.com/forums/gallery/image/3109-img-1322/

Edited March 12, 2017 by Maserface

[dagabu]

I agree with everything you've said Dave although I've had issues with the shim stock. I've streched out the brass on several types of stock causing a bulged bottom so I abandoned the idea. I used very small measured increments, never exceeding 1/8", must have taken 50 presses.

Another limitation I am dealing with is a press capacity of 8000#. This is the reason for such small increments with long dwell times. The whistle fuel doesn't seem to have much comppressability but I do believe the tube walls are absorbing the compression.

The only place the grain is relaxing is on the lower part of the spindle so it may be beneficial to decrease the pressure on the bottom half of the motor in proportion to the pressing surface area of each rammer.

The next goal is to press a motor with increased phlegmatizers, at the current 2% it is just too dry to make a solid grain without extreme hi pressures.

 

I only read up to this post, I will get to the rest of the posts after but I wanted to comment first. Using 0.008" brass shim stock, 60" long, I can press 20,000 LPI on a #3 motor with no bulge using only a 1" section of masking tape to hold is closed.

 

Not saying you didn't bulge the shim stock but there has to be another variable in there causing it, Dave and I have just not found this to be true of clean stock appropriately wound.

[dagabu]

Dag, in post #34 I asked about your auto-eject or Acme screw-type spindle release method(s). Did you miss that or is it not something you want to elaborate on? Also, now that I have used my supports for a long time, I can recommend using finger-tightening instead of any kind of tool. I stick the appropriate finger inside the tube. A medical glove adds friction if needed. It works for waxed tubes just as well. I always make sure to insert the end of the tube in the support before dampening it.

 

NeighborJ, I have to wonder how you damaged the brass shim stock support. The plastic washer underneath is important to keep the bottom edge from deforming during pressing. Also, I do NOT recommend Ned's approach of hacking the piece of brass up to make 2 supports out of one piece! I use the 120" length it comes in, always. I've pressed rockets to pretty high forces and never deformed one-? My stock is .005" thick.

 

Dave, I'm sorry that I didn't reply, a LOT has been going on (all of it is good) and I have been pulled away at times. I would be happy to comment.

[dagabu]

I am going to send my designs off to Caleb at some point to produce for me personally. With whistle motors, either one of these designs will allow for much safer spindle removal. I tried to use the spindle removers that use the screw in the base but I stripped the threads out each time. It is also a hassle to do remove the spindle that way. I like the VERY fast and much safer designs myself.

[NeighborJ]

OK I've ordered the shim stock from the link OM posted and made up a new batch of fuel. Benzo this time RIO catylized and with 3.5% mineral oil. It's too cold to make the wax version, there's still 3" of snow on the ground and more on the way so not having a proper workshop anymore is hindering my efforts.

I still haven't gotten a reason why the split pipe support is no good, I spent a lot of time boring it out to fit properly so I'm kinda vested in its implementation.

Edited March 13, 2017 by NeighborJ