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Air pockets in r-candy


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#1 JMan

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Posted 07 November 2017 - 07:39 PM

Using recrystleization method, I always seem to get air pockets in my fuel grains (1 in diamater). I was wondering if theres any way to help get the fuel less airy? I had three thoughts on how to get less air bubbles.
Make the fuel more liquidy so it can be poured and air bubbles can work their own way out.
Extrude the fuel so you dont pack the fuel in one inch chuncks (air gets trapped between these globs of fuel for me).
Make a vacuum chamber so the space between the fuel is negligible once removed.
If anyone has experience fixing air bubbles in rcandy please help me. My problems usually dont cause catos but its not rare that an air bubble ruins my launch.

#2 greenlight

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Posted 07 November 2017 - 07:51 PM

How about melting the fuel as liquid and fluid as you safely can and then vibrating it as it sets. The vibration should push the air bubbles to the surface and out.
Maybe some sort of household motor or something could provide the vibration (lawnmower).

Im not that experienced with rockets but I have read of the method being used to cast molten TNT.

#3 JMan

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Posted 07 November 2017 - 10:44 PM

Ill give it a try on my standard rockets but I think its too thick (and cools too fast) to be noticeably effective. However, it sounds much simpler than building some sort of extrusion machine.
Thanks for the suggestion

#4 JMan

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Posted 08 November 2017 - 11:21 PM

Ive been researching and sorbitol (15 dollars per kilo is a good price on amazon) has a much lower melting point (and dosent caramelize or absorb as much water YES).
Can anyone who has used both KNSU and KNSB comment on the viscosity of the two mixtures? Im thinking the lower melting point (and the fact that I can heat it past the melting point with out worry) would make it much more of a liquid. Thank you for any other comments on sorbitol you might have.

#5 stix

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Posted 10 November 2017 - 01:32 AM

Hi Jman, I've done some testing using Sorbitol - this was around 2 years ago. I've made some grains, but never got around to making an actual motor with it... yet!!.

 

Your post has prompted me to check out some of the sample strands that I made (2yrs+ ago) - some are ok, some have been ruined by moisture. The grains look ok. I should get off my arse and make a couple of motors to test.

 

Anyway, Sorbitol - yes it does melt at a lower point (115C/235F) than Sucrose. But I don't think that fact is going to help you pour/cast it. I've made motors using KNSU, KNDX (Dextrose) and various others and the best candidate for pouring was Xylitol but that was pretty expensive.

 

The main issue with "pourability" or low viscosity comes down to the particle size of the KNO3 and not so much to do with the sugars. I have tested this and it holds true and also makes sense when you think about it.

 

For example, let's say you are using the melted method but you decide to melt the sugars first, then mix in the KNO3. Taken to the extreme, lets imagine the KNO3 particles are 2mm(1/16") diam. and you mix it into the now melted liquid mass - the KNO3 won't melt, so what you have is a somewhat "pourable" fuel mixture. It probably wouldn't burn well, if at all.

 

Taken to the other extreme, if you add finely ball-milled KNO3, you end up with a "putty" and certainly not pourable - but a highly integrated mix than burns well. There is probably a good happy medium.

 

What also compounds the "pourability" of your fuel can depend on how big the mix is. If you are making a mix of around a couple of kilos, then the larger mass helps keep the whole thing hot, and when you pour it also drags the rest with it. A small mix of the same fuel would not pour. You could add a surfactant which helps lower the surface tension but I haven't read of any great success in this area.

 

So what does it all mean?  Well to me it meant giving up on finding a suitable "pourable" sugar-fuel, and I concentrated on the "Putty" method, whereby you roll strands/balls and wrap, insert and press into your forming tool to create the grains.

 

This method has worked well for KNDX (Dextrose) because the dextrose melts at around 145C. I've made many successful motors using this method and Dextrose. A couple of years back I came across some reasonably cheap Sobitol which is what I would always have preferred because of the lower melting temp and therefore extended "setup" time.

 

I did a couple of months of testing using various formulas. I came up with a mix that is a putty which is able to be formed and has a setup time of around 5mins which is very good. However, I did find that Sorbitol will make the fuel more brittle than Sucrose or Dextrose.

 

These are my findings and hopefully there is something there that is useful to you and others. Happy to answer any questions - or criticisms :) you or anyone else may have.

 

Cheers.


Edited by stix, 10 November 2017 - 01:36 AM.

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#6 Sparx88

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Posted 10 November 2017 - 02:49 AM

Thank you stix. I just recently started to really try sugar rockets this time and what you said answered a couple of things.

 

what I have in mind for getting the air bubbles out of poured mixes is donating a playstation controller to the cause and using the rumble/vibrate motors wired to a 9 volt battery and momentary switch. Might work out. Since I don't own a playstation anymore but have some old controllers for the ps2, why not. 


Edited by Sparx88, 10 November 2017 - 02:55 AM.

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#7 stix

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Posted 10 November 2017 - 06:13 AM

In a heated vacuum chamber, that sounds like a good possibility.


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#8 JMan

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Posted 10 November 2017 - 01:33 PM

Thank you very much Stix. I never though about the kno3 size but that does make sense. I've ordered some sorbitol and it will be here next week ill be sure to update you guys on the fuel when I test (I don't have the materials to do real quantitative tests so they'll have to be qualitative). I plan on trying four tests with 1 inch diameter grains

 

1) pouring kno3 in liquid sorbitol (kno3 is about .1 mm grains).

 

2) curing above method in a shaky vacuum chamber (a mason jar fixed atop my shaky vacuum pump).

 

3) dissolving kno3 in water and recrystallizing in liquid sorbitol.

 

4) curing above method in a shaky vacuum chamber.

 

ps. I might do some tests with mixes of sorbitol and sucrose as I've read about some people using sorbitol as a binder in KNSU.


Edited by JMan, 10 November 2017 - 01:34 PM.


#9 mikeee

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Posted 10 November 2017 - 03:02 PM

We have a customer that makes large R-Candy fuel grains for big motors who uses our Erythritol sweetener

product. This product has a lower melting temperature and he has had good luck with using this product for

a number of years. He uses a Presto cooker and pours his fuel grains in a liquid form and then lets them cool

and removes them from the form.



#10 MadMat

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Posted 10 November 2017 - 05:38 PM

I usually make 3/4" i.d. rockets and have never had problems with air pockets (I've had other problems though!). I don't fill my tubes all at once, but rather fill them in approx 5-6 stages and press in between each amount. I've found that the tool you use for ramming/pressing is kind of finicky in the desired fit. It needs to be close to the i.d., but not tight; I figure you need room for any air to escape. I usually press my rockets with just the pressure I can muster by hand. Once the grain is in a cardboard tube, it stays hot for a good while, so I haven't had any problems with it hardening up too soon. BTW, I add water to my KNSU and boil it down. From everything Ive read the dry method is supposed to have a lower viscosity than boiling down a water solution, but my experiences have been exactly the opposite; hmm.  So, thats my two cents worth.


Edited by MadMat, 10 November 2017 - 05:41 PM.


#11 stix

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Posted 12 November 2017 - 12:28 AM

Thank you very much Stix. I never though about the kno3 size but that does make sense. I've ordered some sorbitol and it will be here next week ill be sure to update you guys on the fuel when I test (I don't have the materials to do real quantitative tests so they'll have to be qualitative). I plan on trying four tests with 1 inch diameter grains

 

1) pouring kno3 in liquid sorbitol (kno3 is about .1 mm grains).

 

2) curing above method in a shaky vacuum chamber (a mason jar fixed atop my shaky vacuum pump).

 

3) dissolving kno3 in water and recrystallizing in liquid sorbitol.

 

4) curing above method in a shaky vacuum chamber.

 

ps. I might do some tests with mixes of sorbitol and sucrose as I've read about some people using sorbitol as a binder in KNSU.

 

 

Jman - I had a look at my notes and this is my formula using un-milled KNO3 (done mid 2015):

 

KN65/SB35  KNO3 is Un-Milled.

(ie. use the powder as supplied - similar to castor sugar)

All components are manually mixed.

Combined powder is melted in frypan whilst mixing and slowly bringing up the temperature to 100-120C (leave for 5mins). Sorbitol does not caramelize.

The fuel is then thoroughly incorporated by mixing in the pan.

1. AT AROUND 110C, IT COULD EASILY BE POURED, GIVEN THE CORRECT TOOLING.

2. BACK THE TEMP DOWN TO AROUND 60C FOR PUTTY TYPE ROLLING.

Results: Leaves too much residue - Don't bother with this formula.

 

 

If you read my point 1, which is what your point 1) refers to, I mention that it could easily be poured. I also mention that it leaves too much residue when burned.

 

However, I was only rolling strands when testing, so under the correct conditions, ie. an actual motor under pressure and higher temps it may well leave little residue. Also the fact that you will be making 1" grains will be a lot easier that trying to pour 3/4" ones.

 

 

I've also tried the re-crystalzed method as per your 3). The results were odd and unexpected:
 

27/5/15: KN65/SB35 Recrystalised Method.

Dissolve in enough water.
Raise temp to 10-110C to boil off remaining water.
Mix thoroughly to the 'mashed potato' stage.
Leave at 100C to ensure all water is driven off.
Should create a roll-able putty.

 

Results:

 

Overall not very good.

The strands aren't that hard and pretty easy to snap.
Burn test: Not that fast and leaves some residue - I'm surprised, I thought it should have burnt very fast - The "recrystalised" method for this fuel may not be good.

Anyway, not worth bothering with again.

 

 

I found for some unknown reason, Sorbitol (and some other sugars like Xylitol and Erythritol) react differently to the recrystalised method compared to just a straight melt. From memory I ended up with a "crumbly mess". I then put the temp up to melt it, which it did eventually, but now above what would have normally been the melting temp - I ended up being able to roll test strands but they didn't perform the same.

 

These were my experiments and I enjoyed doing it. It's always fun experimenting, and it kept me entertained for many months.

 

It will be great to see your results. Make sure you keep notes.

 

I have a database of my formulas and what methods were used including the results (although there are bits missing). If you're interested (or anyone else), I could post a copy of the database. With it you will also be able to create your own formulas and enter test results.

 

HJDPqZY.jpg

 

You can also use it for other pyrotechnic formulas. It makes it very easy to measure parts & total mix etc.

 

If anyone is interested, I'll see how I can post it on this forum. It would be a shame for a lot of past effort not to be of benefit to others.

 

Cheers.


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#12 chuckufarley

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Posted 12 November 2017 - 03:30 AM

I would be very interested in that stix.

#13 stix

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Posted 12 November 2017 - 04:19 AM

Ok Charley.

 

I'll say this, IF there are at least 3 people that want this, then I'll do it.

 

I say that not just because I'm an a'hole, but because I have to check on another older computer and then create a "build version". A reasonable amount of work for me but happy to take the time to do that if more people are interested.

 

Also worth pointing out that the components, ie. Component_1 is a drop-down list that is derived from a list of chems that you can add to:

 

wCelC0D.jpg

 

It's also un-finished but it works as a very useful tool as it is.

 

btw. I don't wish to diminish or hijack JMans original thread, so I'll move this to my own thread if that is more appropriate.

 

Cheers.


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#14 CoalesceRockets

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Posted 12 November 2017 - 09:54 PM

Hey guys, first post for me...

 

So what is the consensus on max thrust sugar mixture? Cane sugar? Powdered sugar? I ordered some glucose paste to try. 

 

Results on hard packing fine powder vs. KNO3/sugar melting?

 

What are the comments about adding aluminum powder to such mixtures? Too toxic due to thermite? I've seen conflicting remarks on this.

 

Thank you!



#15 stix

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Posted 12 November 2017 - 11:58 PM

Hi CR,

 

Best you post this as a new topic under the Rocketry section.

 

Cheers.


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#16 JMan

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Posted 14 November 2017 - 05:23 PM

Hi. Starting to think that I should start a new thread on "beginners guide/walk-through to sorbitol rockets"

 

Anyways my vacuum pump kind of sucked up water and seized, so, no vacuum tests for a while.

 

Today I dissolved kno3 into water and added sorbitol boiled it off. Took longer than expected (about an hour and a half). Upon the fuel becoming more solid it acted just like sucrose. It didn't melt until about 200c and caramelized (yes it is 100% sorbitol). I packed the rocket and lit it off and personally I though it had more power. I filled a 1 in diameter 2 inch length rocket with 1/8 in core (and nozzle). My normal sucrose fuel would not fly this thing, but the sorbitol flew about 100 meters high! I'm going to try and experiment more with the melting temp of sorbitol since this fuel melted around 200c. I blame the recrystallized method. I think it made the fluid more viscous and appearing solid when the sugar was actually melted.



#17 JMan

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Posted 15 November 2017 - 07:33 PM

Ok I just did the dry melt method and I would swear by it from now on. The fuel is like play-dough at body temp (so you can roughly mold/shape it in your hand), like syrup at about 100-125 and egg whites? Idk what to call it but between water and syrup. It fills all voids no air and I truly believe it is more powerful than surcrose
I know mathematically surcrose is more powerful but I think the degradation of it causes it to be less powerful than sorbitol.
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#18 stix

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Posted 17 November 2017 - 01:07 AM

. . .  I blame the recrystallized method. I think it made the fluid more viscous and appearing solid when the sugar was actually melted.

 

 

Ok I just did the dry melt method and I would swear by it from now on. The fuel is like play-dough at body temp (so you can roughly mold/shape it in your hand), like syrup at about 100-125 and egg whites? Idk what to call it but between water and syrup. It fills all voids no air and I truly believe it is more powerful than surcrose
I know mathematically surcrose is more powerful but I think the degradation of it causes it to be less powerful than sorbitol.

 

Sounds like you experienced the same odd behavior I had with the recrystallized method with sorbitol. I wonder why it does this? Might be worth asking the question in the chemicals section.

 

In any case, the melted method is far superior IMO.


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#19 pyropro

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Posted 17 November 2017 - 08:11 AM

atmospheric pressure could be the blame.Trying melting to a liquid and pour into molds using a toothbrush as a source of vibrating. I made many a large candy rockets and never experienced airpockets.There is an alternative also.After your candy has become rock hard rub it on a cheese grater once its flaked press as you would a bp rocket but with much less pressure.I made hundreds of candy rockets this way and got very good lift qualities.


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#20 stix

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Posted 18 November 2017 - 02:32 AM

atmospheric pressure could be the blame.Trying melting to a liquid and pour into molds using a toothbrush as a source of vibrating. I made many a large candy rockets and never experienced airpockets.There is an alternative also.After your candy has become rock hard rub it on a cheese grater once its flaked press as you would a bp rocket but with much less pressure.I made hundreds of candy rockets this way and got very good lift qualities.

 

I've heard of this technique before. I did try something similar a while back by crumbling into small granules then ramming hard with a hammer. That experiment ended with a big bang!! (fortunately not whilst hitting it!!). Exciting in one way, but not the result I was after. The crystals must have been too hard to compress and had tiny tiny voids for the flame to propagate.

 

I'd imagine that the grated fuel has to be pressed immediately - or can you store it in that form?

 

. . . The fuel is like play-dough at body temp (so you can roughly mold/shape it in your hand) . . .

 

I've found that even in that play-dough state it burns extremely well.

 

One thing I've also done is add a small amount of carbon black. This helps the mix to retain heat and remain softer for longer. Being an opacifier, It also helps (I believe) to slow down the burn rate of an internal (cored) motor - if that's what you want.

 

JMan, you also mentioned:

 

I might do some tests with mixes of sorbitol and sucrose as I've read about some people using sorbitol as a binder in KNSU.

 

Don't know if you read one of my old posts but my current composition includes powdered sucrose. I can't find much documentation as to exactly why I thought this was a good idea, but I think it was to do with trying to find a way to strengthen the standard KNSB mix. It also helps to make the mix more pliable and has the added benefit of reducing the (sugars) cost by approx. half.

 

At the lower temperature, the sugar does not melt/decompose much, and therefore is suspended within the sorbitol which acts as the binder.

 

My current composition, although not tested in a motor as yet, is:

 

NXgi9Kc.jpg

 

The Carbon Black amount is just a guesstimate. I'd say a standard match heads volume (or less) for every 100 grams. It makes the fuel look a nice dense black - perhaps it doen't do anything, but it sure does look good. :)

 

The powdered sugar should be "pure" as some contain starch or other ingredients to help it not clump and also help it set quicker - or something to that effect. I also decreased the KNO3 and increased the sugars from the standard KNSU-65/35 mix to 62/38 which also lowers the viscosity. The strand burn tests I did left almost no residue, so in that sense this composition is looking very positive. I've cast some grains (2yrs old) but still have not tested in an "Actual Motor".

 

I've found this mix so silky smooth that one night, when asked to go out with friends, I decided to stay home and fondle it's silky smoothness instead. Although, come to think of it, I probably should get out more. :)

 

We all have our crazy ideas for making the best sugar-rocket-fuel. In my view, the fun part is in experimenting.

 

Cheers.


Edited by stix, 18 November 2017 - 02:37 AM.

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