Re-melting r candy

[Redrocketman]

I am wondering if those out there using kno3/Su fuel have any sound knowledge as to what % of performance degredation would result from re-melting previously cooked r candy fuel? I am reluctant to throw away good fuel, and so have stored what was left from previous batches, which has ended up a reasonable quantity. I have blended all the leftovers together and have reduced the said fuel to a reasonably fine product, knowing that all batches are mixed at the same identical ratio & same procedure.

I understand that some degredation will result ( of Su, or chosen fuel ) from any heating, but am curious as to whether it would be very, if at all noticeable seeing as it would effectively be cooked twice...

[NeighborJ]

I've made a lot of sugar rockets and it was common practice for me to melt more than I needed and remelt leftovers into it. I've never noticed a difference unless the leftovers were caramelized, in which case it didn't seem to decrease performance but it was more brittle and had a higher likelihood of cato. If I suspected this I would add a small amount of corn syrup as a precaution and I still would not use it in my good rockets.

[MadMat]

As long as you don't over-cook and caramelize the sugar (you will notice by the brownish color change) you should be fine re-melting Rcandy. Some caramelization won't hurt (and is probably unavoidable), but too much will drop the performance.

Edited August 5, 2016 by MadMat

[Redrocketman]

Cheers. Just finished casting two 7.5 X 1 inch cored grains, they turned out fine. After re-melting the fuel was much more like the old mash potatoes style though, like Dissolving in water method. Not pourable. Though I have just got a different electric pan, may not have had temp exactly right. I use corn syrup in all my fuel so that helped it stay pliable as it cooled. Definitely still a pain in the ass to cast small grains as opposed to fresh fuel, still, that could be due to me not being used to the new pan

[NeighborJ]

7.5" long Bates grains? 1/2" core I assume? Am I misunderstanding this? Grains that long would have surely cracked under pressure in one of my motors. I would use a chart outlined in the Jacobs rocketry website, where the 1" grains were all 1.75" long, multiple grains were used to increase surface area. No wonder it's such a pain too make those grains. On my chart the impulse is somewhere around a G160 with a nozzle dia of 23/64" that would make a big boom. I'm curious where you got this design, and if it works I might just have to pull my skillet out and try it.

[Redrocketman]

You read right. For my PVC G & H class motors I use a single cored grain. I - K multiple bates grains. I only build PVC motors now I have polished the fine details, no case failures, not even a nozzle fail bar some expected erosion.

 

7" X 1" X 7/16core single grains G & H

Same dimensions x2 For I class

4" X 2" X 1/2"core bates grains for J & K class. ( 4 & 5 )

 

Yes, the K motor is 20" long + nozzle & retainer!!

 

I have had brilliant results all being its a pain to cast ( I usually prep fuel to a pourable state )

 

Have gone through designs with Richard Nakka & he's seen the vids - was real impressed.

[Redrocketman]

Sorry English isn't my forte, I think I used the term bates when I ment single in the OP!! Edited August 6, 2016 by Redrocketman

[NeighborJ]

4" casings? Wow, I gave up on anything larger than 1 1/2" because I was plagued by a rash of catos and it was getting expensive replacing the electronics. They fired well on the test stand but I believe the hot summer sun accelerated the burn characteristics of the sugar. I used rebuildable apcp after that. The guys at the club would roll their eyes and stand back a little farther when I pulled out a sugar motor.

[Redrocketman]

Bugger. I live in a cold climate so have never struck that issue. I will admit I suffered my 1st CATO today on the stand, due to my own, I suppose complacency... Coring rod was off centre so after loading the grain, the core was offset from the nozzle centre. I thought I'd get away with it, no sir re. It fired and burnt for about 1 sec, then poof. Though it was a tad more than a poof!!! I will swear by dagabus wisdom that distance is your safest barrier!!!!

I'm on a mission to go large and really exploit the capabilities of PVC. There is a lot of room to improve I think, but u do have to be very careful.

Isn't that part of the passion tho!!!

[Redrocketman]

Ps, u may have mistaken my dimensions.

 

4" length x 2" width with 1/2 core.

 

Is that a bit more reasonable!?

[NeighborJ]

That off center core would certainty be a problem on these rockets. Since my grains were short and many, I'd place those off center ones at the top so as to not create obstructions. I also found it easier to cast the grain solid then drill it out on the press using a centering bushing. Mabe not as safe but it worked well with spade bits in small increments.

The 2"x 4"l makes grains make more sense now. That was about were I found were the limits of my ability. I can't remember the exact data but as pipe size goes up, it's burst pressure goes down. This forced me to derate the larger motors almost to the point where they become useless for lifting large rockets. I had bought aluminum casing tube to machine for them but I got sidetracked by pyrotechnics and have gotten lost in all these firework motors. In having a blast though.😁🎆🎆🎆😛.

It has long been a suspicion of mine that the remelted fuel actually burns hotter then the first melt and I believe it has to do with better homogenization of ingredients. I have always had a higher Cato rate on 100% remelt. This could also be caused by its increased brittleness or air bubbles trapped under the hard flake remelt chips. This is why I add a little extra corn syrup, to help fill voids and prevent brittleness. If I am catalyzing with RIO I simply don't add any to the virgin melt and rely on the smaller amount left in the remelt. I generally didn't exceed 50% of remelt in an attempt to maintain consistency.

Edited August 7, 2016 by NeighborJ

[Redrocketman]

I agree wholly that burn rate is higher after 2nd heating. I did a strand test yesterday and when it got about 15mm from the end it zipped into the air like a little rocket!! I too use RIO, but in this new design it's not really necessary. My girls just love the 'Turkish Delight' coloured pink grains Though!! The residual water in the corn syrup must get evaporated, as they are much more brittle 2ndtime around.

I was spewing yesterday, I also put together a 1"X 16" motor, using 2 spaced 7.5" X 1" grains. Just doubled length of a H motor. 1grain slid in OK, 2nd was tight so I had to use some persuasion... Crack. So I cut it back to a H motor. Glad, case that was the one that CATOed

Yes, the larger dia PVC you go, the lower the pressure it can handle. Really though, these things are that powerful there is no need at all to run them on the limit. Or use RIO. Still to this day, after firing numerous motors I get a bit anxious as I hit the arm switch, knowing what is about to be unleashed!!! Clubs wont not accept them here, maybe the od special day.

 

I'm going to remake my casting stand today, machining a coring rod alignment cap. Then il just fit the cap, push the rod right though, knowing every time it will align with the centre hole in the base. Then long grains won't be an issue at all

[Redrocketman]

Off the topic a bit, but Rick Maschec has advised me to use copper thermite igniters for large motors. I've never made that breed before, and most people, dugabu Dave as well emphasise it is very unstable, explosive and dangerous. Now, Rick and many know 1st hand my safety & quality of work is exceptional (. I try to sound a bit simpler than I Am on this forum!! ) therefore they trust I will not hurt anyone or myself. Have you any experience with this type of thermite? Bugger it, I'll start a new post

[stix]

It's always going to depend on how much the first batch was melted/decomposed/caramelised in the first place.

 

I've found that the methods will always vary too much - so an answer to that question is as varied as the methods themselves. If you want to have a better understanding then you need to accurately measure your fuel mixes with "real and measurable" results, and go from there.

 

Retained water or lack of, is absolutely crucial to burn rates with Sugar Rocket Fuels. Unless you think that karo/glucose syrup has some sort of magical property that does not contain water, then I guess you could re-melt it infinitum.

 

Perhaps Poseidon is not just a mythical fantasy, but a rule needing more consideration?...

 

 

[NeighborJ]

Wow stix, who s##t in your cornflakes? I think everyone here understands the meaning of hydroscopic. The extra syrup just helped to slow it down a little and possibly to counteract the inherently brittle nature of the remelt. I didn't say dump the whole bottle in. Besides your gonna need to dump water in the skillet anyway to keep it from caramelizing too much. It's all good.

[Redrocketman]

After some burn strand tests I I'll conclude that the re-melted batches burn quicker @ atmospheric pressure, have made 3 motors, weighed grains and will test then in the next few days. I'm confident that it will make no noticeable difference or up the chance of failure. Only testing will tell, interested to find our how it performs under pressure.

As for the Karo, as neighbor j said, it only added to reduce brittleness, yes apparently there is a small % water in it but it such a small% I don't see any lack of performance. No I do not add any waster, I used to, but now with careful temp control it is not necessary. Makes fuel pourable, which is what I require for the grain dimensions I make. Example, next motor is a K500, with a 30.5" X 2" grain. Yes that's right. There is the reason for the Cu thermite igniters

[NeighborJ]

Wow that "K" sounds fun. And for the no water thing, I often thought about using some sort of steam hot plate. I once had a pan of candy fuel ignite in the pan from a faulty element, no real damage but it did singe the hair on my beard and I had to shave it off. The element developed a hot spot at one end, and so that is why I used water and a high quality skillet from then on.

I also have mabe 5 or 6 lb of Rio catalyzed shavings from coring grains. I was going to try using them in a press and skip the whole remelt process. I'm just afraid that even if I lube the core it will get stuck.

There are other options for igniters such as hot primes with silicon or titanium. But I can't think of much that will throw as much molten metal as the termite.

[OldMarine]

Wow stix, who s##t in your cornflakes? I think everyone here understands the meaning of hydroscopic. The extra syrup just helped to slow it down a little and possibly to counteract the inherently brittle nature of the remelt. I didn't say dump the whole bottle in. Besides your gonna need to dump water in the skillet anyway to keep it from caramelizing too much. It's all good.

UHHH... do you mean hygroscopic? Sorry, didn't mean to shit in your cornflakes.

[NeighborJ]

OM it's OK you can use my cornflakes as a latrine if you want I'm lactose intolerant.

[patsroom]

Leave the cornflakes out of this you guys!...Pat

 

I don't even like cornflakes that much

[patsroom]

Come to think of it leave the shit out of it too. I doubt that it would be any better. .......Pat

[Redrocketman]

Would go much better with coco pops. Mmm yum!!

[Redrocketman]

Neighbor j, I'll let ya know when I've got the beast ready!!

[NeighborJ]

You'll get it right. I'll post a pic of what was left of my last 2" rocket. It was all brand new, with a new GPS locator, camera and altimeter. Now it's just new trash for the landfill.😭

I thought I had it all worked out but it was almost 100degrees f in the shade on launch day. The pics I recovered wouldn't fill a shoe box.

Edited August 10, 2016 by NeighborJ

[Redrocketman]

Bugger.... The last one that popped was identical!! Won't let it happen again, all I found was the cap like that one, and the throat washer stack. Don't attempt to pick them up either, their hot....