kyanite vs. grog

[Swede]

My very first exposure to higher-quality homemade BP rockets came from a Skylighter ad for their Stinger Missile kits. On a bit of a rampage, I ordered most of the items necessary to make them. For the nozzle mix, I ended up with bentonite, kyanite, and grog.

 

I know you can use clay kitty litter. When my bentonite runs out, I'll be using that, but for now I have some good clay.

 

I made my first batch of nozzle mix for some small rockets using bentonite, grog, and toilet wax in the ratio 30:15:4. It seems to ram and perform well, but the grog was expensive for what I got... seemingly a small cup full of crushed pottery. Much of it was far too coarse for my liking, and I ended up screening and discarding the coarse stuff. I'd like to try kyanite for my next mix.

 

What ratios do you guys like to use in your nozzle mixtures? Can I substitute the grog 1:1 with the kyanite? And are there any special attributes of kyanite that make it better (or worse) than grog? As always, I really appreciate the collective wisdom here! Thanks!

[psyco_1322]

Not sure what kyanite is but it seems to be a suppliment for grog in throwing clay. Essentailly thats all grog is, just fired clay that has been crushed up and added back to the building clay to add strength and resistance to shock and heat when firing.

 

Personally I dont think that one really needs grog in the nozzle mix at all. I had a mix of nozzle mix I bought from UN a long time ago and it had some grog in it with other fire clays. I fould it kinda rough feeling, possible scratching up my tooling. Beating ceramics into my Al tooling doesnt sound to nice to me. Ive been using straight bentonite powder from Firefox for a year or so. Ive never had any problems with nozzles coming out. It sticks very well just by inself to paper tubes, as Ive tryed to get it out of them a few times. The only time the nozzles come out is when the rockets come completely apart, aka EXPLODE! So I suggest just trying it without anything else. A bit of graphite dust in there will help a bunch in the removal of the spindle. Plus black kitty litter looks cool. I think I will be switching over to kitty litter soon because its granulated compaired to the messy dust Ive been using. Same stuff different size.

[lnstantkarma]

I've used benonite for a while, I like it because it makes cleaner looking nozzles than cat litter. I've thought about making some grog because there are a bunch of old fired ceramics up in my attic but I've never had a nozzle just blow out so my mix doesn't need any more grip which is what grog is for.

 

Now I use a 50/50 mix of clay and kyanite. I think I like it better because I've found less erosion for my drivers and saxons than straight clay. I think kyanite is basically this super fire resistant stuff and it makes the benonite better.

[psyco_1322]

Cat litter is made up of bentonite. I kinda like that look of it if pressed after being graphite coated, like looks like the pieces are still there but smashed.

[DeepOvertone]

I was having serious problems with my bentonite nozzles eroding from high temp gerb comps. I was going to buy grog from skylighter but I didnt like the sound of "pea sized chunks" and started to look elsewhere for something that was cheap and would work good. I ended up buying 5 lbs of crushed alumina from a company that I found online. Its basically the consistency of coarse sand. The guy was very helpful and it was only a couple bucks a lb. Since making nozzle mix with this stuff and wax, I havent had any more problems with erosion. I will say this stuff is hard as nails and will eat up your tooling.. especially if its aluminum. I dont remember the exact name of the company right off but I'm sure I can find it if anyone is interested. I think its High Temp Materials or something like that.

[Swede]

Deep, that is an AWESOME suggestion... most every town has a place that sells sand blast cabinets and equipment. The stuff they sell that goes into the blast cabinets is nothing but pure aluminum oxide, and can come in differing granulations. I'll bet that stuff would make a superb nozzle supplement, and dirt cheap to boot. The note on tool erosion is a good one, though, this stuff is designed to erode metal. But if your tooling can stand it, I'll bet it'll be great. Thanks!

[Sylar]

I have some fine Al2O3 from a ceramics place which I believe could do a smashing job when mixed with bentonite and pressed to nozzles ...

 

Al2O3 is really everywhere to be found, but it has alot of diffirent forms. The stuff I have is a (relatively) pure flour like white powder.

It can also be in the form of extremely hard clear or dark (purity!) crystals. Purity doesn't matter much for this application though.

[DeepOvertone]

Swede, I the stuff you are referring to is aluminum oxide grit. Its pretty hard and might work. The stuff that I have is pure Alumina. Its a white ceramic. Same stuff that some ball mill media is made of. I tried to find where I bought it from and I'm having a bit of trouble. All my business was done on the phone and I found them on ebay but I cant seem to find them again. I will keep searching though.

[DeepOvertone]

Ok I tracked them down for those who might be interested. They dont have a website that I can find but their phone number is 1-800-325-2492. I think the material I bought was 40 mesh but I think I would go finer the next time around. Their ebay store name is High-Temp Refactory Store.

[Swede]

Thanks for the hookup. Is there a difference between "alumina" and aluminum oxide? For some reason I thought they were the same thing. Ideally, I think you'd want the powder to be pretty darned fine unless you are making some really large rockets. That is what irked me about the skylighter grog - really chunky. Probably 1/2 of it by weight was unuseable for my small rockets.

[DeepOvertone]

You are right swede, they are the same thing. But I've never seen that stuff for sale in a blasting shop. But I could be very wrong on this also. So its definitely worth looking into.

[Swede]

I checked out the store on eBay. They have some cool stuff, both grog-like materials for rocketeers, and casting supplies for backyard foundries, which I enjoy doing on occasion.

 

They have Kyanite in three mesh sizes. At 90 cents per pound, you not only get to choose what mesh you want, it's 1/3 the price of Pyro suppliers. They also have the stuff I think you are referring to, White fused alumina.

 

They show these "mesh" sizes...

 

3x6m, 6x14m, 14x28m, 28x48m, 48m, 100m, 325m

 

I'm not sure how to interpret something like 28X48 mesh. Does that mean it is an elogated grain? The 100 mesh stuff might be good for small rockets, while the 48 mesh would be best for larger.

 

The prices seem to be $5 to $20 for a ten pound bag, and I'm sure the cheaper stuff would be all that's needed.

[jacob]

You guys should check out This thread.

Apparently "Fresh step" brand cat litter is about the best stuff you can make a nozzle out of.

 

Has anyone tried a nozzle made out of straight Graphite? seems like it would work good, and be easy on your tooling.

 

Aluminum oxide soulds like it would work great to, I wonder if you could use other metal oxides?

[Mumbles]

24x48 mesh would be the equivalent of us writing -28+48 mesh. It's a shorthand notation for the mesh fraction.

 

If using it as a grog type of material, with it biting into the walls, I'd think the -28+48 would be pretty good. For just adding it for errosion protectio, the finer the better I would imagine.

[DeepOvertone]

Yah I got the 48 mesh stuff. Its pretty big. I'm using it in 3lb rockets though so its acceptable. I would have liked to get it a bit smaller though. But just out of curiosity I tried it with my 1/4" bottle rocket tooling and it still made a smooth nozzle. Regardless, something the size of sand would have been better.

[Mumbles]

That should be finer than normal beach sand. Beach sand is normally around 28 or 30 mesh. Fine sand around 60 mesh.

[DeepOvertone]

wow... Mesh sizes are something I have no frame of refrence on. I was going off of memory when I said i got the 48 mesh size. Eventually I'll be able to get some nice screens and I'll have a better clue as to what the heck I'm talking about. Untill then I guess I'll have to use common materials for my description. For example, The stuff I got was about the size of pretzle salt. Any idea what that size would be?

[cplmac]

I've always used straight bentonite powder and never had a problem that could not be attributed to operator error. Also, Menards sells 50 pound bags of black sandblasting media the consistency of medium sand for twenty bucks if I remember right, just bought some a month ago for some sandblasting I needed to do. When I'm pressing clay into one of the big rockets for a report head I use a 2:1 ratio of bentonite:grog. The grog is very scratchy, feels nasty and I don't think I would use it for a nozzle on anything besides a big rocket where you NEED the added gripping power.

[Swede]

There's some good thoughts here. I can't see the harm in always using a finer grog/alumina as it would definitely strengthen the nozzle and help with erosion. Perhaps test a few, and if there are problems with nozzles being blown out, then, and only then, add coarser stuff to get some gripping power.

 

If you are using a press, I think you can avoid coarse materials entirely. If you are limited to a mallet, then the coarse stuff may be necessary to get a good wall bite.

[Mumbles]

The finer the grog, the less it can bite into the tube and hold it in place. There is definitely a limit, both large and small, for useful granulation. Think about it. A coarse grit sand paper is much harder to get moving than a fine.

[psyco_1322]

I swear I seen someones sight that should some nozzles being machined out of a chunk of graphite, I thought it was Yawns page but I guess he was just doing Al. Hmmm wonder where that was.....

 

There was one wierd thing I experienced with pressing straight bentonite dust nozzles. It was when I was making rockets with my fountain tooling and would press a increment and remove the motor from the spindle to see if the nozzle was thick enough. It quite frequently broke the nozzle in half, like the was half of it in the tube and the other half on the spindle. It usually came apart in a cone shape with this strange crystalized jagged look to it, virtical lines all around where it had I guess sheared apart. I removed the spindle with a twisting motion as always and it looks as if I literally pull the nozzle in two. Never got it to re-press back together without conpletely breaking it all out and starting over. I seemed to help when I used the pressed pieces I broke out also. It only happened with press though. Maybe Ill get bored in the next few days and see if I can screw one up and get a pic.

[TheSidewinder]

psyco, I've seen that site (or one like it) as well.

 

Machined Graphite nozzles ARE used in Amateur Rocketry for APCP motors. If you get a great deal on Graphite rod stock and have a lathe, you COULD do the same thing for pyro rockets which use APCP fuel or even BP motors, though unnecessary, and the "cost per motor" would be relatively high. Dave Sleeter's book mentions graphite nozzles, IIRC.

 

From the information I was able to gather, the general concensus is:

 

Machine the nozzle, cutting one or two additional grooves around the perimeter of it, to provide a "ledge" for additional "grip" by whatever glue you choose to construct the motor with.

 

A few options and some observations:

 

It seems that the most reliable method is to epoxy the nozzle into your motor casing, using the same epoxy that the APCP is mixed with. NOTE: I'm using "epoxy" generically. Nearly all of the HTPB, CTPB, or other Polyester Resins, and their respective curatives, can be used. Use caution with some of them as they produce toxic vapors while curing (same with the grains you make). If you already have it, there's no need to buy another glue. Allow to cure FULLY before casting your grain into the motor casing.

 

White Glue, or Carpenter's Glue (brown stuff) should work, though I've seen it questioned whether it will hold up due to the high heat. In a pyro rocket, the burn duration MAY be short enough to make this irrelevant.

 

Rubber Cement will not work.

 

Gorilla Glue will not work well, or at all, because it expands a fair bit as it cures.

 

Just a little "shotgun info" there, but may prove useful to some.

[DeepOvertone]

Psyco, Are you using clay with your bentonite? I was having a similar problem with the nozzle breaking when I would pull it off of the spindle. After making with wax and grog.. NADA... They look beautiful. I think it makes them pack together better and hold together better verses no wax.

[psyco_1322]

See I knew I wasnt pyscho, I seen it somewhere.

 

No I use straight bentonite clay. Bentonite is a clay, or so its called. I take it you ment grog or something. But no, just straight benti.

[DeepOvertone]

HAHA I cant believe I put that. I meant are you using wax with your bentonite. Because like I said earlier it really helped me out with the nozzles sticking together and being more durable. You should try it out. I followed the recipe on skylighters website to make mine and its just improved my nozzles 200%. Even if you dont add any grog I definitely recommend adding wax to the mix.