(Can we PLEASE get sugpro up and running on freelists.org??)The last time this issue came up on sugpro, the suggestion was to use one of those drywall sanders that run the air through water before exhausting it. I don't have a link handy, but as I recall the item wasn't that expensive and was available at home improvement stores and the like.
--SteveOn 05/07/2014 04:15 AM, (Redacted sender monsieurboo@xxxxxxx for DMARC) wrote:
Because I occasionally machine graphite and this is the first time I've seen this particular concern raised, I did an online search for info. I'd characterize it as showing broad consensus but not unanimity. Based on that, I've formed my own conclusion but really think anyone who creates graphite dust should review the literature yourself and assess your own operations accordingly -- always keeping safety foremost.That's a fascinating and clever use of graphite in mining. LOX, like other highly concentrated oxidizers, will sensitize most organics so I can certainly see a combination of tamped graphite saturated with LOX being effective. Here we have three separate cases (the mining case, graphite dust dispersed in workspace air, and graphite dust dispersed in the shopvac canister or bag). The fuel density and A/F ratios are different for each case, as is the likelihood of an ignition trigger. It's certainly interesting to juggle the variables involved while pondering the importance of "safety first".I rarely cross-post but this might be a good question to pose on arocket. It's been pretty quiet over there for the past week and the response from that bunch could be informative. Any objections?Cheers, Mark L. -----Original Message----- From: Cliff Bates <cliff@xxxxxxxxxxxxxx> To: sugarshot <sugarshot@xxxxxxxxxxxxx> Sent: Wed, May 7, 2014 12:54 am Subject: [SS2S-Main] Re: Material for Nozzle fabricationI might suggest here that carbon dust is "extremely" explosive if mixed with the proper amount of air and ignited. In fact carbon dust was used back in the 1920's in mining to replace dynamite. A cardboard tube of packed carbon dust was soaked in liquid oxygen for 15 minutes, then stuck in the blasting hole. If the charge failed to go off for some reason, after 30 minutes the O2 evaporated enough that the explosive aspects of the charge became inert, so it could be drilled out. Unlike the dynamite filled holes that the "new guy" got to dig out........... alone. Machining graphite is extremely dirty if a vacuum cleaner is not used, as someone earlier pointed out. THE THING TO WATCH is the arcing brushes on the vacuum cleaner motor igniting the dust if the vacuum cleaner exhausts through the motor housing, as most do. I'd strongly suggest that the vacuum cleaner bag be double bagged to assure the dust is all caught inside the can. If not, a dust explosion could very likely occur from the arcing motor brushes as the air/carbon mixture flows by, and it will not be a nice thing. Years ago I accidentally sucked some coal gas fumes into my 5 gallon shop vac while cleaning up after some blacksmithing. The vacuum exploded, splitting the can wide open and throwing the lid with a 1 horse motor still attached, about 30 feet in the air. Graphite/carbon dust is much more energetic than coal gas fumes, and why air powered drills are used in coal mining. If you doubt this, take a large coffee can with a slap on lid. Drill a hole in the side of it to fit a small 1/4" hose. Attach a small funnel to the hose inside the coffee can and put a small amount, half a teaspoon, of flour in the funnel set up vertically. Take a birthday candle and put it in the can. Light the candle, then snap on the lid. Quickly blow into the hose to mist the flour before the candle burns up all the O2 and goes out. Be sure to be back about a meter or so from the can due to the exiting lid. You can use this method to test various dust samples, including powdered sugar, coal, graphite, flour, corn meal, fine wood dust, etc., etc. A larger can with the same amount of "fuel" and candle will usually produce a more energetic response than a large coffee can due to more air being available to burn the fuel. However the idea here is not to level your shop, but just some food for thought about something that is normally not considered..Cliff ----- Original Message ----- *From:* Hans Olaf Toft <mailto:hot@xxxxxxxxxxxxx> *To:* sugarshot@xxxxxxxxxxxxx <mailto:sugarshot@xxxxxxxxxxxxx> *Sent:* Tuesday, May 06, 2014 9:11 AM *Subject:* [SS2S-Main] Re: Material for Nozzle fabrication When using graphite for nozzles - keep in mind that it is a surprisingly good heat conductor. Hans On 05/06/2014 02:39 PM, Steve Peterson wrote:The Graphite Store (www.graphitestore.com). Right now, 2" rod, 48" long (medium extruded) is selling for $66.50. That much steel would be a lot more expensive. Unfortunately, I don't see any smaller diameters in the medium-grained; they do have smaller diameters in the fine-grained but it's more expensive--for instance 1" diameter by 24" long is $43.90. I would not recommend trying to machine away a 2" diameter chunk if all you need is 1" diameter--a vacuum helps control the dust, but it's still messy. I used 12L14 for years before I switched to graphite and I still make steel nozzles on occasion. I never saw any erosion with sugar propellant. If you do go with graphite you can make a "form tool" for the convergent and divergent sections which makes the turning go much quicker--just grind down a spade bit, it doesn't have to be that sharp to get the job done. --Steve On 05/06/2014 03:59 AM, (Redacted sender monsieurboo@xxxxxxx for DMARC) wrote:Strangely enough, the mid-grade (medium-grained) graphite tendsto do the job better than the high-end, fine-grained material. Less erosion, perhaps due to larger grains interlocking betterand being ablated more slowly. And of course, less expensive. Graphite's definitely the way to go, but you don't want conductive, fine dust getting into any electronics (such as a benchtop mini-lathe) so try to capture the dust at its source. Cheers, Mark L. -----Original Message----- From: Hayk Azatyan <dmarc-noreply@xxxxxxxxxxxxx> To: sugarshot <sugarshot@xxxxxxxxxxxxx> Sent: Tue, May 6, 2014 5:53 am Subject: [SS2S-Main] Re: Material for Nozzle fabrication Thanks for your input Jeff. Where do you recommend I buy graphite from? On Monday, May 5, 2014 4:58 PM, Jeff Moore <tnetcenter@xxxxxxxxx <mailto:tnetcenter@xxxxxxxxx>> wrote: Graphite would probably be the most affordable of materials to use. We had a machinist in our local group at one point and he made a titanium nozzle as a proof of concept. That would more than likely be rather pricey for this project ( his was for a 54mm motor). Aluminum is a good material to practice on or do mockups with, but I suspect that it's melting point is way too low to be used as the actual nozzle. It might work as a carrier for a graphite or ceramic insert though. Jeff Moore Bend, Oregon On Mon, May 5, 2014 at 4:10 PM, Hayk Azatyan <dmarc-noreply@xxxxxxxxxxxxx <mailto:dmarc-noreply@xxxxxxxxxxxxx>> wrote: Hello all, Would you all happen to know where I can get my hands on some scrap circular steel bars for rocket nozzle fabrication?And if you have any suggestions on the material I should use please let me know. I have already started using the lathe, and currently I am machining a nozzle out of aluminum. Although I will not be using this particular nozzle for flight I figured I should practice making one out of some scrap metal that I found(in this case aluminium). I know that you guys make some of your nozzles out of graphite, but for now I am learning to machine metal nozzles just for educational purposes. Thank you guys! -Hayk Azatyan
