Thanks Steve , i have just ordered one ,and should get it by the end of September , i’m not sure if it will hold up any better than the Boron carbide one i tried, but i have gone this far on my search for the holy grail of nozzles so why stop now .
Will update when i get around to testing this one out , should be ready for a new nozzle in about 4 or 5 weeks if the one i have in is anything like the Boron one i took out the other day .
Dave
Great spirit…
I have read another one, forgot whom’s…
“Don’t bother to live near me for a day, try to imagine being in my brain and hold out for 10 seconds…”
Yup, the holy grail has many forms…
@ Steve, Smaresca: wow, great find
Steve,
How would you attach this to something? Might make good nozzles for a ceramic blanket wood gasifier.
Rindert
@r_wesseling I’ve been chewing on that question myself. I think it would be feasible to fix it within a containing (probably sacrificial) tube using refractory mortar of some kind. Cutting a groove in the outer surface of the cylinder would probably help too.
I think these alumina bushings are another potentially viable solution because they have a step that would make it easy to be held in a pipe cap or something.
Other stuff from the glass working industry is likely to be helpful…molten glass chemistry is extremely weird at high temp, and the materials involved tend to be super tough.
On the other hand, such things are usually considered consumables…which is probably the most useful hint here despite the temptation to find a long-lasting nozzle material: Simple and replaceable nozzles are probably the best route, even if some of the more exotic materials would suffice. Of course, if we find that some carbide or alumina material lasts years, then that’s probably a great trade-off.
Steve,
A factor that we have to consider is the different rates of thermal expansion for different materials. Alumina - 8.1, Steel - 11-12.5, Silicon Carbide 2.77 units (10-6 m/(m K)).
https://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html
Still, I know it can be done somehow. A.S Richards, see post #87, is attaching silicon carbide to steel. And I have seen a lot of silicon carbide grinding cones with a steel insert that allow them to be used with an angle grinder.
Rindert
I ordered a couple of these as well. BTW, so far no degradation on my copper nozzle with 1/4 wall thickness, but I only have 100+ miles on my MGB. Also no corrosion on one-ended horizontal copper nozzle run for a few hours with no EGR on a small gasifier. I am looking for something other than copper for those wanting a less expensive, but durable option for small engines.
I’m thinking that I will slip the silicone carbide tube about half way over a 1/2" SS nipple. The expansion of SS is far greater than the silicon carbide so must be much smaller diameter than the nozzle. My thinking is that 1/2" will give good air velocity and the carbide will take the reaction temperature and prevent catastrophic oxidation of the recessed SS nipple.
The nozzle will hang loosely in a refractory cradle/notch allowing back and forth/end to end movement without crawling off of the nipple. The slight venturi effect sucking in CO2 from reaction into the nipple end of the nozzle should not overwhelm the entering air volume and might even help cool the reaction a bit?
Other’s thoughts are welcome.
An insert for grinding isnt surprising, as the grinding and spinning in air will largely dissipate grinding heat. If you applied heat to the steel mandrel I wouldn’t be surprised to see it split the carbide.
@taitgarry00 Agree, definitely critical given the wildly different expansion coefficients between the materials (and the relative brittleness of carbide ceramics).
@bsoutherland’s idea (post 106) could work here because it can tolerate some degree of slop. And Bruce a passing thought – given the movement/vibration while driving in the MG, probably want to cushion with a bit of ceramic wool or something so it doesn’t bang around too much when everything is at operating temp.
Garry, Steve,
The website I found for A.S. Richards in post #87 seems to have gone dead. Maybe they found out I was talking about them.
But here is one with a reinforcing pipe in the center. https://www.jms-se.com/catalog/Silicon_Carbide_Silicon_Nitride_Protection_Tubes_Ordering_Page.pdf
How is this even possible? Are ALL these guys playing shenanigans?!?!
Rindert
When i bought my bag of refractory cement they asked me what grade i wanted and explained the alumina content in each type , so i explained what i wanted it for , and they mentioned that 90% alumina content would probably be too much because of the thermal shock of the material and they suggested trying a 76% alumina filled bag instead , i have made about 8 nozzles so far since buying it and so far they all stood up to the temp change that water drip causes and heating and cooling off of the nozzles , and only changed them over when they had more or less melted away , and thats around the 120 hour of use time .
Bruce instead of slipping the carbide over the SS tube why don’t you slip the silicon carbide just a few mm inside of a SS tube thats ground out to a plug fit for the carbide ,thats how i have done mine and no problem with expansion at all .they all seem to stay in place, plus when they have oxidized away down close to the SS nipple the shut of tap on the air inlet gets warm/hot and thats a early sign that the nozzle needs changing .
Dave
From the schematic it appears the metal tube is discontinuous, perhaps a spiral wrap?
Thats the kind of REAL experience we need more of around here. Thanks Dave.
I looked at the drawing again and I don’t think it is a spiral wrap, just a convention that mechanical draftsmen use. Anyhoo, the A.S. Richards link is back on line and hasn’t changed, so maybe these guys are okay.
I sooo like Dave’s method of putting the refractory/ SiC inside steel because the steel is going to expand faster. The SiC piece might be slightly loose in the steel but I think it will still be functional.
Rindert
Steve, I really like the ceramic wool idea. I like my MGB copper nozzle as it is. I’m just looking for something cheaper, simpler for small engine gasifiers.
Dave, I’m glad that you’ve had good success putting carbide over SS. Since the SS has a much higher expansion, I don’t see how that is possible. Your experience is still tops. You have so many long runs with such good results. Thank you for sharing!
Oops, I meant “putting carbide Inside SS.”
I have also cast refractory cement Around 1 inch copper, SS & mild steel tubes , not one casting broke due to expansion & contraction of the inner metal pipe going into it , but i think the main reason it worked for me is that the length of my refractory nozzles are around 4 inches long by 2 and 3/4 inches dia , but i only allow the pipe to go into the refractory nozzle around 2 inches and so when the nozzle gets to extream heat at the tip there is nothing inside there to expand . the last few nozzles i made i used TIG nozzle’s for the last 1 and a half inches and that really didn’t affect the life of the nozzles by much really .
Dave
I would think those TIG nozzles might last a long time. Did they?
Rindert
The TIG nozzles always seem to last around the 120 hour run time mark ,there would sometimes be a little bit of the end left in the refractory when i took them out to replace with a new nozzle , i normally only change the nozzle when the end of the pipe nipple starts to get hot on the outside of the gasifier where the tap is screwed onto it on shut down ,so thats about 1 and a half too 2 inches in length , now i am just trying types of carbide nozzles without any refractory surrounding it , and once i can reach the 150-200 hour mark i will be happy so there is still plenty of ways i can still play at it , now days i am using the nozzles vertically, and i am getting better results due to the formation of slag build up around the top end of the nozzle , and as long as i can keep the hole free from molten build up they seem to work fine .
Dave
Thanks for good info. I sure hope your carbide nozzles work well for you.
Rindert
