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Post by turbochris on Sept 22, 2011 17:52:49 GMT -5
maybe you should buy a piece of inconel plate instead of rod if you need 5 inch blanks
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Post by Johansson on Sept 22, 2011 23:55:25 GMT -5
An you wouldn´t really need inconel for the NGV since SS2368 or some other heat resistant stainless would easily survive the temps.
Does anyone know how much an "DIY" axial turbine made from sheet inconel with bent and grinded blades would suffer in max rpm´s and efficiency compared to a cast one, given that the blade angles are the same and the DIY wheel is carefully built?
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Post by propellanttech on Sept 23, 2011 13:28:30 GMT -5
An you wouldn´t really need inconel for the NGV since SS2368 or some other heat resistant stainless would easily survive the temps. Does anyone know how much an "DIY" axial turbine made from sheet inconel with bent and grinded blades would suffer in max rpm´s and efficiency compared to a cast one, given that the blade angles are the same and the DIY wheel is carefully built? Theoretically, the sheet Inconel if hardened (aged) after construction, should survive just as much as the machined or cast. I didn't think about using a different alloy for the NGV. That is a good idea. I'm not up to date on my high temperature alloys. James
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 23, 2011 16:19:39 GMT -5
For our desired operating TIT's (since we don't have the nice cooling air flow holes in the blades to let us run any higher...) you can get away with running 316 stainless. 304 would also work, but the price difference is mild between the two and for higher temperature tolerance, the molybdenum in the 316 will aid in higher corrosion resistance at those temperatures. Both have similar melting points, the big difference is just corrosion resistance.
Since 300 series stainless is the most common stainless alloy out there, it can be obtained for reasonable costs as opposed to nickel superalloys, also they don't require the heat treating that inconel would need prior to service.
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Post by Johansson on Sept 24, 2011 1:01:40 GMT -5
The problem isn´t that stainless is less heat resistant than inconel, but the fact that stainless creaps more. At high revs the stainless steel tends to stretch and rub the housing while inconel is more constant.
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Post by propellanttech on Sept 24, 2011 1:06:20 GMT -5
The problem isn´t that stainless is less heat resistant than inconel, but the fact that stainless creaps more. At high revs the stainless steel tends to stretch and rub the housing while inconel is more constant. But if using Stainless for the NGV, it shouldn't be a problem. I would never use stainless for a turbine, just a personal choice. I don't think it would hold up to my abuse. ;D James
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 24, 2011 10:31:33 GMT -5
True the gamma prime you get after heat treating inconel (especially 718) does give it ridiculous creep resistance...
I should sit down and crunch some numbers to get the centripetal force on a turbine and solve for some rough stress values, would be nice to know if that much creep resistance is really needed for most DIY turbines
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Post by racket on Sept 24, 2011 17:17:16 GMT -5
Hi Wolf
Heh heh , we always end up wanting more power from our DIY engines , so the stresses get bigger and bigger as development progresses ..................probably a good idea to start with the best material available and save having to do the job twice .
Some of our DIY engines get punished rather hard :-)
Cheers John
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wolfdragon
Senior Member
Joined: April 2011
Posts: 287
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Post by wolfdragon on Sept 25, 2011 8:55:49 GMT -5
I did a VERY rough calculation, a mm+ of stretch on 316 is very possible... especially if you aren't the best at maintaining a proper TIT
I agree with you John, cheaper and safer to get Inconel in the first place...
I am a bit worried about that mill you linked James, I think Inconel is going to take a bit more than what those (even the expensive ones) desktop CNC machines can do...
Worked in the machine shop that handled repair of space shuttle parts before that program closed out, 300 series stainless was a breeze, inconel took a bit of finesse and very expensive cutters (usually ceramic, sometimes could get away with carbide), and we had machines that were the size of a small truck making 3" parts
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Post by propellanttech on Sept 25, 2011 15:28:52 GMT -5
I did a VERY rough calculation, a mm+ of stretch on 316 is very possible... especially if you aren't the best at maintaining a proper TIT I agree with you John, cheaper and safer to get Inconel in the first place... I am a bit worried about that mill you linked James, I think Inconel is going to take a bit more than what those (even the expensive ones) desktop CNC machines can do... Worked in the machine shop that handled repair of space shuttle parts before that program closed out, 300 series stainless was a breeze, inconel took a bit of finesse and very expensive cutters (usually ceramic, sometimes could get away with carbide), and we had machines that were the size of a small truck making 3" parts That is a possibility. I have been reading about machining inconel 718 and there is hope. There are new techniques for using a light machine, but the software is quite expensive. The technique requires a constant cutting angle while the tool never leaves the material. Also coated cobalt has been stated to be the best tool for cutting inconel on a light machine. I am in contact with the machine manufacturer, and I'm am sure they will be willing to at least try it. It may be just necessary to cast the turbines. James
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Post by twenglish1 on Sept 28, 2011 15:53:51 GMT -5
Very nice drawings! What program did you use? Autodesk Inventor?
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Post by propellanttech on Sept 28, 2011 17:37:20 GMT -5
Very nice drawings! What program did you use? Autodesk Inventor? Yes. I use Inventor 2011. The turbine and NGV are not 100% accurate, but close enough for the drawing. (They are purchased parts in that design anyway). I have yet to do the lubrication for the bearings, and the total fuel manifold. I also need to do some representation of the compressor. It is getting close to being 100%. I am worried though. I emailed the contact for the purchased parts, but never got a response. I need to try the person again. I'm also trying to up size the design to a JT84, but I can't get anyone to give me dimensions. The diffuser is of my own design. I need to go back and draw the original as in the plans. James
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Post by twenglish1 on Sept 28, 2011 19:26:37 GMT -5
Do you think you could email me your designs? i would be very interested in taking a look at that
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Post by propellanttech on Sept 28, 2011 20:40:14 GMT -5
Do you think you could email me your designs? i would be very interested in taking a look at that Sure, but I need an email address, and it will probably be large. I could zip it to make it smaller. James
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