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Post by racket on Dec 5, 2014 21:10:05 GMT -5
Hi Mitch If you only rev your homemade freepower to 15,000 rpm , the limit for the chain , then its possible to weld blades onto a steel hub and have it survive . The freepower for my turboprop PJ www.youtube.com/watch?v=uqMn0A2aUdo was a "welded" unit , segments of stainless tubing were welded ( rather poorly) to a steel hub , during "destruction testing" of the freepower without the prop attached, but redux chain, sprockets, and prop drive shaft in situ , it was spun to ~22,000 with temperatures of >1,700 F (EGT gauge pegged out) , the blades were in a poor state after the testing , bent, burnt and twisted, but still "sorta" attached . Cheers John
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mitch
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Post by mitch on Dec 6, 2014 11:27:19 GMT -5
That is impressive racket, especially considering the free power turbine is not usually exposed to egt's that high during normal operation, (right?). I planned on using 10 ga. Mild steel for the free power, and using a small scale to get all of the turbine blades within 1/10 of a gram of each other for balance purposes.
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Post by racket on Dec 6, 2014 16:53:19 GMT -5
Hi Mitch
I'd suggest using stainless for the blading , whilst steel for the disc is OK , the stainless will have much better strength once the temps are up , you'll need reasonable thickness at the blade root to produce a reasonable weld, my 1.6mm - 0.060" " thick tubing I used for cutting the blades from meant there was some "undercutting" at the weld which left the blades a bit weakened , I think 2mm - 0.080" would have been better.
LOL .........I didn't worry too much about balance , as long as each blade was roughly the same size I welded them on , at a mere 15,000 rpm the ball bearings could easily cope with the out of balance forces .
Cheers John
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mitch
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Post by mitch on Dec 6, 2014 20:16:32 GMT -5
Hahaha, okay. I might have to just go with a thicker gauge mild steel, since I would have to go get another welding tank, fill it with the appropriate gas for stainless mig, new wire, etc. When it comes to these home made free power turbines, what kind of efficiency are we talking? I would assume that the housing also has a great deal to do with the overall efficiency of the turbine too.
and as for your free power turbine, that makes me laugh. Here I was assuming that the blades needed to be precisely measured and cut!
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Post by racket on Dec 6, 2014 21:19:40 GMT -5
Hi Mitch
All I did was cut a cardboard template of the blade , wrapped it against the stainless tube and with a fine tipped marking pen marked where I needed to cut the tube with the thin bladed side grinder.
I worked on the principle of randomness , some a bit bigger here and there, whilst some a bit smaller , so when welded on there was a general "balance" , .......it was close enough that when the shafting was set up on a couple of straight edges the shaft didn't roll over with a heavy point , if it had I would simply have ground a bit off on the heavy side , a rough "static" balance is plenty for such slow rpm .
Your best bet would be a Cummins ST-50 turbo , remove the comp , fit a ball bearing next to the sprocket and go :-)
Cheers John
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mitch
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Post by mitch on Dec 6, 2014 22:03:20 GMT -5
Haha that is what I would like to do! I am having trouble finding a decent price on one hopwever. (one that doesn't require a rebuild). That is a good idea with using a tube to cut the blades out of. I'll have my brother turn the shaft I choose on a metal lathe to get a even surface for the ball bearings. Anything I should look for when buying ball bearings?
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Post by racket on Dec 6, 2014 22:57:51 GMT -5
Hi Mitch
Use C3 bearings , they have a bit more clearance between ball and raceways which helps at higher rpm .
If you use C3 25mm or 1 inch ID by 12mm-1/2" wide bearings , they'll easily cope with 15 - 20,000 rpm , 20mm ID to >20,000 , we'll in excess of the chain rpm limits .
And use bearings with metal seals , not the plastic ones as the heat can cause problems .
Cheers John
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mitch
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Post by mitch on Dec 7, 2014 0:26:55 GMT -5
Ahh okay thanks, I was looking at bearings earlier and I did not think about metal vs plastic seals. You think I will need a 1 inch power turbine shaft? Also, I made a couple turbine blades tonight. I weighed them (even though racket said it is not necessary, I am still curious and want to get them close to the same weight ), and the smaller one weighs in at 16.75 grams, and the larger at 28.020 grams. Of the two, which design should I use? They are both the same length, and will equal a 125mm turbine wheel when fastened to the 2" center piece. Here are some pics of them: Here is a pic of the two blades side by side for comparison And a bottom view to show the curvature:
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Post by racket on Dec 7, 2014 1:33:08 GMT -5
Hi Mitch Are you attempting to make a radial inflow turbine wheel ?? Its much easier to make an axial wheel as the disc is just that , whereas a radial inflow is much more complex regarding its shapes and areas . Checkout this axial wheel build www.rcdon.com/html/gr-5_turboshaft_engine_project.htmlCheers John
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mitch
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Post by mitch on Dec 7, 2014 11:35:26 GMT -5
Racket, it is funny that you say that. Last night I was thinking about making the turbine housing for a radial turbine, and I thought about making an axial flow similar to RC don's. I think I will go with the axial flow turbine now, the hardest part of the build for me, will probably be getting the bearing tube hole centered in the housing. Would I need a set of stators like he used?
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Post by racket on Dec 7, 2014 15:31:44 GMT -5
Hi Mitch
Yep , you'll need some way of getting the gas flow turned so that its at the correct inflow angle , theres a fair bit of work whichever way you go , thats why I feel you're better off using a ST-50 turbo .................the Cummins ST-50 has a fairly large diameter inducer ( 4.7" ) on the turb wheel for the mass flow being processed , and as you're rpm limited by the chain it pays to use as large a diameter as possible to increase the tip speed to maximise potential horsepower output at those limited rpm .
The only time I'd recommend someone make their own turb wheel is if theres nothing available that could do the job , but I feel the Cummins turbo would be ideal for your situation ,....... having made a few freepower setups I know just how much work is involved , if there was an "off the shelf" alternate I would have happily used it.
Cheers John
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mitch
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Post by mitch on Dec 7, 2014 20:03:23 GMT -5
Racket, You are right, after researching and mocking up a few designs, it would be a better use of my time to just find an st-50. The st-50 will save me time, money, and will be much more efficient than what I could create in my shop, with only hand tools and a mig welder, haha. I just bid on this: www.ebay.com/itm/231408080280?item=231408080280&viewitem=&vxp=mtrHopefully I can get it for that price (seems cheap to me, and it came off a running truck, says it has no shaft play!). Only thing I am not looking forward to with this, is the fact that I will need to improve my oiling system to keep up not only with the gas producer's bearings, but the free power turbine's bearings as well.
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mitch
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Post by mitch on Dec 11, 2014 0:02:38 GMT -5
I ended up not winning the auction for the st50 on ebay, but good news is that I found a large turbo upgrade/ repair shop about 40 minutes from me, so I will be heading there soon to have a look at some of their cores. Hopefully they will have something big enough!
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Post by racket on Dec 11, 2014 0:14:12 GMT -5
Hi Mitch
That is good news :-)
A ST50 or VT50 with a wrecked comp wheel is all you need , as long as the turb wheel is still intact she'll do the job .
Cheers John
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mitch
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Post by mitch on Dec 12, 2014 13:18:32 GMT -5
Hey everyone, quick question. Looked at an st50 today, for $100, only problem was that it was completely seized and the turbine wheel and compressor wheel did not turn at all. Should I still buy it? Would fitting ball bearings to the internal dimensions be too difficult?
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