Steam turbine generator

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jscarmozza
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Re: Steam turbine generator

Post by jscarmozza »

HI Wolfgang, I was trying for 31 buckets, I made the cutter 0.050" wide and the wheel diameter just under 1" so that I could get 0.050" equal thickness voids and vanes around the wheel? I'm just playing around with scrap for now trying to get my set up and procedure refined, no thought yet on the nozzle. However, I'm thinking about having it come in at a slight angle not tangent. After reading the information you posted, I finally understood the 180 degree change of direction/change of momentum concept. Before that I thought the exhaust had to be 180 degrees from the inlet (duh). Thanks, John
Kimball McGinley
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Re: Steam turbine generator

Post by Kimball McGinley »

I designed miniature "Pelton Wheel" turbines for Dental High-Speed handpieces in a past position. These were just 6 buckets formed by plunging a .156" dia. endmill downward with one side about tangent to the vertical centerline. They were about .350" diameter x .160" wide and turned 450,000 RPM on about 35 PSI compressed air. I don't think my phone can capture the sample I still have, but I could re-model and post if anyone is interested.
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Harold_V
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Re: Steam turbine generator

Post by Harold_V »

Kimball McGinley wrote:I designed miniature "Pelton Wheel" turbines for Dental High-Speed handpieces in a past position. These were just 6 buckets formed by plunging a .156" dia. endmill downward with one side about tangent to the vertical centerline. They were about .350" diameter x .160" wide and turned 450,000 RPM on about 35 PSI compressed air. I don't think my phone can capture the sample I still have, but I could re-model and post if anyone is interested.
I'd enjoy seeing a picture if it's not too much trouble! 8)

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Wolfgang
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Re: Steam turbine generator

Post by Wolfgang »

Kimball McGinley wrote:I designed miniature "Pelton Wheel" turbines for Dental High-Speed handpieces in a past position. These were just 6 buckets formed by plunging a .156" dia. endmill downward with one side about tangent to the vertical centerline. They were about .350" diameter x .160" wide and turned 450,000 RPM on about 35 PSI compressed air. I don't think my phone can capture the sample I still have, but I could re-model and post if anyone is interested.
Hello Kimball,

I, also, would be interested in seeing some photos of your turbine wheel. If you are able I'd appreciate your opinion on the following:

1) Are your wheels balanced statically or dynamically? If so, how?
2) What kind of bearings do your wheels run on? What is the life expectancy?

Thank you very much for any information you can supply.

Wolfgang
Asteamhead
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Re: Steam turbine generator

Post by Asteamhead »

Hello John,
Asteamhead, is my understanding correct, your turbine rides on the piston style ring seals and has no bearings? If that is correct, brass body with cast iron rings I would assume. I don't have any CNC machines, everything I do is manual, so I have to keep it simple. John
The turbine wheel is pressed carefully on the shaft of the brushless servo with stainless ball bearings inside (used as generator). It can be removed by means of a thread inside the wheel. The piston rings on the enlarged wheel are pushed inside the case. They will settle after some revolutions with no contact remaining to the 'piston' :lol: ! It's made similar to the method used with most prototypes. All parts are made of bronze.
The minor leakage of steam towards the generator is thrown outside by means of a rotating disk, mounted on the shaft, too.
Thus the whole unit may be inserted or removed from the outer case without touching the rings or the stainless bearings of the generator.
By the way: No CNC or precision mill necessary due to use of a simple gearwheel as turbine - please try!
Asteamhead
jscarmozza
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Re: Steam turbine generator

Post by jscarmozza »

Thanks for the clarification Asteamhead, I suspected that everything was riding on the 'generator' bearings but wasn't 100% sure. I like the overall idea, I'm going to try and make something similar.

Back to the wheel, I attached a photo of today's failure. Things were going along well until my gashing tool broke. I got about 3/4 of the way through the process when the tool broke (the same thing happened yesterday). I think my heat treating is to blame; I suspect that the thin cutting section is getting over heated and brittle. I'm going to try just hardening the cutter on the next one I make. I ran out of 1" diameter brass scrap, so I used 303 stainless steel and was surprised at how nicely it machined; I think I'll make my prototype wheel from it rather than brass. Since you brought the matter up, how well does the spur gear work as a turbine wheel? If my tools keep breaking I may switch to the gear form. Looking forward to further discussion and comments, thanks to all. John
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Kimball McGinley
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Re: Steam turbine generator

Post by Kimball McGinley »

I modeled up the Dental Pelton Wheel I designed because I just could not get a good photo with my phone camera. Its six buckets were formed by walking a 5/32" dia. end mill in from the side, not plunging vertically as I said earlier. These were fed air basically tangent, in and out at 180 degrees. The exhaust air has to go back down alongside the same supply hose it came in on because it couldn't exhaust into the patient's mouth. The exhaust line was larger than the supply.
The best miniature ball bearings used ceramic balls, but another company managed to gab a patent on that for Dental Handpieces, so we used New Hampshire Bearings with high-grade SS bearing balls. Interestingly, bearing failure occurred when the spacers wore out, allowing the ball spacing to become non-regular. NHBB then made a bearing with seven balls instead of 8, its life rose about 15% correspondingly. The two bearings were end-loaded with a wave spring to keep the balls from ruinous sliding: they have to be loaded at all times.
A Ball bearing design engineer told me that they consider Dental High-Speed Handpieces to be the toughest application for ball bearings due to scarcity of lubricant, extremely high speeds (450,000 rpm) and steam sterilization by Autoclave. They learn a lot from the Dental industry.
The turbine and 1/16" 3-jaw collet/closer were balanced by an outside company; they were spun and small drills removed tiny amounts of material.
I am attaching a view of the model and a photo showing all the parts posed around a penny, from 12:00; Pelton Wheel, two bearings, wave washer, shaft/closer, 3-jaw collet, collet spring, housing (showing inlet and outlet holes) and cartridge top. The dental burr on top of the penny has a 1/16" shank; the business end is a miniature six-flute ball end mill with serrated flutes.
Attachments
Set.jpg
Dental Pelton Wheel .JPG
Wolfgang
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Re: Steam turbine generator

Post by Wolfgang »

Kimball,

Definitely food for thought; thanks for your information.

Did you experiment with different number of buckets?

Wolfgang
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Harold_V
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Re: Steam turbine generator

Post by Harold_V »

Kimball,
Thanks for the information. I specialized in small work when I ran my humble shop, and have great appreciation for such work. Most machinists don't like it, and have little success in getting it done. Requires a great deal of patience, something this normally impatient person seems to have when on a machine.

Very nicely done, by the way! :wink:

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Kimball McGinley
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Re: Steam turbine generator

Post by Kimball McGinley »

As to Wolfgang's question about more buckets; we did try 8, 10, and 12, I think, but with this design the geometry means that they have to get shallower, so it seemed that the torque went down and the cost of machining went up. Bearing life was probably a few dozen hours; but that was adequate as it was a few hundred uses.
jscarmozza
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Re: Steam turbine generator

Post by jscarmozza »

I made two of the turbine wheel forms that have been discussed, both wheels are 1" diameter and 7/16" thick. The bucket depth in the crescent form proposed by Karl and Ken is 0.070", the bucket depth in the form proposed by Kimball is 0.065". I spun both between centers and they really scream. Is there any way to test them to determine which produces the most torque? John
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Bob D.
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Re: Steam turbine generator

Post by Bob D. »

I would think there would be an inherent design difference between a rotor intended to absorb available energy from compressed air and one from that is intended for live steam. Obviously there is more energy in 75 psi of steam thru a jet than there is from compressed air.
It looks like you have made fine examples of each. What might be an easy test mule dyno would be to utilize a bicycle wheel driven dynamo. Add light bulbs to increase the load and see what each rotor can deliver on air. Any DC brushed motor would work. The RC car hobby has some pretty high rpm motors for pretty cheap. Knowing the bulb wattage will ballpark the load generated by the rotor. Really just knowing one setup can light 6 bulbs and the other can do 8 gives you good info without knowing any other details.
Definetely something that interesting to experiment with. Great project!

Bob
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