turbodisplay
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| posted on 22/10/09 at 07:55 AM |
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High speed 7 - 10mm bearings required
Anyone know where i can get some high speed bearings that can operate at 50,000 - 100,000 rpm?
Looking to make up a supercharger using a turbo.
Got the gears lined up, as well as making as case etc.
Only problem is that i have found bearings that will operate at 26,000 that can operate at 56,000 for £4 (it won`t last long at that speed).
Found some spindel bearings rated to 100,000 cost of £56 each.
Looking for a better price if pos. or if anyone can point me to a place that sells high speed beaings.
Thanks
Darren
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flak monkey
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| posted on 22/10/09 at 08:33 AM |
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This is why most turbos run on ceramic bearings with a pressurised oil feed.
Centrifugal superchargers have the same kind of thing too.
I dont know of any rolling element bearings which will withstand that rpm without an oil feed. Those that will are have ceramic rolling elements to
avoid excessive expansion due to the heat. Once you get to these the price starts getting very high. These bearings still need an oil feed, usually
through an oil mist in compressed air.
Also bear in mind that your gears/drive system will need to be extremely well designed to take those speeds on the output side. If its not it will
simply eat itself.
We did some playing around to do a similar thing at uni but couldnt make a drive system which was reliable for more than about 10 hours.
David
[Edited on 22/10/09 by flak monkey]
Sera
http://www.motosera.com
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Toprivetguns
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| posted on 22/10/09 at 08:39 AM |
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quote:
Originally posted by flak monkey
This is why most turbos run on ceramic bearings with a pressurised oil feed.
[Edited on 22/10/09 by flak monkey]
Definetly agree ! Lubrication will be needed. Most aircraft APU's run at 25,000RPM and then some. They all have a pressurized oil system.
Only drive as fast as your angel can fly... !
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richardlee237
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| posted on 22/10/09 at 08:40 AM |
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Not wishing to put a damper on your enthusiasm, but a gear driven assembly at 50k rpm plus is asking a lot.
The original turbo has very light lateral shaft loads due to the balanced nature of the system, a gear drive will impart a lateral load due to the
teeth angles. Even if you can make a gear to hold together at these speeds the losses will be bad.
The losses on these small impellers are substantial, but this is not important if the driving power is free (Turbine driven by exhaust) but if it is
parasitic on the engine you might find that it takes all your gain to drive the compressor. This is why most superchargers are large with low
velocities.
If you do build it, make sure you have some hefty steel work around the drive !!
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
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turbodisplay
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| posted on 22/10/09 at 09:32 AM |
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I agree about protection. The bearings I was looking at were sealed yet rated to 70 - 90,000rpm. The cheaper one require lubrication.
I am using a ct26 turbo so quite large compressor, so lower speed required.
I only want a system to reduce lag (turbo/ supercharger), might not be too important on a 1 ton car with a 2.9 engine.
I might get more life using an a/c electric clutch, then it will only be switch on for at most 1 minute every hour.
Gear width is 17mm en8 steel.
Flak monkey what specs were you drive unit and waht speed/ turbo did you use?
Thanks
Darren
[Edited on 22/10/09 by turbodisplay]
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flak monkey
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| posted on 22/10/09 at 09:51 AM |
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The main drive issue has already been mentioned, its the sideways forces generated by the gears at that speed which causes the problems with the
bearings. There is also a lot of heat to dissipate and you cant run the gears in an oil bath (as you normally would) as the drag at those speeds is
huge.
Loads can get quite high on high speed gear systems and most high speed bearings are rated at 0 or very low axial load.
I didnt get heavily involved in the uni project, but we started off with a holset I belive then tried various drive systems from helical and straight
cut gears to toothed belts. None of which were particularly reliable above 30,000rpm. At which speed the efficiency was pretty poor, a lot of
heat/noise in the drive system and not enough speed on the impellor to move enough air to generate any significant boost pressure. You may be able to
overcome this with the correct sized impellor though (see below)
If you look at the rotrex drive system its rather complex to achive 120,000rpm impellor speeds. If you can find some cut away pics you'll see
what I mean. They also have a pressurised lube system, albeit pumped by the supercharger itself.
There are other companies in the US using toothed belt and gear systems to generate impellor speeds of up to 50,000rpm which coupled with the right
sized impellor can generate moderate boost levels. Have a look at Paxton and Powerdyne for examples.
Although it is a nice excercise, personally knowing the problems, I wouldnt attempt a high speed homebrew drive system for a supercharger. I would
either save up for the rotrex kit or go with the rootes/eaton type if you want the cheaper option.
David
[Edited on 22/10/09 by flak monkey]
Sera
http://www.motosera.com
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turbodisplay
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| posted on 22/10/09 at 10:08 AM |
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Thanks for your replies.
I look at the project as an experiment, if it works great, if not well at least i can try out my dashboard speed measuring capabilities. (providing it
lasts am minute that is).
I`m going to use 10mm steel laser cut to hold the bearings so it should be accurately placed.
Looked at Paxton they seen to rotate at 50,000 with helical gears, ie less noise but more thrust and less efficeint.
I think i might fail iva because of noise of the gears alone by using stright cut!
Thanks
Darren
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britishtrident
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| posted on 23/10/09 at 06:48 PM |
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You just won't get it to work truly enormous problems are involved ---- how are you going to drive something at that RPM from a crankshaft doing
6,000 rpm. Then you have the effects of rotational inertia of turbine wheel trying to to drive the crankshaft, the result is very high amplitude
forces in the gear drive train. Even you do get it to work the working power band will be very narrow right at the top end.
[Edited on 23/10/09 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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