Axial Thrust

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NFLD
Bilge Dweller
Posts: 3
Joined: Mon Apr 01, 2013 11:47 pm

Axial Thrust

Postby NFLD » Tue Apr 02, 2013 10:01 pm

Need some help in understanding axial thrust and how it is dealt with?

Thanks

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Big Pete
Engineering Mentor
Posts: 813
Joined: Fri Apr 24, 2009 11:18 pm
Currently located: Solihull, England

Re: Axial Thrust

Postby Big Pete » Wed Apr 03, 2013 12:12 am

Axial thrust is thrust along the axis of the shaft.
For instance a propeller driving a ship generates thrust to push the ship forward by pushing water backwards. This thrust is transmitted from the propeller through the propeller shaft, if this was just connected to the crankshaft of an engine it would push the crankshaft forward into the engine until the engine seized. A thrust bearing has to be fitted to transmit the forward (and astern) thrust to the HULL of the ship, while allowing the engine to transmit torque to the propeller.
With medium speed engines the thrust block is usually incorporated into the gear box.
With slow speed engines a seperate thrust bearing can be fitted between the engine and the propeller, or incorporated into the engine. The Mitchell thrust bearing used to be very common with tiltng kidney shaped white metal pads acting on a flange on the shaft.
Axial thrust also occurs in axial flow pumps and ventilation fans, in these cases a thrust bearing is usually incorporated in the electric motor driving the unit. These will usually only absorb thrust in one direction. This is why you will sometimes see ER fans with a capability to run in reverse, to clear smoke from the ER after a fire, with warnings on them that they are only to be run in reverse for very short periods.

Hope this helps.

BP.
It is always better to ask a stupid question than to do a stupid thing.


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