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REPAIR OF MAGNESIUM GEAR BOX CASING

(-----) 2006

DEAR SIR,
WE ARE FACING A PROBLEM IN THE REPAIR IF GEAR BOX CASNG.THE PROBLEM IS THAT AFTER THE BEARINGS AARE REMOVED FROM THE CASING THE BORE SIZE ETS ENLARGED BY 15 TO20 MICRONS.
WE CANNOT DISCARD THE CASING SINCE IT IS VERY COSTLY.

SATHYA PRAGASH
HELICOPTER DIVISION - BANGALORE, INDIA
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First of four simultaneous responses -- 2006

You can not just make any repair. You must follow the overhaul instructions of the OEM for that repair. Typical would be to mill it appropriately oversize, plate it and then grind to final size. Thermal spray has replaced some chrome and nickel applications.

James Watts
- Navarre, Florida
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Second of four simultaneous responses -- 2006

One approach would be to machine the bearing housing oversize, then install a bush to bring it back to the required ID to suit the bearing OD.

Bill Reynolds [dec.]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
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Third of four simultaneous responses -- 2006

It may be possible to build up the bore area with a hard anodic coating such as Magoxid-Coat(r).

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

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Fourth of four simultaneous responses -- 2006

One common way of dealing with oversize bores during repair and overhaul is to machine the bore first to regain concentricity and then fit a liner of the appropriate size to bring the bore back to operational tolerance. The liner may be interference fitted in most cases.
The choice of material for the liner will depend on the application of the bore.

Brian Terry
Aerospace - Yeovil, Somerset, UK
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2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Sir,

this is problem regarding magnesium alloy (rz5) housing bores which are being oversized when they are coming for overhaul after 500 hours of servicing. helicopters using magnesium alloy housings for its gear boxes is facing this problem. the oversizing is around 65microns. so please suggest how to develop material/ protective coating to avoid oversize/ any other procedures which makes use of rejected housings.

thanking you sir,

Kothara Srinivasa Rao
aeronautics - India
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