This document describes a patent application filed in 1957 relating to improvements in axial-flow compressors. Specifically, it describes using softer aluminum alloy sealing rings between compressor stages to prevent damage to steel rotor rims from interference during operation. The soft rings are installed at a small initial clearance so that they deform away from the rotor to maintain a minimum gap without scoring the thin rim. Tests showed aluminum rings could satisfactorily wear away under high rim velocities over 800 feet per second due to their higher hardness and melting point compared to steel.

1. * GB780137 (A)
Description: GB780137 (A) ? 1957-07-31
Improvements relating to axial-flow compressors
Description of GB780137 (A)
-PATEN S
P ATENT SPECIFICATION
Inventor: FREDERICK R. SHORT 7O0,137 No. 196 Comnplet Application and
filing Complete Specification: July 7, 1955.
e Specification Published: July 31, 1957.
Index at acceptance:-Class 110(1), D2H.
International Classification:-FO4d.
COMPLETE SPECIFICATION
Improvements relating to Axial-Flow Compressors We, GENERAL MOTORS
CoRpoRATIoN, a Company incorporated under the laws of the State of
Delaware, in the United States of America, of Grand Boulevard, in the
City of Detroit, State of Michigan, in the United States of America
(Assignees of FREDERICK R. SHORT), do hereby declare the invention,
for which we pray that a patent may be granted to us, and the method
by which it is to be performed, to be particularly described in and by
the following statement:-
This invention relates to axial flow air compressors and more
particularly to interstage seals for such compressors.
The scope of the invention is defined by the appended claims. How the
invention may be carried out will now bedescribedwith reference to the
accompanying drawing which represents a partial section taken
longitudinally of a multi-stage axial-flow air compressor.
Referring now to the drawing, a disk-type compressor rotor 1 is shown
in the annular casing 3; only so much of the compressor being shown as
is necessary to illustrate the present invention. The rotor 1 is built
of a number of disks 5 that are flanged at their rims to fit one
against the other. The disks are held together by a tie bolt (not
shown) in a known manner and the thin flanges 7 are splined together
as at 9 so that torque may be transmitted between them. Non-integral
spacer rings may be used to separate the disks 5, if desired, rather

2. than the integral flanges 7 illustrated. The disks 5 are formed with
dovetail slots across the rims to carry the rows of blades 11. The
stator vane rows 13 extend inwardly from the casing 3 and are
supported by the rings 15 which are suitably secured in annular
grooves in the casing 3. Flanged rings 17 and 19, fixed to the inner
ends of the stator vanes 13 by upsetting tangs 20 extending from the
blades through the rings, carry inter - stage sealing rings 21. As
shown, the sealing rings 21 are pinched between the flanged rings 17
and 19, [Price 3s. 6d.J but they may be supported in the stator
assembly in various alternative fashions. The flange 7 have peripheral
ridges 23 as a further means of reducing air leakage past the 50
sealing rings 21.
The sealing rings 21 are fashioned of a material that is materially
softer than the rotor rim material and in the construction illustrated
they are also angled to lie nonperpendicularly with respect to the
rotor rim. The sealing rings 21 are initially set at a predetermined
clearance so selected that some interference will probably result
between the rotor rim and rings during operation. Such interference or
rubbing will not score the thin rotor rim because the conical
configuration of the softer sealing rings allows the rings to easily
deform away from the rotor rim and because any rubbing or 65 wearing
away of material takes place in the softer rings rather than in the
rotor rim.
The rotor disks 5 are made of high strength alloy steel and the
sealing rings 21 are made of aluminium base alloys (that is, alloys
having at least 85% aluminium), or aluminium of commercial purity. To
understand the desirability of utilising aluminium sealing rings with
steel rotors, it is necessary to visualise the effects of
interferences between the 75 rings and rotors when the rings are
initially installed with such small clearances as to result in
interferences. Interference results in the wearing away of the rings
to a minimum clearance without scoring the thin rim of the 80, rotor,
for the rings are materially softer than the rotor. The rate of wear
varies in accordance with the relative hardness and particular
composition of the rings and rotor rims.
Tests at rim velocities in excess of 800 feet 85 per second indicate
that practically any high aluminium content ring, regardless of its
temper, will perform satisfactorily due to the inherently higher
hardness and melting point of the steel rotor rim. The thin rotor rim
90 will remain undamaged even under interferences that exceed the
capacity of the rings p to wear away, for in such instances the
frictional surface of the ring will melt away from the rotor rim. The
melting points of high aluminium content rings (around 1,250-) thus
satisfy two prerequisites, that is, they are higher than the maximum

3. air temperatures usually developed in axial-flow compressors and lower
than the melting points of the rotor rim materials.
The interference wear of the rings 21 is reduced by angling the rings
in non-perpendicular relation with the flanges 7 of the rotor rim, as
shown in the drawing. Because of the excellent spinning properties of
aluminium the conical rings 21 will readily deform when interference
arises.
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