Note: Descriptions are shown in the official language in which they were submitted.
"` llZ541~3
Method and Apparatus for Securing a Wheel to
a Rotatable Shaft of a Turbomachine
This invention relates to method and apparatus for securing a
wheel member of a turbomachine to a rotatable shaft, and in
particular to an arrangement which positively secures the wheel to
the shaft without generating torsional forces.
Rotors of turbomachinery, such as centrifugal compressors and
turbines, are at times manufactured as a composite structure,
wherein the discs or wheels of the turbomachine are attached to
stub shafts, which are fixed to the ends of a thru-bolt, sometimes
; 10 referred to as a tie-bolt. In achieving the composite structure,
heat has been applied to the thru-bolts for developing forces to
positively secure the wheels to the shafts. In order to apply the
heat, holes have been drilled through the entire length of the
shafts, destroying the integrity of the shafts and increasing the
problems associated with achieving dynamic and static balance of
the rotor. In addition, alignment of the shaft journals has been
difficult to achieve without complicated and relatively expensive
manufacturing techniques. It has been suggested that the heating
step used to positively secure the wheels to the shafts be
; 20 eliminated, and that compression and torsional forces developed
through the use of appropriate bolt and nut arrangements be used
to achieve the desired joining of the disc and shaft.
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However, turbomachinery employed in many applications, such as
power recovery installations, operate at relatively high
temperatures. Thus, the working strength of the various elements
of the turbomachine are reduced as the working strength of a
metallic component generally varies inversely to the temperature
of the environment in which the component operates. The torsional
forces developed in securing the disc to the shaft will generate
torsional stresses. Such stresses may result in the failure of
one or more of the bolts due to the relatively low value of the
working strength of the bolts. Generally speaking, the shear
strength of the bolts to withstand the torsional stresses is
approximately one-half the tensile strength of the bolts at any
given temperature. As is obvious, a failure of a connecting bolt
may result in maior damage to the turbomachine.
Accordingly, it is an object of this invention to eliminate
torsional stresses developed in the means employed to secure a
wheel to a shaft of a turbomachine rotor.
It is a further object of this invention to utilize tensile and
compressive forces to secure the wheel to the shaft.
It is a further object of this invention to positively secure a
wheel to a shaft without creating torsional stresses.
It is yet another object of this invention to provide a wheel
secured to a shaft suitable for use in high temperature
environments.
It is yet another object of this invention to secure and
accurately attach the wheel to a shaft through a relatively
inexpensive arrangement and method.
The foregoing problem is solved according to the invention in
apparatus for securing a wheel to a shaft of a turbomachine
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characterized in that a piston~like member is provided
adjacent one side of said wheel; securing means joins the
wheel between opposed sides of the shaft and piston-like
member; force generating means to move the piston-like
member relative to the wheel for providing a space between
the opposed sides thereof; and compression means secured
within the space, with one side thereof being in contact
with the wheel for placing a compressive force on the wheel
to positively secure the wheel to the shaft.
The present invention further includes a method of securing
a wheel member to a rotatable shaft which includes the steps
of securing the wheel between a first member and an end of
the shaft; the member is moved relative to the wheel to form
a space between opposed sides of the wheel and of the member;
and a spacing member is placed in the space formed between
the wheel and the movable member to place a compressive
force on the wheel for positively securing the wheel to the
shaft.
Figure 1 of the drawings depicts a sectional view of a
portion of a turbomachine illustrating a first embodiment of
the present invention.
Figure 2 of the drawings depicts a sectional view of a
portion of a turbomachine illustrating a second embodiment
of the present invention.
Referring now to the drawings, there are disclosed preferred
embodiments of the present invention. In referring to the
two figures o~ drawings, like numerals shall refer to like
parts. In particular, and with specific reference to Figure
1, there is disclosed a portion of a turbomachine 10 comprising
a wheel member such as disc 12 and an axial, rotatable shaft
14. Wheel 12 is secured to a forward, axial surface of
shaft 14, the disc and shaft forming in combination the
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rotor section of the turbomachine. Suitable axially extending
seals, as for example labyrinth seals 16 are provided about
shaft 14 to maintain leakage of the motivating fluid to a
minimum. Shaft 14 is formed with a plurality of tapped
holes 18, each of the tapped holes receiving therein a
threaded end 26 of a bolt or stud 24. Disc 12 includes a
plurality of drilled holes or apertures 17, provided in
axial alignment with threaded holes 18. Suitable torque
transmitting means, such as coupling 50 join disc 12 to
shaft 14 resulting in the joint rotation of the shaft and
disc.
Turbomachine 10 may be a centrifugal compressor, an axial
compressor, a radial`or axial turbine. Wheel member 12
takes the form of an impeller when machine 10 is a centrifugal
compressor and takes the form of a bladed disc when the
machine is an axial compressor or turbine.
A piston-like or outside member 22 is located axially forward
of wheel 12 and is supported by the wheel for axial movement
relative thereto, and surfaces of the wheel and outside
member 22 define an expansible chamber 38. Chamber 38, more
particularly, is bounded or defined by first and second
opposite radial surfaces of wheel 12 and outside member 22,
and first and second opposite annular surfaces of the wheel
and the outside member respectively. Preferably, as shown
in the drawings, the above-mentioned first annular surface
is radially outside the second annular surface. The piston
also includes a plurality of holes or apertures 23 provided
in axial alignment with holes 17 and 18 respectively provided
in wheel 12 and shaft 14. Bolts 24 thus extend axially
through the pis~on-like member, the rotor disc, and terminate
in the threaded hole formed in shaft 14.
Piston-like member 22 further includes a fluid opening 46.
Opening 46 connects with a suitable conduit (not shown) to
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provide a high pressure fluid from a source thereof (not
shown) to chamber 38. A suitable seal such as O-ring 40 is
provided to prevent leakage of the high pressure fluid from
chamber 38.
When wheel member 12 is positively secured to shaft 14, as
for example when the rotor section is installed in the
turbomachine's casing, the rotor includes annular shim
member 28, provided between opposed sides 42 and 44 respectively
of piston-member 22 and wheel member 12. The diameter of
the shim member is equal to or less than the diameter of the
piston-like member. A shim cover plate 30 is suitably
attached, as for example by screws 32 to piston-like member
22.
As noted previously, it is desirable to minimize torsional
stresses generated in the bolts used to secure the wheel to
the shaft. The minimization or elimination of torsional
stresses is particularly important in turbomachines utilized
with relatively high temperature motivating fluids.
In securing outside member 22, wheel 12 and shaft 14, wheel
12 is coupled to a forward, axial end of shaft 14, member 22
is located axially forward of the wheel, with apertures 17,
18 and 23 aligned, and bolts 24 are passed through these
aligned apertures. The bolts are only lightly torqued to
maintain the initial integrity of the rotor section. First
ends 26 of bolts 24 are securely anchored within holes 18 of
shaft 14 due to the mating engagement of threaded sections,
and second ends of the bolts are brought into abutting
engagement with the outside member, specifically an axially
forward surface thereof. Shims 28 are not placed within the
assembly at this time; opposed sides 42 and 44 are in direct
contact with each other. High pressure hydraulic fluid is
thence delivered to chamber 38 through connection 46. The
fluid generates a force in the chamber to move piston-like
member 22 relative to wheel 12 to expand the volumetric size
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of chamber 38. The movement of piston 22 results in thestretching of bolts 24 to a stretched position and the
compression of wheel 12. A shim space is formed between
the opposed sides of the wheel and piston, preferably
radially outside expansible chamber 38, with shim 28
being placed in the shim space to maintain bolts 24 in
the stretched position. Shim 28 is in direct contact with
the opposed sides of piston 22 and wheel 12. Shim cover
plate 30 is then attached to piston 22, and the cover plate
30 extends over shim 28 to maintain the shim in the shim
space. After the bolts 24 have been stretched to their de-
sired,stretched length, and shim 28 has been positioned to
maintain the bolts in their stretched position, the fluid
is exhausted from chamber 38 whereby the bolts apply a
compressive force to compress wheel 12 against shaft 14.
By stretching bolts 24, the bolts are placed in tension.
The tensile force thus developed is transmitted through
piston member 22 and shim 28 as a compressive force acting
against wheel 12 to maintain the wheel positively secured to
shaft 14. Essentially, the only force acting on bolts 24 is
the tensile force developed during the stretching of the
bolts. Thus, the working strength of the bolts will not be
decreased as a result of the generation of torsional forces
and thus stresses acting thereon.
When it is desired to remove wheel 12 from shaft 14, hy-
draulic fluid is reintroduced into chamber 38. The hydrau-
lic fluid generates a force in chamber 38 compressing wheel
12 against shaft 14 and urging piston member 22 outward,
away from the wheel. Member 22, in turn, applies a stretch-
ing force on bolts 26, relieving the stress on shim 28.
Shim 28 may then be removed. Then the hydraulic fluid is
exhausted from chamber 38, relieving the stretching force
on bolts 26 and the compressive force on wheel 12. Bolts 26
return to their normal, unstretched position, and the bolts
and wheel 12 may then be removed from turbomachine 10.
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Referring now to Figure 2, it will be observed that the side
54 of wheel 12 remote from shaft 14 includes a rotor end cap
60 attached thereto through suitable coupling means 52.
Alternatively, the rotor end cap may be made integral with
the wheel thereby eliminating the need for coupling 52.
Rotor end cap 60 includes a plurality of holes 67 axially
aligned with holes 17 in wheel 12 and holes 18 in shaft 14.
A piston-like member 22 is movably disposed in a chamber 38
defined by axially extending flange 68 of rotor end cap 60.
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The piston includes a plurality of holes or apertures 63
provided in axial alignment with the holes and apertures
respectively provided in end cap 60, wheel 12 and shaft 14,
and a plurality of connecting or bolt means axially extend
through these aligned apertures. With the embodiment shown
in Figure 2, these bolt or connecting means includes studs
64, outside nuts or bolt heads 74 and intermediate nuts 76.
Studs 64 extend axially through the aligned holes in the
piston-like member, the rotor end cap, and the wheel and
terminate in the threaded holes formed in shaft 14. As
noted previously, one end 26 of stud 64 is threaded for
mating engagement with the threads formed in hole 18; likewise
the other end 65 of stud 64, extending through hole 63 in
piston 22, is also threaded. As an alternate construction,
stud 64 may be attached to shaft 14 via a thread-nut arrangement
in lieu of the thread-tapped hole construction shown.
Piston-like member 22 further includes a fluid opening 46.
Opening 46 connects with a suitable conduit (not shown) to
provide a high pressure fluid from a source thereof ~not
shown) to chamber 38. A suitable seal, such as O-ring 40,
is provided to prevent leakage of the high pressure fluid
from chamber 38.
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Ends 65 of studs 64 extending through the piston-like member
are provided with threads, an outside nut 74 is releasably
mounted thereon axially forward of outside member 22, and an
intermediate nut 76 is movably mounted on ends 65 of studs
64, between piston-like member 22 and end cap 60 of wheel
12. Nut 74 secures the end of stud 64 to piston-like member
22. As noted previously, it is desirable to minimize torsional
stresses generated in the studs used to secure the wheel to
the shaft. The minimization or elimination of torsional
stresses is particularly important in turbomachines utilized
with relatively high temperature motivating fluids.
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In positively securing wheel 12 to shaft 14, nuts 76 are
in:itially placed in firm contact with side or face 61 of
rotor end cap 60. Thence, high pressure hydraulic fluid is
delivered to chamber 38 through fluid flow connection 46.
The fluid generates a force in the chamber acting against
face 42 of member 22 to move the member relative to the
wheel to expand the volumetric size of chamber 38. The
movement of piston 22 results in the stretching of studs 64
attached thereto. In addition, the hydraulic force acts
against face 44 of the rotor end cap thereby generating a
compressive force on the end cap which is transmitted to the
wheel.
By stretching studs 64, the studs are placed in tension.
The tensile force thus developed is transmitted through nuts
76 and the rotor end cap 60 as a compressive force acting
against~wheel 12 to maintain the wheel positively secured to
shaft 14. Once the studs have been stretched to their
desired length, nuts 76 are brought into firm engagement
with the opposed side of the rotor end cap to maintain the
compressive force developed during the stretching of the
studs acting against the wheel and shaft. The hydraulic
fluid is exhausted from chamber 38 once the desired compression
of the components has been achieved. Piston-like member 22
can be withdrawn from chamber 38 by removal of nuts 74 from
studs 64 and then axially sliding the piston-like member
outward along studs 64. Thus, a single piston-like member
22 may be used with more than
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one turbomachine to achieve the desired positive locking of
the wheel to the shaft.
Since the only forces acting on studs 64 is the tensile
force developed during stretching of the studs, the working
strength of the studs will not be decreased as a result of
the generation of torsional forces and thus stresses acting
thereon.
With this embidiment, when it is desired to remove wheel
12 from shaft 14, piston member 22 is remounted on stud 64,
axially slid forward therealong to form chamber 38, and
then secured in place by nuts 74. Hydraulic fluld is re-
introduced into chamber 38 compressing wheel 12 against
shaft 14 and urging piston member 22 outward away from the
wheel. Member 22 urges nuts 74 outward, and nuts 74 apply
a stretching force on studs 64, relieving the stress on nuts
76. Nuts 76 may be moved away from rotor end cap 60. Then
the hydraulic fluid is exhausted from chamber 38, relieving
the stretching force OIl bolts 64 and the compressive force
on wheel 12. Nuts 74, piston member 22, studs 64, and wheel
12 may all then be removed from turbomachine 10.
The arrangements and methods herein disclosed provide a
relatively inexpensive means for positively securing the
wheel of a turbomachine to a shaft. The invention finds
particular applicability in turbomachines having relatively
high temperature working fluid flowing therethrough where
it is particularly important that torsional stresses be
maintained at a minimum to prevent material fatigue.
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