CA1125483A

CA1125483A - Method and apparatus for securing a wheel to a rotatable shaft of a turbomachine and apparatus for securing a wheel to a rotatable shaft of a turbomachine

Info

Publication number: CA1125483A
Application number: CA336,876A
Authority: CA
Inventors: Carl H. Geary, Jr.; Norman A. Samurin; William A. Straslicka
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 1978-10-27
Filing date: 1979-10-03
Publication date: 1982-06-15
Also published as: GB2109896A; IT7926716A0; JPS6210401Y2; JPS592901U; CH643634A5; GB2033541B; GB2033541A; GB2109896B; IT1125568B

Abstract

ABSTRACT

A wheel of the turbomachine is secured to a shaft of the machine by initially securing the wheel between one end of the shaft and a piston-like member. A space is formed between opposed sides of the member and wheel by moving the member relative to the wheel. A compression member is placed in the space for placing a compressive force on the wheel for positively securing the wheel to the shaft.

Description

"` 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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llZ5483 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 , ' , : '`~ ' ' ~ `

11'~548~3 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 548;~

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 --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.

-6a-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.

;'7 , -~lZ5483 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.
, 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.

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 ~..S ~

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ll'Z~i483 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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for securing a wheel to an axial, rotatable shaft of a turbomachine comprising: an outside member disposed axially forward of the wheel, wherein surfaces of the wheel and the outside member define an expansible chamber; a plurality of connecting means axially extending through aligned apertures defined by the shaft, the wheel, and the outside member, with a first end of the connecting means secured to the shaft and a second end of the connecting means engaging the outside member; means for generating a force within the expansible chamber to move the outside member relative to the wheel to apply a stretching force to the connecting means and a compressive force to the wheel, axially compressing the wheel against the shaft; and means for maintaining the stretching force on the connecting means and the compressive force on the wheel to allow removal of the force generating means.

2. Apparatus in accordance with claim 1 wherein the expansible chamber is defined by a first radial surface defined by the wheel, a second radial surface defined by the outside member opposite to the first radial surface, a first annular surface defined by the wheel, and a second annular surface defined by the outside member opposite to the first annular surface; and further including a seal located between and engaging the first and second annular surfaces to prevent fluid leakage from the expansible chamber.

3. Apparatus in accordance with claim 2 wherein the connecting means are located radially outside the expansible chamber.

4. Apparatus in accordance with claim 3 wherein the first annular surface is radially outside the second annular surface.

5. Apparatus in accordance with claim 1 wherein:
the force generating means includes means for generating a force to move apart surfaces of the outside member and the wheel to define therebetween an axial shim space radially outside the expansible chamber; and the maintaining means includes shim means secured within the shim space and in contact with opposed surfaces of the outside member and the wheel for maintaining the compressive force on the wheel to secure the wheel positively to the shaft.

6. Apparatus in accordance with claim 5 further including a shim cover plate secured to the outside member and extending over the shim means to maintain the shim means in the shim space.

7. Apparatus in accordance with claim 6 wherein:
the connecting means includes a plurality of bolts; first ends of the bolts are anchored within the shaft; and second ends of the bolts abut against a forward surface of the outside member.

8. Apparatus in accordance with claim 1 wherein the maintaining means includes nut means movably mounted on the connecting means between the wheel and the outside member for engaging the wheel to maintain the stretching force on the connecting means and the compressive force on the wheel.

9. Apparatus in accordance with claim 8 wherein the connecting means includes: a plurality of studs, with first ends of the studs secured to the shaft and second ends of the studs axially extending axially forward of the outside member; and a plurality of outside nuts releasably secured to second ends of the studs and abutting against a forward surface of the outside member.

10. A method of securing a wheel to an axial shaft of a turbomachine comprising the steps of: coupling the wheel to a forward, axial end of the shaft; positioning an outside member axially forward of the wheel; forming an expansible chamber between the wheel and the outside member;
passing a plurality of bolt means through aligned apertures defined by the outside member and the wheel and into holes defined by the shaft; securing a first end of each bolt means to the shaft; engaging the outside member with a second end of each bolt means; moving the outside member relative to the wheel by delivering a pressurized fluid into the expansible chamber to stretch the bolt means to a stretched position and to compress the wheel against the shaft; maintaining the bolt means in the stretched position;
and exhausting the pressurized fluid from the expansible chamber whereby the bolt means apply a compressive force to compress the wheel against the shaft.

11. A method as defined by claim 10 wherein: the moving step includes the step of forming a shim space be-tween the outside member and the wheel; and the maintaining step includes the step of placing a shim means within the shim space in contact with opposed surfaces of the wheel and the outside member.

12. A method as defined by claim 11 wherein the maintaining step further includes the step of covering the shim means to maintain the shim means in the shim space.

13. A method as defined by claim 10 wherein the maintaining step includes the steps of: mounting a plurality of intermediate nuts on the bolt means and locating the intermediate nuts between opposed surfaces of the outside member and the wheel prior to stretching the bolt means to the stretched position; and bringing the intermediate nuts into engagement with a forward surface of the wheel after stretching the bolt means to the stretched position.

14. A method as defined by claim 10 further including the step of removing the outside member.

15. A method as defined by claim 14 wherein: the engaging step includes the steps of releasably mounting a bolt head on the second end of each bolt means, and bringing the bolt heads into firm contact with the outside member;
and the removing step includes the steps of removing the bolt heads, and axially sliding the outside member along and off the bolt means.