US2846183A - Retaining devices for turbine blades - Google Patents

Description

4 w. c. MORGAN RETAINING DEVICES FOR TURBINE BLADES Aug. 5, 1958 Filed July 18, 1952 WILLIAM G. MORGAN RETAIN NG DEVKCES FOR TURBINE BLADES William C. Morgan, Westlake, Ohio Application July is, 1952, Serial No. 299,786

Claims. (Cl. 253-77) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be used and manufactured by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to wheel blades usable in turbines and compressors with special reference to supporting structure for firmly but detachably holding the blade secured to the wheel rim.

Various means have been used hereofore in securing blades to wheel rims including wire attachment, pin fastening and slide engagement with peened locks. One of the chief difliculties with these prior methods has to do with lack of ease and speed of assembly and disassembly.

One of the primary objects of the invention, therefore, is to provide an attachment device for turbine wheel blades which may be employed with facility and speed. Another object is to provide a blade attachment device which may be employed without physical deformation of the wheel or blade structure. Still another object is to provide a blade attachment which, when in use, as 3 on a turbine wheel, is subjected to forces tending to resist separation of blade and wheel. A further object is to provide a blade attachment which will permit free movement of the blade through small angles in the plane of rotor rotation.

Other objects and features of the invention will become apparent to those skilled in the art on consider-' ation of the following description of a preferred embodiment of the invention in connection with the accompanying drawings, in which- Fig. 1 is a side view of a part of the blade and a section of the wheel rim, showing a mode of blade attachment;

Fig. 2 is an elevational view of the blade-rim attachment taken at right angles to the view of Fig. 1;

Fig. 3 is a sectional detail of the fir tree assembly of blade and rim; and

Fig. 4 is a detail view showing a modified locking device for the assembly.

The wheel in the drawings is indicated by the numeral and includes the wheel hub 11 and the blades 12. The blade root vor base 13 is formed in tapered triangular contour with spaced ridges 14 running parallel to the Wheel axis on the flat faces of the base taper, forming what is often referred to as a fir tree construction.

In the rim edge 15 are cut a series of transverse channels or recesses 16, shaped similarly to the blade base, with axial grooves 17 so spaced and sized that when the blade base 13 is applied to the sides of these recesses,

blade ridges l4 slide into complementary registry with 65 the hub recess grooves 17. Preferably, as shown in Fig. 3, there is some clearance between the blade ridges and the hub recesses so that there is a small play between these elements permitting a small amplitude swing of each blade with reference to the hub; and by so doing 70 it has been found that blade vibration, with its attendant disadvantages, is substantially reduced.

2,46,183 Patented Aug. 5, 1958 It is apparent that this type of assembly insures complete elimination of loosening or detachment arising from centrifigual forces developing in use of the bladed structure.

In order to lock the assembled parts when properly centered, as shown in Fig. 1, there is provided a ball-lock device which may be readily and quickly manipulated to lock or release the blade. A tube 20 is cut in the hub rim, extending from a point at the base of each of the rim recesses 16, centrally positioned both as to length and width, to a point on the hub side displaced inwardly from the recess 16. This inclined tube is preferably formed in two sections, the outer section 21 being smaller than section 22 and threaded to receive a set screw 23, and a lock screw 24, each of these screws being provided with driver grooves 25. The larger section 22 of the tube is smooth walled to receive in sliding engagement a ball retainer 26, having a cylindrical slide section 27 for tube wall engagement, and a frusto-conical tip section 28 provided with a flattened or recessed tip bearing area adapted for engagement with the bearing ball 29.

In order to provide a complementary holding element in the blade base, a conical cavity is formed centrally of the base 13, the cone dimensions being such as to form a receptacle for the locking element in the form of bearing ball 29, with the ball protruding about half of its diameter into the cavity with the blade in attached position.

It is now apparent that when the complementary blade and rim elements are slidably engaged and centered, with the set screw 23 retracted to clear the hub recesses for assembly, and the bearing ball 29 then moved snugly into the conical recess 30 and locked therein by lock screw 24, that the slidable parts are firmly secured and a fast connection is made between the blade and hub.

It is apparent that the degree of looseness in the bladerim connection can be readily controlled by adjustment of locking and set- screws 23 and 24, so that the best ball position for vibration control can be obtained.

In removal, it is necessary only to remove the ball holding screws and slide out the blade, the loose fit facilitating this action, there being no peened parts, pins, or wires to be released requiring extensive manipulation. It is noted that the described mode of blade-rim 'connection is aided by the centrifugal forces of rotation in that the blade-root ridges are held firmly against the complementary grooves in the hub rim.

Alternative connective structure may be employed. For example, as shown in Fig. 4, the ball tube may be formed radially of the hub at the transverse center of the rim recess 16. Connecting with this tube 60 is a transverse threaded tube 61, extending from the rim side face. In tube 61 are two screws, the set screw 62 having a protruding section 63, and a locking screw having the usual driver groove 66. The screw 62 is so related to the coacting tube thread that when fully entered into the tube 61, the tip 63 of screw section 62 seats in terminal recess 67, formed in the wall of tube 60 in line with screw section 63.

A strong coil spring 70 is provided of a diameter permitting insertion in tube 60 and of a length such that when in place in the tube with the spring end resting on screw section 63 and the upper end engaging the bearing ball 29, the ball projects half of its diameter from the tube end and into conical cavity 71 formed in the root of the blade.

In using this modification the spring 70 and ball 29 are placed in screw-held position before blade engagement with the hub. The blade is then slid into central position and there retained by the spring action on ball 29. To remove the blade the screws 62 and are moved outwardly until the seat section 63 is free of tube 60, when the spring drops into the lower space of the tube 60 releasing ball 29 from cavity 71. Thereupon, the blade may be removed.

The-description hereinabove'has been restricted to a wheel-with hub and blade sections, but obviously, the

' practiced otherwise than as specifically described.

-What is claimed-is:

1. A wheel blade mounting comprising a rotor hub "having a rim, a transverse channelin the outer surface ofsaid 1 rim'provided with transverse grooves in the channel surfaces, ablade having a base conforming in shape to said rim channel and provided with transverse ridges formed for loose interlocking sliding engagement with the rim channel grooves whereby a locking interengagement of blade and rim is secured, and means for.

holding said blade and rim members from relative transverse sliding movement and for controlling the degree of looseness in the groove-ridge connectionbetween said blade and rim, said means including a cylindrical tube formed in the rim between the channel base intermediate the ends thereof and a'point-on the rim side, said tube having an inner smooth Walled-section and 'anouter threaded section, a ball movably mounted inthe smooth- Walled inner section of said tube, a cylindrical ball retainer having blunt ends slidably mounted in the smooth walled section of said tube with one end normally in engagement with said ball, a set screw having a blunt inner contact end adapted to engage the'outer end of said ball retainer, said screw being-in threaded engagement with the outer threaded section of the tube'adapted on rotation to move said ball'into a conforming conical cavity formed on the base end of the blade, and means including a lock screw in threaded engagement with the outer tube section external to said set screw for holding said set screw at adjusted points, whereby the degree of looseness in the connection between said riin and blade may be controlled.

2. A wheel blade mounting comprising a hub having a peripheral transverse surface channel provided with parallel axially extending grooves "in the wall thereof and a tube extending from said channel at apoint intermediate its ends to a point in the side surface of said hub such that the tube lies at'an angle relative to the channel axis, a blade having a base conforming to said hub channel and provided with parallel ridges adapted to have loose interlocking engagement with said channel grooves and a conical cavity adapted to overlie said hub tube at its channel end when said blade and hub are in interlocking engagement, a lock element freely movable inside the wall of said hubtube and into said blade cavity for holding the blade from transverse movement relative to said hub, means adjustably attached to the wall of said tube for moving said lock element into and out of said blade cavity, and means adjustably attached to said hub tube wall and abutting said lock element moving means for locking said lock element at' adjusted 'points, whereby the degree of looseness of the rim-blade connection may be controlled.

3. A wheel blade mounting comprising a hub having a peripheral transverse surface channel provided with axially extending grooves in the wall thereof and a cavity extending radially from said channel at a point intermediate its ends to a point in said hub wall, a blade having a base conforming to said hub channel and provided with parallel ridges adapted to have interlocking engagement with said channel grooves and a cavity adapted to overlie said hub cavity when said hub and blade are in normal interlocking engagement, a ball movable in said hub cavity and partially into said blade cavity for holding the blade from transverse movement relative to" said hub, a tubular opening in said hub wall connecting with said hub cavity from the outside hub wall surface, a screw having a protruding section threaded into said opening and adapted for movement across said hub cavity within the hub wall, means connected to said cavity permitting movement of said protruding section to block said cavity, and a spring extending between said screw and ball when the blade is attached to said hub and adapted to move to the hub cavity base limit on retraction of said screw, whereby the blade may be removed from said hub.

4. A blade mounting comprising a hub having a rim, a transverse channel in the outer surface of said rim provided with transverse grooves in the channel surfaces, a blade mounted in said rim channel and having a base conforming in shape to said rim channel and provided with transverse ridges formed for loose interlocking sliding connection with the rim channel grooves, a lock element interposed between said hub rim and blade base and engaging said rim and blade base for preventing transverse sliding movement of said ridges in the rim grooves, and adjustable means attached to said hub and engageable with said lock element for fixing the spacing between said ridges and grooves, whereby the rocking movement of the blade relative to the drum may be controlled.

5. The wheel blade mounting as defined in claim 4, said means for holding the blade from transverse movement including a ball nesting in a shallow conical opening in the base end of said blade and movable in a tube formed in said rim, and means attached to the tube wall and engageable with said ball for retaining said ball at a fixed adjusted position in joint engagement with said conical recess and tube wall, and for releasing said ball at will without structural deformation of said blade or llIIl.

References Cited in the file of this patent UNITED STATES PATENTS 894,659 Kallberg Jilly 28, 1908 1,095,587 Mcintosh May 5, 1914 1,891,948 Rice Dec. 27, 1932 1,940,455 Kilpela Dec. 19, 1933 2,618,460 Williams Nov. 18, 1952 2,646,920 Butcher July 28, 1953 2,651,494 Persson Sept. 8, 1953 FOREIGN PATENTS 976,790 France Mar. 22, 1951 OTHER REFERENCES SAE Journal, February 1948, page 32.

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