US2919889A

US2919889A - Blade mounting

Info

Publication number: US2919889A
Application number: US491887A
Authority: US
Inventors: Herbert J Rubel
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1955-03-03
Filing date: 1955-03-03
Publication date: 1960-01-05
Anticipated expiration: 1977-01-05

Description

Jan. 5, 1960 H. J. RUBEL 2,919,839

BLADE MOUNTING Filed March 3, 1955 F/GZ uws/vro/e HERB n-r J. RUBEL Byway 44M,

AT TOPNE) United States Patent BLADE MOUNTING Herbert J. Rube], Bloomfield, Coun., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation ol? Delaware Application March '3, 1955, Serial No. 491,887

9 Claims. (Cl. 253-77) This invention relates to a blade mounting for a compressor or turbine and more particularly to a compressor blade attachment by which to eliminate certain bending stresses in the blade resulting from vibrations of the blade.

One problem in high speed axial flow compressors is the attachment of the blades so that they will not be bent or broken off by the vibrations set up in the blades as the compressor operates. One feature of this invention is a flexible connection between the blade and supporting rotor by which to eliminate bending of the blade resulting from certain vibration frequencies. Another feature is a hinge or pivotal connection for the blade which will permit circumferential rocking movement of the blade without bending the blade.

' More specifically one feature of the invention is a blade having strands of material extending radially inward from the base of the blade and which cross substantially along a line parallel to the rotor axis at a point between the blade base and the attachment of the strands to the disc to form a hinge or pivotal connection for the blade.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is a side elevation with parts broken away of a portion of a compressor disc with attached blades incorporating the invention.

Fig. 2 is a sectional view substantially along the line 22 of Fig. 1.

Fig. 3 is a view similar to Fig. 1 showing a modification.

Fig. 4 is a sectional view along the line 44 of Fig. 3.

Referring first to Figs. 1 and 2, the disc 2 has peripheral radially extending flanges 4 and 6 defining therebetween a groove 8. The disc may also have a centrally positioned radially extending flange 10 midway between and shorter than the flanges 4 and 6. The disc carries a row of radially extending blades 12 on its periphery with the base 14 of each blade positioned between the outer ends of the flanges 4 and 6. Each blade base 14 extends circumferentially on opposite sides of the blade nearly to the adjacent blade base or platform, as best shown in Fig. 1 thereby forming a circumferentially extending platform radially outward of the disc periphery.

The blades 12 may be made from a thermoplastic material or any other suitable material which may be cast around a series of twisted wires 16, each of which has a flexible loop 18 extending radially inward from the blade base or platform 14. Each wire is twisted around axially extending rods or wires 20 positioned in radially spaced relation to each other within the blade. The wires are twisted together at their outer ends 23 to retain the twist of the wire around the rods 20. The material forming the blade is preferably cast around the rods 20 and wires 16 so that they are completely embedded within the blade. Each wire 16, with its centrally formed loop 18 is in effect two strands of wire extending outwardly from the loop and twisted together, thus, in effect the strands are arranged in pairs, the strands of each pair being twisted together.

The several wires 16 are preferably arranged in closely spaced axial relation to each other and the several loops or other flexible looped tension members 18 are equal in length to extend around and engage with an axially extending pin 22 supported in openings 23 in the flanges 4 and 6 and also in an opening 23 in the centrally located flange 10. The strands of wire forming each flexible loop 18 cross each other at a point 25 below the blade platform 14 and the points where the several strands cross are located substantially along an axially extending line parallel to the rotor axis. The point where the wires of each loop 18 cross is adjacent to the blade platform 14 thereby producing a hinge or pivotal connection along said axially extending line for the blade which will permit the blade to rock in a circumferential direction. The rocking movement of the blade is limited by inwardly'extending ribs 24 on the flanges 4 and 6 which are spaced radially inward from the inner surface 26 of the blade platform but are in a position to engage with the blade platforms after a predetermined rocking movement of each blade and thereby function as stops engaging with the blade to prevent excessive blade rocking.

In the arrangement shown in Fig. 2 the loops 18 are arranged in two sets which are located on opposite sides of the center flange 10.

In the arrangement shown in Figs. 3 and 4 the loops 18' are formed and connected to the blade in the manner described above. In this arrangement, however, the rotor 2 has axially extending dovetail slots 27 adjacent to the periphery which communicate with the periphery through slots 28 which are narrower than the dovetail slots. Each dovetail slot receives a similarly shaped dovetail pin 30 around which the loops 18' are positioned. As in Figs. 1 and 2, the strands of wire that form the loop 18' intersect along an axial line close to the blade platform but spaced slightly radially inward from the blade platform to form a pivotal connection about which the blade is free to rock in a circumferential direction. The pin 30 has circumferential grooves 32 therein which, on the converging surfaces 33 of the pin, these surfaces being in engagement with the side walls of the slot 27, are deeper than the thickness of the wire to hold the several loops in uniformly spaced relation to each other and also to avoid any wedging action between the pin and the slot. In this arrangement, the rocking movement of each blade is limited by engagement of the underside 26' of the blade platform 14' with the peripheral surface 34 on the rotor.

This type of blade mounting eliminates the first bending frequency which determines the chordal dimension of the blade. Running frequency of a blade is given by the equation ;f,= /f +/3N where f is the static frequency, 3 is a constant for a given hub-tip ratio and N the r.p.m. of the engine.

With a flexural joint as above described, the static frequency is zero so that f =N /fi which in plotting frequency against speed produces a straight line starting at the origin of the plot. Since the second order excitation is also a straight line starting at the origin of the plot the two lines do not intersect at any operating speed. This flexure joint thus permits the chordal dimension of the blade to be established only on a tensile stress consideration instead of on a vibration basis.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In a blade mounting, a disc having a transversely extending pin, a blade extending radially outward from and having radial clearance with respect to the disc, and fiexible looped tension members attached to and extending radially inward from the blade and crossing between said blade and pin and extending around said pin, said looped tension members being closely spaced from each other axially of the disc and being substantially parallel to each other, said looped tension members being the sole support for said blade.

2. In a blade mounting, a disc, a blade extending radially outward from the periphery of the disc and having radial clearance with respect to the disc, and strands of material extending radially inward from the blade and secured to said disc, said strands crossing each other substantially along a line parallel to the axis of the disc and between the disc and the blade thereby forming a pivotal axis for the blade with respect to the disc.

3. In a blade mounting, a disc having a transversely extending pin, a blade extending radially outward from and having radial clearance with respect to the disc, and wire strands extending radially inward from the blade to form loops around said pin, said strands being arranged in pairs, the strands of each pair crossing each other substantially along a line parallel to the axis of the disc and between the pin and the blade thereby forming a pivotal axis for the blade with respect to the disc.

4. In a blade mounting, a disc, a row of blades extending radially outward from the periphery of and having radial clearance with respect to the disc, said blades being of thermoplastic material, and wire strands embedded in each of said plastic blades and extending radially inward from the blades, said strands being secured to said disc, said strands being arranged in pairs, the strands of each pair crossing each other substantially along an axially extending line radially inward from each of said blades thereby forming a pivotal axis for the blade with respect to the disc.

5. In a blade mounting, a disc, a plurality of blades extending radially outward from the periphery of and having radial clearance with respect to the disc, each blade having a platform at its inner end, wire strands extending radially inward from the blade and secured to said disc, said wire strands being arranged in pairs, the strands of each pair crossing each other substantially along an axially extending line between the blade and the disc, thereby forming a pivotal axis for the blade with respect to the disc and stops on the disc engageable with said platform as the blade pivots for limiting the movement of the blade in a circumferential direction.

6. In a blade mounting, a disc having a transversely extending pin adjacent to the periphery thereof, a blade extending radially outward from and having radial clearance with respect to the disc, and a plurality of pairs of crossed wires extending around said pin and from said pin to said blade, said crossed wires intersecting approximately along a line extending substantially parallel to the axis of the disc and between the disc and blade thereby providing along said line a hinge joint between said pin and blade about which the blade may pivot.

7. In a blade mounting, a disc, a row of blades extending radially outward from the periphery of and having radial clearance with respect to the disc, and a plurality of pairs of crossed wires extending inwardly from each of said blades to said disc and being fixed in said blade and disc, said pairs of crossed wires being closely spaced apart in an axial direction and being arranged substantially parallel to each other said crossed wires crossing each other along a substantially axial line between blade and disc thereby providing along said line a hinge joint for each of said blades about which each of said blades may pivot.

8. In a blade mounting, a disc having a transversely extending pin adjacent to the periphery thereof, a blade extending radially outward from and having radial clearance with respect to the disc, and a plurality of pairs of crossed wires extending from said pin to said blade, said crossed wires of each pair intersecting approximately along a line extending substantially parallel to the axis and between the blade and the disc, said pairs of wires being axially spaced apart and arranged in a row axially thereby providing, where said wires intersect, an axially extending hinge joint between said pin and blade about which the blade may pivot, said blade having a platform at its inner end for engagement with the disc to limit the pivotal movement of the blade about said hinge joint.

9. In a blade mounting, a disc having a transversely extending pin, a blade extending radially outward from the disc, and a plurality of axially spaced flexible loops extending radially inward from the blade and around said pin, said pin having parallel grooves receiving and positioning said loops and having surfaces in engagement with the disc, said grooves at least along the surfaces of the pin in engagement with the disc being deeper than the thickness of the material forming the loops, said loops being the sole support for said blade, said pin being substantially dovetail in shape, and said disc having correspondingly shaped slots receiving the pin.

References Cited in the file of this patent UNITED STATES PATENTS 1,035,364 Leblanc Aug. 13, 1912 1,802,648 Heath Apr. 28, 1931 2,404,678 Wuensch July 23, 1946 2,405,283 Birmann Aug. 6, 1946 2,625,366 Williams Ian. 13, 1953 2,630,868 Ellenberger Mar. 10, 1953 FOREIGN PATENTS 606,151 Great Britain Aug. 6, 1948 621,315 Great Britain Apr. 7, 1949 758,097 Germany Feb. 22, 195.4 872,416 Germany Apr. 27, 1953