US3042369A

US3042369A - Pinned blade sealing means

Info

Publication number: US3042369A
Application number: US792664A
Authority: US
Inventors: Harvey W Welsh
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1959-02-11
Filing date: 1959-02-11
Publication date: 1962-07-03
Anticipated expiration: 1979-07-03
Also published as: GB871098A

Description

July 3, 1962 H. w. WELSH 3,042,369

PINNED BLADE SEALING MEANS Filed Feb. 11, 1959 INVENTOR.

ATTORNEY United States Patent 3,042,369 PINNED BLADE SEALING MEANS Harvey W. Welsh, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Feb. 11, 1959, Ser. No. 792,664 3 Claims. (Cl. 253-77) This invention relates to a gas seal and vibration damping means.

More particularly, this invention relates to a gas seal and vibration damping means for use in combination with a rotor and blade assembly wherein each of the blades is secured to the rotor by a pin, and an annular seal member is mounted between the rotor and blades on the pins to control the circulation of gas from the downstream to the upstream side of the assembly.

Therefore, it is an object of this invention to provide a gas seal and vibration damping means in combination with a pinned rotor blade assembly to control the circulation of gas from one portion of the assembly to another, and to dampen the blade vibration.

Other features, advantages and objects will become apparent by reference to the detailed description of the invention and to the drawings wherein there is shown the preferred embodiments of this invention.

In the drawings:

FIGURE 1 is a front elevational view with parts broken away and sectioned of a portion of a rotor assembly embodying this invention,

FIGURE 2 is a cross-sectional view of the rotor assembly of FIGURE 1 on a plane indicated by the lines 2-2 of FIGURE 1, and

FIGURE 3 is a front elevational view of a detail of FIGURE 1.

Referring now to the drawings and more particularly to FIGURE 1, there is shown therein a portion of a rotor assembly of an axial flow type compressor, the rotor assembly including a rotor or disk 12 having a plurality of circumferentially spaced blades 14 secured thereto. Each of the blades includes a platform 18 integral therewith, the platform having two tangs 20 depending therefrom to define a blade stalk, the axial distance between the tangs being slightly greater than the thickness of the rim portion 22 of the rotor 12 with which they are adaped to cooperate. As seen in FIGURE 2, the tangs 29 have holes 24 axially aligned with each other and adapted to be aligned with holes 26 in the rim 22 of the rotor for the insertion therethrough of pins 28 to secure the blades to the rotor upon straddling of the rotor rim 22 by the tangs 20. Axial displacement of the pins is prevented by the abutment of head 29 and nuts or other retainers 30' against the tangs.

As shown more specifically in FIGURE 1, the blade platforms 18 have edges 40 extending circumferentially beyond the tangs 20 into close proximity to each other upon assembly to the rotor, a nominal circumferential clearance being provided therebetween. Each of the grooves 42 between the blade tangs extends radially outward a distance sufficient to provide a small clearance 44 between the periphery of the rotor rim 22 and the base 43 of the groove together with the clearance between adjacent platforms permitting a slight relative rotation between the blade and rotor on the pin 28 under the influences of the gas bending and centrifugal forces acting on the blades. Slight axial clearances or spaces 45 are also provided between the rotor rim 22 and the blade tangs.

Since a pressure rise is effected from the upstream edge 46 as seen in FIGURE 2 to the downstream edge 47 of the compressor, and since the substantially abutting blade platforms do not constitute a seal, any openings or clearances large enough to bleed air therethrough, such as the opening 48 between adjacent blade tangs and platforms and rotor rim, as well as

clearances

44 and 45, will permit a reverse circulation of the gas or air from its normal path because of the differential in pressures of the air on opposite sides of the platforms. This reverse circulation of air causes a loss of compression resulting in lower compressor efliciency. Accordingly, a gas seal constituting the subject of this invention is inserted between the rotor rim and blade tangs are shown in FIGURE 2. The seal comprises a thin (.005.010" thick, for example) annular sheet metal plate 32 having a continuous inner rim 34, an outer stepped rim 36, and a plurality of circumferentially spaced holes 38 aligned with the holes 24 and 26 in the tangs and rotor rim. The outer rim 36 has radially projecting circumferentially spaced portions 50 of a circumferential length equal to the distance between blade tangs of adjacent blades, i.e., equal to the length of the combined overhang of adjacent blade platforms. The space between projections 50 therefore provides recesses 52 of a circumferential length equal to the circumferential length of the stalk portions of each blade assembly. The seal 32 is inserted between the rotor rim 22 and the downstream tang 20 extending radially into close adjacency with the bottom of groove 42 as seen best in FIGURE 2 and the underside of the blade platforms 18 as seen best in FIGURE 1, effectively preventing the reverse flow of air from the downstream to the upstream portions of the blade assembly. A nominal radial clearance is provided between the bottom of the groove and the underside of the platforms with respect to the periphery of the seal to permit a slight relative roation between the parts, this clearance being sufficient to prevent an interference fit while, however, maintaining a good seal.

In addition to controlling the circulation of air, plate 32 also constitutes a vibration damping means. In a pinned blade connection of this kind, it frequently occurs that the blades are tuned to an exciting engine order of vibration, which can result in damage to the engine at certain predetermined speeds. The seal 32, however, in the position indicated, constitutes a dry friction damper to dampen these undesirable vibrational frequencies and therefore permit operation of the engine at speeds otherwise unobtainable, i.e., the range of objectionable vibrations is raised therefore raising the permissible safe engine speed. Since the reaction loads on the assembly tends to push the assembly upstream, the seal is inserted between the downstream tangs and the rim so that the tangs and seal are pressed against the rim permitting the seal to effectively dampen the objectionable vibrations. The seal therefore acts as a bearing surface upon relative movement of the tangs with respect to the rim, i.e., the upstream faces of the tangs and the downstream face of the rim rub against the opposite faces of the seal as they pivot about each other due: to the cenrifugal and gas bending forces acting on the blades. The tendency of the assembly to be moved upstream because of the reaction loads also maintains the clearance between the upstream tangs and the rim for the relative rotation between the rim and tangs.

While the invention is believed to be clear from an inspection of the drawings, a brief description of the assembly thereof is as follows. The seal 32 is abutted against the rotor rim 22 with the

holes

26 and 38 axially aligned. Each of the blades with its depending tangs 20 is then slipped over the seal and rim with the stalks fitting in the slots or recesses 52 and the underside of the platform edges 40 cooperating with the projections 50. Pins 28 are then inserted through the axially aligned holes and secured against axial displacement. The assembly is then complete, and the seal effectively prevents reverse circulation of air from the downstream to the upstream side and dampens the vibrations imposed on the blade assemblies.

While the invention has been described in its preferred form for use in an axial flow type compressor, it will be clear to those skilled in the art that many modifications can be made thereto without departing from the scope of the invention.

I claim:

1. A rotor assembly comprising a rotor, a plurality of blades pivotally secured to and circumferentially spaced around the outer rim of said rotor, said blades each having a tang depending from a platform, pin means pivotally mounting each of said blade tangs in overlapping relationship to the rim of said rotor, each of said platforms extending circumferentially beyond said tangs and substantially abutting adjacent platforms, the construction and arrangement of said platforms and tangs defining openings between the rotor rim and adjacent tangs and the undersides of said platforms through which fluid may pass, and a combined vibration damping and fluid seal member mounted on all said pin means against said rotor and tangs between said tangs and rotor and extending radially into substantially abutting relationship to said platforms covering said openings, said member damping blade vibrations and blocking the flow of fluid through said openings.

2. A rotor assembly comprising a rotor, a plurality of blades pivotally secured to and circumferentially spaced around the outer rim of said rotor, said blades each having a stalk depending from a platform and a blade tang depending from said stalk, pin means pivotally mounting each of said blade tangs in overlapping relationship to the rim of said rotor, each of said platforms extending circumferentially beyond said stalks and tangs and substantially abutting adjacent platforms, the mounting of said blade tangs on said rotor providing openings between said rotor rim and blade stalks through which fluid may pass, the construction and arrangement of said platforms and tangs defining other openings between the rotor rim and adjacent tangs and the undersides of said platforms through which fluid may also pass, and a combined vibration damping and fluid seal member mounted on all said pin means against said rotor and tangs between said tangs and rotor and extending radially into substantially abutting relationship to said platforms and stalks to cover all said openings, said member damping blade vibrations and blocking the flow of fluid through said openings.

3. A rotor assembly as in claim 2, wherein said member comprises a flat disc having a circumferentially slotted outer rim providing spaced radial projections of a circumferential length and radial extent suflicient to cover said other openings, the portions of said disc between said projections blocking said first-mentioned openings.

References Cited in the file of this patent FOREIGN PATENTS 202,528 Australia July 13, 1956 701,263 Great Britain Dec. 23, 1953 724,281 Great Britain Feb. 16, 1955 745,073 Great Britain Feb. 22, 1956 777,612 Great Britain June 26, 1957 1,097,487 France Feb. 16, 1955 1,136,390 France Dec. 29, 1956