Blade damper

This invention relates to the construction of a turbine rotor having a rotor disc with a plurality of blades, said blades having roots fitted into slots around the periphery of the disc with each blade engaging a stop means to properly position it, said blades being held in place by a cover plate fixed to the rotor disc and said stop means; a pocket is formed on the front face of each blade while an annular groove on said cover plate is positioned over said circumferential ring of pockets. Each pocket has an outer flat surface placed at an angle so that each surface intersects the outer surface of the annular groove; a stiff solid damper having a rectangular surface is positioned in each pocket so that one end of said surface will be supported by the outer surface of the annular groove while the other end of said surface will be supported by the outer surface of the pocket when the damper is thrown outwardly by centrifugal force.

TECHNICAL FIELD 
This invention relates to blade damping and more particularly to loosely 
mounted vibration dampers used with gas turbine blades exposed to high 
temperatures. 
BACKGROUND ART 
In the past, various means of blade damping have been used. One of the 
accepted blade damping schemes is a toggle device. A toggle is a 
non-structural member which is held in physical contact with a turbine 
blade by centrifugal force during rotation of the turbine engine. The 
toggle reduces the vibratory action of the blade by imposing a retarding 
force due to friction on the blade at the point of contact between the 
toggle the blade. Loosely mounted vibration dampers have been used and two 
such constructions are shown in U.S. Pat. No. 3,666,376 and U.S. Pat. No. 
4,182,598. 
DISCLOSURE OF INVENTION 
The primary object of this invention is to dampen the vibrations in a 
turbine blade by placing a damper shaped in the form of a rectangular 
solid between a portion of the blade and a portion of a cover plate, said 
damper being essentially square in cross-section and rectangular in 
circumferential direction; the damper is positioned in a four-sided pocket 
in a portion of the blade facing the cover plate and extends into an 
annular groove in the cover plate. Since the outer flat surface of the 
pocket is at an angle crossing the outer surface of the annular groove, 
under centrifugal force one location at one end of the damper is supported 
by the outside diameter of the annular groove in the cover plate and 
another location at the other end of the damper is supported by the outer 
surface of the pocket. 
Another object of this invention is to provide a blade damping device 
wherein the damper can be properly placed between the blade and cover 
plate which simplifies means for locating the damper and eliminating 
expensive locating features. 
A further object of this invention is to provide a mechanical damper with a 
large degree of stiffness. The damper transmits load directly into a stiff 
cover plate. The weight of the damper can be controlled by varying its 
thickness or by placing a hole along its length.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows a portion of a turbine disc 10 of a gas turbine engine with 
axially extending slots 11 on its periphery, each of which receives the 
root 12 of one of the blades 4. Fixed vanes 2 are located upstream of the 
blades 4 and fixed vanes 3 are located downstream of said blades. A 
portion of a blade tip seal member 30 is shown which is fixed to a casing 
member, not shown, for completing a housing. A similar construction is 
shown in U.S. Pat. No. 3,836,279. Each blade has a projection 44 extending 
to one side thereof from an extended neck section 15 between the root 12 
and the platform 16. To provide a stop for the projection 14 of each 
blade, a projection 18 extends outwardly from the periphery of the turbine 
disc 10 between each of the slots 11. When the projection 14 engages the 
stop 18, the blade 4 is properly positioned with respect to the disc 10 to 
receive a cover plate 20 which engages the forward face of the outer 
periphery of the disc 10 and engages the forward faces 19 of buttress 
members 22 of blades 4. A buttress member 22 extends inwardly from the 
forward edge of each platform 16 and extends for the width of the platform 
16 forming part of the extended neck section 15 where they meet. Each 
buttress member 22 abuts the adjacent buttress member 22 on adjacent 
blades 4. The cover plate 20 can be affixed to the outer periphery of the 
disc 10 by any means desired, such as by bolts 24. 
The forward face 19 of each buttress member 22 includes a pocket, or 
opening, 32 for receiving a damper member 34. Said cover plate has an 
annular groove 36 located therearound which faces the annular ring of 
pockets 32 formed by the plurality of blades 4 positioned around the disc 
10. This annular groove 36 is shown in phantom in FIG. 2. Each pocket 32 
is formed as a four-sided figure, with the inner surface 38 shown aligned 
with the inner surface 40 of the annular groove 36. While the inner 
surfaces are shown aligned, this alignment is not necessary for the 
damping action. The side surfaces of each pocket 32 are formed straight 
and approximately lying on a radial line extending outwardly from the 
center of the disc 10. The outer surface 42 of each pocket 32 is formed at 
an angle to the outer surface 44 of the annular groove 36 so as to 
intersect it. In FIG. 2, the outer surface 42 of the pocket 32 can be seen 
crossing the outer surface 44 of the annular groove 36 at A. 
The damper member 34 is formed approximately square in cross section (see 
FIGS. 1, 3 and 4) with rectangular surfaces in the circumferential 
direction (see FIG. 2). This solid damper member shape prevents it from 
being assembled incorrectly. It can be seen that the damper member 34 is 
supported at one end at point B by the outer surface 44 of the annular 
groove 36 (see FIG. 2), while the other end of the damper member 34 is 
supported at the other end at point C by the outer surface 42 of the 
pocket 32 (see FIG. 2), when the dampers are thrown outwardly by 
centrifugual force. When a blade 4 bends about its attachment, sliding can 
occur at either point B or C, providing friction damping. The weight of 
the damper 34 can be reduced, if desired, by drilling a hole 50 therein. 
For a high spring rate it is desired that the cover plate be a complete 
ring and not segmented.