GAS TURBINE BLADE RETENTION

Abstract: Gas turbine blades (14) are slid axially into disc (12) with a retention tang (22) on each blade abutting the disc. An axially extending space (18) between blade platforms (26) and the disc receives elongated strip (30). With prebent end (34) resiliently held against the disc the opposite end (36) is bent radially outward against the roots of adjacent blades. A bow (38) biases the blades outwardly, deterring vibration.

Description: Gas Turbine Blade Retention Technical Field The invention relates to retention of gas turbine blades on a disc, and in particular to a clip which retains, dampens and seals the arrangement. Background of the Invention It is conventional to secure gas turbine blades to the disc of a gas turbine with dove tail fir tree grooves in the disc. A fir tree root on the blade engages these grooves. Precise location of the blade in the radially outward direction is established by precise locations on the two fir trees. Therefore it is designed to bear against the support surface with the blade in its radially outermost position. Inboard clearances are of course required to permit insertion of the blade. In such an arrangement some means are required to axially retain the blade at its desired position. At high rpm's centrifugal force will establish the blade in its outer position. However it is required that the blade have substantially the same position at balancing speed (1000 rpm) and also at tip grinding speed (100 rpm). Sealing is required to deter gas passage from the gas path upstream of the blade, between blade plat orms, to the space under the blade at the downstream side thereof. Damping of the blades is also a benefit to reduce vibratory stresses of blades during operation. Summary of the Invention The gas turbine blade retention arrangement comprises a gas turbine disc with dove tail recesses around the periphery of the disc, leaving dead load material between the recesses. A plurality of gas turbine blades each having a root conforming to the SUBSTITUTE SHEET dove tail recesses is located in one of each of the recesses. A retention tang on one side of the blade abuts a first side of the rim. A circumferentially extending platform is located on each of the blades. An axially extending space is located between the disc and the adjacent platforms. An elongated retention strip is located in this space with the end at the first side bent radially outward in contact with the adjacent gas turbine blades, this bending occurring after the retention strip is installed. The other end of the retention strip is bent radially inward prior to installation and remains in resilient contact with the dead load material of the disc. Accordingly the resilient end exerts a force against the disc so that the bent tab at the other end retains the gas turbine blades. The retention strip is also bowed in the radial direction so that it is resiliently biased against the blades, continuously urging them radially outward. Brief Description of the Drawings Figure 1 is a view of the disc, the gas turbine blades and the blade platform looking radially inward from outside the gas turbine stage; Figure 2 is a view circumferentially taken through section 2-2 of Figure 1 ; Figure 3 is an axial view of Figure 2 looking upstream; Figure 4 is an axial view of Figure 2 looking downstream; Figure 5 is a side view of the retention strip before insertion; and Figure 6 is a top view of the retention strip before insertion. Description of the Preferred Embodiment Referring to Figure 1 the gas turbine blade retention arrangement 10 includes a gas turbine disc 12 and a plurality of gas turbine blades 14 located in gas flow 15. Referring also to Figures 2, 3 and 4 it can be seen that there are a plurality of dove tail recesses 16 located around the periphery of the disc. These leave dead load material 18 between the recesses. Each gas turbine blade has a root 20 conforming to the dove tail recesses 16. Each root conforms to and is located in one of the recesses. A retention tang 22 is located on one side of each blade abutting the first side 24 of the SUBSTITUTE SHEET disc. The blades are inserted by sliding them into the recesses from this side until tang 22 stops movement of the blade. Circumferentially extending platforms 26 are located on each blade. Axially extending space 28 is located between the disc and adjacent blade platforms. An elongated retention strip 30 is located in this space. It is inserted by sliding it in from the second side 32 of the rim. The resilient tab 34 is formed on the retention strip prior to installation of the strip. The strip is inserted until resilient contact is made with surface 32. Additional force is then applied to further increase resilient contact. While holding the strip in this location, tab 36 at the first end is bent upwardly or outwardly in contact with adjacent turbine blades. When the force is released resilient contact between resilient tab 34 in the face continues thereby maintaining a constant force on the gas turbine blades operating against the force applied on tab 22. Only the extreme end 35 of tab 34 is in contact with the disc. Figure 5 and 6 show the retention strip 30 in its formed condition prior to installation. End 34 which will be in resilient contact with the disc has already been bent. It is also noted that there is a bow 38 in the strip. Referring to Figure 2 this creates a force resiliently biasing the blades radially outward at location 40. This urges the blades outwardly maintaining them in position during tip grinding of the blades at 100 rpm approximately, and during balancing of the gas turbine section at about 1000 rpm. This force against the blades combined with the resilient retention of the strip also dampens vibration as a blade to blade damper. The retention strip also tends to restrict flow through gap 42 where flow shown by arrow 44 in Figure 2 would otherwise pass form zone 46 in the gas passage upstream of the blade, through the gaps 42 to area 48 which is the space under the blade and downstream thereof. Figure 6 is a top view of the retention strip 30 also showing the tab 36 in its unbent condition. The invention retains the turbine blades in the turbine disc and also provides a seal where the blade is secured to the disc. It acts as a blade to blade damper, and also generates a radial load to aid in balancing and tip grinding. SUBSTITUTE SHEET

Claims: In the Claims 1. A gas turbine blade retention arrangement comprising: a gas turbine disc 12; dove tail recesses 16 around the periphery of said disc leaving dead load material 18 between said recesses; a plurality of gas turbine blades 14, each having a root 20 conforming to and located within one of said recesses 16; a retention tang 22 on one side of each blade abutting said first side 24 of said disc 12; circumferentially extending blade platforms 26 on each of said blades; an axially extending space between 28 said disc and adjacent said blade platforms; an elongated retention strip 30 located in said space with the end 26 at the first side of said rim bent radially outward in contact with two adjacent gas turbine blades; and the other end 34 of said retention strip bent radially inward and resilient contact with said dead load material 18 of disc. 2. An arrangement as claim 1 further comprising: said retention strip being resiliently biased 38 radially between said disc and said blade platforms. 3. An arrangement as in claim 1 comprising: only the extreme end 35 of said other end in contact with said disc. SUBSTITUTE SHEET 4. An arrangement as in claim 1 wherein: said tang 22 is located on the downstream side 24 of said gas turbine blades with respect to gas flow 15 through said turbine. 5. A retention arrangement as in claim 1 wherein: said root 20 is a fir tree. 6. A method of assembling a gas turbine engine blade retention arrangement comprising: axially sliding a first gas turbine blade from a first side into engagement with a turbine disc and against a stop; axially sliding a second gas turbine blade from said first side into engagement with said turbine disc against a stop; axially inserting from a second side of said gas turbine disc a retention strip between said disc and both said first and second blades, with a portion of said strip in resilient contact with said disc on said second side; applying a force from said second side of said strip and further increasing the resilient contact; bending an end strip into contact with said first and second gas turbine blades on said first side while maintaining said applied force; and releasing said applied force leaving said strip and resilient contact with said disc. SUBSTITUTE SHEET

Inventors: MODAFFERI MARIO, MODAFFERI, MARIO
Applicants: PRATT & WHITNEY CANADA, PRATT & WHITNEY CANADA INC.
Application year: 1995
Main classification: F01D5
IPC codes: F01D5, F01D11