Blade Lock Screw

1. Technical Field

This invention relates to compressor rotors for gas turbine engines and particularly to the means for securing the compressor blades to the drum of the drum rotor or rotor disk.

2. Background Art

The locking means for securing the blades to the drum rotor of the compressor of gas turbine engines has over time seized and as experienced it was virtually impossible to remove without having it drilled out. This had the propensity to cause damage to the drum rotor or rotor disk should there be an inadvertent slip of the drill bit or if the screw put up an inordinate amount of resistance to being removed.

An example of a blade locking assembly is disclosed in U.S. Pat. No. 3,721,506 granted to B. J. Anderson on Mar. 20, 1973 and entitled "Split-Nut Blade Lock Assembly". This patent discloses a blade lock which includes a split nut that threadably engages a set screw. In spite of the fact that the nut was split, it also had a tendency to seize over time and require extraordinary means for its removal.

U.S. Pat. No. 3,930,751 granted to W. A. Straslicka et al on Jan. 6, 1976 and entitled "Bucket Locking Mechanism" is another example of a blade locking device. This assembly includes locking means for a rotor that includes a plurality of blades supported to a rotor disk by fitting the blades in fir tree slots formed in the disk and utilizing a pin-set screw assembly to hold the blade in place.

There are a number of patents that show screws that are fabricated with axial slots extending the length of the threaded portion of the screw. U.S. Pat. No. 4,712,957 granted to W. Edwards et al on Dec. 15, 1987 and entitled "Adhesively Secured Fastener" exemplifies these types of devices. Typically, the side slots serve to allow the passage of adhesive to lock the crew in place or chips or metal slivers that are removed when screwing the screw in place.

This invention contemplates the combination of the slotted screw and a blade lock member that has proven to be capable of being removed without having to go through the extraordinary removal process heretofore required.

An object of this invention is to provided an improved blade lock for the blades of a drum rotor used in a gas turbine engine.

A feature of this invention is the slotted screw adapted to fit into a locking member to engage the bottom surface of the recess in the drum of the drum rotor to urge the locking member upwardly to bear against the surface of shoulders formed in the dovetail groove of the drum rotor or rotor disk to hold the blades in place where the slot is accessible at the top surface of the screw to allow admittance of lubricant to penetrate the threads for ease of removal.

The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings.

FIG. 1 is a developed partial view showing the top view of the assembled drum rotor of a gas turbine engine,

FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1,

FIG. 3 is a side elevation view of the slotted screw of this invention,

FIG. 4 is a top view of the screw shown in FIG. 1 illustrating one type of tool receiving slot, and

FIG. 5 is a top view illustrating another tool receiving slot.

While this invention is described in its preferred embodiment of being used in a drum rotor for a gas turbine engine it will be appreciated by one skilled in this art that the invention has utility in other applications. The invention can best be understood by referring to FIGS. 1 and 2 which show a portion of a drum rotor as is typically used in a gas turbine engine generally indicated by reference numeral 10 supporting a row of axially flow compressor blades 12. As is typical in these types of installations the root section 14 of blades 12 are fitted into the circumferential dovetail slot 16 formed in the outer periphery of the drum 18. Once slid into position in the dovetail groove or slot 16, the blades are secured by snap rings 17 and 19 formed in circumferential slots 21 and 23, respectively. The blades then must be locked into place by means that are capable of withstanding the circumferential component of the aerodynamic loads developed during engine operation. The locking means must be capable of permitting the assembly and disassembly of blades with relative ease. As mentioned in the above experience has shown that heretofore locking means have seized over time requiring extraordinary measures for their removal with a consequential damage to the surrounding hardware.

According to this invention two locking means generally illustrated by reference numeral 20 serve to prevent circumferential movement of the blades 12 and secure them in place. The locking means includes a wedge member 22 and a set screw 24. Wedge member 22 is generally cylindrical in shape and includes a central threaded bore 26, a smaller diameter neck section 28 and a wider diameter locking section 30. The set screw 24 includes a platen 32, a smaller diameter neck section 34, and a threaded body 36. Installed, the locking means is fitted into the dovetail groove or slot 16 and the upper end of the neck section protrudes through drilled aperture 40 formed in the blade's platform 42. Set screw 24 includes a tool receiving recess 44 formed on the top surface remote from the platen 32 that can be made to accommodate existing Allen wrenches or can be splined (as shown as recess 40' in FIG. 5) if additional removing torque is required. To assemble the locking mechanism the locking member or wedge member is installed in the dovetail groove 16 and the set screw is installed to threadably engage the threads in the central bore 26. With the use of the tool, the set screw is torqued down so that the platen 32 bears against the surface 46 of the dovetail groove 16 and forces the wider diameter locking section 30 of wedge member 22 to engage the shoulder 48 formed in the drum 18. This serves to prevent the blades 12 from moving while being capable of withstanding the aerodynamic loads encountered during operation.

As noted and according to this invention the set screw 24 includes three equally spaced axial grooves 50 extending from the top surface to the neck 34. This serves to allow for the ease of removal during teardown after considerable operation time of the engine without the necessity of relying on extraordinary means for removal as has been experienced in the past. The axial slots 50 not only help in reducing torquing loads but also enhances thread cleaning capability and allows the penetration of lubrication fluids during teardown.

Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.