Shuttle for a Tumbling Operation

1. Technical Field

A shuttle is constructed to support an irregularly shaped object such as a compressor blade or vane during a tumbling operation with a masking device protecting a selected area of the object from a tumbling action without direct contact with the object.

2. Background Art

Many mechanical parts for example compressor blades and vanes for gas turbines are given a desirable surface finish by a tumbling action in which the parts are placed in a tumbling barrel with a tumbling media which may or may not be abrasive and the barrel is then rotated to obtain the desired action from the pieces being tumbled. Different barrel configurations and different tumbling media control the aggressiveness of the tumbling action in order to produce the desired surface edge geometry.

It is well known that tumbling operations are most effective on corners and edges of the part being treated and when the part is irregular in shape, one part may be more vigorously acted upon by the tumbling medium. This is particularly true with compressor blades or vanes where the leading edge and trailing edge may be dissimilar. For best results two tumbling operations are desirable, one to produce the desired surface finish at and adjacent the trailing edge and another to produce the desired surface finish at and adjacent the leading edge. These separate tumbling operations use either different timings or different media for the desired result. When treating one edge of a part such as a compressor blade, the other edge must be protected from the tumbling action. Masking one edge has been attempted but it has been generally unsatisfactory because the tumbling action is effective in removing the masking material thus exposing the masked edge. If the masking material stays in place there is a sharp line of demarcation at the edge of the masked area and this is generally undesirable.

A feature of the invention is a shuttle arrangement for the parts to be treated with protection for a selected area that is not in contact with the area. Another feature is a protective or masking device that will not leave a line of demarcation on the finished part. Another feature is a protective device that may be used repeatedly on successive parts with full effectiveness.

According to the invention the part to be tumbled which may be a compressor blade or vane for example is mounted in a shuttle that engages the root or end shroud on the blade or vane and has a projecting spar thereon that extends in parallel relation to the edge of the part to be protected but out of contact therewith so as to leave no demarcation line on the part. The clearance between the spar and the edge of the part is such that the tumbling media does not pass readily between the spar and the part and thus causes no significant action on this area of the part. In this way the shuttle and spar may be used repeatedly on successive parts with complete effectiveness.

FIG. 1 is an elevation of a shuttle incorporating the invention.

FIG. 2 is a plan view of the device.

FIG. 3 is a perspective view of the device.

Referring to FIG. 1 the compressor blade 2 to be treated has a root 4 thereon that is positioned in a shuttle 6. This shuttle has a hollow rectangular base 8 to receive the blade root and the root is held securely in one corner of the hollow part of the shuttle base as by set screws 10 and 12 in adjacent sides of the base. These set screws when tightened have their slot receiving outer ends flush with or below the shuttle surface to prevent tumbling action on these screws that would affect the ability to remove the screws.

Projecting upwardly from the base of the shuttle is a spar 14 which may be generally of triangular cross section and positioned so as to extend in parallel spaced relation to the edge of the airfoil portion of the blade, that is to say that portion of the blade that is to be protected against the tumbling action. The spacing is relatively close and gaps up to 1/100 of an inch have been used effectively. The spar extends the length of the airfoil portion as will be apparent.

It is not usual to have a rectangular base on the blade or vane and to make the blade or vane fit within the shuttle with the edge of the vane in proper relation to the spar the root of the blade 4 represented by the dotted lines in FIG. 2 may thus have a false root 15 cast around the blade root to provide the desired shape to fit with and be clamped in the base of the shuttle. The same would be accomplished with a vane which instead of a root may have a shroud at either end around one of which a false shroud or root portion could be cast.

In a tumbling action on several blade shapes it is desirable to give a different tumbling action on the trailing edge than on the leading edge. In this event one shuttle would be used as shown in which the leading edge is positioned in closely spaced relation to the spar for one tumbling action. The blade would then be remounted in the same shuttle or in a similar shuttle with the trailing edge closely spaced from the spar for second tumbling action on the leading edge. With differently shaped leading and trailing edges it is frequently desirable to use a different cycle and/or a different tumbling medium on the two edges and this arrangement makes possible the different tumbling operations.

Although the surface of the spar adjacent to the blade edge is shown as flat and having a significant width close to the edge of the blade, this flat surface is not critical so long as the shape is such as to prevent action of the tumbling medium on the protected edge of the blade.

In operation, the properly shaped shuttle has the part mounted therein. As shown the part is a compressor blade which is clamped in position in the shuttle base and with the appropriate edge of the blade in closely spaced relation to the spar. That is to say, the edge of the blade to be protected from the tumbling operation is positioned close to the spar. The shuttle and the part are then placed as a unit in the tumbling barrel with the appropriate tumbling medium and tumbled in the appropriate tumbling cycle. Because of the spar the tumbling medium performs the desired operation on the unprotected edge of the blade but is ineffective on the protected edge adjacent to the spar because the medium is prevented from operative contact with this edge.

After one edge of the blade is suitably treated the blade is removed from the shuttle and replaced in the same or a different shuttle with the treated edge close to the spar and the untreated edge unprotected so that it may have the appropriate tumbling operation performed thereon. This is particularly desirable where the two blade or vane edges are of a different shape and require somewhat different tumbling treatments either by the use of different tumbling materials, either grain size or consistency for example, or a longer or shorter or slower tumbling action.

A particular advantage is that there is no need for masking operation of any type with the attendant problems and no direct contact between any portion of the blade being tumbled and the protecting spar so that no line of demarcation will appear on the article after the tumbling operation is completed.

Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that other various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.