US2730794A - Method and apparatus for finishing turbine blades - Google Patents

Description

Jan. 17, 1956 c, SCHQRNER 2,730,794

METHOD AND APPARATUS FOR FINISHING TURBINE BLADES Filed July 17, 1.951

Fig. 1.

INVENTOIZ,

CHRISTIAN Scnb'wea BY WKWMM ATTORNEYS United States Patent METHOD AND APPARATUS FOR FINISHING TURBINE BLADES Christian Schorner, Augsburg, Germany, assignor to Maschinenfabrilr Augsbnrg-Niirnberg A. G., Augsburg, Germany, a corporation of Germany Application July 17, 1951, Serial No. 237,228

Claims priority, application Germany lanuary 20, 1951 13 (Zlairns. (Cl. 29-156.8)

This invention relates to a method and apparatus for aligning and machining sets of ceramic blades for turbine rotors.

The tight fit of the ceramic blades in the annular groove of the steel rotor is an important requirement for a reliable fixing of the blades which are exposed to very exacting conditions of operation. Special measures are required to take care of the different specific thermal expansions of the assembled constructional materials. In view of the variations occurring in constructional elements of ceramic material owing to the shrinking in the firing operation, depending on their structure, composition, shape etc., it is difricult to ensure the requisite uniformity among the blades of a set of blades with reasonable expenditure, especially in case of series production.

Therefore, it is preferred to machine the seating surfaces of the blades by grinding them in an assembled condition of the complete set of blades. In assembling the blades, all possible causes of injuries of the brittle constructional elements of ceramic material must be strictly precluded, the more so as such injuries while oftentimes being difiicult to ascertain, even with the test methods used for testing steel, would tend to cause troubles in operation.

It is an object of the present invention to provide methods and means for assembling the blades into a selfcontained unit for machining the seating surfaces and the tips of the blades, in such a way that mechanical injuries of the blades are strictly avoided.

With this and further objects in view, according to the present invention the blades are aligned in a dummy having an annular groove corresponding to the annular groove of the rotor, and the blade grid region is filled up, within a sectional cage centered on the dummy, with a compound mass melting at moderate temperatures. After the aligning of the blades in the dummy groove and the fitting in of the filling mass into the blade grid the existing gaps, irregularities, cavities etc. on the seating surfaces of the blades are equalized by filling in a thinly liquid, self-hardening deposit mass, e. g. a ceramic mass or cement. On removal of the dummy the cage with the blade rim embedded therein is used as a centered holder for machining the root of the blades. Finally, on removal of the cage and fitting of the blade rim in the turbine rotor the compound mass serves to hold and support the blades when grinding their tips.

It has been found that ceramic blades aligned and machined in this way ensure faultless running characteristics of the turbine rotor.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and appear in the appended claims forming part of the application.

In the accompanying drawings a now preferred embodiment of the invenion is shown by way of illustration and not by way of limitation.

, Fig. 1 is an axial section through a device for carrying out the invention, including the dummy rotor with the blades inserted in the groove thereof, and the casting cage,

Fig. 2 is a similar section, but showing only the casting cage with the blades embedded therein, with the dummy rotor removed, and

Fig. 3 is a section through he turbine rotor with the blade rim inserted therein.

Similar reference numerals denote similar parts in the different views.

Referring now to the drawing in greater detail, and first to Fig, 1, it will be seen that the root portions 11 of the fired ceramic blades 1 are inserted in a bi-partite dummy rotor 2a, 2b with the blade portions 12 thereof protruding radially outwardly. The contours of the annular groove of the dummy 2a, 2b especially as regards the seating surfaces of the roots ll of the blades correspond exactly to the corresponding contours of the actual turbine rotor 3, see Fig. 3. The projecting operating portions 12 of the blades 1 are encased in a bipartite cage 4a, 4b concentrically engaging the dummy 2a, 2b which is mounted on a table 5, by means of a roller bearing 6, so as to be easily rotatable by means of shaft it The two halves 2a, 2b of the dummy rotor are releasably held together as by bolts 13, while the two halves of the cage 4a, 4b are releasably interconnected as by bolts 14.

In order that the blades 1 may be inserted in a position ensuring optimum stressing conditions in operation, i. e., in such a way that the centers of gravity of the successive cross sections of each blade if possible come to lie along a common radial line, the dummy is rotated at a. pcripheral speed which is rated so that the blades are able to set themselves into the correct position, thereby effecting alignment of said blades under centrifugal force. This is important because in spite of the use of negative supports, deformations of the thin portions of the blade may occur in firing the blades and it is desirable to reduce as much as possible the deleterious effect upon the stresses in operation caused thereby.

in blade welding devices for grid rings of steel, special measures for ensuring an accurate pitch are usually ap plied. Such measures, however, in most instances require very accurate dimensions of the profile of the blades and, therefore, it is preferred in connection with the method according to the present invention to apply such measures only to achieve a uniform distribution of the blades on the circumference of the set of blades but not in regard to the alignment of the blades, since in case of ceramic material deviations must be expected even in case of an absolutely uniform treatment in the producion. It is also important to apply only thin and uni form additional layers on the seating surfaces of the root part for the purpose of corrections; therefore, it is not advisable to adjust the blades according to the position of their operative portions. it depends on the shape of the grid or of the root of the blade or of the additional elements for positive engagement of the root independently of the temperature, which point of the blade will be relied upon for said one-time positioning of the blade pitch or spacing. However, this is of an inferior importance for the present invention. In order to facilitate adjustment of the blades according to the radial direction it is preferred to support the seating surfaces of the root portions on slightly projecting points which are provided for each blade on a line passing through the root cross section, on the two halves of the dummy. On the right hand side of Fig. l the points 9 for supporting the roots of the blades are indicated in the seating surfaces of the dummy halves 2a, 2b. Once the blades 1 are thus aligned in the annular groove of the dummy, the grid region is filled up with a compound 7 adapted in the upper half 4a of the bipartite cage.

, 3 to be removed later by melting at a moderate temperature. The properties of this compound should be such that it absolutely preserves its shape at normal working temperatures and also duringthe machining ofthe set of blades. This is supported bythe metal cage 41:, lb

which also serves as a holder for the machining since it is coaxial with the dummy. The meltable compound 7 is introduced among and around the blade vanes 12 by pouring through a plurality of openings 15 provided Such pouring may conveniently be facilitated by providing a circular dam or weir 16.

On solidification of the compound either the dummy is removed for applying a'suitable metal layer onthe sea ing surfaces of the roots of the blades, which metal layer is then machined according to the desired contour of the annular groove of the rotor, or the dummy'is directly used as an accurate mould for application of a cast-on material of a ceramic or cement-like nature. This mass may be composed in such a way that it will harden at room temperature without burning, compensating all existing irregularities. It is also possible that in special instances for obtaining the required mechanical strength of the cast-on material a kind of glazing firing or glaze baking has to be inserted. To this end of course, the grid compound mass has to be removed by melting and recast into the device afterwards for the further machining. Moreover, it is also possible to apply a metal coating additionally on this compensating layer. Where it is intended to grind the seating surfaces thus produced, the contours of the dummy may have slightly excessive dimensions. The cast-on mass should be adapted to be cast in a liquid state and set by itself. An unexceptional slip consistency is desirable in order that all gaps in the seating groove are also filled up by the centrifuging action in the casting operation. It will be understood that care has to be taken to specially prepare the dummy surfaces which have to be detached from the compound after the machining. Scaling of the thin deposit layer on incorporation of the set of blades in the turbine rotor has to be strictly prevented, since in operation at high temperatures the positive engagement of the surfaces while being maintained in the meridian plane by the special contours of the annular groove, is not preserved in the peripheral direction where on the contrary gaps will occur between the adjacent roots of the rim of blades. Therefore, careful insulation of the contact surfaces between adjacent blade roots is advisable so as to prevent their growing together with the compound mass.

When the machining of the seating surfaces of the blades is finished, the set of blades together with the compound mass in the grid range is fitted in the turbine rotor. The supporting members 8, Fig. 3, are likewise fitted on the inner side of the root of the blades so as to secure the blades tightly in their normal position in the rotor for further machining of the blades. Now, the tips of the blades are ground to their accurate outside diameter, on removal of the cage 4a, 4b. Since the blades are fixedly embedded in the compound, this grinding process will take place without shocks and impacts, so that the danger of breakage during the grinding of the outside diameter of the blade tips is eliminated.

Finally the compound is melted out at a relatively low temperature and the rotor with the rim of ceramic blades on balancing is ready to be fitted in the turbine. The method according to the invention permits a quick and accurate machining of the ceramic blades, avoiding waste as a result of their high sensibility to impacts and shocks.

While the invention has been described in detail with respect to a now preferred example and embodiment of the invention it will be understood by those skilled in the art after understanding the invention that various 4 intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. in a method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades adapted to be carried around the rim of a turbine rotor, the steps which comprise fitting a portion of each said blade into a rotor dummy, spinning said rotor dummy and said blades effecting automatic alignment of said blades under the action of centrifugal forces thereon, fastening together portions of said blades outside said dummy into a rigid blade unit while maintaining said alignment'of said blades in said rotor dummy, shaping said blades into said close tolerance while all said blades are fastened together in aligned position in said unit, and thereafter mounting said blades in a rotor.

2. In a method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades adapted to be carried in an annular groove around the rim of a turbine rotor, the steps which comprise fitting a portion of each said blade into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades eifecting alignment of said blades under the action of centrifugal forces thereon, filling hollow spaces between said aligned blades with a hardenable plastic binding material, effecting hardening of said material forming said aligned blades into a rigid .blade unit, finally shaping said blades uniformly to said close-tolerance while said blades are bound together as said unit, removing said rotor dummy from said blades, and thereafter removing said binding material from said blades to form said plurality of separate blades each with said uniform close tolerance finishing and fitting.

3. In a method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including rootportions adapted to be carriedin an annular groove around the rim of a turbine rotor, the steps which comprise fitting said root portions into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades effecting automatic alignmentof said blades under the action of centrifugal forces thereon, filling hollow spaces between said aligned blades with a hardenable plastic binding material forming said blades into a rigid blade unit, removing said rotor dummy from said root portions, uniformly finishing'all said root portions while in said rigid unit imparting uniformly thereto said close tolerance fitting, and thereafter removing said binding material. e

4. In the method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annulargroove around the rim of a turbine rotor, the steps'which'comprise inserting said root portions of said blades into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades elfecting alignment of said blades under the action of centrifugal forces thereon, filling hollow spaces between said aligned blades with a hardenable plastic binding material forming said blades into a rigid blade unit, introducing into said V groove in said rotor dummy a fluid ceramic coating material for imparting to all said foot portions said uniform close tolerance fit corresponding to said groove in said rotor dummy, removing said rotor dummy from said root portions, and thereafter removing said binding material.

5. In the method of. imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove aroundthe rim of a turbine rotor, the steps which comprise inserting said root portions of said blades into a rotor dummy'having an annular groove substantiallyequivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades effecting automatic alignment of said blades under the action of centrifugal forces thereon, filling hollow spaces between said aligned blades with a hardenable plastic binding material forming said blades into a rigid blade unit, removing said rotor dummy from said root portions, machining root portions of all said blades in said unit to impart uniformly thereto said close tolerance fitting, and thereafter removing said binding material.

6. In the method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove around the rim of a turbine rotor, the steps which comprise inserting said root portions of said blades into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades effecting alignment of said blades under the action of centrifugal forces thereon, filling hollow spaces between said aligned blades with a hardenable plastic binding material forming said blades into a rigid blade unit, removing said rotor dummy from said root portions, depositing on said root portions a machineable coating layer, machining root portions of all said blades in said unit to impart uniformly thereto said close tolerance, and thereafter removing said binding material.

7. In a method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove around the rim of a turbine rotor, the steps which comprise inserting said root portions of said blades into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades effecting automatic alignment of said blades under the action of centrifugal forces thereon, enclosing radially outer portions of said blades in a casing while maintaining said alignment of said blades in said rotor dummy, filling hollow spaces between said blades in said casing with a hardenable plastic binding material forming said blades into a rigid blade unit, removing said rotor dummy from said root portions, uniformly finishing all said root portions while in said rigid unit imparting thereto said close tolerance, removing said casing, uniformly finishing radially outer portions of all said blades while in said rigid unit imparting uniformly thereto said close tolerance, and thereafter removing said binding material.

8. In a method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove around the rim of a turbine rotor, the steps which comprise inserting said root portions of said blades into a rotor dummy having an annular groove substantially equivalent to said groove in said turbine rotor, spinning said rotor dummy and said blades effecting automatic alignment of said blades under the action of centrifugal forces thereon, enclosing radially outer portions of said blades in a casing while maintaining said alignment of said blades in said rotor dummy, filling hollow spaces between said blades in said casing with a meltable plastic binding material forming said aligned blades into a rigid blade unit, removing said rotor dummy from said blades, machining root portions of all said blades in said unit to impart uniformly thereto said close tolerance fitting, removing said casing, machining radially outer portions of all said blades in said unit to impart uniformly thereto said close tolerance fitting, and thereafter melting away said binding material.

9. The method of imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades adapted to be carried around the rim of a turbine rotor with root portions of said blades inserted in an annular groove in said turbine rotor, which comprises the steps of inserting root portions of said blades into a rotor dummy having an annular groove substantially dimensionally equivalent to said annular groove in said turbine rotor, spinning said rotor dummy and said blades at a predetermined speed effecting alignment of said blades under the action of centrifugal forces thereon, enclosing radially outer portions of said blades in a casing while maintaining said alignment of said blades in said rotor dummy, filling hollow spaces between said blades in said casing with a hardenable plastic binding material, effecting hardening of said material for firm clamping of said blades in said aligned position, removing said rotor dummy from said blades while maintaining blades aligned in said casing, depositing a mechineable coating on said root portions of said blades while aligned, machining root portions of all said blades to said uniform close tolerance fit while all said blades are bound as a unit in said casing, mounting said blades in a turbine rotor, removing said casing, machining radially outer ends of said blades to said uniform close tolerance fit, and melting away said binding material while maintaining said alignment and close tolerance finishing and fitting characteristics imparted to said blades.

10. In apparatus for imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades adapted to be carried in an annular groove around the rim of a turbine rotor, the combination which comprises a rotor dummy, rim portions on said dummy defining an annular groove substantially equivalent to said annular groove in said turbine rotor, means for receiving and retaining said turbine blades in said rotor dummy annular groove, means for spinning said rotor dummy effecting automatic alignment under centrifugal force of turbine blades inserted into said groove, and means for releasing all said blades from said groove while maintaining said aligned condition of said blades,

11. In apparatus for imparting uniform. close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove around the rim of a turbine rotor, the combination which comprises a rotor dummy, rim portions on said dummy defining an annular groove substantially equivalent to said annular groove in said turbine rotor, means for receiving and retaining said root portions of said blades in said rotor dummy annular groove, means for spinning said rotor dummy effecting alignment of said blades inserted into said groove, means for fastening radially outer portions of said aligned blades to form a rigid blade unit, and means for releasing all said blades from said dummy while maintaining said aligned condition of said blades in said rigid unit.

12. In apparatus for imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades including root portions adapted to be carried in an annular groove around the rim of a turbine rotor, the combination which comprises a rotor dummy, rim portions on said dummy defining an annular groove substantially equivalent to said annular groove in said turbine rotor, means for receiving and retaining said root portions of said blades in said rotor dummy annular groove, means for spinning said rotor dummy effecting alignment of said blades inserted into said groove, a casing for en closing radially outward portions of said aligned blades in said dummy, means in said casing for receiving a hardenable plastic binding material between said blades forming said aligned blades into a rigid blade unit, means for releasing all said blades from said groove in said dummy while maintaining said alignment of said blades in said rigid unit, and means for releasing said casing from said rigid blade unit while maintaining said alignment of said blades.

13. In apparatus for imparting uniform close tolerance finishing and fitting to a plurality of nonuniform turbine blades adapted to be carried in an annular groove around the rim of a turbine rotor, the combination which comprises a pair of substantially circular dummy rotor eleifi'efits, meansfor releasably aflixing Said eleinnts t0- g'ether in substantially coaxial'alignment, rim ortions 'oneaCh of-sa'id dummy elements mutually defining an 'ilinig Said 'd'fim'my rotor andsaid-blades effecting alignment of'sa'id blades 'u'nder centrifugal force, and means separate from said d'uminy rotor for retaining said blades in said aligned condition upon separation of said d'ufnmy elementsfrom said blades.

-Referenc'es Cited in the file of this patent UNITED STATES PATENTS 585,696 Player July 6, 1897 Steenstrup Oct. 9, 1923 SteejnStr'uP Aug. 25, 19-25 McCall Jan. 26, 1926 Hodgkinson June 5, 1928 Wahlstn Jline 27, 1933 Lysholm June 27, 1933 Smith 1 Nov. 17, 1936 Rubissow -J-uly 16, 1940 Dodge Oct. 30, Rockwell Mar. 30, 1948, Cronstedt Aug. 16, 1949 Eastman July 3, 1951 FOREIGN PATENTS France Oct. 30, 1939

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