US2946104A - Method of making cores for casting bladed members - Google Patents

Description

July 26, 1960 a. MARTIN METHOD OF MAKING CORES FOR CASTING BLADED MEMBERS 2 Sheets-Shet' 1 Filed June 3. 1957 INVENTOR. moms a. MART/IV /WZ W ATTORNEYS y 1960 T. B. MARTIN 2,946,104

' mzmob OF MAKING CORES FOR CASTING BLADED MEMBERS Filed June 3, 1957 2 Sheets-Sheet 2 .Izg. 6. 79 z/ X T 7 alaz THOMAS E. MART/IV hww fiwwd ATTORNEYS Unite States Patent METHOD OF MAKING CORES FOR CASTING BLADED MEMBERS This invention relates to a new and improved method and apparatus for casting bladed members and the like and more particularly relates to method and apparatus for making bladed wheels and bladed annuli by casting walls around a blade-holding plaster core.

The present invention is concerned with a method of casting members to which blades are attached, as in the construction of turbines and the like wherein a plurality of blades are attached to Wheels or annuli and wherein it is desirable to fabricate the blades separately and subsequently to cast the fabricated blades into the Wheel or annulus which receives the same.

=Heretofore the problem in casting fabricated blades into a hub arose from not having a convenient method of holding the extended ends of the blades, which ends are to be embedded in the casting in a core box which defines the shape of the walls into which the blade ends are to be embedded. The problem is even more severe when the blades are to be embedded at their inner ends into an inner hub and at the opposite ends into a shroud ring. The present invention involves first casting the blades in a plaster core with one or both ends of the blade projecting from the core and then casting the walls about the core in such manner that the projecting ends are fused or bonded to the walls.

The present invention has a principal advantage in that it imposes no limitations or restrictions on the shape, number or position of the blades, and further that it imposes only relatively insignificant limitations on the shape of the hub and the ring walls in the region of the blades.

Still another feature of the invention is that the apparatus is relatively inexpensive and easy to build.

Still another feature of the invention is the low cost of manufacture of bladed members in accordance with this invention.

' Still another feature of the invention is the flexibility of the method in that complicated molds'are not reeach of the several views.

In the drawings:

Fig. 1 is a'plan view of a plurality of blades held in retaining rings;

Fig, 2 is a vertical sectional view through a casting machine showing the centrifugal casting of a plaster core;

Fig. 3 is a vertical sectional view through a portion of a mold employed to cast the device;

Fig. 3a is a vertical sectional view of a device cast in accordance with this invention and removed from the mold;

Fig. 4 is a view similar to Fig. 2 of a modification of ice the invention for casting both a hub and a shroud ring with blades interconnecting the same;

Fig. 5 is a vertical sectional view showing the next step in sequence to that of Fig. 4; j

Fig. 6 is a vertical sectional view of a core formed as the result of the operations illustrated in Figs. 4 and 5; and

Fig. 7 is a vertical sectional view simil-arto Fig. 3 showing casting of the shroud ring and hub with the core of Fig. 6 installed therein.

The present invention is employed to cast blades 11 extending substantially radially from a hubf12, the external surface 13 of which is substantially parabolic. Blades 11 are first fabricated from sheet metal or other desired material in the required shape and the innerend 14 thereof which projects into and is anchored in hub 12is elongated, the amount of elongation of inner end 14 being the portion of plate 11 which is anchored in the hub. To assist in anchoring blades 11 in the hub a plurality of anchor. holes 16 may be formed in extension 14 so that the molten metal may pass through holes 16. It will be understood, however, that anchor holes 16 may be eliminated or any other shape of anchor device substituted.

Preliminarily blades 11 are nested in a fixture (not shown) which locates them in proper position with respect to'each other. A variety of different means may be employed to hold blades 11 in place after they are removed from the fixture and before the castings are made. As illustrated in Fig. 1, a plurality of annular blade- holding rings 17, 18, 19 are employed. As illustrated, there are three rings, two of which, 17, 19, are secured to the bottom edges of blades 11 and third ring 18 being secured to the top edge. The edges of the rings are notched to grip the edges of the blades.- Rings 17, 1'8, 19 may be formed of rubber or any suitable material which is easily removed after the core has hardened. In

the modification shown in Fig. 4, a. metal ring 21 is employed which is soldered or cemented to blades 11 or 11* at about the middle of its span. The assembly of blades 11 and rings 17, 18, 19 or 21 is removed from the fixture and then placed in a rotatable core box 26 which is supported on a pedestal 27 at the upper end of rotatable shaft 28. Shaft 28 is rotated by a motor (not shown), preferably with an adjustable speed control, so that the speed of rotation may be accurately controlled and held for a long period of time at the pre-selected speed. The shape of core box 26 depends on the shape of the final article to be cast. As illustrated in Fig. 2, box 26 is formed with a cavity having a bottom step 29 of considerable depth and an outer annular step 31 of lesser depth, but such construction is merely for convenience in casting the parabolic hub 12. The surface of step 31 may be formed with one or more grooves 32, 32 which receive the bottom edges of rings 19 and 17, respectively, and thus form a support for blades 11. Core box 26 is provided with a top 33, the bottom sur-v face of which is formed with an annular groove 34 which receives ring 18. Thus when top 33 is placed on box 26 with the assembly of Fig. 1 installed therein, blades 11 are accurately spaced and positioned in the cavity of box 26. Top 33 is formed with a central aperture, the edge 36 of which is preferably bevelled to form a spill lip. The diameter of spill lip 36 is one of thelimit-ations on the shape of cavity 37 to be cast in core 38. Thereupon a liquid casting plaster is prepared. Pumice, may be added to the casting plaster to improve the smoothness of the surface.

It will also be understood, as will be apparent to one skilled in the art, that core 38 may be made in two operations, one employing a relatively large grain plaster which is made in a core slightly undersized and followed by a 3 second casting made of a fine grain plaster to complete the final shape of core 38.

After the plaster is prepared, box 26 is rotated by rotation of shaft 28 at a predetermined rpm. and while being thus rotated the plaster or other liquid cum solid core material is poured into cavity in box 26. By reason of the fact that box 26 is rotated, a central cavity 37 is created in the liquid plaster, the margin 39 of which is a paraboloid of revolution. The precise shape of margin 39 is dependent upon the speed of revolution of shaft 28 and the diameter of spill lip 36. The higher the speed, the more nearly marginal wall 39 approaches a cylinder, as distinguished from a conventional paraboloid. In any event, it is an important feature of this invention that extensions 14 of blades 11 project into cavity 37. Filling of the cavity in box 26 is continued until the plaster runs out over spill lip 36, which indicates that core 38 is full. Rotation is continued until the core sets firm, which requires upwards of 20 minutes. 'It has been found that for ordinary parabolic shapes, such as illustrated in Fig. 2, a speed of the order of 100 r.p.m. is suitable, whereas if a cylindrical or cone-shaped cavity is required, speeds of up to 1000 r.p.m. may be required.

In order to prevent chalking of the finished plaster core, it is desirable that the casting operation be conducted in a saturated atmosphere, such as a humidified room, or core box 26 may be surrounded by a casing 41 into which humidified air is forced.

After plaster core 38 has set, it is removed and placed in a drag 51 of foundry sand or other suitable molding material, as shown in Fig. 3. A cope 52, also of foundry sand, is installed on top of drag 51. The boxes in which the patterns are placed are not illustrated in Fig. 3, but their construction will be understood by one skilled in the art. If an internal core is desired in the finished product, a core 53 may be attached to the bottom of cope 52 and extending into cavity 37. Molten metal is then poured through a pouring gate 54 in cope 52 and into cavity 37 in cope 38 to form hub 12. Surface 39 thus governs the external shape of hub 12 and is parabolic in form. Blades 11 are secured to hub 12 as the metal is poured into the mold, anchor holes 16 assisting in this operation. Casting of the metal is accomplished by any of the well recognized casting methods required in any particular case.

After the metal has solidified, core 38 and rings 17, 18, 19 are removed, leaving hub 12 having projecting blades 11. The metal of hub 12 may be steel, aluminum or any conventional metal. If the metal of hub 12 has a lower melting point than blades 11, it flows through anchor holes 16 and mechanically secures the blades to the hub. If the metal of hub 12 has the same or a higher melting point than blades 11, the blades are fused or melted into the hub. For example, in certain types of turbines, titanium or molybdenum blades 11 may be required by the operating conditions of the turbine. Such blades may be fabricated from sheets and then cast into a hub 12 or hub 12 may be of aluminum, steel or any other suitable metal. Depending upon the relative melting points of blades and hubs, blades are either mechanically secured to the hub or fused therein.

In the modification of the invention illustrated in Figs. 4-7, inclusive, blades 11 are to be attached at their inner ends to hub 61 and at their outer ends to a ring 62. Accordingly, blades 11 are provided with two integral extensions 14- and 14 which are secured to hub 61 and ring 62, respectively.

Blades 11 are initially fabricated with extensions 14 and 14 which optionally are provided with anchor holes 16. Blades 11 are secured in a fixture (not shown) and ring 21 is either welded or soldered thereto, or rings 17, 13, 19 are secured thereto as illustrated in Fig. 1.

The assembly of blades 11 and ring 21 are then installed in an apparatus as illustrated in Fig. 4 wherein a core box consisting of base 63. and sides 64 are mounted on pedestal 29 at the upper end of rotatable shaft 28. The annular inner surface 66 of sides 64 determines the ultimate outer shape of ring 62. A groove 67 is formed in the top surface of bottom 63 to receive ring 21. Top 68 having a spill lip 69 is installed above side 64. Shaft 28 is then rotated at a predetermined speed and plaster poured into the central cavity until it runs up over spill lip 69. Accordingly a ring 71 of plaster is produced in which extensions 14 are embedded. The outer surface of ring 71 conforms to surface 66 of sides 64 while the inner surface 72 is a paraboloid of revolution. By reason of the speed of revolution of shaft 28, surface 72 is substantially conical or cylindrical, but nevertheless is a section of a paraboloid of revolution, as is shown by reference line 73 which illustrates the parabolic nature of surface 72. Plaster ring 71 is permitted to solidify and the assembly is then established in the relationship shown in Fig. 5. Surface '72 is first coated with a parting compound so that plaster subsequently applied, as hereinafter described, will not adhere thereto. Sides 64 are inverted from the position shown in Fig. 4 by reason of the desired ultimate shape of the final product. Top 74 differs from top 68 in having a spill lip 76 which is of lesser diameter than spill lip 69, which is installed above sides 64. Ring 21 is received in a groove 77 in the bottom surface of top 74.

After the parts have been positioned in the apparatus of Fig.5, shaft 28 is rotated and plaster is poured in while shaft 28 rotates at a speed less rapid than in the operation illustrated in Fig. 4. A plaster core 78 is produced. The inner surface 79 of core 78 is a paraboloid of revolution, the shape of which is determined by the diameter of spill lip 76 and the speed of shaft 28. The outer surface 72a matches surface 72. Extensions 14 project into the central cavity 81.

Again core 78 is allowed to harden and thereafter plaster ring 71 is broken away, which leaves the core shown in Fig. 6 wherein there is provided a central core 78 having an outer surface 72 corresponding to the surface 72 shown in Fig. 4 and having an inner surface 79 corresponding to the similar surface shown in Fig. 5. Embedded in core 78 is a plurality of blades 11 each having inwardly extending projections 14 and outwardly projecting extensions 14 which extend beyond surfaces 79 and 72, re spectively. Blades 11 are held by ring 21.

The core shown in Fig. 6 is then ready for casting, as shown in Fig. 7. Core 78 is embedded in a drag 82 on top of which is mounted a cope 83. The box confining the foundry sand for members 82 and 83 is omitted in the drawings. To gates 84 and 86 are employed in cope 83 and metal is poured through each thereof so as to produce an inner hub 61 and an outer ring 62, with inner extensions 14 and outer extensions 14 of each blade 11 embedded therein, respectively.

After the metal of hub 61 and ring 62 has solidified, core 78 is broken away and ring 21 removed, thereby producing the final product. Hub 61 has an external parabolic surface 79 corresponding to the paraboloid of revolution of similar reference numerals shown in Fig. 5. Shroud ring 62 has an inner surface 72b which is likewise a paraboloid of revolution and is determined by the shape of the surface 72 in Fig. 4. The outer surface 87 of ring 62 is determined by use of a pattern (not shown) forming a cavity in drag 82. Thus the method illustrated in Figs. 4-7 makes possible the casting of bladed annuli having conical or parabolic walls both inside and out by casting the walls around a blade-holding core of plasterlike material.

It will be understood that the parabolic wall shapes apply only in the region of the blades and that the extensions in either direction may be of any desired shape.

One of the features of the invention is that the inner wall of the poured plaster core is always a paraboloid of revolution if the core box rotation is vertical with respect to gravity. Where the shape of the hub is for a spinner nose or the like having a rounded shape, the core box speed of rotation is relatively low and short sections of such a parabola are nearly conical, for practical purposes. If a substantially cylindrical duct or hub walls are required, the core box speed is increased and for practical purposes a cylindrical wall can be obtained within reasonable limits. The axis of the core box rotation might be disposed horizontally, thereby eliminating the effect of gravity on the shape of the core and more cylindrical wall shapes might thus be obtained.

Inasmuch as plaster is not truly liquid when poured, the surface may not be entirely smooth. The imperfections can be reduced by vibrating the box as it is rotated, as well understood in the casting art, or by applying a second thin coat of a plaster mix formulated to produce an especially smooth surface as hereinbefore described. It will further be understood that in accordance with conventional foundry practice, the cores may be baked at moderate temperatures before final casting of the metal in order to drive out moisture.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is understood that certain changes and modifications may be practiced within the spirit of the invention and scope of the appended claims.

I claim:

1. A method of preparing a core for a cast bladed hub and annulus wherein a plurality of blades interconnect said hub and annulus comprising preparing a plurality of blades each having an inner extension to project into said hub and an outer extension to project into said annulus, locating said blades in predetermined position relative to each other, preparing a core box dimensioned to receive said blades, positioning said blades located in predetermined position centrally in said core box, positioning a centrally apertured first cover on said core box, the aperture of said first cover having a diameter substantially equal to the inner diameter of said annulus, revolving said core box at a predetermined first speed, pouring first casting material into said core box, partially filling said core box, discontinuing filling said core box when said casting material runs out the aperture in said first cover while continuing to revolve said core box at said first speed until said first casting material has set, applying parting compound to said first casting material, positioning a centrally apertured second cover on said core box, the aperture of said second cover having a diameter substantially equal to the outer diameter of said hub, revolving said core box at a predetermined second speed, pouring second casting material into said core box until said second compound runs out the aperture in said second cover while continuing to revolve said core box at said second speed until said second casting material has set, and breaking away said first compound.

2. A method according to claim 1 in which said first predetermined speed is adjusted to provide a first inside wall of casting material having the configuration of a first paraboloid of revolution intersecting the margin of the aperture of said first cover and passing through the boundaries between said outer extensions of said blades and the remainder of said blades.

3. A method according to claim 1 in which said second pre-determined speed is adjusted to provide a second inside wall of casting material having the configuration of a second paraboloid of revolution intersecting the margin of the aperture of said second cover and passing through the boundaries between said inner extensions of said blades and the remainder of said blades.

References Cited in the file of this patent UNITED STATES PATENTS 669,119 Krank Mar. 5, 1901 1,095,230 Rockwell May 5, 1914 1,187,446 Moore June 13, 1916 1,620,974 Klenk Mar. 15, 1927 1,621,002 Dimberg Mar. 15, 1927 2,005,408 Allan June 18, 1935 2,097,314 Wales Oct. 26, 1937 2,270,822 McCarroll et a1 Jan. 20, 1942 2,304,067 Anderson Dec. 8, 1942 2,639,886 Townhill et a1. May 26, 1953 2,690,132 Misch Sept. 28, 1954

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