Method And Apparatus For Casting Directionally Solidified Discs And The Like

Abstract

Apparatus and method for inducing radial directional solidification in parts having a relatively large dimension at right angles to the major axis such as discs and the like, in which, for example, a [010] radial and [100] tangential orientation is generated.

Description

BACKGROUND OF THE INVENTION

The U.S. Pat. No. 3,260,505 to VerSnyder describes the casting of directionally solidified parts with a particular orientation of the crystalline growth with respect to the longitudinal axis of the part. In casting large diameter parts it is desirable to control the orientation of the dendritic growth in order to control the strength characteristics. In casting large diameter parts it is desirable to control the solidification to produce the desired crystalline orientation throughout the disc in order to obtain the desired strength or other characteristics in the desired direction within the disc.

SUMMARY OF INVENTION

One feature of the invention is an arrangement by which to cast a relatively flat directionally solidified article in which the dendritic growth has the selected orientation therein. Another feature is a method by which to produce such a cast article. One feature of the invention is the production of directionally solidified cast articles having substantially a 8 100] tangential orientation.

One particular feature is a method and apparatus for producing discs adapted to be loaded in a radial direction, for example, turbine discs in which the dendritic orientation is substantially in a radial direction and in a tangential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view partially schematic of apparatus embodying the invention.

FIG. 2 is a fragmentary sectional view similar to a portion of FIG. 1 showing a modification.

FIG. 3 is a schematic view showing the dendritic orientation.

FIG. 4 is a vertical sectional view of a mold for producing a complete turbine disc including blades.

FIG. 5 is a fragmentary sectional view along line 5-5 of FIG. 4.

FIG. 6 is a view similar to FIG. 1 of another modification.

FIG. 7 is a horizontal sectional view of the modification of FIG. 6.

FIG. 8 is a vertical sectional view similar to FIG. 6 of another modification.

FIG. 9 is a fragmentary horizontal view through the mold of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the apparatus includes a chill plate 10 supporting a mold 12, the latter having a relatively large horizontal dimension, and shown as a mold for producing a disc. At one side of the mold an axial projection 14 extends downwardly to engage the chill plate, and an upwardly extending axial projection 16 provides a filling opening for the mold. The mold is shown as a split-shell mold, being in two parts 12a and 12b although a single piece shell mold may be utilized. The mold may be enclosed in part by insulation 18 around the axial extension 14 and the disc forming portion is covered from the periphery inwardly by insulation 20 that decreases in thickness toward the center of the disc. Annular heating coils 22 and 24 are positioned above and below the mold adjacent to the axial projections, and other heating coils 26 and 28 are located above and below the mold nearer to the periphery and concentric to the coils 22 and 24. A heating coil 30 surrounds the periphery of the mold, as shown.

In operation, the technique described in U.S. Pat. No. 3,260,505 to VerSnyder is followed to obtain a directionally solidified casting. The mold is positioned within a heating chamber, not shown, to raise the temperature of the entire mold above the melting point of the alloy to be poured and, when adequate heating is accomplished, the molten alloy, superheated to at least 100.degree. above the melting point is poured into the mold through a sprue 32, and coolant is supplied to the chill plate to establish a steep temperature gradient within the mold. This causes the formation of vertically oriented directionally solidified grains in the axial projection 14 and solidification proceeds upwardly.

While this is occuring heat has been supplied to the mold by the heating coils thereby maintaining the portion of the mold peripherally out from the axial projections and the metal thereon above the melting point. As solidification begins to take place into the portion of the mold directly above the axial portion 14 the grain growth continues vertically by reason of the heat loss to the chill plate and the vertical grains on the periphery of the solidifying portion begin to grow radially outward. When the solidification reaches a position represented by the dotted line 34, a radial thermal gradient is produced in the disc portion of the mold by gradually reducing the heating effect from the axis outwardly toward the periphery of the disc. Thus the power to coils 22 and 24 is reduced first then the power to coils 26 and 28, and finally to coil 30. The radial thermal gradient thus produced causes radial growth of the dendrites in the peripheral vertical columnar grains extending upwardly from the axial portion 14 and the radial competition between the several orientations of dendrites in the several grains will result in the radially oriented grains growing the fastest and producing substantially radially arranged dendrites in the entire disc. The radial thermal gradient produces the radial growth within the disc in the same way that the vertically oriented grains outgrow the other grains in the axial portion 14. This effect is described in the U.S. Pat. No. 3,260,505 to VerSnyder. Grain growth occuring in this manner produces an [010] radial orientation and [100] tangential orientation.

Much the same arrangement may be used in producing a more idealized orientation of grain structure. As shown, in FIG. 2, the axially extending portion 14' of a mold 12' which is otherwise arranged as in FIG. 1 has a seed 36 therein resting on the chill plate. This seed is made up of wedges 38 each having the desired orientation for the portion of the disc extending outwardly therefrom. In operation the same procedure is followed as above. When the molten alloy is poured into the mold, the seed wedges cause vertical dendritic growth with each of the several seed wedges providing the desired horizontal orientation for the adjacent portion of the cast disc.

The resulting orientation is shown in FIG. 3 where the seed 36 is made up of wedges, for example, as shown, the seed is made up of eight wedges each of 45.degree. and each having the orientation indicated. The result is a disc made up of interacting dendritic growths producing approximately a [010] radial and a [100] tangential orientation. Use of many more wedge elements will produce a more precisely radial grain distribution within the disc. Obviously the controlled radial thermal gradient provided by the structure of FIG. 1 permits controlled grain growth through the entire disc to its periphery.

One particular article that may prove particularly useful in a casting of this character is represented by FIGS. 4 and 5. In these figures is a mold 40 defining a disc-shaped cavity 42, and having the downwardly extending axial projection 44 corresponding to the extension 14 of FIG. 1. Projecting outwardly from the periphery of the mold 40 are blade forming projections 46 defining blade-shaped cavities 48 communicating with the disc cavity as shown in FIG. 5. Following the method above described, and using the heat controlling arrangement of FIG. 1, the disc and blades for a turbine disc may all be cast in a single piece with the preferred orientation of the grain growth in the disc and with the desired [010] radial orientation in the blades for the desired strength characteristics. In this arrangement the number of seed wedges would be selected to insure the precise radial grain growth in the blades. Thus, for example, the seed used would have possibly one wedge for each two blades, the orientation of the several wedges being carefully selected for precise radial grain growth.

Another alternative is shown in FIGS. 6 and 7 where the mold is made up of individual mold elements 50 extending radially outward from a central casting cavity 52 surrounding a vertical cylindrical chill 54. The chill 54 is surrounded by seed segments 56, one for each mold element 50 and these segments establish the direction of the grain growth in each mold. The grain growth proceeds radially outward in each mold 50 and its connecting mold passage 58, with the temperature gradient in a radial direction controlled by the central chill and the use of annular heating coils as in FIG. 1. This controlled thermal gradient which will produce directionally solidified alloy in each mold element 50 with the direction of the grains radial in each cast article, is described in U.S. Pat. No. 3,260,505 to VerSnyder above referred to. The cast articles are represented as turbine blades and would be cast from the type of high temperature alloy of which several examples are given in the VerSnyder patent.

An alternate proposed method of producing discs, with or without integral blades, is shown in FIG. 8 in which the mold 60 has an annular disc cavity 62 and surrounds a central vertical cylindrical chill 64. The periphery of the mold may have recesses 66 therein for forming the individual blades on the periphery of the disc when the cast article is intended as a bladed turbine disc. A ring 68 of individual seed segments 70, each of directionally solidified material with properly oriented grains surrounds the chill at the disc level to control the directional orientation of the grain growth in the disc. Obviously annular heat control coils similar to those in FIG. 1 are used here to produce the desired radial thermal gradient. By using the appropriate number of seed segments the precise radial grain growth desired may be obtained throughout the disc and into the individual blades.

Claims

We claim:

1. Apparatus for casting relatively flat articles with a selected grain orientation including a chill plate, a mold having an article-shaped cavity and a centrally located downward extension forming a vertically positioned cavity communicating with said first cavity and opening onto the chill plate, and a plurality of heating means adjacent to the mold and arranged on top and bottom of the article cavity and in steps outwardly from the downward extension to the remote edge of the mold to establish a thermal gradient radially outward from the extension toward the remote edge of the mold.

2. Apparatus as in claim 1 in which the heating means are arranged in concentric rings from the extension to the periphery of the mold.

3. Apparatus as in claim 2 in which insulation is placed on the mold from the extension to the periphery in gradually decreasing thickness from the periphery toward the extension.

4. Apparatus as in claim 1 in which a selectively oriented seed is placed on the chill plate and within the extension.

5. Apparatus as in claim 1 in which a seed having multiple orientations is placed on the chill plate and within the extension.

6. The method of casting discs and the like including the step of providing a mold having an article forming cavity and a downward extension thereon forming a vertical cavity communicating with said first cavity and open at the bottom, providing a chill plate on which the downward extension rests, heating the mold to a point above the melting point of the alloy, pouring the alloy into the mold, cooling the chill plate to remove heat from the alloy, and cooling the mold in steps radially outward from the extension thereby providing a radially outward thermal gradient from the downward extension of the mold to the outer periphery of the mold laterally remote therefrom.

7. In the method of claim 6 in which the mold cavity is relatively flat, the extension is located centrally of the cavity, and the step of cooling the mold in steps radially outward produces a radial thermal gradient horizontally from the central extension to the periphery of the annulus thereby promoting a radial grain growth horizontally in the mold.

8. In the method of claim 6 the step of providing a seed in the extension before pouring the alloy with the orientation of the grain of the seed in the desired orientation for the solidified alloy in the cast article.

9. In the method of claim 7 the added step of providing a suitably oriented seed in the extension before pouring the alloy.

10. In the method of claim 7 the added step of providing a seed made up of wedges each of radially oriented grains to produce an annulus in which the grains are substantially all radially oriented.

11. Apparatus for casting relatively flat articles with a selected grain orientation including a chill, a mold defining a ring-shaped cavity, one surface of which is defined by the chill, and a plurality of annular heating means adjacent to the mold and arranged in steps radially outward outwardly from the axis of the ring and on opposite sides thereof to establish a thermal gradient from the axis to the periphery of the mold.

12. Apparatus as in claim 11 in which the chill is a cylinder extending axially of and surrounded by the mold.

13. Apparatus as in claim 11 in which the cavity defines a plurality of radially extending article forming cavities all communicating with a central cavity in contact with the chill.

14. Apparatus as in claim 11 in which the chill is a vertically extending centrally located chill surrounded by the mold, and in which a seed made up of properly oriented segments surrounds the chill within the cavity.