US 3488766 A
Description (OCR text may contain errors)
Jan. 6, 1970 w. WILLIAMS ETAL METHOD OF CASTING ELBOWS Filed Feb. 15, 1967 INVENTORS WARREN WILLIAMS THOMAS c. ROONEY GERALD w." JAY v RONALD E. BARRY United States Patent US. Cl. 29157 Claims ABSTRACT OF THE DISCLOSURE In the method of casting a hollow, curved article, forming a pair of molds each. having a surface which is curved in a plane containing its central axis and circular in a plane normal to its central axis. One of the surfaces is convex, and the other concave, with the edges of the surfaces being substantially complementary. A quantity of metal is disposed in each of the molds, and each is rotated about its respective central axis until a shell of solid metal forms in each of the surfaces with the concave mold being stopped and the excess metal removed prior to the complete solidification thereof. The shells are then removed from the molds, and joined along the complementary edges after the removal of excess material to form a hollow toroidal member which may be cut into desired sections.
This invention relates to the art of casting metals and more particularly to the method of making hollow curved elbows, by centrifugal casting in semi-permanent molds of metal or graphite.
The benefits of centrifugal casting are well known. The principal benefit of which is the producing of castings of high quality. Hollow, tubular members having various outside shapes have been made by this method of casting but for the most part have been limited to straight linear axis type castings. Where a curved hollow shape is required, it is usually statically cast usingcores, etc. to make the desired shape. This method is frequently unsatisfactory due to the problems, such as internal shrink, entrapped dirt. slag, etc., encountered in parts made by the static cast method.
One of the principal objects of the present invention is to provide a method for casting hollow tubular members that takes advantage of the centrifugal casting method in which internal shrink and entrapment of foreign material, etc. are substantially eliminated.
Another object of the present invention is to provide a method for making the outer shell for a hollow curved member.
Another object of the present invention is to provide a method for making a hollow tubular member in which a substantial saving is achieved through the reclamation of the unused metal.
A further object of the present invention is to provide an improved hollow tubular member which has greater strength characteristics at the areas of greatest stress.
A still further object of the present invention is to provide a method of making hollow curved members that is simple to manufacture and relatively easy to assemble.
A still further object of the present invention is to provide a method for casting hollow curved members which are to be used under conditions where the inherent high temperature characteristics of cast materials are required.
The article which is cast to accomplish the above objects is best described as a hollow torus or variations thereof. The outer half section of this article is cast separately from the inner half section and the two sections are then welded together. The outer half section 3,488,766 Patented Jan. 6, 1970 is cast in a circular die that is rotated on its axis so that the molten metal in the die will be thrown outward against the curved surface of the die. The die is rotated only long enough for the molten metal on the surface of the die to set and it is then stopped to allow the still molten metal to flow into a reservoir provided at the lower end of the die. This metal is cooled in the reservoir and then removed from the reservoir for reuse.
In practicing the method of the invention, the surface of the die is heated by any appropriate means such as a torch to bring the surface up to a predetermined temperature. A ceramic coating may be applied to the surface of the die to prevent adherence or any reaction with the die material. The metal which is to be used to make the shell is then poured into the die while the die is rotating so that the metal is thrown outward by centrifugal force against the inner curved surface of the die. Rotary motion is continued for a predetermined period of time to allow the molten metal to freeze or set on the surface of the die. The die is then stopped and the metal which is still molten will drain into the reservoir at the bottom of the die. This metal is cooled and then reclaimed from the reservoir when the die is opened. Once the shell has been removed from the die the surfaces of the shell are finished by any of the well known finishing means such as machining or grinding.
The inner half section is also made in substantially the same manner, except that the surface of the die for the inner half section must have a convex curvature. However, none of the molten metal used to cast the inner half section is drained into a reservoir. The inner section after machining, grinding or finishing in some other manner is then welded to the edges of the outer half section to form a complete hollow torus. When the torus is completed it can then be cut to the desired degree of curvature, for example four elbows or two elbows.
Other objects and advantages will become more readily apparent from the following description when read in connection with the accompanying drawings, in which:
FIG. 1 is a side view in section of a die used to form the outer half section for the curved casting.
FIG. 2 is a side view in section of a die used to form the inner half section for the curved casting.
FIG. 3 is a cross-sectional view of the shell showing the welded connection.
FIG. 4 is a top view of the completed shell shown cut at 90 angles.
FIG. 5 is a view of a finished 90 tubular elbow.
Referring to the drawings, the centrifugal die shown in FIG. 1 is made up of an upper part 10 and a lower part 12 which are secured together in a conventional manner on line 14 to form a completely symmetrical curved die. The means of securing said dies together is well known in the centrifugal casting art and does not form a part of this invention, so no further description is provided herein. The method for mounting the die for centrifugal casting is also well known and involves merely the placing of the die in a standard rotating device so that it will be rotated on its vertical axis. The die parts have concave curved inner surfaces 16 and 18 which have identical radius of curvature. These surfaces define the outer surface of the article to be cast. A circular reservoir 20 is formed below the casting surfaces in the center of the lower die and has sloping curved walls 22 and 24. A circular opening 26 is provided in the top of the upper die and is used to allow the molten metal to be poured into the die.
It should be apparent that although upper and lower dies are shown in the drawing, it is also possible to use a vertically split die having identical half sections. A
reservoir would also have to be provided in the bottom of such a die.
Prior to pouring the molten metal into the die, the surfaces 16 and 18 may be heated to a temperature between 200 to 600 F. This can be done with a torch or any other appropriate means. A commercial ceramic coating may be applied to the heated surface to minimize the adherence of the cast metal to the surface of the die. The temperature of the metal should be 100 to 300 F. above its melting temperature at the time of pouring and in the present example the temperature of the molten metal was 2850 F. when poured into the die. The molten metal is preferably poured into the die while the die is rotating so that the metal is thrown outwardly by centrifugal force against the inner curved surface of the die. It will be appreciated, however, that rotation of the die may also be commenced after the metal is poured into the die. In either case rotation of the die continues to allow the molten metal adjacent the die surface to solidify a thickness of approximately one inch. All of the molten metal in the die will be thrown outward by centrifugal force against the surfaces 16 and 18. Since the surface temperature is approximately 300 F. and the molten metal temperature is approximately 2850 F. a fast set will occur on the surface producing a shell of solidified metal on the surfaces 16 and 18. The period of time of rotation is selected to allow this shell to set until it is approximately one inch thick. In this example this will take approximately 40 to 45 seconds. The die is stopped and the molten metal remaining in the die will flow down the Walls 22 and 24 filling reservoir 20. It will be appreciated that all of the molten metal will have drained away from the die surface before the die actually comes to a complete stop. In the present example a molten metal charge of approximately 560 lbs. was poured into the die and when the die was stopped about 400 lbs. of the original metal was reclaimed in the reservoir. Once the die is stopped and the molten metal cooled sufiiciently to freeze or set the shell or casting 28 formed in the die the upper die is removed and the shell removed from the lower die. The surfaces of the shell are finished by machining or grinding to the desired dimensions. The reclaimed metal in the reservoir is also removed from the lower die for reuse as melting stock.
The inner half section of the casting is formed in a centrifugal die as seen in FIG. 2. Dies 30 and 32 are formed by securing parts 30a, 30b and 300 and 32a, 32b and 320 together and then assembling the dies on line 34. The die is formed with inwardly sloping surfaces 36 on part 300 which terminate at a curved surface 37, which has substantially the same curvature as the shell 43. The upper and lower surfaces 39 and 40 are made substantially parallel to surfaces 36. The space between surface 36 and surfaces 39 and 40 will allow the cast metal to shrink without creating any stresses in the cast piece shown dotted in FIG. 2. The metal is poured into this die through circular opening 41 under substantially the same temperature conditions as described above, but is rotated until all of the molten metal has frozen or set up in the die. The cast metal shown shaded at 35 must be machined or removed in some other manner to form the surface of the circular ring shown dotted at 43. After the metal has set or frozen the die parts 30a, 30b, 30c and 32a, 32b and 32c are removed. When this section has been completed it is positioned within the inner circumference of the finished casting 28 formed in dies and 12 and welded t 42 o fo m a h o o us.-
Referring to FIG. 4, the complete hollow torus is shown cut along lines 46, 48, 50 and 52 to form four 90 hollow elbows A, B, C and D. A completed tubular elbow is shown in FIG. 5. The degree of curvature can be varied to provide two 180 elbows, six 60 elbows or even twelve 30 elbows.
It should be noted that the weld is located at the top and bottom of the casting. The casting will then present a continuous surface 56 at the area Where the greatest flow is anticipated. It should be apparent that the outer shape can be varied as well as the cross-sectional shape.
Although only one embodiment of the present invention has been shown and described it should be apparent that various changes and modifications can be made herein without departing from the scope of the appended claims.
What is claimed is:
1. In the method of making a curved tubular article, the steps of forming a die having a concave mold surface which is curved in a section taken in a plane which contains its central axis and circular in a section taken in a plane which is normal to the central axis, rotating the die at a predetermined speed, pouring a predetermined quantity of molten metal into said die while it is still rotating to solidify a portion of said molten metal on said mold surface, stopping the rotation after a predetermined period of time so that a shell is formed on said mold surface and allowing the still molten metal to drain from the mold surface whereby a layer of metal will be left on the inside surface of the die.
2. The method of claim 1, including the steps of forming a second die having a convex annular mold surface which is curved in a section taken in a plane which includes its central axis and circular in a plane normal to said central axis, the edges of said convex and concave surfaces being substantially complementary, disposing a quantity of molten metal in said second die, rotating said second die about its central axis to solidify at least a portion of said molten metal on said convex surface to form the second of a pair of members each of which has an edge substantially corresponding to the edges of its respective mold, removing said members from said molds and joining said members along the complementary edges to form a composite member.
3. The method of claim 2 and including the steps of removing excess metal from said composite member and segmenting said member.
4. The method set forth in claim 2, wherein the surfaces of said dies are preheated to a temperature substantially less than that of the molten metal.
5. The method set forth in claim 2, wherein the central axes of said dies are disposed substantially vertically during rotation.
References Cited UNITED STATES PATENTS 5/1914 Rockwell 164-l14 7/1937 Larsen l6477 X US. Cl. X.R.