US3520350A - Pattern assemblies for use in the lost wax process of investment casting - Google Patents

Description

July 14, 1970 c, WATTS 3,520,350

PATTERN ASSEMBLIES FOR USE IN THE] LOST WAX' PROCESS OF INVESTMENT CASTING Original Filed Feb. 28, 1966 2 Sheets-Sheet l Fig. 2 I

Fig. 2A

Fig. 5

I NVENTOR. CLAUDE H. Wmrs ATTOQNEYS.

July 14, 1970 C. H. WATTS PATTERN ASSEMBLIES FOR USE IN THE LOST WAX PROCESS OF INVESTMENT CASTING Original Filed Feb. 28, 1966 Fig. 4

2 Sheets-Sheet Fig. 3

INVENTOR. CLAUDE H. WATTS ATTORNEYS.

United States Patent 3,520,350 PATTERN ASSEMBLIES FOR USE IN THE LOST WAX PROCESS 0F INVESTMENT CASTING Claude H. Watts, Lyndhurst, Ohio, assignor to Precision Metalsmiths, Inc.

Originai application Feb. 28, 1966, Ser. No. 530,488, now Patent No. 3,433,627, dated May 13, 1969. Divided and this application Oct. 7, 1968, Ser. No. 765,477

Int. Cl. B22c 7/02 US. Cl. 164244 19 Claims ABSTRACT OF THE DISCLOSURE A pattern assembly for use in the lost wax process of investment casting comprising a sprue member and a plurality of patterns attached to the sprue member, the sprue member including a tube and a corrugated sleeve around the tube. A pattern assembly for use in the lost wax process of investment casting comprising a sprue member having visible markings for locating the positions of patterns attached thereto.

CROSS REFERENCE TO RELATED APPLICATION This application is a division of a co-pending application Ser. No. 530,488 of Claude H. Watts, filed Feb. 28, 1966 and entitled Method of Making a Pattern Set-up for Use in an Investment Casting, now Pat. No. 3,433,- 627, issued May 13, 1969.

This invention relates generally to the lost wax process of investment casting, and more specifically to the formation of the pattern assemblies used in such a process.

In the so-called lost wax process, a pattern assembly, commonly referred to as a set-up or tree, is prepared by attaching a plurality of patterns to a suitable sprue member. The patterns, which are replicas of the parts to be cast and include the necessary gates and risers, are made of an expendable material, such as wax, a synthetic resin or a combination of wax and synthetic resin. The set-up or tree is coated or invested with a suitable slurry which is allowed to harden to form a refractory mold. Thereafter, the patterns are destroyed, such as by subjecting the mold to heat or a solvent for the pattern material or both, to form the mold cavities.

With specific regard to the formation of the set-up or tree, the usual sprue member is cylindrical in shape and is formed either as a solid, massive piece or as a tube from an expendable material such as wax. According to another technique, the sprue member may be a hollow metal tube coated with a low melting point wax. The typical procedure which is followed in attaching the patterns involves the steps of melting or softening the ends of the patterns and/or the wax on the outside surface of the sprue member at selected locations, as by use of a Wax welding tool. Each pattern is then held against the sprue member until the wax hardens. These operations are manually repeated until the desired number of patterns have been attached in rows extending around and along the length of the sprue member.

The location of the several patterns on the sprue memher is critical. From the standpoint of obtaining the maximum yield of castings from a mold, it is desirable to use a large number of patterns in a set-up. On the other hand, the patterns cannot be so close together as to prevent the mold from being properly formed. For example, ceramic shell molds are made by dipping a set-up in a slurry, sanding the slurry coated set-up with coarse refractory particles and then drying the coating to form a hard refractory layer. These operations are repeated until a refractory shell of the desired thickness has been built up around the Patented July 14, 1970 set-up. When the patterns are too close together on the sprue member, it may be impossible to obtain a satisfactory uniform coating of the slurry over the patterns. Further, a substantial amount of slurry may be retained between closely spaced patterns to form thick wall sections which are difiicult to dry properly so as to prevent cracking when the mold is subsequently heated, such as during the pattern removal operation or when the mold is fired prior to casting.

The exact location of the patterns on the sprue member depends on several factors, including the size and complexity of the patterns, the size of the mold and the sprue, the size of the gate required for each pattern shape, and the metal from which the parts are to be cast. Because of the criticality involved in forming the set-up, the operation has required skilled and experienced personnel. The operation also has been extremely tedious and time-consuming. These problems have become particularly acute in the light of recent advancements in the lost wax process, particularly the invention of the hollow sprue disclosed in the US. Pat. No. 3,015,138, which have made it possible to cast several thousand parts in a single mold.

In order to facilitate proper positioning of the patterns when assembling a set-up and to provide for production control in the foundry, there has been a need for an efficient way of calculating the number of parts which can be cast in a mold and laying out the positions of the patterns on the sprue member before the actual fabrication of the set-up. There has also been a need for a means of enabling the person assembling the set-up to locate the patterns in accordance with the predetermined optimum layout without the skill and time which have been required in the past.

The inventions disclosed in the above-identified, copending application Ser. No. 530,488 satisfy the foregoing needs and overcome the problems theretofore involved in making a set-up for use in the lost wax process by providing means and techniques for calculating the number of parts which can be cast in a mold, the proper position of the patterns on the sprue member, the length of the pattern gates which will result in the desired spacing and the highest yield of castings from the mold and the amount of metal required to cast the mold. The disclosed inventions also provide means which enables relatively unskilled personnel quickly and precisely to attach the patterns in the predetermined optimum positions.

The preferred embodiment of one aspect of the inventions described in co-pending application Ser. No. 530,488 comprises two layout scales. One of these scales is proportioned to the circumference of the particular sprue member to be used in making a mold, and the other scale is proportioned to the length of the sprue member. Using these scales, the layout engineer is able to determine the required spacing of the patterns and the precise locations at which the gates of the patterns should be connected to the sprue member. It is also possible to calculate the length of the gate which will result in the desired circumferential spacing of the patterns and the optimum yield of the castings from the mold, the total number of patterns which can be connected to the sprue member, and the volume of metal required to cast the mold. The invention thereby provides for eflicient layout and production control.

In accordance with one aspect of the invention claimed in the present application, the sprue member itself may be formed with visible markings, such as circumferential and longitudinal grid lines, on its outer surface. When provided with such longitudinal and circumferential grid lines, the spacing of the lines preferably corresponds to the spacing of the markings or graduations of the two layout scales. In assembling the set-up, the gate ends of the patterns are attached to the sprue member using the grid lines to locate the patterns around and along the length of the sprue member. Since the proper positions of the patterns have been determined in advance by the layout engineer, it is possible for the person assembling the set-up precisely to position the patterns by counting the predetermined number of grid lines between each pattern. Thus, the present invention makes it possible accurately to assemble a set-up in a more eflicient manner than in the past.

Another feature of the present invention resides in the structure of a novel sprue member which is useful in forming a pattern set-up or tree for the lost wax process on investment casting and which is of particular utility in carrying out the techniques generally described above. In one preferred embodiment the sprue member comprises a tube formed of a stiii material, such as cardboard or the like, and a separate corrugated cardboard sleeve around the tube. Preferably, the sleeve has axial corrugations only in its inner surface. The outer wall surface of the sleeve is smooth and is provided with a thin layer of wax to which the gate ends of the workpiece patterns may be attached. A sprue member constructed in this manner is inexpensive, light in weight, and has the necessary strength to permit handling of the set-ups or trees. At the same time, the sprue members can be easily removed from either ceramic shell molds or conventional bulk investment molds. Another advantage is that the use of the novel cardboard sprue eliminates the time heretofore required during pattern removal operations for destroying conventional sprue members formed of wax or the like.

When employing the novel cardboard sprue member in the layout technique described above, the horizontal and vertical grid lines can be printed either directly on the outer surface of the corrugated sleeve or on the separate paper which is wrapped around the wax-coated sleeve. According to another embodiment of the invention, the sprue member may comprise a tube of wax, plastic or other expendable material and a sheet of preferably porous grid paper which surrounds the tube.

Other advantages and a fuller understanding of the invention will be had from the following detailed description taken in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a perspective View of an exemplary set-up or tree;

FIG. 2 is a perspective view of a sprue member formed with grid lines in accordance with this invention;

FIG. 2a is a view showing a paper having grid lines which may be used in forming the sprue member;

FIG. 3 is a view showing one layout scale;

FIG. 4 is a view showing the other layout scale; and

FIG. 5 is a view showing a modified form of the sprue member.

Referring now to the drawings, and to FIG. 1 in particular, the exemplary set-up is designated by reference numeral 10. The set-up is comprised of a central sprue member 11 and a plurality of workpiece patterns 12 projecting from the outside wall of the sprue member.

In accordance with conventional practice, the patterns 12 and at least the outer wall portion of the sprue member 11 are formed of an expendable material, such as wax, a synthetic resin, or a wax and synthetic resin composition. The sprue member 11 is preferably cylindrical and may be solid in cross section or in the form of a tube. Each of the patterns 12 includes a main portion 13 which defines the shape of the part to be cast in metal and a gate 14 which has its root end attached to the wall of the sprue member.

As shown in FIG. 2, the outside of the sprue member 11 is covered with uniformly spaced vertical grid lines and uniformly spaced circumferential grid lines 21, the lines having been eliminated from FIG. 1 for the sake of clarity. The exact distance between the vertical and 4 horizontal lines is not critical, but may be on the order of one-eighth or an inch in order that the lines are easily discernible and can be quickly counted. If desired, certain vertical and circumferential lines, for example, every eighth line, may be heavier or darker than the rest.

The lines 20 and 21 may be imposed on the sprue member 11 in several different ways. One preferred technique is to provide a thin, relatively porous sheet of paper 22 (FIG. 2a) on which the lines 20 and 21 are suitably printed. The porosity of the paper 22 is such as to permit the materal forming the outer wall surface of the sprue member 11 to pass through the paper when the material has been heated to a flowable state. In forming a wax sprue member 11, the paper 22 is rolled into a tube against the inside surface of the usual wax injection mold and the wax is simply injected into the mold within the rolled paper tube. Alternately, a wax sprue member 11 can be injection molded and the paper 22 thereafter wrapped around the sprue member and secured in place by any suitable means, as by tape, adhesive or the like.

Another preferred construction of the sprue member is shown in FIG. 5. In this embodiment, the sprue member 30 comprises an internally corrugated cardboard sleeve 31 having a smoother outer wall surface. The vertical grid lines 20 and the circumferential lines 21 may be printed on the smooth outer wall surface of the sleeve 31. The internally corrugated sleeve 31 is placed around a rigid cardboard tube 32 and the assembly is provided with an outer cylindrical wall formed by a thin coating of a low melting point wax (not shown). The wax can be coated on the sleeve 31 by rotating the sprue member 30 on a horizontal axis in a molten wax bath. The thickness of the wax coating which is formed is sufiicient to permit the patterns (not shown in FIG. 5) to be secured to the sprue member 30 by locally heating the wax coating to affix the gate ends of the patterns. Preferably, the thickness of the wax coating is in the range of from about of an inch to about A of an inch. As in the embodiment of FIG. 2, the sprue member 30 can be modified to comprise a wax coated assembly including the sleeve 31 mounted around the tube 32 and the porous paper 22 wrapped around the sleeve 31. After a mold (not shown) has been formed around a pattern set-up including the sprue member 30, the tube 32 can be easily slipped from the sleeve 31 and the sleeve stripped from the inside of the mold.

Referring now to FIG. 3, there is shown a layout scale 48 which is adapted to be used in laying out the circumferential positions of workpiece patterns on a sprue member before assembling the set-up. As shown, the scale 48 is in the form of an annulus and includes a circular line 49. The diameter of the circle 49 is in proportion and is preferably approximatelyequal to the outside diameter of the particular sprue member to be used in the set-up. The scale 48 also includes uniformly spaced radial markings or graduations 50 which intersect the circle 49. The number of graduations 50 and the spacing between the lines at the points of intersection with the circle 49 is preferably equal to the number and spacing the vertical lines 20 on the sprue member. The spaces between the graduations 50 are sequentially numbered clockwise around the circle 49. It will be apparent that all of the numbered spaces on the scale 48 will be of equal size when the number and spacing of the graduations '50 is evenly divisible into the circumference of the circle 49. When the selected uniform spacing of the graduations 50 clockwise around the circle 49 is not evenly divisible into the circumference of the circle, the last numbered space on the scale will be smaller than the other spaces.

The second layout scale which is used to determine the longitudinal spacing of the patterns 12 is designated in FIG. 4 by reference numeral 60. The layout scale 60 has a length in proportion to the length of the sprue member and is comprised of a series of parallel graduations or lines 61 which are uniformly spaced apart a distance equal to the spacing between the circumferential lines 21 on the sprue member. The spaces between the graduations 61 are sequentially numbered from one end of the scale 60 to the other. The number of the graduations 61 may equal or exceed the number of lines 21 on the particular sprue member, and, if desired, the scale '60 may be marked off in inches as shown at the left in FIG. 4 to facilitate use of the scale with sprue members of different lengths.

When laying out a pattern set-up, two patterns 12a and 12b of the type to be used in the set-up are placed on the circular scale 40 so that the root ends of the gates 14 abut the line 49 and the main portions 13 are radially outward of the line 49 over the lines 50. As shown in FIG. 3, the pattern 12a is positioned so that the left edge of the main pattern portion 13 is slightly to the right of the radial line between spaces zero and one. In this position the right hand corner of the gate 14 of the pattern 12a lies approximately on the line between the number five and the number six spaces, and the extreme right edge of the main pattern portion is within the number seven space.

The second pattern 12b is positioned adjacent the pattern 12a so that the main portions of the patterns are spaced apart a selected distance. As pointed out above, this distance will vary with the part design and other considerations, but it is usually on the order of 7 of an inch or slightly less. In the illustrated example, the spacing is approximately A; inch. When the pattem 12b is placed in the desired position, it is observed that the right ahnd corner of its gate lies on the line between numbered spaces 12 and 13.

In the usual situation where the last numbered space of the scale 48 is smaller than the other spaces, the number of patterns which can be placed around the sprue member is calculated by determining the number of spaces between corresponding portions of the two pattern gates and dividing this number into one less than the total number of spaces on the scale 48. In the illustrated example, there are 7 spaces between the right hand corners of the pattern gates. Assuming that there are 219 spaces on the scale 48, it can be determined by dividing 218 by 7 that 31 patterns can be placed around the sprue member.

It will be apparent that the number of patterns which can be placed around the sprue member can be increased while maintaining a desired spacing between the main pattern portion simply by lengthening the gates. Thus, the person making the layout can determine what the proper length of the gate should be to obtain a maximum yield of castings from the mold. The length of the gate will vary depending upon the design of the part, the metal to be cast and the feeding requirements.

In determining the number of patterns which can be attached lengthwise of the sprue member, the end surfaces of the gates 14 of the patterns 12a and 12b are placed against the layout scale 60, as shown in FIG. 4. The pattern 12a is positioned so that the entire main portion (not shown) is above the first line of the scale. In this position, the bottom edge of the gate is slightly above the first line on the grid and the top edge of the gate lies on the line between spaces two and three. The second pattern is stood on end and is spaced from the pattern 12a to allow the proper distance between the main portions of the patterns (not shown in FIG. 4). As noted above, this distance is usually on the order of of an inch or slightly less. Thus positioned, it is observed that the bottom edge of the gate of the pattern 12b is within space four and that the top edge is on the line between spaces five and six.

The number of patterns that can be placed along the length of the sprue member is calculated by determining the spaces between corresponding portions of the two pattern gates and dividing that number into the number of spaces corresponding to the usable length of the sprue member. When positioned as shown in FIG. 4, the number of spaces between corresponding edges of the pattern gates is three. Assuming that the sprue member has a usable length of 14 inches, the number of patterns in each vertical row on the set-up will be 112 divided by three or 37.

It will be apparent from the foregoing that the total number of patterns to be used in the illustrative set-up can be determined to be 1147 by multiplying the number of patterns in a horizontal row by the number of patterns in a vertical row. By making it possible for a person to determine in advance the total number of patterns which can be cast in a single mold using a sprue member of any given size, the invention facilitates efiicient production planning and layout control.

It will also be apparent that the invention facilitates the actual assembly of the set-up. The person making a.set-up positions the first pattern at the end of the sprue member so that the right hand edge of the gate is on one of the lines 20 and the bottom edge of the gate is on one of the lines 21. In positioning the patterns around the sprue member, the second pattern is positioned so that the right hand edge of its gate is spaced from the corresponding edge of the first pattern gate by the number of spaces previously determined by use of the layout scale 48. Thus, in carrying out the described eX- ample of the invention, the location of the right side edge of each pattern in a circumferential row is determined by counting seven spaces from the right hand side edge of the previously positioned pattern gate. In a similar manner, the location of each subsequent horizontal row of patterns is determined by counting the number of spaces previously determined by use of the scale 60. For example, if the desired vertical spacing between patterns was determined to be three spaces, the location of the bottom edges of the gates of each horizontal row of patterns is determined by counting three spaces down from the bottom edges of the previously attached patterns.

Many other modifications and variations of the invention will be apparent to those skilled in the art in View of the foregoing detailed description. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically shown and described.

What is claimed is:

1. A pattern set-up for use in the lost pattern process of investment casting comprising a sprue member and a plurality of workpiece patterns projecting outwardly therefrom, said sprue member including a tube and a corrugated sleeve around said tube.

2. A pattern set-up as claimed in claim 1 including a coating of an expendable material on the outside of said sleeve.

3. A pattern set-up as claimed in claim 1 wherein the inner surface of said sleeve engaging said tube is corrugated and the outer surface of said sleeve is smooth.

4. A pattern set-up as claimed in claim 3 wherein the corrugations of the inner surface of said sleeve extend axially of said sprue member.

5. A pattern set-up as claimed in claim 3 including an outer thin wax coating on said sprue member.

6. A pattern set-up for use in the lost pattern process of investment casting comprising a sprue member shaped to form sprue passage means in a refractory mold, and a plurality of outwardly projecting patterns attached to said sprue member around its outside and along its length, said sprue member having a plurality of regularly spaced visible markings for use in locating the positions of patterns on the sprue member so as to permit proper formation of mold walls between adjacent patterns,

7. A pattern set-up as claimed in claim 6 wherein said sprue member includes a porous paper and a coating of expendable material, said paper being pervious to said expendable material when heated to a flowable state, and said markings being inscribed on said paper.

8. A pattern set-up as claimed in claim 7 in which said markings on said paper comprises longitudinal and circumferential grid lines.

9. A pattern set-up as claimed in claim 7 wherein said sprue member is comprised of a tube and a corrugated sleeve surrounding said tube.

10. A pattern set-up for use in the lost pattern process of investment casting comprising a sprue member shaped to form sprue passage means in a refractory mold, and a plurality of outwardly projecting patterns attached to said sprue member, said sprue member including a tube, a sleeve surrounding said tube, a paper around said sleeve, said paper having spaced markings for use in locating the positions of patterns on said sprue member so as to permit proper formation of mold walls between adjacent patterns, and a wax coating.

11. A pattern set-up for use in the lost pattern process of investment casting comprising a sprue member shaped to form sprue passage means in a refractory mold, and a plurality of outwardly projecting patterns attached to said sprue member around its outside and along its length, said sprue member being provided With a first series of regularly spaced parallel lines for use in locating positions of patterns with respect to one another on said sprue member so as to permit proper formation of mold walls between adjacent patterns.

12. A pattern set-up as claimed in claim 11 in which said sprue member comprises an inner tube and a corrugated sleeve around said tube, said sleeve being imprinted on its outer surface with said lines, and a coating of expendable material on said sleeve.

13. A pattern set-up as claimed in claim 11 in which said sprue member is provided with a second series of parallel lines extending transversely to said first series of lines.

14. A pattern set-up as claimed in claim 13 in which said first series of lines extends circumferentially of said sprue member and wherein said second series of lines extends longitudinally of said sprue member.

15. A pattern set-up for use in the lost pattern process of the investment casting comprising a sprue member shaped to form sprue passage means in a refractory mold, and a plurality of outwardly projecting patterns attached to said sprue member, said sprue member including a tube, a corrugated sleeve surrounding said tube, and a plurality of visible markings for use in locating positions of patterns with respect to one another on said sprue member so as to permit proper formation of mold walls between adjacent patterns.

16. A pattern set-up as claimed in claim 15 including a thin coating of expendable material on the outside of said corrugated sleeve.

17. A pattern set-up as claimed in claim 15 in which the corrugations of said sleeve extend axially and are located internally thereof, the outer surface of said sleeve being smooth.

18. A pattern set-up for use in the lost pattern process of investment casting comprising a sprue member shaped to form sprue passage means in a refractory mold, and a plurality of outwardly projecting patterns attached to said sprue member around its outside and along its length, said sprue member having a plurality of visible markings uniformly spaced around said sprue member and along its length for use in locating the positions of patterns with respect to one another on the sprue member so as topermit proper formation of mold walls between adjacent patterns.

19. A pattern set-up as claimed in claim 18 wherein said visible markings comprise grid-like indicia.

References Cited UNITED STATES PATENTS Re. 26,495 12/ 1968 Watts et al 164-34 X 3,139,656 7/1964 Watts et a1. 164-244 3,254,379 6/1966 Poe 164-34 X J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner

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