US2770858A - Supporting shell molds during metal pouring operations - Google Patents

Description

Nov. 20, 1956 A. J. ANDERSON 2,770,853

SUPPORTING SHELL MOLDS DURING METAL. POURING OPERATIONS 2 Sheets-Sheet 1 Filed April 12, 1952 SnDenbr Nov. 20, 1956 A. J. ANDERSON SUPPORTING SHELL MOLDS DURING METAL POURING OPERATIONS Filed April 12, 1952 2 Sheets-Sheet 2 aw M67233 (Clitorm s United States Patent SUPPORTING SHELL MOLDS DURING lVIETAL POURING OPERATIONS Arthur J. Anderson, Bedford, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware This invention relates to metal casting operations using shell molds and particularly to a machine for supporting or backing up shell type sand-resin molds during pouring of the molten metal.

Recently developed techniques in foundry practice employ thin-walled dispensable molds and cores composed of sand and plastic binders. These procedures, generally referred to as shell molding, are particularly suited for the production of precision castings in a wide variety of metals.

Essentially the shell molding process consists of using a thermosetting plastic or resin as a binder for the sand grains to form rigid molds having high gas permeability, good surface smoothness and dimensional stability. The molding material, which is generally a dry mixture of a major proportion of silica sand and a minor proportion of a plastic binder, is used in powder form with no water being added. Phenol formaldehyde and melamine formaldehyde resins are typical examples of the type of thermosetting binders preferably used. The sand employed is preferably free of metal oxides, clay, moisture and organic matter.

These sand-resin molds are prepared by allowing the dry mixture of sand and resin powder to come into contact with a hot metal pattern for a short period of time. A layer of the mix adheres to the metal surfaces due to the heating of the resin which entraps the sand with which it is intimately mixed, thereby accurately reproducing pattern details. Metal patterns must be employed because they are subjected to elevated temperatures. Pattern temperatures in the range between 250 F. and 3 50" F. are typical, but temperatures up to 600 F. may be advantageously employed under particular conditions. The half patterns, gate and runner are usually all permanently fixed on metal plates. The pattern temperature and the length of time the molding material is allowed to remain in contact with the hot pattern surfaces determine the resulting thickness of the mold. Mold build-up times ranging from a few seconds to approximately one minute are appropriate for various applications. I

After this short time interval, the excess dry sand and resin are removed, and the closely adhering sand-resin layer preferably is cured by heating in a recirculating air oven at a temperature within the range of approximately 300 F. to 900 F. for a short period of time, usually from a few seconds to five minutes, while in contact with the metal pattern. This baking operation results in the conversion of the resinous material to a hard insoluble binder which securely bonds the sand grains together. After the removal of the pattern and formed mold from the curing oven, the mold is stripped from the pattern.

. The formed molds are, in effect, thin shellsv which usually have suflicient strength and stiffness to make them suitable for many casting operations if these shells are suitably reinforced or backed up while the molten metal isbeing' poured. If inadequate backing means is provided, these thin shell molds, because of inadequate 2,770,858 Patented Nov. 20, 1956 rigidity, frequently tend to bulge, crack, or otherwise become distorted by the pressure of the molten metal during or immediately after pouring. Not only does such mold distortion prevent casting to very close dimensional tolerance, but it also results in excessive finnin-g at the mold parting line.

Shell molds contain a relatively large amount of resin binder, this binder normally constituting between 4% and 20% by weight of the molding material. Hence, upon contact of the molten metal with the cured shell molds, a considerable volume of volatiles is given off; and if these gases are not properly vented, distortion of the resultant casting or occlusion of gases therein results. It is therefore necessary that the mold-backing means not only rigidly supports the mold, but also that this means provides for adequate venting of the formed mold gases.

The back-up bedding materials heretofore used, such as steel shot or sand, which meet this permeability requirement, frequently fail to adequately support these molds with the result that close dimensional tolerances in the mold cavity are not maintained. Moreover, the mechanical handling of such bulky bedding material is a cumbersome and expensive procedure.

Accordingly, a principal object of the present invention is to provide an apparatus for supporting assembled shell molds so as to eliminate the use of the aforementioned unsatisfactory types of backing means and the resultant casting difiiculties.

These and other objects are attained in accordance with this invention by the use of an apparatus having a pair of metallic mold-supporting members, one of which is reciprocably mounted to provide for the rapid engagement and disengagement of these members and to accordingly permit a substantial increase in the rate of metal pouring. Moreover, these supporting plates or platens are provided with mold-contacting projections having recesses therebetween which permit the mold gases formed during the pouring operation to escape into the atmosphere. The resultant castings have very smooth as-cast surfaces, thereby considerably reducing the number of machining operations necessary for precision parts. Furthermore, the precision castings formed by the use of my shell mold supporting machine are almost completely devoid of fins.

Most efiicient use of this back-up machine is now possible because of the recent development of machines which form shell molds having suflicient uniformity of thickness to permit the molds to be taken directly from the mold-forming machine, baked in a curing oven, and placed in the back-up machine. An example of this type of mold-forming machine is disclosed in my copending patent application Serial No. 248,424, which was filed September 26, 1951.

Other objects and advantages of this invention will more fully appear'from the followingdescription of the preferred embodiment of the invention shown in the accompanying drawings, in which:

Figure l is a diagrammatic front elevational View, with parts broken away, of a mold back-up machine embodying my invention, the mold-supporting plates being shown in their disengaged positions;

Figure 2 is a diagrammatic fragmentary front elevational view of the back-up machine shown in Figure 1 with the mold-supponting plates shown in their closed ositions;

Figure 3 is a diagrammatic fragmentary top elevational view, with parts broken away and in section, of the machine shown in Figures 1 and 2;

' Figure 4 is an enlarged elevational end View of the stationary mold-supporting plate of the machine; and

Figure 5 is a sectional view generally along the line 55 of Figure 4, showing the details of the stationary mold-supporting plate and the position of the supported shell mold relative to it.

Referring more particularly to the drawings, in Figure l is diagrammatically shown a shell mold back-up machine embodying the invention and including a base 10. Mounted upon this base near opposite ends thereof are a vertical frame member or stationary bolster 12 and a second vertically extending frame member 14. Members 12 and 14, which are preferably formed of steel or cast iron, are shown as provided with horizontally extend ing bottom flanges .16 and 18 respectively, which are rigidly secured to the base by bolts or other appropriate attaching means.

Positioned upon the base 10 between the frame members 12 and 14 is a reciprocable bolster 20. A longitudinally extending short connecting rod 22 is attached by bolts or other suitable means, not shown, to one face of the movable bolster 20. The opposite end of the connecting rod 22 is secured by means of a pin 24 to a bifurcated connecting member 26 which is attached to an end of a reciprocable elongated plunger shaft 28. This shaft extends through and reciprocates in an opening, not shown, in the vertical frame member 14.

Mounted on the outer surface of the frame member 14 by longitudinally extending tie rods 30 provided with nuts 32 is an air cylinder 34 which is adapted to reciprocate the shaft 28 by means of a conventional plunger attached to the end of the shaft. Each of the tie rodshas one end secured to the frame member 14 and the other end secured to the end plate 36 of the cylinder 34.

Appropriate pipes 38 communicate through pipe 39 with a source of compressed air, not shown, and with the ends of the cylinder 34 for conveying the compressed air to and from the cylinder. A suitable controlling mechanism or valve 40 is mounted on the upper end of the frame member 14 and is provided with an arm or handle 42 to operate the valve and alternately direct the compressed air from pipe 39 into and out of the appropriate end of the cylinder 34 to reciprocate the plunger shaft 28. Of course, the plunger shaft 28 and movable bolster 20 could equally well be reciprocated by a hydraulic liquid cylinder or other suitable means.

The base 10 is shown in Figure 3 as including longitudinally extending railings 44 upon which the aforementioned stationary frame members are mounted. These railings have a portion of their upper surfaces recessed, as shown at 46 in Figure 2, to function as lower sills for the movable bolster 20. Secured to the outer sides of these railings and .the side surfaces of the frame members 12 and 14 by means of metal screws or bolts 48 and 50,

respectively, are a pair of longitudinally extending metal guide members 52 of L-shaped cross section. The movable bolster 20, which is reciprocable by the shaft 28, has its bottom portion provided with outwardly extending transverse flanges or runners 54 which slidably engage the upper recessed surfaces 46 of the base railings 44. Hence, the inwardly extending horizontal flanges 56 of the guide members function as upper sills for the runners 54. These runners, when the bolster 20 is reciprocated by the shaft 28 in response to actuation of the hydraulic cylinder 34, thus are slidable within the grooves 58 formed between the base railings 44 and the guide members 52.

Mounted on the inner vertical face of the fixed bolster 12 by bolts or other suitable means which are not shown is a mold-supporting plate or platen 60. This stationary mold-supporting plate is preferably of metal and, as best shown in Figures 4 and 5, has its outer edges provided with flanges 62 extending longitudinally toward the movable bolster. Outwardly extending lugs 64 are preferably formed on the outer surfaces of the side portions of these flanges and are provided with longitudinal metal aligning pins or dowels 66. A plurality of transversely extending and vertically spaced ridges 68 are shown as formed on the inner surface of the mold-supporting plate .60 and are adapted to project into contact with the shell mold 63 to be supported. A pair of cutaway portions or openings 70 are provided in the upper horizontal portion of flange 62 to enable the operator to more easily locate the mold on the plate 60 and to permit the escape of the mold gases formed during the metal pouring operation. As shown in Figures 4 and 5, the vertical wall portion of plate 60 has ducts 72 which extend through this wall and also function as gas escape vents for the formed mold gases. Communicating apertures, not shown, likewise may be provided in the stationary bolster 12, or recesses 74 may be formed between flanges 76 projecting from the back face of plate 60 to allow the mold gases which are vented through the ducts 72 to escape through these recesses to the atmosphere.

A second mold-supporting plate 78 having a construction which is generally similar to the stationary platen 60 is attached to the adjacent vertical face of the reciprocable bolster 20. Like platen 60, the movable moldsupporting plate 78 is provided with side flanges having lugs 80 projecting outwardly therefrom. Longitudinal openings, not shown, are formed through these lugs and, upon reciprocation of the movable mold'supporting plate 78 into engagement with the stationary plate 60 and the supported shell mold 63, the dowels 66 extend into the openings in the lugs 80 to thereby properly align the two mold-supporting plates.

A plurality of spatially separated projections or ridges similar to those on the stationary plate 60 are likewise formed on the mold-engaging face of the movable platen 78. These projections are also so formed that, upon contact with the mold 63, their mold-contacting edges apply uniform pressure to the mold at the areas of contact to maintain the mold halves in assembled position. In general, it is preferable if the ridges or projections on the two mold-supporting plates are in approximately alignment relative to the longitudinal axis of the machine in order to best obtain this uniformity of pressure application and to avoid cracking the mold by the creation of excessive localized pressure areas. The details of plate 78 are not shown in the drawings in view of the sub stantial similarity in construction between it and plate 60.

As shown in Figures 1 through 3, clamps 82 are attached by bolts or other suitable means to the outer side surfaces of the stationary platen 60. Each of these clamps is shown as consisting of an arm or book 84 which is pivotally mounted on a base or bracket portion 86 of the clamp. A handle 88 is connected to the hook and may be pivoted to lock the latter in mold-retaining position.. The details of clamps 82 are not shown in the drawings, and the construction of the clamping means employed to retain the molds is not critical insofar as this invention is concerned. For example, these clamps may be provided with spring means so as to avoid applying undue pressure to a mold of excessive thickness when the latter is mounted in position on the mold-supporting plate 60.

After the shell mold halves 63 have been removed from the curing oven, their smooth castingdefining faces are placed into contact with each other, and this mold assembly is positioned against the ridges 68 and the edges of the flange 62 of the stationary platen 60, as shown in Figure 1. The handles 88 and the attached hooks 84 of the clamps 82 are then pivoted so that the hooks engage the surface of the assembled mold opposite the platen 60 near its edges and lock the mold in position.

In order to facilitate assembly of the shell mold halves 63 on the stationary mold-supporting plate 60 and to provide these mold halves with perfect vertical alignment,

thus eliminating the possibility of applying undue 10- calized pressure to the mold upon contact with the ridges 68 on the mold-supporting plates, the stationary moldsupporting plate 60 has a transversely extending horizontal bar 92 suitably fixed, as by welding 94, to the lower horizontal portion of the flange 62. In this mannerthe two mold halves may be quickly placed in position on the bar 92 and maintained by it in perfect vertical alignment. Lateral movement of the mold is shown as further prevented by a generally'semicircular opening or cutawayportion 96 in the upper horizontal portion of flange 62, the edges of this opening snugly engaging the outer peripheral surface of the sprue portion 98 of the mold. Of course, movement of one of the mold halves relative to the other is eliminated in the usual manner by the provision of suitable mold prints on these mold halves.

After the cured core halves 63 are positioned on the stationary mold-supporting plate 60 and aflixed thereto by means of clamps 82, the valve 40 is regulated by means of the handle 42 to direct the compressed air through the pipes 38 into the outer end of the cylinder 34. The compressed air, driving the plunger and shaft 28, moves the reciprocable bolster 20 and the attached core-supporting plate 78 toward and into engagement with the adjacent face of the shell mold 63, as shown in Figures 2 and 3. Suitable notches or slots 100 are shown as formed in the side flanges of plate 78 to provide clearance for the inwardly extending hooks 84 of the clamps 82. The ridges or projections on the movable core-supporting plate 78 thus engage the outer surface of the shell mold and evenly apply pressure thereto so as to prevent warping or distortion of the shell molds upon pouring of the molten metal. In this manner close dimensional tolerance of the resultant casting is maintained.

The relative positions of the stationary mold-supporting plate 60 and the shell mold when so engaged are shown in Figure 5. The broken lines show the location of the mold with respect to plate 60 and indicate that, except for contact with the flange 62 and ridges 68, the mold is spatially separated from the plate because of the recesses 99 formed between these ridges and flange. These recesses serve as vents to permit the mold gases to escape through ducts 72. The position of the reciprocable mold-supporting plate 78 relative to the mold is similar to that of the fixed plate 60 and is therefore not shown in detail.

It will be understood that, depending upon the contour of the particular mold being used, the ridges or projections 68 could be formed at various locations relative to the mold. Moreover, of course, the ridges can be fabricated in a variety of shapes or forms and do not have to be shaped as shown in the drawings.

It also will be understood that the shell mold supporting machine described above could equally well be designed so that one shell mold half is retained in position on each of the mold-supporting plates prior to closure of these plates. However, the modification shown provides for perfect alignment of the mold halves and eliminates any possibility of even slight misalignmlent caused by attrition of mold prints due to relative movement of the mold halves upon closure of the mold-supporting plates.

Upon pouring the liquid metal through the mold sprue 98 and into the mold cavity in the usual manner, the hot metal, on coming into contact with the mold, burns the plastic binder of the shell mold to essentially carbon. The gases which are generated readily escape through the highly permeable sand-resin shell and are vented from the mold through the recesses 99, the ducts 72 and the openings 70 in the flange 62. A hood 102 of conventional design is shown as located above the back-up machine to exhaust these gases from the vicinity of the machine. After the casting has been permitted to solidify, the reciprocable bolster 20 and the attached mold-supporting plate 78 are moved out of engagement with the shell mold and return to the position shown in Figure 1, thus completing the operating cycle of the machine. The solidified casting and adhering shell mold halves are then removed by metal tongs or other appropriate means. As

a result of the breakdown of the thermosetting resin binder inthe mold, as hereinbefore described, the shakeoutv is readily accomplished, and the mold is ready for use ornsubsequent finishing operations.

Inasmuch as shell molds, if properly supported in the above-described manner during pouring of the molten casting metal, faithfully reproduce pattern details and maintain good dimensional tolerance, they can be used to provide cast metal parts with extremely thin section which can be cast to almost the precise dimensions ultimately desired. The resultant castings have unsuallv smooth and clean surfaces, true dimensions, and a minimum of fin at the mold parting line. These desirable qualities result from the unusual surface smoothness and excellent gas permeability of shell molds and their high rigidity when they are supported as hereinbefore described during metal pouring operations.

The surfaces of these castings are also free of residual mold material, thereby generally eliminating the necessity of shot blasting. Hence the use of shell molds which are properly supported in the above manner permits the production of sound precision castings in a variety of metals over a wide range of casting temperatures.

Various modifications in the arrangement and details of the embodiment of the invention described and shown herein will be apparent to those skilled in the art and are contemplated as within the scope of the present invention as defined in the claims appended hereto.

I claim:

1. An assembly of a shell mold and support therefor for use during metal pouring operations, said assembly comprising a base, a pair of mold-supporting plates mounted on said base, each of said plates being provided with a plurality of spatially separated projections of varying longitudinal extension with respect to the plane of said plate, a thin-walled shell mold formed of sand and thermosetting resin binder mounted on one of said plates against the projections on said plate, at least one of said plates being reciprocably mounted on said base and movable relative to the other of said plates so as to cause the projections on said plates to apply pressure to opposite exterior surfaces of said mold supported between said plates, and means associated with the plate on which said mold is mounted for maintaining said mold in position against the projections on said plate prior to contact between the other ofsaid plates and said mold.

2. An assembly of a shell mold and support therefor for use during metal pouring operations, said assembly comprising a base, a mold-supporting plate mounted on said base and provided with a plurality of spatially separated projections of varying longitudinal extension with respect to the general plane of said plate, a thin-walled shell mold mounted on said plate against said projections, a second mold-supporting plate reciprocably mounted on said base and movable into abutment with the exterior surface of said mold opposite said first-mentioned moldsupporting plate, and means associated with said firstmentioned mold-supporting plate for maintaining said mold in position against the projections on said plate prior to contact between said reciprocably mounted plate and said mold, said reciprocably mounted plate being similarly provided with a plurality of spatially separated mold-contacting projections of varying longitudinal extension with respect to the general plane of said reciprocably mounted plate.

References Cited in the file of this patent UNITED STATES PATENTS 633,872 Mackin Sept. 26, 1899 1,300,723 Gutmueller Apr. 15, 1919 1,321,812 Drumm Nov. 18, 1919 (Other references on following page) 7 UNITED STATES PATENTS Pettis -2 June 16,1925 Frantz Oct. 4, 1932 Baldwin May 12, 1936 Lannert Sept. 5, 19,39 Hagemeyer Jan. 9, 1940 Hagemeyer Apr. 23, 1940 8 2,476,374 Hodes July 19, 1949 2,651,822 Davis Sept. 15, 1953 2,660,770, Davis Dec. 1, 1953 OTHER REFERENCES Metal Industry, page 506, December 19, 1947.

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