COUNTERGRAVITY CASTING APPARATUS

Abstract: Apparatus for the vacuum, countergravity casting of metal in shell moulds including a gas-permeable shell mould (6) secured to a mouth of a vacuum box (22) by a plurality of keepers (28) on the ends of rotatable shafts (34) reciprocably slidable through a ceiling (32) of the vacuum box (22), which keepers (28) are adapted for insertion into and rotation within respective anchoring cavities (26) in the mould (6) such that each keeper (28) engages a portion (40) of the mould (6) overhanging the respective cavity (26) to secure the mould (6) to the box (22).

Description: This invention relates to apparatus for the vacuum, countergravity casting of metal in gas-permeable, shell moulds as specified in the preamble of claim 1, for example as disclosed in US-A-4,616,691, and, more particularly, to means for anchoring the mould to the vacuum chamber used therewith. Background of the Invention The vacuum, countergravity, shell mould casting process is particularly useful in the making of thin-walled castings and involves: sealing a bottom-gated mould, having a gas-permeable upper portion, to the mouth of a vacuum chamber such that the chamber confronts the upper portion; immersing the underside of the mould in an underlying melt; and evacuating the chamber to draw melt up into the mould through one or more gates in the underside thereof. Such a process is shown in United States patent 4,340,108 wherein the mould comprises a resin-bonded-sand shell having an upper cope portion and a lower drag portion sealingly bonded together and attached to the vacuum chamber by means of spring clips which engage a peripheral abutment on the outside of the vacuum chamber. United States patent 4,340,108 seals the mould to the vacuum chamber on top of the cope such that the parting line between the mould halves lies outside the vacuum chamber. United States patent 4,632,171 seals the mould to the vacuum chamber on top of the drag such that the parting line between the cope and drag falls within the vacuum chamber. United States patent 4,632,171 uses spring-biased bolts engaging the underside of the drag and extending along the outside of the vacuum chamber to secure the mould to the vacuum chamber. The heads of the bolts are immersed in the melt and accordingly have a very short useful life. G.D. Chandley, "Automatic Counter Gravity Casting of Shell Moulds", Modern Casting, October 1983 pages 29-31, describes a technique for mounting round moulds to a round vacuum chamber wherein the inside surface of the vacuum chamber includes self-tapping threads which screw into the periphery of the round mould. The latter technique has been restricted to relatively small moulds and cannot be used with moulds which are rectangular or have other than a round exterior. United States patent 4,658,880 describes the use of shafts having self-tapping threads on the ends thereof engaging the mould inside the vacuum chamber. It is an object of the present invention to provide apparatus for the vacuum, countergravity casting of shell moulds including improved means for quickly, simply, and reliably mounting the shell mould to the mouth of the vacuum box regardless of the shape or size of the mould and the vacuum chamber. This and other objects and advantages of the present invention will become more readily apparent from the detailed description thereof which follows. Brief Description of the Invention An apparatus for the vacuum countergravity casting of molten metal according to the present invention is characterised by the features specified in the characterising portion of claim 1. The invention comprehends an improved vacuum, countergravity casting apparatus including: a mould having a porous, gas-permeable upper shell and a bottom-gated lower portion secured to the upper shell; a vacuum box defining a chamber confronting the upper shell for evacuating the mould through the shell, which box comprises a peripheral wall having a lip on the underside thereof for sealingly engaging the mould and a ceiling overlying the mould; a plurality of anchoring cavities recessed in the mould, each of which is defined in part by at least one shelf-like, overhang portion(s) of the mould overlying the anchoring cavity; an opening in the mould contiguous the overhang providing access to the anchoring cavity; and anchoring means reciprocably slidable through the ceiling of the box, which anchoring means comprises (1) a plurality of shafts extending through the ceiling of the box, (2) a keeper on the lower end(s) of each shaft adapted for insertion through the opening(s) in the mould and into the cavity(s) and rotation therein to engage the underside(s) of the overhang portion(s), and (3) a means for rotating each shaft and keeper into engagement/disengagement with the underside of the overhang for mounting and demounting the mould to/from the vacuum box. The anchoring cavity is preferably defined by two overhang portions which flank the access opening to the cavity. The keeper is preferably an elongated bar welded or otherwise secured to the lower end of the shaft midway on the bar so that, upon 90° rotation of the shaft, one half of the bar engages the underside of one of the overhangs and the other half of the bar engages the underside of the other overhang. All the shafts will preferably be appropriately mechanically linked or pneumatically/hydraulically coupled together for simultaneous/en masse rotation. The invention may better be understood when considered in the light of the following detailed description of certain specific embodiments thereof which is given hereafter in conjunction with the accompanying drawings. Brief Description of the Drawings Figures 1, 4 and 6 are partially-sectioned front or side (i.e., Figure 4) elevational views through different embodiments of vacuum, countergravity metal casting apparatus in accordance with the present invention; Figure 2 is a top view taken in the direction 2-2 of Figure 1; Figure 3 is an enlarged bottom view in the direction 3-3 of Figure 1; and Figure 5 is a top view in the direction 5-5 of Figure 4. Figure 7 is a partially sectioned elevational view of another embodiment of the present invention; Figure 8 is a top view in the direction 8-8 of Figure 7; and Figure 9 is an enlarged perspective view of one corner of the apparatus of Figure 7. Detailed Description of Specific Embodiments In the drawings, like reference numerals are used for like parts in all of the Figures. The several Figures show a pot 2 of metal melt 4 which is to be drawn up into a mould 6. The mould 6 includes a gas-permeable, upper portion 8 secured (e.g., glued) to a lower portion 10 along parting line 12 and a moulding cavity 16 therebetween. The lower portion 10 includes a plurality of ingates 14 on the underside thereof for supplying melt to the mould cavity 16 when the cavity is evacuated. The lower portion 10 of the mould 6 is sealed (i.e., via a high temperature gasket material 24) to a mouth 18 of a vacuum chamber 20 which is defined by vacuum box 22 such that the gas-permeable upper portion 8 of the mould 6 is contained within the chamber 20. The vacuum chamber 20 communicates with a vacuum source (not shown) via conduit 23. The upper (i.e., cope) portion 8 of the mould 6 comprises a gas-permeable material (e.g., resin-bonded-sand, or a ceramic, material) which permits gases to be withdrawn from the casting cavity 16 when a vacuum is established in the chamber 20. The lower portion 10 of the mould 6 may conveniently comprise the same material as the upper portion 8, or other materials, permeable or impermeable, which are compatible with the upper portion material. In accordance with one embodiment of the present invention (see Figures 1-3), a plurality of anchoring cavities 26 are provided in the mould 6 and are adapted to receive keepers 28 on the ends of anchoring means 30 (i.e., one at each corner of the mould 6) which extend through a ceiling 32 of the vacuum box 22. More specifically, each of the anchoring means 30 comprises an axially and rotatably movable shaft 34 having an elongated keeper bar 28 secured at about its centre onto the lower end of the shaft 34. The keeper bar 24 passes through an elongated, substantially complementary-shaped, access opening 36 to the cavity 26 in the mould 6. The opening 36 is flanked on both sides by portions 38 of the mould 6 which overhang and partially define the respective cavity 26. After insertion into the respective cavities 26, the keeper bars 28 are rotated under the overhang portions 38 to engage undersides 40 of the overhang portions 38. Alternatively, a single overhang and a keeper comprising a half-bar, as it were, secured at its end to the shaft 34 may also be used to engage a single overhang portion. However, the full bar keeper and dual overhang shown is preferred for providing the most reliable anchoring. In the embodiment shown in Figure 1, the several anchoring means 30 are each manually operated so as to mate with the several anchoring cavities 26 one at a time. To this end, a handle 42 is provided on the end of the shaft 34 opposite the keeper 28. The shaft 34 slides through an elongated bushing 44 welded to the ceiling 32 of the box 22 which serves not only to keep the shaft registered with the openings 36 but also to prevent any significant loss of vacuum from the chamber 20 along the shaft 34. Compression springs 46 are provided between the bushing 44 and the handle 42 to bias the mould 6 tightly against the mouth 18 of the box 22 after the keepers 28 have been inserted through the openings 36 into the respective cavities 26 and rotated under the overhanging ledges 38. In Figure 1, the anchoring means 30 on the left side of the drawing is shown in the anchoring position engaging the overhang portions 38 whilst on the right side of the drawing, the anchoring means 30 is shown positioned above the opening 36 prior to insertion therein. In accordance with the most preferred embodiment of the invention (see Figures 4 and 5), the several anchoring means 30 are all mechanically linked together by linkage means 50 adapted to engage/disengage the several keepers with/from the mould en masse. More specifically, linkage means 50 includes a frame comprising support members 52 secured to and carried by a tubular steel cross-member 54 via brackets 56. An air cylinder 58 is detachably secured (e.g., bolted) to the centre of the cross-member 54 via a mounting bar 60 to raise and lower the linkage means 50 as required to engage/disengage the keepers 28 from the mould 6. The shafts 34 are axially slidable through bushings 62 which are fitted for rotation in the ends 64 of the support members 52. Exterior splines 78 on each shaft 34 mate with interior splines (not shown) in the respective bushing 62 to allow axial movement of the shafts 34 yet still permit rotation of the shafts 34 when the bushings 62 are rotated as will be discussed hereafter. Yokes 66 include upper arms 68 fixed securely, but adjustably, to upper ends 70 of the respective shafts 34 and lower arms 72 which may be threaded onto threads 74 on the respective shafts 34. Compression springs 76 bias the yokes 66 upwardly relative to the supports 52 to hold the mould firmly, yet resiliently, in place in the chamber 20. Bushings 102 secured to the top of the box 22 permit the shafts 34 to slide axially therethrough as well as rotate therein without substantially reducing the vacuum in the chamber 20. When the mould 6 is to be secured in chamber 20, the air cylinder 58 is energized to extend the rod 59 to as to move the support members 52 downwardly which in turn push on the lower arms 72 of the yokes 66. This causes the shafts 34 to slide axially in the bushings 102 to insert the keepers 28 in the respective openings 36 above the cavities 26. Toggles 90 and 92 and lever arms 98 and 100 are rigidly secured to the respective bushings 62 so as to effect rotation thereof when the toggles 90, 92 are moved. Thereafter, an air cylinder 80, which is rigidly anchored to the cross member 54 via support arm 82, is energized to retract a cylinder rod 84. As the rod 84 moves to the left (see Figure 5), link 86 which is attached thereto at joint 88 also moves to the left and causes the toggles 90 and 92 to rotate clockwise 90°. At the same time, shorter links 94 and 96, which are rotatably coupled to the toggles 90 and 92, act on lever arms 98 and 100 to also rotate them through 90°. Once the keepers 28 have been rotated into their respective anchoring positions, air cylinder 58 is retracted causing the anchoring means 30 to firmly, but resiliently (i.e., against the springs 76), hold the mould 6 in place in the chamber 20. Figure 6 depicts still another embodiment of the present invention wherein individual air motors 110 on the upper ends of each of the shafts 34 are actuated substantially simultaneously from a common air source (not shown) to both insert the keepers 28 in the anchoring cavities 26 as well as rotate them therein for anchoring the mould in the chamber 20. In this embodiment and unlike Figure 1, the keepers 28 engage cavities 26 formed in upstanding portions 112 formed on a drag portion 114 of the mould 6. Caps 116 having keeper-receiving openings 118 therein are glued or otherwise secured on top of the upstanding portions 112 to provide the requisite cavity overhanging portions needed to engage the keepers 28. Figures 7 and 8 depict another embodiment of the present invention wherein the means for anchoring the mould to the vacuum chamber lie on the outside of (i.e., outboard) the chamber, the anchoring cavities are formed from the underside of the bottom portion of the mould and the mouth of the anchoring cavity (i.e., where it opens to the underside of the mould) is plugged with mould material or similar material to protect the keeper from the deleterious effects of the melt when the mould is immersed therein. More specifically, the Figures shown a lower portion 120 of the mould secured to an octagonal vacuum chamber 122 and immersed in the melt 4 in the pot 2. The lower portion 120 includes four towers 124 extending upwardly from the corners of the mould for housing anchoring cavities 126 which are formed in the towers 124 from the underside 128 of the lower mould portion 120. Forming the cavities from the underside of the mould simplifies the cavity-forming process and particularly eliminates the need for a separate cap such as cap 116 in Fig. 6. The mouth 130 of each cavity 126 where it opens to the underside of the mould 128 is preferably closed-off with a plug of mould material 132 to protect a respective keeper 134 from contacting the melt 4. An upstanding levee 136 circumscribes the junction between the chamber 122 and the lower portion 120 of the mould to protect the junction from the melt as described and claimed in U.S. patent 4,745,962. In the embodiment shown in Figures 7-9, the anchoring means 30 is adapted to engage the bottom portion 120 of the mould on the outside of the vacuum chamber 122. More specifically, shafts 138 of the anchoring means 30 reciprocate and rotate in ball-bushings 140 and guide rings 142 which stabilize and guide the shafts 138 and keepers 134 into respective openings 144 to the cavities 126. Flexible couplings (e.g., U-joints) 146 on the upper ends of the shafts 138 allow for any misalignment between the shafts 138 and the actuating means 148 and thereby serve to prevent binding of the shafts in the bushings 140 and/or guide rings 142. Rods 150 extend from the other end of each coupling 146 into engagement with the actuating means 148. External splines 152 engage internal splines in bushings 154 to allow axial movement of the rods 152 yet still permit rotation thereof when the bushings 154 are rotated. Upper springs 156 and lower springs 158 function as shock-absorbers and permit resilient engagement of the mould by the keepers 134 and thereby prevent such damage to the moulds as might otherwise occur were the components of the system too rigid and incapable of adjusting to variations in the mould. Locking collars 160 are movable up or down along the rods 150 to adjust the position of the keepers 134 and the degree of compression on the springs 156 and 158. The mechanism for simultaneously actuating the anchoring means 30 in Figures 7-9 is essentially the same as shown in Figures 4 and 5, in that toggles 90 and 92, lever arms 98 and 100 and links 94 and 96 therebetween move together to rotate the shafts 138 to engage and disengage the mould in the same manner as described above when the mechanism is lowered onto the mould by air cylinder 58 and the air cylinder 80 is actuated.

Claims: 1. Apparatus for the vacuum countergravity casting of molten metal (4) comprising: a mould (6) comprising a porous gas-permeable upper shell (8) at least in part defining a moulding cavity (16), and a bottom-gated lower portion (10;120) secured to said upper shell (8) for admitting said metal (4) into said cavity (16) from an underlying pot (2) of said metal (4); and a vacuum box (22;122) sealingly engaging said mould (6) and defining therewith a vacuum chamber (20) enclosing said upper shell (8) for evacuating said cavity (16) through said shell (8), said box (22;122) having a ceiling (32) overlying said mould (6); characterised in that the apparatus includes a plurality of anchoring cavities (26;126) recessed in said mould (6), each cavity being defined in part by at least one overhang portion (38) of said mould overlying said cavity; a plurality of openings (36;118;144) in said mould (6), each opening being contiguous a respective overhang portion (38) and providing access to the respective cavity (26;126); guide means (44;140,142) engaging said vacuum box (22;122); anchoring means (30) reciprocally slidable through said guide means (44;140,142) and said openings (36;118;144), for engaging said mould (6) so as to anchor said mould (6) in said chamber (20), said anchoring means (30) comprising a plurality of shafts (34,138) extending through said guide means (44;140,142) in registry with said openings (36;118; 144) and a keeper (28;134) on the lower end of each of said shafts (34;138) adapted for insertion into a respective cavity (26;126) through the opening (36;118;144) corresponding thereto and rotation therein to engage an underside (40) of the corresponding overhang portion (38); and rotator means (42;50;110) operatively associated with each of said shafts (34;138) for rotating the respective keeper (28;134) into engagement/disengagement with said underside (40) to respectively mount/dismount said mould (6) to/from said box (22;122). 2. Apparatus from the vacuum countergravity casting of molten metal (4) according to claim 1, characterised in that each of said shafts (34) of said anchoring means (30) extends through said ceiling (32) in registry with a respective one of said openings (36). 3. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 1 or 2, characterised in that each cavity (26,126) is defined by at least two overhang portions (38) of said mould (6), the corresponding opening (36;118;144) is flanked by said portions (38), and each keeper (28;134) is an elongated bar secured to the corresponding shaft (34;138) so as to engage the undersides (40) of both of said overhang portions (38) upon rotation of said keeper (28;134) to mount said mould (6) to said box (22;122). 4. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 1, 2 or 3, characterised in that said rotator means (50;110) substantially simultaneously rotates said shafts (34;138). 5. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 4, characterised in that said rotator means comprises mechanical linkage overlying said box (22;122) including toggle means (90,92) for effecting said rotation and a plurality of links (86,94,96,98,100) coupling said toggle means (90,92) together and to a motor (80) for engaging/disengaging said keepers (28;134) en masse. 6. Apparatus for the vacuum countergravity casting of molten metal (4) according to any one of the preceding claims, characterised in that the apparatus includes spring means (46;76;156) biasing said shafts (34;138) upwards with sufficient force to support and secure said mould (6) to said box (22;122) without breaking away said overhang portions (38). 7. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 4, characterised in that said rotator means comprises individual fluid motors (110) on top of each shaft (34). 8. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 1, characterised in that said anchoring cavities (126) are recessed in regions (124) of said lower portion (120) lying outboard said shell, each cavity (120) being defined in part by at least one overhang portion of said mould overlying said cavity (120); and the guide means (140,142) extend outboard said vacuum box (122) for guiding said anchoring means (30) through said openings (144). 9. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that said cavity (126) is defined by at least two overhang portions of said mould, said opening (144) is flanked by said portions, and said keeper (134) is an elongated bar secured to said shaft (138) so as to engage the undersides of both of said overhang portions upon rotation of said keeper (134) to mount said mould to said box (122). 10. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that the rotator means (50) includes means for substantially simultaneously rotating said shafts (138). 11. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 10, characterised in that said simultaneous rotating means comprises mechanical linkage overlying said box (122) including toggle means (90,92) for effecting said rotation and a plurality of links (94,96,98,100) coupling said toggle means (90,92) together and to a motor (80) for engaging/disengaging said keepers (134) en masse. 12. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that the apparatus includes spring means (156) biasing said shafts (138) upwards with sufficient force to support and secure said mould to said box (122) without breaking away said overhang portions. 13. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that the apparatus includes a flexible coupling (146) on each of said shafts (138) intermediate said rotator means (50) and the respective keeper (134) for preventing said shaft (138) from binding in said guide means (140,142). 14. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that each of said cavities (126) has a mouth (130) opening to the underside of said lower portion (10). 15. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that an upstanding levee means (136) joins said regions (124) one to the other so as to circumscribe a mouth of said chamber where it sealingly engages said mould and protects said chamber mouth from melt (4) during immersion of said lower portion (10) in the melt (4). 16. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 14, characterised in that a plug (132) fills said mouth (130) to shield said keeper (134) from melt (4) during filling of the mould. 17. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 8, characterised in that said anchoring cavities (126) reside in a plurality of towers (124) extending upwardly from said lower portion (10). 18. Apparatus for the vacuum countergravity casting of molten metal (4) according to claim 15, characterised in that said regions comprise towers (124) extending upwardly from said lower portion (10).

Inventors: MERCER, JAMES B., SCHAFFER, GREGORY A., SMITH, JAMES, JR., VOSS, KARL D.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: B22D18
IPC codes: B22D18