US2181157A - Method and apparatus for pressure casting - Google Patents

Description

Nov. 28, 1939. J. N. SMITH METHOD AND APPARATUS FOR PRESSURE CASTING Filed Nov. 16, 1938 4 Sheets-Sheet l EXHAUST r0 HIGH PRESSURE 22 FLU/D \SOURCE T0 PNEUMATIC PREJ'SURE SOURCE INVENTOR. James N. \SMITH.

ATTORNEY.

Nov. 28, 1939. J. N. SMITH 2.18L

- METHOD AND APPARATUS FOR PRESSURE CASTING Filed Nov. 16, 1.938 4 Sheets-Sheet 2 INVENTOR. J/mas N. 6mm.

ATTORNEY.

Nov. 28, 1939. J N. SMITH METHOD AND APPARATUS FOR PRESSURE CASTING Filed Nov. 16, 1938 4 Sheets-Sheet 3 INVENTOR. J4Ms N. 8mm.

ATTORNEY.

Nov. 28, 1939. J Nv M T 2,181,157

METHOD AND APPARATUS FOR PRESSURE CASTING Filed Nov. 16, 1938 4 Sheets-Sheet 4 z F r ro- HYDRAULIC PRESSURE some:

INVENTOR.

034m: A BY m ATTORNEX:

atcnted Nov. 28, 1939 mop AND Aiumin The invention relates to casting metals under or die casting as distinguished from sand mcastinacand'permanent mold casting. The meth- --od":and-i-ap'paratus herein di closed are useful in the pressure casting of aluminum, magnesium, -:'tin,z :zinc,s-lead, and the like. The invention is respecialiy applicable to the casting of the higher niieltiiigkp'ointmetals in this series, aluminum and aimagnesiumiiand will be described principally with referencez-to-the former. This application is a 'i 'continuation in-part of my application Serial No.

99,947,:filed-September 9, 1936.

Pressure castings of the type referred to in the u art as' die' castings generally are produced with machines failihgdnto one or the other of two genera-lclassesg known as the plunger and gooseas he latter is the conventional type astin'g aluminum and its alloys. Ma-

'tliis type utilize a trunnioned ladle or a niber shaped like a gooseneck arfo minersion in molten metal contained tand for movement into engage- =inlet port or gate of the mold.

3 hiriesf usually operate at pressures of ggg 'aboufi iiflo o' fioo pounds per'square inch, being I limited in this respect by the hazards attendant iip"""hiitidli" at higher pressures as well as cessive ostof higher compression. The

at pressure facts directly against the molten l t'a l inane charging chamber or gooseneck, and

- rapidly and forcibly injected -i'nto 1the :niol through a restricted gate opensing ca ting tli mietal with apparatus of this I "po -possesses recognized advantages over perg a5iliiiarieniimiold oasting .where the castings to be prhduce ofldntricate design, or have thin iot'ionsid musttha-ve a smooth surface or sharp definition zatatheediirners and edges, or must be heldii.:tii'icloseiedimensional tolerances, etc. An (important featureihfiithe pneumatic die casting hmethoii is? thaimaz estric-ted gate opening is emqiloyedethroufih whili the metal may be fed into 'ztliein'iol vityaswithxcontrolled flow, at a point adiacenti'c' portion of; the cavity which forms a tiiszithinawalledisectionbwhich is frequently desir- -ablei when theispiiue iseremoved from the casteihgitheieleanirigiahd finishing operations can be liperfoi'med rihore'i eiionoinically and satisfactorily wry ec'asonio-fsthezrestrictedfigate employed in the C60 -Iiastingsoperatioriisee :sgswihil'es did-L castings produced in the convensz-tional maiifiendiscussed above possess advantages aofsdehtmsup'iiacsstructui'e,:Jgood definition, the .zirapidityciwtthiwhich tfiy may be produced, and sii'esultaiiteiow coststhe heavier, sections of such IT sures PAT-ENToF'FicE APPARATUS CASTING "James imsmiui, Wcatficld, N. 1., llllmi' to son mssuaa um Company of America, Pittsburgh, Pa, a corporation of Pennsylvania Application November 18, 1938, Serial No. 240,713

1 Claims. (CI. 22-88) fill the mold cavity before the metal solidifies in any one portion of the cavity, the ca ting operation must be performed rapidly, the metal entering the die through the restricted gate athigh velocity. The flow of the metal through the restricted gate at this high velocity creates turbulence in the metal stream, trapping air in the walls of the casting and resulting in the forma-- tion ofblow holes. The provision of air'vents in the die is only partially effective in alleviating this condition.

(2) It is neces ary to apply a lubricant to the walls of the mold cavity to prevent adhesion of the molten metal. This lubricant vaporizes, and some of the vapor is trapped in the walls of the casting, resulting in the formation of blow holes.

(3) Since the mold acts as a chill, the metal in contact with the surfaces of the mold cavity and cores solidifies first, the metal farthest from these surfaces being the last to solidify. The metal shrinks as it solidifies which results in the formation of voids in those portions of the casting which are remote from the chill surfaces. Thus, while shrink spots are seldom present on the surface of a properly gated and vented die casting, they do occur in the central portions thereof.

A considerable amount of development work has been done in an effort to decrease the interior porosity of die castings produced in the manner described. Those who have attempted the solution of the problem have recognized that the amount of pressure used has a material effeet on the density of the cast metal, the density being increased as the pressure increases. The limitations upon the pressure which is practicable with the pneumatic or gooseneck type of machine have been pointed out hereinabove. Higherpressures are attainable in the type of machine which utilizes a mechanical pump submerged in a pot of molten metal, this pump consisting of a cylinder and piston arrangement in which the cylinder is provided with an inlet port located below the level of the metal in the pot and a passage leading into the gate of the mold. This type of machine usually produces metal pressures of 1,000 to 1,500 pounds per square inch, and is commonly used for low melting point metals, such as tin, lead, and zinc base alloys. It has not been found practicable for use with aluminum or other relatively high melting point die casting metals and alloys, because of the difllculties experienced with the cylinder and plunger when in contact with these metals at the higher casting temperatures. Some of these higher melting point alloys have a corrosive action on the pump, which is a disadvantage.

Other forms of apparatus have been devised for casting metals under the desired higher pressures. The most successful of these have employed a cylinder into which the metal is ladled and then forced into the mold by a plunger reciprocating in the cylinder. This form of apparatus likewise possesses serious disadvantages. It is expensive to operate because it is slow, and because of the necessity of ladling the metal into the cylinder by hand for each casting operation. Furthermore, it has been found that it is necessary to u e large gate and vent openings, the metal being in a pasty condition. These are expensive to remove from the casting, and leave objectionable blemishes- Another difficulty which has been encountered is that large or compiex-castings cannot be made, solidification occurring before the mold cavity is completely filled. Lastly, it has been found that heavy sections of the casting which are not in close proximity to the gate will be porous.

Thus, it will be seen that the methods and apparatuses which have been devised heretofore with view to obviating porosity in die castings in each case have either presented disadvantages of equally serious or more serious a character, or sacrificed advantages inherent in the more conventional die casting procedure. As has been noted, the latest attempt to devise a high-pressure casting machine with the object of decreasing porosity has resulted in a machine which sacrifices (1) the economy and speed of operation of the gooseneck type of machine, (2) the possibility of using restricted gate and vent openings, and (3) adaptability to the production of large and complex castings.

It is an object of my invention to provide a high-pressure die casting method and apparatus which retain the aforesaid advantages of the pneumatic or gooseneck type of machine, and yet make it possible to produce castings of decreased porosity. I aim to provide a die casting method which combines the advantages of pneumatic pressure casting (as performed with a gooseneck type of machine) with the principal advantages of applying a very high pressure to the cast metal (as accomplished with a high-pressure apparatus described hereinabove) I am aware that it has been proposed heretofore to inject metal into a mold at low velocity by gravity feeding, or by creating a vacuum in the mold, or by applying a small pressure behind the metal, and thereafter compressing the metal in the mold by means of a plunger, thus broadly disclosing the feeding of the metal into the mold by one means and compressing it by another. These, however, are merely modified permanent mold processes in which the metal fiows into the mold at low velocity through an unrestricted gate, and castings having thin-walled sections cannot be produced satisfactorily, while those which can do not possess the desirable characteristics of die castings as tosurface density, sharpness of definition, and so on. These proposals are not within the purview of my invention which has the more specific object of combining the step of introducing the metal at high velocity through arestricted gate with the subsequent step of applying pressure to the metal so introduced into the mold cavity. A more specific object of the invention resides in the provision of a method comprising the steps described in which the second step of applying additional pressure is so carried out as to act directly against a thick-walled portion of the casting.

Another object is to provide a method of producing a die or pressure casting having a thinwalled section and 'a thick-walled section which comprises injecting molten metal under pneumatic pressure through a restricted gate into a portion of the mold cavity which is to form a thin-walled section, and after the metal in the restricted gate freezes applying a substantially greater pressure directly to a thick-walled section of the cast metal. A further specific object is to provide apparatus which is adapted to coordinate the operation of the means for injecting the metal under pneumatic pressure and the means for applying additional pressure thereafter, rendering the operation of the last-named means automatic.

Other objects and advantages will appear upon consideration of the following description of the invention as read in conjunction with the drawings in which:

Fig. 1 is a vertical sectional view, taken as indicated by the line 1-1 in Fig. 2, showing apparatus suitable for carrying out my novel method, including a schematic representation of means for coordinating the two pressure-applying steps of the method; Fig. 2 is a vertical sectional view of a part of the apparatus shown in Fig. 1, taken at the plane of parting of the mold;

Fig. 3 is a vertical sectional view, similar to Fig. 1 and taken as indicated by the line III-III in Fig. 4, of another embodiment of the apparatus suitable for carrying out the method wherein core members are utilized in performing the second pressure-applying step; Fig. 4 is a vertical sectional view taken on the line IV-IV of Fig. 3; Fig. 5 is a horizontal sectional view taken on the line V-V of Fig. 4; and Fig. 6 is a vertical sectional view similar to Fig. 1, but showing the invention as applied to apparatus using different means for injecting the metal into the mold cavity.

According to my invention metal is injected forcibly and at high velocity through a restricted gate into a mold cavity. The use of a restricted gate is essential to the attainment of the advantages I have enumerated. A confined body of the molten metal is thus injected into the mold cavity under a pressure (preferably pneumatic) of not less than 250 pounds per square inch. Higher pressures may be employed up to about 600 pounds per square inch, or even higher in some cases, but I prefer to use a pressure of 500 pounds per square inch. The metal in the restricted gate is then allowed to freeze. (This normally requires but a fraction of a second.) Thereafter, but before the cast metal in the mold cavity has completely solidified, the cast metal is subjected to further pressure. This further pressure may be applied by any suitable apparatus, and should be applied directly to a portion of the cast metal the position of which is removed from the gate. Preferably it should be applied to a thick-walled section of the cast metal so as to insure feeding of the metal to the interior of the thick-walled section during solidification, thereby taking care of the shrinkage which occurs as the metal cools. The pressure applied in this step of the method should be on the order of 1,000 to 10,000 pounds per square inch, or greater. There are two aspects to the concept here involved: one is the injection of the metal at high velocity, followed by pressure feeding at a point removed from the gate, and the other is the injection of the metal at high velocity and under substantial pressure, followed by the application of a greater pressure to the cast metal.

I shall now describe one form of apparatus which is suitable for carrying out this method.

In Fig. 1 there is shown a furnace I in which is disposed a melting pot 2. Arranged in and above the melting pot 2 is a trunnioned ladle or pressure chamber 3 adapted for oscillation in the trunnion supports 4 alternately to submerge its nozzle 5 below the surface of the molten metal 6 in the melting pot 2, and then to bring the nozzle 5 into charging engagement with the gate of a mold. In the embodiment illustrated, the pressure chamber 3 is in the form of a conventional gooseneck, and its oscillation in the trunnion supports 4 may be accomplished by suitable actuating mechanism such as that represented generally by the reference numeral 1 and consisting of a cylinder and piston arrangement adapted for fluid operation and control.

The mold as represented comprises complementary metal dies 8, Sproviding therebetween a casting cavity l connected to an inlet port or gate H and to a riser l2 disposed adjacent a portion of the mold cavity which is to form a thick-walled portion of the casting and ate point removed from the gate ll. Dies 8, 9 are supported above the melting pot 2 in a position to register with the nozzle of the gooseneck 3, the fixed die 8 being secured to the stationary platen l3, and the movable die 9 being secured to the reciprocable platen l4 mounted on the rods l5 constituting a part of the main frame assembly of the casting unit. The opening and closing of the die may be accomplished through the hydraulic plunger l6.

Arranged in communication with the riser I2 is a high-pressure plunger ll adapted for hydraulic operation by means of the piston l8 and cylinder I9. The upper end of the gooseneck 3 is connected to a pneumatic pressure source 28, controlled by the operating valve 2|. The hydraulic cylinder I9 is in communication at either end with a high-pressure fluid source 22, controlled by the slide valve 23 which alternately admits the operating fluid to the upper and lower sides of the piston I 8. The slide valve 23 is arranged for operation by a piston 24 within the auxiliary cylinder 25, this auxiliary cylinder being in communication with the upper end of the gooseneck 3 through the pipe 26 and reducing valve 21. The slide valve 23 is arranged to be returned into its upper position in any convenient manner, as by the spring means 28 disposed between the piston 24 and the end of the auxiliary cylinder 25.

My novel method is performed in this embodiment of the apparatus as follows:

With the dies 8, 9 in the position shown in Fig. 1, the gooseneck 3 is lowered to submerge its nozzle 5 below the level of the molten metal 6 in the melting pot 2, whereupon it receives a charge of molten metal for delivery to the mold. The nozzle 5 is then brought into registry with the inlet port of the mold as shown. With the highpressure plunger ll withdrawn sufficiently to allow the metal access to the riser l2 (i. e., in the position shown in Fig. 1), the gooseneck operating valve 2| is opened to admit air into the pressure chamber above the charge of metal. The

pressure used musbe sufiiciently high to cause rapid injection of the metal into the casting cavity III; for aluminum, preferably at a pressure of about 500 pounds per square inch or between about 250 and 600 pounds per square inch. The application of pneumatic pressure is continued until the mold cavity l8 and riser l2 are filled. Thereafter, the slide valve 23 is brought into the position shown in Fig. 1 to admit the high-pressure operating fluid to the upper side of the piston l8, forcing the plunger ll downwardly against the metal in the riser l2 to feed metal into the aforesaid thick-walled section of the casting.

In the embodiment illustrated in Fig. 1, the slide valve 23 is actuated by pneumatic pressure in the charging chamber, acting through the reducing valve 21. I have found that the time lag produced by the interaction, of the air pressure in the chamber of thegooseneck 3 through the reducing valve 21, connecting pipes, auxiliary cylinder 25, slide valve 23, high-pressure cylinder l8, and plunger l1 ordinarily is suflicient to produce the desired timing, allowing the metal injected through the gooseneck 3 to fill completely the casting cavity l8 and riser l2 before the hydraulic plunger l1 comes down against the metal in the riser to feed and compress the metal during solidification. It will be understood, however, that suitable auxiliary mechanical or electrical delay means may be employed between the gooseneck 3'and auxiliary cylinder 25 in order to permit adjustment of the time interval to suit any given set of casting conditions, thus'insuring that the hydraulic plunger is brought into operation at exactly the right moment, while retaining the feature of automatic operation of both the gooseneck and high-pressure plunger upon opening the single valve 2|. 'With proper timing, the highpressure plunger l'l exerts a compressing force directly against the metal in the riser l2 just as the metal in the restricted gate H of the mold 8, 8 freezes.

The dot-dash lines 29 in Fig. 1 indicate the lowermost position of the piston l8, and the dotdash lines 38 indicate its uppermost position. In the operation of a given casting cycle the actual movement of the piston I8 is much less than would be indicated by the limiting positions 23 and 30. The intermediate or full line position and lowermost osition for a given casting cycle are determined in accordance with the position of o 5116 casting cavity and connecting riser, and the size of the casting cavity. The uppermost position 30 of the piston l8 should be high enough to allow the lower end of the plunger IT to clear the top of the mold 8, 9, thus to permit ready cleaning of the mold and make it convenient to change dies.

It isnot always necessary that a riserin the ordinary meaning of the term-be employed. The principal advantages of my invention may be attained with a construction in which the final high pressure is applied through the medium of a movable core. Such a modification is illustrated in Figs, 3-5, in which, to avoid duplication, the furnace, melting pot, gooseneck, and valve mechanism have been omitted. The die sections 3i, 32 provide therebetween a casting cavity 33, into which project core members 34. At the top of the casting cavity 33, and adjacent a portion thereof which is to form a thick-walled section of the casting 40, there is provided a large retractable core 35. Core 35 extends upwardly through a supporting member 36 mounted above the mold. Rigidly secured to the supporting member 38 by means of tie rods 31 is a hydraulic cylinder l9' corresponding to the cylinder I 3 of Figs. 1 and 2. The casting cavity 33 is fed through-the gate 38 and restricted opening 39.

The operation of this embodiment of the apparatus is the same as that described in connection with Figs. 1 and 2. At the beginning of the casting cycle, the core or plunger is withdrawn a predetermined amount from the position shown in the drawings, so that the metal injected into the casting cavity 33 initially fills up the heavy section 40 of the casting cavity. Immediately this has occurred and the metal in the restricted gate 39 freezes, the core 35 is forced downwardly into the heavy section 40, compressing the metal therein to feed it into the casting cavity 33 during solidification of the casting. The extent to which the core 35 should be withdrawn at the beginning of the casting cycle is determined in accordance with the size and shape of the casting which is to be produced, and also in accordance with the amount of solidification shrinkage which is to be expected, as determined from practice. The core 35 is demountable from the hydraulic cylinder and plunger l9 so as to permit cores of other sizes and shapes to be substituted as may be desired in accordance with the form of the casting to be produced. The core 35 serves to simultaneously form a core impression in the casting and exert a substantially greater pressure on the cast metal, maintaining this greater pressure during solidification of the casting.

Although the invention has been illustrated in Figs. 1-5 as applied to the pneumatic type of die casting machine, and is particularly applicable to such machines, the invention may also be utilized advantageously in die casting machines in which the molten metal is forced into the mold by means other than pneumatic pressure.

' Such a modification is illustrated in Fig. 6, which is similar to Fig. 1 except that the gooseneck and other apparatus for forcing the molten metal into the mold cavity have been replaced by a cylinder and a hydraulically operated pressure plunger. In this modification the die sections 4| and 42 form the casting cavity 43 at the'top of which is a riser 44, positioned adjacent to a portion of the mold cavity which is adapted to form a thickwalled portion of the casting. The fixed die 41 is secured to the stationary platen 45, and the movable die 42 is secured to the reciprocable platen 43.. The casting cavity 43 is connected to a gate 41 which communicates with the orifice 43 in the fixed die 4|, which orifice is in registration with the bore of the cylinder 49. The cylinder 49 is secured to the platen and is provided with an opening 50 through which a charge of molten metal may be poured into the cylinder. The pressure plungerv 5i is mounted for reciprocation in the cylinder 49 and is adapted to be actuated by means of the hydraulic cylinder 52 and piston 53, the hydraulic cylinder 52 being in communication with a hydraulic pressure source 54 controlled by the operating valve 55. A high-pressure plunger 56 is mounted in communication with the riser 44. The hydraulic pressure source 54 is in communication, by means of a pipe 51 and the reducing valve 58, with the auxiliary cylinder 59. The slide valve 60 controls the hydraulic operation of the plunger 56 in the same manner as has been described with reference to Fig. 1, for which reason a description of the mechanism involved is not repeated.

In this modification my method is performed as follows:

With the high-pressure plunger 56 withdrawn a predetermined amount so as to allow the molten metal being cast to have access to the riser 44, and with the plunger H in a retracted position, a charge of molten metal is poured into the cylinder .49. While the metal in the cylinder is still molten, the operatingvalve. 55 is opened to admit fluid into the hydraulic cylinder 52. The pressure used may be much higher than that ordinarily used in pneumatic machines; for most purposes a pressure of between 2,000 and 10,000 pounds per square inch is sufficient. The movement of the piston 53 forces the plunger 5| to move forward and inject the molten metal into the casting cavity 43 and riser 44. When this has occurred and the metal in the gate 41 solidifies, the high-pressure plunger 56 is forced downwardly into the riser 44 by reason of the operation of thevalve mechanism '60, forcing the metal from the riser into the casting cavity and compressing the metal. In this modification the pressure applied by the high-pressure plunger 53 should be substantially greater than that applied by the plunger 5| in order to obtaina denser and less porous casting than would otherwise resuit.

The modification of the invention described with reference to Figs. 3-5, in which the highpressure plunger acts as a core, is, of course, adaptable to the modification which is described with reference to Fig. 6.

The embodiments which have been described are adapted to the performance of a casting cycle in which the metal is injected into the mold through a restricted gate at high velocity by the application of pressure directly to a confined body of metal, followed by the application of a substantially greater pressure at a point closely adjacent a thick-walled section of the cast metal, to feed metal thereinto during solidification of the casting. Castings can be produced in accordance with my invention which have the characteristic thin-walled sections and intricate design found only in die castings, yet with greatly decreased porosity over die castings produced in accordance with methods heretofore known. The castings have a smooth surface, sharp definition at the corners and edges, and can be held to close dimensional tolerances. The combination of these well known advantages with the speed of operation common to conventional die casting practice and the improved interior metal structure characterized by greatly decreased porosity can be achieved by following the method I have outlined, as performed with the apparatus described in connections with the specific embodiments.

The term molten metal as used throughout" the specification and claims is intended to include metal in what is sometimes referred to as a pasty" condition, 1. e., the condition obtaining when the metal is very close to its melting point. My invention has been described herein with reference to specific and preferred embodiments in order that it may be fully understood. It will.

adapted for application to center-gated as well as edge-gated molds.

I claim:

1. Method of making castings having a thinwalled section and a thick-walled section which comprises injecting molten metal into a metallic mold through a restricted gate by applying pneumatic pressure directly to a confined body of the molten metal, continuing the application of pneumatic pressure until the mold cavity is filled, sealing the gate by solidification of the metal therein, and thereafter applying a substantially greater pressure at a point closely adjacent a thickwalled section of the castmetalto feed metal thereinto during solidification of the casting.

2. Method of pressure casting which comprises injecting molten metal through a restricted gate into a metallic mold by applying pneumatic pressure directlyto a confined body of the molten metal, continuing the a plication of pneumatic pressure until the mold cavity and a connecting riser are filled, sealing the gate by freezing of the metal therein, and after the metal in the restricted gate begins to freeze applying a'substantially greater pressure to the metal in the mold cavity by a compressing force acting directly against the metal in said riser.

3. Method of pressure casting which comprises injecting molten metal through a restricted gate into a metallic mold by applying pneumatic pressure directly to a confined body of the molten metal, continuing the application of pneumatic pressure until the mold cavity is filled, sealing the gate by freezing of the metal therein, and after the metal in the restricted gate begins to freeze forcing a core member into the cast metal in the mold cavity to simultaneously form a core impression in and exert 'a substantially greater pressure on said cast metal, and maintaining said greater pressure through the force applied to said core member during solidification of the casting.

4. Method of making castings having a thinwalled section and a thick-walled section which comprises injecting molten metal into a metallic mold through a restricted gate by applying pneumatic pressure directly to a confined body of the molten metal, continuing the application of pneumatic pressure until the mold cavity and a riser directly connected to a portion of the mold which forms a thick-walled section are filled, sealing the gate by freezing of themetal therein, and after the metal in the restricted gate begins to freeze applying a substantially greater pressure to the metal in the mold cavity by a compressing force acting directly against the metal in said riser to feed metal back into said thick-walled section during solidification of the casting.

5. Method of making castings having a thinwalled section and a thick-walled section which comprises injecting molten metal into a metallic mold through a restricted gate by applying pneumatic pressure directly to a confined body of the molten metal, continuing the application of pneumatic pressure until the mold cavity is filled, sealing the gate by freezing of the metal therein, and after the metal in the restricted gate begins to freeze forcing a core member into a thickwalled section of the cast metal to simultaneously form a core impression in said thick-walled section and exert a substantially greater pressure on said cast metal, and maintaining said greater pressure through the force applied to said core member during solidification of the casting.

6. Method of pressure casting which comprises injecting molten metal into a metallic mold through a gate by applying directly to a confined body of the molten metal a pressure of 250 to 600 pounds per square inch, sealing the gate by solidification of the metal therein; and during the solidification of the metal so cast in the mold applying thereto a pressure of at least 1,000 pounds per square inch.

7. Method of making castings having a thinwalled section and a thick-walled section which comprises injecting molten metal into a metallic mold through a restricted gate by'applying pressure directly to a confined body of the molten metal, continuing the application of such pressure until the mold cavity is filled, sealing the gate by solidification of the metal therein, and thereafter applying a substantially greater pressure at a point closely adjacent a thick-walled section of the cast metal to feed metal thereinto during solidification of the casting.

a. Method of making castings having a thin-' walled section and a thick-walled section which comprises injecting molten metal into a metallic mold through a gate by applying pressure directly to a confined body of the molten metal, continuing the application of such pressure until the mold cavity is filled, sealing off a thick-walled section of the cast metal by solidification of the metal in a thin-walled section of the cast metal arranged between the said thick-walled section and the gate, and thereafter applying a substantially greater pressure to said thick-walled section to feed metal thereinto during solidification of the casting.

9. Apparatus for the pressure casting of metal comprising a a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, an inlet for molten metal, said inlet being connected to the cavity by a restricted gate, a feeder directly connected to said second-named portion by an unrestricted opening, said unrestricted opening being substantially larger than said restricted gate, means for rapidly introducing molten metal under pneumatic pressure acting directly thereagainst, and means for applying pressure to the metal in said feeder, said restricted gate having a cross-sectional dimension substantially smaller than. the greatest cross-sectional dimension of the said second-named portion of the casting cavity, whereby the molten metal first solidifies within the restricted gate.

10. Apparatus for the pressure casting of metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, an inlet for molten metal, said inlet being connected to the cavity by a restricted gate, means for rapidly introducing molten metal through said inlet and gate into said cavity, said means including pneumatic pressure arranged to act directly against the molten metal, and means including a core member arranged for reciprocatory movement in said second-named portion to apply pressure to the cast metal during solidification thereof, said restricted gate having a cross-sectional dimension substantially smaller than the greatest cross-sectional dimension of the said second-named portion of the casting cavity, whereby the molten metal first solidifies within the restricted gate.

11. Apparatus for the pressure casting of metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a. thin-walled section and whereby molten metal first solidifies within the restricted gate, means for rapidly introducing molten metal through said inlet and gate into said cavity, said means including pneumatic pressure arranged to act directly against the molten metal, and means connected to said secondnamed portion of the casting cavity for applying pressure to the cast metal during solidification thereof, said last-named means including a valve mechanism operated by'pressure passing through a pressure conduit in direct communication with the pneumatic pressure of said first-mentioned means, whereby the last-mentioned means may be brought into operation automatically.

12. Apparatus for the pressure casting oi! metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, an inlet for molten metal, said inlet being connected to the first-named portion of the cavity by a restricted gate having a cross-sectional dimension substantially smaller than the greatest cross-sectional dimension of the second-named portion of the casting cavity, whereby molten metal first solidifies within the restricted gate, means for rapidly introducing molten metal through said inlet and gate into said cavity, said means including pneumatic pressure arranged to act directly against the molten metal, means connected to said second-named portion of the casting cavity for applying pressure to the cast metal therein during solidification thereof, said last-named means including a valve mechanism operated by pressure passing through a pressure conduit in direct communication with the pneumatic pressure of said first-mentioned means, and adjustable means for delaying the operation of said valve mechanism, whereby the application of the final pressure to the .cast metal may be effected automatically after a predeterminable time interval has elapsed following the application of said pneumatic pressure.

13. Apparatus for the pressure casting of metal comprising a mold with a casting cavity, a pneumatic pressure charging chamber, a pressure plunger communicating with said casting cavity, and means for controlling movement of said pressure plunger including a valve mechanism directly operated by pneumatic pressure passing through a pressure conduit in direct communication with the pneumatic pressure in said charging chamber.

14. Apparatus for the pressure casting of metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, a gate for molten metal, means for introducing molten metal through said gate into said cavity, and means connected to said second-named portion for applying pressure to the cast metal at a point removed from said gate during solidification of the metal, said gate having a cross-sectional dimension substantially smaller than the greatest cross-sectional dimension of the said second-named portion ot the casting cavity, whereby the molten metal first solidifies within the gate.

15. Apparatus for the pressure casting of metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, a gate for molten metal, means for introducing molten metal through said gate into said cavity, and means connected to said second-named portion for applying pressure to the cast metal at a point removed from said gate during solidification of the metal, a portion of the casting cavity adapted to the formation of a, thin-walled section being arranged between said gate and the point where said pressure is applied and having a cross-sectional dimension substantially smaller than the greatest cross-sectional dimension of the portion of the casting cavity where said pressure is applied.

16. Apparatus for the pressure casting of metal comprising a metallic mold having a casting cavity therein, said cavity having a portion adapted to the formation of a thin-walled section and another portion adapted to the formation of a thick-walled section, agate for molten metal, means for introducing molten metal through said gate into said cavity, said means including a cylinder and a plunger reciprocable therein, and means connected to said second-named portion for applying pressure to the cast metal at a point removed from said gate during solidification of the metal, said gate having a cross-sectional dimension substantially smaller than the greatest cross-sectional dimension of the said secondnamed portion of the casting cavity, whereby the molten metal first solidifies within the gate.

JAMES N. SMITH.

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