US3504733A - Die casting mold assembly - Google Patents

Description

lnveno r Loren W. Smith his Attorney L. W. SMITH DIE CASTING MOLD ASSEMBLY Filed May 2. 1966 April 7, 1970 FIG. 2

United States Patent O 3,504,733 DIE CASTING MOLD ASSEMBLY Loren W. Smith, Eggertsville, N Y., assiguor to Dresser Industries, Inc., a corporation of Delaware Continuation-impart of application Ser. No. 444,459,

Mar. 31, 1965. This application May 2, 1966, Ser.

Int. Cl. B22d 17/04, 39/00 U.S. Cl. 164-314 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to die casting and particularly to expendable metal mold assemblies for use therein. This application is a continuation-in-part of my copending application Ser. No. 444,459, filed Mar. 3l, 1965, now Patent No. 3,258,818, issued July 5, 1966.

Prior to the invention disclosed in the above application, it was universally thought essential to the cornmercial die casting of metals in metal molds that the molds be permanent and this has been the principal obstacle to the die casting of ferrous and other high melting metals. However, in that application there is disclosed a method by which even the high melting metals can be die cast commercially in metal molds and, most feasibly, in aluminum or like low melting metal molds. According to that method, a run of castings is cast in expendable, usually identical, metal molds, one of which is used and expended in each casting operation.

In die casting metals in the expendable metal molds of the above method, it is contemplated, following usual practice, to inject the molten metal under pressure into each mold from a charging cylinder containing a metered quantity of the metal suiiicient to fill the rnold. Any joint in the connection between the charging cylinder and the mold should of course be sealed against leakage of the liquid metal during the injection.

In conventional die casting in which the metal mold is permanent, this presents no particular problem, since such a joint can readily be sealed by a suitable bonding agent. The use of expendable metal molds, however, presents a very definite problem in this respect, as the need to remove and replace a mold at the end of each casting operation makes it impractical to have a bond between the charging cylinder and each mold. There too is the further problem in casting high melting metals in low melting metal molds that if a sprue and gate leading to the mold cavity are formed in the mold itself, the direct exposure of the mold metal thereabout to the heat of all of the liquid metal injected into the cavity, may well cause it to melt with consequent premature impairment of the molds integrity. It is with these problems that the present in- -vention is concerned.

The primary object of the present invention is to provide in apparatus for die casting metals in expendable metal molds, a mold assembly including for each casting operation the metal mold expended therein, wherein each expendable mold is so releasably connected to the charging cylinder by which liquid metal is injected under pressure into the mold that a joint therebetween will seal itself at the outset of the injection without interfering with subsequent removal of the mold.

Another object of the invention is to provide in apparatus for die casting high melting metals in expendable low melting molds, a mold assembly wherein a mold cavity in the mold expended in each casting operation is so connected to a charging cylinder by which it is filled under pressure with liquid metal as not only to render a joint therebetween self-sealing on injection of the metal without interfering with subsequent removal of the mold but also to prevent premature impairment of the integrity of the mold by the heat of the liquid metal as it is forced through a passage in the rnold to the mold cavity.

Other objects and advantages of the invention will appear hereinafter in the detailed description, be particularly pointed out in the appended claims and be illustrated in the accompanying drawings, in which:

FIGURE l is a longitudinal sectional view of apparatus for die casting metals in expendable metal molds incorporating a preferred embodiment of the improved mold assembly of the present invention; and

FIGURE 2 is an enlarged fragmentary view on the section of FIGURE l, showing in detail the connection between the mold and a charging cylinder.

Referring now in detail to the drawings in which like reference characters designate like parts, the improved mold assembly of the present invention is designed for use in die casting metals in expendable metal molds in accordance with the method of my copending application Ser. No. 444,459. The improved mold assembly includes for each casting operation an expendable metal mold 1 and a connection 2 between a cavity 3 in the mold and a charging cylinder 4 through which liquid metal is injected under pressure into the cavity. As in the method of my copending application, it is contemplated in this invention that a mold be expended in each casting operation. Consequently, while part of the connection 2 may be and preferably is permanent, the expendable mold 1 and any part of the connection attached or secured thereto will be temporary and replaced in the assembly after a singl' casting operation.

The die casting apparatus in which each expendable mold is mounted during the single casting operation in which it is expended, may be of any suitable type. Exemplifying such apparatus, the illustrated apparatus has a base 5 mounting a mold holder 6 having a pair of separable jaws, one 7, stationary and integral with or secured to the base. The other jaw 8 is movable and, if, as preferred, the mold holder 6 is horizontally separable, may be slidable or reciprocable on the base 5 and suitably guided in its movement therealong to maintain its longitudinal alignment with the fixed jaw 7. In the illustrated apparatus the jaws 7 and 8 are relatively reciprocated, to open for insertion and removal of an expendable mold 1 and close for applying clamping pressure to the mold during a casting operation, by a fluid-actuated piston 9 connected to and acting on the movable jaw.

Each expendable mold 1 may have one mold cavity 3 or a plurality of connected cavities, depending on the castings to be made in the particular run and, to facilitate removal of a casting, is split or divided into two parts 10, each removably seated or received during its casting operation in a seat or cavity 11 in one of the jaws and bounding or containing part of the mold cavity. Preferably chargeable or llable with liquid metal from the bottom or a side, with suitable vent holes (not shown) in the mold 1 for venting the air displaced by the liquid metal, the mold cavity 3 of the illustrated mold is chargeable from the side and the consequently horizontally disposed charging cylinder 4 conveniently is mounted on the base 5 on an opposite side of the stationary jaw 7 from the mold. The charging cylinder 4 contains a chamber 12 fed through a feed opening 13 and of a capacity to hold a charge of liquid metal sufficient to ll the mold cavity 3. In a casting operation the liquid metal, by actuation of a iiuid or otherwise suitably actuated plunger 14, is ejected under pressure from the chamber 12 and injected into the mold cavity 3 through a preferably cylindrical outlet nozzle or spout 15 forming part of the charging cylinder 3 and projecting from the chamber toward the mold 1.

The mold cavity 3 is connected to the charging cylinder 4 through an aperture 16 of cylindrical or other suitable cross-section, in and extending horizontally through the stationary jaw 7. While the backs 17 of both of the mold parts may be flush with the confronting faces 18 of the associated or related jaws 7 and 8, that of the mold part mounted in the stationary jaw preferably has a boss 19 projecting or outstanding therefrom and horizontally aligned with and of a cross-section to slideably tit or be received in the inner end of the aperture 16.

While the nozzle of the charging cylinder 4 may extend into the opposite end of the aperture 16, it is preferred that that end slideably tit or receive a stern 20 of a ceramic or other suitable heat-insulating annular collar or sleeve 21 having a head 22 fitting over the end of the nozzle and bearing against or abutting the presented back or outer surfaces 23 of the stationary jaw 7. An axial bore 24, extending through the nozzle 1S and collar 21, leads or connects inwardly to a passage or opening through a side of the mold, formed of a funnelshaped sprue 2S and a suitably cylindrical gate 26 of reduced cross-section relative to the bore, which opens inwardly onto the mold cavity 3.

Confined laterally or radially by the side wall 27 of the aperture 16 in the stationary jaw 7 in which they are seated, the boss 19 and collar stem 20 confront or face at their adjoining ends along a joint 28 bounded inwardly by the outer end 29 of the boss and outwardly by the inner end 30 of the stem. Even if, as preferred, the ceramic collar 21 is interposed between the mold 1 and charging cylinder 4, it ordinarily will have a long effective life and thus can be bonded or otherwise sealingly connected permanently to the nozzle 15 and with the nozzle form, as a permanent part of the connection 2 between the charging cylinder and the mold cavity 3 an axially bored conduit 2a attached or secured to the cylinder and extending to the joint 28 for directing liquid metal to the mold 1. However, no such expedient is available to seal the joint 28, as the removal and replacement of the expendable mold 1 after a single casting operation requires there to be a releasable connection between the mold and the collar 21. Nor is it desirable from the standpoint of preciseness of the castings, to resort to the sometimes proposed expedient of first partly or completely filling the mold by gravity with liquid metal and relying on surface freezing of the metal in the interventing interval to prevent leakage through a joint when the pressure is subsequently applied.

In this invention neither a preliminary gravity filling of the mold 1 nor a precision t between the confronting ends 29 and 30 of the boss 19 and collar stem 20, is depended on for sealing the joint 28. Instead, the joint is deliberately made accessible to liquid metal under pressure in the bore 24 in the collar 21 and the high heat conductivity of the metal of the mold 1 is used to cause any liquid metal entering the joint at the outset of the pressure injection to freeze or solidify substantially instantly or immediately on entry and, by forming a solid metal barrier against ingress of further liquid metal, seal the joint against leakage.

The above result is obtained by predetermining for the temperature and maximum volume containable in the joint 28 of the particular liquid metal being cast and the heat conductivity of the particular mold metal, the surface area of the mold required to freeze the metal and making the joint of such a contiguration and length from its inner end at the bore 24 to its periphery at the side wall 27 of the aperture 16 as to present that area of the mold to the liquid metal. On this basis the confronting ends 29 and 30 of the boss 19 and stem 20 not only need not contact or abut but desirably are slightly spaced so that the joint 28 is initially slightly open, to ensure that the liquid metal will enter and seal the joint at the outset of the injection rather than later.

As exemplary of a suitable self-sealing joint, the illustrated joint 28 between its radial extremities is nonlinear, bent or broken to provide a crooked or zigzag flow path for any entering liquid metal and correspondingly increase, over a radially flat or linear joint, the surface area of the mold 1 presented to the liquid metal. In its preferred form, the joint 28 has two angularly related legs, one, a conical inner or inlet leg 31 sloping or inclined outwardly away from the charging cylinder 4 and generally in the direction of flow of the liquid metal through the bore 24, and the other, a ilat or planar radial outer or outlet leg 32 extending to its periphery. This shape or conguration of the joint 28 is achieved by forming on the outer end 29 of the boss 19 inwardly of its side a central frusto-conical protuberance or convexity 33 containing the sprue 25 and in spaced relation fitting or received in or interiitting with a correspondingly frusto-conical socket or concavity 34 formed centrally in the inner end 30 of the stem 20 outwardly of or about the bore 24. Radially outwardly beyond the protuberance 33 and socket 34, the confronting ends 29 and 3i) are both radially fiat.

The bulk of the liquid metal ejected from the charging cylinder 4 in a pressure injection will be directed or deflected by the sprue 25 through the gate 26 into the mold cavity 3l As opposed to the relatively very small quantity diverted or flowing into and on freezing sealing the joint 28, the ybulk or main body of the liquid metal iiowing or injected into the mold cavity 3, is of such large volume, relative to the areas of the sprue 25 and gate 26 to which it is exposed, as to remain liquid until stopped in its ow by back pressure when the mold cavity 3 is full. Conversely, if the liquid metal is a high melting metal and the mold 1 made of aluminum or other low melting metal, the heat to which the surfaces of the sprue and gate are exposed as the liquid metal ows therethrough, is of such order as to make possible the melting of the part of the mold adjacent thereto. To avoid this possibility, the sprue 25 and gate 26 in such case can be lined with a heat resistant liner or funnel 35 made of the metal being cast or other suitable high melting metal or a suitable ceramic. Either will protect the surrounding part of the expendable mold 1 against premature melting or distortion, a ceramic liner by interposing itself as a heat insulator and a high melting metal liner by the usual abrupt drop in heat conductivity across the interface between it and the mold.

A last element of the mold assembly, unnecessary for a bottom injection but quite desirable for the illustrated side injection, is a controlled burst diaphragm 36 for preventing ow of liquid metal from the charging cylinder 4 into the mold cavity 3 before or prior to actuation of the plunger 14. Preferably made of a metal that will not melt on exposure to the heat of the liquid metal but will rupture or burst under the pressure applied to the liquid metal in an injection, the diaphragm 36, in this application, conveniently is a thin disc seated between the boss 19 and stem 20 in the socket 34 in the stern and closing the adjoining end of the bore 24 in advance of the joint 28. Since, like the mold 1, the diaphragm 36 is expended in a single casting operation, it is removed and replaced by a new one at the end of each operation.

Closed during a casting operation to clamp the mold parts 10 together, the jaws 7 and 8 of the mold holder 6 will be opened after an interval suilicient at least to ensure that the casting in the mold cavity 3 has frozen to shape. Thereupon, the mold 1 and casting will be removed, the former suitably for reuse 0f its metal and the latter for any necessary finishing operations, Joined 0r attached to the casting in the mold cavity 3 by the then frozen metal in the sprue 25 and gate 26, the frozen metal that sealed the joint 28 will be removed incident to the removal of the mold. While effectively sealing the joint 28 during the injection and now joined to the casting, the ring of frozen metal formed in the joint will usually not adhere to the end 30 of the stem 20. However, if there is any likelihood of interference with removal of the mold 1 Iby such adherence, it can readily be avoided by applying a suitable releasing agent to the stems end 30 before placement of the next mold.

From the above detailed description it will be apparent that there has been provided an improved die casting mold assembly which, by having a self-sealing joint in its connection to a charging cylinder, enables that connection to be releasable without permitting liquid metal to leak through the joint during its pressure injection into the mold. It should be understood that the described and disclosed embodiment is merely exemplary of the invention and that all modifications are intended to `be included that do not depart from the spirit of the invention and the scope of the appended claims.

Having described my invention, I claim:

1. In die casting apparatus having a permanent mold holder and a permanent charging cylinder for injecting liquid metal under pressure into a mold, said cylinder being iixedly positioned relative to said holder during both said injection and subsequent removal of said mold, a mold assembly comprising a metal mold held in said holder and expended in and removed after a single casting operation, conduit means attached tothe cylinder and during a casting operating releasably connected to said mold for directing a pressure injection of liquid metal from the cylinder into a mold cavity in said mold through an opening in a wall thereof, a joint about said opening between and coextensive with all confronting surfaces of said conduit means and mold wall, said joint at the outset of said pressure injection being unsealed and open to passage of liquid metal from said conduit means, and a surface on said mold wall bounding one side of said joint and of sufcient area to freeze any liquid metal forced into said joint at said outset and thereby alone seal said joint against leakage of liquid metal therethrough during said injection.

2. A mold assembly according to claim 1, including a bore leading from the charging cylinder to the joint, and wherein the joint has annularly related legs, and an inner of said legs has an inner end adjoining said bore and slopes outwardly therefrom generally in the direction of oW 0f the liquid metal therethrough,

3. A mold assembly according to claim 2, wherein the joint is initially open.

4. A mold assembly according to claim 1 including apertured means between the charging cylinder and mold, and a boss on the mold about the opening therein to the mold cavity, said boss and conduit means being received in opposite ends of an aperture in said apertured means and having ends confronting at the joint.

5. A mold assembly according to claim 4, wherein the conduit means include a ceramic collar sealingly bonded to the charging cylinder, the collar having thereon the end of the conduit means confronting the boss at the joint.

6. A mold assembly according to claim 1, wherein the expendable mold is low melting relative to the liquid metal cast therein, and including a liner lining the opening in the mold wall leading from the joint to the mold cavity and heat resistant to the liquid metal.

7. A mold assembly according to claim 6, wherein the liner is made of the metal being cast.

8. A mold assembly according to claim 6, wherein the joint is initially open.

9. A mold assembly according to claim 4, including a central protuberance on an end of the boss bounding the one side of the joint and about the passage to the mold cavity, said protuberance seating in spaced relation in a correspondingly configured socket in the confronting end of the conduit means about the bore therethrough, and a controlled burst diaphragm seated in said socket and closing the bore in advance of the joint prior to the pressure injection of the liquid metal.

References Cited UNITED STATES PATENTS 1,599,423 9/1926 Lee 249-110 1,940,173 12/1933 Korsrno 249-141 2,928,125 3/1960 Smucker et al. 18-30 3,266,099 8/1966 Bucy 164-305 X J. SPENCER OVERHOLSER, Primary Examiner V. RISING, Assistant Examiner U.S. Cl. X.R. 18-30; 164-69, 133, 337

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