US2305071A - Permanent mold - Google Patents

Description

Patented Dec. i5, 'i942 UNITED STATESI PATENT OFFICE PERMANENT HOLD Everett G. F

The lermold poration of Ohio ahlmaglnkeweoQOhioJldgnerto cilmumclevelaniohlmeoerapplication Februar-yin, 1941, sam N, :sans

(ci. ss-m) Claims.

This invention relates topermanent molds, and more particularly to molds of this character for the casting of metals having a high crystallisation shrinkage, such as aluminum and its alloys.

An object of the invention is to provide an improved mold, simple in design and construction, and inexpensive to manufacture, which facilitates the introduction of molten metal into the mold cavity in a smooth, continuous and uniform flow, so that the resulting casting has desirable physical properties and is substantially free from inclusions of air and other gases.

Another object is to provide a mold of this character in which the poured metal has its initial velocity arrested before flowing into the sprues which distributes the metal to the castma cavity.

A further object is to provide a mold having y one or more risers for holding metal in the molten state during solidication of the casting in which the pouring sprues are arranged so that metal introduced into the casting cavity heats the walls of the risers so that the metal retained therein after completion of the pouring of the casting solidifles subsequently to the solidiiication of the metal ofthe casting,

A still further object is to provide a mold for the casting of metallic articles in which the quantity of metal in the sprues, gates and risers is minimized, so that there is a larger proportion of metal in the finished casting with respect to the amount of scrap to be trimmed and remelted, and which produces a casting having the sprues, gates and risers so positioned as to facilitate their removal and the trimming of the rough casting.

More speciiicalLv, the invention provides a mold for the casting of hollow, cup-shaped articles having a relatively-#thick head section in a position such that the opening of the cup is faced downwardly,

Other objects and advantages will become apparent from the following detailed description of the invention, which is illustrated as applied to the casting of a piston, such, for example, as an aluminum piston for use in an internal combustion engine. In the casting of this article it is desirable that the relatively thick section of metal at the head of the piston be uppermost in the mold, and that one or more risers be provided in communication with this thick section of metal to feed it during solidification. According to the present method the functions of pouring sprue and riser are advantageously combined after completion of the tokeepthexnetalintherisermolten untilsolidimation oi' the metal in the casting cavity is complete and to produce a casting which may be readily removed from the mold.

In the drawing: 1

Figure 1 is a perspective view, with parts removed and with parts broken away, of a permanent mold for casting an aluminum piston in an upright position;

Fig. 2 is s, fragmentary elevational view, in sectaken on the parting line of the mold, indicated at 2 2 of Fig. 1;

Pig. 3 is a fragmentary sectional view taken substantialivonthelmeJ-B ofFig.1; and

Fig. 4 is a fragmentary detail view, in perspective, illustrating the appearance of the scrap metal comprising the spruce and risers at the `topofthecasting,lndwhichistobetrimmed therefrom in iinishing the latter.

Referring to the drawing by numerals of reference, which indicate like parts in the several views, the mold comprises a pair of mating mold sections I and 2, which rest upon a mold base (not shown) in accordance with the usual practice in permanent mold foundries. These sections cooperatively denne a casting cavity 3 corresponding in shape to the outer surface or contour ofthe article or piston to be cast.

Indicated at 4 is a multi-part core. which extends upwardly through an aperture in the mold base and is positioned centrally in the cavity I. This core is constructed in accordance with standard practice, and mounted for vertical movement in the mold so that it may be retracted casting operation to release the casting. 'I'he mold sections i and 2 have faces i which meet lone another at a parting line l of the mold.

A plurality lof depressions are formed in the faces i of the mold .setiona above the casting cavity 8. When the nti'old is closed the depressions on one face cooperate with those on the opposing mold section face to denne a pair of risers I and I and a pouring chamber or distributing sprue il. The risers I and 8 are spaced apart from one another, and each has an opening of relatively large cross-sectional area at the top of the mold. From the top of the mold the risers cavity 3 through Ii in the top wall opposite margins l. 'I'his chamber has a mouth Il which opens upwardly through the top of the mold, and a closed, substantially spherical-shaped bottom l2, which, in the present instance, is disposed a short distance above the top wall I2 of the casting cavity, and separated therefrom by small portions of the faces 6, which form lands i6.

Each of the risers I and i communicates with the pouring chamber Il through a relatively narrow, elongated and vertically extending passage Il. These passages are formed by removal to a relatively slight depth of portions of the face t of one or both of the mold sections l and 1, positioned between the side Walls of the pouring chamber I and risers 8 and 9. As shown in Figs, 3 and 4, the width of the es Il is considerably less than the width of the risers I and I and the pouring chamber Il. However, the passages are of considerable depth and communicate with the pouring chamber il throughout the greater portion of its depth. If desired, the passag may extend to the top of the mold, thus forming a continuous opening across the top of the mold from anoutermarginal wall Il oftheriser toanouter marginal wall I9 of the riser l. The bottom of the passages Il are dened by portions of the land I6, which preferably has rounded upper margins 2| merging into a downwardly sloping.portion 22 extending to the openings il at the bottom of the risers 8 and 9. Preferably, the rounded upper margins ZI of the lands i8 are disposed above the level of the bottom II of the pouring chamber il, so that molten metal poured into the latter has its initial pouring velocity substantially arrested before nowing into the risers 8 and l.

`In operating the mold, the cavity 3 is prepared in accordance with usual permanent mold foundry practice and the sections I and Zbrought to a suitable operating temperature. With the mold sections together, so that their faces 8 meet at the parting line 1, and the core 4 properly positioned in the cavity I, molten metal is introduced into the pouring chamber II through its mouth i4 in the usual manner, such as by pouring from a ladle. The downward velocity of the poured metal is arrested'by the bottom wall l5 of the pouring chamber, and as the pouring continues molten metal ows sideways or radially from the pouring chamber through the passages Il over the bottom wall 2i thereof and the gradually sloping surface 22 into portions of the casting cavity through the openings il.

0n account of the bottom 2i of the passages Il being above the level of the bottom l5 of the pour- .ing chamber, the relatively high velocity of the metal being poured is checked by impact in the pouring chamber, so that the radial flow through the passages l1 is relatively smooth and even, and caused primarily by a differential in the height of the metal in the pouring chamber IB relative to the height of the metalin the passages I1 and risers l and I.

During the flow through the passages IIlthe molten metal is quieted and smoothed to eii'ect a ,more uniform how, and the turbulence present in that sound castings, having uniform and improved physical properties, are produced.

After the mold cavity 3 is filled, continuous pouring of molten metal into the pouring chamber il fills the latter and the risers 8 and i to provide relatively heavy sectioned bodies of metal 26 andiintherisersandilinasimilarheavysectioned body 2l in the pouring chamber il, which is connected to the portions 26 and 21 through the relatively thin-sectioned portions 2l in the passages il.

On account of the relatively thin sections of the metal forming the skirt 23 of the piston, and because this portion of the metal was that which was first introduced into the cavity and gave up considerable of its heat in flowing to the bottom of the casting cavity, it freezes or solidiiles before the relatively thick-sectioned head 24, so that there is a. progressive upward freezing of the metal in the casting cavity. Because ofthe relatively high crystallization shrinkage of metal, such as aluminum and its alloys, employed in the casting of pistons of the character contemplated by this invention, the relatively large body of metal indicated by the numerals 26 through 2l, and disposed in the risers and pouring chamber of the mold, is drawn upon to feed the shrinking metal in the casting chamber during the solidiiication of the piston.

In connection with this feeding of the casting from the risers during solidication, there is a feature of the present mold which is of particular advantage. During the flow of molten metal over the curved portion 22 at the bottom of each of the risers 8 and 8, and through the openings Il, the adjacent portions of the mold absorb considerable heat from the metal and become elevated in tem-Y perature. Accordingly, when the metal is substantially at the level indicated in Fig. 2, the mold surfaces surrounding the relatively thin section of metal, indicated at 30, through which the risers 8 and 8 communicate with the casting cavity, are at relatively high temperatures so that the probability of these portions of the metal freezing and preventing feeding of the casting by the risers during solidication of the former is minimized.Y

uniform height of molten metal in the pouring chamber l 0, produce a succession of castings under substantially identical conditions of time and rate of pour. Furthermore, on account of the variable capacity of the passages l1, the molder can. by alternately raising or lowering the effective height of the molten metal in the pouring chamber I0 during the pouring of a single casting, regulate the rate of feed of the molten metal into the cavity, as desired. As the height of metal in the pouring chamber lil increases, the

rate of iiow through the lpassages I1 likewise increases. Conversely, as the height of molten metal in the pouring chamber decreases, the rate of ow through the passages i1 proportionately decreases. This latter feature is utilized, for example, when it is desired to initially pour at a relatively slow rate during the lling of the lower portion of the casting cavity 3 which forms the skirt 23 of the piston. Thus, as the level of metal which gradually rises .uniformly in the casting cavity reaches the relatively thick sections at the head 24, it may be advantageous to increase the rate of flow and hasten the completion of the casting operation.

v On account of the relatively small surface area of the scrap metal in the rough casting produced in the above described mold, and which is represented by the portions of metal numbered 28 through 2l, the separation oi' the mold sections I and 2, after the setting of the metal, is accomplished with a minimum of effort. Also, these portions o1' scrap metal are a relatively small proportion of the total metal poured into the mold, on account of the elimination of long feeding sprues and the combining of the function of sprue and riser, thus effecting a substantial economy in scrap losses. Another economy is realized in trimming the rough castings. The relatively small section portions, indicated at Il, oi the risers 8 and I, which connect the risers to the top oi the piston head, need only be severed to separate the scrap metal from the cast article.

The method and mold of the present invention, illustrated in the drawing and described above, are given for purposes of illustration. They are subject to considerable variations and numerous modifications and alterations are contemplated and intended to be included within the Scopeyof the appended claims. V

What I claim is:

l. In a permanent mold having a cavity for casting cup shaped articles with their openings directed downwardly, a plurality of risers extending upwardly from gates into the cavity at substantially the outer periphery of the cavity and opening through the top of the mold, a pouring chamber formed in the lmold above the cavity and centrally disposed between the risers, said chamber also opening through the top of the mold and having a closed bottom, and narrow passages of greater height than width extending between the pouring chamber and the risers,

said passages each being of less width than the chamber and the risers and sutliciently narrow to retard the flow 'of molten metal from the pouring chamber into the risers whereby the poured metal accumulates in the pouring chamber durlng the pouring operation to a height substantially above the level of the metal in the risers.

2. In a permanent mold having a cavity for casting cup shaped articles with their openings' directed downwardly, a plurality o! risers extending upwardly from gates into the cavity at substantially the outer periphery of the' cavity and opening throughvthe top of the mold, a pouring chamber formed in the mold above the cavity and centrally disposed between the risers, said chamber also opening through the top of the mold and having a closed bottom,and narrow passages of greater height than width extending between the pouring chamber and the risers, said passages each being of less width than-the chamber and the risers and suiiiciently narrow to retard the flow of molten metal from the pouring chamber into the risers whereby the poured metal accumulates in the pouring chamber during the pouring operation to a height substantially above the level of the metal in the risers, the bottoms of the narrow passages being inclined downwardly in continuous runs substantially from the pouring chamber to the openings of the risers into theA top of the cavity whereby the molten metal ilowing intothe mold cavity is directed by the inclination o! the passages to now across said risers and gates to the outermost portions of the cavity.

3. In a permanent mold having a cavity for casting articles of high crystallization shrinkage metal, a riser extending upwardly from a gate into the cavity adiacent the periphery of the latter and opening upwardly through the top ot the mold, a pouring chamber formed in the mold above the cavity and to one side of the riser, said 4,chamber also opening 4through the top of the mold and having a closed bottom, and a narrow passage of greater height than width extending between the pouring chamber and the riser, said passage opening into the chamber through one side thereof and having a bottom inclined downwardly in a continuous run substantially from the pouring chamber to the gate into the top oi' the cavity whereby the molten metal flowing into the mold cavity is directed by the inclination of the passage to now across the riser and gate to the outermost portion of the cavity.

4. In a permanent mold having a cavity for casting articles of high crystallization shrinkage metal, a riser extending upwardly from a gate into the cavity and opening through the top o! the mold. a pouring chamber formed in the mold above the cavity and to one side of the riser, said chamber also o'pening through the top of the mold and having a closed bottom, and a narrow passage ot greater height than width extending between the pouring chamber and the riser, said i passage opening into the sides of the chamber and the riser and being of less width than the chamber and the riser to retard the flow of molten metal from the chamber into the riser,

Y' the top of said passage opening through the top oi' the mold to provide a continuous mold opening across the tops oi' the pouring chamber, nowretarding passage and riser for continuous visual observation of molten metal poured into the chamber and flowing thence into the riser through the narrow passage, said retarding o! the ilow by the narrow passage effecting an aocumulation of molten metal in the pouring chamber and a. variation in the height oi' metal flowing in the narrow passage which varies directly with the rate of pouring into said chamber.

5. A permanent mold for casting a substantially cylindrical piston comprising metal mold sections cooperatively formed to provide a piston defining cavity in which' the longitudinal axis of the piston is vertical and the head portion of the piston is uppermost, said sections having meeting faces above the cavity cooperatively formed to provide an open'top pouring chamber having I a closed bottom disposed directly above the head forming portion of the cavity and at least one riser spaced laterally from the pouring chamber above the head forming portion of the cavity and communicating with the upper part of the cavity to feed metal directly into the head forming portion of the cavity, a relatively narrow passage oi greater height than width extending between the pouring chamber and the riser and opening into the chamber through one side of the latter to eiiect a change of direction in the flow of metal poured into the mold from substantially vertical in the chamber to substantially horizontal in the passage, and said passage being of less width than the pouring chamber and the riser to retard the now of molten metal from the pouring chamber into the riser, the location of the pouring chamber, riser, and passage serving to maintain the e, reservoir for a. body of molten metal directly above the head of e, cast pieton to supply heat directiy to the piston heed by conduction during freezing of the casting and to feed the head thereby compensating for crystallization shrinkege.

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