US3238578A

US3238578A - Chill mold casting method

Info

Publication number: US3238578A
Application number: US460910A
Authority: US
Inventors: Reinemann Werner
Original assignee: Piel and Adey
Current assignee: Piel and Adey
Priority date: 1961-05-15
Filing date: 1965-06-03
Publication date: 1966-03-08
Anticipated expiration: 1983-03-08

Description

March 8, 1966 w. REINEMANN 3,238,578

CHILL MOLD CASTING METHOD Filed June 5, 1965 2 Sheets-Sheet l Fig.3

/5 3\ F' I I; l, 9

; Ill Ii INVENTOR WEfiA/EK QEl/V'MAAI/V March 8, 1966 w. REINEMANN 3,238,578

CHILL MOLD CASTING METHOD Filed June 5, 1965 2. Sheets-Sheet 2 F ig.4

4/ IN VENTOR 0,2mm BY ozgq wan/x United States Patent 6 Claims. (a. 22-200 This application is a continuation-in-part of my application Serial No. 194,337 filed May 14, 1962, now abandonecl.

The manufacture of cast parts by casting of heavy metals in chill molds involves difliculties that have called for special care and experience. As the specifications for cast articles become more and more exacting and greater demands are placed on chill mold casting especially as regards homogeneity, precision and shape, increased difiiculties arise, particularly in the casting of heavy metals, such as copper and copper alloys, which are subject to the formation of fissures and air occlusions in the cast parts so that a high scrap-to-finish product ratio results, and whereby the casting of complex parts is made all but impossible.

Although some defects may be prevented by suitable construction of the mold, and by skill in casting, many defects in this area are fundamentally caused less by the nature of chill mold casting than by the inherent properties of the material to be cast. This is particularly the case with respect to highly developed special materials. The defects are essentially attributable to differences of wall thickness, shrinkage strains and to the occurrence of occlusions of air residues trapped by the material flowing into the chill mold.

In flat cast parts having a large surface area, as Well as in closed, casing-like castings, the shrinkage strains that occur during cooling of the metal are particularly destructive. These strains create much difficulty inasmuch as the casting contracting during the cooling stage cannot freely shrink in the chill mold, especially when it has a complicated shape. For this reason, the casting must stretch at some points in an amount corresponding to its contraction.

If the casting is hollow, or will have cast-in openings, it follows that the casting will surround or enclose certain core portions of the mold. In this case, the casting process becomes even more critical since the surrounding hot metal transfers its heat to the metallic core and shrinks while the core heats and expands in conformity with the absorbed heat. Therefore, the strength of the metal of the casting must be quite high in that it must compensate for the consequent shrinkage strains of the alloys that are used extensively in chill mold casting. But each chain is only as strong as its weakest link and this applies also to the casting which is cooling in the chill mold. The weakest portion is, as a rule, that which is the hottest, and, for this reason, has the least strength. Such portions are, for example, adjacent to the sprue, or where larger amounts of heat are present due to an accumulation of metal, or where an insulating cushion is formed by enclosed air pockets so that the otherwise normal transfer of heat to the wall of the chill mold is considerably reduced, or prevented. The strain caused by shrinkage thus is not, as would be desirable, distributed uniformly over the entire surface area of the casting, but on the contrary, is uneven, being at a maximum at the hottest portion. The strength of this portion quite often is not sufficient to absorb the occurring forces, with the result that the casting structure may be broken.

Several methods already have been developed to prevent the occurrence of the above-mentioned flaws in castice ing, but these methods have only partially solved the problem and show deficiencies in their application which create additional difficulties in the process.

The aforesaid deficiencies and difficulties may be overcome in accordance with the present invention. It is an essential feature of the present invention that channels or grooves are provided at the surface, at least of those parts of the chill mold, and especially, of the cores, which come in contact with the molten metal at critical portions of the castings. In accordance with the present means and method, the disadvantages of known methods are overcome, and the risks of chill mold casting, especially of heavy metals such as copper and copper alloys, are considerably reduced.

It is an object of this invention to provide a new and improved chill mold.

It is another object of this invention to provide a new and improved chill mold which eliminates many of the strain and occlusion problems encountered in the use of prior art molds.

It is a further object of this invention to provide a new and improved chill mold which includes means providing for the escape of entrapped air.

It has been found that by means of the channels or grooves provided according to the present invention, the shrinkage which causes the strain which is largely concentrated at the hottest portion of the forming casting, may be greatly reduced or prevented to become effective at the weakest portions of the casting. By means of the grooves which are provided according to the present invention, shrinkage may be greatly avoided or retarded.

Inasmuch as the poured-in metal enters partly into the channel depressions, to this extent, a toothing of the still hot metal at the inner face thereof with the wall of the chill mold, takes place. This toothing causes a halting or retardation of the shrinkage strain. In this, that portion of the casting which may be endangered by an accumulation of material or the like, is essentially relieved of the full effect of the total shrinkage strain since the casting material by even a dimensionally slight toothing is hindered in transferring the strain in the usual man ner to adjacent portions of the casting; the critical portion is thereby isolated from the total strain and the danger of formation of cracks in the casting body is eliminated. The advantageous effect of the arrangement according to the present invention is explainable by considering that the loci of strain are subdivided by the toothing or ridges on the casting which are formed by the grooves on the walls of the mold, in this avoiding the possibility of the strains at various points uniting forces.

In addition to retarding the effects of shrinkage, the grooves serve also in contributing to an enlarged surface at the endangered portions of the casting, thereby ac celerating the rate of transfer of heat from the casting, thus increasing the power of resistance to strain. This brings about an effect on the surface of the metal casting which avoids the formation of surface cracks of relatively small depth which are, according to prior practice, primarily created by changes of cross-sectional surface area thereof.

It will be understood that the term mold herein embraces all mold parts including especially the core portion.

When pouring the liquid metal into the chill mold, it is in accordance with the teachings of the present invention a highly desirable aim to insure that air contained therein must be removed. Inasmuch as the air in the mold moves only in a comparatively slow manner while the molten metal flows in quickly, the result hitherto encountered is that the mold, especially in the case of complicated casting, fills with molten metal before all the air can escape.

Thereby there are formed air inclusions enclosed or entrapped between the surface of the casting and the wall of the chill mold. The occurrence of these residues is very difficult to prevent. Moreover these residues or air pockets once formed cannot escape inasmuch as the chill mold, in contrast for example with a sand mold, is impermeable to air. The air pockets therefore constitute bubbles or cushions between the contacting surfaces and are quite apt to form blow holes in the casting or at the surface of the casting.

The provision of grooves according to the present invention has the following effect. The molten metal enters the grooves thereby forming corresponding ribs on the surface of the casting. It is found however that the metal does not completely fill the grooves but enters only partially thereinto due to the small size of the grooves and to surface tension of the metal. This is a surprising effect, especially in view of the high specific weight of the copper and copper alloy metals. There thus remains in each groove a portion which does not contain metal but only air. In other words, there are formed in the grooves air channels and these air channels permit the escape of the air, otherwise trapped, to the atmosphere.

The several advantages and effects of the ribs on the casting and of the channels in the mold may beeffective either separately or in combination. The channels or grooves according to the present invention may be provided in various ways. Depending upon the size and shape of the casting, even one or two such grooves may prove to be sufficient. On the other hand, it may be necessary to distribute a relatively large number of grooves over a single area of the chill mold or over the whole of the chill mold surface. It may be found desirable to concentrate a plurality of grooves in a small space or on a small surface. In some cases it has been found desirable to provide a whole network of grooves, particularly if the strains encountered operate in two directions. The density of the network provided is dependent upon the forces to be encountered.

The grooves according to the present invention may be distributed over the surface of the mold and mold core in various determinable ways. The length of the grooves will be determinable without special difficulty dependent upon the size of the mold, bearing in mind that in order to permit most favorable vent of air they preferably should terminate above the surface of the molten metal. The grooves in width and depth should be such that the entry of the molten metal thereinto will be only part way, i.e., to the extent which in the final analysis will be determined by the surface tension of the molten metal. Within certain limits a degree of variation in cross sectional groove size and shape is permissible. A favorable depth has been found to be about 0.4 mm. when using copper and copper alloys, and a favorable shape that of a V in cross section. It has been found that these conditions provide for entry of the molten metal into the groove to a depth of approximately 0.2 mm., or, otherwise viewed, for the provision of ribs of 0.2 mm. height. The remaining space inthe groove thereby will consequently be about 0.2 mm. in depth, and will constitute between the cooling metal and the contiguous face of the mold a space or channel for air. The slight toothing of the casting afforded by ribs of aforesaid size has been found sufficient to afford an effective grip on the mold.

In event the grooves provided are not continuous, the beneficial effect will be largely limited to relieving the strain and not to the escape of entrapped air.

By the arrangement of channels or grooves according to the present invention, a simple and secure means for the prevention not only of cracks but air occlusions also,

is obtained. The success of casting in chill molds is made less dependent on the skill of the caster. A further advantage of the invention consists in that the required grooves may be manufactured in a simple manner. The durability of the chill molds is not affected. The accuracy of size of the castings is not damaged and the maintenance of the chill molds is not rendered more difficult.

By way of illustration reference is now made to the drawings which illustrate various embodiments of the invention.

FIG. 1 shows in section a chill mold casting manufactured in a chill mold according to the present invention.

FIG. 2 is a top plane view of the casting shown in FIG. 1.

FIG. 3 is a bottom view of the casting shown in FIG. 1.

FIG. 4 shows insection another embodiment form of casting manufactured according to the invention.

FIG. 5 is a plane view of the casting shown in FIG. 4.

FIG. 6 shows a core in elevation which may be used in conjunction with a further embodiment of the invention.

FIG. 7 is an enlarged view of the circled portion VII of the core of FIG. 6.

With particular reference to the embodiment shown in FIGS. 1, 2 and 3 of the drawings, casting 1 has on its floor surface 2 as well as on the inner cylindrical wall 3

small ribs

4 and 5 which are formed by corresponding grooves provided in the core of the chill mold. On the surface of the core (not illustrated) corresponding to surface 2, the grooves extend in a radial direction. To bring about the proper casting of heavy metal, a few grooves are sufiicient. The surface of the core forming the partially tapered surface 7 of the casting is likewise provided with grooves which appear on the casting as small ribs 6 (FIG. 3). These ribs are not disturbing. The depth and size of the grooves depends on the size of the casting. As best seen in FIG. 2, in addition to the longitudinal ribs 5 radial ribs extend along the floor 19 of the casting and along the bottom 20 thereof. In the illustrated embodiments, the grooves are taken to have a depth of about 0.4 mm., and the depth of penetration of the heavy metal thereinto amounts to about 0.2 mm.

In the case of the casting of FIGS. 4 and 5, the bottom surfaces 9 are provided with a network of grooves which appear on the casting as a rib-like arrangement 10. Such network acts, according to the invention, as a shrinkage retardation means so that the portions of the casting which otherwise would be endangered by an accumulation of material, are no longer subjected to the formation of harmful cracks. The grooves forming ribs 12 of the net- 'work open in the withdrawal direction of the casting and merge with the aforesaid radial ribs on the bottom surface 9. Besides the reduction of the destructive effects of shrinkage strain, escape of air otherwise pocketed between the casting surface and the wall and bottom of the chill mold also is taken care of.

Referring particularly to FIG. 6 there is illustrated a core member 13 provided with laterally extending grooves 14 and vertically extending grooves 14a. These form a rectangular network on the surface of the core and produce corresponding ribs on the inner wall of the casting. In FIG. 7 there is illustrated in detail the formation of ribs. There is shown an enlarged view if a V-shaped groove 17 extending circumferentially around the core 13, the core surface 16 being in direct contact with the metal 15 which has been poured into the mold. The metal 15 in the molten state enters the groove 17 only to a partial extent due to the surface tension of the molten metal. There is thus preserved a space 18 at the narrowest part of the groove which serves as an air channel. In the illustration of FIG. 7 the depth of the groove is 0.4 mm. and the depth of penetration of the metal into the groove is 0.2 mm. It has been found that for castings substantially of the size and shape of that of FIG. 1, these dimensions are quite satisfactory. However, the groove and the corresponding rib may vary from these particular dimensions. In general the dimensions of the groove should be sufliciently shallow to permit entry of the molten metal thereinto only partway and to maintain a continuous air passage through the channel portion.

When, therefore, it is said that the grooves are a depth of approximately 0.4 mm., it will be understood that this figure is not being employed in a strictly limiting sense, but embraces dimensions not greatly larger or smaller thereof depending upon the dimensions of and the material of the casting.

In all of the illustrated embodiments herewith, longitudinal passages are provided, i.e., grooves which extend in the direction of removal of the casting. When radial or transverse grooves are present, these normally interconnect with the longitudinal grooves, the latter opening to the atmosphere whence the air may escape.

With the foregoing improvements, the operation of casting may be carried out in a manner comparable to that which is conventional in the art. As will be under stood, the chill mold may well be composed of several parts to be assembled and held in position by suitable closure means known to the art. Thus, at one or several places, the mold may be provided with a conventional sprue opening. Further openings may serve as risers. The molten metal will be poured in the usual manner into the mold when it is closed on all sides. The grooves in accordance with the present invention are provided preferably both on the inner walls of the mold itself, and on the peripheral surfaces of the inner member of the core.

In order to facilitate the removal of the casting from the mold, the grooves, as illustrated in the several figures of drawing, extend in the longitudinal direction, i.e., in the direction of removal of the casting from the mold. On the other hand, if the core of the mold or the inner surface of the circumferential wall, i.e., that portion which shapes the interior surface of the casting, is provided with transverse grooves (FIG. 6), the removal of the casting has been found not to present any great difliculty. The grooves according to the present invention are of small depth and the ribs produced thereby are of even smaller height.

Therefore there are produced ribs with cross sectional dimensions so slight as to be substantially negligible, and it is within the skill of the art to so dimension these ribs and grooves so as to perform the aforesaid functions, and at the same time ofter quite small obstacle to being removed from the mold. This is surprising in the case of one-piece molds, but on the other hand, molds may be used if desired which are in separable portions. As a matter of practice no serious difficulty in removal of the casting has been encountered.

What is claimed is:

1. The method of chill mold casting metals of the class consisting of copper and copper alloys to form casting having a recess therein comprising the following steps:

(a) forming at least on the surface of the mold core, spaced grooves at critical shrinkage areas of said article, said grooves having a crosssectional area of a dimension sufficient to permit flow of molten metal thereinto to a depth partway into said grooves as determined by the surface tension of said molten metal;

(b) inserting said core in said chill mold and forming therebetween a space conforming in shape to the shape of a finished article to be molded; and

(c) pouring molten metal of the aforesaid class into said space formed by said chill mold and said core, and forming a finished article by restraining the outer and inner surfaces of casting at the critical shrinkage areas thereof against radial movement during cooling and releasing trapped air from both the inner and outer surfaces of said mold and said core through said grooves.

2. The method according to claim 1 wherein said grooves are formed in the inner surfaces of the mold as well as in the surfaces of said core.

3. The method according to claim 1 wherein said grooves are V-shaped in cross section.

4. The method according to claim 1 wherein said grooves are approximately 0.4 mm. in depth.

5. The method according to claim 1 wherein said grooves are formed as an intersecting network.

6. The method according to claim 1 wherein the grooves extend above the top of the casting being molded.

References Cited by the Examiner UNITED STATES PATENTS 922,678 5/1909 Dimmick 22-171 1,296,588 3/ 1919 Bamberg 22-168 2,018,762 10/ 1935 Kauifman 249174 2,221,947 11/1940 Kaufi'man 249174 2,221,948 11/ 1940 Kauffman 249174 2,518,055 8/1950 Olsen et al. 22183 2,806,267 9/ 1957 Jansen 22l93 J. SPENCER OVERHOLSER, Primary Examiner.

Claims

1. THE METHOD OF CHILL MOLD CASTING METALS OF THE CLASS CONSISTING OF COPPER AND COPPER ALLOYS TO FORM CASTING HAVING A RECESS THEREIN COMPRISING THE FOLLOWING STEPS: (A) FORMING AT LEAST ON THE SURFACE OF THE MOLD CORE, SPACED GROOVES AT CRITICAL SHRINKAGE AREAS OF SAID ARTICLE, SAID GROOVES HAVING A CROSS SECTIONAL AREA OF A DIMENSION SUFFICIENT TO PRMIT FLOW OF MOLTEN METAL THEREINTO TO A DEPTH PARTWAY INTO SAID GROOVES AS DETERMINED BY THE SURFACE TENSION OF SAID MOLTEN METAL; (B) INSERTING SAID CORE IN SAID CHILL MOLD AND FORMING THEREBETWEEN A SPACE CONFORMING IN SHAPE TO THE SHAPE OF A FINISHED ARTICLE TO BE MOLDED; AND (C) POURING MOLTEN METAL OF THE AFORESAID CLASS INTO SAID SPACE FORMED BY SAID CHILL MOLD AND SAID CORE, AND FORMING A FINISHED ARTICLE BY RESTRAINING THE OUTER AND INNER SURFACES OF CASTING AT THE CRITICAL SHRINKAGE AREAS THEREOF AGAINST RADIAL MOVEMENT DURING COOLING AND RELEASING TRAPPED AIR FROM BOTH THE INNER OUTER SURFACE OF SAID MOLD AND SAID CORE THROUGH SAID GROOVES.