US3186678A - Metal casting art - Google Patents

Description

J- H. KEATING METAL CASTI-NG ART June 1, 1965 2 Sheets-Sheet 1 Filed Oct. 19, 1961 INVENTOR. JOHN H. KEATING mTm ibkk ATTORNEYS June 1, 1965 H. KEATING 3,186,678

METAL CASTING ART Filed bot. 19. 1961 2 Sheets-Sheet 2 FIG. 4

IN V EN TOR.

JOHN H. KEATING BY wsmmmljfimuz ATTORNEYS United States Patent 3,186,678 IVETAL CASTING ART John H. Keating, Cleveland, Ohio, assignor to Monarch Aluminum Mfg. (30., Cleveland, Ohio, a corporation of ()hio Filed Get. 19, 1961, Ser. No. 146,183 6 Ciainis. ((11. 249-416) By prior art practice it is usual to utilize a permanent or die casting mold, to the mold cavity surfaces of which is applied a coating or mold release agent adapted to further production of a better product surface, especially by furthering venting of the cast metal or a ready release of the cast object from the mold and to permit the use of iron or steel dies and molds which otherwise would be severely and unacceptably eroded by molten metal, especially aluminum. However, in a relatively short time, not unusually, for example, one shift or Working day, it has been found necessary that molds be scoured of the coating by sandblasting or the like, and the coating replaced.

Such prior practice involves economic loss not only in the operations of removing and replacing the mold coatin" and in the resulting down-time of the mold; but also from the fact that the repeated scouring or cleaning operations change the mold cavity surfaces to an extent efiectively destroying the mold in consequence of changed dimensions or configuration of the ultimate product.

By the present invention there is provided in a mold of the character described a novel coating advantageously obviating many untoward features to be ascribed to the prior art mold coatings. More particularly at least the cavity, i.e., the article forming surfaces of the mold, is provided with a plated porous hard chromium surface. This has been found first to eliminate the need for the prior used coatings of the type previously described and consequently the subsequent usual scouring and recoating operations along with the detrimental physical and economic results hitherto arising.

Also a product is obtained by this invention having, throughout the life of the plating, a surface consistently better reproducing the mold cavity surface. This of course substantiallyeliminates grinding, or other operations on the product previously required in consequence of variations of successive objects from intended form. The finish resembles that 011 die castings of much lower melting point alloys. It is generally possible better to cast a desired surface finish in theobject; whether a smooth surface or one having particular decorativecontours or configurations formed in the mold cavity; The cast surfaces produced by this invention also generally have a finer grain structure, therefore resulting in more reflective surfaces and also surfaces to which various coatis consequently achieved a better metal section, and a minimization of scrap due to holes in or at the surface of the product.

Further where the prdouct is ultimately to be coated with an application of afired ceramic-type, or of a plastictype such as Teflon, it appears that casting in the improved molds is conducive .to a ready application of a sound final coating.

The general object of the present invention is. an improvement in the art of metal casting with permanent molds or die casting molds.

Another object is to provide an improved mold of the character described which obviates need of frequent removal and replacement of mold cavity coatings.

Another object is provision of a mold cavity surface resulting in a longer ultimate mold life as well as longer periods between maintenance operations on the cavity.

A still further object is the provision of a mold producing castings of consistently better and more uniform surface than obtainable by comparable prior practice.

Other objects and advantages will appear from the following description and drawings wherein:

FIGURE 1 is a fragmentary representation in section of two mold components;

FIGURE 2 is a perspective view of a cast frying pan 'having a figured surface for the production of which this invention is particularly advantageous;

FIGURE 3 is a fragmentary section, similar to FIG- URE 1 through a mold for producing the pan of FIG- URE 2, with metal cast therein, the mold configuration being exaggerated and certain casting layers omitted for clarity; and

FIGURE 4 shows another object, in the casting of which the present invention is advantageously used.

In fragmentary form, FIGURE 1 of the drawing represents two spaced mold components 10' and 11 defining therebetween the cavity into which the' metal is .cast to' form the desired product. Each mold component has a respective coated portion or layer as Hip, H p; at least one of which is a porous hard chromium plating or layer, for producing that surface or surfaces of the casting where best definition of surface configuration or best surface finish is desired, while the opposite or remaining cavity surface may be a usual coating of the prior art. q

A cast aluminum frying pan 13 is shown in FIGURE 2, having an inside bottom surface 14, which is cast between opposed mold components 16, 17 (see FEGURE 3). The component 17 on its cavity surface has a -multitude of shallow closely spaced concentric lands 18 and grooves 19, here smoothly curved in cross'section;

which define complementary lands and grooves in the cast metal and result in the figured bottom surface 14.

Here the lands and grooves are greatly exaggerated in size relative to the thickness of the cast section and the portion analogous to 10p, 11p in FIGURE 1 are omitted for clarity'of the drawing. However, it is to be understood that with the cavity. surface of member 17 coated or plated with porous chromium and even with the cavity surface of 16 provided with a coating of the prior art suitable for casting such an aluminum object, good definition of the cast pattern on the surface 14 is obtained where the grooves are on the order of 0.002 inch in depth and .003 inch in spacing. V

The cast aluminum chair base of FIGURE 4 represents another object difficult to obtain in uniform production by prior methods. Particularly the concave regions at hub between the adjacent legs are subject to non-uniformity of surface characteristics, varying in smoothness and requiring grinding operations to get them into acceptable form for subsequently applied finishes. The grind- 3, e ing or finishing operationsientail considerable labor costs. Generally with conventional molds, there is required a fast grind with a coarse wheel, followed by another with a less coarse Wheel, and finally a finish grind with a fine grain wheel. The multiple operations are necessitatedby the fact that working immediately with the fine grain wheel would take a considerable time, cause overheating of and deterioration of the Wheel and also undue heating and deformation of the casting, which is eliminated by previous useof a fast cutting coarse wheel, and an intermediate-wheel to remove the grain marks fromthe first operation. On the other hand, where the correspond ing mold surfaces have, according to the present invention, a hard porous chrome surface, only little grinding.

with a fine grained finishing wheel is required, even over extended production runs, to provide a surface suitablefor plating, or other finish applications on the casting.

The hard porous chromium plating has been found.

quite suitable for the casting, for. example, of aluminum, zinc or .brass objects desired tohave relatively smooth finishes and also for the reproductionof the cast objects even of mold surfaces having closely spaced configurations.

Notonly is the invention applicable to permanent mold casting but also to die casting where again the die life is improved, and especially for brass casting, where be- Generally the same ranges of plating thickness and porosity are applicable for metals such as zinc, aluminum and brass. The upper limit in thickness of the plating is dictated as in general plating considerations by the tendency of the layer to peel'from the cavity surface,-

a maximum chrome thickness on the order of about 0.005 inch being generally safely adherent, while giving a long mold life. The etching of a 0.005 inch plating is carried out to an average depth of about 0.002-0.003 inch in the etched voids and to the extent of about 60% to 80% voids in the surface area of the chromium layer. At about 60% voids the threshold seems to be reached of the porosity requisite for wetting by and therefore venting of the cast metal, while etching to above 80% voids leads to veining between voids, i.e., a marked joining of voids by veins or fissures penetrating to a fraction, say,

one-half to three quarters of the chromium thickness,

which results in diminishing life of the porous chrome surface.

It should be noted, however, that the thinner the .base,

plated according to this invention to obtain fine definition, for example, a name plug in a larger mold, a relatively shallow etc, say to a depth of 0.001 inch suffices; but where a larger fiat area is plated, for example, corresponding to a pan bottom thirteen inches in diameter, a deeper etch, say about 0.002 inch, is indicated.

I claim:

'1.,A non-porous mold defining a metal cavity adapted to receive a molten metal to be cast comprising a mold coating of hard chromium adhering to the mold cavity in physical contact with the metal being cast and having a surface porosity defined by a network of voids extending uniformly over about 60% of the mold coating area and to an average depth of at least 0.002 inch whereby entrained gases in the metal are vented through the coating.

2. A non-porousmoldas set forth in claim 1 wherein said surface porosity is formed by electroetching the chromium coating.

3. A non-porous mold as set forth in claim 2 wherein thethickness of the chromium coating is'approximately 0.005 inches.

4. A non-porousmold as set forth in claim 3 wherein the network of voids extends over about 60% to of the coating area and to anaverage depth of between 0.002 and 0.003 inches.

5. A non-porous mold defining a mold cavity adapted to receive a molten metal to be cast comprising an electro-deposited mold coating of hard chromium adhering to the mold cavity andin physical contact with the metal being cast and having an electroetched surface porosity defined by a network of voids extending uniformly over about 60% of the mold coating area and to an average depth of at least 0.002 inches whereby entrained gases in the molten metal are vented through the coating.

6. The method of making a self-venting, non-porous mold having a mold cavity adapted to receive a molten metal to be cast therein comprising the steps of: electroplating a portion of the cavity with a hard chromium layer having a thickness of approximately 0.005 inches.

and anodically etching the chromium layer for a period sufiicient to produce a surface porosity therein defined by a network of voids extending uniformly over about 60% of the chromium layer and to an average depth of at least 0.002 inches whereby entrained gases. in the metal are vented through the chromium plate.

References Cited by the Examiner,

UNITED STATES PATENTS 1,678,117 7/28 Homberg 106-3 8;27 1,794,536 3/3 1 Quinn 117--5.3 1,809,872 -5/27 Soderberg 106-3827 2,031,568 *2/36 Lemmerman 22-2165 2,217,802 10/40 Koehring 10638.27 2,363,337 11/44 Kelly 106-3827 2,479,364 8/49 Jocelyn 22216.5

OTHER REFERENCES Metal Handbook, 1948 Ed., Porous Chromium, page 719.

MICHAEL V. BRINDISI, Primary Examiner.

MARCUS U. LYONS, Examiner.

Claims (1)

1. A NON-POROUS MOLD DEFINING A METAL CAVITY ADAPTED TO RECEIVE A MOLTEN METAL TO BE CAST COMPRISING A MOLD COATING A HARD CHROMIUM ADHERING TO THE MOLD CAVITY IN PHYSICAL CONTACT WITH THE METAL BEING CAST AND HAVING A SURFACE POROSITY DEFINED BY A NETWORK OF VOIDS EXTENDING UNIFORMLY OVER ABOUT 60% OF THE MOLD COATING AREA AND TO AN AVERAGE DEPTH OF AT LEAST 0.002 INCH WHEREBY ENTRAINED GASES IN THE METAL ARE VENTED THROUGH THE COATING.

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