US1926573A - Casting method and apparatus - Google Patents

Description

Sept, l2, y1933. D WILLCCX 1,926,573

I CASTING METHOD AND APPARATUS Filed DSC. 24", '1951 Patented Sept. 12, 1933 UNITED STATES PATENT OFFICE CASTING METHOD AND APPARATUS Application December 24, 1931 Serial No. 582,989

4 Claims.

My invention deals with a method of melting and casting metals and alloys, particularly those of a high temperature melting point, and has as its main purpose the adaptation of crucible and 5 mold for a very rapid transfer of charge.

Another purpose is to provide pre-heating or pre-cooling for .the mold so that the charge may be made to solidify at a denite rate, or to prevent the chargefrom solidifying before it has lled the mold to the desired extent.

The invention embodies the design of the furnace which is so constructed that molds may be made of a variety of materials and removed or replaced quickly.

In practicing my invention, I make use of an induction electric furnace of the usual form and have referred to show one figure by way of illustration.

In the casting of low temperature melting substances, it is relatively unimportant whether the crucible and mold are adapted for quick pouring, and generally speaking, the temperature of the mold proper is o f only minor consideration, pro.- viding it is dry or free from substances which might form gas holes in the product being cast.

Thus far it has been very diicult to make good castings of the extremely high temperature melting substances, because the material frequently solidies on the crucible walls before a pour may be made, or it makes at best a poor casting in the mold because of solidication or oxidation during the casting operation.

Iron and steel melt at approximately 1500 C. and are poured into molds which generally run 5 from 200 to 600 C.- The diiference in temperature between charge and mold therefore varies from 900 to l300 C. In high temperature work, such as the melting of tungsten carbide, the melting temperature is nearer 2500" C., and to establish even an approximately equal difference between charge and mold temperature,l asin the case of iron or steelas above cited, the mold must be heated considerably over 1000 C.

A method of overcoming the difficulty of premature freezing or solidication of the charge has been to allow the melt to solidify within the melting chamber, and to regulate the cooling by usual means. In this operation, however, the crucible becomes wornv or damaged; it loses its sharp corners and edges during the melting operation, and at best is good for only one casting which must be broken out-and ground to shape.

Lately, the use of tungsten carbide and carbides of other metals have been found to be of great 5 advantage for tool making. Carbon and tungsten powders together with bonding materials of a temporary or permanent nature are compressed to the dimensions desired and are sintered to hardness at a comparatively low temperature. The pieces attain an extreme hardness by this process and are used as dies on cutting tools.

The melting point of tungsten carbideapproximates 2500"l C. It has been found that samples melted and cast have a hardness approximating that of the sintered product but because of the diiliculty of getting accurately shaped pieces, or pieces properly solidified and cooled, the cast product has not found as much favor in the industry as the sintered product.

By my method of casting, I have reduced the casting operation to commercially feasible routine. The charge may be melted, if preferred, in a controlled atmosphere; it may be poured into a clean cut mold shaped to the dimensions of the nished product; and pre-heated if desired. After casting, the mold may be cooled as desired to obtain the grain or crystal structure found best. Neither crucible nor mold are damaged for future melts and such melts may be made in regular succession.

If desired the crucible and mold may be evacuated during melting or casting, thus insuring against contamination by injurious gases.

In the igure I have shown a graphite crucible (l) containing a charge (2) so proportioned as to fill but not overflow the mold (3) when the assembly is inverted. The mold is made to slide into the crucible along the Wall surface and to form a tight joint at the point (4) where a seat has been adapted to receive it. Crucible and mold are both shown here to be graphite or carbon, but my invention is not limited to apparatus of this sort. I have shown graphite preferably because it has been found most advantageous in high temperature work and because of its electrical conducting characteristic. If crucible and mold are of graphite, they will absorb energy and become heated. If they are of electrically nonconducting materials, the metallic charge absorbs the energy. In the case shown, the mold will be heated by energy absorbed directly from the inducing coil (5). In the case Where the mold is non-conducting, it will become heated by radiation andconduction from the charge below it.

In the figure, the crucible and charge are shown packed in heat insulating refractory material (6) Where graphite crucibles are used this material is preferably thermatomic carbon; a grade of carbon black used extensively in the rubber industry and characterized by its readiness to be tremely high temperature. Powdered silica or other non-carbon heat insulators may be used if desired in certain cases.

'I'he crucible and refractory are contained in an i electrically insulating sleeve (7) which may be a quartz tube or mica sheet or the like.

Inductor coils (8) and (5) are wound to surround the assembly as shown. Coil (8) is made to supply energy to `the crucible proper and charge, while coil (5) may be used to heat the upper portion of the crucible or mold. Coil (5) may, if preferred, be wound closer to the mold so that when deenergized the water cooling with which-both c oils are adapted, may be used to cool the mold.

Coil and crucible assembly are mounted in a cylindrical frame member 19 with a bottom meinber 11 fastened to it by bolts and angles as at 14. A top piece similar to the bottom is provided with an opening and with a hinged cover 13. Braces or supports 10 are provided to h'old the coil in place vertically and laterally and are themselves Aheld in place by the top, the bottom and theoutside case. These braces may be tied to the coil turns with asbestos string and they may be bolted directly to the coil turns if desired. Top, bottom, hinged cover and sides can conveniently be 'made of asbestos lumber.

The cover is arranged to operate on a hinge (l5) and to be held inthe closed position by screw clamp (16). Refractory blocks (1'7) are used to hold the mold down against the crucible, and a refractory cement topping (12) may be used to seal in the crucible packing.

Trunnions 18 arebolted to the frame at points on opposite sides of the assembly and approximately on a line which would intersect its center of gravity. The furnace as a whole is arranged to tilt or rotate about an axis through these trunnions so that the charge may be poured from the crucible into the mold.

After the furnace has been inverted about the trunnions and the charge has had opportunity to solidify'in the'mold, the clamp (16) Ymay be released and the mold (3) removed. 'A new charge and crucible may be inserted, and the operation repeated. If a split mold is used, the casting may be removed at once and the same mold returned to the assembly.

It is not necessary that the crucible proper form the guide for the mold as the heat insulation may be of rigid or sintered material to serve as the necessary guide.

Having described my invention vso dthat others sklliedintheartmaybeenabledtocopythe same, what I desire tosecure by Letters Patent is described in what is claimed.

c 1. A casting mechanismfor metals having a -packed and by its gas free qualities evan at exmelting temperature in excess of 1800 degrees centigrade comprising a crucible, a replaceable mold held inverted directly over and in contact with said crucible, refractory heat insulation and electrical insulation surrounding said crucible and mold, an artificially cooled inductor means for heating and cooling said crucible and mold or said crucib1e`a1one supports and housing for said assembly and diametrically opposed trunnions secured to the housing about which the whole assembly may be inverted to cast a molten charge from the crucible into the mold.

2.v Apparatus for casting metals having a melting temperature in excess of 1600 degrees centigrade comprising a crucible. a replaceable :holdv mounted in inverted relation to said crucible so that its open end is removably secured to the open end of said crucible, a water cooled inductor heating coil operatively surrounding said crucible, a second combined inductor heating andcooling coil surrounding the mold, electrical and heat insulation between coil and crucible and between lcoil and mold, supporting means and housing for said 'assemblyand two diametrically opposed trunnions secured to said housing about which the whole apparatus may be rotated to pour a charge from the crucible into the mold.

3. Apparatus for casting metals having a melting temperature in excess of 1600 degrees centigrade comprising a graphite crucible, a replaceab'le graphite mold mounted in inverted relation to said crucible so that its open end is removably secured to the open end of said crucible, a water cooled inductor heating coil operatively surrounding ,said' crucible, a second combined in- 110 ductor heating and cooling'coil surrounding the mold, electrical and heat insulation between coil and crucible and between coil and mold, supporting means andhousing f or said assembly and two diametrically opposed trunnions secured to'115 said housing about which the whole apparatus may be rotated to pou: a charge from the crucible into the mold.

4. Apparatus forcasting metals having a melting temperature in excess of 1600 degrees centi- 0 vgrade comprising a graphite crucible, a replacevsecured to the open end of said crucible. a water cooled inductor heating and cooling means operatively surrounding said crucible, a support and mousing forsaid crucible coil and mold assembly, lelectric and heat insulating means between said coil and said crucible and mold assembly and two diamecriemy opposed trunnions secured 13 to the housing about which the whole assembly may be rotated to pour a charge from the crucible into the mold.

- DUDLEY WILLCOX. 135

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