US2688169A - Method for melting metal powders - Google Patents

Description

Sept. 7, 1954 B. A. GRUBER ETAL 2,688,169

METHOD FOR MELTING METAL POWDERS Filed July 11, 1952 are | I i Is ea 4 o 686" as o o 0 o 9 -lw SE3 3/ .19 E wifoflmey Patented Sept. 7, 1954 UNITED STATES PATENT OFFICE METHOD FOR MELTING METAL BOWDERS Bernard A. Gruber, Lynnfield, and Lewis W. Davis, Beverly, Mass., assignors to Metal Hydrides Incorporated, Beverly, Mass., a corporation of Massachusetts Application July 11,

2 Claims.

This inventionrelates to melting metal powders to form castings or ingots of such metal and, more particularly, to a method for melting powders of metals, such as titanium, zirconium, vanadium, etc, which react with crucible materials or absorb components of crucible materials when melted therein.

When certain metal powders, such as titanium, zirconium and their alloys, are melted in graphite crucibles, the metal absorbs considerable carbon. When such metal powders are melted in ceramic crucibles, the metal absorbs oxygen or other elements. In either case, the casting produced contains considerable amounts of foreign material which decreases the ductility of the casting or is objectionable for other reasons. It is highly desirable, therefore, to provide a method for melting metal powders to form castings or ingots without introducing undesirable elements therein. This has been made possible by the present invention.

In accordance with the present invention, portions of the metal powder to be melted are compacted under heavy pressure to form self-sustaining blocks each provided with complementary interlocking means on two opposite sides, such for example as a projection having the cross sectional shape of a truncated triangle and extending from one face or side and a complementary groove in the opposite side. Thus, by interlocking a plurality of such blocks together a rod of any desired length may be formed. The rod thus formed may be suspended vertically in a furnace unit having a melting zone provided by electrical induction coils and the rod may be fed downward progressively at a desired rate into the melting zone where the rod is melted progressively, the melted metal falling into a quick freeze mold to form a casting or ingot.

By suspending the rod in the furnace unit it may be maintained out of contact with the furnace walls and the induction coils, the melted metal dripping from the remaining unmelted rod and falling directly into the mold without contacting any other portion of the furnace unit. The mold may be a water cooled thin sheet metal mold, such as copper, and the melted metal is cooled so rapidly in the mold that the metal casting does not become contaminated by foreign elements. An inert atmosphere, such as vacuum or a monatomic gas, should be maintained within the furnace unit during melting of the rod and cooling of the melted metal.

While the method of the invention is most advantageous for melting metal powders, such as 1952, Serial No. 298,394

titanium, zirconium, vanadium and alloys of such metals, which react with crucible materials, it is obviously applicable for melting powders of other metals which have a lesser tendency to react with crucible materials.

The invention will be more clearly understood from the following description in conjunction with the accompanying drawings: in which,

Fig. 1 is an elevational View, partly in section, of a furnace suitable for use in the practice of the method of the invention; and

Fig. 2 is a perspective View of a compacted self-sustaining block of a metal powder.

As illustrated in the acompanying drawing, a suitable furnace unit for use in the practice of the invention may comprise a cylindrical vertically disposed tube IQ of stainless steel provided with a water jacket I I. The water jacket I I is connected to a water inlet I2 and a water outlet I3. A conduit I4 provides communication with the interior of the tube iii and may be connected with a vacuum pump or a source of an inert gas, such as argon, or both. The tube It is provided with outwardly extending flanges I5 and I6 at its top and bottom respectively. A cover plate I! is secured to the flange I5 as by bolts I6 with a suitable gasket interposed therebetween. A vertical steel tube I 8 is secured and hermetically sealed to the plate I1 and communicates with the interior of the tube or chamber It. The upper end of the tube I8 communicates with the interior of a closed box I9 forming part of a conventional mechanical feeder, such as that of the Wobblerbellows type, for imparting longitudinal movement vertically in either direction to a flexible wire 20 for a purpose described hereinafter. The cover 8 of the box I 9 is detachably secured thereto as by bolts 9.

An annular series of water cooled induction coils 2! providing a central passage 22 therethrough are suitably supported within the chamber I0 so that their central passage, which provides a high temperature melting zone, is in vertical alignment with the passage in vertical tube I8.

A quick freeze casting mold 23, which may be formed of thin sheet copper, is positioned below and in alignment with the tube I8 and the passage 22 through the induction coils 2|. The mold 23 is provided with an annular flange 24 which is detachably secured to the flange I6 as by bolts 25 With a suitable gasket interposed therebetween. The mold 23 is provided with a water jacket 26 having a water inlet 2'! and a water outlet 28.

In accordance with one method for practicing the invention, portions of the metal powder to be melted are compacted under heavy pressure, such as a pressure of about tons per square inch, in a suitable mold to form self-sustaining blocks 36 of any desired size each provided with parallel fiat faces 32 and 34. Each block also is provided with a projection 3| extending from face 32 and a complementary groove 33 in its opposite face 34. The projection 31 has two flat sides 35 which intersect the face 32 along spaced parallel lines and incline outwardly therefrom away from each other. By sliding the projection 35 of one block into the groove 33 of another block, the two blocks may be fitted together or interlocked against relative movement along a line passing through both blocks and perpendicular to the faces 32 and 34. Thus, by fitting a plurality of blocks together in this manner, a self-sustaining rod 36 of any desired length may be formed. The length of the rod 36 should be slightly longer than is necessary, when melted, to form a. casting or ingot of the size desired.

After the rod 36 has been inserted in the tube i8 and suspended therein out of contact with the wall of the tube by being fastened to wire 20 through an eye 3'! or the like secured to the top end of the rod 36, the cover 8 is replaced and secured upon the box 19. The furnace unit then is evacuated to remove air and moisture. Electric power is supplied to the induction coils 2| while maintaining a high vacuum within the furnace unit. The rod 36 then is progressively lowered into the melting zone 22 while being maintained out of contact with the induction coils 21 and the well of tube [8 and is progressively melted. The melted metal drips from the rod 35 and falls directly into the mold 23 where it is quickly solidified. When a casting of desired size has been formed in the mold 23, the electrical power to the induction coils is shut off. When the casting is sufficiently cool, the vacuum is discontinued and the mold 23 removed from the furnace unit. During melting of the rod 36 and cooling of the casting, an inert atmosphere is maintained within the furnace unit. This may be accomplished by maintaining a high vacuum therein by means of a vacuum pump connected to the conduit [4 or by introducing an inert gas, such as argon, under a pressure slightly greater than atmospheric pressure after the furnace has been evacuated to remove air and moisture.

We claim:

1. The method for forming an ingot by melting a powder of a metal which reacts with crucible materials which comprises forming a selfsustaining rod consisting of particles of said. metal powder, moving said rod progressively into the melting zone of a closed furnace while out of contact with the furnace walls and in the presence of an inert atmosphere, said furnace having a casting zone beneath and vertically aligned with said melting zone, the progressive movement of the rod being at a rate to cause adjacent portions of the rod to melt progressively and the melted metal to fall by gravity into said casting zone, and causing the melted metal to solidify in the casting zone as an ingot.

2. The method for forming an ingot by melting a powder of a metal which reacts with crucible materials which comprises forming a self-sustaining rod by interlocking a plurality of selfsustaining blocks consisting of the metal powder, moving said rod progressively into the melting zone of a closed furnace while out of contact with the furnace walls and in the presence of an inert atmosphere,said furnace having a casting zone beneath and vertically aligned with said melting zone, the progressive movement of the rod being at a rate to cause adjacent portions of the rod to melt progressively and the melted metal to fall by gravity into said casting zone, and causing the melted metal to solidify in the casting zone as an ingot.

References Cited in the file of this patent Dunlap May 6, 1952

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