US 3345059 A
Description (OCR text may contain errors)
Oct. 3, 1967 J. K. SWINDT CRUCIBLE FOR HOLDING MOLTEN METAL Filed March 12, 1965 mus/won JOSEPH K. SW/IVDT r M Attorney United States Patent C) 3,345,059 CRUCIBLE FOR HOLDING MOLTEN METAL Joseph K. Swindt, Manhattan Beach, Calif, assignor to United States Steel Corporation, a corporation of Delaware Filed Mar. 12, 1965, Ser. No. 439,238 1 Claim. (Cl. 266-39) ABSTRACT OF THE DISCLOSURE A crucible for holding molten metal includes a metal container in a double-walled vessel, the Walls being of thermally insulating material and separated by a cushioning layer. The insulation Walls are confined in an outer box lined with insulation powder.
This invention relates to a crucible and, in particular, to a crucible specially adapted to hold molten metal while the surface thereof is being heated sufficiently to effect rapid evolution of the vapor of the metal.
In the coating of material with metal by vapor deposition in a vacuum, the prime requisite is a satisfactory crucible for holding the molten coating metal, e. g. aluminum, while the surface thereof is heated, as by electron bombardment, to effect vaporization at a rapid rate. The problem of providing a satisfactory high-temperature crucible as a source is rendered acute by the fact that many otherwise suitable refractory materials are subject to cracking from sudden thermal expansion and contraction, and are thus not leakproof. Others are subject to attack by the molten metal. Artificially cooled crucibles have a low thermal efiiciency.
I have invented a novel composition crucible which permits expansion and contraction incident to cyclical heating and cooling and yet takes care of leakage of molten metal, in the event of a crack, in such manner as to permit continued operation. In a present preferred embodiment, my crucible comprises an inner receptacle or container of highly refractory material surrounded by a vessel of thermal insulation. The vessel has double walls of insulation with an intermediate layer of compressible refractory or thermal insulation. The entire crucible is disposed within a binding of metal plate but is separated therefrom by a layer of packed refractory powder.
A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawing illustrating the present preferred embodiment. In the drawing the single figure is a perspective view of a crucible according to my invention, showing a transverse section therethrough.
Referring now in detail to the drawing, an inner receptacle or container is dimensioned to hold a charge of molten metal 11 to be evaporated. The crucible may be of any desired shape in plan but will usually be rectangular. It is composed of a highly refractory material such as the nitride of boron, aluminum or silicon, but need not be free from cracking on heating and cooling.
Container 10 is positioned within a double-walled vessel 12 composed of separate walls or shells 12a and 12b of thermal insulation, having a cushioning or expansion layer 13 therebetween. Shells 12a and 12b are preferably made of a castable insulation having a high alumina content. The expansion layer 13 between the side walls of these spaced shells is preferably aluminum-silicate fibers, refractory pebbles or crushable shapes. In any event, it is compressible so as to permit expansion of shell 12a without materially stressing shell 12b. The bottoms of shells 12a and 12b are spaced by a layer 14 of granular material, e.g. alumina powder.
A binding of metal plate such as box 15 surrounds the entire crucible structure but is separated therefrom by a densely packed layer 16 of powdery material, such as alumina, similar to that of layer 14.
It will be evident from the foregoing that I have provided a crucible comprising an innermost vessel of refractory material, confined within a double wall of insulation, the walls being separated by a compressible filling, the entire crucible structure having an outside binding or vessel spaced from it by a densely packed refractorypowder layer.
The advantage of such crucible is that, in the event of a crack in vessel 10, leakage of molten metal therethrough is confined by the insulation walls 12a and 12b or, if not, is caused to solidify by reason of the steep temperature gradient between the space inside and that outside of the double-walled insulation vessel. Any such leak is thereby plugged by a cementing or self-healing action and exerts no ill effect on continued operation of the crucible. The tendency of the molten metal to react with the crucible parts is much inhibited at the reduced temperature on the exterior of insulation shell 12b. Vessel 10 may therefore be of material resistant to such reaction, regardless of whether it cracks on repeated heating and cooling.
Layer 13, of course, permits expansion and contraction of shell 12a independently of shell 12b while shell 12b aflfords a rigid refractory support for shell 12a. Separating layer 16 further seals against possible contact of a leak of molten metal with binding 15.
Although I have disclosed herein the preferred embodiment of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention as set forth in the claim.
A crucible for holding molten metal comprising a metal box, a lining of thermal-insulation powder therein, an outer shell of solid thermal insulation seated in said lining, a second lining of thermal-insulation powder in said outer shell, an inner shell of solid thermal insulation seated in said second lining and a container of refractory metal seated in the said inner shell.
References Cited UNITED STATES PATENTS 2,557,834 6/1951 McMullen 266-43 X 3,079,136 2/1963 Soine 266-39 3,227,431 1/ 1966 Steeves 263--48 J SPENCER OVERHOLSER, Primary Examiner.
E. MAR, Assistant Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,345,059 October 3, 1967 Joseph K. Swindt It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
I Columml, line 35, for "composition" read composite column 2, line 53, for "metal" read material Signed and sealed this 29th day of October 1968.
EDWARD J. BRENNER Edward M. Fletcher, Jr.
Commissioner of Patents Attesting Officer