US2378539A - Process of making shaped bodies capable of being sintered - Google Patents

Description

June 19, 1945. w -1 2,378,539

\ PROCESS OF MAKING SHAPED BODIES CAPABLE OF BEING SINTERED Filed se xl 4, 1941' Inventor: .Walther Dawihl '10s JWZW His Attorney;

Patented June 19, 1945 PROCESS OF MAKING SHAPED BODIES CAPABLE OF BEING SINTERED Walther Dawihl, Kohlhasenbruek. near Berlin,

Germany; vested in the dian Alien Property Custo- -Applieation September 4, 1941, Serial No. 409,501

. In Germany June 4, 1940 3 Claims.

Shaped bodies particularly of the kind made of hard metal alloys have heretofore usually been produced in such a way that a powder, for instance a mixture of powdered tungsten carbide a p wdered cobalt, was placed into molds either in the dry state or with an addition of a moistening liquid, such as water or acetone, and subsequently pressed, after which a greater number its plasticity the extruded bar can readily be seetioned by customary means, such as knives or cutting wires. It is possible by means of the novel method to produce per hour many hundreds .of

units of shaped bodies of uniform size, measuring for instance by 10 by mm. along the edges,

such as are frequently used as blanks for cuttingof the smallpressed-powder bodies thus obtained were sintered conjointly in a furnace and then,

after being machined, again placed in a furnace intervals in order that a portion of the mass, While retained in thepres's during its stand-still, can first be de-aerated and then suddenly set'under an air or gas pressure, if necessary, of several atmospheres. Each section of the forward movement of the flowing mass corresponds in length to the section of the mass that is being acted upon by vacuum, airor gas. Therefore, the bar extruded from the mouth-piece of the press has been uniformly subjected over its entire length to the action of the vacuum, air or gas. Further more. the extruded bar is divided in manner known per se into sections of the required length. Such sections are subsequently sintered, machined to the desired shape, and finish-sintered. As a binder, use can be made of Wate Or c iq d such as for instance lycerine or mixtures containing glycerlne, or also solutions, for instance, of resins in, the liquids just referred to. In consequence of de-aeration, the air trapped in the tips insert-pieces and pins.

In order that the invention may be readily understood, one example of construction of an ex- .trusion press suitable for carrying out the process is represented diagrammatically on the accompanying drawing-showing a vertical section.

The extrusion press consists of a cylindrical casing 5 having a tapered front portion, and which encloses a longitudinall arranged shaft 2 as well as a worm gear 56 secured thereto. At the rear end of the casing i, a feed hopper 4 is provided for the powder which is mixed with a binder, for instance water or glycerine. Said hopper may contain, as shown, a piston 5, the action of which presses the powder t into the casing I, avoiding the inclusion of an unduly great amount of air. The central portion of the casing i is separated from the rear and front parts of the casing by means of two screen plates 8 inserted therein and secured to bushings l of the shaft 2. To the wall of said central portion is fitted a tube 9 communicating, on the one side, with a pressure chamher by means of a shut ofl valve iii and, on the other side, with a vacuum source by means of a shut-ofl valve H so that eitherthe air contained in the space between the two screen plates 8 can be exhausted or the space itself set under pressure. In this case, layers of the moist pasty powder-mixture, adhering to the screen plates 8,

- form a sufliciently tight air seal in the central pores of the hard metal mass is first exhausted and then, owing to the sudden stream of gas entering under sumcient pressure, the total mass is.

compressed, and the cavities which wer filled with the vapour from the moistening liquid dur-- ing the de-aeration, are compressed to a large extent and closed, thus liquefying such evaporated parts. The gas used can either be air or, in the case of powders sensitive to oxygen, hydrogen or other gases. In general, the pressure of the gas introduced will be adjusted to one atmosphere; however, in certain cases, pressures of several atmospheres may also be adopted. Owing to portion of the casing, so that the action of the vacuum or of the pressure, as the case may be,

can only become eflective in the said central portion of the casing. In the mouth-piece [2 of the extrusionpress is inserted a spring sleeve IS, the rear part M of which is attached to the inner wall of the mouth-piece l2, for instance by soldering, welding, or riveting. The front end of the sleeve I3 is subjected to the pressure exerted by a lubrieating liquid, such as water or oil, introduced into the mouth-piece by means of two tubes l5. At

the front end of the sleeve l3, the lubricatin liquid is projected onto the bar, preventing the latter from adhering to the inner wall of the mouth-piece, which is an important featurein view of the risk involved for the bar to stick to the mouth-piece during each interruption of the forward movement of the bar. However, the lubricating liquid which is continuously ied onto the surface oi'the' bar, through the medium of the spring sleeve i3, causes the bar to be extruded very reliably in a constantly uniform' condition from the mouth-piece l2. Directly in front of said mouth-piece, cutting tools of any desired description'may be arranged to cut the bar into small shaped bodies. If desired, the piston 5 may be inserted with a perfectly tight flt to permit of the press chamber being set under vacuum or pressure as far as the said piston. .With this arrangement, the first of the two screen plates may be dispensed with.

What I claim as new and desire to secure by Letters Patent 0! the United States is:

1. The process or making shaped forms oi. sinterable powder mixtures of hard metal alloys and the like which comprises intermittently advancing the powdered mixtures longitudinally through a press having three successive zones divided by transverse screens, interrupting the advance of the material at short intervals and during said interruption subjecting the material in the intermediate zone between the screens to de-aeration by vacuum, subjecting the material to superatmospheric gas pressure and finally extruding the treated material.

2. The process oi making shaped forms of sinterable powder mixtures 01' hard metal alloys and the like and a liquid binder, which comprises intermittently advancing the powdered mixtures longitudinally through a press having three successive zones divided by transverse screens, interrupting the advance of the material at short intervals and during said interruption subjecting the material in the intermediate zone between the screens to de-aeration by vacuum, subjecting the material to superatmospheric gas pressure and finally extruding the treated material.

3. The process of making shaped forms of sinterable powder mixtures of hard metal alloys and the like and a liquid binder, which comprises intermittently advancing the moistened powder mixture longitudinally through a press having three successive zones divided by transverse screens, interrupting the advance of the material so that each successive portion will pause 1n the intermediate zone between the screens, subjecting such portion to de-aeration by vacuum and subsequently to superatmospheric gas pressure, advancing the material and finally extruding said treated material.

WALTHER DAWIHL.

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