US 3594302 A
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July 20, 1971 H E. RORDORF 3,594,302
APPARATUS FOR IMPROVING THE CHEMICO-THERMAL SURFACE TREATMENT OF TUBES Filed June 10, 196B IN VE N TOK Ho sr EDMUND Roam/9F Mam A TTORNE YS United States Patent Oflice 3,594,302 Patented July 20, 1971 3,594,302 APPARATUS FOR IMPROVING THE CHEMICO- THERMAL SURFACE TREATMENT OF TUBES Horst Edmund Rordorf, Weiningen, Zurich, Switzerland, assignor to Elektrophysikalische Anstalt Bernhard Berghaus, Vaduz, Liechtenstein Filed June 10, 1968, Ser. No. 735,675 Int. Cl. B01k 1/00 US. Cl. 204-312 2 Claims ABSTRACT OF THE DISCLOSURE Hardening by ionitriding of workpieces made of iron and steel means of ammonia has in many years been developed to technical perfection by the applicant and is now established as a perfect hardening process with excellent quality properties.
Particular difficulties were met within hardening tubes, particularly gun barrels, to achieve entirely uniform hardening of the interior of the tube. The uneven hardening of the tube was first attributed to certain irregularities of the glow-discharge which appeared to be irregular particularly in the interior of the tube. Accordingly, a counter-electrode was placed in the axis of the tube which was later designed, according to German Pat. No. 1,141,850 of applicant, as a narrow metallic pipe passed by a coolant. However, it proved that imperfect hardening was obtained in the interior of the tube despite that in places, and that production losses had to be accepted.
Also known is a method of gas plating, i.e. of coating objects with a thin metal film at an elevated temperature, the metal-gas compound, e.g. nickel carbonyl, being supplied to the surfaces to be metallized through a ceramic tube. However, the present invention does not relate to such a gas plating method since it is based on plasmametallurgical processes.
The present invention eliminates the said disadvantages and entirely avoids production losses.
This invention relates to a method of hardening tubes by ionitriding, particularly gun barrels, made of iron and steel, by means of an electrical glow discharge in a metallic vacuum container with a cathode and an anode located inside the said container, the cathode carrying the workpiece, e.g. a gun barrel, to be hardened, and a gas supply pipe and a gas exhaust pipe. The invention is characterized by the fact that the gas employed in the treatment, particularly ammonia, is supplied to the interior of the tube to be hardened. The invention further relates to a device for the performance of the said method characterized by a metallic gas supply pipe passed coaxially through the center of the tube to be hardened and closed at its interior end, the said pipe being provided with a plurality of nozzle-type bores from which the gas used in the treatment can preferedly pass to the portions of the tube interior subject to the greatest wear, and by baflie plates arranged at a small distance in front of the gas outlet nozzles. The axial gas supply pipe may operate as the anode of the glow discharge or it may have no connection with the voltage source.
An embodiment of the device according to this invention is described in greater detail with reference to the attached drawing which is a longitudinal section of a suitable vacuum container in diagrammatic representation.
The container consists of the metallic wall 1 and the cover 2 and base plates 3 secured to its in airtight relationship. The interior of the container is connected to a vacuum pump (not shown) for evacuation by means of a gas exhaust pipe 4. Attached to a current lead-in comprising the metal sleeve 5, the insulator 6 and the metallic interior conductor 7, which is mounted in gas-tight relationship on the cover plate 2, is a so-called centering body 8 which in turn carries the workpiece to be treated, here by way of example a steel tube 9 of which the inner wall is to be hardened. The steel tube 9 is electrically connected with the interior conductor 7 in a suitable manner, here indicated merely by the lead 10. Arranged at the lower end of the steel tube 9 is a further centering body 11. The interior of the tube 9 is connected, via the openings 12 and 13 respectively in the walls of the centering bodies 8 and 11 respectively, with the interior of the container 1, 2, 3 and can thus be evacuated along with the said container. The centering bodies 8 and 11 hold a metallic gas supply tube 14 which is arranged in coaxial relationship with the steel tube 9 and connected, in the upper centering body 8, with the elbow 15 which leads to the insulated gas lead-in, arranged in air-tight relationship in the cover plate 2, which comprises the metal sleeve 16, the insulating ring 17 and the connection pipe 18. Located in the wall of the gas lead-in 14 are lateral bores 19, preferably in the vicinity of such portions of the tube interior which should be most reliably and durably hardened, here, by way of example, in the central area of the steel tube 9. The bores 19 are covered by a metal sleeve 20 enclosing them at a small distance. These bafiie plates prevent a gas jet emerging from the nozzle-type bores 19 from directly impinging on the inner wall of the steel tube 9. The gas supply tube 14 is closed at its lower end or beyond the last bore 19; by way of example it is designed, in its lower portion, as a cylindrical bar which is held by the centering body 11. When gas for the treatment, e.g. ammonia, is supplied through the connection 18 and removed via the exhaust 4, a gas flow enters the interior of the tube 9 through the nozzle-type bores 19, the baffle plates 20 deflecting it in the direction indicated by the broken lines.
In order to obtain hardening of the inner wall of the tube 9 by ionitriding in a nitrogenous gas atmosphere, an electrical glow discharge must be produced in the interior of the tube 9 in addition to maintaining a suitable underpressure in the container 1, 2, 3 and a continuous supply of nitrogenous gas via the connecting pipe 18. In the embodiment shown, the interior conductor 7 of the current lead-in is connected to the negative pole; the connecting pipe 18, with the positive pole of a voltage source 22 having a suflicient voltage.
The conventional supply of the treating gas to the container, as by a supply pipe in its cover plate leading into the interior of the container in which the tubes to be treated are located, causes the gas to permeate the entire space but fails sufficiently to penetrate into the interior of the tube so as to ensure an adequate supply of nitrogen to the inner portions of the tube. Only the arrangement, according to this invention, of nozzle-type bores in the interior of the tube, from which the treating gas can emerge, is directly supplied to the tube areas to be hardened and causes a gas flow in the interior of the tube brought as surprising improvement and enabled flawless production. The gas supply pipe may be connected, as is the case in the embodiment represented, as the anode of the electrical glow discharge. If several tubes are treated simultaneously with three-phase AC in a container, the individual gas supply pipes may be interconnected so as to ensure an even gas supply, no electrical connection with the voltage source being required. As it emerges from the nozzles, the gas is already pre-ionized and preheated so that it very intensively acts upon the inner wall of the tube connected to form the cathode and produces the hardening effect. In order to avoid excessive gas supplies to the tube portions located opposite the nozzles, it has proved to be advantageous to arrange the bafiie plates described in front of the nozzle mouths.
The device may naturally be designed in a manner different from the embodiment shown, particularly in respect of the suspension of the tubes and the attachment of the gas supply pipes. By way of example, the centering bodies 8 and 11 may be formed of a metallic sleeve in which an insulating body carrying the gas supply pipe is located, the said body being protected against the attack of the destructive ionized gases in the inside of the tube 9 in the known manner by a narrow protective gap; in that case, the elbow 15 of the upper centering body 8 must be insulatedly passed through the metal sleeve and the insulating material protected by narrow gaps at this point as well.
What is claimed is:
1. Apparatus for hardening, by ionitriding, the interior surface of a tube formed of iron and steel by means of an electrical glow discharge in gas in a metallic vacuum container having a cathode and an anode therein, comprising:
means on said cathode for holding said tube in said container;
a gas supply pipe positioned to extend axially within and spaced from the sides of the tube held by said cathode, said gas supply pipe having gas discharge means intermediate the ends of said tube;
a gas exhaust conduit leading from said container, the interior of said container being in communication with opposite ends of said tube; and
said gas supply pipe comprising said anode.
2. Apparatus as defined in claim 1 wherein the inner end of said gas supply pipe is closed;
said gas discharge means comprising nozzle-type openings in the sides of said pipe adjacent said closed end for directing gas therefrom generally radially outwardly toward the inner surface of said tube; and
baffle means, of limited area, between said openings and said tube to prevent direct impingement of gas jets from said openings onto the surface of said tube.
References Cited UNITED STATES PATENTS 2,927,231 3/1960 Bucek l48-16.5
JOHN H. MACK, Primary Examiner N. A. KAPLAN, Assistant Examiner US. Cl. X.R.