JP2005111562A - Method for cold-deformation processing of molybdenum using backward extrusion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a molybdenum molding member without a crack nor a break by cold-deformation processing using backward extrusion. <P>SOLUTION: A molybdenum work piece is completely recrystallized at a temperature exceeding 1,400 degree C under vacuum and/or under protection gas and is cooled under vacuum and/or under protection gas. Then, the molybdenum work piece is subjected to the cold-deformation processing using backward extrusion at room temperature. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for cold deformation of molybdenum by backward extrusion.

  Molybdenum is used in lighting engineering due to its thermal, electrical and chemical properties. Molybdenum is a brittle material at room temperature, and the previous and semi-finished products are generally deformed hot. Molybdenum molded parts, such as tubes or caps used in lighting engineering, can be made from plate and strip by deep drawing at room temperature. Deep drawing means tension / compression deformation (Zugdruckumformen) from a plate material to a hollow body or molding of a hollow body with a smaller outer periphery from a large outer peripheral hollow body. In this case, the plate thickness cannot be changed intentionally. The cut | disconnected board | plate material is set | placed in an accommodating part. The presser presses the plate material toward the drawing die, thereby preventing wrinkle formation during deep drawing. The squeezing ram that descends presses the plate into the drawing die, thereby forming the plate into a desired workpiece. If the drawing ratio is high, deep drawing can be performed in many steps. The drawing ratio means the ratio of the diameter of the cut plate material to the diameter of the workpiece. Intermediate annealing may be performed during the deep drawing step.

  Deformation of the previous product and the semi-finished product is generally hot, ie preferably immediately after sintering (see US Pat. No. 5,158,709) (or after hot forging in electron beam melted molybdenum) or This is performed by thermomechanical deformation (see US Pat. No. 5,051,139). There are also advantageously cold deformation methods for small dimensions. In this case, however, the molybdenum is not completely recrystallized so that cracks or breaks do not occur under tensile stress during processing. Conventional doctrine says that the material must not be completely recrystallized. This is because, in this case, the tensile stress necessary for deformation processing may cause destruction (shrinkage or cracking) of the material in the recrystallized soft annealed state.

  Further, a method in which deformation processing, recrystallization and heat treatment are alternately performed is known (see, for example, US Pat. No. 4,600,466).

A method for cold deformation processing of recrystallized or stress relieved brittle materials (to which molybdenum belongs) by extrusion is described in US Pat. No. 3,552,996. Yes. This method is also known as forward extrusion. Extrusion is a cold deformation method for producing a hollow body or solid body. A compact pre-material (billet) is pressed through the die ( forward ) by the ram, similar to extrusion, or the ram is pressed into the pre-material and the material flows backward along the ram. The difference to extrusion is that individual parts are produced, not semi-finished strands, by processing temperature and extrusion. In this case, complex shapes can also be produced. The advantage of the method is high working speed with low mold cost, high mold life and cycle time of about 30-150 pieces / min. The surface quality is good and suitable for subsequent surface treatment. The main field of use is aluminum alloys. The main focus is in the avoidance of steep tear edges in the extrusion die in the method described in US Pat. No. 3,552,996. This avoids abrupt stress transition after deformation. However, the above-described method is only actually ensured for TZM alloys, and in this way, a partially crack-free molded body can be formed anyway (see the example).
United States Patent No. 5,158,709 US Pat. No. 5,051,139 United States Patent No. 4,600,466 US Pat. No. 3,552,996

  The object of the present invention is therefore to improve the method for cold deformation of molybdenum by backward extrusion of the type mentioned at the outset so that molded parts without cracks or breaks can be produced.

  In order to solve this problem, in the method of the present invention, complete recrystallization is performed before cold deformation.

  Now, in the present invention, a method for cold deformation of molybdenum by backward extrusion is described. It has been surprisingly found that molybdenum, despite its fragility, can be deformed by backward extrusion without causing cracks or breaks. At the time of extrusion, energy is applied by pressing stress. Molybdenum is completely recrystallized by heat treatment in advance so that it does not exceed the yield point of the material with sufficiently little stress. At the time of recrystallization, it is desirable to remove all grid stress previously generated by deformation processing. In this case, the material reaches its yield point with relatively little force. The recrystallization is preferably carried out at temperatures above 1300 ° C., in particular above 1400 ° C. (molybdenum has a melting point of 2623-5 ° C.).

  The present invention therefore relates to a method for cold deformation of molybdenum by backward extrusion. In this case, complete recrystallization is performed in advance. The method is advantageously carried out as follows.

  Later the molybdenum wire in the diameter range of the finished product is completely recrystallized at a temperature above 1400 ° C. under vacuum or under protective gas and cooled under vacuum or under protective gas. The sections of recrystallized material are extruded at room temperature to form a rotationally symmetric finished product.

  Major advantages of the method: First, the material can be used significantly better than in deep drawing. Furthermore, a member with a thicker or molded bottom can be produced by backward extrusion. The method is also suitable for other brittle metals or their alloys, such as chromium or tungsten.

  Industrially, the method can be used to fabricate molybdenum caps used, for example, in lighting engineering. The member thus manufactured can be used as a current guide and an emitter electrode that penetrates a glass bulb or a ceramic bulb in a CCFL (Cold Cathode Fluorescent Lighting) lamp or a cold cathode lamp (KKL). Cold cathode lamps or CCFL lamps are fluorescent lamps and use the principle of low pressure discharge. This excites a lean gas mixture (eg, Ar / Hg). The electrodes are not heated and a high voltage is first applied to the tube, which ionizes the gas mixture and makes it conductive. Electrical energy excites gas atoms and releases excess energy again in the form of UV and visible light. A phosphorus-based coating layer provided on the inner surface of the tube converts UV radiation into visible light. The electrodes are made from a refractory metal, usually molybdenum. Molybdenum is particularly suitable because of its property of easily releasing electrons. During AC operation, the electrodes function alternately as a cathode and an anode.

  In the following, the best mode for carrying out the invention will be described in detail with reference to the drawings.

  From a 1 mm molybdenum wire segment recrystallized under vacuum at a temperature higher than 1400 ° C. and cooled under vacuum, the molded cap is extruded backwards in a press at room temperature under a pressure of about 1500 MPa. The

  Such a cap can be used for a CCFL (cold cathode tube) lamp as an emitter electrode.

  By the method described, the material used is deformed 100% without waste.

  The microscopic level cross section of the cap shown in FIG. 1 produced by this method shows that a rotationally symmetric molded member without cracks can be produced by this method.

FIG. 3 shows a longitudinal section of a molybdenum cap made by the method according to the invention on a 50: 1 scale.

Claims (7)

  A method for cold deformation of molybdenum by backward extrusion, characterized in that complete recrystallization is performed before cold deformation in a method for cold deformation of molybdenum by backward extrusion.   The process according to claim 1, wherein the recrystallization is carried out under protective gas and / or under vacuum.   The process according to claim 1 or 2, wherein the recrystallization is carried out at a temperature above 1300 ° C. A) completely recrystallizing the molybdenum workpiece under vacuum and / or under protective gas at a temperature above 1400 ° C.
B) cooling the workpiece under vacuum and / or under protective gas,
4. A method according to claim 1, wherein the section comprising the workpiece thus recrystallized is extruded at room temperature to form a finished product.   5. A method according to claim 4, wherein the finished product is pressed rotationally symmetrically.   The method according to claim 1, wherein the molybdenum molded member extruded by the method is used for lighting engineering.   7. The method according to claim 6, wherein the method is used for the production of current guides or emitter electrodes through glass or ceramic bulbs in CCFL lamps or cold cathode lamps.