DE1195871B - Sheathed wire for grid of electrical discharge tubes - Google Patents

Description

Sheathed wire for grids of electric discharge tubes The grids electrical discharge tubes often have to operate at high temperatures, e.g. B. at 1500 ° C and more, work. They are usually made from a molybdenum or tungsten wire made, which is plated with platinum. The platinum plating is capable of that To keep primary lattice emissions very low, a property that is whose grids often take on very high temperatures, is of particular importance. The disadvantage of platinum now has a considerable vapor pressure. At one temperature from about 1500 ° C and more, the surface of the grids begins to deplete of platinum. A platinum-molybdenum or platinum-tungsten alloy is formed on the surface of the grid, which is unsatisfied for electronic reasons.

It is now known that iridium does not turn into molybdenum or tungsten as quickly diffused. It has a high work function for electrons and good strength at high temperatures and a lower vapor pressure than platinum. So far it was however, it is not possible to produce an iridium coating on molybdenum or tungsten wires. So it is z. B. difficult to deposit iridium by electroplating. On the other hand, iridium is so brittle that it is difficult to process mechanically.

From the powder metallurgical working processes to be considered ago it is known z. B. for plating round profiles during a drawing process onto the roughened surface of a rod to be clad made of the cladding metal to press on existing powder. Composite metal wires can also be produced in this way that rods or blocks are embedded in metal powders obtained from carbonyls, the whole thing by heat treatment, if necessary with the application of pressure, into one Piece connected and then deformed to the desired size. In the end can, as is known, also metal wires, e.g. B. as core wires for coated welding electrodes, manufacture from a sintered metal powder compact,. the by hammering or Rolling is compacted and then drawn to its exact size.

The known methods lead to an intimate connection of the jacket and core of the wires, which particularly favors the diffusion process, so that, they for the production of electric discharge tube grids exposed to high temperatures have to retire.

The subject matter of the invention, on the other hand, consists of a tungsten or Molybdenum core and one; Existing coated wire made of noble metal for grids electric discharge tube, which is characterized in that its jacket is made of Iridium exists, which is in direct contact with the nucleus, but not with it is firmly connected.

The production of the wire according to the invention is done by that the core consisting of tungsten or molybdenum is made of a tube made of sintered Metal powder surrounded in a known manner with a sliding fit, together with the tube forged on a rod and then drawn into wire. According to the invention should now the tube made of sintered iridium has a hardness of 220 to 310 VPN (Vickers hardness), the tungsten core has a Vickers hardness of 480 to 540 and the molybdenum core has a Vickers hardness from 330 to 400. It is essential that the tube and the one fitted with a sliding fit Core can only be processed into wire with such forging and drawing pressure, that shell and core are not firmly bonded to one another even after deformation are. The resistance to deformation of the tube and the core must be essentially the be the same. It is roughly proportional to the tensile strength and hardness of the material. Good deformation properties result when the tensile strength of both the pipe as well as the core are in the range of about 3.5 to 8.5 kg / mm2. But when it's difficult is to measure the tensile strength, while the hardness is easier can be determined, then it is recommended. the required relationship by the pyramid pressure test to be determined according to V i c k e r s (VPN). The hardness of the iridium tube should be 220 to 310 VPN and, if the core is made of tungsten, its hardness is 480 to 540 VPN. A core made of molybdenum must have a hardness of 330 to 400 VPN.

Drawn tungsten wire has too great a tensile strength and a deformation resistance too high. Rods made of tungsten produced by sintering can but can be used. It turned out that good products are made when the density of the sintered iridium is 16-20 g / cm3 and that of the sintered one Tungsten be 14 to 17 g / cm3. If the sintered density of the iridium is in the Is close to the lower limit value, then that of tungsten should preferably also are close to the lower limit. The corresponding hardness values are for the Iridium 220 to 280 VPN and for the Wolfram 480 to 520 VPN.

Since molybdenum, as a metal, is not as strong as tungsten, it can be drop-forged Use molybdenum rods to achieve the desired resistance to deformation to achieve consistency. Preferably, the molybdenum rod is made after forging drawn because then its hardness and its resistance to deformation of the hardness and resistance to deformation of the iridium are better matched. The density of molybdenum should be around 10.2 g / em3 be. The core of the finished wire preferably has a fibrous structure which he should also keep in use. If the rod is now used as a grid in a electric discharge tube is used and here to a temperature of about 1500 ° C, then a core consisting of: pure molybdenum can recrystallize, so that its fibrous structure is lost. But if the molybdenum is low Content of titanium, e.g. B. 0.5% titanium, then the recrystallization temperature increases. It is therefore preferable to use such molybdenum. Containing titanium Molybdenum has a hardness of 337 VPN in the drop-forged bar and in the forged bar and drawn rod a hardness of 372 VPN.

The sintered iridium tube can be made by pressing the iridium powder with subsequent sintering of the tube in air or preferably in a vacuum will.

Below is the preferred manufacture of one encased with iridium Tungsten wire described: Iridium powder exhibiting good sintering properties, d. H. a powder, the surface area of which is about 0.3 m2 / g, is applied with a pressure of 23.6 kg / mm2 by a polished molding made of soft steel Diameter of 6 mm pressed. The molding, which has a flange at one end, is surrounded by a latex (rubber) sleeve into which the powder is inserted. The green, d. H. not sintered compact consists of an iridium tube, the one Length of about 100 mm, an inner diameter of 6 mm and an outer diameter of 9 mm. The tube is then at a temperature of 1500 ° C in a vacuum sintered. This results in a linear shrinkage of about 16% and a tube its sintered density is 18 g / cm3 and its hardness is 305 VPN.

A sintered tungsten rod with a density of 15 to 16 g / cm3 and no more than 17 g / cm3 is now sanded to such a degree that it becomes with Slidably fits into the sintered iridium tube, and the filled tube afterwards drop forged at a temperature of 1500 ° C to a diameter of 3 mm. To the To avoid excessive heat loss, forging must be done quickly. Then the rod is drawn hot at 750 to 650 ° C onto a wire of about 2.5 mm. Thereon the wire is drawn at 600 ° C. to 0.5 mm and finally at 550 to 500 ° C to 0.25 mm. The pulling speed varies between 0.3 and 0.6 m / min at the beginning and about 3.7 m / min when the wire diameter is 0.5 mm or less. With this finished, 0.25 mm thick wire, the iridium coating is 0.0125 mm, but generally 0.025 to 0.050 mm thick. Thinner sheaths than expected are given a ratio of the initial diameter of the iridium to the tungsten of Achieved 5: 3 to 2: 1 because the iridium changes from 0.75 mm to 0.25 mm when drawn more deformed than tungsten, despite their similar resistance to deformation.

A wire produced by this method has an outside diameter of 0.25 mm, a core diameter of 0.18 mm, a jacket hardness of 582 VPN and a core hardness of 803 VPN.

If the tungsten core is inserted into the iridium tube, then can locked with iridium plugs at each end. That is but only essential if the heating takes place under oxidizing conditions.

If the core is made of molybdenum, then the iridium tube is preferred made in the same way as a core made of tungsten. That The ratio of the outside diameter of the tube and the rod is preferably 2: 1 Sintered iridium tube, for example, has an outside diameter of 3.75 mm. A drop forged and then drawn bar made of 0.5% titanium Molybdenum with a hardness of 375 VPN was fitted into the tube so that the Rod in direct contact with the iridium surface of the tube found. Then the ends of the tube were made to prevent oxidation Iridium existing stopper sealed and the filled and sealed tubes then brought to a diameter of 0.3 mm by hot forging and hot drawing. The final diameter of the core made of molybdenum was 0.125 mm, the hardness of the sheathed finished wire 698 VPN and the core hardness 386 VPN.

It was found that the composite wires were not bonded exists between the core and the iridium. The sheathing of the wire can be easily be peeled off. This shows that there is none between the core metal and the iridium Diffusion has taken place so that the wires are particularly useful for purposes in which, from the electrical point of view, diffusion between the two metals is undesirable.

The invention comprises as a new product a sheathed wire, which consists of a core made of tungsten or molybdenum, which is connected to a contiguous, drop forged and thereafter drawn coat made of iridium, which is in direct contact with the core of the wire stands, but does not adhere firmly to it.

Claims (6)

Claims: 1. Sheathed wire, consisting of a tungsten or molybdenum core and a noble metal jacket, for grid of electrical discharge tubes, characterized in that its sheath consists of iridium, which is connected to the core in is in direct contact, but is not firmly attached to it. 2. Procedure for producing the wire according to claim 1 from one of tungsten or molybdenum existing core made of a tube of sintered metal powder with a sliding fit is surrounded, tube and core are forged together in the die to form a rod and the rod is then drawn into wire, characterized in that a by sintering tube made of iridium powder with a hardness of 220 to 310 VPN (Vickers hardness), a tungsten core with a Vickers hardness of 480 to 540 or a molybdenum core a Vickers hardness of 330 to 400 is used, the core with a sliding fit in the Tube fitted and the forging and drawing pressure only adjusted to this level that the sheath and core are not firmly adhered to one another even after the deformation are connected. 3. The method according to claim 2, characterized in that the density of the sintered iridium tube 16 to 20 g / cm3 and the density of one sintered from tungsten Core is 14 to 17 g / cm3. 4. The method according to claim 2, characterized in that that the core is made from a bar of drop forged or drop forged and drawn molybdenum, the density of which is about 10.2 g / cms. 5. Procedure according to claim 3 or 4, characterized in that the starting diameter of the iridium tube to the starting diameter of a tungsten rod such as 5: 3 and to the starting diameter of a molybdenum rod behaves like 2: 1. 6. The method according to claim 5, characterized in that that molybdenum containing titanium is used as the core material. Considered Publications: German Patent Specifications No. 598 766, 958 073; Swiss patent specification No. 301059.