DE1253919B - Process for the powder metallurgical production of shaped bodies from tungsten and copper - Google Patents

Description

Process for the powder metallurgical production of molded bodies Tungsten and Copper The present invention relates to a method for powder metallurgy Manufacture of spark erosion-resistant molded bodies or finished parts made of tungsten and copper or a copper alloy with at least 88 weight percent copper.

Moldings of this type, the composition of which is known, have different ones Uses, especially one uses the same as the metal for electrical Contacts. In electrical devices, these contacts close the circuit, so the current can flow through; by separating them from each other, the circuit becomes interrupted again. Sparks occur when the contacts are closed and interrupted on. The metal of these contacts must therefore be carefully selected to avoid spark erosion as well as resisting oxidation. The alloys of tungsten and copper or made of tungsten and a copper alloy allow the solution of a large number of Problems associated with the use of electrical contacts. For Another use is made of these alloys for electrodes Projection welding. In particular, this welding process allows, for example, to weld a thin sheet to a heavy sheet, the ratio of the sheet thicknesses can go beyond 5. With this type of welding there will be sparking the electrodes before the pieces to be welded are in contact with each other brings, put under tension. The latter are then brought closer to one another, and indeed at first slowly, then gradually faster and faster, to finally when the two parts to be welded together are hot enough to apply sudden pressure exercise. This method requires the use of alloy electrodes of tungsten and copper or one of tungsten and a copper alloy; they are particularly suitable for such welding work due to the juxtaposition of a heat-resistant metal with high resistance to flow, namely des Tungsten, with a metal that conducts electricity and heat well, namely the copper. These alloys are also used as Electrodes for machine tools using spark erosion. the end Because of the cheap material, these electrodes are generally made of copper manufactured. The alloys of copper and tungsten are very expensive, whereby their use remains limited. The high price of these alloys is but not actually due to the price of one component, but rather mainly due to the high cost of manufacturing the alloy, as well as its Machining or shaping, in particular on the energy consumption during manufacture of the molded body and, to a lesser extent, the processing time during manufacture of the electrodes.

With the method according to the invention, the cost price for the production of these materials is reduced quite considerably, as a result of which the possible uses become far more numerous. To date, these alloys have been manufactured or processed using two methods. In one of these processes, a mixture of copper powder and tungsten powder or a mixture of the powder of a copper alloy and tungsten powder was pressed into compacts, which were then sintered and then processed. It has now been recognized that this process gives products of unsatisfactory quality; in fact, their porosity is never less than 80 / ", which means that the mechanical and electrical properties are mediocre and incompatible with the quality required for normal use in the various uses envisaged. The residual porosity is due to the fact that the two metals cannot be alloyed with one another and that their melting points are very far apart.

The second of these methods is that you have tungsten powder too Pressed compacts, which are then sintered at a temperature of 1350 to 1500 ° C be, d. H. at a temperature at which the compacts also after sintering still remain porous. The porous tungsten compact is then impregnated with copper or with a copper-containing one Alloy by placing it in immerses a melt of copper or a copper alloy under one reducing atmosphere. The compacts are sometimes still after soaking hammered while warm and then machined to get the correct dimensions.

In the "Zeitschrift für Metallkunde", Vol. 48 (1957), p. 189, is next to the one described above also mentioned another method, namely by Soaking a pressed, unsintered tungsten powder without subsequent cold or Hot deformation to come to the desired moldings. From the basic work von K i e f f e r and H o to p, »Powder Metallurgy and Sintered Materials« (1943), However, on p.325 it can be seen that the hardness values of the composite bodies produced therewith are inadequate for the practical requirements and also in the case of a condensing Post-treatment by extrusion compared to the products from the other two are still inferior to the procedures described. From the number table 78 of this reference it is also evident that only relatively coarse grains are used for this impregnation process Powders with a grain size of 100 to 400 µ were considered.

It is particularly disadvantageous that all previous methods of post-processing required to achieve the desired final shape. This is because the process of impregnating the tungsten powder with molten copper and the sintering process the mixture of tungsten powder with copper powder only results in porous process products lead that have to be redensified, and that with the most favorable method so far the impregnation of the sintered tungsten compact, the process products first must be produced in an oversize to avoid the unpredictable loss of volume to be taken into account during sintering. But especially the latter processing of the oversize Using hard metal tools is extremely time-consuming and inconvenient.

The aim of the present invention is to produce these composite bodies made of tungsten and copper in the most direct way possible and in the final form, without further processing being necessary, according to a very simple procedure, at a cost price that is much lower than the previously known A method, the method comprising only two operations, namely deforming of the tungsten by pressing and soaking the molded piece obtained in this way with molten copper or with the melt of an alloy rich in copper is.

The object of the invention accordingly consists in a process for the powder-metallurgical production of spark erosion-resistant molded bodies or finished parts made of tungsten and copper or a copper alloy with at least 88% copper by pressing tungsten powder into the desired shape and impregnating the unsintered compact, which is characterized by that the pressed body to be impregnated is made of fine-grain tungsten powder provided with a lubricant, with a tungsten powder with 40,000 to 80,000 cm2 / cm3 specific surface and 0.5 to 3 #t for a copper or copper alloy content of the composite body of 15 to 25% Particle size of 42 to 120 kg / mm2 is pressed, for a copper or copper alloy content of 25 to 38% an identical tungsten powder is pressed with 8 to 46 kg / mm2 and for a copper or copper alloy content of 35 to 45% a tungsten powder with 80,000 to 180,000 cm2 / cm3 specific surface and 0.1 to 0, 75 [. Particle size is compressed with 5 to 12 kg / mm2.

The lowering of the cost price results from this novel Method from the fact that the operation of sintering at high temperature, which the most costly one can be avoided. The present invention is based on the discovery that sintering is not necessary for the toughness of the alloy provided that the structure and grain size of the tungsten powder is careful can be selected depending on the composition desired for the finished alloy and that the pressure applied for pressing depends on both the properties the powder as well as the composition desired for the finished alloy is determined.

The state, which the tungsten powder for the implementation of the invention Procedure is determined by the average size of the particles, the specific surface area and the apparent density, the latter already being is essentially determined by the first two measured variables.

The specific surface area of the granules, i.e. H. the surface of the same in square centimeters per cubic centimeter of powder, is determined by the measure of the Permeability of a powder layer to the air. This permeability is inferior the modified equation of Koseny in relation to the porosity of the layer as well as the specific surface.

The mean size of the tungsten grains is measured with the device from R i g d e n determined.

Apparent density is determined by measuring the bulk of a known weight of tungsten powder after shaking the powder in a graduated Measuring glass.

Hammering is also superfluous with the new process. The elimination the sintering of the tungsten compacts, which up to now could never be omitted with another very important advantage over the older method. The dimensions of the finished parts obtained by the method according to the invention are namely the dimensions obtained when pressing the tungsten compact. So you can Parts with the required dimensions ready for use directly without any processing manufacture or at least parts that do not require any further processing on the outside, which was not possible with the usual method, since it was sintered at one temperature of about 1400 ° C the tungsten compact one cannot be foreseen with accuracy Was subject to shrinkage.

So the very significant advantages of the novel process are the following: Elimination of the most costly operation, namely sintering of the tungsten compact, no hammering, the possibility of pressing the parts with the final dimensions, without further processing.

For example, an alloy with a copper content of 30% and 70% tungsten, one proceeds in the following way: One uses a tungsten powder whose specific surface area is 50,000 cm2 / cm3, the average Size of the particles to 1.2 V, and the apparent density after shaking up 5.5 g / cm3. This powder is mixed with a lubricant, to make pressing easier. Various known methods of Lubrication of metal powders can be used, especially the addition of 1.5% Paraffin to the tungsten powder, the paraffin in a volatile solvent, for example a light gasoline is dissolved. This solution is applied to the tungsten powder poured, whereupon the solvent is evaporated. That prepared in this way Tungsten powder is placed in a die under a pressure of 10 kg / mm2 to the desired Pressed shape. The compact obtained in this way is then melted in a bath Immersed in copper under a hydrogen atmosphere. In the process of soaking with copper, the dimensions of the tungsten compact do not change; as a result, that has Finished part after soaking, d. H. upon completion of the procedure, the initial Dimensions of the compact.

To obtain an alloy with a copper content of 200 /, turn the same procedure is used, but the tungsten powder has the same characteristics as in the first example then pressed under a pressure of 80 kg / mm2.

With copper contents of over 380 /, the tungsten powder to be used is characterized by a larger specific surface, about 120,000 cm2 / cm3, the average size of the particles being 0.5 #t and the apparent density after shaking in at 2 g / cm3 amounts to.

To generalize and to cover the main cases of use, one can say: a) Alloys with a content of 15 to 250 /, pure copper or up to 12% alloyed copper: The pressure for pressing a tungsten compact is 42 to 120 kg / mm9 for a carefully lubricated tungsten powder whose specific surface area is 40,000 to 80,000 cm2 / cm3, the average size of the particles is 0.5 to 3 #t and the apparent density after shaking is 4 to 6 g / cm3 .

b. Alloy containing 25 to 38 ° / o pure copper, or up to 12% alloyed copper: The pressure for pressing a tungsten compact amounts to 8 to 46 kg / mm2 for a tungsten powder soaked with a lubricant the same parameters as under a).

c) Alloys with a content of 35 to 450 /, pure copper or up to 12% alloyed copper: The pressure for pressing a tungsten compact amounts to 5 to 12 kg / mm2 for a carefully lubricated tungsten powder, its specific surface area is 80,000 to 180,000 cm2 / cm3, the average Particle size to 0.1 to 0.75 [. and the apparent density after shaking amounts to 1.5 to 2.5 g / cm3.

Claims (1)

Claim: Process for the powder metallurgical production of Spark erosion-resistant moldings or finished parts made of tungsten and copper or a copper alloy with at least 88% copper by pressing tungsten powder into the desired shape and impregnation of the unsintered compact, characterized in that that the compact to be impregnated made of fine-grained, provided with a lubricant Tungsten powder is made, with a copper or copper alloy content of the composite body from 15 to 25% of a tungsten powder with 40,000 to 80,000 cm2 / cm3 specific surface and 0.5 to 3 #t particle size with 42 to 120 kg / mm2 pressed is the same for a copper or copper alloy content of 25 to 38% Tungsten powder with 8 to 46 kg / mm2 is pressed and for a copper or copper alloy content from 35 to 45% a tungsten powder with 80,000 to 180,000 cm2 / cm3 more specific Surface and 0.1 to 0.75 #t particle size with 5 to 12 kg / mm2 is pressed. Publications considered: Zeitschrift für Metallkunde, Vol. 48 (1957), P. 189; Berg- und Hüttenmannische Monatshefte, Vol. 94 (1949), pp. 284 to 294; R. K i e f f e r and W. H o to p, Powder Metallurgy and Sintered Materials, 1943, p. 27, 33, 34, 82, 228, 325.