# Patent

## Title
Dental tools

## Abstract

This is a division of application Ser. No. 112,979, filed Feb. 5, 1971, now U.S. Pat. No. 3,927,990, issued Dec. 23, 1975.

## Background
Our invention relates to a contact member for high electrical loads which is especially suited for high-duty power purposes. Our invention also relates to a method of manufacturing such a contact member.

Contact members which are needed in electric power applications, for example for high voltage high powered circuit breakers, have two tasks which must be fulfilled. For the conduction of current, the contact members must have a high electrical conductivity and a small contact resistance. And, when switching high loads, these contact members must have a high burn-off strength at locations of the circuit breaker at which the light arc continues. The switching apparatus can then be arranged in two portions one of which carries the continuous current in the closed position of the contact member and one region which is subjected to the arcing load and stress during switching.

Contact members are known wherein components of burn-off resistant materials are provided, for example tungsten, molybdenum or rhenium. Also in the known contact members, these metals are provided with the metal having high electrical conductivity such as copper and silver to increase the electrical conductivity. Since an even distribution of the components is required in the contact members and since the mentioned metals are insoluble in each other, sinter technology or sinter impregnation technology is used to manufacture the contact members. However, with the known contact members a large use of costly burn-off resistant materials is unavoidable since the burn-off resistant component is contained in the entire volume of the contact member although it would suffice to have this component located out at the locality subjected to the arc. Hence, the known contact members, while meeting largely the technical requirements, are nevertheless relatively expensive to use.

Accordingly, it is the object of our invention to provide a contact member which can be manufactured with the highest possible saving in expensive materials.

It is another object of our invention to provide a contact member of which at least a portion thereof is easily machinable.

It is also an object of our invention to provide a method of manufacturing the above contact member.

According to a feature of our invention, a contact member is made up of a plurality of component parts. One of these parts is made of non-welding material resistant to burn-off and another one of the parts is made of a solderable material having electrically conductive properties. In addition, the material of each of these parts is configured as a porous skeleton structure and the parts are disposed next to each other. An impregnating metal impregnates both of the parts to preclude the occurrence of a boundary layer at the interface between the parts.

The sinter structure portion of a burn-off resistant part can be made of tungsten, molybdenum or an alloy of these metals. The portion of tungsten, molybdenum, rhenium or the alloy amounts to 40 to 80% by volume referred to the volume of the component part. The sinter portion of the shaped sinter structure portion of the solderable component part may contain a metal or a metal alloy with a high melting point such as copper and an electrical conductivity and solderability or fuseability superior to tungsten, molybdenum or rhenium. A metal suitable for use for the shaped sinter structure portion of the solderable component part can be selected from the group consisting of iron, nickel, cobalt, non-magnetic steel or an alloy of these metals. The portion of the metals or the alloy amounts to 60 to 90% by volume with reference to the volume of the component part. The impregnating metal can be silver or copper or a silver-copper alloy.

With the contact member according to the invention savings are realized with expensive materials such as tungsten, copper, molybdenum or rhenium which can be replaced by inexpensive materials such as iron, since the burn-off resistant component must only be provided in the part of the contact member subjected to the light arc. At the same time, the electrical conductivity of the contact member is increased since the conductivity of one or more component parts is increased. Difficulties associated with soldering or welding of the contact member with a contact carrier as is the case with known contact members do not occur, since the contact member can be secured onto a solderable or fusion-bondable component part. In addition, the contact member can be readily machined without substantial wear of a machine tool on the fusion-bondable component parts.

In a preferred embodiment of the contact member according to the invention, the shaped sinter portions are prefabricated according to fit and the shaped sinter portions positionably fixed next to each other and thereafter in a single process step the shaped sinter portions are bonded with the penetrating impregnating metal. This manufacturing method is simple and is suitable for assembly line procedures. By means of the economy realized through this saving of expensive work materials the contact member according to the invention is therewith further augmented by the simple manufacturing process.

The invention will now be described with reference to the drawings, wherein:

FIG. 1 illustrates in section a configuration of a switching member tip provided with an armor coating of burn-off resistant material;

FIG. 2 illustrates in section another embodiment of a burn-off tip according to the invention;

FIG. 3 illustrates, in section, a preferred embodiment of the contact member of the invention comprising a sleeve of burn-off resistant material mounted on a bushing of fusion-bondable material;

FIG. 3a is a fragmentary view of the embodiment of FIG. 3 taken along the line IIIA - IIIB to illustrate means for fixing the position of the sleeve member and bushing with respect to each other;

FIG. 4 is a sectional view of an embodiment of a burn-off ring made according to the invention; and

FIG. 5 is a sectional view of an embodiment of a burn-off lamination made according to the invention.

FIG. 1 illustrates the tip or armoured portion of a switching member which consists of a part 1 having a material resistant to burn-off and a part 2 which comprises good electrically conductive, solderable material. The through pores of the sinter structure portion of part 1 as well as the sinter structure portion of part 2 are filled with copper as the impregnating metal. In the manufactured contact member, part 1 comprises WCu30 which contains 30% by weight of copper and 70% by weight of tungsten and part 2 comprises FeCu40 which contains 40% by weight of copper and 60% by weight of iron. At the interface of parts 1 and 2, the impregnating metal copper merges as a boundary layer with the neighboring regions. Therefore, under the boundary layer there is a jump in the concentration of the impregnating metal portion which is located between the sinter structure portion of part 1 and the sinter structure portion of part 2.

FIG. 2 illustrates a section of another construction of a burn-off tip which likewise consists of parts 1 and 2. Part 1 is the contact layer and part 2 is the carrier portion of the burn-off tip. As opposed to a full tip of WCu, expensive burn-off resistant material is saved with the burn-off tip according to FIG. 1 as well as with the burn-off tip according to FIG. 2.

This saving can amount to as much as 60%. In addition, the good workability of the part 2 offers considerable advantages, since a screw thread 4 can be provided on the stub 3 of part 2 in a simple manner. Whereas, with a full tip of WCu, there occurs a considerable abrasion of the lathe tool because of the hardness of the tungsten, a material of FeCu40 by weight can be worked with a cutting die and part 2 is comprised of the latter FeCu40 material. Although the hardness of the FeCu 40 material with approximately 100 kilos per mm.sup.2 is relatively high, this material can be nicely machined and a long duration of operation is assured for the machining tool.

Another embodiment of the burn-off tip is illustrated in section in FIG. 3 wherein part 1 with a burn-off resistant contact material is a sleeve and part 2 comprising a solderable, easily workable material is a bushing. With reference to this burn-off tip, a more detailed example of the material composition and the method of fabrication of the parts will now be given.

The sinter structure portion of the outer sleeve 1 is fabricated from a WCu power mixture. The copper portion of this powder mixture amounts to approximately 2 to 10, preferably 5 to 10, percent by weight. To improve the wettability of the finished sinter structure portion with the carrier metal, it is preferable to add a powder mixture of nickel of 0.01 to 5%, preferably 0.01 to 0.2%, by weight. The powder is pressed into the required mold with a press machine. In this way, pressing pressures between 0.5 and 6, preferably between 1 and 4, metric tons/cm.sup.2 are applied. It is to be noted that the necessary pressing pressure is dependent upon the geometry of the sinter structure portion. The pressed portion is sintered with a temperature of between 1200.degree. to 1500.degree., preferably between 1250.degree. and 1300.degree.  C. For an outer ring having an inner diameter of approximately 1 centimeter and an outer diameter of approximately 3 centimeters and which consists of tungsten 89.95% and copper 10% and nickel 0.05%, a pressing pressure of from 2.5 metric tons/cm.sup.2 is needed. The pressed body is sintered at 1250.degree. C.

The shaped sinter structure portion of the inner sleeve 2 is fabricated from iron powder. Copper and nickel can be added to the iron powder. The pressing and sintering of such shaped portions is known. In this connection, reference may be had to the book of Kieffer and Hotop entitled: "Sintereisen und Sinterstahl", Springer Verlag 1948, with special reference to pages 128 to 131 and 148 to 185. It has been shown expeditious to use iron powder reduced from iron ore which is produced according to the Hoeganes method and has a particle size smaller than 150 micrometers. This powder, to which is added 5 to 8 percent by weight of copper powder, is pressed with a pressing pressure of 2.8 metric tones/cm.sup.2 and is sintered for 1 hour in a hydrogen atmosphere at 1200.degree. C. The shrinkage occurring during the sintering procedure amounts to 0.65%. In this connection it is noted that for the fabrication of the shaped sinter portion, it is an advantageous commercial practice to use shrinkage compensated powder compositions. One such powder, for example, is put together from iron with a maximum of 8% by weight of copper and a maximum of 2% by weight of nickel.

The shaped sinter portions for parts 1 and 2 are fabricated to fit to each other. In the instant embodiment, the inner sleeve 2 is inserted in the outer sleeve 1. The tolerance of the fit can be adjusted with respect to the geometry of the pressing tool and in the instant embodiment, the adjustment is made with respect to the diameter of the pressing tool and the sinter conditions. The tolerance to be held for the fit is a gap spacing of 40 to 200 .mu.m between mutually adjacent shaped sinter parts. In the instant embodiment, the gap width is the difference of the outer radius of the inner sleeve 2 and the inner radius of the outer sleeve 1.

FIG. 3a illustrates that one of the shaped sinter portions can be provided with a protrusion 11 and that the second shaped sinter portion can be provided with a corresponding recess 12, whereby the shaped sinter portions are positionally fixed with respect to each other. In addition, a meshing of the two portions can be obtained by applying a proper profile for example to the outer surface of the shaped sinter portion of inner housing 2 or the inner surface of the shaped sinter portion of the outer housing 1 in order to balance out the voltages resulting from different thermal expansion coefficients and to raise the strength.

After the shaped sinter structure portions for the outer sleeve 1 and inner sleeve 2 are put together, the sinter structure portions are impregnated with copper. The final composition of the parts 1 and 2 and therewith the contact member itself is dependent upon the porosity of the shaped sinter structure portions.

For the part comprising the material of excellent contact characteristics, the porosity should be between 10 and 50%, preferably 40%, by volume and for the member with good solderability and good mechanical workability, the porosity can lie between 20 and 50%, preferably 40% by volume. In the instant embodiment a porosity is selected which ensures a composition of WCu25 to WCu30 for part 1 and of FeCu40 for part 2. These values include the weight percentage for the nickel component added to the tungsten.

It is noted that a copper jacket develops on the outer surface of the contact member when there is a surplus of impregnation material of approximately 5% by weight. Such a copper jacket can, for example, be suitable as a galvanized silvering, since with this copper surface, a very good bond is obtained. It can also be expeditious to use a quantity of copper impregnating material which is less than the quantity required for a complete filling of the pores. The deficiency can be between 2 and 30%, preferably between 5 and 20%, of the total pore volume of the contact member. With these measures, impregnated members can be produced which no longer have to be worked at their outer surface, since they have a clean surface. The small remainder of porosity is distributed evenly over the entire cross section of the contact member. Thorough investigations have revealed that this remaining porosity contributes to no essential reduction of the burn-off value in comparison to completely impregnated contact materials.

The burn-off sleeve of FIG. 3 has a bore 5 which extends through the outer sleeve 1 as well as the inner sleeve 2. In special cases, it can be necessary to provide the burn-off sleeves with several such bores 5 at an angle to the axis 6 so that an extinguishing medium, for example oil, can be directed therethrough during switching operations. By producing such bores in the contact materials of the known type, the drills have only a short operational life because of the hardness of the tungsten particles embedded in the copper. This disadvantage is overcome in a contact member according to the invention. The bores are provided at least in the sinter structure portion of part 1 by the pressing action. With a simple finishing on the assembled sinter portions of parts 1 and 2, the bores 5 can be made to extend through part 2 or, in case bores are already provided in part 2, the bores can be brought into alignment with the bores in the sinter structure portion of part 1. Here, only the easily workable part 2 of the burn-off sleeve must be worked, whereby a long operational life for the drill is likewise ensured.

With sinter portions having bores as well as with sinter portions in which no bores 5 are provided, the common impregnation with copper provides an outstanding bond of high strength at the joining surfaces between the sinter structure portions of the parts 1 and 2. Also with a contact member according to FIG. 3, the cutting of a winding, for example the windings 7 and 8, is greatly simplified, since these windings always are provided on part 2 which is made of easily workable material.

FIG. 4 illustrates a section taken through a burn-off ring which is produced from a part 1 having good burn-off characteristics and from part 2 having the features of good workability and good solder characteristics and, at the same time, good electrical conductivity. In this connection it is expeditious to produce the sinter structure portion of part 2 from non-magnetic steel, for example from chrome-nickel steel, in order to suppress the formation of eddy currents in the burn-off ring.

FIG. 5 is a section through a burn-off lamination consisting of a burn-off resistant contact member 1 and a contact carrier 2 having good electrical conductivity. With these contact members there is obtained a high reliability in contrast to the shaped parts used up to the present time. It is known for such burn-off laminations, to machine the contact member 1 to finished form with a tight tolerance. The contact member 1 could be made, for example, of WCu30. In the same manner, the contact carrier 2 must be finished with a corresponding tolerance for the solder applied in the region of the boundary surfaces between the contact member 1 and the carrier 2. After applying hard solder, both members are heated to the soldering temperature and are thereby joined. In most instances, the burn-off laminations must thereafter be cleansed of surplus solder. In comparison thereto, the burn-off lamination illustrated in FIG. 5 is substantially easier to produce. Finished shaped sinter structure portions are put together and joined with impregnating metal. The joint between the contact member and the carrier is thereby improved and several method steps of the fabrication procedure known up to the present time are eliminated.

The embodiments described with reference to FIGS. 1 through 5 illustrate only a few of the basic forms of the contact member according to the invention. In accordance with the foregoing disclosure, many forms of the contact members can be produced wherewith several regions of the contact member can be made of the material having exemplary contact characteristics and several regions of the contact member can be made, for example, of material having good electrical conductivity or good mechanical workability or good characteristics for joining with the carrier metal. Also, several component parts with different characteristics as discussed in the foregoing can be provided, whereby these characteristics are selected on the basis of the function required for the particular application and the shaped sinter structure portions of the individual component parts are thoroughly joined with the same impregnating metal of high electrical conductivity.

While the invention has been described by means of specific examples and in a specific embodiment, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

## Claims

1. A method of producing a contact member for high electrical loads comprising a plurality of parts, one of said parts comprising a non-welding material resistant to burn-off, another one of said parts comprising a solderable material having electrically conductive properties, the material of each of said parts being configured as a porous skeleton structure, said parts being disposed next to each other, and both of said parts being impregnated with a metal and the interface of said parts being devoid of a boundary layer which comprises pressing a powder mixture of non-welding material resistant to burn-off to form a first part, pressing a powder mixture of solderable electrically conductive material to form a second part, sintering said second part to make the same a porous structure, placing said parts so as to be fixed in position next to each other, impregnating said first and second parts while said parts are fixed in position next to each other with impregnating metal in a single step to join said parts with said metal.

2. The method of claim 1 wherein said parts are pressed and sintered so that one part fits at least in part within the other with a tolerance for the fit of a gap spacing between said parts of from 40 to 200 .mu.m.

3. The method of claim 1 wherein the impregnating metal is copper and wherein the quantity of said impregnating metal includes a surplus of up to 5% by weight such that a copper jacket is formed on the outer surface of the contact member.

4. The method of claim 1 wherein the quantity of said impregnating metal is less than the quantity required for a complete filling of the pores of said parts, the difference of said quantities being a deficiency in the amount of between 2 and 30% of the total pore volume of the contact member.

5. The method of claim 4 wherein said deficiency is between 5 and 20% of the total pore volume of the contact member.