Method For Improved Current Contacting When Welding Using A Current-Carrying Wire Electrode

Abstract

When welding with a consumable wire electrode, current contacting occurs when the electrode wire passes by a readily electrically conductive contact element. In order to improve the current contacting and reduce the wear of the contact element in particular, the invention proposes subjecting contact elements to a cold treatment prior to using same. The cold treatment has a cooling phase during which the temperature of the contact element is reduced to a lower target temperature, a subsequent holding phase in which the contact element is substantially held at the target temperature, and a final heating phase, in which the contact element is brought to an upper target temperature. The use of contact elements treated using the method according to the invention leads to a substantial increase of the wear resistance compared to untreated contact elements.

Claims

1. A method for improving current contacting when arc welding using a current-carrying wire electrode by means of an apparatus for arc welding in which, to pick up current, the wire electrode is passed through a contact element connected to a power source, in which method, before its intended use, the contact element is subjected to a cold treatment, in which the contact element is cooled down to a lower target temperature of below minus 50° C. in a cooling phase and is subsequently heated up to an upper target temperature in a heating phase.

2. The method as claimed in claim 1, wherein the lower target temperature is between minus 50° C. and minus 195° C., preferably between minus 100° C. and minus 185° C.

3. The method as claimed in claim 1, wherein the upper target temperature is between 20° C. and 40° C.

4. The method as claimed in claim 1, wherein, after the cooling phase and before the heating phase, the contact element passes through a holding phase, in which the contact element is kept at the lower target temperature for a duration of at least 30 seconds.

5. The method as claimed in claim 1, wherein the cooling of the contact element in the cooling phase and/or the heating of the contact element in the heating phase take place at a rate of between 1.5 K/minute and 10 K/minute.

6. The method as claimed in claim 1, wherein the cooling phase and/or the heating phase is interrupted for a prescribed time period during which the contact element is kept substantially at a temperature reached.

7. The method as claimed in claim 1, wherein the contact element is heated and subsequently cooled down again one or more times during the cooling phase and/or the holding phase.

8. The method as claimed in claim 7, wherein the temperature to which the contact element is heated during the cooling phase and/or the heating phase is in each case between −140° C. and −186° C.

9. The method as claimed in claim 1, wherein the temperature adjustment of the contact element during the cold treatment takes place by producing a correspondingly temperature-adjusted atmosphere in a cold chamber containing the contact element.

10. An electrical contact element for the current contacting of wire electrodes, wherein the electrical contact element has been subjected to a method for cold treatment as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0021] An exemplary embodiment of the invention is to be explained in more detail on the basis of the drawing. The drawing schematically shows in a temperature (T)—time (t) diagram the variation of the temperature of a contact element during the treatment by a method according to the invention.

DETAILED DESCRIPTION

[0022] A contact element of copper or a copper alloy that is at ambient temperature and for fitting in a welding torch, for example a welding torch for submerged arc or gas metal arc welding, is fed to a cold chamber and the latter is subsequently closed. By successively supplying a refrigerant, for example cold gaseous nitrogen at a temperature of minus 190° C., the temperature of the atmosphere inside the cold chamber is slowly lowered, for example at a rate ΔT/Δt of between 1 K/min and 10 K/min. As a result, the temperature of the contact element falls during a cooling phase K to a lower target temperature T.sub.1 of for example minus 150° C. Following the cooling phase K, the contact element is kept at the lower target temperature T.sub.1 for a time period of for example 1 min to 100 min (holding phase H). Following the holding phase H, the contact element is heated gradually, i.e. at a heating rate that is comparable to the cooling rate in the cooling phase K, to an upper target temperature T.sub.2 (heating phase W) by supplying a gas (for example nitrogen), the temperature of which is higher than the temperature inside the cold chamber. T.sub.2 corresponds for example to the ambient temperature.

[0023] In order to reduce stresses in the treated material occurring on account of the cold treatment, it is advantageous to increase the temperature of the workpiece in the cold chamber temporarily during the cooling phase K and/or the holding phase H. In these interim heating phases A.sub.1, A.sub.2, a temperature increase, by for example 10 K to 50 K, takes place to a value below the initial temperature. In the exemplary embodiment shown here, a first interim heating phase A.sub.1 takes place once the temperature of the wire electrode has reached a value of T.sub.4, and a second heating phase A.sub.2 takes place once the lower target temperature T.sub.1 has been reached. The heating phase A.sub.2 may be followed by a further interim heating phase, or the workpiece remains at the lower target temperature T.sub.1 for a certain time period.

[0024] During the cooling phase K, the supply of the refrigerant may be stopped one or more times and as a result the cooling of the contact element slowed or kept at a prescribed temperature. Similarly, in the heating phase W, the supply of warm gas may be interrupted one or more times, and so the heating rate slowed or the contact element kept at a prescribed temperature. In these intermediate holding phases, therefore, ΔT/Δt<<1 K/min. In the exemplary embodiment shown in the drawing, intermediate holding phases are inserted during the cooling phase K at a temperatures T.sub.3, with T.sub.1<T.sub.4<T.sub.3<T.sub.2, and during the heating phase W at a temperature T.sub.5, with T.sub.1<T.sub.5<T.sub.2. After the cold treatment, the contact element is removed from the cold chamber and fitted into a welding apparatus.