GB1601589A

GB1601589A - Arc welding apparatus

Info

Publication number: GB1601589A
Application number: GB37073/77A
Authority: GB
Original assignee: Svejsemaskinefabrikken Migatronic AS
Current assignee: Svejsemaskinefabrikken Migatronic AS
Priority date: 1977-09-06
Filing date: 1977-09-06
Publication date: 1981-11-04
Also published as: IT7827375A0; FI782734A; DE2838471A1; FR2401736A1; BE870270A; JPS5462947A; ES473131A1; PT68521A; DK391278A; NL7809058A; SE7809391L; NO782977L

Description

(54) IMPROVEMENT IN ARC WELDING APPARATUS (71) We, SVEJSEMASKINEFABRjKKEN MIGATRONIC AIRS, formerly known as R0DBRF & HAASTRUP A/S, a Danish company cf Bonderup, DK-9690 Fjerritslev, Denmark, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to direct current arc welding apparatus and more specifically to arc welding apparatus in which the welding current is obtained from an alternating current mains source or generator.

The current from the mains source or generator is fed through a conventional controlled frequency converter which substantially increases the frequency of the alternating current and then to a transformer and a rectifier for obtaining the welding current in the pulsating direct form. A welding apparatus of the described type has several advantages such as good control of welding parameters, low cost and power consumption and low weight. The only serious drawback of such apparatus is that the pulsating welding current fed to the electrodes causes disturbing sounds of such an intensity that its use hitherto has been restricted.

The present invention aims at minimizing or removing such disturbing sounds when welding and with retention of the above-mentioned advantages. The present invention consists in direct current arc welding apparatus comprising first and second welding electrodes that are supplied with pulsating direct current derived from an alternating current source, the current from the said current source being fed through a controlled frequency converter which substantially increases the frequency of the alternating current and then to a transformer and a rectifier for obtaining the welding current in the pulsating direct form, wherein a smoothing filter for smoothing the pulsating current from the rectifier is connected between the output of the rectifier and the welding electrodes.

In order that the invention may be better understood, some examples of apparatus embodying the invention will now be described with reference to the accompanying drawings, in which: Figure I shows the general assembly of the apparatus comprising the mains current supply, the frequency converter, the transformer, the rectifier and the current control means, coupled in series; Figures 2 - 7 show different solutions of the above-defined problem, embodying the present invention, in the form of circuit diagrams comprising the circuit of the apparatus starting from the secondary part of the transformer.

In Figures 2 - 7, 1 is the secondary part of the transformer; 2 is the rectifier; 3 is a capacitor means shunted between the current supply to the welding electrodes, said capacitor means having a suitable capacity for leveling out the pulsating current components to an extent which is acceptable from the acoustic point of view; 5 is a choke means between said capacitor and the welding electrode of such an inductance that the welding properties are not effected adversely; 4 is a further choke means preventing the capacitor means from exerting damage on or otherwise adversely affecting the rectifier or the frequency converter. The capacity of the capacitor means 3, which preferably is adjustable, is chosen for each welding apparatus as necessary for any desired result and effect. A common value of the capacitor is above 500,u F, preferably 1000 - 5000 ,u F for an apparatus with welding currents of 200 - 400 A. The inductance of choke means 5 is about 50 - 200 ,u H and adjusted to the value of capacitor 3 in order to make the capacitor 3 and the choke 5 act together as a smoothing filter. The welding load gap is indicated by 6.

The embodiment of Figure 3 is in principle equivalent to the embodiment of Figure 4. In the latter, however, the choke means 4 of Figure 3 has been incorporated into the transformer, which results in an especially compact apparatus. The same relationship exists between the embodiments of Figure 5 and 6. In these embodiments, however, the rectifier is of the bridge type. In all these embodiments the further choke means preferably comprises two chokes.

Figure 7 shows an alternative solution embodying the invention which, instead of the capacitor 3 and the choke means 4 and 5, comprises a low-pass filter 7 of the active type for attenuating the pulsating components of the welding current to an acoustically acceptable value. For obtaining optimal welding properties in each individual case the filter can be con tinuously adjusted as regards its parameters.

The term "active" refers to the fact that such a filter comprises active electronic components, i.e. transistors, diodes, thyristors, etc., as well as passive components, i.e. resistors, capacitors, inductances, etc.

It is of course apparent that the rectifier of the embodiment of Figure 7 can also be of the bridge type as in Figures 5 and 6. Furthermore, it is apparent that the active filter 7 may only represent the function of the filter 3, 5 or Figures 2 - 6, while the choke means 4 can be left as a means comprising only passive com- ponents or vice versa. However, preferably the filter 7 represents all of the functions of elements 3, 4, 5.

When the filter 7 is made adjustable the controls are suitably located near or at the welding station, preferably on the welding handle itself.

This enables the operator to directly see what happens when an adjustment of the filter is made. He does not have to leave the welding station to perform a necessary adjustment. The fact that the filter 7 can be continuously controlled makes it possible for the operator to obtain optimal welding results. The filter 7 can also advantageously be arranged so as to automatically adjust its parameters for any desired predetermined welding current.

The details of the design and application of the above-defined circuits can be understood and determined by any expert in this particular field of technology.

WHAT WE CLAIM IS: 1. Direct current arc welding apparatus com- prising first and second welding electrodes that are supplied with pulsating direct current derived from an alternating current source, the current from the said current source being fed through a controlled frequency converter which substantially increases the frequency of the alternating current and then to a transformer and a rectifier for obtaining the welding current in the pulsating direct form, wherein a smoothing filter for smoothing the pulsating current from the rectifier is connected between the output of the rectifier and the welding electrodes.

2. Apparatus as claimed in Claim 1, wherein the smoothing filter comprises a capacitor connected across the rectified output and a choke connected between the output of the rectifier and a first of the welding electrodes.

3. Apparatus as claimed in Claim 2, wherein the second welding electrode is connected through a further choke to the mid-point of the secondary winding of the transformer.

4. Apparatus as claimed in Claim 2, wherein the second welding electrode is connected to the mid-point of the secondary winding of the transformer, the apparatus comprising further choke means connected between end terminals of the secondary winding of the transformer and the rectifier.

5. Apparatus as claimed in Claim 2, wherein the rectifier is of the bridge type and comprising further choke means connected between the end terminals of the secondary winding of the transformer and the rectifier.

6. Apparatus as claimed in Claim 4 or 5, wherein the further choke means is incorporated into the transformer assembly.

7. Apparatus as claimed in Claim 1, wherein an active filter is connected between the output of the rectifier and the welding electrodes.

8. Direct current arc welding apparatus, substantially as herein described with reference to Figure 1, in combination with any one of Figures 2 to 7 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tinuously adjusted as regards its parameters. The term "active" refers to the fact that such a filter comprises active electronic components, i.e. transistors, diodes, thyristors, etc., as well as passive components, i.e. resistors, capacitors, inductances, etc. It is of course apparent that the rectifier of the embodiment of Figure 7 can also be of the bridge type as in Figures 5 and 6. Furthermore, it is apparent that the active filter 7 may only represent the function of the filter 3, 5 or Figures 2 - 6, while the choke means 4 can be left as a means comprising only passive com- ponents or vice versa. However, preferably the filter 7 represents all of the functions of elements 3, 4, 5. When the filter 7 is made adjustable the controls are suitably located near or at the welding station, preferably on the welding handle itself. This enables the operator to directly see what happens when an adjustment of the filter is made. He does not have to leave the welding station to perform a necessary adjustment. The fact that the filter 7 can be continuously controlled makes it possible for the operator to obtain optimal welding results. The filter 7 can also advantageously be arranged so as to automatically adjust its parameters for any desired predetermined welding current. The details of the design and application of the above-defined circuits can be understood and determined by any expert in this particular field of technology. WHAT WE CLAIM IS:

1. Direct current arc welding apparatus com- prising first and second welding electrodes that are supplied with pulsating direct current derived from an alternating current source, the current from the said current source being fed through a controlled frequency converter which substantially increases the frequency of the alternating current and then to a transformer and a rectifier for obtaining the welding current in the pulsating direct form, wherein a smoothing filter for smoothing the pulsating current from the rectifier is connected between the output of the rectifier and the welding electrodes.