CZ9903851A3 - Output choke for direct current welding machine and method of using the same - Google Patents

Abstract

The output choke (50) is designed for DC an electric arc welder (10). Includes high a permeable core (102) with an air gap (g) for inductance control defined by the first and second poles terminated by first and second surfaces opposed to each other and each with two edges and an intermediate region. Said surfaces converge with each other from said intermediate areas towards the edges and thus form specific air gap (g) cross section where output choke (50) Is sufficiently rated for a welding current of at least 100 A.

Description

OUTPUT CHOKE FOR DIRECTIONAL ELECTRIC WELDING MACHINE AND METHOD OF USE

Technical field

The present invention relates to an output choke for a DC arc welder and a method of regulating the inductance in the output circuit of a DC electric welder using the choke.

with a change in length in the past

BACKGROUND OF THE INVENTION

The output circuit of an electric arc welding machine typically comprises a capacitor connected in parallel to the electrode and to the welded object of relatively low inductance to charge the capacitor, since the rectifier or voltage source supplies direct current. This inductance removes the alternating component of the welding current. Arc welder typically uses large chokes rated for high currents of about 50 A and acting as a current regulator to stabilize the arc. As the speed of the electrode shift towards the workpiece and the arc is changed, the welding current, large inductors connected in series with the arc fixed the air gap in the core to maintain a fixed value of the inductance as the current changes. Subsequently, the core saturation significantly reduced the inductance when high welding current values were reached. For this reason, the air gap width in the core has been increased to ensure constant inductance over the operating current of the welder. A certain choke has been selected for a given partial range of operating currents. The range of operating currents, however, was different for different welding activities. Thus, an air gap was chosen that was suitable for most welding operations. For a common choke, a small gap provides high inductance, but saturation occurs at relatively low welding currents. In order to increase the current carrying capacity of the choke, the air volume has been increased. Ová ová · vzduch vzduch vzduch vzduch zvět zvět vzduch vzduch zvět vzduch vzduch zvět zvět zvět zvět zvět vzduch vzduch vzduch · · · · · · · · · · · ·

-2 space to reduce inductance of choke of given size. For this reason, large chokes were produced with strong wires, withstand high currents and with large cross-section cores preventing saturation. The gap was large enough to accommodate a wide range of welding currents. Such chokes were expensive and greatly increased the weight of the welder. In addition, the inductor has a constant inductance up to the point of saturation, or, on the other hand, it is ideal for arc welding if the inductance is inversely proportional to the welding current. To alleviate these problems, an air gap having two to three different widths has been proposed. Thanks to this design a high inductance was achieved up to the moment of saturation of the small air gap. Then a lower inductance was achieved until a larger air gap was saturated. Using this concept of two or three graduated air gaps, the size of the choke could be reduced while increasing the range of choke regulated currents. In addition, an inverse relationship between current and inductance was achieved. The concept of using a graduated air gap of the output choke core allowed a smaller choke size; at the same time, there were one or more inflection points. Changing the feed rate of the electrode or arc length so that the welder works around the inflection points will oscillate the DC welder around the saturation point or around the inflection points, causing the welder to become unstable. A standard inductor with variable inductance was not the solution because the welding current changed too much in the region of the saturation knee. Such inductors with variable inductance were only suitable for small current applications.

At present it is common to use a fixed output choke for DC electric arc welding machines. Such a choke is bulky and the operating point is in the linear part of the inductance, avoiding a significant reduction in the output inductance of the welder. Such a choke is expensive and heavy. By using a graduated air gap, it is possible to reduce the choke size and at the same time increase the range of operating currents; however, the existence of an inflection point

-3 at the moment of saturation of one of the gaps caused less robustness and greater susceptibility of the welder to oscillation at certain arc lengths and electrode feed rates. Consequently, this proposed modification was not commercially acceptable.

The present invention is intended to overcome these drawbacks of the prior art.

SUMMARY OF THE INVENTION

The present invention relates to an output choke for. a DC arc welder that solves the problem of weight, cost and welding instability known for large chokes with a fixed air gap or smaller chokes with a graduated air gap. In accordance with the present invention, the DC reactor output choke comprises a highly permeable core having a region having a cross section with two distal edges and an air gap with continuously varying width at least a portion of the distance between said edges. The air gap therefore extends continuously away from both edges. In a preferred embodiment, the air gap has a rhombic cross-section continuously increasing from the edges towards the center of the core. This diamond core technology of the output choke for a DC electric arc welder gives an output circuit inductance that gradually changes over a given current range according to and is inversely dependent on the welding current. As the welding current increases, the inductance decreases continuously without any interruptions or jumps. Thus, the welding current never reaches the saturation point of the output choke, nor is the saturation elbow achieved. There is also no energy oscillation during welding. The present invention provides a robust welder that can withstand voltage variations of 5-10 V as arc length changes without causing arc instability. Thus, the choke provides current control over a wide range of welding currents without oscillation and without having to use a large output choke.

In accordance with another embodiment of the present invention, the output choke comprises a highly permeable air gap core

Further, an output circuit defined by first and second poles terminated by first and second surfaces opposing each other is provided. Each of these surfaces is characterized by two edges and an intermediate region, wherein said surfaces converge with each other from said intermediate region towards said edges and thus form a specific cross-section of the air gap. This cross-section preferably has a rhombic shape; however, it may also have an oval or other curvilinear shape as long as it maintains a continuous change in inductance as the welding current changes. In the preferred diamond air gap, the intermediate region is located at the center of the poles; however, it is possible for the intermediate region to be located closer to one of the edges of the opposing surfaces. This results in the shape of an uneven quadrilateral. In accordance with another embodiment of the invention, the gap may have a shape converging from one edge of the opposite faces towards the other edge of the opposite faces. This creates a triangular air gap. All of these assemblies result in a choke reacting to varying the output current of the welder by continuously varying the inductance without saturating between adjacent regions causing inflexion points that can lead to a parasitic oscillation or oscillation of the welder at certain electrode travel speeds and arc lengths.

proposes a method of regulating inductance in DC electric arc welder operating at a given range of operating currents and welding by means of an electric current flow through the gap between the electrode and the workpiece to be welded. The method comprises: providing an inductor of generally constant inductance for said current range designed to charge a capacitor connected in parallel to the welding gap or arc; providing an output inductor of continuously variable inductance over a given current range; and connecting the choke in series with said gap or arc between the arc and said capacitor. In said method, said inductance varies in accordance with a generally straight curve inversely proportional to the welding current so that with increasing current the inductance decreases continuously according to a generally straight curve. For arc welding, this relationship is optimal. In general

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The arc welder requires the inductor The straight curve described here has the meaning of a concave or convex linear relationship where the curve has no inflection points that occur at graduated air gaps.

The present invention relates to an arc welder that requires a relatively large output choke. This field is different from the electrical sources used for low power appliances such as light sources, audio devices or video devices. Such miniature power sources do not deliver the high currents or large current ranges required for arc welding.

currents exceeding 50 A. In the present invention, it operates with currents in the range of 100-500 A without saturating its core. The present invention contemplates currents of at least 100A. The foregoing clearly distinguishes the output choke described in the present invention from other inductors used in power supplies.

The present invention is directed to the field of arc welding where optimum operation requires an inverse relationship between inductance and welding current. Small inductors are usually used where the optimal operating relationship between current and inductance is linear. In order to ensure an inverse relationship between current and inductance, it is necessary to operate such small inductors in the region of the knee of the saturation curve. This ensures maximum inductance at low current, which swings to a lower value with increasing current value. Such inductors are referred to as inductors of variable inductance; however, they operate in a relatively small range of currents in the area of the elbow of the magnetic saturation curve and are typically designed to operate at relatively small currents of less than 10 A. Such a small inductor of variable inductance cannot be successfully used as a DC welding machine output choke because Here, the large and welding currents reach extreme values over 50 A.

A primary object of the present invention is to provide an output choke for a DC electric arc welder that:

-6 has a continuously variable inductance for a wide range of currents and is capable of withstanding currents in excess of 50 A and usually in the range of 100-500 A.

In addition, it is a further object of the invention to provide an output choke for a DC electric arc welder as described above, which has no inflection points and which does not cause oscillation of the current source when the electrode movement or arc length changes.

In addition, it is a further object of the invention to provide an output choke for a DC electric arc welder as described above that exhibits no regions of non-linearity and is capable of operating over a wide range of welding currents without saturation.

Another object of the present invention is to provide an output choke for a DC electric arc welder which is generally characterized by a direct current-inductance curve over a wide range of welding currents and a method of controlling the inductance in the output circuit of a DC electric welder using this choke.

In addition, it is a further object of the invention to provide an output choke for a DC electric arc welder and a method of using it as described above that allows a transition between high inductance at low electrode feed rate and low inductance at high electrode feed rate without forcing to another saturation curve for a given choke.

It is a further object of the present invention to provide an output choke for a DC electric arc welder, which is characterized by a diamond shaped cross-section of the air gap, providing said current-inductance relationship.

These and other objects and advantages will become apparent from the following description seen in conjunction with the accompanying drawings.

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BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an electrical diagram of a DC arc welder comprising an output circuit utilizing the present invention; Fig. 2 is a diagram schematically showing a basic standard output choke for a DC welder; Fig. 3 is a current-inductance graph showing saturation curves for different types of air gaps used Fig. 2 is a diagram schematically illustrating a DC reactor output choke designed to eliminate the basic choke problems shown schematically in Fig. 2; Fig. 5 is a current inductance graph showing the choke saturation curve schematically shown in Fig. 4; Fig. 6 is a diagram schematically showing an embodiment of an output choke for a DC welder shown in an exemplary embodiment of the invention; Fig. 7 is a graph of current; Inductance depicting the saturation curve of the choke shown in the exemplary embodiment of the invention and schematically shown in Figures 6, 8, 9 and 10 are details showing the core and air gaps of the various shapes used in the exemplary embodiment of the invention; current-inductance, similar to FIG. 7, illustrating a working curve for the exemplary embodiments of the invention shown in FIGS. 8-FIG. 10, FIG. 12 and FIG. 13 are details showing the choke core and showing air gaps of various shapes that are modifications 8-10, FIG. 14 is a detail showing the electrode core constructed in accordance with the present invention, wherein the diamond shape of the air gap used in the exemplary embodiment of the invention is given by two core parts that contact each other and are fixed to each other.

DETAILED DESCRIPTION OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, which illustrate embodiments of the invention to illustrate them without limiting the invention, FIG.

-8 · · · · · ·

200-1000 A. The power supply 12 shown as a single-phase power supply is connected via a transformer 14 to the rectifier 16. It will be appreciated that the rectifier 16 supplying direct current could also be powered by a three-phase power supply. In accordance with conventional practice, a capacitor 20 having a capacity of 20-150 mF is charged through an induction coil 22 having an inductance of 20 mH. The rectifier 16 charges the capacitor 20 through the inductor 22, which can be replaced by the inductance of the transformer. The output voltage of the rectifier 16 at the terminals 24, 26 corresponds to the voltage at the capacitor 20, which maintains the voltage at the arc gap and between the electrode 30 in the feeder 32 and the workpiece 34. A relatively large output choke 50 connected in an output circuit between the capacitor 20 and the arc gap a is required to provide a uniform flow of current through the arc gap. The invention relates to the design and operation of the output choke 50 to control the output current, as best seen in FIG. 6. In the past, the output choke 50 represented a large choke (as shown schematically in Figure 2), where the choke 100 has a highly dependent core 102 with an air gap g defined by two opposing faces 104, 106. The large current load requires the use of large wire for winding 110. A large number of turns is required to ensure high inductance. For these reasons, the choke 100 is bulky, heavy and expensive. By varying the size of the gap g between the opposing faces 104, 106, the core 102 is saturated with the high welding currents in the winding 110 according to the saturation curves as shown in the graphs of FIG. If the air gap g is relatively small for a given choke, a high inductance is achieved; however, if the welding current is small, the core is saturated. This is illustrated by the saturation curve 120. As the gap size g increases, the inductance decreases and the saturation current increases. This dependence on increasing gap size g is evident from the saturation curves 122, 124 and 126. Each curve has a corresponding saturation elbow or points 120a, 122a, 124a and 126a. When using a fixed air gap DC electric arc welding machine 10 as shown in FIG

-9obr.2 _the need to select a saturation curve in order to accommodate the desired welding currents. In order to meet both requirements, both high inductance and a large output current range, it is necessary to increase the size of the windings 110 as well as the core size. This results in a significant increase in choke size and weight. Reducing the size and weight of the choke also reduces the saturation current, resulting in uneven DC welder functionality. In order to overcome the problems associated with a fixed air gap output choke for regulating the current in the DC arc welding machine output circuit, it has been proposed to use a choke shown schematically in FIG. The choke 200 comprises a highly permeable core 202 with an air gap 210. In this choke, the air gap is graduated by a large gap 212 and a small gap 214 formed by the addition of the pole piece 216. as shown in FIG. This non-linear curve includes a first portion 230 applied until the small gap 214 is saturated and a second portion 232 that applies until the large gap 212. is saturated. These two portions create an effective current-inductance dependency indicated by the dashed line 240. This inverse current-inductance dependency is very beneficial for arc welding. The two-part curve allows adaptation to both low and high welding currents. However, there is an interrupted saturation elbow 232a causing an inflection point 242. In the arc welder operating mode given by the line 240, the inflection point 242 causes oscillation due to a change in feed speed, change in arc length, or change in arc voltage. Thus, a parasitic oscillation occurs around the inflection point 242, which reduces the efficiency of the proposed staged air gap approach, shown schematically in FIG.

The choke 50 of FIG. 1 includes a preferred embodiment of the present invention shown in FIGS. The core 50 of highly permeable material has a sufficiently large cross section, preferably limited by opposing faces, preventing saturation at currents in excess of 50 A and up to 100-500 A. Opposite surfaces 54. 56 of the core 50 are edges 54a, 54b and 56a, 56b. The corresponding edges form a relatively small air gap or touch each other. The intermediate area 58 between the opposing surfaces 54, 56 is characterized by a large air gap. The diamond air gap is located between the edges of the opposing surfaces 54, 56 and is formed by the portions 54c, 54d of the opposing surface 54 and the portions 56c, 56d of the opposing surface 56. The maximum distance of these portions is given by the distance of apexes 54e and 56e of the diamond air gap. Welding 60 with a welding current flow cross section and a number of turns providing the desired inductance leads the welding current around the core 52. Using the diamond air gap shown in Figure 6, the core of the selected size and the selected number of turns, the current-inductance dependency given by curve 70 in FIG. 7. Curve 70 represents a current-inductance dependency ideal for electric arc welding, where the electric current rises from 20 A to 200 A and often reaches values of up to 500-1000 A. As shown in Figure 8, a small air gap between edges 54a, 56a and 54b, 56b tends to saturate at low currents. As the electric current increases, the diamond air gap of the choke 50 cannot be saturated. At high current chokes, saturation occurs in the area of the largest air gap. As indicated by the arrows, saturation of the core through the rhombic air gap occurs in the region of the smaller air gap at a, but does not progress further up through b, c, d. The rhombic peak is selected to prevent saturation even at the highest welding currents . Thus, there is a linear relationship between current and inductance, which gradually changes and is continuous due to the use of a diamond air gap.

Another two preferred embodiments of the invention using diamond air gaps are shown in Figures 9 and 10. In Fig. 9, the poles 300, 302 of the core 52 have opposing surfaces 304, 306 that are curved to form an oval or elliptical air gap. This air gap includes small air holes

-11 • gaps • gaps • gaps 310 312 and a large air gap in the intermediate region 314. This preferred embodiment of the invention is characterized by a linear curve 72 that is slightly concave as schematically shown in FIG. 11. Generally a linear but convex curve 74 characterizes a preferred embodiment of the invention shown in FIG. 10, wherein a core 52 consisting of poles 320, 322 with corresponding opposing surfaces 324, 326. These surfaces are curvilinear with small air gaps 330, 332 separated by an enlarged air gap in the intermediate region 334. As can be seen, the preferred embodiment gaps from the center of the core towards its outer edges. An optimum application of the preferred embodiment lies in the diamond gap as best seen in FIGS. 6 and 8. The oval air gap in Fig. 9 and the curvilinear air gap in Fig. 10 are also characterized by a relatively flat curve of inverse proportion, which indicates the current-inductance relationship for the large currents regulated by the choke 50 used in the DC arc welder shown in Fig. 1.

In preferred embodiments, the air gap narrows continuously and is symmetrical with respect to the core axis. It is also possible to use asymmetric air gaps as shown in Fig. 12 and Fig. 13. The core 52a of the choke 50 in FIG. 12 is formed by opposing portions 350, 352 formed by convergent surfaces 360, 362 and 364, 366. These surfaces define a region of the large air gap 338 that is somewhat offset from the center of the core. Another asymmetric air gap embodiment is shown in FIG. 13, wherein the core 52b is formed by opposing portions 370, 372 with a tapered surface 374 and a perpendicular surface 376. The air gap shown in FIG. 13 is formed by a pole 370 with a flat surface inclined relative to the opposite portion 372. These constructions form air gaps with a small proportion in the left part and a large proportion in the right part. These two asymmetric air gaps give better results than the graduated air gap 210 in Fig. 4; however, they do not provide the desired effects shown in Fig. 11 achieved with »» *

The asymmetric air gap structures shown in the preferred embodiments of Figs. 8-10.

The choke 50 used in practice has the core shown in FIG. Rhombic symmetrical air gap 400 is formed by opposing portions 402, 404 with abutting edge surfaces 406, 408 that are in contact with each other, and is characterized by an intermediate air gap 400 with edge gaps 410, 412 continuously increasing up to the size of large gap 414. Poles 402, The air gap 400 is a diamond-shaped air gap whose dimension is largest at its apex or center and decreases towards both edges of the core. This diamond air gap is characterized by a relatively flat curve of inverse proportion, which indicates the current-inductance relationship that is optimal for arc welding. The air gap 400 may be filled with low permeability encapsulating material for packaging a choke for use in the art.

Claims (20)

PATENT CLAIMS An output choke for a DC electric arc welder, comprising a highly permeable core with an air gap for regulating the inductance defined by first and second poles terminated by first and second surfaces opposed to each other and each characterized by two edges and an intermediate region where said surfaces converge with each other from said intermediate region towards said edges, thus forming a specific cross-section of said air gap. Output choke according to claim 1, characterized in that said cross-section is symmetrical. Output choke according to claim 1, characterized in that said cross-section is rhombic. 4. The output choke of claim 1 wherein said cross section is oval. 5. The output choke of claim 1 wherein said cross section is curvilinear. 6. The output choke of claim 1 wherein said intermediate region is located closer to one of said edges. Output choke according to claim 6, characterized in that said cross-section is rhombic. 8. The output choke of claim 1, wherein said edges of said first surface contact edges of said second surface. • · • · -149. Output choke according to claim 8, characterized in that said cross-section is rhombic. 10. The output choke of claim 9, wherein said cross-section is oval. The output choke of claim 8, wherein said cross section is curvilinear. characterized in that An output choke according to claim said intermediate region being located at the edges. 8, characterized closer to one of the above 13. The output choke of claim 1 wherein said gap is filled with a low permeability material. 14. The output choke of claim 1 wherein said choke comprises a welding current guide winding, wherein said winding and core have a saturation preventing dimension for welding currents of at least 100 A. A method of controlling inductance in an output circuit of a DC electric arc welder operating at a given range of welding currents for welding current through a gap between an electrode and a workpiece and said method comprising: providing an inductive coil of generally constant inductance for said range of currents for charging a capacitor connected in parallel to said gap; providing a coil of continuously variable inductance in said current range; and connecting said choke in series with said gap between said gap and said capacitor. 16. The inductance control method of claim 15, wherein said inductance varies according to a generally straight curve inversely proportional to said welding current. 17. The inductance control method of claim 15, wherein said choke comprises a winding, including a process for conducting a welding current of at least 50A through said winding and said gap. 18. An output welder for a DC electric welder comprising a highly permeable core having a region having a cross section with two distal edges and an air gap in said region, said air gap with a continuously varying width at least a portion of the distance between said edges. 19. The output choke of claim 18 wherein said air gap has a generally rhombic cross section between said distal edges. 20. The output choke of claim 19, wherein said choke comprises a welding current guide winding, wherein said winding and core are at least 100A saturation at a welding current. 21. The output choke of claim 20, wherein said choke comprises a welding current guide winding, wherein said winding and core have a size to prevent a welding current saturation of at least 100 A.