Improved methods and configurations for martensite-free brazing processes

Abstract

In a method of brazing a conductive connecting piece of a conductive material, e.g., a cable shoe, to a workpiece of a conductive material by a temperature controlled brazing process, the heat required for brazing is generated by igniting an electric arc between a carbon electrode and the conductive connecting piece, the voltage and current are electronically controlled by the control electronics to achieve a temperature generation resulting in martensite-free brazing, the applied DC voltage uses the carbon electrode as the negative electrode and the conductive connecting piece as the positive electrode, and the carbon electrode has a tapered, chamfered or pointed end at the end facing the electric arc.

Description

[Technical field]

[0001] The present invention relates to an improved method for brazing connecting pieces of electrically conductive material, for example metal, to metallic surfaces by an improved type of temperature controlled brazing. [Background technology]

[0002] Temperature-controlled brazing methods exist by which, for certain types of materials, e.g. steel, martensite-free brazing can be obtained, i.e. the brazing is achieved without any detrimental structural changes (martensite formation) in the workpieces. Brazed joints are obtained with the parts of the workpieces below the brazed joint being more or less free of martensite formation, e.g. in railway tracks (rails), piping / pipelines, and wind power installations. The present invention relates to an improved method and to an apparatus for carrying out the improved method.

[0003] The development of rail traffic is accompanied by ever-increasing speeds and heavier axle loads. This places increasing demands on the strength of the rail track and its ability to withstand wear, so that rails are manufactured from high alloy steels to meet these more stringent requirements. The materials from which rails are manufactured are sensitive to thermal effects that can cause structural changes (hardening effects) known as martensite formation.

[0004] Martensite formation can lead to the formation of cracks in the rail material and, under higher loads, the rail can break, with catastrophic consequences for rail traffic, so it is very important to robustly braze signalling wiring and cables to the rail using a method that does not lead to the formation of martensite in the rail.

[0005] Prior art in this field includes US Pat. No. 5,393,633, which discloses a method and configuration for a martensite-free brazing process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] British Patent No. 2376202 Summary of the Invention [Problem to be solved by the invention]

[0007] The most serious problem with the current methods employed on railway tracks is that a large amount of heat is generated under the brazed joint, which is caused by the electric arcs generated in the brazing process, creating deleterious structural changes or martensite formation.

[0008] The subject matter of the present invention includes the special shape of the electrodes used in the process and further means for controlling the voltage and current used in the process. Advantages of this method include less heat generation, less power consumption, and the convenient brazing of the connecting pieces due to the larger conductor cross-sectional area than known techniques. Today, known brazing techniques are not capable of brazing large cables, i.e., cables with a cross-sectional area of ​​about 25-35 mm. 2 It is virtually impossible to connect cables with larger cable cross sections without significant martensite formation. 2 Testing of the new proposed method involving conductor cross-sectional areas of 0.1 mm or less shows good results with no or only minimal martensite formation after brazing.

[0009] The present invention relates to a new method of temperature controlled brazing and an apparatus for carrying out said method, which reduces the problem of martensite formation while at the same time reducing power consumption and heat generation. Furthermore, the new method facilitates the brazing of cable shoes to increase the cross-sectional area of ​​the conductors involved.

[0010] The object of the present invention is to generate an electric arc through a carbon electrode and to produce a brazed joint of a workpiece to a rail without the electric arc coming into direct contact with the rail, producing a connection of equal or better quality compared to the prior art, but consuming less power and generating less heat.

[0011] A further object is to facilitate brazing of conductors having a larger area than permitted by the prior art. [Means for solving the problem]

[0012] In an embodiment of the present invention, the carbon electrode itself constitutes the electrical resistance in the brazing process, and the length, diameter and shape of the carbon electrode affect the electrical resistance in the process, and therefore also the current strength and voltage in the brazing process.

[0013] Carbon electrodes offer the best control over the arc length during the brazing process because the carbon material has good refractory properties, whereas the metal electrodes melt, and therefore the carbon electrode experiences negligible change in length during the brazing process compared to the molten metal brazing pin.

[0014] Yet another objective of the present brazing process applied to fasten a cable shoe or other electrically conductive contact connection to a steel rail is to prevent the electric arc from coming into direct contact with the workpiece, which is achieved if the electrically conductive contact connection consists of a solid plate of compact electrically conductive material, for example copper. The brazing process in this context does not include flux or brazing material from any brazing pin forming the electrode. The brazing material does not have to flow through the cable shoe to the underlying workpiece (rail). Due to the structure of the cable shoe, the flux and brazing material are located under the electrical contact connection or cable shoe itself. The entire plate of compact electrically conductive material, for example copper, forms a buffer that prevents too high temperatures, which for example affect the rail and lead to martensite formation. Furthermore, the electrode is not finally forced downwards during brazing, without the risk of adversely affecting the brazed joint.

[0015] Another object of the invention is to control the current intensity during the process. If the electrode is raised, the arc length increases. This leads to a large voltage drop across the arc and a decrease in the current intensity in the electric circuit. The arc length cannot be increased completely arbitrarily, since after a certain length, if the resistance becomes too great, the arc will collapse. A small gap between the electrode and the workpiece, the so-called lift height, reliably prevents the arc from being extinguished during the brazing process. A low current intensity during the process is very advantageous, since this prevents martensite formation.

[0016] While it is preferred in the present invention to use a ceramic guard ring, it is also preferred to use a guard ring made from a combination of metallic and ceramic materials as the combination provides increased protection to the brazing gun.

[0017] From the viewpoint of energy consumption, the material and design of the guard ring play an important role. The guard ring of the embodiment of the present invention is designed with a larger diameter to avoid the guard ring becoming too hot, and also has the advantage of being able to accommodate a larger volume of hot gas.

[0018] The guard ring, together with the gripping sleeve, also prevents the operator from coming into contact with the arc itself or the hot gases that are formed, reducing the need for protective equipment for the operator. It also eliminates the risk of eye injury to operators or others who happen to look towards the arc during the brazing process.

[0019] According to a first aspect of the invention, there is provided a method for brazing a conductive connecting piece of a conductive material, for example a cable shoe, to a workpiece of a conductive material by means of a temperature-controlled brazing process, generating the heat required for brazing by striking an electric arc between a carbon electrode and the conductive connecting piece, said method comprising the steps of: providing a DC voltage between the carbon electrode and a conductive connecting piece, e.g. a cable shoe; measuring the voltage across said arc; measuring the current of the arc; controlling the voltage applied between the carbon electrode and the conductive connecting piece, and therefore across the arc; and calculating in real time, continuously or continuously, the power generated in the arc, the method comprising: - measuring the current in the arc and the voltage across the arc in real time, either continuously or continuously; - continuously or continuously calculating in real time the corresponding generated power as a mathematical product of said current and said voltage; controlling a DC voltage and thereby the generated power; Further comprising: The applied DC voltage uses a carbon electrode as the negative electrode and a conductive connecting piece as the positive electrode. The carbon electrodes have a tapered, chamfered or pointed end on the end facing the electric arc.

[0020] This method is receiving an operator input of a conductor cross-sectional area; using the input to adjust the calculation and controlling the DC voltage to achieve and maintain the proper temperature at the brazing site; It may further include.

[0021] According to a second aspect of the invention, there is provided an apparatus for brazing an electrically conductive connection piece to a workpiece of electrically conductive material by a temperature controlled brazing process, the heat required for brazing being generated by striking an electric arc between a carbon electrode and the electrically conductive connection piece, said apparatus comprising: (a) a means for engaging a conductive connecting piece towards a workpiece, the means for engaging including a guard ring and a carbon electrode; (b) means for supporting the electrode, the means including means for moving the electrode between a position in which the electrode engages the electrically conductive connecting piece and is then engaged by the engaging means, and a retracted position from which the electrode is lifted; and (c) a DC voltage unit for providing and applying a DC voltage of a specific polarity between the conductive connecting piece and the carbon electrode, the DC voltage unit including a voltage adjustment unit; (d) a voltage sensor for measuring a voltage between the conductive connecting piece and the carbon electrode; (e) a current sensor for measuring a current flowing through the carbon electrode; (f) processing means, including means for generating an output signal to control said voltage regulation unit, and further including means for continuously or continuously calculating the power generated at said arc in real time; (g) switching means operable to connect said means for applying a voltage in an electrical circuit to said electrode and such conductive connecting piece, wherein when said means for engaging is applied and the switching means is operated to close said electrical circuit, said means for supporting and moving lifts the electrode from the workpiece and ignites an electrical arc between the electrode and the conductive connecting piece; and Including, (h) the carbon electrode has a first end for the electric arc that is pointed, tapered, or beveled; (i) The DC voltage unit is configured such that the polarity of the applied DC voltage is of a specific polarity using the carbon electrode as the negative electrode and the conductive connecting piece as the positive electrode.

[0022] The apparatus may be further configured to automatically provide heat using a first power during a first portion of the total brazing time and a second power during a second portion of the total brazing time, preferably the first power being set at a value to rapidly heat the brazing site and the second power being at a value lower than the first power to maintain the temperature achieved at the brazing site.

[0023] To further regulate the heating, a process may be provided having three or more distinct periods of different heat supply. The process may, for example, have four periods or steps: step 1 fast heating, step 2 slow heating, step 3 maintaining temperature, and step 4 slow cooling.

[0024] The apparatus may further comprise an input device for setting parameters appropriate for the electrical cross-sectional area of ​​the electrical conductors to be brazed; The processor is configured to calculate the time and voltage for the braze taking into account parameters for providing the appropriate voltage and time to achieve the appropriate amount of heat for the appropriate length of time.

[0025] This has the advantage of more precisely controlling the brazing, for example with regard to time and temperature.

[0026] According to a third aspect, a cable shoe for martensite-free brazing is provided, the front part being formed as a compact plate adapted to be brazed in contact with the workpiece, the rear end being formed to define a cable cavity for the cable, the cable shoe being further designed such that the cable cavity extends into a tapered cavity, giving the cable shoe a uniform cross-sectional area along its length from the compact plate to the beginning of the cable cavity. Tests have shown that advantageously, a cable shoe with an extended cavity reduces the power required to perform the brazing process. Furthermore, the compact plate of the front part may comprise a brazing material, for example a quantity of silver alloy with or without a flux material, which is preferably attached to the compact plate by pressing or melting. Particularly advantageous is to manufacture the cable shoe by pressing a brazing clip comprising a silver alloy towards the compact plate, thereby attaching the brazing clip to the compact plate. [Brief description of the drawings]

[0027] An embodiment of the invention will now be described in more detail with reference to the accompanying drawings.

[0028] [Figure 1A] 1 shows a schematic overview of the brazing process. [Figure 1B] A detail from FIG. 1A is shown. [Figure 1C] 1 shows a schematic diagram of the direction of ion and electron movement in a brazing arc; [Figure 1D] 1C and 1C show diagrammatically the direction of ion and electron movement in a brazing arc of reverse polarity. [Diagram 2] FIG. 1 is a partial side view of a brazing gun embodying the present invention. [Diagram 3] 4B shows a brazing gun in cross-sectional view taken along line III-III of FIG. 4A. [Figure 4] FIG. 2 is a side view showing a brazing gun partially cut in the longitudinal (axial) direction. [Diagram 5] Shows the brazing work on the rails. [Figure 6] 1 shows a brazing operation on a pipeline section. [Figure 7] 1 shows a brazed joint between an outer wheel rim and an inner wheel rim of a railway carriage. [Figure 8] 1 shows a conductive connecting piece in the form of a cable shoe in a side view. [Figure 9] FIG. [Figure 10A] 1 shows the cable shoe as viewed from above. [Figure 10B] FIG. 10B is a rear view of the cable shoe of FIG. 10A. [Figure 10C] FIG. 10B is a side view of the cable shoe of FIG. 10A. [Figure 10D] FIG. 10B is a front view of the cable shoe of FIG. 10A. [Figure 11] FIG. 1 is a voltage / current / temperature diagram of a brazing process according to the prior art. [Figure 12A] FIG. 1 is a voltage / current / temperature diagram of the brazing process according to the new method applied to a first cross-sectional area. [Figure 12B] FIG. 13 is a current / voltage / temperature diagram of the brazing process according to the new method applied to a second cross-sectional area. [Figure 13] FIG. 13 is a front view of the main input panel for entering brazing parameters. [Figure 14A] 1 is a control and regulation flow chart for the brazing process. [Figure 14B] FIG. 2 is a flow diagram through the method steps. [Figure 15A] FIG. 2 is a partial view of the front portion of the brazing gun, partially in longitudinal (axial) section; [Figure 15B] FIG. 2 is a side view of a carbon electrode according to an embodiment of the present invention. [Figure 15C] FIG. 2 is a side view of a carbon electrode according to an embodiment of the present invention. [Figure 15D] FIG. 2 is a side view of a carbon electrode according to an embodiment of the present invention. [Figure 15E] 1 is a top view of a circular cross-section electrode, below a top view of a square cross-section electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Fig. 1A shows diagrammatically the necessary components and the steps of the brazing process itself according to a related embodiment, where the power source typically used is a battery 1 from which the current is conducted to an electronics unit 2. The electronics unit 2 is configured to process data received from the brazing gun 5 via its power and signal cables, as well as data from an external power source. The electronics unit 2 processes all the information and is configured to regulate the current and voltage supply to the brazing gun 5, for example by electronically regulating the voltage level. By said regulation, the time and the current consumption can be controlled during the brazing process, thus, in combination with also the control of the temperature in the substrate / workpiece, a satisfactory brazing can be achieved with a minimum of energy consumption.

[0030] When the circuit breaker 3 closes the electric circuit with the lift magnet in the brazing gun 5, the carbon electrode 6 located in the electrode holder 7 first shorts the circuit with the cable shoe 10, so that the electric arc 8, which is then protected by one or more guard rings 9, operates on the compact and flat surface of the cable shoe 10, so that the cable shoe forms one pole and the carbon electrode 6 forms the other pole. Heat is transferred through the cable shoe 10, activating the flux material between the cable shoe 10 and the brazing material 12, preparing and cleaning the surface for brazing between the brazing material 12 and the cable shoe 10, heating the brazing material 12 activates the flux material 13 on the workpiece 14, and a brazed joint is formed by the brazing material 12 on the workpiece 14. As a result, the cable shoe 10 is firmly brazed to the workpiece 14 without the electric arc 18 coming into direct contact with the workpiece 14.

[0031] Furthermore, because the electrical circuit is formed through the cable of the cable shoe 10 or through the guard ring 9 and not through the workpiece 14 itself, no undesirable sparks / arcs are created between the workpiece 14 and the cable shoe 10.

[0032] In the new brazing process, a whole plate of compact conductive material, for example copper, forms a buffer that prevents high temperatures from affecting, for example, the rail and forming martensite. Copper particles are released from the plate of the cable shoe during the brazing process and are deposited in the form of a thin layer on the carbon electrode (see FIG. 1C). During the brazing process, small cavities may be formed in the cable shoe 10. The cable shoe may be configured to allow this cavities formation without compromising the mechanical strength of the cable shoe to a significant level.

[0033] FIG. 1D shows diagrammatically the direction of ion and electron movement of a brazing arc with reversed polarity compared to FIG. 1C. The oval area indicates the width of the arc, suggesting that a narrower, more focused arc is achieved using the polarity corresponding to the negative carbon electrode of FIG. 1C, whereas a wider or more blurred arc is obtained by connecting the carbon electrode with a positive polarity. Tests have shown that choosing a negative polarity with the carbon electrode allows a reduction in the energy required to perform brazing. The energy reduction is about 30%.

[0034] From an energy point of view, the guard ring plays an important role during the brazing process. The guard ring 9 is formed so as to have a good thermal insulation function. The guard ring 9 may be formed of a ceramic material and equipped with a toothed lower edge. In this case, the hot gases formed during the brazing process are discharged in a radial direction. If the guard ring is formed of metal and has a smooth lower surface, the gases leave the guard ring in an axial direction, so that more heat is transferred to the guard ring 9. The guard ring 9 retains its shape and function and is stable throughout the brazing process. The heat absorbed by the guard ring is conducted to the cable shoe 10. As a result, less electrical energy and / or power is consumed during the brazing process and a martensite-free brazing is performed.

[0035] FIG. 2 is a side view of the brazing gun 5, on whose front side the carbon electrode 6 can be seen. Before starting the brazing process, the gun 5 with the carbon electrode 6 is lowered into the cable shoe 10, whereby the carbon electrode 6 is pressed flush against the lower edge of the guard ring 9. The guard ring 9 is fixed in a ring holder 15. When the circuit breaker or start button 3 is pressed, the circuit is short-circuited, after which the lift magnet raises the electrode 6 to a height above the conductive connection piece 10 and the arc 8 is struck. The guard ring 9 and the gripping sleeve 18 shield the operator from the process. Also shown in the figure are a screw 16 for ejecting the guard ring and a screw 17 for ejecting the electrode. During the brazing process, the guard ring 9 can act as a terminal in a grounding operation if it is made of metal or other conductive material.

[0036] FIG. 3 shows a cross-section of the brazing gun 5 from the front, where the circuit breaker 3 can be seen and, centrally in the mouth of the gun, the carbon electrode 6 in the electrode holder 7, together with the ring holder 15 and gripping sleeve 18, are located.

[0037] FIG. 4 shows a cross section of the end of a brazing gun 5, showing the circuit breaker 3, the carbon electrode 6 in the electrode holder 7, the guard ring 9 of ceramic material in the ring holder 15, the gripping sleeve 18, the screw 16 for ejecting the guard ring and the screw 17 for ejecting the electrode. A very important component in the brazing process is the carbon electrode which forms an electrical resistance, the length, the diameter and the shape of the carbon electrode affecting the electrical resistance in the process. The current intensity and the voltage during the brazing procedure are controlled by the control electronics. The control electronics are configured to provide the voltage and the current as a function of time according to FIGS. 12B, 12C and 12D to achieve a suitable brazing temperature at the brazing site (see below).

[0038] Figure 5 shows a brazing gun 5 used on a rail 14. A conductive piece 10 in the form of a cable clip is brazed securely to the head of the rail. Brazing may also be performed on the web part or on the foot of the rail.

[0039] Figure 6 shows a brazing gun 5 used on a workpiece 14 in the form of a section of piping. An electrically conductive connection piece 10 in the form of a cable shoe is securely brazed to the pipe. Strict requirements apply, among other things, to piping in nuclear power plants, where brazing must be carried out without causing structural changes in the piping material which could lead to crack formation. If the pipe is filled with gas or oil, but also if, for example in the chemical industry, the pipe is filled with temperature-sensitive materials, it is important to be able to function at low temperatures during brazing.

[0040] FIG. 7 shows a railway carriage wheel. The inner wheel 20 is fixed to the wheel axle 21 and a damper 23, for example of rubber material, is arranged between the inner wheel and the outer wheel ring 19, the so-called tread. The figure shows how a connecting piece 22 of electrically conductive connecting material joins the inner wheel 20 to the outer wheel ring 19 so that an electric current can flow from the railway carriage to the railway track. Due to the risk of martensite formation and the associated crack formation, no attempt has been made so far to employ pin brazing in connection with this connection. The present brazing process eliminates martensite formation in any case and makes it possible to carry out brazing in this field as well.

[0041] 8 is a side view of the cable shoe 10, a connecting piece of conductive material in which one can see the terminal connector 24 to the electric circuit. The terminal connector 24 is fixed to an electric cable 25 which leads to the cable shoe 10, and on its opposite side consists of a solid plate 26 of compact material. Around the periphery of this continuous plate 26 of compact material is arranged a brazing clip 27 which is pressed against the plate 26 of the cable shoe 10 itself during manufacture, and between the cable shoe 10 and the brazing clip 27 is provided a flux material 28 which is activated during the brazing process.

[0042] 9 is also a side view of the cable shoe 10, in which on the flat continuous compact plate 26 of the cable shoe 10 the brazing itself is performed by a brazing gun 5, in which one can see the brazing clip 12 pressed against the cable shoe 10, and a flux material 11 is heated between the underside of the cable shoe 10 and the brazing clip 12. Another flux material 13 is provided between the workpiece 14 and the clip 27, which becomes activated when the brazing clip 27 is heated and starts to clean the workpiece 14 before brazing the conductive connecting piece 10.

[0043] The brazing clip 12 has a uniform thickness before it is applied to the workpiece to be fastened. When the brazing material is melted by the heat applied through the compact plate 26 of the cable shoe 10, the surface tension of the molten material wetting the compact plate 26 and the workpiece 14 results in a variation in thickness in the sense that the distance between the compact plate 26 and the workpiece, i.e. the distance of the area occupied by the brazing material, is minimized, thus ensuring a strong bond between the compact plate 26 and the workpiece and good electrical and thermal conductivity. The flux material 11 and 13 fulfills the following tasks and has the following properties: 1) it cleans the surface, 2) it removes any oxides present, 3) it prevents re-oxidation, 4) it is displaced by the molten brazing material, 5) it acts as an electrical conductor when the cable shoe 10 is grounded through the rail, 6) it promotes the dissipation of heat due to the fact that it has good thermal conductivity, and 7) it wets the surfaces to be joined.

[0044] Another requirement is that the flux materials 28 and 29 should be activated within a certain temperature range. The flux materials, the brazing material and the brazing process must be compatible with each other. The flux materials are already activated at the start of the brazing process and remain effective until the brazing is achieved.

[0045] Brazing performed at about 500°C is called hard brazing, as opposed to soft brazing, which occurs at lower temperatures. The brazing material used in the brazing process of the present application is intended for hard brazing. However, flux materials intended for hard brazing are not suitable for the present process, as the process is performed too quickly, in about 2 seconds. In the present brazing process, flux materials 10 are used that are usually suitable for soft brazing and therefore are activated at lower temperatures, but do not disintegrate before the brazing is completed due to the short working time.

[0046] To reach the required brazing temperature but using as little energy as possible, a high power input is required for a short time. Railway tracks, thick-walled pipes and similar metal profiles are effective heat sinks. The high power input creates a heat front that moves down through the cable shoe into the rail, where the temperature is suitable for hard brazing but not for martensite formation.

[0047] The cable shoe 10 is a buffer against localized overheating and produces a relatively smooth temperature distribution over the entire melting surface. Indirect heating is provided by a carbon electrode 6. An electric arc 8 is formed between the carbon electrode 6 and the cable shoe 10. This is in contrast to conventional pin brazing, where the arc acts directly on the rail and / or the molten solder on the rail.

[0048] Figure 10A shows the cable shoe 10 seen from above. The front part is formed as a compact plate 26 to which a brazed clip 27 is attached. The dashed lines show the definition of the cable cavity 31 for the cable. The cable shoe 10 is further designed such that the cable cavity 31 extends into a tapered cavity 33, giving the cable shoe 10 a uniform cross-sectional area from the compact plate to the beginning of the mating cable.

[0049] FIG. 10B is a rear view of the cable shoe of FIG. 10A.

[0050] 10C is a side view of the cable shoe of FIG. 10A, and FIG. 10D is a front view of the cable shoe of FIG. 10A.

[0051] Thus, a cable shoe for martensite-free brazing is provided, the front part being formed as a compact plate adapted to be brazed in contact with the workpiece, the rear end being formed to define a cable cavity for the cable, the cable shoe being further designed such that the cable cavity extends into the tapered cavity, giving the cable shoe a uniform cross-sectional area along its length from the compact plate to the beginning of the cable cavity. Tests have shown that advantageously the cable shoe with the extended cavity reduces the power required to carry out the brazing process. Furthermore, the compact plate of the front part may comprise a brazing material, for example a quantity of silver alloy with or without a flux material, which is preferably attached to the compact plate by pressing or melting. Particularly advantageous is to manufacture the cable shoe by pressing a brazing clip containing a silver alloy towards the compact plate, thus attaching the brazing clip to the compact plate.

[0052] In railway signaling and cathodic protection systems which operate at low voltages and currents, it is particularly important that the brazed joints 50 have an overall low transition resistance to prevent interference in the system.

[0053] At high currents and voltages, high transition resistance can generate heat in the brazed joint, which can damage and / or melt the brazed joint. For this reason, low transition resistance is important in the brazed joint, as the connection must also handle high return currents in rail traffic systems. For similar reasons, low transition resistance is also important in protective earths.

[0054] FIG. 11 is a voltage / current / temperature diagram of a prior art brazing process.

[0055] Figures 12A and 12B are voltage / current / temperature diagrams of the new brazing process. Compared to the existing pin brazing, there is no large current surge as when a short circuit occurs. Both the voltage and current curves are relatively constant over time. This diagram shows that the invention provides optimal control of the brazing process. Therefore, the temperature during the brazing process can also be regulated and controlled, which is a prerequisite for obtaining a martensite-free braze.

[0056] In comparison to some prior art martensite-free brazing, the apparatus and method of the present invention can include a two-phase process in which the voltage is automatically controlled to provide heat using a first power during a first portion of the total brazing time and a second power during a second portion of the total brazing time. Preferably, the first power is set at a value to rapidly heat the brazing site, and the second power is at a value lower than the first power to maintain the temperature achieved at the brazing site.

[0057] FIG. 12A is a voltage / current / temperature diagram of the brazing process according to the new method applied to a first cross-sectional area. A strength of the new method is the ability to achieve brazing of larger cross-sectional areas. The brazed cross-sectional area that produces the diagram of FIG. 12A is 16 mm 2 It is.

[0058] FIG. 12B is a current / voltage / temperature diagram of the brazing process according to the new method applied to a second cross-sectional area. The brazed cross-sectional area which gives rise to the diagram of FIG. 12B is 120 mm 2 It is.

[0059] 13 is a front view of the main input panel for entering brazing parameters. Input buttons, keys, or knobs are provided to enter settings, i.e., by repeatedly pressing the setting button, one can scroll through a list to select different cross-sectional areas, e.g., 10, 16, 25, 35, 50, 70, 95, and 120 mm. 212A and 12B. The panel further includes a display showing the current setting. The panel may further include fuse and / or control indicators and an on / off button. Additionally, the input panel may further have sockets for connecting a plug to a brazing gun, for connecting a ground, and for connecting a charger to charge the battery of the brazing device.

[0060] FIG. 14A shows the regulation and control flow diagram of the brazing process.

[0061] 14B shows a flow chart of the method steps. A method is provided for brazing a conductive connecting piece of a conductive material, such as a cable shoe, to a workpiece of a conductive material by a temperature controlled brazing process, in which the heat required for brazing is generated by igniting 1410 an electric arc between a carbon electrode and the conductive connecting piece, the method comprising: Step 1401 providing a conductive connection piece, e.g. a cable shoe; a step 1401 of providing a workpiece of conductive material; a step 1405 of providing a carbon electrode; Step 1405 of providing a DC voltage between the carbon electrode and a conductive connecting piece, e.g., a cable shoe; a step 1415 of measuring the voltage across the arc; measuring 1420 the current of the arc; a step 1425 of controlling the voltage applied between the carbon electrode and the conductive connecting piece, and therefore across the arc; a step 1430 of continuously or continuously calculating in real time the power generated in the arc; The method includes: a step 1435 of continuously or continuously measuring in real time the current in the arc and the voltage across the arc; a step 1440 of continuously or continuously calculating in real time a corresponding generated power as a mathematical product of said current and said voltage; a step 1445 of controlling a DC voltage and thereby the generated power; Further comprising: The applied DC voltage was measured using a carbon electrode as the negative pole and a conductive connecting piece as the positive pole. The carbon electrodes have a tapered, chamfered or pointed end on the end facing the electric arc.

[0062] The process may further include automatically providing heat using a first power during a first portion of the total brazing time, and providing a second power during a second portion of the total brazing time, preferably the first power being set at a value to rapidly heat the brazing site and the second power being at a value lower than the first power to maintain the temperature achieved at the brazing site.

[0063] 15A shows the front of the brazing gun 5 in cross section with the gripping sleeve 18 in the retracted position and the electrode ejector 40 is shown along with the guard ring ejector screw 16 and the electrode ejector screw 17. The ejected carbon electrode 6 and the ejected guard ring 9 are also shown.

[0064] Figures 15B-15E show alternative shapes of carbon electrodes with different apex angles beta and bevel angles alpha α, as shown in Figure 15F. The carbon electrodes may have a circular or rectangular, especially square, cross section. A circular cross section is preferred. Thus, the carbon electrodes are preferably provided with pointed or bevelled ends with an apex angle beta β of 90-150 degrees, more preferably 100-140 degrees, even more preferably 110-130 degrees, and most preferably 118-122 degrees.

[0065] The basic concept of the present invention is to combine various functions and methods to work together in an improved brazing process. The result of the collaboration is a new brazing process without structural changes or martensite formation, which saves energy and facilitates the brazing of large conductor cross-sections to be brazed. Carbon electrodes are used in the brazing process, the length and diameter of which affect the resistance in the electric circuit, the carbon electrodes are provided with pointed or chamfered ends and act as temperature buffers and heat distributors. Furthermore, an electric arc is maintained between the carbon electrode and the smooth end of the cable shoe (see below), which has a stabilizing effect on the arc and counteracts the tendency of the current to change over time.

[0066] The cable shoe has at least one smooth end of a compact conductive material on which the electric arc from the carbon electrode acts. The underside of the cable shoe has a clip of brazing material that is fixed during manufacture. The brazing produces a large area brazing joint resulting in a low overall electrical transfer resistance. Flux material is present between the cable shoe and the brazing clip, and also between the brazing clip and the workpiece, and the flux material, brazing material and brazing process are suitably matched to each other. The brazing material is suitable for soft brazing and is therefore active over a low temperature range, thereby providing a martensite-free braze.

[0067] The advantage of guard rings in brazing processes, for example made of metal or another similar material, is that less energy is required for the entire process and also that the grounding procedure is easier compared to previous procedures. Grounding via guard rings eliminates the need for special grounding contacts, for example grounding terminals or magnetic grounding contacts, and also the need for special preparation of the ground carrier. Since a new guard ring is used in every grounding situation, it is guaranteed that the contact surfaces are always clean.

[0068] The inventive arrangement reduces the length of the ground circuit and eliminates both extra transition resistance between the cable shoe and the workpiece as well as a source of secondary sparks and arcs. The shape of the guard ring, together with the gripping sleeve, shields the operator from electric arcs and hot gases during the brazing process.

[0069] The use of a metal guard ring affects the brazing procedure due to the fact that it utilizes more of the energy released in the form of heat and directs it to the cable shoe.

[0070] Not much electrical energy needs to be supplied to the brazing process to achieve a satisfactory braze with respect to temperature.

[0071] In previously known methods, the total resistivity in the circuit can be considered constant. A lower energy supply should in fact mean a shorter process time. However, sometimes the time becomes too short to achieve a satisfactory brazing.

[0072] By adjusting the additional resistance and / or adjusting the voltage, the length of the brazing process can be controlled, thus achieving a satisfactory martensite-free braze with minimal energy consumption, and in addition the temperature within the substrate / workpiece can also be controlled.

[0073] Some known methods allow wide margins in terms of the power generated and the total energy released in the process, as well as in terms of the overall length of the process. The current has been limited either by incorporating a fixed electrical resistance in the circuit or by interrupting the process when the required amount of released energy has been consumed. Also, no consideration has been given to variations in battery voltage due to the battery's state of charge, discharge characteristics, or other factors, nor to variations in current in a single brazing operation due to changes in electrode length or arc variations, nor to variations in current between brazing cases due to variations in lifting height. These variations result in variations in time and power output for equivalent brazing processes, with simple inadequate adjustments to estimate the amount of energy released, and difficulties in controlling the temperatures in the materials involved.

[0074] In the above-mentioned new brazing process shown in FIG. 14, the brazing temperature and the martensite formation depending on the brazing temperature can be controlled by calculating the electrically generated power and regulating the power in real time, either by an analog or a high-resolution digital procedure. The generated power is calculated by instantaneously measuring the current and the voltage, and the actual power is calculated as the mathematical product of these quantities. The calculated results are processed and fed to a processing unit, the output signal of which influences the voltage regulation unit. In this way, the voltage and thereby the current are regulated and the generated power is adjusted to an appropriate value. The processing unit, which can either be present as a separate unit or can be integrated into the electronic unit 2, processes data in the form of current and voltage values, data and operational adjustments from the transmitter, externally connected units as well as the measured elapsed time, and handles this data taking into account physical, mathematical and logical structures so that an appropriate adjustment of the generated power is made over time.

[0075] As an example, operator input of conductor cross-sectional area is used by the processor, which is configured to adjust the control signal to control the voltage to generate a current that generates the appropriate amount of power for heating and maintaining the proper temperature during brazing.

[0076] Also, since the regulation does not depend on the resistance of the power circuit, there is no need to have a fixed ground resistor, which therefore generates waste heat, thus saving energy. In addition, at the end of the discharge cycle, the battery can still drive the process despite the failed voltage level, since there is no fixed resistor, so a larger amount of energy can be recovered from the battery. Furthermore, the formation of the arc at the start of the process is promoted for two reasons, on the one hand, because the lift height of the electrodes, and therefore the length of the arc, and therefore the subsequent starting inertia, can be minimized without any risk of excessive currents, which in some previous methods caused temperature problems and regulation technology problems, and on the other hand, much higher current and voltage values ​​than before can be allowed at the start of the process without being limited by a fixed resistor, so that a reliable start to the process can be guaranteed.

[0077] In the above-mentioned new brazing process, the above-mentioned processing unit may also be configured to process signals from external transmitters, such as temperature sensors, whose values ​​affect the output data of the processing unit for operational adjustments. Furthermore, it processes signals from external devices such as chargers, generators, motors, etc., which are also processed in the processing unit when appropriate control signals in the form of output data are generated to adjust such units as well.

[0078] Although only a few embodiments of the invention have been shown in the drawings, it should be pointed out that many other modifications can be envisaged within the scope of the appended claims.

[0079] In a preferred embodiment, the carbon electrodes have tapered, pointed or chamfered ends having an apex angle beta β between 70 and 150 degrees, more preferably between 70 and 110 degrees, and even more preferably between 90 and 110 degrees.

Claims

1. The method for brazing a conductive connection piece (10) of a conductive material, for example a cable shoe, to a workpiece (14) of a conductive material by means of a temperature-controlled brazing process, in which the heat required for brazing is generated by igniting an electric arc (8) between a carbon electrode (6) and the conductive connection piece (10), said method comprising the steps of: - providing (1405) a DC voltage between said carbon electrode (6) and said conductive connecting piece (10), e.g. a cable shoe; - measuring (1415) the DC voltage appearing across the electric arc (8) continuously or continuously in real time; - measuring (1420) the current of said electric arc (8) continuously or continuously in real time; - calculating (1430) continuously or continuously in real time the power generated in the electric arc (8) as a mathematical product of the measured values ​​of the current and the DC voltage; - controlling (1425) the DC voltage applied between the carbon electrode (6) and the conductive connecting piece (10), and thus across the electric arc (8), thereby controlling the calculated power; Including, The applied DC voltage uses the carbon electrode (6) as the negative electrode and the conductive connecting piece (10) as the positive electrode; A method according to claim 1, characterised in that the carbon electrode (6) has a tapered, chamfered or pointed end at the end facing the electric arc (8).

2. The method comprises: Receiving operator input of a conductor cross-sectional area; using the operator input of conductor cross-sectional area to adjust the calculation and control the DC voltage to achieve and maintain the proper temperature at the braze site; The method of claim 1 further comprising:

3. 3. The method of claim 1 or 2, further comprising the step of automatically providing heat with a first power during a first portion of a total brazing time and a second power during a second portion of a total brazing time.

4. 2. The method of claim 1, further comprising the step of lifting the carbon electrode (6) from the workpiece (14) and igniting an electric arc (8) between the carbon electrode (6) and the conductive connecting piece (10).

5. 2. The method of claim 1, wherein the tapered, chamfered or pointed end of the carbon electrode (6) has an apex angle of 90-150 degrees, more preferably 100-140 degrees, more preferably 110-130 degrees, and most preferably 118-122 degrees.

6. 1. An apparatus for brazing an electrically conductive connection piece (10) to a workpiece (14) of electrically conductive material by a temperature-controlled brazing process, the apparatus generating the heat required for brazing by igniting an electric arc (8) between a carbon electrode (6) and the electrically conductive connection piece (10), the apparatus comprising: (a) a means for engaging a conductive connection piece (10) towards a workpiece (14), the means including a guard ring (9) and a carbon electrode (6); (b) a means for supporting the carbon electrode (6), the means including a means for moving the carbon electrode (6) between a position in which the carbon electrode (6) engages the conductive connecting piece (10) and is then engaged by the means for engaging, and a retracted position from which the carbon electrode is lifted; (c) a DC voltage unit (1) for providing and applying a DC voltage of a specific polarity between the conductive connecting piece (10) and the carbon electrode (6), the DC voltage unit (1) including a voltage adjustment unit; (d) a voltage sensor for measuring the DC voltage between the conductive connecting piece (10) and the carbon electrode (6); (e) a current sensor for measuring the current flowing through the carbon electrode (6); (f) processing means, including means for generating an output signal to control said voltage regulating unit (1), and further including means for continuously or continuously calculating the power generated by said electric arc (8) in real time; (g) switching means (3) operable to connect said means for applying a voltage in an electric circuit to said carbon electrode (6) and such conductive connecting piece (10), such that when said means for engaging is applied and said switching means (3) is operated to close said electric circuit, said means for supporting and moving lifts said carbon electrode (6) off said workpiece (14) and ignites an electric arc (8) between said carbon electrode (6) and said conductive connecting piece (10); Including, (h) the DC voltage unit (1) is configured such that the polarity of the applied DC voltage is a specific polarity using the carbon electrode (6) as a negative electrode and the conductive connecting piece (10) as a positive electrode; 10. Apparatus according to claim 9, wherein said carbon electrode (6) is provided with a pointed, tapered or chamfered end facing said electric arc (8).

7. 7. The apparatus of claim 6, wherein the voltage adjustment unit is configured to automatically provide heat with a first power during a first portion of a total brazing time and a second power during a second portion of a total brazing time.

8. 8. The apparatus of claim 7, wherein the first power is set to a value for rapidly heating the brazing site, and the processing means is configured to calculate a value for the second power, lower than the first power, in order to maintain the temperature achieved at the brazing site.

9. said device comprising an input device for setting appropriate parameters for the cross-sectional area of ​​the conductor to be brazed; 7. The apparatus of claim 6, wherein the processor is configured to calculate a time and voltage for brazing taking into account parameters for providing an appropriate voltage and time to achieve an appropriate amount of heat for an appropriate length of time.

10. 10. Apparatus according to any one of claims 7, 8 or 9, comprising a gripping sleeve (18) around the guard ring (9), whereby the guard ring (9) together with the gripping sleeve (18) shields an operator from the electric arc (8) and hot gases.

11. 11. The device according to claim 10, wherein the gripping sleeve (18) ejects the used carbon electrode (6) and the guard ring (9) with a longitudinal movement.

12. Apparatus according to any one of claims 6 to 9, wherein the processing means is further capable of controlling external units such as battery chargers, generators and motors to regulate these units.

13. 10. The apparatus according to any one of claims 6 to 9, wherein the tapered, chamfered or pointed end of the carbon electrode has an apex angle of 90 to 150 degrees, preferably 100 to 140 degrees, even more preferably 110 to 130 degrees, and most preferably 118 to 122 degrees.

14. 10. The device according to any one of claims 6 to 9, in combination with an electrically conductive connection piece (10) for brazing to a workpiece (14), said electrically conductive connection piece (10) having a layer (12) of brazing metal on one side and a flux layer (13) between said workpiece (14) and said layer (12) of brazing metal.

15. The combination of claim 14, wherein the layer of braze metal (12) is provided by a braze clip applied to the workpiece (14).

16. 16. The combination of claim 15 including an electrical connection to said conductive connecting piece (10) to provide a ground contact for said device.

17. A cable shoe (10) having a front portion formed as a compact plate (26) and a rear end formed to define a cable cavity (31) for a cable, said cable shoe further designed such that said cable cavity (31) extends into a tapered cavity (33) to provide said cable shoe with a uniform cross-sectional area along its length from said compact plate (26) to the beginning of said cable cavity (31).

18. A cable shoe according to claim 17, wherein the front portion comprises an amount of brazing material, such as a silver alloy, with or without a flux material, which is preferably attached to the compact plate by pressing or melting.

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