Abstract: A track maintenance machine includes a combustion engine mechanically connected by a drive shaft to an electric generator/motor unit. The electric generator/motor unit is connected by a mechanical drive unit to a hydraulic pump. A power accumulator is connected by an electrical supply line to the generator/motor unit and to drives which can be actuated electrically. It is thus possible to mainly electrically supply all of the drives.

Abstract: A heavy weight drill pipe may include a tube body formed of AISI 1340 alloy steel, and first and second tool joints at respective ends of the tube body, and which are formed of an AISI 41XX series alloy steel. The first and second tool joints may be welded to the tube body at a weld line within a weld region. A Charpy impact toughness at the weld line or surrounding weld region may be least 12 ft-lbs. (16.5 N-m). Yield and tensile strengths at the weld line or weld region may be at least 65 ksi (448.0 MPa) and at least 106 ksi (731.0 MPa), respectively. Material properties at the weld line or weld region may be achieved by heat treating after welding. Heat treating may include austenitizing, quenching, and tempering the weld line and/or the surrounding weld region.

Abstract: First steel material, a carbon sheet, and second steel material are put in a state of being separated from each other, and bonding parts are heated by, for example, applying current from a power supply to the carbon sheet. Alternatively, the bonding parts may be heated by an inductive heating coil. Thereafter, heating is terminated if the bonding parts reaching greater than or equal to the eutectic point and less than the liquidus line temperature is detected in the Fe—C phase diagram. Furthermore, the carbon sheet is made to be sandwiched between the first steel material and the second steel material.

Abstract: A welding apparatus for a controlled welding of steel cord ends. The welding apparatus allows for a controlled welding path from welding period over post-weld period to complete cool-down. In the welding apparatus a direct current source is controlled over time using a programmable controller. By sensing the voltage over the clamps of the welding apparatus and using this as a further input to the programmable controller, a constant power dissipation between the clamps can be achieved in the post-weld period. An associated method for making the weld where during the post-welding period the electric power dissipated between the clamps is held constant. The welds obtained by this procedure have a favourable metallographic structure in that the heat affected zone has more than 50% of pearlite and/or bainite over the total area of that zone.

Abstract: A piston and method of making the same includes providing a piston lower part defining a piston axis and at least a portion of the upper combustion bowl surface, and assembling a piston upper part to the piston lower part. The piston upper and lower parts cooperate to define at least in part a cooling gallery extending annularly about the piston. The method further includes bringing the piston upper and lower parts together along respective upper and lower mating surfaces and inducing an electric current between the upper and lower mating surfaces while the upper and lower mating surfaces are in contact.

Abstract: A purge dam assembly confines a volume within an assembly of pipes, including a distal pipe and a proximal pipe together arranged for butt welding at a seam. A distal disk is covered at its periphery with a distal sock including gasketing material. A proximal disk is covered at its periphery with a proximal sock including the gasketing material. Each disk is sized such that the sock contacts but does not completely seal against an inner surface of one of the tubes or pipes permitting a purging flow of gas from the volume and past each disk. A cross-member having a proximal and a distal end, the proximal end is affixed to the proximal disk and the distal end is affixed to the distal disk to preserve the spatial separation between the proximal disk and distal disks and to maintain the proximal and distal disks in coaxial alignment.

Abstract: The present disclosure is directed to a tip extension assembly for a rotor blade of a wind turbine. The tip extension assembly includes a tip extension having a body with a pressure side surface and a suction side surface. Further, the tip extension is slidable onto a tip of the rotor blade so as to overlap the rotor blade adjacent the tip. In addition, the tip extension defines an extended trailing edge of the rotor blade. Moreover, an edge of the tip extension defines a step profile at a transition region between the tip extension and a trailing edge of the rotor blade. The tip extension assembly also includes at least one chord extension configured for attachment adjacent to the edge of the tip extension so as to minimize the step profile and associated noise caused thereby.

Abstract: A gap is provided at joining faces of a pair of metal works with an uneven shape when the metal works contact one another for joining. An adhesive agent having a chain-reacting curing reaction function is disposed within the gap. The adhesive agent is cured by an autogenously-generated curing reaction heat caused by an outer energy and an additional heat that is successively generated by the autogenously-generated curing reaction heat within the adhesive agent. A welding portion, where the works contact one another substantially directly, is welded by a laser beam, and the above-described energy for causing the autogenously-generated curing reaction heat for the adhesive agent is provided by the laser beam. Accordingly, a joining structure and method of metal works that can have less limitation in a joining location is provided.

Abstract: A method for manufacturing a steel component having a flash butt weld joint, which comprises the step of flash butt welding the joint. The method comprises the step of heating at least part of the component to a temperature above the martensite start temperature before and/or during said flash butt welding step.

Abstract: A method for manufacturing a component from steel, which comprises the step of flash butt welding the component. The steel has a reduction ratio of greater than 5:1.

Abstract: In an operating method for a hob having a plurality of heating elements, an operating action for a heating element, such as heating with an additional region on the cooktop or invoking a parboiling step, is selected in an initial step by providing input to a general input sensor element that is not associated with any specific heating element. In a subsequent step, the selected operating action is allocated or associated with a specific heating element by operating a cooking element specific sensor element, for example when setting the power level for that heating element. Therefore, sensor elements can be provided with an advantageous multiple-use effect for general operating actions. Furthermore, the operating sequence permits simple and convenient operation.

Abstract: Electrode assemblies for plasma reactors include a structure or device for constraining an arc endpoint to a selected area or region on an electrode. In some embodiments, the structure or device may comprise one or more insulating members covering a portion of an electrode. In additional embodiments, the structure or device may provide a magnetic field configured to control a location of an arc endpoint on the electrode. Plasma generating modules, apparatus, and systems include such electrode assemblies. Methods for generating a plasma include covering at least a portion of a surface of an electrode with an electrically insulating member to constrain a location of an arc endpoint on the electrode. Additional methods for generating a plasma include generating a magnetic field to constrain a location of an arc endpoint on an electrode.

Abstract: An improved method for executing a flash butt weld to join first and second rail segments includes applying a voltage to the first rail segment and the second rail segment to establish a voltage difference between the first and second rail segments. The rail end faces are brought into contact, resulting in an electrical current between the first rail end face and the second rail end face, resistively heating material at the interface. As material burns off at the interface, the power consumed at the rail end interface as a function of rail displacement is periodically sampled. If the comparison indicates that the power per unit of rail displacement is not increasing from sample to sample, the burn-off process is terminated. In a further aspect, if the power per unit of rail displacement exceeds a predetermined threshold, the burn-off process is terminated.

Abstract: The continuous rolling method and the continuous rolling apparatus provide good product quality and product yield by successively joining pluralities of traveling hot steel pieces by flash welding, and by rolling thus prepared endless steel piece, thus preventing generation of flaws in the rolling step, thereby manufacture steel rods, wires, and the like by the continuous rolling technology. The method has: a heating step for heating billet to a specified temperature; a flash welding step for joining the trailing end of preceding billet with the leading end of succeeding billet while they are traveling using flash welding; a deburring step for removing burrs from the welded part; a trimming step for trimming corners of cross section of the deburred welded part; and a rolling step for rolling the joined billets.

Abstract: The invention relates to a method of providing a duplex stainless steel strip for an armouring layer of a flexible pipe, said method comprising providing at least two duplex stainless steel pieces each having an end-face, welding said end-faces of said two pieces of duplex stainless steel together to form a welded interface section using resistance welding, such as dual upset welding or flash welding, and providing a controlled cooling of said welded interface section. The duplex stainless steel strip should preferably be heated to a temperature of at least about 1100° C., preferably at least about 1200° C., such as at least about 1500° C. in said interface section, and the controlled cooling of said welded interface section preferably comprises prolonging the cooling of the interface section preferably at least for the cooling from about 800° C. to about 600° C., more preferably at least for the cooling from about 1100° C. to about 600° C.

Abstract: The method is used to produce connecting elements (1). The connecting elements (1) are intended for coupling functional elements for applications in the field of oil drilling technology. The connecting element comprises two end pieces (2, 3) and at least one spacer (4) connecting the end pieces to each other. At least one spacer (4) is connected to at least one of the end pieces (2, 3) by pressure welding.

Abstract: The invention relates to a method of providing a duplex stainless steel strip for an armouring layer of a flexible pipe, said method comprising providing at least two duplex stainless steel pieces each having an end-face, welding said end-faces of said two pieces of duplex stainless steel together to form a welded interface section using resistance welding, such as dual upset welding or flash welding, and providing a controlled cooling of said welded interface section. The duplex stainless steel strip should preferably be heated to a temperature of at least about 1100° C., preferably at least about 1200° C., such as at least about 1500° C. in said interface section, and the controlled cooling of said welded interface section preferably comprises prolonging the cooling of the interface section preferably at least for the cooling from about 800° C. to about 600° C., more preferably at least for the cooling from about 1100° C. to about 600° C.

Abstract: The stretch of rail comprises a railway switch element (12) made from high-alloy steel, in which at least one alloy element has a content equal to at least 5% by weight, and a length of rail (14) made from steel, connected to one another by a weld without deposition of metal. The length of rail (14) is formed from a medium-alloy low-carbon steel of which the carbon content is less than 0.55% by weight.

Abstract: A chuck assembly for a stud welding gun includes a current passing member parallel to and separated from an electrically isolated member forming a stud retaining gap. The current passing member provides a path for a welding current and includes a contact surface for releasably retaining and transmitting the welding current through a shank of a weld stud. The welding current only passes through the current passing member into the shank of the stud.

Abstract: An article with an embossment thereon is fabricated by providing an article precursor, providing an embossment precursor, and flash welding the embossment precursor and the article precursor together, to form the article with the embossment thereon.

Abstract: The invention concerns a method for controlling the butt welding, by flash welding, of two metallic parts (A, A?) in a welding machine of the type comprising two pairs of clamping dies (2, 2?) mounted respectively on a fixed frame (1) and on a mobile frame (1?) for contacting rear (3) and front (3?) ends of both parts (A, A?) and the flow of an electric welding current. According to the invention, on the one hand a set of electric parameters including at least the voltage (Us) and the intensity (Is) of the welding current and on the other hand the relative position of the mobile frame (1?) with respect to the fixed frame (1) are measured at any moment and the travel of the mobile frame (1?) is regulated in position from at least one of the measured value of said electric parameters, in order to control the closing-in speed v(t) of the ends (3, 3?) of both parts (A, A?) taking in account the progress of the welding process, during at least a portion thereof.

Abstract: A resistance butt flash welding machine comprises two work piece clamping platens, at least one of which is movable with respect to the other, an electric servo motor operatively mechanically connected to the movable platen, and a programmable electrical control connected to the servo motor to control the motor, and programmed to regulate the pattern of timing of changes in motion of the movable platen, to control speed of the motion and to control the upsetting force applied to the movable platen required to forge together work pieces clamped in the platens. The process of use of the machine includes programming the programmable control.

Abstract: A method of welding an axle housing surface to a blank surface includes generated heat in one of the two components. Heat is generated from at least one of these surfaces at their interface sufficient to weld them together. The surfaces are then applied together.

Abstract: An article with an embossment thereon is fabricated by providing an article precursor, providing an embossment precursor, and flash welding the embossment precursor and the article precursor together, to form the article with the embossment thereon.

Abstract: The invention relates to a machine for butting two metal bands (M1, M2) and a method for implementing such a machine.

Abstract: A method of flash-butt welding in which the travel speed (Vt) of the machine mobile plate and the welding voltage (U2) are changed (by preset programs) and the travel speed is controlled through negative feedback by welding current, the voltage being changed discretely for each flashing fixed interval of tm duration as a function of the increment of the actual average speed of flashing details of shortening (Va) during the previous flashing interval, Va value being maintained at the present level, lower than Vm. The invention envisages a change of the coefficient of enhancement of the negative feedback in a discrete manner for each preset flashing interval of tm duration as a function of Va increment during the previous flashing interval.

Abstract: A flash-butt welder having a stationary head 41 and a moving head 42, a pair of electrodes 45a, 45b, and 46a, 46b arranged to each of the stationary and moving heads, respectively, wherein power source transformers 12 through 16 are located at the stationary head 41 side, four bus bars 21 through 24 connecting the power source transformers 12 through 16 with the electrodes 45a, 45, 46a, and 46b are arranged at symmetrical positions surrounding a billet 10, while the bus bars, 22 and 24 as half of the number are connected to the electrodes 46a and 46b at the moving head 42 side.

Abstract: A method of flash/butt welding an aluminum bicycle wheel rim, in which an aluminum sleeve having a dielectric anodized hardcoat surface finish is inserted into the center of the rim in order to support the interior walls of the rim during the welding process, is disclosed. The walls of a wheel rim or other similar metal profile defines an inner space in a tubular section of the rim. The sleeve is partially inserted into a first end of the rim and partially inserted into a second end of the rim. During the welding process, an electric current flows across a small space or gap between the two ends. The electric current melts the ends, at which time the two ends are pressed together in order to forge them into a single piece. The metal sleeve supports the inner walls of the profile in order to prevent collapse of the wall during welding. Due to the dielectric coating, the sleeve does not affect the welding circuit.

Abstract: Techniques for assuring the accuracy of the welding of a part including a part calibration cycle, a tap check cycle and a gap detection cycle. The part calibration cycle determines the electrical load presented by the part to the welder transformer. The tap check cycle verifies that the operator has set the correct tap on the primary of the welder transformer, The gap detection cycle finds the actual spacing between the platen when the ends of the part are substantially touching so that the ends of the part can be accurately spaced at the beginning of the weld cycle.

Abstract: A welding method and apparatus for flash butt welding adjacent ends of axially aligned railway rails includes a base frame and fixed and movable platens supported on the base frame. The platens support rail sections and are under the control of controller means operative to automatically move the movable platen through a predetermined distance/velocity relation as electrical power is inputted into the rail ends during straight flashing, preheating, flashing and upsetting phases of a welding cycle. The controller includes PID feedback loops operative to maintain the predetermined platen distance/velocity relation with entry of a single parameter by the operator. Significantly improved quality and repeatability of rail welds are obtained.

Abstract: A method for pressure welding of parts with heating with an arc moving in magnetic field in which the parts (2,3) are placed coaxially with each other with a working gap (.delta.) between their ends magnetic field is created in the gap (67 ) and electric arc (6) is fired to heat the ends of the parts (2,3). A d-c component of voltage of the arc (6) is measured, and when this component reaches its minimum value corresponding to a temperature of the ends of the parts (2,3) at which plastic deformation of the material of the parts can occur, a pulsed increase in the arc current is carried out, with subsequent upsetting of the parts (2,3).

Abstract: A method of flash butt welding high-carbon materials, in particular nodular cast iron wherein the arcing craters produced by intermitting contact of the contact faces have a maximum roughness depth R.sub.T such that this roughness depth lies within the narrowest thickness of the plasticized zone. As a result, when the upsetting pressure is applied, the entire molten material areas on the contact faces are pressed out of the contact faces into the welding bead thereby prohibiting the creation of hardening structures, such as, for example, ledeburite in the welding zone. The method is especially suitable for flash butt welding workpieces having wall thicknesses of over 12 mm.

Abstract: A process and apparatus for leak-proof sealing of a metallic capsule closed by a stopper and joining the capsule to a metal cable by arc welding, wherein a capacitor is charged, the capsule with a striking tip at one end or the stopper with an ignition point and the cable are clamped at their ends, connected to the terminals of the capacitor, moved together and welded together by discharging of the capacitor with the formation of an arc.

Abstract: Apparatus for electrical flash butt welding the ends of metal sheet or strip including a pair of flat faced parallel welding electrodes extending across the full width of the metal sheet or strip, one on each side thereof, and an electrode cleaning device comprising a support assembly having mounted thereon an extendable electrode cleaning means including a cleaning head having a plurality of upward extending cleaning members and a plurality of downwardly extending cleaning members the cleaning head adapted to simultaneously remove dirt and contaminants from the contact surfaces of opposed welding electrodes.

Abstract: A method of flash-butt resistance welding of a batch of like parts in pairs consists in that during flashing off of workpieces (1,2) they are brought apart or together depending on the resulting resistance obtained by comparison of the actual resistance between the workpieces (1,2) being welded with the specific short-circuit impedance of the welding circuit, which is determined during the upsetting of the preceeding pair of workpieces (1,2) after the welding current reaches a constant level.

Abstract: A mobile electric flash-butt welding machine comprises machine frame, undercarriages supporting the machine frame on a railroad track, and a drive for propelling the machine frame along the track. The machine frame carries a hydraulic fluid supply pump, an electric current generator, a motor for operating the pump and the generator, a longitudinally, transversely and vertically adjustable electric flash-butt welding head for selectively welding together the adjacent rail section ends of a respective one of the track rails, the welding head comprising two welding halves movable towards and away from each other in a direction of the rail, hydraulic cylinders for moving the two welding head halves in said direction, a pair of clamping and welding jaws on each welding head half, and a hydraulic clamping cylinder connecting the jaws of each pair.

Abstract: The disclosed process includes the steps of and upsetting the flashing parts being welded. The flashing is conducted with concurrent measurement of useful electric power and an electric parameter of the flashing process which is related to the power by a function which maximizes the useful power at a predetermined value of said electric parameter. Then the value and sign of the power and parameter increments are determined within one and the same period of time. The parts are brought closer together up to the moment when the ratio of the power and parameter increments reverses ints sign. Then the parts begin to be separated up to the moment when the value of said ratio reaches the preset value selected to suit the welding circuit resistance and the cross sectional area of the welded parts.

Abstract: A flash-butt resistance welding process including a flashing of parts being welded and their upsetting. The direction of speed of motion of the parts during flashing is changed by converging and diverging them. The parts being welded are converged up to the moment when the total resistance of elementary contacts arising between the flashed surfaces of the parts becomes equal to 0.4-0.5 of the short-circuit impedance of the welding machine. Then the parts are diverged up to the moment when the summary resistance of elementary contacts reaches 1.4-1.6 of the short-circuit impedance of the welding machine.

Abstract: A method and apparatus for flash welding are disclosed wherein a first predetermined voltage is applied between a pair of workpieces to be welded to generate flashes therebetween, and a second predetermined voltage lower than the first predetermined voltage is then applied between the workpieces to maintain fine flashes when the temperature of weld surfaces of the workpieces has reached a predetermined temperature. The workpieces are upset when the total number of flashes has reached a predetermined value. The pressure welding is maintained with an upsetting pressure sufficient to upset the workpieces and slightly higher than a pressure at which the workpieces are deformed near their recrystallization temperature until the temperature of weld surfaces has decreased to lower than the recrystallization temperature. The applied voltage and the upsetting pressure are controlled in accordance with the weld progress.

Abstract: To attach a nut to a plate-shaped workpiece, especially to a metal sheet, in such a way that it has self-locking properties without additional aids or parts, the force fastening the nut and acting on a free thrust surface of the nut is divided into at least two effective components generating a shearing stress in the nut material, transverse deformation of a part of the nut facing away from the workpiece being produced, and the thread diameter in the thread region deformed for self-locking purposes being reduced, while at the same time the thread pitches are inclined towards the center axis. A nut which can be used either as a locking nut or as a non-locking nut is characterized by a force-deflecting design of the thrust surface.

Abstract: A method for welding by a magnetically driven arc, which comprises placing two objects of welding in butt formation with a small gap between the end edges thereof to form a welding line; parallelly connecting a first electric circuit comprising the two objects of welding and a cable arranged on the surface side of the two objects of welding and a second electric circuit comprising the two objects of welding and another cable arranged on the back side of the two objects of welding to a welding power source; flowing a welding current through the first and second electric circuits to produce an arc in the small gap; moving the arc along the welding line under the effect of an electromagnetic force in the direction of the welding line, the electromagnetic force being produced by the magnetic flux of magnetizing coils provided near the end edges of the two objects of welding and welding current flowing through the arc; and changing the amount of welding current flowing through the first and second electric circuit

Abstract: A joint is made between two pieces of steel which have been preheated to a temperature To (.degree.C.) near their abutting surfaces by subjecting first to flashing and then to upsetting. When the ultimate flashing rate is V (mm/sec.), a current whose density I (A/mm.sup.2) is not lower than ##EQU1## is passed during the upsetting process to melt the abutting surfaces. With a mean upsetting rate of not lower than 50 mm/sec., only the molten metal is rapidly squeezed out from the abutting surfaces. Then, the upset current is cut off while applying a final upsetting force that is as low as under 5 kg/mm.sup.2.

Abstract: In a flash butt welder for joining strip ends, the improvement for improving the quality of flash butt welds made in specialty grade steels, such as high strength low alloy, as well as for considerably reducing the upset current requirement, by applying a protective atmosphere of combustible gas, such as propane, natural gas, or hydrogen during the flash butt welding process. Welds free from any detectable defects can be made with lower upset current densities thus extending the equipment welding capacity.

Abstract: The parts to be welded together are caused to continuously approach each other and their ends are fused by an alternating current, and concurrently an oscillatory motion along the direction of approach is imparted to one of the parts, whereby additional relative movements of the parts towards and away from each other are accomplished. During the stage of a relative movement of the parts being welded together away from each other, the welding voltage is reduced to within the range of 0.7 to 0 of its working value, and during the stage of a relative movement of the parts towards each other, the voltage is restored to its initial value. Reducing the voltage is carried out in a time interval of not less than 1/8 of the period of the oscillatory motion from the beginning of the relative movement of the parts away from each other, and restoring it, in a time interval of not more than 1/8 of the period of the oscillatory motion from the beginning of the relative movement of the parts towards each other.

Abstract: An electrical control circuit which provides means of initiating the start of upset of a flash welding machine at an operator selectable value of flashing electrical energy. The energy signal for this circuit is taken from an energy monitor, such as the output of the circuit shown in U.S. Pat. No. 4,084,075. The control circuit, by means of a single adjustment of electrical switch means, may include a few additional electrical components to enable initiation of the start of upset, or termination of upset, as a function of platen position rather than as a function of flashing energy. Further, by simple adjustment of additional electrical switch means, further electrical components may be included to control the distance the movable platen moves during the upset portion of the welding cycle. Also, a meter may be included in the circuit to display either upset distance or upset initiation.

Abstract: Surfaces of metal workpieces being welded are fused at a constant speed of feeding the workpieces towards each other, and the speed of feeding is, before the upsetting, increased to a final value thereof for a period of (1.0 to 4.0) (.DELTA.max/v.sub.1), where .DELTA..sub.max is the maximum gap between the workpiece surfaces being welded and v.sub.1 is the average speed of feeding the workpieces over the period of its increase. Empirical formulas are given to determine the maximum gap for workpieces of various thicknesses.

Abstract: A method consists in that the workpieces to be welded together are at first continuously moved towards each other with the welding current on and the ends of the workpieces are fused, the thermal state of the ends being monitored in terms of current, or of power, or of fusion time, or of length of the fused portion. After any of said variables has reached a preselected value which corresponds to the predetermined heating of the contact region, oscillatory movements are superimposed on the movement of one of the workpieces being welded towards the other and the fusion process is carried out till upsetting.

Abstract: In a method for flash welding metallic materials comprising a flashing step of applying a commercial alternating voltage or a direct-current voltage resulting from its full-wave rectification to the abutting ends of metal workpieces contacted partly with each other to generate Joule heat at their abutting ends and the vicinity thereof and then to generate sparks between the ends and repeating the procedure, and an upsetting step of press-bonding the ends and supplying an electric current to the metallic workpieces during this time; the improvement wherein the alternating voltage or direct-current voltage is used as a fundamental wave voltage and another voltage is superimposed thereon to modulate the wave form of the fundamental wave to obtain a distorted wave voltage, the distorted wave voltage being such that in each 360.degree. cycle, the Joule heat generating period begins at a phase angle between -45.degree. and 0.degree. and terminates at a phase angle between 45.degree. and 135.degree.

Abstract: Method and apparatus for detecting whether or not the gap in adjoining ends of a ring-like workpiece to be flash welded is of normal size, or is so much larger as to produce an unsatisfactory weld. The invention provides means whereby the amount the movable platen of a flash welder moves in a direction toward the stationary platen is compared with its position when the ends abut and flashing begins. If the ends are not materially beyond a predetermined normal gap, the welding action proceeds; however, if the ends are spaced beyond such normal gap, further action of the flash welding process is aborted, or a signal is activated; or both abortion and signal are provided. The invention is especially adapted for use in welding rings which are formed and welded in high production, such as rings that are further processed to make rims for tires of a vehicle.

Abstract: Work pieces to be joined together by the flash butt welding method are brought together at a preset no-load voltage, the end faces of the work pieces are fused, and an upsetting is accomplished. The amount of the upsetting is determined within from 1.2 to 3.0 of the amount of the maximum gap between the end faces of the work pieces being welded together, which gap forms in the course of fusing the end faces of the work pieces. The maximum gap is determined from the following relation:.DELTA..sub.max =f(U.sub.o,.delta.),where:.DELTA..sub.max =maximum gap;U.sub.o =no-load voltage;.delta.=thickness of the work pieces being welded together.Empirical formulas to determine the maximum gap for work pieces of various thicknesses are presented.