Abstract: A solenoidal induction coil with dynamically variable coil geometry is provided for inductively welding or heating continuous or discontinuous workpieces passing through the solenoidal induction coil in a process line. The coil geometry can change, for example, as the outer dimension of the workpiece passing through the solenoidal induction coil changes or as non-continuous workpieces pass through the solenoidal induction coil in an induction heating or welding process line.

Abstract: In preferred embodiments, a heating coil is provided that includes at least a set of heating conductors, one of which is arranged at a side of a work and the other one is arranged at an opposite side of the work. In addition, a plurality of connecting conductors are provided to connect an end of one of the heating conductors with an end of the other heating conductor, wherein each of the heating conductors is connected with at least two connecting conductors. The connecting conductors extend from an end of each of the heating conductor in a different direction from each other. In the preferred embodiments, the heating coil has a simple structure that enables an even heat treatment to a work in a width direction.

Abstract: An induction heating system includes a power source and an induction head. The converter output is at a voltage that is not greater than the voltage applied to the coil. The induction head includes a housing that houses a conductive coil disposed to induce heat in a workpiece and the coil is wound to be tuned to the output power. The coil is wound in a stacked spiral pattern with at least two turns in each layer. A flux concentrator is disposed about the coil with a potting compound around the concentrator and coil. Spacers maintain a desired separation between the head and the workpiece. The coil is a tube carrying a coolant. The head includes a wear surface that prevents contact of the coil and the workpiece, and a thermal insulator between the coil and wear surface. A non-contact temperature sensor is mounted to the housing.

Abstract: The invention relates to a method for joining two essentially metal sheet-type workpieces. In said method, edge regions of the workpieces to be joined are bent by up to 90° in relation to a plane of the workpiece, the bent edge regions being placed against each other, and the edge regions are then heated to a predefined joining temperature by at least one first frictional element that moves relative to the edge regions, are subjected to a certain contact pressure, and are joined while being deformed.

Abstract: An apparatus for the inductive heating of oil sand and heavy oil deposits by way of current-carrying conductors is provided. The conductors include individual conductor groups, wherein the conductor groups are designed in periodically repeating sections of defined length defining a resonance length, and wherein two or more of the conductor groups are capacitively coupled. In this way, each conductor can be insulated and can include a single wire.

Abstract: A solenoidal induction coil with dynamically variable coil geometry is provided for inductively welding or heating continuous or discontinuous workpieces passing through the solenoidal induction coil in a process line. The coil geometry can change, for example, as the outer dimension of the workpiece passing through the solenoidal induction coil changes or as non-continuous workpieces pass through the solenoidal induction coil in an induction heating or welding process line.

Abstract: Embodiments of the invention provide a system and method for induction heating a helical rotor of a progressing cavity pump in order to reduce the surface roughness of the rotor. In order to heat the rotor most evenly, it is desired to space the coil as closely around the rotor as possible. The invention provides a mechanism for threading the helical rotor through an induction coil having an interior diameter which is less than the major diameter of the rotor. The induction coil may include one loop and overlapping ends. The rotor to be heated is rotated about its longitudinal axis and advanced axially through the coil as it rotates. The axial speed and rotational speed are synchronized so that the rotor moves one pitch through the coil for each complete rotation.

Abstract: An impeder for use in an electric induction welding process is provided. A cooling medium is circulated centrally through the impeder's magnetic material with the impeder entry and exit passages for the cooling medium located on opposite sides of the impeder.

Abstract: An impeder for use in an electric induction welding process is provided. A cooling medium is circulated centrally through the impeder's magnetic material and between the interior of the impeder's high temperature enclosure and the exterior of the magnetic material within the impeder with the impeder entry and exit passages for the cooling medium located on the same side of the impeder.

Abstract: A tapered tube manufacturing apparatus and method of operation comprises an entry station adapted to receive a tapered tube having an open, longitudinal seam with spaced longitudinal edges extending the length of the tapered tube. A feed line section moves the tapered tube from the entry section into a welding station while maintaining the longitudinal seam coincident with a pass center line which defines a direction of movement of the tapered tube through the entry station, the feed line section and the welding station. A pair of squeeze rolls in the welding station move the tapered tube through the welding station where the edges of the seam are heated, squeezing the open seam closed for welding the edges of the seam together, and then move the welded tapered tube into a cooling and transition station while maintaining the welded seam coincident with the pass center line.

Abstract: The present invention provides a method for heat-treating seam-welded constructions of hardenable steel and ferrous alloys with reduced weld-zone hardness and improved weld-zone ductility and toughness. This method consists of heating the seam weld rapidly with a secondary heat source to a temperature greater than the martensitic start temperature but not greater than the lower critical temperature, followed by immediately allowing the seam weld to air-cool. The rapid tempering of this invention is particularly suited to the production of high strength hardenable alloy seam-welded pipe and tubing and other structures.

Abstract: A method and apparatus for detecting a joint between workpieces is provided. At least one light line is recorded by the light section method to detect the three-dimensional course of the joint and a grey-level image of the joint is also recorded. The grey-level image is evaluated to assess the quality of the joint.

Abstract: A method and apparatus for welding polymer components by forming a groove along a surface of a polymer part to be welded, placing a conductive member in the groove, heating the conductive member to a first temperature for a first period, allowing the parts to cool for a second period to form a weldment, heating the conductive member to a second temperature for a third period, and removing the conductive member from the weldment.

Abstract: A welded low carbon dual phase (ferrite plus martensite) and/or low carbon martensitic stainless steel PIPE having requisite yield strength and corrosion and/or erosion resistance is shown. Pipe can be manufactured up to a maximum outside diameter from finished plate or coil by utilizing a high speed-forming mill rather than using the traditional costly seamless pierced billet methods, or utilizing U-O-E or break press. An ERW technique is also used rather than utilizing the traditional laser, tungsten inert gas, gas metal arc, plasma arc, submerged arc or double submerged arc welding methods; or the parameters and procedures for ERW traditionally used to weld carbon steel pipe. Welded pipe dimensions and mechanical properties can be achieved which comply with the heat treatment process and the continuous roll forming mill's capability to produce the yield strengths and dimensional tolerances required to meet the service criteria of the pipe's intended application.

Abstract: The invention concerns a method for controlling the edges (7, 7′) of a foil strip guided in a shaping funnel (5) of a device producing tubular bodies from the foil strip by an overlapping weld seam (13) using a guide wedge (11), said strip being then welded. According to the invention, after welding, the method consists in using a linear infrared sensor for measuring and evaluating a temperature profile perpendicular to the overlapping weld seam (13). In case of variation relative to the specific real profile, a signal is automatically transmitted to rotate the shaping funnel (5) with the guide wedge (11), the welding being produced by the high frequency (HF) and the temperature profile being measured directly after welding.

Abstract: A process for the production of multi-layer metal composite tubes (10), wherein a metal strip is shaped to form a tube (16) and butt-welded along its two longitudinal edges. A plastic inner layer (12) is applied by extrusion in firmly adhering manner to the inside (12) of the metal tube (16) and a plastic outer layer (14) is applied by extrusion in firmly adhering manner to the outside (26) of the metal tube (16).

Abstract: Described is a process for the production of multi-layer metal composite tubes (10), wherein a metal strip is shaped to form a tube (16) and butt-welded along its two longitudinal edges. A plastic inner layer (12) is applied by extrusion in firmly adhering manner to the inside (12) of the metal tube (16) and a plastic outer layer (14) is applied by extrusion in firmly adhering manner to the outside (26) of the metal tube (16).

Abstract: A diffusion bonding method having a step of adjusting ends of material to be bonded before bonding the material after setting the materials in the diffusion bonding apparatus, whereas a diffusion bonding apparatus having a means of finishing ends of materials to be bonded so that both ends face parallel to each other.

Abstract: In high frequency welding apparatus in which high frequency electrical heating current is supplied to metal surfaces to be welded together by contacts engaging the metal which is advanced toward a weld point, the contacts engage the metal in advance of the weld point and have contact faces with downstream edges contacting the metal. The downstream edge of one of the contacts, or the downstream edges of the both of the contacts, is or are skewed with respect to the path or paths of the metal surfaces to be heated so that the downstream edge or edges extend at an acute angle of about 35.degree. to about 55 .degree. with respect to the path or paths of the metal surface or surfaces, the angle being intermediate the contacts and the weld point.

Abstract: In case of producing a welded tube from a metal band by using laser welding, edges of the metal band are preheated so that the temperature at the edges of the metal band before laser welding is not less than a predetermined temperature, the preheated abutting edges of the metal band are laser-welded to form a welded tube and welding beads generated on the outer and/or inner surfaces of the welded tube having been produced are eliminated by cutting. The predetermined temperature is determined depending on the thickness of the metal band and the time from the start of laser welding to the cutting of the welding beads. The edges of the metal band are preheated before welding to prevent the welding beads from being hardened by quick cooling at the welded section after laser welding.

Abstract: A method of producing steel pipes is provided which comprises the steps of providing a steel strip, processing the steel strip into a preheated open pipe, preheating the open pipe at its two opposite longitudinal edges at a temperature higher than about the Curie point, heating the open pipe at the two opposite edges at a temperature higher than about 1,300.degree. C. but lower than the melting point of the steel strip, pressure welding the resultant open pipe with a squeeze roll to thereby form a steel pipe, smoothing the steel pipe at its thick-walled portion formed on an outer surface of the welded seam, and subsequently cutting or winding the resulting steel pipe. An apparatus adapted to form the steel pipes is also provided.

Abstract: Problems associated with accurately positioning a susceptor at the bond line between two or more prefabricated, fiber reinforced, resin composite detail parts to facilitate thermoplastic welding (i.e., fusion bonding) between the detail parts. The integrated susceptor detail part is compatible with Z-pinning along the bond line for the pulloff strength enhancement associated with Z-pin reinforcement. We make the parts by (1) preparing the faying overface of the prefabricated part or prepreg preform for the overlayment of the bond line materials, (2) placing a thermoplastic film on the part or preform, (3) placing the susceptor on the film, and (4) securing the film and susceptor to the part by applying suitable heat and pressure to produce a prefabricated, consolidated detail part having an integrated susceptor in a resin rich region intended as the bond line to other parts in the final assembly.

Abstract: High frequency electrical heating apparatus in which metal parts are heated as they are advanced,either for annealing or forge welding purposes,and in which the electrical heating current is supplied by solid state D.C. to A.C. inverter through a load matching and frequency control circuit which maintains the desired load current and current frequency with changes in the load impedance caused by the metal parts as they are advanced.

Abstract: The side seam of a can is coated and heated inductively by passing it through a medium frequency, oscillating magnetic field generated by an induction coil wound around a core. The core is shaped and oriented so as to have two magnetically opposite poles direct magnetic flux in a concentrated manner from the coil into the side seams of cans traveling along a path of travel. The cores are constructed using individual laminations of high frequency core material, each less than about 0.006 inches thick, individually insulated from each other and bound together to form a U- or E-shaped core directing flux toward the workpiece. The induction coil is constructed using a form of Litz wire and the coil and core are air-cooled. In one embodiment, the core has a plurality of pole pieces each directed toward the path of travel. The induction coil is wound on the core such that sequential ones of the pole pieces along the path of travel have alternatingly magnetically opposite polarities.

Abstract: A method for manufacturing a sweeped tubular bumper reinforcement member having a rear wall formed with an inwardly indented portion in cross-section and a front wall formed in parallel with the rear wall and welded to the inwardly indented portion of the rear wall.

Abstract: A steel pipe having excellent corrosion resistance in an environment containing wet carbon dioxide and a small amount of hydrogen sulfide and having also excellent weldability is produced at a low production cost and with high productivity. The production method comprises heating to a temperature of 1,050.degree. to 1,300.degree. C. a slab containing, in terms of wt %, 0.01 to less than 1.2% of Si, 0.02 to 3.0% of Mn, 7.5 to 14.0% of Cr and 0.005 to 0.5% of Al, reduced C, N, P and S contents, at least one of Cu, Ni, Co, Mo and W, a balance of Fe and unavoidable impurities, and having an MC value of at least 0, finishing hot rolling within an austenite monophase temperature range, coiling the steel sheet as a hot coil having a sheet thickness of 3.0 to 25.4 mm, cooling the coil at a cooling rate of at least 0.01.degree. C./sec to at least 500.degree. C. to convert the steel sheet to a steel substantially consisting of martensite, reheating the steel to a temperature of 550.degree. C. to not more than an A.sub.

Abstract: A method for heating pipes with closely spaced end portions that are to be joined by forge welding or the like. Two diametrically opposed contacts are attached to each end portion for supplying high frequency alternating current for resistance heating of the material in the respective end portions. The contacts for one of the pipes being located in close proximity to and substantially in the same axial plane as the contacts for the other pipe. The contacts for one of the pipes are arranged to form an angle (.alpha.) with juxtaposed contacts of the other pipe so that the projections of the juxtaposed contacts onto the axial plane intersect.

Abstract: A method and apparatus in which edge portions of metal parts, the edge portions being disposed with opposed surfaces, are heated by high frequency electrical currents as the edge portions are advanced and brought together at a weld point. The electrical currents are induced in the edge portions in advance of the weld point by two induction coils, one at one side of the metal parts and the other at the other side of the metal parts, disposed and energized from a high frequency electrical source so that the electrical currents at the opposed surfaces flow in opposite directions at any given time and the currents induced by one coil add to the currents induced by the other coil.

Abstract: Sheet metal edges to be welded are preheated prior to welding. At a given welding speed, this results in a smaller temperature gradient in the material to be welded. Consequently the welding speed can be increased, or material which would otherwise provide poor weld quality can be welded at a high temperature gradient. The preheating is carried out for example by high-frequency excitation of the material to be welded.

Abstract: A multiple component structural member is made by cold roll forming two continuous strips of metal on opposite sides of a third continuous strip of metal. The cold rolling process creates two hollow flange elements with a continuous aperture in which the edges of the third continuous strip of metal is partly extended, followed by resistance or induction welding to create the multiple component structural member.

Abstract: A welding management apparatus for use with a tube production machine. A workpiece fed from a roll of metal strip is formed in a tubular formation having side surfaces opposite to each other. An upsetting pressure is applied to joint the opposite side surfaces of the workpiece at a jointing point. A high frequency power is supplied to the workpiece to weld the opposite side surfaces at the jointing point so as to produce a metal tube member. The welding management apparatus comprises a camera positioned to have a visual field including the jointing point for producing a video signal indicative of an image including an area luminous with a pre-arc produced in the visual field. An image processor converts the video signal into a luminance distribution pattern. An inference unit is provided for inferring a defective welding condition based upon the luminance distribution pattern. The inference unit includes an alarm unit for producing an alarm when a defective welding condition is inferred.

Abstract: A welding management apparatus for use with a tube production machine adapted to form a workpiece fed from a roll of metal strip in a tubular formation having side surfaces opposite to each other, provide an upsetting pressure to butt the opposite side surfaces of the workpiece at a jointing point, and supply a high frequency power to the workpiece to weld the opposite side surfaces at a welding point so as to produce a metal tube. The welding management apparatus comprises a camera positioned to have a visual field including the jointing and welding points for producing a video signal indicative of an image of the visual field. The video signal is converted into a luminance distribution pattern used in controlling the high frequency power to the workpiece.

Abstract: A method for the heating and joining together, preferably for welding, of workpieces by use of a generator. Where, during a heating interval the generator supplies high-frequency energy to at least two electrodes disposed on the workpiece and where the energy supply is controlled by a predetermined time-related curve, with respect to a target value. Accordingly, the energy supply is controlled with reference to the target value by monitoring a first parameter, e.g., high-frequency voltage, high-frequency current or generator anode current. Also, during the heating interval at least one further parameter is monitored, and in the event of an inadmissible divergence in the control system of the first parameter, a subsequent control of the energy supply is carried out.

Abstract: A welding management apparatus for use with a tube production machine. A workpiece fed from a roll of metal strip is formed in a tubular formation having side surfaces opposite to each other. An upsetting pressure is applied to joint the opposite side surfaces of the workpiece at a jointing point. A high frequency power is supplied to the workpiece to weld the opposite side surfaces at the jointing point so as to produce a metal tube member. The welding management apparatus comprises a camera positioned to have a visual field including the jointing point for producing a video signal indicative of an image including an area luminous with a pre-arc produced in the visual field. An image processor converts the video signal into a luminance distribution pattern. An inference unit is provided for inferring a defective welding condition based upon the luminance distribution pattern. The inference unit includes an alarm unit for producing an alarm when a defective welding condition is inferred.

Abstract: A structural member which comprises a pair of hollow end sections and an intermediate web characterized in that each hollow end section is welded to the intermediate web so as to form two weld lines or joins extending along the structural member. Suitably the intermediate web is predominantly planar and the structural member is formed from a unitary sheet of metal having opposed edges whereby a respective edge is located adjacent the intermediate web and is welded thereto form the weld lines or weld joins.

Abstract: A process for the continuous manufacture of seamless tube by confining a selected length of metal strip in the form of a tube and with at least two longitudinal abutting edges and completely melting a selected length of such tubular form to form a seamless tube and cooling the formed seamless tube. The cooling is preferably in a controlled atmosphere of nitrogen and the temperature is reduced to about 700.degree. F. before further processing takes place. In a preferred process the material is a single strip of metal formed into a tube with only one longitudinal seam and it is moved continuously through a mould heated by induction heating selectively controlled to cause the tube to preheat to a selected temperature and then be subjected to a temperature bringing the metal to its molten state to form a seamless tube and while the seamless tube is moving it is cooled downstream from the melting zone solidifying the metal and bringing it to a selected temperature before exiting the mould.

Abstract: A continuous manufacturing method for a metal welded tube and a manufacturing apparatus therefor, which obtains a tubular member by continuously passing a metal band coil through molding rollers, guides the tubular member to abutting rollers to bring the edges thereof in slight contact with each other so as to form a V-throat having the vertex of an edge contact portion at the upstream side of the abutting rollers, disposes an inductor of a high frequency preheating unit aiming at edge preheating at the outer periphery in front of the abutting point of the V-throat and at need disposes an impeder also at the inner surface of the V-throat, and further disposes welding torches in a single or double rows of a welding unit for melting and welding the tubular member by welding high density energy at the upstream side of the abutting rollers including the line connecting the centers thereof.

Abstract: In a method and apparatus of forming a flat metal strip into a tube having generally flat side walls connected by bight portions along their opposite longitudinal edge portions comprising the steps of directing the strip between a pair of form rolls to bend the opposite longitudinal edge portions of the strip into similar generally upwardly curved edge portions; then directing the strip between a second set of rolls which engage the upwardly curved edge portions to center the strip laterally relative to the rolls and bend the strip along its longitudinal center line to form an upwardly rounded bend therealong while maintaining the portions of the strip on the opposite sides of the center bend relatively flat whereby to impart to the strip a V-shaped cross section having a central apex and oppositely upwardly inclined flat legs, each terminating in a laterally inwardly curved edge; directing the V-shaped strip between one or more additional sets of form rolls to increase the circumferential extend of said apex

Abstract: A die-drawing and/or extrusion device is described for producing uniform and tapered metal and composite tubes from flatstock and for reducing the size of solid stock and formed tubes therefrom, and lamination of compatable materials in one operation. The die comprises opposed die elements having curved helical tracks or grooves which follow a central orifice through which the flatstock, solid stock, tubes, etc., are pulled and/or pushed. Wedge-shaped shaping and alignment elements are positioned in the helical tracks in contact with the dies to align the feedstock with the die orifice, and to prevent the metal sheet or tube, rod, etc., from being drawn in between the tangential surfaces of the dies. The extent of product taper is determined by the pull rate applied to the feedstock in conjunction with the rotational rate of the dies, which can be varied continuously.

Abstract: A method of ameliorating the residual stresses in a metallic duplex tube and the like and an apparatus therefor, wherein the duplex tube includes a main tube defining the outer tube, and a thermal sleeve defining the inner tube which is inserted to the outer tube, the thermal sleeve being welded onto the inside of the main tube at its root. The method comprises the steps of supplying cooling water in the duplex tube; fitting a restraining ring externally onto the outer surface of the main tube at a position corresponding to the thermal sleeve root; and heating the main tube from its outer surface so as to generate a temperature difference across the main tube wall.

Abstract: Variations of the output frequency (f(i)) of a high frequency power source (1) for welding a steel tube (7) are detected, the maximum and minimum values of the output as a result of this detection of the variations of the output frequency are obtained, the width (.DELTA.f) of the frequency variation is obtained as the difference between the maximum and minimum values, a target value (.DELTA.f(T)) of the width of the frequency variation is obtained, and the output of the high frequency power source (1) is controlled to make the width (.DELTA.f) of frequency variation equal to the target value (.DELTA.f(T)) of the width of the frequency variation, so that an automatic heat input control apparatus of a high frequency power source used for high quality welding of a tube to be electrically welded is realized.

Abstract: In a method for heating metal elements (1,2) which are to be joined, for example by forge welding, there is used a high frequency resistance heating. The elements are provided with surfaces to be welded and are positioned so that said surfaces constituted a narrow gap (3). The current is conducted from a high frequency current source (11) through a contact (9) into one of the elements (1), wherefrom the current follows the material close to the gap surface (4) and to the opposite side of the element, where the current flows via further contacts (8,9) and a conductor (10) to the other element (2). From here the current follows the other gap surface (5) to another contact (7) and the current source (11). The current will follow a path close to the gap surfaces since these surfaces will give the path of smallest total impedance, the current thereby establishing a narrow and efficient heating zone in the vicinity of said gap surfaces.

Abstract: Methods and apparatus for manufacturing tapered, hollow metal poles which can be used for manufacturing poles of various lengths, tapers and cross-sectional dimensions with the same apparatus. A substantially complete, tapered tube is formed from a plate or sheet of metal having lips at its longitudinal side edges which extend transversely to the major surface of the plate or sheet. The tube is guided at its lip portions to a weld point where pressure is applied to force the lips together by a grooved roller which applies pressure to the oppositely facing surfaces of the lips in directions transverse to such surfaces. The lips are spaced in advance of the weld point, and high frequency, electric heating current is supplied to the tube at opposite sides of the gap between the lips to heat the tube at the lips to welding temperature as it is advanced to the weld point.

Abstract: A conductor is installed along a Vee-angle part of a tube to be welded for producing an electric welded tube by high frequency resistance or induction welding. The conductor is set closely above the Vee-angle part. A high-frequency current having about the same phase as a phase of a high-frequency current for welding is supplied to the conductor. This controls the distribution of the current density on mating surfaces of Vee-angle part so that the welding current does not concentrate in the upper and lower edges of the tube, thus making uniform the current density and heating in the Vee-angle part.

Abstract: A method and apparatus is provided for welding an edge surface of a curved metal brake shoe to a substantially flat metal brake shoe table surface. The apparatus has a positioning mechanism which positions the brake shoe table in longitudinal alignment with the brake shoe web with one end portion of the table surface abutting the brake shoe web surface over a predetermined distance and with the table surface diverging away from the brake shoe web edge forming a vertex where the surfaces abut. A wheel is provided for pressing the abutting surfaces together at the vertex. Conductors are used to contact both the brake shoe web and the brake shoe table to provide a high frequency alternating potential to the pieces to induce current to flow therebetween and thereby heat the interfacing surfaces in the area of the vertex.

Abstract: A method of manufacturing a solar panel element comprising a metal sheet or sheets secured to fluid-tight tubing substantially continuously along its length by metal which has been heated and cooled, e.g. weld metal, in which the tubing and the metal sheet or sheets are held in contact while they are heated to welding temperature, either forge welding or melting temperature. In the preferred methods, the heating is accomplished by high frequency, electric currents using a proximity conductor. Also, in the preferred methods, the tubing is formed with longitudinal lips as the heating is carried out, and the lips are secured together by welding them together simultaneously with the welding of the sheet or sheets to the tubing.

Abstract: The present invention concerns the technique for the manufacture of composite materials.It relates to a process and an apparatus which make it possible continuously to deposit refractory materials, in particular boron, onto a conductive filament heated by means of the Joule effect and by means of a current produced by a high-frequency generator.It also relates to the apparatus for carrying out the said process.This new process has the advantage that it makes it possible, in particular, to obtain a fibre of high tensile strength, while at the same time maintaining a high speed of travel.

Abstract: A process for producing large-sized steel pipe of rectangular or square configuration from a single plate includes providing a predetermined length of steel plate. The plate is bent to form a longitudinally extending base, opposed sidewalls and a top wall. The top wall is constituted by inwardly directed extensions of the sidewalls which terminate in spaced apart longitudinally extending edges. The sidewalls are angularly disposed relative to the base. At least one inner roller having outwardly facing substantially planar surfaces is positioned within the bent plate upon the base thereof. Outer rollers are positioned externally of the bent plate so as to be cooperable with the underside of the base and with the sidewalls. Relative longitudinal movement between the rollers and the bent plate is effected, the outer sidewall rollers are pressed against the planar surfaces of the inner rollers, and the longitudinally extending edges are brought into substantially abutting relationship.

Abstract: A process for producing large-sized square steel pipe includes the steps of continuously paying off steel plate from a roll of the same, removing strain from the plate while conveying the plate, and cutting the plate to predetermined lengths. The lengths of plate are successively bent into a shape resembling a rectangular or square pipe having corner portions with angles slightly larger the 90.degree.. The successive plates are tack-welded and opposed outer rollers are pressed against the outer sides of the plate while the plate is conveyed longitudinally thereof. The opposed edges of the plate are thereafter welded together by high frequency welding.

Abstract: An apparatus for monitoring and controlling a welding phenomenon in an electric resistance welding process, which comprises a welding characteristics measuring instrument for carrying out digital measurement of at least one of high frequency welding characteristics, a welding phenomenon monitor circuit for detecting variations in the welding characteristics, and a welding phenomenon controller circuit for automatically adjusting a parameter of a welding power source or other welding conditions, wherein the welding characteristics include an oscillating frequency and an oscillating period of a high frequency used for the welding, and a phase difference between a high frequency voltage and a current. Changes in the welding characteristics occur in correspondence with the occurrence of periodic fluctuations in the shape of the high frequency welding current circuit formed in the material to be welded during high frequency electric resistance welding process.