Abstract: Disclosed is a machine for flash butt welding of pipes located in the bore of the pipes welded together, a housing (2) whereof is provided with rigidly attached thereto a first supporting disc (3) and a second supporting disc (4) and with a pipe flashing-and-upsetting means (5) which has a carrier (7) and a hydraulic actuator (6) for displacing said means along the housing (2) and also has two pipe clamping means (9, 10) each whereof is provided with a carrier (12 and 13) and self-contained hydraulic actuators (11) imparting axial motion to this clamping means.

Abstract: In an apparatus for the butt welding of hollow molding of aluminum with two contact clamps (4, 5), movable toward each other, for the ends of the moldings to be joined together, one contact clamp (4) is fixed at the machine frame, and the other contact clamp (5) is arranged on a table (3) supported at the machine frame (18) by way of two parallelogram guide arm pairs (19, 20). Trough-like recesses (15) are provided in the mutually opposing end faces of the contact clamps (4, 5), a conduit for the feeding of protective gas during the welding operation terminating in the zone between the contact clamps (4, 5).

Abstract: There is proposed a control device for a flash-butt resistance welding mane, which comprises a welding transformer (1) whose primary winding is in series with a welding current pickup (7) connected to an electrohydraulic drive (30) of the moving electrode of the machine via a drive control unit (12). Said drive control unit (12) comprises two input amplifiers (14) and (15), first inputs thereof being coupled with the output of the welding current pickup (7), while second inputs of the amplifier (14) and (15) are coupled to a control voltage source (13). The output of each input amplifier (14) and (15) is connected, via transistor (21) or (22) and a voltage divider, to the input of an operational amplifier (29) whose output is connected to the input of the electrohydraulic drive (30), a welding voltage stabilizing unit being inserted into the primary circuit of the welding transformer (1), the control input of said stabilizing unit (6) being connected to the secondary winding of the welding transformer (1).

Abstract: Flash-butt welder in which the piston rod of a pneumatic cylinder is connected to one end of a pivotable lever arm. A pneumatic system sequentially supplies air at two different pressures to the cylinder. Fixed and movable platens, each with a work piece clamping jaw, are fitted onto a unitary shaft which is mounted in laterally spaced and generally parallel relationship with the pneumatic cylinder. The movable platen is moved by the opposite end of the lever arm along the shaft toward the fixed platen. The movable platen includes a laterally extending arm portion for angular orientation of the platen on the shaft. A switch is disposed to be actuated by the lever arm as it advances to a predetermined position which energizes a solenoid valve to supply substantially higher pressure air to the cylinder. An hydraulic cylinder, disposed in spaced parallel relation to the shaft, includes a piston rod engaged with a pivotable linkage carried by the arm portion of the movable platen.

Abstract: A welding apparatus for welding a trailing end of a preceding strip and a leading end of a subsequent strip including a shear device for cutting them in parallel and a back bar device for supporting the ends of the strips. Provision is made to detachably connect the shear device and the back bar device and move them along a common rail between the strip ends.

Abstract: The apparatus possesses work locating fixtures or clamping devices for clamping edge areas of hollow cylindrical blanks as well as a facility for pressing together the mutually confronting edges of axial slits of the blanks. One of the jaws of each work locating fixture or clamping device is connected to a source of welding current. To prevent substantial elastic deformations of the apparatus caused by the very high clamping forces of the work locating fixtures or clamping devices as well as compression forces before, during and after welding and to render possible a feeding and removing of the blanks or wheel rim hoops, transverse to the axis of the blanks, each work locating fixture or clamping device possesses two movable clamp or pincer-type partial jaw members which cooperate with an associated fixed clamping jaw.

Abstract: A rail alignment device and a shear head are suspended from a trolley running over a rail welding machine. The alignment device comprises structure forming a downwardly-opening bight and carrying locating stops, clamping cylinders and transducers with sensing plungers all of which project into the bight. The rail ends to be butt-welded are received within the bight for alignment. One of the rails is clamped against the stops by the cylinders. The location of the other rail relative to the structure is sensed by the transducers and the machine clamps are adjusted until those transducers indicate alignment of the rails. The device is then removed and stored remote from the gap, with the shear head, during welding. The shear head comprises a horseshoe-shaped back plate which carries three cutting tools. An arm, which is pivotally mounted on one of the ends of the back plate and adapted to be latched to the other end to close the bight of the back plate, carries a fourth cutting tool.

Abstract: A flash welding machine for butt welding the trailing edge of a preceding metal strip to the leading edge of a following metal strip in a rolling mill or the like. A preceding carriage and a following carriage are provided, movably mounted on a common set of rails. Each carriage is provided with electrodes capable of clamping respective ones of the preceding strip and the following strip when the two strips are in abutment with on another. Welding cylinders are provided for selectively joining the two carriers when the two strips are in abutment and the welding operation is to be performed, and then releasing the carriers from one another.

Abstract: The average winding diameter of a finite roller band length wound on a supply coil is increased by having the roller band rewound from the supply coil to a storage coil of a larger than the winding diameter, which encloses the supply coil concentrically. During the uncoiling of the band stored on the storage coil for purposes of a continuous manufacturing operation, a welding device is arranged in the annular area between the external diameter of the supply coil and the internal diameter of the storage coil and welds the band trailing end of the storage coil together with the band and leading end of the supply coil. The contents of the supply coil are then taken over by the storage coil, and while this material is uncoiled, a further supply coil is inserted and its leading edge welded to the end of the storage coil.

Abstract: A machine for electrical resistance welding of chain links has upsetting bars (10) which are engaged against the arcuate ends of a chain link (1). On either side of the welding zone the legs of a link are gripped by pairs of electrodes (12) attached to the ends of a two-armed clamp (14). The arms (13) of the clamp are mounted for pivoting in a plane at right angles to the chain link, and also about an axis in this plane extending at right angles to the upsetting direction and passing through journalling head (20) attached to the end of a piston rod (21) of a counteraction cylinder (20). The ends remote from the electrode jaws (12) of the clamp arms (13) are acted on by an operation cylinder (30) which, via a link system (16, 16), gives the clamp a gripping movement about the link leg. The cylinder (20) with cylinder (30) and the clamp (14) commonly form a welding head which is pivotable about an axis (z-- z) at right angles to the upsetting direction.

Abstract: A welding apparatus includes a mechanical hand assembly suspended from a support assembly rotatably mounted on a movable base. The hand assembly includes a first pair of mechanical hands connected to a hydraulic cylinder and a second mechanical hand coaxially movable relative to the first mechanical hand. Each mechanical hand functions as an electrode during welding, and comprises a movable gripping member pivoted relative to a fixed gripping member by a hydraulic actuator. The support assembly comprises an elongated, counterbalanced beam which is length-adjustable relative to a rotatable support pedestal mounted on a movable base, and may include a pulley and cable supporting the hand assembly to provide adjustment in the vertical position of the handling assembly. The hydraulic system includes controls to effect grasping by the mechanical hands of the elements to be welded and coaxial longitudinal movement of the hands to bring together the elements for joining.

Abstract: In solid phase or pressure welding of adjacent pipe ends wherein a burner ring or other heating element extends circumferentially around the pipes adjacent the joint therebetween, an axial flow of air is directed along the pipe adjacent the weld zone whereby the adjacent pipe ends may be more uniformly heated and thereby produce a better weld.

Abstract: The apparatus comprises a current transformer coupled to the welding tranrmer primary and connected with an analog transmitter of the welding current and with a digital transmitter of the duration of short-circuits in the welding circuit, having a memory element at the output.

Abstract: Disclosed are welding current pick-ups which are switched into welding circuits. Outputs of these pick-ups are connected to inputs of a logical coincidence unit having its output connected to a control input of a welding program control unit whose output is connected with a drive adapted for moving the workpieces being welded.

Abstract: Two coaxially aligned workpieces of ferromagnetic material, axially separated by a narrow peripheral gap across which a weld seam is to be formed with the aid of an arc moving along that gap, are engaged by holders including at least one set of two or more ferromagnetic gripper jaws whose confronting faces are magnetized with like polarity by respective excitation windings surrounding extensions of these jaws. The resulting magnetic field extends axially within the workpiece held by the gripper jaws in a loop which passes generally radially through the peripheral gap, either on account of a bucking magnetic field (which may be generated by a similar set of jaws gripping the other workpiece) or by virtue of pole shoes of the opposite polarity juxtaposed with the jaw extensions and approaching the gap.

Abstract: A pipe resistance butt welding apparatus comprises a body with an elongated arrying member and two internal expanding clamps including current-feeding shoes. One of the clamps is rigidly attached to the body, whereas the other is movably mounted on the elongated carrying member and connected with a drive intended to communicate reciprocating motion to the other clamp. A trimming mechanism for removing flash is mounted on at least one of the internal expanding clamps. The body of the apparatus mounts centering supporting rollers and driving wheels, the former and the latter being secured thereto by means of spring-loaded levers. The driving wheels are connected with a rotation drive intended to rotate the wheels. The body carries a powder cylinder and spring-loaded three-arm rockers, the latter being turnably mounted. The first arm of each of said three-arm rockers carries a driving wheel, the second arm carries an additional supporting roller, and the third arm is connected with a rod of the power cylinder.

Abstract: The primary winding of a welding transformer is provided with controlled rectifiers and the primary winding of a current transformer. The secondary winding of the current transformer is connected to a welding current pick-up. The phase angle of opening of the controlled rectifiers is varied through a phase shifter and a programmer. A pulse shaper is provided for shaping pulses synchronized with the voltage of a supply circuit and has an output connected to a phase delay unit. An OR circuit is provided having inputs connected to the output of the welding current pick-up and to one output of the programmer, and an output connected together with the output of the phase delay unit through AND logical circuits and an inverter to the inputs of a voltage switching flip-flop having outputs each being connected in pair with another output of the programmer through additional AND circuits to corresponding inputs of the phase shifter.

Abstract: A method and apparatus for forming a continuous railroad track including a mobile welding plant which is comprised of, for example, a string of flat cars for transporting a number of already formed continuous rails, another flat car or the like carrying means such as a winch and other related apparatus for delivering the individual continuous rails to the mobile welding plant, and another flat car or the like transporting a puller or pusher apparatus for controlling the movement of the continuous track which is formed, in and from the mobile welding plant.

Abstract: A machine for flash welding rails having two gripping clamps with conductive jaws pivoted on a common shaft, at least one clamp being able to slide along said shaft relative to the second clamp under the action of a jack and being guided along rods disposed laterally to the rail, which rods also serving as jack rods in which the machine has flash removing cutters mounted on a flash removing clamp independently of the gripping clamp, which flash removing clamp has two clamp halves pivotally and slidably mounted on the same shaft and on the same rods as the gripping clamps.

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: A welding apparatus comprises a pair of clamping devices for clamping the workpieces to prevent slip under applying significantly large force to the butting surfaces for the butt welding operation and a pair of electrode tables for feeding a welding current. The welding apparatus need not comprise a step gauge bar nor an auxiliary clamp in order to set the projecting degree.

Abstract: A pipe resistance butt welding apparatus disposable within the pipes to be welded comprises a fixed expanding clamp and a movable expanding clamp, provided with clamping elements and actuating cylinders and intended to fix the pipes to be welded with respect to the apparatus. A cylinder to effect an axial movement of the movable expanding clamp is installed at the end at which this expanding clamp is located; the axial movement provides for drawing together the ends of the pipes to be welded in the course of fusion and upsetting. The cylinder for the axial movement of the movable expanding clamp is coupled with the actuating cylinder of the same clamp and with the clamping elements. The devices making up the apparatus and the cylinders are coaxially installed within a body wherefrom the clamp elements extend outwardly to engage the inner surface of the pipes being welded. Modifications of the apparatus for weld-joining of medium and large diameter pipes respectively are also described.

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: A porous, laminated metal fabrication includes first and second porous walls, each having laminae therein with a free edge portion across at least one end thereof; each of the first and second walls including an outer lamina with a first preformed hole pattern therein, each of the first and second walls further including an inner lamina having a second preformed hole pattern therein combined to form a tortuous air flow path through the first and second walls for cooling the metal therein; and each of the lamina in the laminae including a solid metal annulus therein of uniform density for welding; the annulus being located between the hole patterns and the free edge portions to define a weldable region between the first and second walls having an axial width limited to the axial width of the solid metal annulus whereby air flow through the first and second walls will flow freely throughout the full extent of all the performed hole patterns therein so as to maintain full coolant flow from exteriorly of the poro

Abstract: A machine for continuous flash butt welding comprises control devices for the control of beginning-of-upset operation and upset value, respectively, and such control devices are provided in one unit (a computer). Also provided are a control device for automatically controlling the flashing-off speed and a welding current meter connected to a welding transformer. A sensor connected to the meter detects short-circuit duration in the welding circuit in response to outputs of a welding control enabling signal generator actuated at the final stage of flashing and in the course of upsetting. The inputs of the latter are coupled to the computer and the output is connected to an upset value deviation control circuit. The latter receives inputs from a circuit which detects slippage of the parts in the clamping jaws during welding. The upset value deviation control circuit is further connected to a sensor means for detecting misalignment of a rod of the follow-up slide valve relative to its body.

Abstract: A welder arranged inside pipes to be welded comprises a housing with the longitudinal axis thereof matched with the axis of the pipes. On the housing are a welding transformer and two mechanisms clamping the pipes, each having a drive moving the mechanism along the axis of the housing, and each being electrically connected to the transformer. The housing has mounted thereon a pipe flashing and upsetting mechanism with its own hydraulic drive, kinematically coupled to one of the pipe clamping mechanisms, a hydraulic pump supplying fluid to the drives, and a mechanism driving the welder along the pipes' axis. The housing carries two bearing discs secured at opposite ends and three clips mounted on roller supports and movable along the housing's axis. Two clips are incorporated in the first and second clamping mechanisms, respectively, and the third is part of the flashing and upsetting mechanism.

Abstract: A welding apparatus including, generally, a vertical clamping assembly having an upper and a lower clamping assembly for each of two rail sections to be welded together. These vertical clamping assemblies clamp and vertically align the running surfaces of the two rail sections, by establishing the running surfaces at a pre-determined stop level. The welding apparatus also includes a horizontal centering and aligning apparatus which has a first pair of clamping arms which engage the rail base and pre-center the rail sections with respect to one another and to the welding apparatus. The apparatus also includes a pair of spaced apart clamping arms associated with each of the rail sections which are operable to both laterally clamp the rail heads of the respective rail sections and to horizontally or laterally align the rail sections with respect to one another. Once aligned, the ends of the rail sections are welded together.

Abstract: An electric resistance heating element is formed by a molybdenum disilicide wire loop formed by separate lengths of the wire having ends positioned together and butt welded to the end of a molybdenum disilicide connecting wire of larger diameter than that of the lengths. The lengths diverge from each other so they are electrically separated. Electrical connections with the free ends of the separate lengths of wire can provide for electrically powering the loop.

Abstract: A flash butt welder with an operating lever connected to the movable platen and control mechanism therefor including a rotatable cam member having an arcuate cam surface with a flash portion followed by a radially inwardly extending upset portion, a cam member driving wheel mounted on the operating lever in contact with the flash portion of the cam surface for rotating the cam member and a snubbing device for controlling the rotation of the same member.

Abstract: A device for controlling a butt welding machine includes a pressure equalizing hydraulic slide valve connected to a manifold between the rod space of a clamping hydraulic cylinder and a reversible hydraulic slide valve coupled to both the delivery and drain manifolds of a hydraulic fluid supply system. Upon upsetting, the rod space communicates through the pressure equalizing hydraulic slide valve with the drain manifold, providing the same pressure above and beneath the piston and releasing a part of the clamping force. Provision is made for a programmed control unit or timer for energizing electromagnets adapted for switching the pressure equalizing hydraulic slide valve and a follow-up or tracking slide valve of a hydraulic drive adapted for carrying welded parts.

Abstract: An apparatus for welding two profile or section rods by means of electrical resistance welding, especially an apparatus for welding two rails. There is provided for each of the profile or section rods a clamping device having contact electrodes for infeeding the welding current. Both of the clamping devices are displaceable relative to one another in the direction of the profile or section rods, in order to exert a pressure force at the weld joint. To prevent distortion or displacement of the end regions of the profile sections directly neighboring the weld joint, a centering device is arranged between both of the clamping devices. This centering device can be brought into engagement with the end section of both the one as well as the other profile rod and fixedly retains such end sections. The centering device can comprise two similarly constructed pivotal arms rotatable about a common centering shaft.

Abstract: According to the invention, the continuous flash butt-welding machine supplied with power from a mobile diesel-generator power plant comprises a rectifier-charger the input of which is connected to the diesel-generator. The machine has a storage battery provided with a charge-discharge sensing element connected to the rectifier-charger. The machine also has an inverter with a unit for controlling the frequency and amplitude of the voltage at the inverter output. The inverter is connected to welding transformers and to a current transducer. The control unit is connected to the charge-discharge sensing element, the current transducer and a flashing value sensing element. The proposed invention makes it possible to reduce the installed power of the diesel-electric units of mobile power plants and to increase the life of the diesel engines and the thermal efficiency of the welding process.

Abstract: A welding apparatus comprises a pair of suspension type electrode press devices for clamping an upper electrode and a lower electrode in perpendicular relation to workpieces for synchronizing them, whereby a clamping force is treated as the inner force of the pushing mechanism and the apparatus can be miniaturized. The surfaces of the workpieces can be uniformly clamped by the upper and lower electrodes whereby the consumptions of the upper and lower electrodes are substantially the same and the calibration of the positions of the upper and lower electrodes for consumption is not required.The welding apparatus is especially effective for continuous rolling in single or plural lines of a rolling apparatus for rolling hot steel billets, etc. and welding them.

Abstract: A method of making knives in which a separate blade and handle are bonded together by electron-beam welding which reduces the susceptibility to corrosion at the weld area and thereby increases the knife life. In addition, the blade can be unhardened when welded, and hardened after welding to reverse any structural changes occurring in the metal adjacent the weld and thereby more reliably reduce the susceptibility to corrosion at the weld area. The step of hardening the blade after welding can be used to provide satisfactory corrosion resistance in knives where separate blades and handles are joined by other welding techniques such as electrical seam and oxyacetylene welding.

Abstract: A strip flash welder having a guillotine shear unit which is movable from a position out of the strip flow path into a position for shearing strip ends between the main clamping dies of the machine.

Abstract: A welding machine auxiliary transfer clamp for pushing the end of a coil against a spacer bar and including a pair of clamping elements, each including a cylindrical ram operated by fluid cylinder, there being a ball connection intermediate each fluid cylinder and its respective ram to enable the upper and lower rams to pivot freely about their longitudinal axis so as to prevent occurrence of a gap otherwise formed by lateral tilting of the coil, whose end is to be welded.

Abstract: A welding machine for automatically welding abutting workpiece portions in which the workpiece portions are aligned by a gauge and after being clamped in such a position, the gauge is automatically removed and the clamped ends are moved into abutting relationship to each other to be welded together. After the weld is completed the gauge is moved automatically to engage and eject the welded part and at the same time position the gauge and place the machine in condition to receive the next part to be welded.

Abstract: Welding apparatus for welding railroad rails of a construction such that it is movable plus or minus approximately two feet to compensate for the position of the continuous rail, i.e., the already welded together rail sections, as the latter is removed from the welding apparatus. Accordingly, the entire length of the continuous rail need not be moved to properly position it with respect to the welding apparatus to form or make a subsequent weld.The welding apparatus also is provided with a vertical clamping and aligning system and a horizontal clamping and aligning system, each of which contain pairs of hydraulic cylinders, one of which is larger than the other, with the larger cylinder in each case being operable to a set position with respect to the rail line of the apparatus, to position the rail. The smaller cylinder than operates to effectively clamp the rail against an arm operated by the larger cylinder. Both of the pairs of cylinders are fed from the same source of hydraulic power.

Abstract: The present invention discloses a full-automatic flash welding apparatus wherein the trailing edge of the preceding strip and the leading edge of the succeeding strip are automatically accurately positioned, rigidly clamped and simultaneously cut off, the new trailing and leading edges are automatically machined and then butt welded, and thereafter the flash on the upper and lower surfaces of the joined strips is automatically removed.

Abstract: Wheel rim blank manufacturing apparatus comprises an elongated mandrel passing through Coiling, Welding and Machining Stations. Flat stock is fed transversely for coiling to cylindrical rim blanks about the mandrel. A transfer slide advances and maintains orientation of coiled rim blanks from the Coiling Station to the Welding Station. At the Welding Station clamps secure the blanks for resistance or high frequency current penetration welding. Internal clamps at the Welding Station have small shoulders for transferring the blanks past a Machining Station where a scarfing tool engages their welded areas. The method includes feeding stock transversely, coiling about a mandrel, advancing blanks along the mandrel, welding, again advancing the blanks, and machining weld areas.

Abstract: A butt welding device wherein the trailing edge of a first or preceding strip and the leading edge of a second or succeeding strip are clamped in position, simultaneously cut off, and joined together by flash butt welding and thereafter the flash and upset are removed by machining.

Abstract: A method for controlling flashing speed during resistance butt welding comprises measuring values of current density for at least two joints between parts being welded, converting them into d-c. voltages, detecting a maximum voltage value, comparing it to a preset d-c. voltage, the resultant difference value being used as flashing speed control parameter. An apparatus for carrying out the method comprises electric circuits whose number is equal to the number of joints being welded. Each circuit comprises a welding transformer and a circuit for conversion of flashing current density into d-c. voltage. A maximum signal detector comprises circuits for conversion of current density into d-c. voltages, whose number is equal to the number of joints being welded. The detector output is connected to the circuit for comparing a current voltage value to the preset one.

Abstract: A plurality of individual pre-shaped cores or pins are initially positioned in a prearranged orientation upon an outlet surface of a die body by means of a plate of photosensitive glass or glass-ceramic material which has been etched to form a mask with the desired pattern or arrangement of openings for orienting said cores or pins upon said die surface for subsequent securement thereto such as by welding.

Abstract: The machine disclosed is provided with a manipulator which aligns and moves pipes in course of welding and incorporates a hollow rod for the movement of the manipulator relatively to the pipe joints. The rod is immovably attached to the body of the manipulator and is provided with a partition subdividing the rod bore into two spaces. One of the spaces is intended to be filled with a working fluid and the other accommodates on the partition a hydraulic system for feeding and controlling both actuators of pipeholding clamps and a means for moving the pipes in the course of welding, the means comprising hydraulic cylinders whose bodies are immovably attached to the body of a movable aligning unit between hydraulic cylinders which are mounted on the unit to actuate the clamps holding fast one of the pipes being welded whereas piston rods of the hydraulic cylinders that move the pipes are immovably attached to the body of the manipulator insulated electrically from an immovable aligning unit.

Abstract: Welding apparatus for welding railroad rails is movable plus or minus approximately two feet to compensate for the position of the continuous rail, i.e., the already welded together rail sections, as the latter is removed from the welding apparatus.The welding apparatus also is provided with a vertical clamping and aligning system and a horizontal clamping and aligning system, each of which contain pairs of hydraulic cylinders, one of which is larger than the other, with the larger cylinder in each case being operable to a set position with respect to the rail line of the apparatus, to position the rail. The smaller cylinder then operates to effectively clamp the rail against an arm operated by the larger cylinder. The cylinders are connected in a parallelogram-type arrangement, with the entire arrangement being adjustable by means of still another hydraulic cylinder, for a final alignment adjustment.

Abstract: Apparatus for welding parts, such as pipes, end to end by means of an electric arc which is caused to rotate along the adjacent edges of the pipes. Two separate magnetic fields are used to cause the arc to follow a spiral path along the edges so that pipes having a wall thickness greater than one quarter of an inch may be welded.