Abstract: There has been provided a process for spot welding a stack of thin metal strips or layers with a non-depositing welder gun. The process involves forming a stack of thin metal layers, compressing the layers between the jaws of a press, one of which has at least one receptacle for and adapted to receive the non-depositing welder gun tip, placing the gun in the receptacle, optionally flooding with an inert gas, and applying electrical power to the gun for a period of from 1 to 10 seconds. The process is especially useful in the formation of a stack of thin metal strips for making a multicellular honeycomb converter body for removing pollutants from the exhaust of an internal combustion engine.

Abstract: A welded bracket for use in repairing a shroud in which one or more shroud girth seam welds have experienced stress corrosion cracking. A plurality of the welded brackets are placed around the outer circumference of the shroud at a plurality of azimuthal positions at the elevation of the top guide support ring. Each bracket is constructed by welding curved plates. Welding productivity is increased by using an extremely thin weld joint design with a non-circular cylindrical, thin welding electrode having an elongated cross-sectional shape. During welding, the elongated dimension is aligned parallel with the length of the weld joint. This combination enables joining of the welded bracket parts with both the initial weld joint preparation and the completed weld having a uniquely thin width and with a high aspect ratio of depth to width. This high aspect ratio reduces the number of weld beads needed to build the weld joint.

Abstract: A welding apparatus and method for forming arc welds of thin sheet material. The apparatus forms a first pool of molten material and then discontinues the welding to permit a portion of that pool to solidify and then reestablishes a new arc at point along the periphery of the solidified previous pool and continuing this operation to form the finished weld bead. Thus, lower welding heats may be employed and greater tolerance in the welding method and apparatus is possible.

Abstract: Joining of two elements of aluminium or aluminum alloys, where at least one element is the outer layer forming a part of a composite. The connection is made via a weld bead made by fusion welding at least one outer layer of the one element to the second element. The invention is particularly well suited for manufacturing complex, mechanically stable, load bearing structures of any desired shape that contain composites. The invention also concerns the method for fusion welding composites in which the preparation of the weld bead area is of decisive importance.

Abstract: In laser butt welding of metal sheets, in particular sheets of unequal thicknesses, the temperature is measured at two points behind the liquid-solid interface. From combination of the two readings obtained a series of process data can be derived whereby the welding process can be monitored.

Abstract: A plate body is formed from two plane metal plates each at least 5 mm thick and having an edge at least 10 meters long, by machining each plate along its edge to form a welding groove with high accuracy relative to the dimensions and shape of the groove and with a smooth groove surface. The groove extends from a first side of each plate through only part of the thickness of the plates to leave a root area at the second side of the plate. The plates are supported in the vicinity of the welding groove from the second side of the plates by a support bed and are retained by use of suction in relative positions such that the root areas of the two plates are in confronting and contacting relationship. A weld is created in the welding groove by butt joint welding from the first side only of the plates.

Abstract: Process for welding a weld-in part in a weld point comprising a metal plate and a metal covering lying thereon with two tools of which one is formed by a welding head and the other by a drill for preparing the weld point by a drilling process. The drill attached to a revolving device initially in one operating position, by means of a lifting motor which can be moved in a controlled manner between a return position and a machining end-position and vice versa, performs the process at least until the metal plate is drilled (machining end-position) in preparation of the weld point. By pivoting of the revolving device, a welding head arranged on the revolving device and equipped with the weld-in part is then brought into an operating position above the prepared weld point to perform welding, meanwhile the drill is coupled to the lifting motor when the welding head is coupled to the lifting motor when the drill is uncoupled to perform welding on completion of the drilling process.

Abstract: Substantial surface areas can be treated by continuously magnetically moving an electric arc around a general loop direction such as a circle, ellipse or oval and moving the surface so that the arc treats a substantial surface area. The arc treatment can be used to clean or increase surface area, or both, and a reactant or treatment agent can be brought to the arc contact site to alter the surface treated with the arc. Auxiliary treatments for the surface can precede or follow the arc treatment, or both. The invention produces very desirable surface properties including a mild roughness or matte condition suitable even for critical applications such as aluminum lithoplate. Other surface characteristics can include one or more of: capillarity, adhesion, emissivity, stable oxide, paintability, and others.

Abstract: An apparatus and method for pacing the application of a manual weld along the weld line generates beeps or light flashes at a rate which can be correlated by the welder with markings along the weld line. As each beep or flash is perceived, the welder should reach the next marking. Spacing between the markings determines the desired rate at which the weld is being applied. Alternatively, sequentially lightable areas are distributed along the weld line and sequentially lit a desired rate. The welder chases the sequence along the weld line to achieve the optimum rate of welding.

Abstract: A method of welding a soft-iron guide band on a steel projectile body includes the steps of applying a layer of nickel or a nickel alloy to the projectile body and applying a soft-iron wire as the guide band to the layer by electric protective gas welding.

Abstract: A TIG welding system for controlling the weld shape for the seal welding of a small pressurization hole in the end plug of nuclear fuel rods. The controlled shape of the seal weld enables improved ultrasonic detection capabilities. The system achieves the desired weld shape by controlling the pressure differential between the interior and exterior volumes of the fuel rod. The weld box pressure is decreased in accordance with Boyle's law while the weld material for sealing the hole is molten. The system uses an output from the weld electronics as an input to a programmable logic controller ("PLC"). After a programmed time delay, the PLC outputs a signal to a solenoid valve to open a "ballast" volume. The expansion of gas from the weld box into the ballast volume causes a sudden drop in pressure to a level below the pressure inside the fuel rod. As a result of this pressure differential, the molten weld material forms a concave weld upon solidification.

Abstract: The present invention is a method for welding difficult-to-weld metal components as illustrated in the welding of a receiver for a weapon. The method reduces net distortion by a number of techniques, including: (1) cooling the weld with Carbon Dioxide (CO.sub.2) preheated with the welding torch tip; (2) use of not more than approximately 4% oxygen in the shield gas to enable hotter, faster welding; (3) the use of a reduced voltage and wire feed rate at the end of a weld to avoid cracking; (4) the intentional use of distortion to reduce net distortion; and (5) sequencing of welds to reduce distortion. Distortion can be introduced in the stamped parts as they are made or when placed in a fixture for welding that, when welded, have less distortion than before. Distortion can also be countered by welding parts in a sequence where a subsequent weld reduces the distortion of a previous weld.

Abstract: This invention is of a Cr--Mo steel pipe of a wall thickness of 13 mm or less, containing C: 0.03-0.10 wt %, Si: 0.50-1.00 wt %, Mn: 0.30-0.60 wt %, P.ltoreq.0.007 wt %, S.ltoreq.0.020 wt %, Cr: 1.00-1.50 wt %, Mo: 0.45-0.65 wt %, Al: 0.002-0.010 wt % and N: 0.002-0.010 wt % and the remainder consisting of Fe and unavoidable impurities for which preheating and postheating treatments for the prevention of weld cracking and stress corrosion cracking can be effectively omitted, said steel pipe of this invention being suitable for steam piping applications such as STPA23 used in power generation plants, etc.

Abstract: A method and apparatus especially useful for supplying inert gas to a highly pressurized pressure vessel, such as a hybrid inflator for an automotive airbag module, and weld sealing the gas passage or opening therein to avoid or substantially eliminate weld cracks. The apparatus for accomplishing same comprises no moving parts and the welding is accomplished by utilizing a groove feature formed into the surface of the pressure vessel wall surrounding the gas passage or opening so that no additional filler material is required to obtain the weld seal. The method and apparatus may also be used to weld seal low or non-pressurized vessels as well as vacuum vessels.

Abstract: A method for thermal insulation of a wet shielded metal arc welds including insulating a weld joint between workpieces to be welded with a synthetic insulator is provided. An apparatus for thermally insulating a wet shielded metal arc weld including a synthetic insulator is also provided.

Abstract: A welding enclosure includes a central work chamber; a plurality of horizontally spaced welding work stations within the central work chamber; an exhaust chamber beneath and generally coextensive with the central work chamber; a floor over the exhaust chamber, underlying and substantially coextensive with the central work chamber, and including vents operative to allow air to pass through the floor between the central work chamber and exhaust chamber; an exhaust fan for exhausting air from the exhaust chamber; a blower arranged to establish a positive air pressure in the plenum chamber; and a ceiling over and substantial coextensive with the central work chamber, underlying the plenum chamber, and including air registers operative to pass air downwardly through the ceiling from the plenum into the central work chamber for passage downwardly through the central work chamber and through the floor vents into the exhaust chamber for removal by the exhaust fan.

Abstract: A process to avoid or limit corrosion at the junction of two piping comprising devices welded together, said piping comprising devices being adapted to flow corrosive gases through them, said process comprising the steps of:a) providing a first piping comprising device and connecting it to an inert gas source;b) purging it with an inert gas comprising substantially not more than 10 ppb of an oxidizing gas selected from the group consisting of oxygen, carbon dioxide, water vapor or mixtures thereof, said inert gas flowing from a first opening to a second opening of said piping comprising device;c) providing a second pipe comprising device in flow communication with the first one, while continuing to purge the first piping comprising device;d) welding the two piping comprising devices, said welding being carried out under an inert gas atmosphere; ande) repeating steps c and d if necessary.

Abstract: Narrow groove welding is practiced using conventional welding apparatus including a torch block supporting an electrode and a primary, circular gas cup which directs a first flow of cover gas along the electrode, in combination with a rectangular, secondary gas cup detachably mounted coaxially with the primary gas cup and which directs a second, greater flow of cover gas around the flow of cover gas from the primary gas cup. The broad envelope of laminar flow cover gas thus produced is effective for making deep narrow groove welds and is stable enough for completing the weld cap.

Abstract: An end portion of a steel bar such as a reinforcing bar is planed at an angle to form a oblique tip surface having a prescribed angle for an arc welding. The end portion of the steel bar is fitted within a guide member comprising a butting tab that extends forward, guide edge portions that start from diametrically opposite sides of a base portion of the butting tab and extend backward from a position at a distance from a surface to which the bar is to be welded, but protrude further outward than the oblique tip surface, and a slit formed in the axial direction of end portions of the guide edge portions. An end portion of the butting tab is trimmed into an end shape in accordance with a surface to which the bar is to be welded and is butted against that surface. Weld beads are then built up in sequence from the inner surface of the butting tab and between the surface to which the bar is to be welded and the oblique tip surface at the end portion of the steel bar, to form a single weld.

Abstract: A weld support (50) for use with a center sill assembly (16) for supporting a cradle pad (12) used to support the end of a railway tank car body (B). The center sill assembly includes first and second spaced apart side plates (18, 20) spaced to either side of the car body, and a top plate (28). The weld support comprises first and second support members (52, 54) installed on opposite sides of the assembly. A pocket (56) is formed in the center sill assembly on each side thereof. A respective weld support member is attached to the top plate adjacent the respective pockets, for the weld support members to extend above the upper surface of the top plate. The weld support members each provide a substantial contact surface with the cradle pad. Each weld support member also helps pool welding material in the respective pockets to effect a strong weld between the cradle pad and center sill assembly.

Abstract: Disclosed are a device and a method for inert gas plasma welding in a low pressure or vacuum environment.

Abstract: A method of modifying qualities of a metallic article at a particular surface of the article comprises the step of melting the surface by imparting a flux of high density energy to the surface to form a molten metal layer and the step of adding heat resisting element to the molten metal layer by performing overlay welding to the molten metal layer.

Abstract: Apparatus for the deposition welding or the joint welding of a workpiece made of a superalloy by an arc welding process in which the workpiece is supported in a protective-gas container into which is placed a welding electrode and an induction coil for preheating the workpiece. Material of the same type of the workpiece is applied to the surface of the workpiece or to a welding joint thereof by arc welding produced by the welding electrode. The apparatus and associated method are particularly suitable for repairing age-hardened superalloys of engine blades.

Abstract: A method for exactly and effectively correcting an unbalance of a rotating body such as a turbine assembly for a torque converter without worsening a quality of the rotating body. A filler metal is brazed to a welding position by TIG welding while changing an intensity of produced arc by pulse control under an inert gas atmosphere created at a backside of the welding position of the rotating body.

Abstract: A cold-welding process that eliminates heat treatment of welds in hardenable steel or hardened steel, alloy steel, high alloy steel, high carbon forged steel, bi-metal union, manganese steel such as Hadfield steel, and so on, without hardening the deposited weld, whereby also the transition area of the deposited weld is not hardened, thus preserving the mechanical and physical characteristics of the basic material, and maintaining the deposited weld fileable and machineable, by using specific AWS-307, AWS-309, AWS-312 and AWS-8018 through 10018 electrodes. The temperature of the welded parts should never exceed 100.degree. C. during the welding process. This control of maximum temperature is obtained by welding a series of relatively short fillets instead of a single long fillet extending the length of the joint. The short fillets are followed by open spaces without a weld, and those open spaces are filled with weld fillets once the interrupted welding is completed for that weld pass.

Abstract: A combination of a layered leather pouch and a flat flexible unified structure of a heater utilizing an exothermic composition for the purpose of creating and maintaining an arc welding rod inside the pouch at a temperature range between about 28 degrees C and about 139 degrees C, the pouch having a walled off compartment made of specifically perforated suede, the compartment being adapted to receive and hold one or more heaters having sufficient heat generating capacity to maintain the rod in the temperature range for an extended period of at least 3 hours and to be portably and safely worn adjacent a welder on his belt.

Abstract: A process for welding mechanically and/or thermally treated alloy pipes to achieve the full tensile capacity of the unwelded base alloy across the welded pipe joint is disclosed. The process comprises welding the pipes together at the beveled pipe ends to form a cap of weld metal. The weld metal cap overlaps that portion of the heat-affected zone which is created in the base alloy adjacent to the bevel of each pipe during welding. To further increase the tensile capacity of the welded joint, a low-heat buffer bead layer can be deposited on the outer surface of each pipe proximate the outer edge of each bevel, prior to depositing the weld metal between the bevels. The buffer bead layers serve to reduce the thickness of that portion of the heat-affected zone which is formed in the base alloy under each toe of the weld metal cap (upon formation of the weld metal cap) to a level having no significant reduction in the overall tensile capacity of the welded joint.

Abstract: A metallic sealing ring which in radial cross-section is hollow and of sinuous profile having axial end faces sinuously curved so as each to define an axially outward facing deep peripheral groove, the interior of the ring profile being in communication with the exterior thereof.

Abstract: A process for manufacturing a slotted hole screen made by mechanically joining a plurality of longitudinal members to a plurality of cross bars reduces joint roughness, burrs and recesses by including a step of covering the joints with a covering material which has a smooth exterior surface. The covering material is liquefied and has sufficient surface tension to form the smooth surface. In an alternative embodiment, the joints in a slotted screen formed by welding a plurality of longitudinal members to a plurality of cross bars are smoothed by selectively remelting the joints to form the smooth exterior.

Abstract: A fatigue-resistant welded joint between structural members and process for making same, as for an automotive bracket, are shown. A filler metal-containing reprocessing weld is applied over at least part of a toe of a small primary structural weld at the joint, the reprocessing weld extending onto the weld face area and onto the structural member area immediately adjacent to the covered toe portion. The total welding energy input used for the reprocessing weld is less than the welding energy input used for making said primary structural weld, and the cross-sectional area of the reprocessing weld is less than the corresponding cross-sectional area of the primary structural weld.

Abstract: An improved method and apparatus for welding heavy gages of high strength steels and alloys relatively quickly and inexpensively, while producing joints which are extremely strong and durable and have high fracture toughness.

Abstract: A crucible for containing molten mixtures of magnesium and magnesium chloride comprises an outer relatively thick base layer of austenitic stainless steel covered inside with a relatively thin layer of mild carbon steel. The stainless layer provides strength and good creep resistance at 850.degree. C., and the mild steel layer protects the stainless layer from chemical attack by liquid magnesium. The carbon steel lining is applied by weld overlaying.

Abstract: A plasma arc welding process for welding metal of increased thickness with one pass includes operating the plasma arc welding apparatus at a selected plasma gas flow rate, travel speed and arc current, to form a weld having a penetration ratio to weld height to weld width, and maintaining the penetration ratio at less than 0.74. Parameters for the plasma gas flow rate, travel speed and arc current are adjusted to a steady state condition during a start up period and maintained during the steady state condition to complete a weld. During a terminal stopping period, the travel speed is stopped and instantaneously replaced by filler wire which adds material to fill the keyhole that had been formed by the welding process. Parameters are subsequently adjusted during the stopping period to terminate the weld in a sound manner.

Abstract: Argon having a high degree of purity or else a mixture having a high degree of purity consisting of argon, helium, hydrogen, oxygen and/or carbon dioxide are used as the inert gas for TIG, MIG, MAG and plasma welding. For purposes of improving the welding result, 80 ppm to 250 ppm, preferably 120 ppm to 180 ppm of nitrogen are added to the inert gas.

Abstract: A shielding gas for the arc welding of aluminum consists of argon or mixtures of argon and helium. The shielding gas also includes an admixture of 80 ppm to 250 ppm of nitrogen.

Abstract: The instant invention relates to the point welding of a highly corrosion-resistant metal cover plate to a less corrosion-resistant support and provides for the highly corrosion-resistant cover plate to be provided with holes and to be bonded at the same time to the support by a first build-up weld in the holes. The first weld layer is then covered by a second build-up weld. build-up welding is effect by means of metal-inert gas welding with wire electrode.

Abstract: A root pass bead welding method for joining two metal base members includes forming a dike bead by welding on a rear surface of one metal base member, and placing the dike bead against or in the vicinity of a distal end of a rear surface of another metal base member to define a groove open at the front surface of the same. Then welding is performed from the front surface of the other metal base member at the groove to form a root pass bead extending between the dike bead and the rear surface of the other metal base member.

Abstract: A process for welding a rotatable machine component is provided which includes the steps of rotating the component about a longitudinal axis of rotation thereof; preheating an area of the component to be welded; depositing a plurality of weld beads in the area; post weld heat treating the area; and cooling the area to room temperature. During the entire process from preheating through cooling, the component is continuously rotated about its longitudinal axis.

Abstract: A method for welding a structure containing a gap which is exposed on either side of the gap is disclosed. The method is ideally suited for welding the gap which exists between the inner cylinder and nozzle chamber of a steam turbine during manufacture and repair. The method is accomplished by applying a refractory material into one side of the gap, preferably with the aid of gravity while the structure is inverted. When the refractory material is in place, the gap is welded. Upon completion of the welding procedure, the refractory material is preferably removed. In accordance with the present invention, a substantially uniform weld can be made upon a gap which is exposed on either side without the need for a controlled precision initial root weld.

Abstract: A method of welding a first metal plate to a second metal plate including the steps of affixing a back-up bar by use of spaced welding tacks to the flat surface of a first metal plate, forming an abutting edge on the second metal plate a series of alternating lands and slots, the slots extending through the entire thickness of the second metal plate and the length of the slots being substantially greater than the length of the lands, positioning the formed edge of the second metal plate so that the lands thereof engage the flat surface of the first metal plate and a substantially continuous slot is formed between the plates and in which the second metal plate is in engagement with the back-up bar to form a joint, arc welding with a consumable electrode in the substantially continuous slot to form a weld, the weld penetrating portions of the flat surface of the first metal plate, the entire abutting edge of the second metal plate and a portion of the back-up bar and melting the lands and the welding tacks and

Abstract: A method of welding stainless steel, such as a stainless steel end plug into a stainless steel nuclear fuel rod is disclosed. The welding process has a reduced arc wander and deeper arc penetration. A treated welding electrode for practicing the method also is disclosed. A layer of stainless steel is placed on the working arc discharge end of a nonconsumable tungsten arc welding electrode before welding. The stainless steel coating on the electrode reduces arc wander and permits deeper arc penetration. Approximately 0.001 to 0.005 inches of stainless steel is placed on the working arc discharge end of the electrode. The electrode coating can be formed by positioning the working arc discharge end of the electrode into close proximity to a grounded piece of stainless steel and then electrically shorting the electrode to the stainless steel so that the working arc discharge end sticks to the stainless steel.

Abstract: A method and apparatus of welding along a pass line on a steel workpiece, which method and apparatus comprises simultaneously feeding two welding wires in generally parallel relationship toward a workpiece with extended welding wires generally intersecting the workpiece at individual points spaced from each other a distance in the range about 3/16 inch to about 3/8 inch; then creating a separate arc between each of the wires and the workpiece; passing a single protective envelope of shielding gas axially along two welding wires simultaneously and around said two separate arcs extending between welding wires and the workpiece; and, causing relative movement between the two gas shielded welding wires and the workpiece in the direction corresponding to the desired pass line on the workpiece.

Abstract: A method produces hollow gas exchange valves, in particular with a cooling medium introduced into the hollow valve stem. The hollow of the valve stem is preferably drilled from the valve head side and, after the introduction of the cooling medium, sealed again by surfacing. A thin filling piece is inserted to a defined depth into the drilled hole temporarily holding the weld pool of the surfacing weld. By means of surfacing, it is possible to achieve cost savings over other sealing methods. The surfacing is preferably performed by a welding method in which the workpiece is not part of an electric circuit through which the welding energy flows. Preferable methods include gas welding, electron beam welding or laser welding. With these methods, so-called edge effects can be avoided.

Abstract: A method of consumable electrode arc welding is shown wherein the leading consumable electrode wire is mounted in parallel with a trailing filler wire, the latter inserted into a molten metal bath. Welding current is divided between the consumable electrode wire and the filler wire. These modifications improve the wettable boundary of the molten metal bath, prevent defects in the weld, and provide a high speed, highly efficient and high quality method of welding carbon steels, alloy steels, as well as aluminum and its alloys in a fully automatic as well as a semiautomatic operation. In an apparatus utilizing the above method, a single torch contains the consumable electrode and filler wire. One or more insulating contact tubes containing filler wire are mounted in a gas shield in parallel with a conductive contact tube containing consumable electrode wire. The unit is small in size and light-weight, and thus convenient for a welder to carry or hold during operation.

Abstract: The invention provides a composition for preventing the formation of scales in resistance welding, the composition containing as the active component a reaction product prepared by reacting 1 mole of tetraethyl silicate and about 0.5 to about 1.5 moles of water, and a composition for preventing the formation of scales in arc welding, the composition containing as the active component a reaction product prepared by reacting 1 mole of tetraethyl silicate, about 1 to about 30 moles of triethyl borate and about 0.5 to about 1.5 moles of water.

Abstract: An arc-melting method is taught for the formation of metallic-second phase composite materials. The method involves the formation of an intermediate composite material comprising a relatively high loading of second phase particles dispersed in a metal matrix. This intermediate material is then combined with an additional amount of metal and arc-melted to form a final composite comprising a lower loading of the second phase particles dispersed in a final metallic matrix. The final metallic matrix may be comprised of a metal, metal alloy, or intermetallic, while the second phase particles may comprise ceramic materials such as borides, carbides, nitrides, silicides, oxides or sulfides.

Abstract: This invention discloses a novel shielding gas mixture for use in gas shielded arc welding processes. The shielding gas of this invention may be used in a wide variety of processes when welding various superalloy compositions. In the broad range, the composition contains, in percent by volume, 5 to 12 helium, 0.1 to 0.9 carbon dioxide and the balance argon. The typical composition contains about 10 helium, about 0.25 to 0.55 carbon dioxide and the balance argon plus impurities.

Abstract: In a process for welding a pipe string driven horizontally into the ground to a follower pipe, the pipe string buried in the ground and the follower pipe are rotated. A welder then does not need to make vertical welds but can form the weld seams in a position that is most comfortable for him.

Abstract: A method is provided for applying grooved bands of hardsurfacing on a tool joint for earth boring drill pipe. The hardfacing of the tool joint has tungsten carbide granules in an alloy steel matrix. The tool joint is rotated and an arc between an electrode and the tool joint is provided to create a weld puddle. The electrode is reciprocated parallel to the tool joint axis and the granules are fed into the weld puddle with the puddle being applied to the grooved bands around the exterior of the tool joint to a groove depth of from between about 0.75 inches to about 0.150 inches. The feed of the granules into the weld puddle is discontinued and the weld puddle is continued to be applied around the tool joint and in the grooved bands to provide a protruding substantially tungsten carbide free hardfacing surface about the outer diameter of the tool joint of from between about 0.050 inches to about 0.175 inches, and the hardfacing surface is machined down to substantially the outer diameter of the tool joint.

Abstract: A method of submerged arc welding of thick steel plates with a large heat input and flux for submerged arc welding which comprises: forming a groove having a multi-angle shape which has at least two different angular inclination when a single side submerged arc welding for perfect penetration is conducted under a condition of an welding heat input of 100 to 1000 kJ/cm; using submerged arc welding flux SiO.sub.2 : 5 to 28% by weight, MgO: 15 to 35% by weight, CaO: 5 to 15% by weight, CaF.sub.2 : 2 to 20% by weight, Al.sub.2 O.sub.3 : 5 to 15% by weight, and TiO.sub.