Abstract: A method for making a metal-hydride slurry includes adding metal to a liquid carrier to create a metal slurry and hydriding the metal in the metal slurry to create a metal-hydride slurry. In some embodiments, a metal hydride is added to the liquid carrier of the metal slurry prior to hydriding the metal. The metal can be magnesium and the metal hydride can be magnesium hydride.

Abstract: An apparatus and method for thermal spraying a metal coating on a substrate is accomplished with a modified pulsejet and optionally an ejector to assist in preventing oxidation. Metal such as Aluminum or Magnesium may be used. A pulsejet is first initiated by applying fuel, air, and a spark. Metal is inserted continuously in a high volume of metal into a combustion chamber of the pulsejet. The combustion is thereafter controlled resonantly at high frequency and the metal is heated to a molten state. The metal is then transported from the combustion chamber into a tailpipe of said pulsejet and is expelled therefrom at high velocity and deposited on a target substrate.

Abstract: A wire arc spray system use at least one first wire and second wire that include a composite wire including a first material at a core region thereof and a cladding including a second material surrounding the core region. A controller controls operation to propel heated material created by the arcing of the first wire and the second wire at the arc point to a surface to be coated. A wire arc spray methodology for creating a porous metal coating with all-metal wires is also provided.

Abstract: A torch introduces oxidizer into a passage so as to swirl the oxidizer about a central axis, while fuel is introduced at a location spaced apart from the central axis, where the swirling action of the oxidizer is strong, resulting in rapid mixing of the fuel and oxidizer. In practicing the method, the length of a bore through which the fuel and oxidizer pass is maintained short enough that a sheath of unmixed oxidizer surrounds the combusting mixed fuel and oxidizer, eliminating any need for water cooling. The lengths of torches of the present invention can be significantly shorter than those of the prior art, making the torches well suited for use in confined spaces, and the torches have been found to allow spraying materials at a greater rate than torches of the prior art. The reduced length also facilitates introducing into the passage material to be spray-coated.

Abstract: Shaping the feed wire for a combustion wire thermal spray process improves the operating capability of the combustion wire gun through higher feed rates and high operating efficiencies. The efficiency of the wire melting is increased over conventional systems through increasing the surface area of the wire cross section and exposing more of the wire material directly to the burner jets.

Abstract: A valve for a combustion spray gun. An apparatus includes a torsion element rotatable relative to a housing of the combustion spray gun to a charged position. The apparatus also includes a biasing element applying a force to the torsion element, which force urges the torsion element to move a valve core to an off position. The apparatus further includes an engagement mechanism configured to selectively engage and hold the torsion element in the charged position.

Abstract: An apparatus and method for thermal spraying a metal coating on a substrate is accomplished with a modified pulsejet and optionally an ejector to assist in preventing oxidation. Metal such as Aluminum or Magnesium may be used. A pulsejet is first initiated by applying fuel, air, and a spark. Metal is inserted continuously in a high volume of metal into a combustion chamber of the pulsejet. The combustion is thereafter controlled resonantly at high frequency and the metal is heated to a molten state. The metal is then transported from the combustion chamber into a tail pipe of said pulsejet and is expelled therefrom at high velocity and deposited on a target substrate.

Abstract: The present invention provides an improved combustion head and combustion chamber for use with known flame spray apparatus. The combustion head includes a body portion defining a combustion opening for receiving an outlet end of the combustion chamber and an interior chamber extending from the combustion opening into the body portion. The body portion also defines a material feed conduit extending through the body portion along a longitudinal axis thereof. The body portion being substantially hollow wherein the interior chamber extends from the combustion opening throughout substantially the entire body portion including adjacent the material feed conduit. The body portion defining coolant channels on an outer surface thereof of varying depth such that the wall thickness of the body portion at the coolant channels is substantially uniform. The combustion chamber having a flange formed on an outer surface thereof for limiting insertion of the combustion chamber into the combustion head.

Abstract: A thermal spraying device with a first blowing mechanism for lengthening a droplet formed near the tips of thermal spraying materials by arc, and a second blowing mechanism for a blowing a tip portion of the lengthened droplet to atomize it into droplets and to scatter atomized droplets towards a face to be thermally sprayed. The first blowing mechanism lengthens the droplet so that the second blowing mechanism propels air to the tip portion of the lengthened droplet that is separated from a location where the tips of thermal spraying materials are adjacent and the arc is generated. Arcing between the tips of the thermal spraying materials continues stably, and satisfactory thermal spraying is possible.

Abstract: Shaping the feed wire for a combustion wire thermal spray process improves the operating capability of the combustion wire gun through higher feed rates and high operating efficiencies. The efficiency of the wire melting is increased over conventional systems through increasing the surface area of the wire cross section and exposing more of the wire material directly to the burner jets.

Abstract: An electric arc spraying system includes a spraying gun for thermally spraying an inner surface of an object such as a cylinder block by blasting compressed gas substantially perpendicularly to the supplying direction of target wires. The spraying gun is rotated by a spraying gun rotation mechanism. The target wires are loaded in and supplied from wire supplying sources. A wire feeder rotation mechanism is provided for rotating the wire supplying sources synchronously with the spraying gun in rotation. Wire feeders are provided at the spraying gun or adjacent to the wire supplying sources for feeding the target wires. Wire support cables are configured to guide the target wires from the wire supplying sources to the spraying gun.

Abstract: The invention relates to an electric arc wire burner for spraying an electric arc, comprising at least two burner tubes (3) for feeding electrodes which are embodied in the form of wire (5). Said electrodes are guided through the burner tube (3) in the direction of the surface of the object which is to be coated. The wire (5) is guided by a deflection device (7) comprising a number of rotationally mounted guiding elements and/or sliding elements (8) and the wire (5) is deformed in an elastic area.

Abstract: A product dispenser and carrier (10, 110, 210, 310, 410, 510) for attachment to a surface such as a dryer fin includes a plate member (11, 111, 211, 311, 411, 511) and a product carrier (21, 121, 221, 321, 421, 521). The plate member (11, 111, 211, 311, 411, 511) attaches to the surface and the product carrier (21, 121, 221, 321, 421, 521) releasably attaches to the plate member (11, 111, 211, 311, 411, 511). Product (31, 131, 431, 531) is operatively connected to the product carrier (21, 121, 221, 321, 421, 521).

Abstract: A microprocessor controlled arc metalizing unit includes a wire cassette and a drive mechanism cassette engaged in a separable manner. By disengaging the wire cassette and drive mechanism cassette, an operator has much greater control of the unit since the wire loaded wire cassette is fixed and the operator need only maneuver the lightweight drive mechanism cassette. To improve the safety of the arc metalizing unit, a “dead-man” switch acts to automatically shut down the arc metalizing unit should any number of preestablished safety conditions be breached. In addition, one or more composite housings enclose the operational components of the arc metalizing unit to improve safety. Reliability is improved through a tension control unit that eliminates any rotational fluctuations associated with wire spools. The arc metalizing unit further incorporates a touch pad control with a display for operating the unit and displaying the status of the unit.

Abstract: In a thermal spray process, a wire is fed into a flame-jet to heat said wire to the melting point, atomize and projected high velocity the droplets so formed against a surface to buildup a coating of material on the surface. The wire is fed into the flame by aligning the cast-plane of the wire with the flame-jet by using a tubular member formed into a circular shape to provide sufficient length to guide wire and to provide the necessary twist amount to the wire to align the cast-plane with the axis of the flame-jet.

Abstract: An electric arc metalizing apparatus includes a wire drive unit within a housing unit, a device for attaching at least two spools of wire within the housing unit such that the wire can be led through the wire drive unit, a spray gun spatially moveable with respect to the housing, the wire drive unit having at least one drive roller advancing the wire to the spray gun, the drive roller having a knurled surface engaging the wire for avoiding slippage and removing contaminations like corrosion layers, and within the housing unit at least one wire cleaning/lubrication mean position downstream from said drive unit.

Abstract: The method for thermal spraying, especially of metals, for the coating of surfaces, wherein the material employed for coating is supplied in the form of a wire, molten and sprayed, uses a plasma arc.

Abstract: An arc spray gun has a pair of wire guides that guide two metal wires to an arc zone near the wire tips where an electric current through the wires effect an arc, thereby melting the wire tips. The wire guides are of a two-part design. One part is easily removable without the need for tools. Generally, each removable part of the wire guide is temporarily held within a stationary wire guide by an O-ring. A retainer then holds the removable wire guide firmly in place. A gas cap keeps the retainer firmly against the removable wire guides while the gun is in use.

Abstract: A torch for thermal spraying stored rotatably in the front portion of a nozzle and having a discharge member with a droplet passage at the center, wherein a projection is formed at the tip of the discharge member, an air jet space allowing rotating air to be blown therein is formed at the rear of the discharge member projectedly from the discharge member by integrally forming with each other a plurality of arms disposed in an air jet cylinder, and a rotating force is given to the discharge member by the air blown from an air jet port disposed on the outside of the air jet space, so as to bring the rotational speed of the discharge member into the range of 800 to 6000 rpm, whereby thermal spraying can be performed on the internal surfaces of pipes and cylinders, and the thickness of a thermal spraying film can be optimized.

Abstract: A thermal spray or welding apparatus including a cored wire electrode with a sheath and a multiplex powder composite. The composite comprises micron-sized particles and sub-micron sized particles, including nano-scale particles, the particles mechanically cooperating to promote smooth powder flow, which facilitates compaction of the cored wire electrode. The invention also includes a method of manufacture of the apparatus including the cored wire electrode and its method of use to deposit a low porosity coating with high levels of alloyed refractory elements that is adherent and low in oxide content.

Abstract: A thermal spraying method involves the creation of a coating comprising titanium wire in the presence of nitrogen. The apparatus of the invention comprises a nozzle which has a cylindrical throat, with feedstock guides which guide the feedstock wires to a point of intersection in the throat. A current is passed through the wires to cause an arc in the throat, and a nitrogen rich gas under pressure is forced through the throat, generating a spray of molten particles which is used to coat a substrate. In a variation of the method, one of the feedstock wires comprises a binder metal, which produces a coating having enhanced toughness.

Abstract: An electric arc metalizing apparatus includes a wire drive unit within a housing unit, a device for attaching at least two spools of wire within the housing unit such that the wire can be led through the wire drive unit, a spray gun spatially moveable with respect to the housing, the wire drive unit having at least one drive roller advancing the wire to the spray gun, the drive roller having a knurled surface engaging the wire for avoiding slippage and removing contaminations like corrosion layers, and within the housing unit at least one wire cleaning/lubrication mean position downstream from said drive unit.

Abstract: Method of thermally depositing metal at increased rates onto a target surface, comprising: establishing and operating a high velocity plasma transferred wire arc between a cathode and the free-end of a consumable wire electrode, the energy of such plasma and arc being sufficient to not only melt and atomize the free-end of the wire into metal particles, but also project the particles as a column onto the target surface at an enhanced deposition rate for continuous periods in excess of 50 hours; surrounding the plasma and arc with high velocity and high flow gas streams that converge beyond the intersection of the wire free-end with the plasma-arc to limit turbulence of the plasma-arc, avoid direct impingement with the wire and assist the projection of the particles to the target surface; and impinging a low velocity gas flow along the axis of the advancing wire to counteract any destabilizing fluid dynamic forces attempting to move melted particles back along the wire away from the wire free end.

Abstract: A thermal spraying method involves the creation of a coating comprising titanium wire in the presence of nitrogen. The apparatus of the invention comprises a nozzle which has a cylindrical throat, with feedstock guides which guide the feedstock wires to a point of intersection in the throat. A current is passed through the wires to cause an arc in the throat, and a nitrogen rich gas under pressure is forced through the throat, generating a spray of molten particles which is used to coat a substrate. In a variation of the method, one of the feedstock wires comprises a binder metal, which produces a coating having enhanced toughness.

Abstract: A welding torch with an inert gas injection nozzle provided around a distal end of an electrode and a fume collecting hood defining a suction port disposed around the distal end of the nozzle. The fume collecting hood has an exhaust port and the fume collecting hood preferably defines an open interior space in the hood so as to form an unobstructed passage for suction gas between the suction port and the exhaust port. The suction port is preferably provided with a flange disposed around a peripheral edge of thereof.

Abstract: The high-velocity oxygen-fuel or air-fuel apparatus and method to apply low-oxidized and high-density coatings and bulk materials by spraying of non-fused particles, said apparatus comprises a catalytic member in internal burner. Metallic or ceramic catalyst of the catalytic member allows stable combustion at gas temperatures below the melting point of spraying material. Lowering of combustion temperature occurs when increasing the pressure and flow rate of the oxidizer or fuel over stoichiometrical or when adding an inert gas into combustible mixture. The catalytic member contains a catalyst selected from the group of noble metals, or binary oxides of the noble metal and rare earth metal, or other high temperature resistant catalyst capable to lower an ignition temperature of the oxidizer and fuel mixture.

Abstract: A metallizing device for vacuum metallizing arrangements is disclosed having a vaporizer (3) heated by an electrical heating rod (8). This vaporizer (3) is connected to a nozzle element (1) in the form of a hollow body. For the purpose of vaporizing a substrate, vapor flows out of the vaporizer (3) into the nozzle element (1) and from there out of a nozzle gap (2) toward the substrate.

Abstract: A wire thermal spray gun such as a two-wire arc gun has a speed regulator for a DC pull motor in the gun. Armature current corresponds to pulling torque on the pull motor depending on load resistance of the wires. A DC push motor is between a wire supply and the gun, with wire conduits connecting to the gun. A controller provides the push motor with a controlled pushing torque. Feedback of the armature current of the pull motor to the controller adjusts the pushing torque in direct response to change in the pulling torque, such that load sharing is maintained between the push motor and the pull motor.

Abstract: An apparatus for coating a part with a metallic coating comprising at least two consumable electrically conductive metallic wire electrodes converging to converging point at their ends, an electric current into said wires creating an arc and melting said wire ends forming an arc ball, an atomizing gas supply supplying gas to said converging point of said wires to convert said arc ball into a molten particle stream, and a deflecting gas valve assembly disposed outwardly of said consumable wires, said deflecting gas valve assembly deflecting gas from a direction which is rotatable relative to said two wires, said deflecting gas valve assembly containing a plurality of ports relative to and behind said molten particle stream supplying a steady flow of deflecting gas thereby deflecting said molten metal particle stream radially outward towards a surface to be coated.

Abstract: A method of thermal spray coating a surface with a metal coating material includes the provision of a nozzle about a thermal spray coating apparatus, such as a two wire electric-arc apparatus. The nozzle includes a plurality of ports facing generally radially inwardly towards a coating material particle stream, such as an atomized molten metal stream of a two-wire arc thermal spray apparatus. The ports sequentially receive a deflecting gas flow, such that the direction moves circumferentially about the axis of the particle stream. The deflecting gas entrains the coating material and carries it radially to the surface of the part to be coated or the nozzle assembly. By utilizing a plurality of valve ports, one simplifies the assembly over prior art systems which have rotated the part to be coated. In one embodiment of this invention, a valve disk selectively communicates a compressed gas to the ports sequentially.

Abstract: An atomizing method for atomizing a fluid atomizing material feeds fluid atomizing material into jet air. A pair of planar air jets flow through nozzle tips towards a center axis of an atomization material supply. This forms an air chamber which converges in front of the atomization material supply. The interior edge of the converged air jets has a zone of slow moving air that draws the fluid atomizing material into the converging air jets. The material is thus atomized and evenly distributed. The atomization material supplied includes such fluidized atomizing materials as molten metal droplets fused by arc heat, paints, blast materials, adhesives, powders, etc.

Abstract: A nozzle 22 is used for a torch 5 which effects arc welding in a shield gas atmosphere using welding wire 26 that is continuously supplied from a wire support 23 that extends in one direction. The nozzle main body is disposed around and is separated by a space from the wire support 23. Air blow adapters 24 are fixed to the outer side of the nozzle main body and serve to supply into the nozzle main body fluid for removing sputter, and they have air introduction passages 33 that are directed to the central tip end.

Abstract: A method and apparatus for coating piston rings by producing droplets of molybdenum and stainless steel from these materials in wire form which are sprayed, preferably in equal amounts to coat the outer surfaces of the rings. A plurality of rings are mounted on a body which are moved in a helical path during the spraying. A nozzle is used having a central passage through which the wire is fed and two sets of passages, one set for an oxy-acetylene mixture and the other for compressed air, with the outlet orifices of the two sets of passages arranged in concentric rings around the central passage outlet orifice.

Abstract: The present invention is directed to an atomizing method for atomizing a fluid atomizing material. The method includes feeding the fluid atomizing material into jet air. According to a feature of the instant invention, there is provided a method which includes jetting a pair of planar jet air flows through nozzle tips towards a center axis of an atomization material supply means, forming an air chamber which converges at a forward end, followed by supplying the, thus formed, air chamber with the fluid atomizing material in a non-atomizing form. The atomization material supply means includes fluid atomizing material such as molten metal droplet fused by arc heat, paint, blast material, adhesive, powder, etc.

Abstract: A method and apparatus for arc spraying a pair of wires is disclosed. The invention includes feeding the wires to an arc at a controllable rate, where the rate is controlled in response to the current magnitude, or some other parameter of the arc. The arc is also monitored and the condition of the arc--whether there is a wire shortage or arc outage--is indicated to the user.

Abstract: A plasma jet or a supersonic flame jet emanating from an internal burner combusting compressed air and fuel is applied to a solid rod coaxially within the flame or plasma jet to heat, atomize and project a spray of initially liquid droplets of the rod material separating from the tip of the rod in the direction of a workpiece for impact against a workpiece surface for solidification to form a coating thereon. The process involves the control of the transit of the initially liquid droplets from the tip of the rod over the path of travel to the surface of the workpiece to ensure that at the moment of impact against the surface of the workpiece the rod material particles are least partially solid. The stand-off distance may be set to ensure that the initially liquid droplets pass through an upstream liquid region and a contiguous downstream transit region to effect the partial solidification of the molten liquid droplets prior to impact.

Abstract: A flame spray device of the internal burner type has a fuel and oxidizer mixture combusted within a combustion chamber feeding products of combustion to a discharge nozzle passage of reduced inner diameter. An axially aligned metal piece injector has a centrally disposed injection bore hole positioned upstream of the combustion chamber and is provided with particles which are fed through the centrally disposed injection bore hole with the injection bore hole opening near the entrance of the nozzle passage. The metal piece terminates in a cone-shaped section with a reduced diameter end proximate to the entrance to the nozzle passage. A knife-edge terminal face is thereby produced intersecting the injector bore hole to minimize turbulence and rotation of the stream of carrier gas containing the powder exiting the injector metal piece injection hole.

Abstract: A projection device for depositing by projection a fused coating material onto a substrate. The projection device includes a projection nozzle having a central part defining a central passage for the coating material to be fused and projected. The central passage opening at a distal end thereof into a central orifice. The central part being fitted in a peripheral part. Ejection openings of ducts of oxycombustible mixture being distributed around the central orifice according to at least two series which are alternatingly offset from one another with respect to a main axis of the nozzle. The ducts include channels which are milled in the periphery of the central part. The carrier gas contains between 1 and 10% oxygen with the remaining portion consisting of nitrogen. The carrier gas being supplied by a unit for the separation of inert gas from air by adsorption or permeation. The projection device is particularly suited for the formation of the anti-corrosive deposits based on zinc.

Abstract: A method for regulating the flow of liquid metal to an atomization zone is provided. The regulation is effected by imparting a high density flux to a stream of liquid metal as it descends toward the atomization zone. The high density flux is applied by a flux concentrator. The flux concentrator is a small sleeve-like element attached by parallel conductors to a larger sleeve-like element which acts as a secondary to primary coil extended through the larger sleeve element. By imparting high density flux to initiate a stream passing through the flux concentrator the cross sectional dimensions of the melt stream and the rate of flow of melt through the concentrator is regulated to values which are appropriate for a spray-form type of action.

Abstract: A method of improving an arc spray process for making metal matrix composite monotapes by providing an AC power supply and individually controlled wire feeds to promote even melting of the wires particularly wires formed of metals and alloys having high temperature melting points.

Abstract: A thermal spray gun, for spraying wire and powder simultaneously at high velocity to produce a dense and tenacious coating, comprises a nozzle and a gas cap extending from the nozzle. Combustible gas is injected from the nozzle coaxially into the combustion chamber in the gas cap. An annular outer flow of pressurized air is injected into the chamber adjacent to the gas cap. Heat fusible wire is fed axially from the nozzle into the combustion chamber. An annular inner flow of pressurized air is injected into the combustion chamber adjacent to the wire. Powder in a carrier gas is fed annularly from the nozzle into the combustion chamber coaxially between the combustible mixture and the inner flow, such that a spray stream containing the powder and the heat fusible material commingled in finely divided form is propelled through the open end.

Abstract: A method and device for dispersing molten metal into fine particulate spray, the method comprises applying an electric current through the molten metal and simultaneously applying a magnetic field to the molten metal in a plane perpendicular to the electric current, whereby the molten metal is caused to form into droplets at an angle perpendicular to both the electric current and the magnetic field. The device comprises a structure for providing a molten metal, appropriately arranged electrodes for applying an electric current through the molten metal, and a magnet for providing a magnetic field in a plane perpendicular to the electric current.

Abstract: An improved combustion head for use with flame spray apparatus constructed according to the principles described in U.S. Pat. No. 4,416,421 is provided with a recess in the floor of the counterbore receiving hot pressurized combustion gases from the combustion chamber. The recess is of depth sufficient to redistribute the heat of the combustion gases to prevent local hot spots in the counterbore and to avoid cracking and erosion in the combustion head by reducing thermal fatigue which occurs in cyclic use of the flame spray apparatus. The improved combustion head is also provided with radially spaced longitudinal channels extending inwardly from the periphery thereof, along which channels cooling water is passed to cool the improved combustion head.

Abstract: A flame spray torch which comprises a torch body and a torch head exchangeably connected with each other. Injectors are inserted in recesses of the torch body partly projecting therefrom and extending into recesses of the torch head. Each injector communicates with a respective supply duct for combustion gas and oxidation gas, mixing chambers being provided respectively in each injector and in the torch head, the latter being provided with means to improve the gas mixing. The torque reduces the risk of back-firing and allows the attainment of optimum spraying conditions for a great variety of applications by permitting an easy exchange, particularly with respect to the injectors.

Abstract: For uniformly coating a substrate with a spray, a stream of liquid falls past a point towards which a plurality of nozzles in a bank are all directed but at different angles. Bursts of atomising gas are sprayed through the respective nozzles in a repeated sequence, such as to cause a repeated sequence of equal durations of spray in a plurality of directions.

Abstract: An apparatus and method for spraying molten metal that is light weight, requires low maintenance and is quick and simple to operate. A feed system is provided that uses an electric motor and control system to push the electrodes to the head and to prevent system failure, by temporarily stopping the feed, upon the occurrence of the feed wires becoming shorted or welded together. A portable head is provided that employs parallel lead guides that allows complete head manipulation without electrode mismatch. An atomizing gas nozzle is also provided that permits lower air pressure and compensates for arc wander. A lead system is provided that combines into one lead the feed wire guides, current leads and the atomizing gas. The atomizing gas also becomes a cooland allowing lighter current leads for arc metal spraying.

Abstract: A method for making an aluminum nitride powder comprises atomizing a molten aluminum into a nitriding atmosphere of N.sub.2 gas of elevated temperature and solidifying the finely divided liquid particles of aluminum which have been nitrided.

Abstract: An internal burner or equivalent device for discharging the hot products of combustion as an axial flame from the discharge end of a venturi type nozzle has a flexible or relatively inflexible wire rod presented to the combustion product stream in the vicinity of the flame jet immediately beyond the exit of the nozzle at an angle less than a critical angle such that the wire is melted and atomized as though the wire has been fed axially into and along the flame jet axis. With a flexible wire rod, the impingement by the flame spray causes the wire rod to curve so that the tip of the wire is axially aligned with the flame jet axis. Where the wire rod is rigid, the intersection of the wire rod and the flame jet at an angle less than the critical angle causes melting and uniform breaking away of the melted particles of the wire rod as very fine droplets uniformly distributed within the flame jet gas flow.

Abstract: A gas burner for a metal-spraying pistol wherein wire is melted and the melt is atomized by gas flame. The burner is characterized in that a jet insert of abrasion resistant material which is positioned in the jet and serves for the advance of the wire, is separated on most of its surface from the jet, or from other parts of the burner, by an air gap which communicates, on the one hand, with a pressure air supply and, on the other hand, with a space provided between the jet insert and the wire.

Abstract: The products of combustion of compressed air and fuel fed to an internal burner issue through one or more orifices into a single large diameter expansion or nozzle bore open to the atmosphere. Solid rod or solid particle material to be sprayed is passed concurrent with the products of combustion through the large diameter chamber with the material being heat softened or melted to form a spray which is impacted against a workpiece after acceleration to high velocity. The pressure within the large diameter chamber is maintained sub-atmospheric. By aspirating atmospheric air flow bearing particulate material or by leaking air about a solid rod to the sub-atmospheric chamber pressure, pre-melting of the wire or particulate material within the material feed passage upstream of the chamber and prevented via hot combustion product gas back flow.