Patent Publication Number: US-2012037728-A1

Title: Dual nozzle cap for thermal spray coating

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a dual nozzle cap for thermal spray coating, and more particularly to an apparatus which is attached to a region of a spray gun around a flame spray hole and thus allows subsidiary gas separately injected to be sprayed together with sprayed flame so as to adjust velocity, temperature, and purity of the sprayed flame. 
     2. Description of the Related Art 
     As is generally known, thermal spraying is carried out through a thermal spray coating method in which a coating material, such as a linear material or metal powder, is melted at a high temperature and then is sprayed to perform coating, and a kinetic spray coating method in which powder for coating is melted by collision energy, generated when the coating powder is sprayed toward the surface of a base material to be coated at a high pressure and a high velocity and thus collides with the surface of the base material, to perform coating. Such a thermal spray coating method is divided into a gas type and an electric type according to the kind of a heat source used to heat the coating material. The gas type thermal spray coating method includes flame spraying, detonation spraying, and high velocity oxygen fuel (HVOF) spraying, and the electric type thermal spray coating method includes arc spraying, plasma spraying, wire explosion spraying, and laser spraying. Recently, techniques for plasma spray which enables miniaturization of an apparatus and generates high-temperature heat, and thus uses a coating material having a high melting point, such as W or Mo, have been vigorously developed. For example, there is Korean Patent Laid-open Publication NO. 10-2008-0082283 (Title: Plasma Spray Coating Method; hereinafter, referred to as ‘Cited Reference’). 
     A thermal spray process includes performing pre-treatment or roughing the surface of a base material to be coated by applying impact to the surface of the base material so as to obtain weld-strength of the base material, forming a coating layer on the surface of the base material by melting and spraying a coating material, such as a linear material or metal powder, and performing post-treatment to improve coating properties of the coating layer after spraying. In such a thermal spray process, if the base material is a general crystalline metal, impact or heat generated during the pre-treatment or the spraying causes fine cracks between crystals of the metal or peeling-off of fine crystals of the metal to form an uneven surface of the base material having depressions, and the molten coating material is sprayed and fills the cracks or the depressions, thereby achieving a coating layer. On the other hand, a plasma spray coating process disclosed in Cited Reference further includes preparing a substrate, one surface of which is substantially parallel with a direction of gravity, so as to increase a coating density without re-absorption of scattered particles reflected due to collision with a base material during plasma spray coating, and spraying a plasma flame, which is generated due to a pressure difference between a cathode and an anode and mixed with molten ceramic powder, onto the surface of the substrate in a direction perpendicular to the direction of gravity. 
     However, new materials, i.e., amorphous metals having far higher strength and repulsive force than conventional crystalline metals, have been developed. If such an amorphous metal is applied to the conventional thermal spray coating method as in Cite Reference in which ceramic powder is mixed with the coating material or a spraying direction is varied, the amorphous metal oxidizes and thus the amorphous property of the amorphous metal is rapidly lowered. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a dual nozzle cap for thermal spray coating in which a kinetic spray coating method is applied to a thermal spray coating-type spray gun so as to increase directionality in spraying and spray velocity. 
     In accordance with the present invention, the above and other objects can be accomplished by the provision of a dual nozzle cap for thermal spray coating, which is mounted at the front end of a spray gun, the dual nozzle cap including a nozzle unit including an inner nozzle and an outer nozzle, a gun insertion hole, into which the front end of the spray gun is inserted, formed at the center of the nozzle unit, and a gas connection hole formed through one surface of the nozzle unit to supply high-pressure subsidiary gas, wherein, in a space between the inner nozzle and the outer nozzle of the nozzle unit, a gas collection part to distribute the high-pressure subsidiary gas, injected through the connection hole, throughout the inside of the nozzle unit, a neck part to apply pressure to the high-pressure subsidiary gas filling the gas collection part so as to elevate the pressure of the high-pressure subsidiary gas, accelerate the high-pressure subsidiary gas, and provide directionality when spraying the subsidiary gas, and a gas spray hole formed in a ring-shaped space at the end of the nozzle part to spray the subsidiary gas, provided with the elevated pressure and accelerated velocity by the neck part, together with a material sprayed from the spray gun are sequentially formed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating a detailed configuration of a dual nozzle cap for thermal spray coating in accordance with the present invention; 
         FIG. 2  is a sectional perspective view illustrating an internal structure of the dual nozzle cap for thermal spray coating in accordance with the present invention; 
         FIG. 3  is a sectional view of the dual nozzle cap for thermal spray coating in accordance with the present invention; and 
         FIG. 4  is a sectional view of the dual nozzle cap for thermal spray coating, which is connected with a spray gun, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, a preferred embodiment of the present invention will be described in detail with reference to the annexed drawings. 
       FIGS. 1 to 3  illustrate an overall configuration of a dual nozzle cap for thermal spray coating in accordance with one embodiment of the present invention. 
     As shown in  FIGS. 1 to 3 , the dual nozzle cap for thermal spray coating in accordance with the present invention is mounted at a front end of a spray gun  10 . The dual nozzle cap for thermal spray coating includes an inner nozzle  40  provided with a gun insertion hole  51 , into which the front end of the spray gun  10  is inserted, formed at the center of the inner nozzle  40 , and an outer nozzle  50  surrounding the outer circumferential surface of the inner nozzle  40  and concentrically connected with one side of the inner nozzle  40 . A ring-shaped space is formed between the inner nozzle  40  and the outer nozzle  50  so as to accelerate subsidiary gas  21  injected into the space between the inner nozzle  40  and the outer nozzle  50 . 
     Here, as the spray gun  10 , any conventional spray guns, including a thermal spray gun, a plasma spray gun, a flame gun, and an arc spray gun, may be used. Further, a connection nozzle to connect the front end of the spray gun  10  to the dual nozzle cap in accordance with the present invention may be interposed between the front end of the spray gun  10  and the dual nozzle cap. 
     Hereinafter, the respective components of the dual nozzle cap in accordance with the present invention will be described in more detail. 
     A connection hole  42 , to which a connector  20 , such as a gas supply pipe, through which the subsidiary gas  21  of a high pressure is supplied to the dual nozzle cap, is connected, is formed through one surface of either of the inner nozzle  40  or the outer nozzle  50 . The connection hole  42 , as shown in  FIGS. 2 and 3 , may be formed in parallel with the gun insertion hole  41  so that injection force of the high-pressure subsidiary gas  21  injected from the connector  20  is applied to a neck part  70  so as to further raise the elevated pressure. On the contrary, the connection hole  42  may be formed perpendicularly to the gun insertion hole  41  so that the high-pressure subsidiary gas  21  injected into the dual nozzle cap is momentarily distributed uniformly. Further, as needed, two or more connection holes  42  may be formed. 
     In the dual nozzle cap in accordance with the present invention, as shown in  FIG. 3 , the inner nozzle  40  and the outer nozzle  50  are interconnected so as to sequentially form a gas collection part  60 , the neck part  70 , and a gas spray hole  80  between the inner nozzle  40  and the outer nozzle  50 . The gas collection part  60  uniformly distributes the high-pressure subsidiary gas  21 , injected through the connection hole  42 , throughout the space between the inner nozzle  40  and the outer nozzle  50 . The neck part  70  applies pressure to the high-pressure subsidiary gas  21  filling the gas collection part  60 , thereby elevating the pressure of the high-pressure subsidiary gas  21  and accelerating the velocity of the high-pressure subsidiary gas  21 . The gas spray hole  80  is formed in a space having a ring-shaped cross section between other ends of the inner nozzle  40  and the outer nozzle  50 , and sprays the subsidiary gas  21  provided with the elevated pressure and accelerated velocity by the neck part  70  with a designated directionality while preventing diffused spray of a material from the spray gun  10 . 
     Further, the inner nozzle  40  and the outer nozzle  50  may not be formed separately, but may be integrated into a single nozzle unit such that the above-described gun insertion hole  41 , connection hole  42 , air collection part  60 , neck part  70 , and air spray hole  80  may be formed within the nozzle unit. 
     Here, the above neck part  70 , as shown in  FIG. 3 , includes a first neck region  71  rapidly narrowed from one side of the gas collection part  60  so as to elevate the pressure of the subsidiary gas  21  within the gas collection part  60 , and a second neck region  72  gradually narrowed and then gradually widened from the first neck region  71  to the air spray hole  80  so as to prevent diffused spray of the subsidiary gas  21  with the elevated pressure, introduced from the first neck region  71 , and to uniformly maintain directionality when spraying the subsidiary gas  21 . Thereby, when the subsidiary gas  21  injected to the inside of the dual nozzle cap through the connection hole  42  at a high pressure fills the gas collection part  60 , the subsidiary gas  21  is continuously supplied into the dual nozzle cap, the subsidiary gas  21  flows to the neck part  70  formed at one side of the gas collection part  60 . Then, the pressure of the high-pressure subsidiary gas  21  is elevated by the first neck region  71  rapidly narrowed from the side of the gas collection part  60  in the same manner as the principle of a jet engine, and thus the subsidiary gas  21  is accelerated and flows at a superhigh velocity. 
     Thereafter, when the subsidiary gas  21  flows along a gradually narrowed section of the second neck region  72 , gradually narrowed and then gradually widened from the first neck region  71  to the air spray hole  80 , the pressure of the subsidiary gas  21  is continuously elevated and thus the subsidiary gas  21  is accelerated, and then when the subsidiary gas  21  flows along a gradually widened section of the second neck region  72 , the diffused subsidiary gas  21  is concentrated in a spray direction so as to uniformly maintain directionality when spraying the subsidiary gas  21 . Therefore, the superhigh-velocity/superhigh-pressure subsidiary gas  21  having the uniform directionality when spraying the subsidiary gas  21  is sprayed through the gas spray hole  80 . 
     Further, the gas spray hole  80  provided at the end of the second neck region  72 , as shown in  FIG. 2 , is formed in a ring-shaped space around the other end of the inner nozzle  40  having a narrow outer surface. Therefore, as shown in  FIG. 4 , the superhigh-velocity/superhigh-pressure subsidiary gas  21  sprayed from the gas spray hole  80  surrounds the material sprayed from the spray gun  10  so as to prevent the sprayed material from coming into contact with oxygen in the air, has uniform directionality, and is sprayed at a much greater velocity than the sprayed material so as to concentrate the diffusedly sprayed material in the spray direction and accelerate the sprayed material to a superhigh velocity, thereby suppressing oxidation of an amorphous metal, an amorphous property of which is rapidly lowered due to oxidation, and thus producing a high-quality thermal spray coating layer having a high amorphous property. 
     Although  FIG. 4  exemplarily illustrates that the conical dual nozzle cap in accordance with the present invention is mounted at the front end of the thermal spray gun  10 , which melts metal powder  30  using heat of combustion, generated from combustion of fuel gas  31 , such as methane, ethane, propane, butane, or ethylene, with oxygen, and then sprays the molten powder  30 , the dual nozzle cap in accordance with the present invention may be applied to other types of spray guns, such as a plasma spray gun. 
     Here, the powder  30  may be a coating material for thermal spray coating, such as one of thermoplastic polymeric materials, i.e., thermopolymers, which may be melted without serious degradation, as well as a metal. Such thermopolymers include polyethylene (low density or high density), polypropylene (low density or high density), polyurethane (Low density or high density), nylon (for example, nylon 6 or nylon 11), nylon copolymer, EVA, EEA, ABS, PVC, PEEK, PVDF, PTFE (for example, Teflon®) and other fluorocarbon polymers, polycarbonate, acrylics, polyether, polyester, epoxy resins, silicon, and their chemical or physical combinations. In addition, the themopolymers may include zinc, aluminum, zinc-aluminum alloys, ferrous metal alloys, clad powder of copper and copper alloys, ceramics, carbon, graphite, electromagnetic shielding materials, electric conductors, fluorescent materials, phosphorescent materials, reflective materials, radar absorbing materials, and functional components, such as UV protectors and anti-microbial agents. 
     A base material, to which the coating layer is applied, includes porous or non-porous metals (for example, steel and aluminum), wood, cork, glass, ceramics, solid or foamed polymeric materials, and paper-containing materials. 
     Thermal spray coating using the dual nozzle cap in accordance with the present invention may be applied to bridges, transportation facilities, buildings, road signs, or various constructions in marine environments, such as wharfs or piers. That is, when the dual nozzle cap in accordance with the present invention is applied to a conventional thermal spray gun, the dual nozzle cap may achieve temperature adjustment and prevention of contact of a material sprayed from the thermal spray gun with oxygen in the air, thereby allowing the above-described materials, which were not sprayed with the conventional thermal spraying or spray velocity, to be sprayed, and enabling a wide selection range of subjects to be coated. 
     As apparent from the above description, a dual nozzle cap for thermal spray coating in accordance with the present invention provides uniform directionality when spraying subsidiary gas and continuously applies pressure to the subsidiary gas through a gas collection part and a neck part so that the superhigh-velocity subsidiary gas sprayed through a gas spray hole is sprayed together with a material sprayed from a spray gun while surrounding the material, thus accelerating the sprayed material to a superhigh velocity and concentrating a spraying direction. Thereby, the dual nozzle cap in accordance with the present invention prevents the sprayed material from coming into contact with oxygen in the air, increases spray pressure and velocity, and reduces spray temperature, thereby allowing an amorphous metal having high strength and repulsive force to be sprayed. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.