Patent Publication Number: US-2021164108-A1

Title: Cold spray nozzle and cold spray device

Description:
TECHNICAL FIELD 
     The present invention relates to a nozzle for cold spray and a cold spray apparatus. 
     BACKGROUND ART 
     A cold spray apparatus is known, which sprays metal particles onto a base material to form a metal film by plastic deformation of the metal particles. A nozzle for cold spray including a tubular nozzle main body and a cooling member capable of cooling the nozzle main body is also known as the nozzle used for the cold spray apparatus to spray the metal particles (see Patent Document 1, for example). 
     This nozzle for cold spray cools the inner surface of the nozzle body main by cooling the outer surface of the nozzle main body, which is made of a heat conductive material, with a fluid circulated in the cooling member. This suppresses the adhesion of metal particles in the nozzle main body and prevents the nozzle main body from being blocked due to the adhesion and deposition of the metal particles. 
     PRIOR ART DOCUMENT 
     Patent Document 
     [Patent Document 1] JP2009-000632A 
     SUMMARY OF INVENTION 
     Problems to be solved by Invention 
     Unfortunately, however, the above nozzle for cold spray has a problem that the fluid used as a refrigerant leaks from the cooling member. For example, when water is used as the fluid and the water leaks from the nozzle for cold spray and adheres to the metal film, this causes poor quality, poor interfacial adhesion, and the like of the metal film. This fluid leakage occurs due to a gap being created in the seal for a passage through which the fluid flows, such as by the vibration of the nozzle main body in association with the spray of metal particles or the misalignment of the nozzle main body due to movement and stop of movement of the nozzle for cold spray. 
     A problem to be solved by the present invention is to provide a nozzle for cold spray and a cold spray apparatus that are able to prevent the leakage of refrigerant, such as due to the vibration or misalignment of the nozzle main body. 
     Means for Solving Problems 
     The present invention solves the above problem through configuring a nozzle for cold spray so as to include a tubular nozzle main body and a cooling jacket that surrounds the nozzle main body to form a flow path for a refrigerant, providing the cooling jacket with a seal retaining portion that retains a seal member for the flow path, and joining the seal retaining portion with the nozzle main body in a socket-and-spigot joint fashion. 
     Effect of Invention 
     According to the present invention, the socket-and-spigot joint between the nozzle main body and the cooling jacket can suppress the vibration, misalignment, and the like of the nozzle main body, thus preventing the leakage of the refrigerant. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of an internal-combustion engine including a cylinder head in which valve seat films are formed using the cold spray apparatus and the nozzle for cold spray according to one or more embodiments of the present invention. 
         FIG. 2  is a cross-sectional view of the periphery of valves of the internal-combustion engine including the cylinder head in which the valve seat films are formed using the cold spray apparatus and the nozzle for cold spray according to one or more embodiments of the present invention. 
         FIG. 3  is a schematic view illustrating the configuration of the cold spray apparatus according to one or more embodiments of the present invention. 
         FIG. 4  is a perspective view illustrating the nozzle for cold spray according to a first embodiment of the present invention. 
         FIG. 5  is a perspective view illustrating a state in which the nozzle for cold spray according to the first embodiment of the present invention is detached from a cold spray gun. 
         FIG. 6  is an exploded perspective view illustrating the configuration of the nozzle for cold spray according to the first embodiment of the present invention. 
         FIG. 7  is a cross-sectional view in which the nozzle for cold spray according to the first embodiment of the present invention is cut along the spraying direction of a raw material powder. 
         FIG. 8  is a cross-sectional view of the nozzle for cold spray along line VIII-VIII of  FIG. 7 . 
         FIG. 9  is an enlarged cross-sectional view illustrating a socket-and-spigot joint portion of the nozzle for cold spray illustrated in  FIG. 7 . 
         FIG. 10  is a process chart illustrating a procedure of manufacturing a cylinder head using the cold spray apparatus and the nozzle for cold spray according to the first embodiment of the present invention. 
         FIG. 11  is a perspective view of a semimanufactured cylinder head in which the valve seat films are formed using the cold spray apparatus and the nozzle for cold spray according to the first embodiment of the present invention. 
         FIG. 12A  is a cross-sectional view illustrating an intake port along line XII-XII of  FIG. 11 . 
         FIG. 12B  is a cross-sectional view illustrating a state in which an annular valve seat portion is formed in the intake port of  FIG. 12A  in a cutting step. 
         FIG. 13  is a perspective view illustrating the configuration of a work rotating apparatus used for moving the semimanufactured cylinder head in a coating step of  FIG. 10 . 
         FIG. 14  is a cross-sectional view illustrating a state of forming a valve seat film in the intake port of  FIG. 12B  using the nozzle for cold spray according to one or more embodiments of the present invention. 
         FIG. 15A  is a cross-sectional view illustrating the intake port in which the valve seat film is formed using the nozzle for cold spray according to one or more embodiments of the present invention. 
         FIG. 15B  is a cross-sectional view illustrating the intake port after a finishing step of  FIG. 10 . 
         FIG. 16  is a perspective view illustrating a nozzle for cold spray according to a second embodiment of the present invention in which the tip portion of a nozzle main body is formed with a tapered portion. 
         FIG. 17  is an enlarged cross-sectional view illustrating a socket-and-spigot joint portion of the nozzle for cold spray according to the second embodiment of the present invention. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. First, an internal-combustion engine  1  will be described, which includes valve seat films formed using the nozzle for cold spray and the cold spray apparatus according to one or more embodiments of the present invention.  FIG. 1  is a cross-sectional view of the internal-combustion engine  1  and mainly illustrates the configuration around the cylinder head. 
     The internal-combustion engine  1  includes a cylinder block  11  and a cylinder head  12  that is mounted on the upper portion of the cylinder block  11 . The internal-combustion engine  1  is, for example, a four-cylinder gasoline engine, and the cylinder block  11  has four cylinders  11   a  arranged in the depth direction of the drawing sheet. The cylinders  11   a  house respective pistons  13  that reciprocate in the vertical direction in the figure. Each piston  13  is connected to a crankshaft  14 , which extends in the depth direction of the drawing sheet, via a connecting rod  13   a.    
     The cylinder head  12  has a mounting surface  12   a  for being mounted to the cylinder block  11 . The mounting surface  12   a  is provided with four recesses  12   b  at positions corresponding to respective cylinders  11   a . The recesses  12   b  define combustion chambers  15  of the cylinders. Each combustion chamber  15  is a space for combusting a mixture gas of fuel and intake air and is defined by a recess  12   b  of the cylinder head  12 , a top surface  13   b  of the piston  13 , and an inner circumferential surface of the cylinder  11   a.    
     The cylinder head  12  includes ports for intake (referred to as intake ports, hereinafter)  16  that connect between the combustion chambers  15  and one side surface  12   c  of the cylinder head  12 . The intake ports  16  have a curved, approximately cylindrical shape and supply intake air from an intake manifold (not illustrated) connected to the side surface  12   c  into respective combustion chambers  15 . 
     The cylinder head  12  further includes ports for exhaust (referred to as exhaust ports, hereinafter)  17  that connect between the combustion chambers  15  and the other side surface  12   d  of the cylinder head  12 . The exhaust ports  17  have a curved, approximately cylindrical shape like the intake ports  16  and exhaust the exhaust gas generated by the combustion of the mixture gas in respective combustion chambers  15  to an exhaust manifold (not illustrated) connected to the side surface  12   d.  In the internal-combustion engine  1  according to one or more embodiments of the present invention, one cylinder  11   a  is provided with two intake ports  16  and two exhaust ports  17 . 
     The cylinder head  12  is provided with intake valves  18  that open and close the intake ports  16  with respect to the combustion chambers  15  and exhaust valves  19  that open and close the exhaust ports  17  with respect to the combustion chambers  15 . Each intake valve  18  includes a round rod-shaped valve stem  18   a  and a disk-shaped valve head  18   b  that is provided at the tip of the valve stem  18   a.  Likewise, each exhaust valve  19  includes a round rod-shaped valve stem  19   a  and a disk-shaped valve head  19   b  that is provided at the tip of the valve stem  19   a.  The valve stems  18   a  and  19   a  are slidably inserted into approximately cylindrical valve guides  18   c  and  19   c,  respectively. This allows the intake valves  18  and the exhaust valves  19  to be movable with respect to the combustion chambers  15  along the axial directions of the valve stems  18   a  and  19   a.    
       FIG. 2  is an enlarged view illustrating a portion in which a combustion chamber  15  communicates with an intake port  16  and an exhaust port  17 . The intake port  16  includes an approximately circular opening portion  16   a  at the portion communicating with the combustion chamber  15 . The opening portion  16   a  has an annular edge portion provided with an annular valve seat film  16   b  that abuts against the valve head  18   b  of an intake valve  18 . When the intake valve  18  moves upward along the axial direction of the valve stem  18   a , the upper surface of the valve head  18   b  comes into contact with the valve seat film  16   b  to close the intake port  16 . When the intake valve  18  moves downward along the axial direction of the valve stem  18   a,  a gap is formed between the upper surface of the valve head  18   b  and the valve seat film  16   b  to open the intake port  16 . 
     Like the intake port  16 , the exhaust port  17  includes an approximately circular opening portion  17   a  at the portion communicating with the combustion chamber  15 , and the opening portion  17   a  has an annular edge portion provided with an annular valve seat film  17   b  that abuts against the valve head  19   b  of an exhaust valve  19 . When the exhaust valve  19  moves upward along the axial direction of the valve stem  19   a,  the upper surface of the valve head  19   b  comes into contact with the valve seat film  17   b  to close the exhaust port  17 . When the exhaust valve  19  moves downward along the axial direction of the valve stem  19   a , a gap is formed between the upper surface of the valve head  19   b  and the valve seat film  17   b  to open the exhaust port  17 . 
     In the four-cycle internal-combustion engine  1 , for example, only the intake valve  18  opens when the corresponding piston  13  moves down, and the mixture gas is introduced from the intake port  16  into the cylinder  11   a.  Subsequently, in a state in which the intake valve  18  and the exhaust valve  19  are closed, the piston  13  moves up to compress the mixture gas in the cylinder  11   a,  and when the piston  13  approximately reaches the top dead center, the mixture gas is ignited to explode by a spark plug, which is not illustrated. This explosion makes the piston  13  move down to the bottom dead center and is converted into the rotational force via the connected crankshaft  14 . When the piston  13  reaches the bottom dead center and starts moving up again, only the exhaust valve  19  is opened to exhaust the exhaust gas in the cylinder  11   a  to the exhaust port  17 . The internal-combustion engine  1  repeats the above cycle to generate the output. 
     The opening portions  16   a  and  17   a  of the cylinder head  12  have respective annular edge portions, and the valve seat films  16   b  and  17   b  are formed directly on the annular edge portions using a cold spray method. The cold spray method refers to a method that includes making a supersonic flow of an operation gas having a temperature lower than the melting point or softening point of a raw material powder, injecting the raw material powder carried by a carrier gas into the operation gas to spray the raw material powder from a nozzle tip, and causing the raw material powder in the solid phase state to collide with a base material to form a metal film by plastic deformation of the raw material powder. Compared with a thermal spray method in which the material is melted and deposited on a base material, the cold spray method has features that a dense film can be obtained without oxidation in the air, thermal alteration is suppressed because of less thermal effect on the material particles, the film formation speed is high, the film can be made thick, and the deposition efficiency is high. In particular, the cold spray method is suitable for use for structural materials such as the valve seat films  16   b  and  17   b  of the internal-combustion engine  1  because the film formation speed is high and the films can be made thick. 
       FIG. 3  illustrates the schematic configuration of a cold spray apparatus  2  according to one or more embodiments of the present invention. The cold spray apparatus  2  is used for the formation of the above valve seat films  16   b  and  17   b.  Conventional cold spray apparatuses are used for repair and the like of metal mechanical components and structural components and are thus often used for film formation on a relatively large area. On the other hand, the cold spray apparatus  2  according to one or more embodiments of the present invention is applied to film formation on a site having a relatively small area, such as the valve seat films  16   b  and  17   b  of the cylinder head  12 , and therefore includes a nozzle for cold spray that is reduced in size than those of the conventional cold spray apparatuses. 
     The cold spray apparatus  2  according to one or more embodiments of the present invention includes a gas supply unit  21  that supplies an operation gas and a carrier gas, a raw material powder supply unit  22  that supplies a raw material powder of the valve seat films  16   b  and  17   b,  and a cold spray gun  23  that sprays the raw material powder as a supersonic flow using the operation gas having a temperature equal to or lower than the melting point of the raw material powder. The gas supply unit  21 , the raw material powder supply unit  22 , and the cold spray gun  23  correspond to the gas supply means, the raw material powder supply means, and the spray means according to the present invention. 
     The gas supply unit  21  includes a compressed gas cylinder  21   a,  an operation gas line  21   b,  and a carrier gas line  21   c.  Each of the operation gas line  21   b  and the carrier gas line  21   c  includes a pressure regulator  21   d,  a flow rate control valve  21   e,  a flow meter  21   f,  and a pressure gauge  21   g.  The pressure regulators  21   d,  the flow rate control valves  21   e,  the flow meters  21   f,  and the pressure gauges  21   g  are used for adjusting the pressure and flow rate of the operation gas and carrier gas from the compressed gas cylinder  21   a.    
     The operation gas line  21   b  is installed with a heater  21   i  heated by a power source  21   h.  The operation gas is heated by the heater  21   i  to a temperature lower than the melting point or softening point of the raw material powder and then introduced into a chamber  23   a  of the cold spray gun  23 . The chamber  23   a  is installed with a pressure gauge  23   b  and a thermometer  23   c,  which are used for feedback control of the pressure and temperature. 
     On the other hand, the raw material powder supply unit  22  includes a raw material powder supply device  22   a,  which is provided with a weighing machine  22   b  and a raw material powder supply line  22   c.  The carrier gas from the compressed gas cylinder  21   a  is introduced into the raw material powder supply device  22   a  through the carrier gas line  21   c . A predetermined amount of the raw material powder weighed by the weighing machine  22   b  is carried into the chamber  23   a  via the raw material powder supply line  22   c.    
     The cold spray gun  23  includes a nozzle for cold spray  25  according to one or more embodiments of the present invention at the tip portion of the cold spray gun  23 . The cold spray gun  23  sprays the raw material powder P, which is carried into the chamber  23   a  by the carrier gas, together with the operation gas as the supersonic flow from the tip of the nozzle for cold spray  25  and causes the raw material powder P in the solid phase state or solid-liquid coexisting state to collide with a base material  24  to form a film  24   a.  In one or more embodiments of the present invention, the cylinder head  12  is applied as the base material  24 , and the raw material powder P is sprayed onto the annular edge portions of the opening portions  16   a  and  17   a  of the cylinder head  12  using the cold spray method to form the valve seat films  16   b  and  17   b.    
     The valve seats of the cylinder head  12  are required to have high heat resistance and wear resistance to withstand the impact input from the valves in the combustion chambers  15  and high heat conductivity for cooling the combustion chambers  15 . In response to these requirements, according to the valve seat films  16   b  and  17   b  formed of the powder of precipitation-hardened copper alloy, for example, the valve seats can be obtained which are excellent in the heat resistance and wear resistance and harder than the cylinder head  12  formed of an aluminum alloy for casting. 
     Moreover, the valve seat films  16   b  and  17   b  are formed directly on the cylinder head  12 , and higher heat conductivity can therefore be obtained as compared with conventional valve seats formed by press-fitting seat rings as separate components into the port opening portions. Furthermore, as compared with the case in which the seat rings as separate components are used, subsidiary effects can be obtained such as that the valve seats can be made close to a water jacket for cooling and the tumble flow can be promoted due to expansion of the throat diameter of the intake ports  16  and exhaust ports  17  and optimization of the port shape. 
     The raw material powder P used for forming the valve seat films  16   b  and  17   b  is preferably a powder of metal that is harder than an aluminum alloy for casting and with which the heat resistance, wear resistance, and heat conductivity required for the valve seats can be obtained. For example, it is preferred to use the above-described precipitation-hardened copper alloy. The precipitation-hardened copper alloy for use may be a Corson alloy that contains nickel and silicon, chromium copper that contains chromium, zirconium copper that contains zirconium, or the like. It is also possible to apply, for example, a precipitation-hardened copper alloy that contains nickel, silicon, and chromium, a precipitation-hardened copper alloy that contains nickel, silicon, and zirconium, a precipitation-hardened copper alloy that contains nickel, silicon, chromium, and zirconium, a precipitation-hardened copper alloy that contains chromium and zirconium, or the like. 
     The valve seat films  16   b  and  17   b  may also be formed by mixing a plurality of types of raw material powders; for example, a first raw material powder and a second raw material powder. In this case, it is preferred to use, as the first raw material powder, a powder of metal that is harder than an aluminum alloy for casting and with which the heat resistance, wear resistance, and heat conductivity required for valve seats can be obtained. For example, it is preferred to use the above-described precipitation-hardened copper alloy. On the other hand, it is preferred to use, as the second raw material powder, a powder of metal that is harder than the first raw material powder. The second raw material powder for application may be an alloy such as an iron-based alloy, a cobalt-based alloy, a chromium-based alloy, a nickel-based alloy, or a molybdenum-based alloy, ceramics, or the like. One type of these metals may be used alone, or two or more types may also be used in combination. 
     With the valve seat films formed of a mixture of the first raw material powder and the second raw material powder which is harder than the first raw material powder, more excellent heat resistance and wear resistance can be obtained than those of valve seat films formed only of a precipitation-hardened copper alloy. The reason that such an effect is obtained appears to be because the second raw material powder allows the oxide film existing on the surface of the cylinder head  12  to be removed so that a new interface is exposed and formed to improve the interfacial adhesion between the cylinder head  12  and the metal films. Additionally or alternatively, it appears that the anchor effect due to the second raw material powder sinking into the cylinder head  12  improves the interfacial adhesion between the cylinder head  12  and the metal films. Additionally or alternatively, it appears that when the first raw material powder collides with the second raw material powder, a part of the kinetic energy is converted into heat energy, or heat is generated in the process in which a part of the first raw material powder is plastically deformed, and such heat promotes the precipitation hardening in a part of the precipitation-hardened copper alloy used as the first raw material powder. 
     FIRST EMBODIMENT 
     The nozzle for cold spray  25  according to a first embodiment of the present invention will then be described. In a conventional cold spray apparatus, when the spray of the raw material powder is continued for several minutes or more, for example, the raw material powder may adhere and deposit in the nozzle for cold spray to block the inside of the nozzle for cold spray. Moreover, in the conventional cold spray apparatus, the deposited material of the raw material powder removed from the inside of the nozzle for cold spray may be sprayed by the operation gas to form a part of the film. The deposited material of the raw material powder has a very porous structure, and the formed film therefore has a non-uniform structure. 
     The reason that the raw material powder adheres inside the nozzle for cold spray is because the raw material powder collides with the inner surface of the nozzle for cold spray at high speed thereby to plastically deform the raw material powder and the nozzle for cold spray, thus breaking the oxide films of the raw material powder and the nozzle for cold spray, and the newly-formed surfaces of the raw material powder and the nozzle for cold spray come into contact with each other to form metal bond. Accordingly, in a small nozzle for cold spray used for forming a film on a site having a relatively small area, such as the above-described valve seat films  16   b  and  17   b,  the ratio of the wall surface to the nozzle internal area is relatively large, and the friction between the nozzle and the raw material powder is relatively remarkable, which increases the nozzle temperature. Such an increased temperature of the nozzle causes its plastic deformation to readily occur due to collision with the raw material powder, and the adhesion and deposition of the raw material powder take place more remarkably. Moreover, the flow rate of the raw material powder rises to a supersonic speed in the nozzle for cold spray, and the adhesion of the raw material powder therefore becomes remarkable at the nozzle tip portion at which the flow rate is the fastest. 
     The nozzle for cold spray  25  of the present embodiment is made smaller than the conventional cold spray apparatus in order to be applied to the film formation on a site having a relatively small area. To prevent the adhesion and deposition of the raw material powder P, the nozzle for cold spray  25  has a function of cooling the nozzle for cold spray  25 . By cooling the nozzle for cold spray  25 , the temperature inside the nozzle for cold spray  25  is lowered as compared with the temperature before cooling; therefore, even when the raw material powder P collides with the nozzle for cold spray  25 , a sufficient amount of plastic deformation for adhesion is not obtained, and the raw material powder P is less likely to adhere. 
       FIG. 4  is a perspective view illustrating a state in which the nozzle for cold spray  25  of the present embodiment is attached to a nozzle attaching portion  231  of the cold spray gun  23 . The nozzle attaching portion  231  has a cylindrical shape and holds the nozzle for cold spray  25  on the tip side of the nozzle attaching portion  231 . The nozzle attaching portion  231  corresponds to the main body portion of the cold spray apparatus in the present invention. A nozzle fixing ring  232  is attached on the tip side of the nozzle attaching portion  231  to fix the nozzle for cold spray  25  to the nozzle attaching portion  231 . The nozzle attaching portion  231  connects the nozzle for cold spray  25  and the chamber  23   a  of the cold spray gun  23 . Thus, the cold spray gun  23  supplies the raw material powder P and the operation gas in the chamber  23   a  to the nozzle for cold spray  25  through the nozzle attaching portion  231  and sprays the raw material powder P and the operation gas from a spray port  25   a  provided at the tip of the nozzle for cold spray  25 . 
     The nozzle for cold spray  25  includes a spray portion  25   b  and a base portion  25   c . The spray portion  25   b  has the spray port  25   a  for the raw material powder P at the tip of the spray portion  25   b.  The base portion  25   c  is attached to the nozzle attaching portion  231 . The spray portion  25   b  has a cylindrical shape and projects from the tip side of the nozzle attaching portion  231 . A spray passage  25   d  is provided in the spray portion  25   b  to accelerate the raw material powder P, which is supplied from the chamber  23   a,  together with the operation gas to a supersonic flow. The spray port  25   a  is provided at the end of the spray passage  25   d.  To spray the raw material powder P to a site having a relatively small area, such as the valve seat films  16   b  and  17   b,  the spray portion  25   b  is made to have a smaller diameter than that of the conventional nozzle for cold spray. The base portion  25   c  is in a cylindrical shape having a larger diameter than that of the spray portion  25   b  and is attached to the nozzle attaching portion  231 . The nozzle fixing ring  232  fixes the base portion  25   c  so that the nozzle for cold spray  25  does not drop off from the nozzle attaching portion  231 . 
     The nozzle for cold spray  25  includes a flow path  25   e  (see  FIG. 7 ) through which a refrigerant (for example, water) R flows. The nozzle for cold spray  25  includes a refrigerant introduction part  251  at the upper portion of the spray portion  25   b  on the tip side. The refrigerant introduction part  251  introduces the refrigerant R into the flow path  25   e . Furthermore, the lower portion of the nozzle attaching portion  231  is provided with a refrigerant discharge part  233  that discharges the refrigerant R in the flow path  25   e.  The nozzle for cold spray  25  cools the spray passage  25   d  of the nozzle for cold spray  25  through introducing the refrigerant R from the refrigerant introduction part  251  into the flow path  25   e , allowing the refrigerant R to flow in the flow path  25   e,  and discharging the refrigerant R from the flow path  25   e  via the refrigerant discharge part  233 . 
       FIG. 5  is a perspective view illustrating a state in which the nozzle for cold spray  25  is detached from the nozzle attaching portion  231  of the cold spray gun  23 . A recessed nozzle accommodating portion  231   a  is provided on the tip side of the nozzle attaching portion  231 . The base portion  25   c  of the nozzle for cold spray  25  is inserted into the nozzle accommodating portion  231   a.  The outer peripheral surface of the nozzle attaching portion  231  on its tip side is provided with a threaded portion  231   b  to which the nozzle fixing ring  232  is attached. 
     The nozzle attaching portion  231  includes a cylindrical nozzle connecting portion  231   d  at a bottom surface portion  231   c  of the nozzle accommodating portion  231   a  on the rear end side. The nozzle connecting portion  231   d  is connected to the nozzle for cold spray  25 . 
     The central portion of the nozzle connecting portion  231   d  is provided with a chamber connecting path  231   e  that connects the chamber  23   a  of the cold spray gun  23  and the nozzle for cold spray  25 . 
     A discharge path  231   f  is provided below the nozzle connecting portion  231   d  to connect the flow path  25   e  of the nozzle for cold spray  25  and the refrigerant discharge part  233 . An O-ring  231   g  is incorporated in the outer periphery of the discharge path  231   f  to seal the connection portion between the flow path  25   e  of the nozzle for cold spray  25  and the discharge path  231   f.    
     The nozzle fixing ring  232  has a cylindrical shape and includes a nut portion  232   a  on the inner surface. The nut portion  232   a  is screwed with the threaded portion  231   b  of the nozzle attaching portion  231 . A nozzle pressing portion  232   b  is provided on the tip side of the nozzle fixing ring  232 . The nozzle pressing portion  232   b  is provided with a hole into which the spray portion  25   b  of the nozzle for cold spray  25  is inserted. When the nozzle fixing ring  232  is attached to the nozzle attaching portion  231 , the nozzle pressing portion  232   b  presses the base portion  25   c  of the nozzle for cold spray  25 , and the rear end portion of the nozzle for cold spray  25  is pressed against the bottom surface portion  231   c  of the nozzle accommodating portion  231   a.  This allows the spray passage  25   d  and the chamber connecting path  231   e  to be connected without a gap and also allows the flow path  25   e  and the discharge path  231   f  to be connected without a gap. 
     The refrigerant introduction part  251 , which introduces the refrigerant R into the flow path  25   e  of the nozzle for cold spray  25 , includes an introduction pipe connecting portion  251   a  provided on the spray portion  25   b  of the nozzle for cold spray  25 , an introduction pipe  251   b  connected to the introduction pipe connecting portion  251   a,  and a fixing nut  251   c  that fixes the introduction pipe  251   b  to the introduction pipe connecting portion  251   a.  The introduction pipe connecting portion  251   a  includes a cylindrical pipe insertion part  251   d  inserted into the introduction pipe  251   b,  which is made of a steel pipe, a hose, or the like, and a fixing screw  251   e  provided below the pipe insertion part  251   d.  The inner diameter portion of the pipe insertion part  251   d  penetrates into the nozzle for cold spray  25  and is connected to the flow path  25   e.  The fixing nut  251   c  is screwed with the fixing screw  251   e  of the introduction pipe connecting portion  251   a,  and the outer periphery of the introduction pipe  251   b,  into which the pipe insertion part  251   d  is inserted, is pressed and fixed by a pipe insertion hole  251   f.  The introduction pipe  251   b  is connected to a refrigerant circulation circuit  27  (see  FIG. 3 ) that circulates the refrigerant R between the refrigerant introduction part  251  and the refrigerant discharge part  233 , and the refrigerant R is introduced into the introduction pipe  251   b  from the refrigerant circulation circuit  27 . 
     The refrigerant discharge part  233 , which discharges the refrigerant R from the flow path  25   e  of the nozzle for cold spray  25 , includes a discharge pipe connecting portion  233   a  provided on the nozzle attaching portion  231 , a discharge pipe  233   b  connected to the discharge pipe connecting portion  233   a,  and a fixing nut  233   c  that fixes the discharge pipe  233   b  to the discharge pipe connecting portion  233   a.  The discharge pipe connecting portion  233   a  includes a cylindrical pipe insertion part  233   d  inserted into the discharge pipe  233   b , which is made of a steel pipe, a hose, or the like, and a fixing screw  233   e  provided above the pipe insertion part  233   d.  The inner diameter portion of the pipe insertion part  233   d  is connected to the discharge path  231   f  arranged in the bottom surface portion  231   c  of the nozzle attaching portion  231 . The fixing nut  233   c  is screwed with the fixing screw  233   e  of the discharge pipe connecting portion  233   a,  and the outer periphery of the discharge pipe  233   b,  into which the pipe insertion part  233   d  is inserted, is pressed and fixed by a pipe insertion hole  233   f.  The discharge pipe  233   b  is connected to the refrigerant circulation circuit  27 , and the refrigerant R is discharged from the discharge pipe  233   b  to the refrigerant circulation circuit  27 . 
       FIG. 6  is an exploded perspective view illustrating the configuration of the nozzle for cold spray  25 . The nozzle for cold spray  25  includes a nozzle main body  252  having the spray port  25   a  and the spray passage  25   d  and a cooling jacket  253  having the spray portion  25   b  and the base portion  25   c.  The nozzle main body  252  is inserted into the cooling jacket  253  from the rear end side of the cooling jacket  253 , and the tip portion having the spray port  25   a  protrudes from the tip of the cooling jacket  253 . 
     The nozzle main body  252  has an elongated cylindrical shape and includes the spray passage  25   d  inside. The nozzle main body  252  includes a connecting portion  252   a  at the rear end portion on the opposite side to the spray port  25   a.  The connecting portion  252   a  has a diameter larger than that of the other portions. When the nozzle main body  252  is inserted into the cooling jacket  253 , the connecting portion  252   a  defines the position of the nozzle main body  252  in the cooling jacket  253 . When the nozzle for cold spray  25  is attached to the nozzle attaching portion  231 , the nozzle main body  252  is supported so that the connecting portion  252   a  is interposed between the cooling jacket  253  and the nozzle attaching portion  231 . The connecting portion  252   a  of the nozzle main body  252  comes into contact with the nozzle connecting portion  231   d  thereby to connect the spray passage  25   d  and the chamber connecting path  231   e.  The nozzle main body  252  is made of a material having heat conductivity; for example, a metal such as stainless steel. This allows the inner spray passage  25   d  to be cooled by cooling the outer peripheral surface of the nozzle main body  252  with the refrigerant R. 
     The cooling jacket  253  includes the introduction pipe connecting portion  251   a  at the upper portion of the spray portion  25   b  on the tip side. The cooling jacket  253  also includes an inner diameter portion  253   a  into which the nozzle main body  252  can be inserted. The cooling jacket  253  surrounds the nozzle main body  252 , which is inserted from the rear end side, to form the flow path  25   e  for the refrigerant R between the cooling jacket  253  and the outer peripheral surface of the nozzle main body  252 . 
       FIG. 7  is a cross-sectional view in which the nozzle for cold spray  25  attached to the nozzle attaching portion  231  of the cold spray gun  23  is cut along the spraying direction of the raw material powder P. The spray passage  25   d  of the nozzle main body  252  is provided with a convergent portion  252   b,  a throat portion  252   c,  and a divergent portion  252   d  in this order from the rear end side. The convergent portion  252   b  is a conical passage whose cross-sectional area is gradually reduced toward the tip. The divergent portion  252   d  is a conical passage whose cross-sectional area is gradually increased toward the tip. The throat portion  252   c  is a connecting portion between the convergent portion  252   b  and the divergent portion  252   d  and has the smallest cross-sectional area in the nozzle main body  252 . The nozzle main body  252  sprays the raw material powder P as a supersonic flow from the spray port  25   a  through compressing the operation gas, which is supplied together with the raw material powder P from the chamber  23   a,  in the convergent portion  252   b  and releasing the pressure of the operation gas in the divergent portion  252   d.    
     The inner diameter portion  253   a  of the cooling jacket  253  has an inner diameter larger than the outer diameter of the nozzle main body  252 . The cooling jacket  253  therefore surrounds the nozzle main body  252 , which is inserted from the rear end side, to form a gap between the inner diameter portion  253   a  and the nozzle main body  252 . The gap serves as the flow path  25   e  for the refrigerant R. The flow path  25   e  is provided so as to extend from the tip side to the rear end side of the nozzle main body  252 . As illustrated in the cross-sectional view of  FIG. 8  along the line VIII-VIII of  FIG. 7 , the flow path  25   e  is provided so as to surround the entire circumference of the nozzle main body  252 . 
     As illustrated in  FIG. 9  in an enlarged manner, a seal retaining portion  253   c  is provided on the tip side of the inner diameter portion  253   a  of the cooling jacket  253 . The seal retaining portion  253   c  retains an O-ring  253   b.  The O-ring  253   b,  which corresponds to the seal member of the present invention, is in close contact with the outer peripheral surface of the nozzle main body  252  to seal the flow path  25   e.  The seal retaining portion  253   c  includes a front wall  253   d  and a rear wall  253   e  that are annularly projected from the inner surface of the inner diameter portion  253   a  of the cooling jacket  253  toward the central axis of the cooling jacket  253 . The O-ring  253   b  is retained in an annular groove provided between the front wall  253   d  and the rear wall  253   e.    
     The nozzle main body  252  receives force that acts in the spraying direction of the raw material powder P due to the frictional force between the spray passage  25   d  and the operation gas which sprays the raw material powder P. The nozzle main body  252  therefore vibrates along the arrow V direction in  FIG. 9 . The cold spray gun  23  moves and stops moving in order to direct the nozzle for cold spray  25  to the film formation position. At that time, the tip portion of the nozzle main body  252  is misaligned in the I direction approximately orthogonal to the central axis of the nozzle main body  252  due to the inertial force caused when the cold spray gun  23  moves and stops moving. 
     To suppress the vibration in the V direction and the misalignment in the I direction which occur at the tip portion of the nozzle main body  252  during the film formation, the front wall  253   d  and rear wall  253   e  of the seal retaining portion  253   c  are joined with the outer peripheral surface of the nozzle main body  252  in a socket-and-spigot joint fashion. As used herein, the socket-and-spigot joint refers to a joint in which two members, such as represented by a recessed portion and a projected portion, are fitted without a gap thereby to ensure their relative positions so that no play occurs after the fitting. 
     Here, with regard to the dimensions and tolerances of the nozzle main body  252  and the seal retaining portion  253   c,  the outer diameter D 1  of the nozzle main body  252  is, for example, φ11.2 mm, and the outer diameter tolerance is the minimum +0.02 to +0.04 mm. Additionally or alternatively, the inner diameter D 2  of the front wall  253   d  and rear wall  253   e  of the seal retaining portion  253   c,  which is joined with the nozzle main body  252  in the socket-and-spigot joint fashion, is, for example, φ11.3 mm, and the inner diameter tolerance is, for example, −0.01 to −0.03 mm. 
     The socket-and-spigot joint with such dimensions and tolerances allows the gap generated between the nozzle main body  252  and the seal retaining portion  253   c  to be very small, such as 0.015 to 0.035 mm. The nozzle main body  252  and the seal retaining portion  253   c  can therefore be joined with no play after the fitting while ensuring their relative positions. 
     Moreover, the nozzle main body  252  and the seal retaining portion  253   c  are joined in the socket-and-spigot joint fashion; therefore, when the nozzle main body  252  is blocked and needs to be replaced, or when the O-ring  253   b  of the seal retaining portion  253   c  deteriorates and needs to be replaced, for example, the nozzle for cold spray  25  can be disassembled to detach the nozzle main body  252  from the cooling jacket  253 . The above-described dimensions and tolerances of the nozzle main body  252  and the seal retaining portion  253   c  are merely examples, and it is preferred to appropriately set the tolerances for the socket-and-spigot joint in accordance with the dimensions of the nozzle main body  252  and the seal retaining portion  253   c.    
     If it is not necessary to disassemble the nozzle for cold spray  25 , or if the disassembly frequency is low, the nozzle main body and the cooling jacket may be joined using interference fit instead of the socket-and-spigot joint. As used herein, the interference fit refers to a joint in which two members, such as represented by a recessed portion and a projected portion, are designed with a slightly larger size of the projected portion than the size of the recessed portion and the projected portion is pressed into and fitted with the recessed part thereby to ensure their relative positions so that no play occurs after the fitting. When the interference fit is applied to the nozzle for cold spray  25 , the outer diameter D 1  of the nozzle main body  252  is made slightly larger than the inner diameter D 2  of the front wall  253   d  and rear wall  253   e  of the seal retaining portion  253   c,  and the nozzle main body  252  is pressed into and fitted with the seal retaining portion  253   c.  Thus, also when using the interference fit, the nozzle main body  252  and the seal retaining portion  253   c  can be joined with no play after the fitting while ensuring their relative positions. 
     As illustrated in  FIG. 7 , the cooling jacket  253  also includes a seal retaining portion  253   g  that retains an O-ring  253   f  on the rear end side of the inner diameter portion  253   a.  However, the rear end side of the nozzle main body  252  is supported so that the connecting portion  252   a  is interposed between the cooling jacket  253  and the nozzle attaching portion  231 , and the vibration and misalignment occurring on the rear end side are very small as compared with those occurring on the tip side of the nozzle main body  252 . For this reason, the seal retaining portion  253   g  of the cooling jacket  253  on the rear end side is not joined with the nozzle main body  252  in a socket-and-spigot joint fashion. The base portion  25   c  of the cooling jacket  253  is provided with a discharge connection path  253   h  that connects the flow path  25   e  to the discharge path  231   f  of the nozzle attaching portion  231 . 
     The refrigerant circulation circuit  27  which circulates the refrigerant R into the flow path  25   e  of the nozzle for cold spray  25  will then be described with reference to  FIG. 3 . The refrigerant circulation circuit  27  includes the above described introduction pipe  251   b  and discharge pipe  233   b,  a tank  271  that stores the refrigerant R, a pump  272  that is connected to the introduction pipe  251   b  and flows the refrigerant R between the tank  271  and the nozzle for cold spray  25 , and a cooler  273  that cools the refrigerant R. The cooler  273 , which is composed of a heat exchanger or the like, for example, cools the refrigerant R having a raised temperature after cooling the nozzle main body  252  by exchanging heat between the refrigerant R and a cooling medium such as air, water, or gas. 
     The refrigerant circulation circuit  27  sucks the refrigerant R in the tank  271  using the pump  272  and supplies the refrigerant R to the refrigerant introduction part  251  via the cooler  273 . The refrigerant R supplied to the refrigerant introduction part  251  flows through the flow path  25   e  in the nozzle for cold spray  25  from the tip side to the rear end side, and during that time, exchanges heat with the nozzle main body  252  to cool it. The refrigerant R having flowed to the rear end side of the flow path  25   e  is discharged into the discharge pipe  233   b  via the refrigerant discharge part  233  and returns to the tank  271 . Thus, the refrigerant circulation circuit  27  cools the nozzle main body  252  by circulating the refrigerant R while cooling it, and it is therefore possible to suppress the adhesion of the raw material powder P to the spray passage  25   d  of the nozzle main body  252 . 
     A method for manufacturing the cylinder head  12  including the valve seat films  16   b  and  17   b  will then be described.  FIG. 10  is a process chart illustrating the processing steps for the valve sites in the method for manufacturing the cylinder head  12  of the present embodiment. As illustrated in this figure, the method for manufacturing the cylinder head  12  of the present embodiment includes a casting step (step SD, a cutting step (step S 2 ), a coating step (step S 3 ), and a finishing step (step S 4 ). Processing steps other than those for the valve sites will be omitted for simplicity of the description. 
     In the casting step S 1 , an aluminum alloy for casting is poured into a mold in which sand cores are set, and a semimanufactured cylinder head having intake ports  16  and exhaust ports  17  formed in the main body is cast-molded. The intake ports  16  and the exhaust ports  17  are formed by the sand cores, and the recesses  12   b  are formed by the mold. 
       FIG. 11  is a perspective view of a semimanufactured cylinder head  3  having been cast-molded in the casting step S 1  as seen from above the mounting surface  12   a  which is to be mounted to the cylinder block  11 . The semimanufactured cylinder head  3  includes four recesses  12   b,  two intake ports  16  and two exhaust ports  17  provided in each recess  12   b,  etc. The two intake ports  16  and two exhaust ports  17  of each recess  12   b  are merged into respective ones in the semimanufactured cylinder head  3 , which communicate with openings provided on both side surfaces of the semimanufactured cylinder head  3 . 
       FIG. 12A  is a cross-sectional view of the semimanufactured cylinder head  3  taken along line XII-XII of  FIG. 11  and illustrates an intake port  16 . The intake port  16  is provided with a circular opening portion  16   a  that is exposed in the recess  12   b  of the semimanufactured cylinder head  3 . 
     In the subsequent cutting step S 2 , milling work is performed on the semimanufactured cylinder head  3  as illustrated in  FIG. 12B , such as using an end mill or a ball end mill, to form an annular valve seat portion  16   c  around the opening portion  16   a  of the intake port  16 . The annular valve seat portion  16   c  is an annular groove that serves as the base shape of a valve seat film  16   b,  and is formed on the outer circumference of the opening portion  16   a.  In the method for manufacturing the cylinder head  12  of the present embodiment, the raw material powder P is sprayed onto the annular valve seat portion  16   c  using the cold spray method to form a film, and the valve seat film  16   b  is formed based on the film. The annular valve seat portion  16   c  is therefore formed with a size slightly larger than the valve seat film  16   b.    
     In the coating step S 3 , the raw material powder P is sprayed onto the annular valve seat portion  16   c  of the semimanufactured cylinder head  3  using the cold spray apparatus  2  of the present embodiment to form the valve seat film  16   b.  More specifically, in the coating step S 3 , the semimanufactured cylinder head  3  and the nozzle for cold spray  25  are relatively moved at a constant speed so that the raw material powder P is sprayed onto the entire circumference of the annular valve seat portion  16   c  while keeping constant the posture of the annular valve seat portion  16   c  and the nozzle for cold spray  25  of the cold spray gun  23  and the distance between the annular valve seat portion  16   c  and the nozzle for cold spray  25 . 
     In this embodiment, for example, the semimanufactured cylinder head  3  is moved with respect to the nozzle for cold spray  25  of the cold spray gun  23 , which is fixedly arranged, using a work rotating apparatus  4  illustrated in  FIG. 13 . The work rotating apparatus  4  includes a work table  41 , a tilt stage unit  42 , an XY stage unit  43 , and a rotation stage unit  44 . The work table  41  holds the semimanufactured cylinder head  3 . 
     The tilt stage unit  42  is a stage that supports the work table  41  and rotates the work table  41  around an A-axis arranged in the horizontal direction to tilt the semimanufactured cylinder head  3 . The XY stage unit  43  includes a Y-axis stage  43   a  that supports the tilt stage unit  42  and an X-axis stage  43   b  that supports the Y-axis stage  43   a.  The Y-axis stage  43   a  moves the tilt stage unit  42  along the Y-axis arranged in the horizontal direction. The X-axis stage  43   b  moves the Y-axis stage  43   a  along the X-axis orthogonal to the Y-axis on the horizontal plane. This allows the XY stage unit  43  to move the semimanufactured cylinder head  3  to an arbitrary position along the X-axis and the Y-axis. The rotation stage unit  44  has a rotation table  44   a  that supports the XY stage unit  43  on the upper surface, and rotates the rotation table  44   a  thereby to rotate the semimanufactured cylinder head  3  around the Z-axis in an approximately vertical direction. 
     The tip of the nozzle for cold spray  25  of the cold spray gun  23  is fixedly arranged above the tilt stage unit  42  and in the vicinity of the Z-axis of the rotation stage unit  44 . The work rotating apparatus  4  uses the tilt stage unit  42  to tilt the work table  41  so that, as illustrated in  FIG. 14 , the central axis C of the intake port  16  to be formed with the valve seat film  16   b  becomes vertical. The work rotating apparatus  4  also uses the XY stage unit  43  to move the semimanufactured cylinder head  3  so that the central axis C of the intake port  16  to be formed with the valve seat film  16   b  coincides with the Z-axis of the rotation stage unit  44 . In this state, the rotation stage unit  44  rotates the semimanufactured cylinder head  3  around the Z-axis while the nozzle for cold spray  25  sprays the raw material powder P onto the annular valve seat portion  16   c,  thereby forming a film on the entire circumference of the annular valve seat portion  16   c.    
     While the coating step S 3  is being carried out, the nozzle for cold spray  25  introduces the refrigerant R supplied from the refrigerant supply unit into the flow path  25   e  via the refrigerant introduction part  251 . The refrigerant R cools the nozzle main body  252  while flowing from the tip side toward the rear end side of the flow path  25   e.  The refrigerant R having flowed to the rear end side of the flow path  25   e  is discharged from the flow path  25   e  via the refrigerant discharge part  233  and recovered by the refrigerant recovery unit. 
     The nozzle main body  252  vibrates along the spraying direction of the raw material powder P, that is, along the arrow V direction of  FIG. 9  due to the friction between the spray passage  25   d  and the operation gas which sprays the raw material powder P. Additionally or alternatively, the tip portion of the nozzle main body  252  is misaligned in the direction approximately orthogonal to the central axis of the nozzle main body  252 , that is, in the I direction of  FIG. 9  due to the inertial force caused when the nozzle for cold spray  25  moves and stops moving. The vibration in the V direction and the misalignment in the I direction of the nozzle main body  252  is suppressed by the socket-and-spigot joint between the outer peripheral surface of the nozzle main body  252  and the seal retaining portion  253   c  of the cooling jacket  253 . 
     The work rotating apparatus  4  temporarily stops the rotation of the rotation stage unit  44  when the semimanufactured cylinder head  3  makes one rotation around the Z-axis to complete the formation of the valve seat film  16   b.  While the rotation is stopped, the XY stage unit  43  moves the semimanufactured cylinder head  3  so that the central axis C of the intake port  16  to be subsequently formed with the valve seat film  16   b  coincides with the Z-axis of the rotation stage unit  44 . After the XY stage unit  43  completes the movement of the semimanufactured cylinder head  3 , the work rotating apparatus  4  restarts the rotation of the rotation stage unit  44  to form the valve seat film  16   b  for the next intake port  16 . This operation is then repeated thereby to form the valve seat films  16   b  and  17   b  for all the intake ports  16  and the exhaust ports  17  of the semimanufactured cylinder head  3 . When the valve seat film formation target is switched between an intake port  16  and an exhaust port  17 , the tilt stage unit  42  changes the tilt of the semimanufactured cylinder head  3 . 
     In the finishing step S 4 , finishing work is performed on the valve seat films  16   b  and  17   b,  the intake ports  16 , and the exhaust ports  17 . In the finishing work performed on the valve seat films  16   b  and  17   b,  the surfaces of the valve seat films  16   b  and  17   b  are cut by milling work using a ball end mill to adjust the valve seat films  16   b  into a predetermined shape. 
     In the finishing work performed on the intake ports  16 , a ball end mill is inserted from the opening portion  16   a  into each intake port  16  to cut the inner surface of the intake port  16  on the opening port  16   a  side along a working line PL illustrated in  FIG. 15A . The working line PL defines a range in which the raw material powder P scatters and adheres in the intake port  16  to form a relatively thick excessive film SF. More specifically, the working line PL refers to a range in which the excessive film SF is formed thick to such an extent that affects the intake performance of the intake port  16 . 
     Thus, according to the finishing step S 4 , the surface roughness of the intake port  16  due to the cast molding is eliminated, and the excessive film SF formed in the coating step S 3  can be removed.  FIG. 15B  illustrates the intake port  16  after the finishing step S 4 . 
     Like the intake ports  16 , each exhaust port  17  is formed with the valve seat film  17   b  through the formation of a small-diameter portion in the exhaust port  17  by the cast molding, the formation of an annular valve seat portion by the cutting work, the cold spraying onto the annular valve seat portion, and the finishing work. Detailed description will therefore be omitted for the procedure of forming the valve seat films  17   b  on the exhaust ports  17 . 
     As described above, according to the cold spray apparatus  2  and the nozzle for cold spray  25  of the present embodiment, the outer peripheral surface of the nozzle main body  252  and the seal retaining portion  253   c  of the cooling jacket  253  are joined in a socket-and-spigot joint fashion so as not to form a gap, and it is therefore possible to suppress the vibration in the spraying direction of the raw material powder P (V direction of  FIG. 9 ) and the misalignment in the direction approximately orthogonal to the central axis of the nozzle main body  252  (I direction of  FIG. 9 ) which occur in the nozzle main body  252 . Moreover, in the cold spray apparatus  2  and the nozzle for cold spray  25  of the present embodiment, even if the vibration in the V direction and/or the misalignment in the I direction occur in the nozzle main body  252 , the socket-and-spigot joint between the outer peripheral surface of the nozzle main body  252  and the seal retaining portion  253   c  does not cause a gap at the seal retaining portion  253   c,  and it is therefore possible to prevent the refrigerant R from leaking from the flow path  25   e  of the nozzle for cold spray  25 . 
     The flow rate of the raw material powder P and the operation gas becomes high on the tip side of the nozzle main body  252 , and the friction between the spray passage  25   d  and the raw material powder P and operation gas becomes large; therefore, the temperature on the tip side of the nozzle main body  252  is higher than that on the rear end side. Accordingly, the raw material powder P is more likely to adhere to the nozzle main body  252  on the tip side than on the rear end side. However, fortunately, the cold spray apparatus  2  and the nozzle for cold spray  25  of the present embodiment introduce the refrigerant R from the tip side of the nozzle main body  252  into the flow path  25   e  via the refrigerant introduction part  251  provided on the tip side of the nozzle for cold spray  25 , and the tip side of the nozzle main body  252  can therefore be effectively cooled using the refrigerant R which does not undergo the temperature rise due to the heat exchange with the nozzle main body  252 . It is thus possible to suppress the adhesion and deposition of the raw material powder P to the spray passage  25   d  of the nozzle main body  252 . 
     Furthermore, in the cold spray apparatus  2  and the nozzle for cold spray  25  of the present embodiment, the cooling jacket  253  is attached to the nozzle attaching portion  231  which is the main body portion of the cold spray apparatus  2 , and the nozzle main body  252  is supported so that the connecting portion  252   a  on the rear end side is interposed between the cooling jacket  253  and the nozzle attaching portion  231 . That is, the cooling jacket  253  is not attached to the nozzle main body  252 . Thus, the cooling jacket  253  is not affected by the vibration and misalignment of the nozzle main body  252 . The nozzle for cold spray  25  of the present embodiment can therefore effectively suppress the vibration and misalignment of the nozzle main body  252  owing to the cooling jacket  253 . 
     Moreover, in the cold spray apparatus  2  and the nozzle for cold spray  25  of the present embodiment, the flow path  25   e  for the refrigerant R is provided so as to extend from the tip side to the rear end side of the nozzle main body  252  and surround the entire circumference of the nozzle main body  252 , and the nozzle main body  252  as a whole can therefore be cooled from the outside. It is thus possible to suppress the adhesion and deposition of the raw material powder P to the spray passage  25   d  of the nozzle main body  252 . 
     SECOND EMBODIMENT 
     The nozzle for cold spray according to a second embodiment of the present invention will then be described. This embodiment is different from the first embodiment in a form of the socket-and-spigot joint portion between the nozzle main body and the seal retaining portion of the cooling jacket, but other configurations are the same as those in the first embodiment, so the detailed description of the same configurations as those in the first embodiment will be omitted with the use of the same reference numerals. 
       FIG. 16  is an exploded perspective view illustrating the configuration of a nozzle for cold spray  26  according to the present embodiment. The nozzle for cold spray  26  includes a nozzle main body  261  and a cooling jacket  262 . The outer peripheral surface of the nozzle main body  261  on the tip side is formed with a tapered portion  261   a  that gradually tapers in the spraying direction of the raw material powder P. That is, the diameter of the tapered portion  261   a  gradually decreases in the spraying direction of the raw material powder P. The tapered portion  261   a  corresponds to the portion of the nozzle main body to be joined with the seal retaining portion in the present invention. 
       FIG. 17  illustrates the tip portion of the nozzle for cold spray  26  in the cross-sectional view in which the nozzle for cold spray  26  is cut in the spraying direction of the raw material powder P. A seal retaining portion  262   c  is provided on the tip side of an inner diameter portion  262   a  of the cooling jacket  262 . The seal retaining portion  262   c  retains an O-ring  262   b.  The O-ring  262   b,  which corresponds to the seal member of the present invention, is in close contact with the tapered portion  261   a  of the nozzle main body  261  to seal the flow path  25   e.  The seal retaining portion  262   c  includes a front wall  262   d  and a rear wall  262   e  that are annularly projected from the inner surface of the inner diameter portion  262   a  of the cooling jacket  262  toward the central axis of the cooling jacket  262 . 
     The O-ring  262   b  is retained in an annular groove provided between the front wall  262   d  and the rear wall  262   e.  The front wall  262   d  and rear wall  262   e  of the seal retaining portion  262   c  correspond to the joint part of the seal retaining portion of the present invention. 
     To suppress the vibration in the V direction and the misalignment in the I direction which occur at the tip portion of the nozzle main body  261  during the film formation, the front wall  262   d  and rear wall  262   e  of the seal retaining portion  262   c  are joined with the tapered portion  261   a  of the nozzle main body  261  in a socket-and-spigot joint fashion. That is, the front wall  262   d  and rear wall  262   e  of the seal retaining portion  262   c  have tapered shapes along the tapered portion  261   a  of the nozzle main body  261 , and the seal retaining portion  262   c  of the cooling jacket  262  and the tapered portion  261   a  of the nozzle main body  261  are therefore fitted without a gap thereby to ensure their relative positions so that no play occurs after the fitting. 
     Here, the dimensions and tolerances of the nozzle main body  261  and the seal retaining portion  262   c  will be described. In the nozzle main body  261 , the length L 1  of the tapered portion  261   a  may be 10 mm, the outer diameter D 1   a  of the large-diameter part of the tapered portion  261   a  may be φ11.2 mm, and the outer diameter D 1   b  of the small-diameter part of the tapered portion  261   a  may be φ10.2 mm. The outer diameter tolerance of the outer diameters D 1   a  and D 1   b  may be +0.02 to +0.04 mm. Additionally or alternatively, in the seal retaining portion  262   c  which is joined with the nozzle main body  261  in a socket-and-spigot joint fashion, the length L 2  may be 5 mm, the inner diameter D 2   a  of the large-diameter part may be φ11.2 mm, and the inner diameter D 2   b  of the small-diameter part may be φ10.7 mm. The inner diameter tolerance of the inner diameter D 2   a  may be −0.01 to −0.03 mm, and the inner diameter tolerance of the inner diameter D 2   b  may be +0.02 to +0.04 mm. 
     The socket-and-spigot joint with such dimensions and tolerances allows the gap generated between the nozzle main body  261  and the seal retaining portion  262   c  to be very small, such as several dozen μm. The nozzle main body  261  and the seal retaining portion  262   c  can therefore be joined with no play after the fitting while ensuring their relative positions. 
     As described above, according to the cold spray apparatus  2  and the nozzle for cold spray  26  of the present embodiment, the nozzle main body  261  is formed with the tapered portion  261   a  which gradually tapers in the spraying direction of the raw material powder P, and the seal retaining portion  262   c  of the cooling jacket  262  has a tapered shape along the tapered portion  261   a  of the nozzle main body  261 ; therefore, when vibration in the spraying direction of the raw material powder P (V direction of  FIG. 17 ) occurs in the nozzle main body  261 , the socket-and-spigot joint between the tapered portion  261   a  and the seal retaining portion  262   c  is more tightened. Thus, the nozzle for cold spray  26  of the present embodiment can prevent the refrigerant R from leaking from the flow path  25   e.    
     Moreover, according to the cold spray apparatus  2  and the nozzle for cold spray  26 , the tapered portion  261   a  of the nozzle main body  261  and the seal retaining portion  262   c  of the cooling jacket  262  are joined in a socket-and-spigot joint fashion so as not to form a gap, and it is therefore possible to suppress the vibration in the V direction and the misalignment in the direction approximately orthogonal to the central axis of the nozzle main body  261  (I direction of  FIG. 17 ) which occur in the nozzle main body  261 . Moreover, in the cold spray apparatus  2  and the nozzle for cold spray  26  of the present embodiment, even if the vibration in the V direction and/or the misalignment in the I direction occur in the nozzle main body  261 , the socket-and-spigot joint between the outer peripheral surface of the nozzle main body  261  and the seal retaining portion  262   c  does not cause a gap at the seal retaining portion  262   c , and it is therefore possible to prevent the refrigerant R from leaking from the flow path  25   e  of the nozzle for cold spray  26 . 
     In the above first embodiment, the nozzle main body  252  and the seal retaining portion  253   g  of the cooling jacket  253  on the rear end side are not joined in a socket-and-spigot joint fashion, but if there is a concern that the refrigerant R may leak from this portion, the nozzle main body  252  and the seal retaining portion  253   g  may be joined in a socket-and-spigot joint fashion. The first embodiment has been described for an example of the small nozzle for cold spray  25  suitable for the film formation on a site having a relatively small area, such as the valve seat films  16   b  and  17   b  of the cylinder head  12 , but the present invention can also be applied to a nozzle for cold spray that is used for repair and the like of metal mechanical components and structural components and thus used for the film formation on a relatively large area. Furthermore, water has been described as an example of the refrigerant R, but a liquid other than water or a gaseous matter such as a gas may also be used as the refrigerant. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1  Internal-combustion engine
         12  Cylinder head     16  Intake port
             16   a  Opening portion     16   b  Valve seat film     16   c  Annular valve seat portion   
             17  Exhaust port
             17   a  Opening portion     17   b  Valve seat film   
             18  Intake valve     19  Exhaust valve   
     
           2  Cold spray apparatus
         21  Gas supply unit     22  Raw material powder supply unit     23  Cold spray gun
             231  Nozzle attaching portion     232  Nozzle fixing ring     233  Refrigerant discharge part   
             25  Nozzle for cold spray
             25   a  Spray port     25   d  Spray passage     25   e  Flow path     251  Refrigerant introduction part     252  Nozzle main body
                 252   a  Connecting portion   
                 253  Cooling jacket
                 253   b  O-ring     253   c  Seal retaining portion     253   d  Front wall     253   e  Rear wall   
               
             26  Nozzle for cold spray
             261  Nozzle main body
                 261   a  Tapered portion   
                 262  Cooling jacket
                 262   b  O-ring     262   c  Seal retaining portion     262   d  Front wall     262   e  Rear wall