Abstract:
An improved kinetic spray system and a method for using the same in a high speed manufacturing environment are disclosed. The improved kinetic spray nozzle system comprises: a gas/powder exchange chamber connected to a first end of a powder/gas conditioning chamber having a length along a longitudinal axis of equal to or greater than 20 millimeters; a converging diverging supersonic nozzle, the supersonic nozzle having a converging section separated from a diverging section by a throat, the diverging section comprising a first portion and a second portion, with the first portion having a cross-sectional area that increases along a length of the first portion and with the second portion having a substantially constant cross-sectional area along a length of the second portion; and the converging section connected to a second end of the powder/gas conditioning chamber opposite the first end. The method includes: use of the disclosed nozzle system with the addition of hard particles that permit maximum enhancement of particle temperature while not permitting clogging of the nozzle; use of controlled particle feed rates to match the desired very high traverse speeds; and use of pre-heating of the substrate to clean it an to enhance particle bonding. With the disclosed nozzle system coupled with the disclosed methods one can apply kinetic spray coatings at traverse speeds of over 200 centimeters per second with a deposition efficiency of over 80 percent.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to coating a substrate by a kinetic spray process, and more particularly, to an improved nozzle system to permit high speed continuous in-line coating deposition using a kinetic spray system.  
       INCORPORATION BY REFERENCE  
       [0002]     U.S. Pat. No. 6,139,913, “Kinetic Spray Coating Method and Apparatus”, and U.S. Pat. No. 6,283,386 “Kinetic Spray Coating Apparatus” are incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0003]     The prior art for kinetic spray systems generally discloses a kinetic spray system having a nozzle system that includes a gas/powder exchange chamber directly connected to a converging diverging deLaval type supersonic nozzle. The system introduces a stream of powder particles under positive pressure into the exchange chamber. Typically, the powder gas, which is used to drive the powder to the exchanger chamber, is not heated to prevent powder from clogging the powder pipeline. A heated main gas is also introduced into the exchange chamber under a pressure, which is set lower than the pressure of the powder particle stream. In the exchange chamber the heated main gas and the particles mix and because of the very short residence time, the power particles are heated only slightly and significantly below their melting point even when the main gas is at a temperature that is several fold above the melting temperature for certain low melting temperature materials. The heated main gas and the particles flow from the exchange chamber into the supersonic nozzle where the particles are accelerated to a velocity of from 200 to 1,300 meters per second. The particles exit the nozzle and adhere to a substrate placed opposite the nozzle provided that a critical velocity has been exceeded.  
         [0004]     The critical velocity of a particle is dependent upon its material composition and its size. Harder particles generally need a higher velocity to result in adherence and it is more difficult to accelerate large particles to high velocities. The prior art system has been shown to work with many different types of particles, however, some particle sizes and material compositions have not been successfully sprayed to date. Prior to the present invention numerous attempts have been made to coat substrates with harder particles or larger particles. These attempts have been largely unsuccessful. In addition, the coating density and deposition efficiency of the particles can be very low with harder to spray particles. The particle velocity upon exit from the nozzle varies approximately inversely to the particle size and the particle density. Increasing the velocity of the main gas by increasing its temperature should increase the particle velocity upon exit. There is a limit, however, to the main gas velocities and temperatures that can be achieved within the system. If the main gas temperature is too high the powder particles begin to adhere to the inside of the nozzle, which causes poor deposition and requires a nozzle cleaning.  
         [0005]     A recent improvement in the ability to spray difficult to deposit particles is disclosed in co-pending U.S. application Ser. No. 10/808,245, filed on Mar. 24, 2004. The co-pending application discloses an improved nozzle design that incorporates a powder/gas conditioning chamber into the nozzle. This leads to a dramatic ability to spray previously difficult to spray powders at higher deposition efficiency. Although the co-pending system improved the deposition efficiency for difficult to spray powders by increasing the particle temperatures it, however, has limitations for some very hard powders, powders that are hard with low melting temperatures, or with very large particles. Certain particle populations such as brazing alloys formed from, for example, aluminum, silicon, and zinc, still are difficult to deposit because they become gummy in the nozzle and stick to its interior when the particle temperatures are too high, which reduces deposition efficiency. As a result, the traverse speeds of substrates need to be reduced greatly to obtain a coating with adequate thickness and mass loading. For example, one has to use a traverse speed of from 1.25 to 2.5 centimeters/second to deposit a ternary braze alloy of AL-Sn-Zi that is equivalent to a monolayer of prayed particles. Such traverse speeds are far too slow to make them useful when a manufacturing environment requires high deposition efficiency with high traverse speeds in the range of 25 to 250 centimeters per second. Thus, there is a critical need to develop a suitable kinetic spray system that will allow for high deposition efficiency of a wide range of materials at high traverse speeds of 25 centimeters per second and higher while keeping the nozzle clean.  
       SUMMARY OF THE INVENTION  
       [0006]     In one embodiment, the present invention is a method of kinetic spray coating a substrate comprising the steps of: providing particles of a powder; injecting the particles into a gas/powder exchange chamber and entraining the particles into a flow of a main gas in the gas/powder exchange chamber, the main gas at a temperature insufficient to heat the particles to a temperature above a melting temperature of the particles; directing the particles entrained in the main gas in the gas/powder exchange chamber into a powder/gas conditioning chamber having a length along a longitudinal axis of equal to or greater than 20 millimeters; directing the particles entrained in the flow of gas from the conditioning chamber into a converging diverging supersonic nozzle, said nozzle having a diverging section comprising a first portion and a second portion, said first portion having a cross-sectional area that increases along a length of said first portion and said second portion having a substantially constant cross-sectional area along a length of said second portion; and accelerating the particles to a velocity sufficient to result in adherence of the particles on a substrate positioned opposite the nozzle.  
         [0007]     In another embodiment, the present invention is a kinetic spray nozzle system comprising: a gas/powder exchange chamber connected to a first end of a powder/gas conditioning chamber having a length along a longitudinal axis of equal to or greater than 20 millimeters; a converging diverging supersonic nozzle, the supersonic nozzle having converging section separated from a diverging section by a throat, the diverging section comprising a first portion and a second portion, the first portion having a cross-sectional area that increases along a length of the first portion and the second portion having a substantially constant cross-sectional area along a length of the second portion; and the converging section connected to a second end of the powder/gas conditioning chamber opposite the first end. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic layout illustrating a kinetic spray system for using the nozzle of the present invention;  
         [0009]      FIG. 2  is an enlarged cross-sectional view of a nozzle system designed in accordance with the present invention for use in a kinetic spray system;  
         [0010]      FIG. 3  is a photomicrograph of a substrate sprayed via a kinetic spray nozzle designed in accordance with the prior art;  
         [0011]      FIGS. 4A and 4B  are scanning electron micrographs of the coatings shown in  FIG. 3  strips a and g, respectively;  
         [0012]      FIGS. 5A and 5B  are photomicrographs of an exit end of the prior art kinetic spray nozzle before  FIG. 3  strip a was sprayed and after  FIG. 3  strip h was sprayed, respectively;  
         [0013]      FIG. 6A  is a graph demonstrating the effect of the level of silicon carbide addition on the ability to coat a substrate according to the present invention;  
         [0014]      FIG. 6B  is a graph demonstrating the effect of the level of silicon carbide addition on the coating deposition efficiency on a substrate according to the present invention;  
         [0015]      FIG. 7  is a schematic diagram showing one use of the present invention as an in-line addition to a condenser tube extrusion process;  
         [0016]      FIG. 8  is a schematic diagram showing one use of the present invention as an in-line addition to a condenser tube spool to spool process;  
         [0017]      FIG. 9  is a scanning photomicrograph of a cross-section of a condenser tube to condenser core braze joint prepared according to the present invention; and  
         [0018]      FIG. 10  is a graph showing the effect of preheating the substrate on the amount of coating that adheres to the substrate sprayed according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     The present invention comprises a dramatic improvement to the kinetic spray process and nozzle system as generally described in U.S. Pat. Nos. 6,139,913 and 6,283,386.  
         [0020]     Referring first to  FIG. 1 , a kinetic spray system for use of a nozzle designed according to the present invention is generally shown at  10 . System  10  can include an enclosure  12  in which a support table  14  or other support means is located. A mounting panel  16  fixed to the table  14  supports a work holder  18 . Work holder  18  can have a variety of configurations depending on the type of substrate to be coated. For example, work holder  18  can be configured for the present invention as a plurality of high speed rollers capable of moving a substrate past a nozzle  34  at traverse speeds in excess of 250 centimeters per second. In other embodiments, work holder  18  can be capable of movement in three dimensions and able to support a suitable workpiece formed of a substrate material to be coated. The enclosure  12  can include surrounding walls having at least one air inlet, not shown, and an air outlet  20  connected by a suitable exhaust conduit  22  to a dust collector, not shown. During coating operations, the dust collector continually draws air from the enclosure  12  and collects any dust or particles contained in the exhaust air for subsequent disposal or recycling.  
         [0021]     The spray system  10  includes a gas compressor  24  capable of supplying gas at a pressure up to 3.4 MPa (500 psi) to a high pressure gas ballast tank  26 . Many gases can be used in the present invention including air, helium, argon, nitrogen, and other noble gases. The gas ballast tank  26  is connected through a line  28  to both a high pressure powder feeder  30  and a separate gas heater  32 . The gas heater  32  supplies high pressure heated gas, the heated main gas, described below, to a kinetic spray nozzle  34 . The powder feeder  30  mixes particles of a powder to be sprayed with heated or unheated high pressure gas and supplies the mixture to a supplemental inlet line  48  of the nozzle  34 . In some embodiments the powder gas is heated and in others the powder gas is not heated to prevent powder lines from clogging. A computer control  35  operates to control the pressure of gas supplied to the gas heater  32 , the pressure of gas supplied to the powder feeder  30 , the temperature of the gas supplied to the powder feeder  30 , and the temperature of the heated main gas exiting the gas heater  32 .  
         [0022]      FIG. 2  is a cross-sectional view of a nozzle  34  designed in accordance with the present invention for use in the system  10  and its connections to the gas heater  32  and the supplemental inlet line  48 . A main gas passage  36  connects the gas heater  32  to the nozzle  34 . Passage  36  connects with a premix chamber  38  which directs gas through a flow straightener  40  and into a mixing chamber  42 . Temperature and pressure of the heated main gas are monitored by a gas inlet temperature thermocouple  44  in the passage  36  and a pressure sensor  46  connected to the mixing chamber  42 . The premix chamber  38 , flow straightener  40 , and mixing chamber  42  form a gas/powder exchange chamber  49 .  
         [0023]     A mixture of high pressure gas and coating powder is fed through the supplemental inlet line  48  to a powder injector tube  50  having a central axis  52  which is preferably the same as a central axis  51  of the gas/powder exchange chamber  49 . The length of chamber  49  is preferably from 40 to 80 millimeters. Preferably, the injector tube  50  has an inner diameter of from about 0.3 to 3.0 millimeters. The tube  50  extends through the premix chamber  38  and the flow straightener  40  into the mixing chamber  42 .  
         [0024]     Mixing chamber  42  is in communication with a powder/gas conditioning chamber  80  positioned between the gas/powder exchange chamber  49  and a supersonic nozzle  54 . The powder/gas conditioning chamber  80  has a length L along its longitudinal axis. The axis  52  is the same as axis  51  in this embodiment. Preferably the interior of the powder/gas conditioning chamber  80  has a cylindrical shape  82 . Also preferably its interior diameter matches the entrance of a converging section of the supersonic nozzle  54 . The powder/gas conditioning chamber  80  releasably engages both the supersonic nozzle  54  and the gas/powder exchange chamber  49 . Preferably, the releasable engagement is via correspondingly engaging threads on the gas/powder exchange chamber  49 , the nozzle  54 , and the powder/gas conditioning chamber  80  (not shown). The releaseable engagement could be via other means such as snap fits, bayonet-type connections and others known to those of skill in the art. The length L along the longitudinal axis is preferably at least 20 millimeters or longer. The optimal length of the powder/gas conditioning chamber  80  depends on the particles that are being sprayed and the substrate that is being sprayed with the particles. Preferably the length L ranges from 20 to 450 millimeters. With the insertion of the powder/gas conditioning chamber  80 , the distance between the exit of the injector tube  50  and the adjacent end of the nozzle  54  is significantly increased compared to the prior art. The increased distance permitted by the conditioning chamber  80  allows for a longer residence time of the particles in the main gas prior to entry into the supersonic nozzle  54 . This longer residence time leads to a higher particle temperature, more homogeneous main gas powder intermixing, and a more homogeneous flow of the gas powder mixture. Thus, it is predicted that particles will achieve a higher temperature, closer to but still well below their melting point, prior to entry into the supersonic nozzle  54 .  
         [0025]     Supersonic nozzle  54  is a de Laval type converging diverging nozzle  54 . The nozzle  54  has an entrance cone  56  that decreases in diameter to a throat  58 . The entrance cone  56  forms a converging section of the nozzle  54 . Downstream of the throat  58  is an exit end  60 . The largest diameter of the entrance cone  56  may range from 10 to 6 millimeters, with 7.5 millimeters being preferred. The entrance cone  56  narrows to the throat  58 . The throat  58  may have a diameter of from 1.0 to 6.0 millimeters, with from 2 to 5 millimeters being preferred. The nozzle  54  also includes a diverging section that extends from a downstream side of the throat  58  to the exit end  60 . In the present invention the diverging section has been modified from the prior art. The diverging section includes a first portion  59 A adjacent the throat  58  and a second portion  59 B adjacent the first portion  59 A. In the first portion  59 A the cross-sectional area of the nozzle  54  rapidly expands. In the second portion  59 B the cross-sectional area of the nozzle  54  remains substantially constant and does not expand. The prior art only has the first portion  59 A of the nozzle  54 . Preferably the overall length of the diverging section is from 350 to 1000 millimeters and more preferably from 400 to 800 millimeters. Preferably the first portion  59 A is from 200 to 400 millimeters in length and preferably the second portion  59 B is from 150 to 800 millimeters in length. The diverging section may have a variety of shapes, but in a preferred embodiment it has a rectangular cross-sectional shape. At the exit end  60  the nozzle  54  preferably has a rectangular shape with a long dimension of from 6 to 24 millimeters by a short dimension of from 1 to 6 millimeters.  
         [0026]     As disclosed in U.S. Pat. Nos. 6,139,913 and 6,283,386 the powder injector tube  50  supplies a particle powder mixture to the system  10  under a pressure in excess of the pressure of the heated main gas from the passage  36 . Preferably the gas supplied to the powder feeder  30  is at a pressure sufficiently high enough that the powder particles leave the injector tube  50  at a pressure that is 15 to 150 pounds per square inch above the main gas pressure, more preferably at a pressure that is 15 to 75 pounds per square inch above the main gas pressure. In some embodiments the gas supplied to the powder feeder is heated to a temperature of from 40 to 200° C.  
         [0027]     The nozzle  54  produces an exit velocity of the entrained particles of from 200 meters per second to as high as 1300 meters per second. The entrained particles gain primarily kinetic energy during their flow through the nozzle  54 . It will be recognized by those of skill in the art that the temperature of the particles in the gas stream will vary depending on the particle size and the main gas temperature. The main gas temperature is defined as the temperature of heated high-pressure gas at the inlet to the nozzle  54 . The main gas temperature can be substantially above the melting temperature of the particles being sprayed. In fact, the main gas temperature can vary from about 200 to 2000 degrees Celsius or as high as several fold above the melting point of the particles being sprayed depending on the particle material. Despite these high main gas temperatures the particle temperature is at all times lower than the melting point of the particles. This is because the powders are injected into the heated gas stream by the powder gas and the exposure time of the particles to the heated main gas is relatively short. Therefore, even upon impact there is no change in the solid phase of the original particles due to transfer of kinetic and thermal energy, and no change in their original physical properties. The particles are always at a temperature below their melting point. The particles exiting the nozzle  54  are directed toward a surface of a substrate to coat it.  
         [0028]     Upon striking a substrate opposite the nozzle  54  the particles flatten into a nub-like structure with a varying aspect ratio generally depending on the types of sprayed materials. When the substrate is a metal and the particles are a metal the particles striking the substrate surface fracture the surface oxide layer and subsequently form a direct metal-to-metal bond between the metal particle and the metal substrate. Upon impact the kinetic sprayed particles transfer all of their kinetic and thermal energy to the substrate surface and stick onto the substrate. As discussed above, for a given particle to adhere to a substrate it is necessary that it reach or exceed its critical velocity which is defined as the velocity at which it will adhere to a substrate when it strikes the substrate after exiting the nozzle  54 . This critical velocity is dependent on the material composition of the particle and the material composition of the substrate. In general, harder materials must achieve a higher critical velocity before they adhere to a given substrate and harder substrates must be struck at a higher velocity. It is not known at this time exactly what is the nature of the particle to substrate bond; however, it is believed that for the metal particles incident on a metal substrate, a portion of the bond is metallic or metal to metal due to the particles plastically deforming upon striking the substrate and thereby fracturing oxide layers exposing the underlying metal.  
         [0029]     As disclosed in U.S. Pat. No. 6,139,913 the substrate material may be comprised of any of a wide variety of materials including a metal, an alloy, a plastic, a polymer, a ceramic, a wood, a semiconductor, and mixtures of these materials. All of these substrates can be coated by the process of the present invention. Preferably the stand off distance from the substrate is from 5 to 60 millimeters, and more preferably from 10 to 50 millimeters. The particles used in the present invention may comprise any of the materials disclosed in U.S. Pat. Nos. 6,139,913 and 6,283,386 in addition to other know particles. These particles generally comprise a metal, an alloy, a ceramic, a polymer, a diamond, a metal coated ceramic, a semiconductor, or mixtures of these. Preferably, the particles have an average nominal diameter of from about 1 to 250 microns. One preferred use of the present invention is to deposit brazing alloys onto surfaces. Preferably the brazing alloys are mixtures of aluminum, silicon, and zinc. In one embodiment it is preferred that the alloy comprise from 50 to 78% by weight aluminum, 5 to 10% by weight silicon, and 12 to 45% by weight zinc based on the total weight.  
         [0030]      FIG. 3  is a photomicrograph of a substrate kinetically sprayed using a prior art kinetic spray process. Lanes a and b were sprayed right after the nozzle had been cleaned, as shown in  FIG. 5A . Lanes c-h were sprayed right after lanes a and b. The nozzle interior after lane h is show in  FIG. 5B . Notice the heavy particle build up in the nozzle and the poor deposition quality. The spray parameters were as follows: main gas pressure 300 psi, powder gas pressure 350 psi, main gas temperature 650° C., powder feed rate of 0.5 grams/second, stand off distance of 20 millimeters and a traverse speed of 1.25 centimeters per second. The powder particles were a brazing alloy mixture of aluminum, silicon, and zinc. In  FIGS. 4A and 4B  scanning photomicrographs of the coating surfaces in lanes a and g are shown. Note the low density of the particles that stick to the substrate in  4 B versus  4 A. In  FIG. 4A , the particles become highly deformed and closely packed, a clear indicator of high particle velocities and high deposition efficiency. In the case of  FIG. 4B , the majority of the particles that strike the substrate fall off after collision, which is evidenced by the high density of crater marks. The deposit of alloy on the nozzle walls, as shown in  FIG. 5B , is believed to cause the boundary layer to thicken and to reduce the particle velocities.  
         [0031]     In an attempt to improve the ability to spray these brazing alloys the present inventors incorporated an additional hard component into the alloy, namely a ceramic. A diamond or other hard material is also believed to be suitable. The ceramic chosen was silicon carbide; however, other ceramics will also work. The importance is that the second population of particles be too hard to adhere to the substrate under the spraying conditions, it instead serves to scour the inside of the nozzle and keep it clean. It is preferable that the hard particle, such as silicon carbide, be included at levels of from 1 to 20% by weight based on the total weight. The same particle sizes can be used. In  FIGS. 6A and 6B  the dramatic improvement using a nozzle designed according to the present invention and silicon carbide is shown. Using a prior art nozzle the main gas temperature was limited to 650° C., a traverse rate of 1.25 centimeters per second and a deposition efficiency of from 3 to 5%. In the results shown in  FIGS. 6A and 6B  the spray parameters were as follows: main gas pressure 300 psi, powder gas pressure 320 psi, main gas temperature 1000° C., powder feed rate 1.00 grams per second, stand off distance of 20 millimeters, and traverse rate of 60 centimeters per second. In reference lines  100 ,  102 ,  110 , and  112  the silicon carbide particles have an average nominal diameter of from 25 to 45 microns. In the other reference lines the average nominal diameter is from 63 to 90 microns. Reference lines  100  and  110  show the effect of 4% by weight of silicon carbide. In reference lines  102  and  112  the effect of 7% by weight of silicon carbide is shown. In reference lines  104  and  114  the effect of 4% by weigh of silicon carbide is shown. In reference lines  106  and  116  the effect of 7% by weight silicon carbide are shown. In reference lines  108  and  118  the effect of 10% by weight silicon is shown. Generally it is preferred that the loading on a condenser tube be from 40 to 80 grams per square meter. The results show that small amounts of the harder silicon carbide provide dramatic improvements in the ability to deposit a gummy material like an alloy of aluminum, silicon, and zinc. The traverse speed was set 24-fold higher, the main gas temperature could be increased by 400° C., the deposition efficiencies were at least 12 fold higher, and the loading was well above that need to effectively coat condenser tubes.  
         [0032]     Using the sort of data shown in  FIGS. 6A and 6B  one is able to calculate the required powder feed rates that are necessary to sustain a loading of at least  80  grams per square meter onto a condenser tube 18 millimeters wide at any of several assumed deposition efficiencies and traverse speeds. The results of such calculations are shown in Table 1 below.  
                                             TABLE 1                       Traverse speed   Feed rate at   Feed rate at   Feed rate at       (centimeters/   100% DE   80% DE   50% DE       second)   (grams/second)   (grams/second)   (grams/second)                                30   0.45   0.56   0.90       60   0.90   1.13   1.80       90   1.35   1.70   2.70       120   1.80   2.25   3.60       180   2.70   3.38   5.40       200   3.00   3.80   6.00                  
 
         [0033]     Given the dramatic improvement in the ability to deposit coatings efficiently at very high traverse speeds provided by the present invention one can see its use in high speed manufacturing environments. Examples of such are shown in  FIGS. 7 and 8 .  FIG. 7  is a schematic diagram showing an in-line inclusion of the present invention in an extrusion line for condenser tubes. The substrate could be any high speed extrudate material. In  FIG. 7  an extruder  120  continuously extrudes a condenser tube  122  at a temperature of approximately 550° C. The extruded tube  122  passes past a pair of air coolers  124  and then past a pair of kinetic spray nozzles  34  designed according to the present invention where the tube  122  is coated by the nozzles  34 . The coated tube  122  passes through a cooling water bath  126  and then is taken up on a wrap spool  128 . The wrapped tube can subsequently be straightened and cut to size  130 . In another embodiment the nozzles  34  of the present invention are used in a spool to spool operation as shown in  FIG. 8 . A spool  140  contains wrapped extruded tube  142  which is removed from the spool  140  by drive rollers  144 . The drive rollers  144  feed the tube  142  past heaters  146  and then past a pair of nozzles  34  designed according to the present invention. The nozzles  34  coat the tube  142  which is subsequently coiled onto another spool  146 . Later the coated tube  142  can be straightened and cut to length  148 . The proposed continuous in-line manufacturing process combined with the advanced kinetic spray process is the key enabler to minimize the cycle time and manufacturing cost while improving the coating quality and deposition efficiency. This continuous in-line process also can eliminate the need for pre-heating the substrate. The pre-heating of the substrate can improve deposition efficiency. In the example shown in  FIG. 7 , the substrate temperature is fairly high, near 550° C., right after the extrusion and in this in-line process no pre-heating is required before the substrate is passed in front of the nozzles  54 .  
         [0034]     In  FIG. 9 a  photomicrograph of a cross-section of a radiator core  154  brazed according to the present invention is shown. The brazing alloy applied according to the present invention was an alloy of aluminum, silicon, and zinc premixed with the hard silicon carbide. The spray parameters were as follows: main gas pressure 300 psi, powder gas pressure 330 psi, main gas temperature 1100° C., powder feed rate 4.00 grams per second, stand off distance of 22 millimeters, powder/gas conditioning chamber length 131 millimeters, and traverse speed of 200 centimeters per second. The condenser tube  150  shows an excellent braze joint  152  to the core  154 .  
         [0035]     In  FIG. 10  the effect of mild heating of the substrate is shown. In all cases the substrate was condenser tubing and the spray parameters were as follows: main gas pressure 300 psi, powder gas pressure 330 psi, main gas temperature 1100° C., powder feed rate 4.00 grams per second, stand off distance 22 millimeters, powder/gas conditioning chamber length 131 millimeters, and traverse speed of 200 centimeters per second. In reference line  160  the tubing was at room temperature when sprayed. In reference line  162  the tubing was heated to 40° C. and then sprayed. In reference line  164  the tubing was heated to 160° C. and then sprayed. The results demonstrate that heating of the substrate prior to spraying increased the loading and therefore deposition efficiency. The continuous in-line manufacturing process of the present invention improves coating quality and the deposition efficiency in part due to high substrate temperature out of the extrusion. Key benefits include: improved cycle time; improved deposition efficiency; improved coating quality; and no need to pre-heat the substrate.  
         [0036]     The present invention has been described with respect to its use in high speed manufacturing environments and, more specifically, in the use of the invention to coat condenser tubes. The invention is not, however, so limited. It will find use in virtually all high speed manufacturing environments as will occur to those of ordinary skill in the art.  
         [0037]     The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.