Patent Publication Number: US-7717703-B2

Title: Combustion head for use with a flame spray apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application No. 60/656,497 filed on Feb. 25, 2005 and titled “Combustion Head For Use With A Flame Spray Apparatus”. The disclosure of the Provisional Application is incorporated in its entirety herein by reference. 

   FIELD OF THE INVENTION 
   The present invention generally relates to flame spray apparatus for spraying molten or heat softened material onto a workpiece at high velocities by means of hot combustion gases. In particular, the present invention is directed to an improved combustion head and combustion chamber for use with a flame spray apparatus which together work to deliver hot combustion gases and heated coating material to the inlet of a spray nozzle of the apparatus. 
   BACKGROUND OF THE INVENTION 
   In general, flame spray apparatus operated by hot combustion gases for coating a workpiece with metal are well known in the art. For example, U.S. Pat. No. 4,416,421 to Browning (hereinafter referred to as “Browning”) discloses a high velocity flame spray apparatus. The Browning apparatus includes a combustion chamber receiving at one end thereof a supply of pressurized fuel and oxygen. Ignition means, such as a spark plug, is provided to ignite the fuel. Pressurized hot combustion gases resulting from ignition of the fuel are discharged from an outlet of the combustion chamber through a plurality of ports leading to the inlet of a relatively long nozzle having a converging throat. A coating material is fed into the throat of the nozzle along the longitudinal axis of the nozzle. 
   The plurality of ports conveying the pressurized combustion gases from the combustion chamber to the inlet of the nozzle are radially spaced around and inclined toward the axis of the nozzle so that the hot combustion gases propel the coating material through the nozzle and also melt or at least heat-soften the material. The molten or heat-softened material exits the nozzle at high velocity and is projected onto the surface of a workpiece thereby to provide the workpiece with a coating of the material. Passageways for cooling water are provided around the exterior of the nozzle. 
   A commercial embodiment of the flame spray apparatus disclosed in the Browning patent includes a combustion head which is provided as a transition piece between the outlet of the combustion chamber and the inlet end of the nozzle. The combustion head defines a counterbore which receives the hot combustion gases from the combustion chamber. 
   One known problem associated with the combustion head of the Browning flame sprayer is that a floor of the counterbore receiving the hot combustion gases from the combustion chamber cracks and erodes after a short period of use, thus, severely limiting the useful life of the combustion head. Such cracking and erosion occurs due to the development of local hot spots in the counterbore and thermal fatigue of the body of the combustion head adjacent to the counterbore. 
   U.S. Pat. No. 4,911,363 to Webber (hereinafter referred to as “Webber”) discloses an improved combustion head for use with flame spray apparatus such as those described in the Browning patent. The Webber patent discloses a combustion head that defines a recess in the floor of the counterbore which receives the continuous flow of hot pressurized combustion gases from the combustion chamber of the flame spray apparatus. The depth of the recess being sufficient to redistribute the heat of the combustion gases to prevent local hot spots in the counterbore. The recess is provided to avoid cracking and erosion in the combustion head by reducing thermal fatigue which occurs in cyclic use of the flame spray apparatus. Similar to the Browning device, the Webber combustion head also provides a plurality of inclined passages for transporting the combustion gases from the combustion chamber to the inlet of the nozzle of the flame spray apparatus. 
   In use, the Webber combustion head is coupled to a combustion chamber wherein an open end of the combustion chamber extends into and is fully inserted into the counterbore of the combustion head engaging the floor of the counterbore. 
   Additionally, the Webber combustion head defines a plurality of radially spaced recesses or channels extending longitudinally along the length of the outer surface of the combustion head through which water is passed for cooling the combustion head. 
   One disadvantage associated with the above-identified prior art combustion heads is that the floor of the counterbore, even with the recess therein as disclosed by Webber, includes a substantial mass of material which receives the hot combustion gases from the combustion chamber and is therefore susceptible to cracking due to the expansion and contraction of the combustion head during the heating and cooling thereof. The mass of the floor of the counterbore also adds to the overall mass of the combustion head thereby contributing to the thermal fatigue of the combustion head over the life thereof due to the cyclic operation of flame spray apparatus under high temperatures. 
   Additionally, combustion gases contacting the floor of the counterbore cause the floor of the counterbore to erode enlarging the inlets of the combustion gas passages adjacent the counterbore resulting in an uneven flow of gases through the gas passages of the combustion head. Thus, the pressure of the combustion gases conveyed through each of the plurality of inclined gas conduits is not constant therebetween. This uneven pressure in the inclined gas conduits causes the coating material entering the nozzle of the apparatus to be pushed towards the side of the throat of the nozzle opposite the inclined gas conduits with the greatest pressure which causes erosion of the throat of the nozzle and shortens the useful life thereof. 
   Accordingly, the cracking and erosion of the floor of the counterbore present in the above-describe prior art combustion heads limits the useful life of the combustion head and parts associated therewith. 
   The floor of the counterbore in the above-identified prior art combustion heads also obstructs the flow of combustion gases entering the combustion head thereby increasing the amount of turbulence associated with the combustion gases entering the combustion head. This turbulence increases the occurrence of uneven erosion, cracking and wear of the material of the combustion head. Additionally, uneven pressure in the gas conduits exiting the interior chamber of the combustion head is increased due to the disrupted flow of the combustion gases entering the combustion head. Thus, the presence of the floor of the counterbore reduces the overall life of the above-identified prior art combustion heads. 
   Another disadvantage of the above-identified prior art combustion heads, is that a seal provided to retain coolant within a housing of the flame spray apparatus and disposed between the housing in which the combustion head is used in assembly therewith and a material feed passage of the combustion head often fails due to overheating under heavy use conditions. Typically, failure of this seal causes a shut down of a coating operation in which the flame spray apparatus is being used so that the seal can be replaced. The Webber combustion head includes coolant channels extending longitudinally along the length of the outer surface of the combustion head through which water is passed for cooling the combustion head. However, the coolant channels disclosed by Webber do not effectively maintain the inlet to the material feed passage and the seal disposed between the material feed passage and the housing of the flame spray apparatus at an operating temperature low enough to avoid the seal from failure due to heat damage under heavy use conditions. 
   Based on the foregoing, it is the general object of the present invention to provide an improved combustion head and combustion chamber for use with known flame spray apparatus that improves upon, or overcomes the problems and drawbacks associated with prior art combustion heads. 
   SUMMARY OF THE INVENTION 
   The present invention provides an improved combustion head and combustion chamber for use with known flame spray apparatus. The combustion head includes a body portion defining a combustion head opening for receiving an outlet end of the combustion chamber and an interior chamber extending from the combustion head opening into the body portion. The body portion also defines a material feed conduit extending through the body portion along a longitudinal axis thereof. The longitudinal axis extending generally perpendicular to the combustion head opening. The material feed conduit having an inlet and an outlet defined by first and second opposing sidewalls or ends of the body portion respectively. The inlet and outlet of the material feed conduit being aligned concentric with longitudinal axis of the body portion. 
   The interior chamber extends into the body portion on opposing sides of the material feed conduit and is defined in part by arcuate interior sidewalls of the body portion. The body portion being substantially hollow wherein the interior chamber extends from the combustion opening throughout substantially the entire body portion including adjacent the material feed conduit. The floor of the counterbore present in prior art combustion heads is eliminated in the present invention. The elimination of the floor of the combustion head reduces the total mass of the present invention combustion head relative to the prior art devices. Accordingly, the occurrence of cracking and erosion of the combustion head especially at the floor of the counterbore that is present in the prior art combustion heads discussed hereinabove is greatly reduced in the combustion head of the present invention. Additionally, elimination of the floor of the counterbore reduces the turbulence in the flow of combustion gases entering the combustion head as will be discussed further below. 
   The combustion head also includes a plurality of cooling channels defined by an outer surface of the body portion extend through the length of the body portion. The cooling channels are spaced radially about the longitudinal axis of the body portion. Each of the cooling channels having a varying depth along the length thereof defining an arc corresponding to the arcuate sidewalls of the interior chamber such that the sidewalls of the body portion formed between the interior chamber and the plurality of cooling channels are substantially uniform in wall thickness adjacent the interior chamber. The relative uniformity of wall thickness of the combustion head at the cooling channels allows for increased uniformity in the operating temperature over the entire mass of the combustion head during the use thereof than prior art combustion heads. Thus, the cooling channels of the present invention combustion head and the relatively uniform wall thickness formed in part thereby, help to reduce the occurrence of stress fractures in the combustion head due to thermal fatigue and thereby increase the overall life of the combustion head. 
   The present invention combustion head further includes a plurality of combustion gas conduits extending from the interior chamber through the second end of the body portion. In a preferred embodiment of the present invention combustion head, the gas conduits are arranged radially about the material feed conduit and extend through the second end of the body portion converging towards the material feed conduit throughout a length thereof. The gas conduits transport hot combustion gases from the interior chamber into an inlet of a nozzle coupled to the body portion adjacent the second end of the body portion. 
   An improved combustion chamber is also provided for assembly with the combustion head disclosed herein. The combustion chamber having an inlet and an outlet at opposed ends thereof. The inlet for receiving a supply of pressurized fuel and oxygen. Ignition means, such as a spark plug is provided to ignite the fuel as set forth in both the Browning and Webber patents. The combustion chamber includes a flange formed on an outer surface thereof near the outlet end thereof. The flange for engaging a surface of the combustion head surrounding the combustion head opening and limiting the insertion of the combustion chamber into the interior chamber of the combustion head. The restricted insertion of the combustion chamber into the combustion head opening provides that the outlet of the combustion chamber remains spaced apart from the outer surface of the material feed conduit when the combustion chamber is engaged with the combustion head and during use thereof in a flame spray apparatus. 
   One advantage of the present invention combustion head and combustion chamber assembly is that the combustion head includes a substantially less amount of material mass as compared to prior art combustion heads. In the prior art combustion heads, the floor of the counterbore was designed to engage the outlet end of the combustion chamber and support the same thereby in part establishing the proper insertion of the combustion chamber into the combustion head. Whereas, in the present invention, the floor of the counterbore is eliminated and the insertion position of the combustion chamber into the combustion head is established and supported by the flange on the outer surface of the combustion head engaging a flat surface on a lower side of the combustion head. The flange eliminates the need for the combustion chamber to abut against the floor of the combustion head, thereby allowing the floor of the counterbore to be eliminated. As set forth above, elimination of the floor of the counterbore results in a substantially larger interior chamber of the combustion head when compared to the prior art. Further, the elimination of the floor of the counterbore in the present invention, results in the material mass present in the body portion of the combustion head being significantly less than that of prior art combustion heads. When compared to prior art combustion heads, the reduction in the amount of material mass inside the combustion head allows it to operate at a reduced temperature, thereby greatly reducing the occurrence of a failure of the combustion head due to thermal stress and fatigue in the body of the combustion head caused by thermal expansion of the material mass thereof. 
   The foregoing and still other objects and advantages of the present invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawings wherein throughout the figures, like reference numerals describe like elements of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a typical flame spray apparatus employing a combustion head and combustion chamber in accordance with the present invention. 
       FIG. 2  is a perspective view of the combustion head and combustion chamber of the present invention shown coupled to a prior art nozzle and as used in the flame spray apparatus of  FIG. 1 . 
       FIG. 3  is a partial cross sectional side view of the flame spray apparatus of  FIG. 1  including the combustion head and the combustion chamber of the present invention mounted therein. 
       FIG. 4  is side elevational view of a combustion head and combustion chamber according to the present invention. 
       FIG. 5  is a top view of the combustion head and combustion chamber of  FIG. 4 . 
       FIG. 6  is a cross-sectional view of the combustion head and combustion chamber of  FIG. 5  taken at line B-B of  FIG. 5 . 
       FIG. 7  is a perspective view of the combustion head of  FIG. 4  showing the combustion head opening and interior chamber thereof. 
       FIG. 8  is a bottom view of the combustion head of  FIG. 4  showing the combustion head opening and interior chamber thereof. 
       FIG. 9  is a perspective view of the combustion head of  FIG. 4  showing the combustion head opening and interior chamber thereof. 
       FIG. 10  is an enlarged of the combustion head of  FIG. 4  shown mounted to a combustion chamber in accordance with the present invention. 
       FIG. 11  is an enlarged sectional view of the combustion head of  FIG. 4  in assembly with a combustion chamber of the present invention, and mounted in a flame spray apparatus. 
       FIGS. 12 and 13  are elevation side and sectional views respectively of a combustion chamber in accordance with the present invention. 
       FIG. 13  shows a sectional view taken at the line C-C of  FIG. 14 . 
       FIG. 14  is a top view of the combustion chamber of  FIG. 12 . 
       FIG. 15  includes a bottom view of the combustion head of  FIG. 4  showing section line D-D and a cross-sectional view of the combustion head of  FIG. 4  taken at the line D-D. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the  FIG. 1 , the present invention combustion head and combustion chamber are designed for use with a typical flame spray apparatus, generally referred to with the reference numeral  10 . The flame spray apparatus  10  includes a housing  12 . The housing  12  includes a coolant inlet  14  and outlet  16  for cooling the apparatus  10  as well as the combustion head and combustion chamber as shown in  FIG. 2  and referenced generally by reference numerals  18  and  20  respectively. 
   As shown in  FIG. 2 , the combustion head  18  and combustion chamber  20  of the present invention are coupled together as set forth in detail following. A nozzle  21  is also coupled to the combustion head forming an assembly for use in a flame spray apparatus  10 .  FIG. 3  illustrates the combustion head  18  and combustion chamber  20  of the present invention coupled together and mounted in the housing  12  of the flame spray apparatus  10 . 
   Referring to  FIGS. 3-11 , the combustion head  18  includes a body portion  19  having a bottom wall  22  defining a combustion head opening  24  therethrough. The combustion head opening  24  is in fluid communication with an outlet  26  of the combustion chamber  20  and an interior chamber  23  defined by the body portion  19  of the combustion head  18 . The combustion chamber  20  includes an outlet end  28  received in the combustion head opening  24  thereby coupling the combustion chamber to the body portion  19 . 
   The body portion  19  further defines a pair of circular recesses  30 ,  30  extending outwardly from the combustion head opening  24  for supporting a pair of corresponding O-rings  32 ,  32  engageable with the outlet end  28  of the combustion chamber. The O-rings  32 ,  32  seal the joint between the outlet end  28  of the combustion chamber  20  and the interior chamber  23  of the combustion head  18 . Although, two O-rings are utilized in the illustrated embodiment of the present invention, in other embodiments, only one O-ring or other type of seal known to one skilled it the art may be employed. 
   The combustion chamber  20  includes a flange  34  extending outwardly from an outer surface of the combustion chamber  20  which limits the insertion of the outlet end  28  of the combustion chamber into the combustion head opening  24  and interior chamber  23  of the combustion head. Referring to  FIGS. 12 and 13 , in a preferred embodiment, the flange  34  is formed by turning the outlet end  28  of the combustion chamber  20  and the body  35  of the combustion chamber down to a smaller diameter than the flange  34 . The flange  34  could also be formed on the outer surface of the combustion chamber  20  using other methods know to one skilled in the art.  FIG. 14  illustrates a top view of the combustion chamber  20  and flange  34  in accordance with the present invention. 
   Referring to  FIG. 7 , the bottom wall  22  of the combustion head is substantially flat engageable with the flange  34  of the combustion head. The flat bottom wall  22  provides for ease of insertion of the combustion chamber  20  into the combustion head opening  24  while both of the combustion head  18  and combustion chamber are disposed in housing  12  as the joint therebetween is viewable through a nozzle opening of the housing  12 . The ability to view the engagement between the flange  34  and the bottom wall  22  of the combustion head  18  inside of the housing  12  also allows a user to confirm that the combustion chamber is properly coupled to the combustion head. This constitutes a further improvement in the present invention combustion head when compared to that disclosed by Webber. In the Webber combustion head, the lower surface adjacent the combustion opening is round such that the joint between the combustion chamber and the combustion head is not viewable when the combustion head and chamber are installed in the housing of a typical flame spray apparatus. 
   The combustion head  18  further defines a material feed conduit  36  extending through the length of the body portion  19  along a longitudinal axis X-X of the body portion. (See  FIGS. 3 and 11 ). The material feed conduit  36  includes an end portion  38  extending outwardly from a first end  40  of the body portion  19  and defining an inlet  42  of the material feed conduit. As shown in  FIG. 6 , the inlet  42  includes a threaded opening  43  wherein a material feed supply line (not shown) is coupled to the combustion head  18  during use of the apparatus  10 . An outlet  44  of the material feed conduit  36  is defined by a second end  46  of the body portion  19 . The outlet  44  of the material feed conduit  36  is in fluid communication with an inlet of the nozzle  21  when the combustion head  18  is coupled to a nozzle  21  as shown in  FIG. 2 . 
   Referring to  FIG. 7 , the interior chamber  23  of the body portion  19  includes areas  25 ,  25  extending into the body portion on opposing sides of the material feed conduit  36  and substantially throughout a height h of an outer surface of the material feed conduit. The interior chamber  23  being in fluid communication with the outlet  26  of the combustion chamber  20  functions as an extension of the combustion chamber for receiving combustion gases discharged therefrom. 
   As shown in  FIG. 7 , apart from the material feed conduit  36 , the interior chamber  23  occupies nearly the entire interior area of the body portion  19 . Thus, combustion gases discharged from the combustion chamber  20  flow substantially undisturbed into the interior chamber  23  of the combustion head  18  and exit through a plurality of gas conduits  27  ( FIG. 9 ). In contrast to the above-identified prior art combustion heads, the present invention combustion head  18  does not include a counterbore having a floor wherein the floor of the counterbore receives a portion of the combustion gases discharged from the outlet of the combustion chamber  20 . In the prior art combustion heads, the floor of the counterbore is provided in part to engage the outlet end of the combustion chamber and provide support to the same. Additionally, the floor provides additional mass to retain the heat of the combustion head. However, the mass of the floor of the counterbore present in prior art combustion heads adds to the overall mass of the combustion head thereby increasing the occurrence of erosion and cracks in the combustion head due to thermal fatigue of the material thereof. 
   As shown in  FIGS. 6 and 11 , the combustion head  18  in accordance with the present invention includes the combustion head opening  24  which provides an unobstructed opening to the interior chamber  23  of the body portion  19 . Further, as set forth above, the flange  34  of the combustion chamber limits the insertion of the combustion chamber into the interior chamber  23  such that the outlet end  28  of the combustion chamber remains spaced apart a distance Y from an outer surface  48  of the material conduit  36 . Accordingly, the combustion gases entering the interior chamber  23  pass unobstructed from the combustion chamber  20  through the combustion head opening  24  and into the interior chamber  23  and extended areas  25 ,  25  of the interior chamber surrounding the material feed conduit  36 . Thus, in the combustion head  18  of the present invention, the combustion gases entering the interior chamber  23  of the body portion  19  are evenly dispersed throughout the interior chamber and about the outer surface of the material feed conduit  36  and therefore uniformly heat the material feed conduit throughout the length of the body portion  19  of the combustion head. 
   Additionally, in the present invention combustion head  18 , the mass of material forming the floor of the counterbore that is present in prior art combustion heads is eliminated, thereby reducing the overall mass of the combustion head. This reduction in the overall mass of the combustion head reduces the occurrence of cracking and erosion of the combustion head due to thermal fatigue of the material of the combustion head caused by the heating and cooling of the combustion head during the cyclic use thereof. Thus, due to the elimination of the floor of the counterbore, and reduced mass resulting therefrom, the present invention combustion head  18  has a longer useable life when compared with that of the above-identified prior art combustion heads. 
   The presence of the flange  34  on the combustion chamber  20  along with the absence of the floor of the counterbore in the combustion head  18  of the present invention render both the combustion head  18  and the combustion chamber  20  not useable interchangeably with corresponding prior art devices including the Webber device. 
   Referring to  FIGS. 4 ,  5  and  6 , a spray nozzle flange  50  is coupled to the second end  46  of the body portion  19  of the combustion head  18 . The spray nozzle flange  50  defines an opening  52  on a side opposite the second end  46  for receiving an inlet portion  56  of a nozzle  21  therein. The spray nozzle flange  50  defines a recess  51  surrounding the opening  52  for receiving a seal for sealing the coupling between an inlet of the spray nozzle  21  and the spray nozzle flange  50 . 
   Referring now to  FIGS. 9 and 10 , the body portion  19  defines a plurality of intersecting coolant channels including longitudinal coolant channels  64  and circumferential coolant channels  66  on the outer surface thereof for transporting coolant adjacent to the body portion for cooling the combustion head  18  during use of the flame spray apparatus  10 . As shown in  FIG. 1 , the housing  12  of the flame spray apparatus  10  includes a coolant inlet  14  and outlet  16  for cooling the apparatus including the combustion head  18  during use thereof. The plurality of longitudinal coolant channels  64  are spaced apart radially about the longitudinal axis X-X of the body portion  19  and extend throughout the length of thereof. Each of the cooling channels  64  having a varying depth along the length thereof defining an arc  65  corresponding to the arcuate sidewalls  68  of the interior chamber  23  and extended portions  25 ,  25  thereof, (See  FIGS. 7 and 9 ) such that the sidewalls of the body portion  19  formed between the interior chamber and the plurality of cooling channels  64  are substantially uniform in wall thickness adjacent the interior chamber throughout the length of the body portion. 
   Referring to  FIG. 15 , the illustrated embodiment of the combustion head  18  includes a wall thickness of substantially the same dimension at the coolant channels  64  throughout the length of the combustion head. The illustrated embodiment of the combustion head  18  includes the following wall thicknesses at section D-D: 
   D-1=0.141 inches 
   D-2=0.105 inches 
   D-3=0.131 inches 
   D-4=0.088 inches. 
   Thus, in the illustrated embodiment, the sidewalls of the body portion  19  of the combustion head  18  formed between the interior chamber  23  and the plurality of longitudinal coolant channels  64  have a wall thickness in a range of about 0.088 inches to about 0.141 inches with an average wall thickness of about 0.116 inches. 
   In a more preferred embodiment of the present invention combustion head  18 , the wall thickness of the body portion  19  at the plurality of longitudinal coolant channels  64  averages approximately 0.125 inches. 
   The substantially uniform wall thickness of the body portion  19  at the longitudinal coolant channels  64  throughout the length thereof allow the combustion head  18  to be maintained at a more uniform operating temperature throughout the mass thereof when compared to prior art combustion heads having much greater variances in the wall thicknesses thereof. 
   Additionally, the circumferential coolant channels  66  defined by the outer surface of the present invention combustion head  18  further add to the surface area of the outer surface of the combustion head thereby increasing the effect of a coolant passing over the combustion head and allowing the combustion head to operate at lower temperatures than prior art combustion heads. The circumferential coolant channels  66  of present invention combustion head  18  provide an increased heat transfer coefficient for the present invention combustion head compared to prior art combustion heads. 
   Referring again to  FIG. 10 , the longitudinal coolant channels  64  of the present invention extend at the first end  40  of the body portion proximate to a shoulder  70  formed around a base of the end portion  38  of the inlet  42  of the material feed conduit  36 . The shoulder  70  maintains a space between an inner surface of the housing  12  and the first end  40  of the combustion head when the combustion head is mounted in the housing  12  so that a coolant can pass therebetween. 
   In the combustion head  18  of the present invention, the end of the coolant channels  64  near the inlet  42  of the material feed conduit  36  ensure that coolant directly contacts the shoulder  70  formed around the end portion  38  of the material feed conduit. Thus, the shoulder  70  and end portion  38  are maintained at lower operating temperatures than prior art combustion heads wherein the coolant channels do not extend proximate a shoulder of the inlet of the material conduit. Due to the cooler operating temperatures of the end portion  38  of the present invention combustion head, a seal  72  (See  FIGS. 3 and 11 ) disposed between the end portion  38  and the housing  12  is also maintained at lower operating temperatures when used with the present invention combustion head  18  compared to that of the prior art. Accordingly, a seal  72  which often fails due to heat damage in flame spray apparatus employing prior art combustion heads lasts longer and fails less when used with the present invention combustion head. This further adds to the efficiency of the present invention combustion head  18  over those of the prior art. 
   The flame spray apparatus  10  equipped with the present invention combustion head  18  is used to apply a coating material to a workpiece. In operation, a continuous supply of pressurized fuel mixed with oxygen is ignited in the combustion chamber  20  such that hot pressurized combustion gases discharged from the outlet  26  of the combustion chamber enter the interior chamber  23  of the body portion  19  of the combustion head  18  via the combustion head opening  24 . The combustion gases entering the combustion head  18  are forced through the gas conduits  27  and exit through the nozzle  21  of the apparatus at a high velocity. Simultaneously, a supply of pressurized coating material is projected through the material conduit  36 . 
   Upon exiting the combustion head  18  through the nozzle  21 , the coating material is enveloped by the combustion gases exiting the gas conduits  27  which propel the coating material through the throat of the nozzle. 
   The foregoing description of embodiments of the present invention have been presented for the purpose of illustration and description and are not intended to be exhaustive or to limit the invention to the form disclosed. Obvious modifications and variations are possible in light of the above disclosure. The embodiments described were chosen to best illustrate the principals of the invention and practical applications thereof to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.