Abstract:
A convection oven that achieves a substantially enhanced degree of air flow through the use of a special nozzle design. Turbo flow air nozzles create an air flow pattern to provide higher velocity airflow with a smaller fan size and ductwork. The turbo flow air nozzles include main supply nozzles that direct high velocity air through air entrainment and mixing sections that entrain air from the oven interior to generate the increased air flow in a heat transfer zone of the oven. Appropriate ductwork is provided to direct air from a fan or fans to the supply nozzles to generate a high velocity air flow therethrough.

Description:
FIELD OF THE INVENTION 
   This invention pertains generally to ovens, particularly industrial convection ovens, and more particularly to systems and methods for enhancing air flow within such ovens. 
   BACKGROUND OF THE INVENTION 
   A variety of different industrial ovens are used for a variety of different purposes. For example, industrial ovens are used to cure powder painted steel sheets and other parts. In this application, and all others, it is necessary to keep the work piece within a desired temperature range for a desired period of time to achieve the desired result. If the work piece temperature is allowed to climb too high the work piece will be damaged. If the work piece temperature is too low or inconstant the work piece may not be cured properly, or at least the time required to cure the work piece, and thus the flow of work product through the oven, is reduced. Maintaining optimum work piece temperatures is made more complicated for certain work pieces, such as metal articles, which act as heat sinks affecting the oven temperature, often significantly. 
   Convection ovens use a fan or fans to re-circulate air in the oven to enhance the heating characteristics of the oven. Movement of heated air over the work piece to be heated enhances oven operating efficiency. It has been found that oven operating efficiency can be increased by increasing air flow velocity over the work piece. One way to achieve this result is to increase air flow throughout the oven. However, the fan size and ductwork needed to provide the required air velocity throughout an oven is often expensive and inefficient. 
   As an alternative, attempts have been made to increase air velocity in an oven specifically through a heat transfer zone of the oven where the work piece is to be placed or through which the work piece is to be moved. For example, some ovens have an air supply duct located in the bottom of the oven with air nozzles that discharge air upward over the work piece being heated in the heat transfer zone of the oven. Other ovens have two air supply ducts, one located in the upper corner on each side of the oven. High velocity nozzles are used to blow air vertically downward along the oven walls where it is then turned upward over the work piece being heated in the heat transfer zone. This design has proven effective in maintaining uniformity of both oven air temperature, and air velocity, across the work piece. It helps to even out the temperature rise of the entire work piece and to minimize flutter of suspended work pieces due to uneven air velocities. An additional benefit is that the oven walls are kept hot, reducing the tendency for condensation to build up. The high velocity nozzles used in this application are designed to induce a venturi effect that draws in a significant amount of the air inside the oven chamber. The result is that the volume of air passing through the work piece is much higher than the capacity of the circulation fans. This enhances temperature uniformity and heat transfer as well as reduces the electrical energy consumption of the circulation fan motors. However, the use of high velocity air nozzles alone is limited in that it does not provide control of the quantity and direction of air flow through the oven. 
   What is desired, therefore, is an improved convection oven that employs turbo flow air nozzles for increasing air flow through the heat transfer zone of the oven and a method of using such an oven to heat work pieces. 
   SUMMARY OF THE INVENTION 
   The present invention provides a convection oven, and method of using same, that achieves a substantially enhanced degree of air flow through the use of a turbo flow nozzle design. Ovens contemplated by the present invention may be used to dry powder coated paint on metal articles or for any other application. A convection oven in accordance with the present invention employs turbo flow air nozzles along with appropriate ductwork to create a specific air flow pattern to provide a high velocity airflow in a heat transfer zone with a smaller fan size and ductwork, and thus may be operated more efficiently than conventional industrial convection ovens. 
   A convection oven in accordance with the present invention employs turbo flow air nozzles that are positioned within the oven. For example, turbo flow air nozzles may be positioned near the top of the oven and to the sides of a heat transfer zone. Alternatively, the turbo flow air nozzles may be positioned at any desired location in the oven to create the desired enhanced air flow in the heat transfer zone. The turbo flow air nozzles include one or more main supply nozzles that direct high velocity air through air entrainment and mixing sections. For example, a plurality of conical main supply nozzles may be employed to direct high velocity air through a rectangular air entrainment and mixing section. Alternatively, main supply nozzles and air entrainment and mixing sections having other shapes may be used to form the turbo flow air nozzles. Appropriate ductwork may be provided to direct air from a fan or fans to the supply nozzles to generate a high velocity air flow therethrough. 
   During operation of a convection oven in accordance with the present invention convection airflow through a heat transfer zone is enhanced by the use of the turbo flow air nozzles. Airflow from a recirculation fan flows through a supply duct to the one or more supply nozzles to produce a high velocity air flow that flows through the air entrainment and mixing section, turns and flows through the heat transfer zone, and flows through a return path, e.g., via a return duct, back to the recirculation fan. Air from the interior of the oven is entrained by the high velocity air directed into the air entrainment and mixing section from the supply nozzles and flows through the air entrainment and mixing section, is directed through the main heat transfer zone, and then turns and flows back into the air entrainment and mixing section. 
   By re-circulating oven air through the heat transfer zone using turbo flow air nozzles in this manner, a convection oven in accordance with the present invention achieves increased air flow through the heat transfer zone using significantly less fan capacity than would be required to achieve the same air flow using conventional air flow nozzles alone. Thus, a less expensive and physically smaller air circulation fan system may be employed, taking up less space in the facility where the oven is installed. Since the increased air flow provides better heat transfer to the work piece, lower temperature air may be used, reducing the risk of overheating the work piece. Also, better heat transfer can reduce the amount of time needed to bring the work piece to the desired temperature. If less time is needed, the overall oven size can be reduced. A smaller oven is less expensive, takes up less space in the facility where it is installed, and has less heat loss through its walls. All of these advantages of a convection oven with turbo flow air nozzles in accordance with the present invention result in a convection oven that is more efficient and less expensive to implement and to operate. 
   Further objects, features, and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a perspective view illustration of an exemplary convection oven in accordance with the present invention employing turbo flow air nozzles to increase airflow therethrough. 
       FIG. 2  is a perspective view illustration of an exemplary convection oven in accordance with the present invention as shown in  FIG. 1  illustrating air flows through the oven when in operation. 
       FIG. 3  is a more detailed perspective view illustration of the air flow through an exemplary turbo flow air nozzle employed in the exemplary convection oven in accordance with the present invention of  FIGS. 1 and 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An exemplary convection oven  10  in accordance with the present invention, incorporating turbo flow air nozzles to increase air flow therethrough, will be described in detail first with reference to  FIG. 1 . The present invention may be embodied in any otherwise generally conventional industrial convection oven design as used for the heating of any type of work piece for any desired purpose. For example, the present invention may be implemented in a conventional tunnel type oven, through which work pieces are moved in a continuous work flow, via conveyors supporting the work pieces from either above or below, or in tunnel or entirely enclosed ovens in which work pieces are placed in position for heating. Such ovens may be heated in any conventional manner. The present invention may be incorporated in all or any selected zones of an oven that includes, for example, one or more come-up zones, used to elevate the temperature of a work piece quickly and uniformly to a desired bake temperature, and one or more bake zones. In particular, the present invention has been found to be very useful for the effective and efficient curing of powder paint on sheet steel parts of various thickness. However, the present invention may be employed for the heating of any type of work piece where increased throughput and/or operating efficiency and reduced cost is desired. 
   A convection oven  10  in accordance with the present invention has an oven interior that is defined by at least side walls  12 , a top wall  14  and a bottom  16 . The walls  12 ,  14 , and  16  of the oven  10  may be formed in a conventional manner of conventional appropriate materials, such as sheet steel, and insulated appropriately to maintain heat in the oven  10 . The bottom  16  of the oven  10  may be a separate wall structure or simply a floor (typically concrete) of the building in which the oven  10  is placed for operation. A portion  18  of the oven  10  forms a heat transfer zone. In the exemplary oven  10  illustrated and described herein the heat transfer zone  18  is formed in the center of the oven. It should be understood, however, that heat transfer zones  18  may be located in other and various locations within a convection oven in accordance with the present invention. Work pieces are placed in or pass through the heat transfer zone  18  where, in accordance with the present invention, heat is transferred efficiently to the work piece to achieve a desired result, e.g., to cure the powder paint coating on a sheet steel product. 
   In accordance with the present invention, at least one turbo flow air nozzle  20  is provided within the oven  10 . In the exemplary convection oven  10  in accordance with the present invention illustrated and described herein, turbo flow air nozzles  20  are provided at or near the top  14  of the oven  10  and near the side walls  12  of the oven  10  and are directed in a generally downward direction. It should be understood, however, that turbo flow air nozzles  20  may be positioned anywhere within a convection oven  10  in accordance with the present invention, e.g., at the center top of the oven, on the sides of the oven, and/or in the bottom of the oven, and directed in any desired direction, e.g., downward, sideways, and/or upward, thereby to generate increased air flow at desired heat transfer zones  18  in the oven  10 . For example, for a convection oven in accordance with the present invention wherein a work piece is conveyed in a serpentine pattern back and forth through the oven, turbo flow air nozzles may be positioned near the top of the oven between each straight section of the serpentine conveyor and directed downward, thereby providing increase air flow in heat transfer zones extending along the length of the conveyor through the oven. 
   The turbo flow air nozzles  20  preferably include at least one high velocity air supply nozzle  22  and an air entrainment and mixing section  24 . The high velocity air supply nozzles  22  are positioned with respect to the air entrainment and mixing section  24  so as to direct air at a high velocity through the air entrainment and mixing section  24 . The air entrainment and mixing section  24  has closed side walls and an open first end  26  and open second end  28 . The open first end  26  of the air entrainment and mixing section  22  is positioned with respect to the air supply nozzles  22  such that high velocity air is directed into the open first end  26  of the air entrainment and mixing section  24  from the air supply nozzles  22 . The open first end  26  of the air entrainment and mixing section  24  also is in fluid communication with the interior of the oven  10  such that the open first end  26  of the air entrainment and mixing section  24  forms an air entrainment lead in section for air in the interior of the oven when in operation, as will be discussed in more detail below. 
   As illustrated, multiple adjacent conical air supply nozzles  22  may be used to provide high velocity air through a single elongated rectangular box shaped air entrainment and mixing section  24 . An outward extending flange  30 , e.g., extending outward from the walls of the air entrainment and mixing section  24 , may be formed around the open first  26  and second  28  ends of the air entrainment and mixing section  24 . Alternatively, each air entrainment and mixing section  24  may be supplied by a single air supply nozzle  22  that provides high velocity air therethrough. For example, a single elongated slot shaped air supply nozzle may be used to provide high velocity air through an air entrainment and mixing section  24  having an elongated rectangular box shape as illustrated herein. 
   It should be understood that the turbo flow air nozzles  20  employed in a convection oven  10  in accordance with the present invention may be formed differently from the nozzles  20  illustrated and described by example herein, as will be known to those skilled in the art. For example, the air supply nozzles  22  may be cylindrical, rather than conical, in shape. Each such cylindrical or conical air supply nozzle  22  may have its own associated cylindrical or conical shaped air entrainment and mixing section  24 . The air entrainment and mixing sections  24  may be separated into separate entrainment sections and mixing sections placed in series and in fluid communication with each other. The separate entrainment sections and mixing sections may have different shapes. For example, the entrainment section may have a conical shape, similar to the shape of the supply nozzles illustrated herein, with the corresponding mixing section having a cylindrical shape. 
   Air flow to the air supply nozzles  22  preferably is provided by a fan  32  via appropriate supply ducts  34 . The size, capacity and position of the fan  32  and supply ducts  34  with respect to the oven  10  will depend upon the specific position, number, and orientation of the turbo flow air nozzles  20  being employed as well as the desired oven operating temperature and air flow to be achieved in the established heat transfer zone or zones therein. For example, for an application as illustrated, with the turbo flow air nozzles  20  positioned near the top  14  and side  12  walls of the convection oven  10 , the supply ducts  34  preferably may be run along the top  14  of the oven, near the side walls  12  thereof. 
   Return air is drawn from the interior of the oven via an appropriate return path. For example, return air may be drawn by the fan  32  from the interior of the oven  10  via a return duct  36 . For the exemplary application of the invention as illustrated herein, the return duct  36  may be positioned at the top  14  of the interior of the oven  10  near the center thereof, i.e., above the heat transfer zone  18 . The return duct  36  is in fluid communication with the interior of the oven  10  via a plurality of appropriate apertures  38  therein. Different or other return paths for the return air from the oven  10  may be established to achieve a desired air circulation pattern in the oven  10 . 
   Improved air flow through the exemplary convection oven  10  in accordance with the present invention as illustrated in  FIG. 1  now will be described in more detail with particular reference to the illustrations of  FIGS. 2 and 3 . During operation, the oven  10  is heated to the desired operating temperature and is maintained at the desired temperature using conventional oven temperature control and feedback systems. A work piece to be heated may be positioned in or passed through the heat transfer zone  18  of the oven  10 . 
   With the fan  32  in operation, supply air  50  is provided via the supply ducts  34  to the supply nozzles  22  of the turbo flow air nozzles  20 . This supply air  50  is directed at a high velocity into the open first end  26  of the air entrainment and mixing section  24  and through the air entrainment and mixing section  24 . Air from the interior of the oven  10  is entrained  52  by the turbo flow air nozzles  20  as the high velocity air flow through the air entrainment and mixing section  24  draws air from the interior of the oven  10  into the open first end or entrainment lead in section  26  of the air entrainment and mixing section  24 . Note that the turbo flow air nozzles  20  preferably may be positioned in the interior of the oven  10  such that air is drawn from all directions into the entrainment lead in section  26  of the air entrainment and mixing section  24 . This entrained air  52  is thus mixed in the air entrainment and mixing section  24  with the supply air  50  from the supply nozzles  22 . 
   The mixed  54  entrained  52  and supply  50  air flows out of the second open end  28  of the air entrainment and mixing section  24  in this case downward toward the bottom  16  of the oven  10 . The mixed air  54  is directed upward from the bottom  16  of the oven through the heat transfer zone  18 , around the work piece to be heated, and then turns and flows back into the air entrainment and mixing section  24  as entrained air  52 . Some of the mixed air  54  flowing upward through the heat transfer zone  18  is drawn as return air  56  into the return duct  36 , to be redirected by the fan  32  through the supply nozzles  22  as supply air. 
   A convection oven  10  employing turbo flow air nozzles  20  in accordance with the present invention thus provides increased air flow to a work piece positioned in the heat transfer zone  18  of the oven  10 . This provides for more efficient, rapid, and better controlled heating of the work piece, thereby increasing work piece throughput. The operating temperature of the oven, fan operating speed, and air flow speed and volume through the turbo flow air nozzles all may be selected to achieve the desired oven operating conditions required for the work piece processing operation to be performed in the oven. The ratio of air flow  54  out of the turbo flow nozzle  20  to supply air  50  provided by the fan  32  through the supply nozzles  22  is equal approximately to the square root of the ratio of turbo flow nozzle flow area to supply nozzle flow area. Thus, the degree of enhanced air flow in the heat transfer zone  18  of the oven  10  can be selected based on selecting the relative parameters of the components of the turbo flow nozzles  20  used and can be achieved using significantly less fan capacity than can be achieved using conventional high velocity air supply nozzles alone. 
   It should be understood that a convection oven  10  employing turbo flow air nozzles  20  in accordance with the present invention may employ various other different or similar conventional systems, fans, nozzles, ductwork, etc. from those illustrated and described in detail herein for providing improved air flow through the interior of the oven  10 . For example, alternative embodiment components of a convection oven  10  in accordance with the present invention are illustrated in dashed lines in  FIG. 1 . In one exemplary alternative embodiment, conventional air nozzles  60  are provided in the bottom  16  of the oven  10  (only a few exemplary conventional nozzles  60  are illustrated in  FIG. 1 .) Air flow from the fan  32 , via an appropriate air supply duct  62 , may be directed upward through the heat transfer zone  18  from these conventional air nozzles  60 , further to increase air flow through the oven  10 . In a further alternative embodiment, a separate fan  64  may be used to direct air through the conventional nozzles  60  located in the bottom  16  of the oven. In this case, a return duct  66  for the air flow passing through the turbo flow nozzles  20  may be located in the bottom  16  of the oven  10 . Thus, the mixed air flow  54  from the bottom  16  of the oven  10  may not include the air flow passing the supply nozzles  22 . The air flow passing through the return duct  66  does not pass through the heat transfer zone  18 . 
   It should be understood that the present invention is not limited to the particular exemplary applications and embodiments illustrated and described herein, but embraces all such modified forms thereof as come within the scope of the following claims.