Abstract:
A multiple-piece seal is used for a cure oven circulating fan. The seal may be readily positioned along the length of the shaft to control the small clearance between the rotating seal and the oven such that there is no contact between the seal and the oven, but the flow of heated air from the oven is substantially reduced and redirected away from the bearings of the circulating fan. The multiple-piece design permits seal replacement without having to disassemble the shaft, so that the seal may be replaced entirely from the outside of the oven, saving substantial down-time.

Description:
This application claims priority from U.S. Provisional Patent Application Serial No. 60/297,227 filed on Jun. 8, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to seals, and in particular to a seal for use on a shaft of a circulating fan in a paint cure oven. 
     Modem automobile and truck body protective coatings are applied as the body passes through a series of coating dip and spray booths and ovens. Coatings are set or initially cured in ovens that include the radiant heat type. Radiant heat ovens have a conveyor that runs the length of the oven to allow the bodies to move from one end of the oven to the other. Radiant heating is achieved by burning natural gas in an interior plenum to the oven. The inner oven side surfaces along the length of conveyor are heated by natural gas. This heated surface then radiates heat toward the body to be cured as it travels along on the conveyor. 
     The oven can be composed of one or more zones (up to 7 is common), each of which can be temperature controlled. Zone heating is used to ensure the quality of the coating. Circulating fans are used to prevent stratification of the heated air in the oven. If stratification were to occur, it could cause variations in the coating cure, which would produce a product of unacceptable quality due to over-cured coatings on upper portions of a vehicle body (hotter) and under-cured coatings on lower portions and in recessed areas of a vehicle body (cooler). Efficient oven operation is obtained with continuous and extended operation, which increases the need for ease of maintenance. Oven temperatures can range from ambient to over 350° F. 
     The circulating fan includes a shaft-mounted impeller, which is driven by an electric motor using V-belts and sheaves. The shaft position is maintained by roller bearings, with the motor, belts, sheaves and bearings all supported on a common frame which is secured to the top of the oven. The fan impeller and part of the fan shaft extend vertically through the top of the oven, with the fan shaft passing through a pipe that is secured to, and extends above, the top of the oven. The outer shell of the oven is insulated for thermal efficiency and to prevent damage to various parts. 
     The pipe through which the fan shaft enters the oven acts as a chimney, drawing hot air from inside the oven and directing it upwardly where the hot air contacts the bearings, drying out the lubricant in the bearings and leading to premature failure. Also, any dirt flying around the shaft area, such as wear pieces from the V-belt drive, may fall through the clearance gap between the shaft and the pipe and into the oven area, possibly contaminating the finish on the pieces being cured inside the oven. 
     SUMKARY OF THE INVENTION 
     The present invention proposes the use of a split-boot seal which clamps around the shaft and caps off the pipe through which the shaft extends, substantially reducing the release of heat from the oven. 
     The seal of the present invention also redirects the flow of heated air which does escape from the oven via the pipe so that the heated air is no longer directed onto the bearings, thus further increasing the life of the bearings on the fan drive. 
     The seal of the present invention is of a two-piece design so it may be readily replaced from outside of the curing oven simply by releasing a clamp, removing the old seal halves, installing new seal halves, and reinstalling the clamp. This seal replacement takes minutes to complete, compared with the hours required to replace a traditional seal which involves entering the confined space of the main oven cavity to disassemble the shaft (and consequently the need to cool down the oven completely before any replacement work can be started). 
     The ease with which the seal of the present invention may be replaced, the fact that this seal substantially reduces the escape of heated air from the oven, and the fact that the heated air which does escape is effectively directed, by the seal, away from the bearings, results in cooler running bearings and permits the use of standard, off-the-shelf bearings instead of special, high temperature bearings for this application. 
     The seal of the present invention is secured to the fan shaft using a clamp and is located directly above the pipe passing through the oven. There is a gap between the seal and the top of the oven such that the seal does not contact any stationary oven part when the fan is in operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic, sectional view of a paint curing oven made in accordance with the present invention. 
     FIG. 2 is a broken away, sectional view of the seal area of FIG. 1; 
     FIG. 3 is an exploded, perspective view of the seal of FIG. 2; and 
     FIG. 4 is an assembled, perspective view of the seal of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a sectional view of a paint curing oven  10  including a conveyor  12  that runs the length of the oven to move components  14  from one end of the oven  10  to the other. The inner oven side surfaces  16  along the length of the conveyor  12  are heated, typically by natural gas burners, and this heat is then radiated toward the components  14  to be cured as they travel along the conveyor  12 . Circulating fans  18  are used to prevent stratification of the air inside the oven  10 . Since warm air naturally rises, without the circulating fan  18 , cooler air would settle at the bottom of the oven  10 , resulting in under-curing of the protective coating in this area, and warmer air would rise to the top of the oven  10 , resulting in over-curing of the protective coating in this area. 
     The fan  18  includes a shaft  20  which enters the oven  10  through an opening  22  created by a hollow pipe  24  which extends through the top wall  26  of the oven  10 . A portion  28  of the pipe  24  extends and projects above the top wall  26  of the oven  10  (as shown in FIG.  2 ). A two-piece, split-boot seal  30  is secured to the shaft  20  and caps the projecting portion  28  of the pipe  24  as will be discussed shortly. Outside the oven  10 , the shaft  20  is rotationally supported by bearings  32 . A V-belt drive arrangement  34  links the shaft  20  to a motor  36 , which drives the shaft  20  and the fan  18 . The motor  36 , the V-belt drive  34 , and the bearings are mounted in a housing  37 . 
     Referring now to FIG. 3, the seal  30  is shown in more detail. The seal  30  includes two symmetrical half sections  40  which, when secured with a suitable clamp  42 , form a seal having a substantially circular cross-section. Once assembled (See FIG.  4 ), the interior surface of the seal  30  defines a first, smaller diameter cylindrical section  44 , which is connected via a flange  46  to a second, larger diameter cylindrical section  48 . The first cylindrical section  44  has an inside surface  50  with a nominal inside diameter which is substantially equal to the outside diameter of the shaft  20 . The outside surface of this first cylindrical section  44  includes an annular indentation  54  between two projections  56 ,  58 . This indentation  54  receives the clamp  42  such that, when the seal halves  40  are assembled onto the shaft  20  to form the seal  30 , the clamp  42  holds the seal halves  40  together and further clamps the seal  30  onto the shaft  20 , sealing against any flow of heated air axially along the shaft  20 . 
     The larger diameter interior cylindrical section  48  has a larger inside diameter than that of the smaller diameter cylindrical section  44 . The inside diameter of the larger diameter cylindrical section  48  is slightly larger than the outside diameter of the pipe  24 , and the seal  30  is positioned on the shaft  20  such that this larger diameter section  48  forms a skirt  60  around the top portion  28  of the pipe  24 , as shown in FIG.  2 . The length of the skirt  60  is preferably approximately equal to the height of the top portion  28  of the pipe  24  that extends above the top wall  26  of the oven  10 , so that the large diameter section  48  encloses most of the top portion  28  of the pipe  24 . 
     The placement of the seal  30  along the shaft  20  is adjustable by loosening the nut  43 A from the bolt  43  of the clamp  42  and sliding the seal  30  down along the shaft  20  until there is only a small clearance between the bottom of the skirt  60  and the top wall  26  of the oven  10 , and then re-tightening the clamp  42  with the nut and bolt  43 A,  43  respectively. In this position, and if the length of the skirt  60  is approximately equal to the height of the top portion  28  of the pipe  24  extending above the top wall  26  of the oven  10 , then there will also be a small clearance between the top end of the pipe  24  and the inside surface  46 A of the flange  46  of the seal  30 . Any heated air traveling axially upwardly along the toroidal opening  22  between the shaft  20  and the pipe  24  is forced to make a 90° turn and travel radially outwardly along the first clearance between the top end of the pipe  24  and the inside surface  46 A of the flange  46  of the seal  30 . The heated air is then forced to make another 90° turn to travel axially downwardly between the skirt  60  of the seal  30  and the outside of the pipe  24 . Finally, the heated air must make yet another 90° turn to travel radially outwardly along a second clearance between the bottom of the skirt  60  of the seal  30  and the top wall  26  of the oven  10 . 
     By adjusting the location of the seal  30  on the shaft  20  such that there is a very small clearance between the bottom of the seal&#39;s skirt  60  and the top wall  26  of the oven  10 , the seal will be free to rotate with the shaft  20  without contacting any stationary part of the oven  10 . At the same time, the very small clearances between the seal  30  and the top of the pipe  24  and also between the seal  30  and the top wall  26  of the oven  10  result in a substantial reduction in the amount of heated air allowed to escape from inside the oven  10 . Finally, any heated air that does escape past the seal  30  is being directed downwardly and outwardly, away from the bearings  32 . 
     Replacement of the seal  30  is very easy, since the entire seal assembly  30  is located outside of the oven  10 , and the two piece design of the seal  30  means that it can be replaced without having to disassemble the shaft  20 , bearings  32 , drive  34 , and so forth. The nut  43 A, bolt  43 , and the clamp  42  are loosened and removed, and the symmetrical half sections  40  are then readily removable without having to disassemble the shaft. Prior art seals used in is similar applications are of the one-piece design, requiring entering the confined area inside the oven  10  to remove the impeller  18  from the shaft  20 , disconnect the V-belt drive  34 , and remove the shaft  20  so that the old one-piece seal may be slid off and the new seal may be slid onto the shaft  20 , all of which is very time consuming. Thus, the present invention significantly reduces both the labor cost and time required for maintenance to service or replace the seal as part of normal use and operation and permits ease of removal for cleaning and inspection. It also removes the need for confined-space entry, thus improving safety. Finally, since the amount of heated air escaping the oven  10  is substantially reduced, and the heated air which does escape is directed axially away from the bearings  32 , the bearings  32  used may be standard off-the-shelf bearings  32  instead of specialty, high-temperature bearings. 
     The seal  30  is preferably manufactured from a material such as Rulon™ (a high temperature Teflon™) or steel. 
     It will be obvious to those skilled in the art that modifications may be made to the embodiment described above without departing from the scope of the invention as claimed.