Abstract:
A flow-through dryer for drying webs of material comprising a rotatable drying drum having a cylindrical drum face and section flanges on the drum ends that enclose an interior space. The drum face is configured as a series of spaced pleated vent plates mounted circumferentially about the outside of drying drum. The pleated vent plates are perforated to allow air flow into the interior space and have an outer edge that is adapted to support the web of material about the drying drum.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a flow-through dryer drum used in paper, non-woven and textile manufacturing. More particularly, it relates to a structure that contains a porous vacuum drum over which webs of material (paper, non-wovens, textiles) pass over a rotating drum. As the drum rotates, air is blown and/or vacuumed through the web of material passing through the dryer or curing purposes. The air may be heated, cooled, or ambient temperature.  
       BACKGROUND OF THE INVENTION  
       [0002]     In many paper-making machines, through-air dryer units are used for evaporative drying of a web of paper. Through-air units may be used on the paper web after or instead of other drying devices, such as Yankee dryers or other pressing devices. Flow-through dryers have been used in past paper or textile manufacturing processes.  
         [0003]     Typically, a flow-through dryer unit  10 , such as the one of the present invention shown in  FIG. 1 , includes a hollow, rotating drying drum  12  having a porous or foraminous cylindrical drum face  14  around which the wet web  16  of paper is partially wrapped as the web is passed through the unit.  
         [0004]     The paper web can either be supported on a continuous fabric  18  or the vacuum drum itself could be covered with a very porous material. A continuous fabric system  18  typically has a plurality of guide rolls  20  about which the fabric  18  is looped for guiding the fabric  18  about a continuous path. The fabric  18  contacts the outer surface of the drum face  14  and guides the web  16  through the flow-through dryer unit  10 . An air supply hood  22  surrounds the portion of the drying drum  12  about which the fabric  18  and web  16  are wrapped and supplies heated, cooled, or ambient air through the fabric  18  and web  16  and through the drum face  14  into an interior volume  24  of the drum  12 . The supply hood  22  is formed of two halves that are movable away from each other by a wheeled track so that the drum  12  can be accessed for service and cleaning.  
         [0005]     Heated, cooled, or ambient air from the supply hood  22  passes through the porous drum face  14  and through the web  16  and fabric  18  so as to cause evaporative drying of the web or cooling of the web. An exhaust vacuum system  26  often located either on the bottom portion of the drum  12  (opposite the supply hood  22 ) or, preferably, on the ends of the drum  12  then exhausts air from the drum  12 .  
         [0006]     In certain past drying drums, the drum face  14  was of a honeycomb design. Such past drying drums are relatively heavy, expensive, difficult to manufacture, and are insufficiently porous. The honeycomb design subtracts from the open surface area of the outer surface such that the surface is only 70-80% open to through-air flow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is an end view of the preferred embodiment of a flow-through dryer unit.  
         [0008]      FIG. 2  is a partially exploded, perspective view of a preferred embodiment of the flow-through dryer drum of the invention.  
         [0009]      FIG. 3  is an inside perspective view of a single quadrant of a preferred embodiment of the flow-through dryer drum.  
         [0010]      FIG. 4  is a cross-sectional detail view of the flow-through dryer drum taken from circle  4  of  FIG. 2 .  
         [0011]      FIG. 5  is a perspective view of a preferred embodiment of a single pleated vent plate of the invention.  
         [0012]      FIG. 6  is a side-view of the preferred embodiment of a single pleated vent plate of the invention.  
         [0013]      FIG. 7  is an end view of the preferred embodiment of a single pleated vent plate of this invention.  
         [0014]      FIG. 8  is a detailed view of the preferred embodiment of a single pleated vent plate taken along circle  8  in  FIG. 6 .  
         [0015]      FIG. 9  is a detailed perspective of the underside of a central portion of the flow-through dryer drum.  
         [0016]      FIG. 10  is a detailed perspective view of the underside of an end portion of the flow-through dryer drum. 
     
    
     DETAILED DESCRIPTION  
       [0017]     A preferred embodiment of the flow-through dryer  12  of the invention is shown in  FIG. 2 . The drum  12  is divided up into four generally identical sections or quadrants  28  as shown more clearly in  FIG. 3 . If a portion of the drum is damaged, at most only one section  28  needs to be replaced. In addition, the drum  12  is easier to manufacture when it is formed of sections. Each end of each section  28  includes an outer radially extending flange  30 . The sections  28  are held together via bolt connections between the flanges  30  and circular end plates  32  that cover opposite ends of the drum  12 .  
         [0018]     The end plates  32  have several circular cutouts. The center cutout journals a drive shaft so that the drum  12  is rotatable about its central axis. The other three cutouts may be used as an access holes for servicing and cleaning.  
         [0019]     As shown best in  FIG. 4 , a series of equally-spaced pleated vent plates  34  are mounted circumferentially along the outside of the drum  12  and between the section flanges  30 . As shown in  FIGS. 5-7 , each pleated vent plate  34  is a perforated  36  plate formed in the shape shown in  FIG. 7 . Preferably, each plate  34  may be comprised of 14-gauge stainless steel perforated  36  such that at least 40-60% of the plate area is open, without compromising the material strength, and formed into the desired shape. Many other cutout patterns  36  could be used and the percentage of open area could also vary as long as the material strength is not compromised.  
         [0020]     As shown in  FIG. 7 , the plates  34  include a base section  38  and a skirt  40 , and, as shown in  FIGS. 5 and 6 , an end portion  42 . The skirt  40  portion includes a series of spaced annular cutouts  44 . Except for the annular cutouts  44  in the skirt  40 , the skirt and the end portions are non-perforated. The non-perforated areas help mount the pleated vent plates  34  to the drum  12 . In addition to skirts  40  and end portions  42 , tips  46  of the plates  34  could be non-perforated so wear of fabric  18  could be minimized. Moreover, if flow-through dryer unit  10  were operated without the use of fabric  18 , tips  46  may preferably be non-perforated so as to limit damage to the web.  
         [0021]     The series of pleated vent plates  34  are mounted circumferentially along the outside perimeter of the drum  12 . The continuous fabric upon which the web  16  rides typically only contacts the drum face  14  at the tips  46  of the plates  34 . Preferably, as shown in  FIGS. 9 and 10 , a circumferential gap of about ⅜″ remains between the base portions  38  of adjacent pleated vent plates  34  when they are welded or otherwise fastened to the sections  30  along the non-perforated end portions  42 . Alternatively, the gap could be eliminated by either positioning the pleated vent plates against each other or by forming the pleated vent plates from a continuous sheet (i.e., making the series of plates integral formed with each other).  
         [0022]     As shown by the airflow arrows in  FIG. 4 , the perforated plates and the gaps therebetween create a large number of airflow paths for air to flow in or out of the interior  24  of the drum  12 . Air may flow through the perforations  36  in the plates  34  or through the gaps between the plates. The drum construction creates a corrugated or pleated structure that increases the open-air surface area of the drum face  14  over the honeycomb designs of the prior art. By pleating the perforated plates, five objectives are achieved simultaneously. First, the combined surface area is more than doubled, thereby increasing the total effective open surface area from about 60% to 120% as compared to the flat circumferential surface area. Second, the pleated design makes the drum strong. Third, the pleated design makes the drum much easier and cheaper to manufacture than past honeycomb designs. Fourth, if damaged the drum can be inexpensively repaired on-site. Finally, this pleated design can be assembled on-site in, for instance, a paper mill quickly, easily, and inexpensively. This is a benefit because some honeycombs can be 14-18 feet in diameter and require special and expensive shipping considerations. This can be extremely expensive as paper machines are located throughout the world. The honeycomb cannot be assembled on-site like the present invention can.  
         [0023]     In addition, the shape of the perforated plates helps prevent one end plate  32  from rotating relative to the other plate  32 . The perforated plates  34  are much lighter than past honeycomb designs. With decreased weight, the material and operating costs of the drum  12  are also reduced.  
         [0024]     As stated above, a preferred cross-section of the pleated vent plate is shown in  FIG. 7 . Many different cross-sectional shapes are suitable, including an inverted V, U, W, Y, etc. These shapes provide an outer edge to support the web while maintaining perforated sides that extend inward (towards the cylinder center) and outward (circumferentially away from the outer edge).  
         [0025]     The plates  34  are supported radially by a series of circular hoops  50  spaced axially along the length of the plates. Preferably, the hoops  50  are welded to the skirts  40  of the plates  34  within the annular cutouts  44 . The hoops are preferably formed of stainless steel rods ½″ in diameter. Other means besides the hoops  50  could be used to provide radial support to the plates  34  to hold the tips at a consistent radius from the center axis of the drum  12 . For instance, the plates could be connected together to provide radial support or another structure could be used to interconnect plates for this same purpose.  
         [0026]     As stated above, an exhaust vacuum system  26  is often located either on the bottom portion of the drum  12  (opposite the supply hood  22 ), as shown in  FIG. 1 , or on the ends of the drum  12 . The exhaust system  26  exhausts air from the drum  12 .  
         [0027]     It will be appreciated that the present invention can take many forms and embodiments. It is not intended that the embodiment of the invention presented herein should limit the scope thereof.