Patent Publication Number: US-6986812-B2

Title: Slurry feed apparatus for fiber-reinforced structural cementitious panel production

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to co-pending applications U.S. Ser. No. 10/666,294 entitled MULTI-LAYER PROCESS AND APPARATUS FOR PRODUCING HIGH STRENGTH FIBER-REINFORCED STRUCTURAL CEMENTITIOUS PANELS and U.S. Ser. No. 10/665,541 entitled EMBEDMENT DEVICE FOR FIBER-ENHANCED SLURRY, filed concurrently herewith and herein incorporated by reference. 
   FIELD OF THE INVENTION 
   This invention relates to a continuous process and related apparatus for producing structural panels using a settable slurry, and more specifically, to a slurry feeder apparatus used in the manufacture of reinforced cementitious panels, referred to herein as structural cement panels (SCP), in which fibers are combined with a quick-setting slurry for providing flexural strength. 
   Cementitious panels have been used in the construction industry to form the interior and exterior walls of residential and/or commercial structures. The advantages of such panels include resistance to moisture compared to standard gypsum-based wallboard. However, a drawback of such conventional panels is that they do not have sufficient structural strength to the extent that such panels may be comparable to, if not stronger than, structural plywood or oriented strand board (OSB). 
   Typically, the cementitious panel includes at least one hardened cement or plaster composite layer between layers of a reinforcing or stabilizing material. In some instances, the reinforcing or stabilizing material is fiberglass mesh or the equivalent. The mesh is usually applied from a roll in sheet fashion upon or between layers of settable slurry. Examples of production techniques used in conventional cementitious panels are provided in U.S. Pat. Nos. 4,420,295; 4,504,335 and 6,176,920, the contents of which are incorporated by reference herein. Further, other gypsum-cement compositions are disclosed generally in U.S. Pat. Nos. 5,685,903; 5,858,083 and 5,958,131. 
   One drawback of conventional processes for producing cementitious panels is that the fibers, applied in a mat or web, are not properly and uniformly distributed in the slurry, and as such, the reinforcing properties resulting due to the fiber-matrix interaction vary through the thickness of the board, depending on the thickness of each board layer. When insufficient penetration of the slurry through the fiber network occurs, poor bonding between the fibers and the matrix results, causing low panel strength. Also, in some cases when distinct layering of slurry and fibers occurs, improper bonding and inefficient distribution of fibers causes poor panel strength development. 
   Another drawback of conventional processes for producing cementitious panels is that the resulting product is too costly and as such is not competitive with outdoor/structural plywood or oriented strand board (OSB). 
   One source of the relatively high cost of conventional cementitious panels is due to production line downtime caused by premature setting of the slurry, especially in particles or clumps which impair the appearance of the resulting board, and interfere with the efficiency of production equipment. Significant buildups of prematurely set slurry on production equipment require shutdowns of the production line, thus increasing the ultimate board cost. 
   An important target area for reducing cementitious panel production line downtime due to premature setting is in the deposition or feeding of the slurry upon a moving web. In conventional cementitious panel production lines, the moving web includes a connected mat or layer of reinforcing fibers. In some applications, the slurry and/or fibers are sprayed upon the moving web. This system raises issues of maintenance of the spray equipment, since nozzles and pressure lines must be periodically purged of preset slurry particles. Also, this system risks uneven deposition of slurry due to the force and spacing of the spray heads. 
   An alternative conventional system for feeding cementitious slurry upon a moving web involves the use of a nip roll feeder. Counter-rotating rollers forming a nip create a reservoir for slurry, which migrates along an underside of one nip-forming roll to a feed roller. This arrangement carries with it the potential problem of slurry droplets prematurely falling upon the web from the underside of the nip roll, causing unwanted premature setting particles and uneven constitution of the finished cementitious panel. In addition, the thickness of the layer of slurry deposited upon the web can be uneven and difficult to control with this type of configuration. Further, this arrangement is believed to foster the collection of prematurely set particles of slurry, which require system shutdown for cleaning. 
   Thus, there is a need for a slurry feed device which is particularly useful in the feeding of cementitious, and /or gypsum-cement slurries of the type used in the production of cementitious construction panels. There is also a need for such a feed device in which the collection and/or clogging of prematurely set gypsum particles is prevented. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The above-listed needs are met or exceeded by the present invention that features a slurry feed apparatus for use in a SCP panel production line or the like application where settable slurries are used in the production of building panels or board. The present apparatus includes a main metering roll and a companion roll placed in close, generally parallel relationship to each other to form a nip in which a supply of slurry is retained. Both rolls preferably rotate in the same direction so that slurry is drawn from the nip over the metering roll to be deposited upon a moving web of the SCP panel production line. A thickness control roll is preferably provided in close operational proximity to the main metering roll for maintaining a desired thickness of the slurry. 
   It is also preferred that the thickness control roll rotates in the same direction as the main and companion rolls. 
   More specifically, the invention provides a feed apparatus for use in depositing a slurry upon a moving web having a direction of travel, and includes a main metering roll and a companion roll disposed in closely spaced relation to the metering roll to form a nip therebetween. The nip is constructed and arranged to retain a supply of the slurry, and the rolls are driven so that slurry retained in the nip progresses over an upper outer peripheral surface of the metering roll to be deposited upon the web. 
   In another embodiment, a feed apparatus is provided for use in depositing a slurry upon a moving web having a direction of travel. The apparatus includes a main metering roll, a companion roll disposed in closely spaced relation to the metering roll to form a nip therebetween. The rolls are disposed generally transversely to the direction of travel of the web. Also, the nip is constructed and arranged to retain a supply of the slurry, and a thickness control roll is disposed in operational relationship to the metering roll for controlling the thickness of a layer of slurry drawn from the nip upon an outer surface of the metering roll. A drive system is provided for driving the metering roll, the companion roll and the thickness control roll in the same direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic elevational view of a SCP panel production line suitable for use with the present slurry feed device; 
       FIG. 2  is a fragmentary enlarged elevational view of the feed device depicted in  FIG. 1 ; and 
       FIG. 3  is a perspective view of the present slurry feed apparatus. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1 , a structural panel production line is diagrammatically shown and is generally designated  10 . The production line  10  includes a support frame or forming table  12  having a plurality of legs  13  or other supports. Included on the support frame  12  is a moving carrier  14 , such as an endless rubber-like conveyor belt with a smooth, water-impervious surface, however porous surfaces are contemplated. As is well known in the art, the support frame  12  may be made of at least one table-like segment, which may include designated legs  13  or other support structure. The support frame  12  also includes a main drive roll  16  at a distal end  18  of the frame, and an idler roll  20  at a proximal end  22  of the frame. Also, at least one belt tracking and/or tensioning device  24  is preferably provided for maintaining a desired tension and positioning of the carrier  14  upon the rolls  16 ,  20 . In the preferred embodiment, the SCP panels are produced continuously as the moving carrier proceeds in a direction ‘T’ from the proximal end  22  to the distal end  18 . 
   Also, in the preferred embodiment, a web  26  of craft paper, release paper, and/or other webs of support material designed for supporting a slurry prior to setting, as is well known in the art, may be provided and laid upon the carrier  14  to protect it and/or keep it clean. However, it is also contemplated that the SCP panels produced by the present line  10  are formed directly upon the carrier  14 . In the latter situation, at least one belt washing unit  28  is provided. The carrier  14  is moved along the support frame  12  by a combination of motors, pulleys, belts or chains which drive the main drive roll  16  as is known in the art. It is contemplated that the speed of the carrier  14  may vary to suit the application. 
   In the present invention, structural cement panel production is initiated by depositing a layer of loose, chopped fibers  30  upon the web  26 . A variety of fiber depositing and chopping devices are contemplated by the present line  10 , however the preferred system employs a rack  31  holding several spools  32  of fiberglass cord, from each of which a length or string  34  of fiber is fed to a chopping station or apparatus, also referred to as a chopper  36 . 
   The chopper  36  includes a rotating bladed roller  38  from which project radially extending blades  40 , and which is disposed in close, contacting rotating relationship with an anvil roll  42 . Preferably, the blades  40  extend the width of the carrier  14  or the web  26 . In the preferred embodiment, the bladed roller  38  and the anvil roll  42  are disposed in relatively close relationship such that the rotation of the bladed roller  38  also rotates the anvil roll  42 , however the reverse is also contemplated. Also, the anvil roll  42  is preferably covered with a resilient support material against which the blades  40  chop the strands  34  into segments. The spacing of the blades  40  on the roller  38  determines the length of the chopped fibers. As is seen in  FIG. 1 , the chopper  36  is disposed above the carrier  14  near the proximal end  22  to maximize the productive use of the length of the production line  10 . As the fiber strands  34  are chopped, the fibers fall loosely upon the carrier web  26 . 
   Referring now to  FIGS. 1 and 2  next, the present slurry feed apparatus, also referred to as a slurry feed station, or a slurry feeder, generally designated  44  receives a supply of slurry  46  from a remote mixing location  48  such as a hopper, bin or the like. While a variety of settable slurries are contemplated, the present process is particularly designed for producing structural cement panels. As such, the slurry  46  is preferably comprised of varying amounts of Portland cement, gypsum, aggregate, water, accelerators, plasticizers, foaming agents, fillers and/or other ingredients well known in the art, and described in the patents listed above which have been incorporated by reference. The relative amounts of these ingredients, including the elimination of some of the above or the addition of others, may vary to suit the application. 
   The preferred slurry feeder  44  includes a main metering roll  50  disposed transversely to the direction of travel of the carrier  14 . A companion or back up roll  52  is disposed in close, parallel, rotational relationship to the metering roll  50  to form a nip  54  therebetween. The rolls  50 ,  52  are disposed in sufficiently close relationship that the nip  54  retains a supply of the slurry  46 , at the same time the rolls rotate relative to each other. While other sizes are contemplated, it is preferred that the metering roll  50  has a larger diameter than the companion roll  52 . Also, it is preferred that one of the rolls  50 ,  52  has a smooth, stainless steel exterior, and the other, preferably the companion roll  52  has a resilient, non-stick material covering its exterior. 
   A pair of relatively rigid sidewalls  56 , preferably made of, or coated with non-stick material such as Teflon® brand material or the like, prevents slurry  46  poured into the nip  54  from escaping out the sides of the slurry feeder  44 . The sidewalls  56 , which are preferably secured to the frame  12 , are disposed in close relationship to ends of the rolls  50 ,  52  to retain the slurry, however the sidewalls  56  are not excessively close to ends of the rolls to interfere with roll rotation. 
   An important feature of the present invention is that the feeder  44  deposits an even, relatively thin layer of the slurry  46  upon the moving carrier web  26 . Suitable layer thicknesses range from about 0.08 inch to 0.16 inch. However, with four layers preferred in the preferred structural panel produced by the production line  10 , and a suitable building panel being approximately 0.5 inch, an especially preferred slurry layer thickness is in the range of 0.125 inch. 
   To achieve a slurry layer thickness in the ranges described above, several features are provided to the slurry feeder  44 . First, to ensure a uniform disposition of the slurry  46  across the entire web  26 , the slurry is delivered to the feeder  44  through a hose  58  or similar conduit having a first end  60  in fluid communication with the slurry mixing tank or reservoir  48 . A second end  62  of the hose  58  is connected to a laterally reciprocating, cable driven, fluid-powered dispenser  64  of the type well known in the art. Slurry flowing from the hose  58  is thus poured into the feeder  44  in a laterally reciprocating motion to fill a reservoir  66  defined by the rolls  50 ,  52  and the sidewalls  56 . Rotation of the metering roll  50  draws a layer of slurry  46  from the reservoir  66 . 
   Next, a thickness control roll or thickness monitoring roll  68  is preferably disposed slightly above the main metering roll  50  and slightly downstream of a vertical centerline of the main metering roll to regulate the thickness of the slurry  46  drawn from the feeder reservoir  66  upon an outer surface  70  of the main metering roll  50 . Another related feature of the thickness control roll  68  is that it allows handling for slurries with different and constantly changing viscosities. As such, the thickness control roll  68  is located in operational relationship to the main metering roll  50  for regulating the thickness of the slurry carried from the reservoir  66  over the outer peripheral surface  70  of the main metering roll  50  for deposition upon the moving carrier web  26 . As is well known in the art, the relative distance ‘t’ ( FIG. 2 ) between the thickness control roll  68  and the main metering roll  50  may be adjusted to vary the thickness of the slurry  46  deposited. Also, while other sizes are contemplated, it is preferred that the thickness control roll  68  has a smaller diameter than the companion roll  52  and a substantially smaller diameter than the main metering roll  50 . 
   Another feature of the present feeder apparatus  44  is that the main metering roll  50 , the companion roll  52  and the thickness control roll  68  are all driven in the same direction, which minimizes the opportunities for premature setting of slurry on the respective moving outer surfaces. A drive system  72 , including a fluid-powered, electric or other suitable motor  74  is connected to the main metering roll  50  or the companion roll  52  for driving the roll(s) in the same direction, which is clockwise when viewed in  FIGS. 1–3 . As is well known in the art, either one of the rolls  50 ,  52  may be driven, and the other roll may be connected via pulleys, belts, chain and sprockets, gears or other known power transmission technology to maintain a positive and common rotational relationship. Further, the thickness control roll  68  is also configured to rotate in the same direction as the rolls  50 ,  52 , and this is preferably achieved through a connection to the drive system  72 , its own motor (not shown) or other arrangement well known to skilled practitioners, depending on the application. 
   As the slurry  46  on the outer surface  70  moves toward the moving carrier web  26 , it is important that all of the slurry be deposited on the web, and not travel back upward toward the nip  54 . Such upward travel would facilitate premature setting of the slurry on the rolls and would interfere with the smooth movement of slurry from the reservoir  66  to the carrier web  26 . To that end, a transverse stripping wire  76  is located between the main metering roll  50  and the carrier web  26  to ensure that the slurry  46  is completely deposited upon the carrier web and does not proceed back up toward the nip  54  and the feeder reservoir  66 . The stripping wire  76  also helps keep the main metering roll  50  free of prematurely setting slurry. 
   Referring now to  FIG. 3 , the reciprocating dispensing mechanism  64  will be explained in greater detail. The second end  62  of the hose  58  is retained in a laterally reciprocating fitting  78  which is connected at each of two sides  80 ,  82  to corresponding ends  84 ,  86  of cable segments  88 ,  90 . Opposite ends  92 ,  94  of the cable segments  88 ,  90  are connected to one of a blind end  96  and a rod  98  of a fluid power cylinder  100 , preferably a pneumatic cylinder. The cable segments  88 ,  90  are looped about pulleys  102  (only one shown) located at each end of the feeder apparatus  44 . The fluid power cylinder  100  is dimensioned so that the travel distance of the rod  98  approximates the desired length of travel of the dispensing fitting  78  in the reservoir  66 . As the cylinder  100  is pressurized/depressurized, the fitting  78  will reciprocate above and along the nip  54 , thus maintaining a relatively even level of the slurry  46  in the reservoir  66 . 
   Referring again to  FIG. 1 , the other operational components of the SCP panel production line will be described briefly, but they are described in more detail in co-pending, commonly assigned US. patent application Ser. No. 10/666,294 entitled, MULTI-LAYER PROCESS AND APPARATUS FOR PRODUCING HIGH STRENGTH FIBER-REINFORCED STRUCTURAL CEMENTITIOUS PANELS which has been incorporated by reference. 
   A second chopper apparatus  110 , preferably identical to the chopper  36 , is disposed downstream of the feeder  44  to deposit a second layer of fibers  112  upon the slurry  46 . Next, an embedment device  114  is disposed in operational relationship to the slurry  46  and the moving carrier web  26  of the production line  10  to embed the fibers  112  into the slurry  46 . 
   While a variety of embedment devices are contemplated, including, but not limited to vibrators, sheep&#39;s foot rollers and the like, in the preferred embodiment, the embedment device  114  includes at least a pair of generally parallel shafts  116  mounted transversely to the direction of travel of the carrier web  14  on the frame  12 . Each shaft  116  is provided with a plurality of relatively large diameter disks  118  which are axially separated from each other on the shaft by small diameter disks (not shown). During board production, the shafts and the disks  118  rotate together about the longitudinal axis of the shaft  116 . As is well known in the art, either one or both of the shafts  116  may be powered, and if only one is powered, the other may be driven by belts, chains, gear drives or other known power transmission technologies to maintain a corresponding direction and speed to the driven shaft. The respective disks  118  of the adjacent, preferably parallel shafts  116  overlap and are intermeshed with each other for creating a “kneading” or “massaging” action in the slurry, which embeds the previously deposited fibers  112 . In addition, the close, intermeshed and rotating relationship of the disks  118  prevents the buildup of slurry  46  on the disks, and in effect creates a “self-cleaning” action which significantly reduces production line downtime due to premature setting of clumps of slurry. By providing two sets of disks  118  which are laterally offset relative to each other, the slurry  46  is subjected to multiple acts of disruption, creating a “kneading” action which further embeds the fibers  112  in the slurry. The preferred embedment device  114  is described in greater detail in corresponding application Ser. No. 10/665,541—entitled EMBEDMENT DEVICE FOR FIBER-ENHANCED SLURRY, which has been incorporated by reference herein. 
   Once the fibers  112  have been embedded, a first layer  120  of the panel is complete. In the preferred embodiment, the height or thickness of the first layer  120  is in the approximate range of 0.05–0.15 inches. This range has been found to provide the desired strength and rigidity when combined with like layers in a SCP panel. However other thicknesses are contemplated depending on the application. 
   To build a SCP panel of desired thickness, additional layers are needed. To that end, multiple production modules, including slurry feeders  44 , chopper stations  36  and embedment devices  114  may be provided for each successive layer. 
   In the preferred embodiment, four total layers are provided to form the SCP panel  122 . Upon the disposition of the four layers of fiber-embedded settable slurry as described above, a forming device  124  is preferably provided to the frame  12  to shape an upper surface  126  of the panel  122 . Such forming devices  124  are known in the settable slurry/board production art, and typically are spring-loaded or vibrating plates which conform the height and shape of the multi-layered panel to suit the desired dimensional characteristics. 
   At this point, the layers of slurry have begun to set, and the respective panels  122  are separated from each other by a cutting device  128 , which in the preferred embodiment is a water jet cutter. Other cutting devices, including moving blades, are considered suitable for this operation, provided that they can create suitably sharp edges in the present panel composition. The cutting device  128  is disposed relative to the line  10  and the frame  12  so that panels are produced having a desired length. Since the speed of the carrier  14  is relatively slow, the cutting device may be mounted to cut perpendicularly to the direction of travel of the carrier  14 . With faster production speeds, such cutting devices are known to be mounted to the production line  10  on an angle to the direction of web travel. Upon cutting, the separated panels  122  are stacked for further handling, packaging, storage and/or shipment as is well known in the art. 
   While a particular embodiment of the present slurry feed apparatus for fiber-reinforced structural cementitious panel production has been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.