Patent Abstract:
An adhesive-free gasket for use on a sector of a disc filter. The gasket comprising a first surface and a second surface. An inner edge on the first and second surface defining at least one aperture therethrough. Two tabs on the periphery of the gasket are suitable to engage an edge of the base plate of the sector without adhesive, whereby the aperture in the gasket will coincide with the opening in the base plate.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority on Canadian Patent Application No. 2,438,096, filed on Aug. 22, 2003, by the present applicant.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to the field of disc filters used in the pulp and paper industry for processing paper machine white water.  
         [0004]     2. Background Art  
         [0005]     A disc filter machine used in the pulp and paper industry is comprised of a hollow central rotating shaft with approximately twenty radially symmetrical sectors connected thereon, and a vat enclosing the sectors and extending along the length of the shaft. The central rotating shaft comprises axial filtrate channels and is connected to a filtrate valve. The filtrate, which is drained via the sectors into the corresponding filtrate channels of the shaft, is vacuumed therein by way of barometric legs.  
         [0006]     The sectors are accessible from a platform through hood doors of the disc filter machine. A sector can be described as a plane figure bounded by two radial edges and an outer arcuate edge therebetween. The radial edges converge to form a neck on the sector. Furthermore, the sector is defined by an arrangement of flow paths for directing filtrate which terminate at an exit opening at the neck of the sector and are connected to corresponding channel openings on the central rotating shaft. The neck of the sector is joined to an arcuate base plate which acts as a means of attachment for the sector onto the shaft. The curvature of the arcuate base plate is identical to the curvature of the shaft, thus enabling the base plate to be superimposed thereon. Further, the arcuate base plate of the sector is bolted onto the shaft at two opposing locations.  
         [0007]     The working principle of the disc filter consists of the sectors rotating by way of the hollow central shaft, thus dipping into a slurry or white water bath in the vat. The slurry or white water consists of a mixture of water, fibre particles and other impurities. As the sectors rotate out of the slurry bath, a fibre residue starts to form under gravity as the sectors are dewatered. The filtrate is drained via the sectors to the corresponding filtrate channels in the central shaft and is directed to a drainage opening where it is removed. Thus, in order to seal the passageway of the filtrate from the sector to the shaft, a gasket is required therebetween.  
         [0008]     The conventional gaskets presently utilized are manually glued onto the arcuate base plate at the end of the neck portion of the sectors to act as a sealing means for the channel connection between the shaft and the sector. In order to replace a used gasket, the sector must be manually unbolted from a distance by way of a pneumatic fastening device. Then, the gasket must be forcibly removed with scraping tools, and finally the concave contact surface of the sector must be thoroughly cleaned to ensure that no fibre particles from the slurry bath or the filtrate remain thereon. The washing is essential because the glue must be applied to a very clean surface in order for it to stick well. Once the glue has been applied and the conventional gasket has been stuck onto the cleaned surface, a curing period is required for the adhesive. During the time the sector is detached, the disc filter machine is not in operation. Thus, the production of quality filtrate from white water only commences when the sector is reattached. In the event that a number of gaskets need to be manually replaced by a single worker, the production downtime is considerable. Furthermore, the additional labour will be expensive.  
         [0009]     Consequently, it is desirable to simplify the method in order to maximize productivity of the disc filter. machine. What is needed is a flexible gasket, propitiously suited for sectors, that is easily applied, easily removed and easily reapplied with the stability required to make an efficient gasket seal.  
       SUMMARY OF INVENTION  
       [0010]     It is therefore an aim of the present invention to provide a method of replacing a gasket on a sector of a disc, filter which substantially overcomes the disadvantages of the prior art.  
         [0011]     It is another aim of the present invention to provide a gasket adapted to be easily installed on an arcuate base plate of a sector.  
         [0012]     It is yet another aim of the present invention to provide a sealing gasket device substantially retaining its structural integrity to remain properly oriented on an arcuate base plate surface between a sector and a corresponding shaft, thus optimising the seal and minimizing deformation and improper orientation of the gasket during installation.  
         [0013]     Therefore, in accordance with the present invention, there is provided an adhesive-free gasket for use on a sector of a disc filter wherein the sector includes a base plate having an opening, the gasket comprising a first surface and a second surface, an inner edge on the first surface and the second surface defining at least one aperture therethrough, at least a first mechanical attachment on a periphery of the gasket, the first mechanical attachment being adapted to engage an edge of the base plate, and at least a second mechanical attachment on the periphery of the gasket, the second mechanical attachment adapted to engage an opposite edge of the base plate, wherein the first and second mechanical attachments are suitable to engage the gasket onto the base plate of the sector without adhesive, and whereby the aperture in the gasket will coincide with the opening in the base plate.  
         [0014]     Further in accordance with the present invention, there is provided a method for replacing a gasket on a sector of a disk filter wherein the sector includes an arcuate base plate having an opening, the method comprising the steps of providing an adhesive-free gasket having a first surface, a second surface, a first mechanical attachment and at least a second mechanical attachment on a periphery of the gasket, the first and second attachments being adapted to engage edges of the arcuate base plate of the sector, and an inner edge on the first surface and the second surface defining at least one aperture therethrough, removing a used gasket from the arcuate base plate of the sector, aligning the inner edge of the gasket with edges of the opening in the arcuate base plate of the sector by superimposing the first surface of the gasket thereon, and engaging the first mechanical attachment onto one of the edges of the arcuate base plate of the sector and engaging the second mechanical attachment onto another one of the edges of the base plate of the sector, wherein the gasket is adapted to be engaged onto the arcuate base plate without adhesive.  
         [0015]     These and other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which:  
         [0017]      FIG. 1  is a perspective view of a gasket in accordance with a preferred embodiment of the present invention;  
         [0018]      FIG. 2  is a top plan view of the gasket according to the present invention;  
         [0019]      FIG. 3  is a perspective view of a sector according to the prior art;  
         [0020]      FIG. 4  is a perspective view of an arcuate base plate of a sector with a conventional gasket glued thereon, according to the prior art; and  
         [0021]      FIG. 5  is a perspective view of a gasket in accordance with an alternative embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     Referring now to  FIG. 4  of the drawings, a sector used on a disc filter machine commonly employed today is illustrated. The sector  10  is defined by two radial edges  12  and an outer arcuate edge  14 . The radial edges  12  converge to form a neck  16  on the sector  10  whereupon an arcuate base plate  18  is joined. In  FIG. 3 , the arcuate base plate  18  of the sector  10 , which acts as a means of attachment for the sector  10  onto the central shaft, is shown with the conventional gasket presently utilized glued onto the contact surface  19  thereof. Further an exit channel aperture  20  of the sector  10  wherethrough filtrate passes is centrally located in the arcuate base plate  18 .  
         [0023]     With concurrent reference to  FIGS. 1, 2  and  3 , a gasket in accordance with the present invention is shown at  22 . The gasket  22  is generally defined by a flexible portion  24 , which is preferably resilient. Referring concurrently to  FIGS. 1, 2  and  4 , the flexible portion  24  comprises inner edges  25 ,  26 ,  27 , and  28  defining a central aperture  29  preferably of similar shape and size as the exit channel aperture  20  of a sector  10 . A raised sealing portion  30  with semi-circular cross-section located on the flexible portion  24  of the gasket  22 , contours the central aperture  29 . The gasket  22  also comprises protruding tabs  32  and hooks  34  on its periphery adapted to be used on the edges of an arcuate base plate  36  of a sector  10 . Furthermore, bands  38  are positioned parallel and adjacent to longitudinal inner edges  27  and  28  of the central aperture  29 , and are provided for maintaining the structural integrity of the gasket  22 .  
         [0024]     Referring more particularly to  FIG. 1 , the flexible portion  24  defines a front surface  40  and a rear surface  42 , both sharing exterior edges  44 ,  45 ,  46 , and  57 . The edges  46  and  47  comprise U-shaped edges  48 , as a preferred embodiment of this invention, positioned at the half way mark. The U-shaped edges  48  ensure proper alignment of the gasket  22  on the connecting arcuate base plate  18  ( FIG. 4 ) of the sector  10  with respect to the attachment bolts, as will be described hereinafter.  
         [0025]     The inner edges  25 ,  26 ,  27 , and  28  defining the central aperture  29  of the flexible portion  24  are parallel to the related exterior edges  44 ,  45 ,  46 , and  47  of the gasket  22 . The central aperture  29  acts as a trough for filtrate passing from the sector  10  ( FIG. 3 ) to the central rotating disc shaft by way of corresponding filtrate channels.  
         [0026]     Referring concurrently to  FIGS. 1, 2  and  4 , both the flexible portion  24  and the central aperture  29  may vary in size depending on the size of the arcuate base plate  18  of the sector  10  and on the size of the exit channel aperture  20  therein. Preferably, flexible portion  24  is designed to cover the entire arcuate base plate  18  surface area of the sector  10 , thus ensuring the most effective seal by reducing the risk of fibre build-up which tends to form along the exterior edges of conventional sealing gaskets. This fibre build-up could develop between the contact surface  19  of the sector  10  and that of the shaft. Advantageously, the present invention is characterized by matching the surface area of the flexible portion  24  with that of the arcuate base plate  18 , consequently reducing the possibility of fibre deposition therebetween.  
         [0027]     Particularly, the flexible portion  24  is preferably made of rubber, or rubber-like material resistant to oil and fluid, such as pellethane 2363-80A. The aforementioned material will compress slightly under pressure, but offers sufficient firmness so as to become firmly seated and form a tight seal between the arcuate base plate  18  and the shaft.  
         [0028]     Furthermore, in a preferred embodiment of the present invention, the gasket  22  comprises protruding tabs  32  as a means of attaching the gasket  22  to the arcuate base plate  18  of the sector  10 , as shown concurrently in  FIGS. 1, 2  and  4 . Due to the fact that the thickness of the arcuate base plate  18  may vary with respect to the type of sector utilized, it is preferable that the tabs  32  be pliable and also variable in length in order to adapt to the thickness of the arcuate base plate  18 . Ideally, the tabs  32  are made of a malleable metallic element such as aluminum, stainless steel or the like.  
         [0029]     In another embodiment of the present invention best illustrated in  FIG. 1 , bands  38  extend parallel to the exterior edges  46  and  47  of the flexible portion  24  of the gasket  22 , and perpendicularly intersect and surpass the opposing exterior edges  44  and  45  to yield the aforementioned protruding tabs  32 . In this embodiment, the bands  38  are integrally joined to the tabs  32  and are also integrally moulded into the flexible portion  24  along a flat plane between the front surface  40  and the rear surface  42 . The bands  38  are preferably made of a malleable metallic element. Further, the bands  38  are adjacent to inner edges  27  and  28  defining the central aperture  29 , extending on both sides thereof to maintain the structural integrity of the gasket  22 . It should be noted that although the bands  38  and the tabs  32  are described as integrally joined and metallic, other alternatives can also readily be used.  
         [0030]     Referring concurrently to  FIGS. 1, 2  and  4 , when the reinforced sealing gasket  22  is positioned on the arcuate base plate  18  of the sector  10  around the exit channel aperture  20  therein, and attached by way of the tabs  32  onto the edges of the arcuate base plate  36 , the bands  38  can be shaped into the curvature of the arcuate base plate  18  to ensure a proper seal. The bands  38  optimize the seal by having the gasket  22  pressed up against the arcuate base plate  18  before the sector  10  is reinstalled onto the cylindrical shaft. Considering that the worker installing the sector  10  on the central rotating disc shaft is positioned away from the arcuate base plate  18 , the bands  38  ensure that the gasket  22  stays in position on the arcuate base plate  18 . Moreover, the risk of an obstruction or any fibres getting between the arcuate base plate  18  and the gasket  22  is reduced. In addition, gasket displacement is avoided during sector reattachment because the bands  38  register the gasket  22  into place at the onset of the installation procedure. The bands  38  act as reinforcing members, minimizing deformation due to friction and compressive forces as well. Thus, the bands  38  help optimize the seal, ensuring that the gasket  22  is fully effective for sealing the sector  10  onto the shaft.  
         [0031]     Moreover, as best seen in  FIG. 2 , the central aperture  29  is outlined by the raised sealing portion  30  with semi-circular cross-section located on the front surface  40  of the flexible portion  24 , whose purpose is to optimize the seal between the sector  10  and the shaft. The raised sealing portion  30  is preferably resilient and accordingly shaped to surround the central aperture  29  as well as the adjacent bands  38 . In  FIGS. 1 and 2 , the raised sealing portion  30  is illustrated in a rectangular formation with rounded corners. The raised sealing portion  30  is an elastomeric liner seal, which when compressed against the arcuate base plate  18  of the sector  10  acts as an added barrier reducing leakage between the arcuate base plate  18  and the gasket  22 .  
         [0032]     In addition, referring concurrently to  FIGS. 1, 2  and  4 , the gasket  22  encompasses pairs of hooks  34  protruding from the exterior edges  46  and  47  of the flexible portion  24 , preferably in juxtaposition with the U-shaped edges  48  thereon. The hooks  34 , symmetrically located on opposing sides of the U-shaped edges  48 , are means of attachment and alignment for the gasket  22  onto the arcuate base plate  18  of the sector  10 . The hooks  34  oppose the tabs  32  on the flexible portion  24 , but essentially have the same function which consists of attaching the gasket  22  to the arcuate base plate  18  of the sector  10 . Advantageously, the hooks  34  ensure that the U-shaped edges  48  are properly aligned with, and centered on the bolt holes  50  ( FIG. 4 ) on the arcuate base plate  18 .  
         [0033]     In another embodiment of the present invention, the gasket  22  is provided with crenellated portions  52  which are best illustrated in  FIG. 1 . More distinctively, the whole crenellated portion  52  can be described as having two merlons  54  and one crenel  56 , and is shown as integrally moulded within the flexible portion  24  and integrally connected to the aforementioned hooks  34 .  
         [0034]     It is pointed out that an alternative configuration can also be effectively employed whereby the crenellated portions  52  are integrally connected to the aforesaid bands  38  and hooks  34 . As shown in  FIG. 5 , the integrally moulded piece  58  is a combination of the crenellated portions  52  connected to the hooks  34  and to the bands  38  which are integrally joined to the tabs  32 . Preferably, the crenellated portions  52  are at right angles with the bands  38 .  
         [0035]     Referring concurrently to  FIGS. 1, 2 ,  4  and  5 , it is preferred that the crenellated portions  52  are in juxtaposition with the U-shaped edges  48  because the crenellated portions  52  act as spacers between the arcuate base plate  18  and the cylindrical shaft. Thus, they protect against over compression of the flexible portion  24 , particularly at the area surrounding the U-shaped edges  48 , whereupon the exerted bolt force is strongest. Due to the fact that the sector  10  is manually reattached from a distance by way of a pneumatic fastening device, it is difficult for a worker to determine the magnitude of the torque applied onto the gasket  22  through the bolts inserted therein. It is important that the compressive force applied to the gasket  22  be of comparable magnitude on both sides to ensure a proper seal. Thus, without the spacers and in the event that one side of the flexible portion  24  is over compressed once the first of two bolts is inserted, the gasket  22  will have a tendency not to adhere as well to the arcuate base plate  18  on the opposing side whereat the bolt has not yet been installed. As a result, this occurrence creates a problem with the seal when the remaining bolt is put into place. This is largely due to the unequal distribution of compressive forces on the bolted sides of the gasket  22 .  
         [0036]     Advantageously, the crenellated portions  52  of the present invention, which are preferably made out of a metallic element, act to oppose the applied bolt force. Hence, a worker can more accurately determine the magnitude of torque needed when using a pneumatic fastening device to render an even distribution of pressure on the gasket  22 .  
         [0037]     Due to the abovementioned embodiments described hereof, the effectiveness of the seal between the arcuate base plate  18  and the cylindrical shaft is thereby optimized. The tabs  32  and hooks  34  are means of attachment and alignment of the gasket  22  onto the arcuate base plate  18 . The bands  38  maintain the structural integrity of the gasket  22 , while the raised sealing portion  30  ensures the integrity of the seal. Finally, the crenellated portions  52  in juxtaposition with the U-shaped edges  48  ensure that the compressive force on both sides of the gasket  22  be of comparable magnitude.  
         [0038]     With concurrent reference to  FIGS. 1, 2  and  4 , the gasket  22  depicted above will now be incorporated into the method proposed in an embodiment of the present invention. With the foregoing arrangement, the gasket  22  is manually attached to the relatively clean arcuate base plate  18  of the sector  10  by way of the following methodical steps. In carrying out this method, the gasket  22  is hooked onto the peripheral edges of the arcuate base plate  36  by way of the hooks  34 , while ensuring that the U-shaped edges  48  are aligned with, and centered around the bolt holes  50  on the arcuate base plate  18 . Thus, the proper positioning of the gasket  22  thereby registers the inner edges  25 - 28  of the flexible portion  24  defining the central aperture  29  with the perimeter of the exit channel aperture  20  of the arcuate base plate  18 .  
         [0039]     Next, the tabs  32  are folded over the opposing exterior edges  44  and  45  to secure and stabilize the gasket  22  into place. Due to the fact that the arcuate base plate  18  is a concave surface, the bands  38  need to be manually form fitted by simply applying pressure so that the gasket  22  takes the shape of the surface. Once the gasket  22  is fixed onto the sector  10 , the latter is reattached to the rotating cylindrical shaft and bolted thereon. The bolts further pin down the gasket  22 , keeping it tightly pressed between the respective surfaces.  
         [0040]     The foregoing description of the preferred embodiments is considered as illustrative only of the principles of the invention. Further, changes and variations which are obvious to those skilled in the art are also included in the scope of this invention because it is not desired to limit the invention to the exact construction and method shown and described.

Technology Classification (CPC): 3