Abstract:
An industrial blade for use in pulp and papermaking processes and method of making such a blade. The industrial blade is typically a doctor blade and is fabricated from a plurality of web layers, each web layer formed from a mixture of polyamide and copolyester, thereby forming a thick felt. A polyurethane coating is applied to an edge of the thick felt and the felt is cut at an angle on the coated edge.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to an industrial blade apparatus for use in papermaking and other manufacturing processes. More particularly, the present invention relates to a doctor blade fabricated from a thick felt having an angled edge coated with polyurethane. 
         [0003]    2. Background Discussion 
         [0004]    Pulp or papermaking machines utilize a variety of components during the pulp or papermaking process. These components include, for example, belts, presses and machine rolls. Machine rolls are used during various aspects of the pulp or papermaking process, for example, forming, pressing, drying and/or calendering operations. 
         [0005]    The operation of machine rolls often requires a device to remove contaminants that form on the roll surface and/or to pull off the sheet from the machine rolls. Failure to effectively remove contaminants or the sheet from a machine roll can have catastrophic effects on the quality of the product being produced. One way of achieving this is through the use of a mechanical device commonly referred to as a doctor or doctor blade. 
         [0006]    Also, during operation of papermaking machines, and particularly during operation of presses, such as in press sections with long nip presses and especially with grooved belts, there is a high risk of inefficient dewatering as the belt surface and grooves may have a film layer of water present as the belt returns to the press nip. Accordingly, a doctor blade may be instrumental in removing excess water from the belt. 
         [0007]    Doctor blades can be of rigid or flexible design depending upon the desired application. Also, doctor blades are typically removable and therefore replaceable when worn out. 
         [0008]    The doctor blade is typically fastened to a structural beam that is adjustably supported across the papermaking machine on which a blade holder and a blade is provided. The doctor blade comes in direct contact with the roll surface to scrape off any contaminants from the roll surface including the whole pulp or paper web sheet or parts thereof. 
         [0009]    For example, European Patent Application EP 1 295 988 by Takeuchi et al., entitled, “Doctor Blade” relates to a doctor blade fabricated from an integrated base material and batt fiber layers. Resin is impregnated into one side of the fibrous laminate. In use, the layer in which the amount of resin is small is in contact with a belt. This application is hereby incorporated by reference in its entirety herein. 
         [0010]    Also, European Patent Application EP 1 298 250 by Takeuchi et al., entitled, “Doctor Blade” relates to a doctor blade with a resin impregnated into a fibrous laminate that includes base materials and batt layers integrated by needle punching. This application is hereby incorporated by reference in its entirety herein. 
         [0011]    Thirdly, European Patent Application EP 1 342 842 by Takeuchi et al., entitled, “Doctor Blade for Removing Water” relates to a laminated, resin-impregnated doctor blade for removing water from a grooved belt. Fibers of the belt-contacting layer are oriented in the direction of travel of the belt. This application is hereby incorporated by reference in its entirety herein. 
         [0012]    Unfortunately, using a doctor blade of the type above for removing water and other contaminants, undesirably wears, or abrades, the grooved belt surface. This wear is typically due to polyester, also referred to as PET herein or glass fibers in the doctor blade, which, when impregnated with a hard resin, cause a hard grinding surface to be in contact with the softer belt surface, usually made of polyurethane resin, also referred to as PUR herein. 
         [0013]    A second source of surface wear of the grooved belt is contaminants or foreign particles such as calcium carbonate (CaCO 3 ) that become trapped or lodged in damaged areas on a doctor blade caused by pitting or bending of the blade. This further exacerbates the grinding on the belts, thereby reducing operational life of the belt. 
         [0014]    Furthermore, the use of transfer belts increases the need for an improved doctor blade over the type described above. The surface of a transfer belt is softer and more compliable than a shoe press belt. Since a transfer belt is in direct contact with a paper web, its surface can pick up contaminants/stickies from the web that must be removed. Prior to entering a press nip, a transfer belt&#39;s surface must be relatively dry in order to minimize loss in dewatering efficiency as well as minimize the thickness of the water film created on the belt surface so as to prevent incipient crushing of the paper web and/or to allow the water film to break up resulting in the paper sheet being released from the transfer belt. Additionally, the transfer belt&#39;s surface cannot be unevenly worn or scored/scratched by a contaminant embedded in the edge of a doctor blade. An unevenly worn transfer belt will cause nonuniform pressure to be applied to the paper web that can affect both sheet dewatering and sheet transfer. A scored/scratched belt will result in a mark on the paper sheet. 
         [0015]    Therefore, it would be an advancement in the art to have a doctor blade with a surface that minimizes wear and abrasion of a surface, which may be a belt or otherwise that the blade contacts, while still satisfactorily performing the blade&#39;s intended function. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is directed toward an industrial blade, such as a doctor blade, having a surface that minimizes the wear of a surface of a component that the blade contacts, thereby increasing the operational life of the component. 
         [0017]    Accordingly, one embodiment of the present invention relates to an industrial blade that includes a plurality of web layers, with each web layer formed from a mixture of polyamide and copolyester. An edge of the web layers also has a polyurethane coating and the blade is fabricated to have an angled portion. 
         [0018]    Another embodiment of the present invention relates to a method of manufacturing a blade. The method includes providing a plurality of web layers, each web layer formed from a mixture of polyamide and copolyester. The plurality of web layers is needled to form a thick felt, which is then calendered. Polyurethane is applied to an edge of the thick felt, and an angled surface is formed on the edge after a predetermined period of time. 
         [0019]    The various features of novelty which characterize the invention are pointed out in particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying descriptive matter in which preferred embodiments of the invention are illustrated in the accompanying drawings in which corresponding components are identified by the same reference numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0020]    Thus by the present invention, its objects and advantages will be realized, the description of which should be taken in conjunction with the drawings wherein: 
           [0021]      FIG. 1  shows a perspective view of a blade, according to the present invention, that may be used in papermaking and pulp making machines; 
           [0022]      FIG. 2  illustrates web layers for fabricating the blade; 
           [0023]      FIG. 3  illustrates a needling process for the web layers; 
           [0024]      FIG. 4  illustrates a hot calendering process of a thick felt; 
           [0025]      FIG. 5  illustrates a polyurethane treatment of a region of the thick felt; 
           [0026]      FIG. 6  illustrates the edge region being cut at an angle; 
           [0027]      FIG. 7  shows an example of dimensions of a blade according to the present invention; 
           [0028]      FIG. 8  shows an example of an installed blade of the present invention; and 
           [0029]      FIG. 9  shows a comparison of abrasion test results for a belt using a conventional blade and using a blade according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The present invention provides an improved doctor blade and a method of manufacturing such a blade. In one embodiment, the present invention addresses the issue of belt wear resulting from a surface of the doctor blade in contact with a softer belt such as one made from polyurethane (PUR). Secondly, the present invention also addresses the issue of contaminants or foreign particles, that become trapped or lodged in a damaged edge of a conventional doctor blade. Such damage can occur from pitting or bending of the blade. Trapped contaminants or foreign particles will not only cause wear of the belt but may result in scoring/scratching of the belt surface ultimately resulting in sheet marking. 
       I. Reduction of Belt Wear Due to Doctor Blade Friction 
       [0031]    Specifically, the present invention provides an improved doctor blade by eliminating PET fibers or glass fibers from the blade and constructing a doctor blade from a fiber mixture of polyamide (PA) and copolyester. This mixture provides a softer and less abrasive surface that contacts the surface being doctored, such as a belt or roll cover. The fibers are mixed and needled to form a thick felt, which is then cut in long strips. 
         [0032]    The strips are then hot pressed or calendered at a sufficiently high temperature (e.g. 200° C. or more) to achieve the required hardness and stiffness characteristics necessary for a desired application, such as papermaking or other manufacturing process that utilize doctor blades. 
         [0033]    Following the hot pressing step, one or more edges of the thick felt is cut at a desired angle, for example an angle between approximately 25 degrees and 80 degrees from a longitudinal axis of the thick felt, and preferably approximately 45 degrees. 
         [0034]    Once the edge of the blade has been formed by the cutting operation, the blade may be mounted in a fixed or flexible manner such as in a doctor mounting or doctor back so that the doctor blade interacts in a desired manner with the surface being doctored, for example a belt or roll cover. 
       II. Particles Filling Interstitial Regions of Doctor Blade 
       [0035]    Another embodiment of the present invention, which may be used in conjunction with the embodiment described above, is that the blade, particularly the blade edge in contact with a belt or roll cover, is resistant to penetration by undesired contaminants or foreign particles. This resistant characteristic is accomplished by treating a region of the blade, typically a region that includes the portion cut at an angle, with polyurethane. Thus, the treatment process seals the blade edge and reduces introduction of foreign particles or contaminants into surfaces of the blade, decreasing the potential of the blade from scoring/scratching a belt surface, ultimately reducing sheet marking. Further, only a desired portion of the angled blade may be treated with polyurethane. In order to achieve a doctor that is more flexible over the prior art as well as one that is resistant to contaminants, only the upper portion of the blade or the portion of the blade in contact with or interacting with the surface being doctored is treated with polyurethane. 
         [0036]      FIG. 1  shows a perspective view of a blade  10 , fabricated according to the present invention that may be used in papermaking and pulpmaking machines. Blade  10  has a body portion  132 . The blade has an upper surface  131 , which typically contacts a belt or other surface for doctoring purposes, for example, to remove water, and a lower portion  133 , which is typically used to secure the blade  10  to a mounting apparatus or guide arm or other support structure (not shown). 
         [0037]      FIG. 2  illustrates web layers  115  for fabricating the blade body  10  according to the present invention. The blade  10  is fabricated from a plurality of web layers  102 ,  104 ,  106 ,  108  and  110 . As shown in  FIG. 2 , web layers  106 ,  108  and  110  are already assembled with web layers  102  and  104  being applied to the upper and lower surfaces, respectively. 
         [0038]      FIG. 3  illustrates a needling process to form a thick felt  130 . Web layers  102 ,  104 ,  106 ,  108  and  110  are assembled to form a stack of web layers,  140 . The stack  140  is needled with material  120  and  122  on the upper and lower surfaces, respectively, to form a thick felt  130 . (For example  122  is in contact with web layer  104  and  120  is in contact with web layer  102 .) 
         [0039]      FIG. 4  illustrates a hot calendering process of the thick felt  130 . The thick felt  130  (from  FIG. 3 ) is calendered using rollers  134 ( a ) and  134 ( b ). As shown in  FIG. 4 , portion  130 ( a ) represents the thick felt prior to a calendering operation and portion  130 ( b ) represents the thick felt after a calendering operation. 
         [0040]      FIG. 5  illustrates a polyurethane treatment of an edge region of the thick felt  130 . A portion  140  of the thick felt  130 , which has been calendered, as shown in  FIG. 4 , above, is coated, or treated, with a material  136  such as polyurethane or other material suitable for the purpose. The coating or treatment process is typically accomplished by soaking the portion  140  with the treatment compound. As shown in  FIG. 5 , the treatment material  136  is absorbed or adhered, as shown by element  138 , to portion  140 . 
         [0041]      FIG. 6  illustrates the edge region  140  being cut at an angle. As shown in  FIG. 6 , thick felt  130  with treated portion  140  is cut an angle α, which is typically between approximately 25 and 80 degrees relative to an axis  141  of member  130 . Preferably, the angle α is between approximately 35 and 55 degrees relative to axis  141  of member  130  and most preferably the angle α is approximately 45 degrees relative to axis  141  of member  130 . Cutting the treated edge of the thick felt  130  results in blade  10 . 
         [0042]      FIG. 7  shows an example of dimensions of a blade  10  according to the present invention. The blade  10  has upper lateral surface  152 , which includes treated region  150 ; first edge portion  154  with treated region  140  and second edge portion  156 . The blade may have dimensions, such as, for example, the length of portion  154  being between approximately 10 centimeters and 20 centimeters; the height of portion  154  between approximately 0.25 centimeters and 3 centimeters; and the length of edge  156  between approximately 2 and 12 meters. Blade stock can be produced at any length and cut down into a plurality of blades of desired lengths. 
         [0043]      FIG. 8  shows an example of an installed blade  10  of the present invention. The doctor blade  10  is disposed relative to a belt  182  that is in contact with roller  180 . The doctor blade  10  has an angle surface, as described herein, that is in contact with the belt  182  to remove water and/or other material from belt  182 . 
         [0044]      FIG. 9  shows a graph  90  of abrasion test results for a general shoe press belt used with a conventional blade and a blade according to the present invention. Specifically, graph  90  has horizontal axis  190 , which represents days of operation and vertical axis  192 , which represents percent of belt grooves present. As shown by line  196 , the standard blade caused increased deterioration or surface degradation of the belt, particularly after two days of use. Line  194  shows that a blade fabricated according to the present invention has improved wear characteristics on the belt and does not degrade the belt as quickly as the other blade (line  196 ). 
         [0045]    Thus, while fundamental novel features of the invention shown and described and pointed out, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in another form or embodiment. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.