Papermaking system including a flexible ceramic member having a pre-loaded tensile force applying means

Abstract

A system for use in papermaking including at least two members one of which is movable relative to the other and in frictional engagement therewith wherein at least one of the members comprises an elongated flexible composite including a plurality of ceramic segments, each segment having at least two opposite surfaces that are flat and parallel. The segments are aligned in stacked relationship with their flat faces in abutting face-to-face relation and forced toward each other in the direction of their composite length with a force which is sufficient to maintain the segments in compression when subjected to conditions of thermal change and/or flexing of the member during use. The ceramic member is provided with a smooth elongated working surface which defines an area of contact between the members of the system. Systems including a papermaking foil or suction device in a papermaking process, or a doctor blade are disclosed. A method for making the ceramic member is disclosed.

What is claimed is: 
     
       1. In a papermaking system including at least two members one of which is movable relative to the other and in frictional engagement therewith, and in which system at least one of said members is subjected to deflection, the improvement wherein said latter member comprises an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfaces that are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpendicular to the composite length of said plurality of segements,   tension means extending between opposite ends of said assemblage and forcing said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means, when said latter member is in an undeflected condition, that is at least the force calculated by the equation:   P = [(E.sub.c A.sub.c)(8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] + [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]     where:     P is the preload of said tension means, in pounds;   E c  is the modulus of elasticity of the ceramic material;   A c  is the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;   d is the maximum anticipated deflection of said assemblage, in inches,   
     
     
       h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches; l is the overall length of said assemblage;   α s  is the coefficient of thermal expansion of said tension means;   α c  is the coefficient of thermal expansion of said ceramic;   ΔT is the degrees of temperature change anticipated, in degrees F.;   A s  is the cross-sectional area of said tension means;   E s  is the modulus of elasticity of said tension means, .[.and   L is the length of a ceramic segment, in inches,.].   but less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength,   an elongated smooth working surface extending along the length of said latter member and defining an area of contact with said other member, and   means supporting said latter member relative to said other member with its longitudinal dimension oriented generally transversely of the direction of relative movement of said members whereby loading forces exerted upon said latter member are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said latter member pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said latter member and by relief of less than all of the compression in those portions of said abutting faces that are disposed along the outside of said line of curvature of said member without physical separation of said segments at their abutting faces.   
     
     
       2. The system of claim 1 wherein said preload force does not exceed a force which will compress said ceramic to greater than about 20 percent of its maximum compressive strength. 
     
     
       3. The system of claim 1 wherein said working surface on said latter member includes a substantially straight and continuous leading edge that is in initial contact with said other member. 
     
     
       4. The system of claim 1 wherein said tension means forcing said segments toward each other is a nonceramic material. 
     
     
       5. The system of claim 1 wherein said ceramic comprises alumina. 
     
     
       6. The system of claim 1 wherein said alumina has a purity of greater than about 85 percent. 
     
     
       7. The system of claim 1 wherein said ceramic segments are substantially identical and each has an opening extending between its opposite flat and parallel surfaces, said openings in said segments being in register and said tension means extending therethrough. 
     
     
       8. The system of claim 1 wherein each of the abutting flat faces of said ceramic segments is flat to within about 0.0002 inches. 
     
     
       9. The system of claim 1 wherein said elongated smooth working surface has a surface smoothness of less than about 20 microinches AA. 
     
     
       10. In a papermaking machine including a moving wire on which a paper web is formed, an improved foil disposed on the bottom side of said wire in frictional engagement therewith comprising an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfaces that are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpendicular to the composite length of said plurality of segments,   tension means extending between opposite ends of said assemblage and forcing said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means, when said assemblage is in an undeflected condition, that is at least the force calculated by the equation:   P = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].] + [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]     where:     P is the preload of said tension means, in pounds;   E c  is the modulus of elasticity of the ceramic material;   A c  is the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;   d is the maximum anticipated deflection of said assemblage, in inches;   h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches;   l is the overall length of said assemblage;   α s  is the coefficient of thermal expansion of said tension means;   α c  is the coefficient of thermal expansion of said ceramic;   ΔT is the degree of temperature change anticipated, in degrees F.;   A s  is the cross-sectional area of said tension means;   E s  is the modulus of elasticity of said tension means, .[.and   L is the length of the ceramic segment, in inches,.].   but less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength,   an elongated smooth working surface extending along the length of said elongated assemblage and defining an area of contact with said moving wire, and   means supporting said elongated assemblage on the bottom side of said moving wire and in frictional engagement therewith with the longitudinal dimension of said assemblage oriented generally transversely of the direction of movement of said wire whereby loading forces exerted upon said assemblage are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said foil pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said assemblage without physical separation of said segments at their abutting faces.   
     
     
       11. In a papermaking machine including a moving fabric having a forward direction of motion, an improved elongated drainage device oriented transversely of the forward direction of said fabric in supporting contact therewith including a suction chamber and means defining a slot along that side of said suction chamber adjacent said fabric, said slot having closed ends and opposite side edges and extending along the length of said device and being in fluid communication with said fabric for the application of suction to that side of said fabric adjacent said slot, the improvement comprising an elongated flexible assemblage disposed on each of said side edges of said slot, including a plurality of ceramic segments, each having at least two opposite surfaces that are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpendicular to the composite length of said plurality of segments,   tension means extending between opposite ends of said assemblage and forcing said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means, when said latter member is in an undeflected condition, that is at least the force calculated by the equation:   P = [(E.sub.c A.sub.c) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].]+ [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]     where:     P is the preload of said tension means, in pounds;   E c  is the modulus of elasticity of the ceramic material;   A c  is the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;   d is the maximum anticipated deflection of said assemblage, in inches;   h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches;   l is the overall length of said assemblage;   α s  is the coefficient of thermal expansion of said tension means;   α c  is the coefficient of thermal expansion of said ceramic;   ΔT is the degree of temperature change anticipated, in degrees F.;   A s  is the cross-sectional area of said tension means;   E s  is the modulus of elasticity of said tension means, .[.and   L is the length of a ceramic segment, in inches,.].   but less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength,   an elongated smooth working surface extending along the length of said assemblage and defining an area of contact with said fabric, and   means supporting said drainage device relative to said fabric with its longitudinal dimension oriented generally transversely of the direction of relative movement of said fabric whereby loading forces exerted upon said drainage device are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said assemblage pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said assemblage and by relief of less than all of the compression in those portions of said abutting faces that are disposed along the outside of said line of curvature of said assemblage without physical separation of said segments at their abutting faces.   
     
     
       12. The drainage device of claim 11 wherein said means supporting said assemblage relative to said fabric comprises an elongated cradle means receiving said assemblage of ceramic segments in substantially fluid tight relation therewith. 
     
     
       13. In a papermaking system including a rotating cylindrical member carrying a paper web on the outer cylindrical surface thereof and an elongated doctor blade disposed adjacent said surface for removing said web from said surface the improvement comprising an elongated flexible assemblage including a plurality of ceramic segments, each having at least two opposite surfaces that are substantially flat and parallel, said segments being aligned with their flat faces in abutting face-to-face relation and in respective planes that are oriented substantially perpendicular to the composite length of said plurality of segments,   tension means extending between opposite ends of said assemblage and forcing said segments toward each other in a direction along their composite length and substantially perpendicular to their respective parallel faces with a preload force on said tension means, when said assemblage is in an undeflected condition, that is at least the force calculated by the equation:   P = [(E.sub.c A.sub.c ) (8dh/l.sup.2 + 4d.sup.2)/2 .[.(L).].]+ [(α.sub.s -α.sub.c) ΔT]/[(1/A.sub.s E.sub.s) + (1/A.sub.c E.sub.c)]     where:     P is the preload of said tension means, in pounds;   E c  is the modulus of elasticity of the ceramic material;   A c  is the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of said assemblage, in square inches;   d is the maximum anticipated deflection of said assemblage, in inches;   h is the dimension of a ceramic segment in the plane perpendicular to the composite length of said assemblage and in alignment with the direction of said deflective force, in inches;   l is the overall length of said assemblage;   α s  is the coefficient of thermal expansion of said tension means;   α c  is the coefficient of thermal expansion of said ceramic;   ΔT is the degree of temperature change anticipated, in degrees F.;   A s  is the cross-sectional area of said tension means;   E s  is the modulus of elasticity of said tension means, .[.and   L is the length of a ceramic segment, in inches,.].   but less than the amount of force which will compress said ceramic to over about one-half of its maximum compressive strength,   an elongated smooth working surface extending along the length of said doctor blade and defining an elongated area of contact with said cylindrical surface, and   means supporting said doctor blade relative to said cylindrical surface with the longitudinal dimension of said doctor blade oriented generally transversely of the direction of rotational movement of said cylindrical member whereby loading forces exerted upon said doctor blade are directed thereagainst in a direction substantially perpendicular to the longitudinal dimension thereof and deflection of said doctor blade pursuant to such loading forces is compensated for in said compressed segments by further compression of said segments in those portions of the abutting faces thereof disposed along the inside of the line of curvature of said assemblage and by relief of less than all of the compression in those portions of said abutting faces that are disposed along the outside of said line of curvature of said assemblage without physical separation of said segments at their abutting faces.