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.
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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 = [(Ec Ac) (8dh/l2 + 4d2)/2 (L)] + [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] where: P is the preload of said tension means, in pounds; Ec is the modulus of elasticity of the ceramic material; Ac 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; αs is the coefficient of thermal expansion of said tension means; αc is the coefficient of thermal expansion of said ceramic; ΔT is the degree of temperature change anticipated, in degrees F.; As is the cross-sectional area of said tension means; Es 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. 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 = [(Ec Ac)(8dh/l2 + 4d2)/2 (L)] + [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] where: P is the preload of said tension means, in pounds; Ec is the modulus of elasticity of the ceramic material; Ac 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; αs is the coefficient of thermal expansion of said tension means; αc is the coefficient of thermal expansion of said ceramic; ΔT is the degrees of temperature change anticipated, in degrees F.; As is the cross-sectional area of said tension means; Es 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. 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 = [(Ec Ac ) (8dh/l2 + 4d2)/2 (L)]+ [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] where: P is the preload of said tension means, in pounds; Ec is the modulus of elasticity of the ceramic material; Ac 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; αs is the coefficient of thermal expansion of said tension means; αc is the coefficient of thermal expansion of said ceramic; ΔT is the degree of temperature change anticipated, in degrees F.; As is the cross-sectional area of said tension means; Es 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. 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 = [(Ec Ac) (8dh/l2 + 4d2)/2 (L)]+ [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] where: P is the preload of said tension means, in pounds; Ec is the modulus of elasticity of the ceramic material; Ac 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; αs is the coefficient of thermal expansion of said tension means; αc is the coefficient of thermal expansion of said ceramic; ΔT is the degree of temperature change anticipated, in degrees F.; As is the cross-sectional area of said tension means; Es 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. 2. The system of
3. The system of
4. The system of
7. The system of
8. The system of
9. The system of
12. The drainage device of
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This application is a continuation-in-part of Ser. Nos. 273,027 filed July 19, 1972; 273,307, filed July 19, 1972; and 377,893, filed 10, 1973, all now abandoned. Further, this application is related to Ser. No. 377,894, filed July 10, 1973length, L (in inches), and a dimension, h (in inches), across the segments, in the direction of the applied deflective force and a cross-sectional area, Ac, in square inches, the preloading on the tension member, e.g. cable 24 (FIG. 1), which will impart to the ceramic segments the necessary compressive force that precludes separation of the segments is calculated using the equation
PD = [(Ec Ac) (8dh/l2 + 4d2)/2 (L)] (1)
where
Ec = the modulus of elasticity of the ceramic;
Ac = the cross-sectional area of a ceramic segment in a plane perpendicular to the composite length of the member, in square inches;
d = the maximum anticipated deflection of the member, in inches;
h = the dimension of a ceramic segment in the plane perpendicular of the composite length of the member and in alignment with the direction of the deflective force, in inches;
l = the overall length of the member. , and
L = the length of a ceramic segment, in inches
With reference to Equation (1), it is noted that the initially determined preloading is divided by 2 to give the preloading to be used in tensioning the cable. This fact arises because of the manner in which the ceramic segments are stressed when the member is deflected while under compression. More specifically, assuming the cable is disposed midway between the ends of the segment dimension h, when the member is in an undeflected state, the stress on each compressed ceramic segment is the same at any point along the dimension h. When the member is deflected, the stress in that portion of a segment on the outside of the line of curvature (on the outside end of the dimension h) is reduced toward zero and the stress in that portion of the same segment on the inside of the line of curvature is doubled. Thus when preloading the aligned segments, the stress imparted to the segments is taken as the average of the stresses along the dimension h when the member is deflected by a maximum amount.
The effect of thermal change upon the ceramic member must also be taken into account. Thermal changes occur most frequently by reason of the ceramic member being manufactured at a first temperature, room temperature for example, and thereafter encountering a substantially higher operating temperature. In such circumstances, the strain in the cable decreases when its temperature increases by reason of the cable expanding when heated. Expansion of the cable cross-section as well as along its length is of importance. The ceramic also expands when heated, but usually to a lesser extent than the cable, so that there is added to the preload calculated for deflection in accordance with Equation (1), an additional preloading which will compensate for the effect of thermal change upon the cable and the ceramic and provide the desired preloading for accommodating deflection up to a maximum temperature. Such additional preloading of the tension means is calculated using the equation.
PT = [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] (2)
where:
αs = the coefficient of thermal expansion of the tension member;
αc = the coefficient of thermal expansion of the ceramic;
ΔT = degrees of temperature change anticipated, in degrees F;
As = cross-sectional area of the tension member, in square inches;
Es = the modulus of elasticity of the tension member
Ac = the cross-sectional area of a ceramic segment in a plane perpendicular to the length of the member, in square inches;
Ec = the modulus of elasticity of the ceramic.
Combining Equations (1) and (2) gives
P = [(Ec Ac) (8dh/l2 + 4d2)/2 (L)] + [(αs -αc) ΔT]/[(1/As Es) + (1/Ac Ec)] (3)
where P is the total preloading of the tension member which will prevent separation of the segments of the member 30 when the member is deflected up to a maximum amount d while at a temperature less than an anticipated maximum temperature it will be noted that in those situations where the ceramic member will not experience a thermal change, ΔT will be 0 and PT [including its equivalent expression in Equation (3)] will be 0 and no additional preloading will be required to account for thermal changes.
Thus, in any given situation where the elongated ceramic member is to be subjected to deflection forces, it is possible to select a composite which exhibits the desired non-separation of abutting segment faces when the composite is deflected along its composite length. As shown in Equation (1), the preloading force (compressive force) applied to the aligned segments, for any given maximum anticipated deflection and total length of the segmented member, depends upon the length of each individual segment and the dimension h of each segment. Thus, if the deflection capability of a given composite of ceramic segments is less than that which precludes physical separation of the abutting faces of the segments under the anticipated deflection, an adjustment can be made, in many instances, in either the length or width of the individual segments, or in both the length and width. Of course, consideration must be given to the added compression experienced by those portions of the abutting segment faces disposed on the inside of the line of curvature of the deflected composite.
The preloading force exerted upon the ceramic segments is kept below that amount of force which will compress the ceramic material to within about one-half, and preferably to within about 20 percent, of its maximum compressive strength to insure that localized stresses which may occur within the composite do not exceed such maximum compressive strength with resultant damage to one or more segments. This preferred preloading also provides a substantial margin of safety against damage to the segments by inadvertent overloading of the segments to produce undue deflection. In any event, the preloading of the segments is sufficient to shorten the length of each segment, hence shorten the overall length of the composite. Further, in the preferred preloading, the segments are sufficiently deformed at the interface between abutting segment faces as results in substantial loss of joint identity at such interface. Such deformation is known to occur when the segments are preloaded to between about 15 and 20 percent of the maximum compressive strength of the ceramic. This substantial loss of joint identity has been found to be important in establishing the working surface on the member in that such allows the composite to be ground to a suitable smoothness. Less preloading is acceptable but at a loss of certainty of achieving the desired properties in the composite. Thus, the preloading of the ceramic segments must be sufficient to maintain the segments abutting when the member is deflected by a maximum amount d but less than that preloading which will compress the ceramic to more than one-half its total compressive strength.
It is understood that in the present discussion each of the segments is substantially identical to each other segment in a given composite. Such is assumed for purposes of simplifying the disclosure. It is not required, however, that all of the segments be identical. For example, it may be desirable to provide a segmented member which is deflected by different degrees along its length. In such an embodiment, the deflective characteristics of the member will differ in different portions of its length and the segments in each such portion may differ in length from the segments in other portions of the length of the member.
As disclosed, one of the members of the system is movable with respect to the other member. In many embodiments, one member is held stationary while the other member moves thereover in frictional engagement therewith. Similarly, in many embodiments the stationary member will be the flexible ceramic member and will include a leading edge which is initialy contacted by the moving member as it moves over the ceramic member. In such instances it is important that such leading edge be straight and free of irregularities such as gaps resulting from chipping of the leading edge inasmuch as such irregularities, among other things, hinder or prevent alignment between the two members and create wear points between the moving members.
The segmented ceramic member, being intended for use in a system where it is in frictional engagement with a further member and there is relative movement between the members, is provided with an elongated smooth working surface (surfaces 46, FIG. 3; surfaces 114 and 116, FIG. 6; surface 230, FIG. 11). This surface extends along the length of the ceramic member and defines an extended area of contact between the relatively moving members. Minimum wear of this surface and of the other of the moving members is obtained by maximizing the smoothness of this working surface. This is accomplished by grinding the working surface after the segments have been formed into the composite and preloaded as described hereinabove.
In a typical grinding operation the segmented ceramic member is anchored on the bed of a grinding machine. A diamond impregnated grinding wheel, preferably of the type having an annular planar grinding surface is used in the grinding process. This grinding wheel is moved into contact with the segmented member with the plane of the grinding surface of the grinding wheel disposed at a slight angle with respect to the plane of the surface to be ground so that only a portion of the rotating grinding surface is in contact with the segments at a given time. Preferably the grinding surface plane is also disposed with respect to the working surface so that grinding of the surface takes place as the annular grinding surface moves onto the surface and little or no grinding takes place as the grinding surface is moving away from the surface being ground.
The rotation of the grinding wheel, when grinding a leading edge of the type shown in FIG. 1, is such that the grinding surface initially contacts the leading edge, e.g. edge 13 of FIG. 1, as the grinding surface moves toward the edge. In this manner, the grinding forces exerted upon the segments are directed inwardly of the segments to aid in preventing chipping of the segments edges during grinding. Preferably, the grinding action at the leading edge is in a direction substantially perpendicular to the leading edge. Variations of greater than about 10° from such perpendicular relationship may provide relatively poor edges.
In the grinding operation the compression of the segments in the direction of their composite length maintains the edges of abutting segments in supporting relationship to each other. In addition to this physical support of one segment by its neighbor, the compression in the segments is sufficient to prevent the force of the grinding operation from placing the segment edges in tension as the grinding wheel drags across the segment, thereby enhancing the resistance of the segments to edge chipping during grinding.
The manufacture of a doctor blade is described hereinafter as illustrative of the manufacture of the disclosed composite ceramic members of the systems described herein. Doctor blades for doctoring a paper web from the surface of a cylindrical dryer shell normally are deflected by different amounts along different portions of their length due to undulations in the dryer shell across its width. In making a ceramic composite doctor blade the most severe anticipated deflection is chosen and the total deflection capability of the blade is made sufficient to accommodate such. In this Example the length, l, of the chosen deflected portion is 50 inches.
The doctor blade in the configuration illustrated in FIG. 1 is made from 1 inch long (L) alumina segments (AD-995 from Coors Porcelain Co.) each having a cross-sectional area (Ac) of 0.78 square inches. The dimension (h), the dimension in the direction of the application of the deflective forces, is 0.875 inch. These segments are aligned with their flat parallel faces abutting and compressed in the direction of their composite length by a stainless steel cable of 0.14 square inches cross-sectional area threaded through aligned openings in the segments.
The maximum anticipated deflection of the doctor blade over the chosen 50 inch length, l, is determined to be 0.027 inch and the anticipated thermal change is from 70° F to 300° F. (ΔT = 230° F). The preloading for the cable which passes through the segments is calculated using Equation (3) as follows: ##EQU1## P = 1579.5 + 2385.19 P = 3964.69 pounds
This preloading imparted a compressive force to the ceramic which is about 1.54 percent of the 330,000 psi approximate maximum compressive strength for AD-995 alumina. This degree of compression provides for the anticipated deflection, occurring at a temperature of 300° F., without complete relief of the compression in those portions of the abutting segment faces furtherest from the longitudinal axis of the member along which the deflection occurs and, importantly, provides for additional compression of those portions of the abutting segment faces nearest the longitudinal axis of the member as necessary to accommodate the deflection.
The working surface 230 of the segmented member 222 is ground while the member is supported along its entire length on the bed of a grinding machine. A 220-grit diamond impregnated wheel, having an annular grinding surface, as sold by the Norton Company is employed in the grinding operation. The grinding wheel has a diameter of 10 inches, and is rotated at approximately 3,600 revolutions per minutes. The wheel is moved along the length of the working surface at a speed between about 10 and 20 feet per minute. The position of the grinding wheel relative to the working surface and its rotational movement is as described above. The grinding operation provides a surface finish of about 20 microinches (AA) with no significant chipping of the leading edge 234.
Another system of the type disclosed herein comprises a foil and a forming fabric of a Fourdrinier papermaking machine. In this system, the elongated foil is disposed beneath the forming fabric and serves to support the fabric and remove water from a slurry of papermaking fibers carried on the fabric. In these functions, the fabric slides over the foil while it is pulled against the foil by suction developed by the foil. There is substantial wear of both the foil and the wire in these systems as known heretofore.
A 200-inch long foil for use in a Fourdrinier papermaking machine is made from 200 l inch long AD-995 alumina segments held in compression by a 0.677 inch diameter stainless steel cable which is passed through an opening located centrally of each segment. Each segment has a cross-sectional area (Ac) of 2 square inches, and a dimension (h) of 2 inches. The maximum anticipated deflection of the foil is 0.5 inch and the anticipated thermal change is from 70° F. to 170° F (ΔT = 100° F).
Using Equation (3), the preloading for the cable for preventing separation of the segments under such conditions is calcuated as follows: ##EQU2## P = 10,746 + 3,557.8
P = 14,304 pounds
The preload force in this example stresses the ceramic to 2.17 percent of its maximum compressive strength.
This foil is provided with a ground elongated working surface having a smoothness of less than about 20 microinches AA in the manner disclosed herein. In use, the foil exhibits excellent wear qualities and does not exhibit gaps between abutting segment faces. Foils of this type when used in a high speed Fourdrinier papermaking machine do not produce streaks in the paper web formed on the forming fabric moving over the foil, as has been experienced by the prior art segmented foils which develop gaps between abutting segments.
A further system of the type disclosed herein comprises a suction device for use in a papermaking machine known as a Uhle Box. This suction device comprises an elongated trough-like device having an elongated slot extending along its length and opening toward a forming fabric or felt moving thereacross. A suction is developed within the Uhle Box so that the fabric or felt is pulled against the edges of the slot and water or other material is pulled from the fabric or felt into the Uhle Box. The edges of the slot are subjected to relatively greater wear forces and the Uhle Box, hence the slot edges, are subjected to substantial deflective forces as the fabric or felt moves across the device in a direction transverse to its length.
A Uhle Box having each of its slot edges made of a flexible ceramic member may be fabricated using the teachings of the invention as follows. Each such slot edge is 200 inches long and made of 1 inch long AD-995 alumina segments held in compression by a stainless steel cable having a cross sectional area of 0.25 square inches which is disposed in aligned openings in the segments. Each segment has a cross-sectional area (Ac) of 0.92 square inch and a dimension of (h) of 1.250 inches.
In calculating the preload for the cable, the maximum anticipated deflection is 3 inches and the maximum temperature anticipated during use is 170° F. The temperature at assembly is 70° F, giving a ΔT of 100° F. Using Equation (3) the preload is determined as follows: ##EQU3## P = 18,605 + 1,771.5 P = 20,376.5 pounds
The preload force in this Example stresses the ceramic to 6.71 percent of its maximum compressive strength.
In addition to the advantages of flexibility and resistance to gaping between segments, the present ceramic member offers the advantage of providing a wear-resistance surface that can be ground smooth to the extent desired. Because the abutting faces of the ceramic segments are held in exceptionally close contact with each other, when the combined top surfaces of the segments are ground smooth, their edges support each other to prevent chipping of their adjacent edges so that in the finished surface, even though the dividing line between segments may be visible as a "hair line" crack, there is no substantial opening or gap therebetween. The wear surface of the disclosed ceramic member is ground and/or lapped smooth to less than about 20 microinches AA and preferably to within a few wavelengths of light to provide exeptionally low-friction contact between the relatively moving members of the system. In this manner, the useful lives of both members are prolonged.
While preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.
Lee, Charles A., Hunt, Robert F.
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| Nov 11 1976 | International Paper Company | (assignment on the face of the patent) | / |
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