U.S. patent number RE29,417 [Application Number 05/740,932] was granted by the patent office on 1977-09-27 for papermaking system including a flexible ceramic member having a pre-loaded tensile force applying means.
This patent grant is currently assigned to International Paper Company. Invention is credited to Robert F. Hunt, Charles A. Lee.
United States Patent |
RE29,417 |
Lee , et al. |
September 27, 1977 |
**Please see images for:
( Certificate of Correction ) ** |
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.
Inventors: |
Lee; Charles A. (Knoxville,
TN), Hunt; Robert F. (Concord, TN) |
Assignee: |
International Paper Company
(New York, NY)
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Family
ID: |
27037947 |
Appl.
No.: |
05/740,932 |
Filed: |
November 11, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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273027 |
Jul 19, 1972 |
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273307 |
Jul 19, 1972 |
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377893 |
Jul 10, 1973 |
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Reissue of: |
455678 |
Mar 28, 1974 |
03871953 |
Mar 18, 1975 |
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Current U.S.
Class: |
162/274; 162/281;
162/374; 15/256.51; 162/352 |
Current CPC
Class: |
B28B
23/22 (20130101); C04B 35/111 (20130101); C04B
35/63 (20130101); D21F 1/483 (20130101); D21F
1/523 (20130101); D21G 3/00 (20130101); D21G
3/005 (20130101) |
Current International
Class: |
C04B
35/111 (20060101); C04B 35/63 (20060101); B28B
23/02 (20060101); B28B 23/22 (20060101); D21G
3/00 (20060101); B32B 18/00 (20060101); D21F
1/48 (20060101); D21F 1/52 (20060101); D21F
001/48 (); D21G 003/00 () |
Field of
Search: |
;162/211,274,281,351,352,363,373,374 ;15/256.51 ;29/452 ;52/227
;138/155 ;174/141R,141C,150 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Modern Ceramics, Edited by J. E. Houe and W. C. Riley, John Wiley
& Sons Inc., 1965, pp. 209-214..
|
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Fisher; Richard V.
Attorney, Agent or Firm: Fitch, Even, Tabin &
Luedeka
Parent Case Text
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, 1973.Iadd., now U.S.
Pat. No. 3,869,344. .Iaddend.
Claims
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:
where:
P is the preload of said tension means, in pounds;
E.sub.c is the modulus of elasticity of the ceramic material;
A.sub.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;
.alpha..sub.s is the coefficient of thermal expansion of said
tension means;
.alpha..sub.c is the coefficient of thermal expansion of said
ceramic;
.DELTA.T is the degrees of temperature change anticipated, in
degrees F.;
A.sub.s is the cross-sectional area of said tension means;
E.sub.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:
where:
P is the preload of said tension means, in pounds;
E.sub.c is the modulus of elasticity of the ceramic material;
A.sub.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;
.alpha..sub.s is the coefficient of thermal expansion of said
tension means;
.alpha..sub.c is the coefficient of thermal expansion of said
ceramic;
.DELTA.T is the degree of temperature change anticipated, in
degrees F.;
A.sub.s is the cross-sectional area of said tension means;
E.sub.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:
where:
P is the preload of said tension means, in pounds;
E.sub.c is the modulus of elasticity of the ceramic material;
A.sub.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;
.alpha..sub.s is the coefficient of thermal expansion of said
tension means;
.alpha..sub.c is the coefficient of thermal expansion of said
ceramic;
.DELTA.T is the degree of temperature change anticipated, in
degrees F.;
A.sub.s is the cross-sectional area of said tension means;
E.sub.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:
where:
P is the preload of said tension means, in pounds;
E.sub.c is the modulus of elasticity of the ceramic material;
A.sub.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;
.alpha..sub.s is the coefficient of thermal expansion of said
tension means;
.alpha..sub.c is the coefficient of thermal expansion of said
ceramic;
.DELTA.T is the degree of temperature change anticipated, in
degrees F.;
A.sub.s is the cross-sectional area of said tension means;
E.sub.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.
Description
This invention relates to papermaking systems including two members
that are movable relative to one another, and more particularly to
a wear-resistant, flexible member which is useful in applications
where the member is to be subjected to conditions of thermal change
and/or forces tending to bend the member along its length.
The physical properties and/or the chemical inertness of ceramic
materials frequently suggest such materials for use in applications
wherein the material is to be subjected to potential physical
and/or chemical degradation as by frictional forces, corrosion, or
other erosive forces. Not infrequently, ceramic elements or members
are of considerable length and subjected to thermal change or
forces, such as vibration or frictional drag, which tend to bend or
deflect the member along its longitudinal axis.
Because of the relatively high cost and difficulty of manufacturing
ceramic members in continuous lengths, for example lengths greater
than about two feet, ceramic materials have heretofore been
generally limited to use in those situations where their relatively
high cost is justified in order to obtain the advantages from the
physical and/or chemical properties of the ceramic materials. Even
in such special situations where ceramic lengths have been
employed, it has been important to assure that the elongated
ceramic members neither bend nor are subjected to localized
stresses, so as to avoid cracking and/or breaking of the elongated
member. Consequently, the circumstances under which elongated
ceramic members could be used heretofore have been severely
limited.
Commonly in papermaking systems, there are two members, one of
which is movable relative to the other and in frictional engagement
therewith. In these systems, at least one of the members will
possess a working or wear surface defining an area of contact
between the members. Examples of such systems include the
combination of elongated drainage devices, such as foils or suction
boxes, in contact with a forming fabric in a Fourdrinier
papermaking machine, a Uhle Box which bears against a forming
fabric or felt in a papermaking machine, and doctor blades for use
in contact with rotating drums or other moving members. In these
systems, the member having the wear surface frequently is of
elongated geometry and has a length as great as 20 to 30 feet, or
greater.
In papermaking machines, e.g. a Fourdrinier machine, a twin wire
machine, or the like, a dilute slurry of wood fibers in a water
medium is deposited on a moving screen known in the art as a wire.
Water drains and/or is withdrawn from the slurry and through the
openings in the wire to produce a self-sustaining paper web. These
wires may be made of a metal or plastic as known in the art.
Various drainage devices have been employed heretofore for aiding
withdrawal of water from the slurry by developing suction on that
side of the wire opposite the slurry carried thereon. Foils are
among such devices. The usual foil comprises an elongated member,
which may be 20 or more feet long, that extends transversely of the
direction of travel of the wire and serves to support the moving
wire incident to its water removal function. The usual foil is
stationarily mounted beneath the wire by means of a support
structure, each end of which is mounted on the papermaking machine,
so that the foil and its support structure is self-supporting along
that portion of its length between the end supports. At least one
of the end mountings provides for expansion and contraction of the
foil and its support structure as their lengths change due to
temperature changes as is known in the art.
Foils usually are provided with a top surface having a leading edge
(facing the inlet end of the papermaking machine) which scraps
water from the bottom surface of the wire, a substantially flat
portion which contacts and supports the moving wire, and a trailing
portion that diverges downwardly away from the wire. The action of
the wire moving over and past the trailing portion develops a
reduced pressure in the area between the wire and the trailing
portion that functions to pull water from the slurry through the
wire. When the foil is geometrically uniform and free of gaps,
cracks or the like along its length, there is an evenly distributed
and generally uniform suction developed along the length of the
coil and a uniform withdrawal of water from the slurry. This aids
in producing a paper web of uniform quality.
It shall be recognized that there is significant frictional
engagement between the wire and the foil or supporting structure as
the wire moves over the foil. This frictional contact between the
wire and the foil is in part due to the suction pulling the wire
against the foil. These frictional and hydraulic drag forces
increase the wear of both the wire and foil. These forces are
aggravated by hydraulic drag forces arising by reason of water on
the surface of the fast moving wire impacting the leading edge of
the foil. These latter forces and the frictional forces are
sufficient in magnitude to cause the foil to flex along its length,
the direction of such flexing being in the direction of movement of
the wire across the foil, i.e. the machine direction. When
installing a foil on a papermaking machine, it is not uncommon that
the foil be adjusted with respect to the papermaking machine
superstructure so as to align the foil with the wire. This may
involve the addition of shims which bring the foil into the desired
alignment, involving flexing of the foil.
In some instances, the wires in papermaking machines are supported
by elongated devices disposed beneath and transversely of the
direction of movement of the wire. Such devices do not necessarily
aid in withdrawing water from the slurry through the wire but are
subject to the wear and flexing problems as are foils. Metal foils,
as introduced to the industry, proved unsatisfactory due to
excessive wear of both the foil and the wire. It was subsequently
suggested that the metal be hardened or that ceramic inserts to
provided in strategic locations of the foil. Neither of these
concepts provided a sufficiently smooth surface so that the wire
was worn excessively. It has also been suggested heretofore that
hard, dense ceramic materials be used in drainage devices for
papermaking machines. These problems relate to the present
incapability of the industry to fabricate ceramic foils of the
required size. In view of the limitations of the industry, it has
been suggested heretofore that drainage devices for papermaking
machines be made of multiple segments of ceramic materials. Ceramic
materials in continuous lengths are economically prohibitive to
manufacture and very susceptible to fracture. Insofar as the use of
ceramic segments in drainage devices is taught in the prior art,
the concepts are not acceptable for the reason that the segments
separate from each other when the device deflects or is subjected
to thermal change thereby opening up gaps or cracks between
adjacent segments with resultant nonuniformity of paper
quality.
In the usual Fourdrinier papermaking machine, the wet paper web
passes from the wire section to the press section for further water
removal. The transfer of the wet paper web from the wire section to
the press section is frequently accomplished by means of a felt.
The paper web, while on the felt, is passed through the press
section where additional free water is removed from the paper web
through the use of various combinations of pressure and suction.
Following the pressing of the paper web, it is separated from the
felt and passed to further processing stations. The felt normally
comprises an endless fabric so that as it is separated from the
paper web following pressing, the fabric is caused to traverse
several return rolls to be directed back to the point where the wet
paper web coming from the wire section is received on the felt.
During the time that the paper web is present on the felt and water
is being removed from the paper web through the felt, the pores in
the felt become plugged by such materials as rosin, clay, starch,
paper fines, bacterial products and so forth. Also, as the felt
passes through the presses, its bulkiness is reduced. To assure
uniform porosity of the felt, hence uniform water removal from the
wet paper web, it is desired that the felt be cleaned on its return
run. Such cleaning is commonly accomplished by suction box devices
over which the felt is caused to move during its return run. The
suction developed by such box restores the bulkiness of the felt as
well as cleaning and drying the felt. Suction boxes of this type
are also useful in the wet end of a Fourdrinier papermaking machine
where they are positioned beneath the wire to aid in withdrawing
water from the paper slurry carried by the wire. For purposes of
this disclosure, the term "fabric" is considered to include felts
and/or wires.
In one common suction box of the type used for cleaning felts,
there is provided an elongated slot which extends the width of the
felt so that as the felt moves transversely across the slot, the
desired cleaning and renewal of the felt is brought about. In an
effort to reduce the wear on the felt and those portions of the
suction box which are contacted by the felt, particularly the edges
of the slot in the suction box, it has been proposed that the slot
edges be provided with ceramic faces, comprising continuous lengths
of ceramic material or adjacent ceramic segments in side-by-side
relation, which provide a smooth, hard and long wearing surface in
contact with the felt.
For reasons of economy, only those portions of these and other
suction box drainage devices in contact with the felt or wire are
made of ceramic material. The remainder of the box is made of
materials that are less expensive and less costly to fabricate,
such other materials, stainless steel for example, providing
support for the ceramic portions which are securely mounted
thereon. As noted above, inasmuch as the ceramic and nonceramic
materials have different coefficients of thermal expansion, in the
instance of the prior art devices having ceramic sections in
side-by-side relation along the edges of the box slot, the thermal
changes normally encountered in papermaking machines cause the
support to expand to a greater degree than the ceramic so that the
ceramic segments no longer remain in abutting relation and become
free to physicaly separate. Such physical separation produces gaps
in the surface of the box over which the felt or wire moves which
cause irregular patterns of air or water flow that manifest
themselves in similar irregularities in the felt surface or in the
paper web formed on the wire. Further, the edges of the gaps
between stress or wear points that cause inordinate wear of the
felt or wire.
In the instance of continuous lengths of ceramic materials provided
along the edges of the box slot, frictional and/or hydraulic drag
forces arising by reason of the felt or wire moving across the box
flex the box along its longitudinal axis and cause the continuous
lengths of ceramic to crack or break transversely thereof. This
develops the undesirable gaps and/or points of wear referred to
above so that these prior art devices also are unsuitable.
Still further, in certain papermaking systems the paper web from
the press section is fed over a cylindrical dryer such as the
well-known Yankee Dryer for further drying of the web. In these
systems the web is trained about a portion of the peripheral
surface of the dryer and dried by heat transferred through the
cylindrical shell thereof. Steam introduced into the interior of
the dryer shell is commonly used to heat the shell. The dry paper
web is doctored from the shell by means of a doctor blade
comprising an elongated blade member extending transversly of the
direction of the rotation of the dryer and frequenctly in contact
with the exterior cylindrical surface of the dryer along a line
extending across the dryer surface substantially parallel to the
rotational axis of the dryer. In operation of these dryers, the
surface of the dryer shell becomes irregular due to it being heated
by the steam. In order to keep the doctor blade in contact with the
shell for doctoring the web from the shell, it is necessary to bend
the doctor blade so that if conforms to the irregularities from the
shell surface. In this and other systems of this type, it is
desired that the elongated blade member be flexible and have a good
wear surface.
It is therefore an object of the present invention to provide an
elongated flexible ceramic member useful in a papermaking system.
It is also an object of this invention to provide an elongated
flexible ceramic member of substantial length wherein the member
comprises a plurality of ceramic segments adapted to accommodate
conditions of thermal change or bending of the member within
predetermined limits. Another object of this invention is to
provide a method for the manufacture of an elongated flexible
ceramic member.
It is also an object of this invention to provide a papermaking
system comprising at least two members one of which is movable with
respect to the other and in frictional engagement therewith and one
of which is an elongated flexible ceramic member.
It is also an object of the present invention to provide a flexible
foil or like elongated supporting structure for the wire of a
papermaking machine which affords the advantages of having a hard,
long-wearing, smooth surface in contact with the wire. It is also
an object of this invention to provide a foil including ceramic
material at least in the wire-contacting portion thereof, it is
another object of this invention to provide a foil including a
plurality of ceramic segments disposed in face-to-face relation to
define an elongated foil which is relatively flexible along its
longitudinal axis and wherein gaps do not develop between the faces
of adjacent ceramic segments when the foil is subjected to thermal
change or bending movements.
It is also an object of the present invention to provide a slotted
drainage device, particularly useful in a papermaking machine, over
which the felt or wire of a papermaking machine passes transversly
thereof, wherein the longitudinal edges of the slot each include a
plurality of ceramic segments disposed in face-to-face
relation.
Other objects and advantages of the invention will be recognized
from the following description and claims, including the drawings
in which:
FIG. 1 is a representation, in perspective and partly cut-away, of
a foil embodying various features of the invention;
FIG. 2 is an enlarged fragmentary view, part in section, showing a
portion of the foil of FIG. 1;
FIG. 3 is an end view, partly cut-away, of the foil shown in FIG.
1;
FIG. 4 is a representation of a segment of the foil shown in FIG.
1;
FIG. 5 is a front view of the segment shown in FIG. 4;
FIG. 6 is a representation, part in section of a slotted drainage
device embodying various features of the invention;
FIG. 7 is an end view, part in section, of the drainage device of
FIG. 6.
FIG. 8 is a fragmentary side view of the drainage device of FIG.
6;
FIG. 9 is a fragmentary side view of an assemblage of ceramic
segments as disclosed herein; and,
FIG. 10 is a fragmentary representation of a support cradle for an
assemblage of ceramic segments as disclosed herein;
FIG. 11 is a representation of an elongated segmented ceramic
doctor blade member embodying various features of the
invention;
FIG. 12 is a representation of a segment of the member shown in
FIG. 11;
FIG. 13 is a representation of one embodiment of a system including
at least two relatively movable members and showing various
features of the invention.
FIG. 14 is a grossly exaggerated representation of a plurality of
segments deflected in a manner to aid in explaining certain
calculations attending the disclosed invention; and
FIG. 15 is a grossly exaggerated representation of a portion of a
deflected composite of ceramic segments.
In accordance with the present disclosure, there is provided a
system that includes two relatively movable members, one of which
comprises an elongated ceramic composite. The ceramic member is
formed from a plurality of segments, each having opposite flat
faces that are aligned with their flat faces in abutting
face-to-face relation, the segements being held in their abutting
relation by tension means which maintains the segments in
compression such that the abutting segment faces do not separate
and form a gap or gaps therebetween when the member is subjected to
flexing forces or to thermal change.
FIGS. 1-5 depict a system including a foil 10 positioned
transversely of and in contact with the wire 15 of a papermaking
machine which moves thereacross with the front edge 13 of the foil
in contact with the wire. The foil includes a trailing edge 17
which diverges from the wire to form an acute angle therebetween.
It has been found that the foil can be provided with the desirable
wear characteristics of a ceramic material and also be made
sufficiently flexible to enable the foil to withstand the maximum
deflection of the foil anticipated in a papermaking machine. In the
present disclosure, the specific reference is not to be considered
as limiting the invention but it is recognized that the disclosed
concepts are applicable to relate or similar two-member
systems.
The illustrated foil 10 comprises a support structure 11 on which
there is mounted an assemblage 14 of ceramic segments or wafers 12,
each being of generally rectangular geometry and having two
opposite parallel faces 16 and 18. The segments are disposed in
face-to-face relation with their parallel faces abutting the
parallel faces of adjacent segments to define an elongated
assemblage 14 of a length sufficient to extend fully across the
width of the wire 15 moving across the foil. As will appear
hereinafter, the abutting faces of adjacent segments are subjected
to a compressive force applied at substantially right angles to the
faces. To prevent cracking or breaking of the segments due to
unevenly applied stresses, the faces 16 and 18 are each
substantially flat and are oriented substantially parallel to each
other and substantially perpendicular to the longitudinal axis of
the assemblage 14. Each of the parallel faces is flat and smooth to
within less than about 20 microinches (AA) so that when the
individual segments are placed in face-to-face relation, the
abutting flat faces of adjacent segments lie in contact with each
other over substantially the entire areas of the abutting faces
without significant open space therebetween. An opening 20
extending between the opposite flat faces 16 and 18 of each segment
is aligned with similar openings of the abutting segments to
provide a channel 22 through the assemblage.
Each illustrated segment further includes a flat top surface 26, a
flat bottom surface 28, and forward and rear surfaces 30 and 32,
respectively. The forward surface 30 extends upwardly from the
bottom surface 28 to join the forward edge of the top surface 26
and define an acutely angled leading edge 34. As indicated, the top
surface 26 of each segment is flat. The rear edge of such flat
surface 26 transists into a diverging trailing surface 36. In the
illustrated segments, the trailing surface 36 is generally arcuate
to provide an increasingly greater acute angle between the trailing
surface 36 and the Fourdrinier wire 15 passing over the foil (see
FIG. 3). It may be desired in certain applications to not use the
foil in withdrawing water, in which case the entire top surface of
each segment may be flat. Alternatively, the trailing surface 36,
itself, may be substantially flat so as to form a constant angle
with the wire.
In producing a foil of given length, a sufficient number of
segments 12 are assembled in face-to-face relation with their
respective openings 20 aligned to obtain the desired foil length.
The assembled segments are secured together with a force applied
substantially in the direction of the length of the assemblage 14
and substantially perpendicular to the flat parallel faces of the
segments. This force is sufficient to place the segments in elastic
compression and is suitably applied as by a tension means applying
a compressive force to opposite ends 37 and 39 of the assemblage
14. One suitable tension means is a cable 24 inserted through the
aligned openings 20 of the assembled segments, pulled to the
required length, anchored at the opposite ends of the assemblage as
by swage fittings 41, and released to exert a compressive force to
the assemblage at its opposite ends. Alternatively, other tension
means may be used to establish the desired compression of the
segments in the assemblage. One such other means includes a rod
disposed in the aligned openings 20 of the segments and fitted with
a nut at one or both of its ends so that tightening of the nuts
tensions the rod and places the segments in compression. One
suitable cable for applying the desired compression force to the
segments is made of carbon steel and of the general type employed
in prestressed concrete structures.
The cable 24 may be chosen with a diametral dimension less than the
diametral dimension of the opening 20 in each segment and after the
segment is in place on the cable the space between the cable and
the inside surface of the opening 20 in the segment may be filled
with a grout 44, such as rigid polyurethane, to position the cable
within the openings 20 and provide added assurance that the
segments do not rotate about the cable and that the faces of
adjacent segments remain flush with each other. One suitable grout
is a liquid casting urethane polymer designated as LD-2699, sold by
E. I. Du Pont de Nemours Company, Trenton, N.J. This grout also
accommodates the axial movement of the segments with respect to the
compression cable during compression of the stacked array.
In one embodiment, the assemblage of segments is provided with a
plate or other means such as a metallic segment 40 at each end of
the assemblage to provide for distribution of the compressive force
over the face of each end segment to protect it from destruction by
localized forces. A plurality of tension means may be employed to
force the segments into the desired compression and in those
instances where the desired compression is relatively great, such
provide greater compression capability. Multiple, spaced apart,
tension means also aid in more evenly distributing the compressive
forces over the abutting faces of the segments.
In the assemblage 14 of segments, the individual segments 12 are
oriented with respect to each other in a manner such that their
common surfaces lie in common planes to combine with each other to
define an elongated substantially flat top surface 46 extending
along the length of the foil and adapted to contact and support a
Fourdriner wire 15 moving thereacross. The combined aligned faces
also define an elongated trailing surface 48 which is a
continuation of the flat surface 46 but diverges downwardly away
from the wire 15 to define a generally triangular (cross-section)
zone 50 between the trailing surface 48 and the Fourdrinier wire
15. It is in this zone 50 that the usual relatively low pressure is
developed which assists withdrawal of water from a slurry of paper
fibers carried on the wire. The elongated assemblage 14 of ceramic
segments further includes an inclined forward surface 52, defined
by the combined forward faces of the segments, that joins the
forward edge of the flat top surface 46 to define an acutely angled
leading edge 13 extending the length of the foil and which
functions to scrape water from the wire as it moves past the
stationary foil. Alignment of the segments so that their common
surfaces combine to provide the described foil surfaces is
accomplished during assembly.
In the illustrated foil 10, the stack 14 of ceramic segments 12 is
mounted in a support saddle 56 which in turn is mounted on existing
superstructure of a usual Fourdriner papermaking machine (not
shown). Such papermaking machines, their structure and operation,
are well known in the art and need not be discussed herein.
Preferably, the support saddle 56 is removably secured in position
on the papermaking machine as by means of bolts 60 that join the
support saddle at spaced apart locations to an elongated bar 58
that extends between opposite sides of the papermaking machine and
which is itself secured at its opposite ends to the papermaking
machine. The support saddle 56 and the bar 58, being securely
joined to each other at relatively closely spaced points, exhibit
thermal expansion characteristics that are some combination of the
individual thermal characteristics of the saddle 56 and bar 58. It
will be recognized that if the saddle and bar are of the same
material, they will exhibit the thermal expansion characteristic of
such material.
The support saddle 56, in the illustrated foil, includes an
elongated bottom portion 82 in FIG. 1 which resides on and is
bolted to the bar 58 to join the saddle to the bar referred to
above. A rear wall portion 64, formed integrally with the bottom
portion, extends upwardly from the bottom portion 62 of the saddle.
The upper surface 66 of the bottom section 62 and the forward
surface 68 of the rear wall 64 receives the bottom surfaces 28 and
at least a portion of the rear surfaces 32 of the stacked segments
to provide support for the segments and position them for
engagement with the wire 15. At the juncture of its surface 66 and
its surface 68, the support saddle is cut away along its length to
accommodate the bottom rear corners 70 of the segments. In the
illustrated support saddle, these surfaces 66 and 68 define an
acute angle therebetween into which the corners 70 of the segments
fit thereby restraining the segments against upward movement out of
the support saddle. Further support and retention of the segments
in the saddle 56 is provided by a plurality of clamps 72 that are
removably attached as by bolts 74 to the bottom portion 62 of the
saddle at locations spaced along the length of the foil. A
generally semicircular (cross-section) groove 76 extending parallel
to the longitudinal axis of the foil is provided on that face 78 of
the clamp next to the segments. A similar groove 80 is provided on
the forward face of each segment so that the two grooves define a
generally circular channel between each clamp and the segments
faced by the clamp. A relatively non-yielding cylindrical rod 82 is
fitted into the channel defined by the grooves 76 and 80 to prevent
movement of the segments with respect to the clamps 72 and thereby
hold the segments in position in the saddle 56.
A further system including a drainage device specifically a Uhle
box), for papermaking is shown in FIGS. 6-10 and this system
comprises a suction box having a longitudinal slot 100 whose
longitudinal side edges each comprise a plurality of ceramic
segments 102 disposed in face-to-face relationship and held
together in an assemblage 104 in the direction of their composite
length with a force sufficient to hold the segments in elastic
compression to the degree sufficient to accommodate anticipated
thermal change and/or flexing without physical separation of the
segments. This is accomplished by forming the side edges of the
slot 102 in the suction box 106, from the respective assemblages
104 and 104', each of relatively thin ceramic segments 102 held
together by means of a nonceramic tension means 120 with a
compressive force applied in the direction of their composite
length.
Various drainage device, e.g., Uhle boxes, suction boxes, etc. may
be supplied with ceramic edges along the sides of the slot therein
as disclosed herein. For simplifying the present disclosure, the
discussion at times refers to a suction box, but such is not to be
deemed to limit the invention.
With reference to FIGS. 6-10, in one embodiment the suction box 106
includes a generally elongated tubular housing 108 having a slot
109 cut in one of its walls 110 so that the slot opens facing a
felt 112 or the like which moves transversely over the slot. Each
of the longitudinal side edges of the slot 100 comprises an
assemblage 104 including a plurality of ceramic segments 102 held
in face-to-face relation to provide ceramic surfaces 114 and 116 in
contact with the felt 112. Each of the ends of the box is closed as
by a plate 118, at least one of which has an outlet conduit 122
leading to a source of suction (not shown) by means of which a
vacuum is developed within the box. The two assemblages 104 and
104' of ceramic segments face each other and define an extension of
the slot 109 in the box. As desired, each end portion 124 of the
slot 100 may be sealed as by means of a deckle 126 whose
construction and function is known in the art.
The suction box 106 is supported at its opposite ends on exiting
papermaking machine superstructure 128, the box being disposed on
one side of the felt with the felt bearing against the ceramic
surfaces as it moves transversely over the box. The vacuum
developed within the box pulls water and other material, such as
felt contaminates, from the felt.
It will be recognized that the suction developed within the box
pulls the felt against the ceramic surfaces 114 and 116 thereby
increasing the frictional drag of the felt against the box. These
frictional forces are aggravated by hydraulic drag forces such as
are developed by water droplets on the the fast moving felt or wire
impinging the leading edge of the box. Such friction and hydraulic
drag forces bend the box along its longitudinal axis in the
direction of felt or wire travel.
As noted, the suction box is subject to exposure to thermal changes
such as may occur during shipment or storage, as well as the
difference in the temperature of the box at the time it is
installed on the papermaking machine and its temperature when the
papermaking machine reaches its operating temperature.
In the illustrated suction box 106 each of the assemblages 104 and
104' comprises a plurality of ceramic segments or wafers 102, each
being generally disc-shaped and having two opposite parallel faces
130 and 132. The segments are disposed in face-to-face relation
with their parallel faces abutting the parallel faces of adjacent
segments to define the elongated assemblage 104, the number of
segments in the assemblage being sufficient to provide a length
sufficient to extend fully across the width of a felt 112 moving
across the box. Abutting adjacent segments are subjected to a
compressive force applied at substantially right angles to their
parallel faces. To prevent cracking or breaking of the segments due
to unevenly applied stresses, the faces 130 and 132 are each
substantially flat and are oriented substantially parallel to each
other and substantially perpendicular to the longitudinal axis of
the assemblage 104. Each of the parallel faces is flat and smooth
to within less than about 20 microinches so that when the
individual segments are placed in face-to-face relation, the
abutting flat faces of adjacent segments lie in contact with each
other over substantially the entire areas of the abutting faces
without significant open spaced therebetween. An opening 134
extending between the opposite flat faces 130 and 132 of each
segment is aligned with similar openings of the abutting segments
to provide a channel through the assemblage.
The ceramic composite of this embodiment is produced in like manner
as the foil referred to hereinbefore, that is a sufficient number
of segments 102 are assembled in face-to-face relation with their
respective openings 134 aligned to obtain the desired length. The
assembled segments are secured together with a force applied
substantially in the direction of the length of the assemblage 104
and substantially perpendicular to the flat parallel faces of the
segments. This force is sufficient to place the segments in elastic
compression and is suitably applied as by a tension means applying
a compressive force to opposite ends 136 and 138 of the assemblage
104. The two assemblages 104 and 104' are substantially identical.
One suitable tension means is a cable 140 inserted through the
aligned openings 134 of the assembled segments, pulled to the
required length, anchored at the opposite ends of the assemblage as
by swage fittings 142, and released to exert a compressive force to
the assemblage at its opposite ends. Alternatively, other tension
means may be used to establish the desired compression of the
segments in the assemblage. One such other means includes a rod
disposed in the aligned openings 134 of the segments and fitted
with a nut at one or both of its ends so that tightening of the
nuts tensions the rod and places the segments in compression. One
suitable cable for applying the desired compression force to the
segments is made of carbon steel and of the general type employed
in prestressed concrete structures.
The cable 140 may be chosen with a diametral dimension less than
the diametral dimension of the opening 134 in each segment and
after the segment is in place on the cable the space between the
cable and the inside surface of the opening 134 in the segment may
be filled with a grout 144, such as rigid polyurethane, as
described hereinbefore. The end segments may be protected from
localized forces by a plate or metallic segment 146, and plural
tension means may be employed as previously described.
In the assemblage 104 of segments, the individual segments 102 are
aligned with respect to each other in a manner such that their
peripheries are flush with each other to define an elongated top
surface 114 extending along the length of the box and adapted to
contact and support a drier felt or Fourdrinier wire moving
thereacross. Employing centerless grinding techniques, the aligned
peripheries of the segments are provided with a collective smooth
surface finish of less than about 20 microinches AA (arithmetic
average) so as to provide for low frictional contact between the
ceramic surfaces 114 and 116 and the felt 112. In this manner, the
wear of the ceramic surfaces and the felt is minimized. It has also
been found that less horsepower is required to move the felt over
the disclosed ceramic surfaces than has heretofore been required
with accompanying savings in power. In the depicted suction box,
the assemblages 104 and 104' of compressed ceramic segments are
mounted on ledges 148 and 150 of the upper wall 110 of the suction
box 106. One suitable mounting is depicted in FIGS. 6 and 10 and
comprises elongated cradles 152 and 154, one on each side of the
slot 100. Each of the depicted cradles includes a first continuous
length clamp 156 extending over substantially the entire length of
the side edge of the slot 100 and shaped to receive an assemblage
of segments 104' therein. The fit between each continuous clamp and
its assemblage of segments along the length of the clamp is
sufficient to form a vacuum seal therebetween. If necessary or
desired a gasket may be employed between each assemblage and its
respective cradle. The assemblage 104 is retained in its continuous
clamp 156 means of a plurality of further clamps 158 each having a
concave face 160 contacting the assemblage and being removably
secured to the continuous clamp as by means of bolts 162. In
addition to holding the assemblage in place, these further clamps
158 force the assemblage against the continuous length clamp 154 to
aid in developing and maintaining a vacuum seal between the
assemblage.
The continuous surfaces 164 and 166 of the clamps 152 and 154 are
disposed facing each other to define an elongated extension of the
slot 100 so that fluid or other matter withdrawn from the felt or
wire is directed into the suction box to be discharged through the
conduit 122. Each of the continuous length clamps 152 and 154 is
removably mounted on its respective ledges 148 and 150 as by screws
168. As necessary, a gasket material 170 is positioned between each
clamp 154 and its supporting ledge 150 to form a vacuum seal
therebetween.
One embodiment of a system which includes an elongated flexible
ceramic member and which includes at least two members, one of
which is movable relative to the other and in frictional engagement
therewith is the doctor system depicted in FIGS. 11-13. This
depicted system includes Yankee Dryer 200 on which a paper web 202
is dried and creped. The web is trained about a portion of the
peripheral surface of the dryer 20 and dried by heat transferred
through the cylindrical shell 204 thereof. Steam introduced into
the interior of the dryer shell is commonly used to heat the shell.
The paper web 202 is doctored from the shell 204 by means of a
doctor blade 206 as is well known in the art to provide a creped
paper web 208. In this embodiment, the dryer shell 204 comprises a
first member of the system and is movable relative to and in
frictional engagement with the doctor blade 206 which comprises a
second member of the system.
In the system depicted in FIG. 13, the doctor blade 206 is
positioned with respect to the dryer surface 204 and to the paper
web 202 by support means shown generally at 210 including a pair of
jaws 212 and 213 having shoulders 214 and 215, respectively, that
engage mating slots 216 and 217 in opposite surfaces of the doctor
blade 206. Other suitable mounting means will be readily recognized
by one skilled in the art.
In operation of the depicted system, the surface of the shell 204
becomes irregular due to its being heated by the steam. In order to
keep the doctor blade in contact with the shell for doctoring the
web from the shell, it is necessary to bend the doctor blade so
that it conforms to the irregularities in the shell surface.
In these and other systems of this type, as disclosed, it is
desired that one of the members be flexible and have a good wear
surface that is engaged by the other of the members. It has long
been desired that such one of the members be made of a ceramic
material to take advantage of the wear resistance of this material.
Continuous lengths of ceramic are prohibitively costly. Members
having small ceramic inserts disposed along the length of the
member to define a wear surface have been tried but such members
develop gaps between the inserts where the member bends during use
so that the edges and/or corners of the separated segments become
points of excessive wear.
The illustrated doctor blade system comprises an elongated flexible
member including a plurality of ceramic segments 220 each having at
least two opposite substantially parallel flat faces 224 and 226
(FIG. 12). Each of the depicted segments 220 further includes an
upper flat surface 230 which joins a forward upright surface 232 to
define a leading edge 234, and an opening 236 extending through
each segment between its opposite flat surfaces 224 and 226. A
plurality of these segments are assembled in face-to-face abutting
relationship with their leading edges aligned to define the doctor
blade 206. As illustrated, the flat faces 224 and 226 of each
segment are disposed substantially perpendicular to the
longitudinal axis, i.e. the composite length, of the composite
member. The aligned segments 220 are forced toward each other by a
tension means 238, anchored to opposite ends of the composite, with
a force which elastically compresses the segments.
Each of the segments of each of the elongated members of the
present disclosure is fabricated from a hard dense ceramic material
that is available at a reasonable cost.
The ceramic preferably is an impervious crystalline material that
combines high mechanical strength with extreme hardness, inertness,
refractoriness, and high chemical resistance properties. Because
these properties are retained over a wide range of application and
environmental conditions that many other materials cannot
withstand, such ceramics suitably serve under conditons adverse to
other materials. Alumina, silicon carbide, boron carbide and
silicon nitride materials possess those properties required in many
industrial applications, and economically feasible for such end
uses. Alumina is particularly suitable and is preferred for use in
the present ceramic member because of its properties and its
availability at relatively low cost when formed in relatively short
segments.
The alumina segment is formed by compacting finely ground oxide
powders with fluxing agents and inhibitors at relatively high
pressures as is known in the art. Forming methods include dry
pressing, isostatic pressing, casting, extrusion, and injection
molding. After forming, the resulting "green" ceramic segment is
fired at a high temperature for a specific length of time. Firing
temperatures vary but usually range between 2,500.degree. F. and
3,250.degree. F. During firing the ceramic shrinks; therefore,
segments are formed while in the green state to allow for the
physical reduction caused by firing. After firing, the ceramic
segment is strong, hard and dense, composed substantially of pure
alumina of controlled crystal size. Machining of the ceramic
segments is possible either before or after firing. Fired segments
are ground or lapped to obtain the desired surfaces thereof.
Grinding usually must be done with diamond-impregnated wheels,
although silicon-carbide or alumina wheels are sometimes used.
Most of those physical properties desired in the ceramic segments
improve as the purity of the ceramic increases, especially
hardness, compressive strength, wear resistance and chemical
resistance. For example, alumina ceramic compositions having
aluminum oxide contents less than about 85% lose certain of their
properties to an unacceptable degree. Preferably, the alumina
ceramics contain about 90.0 percent or more aluminum oxide.
The compressive strength of the ceramics exceed that for most
materials. For example, compressive strengths as high as 550,000
psi have been obtained in certain relatively pure alumina ceramics.
Suitable compressive strengths for the ceramic segments range
upwardly from about 200,000 psi.
Each of the segments is provided with two opposite substantially
flat and parallel faces. The segments are disposed in face-to-face
relation with their parallel faces abutting the parallel faces of
adjacent segments to define the elongated composite of a desired
length and subjected to a compressive force applied at
substantially right angles to the faces. The flatness and
parallelism of the abutting segment faces help to prevent cracking
or breaking of the segments due to unevenly applied stresses or
localized stresses by distributing the compressive forces evenly
over the abutting faces. Abutting segment faces, each of which is
flat to within about 0.0002 inches and has a surface finish of less
than about 20 microinches arithmetic average (AA) have been found
to be suitable for these purposes. When such individual segments
are placed in fact-to-face relation without grout or adhesive, the
abutting flat faces of adjacent segments lie in intimate contact
with each other over substantially the entire areas of the abutting
faces without significant open space therebetween so that the
abutting faces supply support to each other especially when the
surface of the member is being ground as will be described
hereinafter. In one embodiment, each segment is provided with an
opening extending between the opposite flat faces thereof. This
opening in a segment is aligned with similar openings of abutting
segments to provide a channel through the composite for receiving a
tension means for compressing the segments in the direction of
their composite length.
As noted above, in producing an elongated member of given length, a
sufficient number of segments are assembled in face-to-face
relation with their respective openings aligned to obtain the
desired length. The assembled segments are secured together with a
force applied substantially in the direction of the length of the
composite and substantially perpendicular to the flat parallel
faces of the segments. This force is sufficient to place the
segments in elastic compression, and produce a significant
compressive strain, and is suitably applied as by a tension means
applying a compressive force to opposite ends of the composite. One
suitable tension means is a cable inserted through the aligned
openings extending between the opposite faces of each of the
assembled segments, pulled to the required length, anchored at the
opposite ends of the composite as by swage fittings to exert a
compressive force upon the composite at its opposite ends.
Alternatively, other tensioning means may be used to establish the
desired compression of the segments in the composite. One such
other means includes a rod disposed in the aligned openings of the
segments and fitted with a nut at one or both of its ends so that
tightening of the nuts tensions the rod and places the segments in
compression. One suitable cable for applying the desired
compression force to the segments is made of carbon steel and of
the general type employed in prestressed concrete structures.
The cable may be chosen with a cross sectional area less than the
cross sectional area of the opening in each segment and after the
segment is in place on the cable the space between the cable and
the inside surface of the opening in the segment may be filled with
a grout 44 (FIG. 2) such as rigid polyurethane, to position the
cable within the openings. One suitable grout is a liquid casting
urethane polymer designated as LD-2699, sold by E. I. Du Pont de
Nemours Company, Trenton, N.J. This grout also accommodates the
axial movement of the segments with respect to the compression
cable during compression of the composite and/or relative movement
between the segments and the cable in the event the member is
subjected to thermal change during use.
As illustrated, the composite of segments may be provided with a
plate or other means such as a metallic segment at each end of the
composite to provide for distribution of the compression force over
the face of each end segment to protect it from damage by localized
forces. In those instances where the desired compression is
relatively great a plurality of tensions means, e.g. cables,
provides greater compressive capability. In that event, the
plurality of cables are desirably threaded through spaced apart,
aligned openings through the segments. Such construction aids in
more evenly distributing the compressive forces over the abutting
faces of the segments.
The flexibility of the ceramic member is made possible be employing
relatively short segments (e.g. on the order of 1 inch long) held
together with a compressive force such that when the elongated
composite deflects by a distance d, along its length (see FIGS.
14-15), at least a part of the compression, e.g. compressive
strain, in those portions 240 and 242 of the abutting faces 244 and
246 of adjacent segments disposed on the outside of the line of
curvature A of the deflected composite is relieved, permitting
those portions of the segments to expand to accommodate the
deflection without physically separating. Importantly, the
compressive force holding the segments together is less than the
maximum compressive strength of the ceramic material by an amount
which permits those portions 248 and 250 of the abutting faces 244
and 246 of adjacent segments on the inside of the line of curvature
A of the deflected composite to be compressed by an additional
amount, causing these portions of the segments to compress by an
amount sufficient to accommodate the deflection without destruction
of the segments. In addition, the length of the individual segments
is chosen to be sufficiently small as permits their manufacture at
minimized costs taking into consideration the anticipated
compressive forces to which the segments are to be subjected in
order to obtain the desired response of the composite incident to
deflective forces.
In addition to the deflective forces, consideration must be given
to thermal changes affecting the element in that such will usually
produce different responses in the ceramic segments and the tension
member. Such thermal changes can arise by differences in the
start-up and operating temperatures of the machine or system in
which the element is installed, and/or changes in ambient
temperature of the element during assembly, shipping or
installation.
In calculating the compression required to accommodate the maximum
anticipated deflection of a member of given length without
separation of the segments, it is assumed that the deflection of
the member will take the shape of a uniformly loaded simple beam
and that the maximum deflection will be sufficiently small (less
than about 1 percent of the member length) to permit the use of
calculations based on circular arcs, rather than more exact curves.
The latter could be used in those circumstances where more exact
calculations are required; however, it has been found that such is
not necessary in constructing flexible members for most end uses.
More specifically, and with reference to FIGS. 14 and 15, for a
ceramic member of given length, l (in inches), having a
longitudinal axis subjected to a maximum anticipated deflection, d
(in inches), along a line of curvature A, and made up of a
plurality of segments each being of a known .[.length, 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, A.sub.c, 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
where
E.sub.c = the modulus of elasticity of the ceramic;
A.sub.c = 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.
where:
.alpha..sub.s = the coefficient of thermal expansion of the tension
member;
.alpha..sub.c = the coefficient of thermal expansion of the
ceramic;
.DELTA.T = degrees of temperature change anticipated, in degrees
F;
A.sub.s = cross-sectional area of the tension member, in square
inches;
E.sub.s = the modulus of elasticity of the tension member
A.sub.c = the cross-sectional area of a ceramic segment in a plane
perpendicular to the length of the member, in square inches;
E.sub.c = the modulus of elasticity of the ceramic.
Combining Equations (1) and (2) gives
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, .DELTA.T will be 0 and P.sub.T [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.degree. 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.
EXAMPLE I
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 (A.sub.c) 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.degree. F to 300.degree. F.
(.DELTA.T = 230.degree. 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.degree. 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.
EXAMPLE II
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 (A.sub.c) 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.degree. F. to 170.degree. F (.DELTA.T = 100.degree. 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.
EXAMPLE III
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 (A.sub.c) 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.degree. F. The temperature at assembly is
70.degree. F, giving a .DELTA.T of 100.degree. 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.
* * * * *