Note: Descriptions are shown in the official language in which they were submitted.
1:C~~ v«n: : ~ f~ a N,u~;~c.ttrr; urp . o- o- v : i i . a = -s +q.5 F39 ~y_ _
_ . . _ _
06-06-2000 CA 009900533
7
SCREEN GYL1NDER STf~ESS CONCENTRATION RELIEF
BACKGROUND AND SUMIUIARY OF THE INY NTION
In the manufacture of slotted screen cylinders, such as for the pulp and paper
industry (e,g, for screening cellulose pulp having a typical consistency of .5-
5°~0); as
shown in U.S. patents 5,718,826, 5,200,072. 4,2fi4,438, 4,529,52Q, etc., a
plate of steel
or like material is machined to provide a plurality of grooves substantially
parallel to
- each other and to what will be the central axis when a cylinder is made from
the piste,
and a plurality of slats in at least some of the grooves (normally ail of
them) defining d
through-extending flow path of a pre-determined size perpendicular to the
plane of the
plate, with a land area separating grooves, and their associated slots, from
other in-lire
grooves and slots. After the grooves and slots are machined, the plate is
rolled,
utilizing conventional equipment, to form a cylinder. When that rolling takes
place the
surface of the plate that becomes the outer surface of the cylinder is
subjected to
tension stresses, vdhlle the face of the plate that becomes the inner surface
of the
cylinder is subjected to compressive stresses. For outflow type cylinders this
results in
a narrowing ref tl;e width of the slot, while for in flow type cylinders this
results in an
opening up of the slot, in either case, the care taken to machine a slot of a
desired
pre-determined size (e.g. .002-.024 inches in width) is negated to at least
some extent,
causing the slots to Jose their initial machined geometry. Also, at rolling,
cracks oan
appear at the ends of the slots. The ends of the slots typically include
stress risers,
and when combined with the stress of rolling, the stress threshold of the
material rnay
be exceeded, resulting in a poor quality cylinder-
U.S. Patent 3,748,428 relates to the production of a slotted screen by
electrical
a'ischarge machining. The slots are provided in groups in a curved screen
plate of
metal at least one-eighth inch thick immersed in a dielectric liquid. Using
two sets of
electrodes, successively applied, a first set of slots is produced extending
partially
through tt~e plate, and then a second set forming narrot~rer slots extending
from the
base of the first slot so that the remaining thickness of the metal. are
provided. This
technique has not been effectively utilized to produce slots having precisely
controlled
slot width, and of smaller dimension, than in other conventional techniques.
CA 02334572 2000-12-07 AMENDED SHEET
RC~w v;nn; . i-nA ~ej:ENCH1'~.N U6 . Ei- 6- U : 17: '?'~
06-06-2000 -a +49 89 ' CA 009900533
1a
According to the present invention, a method and screen cylinder are provided
which reduce the stress concentration at the slot ends and allow the rolling
of screen
cylinders of smaller diameters without cracking of the Base material at the
slot ends.
This also allows the production of screen cylinders with more precisely
controlled slot
width,
CA 02334572 2000-12-07 AMENDED SHEET
WO 99/64664 PCT/CA99/00533
- 2
which is particularly important for inflow cylinders since according to
the present invention there is less widening of the slots. In the case of
inflow screen cylinders, it is possible to make smaller final actual slots
than earlier possible.
According to the invention, stress relief grooves are provided in
the land area between in-line grooves so as to typically cut away about
10-80% (e.g. about 40-60%) of the thickness of the land area (most
normally about 50%), which cuts the deformation tension and
compression roughly about 50%.
According to one aspect of the present invention a screen cylinder
is provided comprising: A screen plate having first and second surfaces
and a thickness dimension provided between the first and second
surfaces, a plurality of accept flow providing grooves formed in the first
surface, and a plurality of slots extending between the grooves and the
second surface for effecting screening of a slurry to be screened. At least
some of the grooves in substantially end-to-end alignment, and the plate
having land areas between the grooves in substantially end-to-end
alignment. A plurality of stress relief grooves formed in the land areas
each between accept flow providing grooves in substantially end-to-end
alignment, the stress relief grooves each having a depth between about
10-80% of the thickness dimension of the plate. And, wherein the screen
plate is in cylindrical form with one of the first and second surfaces
defining an outer surface of a cylinder, and the other of the first and
second surfaces defining an inner surface of a cylinder.
Each of the stress relief grooves has a bottom, which is a portion of
each of the stress relief groove closest to the second surface, and
preferably at least a plurality of the bottoms are rounded (typically they
all are). A plurality of the stress relief grooves (e.g. all) preferably have
a
depth between about 40-80% of the thickness dimension of the plate, e.g.
about 50%. The stress relief grooves reduce by at least 10% (e.g. by about
30-50%) the magnitude of deformation of the slots due to compression or
tension in the second surface as a result of cylinder formation from the
plate, compared to if the relief grooves were not present.
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26~
WO 99/64664 PCT/CA99/00533
- 3
In situations where an inflow cylinder is provided, that is where
the second surface comprises the outer surface of the cylinder, the slots
may have a smaller actual width impossible for an otherwise identical
cylinder without the relief grooves, e.g. an actual width of between about
.002-.004 inches.
In most situations the thickness dimension of the plate is between
about 2-20 millimeters and the slots have an actual width of between
about .002-.024 inches. The stress relief grooves may have the width that
is the same as that of the accept flow providing grooves substantially in
IO end-to-end alignment adjacent thereto, but the width may also be
different; for example the width of the stress relief grooves may be
between about 40-90% of the width of the accept flow providing grooves.
According to another aspect of the present invention a method of
making a screen cylinder from a screen plate having first and second
surfaces and a thickness dimension provided between the first and
second surfaces, is provided. The method comprises: (a) Forming a
plurality of accept flow providing grooves in the first surface with land
areas between the grooves, some of the grooves in substantially
end-to-end alignment. (b) Forming a plurality of slots extending between
the grooves and the second surface for effecting screening of a slurry to be
screened. (c) Forming a plurality of stress relief grooves in the land areas
between accept flow providing grooves in substantially end-to-end
alignment, so that the stress relief grooves each have a depth between
about 10-80% of the thickness dimension of the plate. And then, (d)
forming the screen plate into cylindrical form with one of the first and
second surfaces defining an outer surface of a screen cylinder, and the
other of the first and second surfaces defining an inner surface of a screen
cylinder.
The procedures (a) through (c) may be practiced in essentially any
order; oftentimes, however, (a) and (c) may be practiced at approximately
the same time, and before (b).
Typically (c) is practiced to provide the stress relief grooves with
bottom portions, closest to the second surface, that are rounded; and (c) is
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
- 4
also practiced to provide at least a plurality of the relief grooves with a
depth between about 40-60% (e.g. about 50%) of the thickness dimension
of the plate. For example (c) is practiced to reduce by at least 10% (e.g.
about 30-50%) the magnitude of deformation of the slots due to
compression or tension in the second surface as a result of cylinder
formation during (d) compared to if the relief grooves were not present.
Also (c) may be practiced so that the stress relief grooves have a width
that is about the same as (that is about 100% of) the width of the accept
flow providing grooves, but alternatively (c) may be practiced so that at
least a plurality of the stress relief grooves have a width of between about
40-90% of the width of the accept flow providing grooves substantially in
end-to-end alignment adjacent thereto.
In the method typically (a)-(d) are practiced to provide an
effectively operable screen cylinder having a diameter smaller than the
diameter of an otherwise identically produced screen cylinder produced
by a method not including (c). Also (a)-(d) may be practiced so as to
provide the second surface as the outer surface of the screen cylinder, and
so that the slots have a smaller actual width than possible if producing
an otherwise identical cylinder without the stress relief grooves.
The method further preferably comprises using the screen cylinder
to screen a cellulose pulp slurry having a consistency of between about
.5-5%.
According to still another aspect of the present invention a screen
cylinder is provided comprising: A screen plate having first and second
surfaces and a thickness dimension provided between the first and
second surfaces, a plurality of accept flow providing grooves formed in
the first surface, and a plurality of slots extending between the grooves
and the second surface for effecting screening of a slurry to be screened.
At least some of the grooves in substantially end-to-end alignment, and
the plate having land areas between the grooves in substantially
end-to-end alignment. A plurality of stress relief grooves formed in the
land areas each between accept flow providing grooves in substantially
end-to-end alignment, the stress relief grooves reducing by at least 10%
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
- 5
the magnitude of deformation of the slots due to compression or tension
in the second surface as a result of cylinder formation from the plate,
compared to if the relief grooves were not present. And, wherein the
screen plate is in cylindrical form with one of the first and second
surfaces defining an outer surface of a cylinder, and the other of the first
and second surfaces defining an inner surface of a cylinder, and
reinforcing elements provided on the outer surface.
It is the primary object of the present invention to release the
stress concentration during the manufacture of screen cylinders from
slotted screen plates, particularly for screening pulp in the pulp and
paper industry. This and other objects of the invention will become clear
from an inspection of the detailed description of the invention and from
the appended claims.
BRIEF DESCRIIrTION OF THE DRAWINGS
FIGURE 1 is a side greatly enlarged cross-sectional view of an
exemplary slotted screen cylinder plate according to the prior art, taken
along lines 1-1 of FIGURE 3;
FIGURE 2 is an enlarged schematic cross-sectional view taken
along lines 2-2 of FIGURE 1;
FIGURE 3 is a side schematic view of an exemplary prior art screen
cylinder;
FIGURE 4A is an end view of a conventional prior art screen
cylinder;
FIGURE 4B is an enlarged view of a portion of the cylinder of
FIGURE 4A;
FIGURE 5 is a view like that of FIGURE 1, taken along lines 5-5 of
FIGURE 7, of a slotted screen cylinder plate according to the present
invention;
FIGURE b is a schematic cross-sectional view taken along lines 6-6
of FIGURE 5;
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99I00533
- 6
FIGURE 7 is a side schematic view of an exemplary screen cylinder
according to the present invention;
FIGURE 8A is an end view of an exemplary screen cylinder
according to the invention; and
FIGURE 8B is an enlarged detail cross-sectional view of a portion
of the screen cylinder of FIGURE 8A.
DETAILED DESCRIPTION OF THE DRAWINGS
FIGURES 1-4B illustrate the prior art over which the invention is
an improvement. FIGURE 1 illustrates a flat plate 10 which is rolled into
a screen cylinder 11 (see FIGURES 3 and 4), as is conventional. The view
in FIGURE 1 is parallel to the central axis 12 (see FIGURES 3 and 4A) of
the screen cylinder 11 ultimately formed, taken along lines 1-1 of
FIGURE 3; while FIGURE 2 shows a cross-sectional view of the plate 10
perpendicular to the axis 12, taken along lines 2-2 of FIGURE 1.
In the conventional plate 10, an accept flow providing groove 13,
which is large and does not function to effect screening, is formed in the
surface 14 of the plate 10, while fine slots 15 -- which do effect screening --
are machined in the face 16 opposite the face 14. The slots 15 control the
cleanliness of the accepts passing through the screen cylinder 11. The
widths of the slots 15 are particularly important for control of accepts
cleanliness. The width 18 (see FIGURE 2) of each slot 15 is typically
between .002-.024 inches, while the plate 10 typically has a thickness 19
(see FIGURE 1) of between about 2-20 mm.
FIGURES 3, 4A and 4B show an outflow screen cylinder 11
produced from the plate 10, in which the surface 14 becomes the outer
surface of the screen cylinder 11, and the surface 16 becomes the inner
surface. If an inflow screen cylinder is constructed from plate 10, then
the surface 14 is the inner surface and the surface 16 the outer one. The
rolling action during cylinder production causes the outflow cylinder, as
seen in FIGURES 3, 4A and 4B, to have a narrower slot 15 width, and can
cause stress cracking at the ends 20 of the slots 15 for both outflow and
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
_ 7
inflow cylinders, while formation of an inflow cylinder can cause the
slots 15 to "open up" and thereby become larger and thereby allow a
larger size material (debris) to pass therethrough than desired.
In the conventional plates 10 and associated cylinders 11 of
FIGURES 1 through 4B, the grooves 13, and the slots 15, are disposed in
rows, the grooves 13 and slots 15 in any one row being substantially in
line with each other along a dimension parallel to the central axis 12 of
the screen cylinder 11 formed thereby, as indicated by the double arrow 12
in FIGURE 1. The solid material of the plate 10 between the ends of
in-line grooves 13, shown generally by reference numeral 21 in FIGURES
1 and 3, is called the "land area".
FIGURES 5 through 8B are views comparable to those of FIGURES
1 through 4B, only showing the practice of the method according to the
present invention, to produce a cylinder according to the present
invention. In FIGURES 5 through 8B structures comparable to those in
FIGURES 1 through 4B are shown by the same reference numeral only
preceded by a "1".
The only major difference between the invention of FIGURES 5
through 8B and the prior art of FIGURES 1 through 4B is the provision
of a stress relief groove 25 in the land areas 121 between the in-line ends
of the accept flow providing grooves 113. The amount of material
removed to form the relief groove 25, which is a partial continuation of
the grooves 113, is typically between about 10-80% of the thickness 119 of
the plate 110, e.g. about 40-60%, preferably about 50% as illustrated in
FIGURES 5 through 8B. That is the land area 121 is machined to have a
thickness 26 (see FIGURE 5) which is between about 20-90% (e.g. about
40-60%, preferably about 50%) of the thickness 119 of the plate 110. Thus
if the plate thickness 119 is 10 mm, the stress relief groove 25 has a height
of about 5 mm, and the land area 12I has a thickness 26 of about 5 mm.
This is of course only one example, and a wide variety of modifications
are possible, the goal being to reduce significantly (by at least 10%, and
typically between about 30-50%, e.g. about 50%) the magnitude of
deformation due to compression or tension of the surfaces 114, 116.
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
_ 8
By cutting the stress relief grooves 25 the neutral axis of the solid
section 121 of the cylinder 111 is displaced toward the slot 115, and thus
upon rolling deformation is reduced or minimized.
The stress relief grooves 25 are preferably about the same width as
the grooves 113, but can be less. For example the width of a stress relief
groove 25 may be about 40-100%, e.g. between about 40-90%, of the width
of the grooves 113 on either end thereof. In FIGURES 5, 6, and 8B the
stress relief grooves 25 have about 100% of the width of the grooves 113,
the groove 25 bottom may be rounded, as seen in FIGURES 6 and 8B, but
also may be flat, or have a wide variety of other configurations.
Although not visible in the drawings, typically the screen
cylinders 111, 11, are contoured. That is contoured accept flow providing
grooves 113 are provided in the inlet side of the screen cylinders 111, the
contoured grooves having an upstream side surface, a bottom, and a
downstream side surface. The contoured grooves -- and the screen
cylinders utilizing them -- may be provided as shown in U.S. patents
4,529,520, 4,836,915, 4,880,540, 5,000,842, or in other ways known in the art.
Such contoured cylinders are commercially available, for example, under
the trademark "PROFILE" from CAE ScreenPlates, Inc. of Lennoxville,
Quebec, and Glens Falls, New York.
When the screen cylinders 11, 111 are constructed they also will
have reinforcing rings shown schematically at 23, 123 in FIGURES 3 and
7, respectively. However the reinforcing rings 23, 123 are typically
applied after cylinder formation and in any event are not significantly
related to the invention. The rings 23, 123 may be provided as shown in
U.S. patent 5,718,826, or the prior art illustrated or discussed therein.
The method and cylinders according to the invention are suitable
for screen cylinder 111 diameters from two inches to 120 inches, for slot
115 widths 118 of from .002-.024 inches, for plate 110 thicknesses 119 of
2-20 mm, and for a wide variety of plate materials including steel,
stainless steel, non-ferrous alloy composites, and others. By practicing
the invention it is possible to reduce stress concentrations (e.g. by about
50%) at the slot 115 ends 120, and allow rolling of cylinders 111 of smaller
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
_ 9
diameters without cracking of the material of the plate 110 at the slot
ends 120, for both inflow and outflow cylinders. The method also allows
rolling of inflow type cylinders with much less widening of the slots 115
so that smaller final actual slots may be obtained than in prior art
machined inflow screen cylinders, and more precise control over the slot
lI8 width for both outflow and inflow cylinders.
According to the present invention a method of making a screen
cylinder 111 from a screen plate having first and second surfaces 114, 116,
respectively, and a thickness dimension 119 provided between the
surfaces 114, 116 comprises, (a) Forming a plurality of accept flow
providing grooves 113 in the first surface 114 with land areas between the
grooves 113, some of the grooves 113 in substantially end-to-end
alignment (as seen in FIGURES 5 and 7 in particular). (b) Forming a
plurality of slots 115 between the grooves 113 and the second surface 116
for effecting screening of a slurry to be screened (e.g. for a cellulose pulp
slurry having a consistency between about .5-5%). (c) Forming a plurality
of stress relief grooves 25 in the land areas 121 between the grooves 113
so that the stress relief grooves 25 each have a depth between about
10-80% of the thickness dimension 119 of the plate; and then (d) forming
the screen plate into a cylindrical form 111 (FIGURES 7, 8A and 8B) with
one of the surfaces defining an outer surface of the screen cylinder (the
surface 114 in the embodiment of FIGURE 8B) and the other the first and
second surfaces defining an inner surface of the screen cylinder (116 in
FIGURE 8B). The procedures (a)-(c) may be practiced in any order, and
are practiced using entirely conventional techniques of milling,
machining, etc. The procedure (d) is also practiced utilizing entirely
conventional techniques.
In the disclosure all broader ranges also specifically include all
specific narrower ranges within the broad range. For example, 30-50%
includes 31-49%, 35-48%, 40-41%, and all other narrower ranges.
While the invention has been herein shown and described in
what is presently conceived to be the most practical and preferred
embodiment it will be apparent to those of ordinary skill in the art that
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
WO 99/64664 PCT/CA99/00533
many modifications may be made thereof within the scope of the
invention, which scope is to be accorded the broadest interpretation of
the appended claims necessary to cover equivalent methods and
products.
5
CA 02334572 2000-12-07 SUBSTITUTE SHEET (RULE 26)
