Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 1 78683
A CYLINDRIC SCREEN BASKET AND A METHOD OF MAKING SAME
Background of the Invention
Field of the Invention
The present invention relates to a cylindric screen for use in pressure
5 screening devices and to a method of producing such a screen. The screens of
this type are used primarily, but not exclusively, in the pulp and paper industry
for screening pulp or paper stock. Typically, the screen is mounted in a
pressurized vessel provided with a system of rotary hydrofoils designed to
generate pulsations in the pressurized stock with which the screen is filled,
10 thus aiding the passage of accepted fibrous stock throu~h the passages
machined in the cylindric screen.
Desc, i~ Iion of Prior Art
In certain applicd~iol1s it has been recognized that the ideal dlldl~elllelll
from the standpoint of providing optimum passa~e of acceptable fibres while
15 securing reliable blocking of the rejects is a device wherein the slots~or
passages throu~h the screen are of the type of a preferably continuous
circumferential slot the width of which may vary depending on a particular
ion, the useful range being app,u.d",dLely between .003 inch to sizes
wider than 0.010 inch. Reference may be had to US Patent 4,155,841
20 (Chupka et al.) the entire specification of which is incorporated herein by
reference .
It is known to provide screens of the type where the slots extend
generally continuously over the periphery of the screen drum. Such screens
have been made, virtually exclusively, as a so-called wedge-wire structure in
25 which a number of wires having a generally wedge-shaped cross section, are
formed and welded into a number of rings and are then connected together to
form the screen. Another known modification replaces the plurality of wedge
wire rings with a continuous wedge wire in the form o. a thraad with a shallow
pitch. The wire is welded to a number of axially arran~ed rods.
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Prior art describing the present state of the art is represented by the
aboveUSPatent4,155,841;CanadianPatent1,185,210(Chupka);Published
Canadian Patent Application No. 2,094,546 (Ehmcke); Published Canadian
Patent Application 2,117,077 ~Malm); US Patent 4,383,918 (Chupka et al.J;
US Patent 4,410,424 (Chupka et al.); US Patent 4,918,807 (Frejborg) and US
Patent 5,190,161 (Koichi). The text of all of the above l~:r~ nces is
incorporated herein by reference.
It is a common drawback of the known cylindric screens with continuous
peripheral or circ~"~,r~r~ ial screening slots that they are difficult to
manufacture with the desired accuracy of the width of the screenin~ slots.
This is due to the fact that the width of the slot is determined by placement
of adjacent wedge-wires relative to each other and weldin~ thus placed wires
to supportin~ ribs. Durin~ the weldin~, the wires are subjected to thermal
stress which ~ives rise to inaccuracies. The welding also provides further
drawback in that rou~h sections may develop at the joinders of the wires and
the axial ribs. Last but not least, the stren~th of the known screens of this type
is often insufficient for hi~h pressure screenin~ devices which are preferred inthe industry.
Summary of the Invention
It is an object of the present invention to advance the art of cylindric
screens of the above type. In particular, it is an object of the invention to
provide a screen with circ~",rt:,~"~i~lly disposed, ~enerally continuous
screeninrJ slots, which is easier to produce than the wed~e-wire screen.
Another object is to provide a screen which can easily be produced without
burrs. In the wed~e wire screens burrs are often present. They attract clusters
of fibres known âS ~fibre stringin~" are detrimental to the homogeneity of the
screened stock.
In general terms, the invention provides a cylil~dric screen of the
aforesaid type which comprises the combination of:
(a) an annular sheet section of a ~enerally cylindric shape and includino~ a
first generally cylindric surface, a second ~enerally cylindric surface, a
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first axial end and a second axial end; a first abutment side and a second
abutment side, the abutment sides extending each ~enerally axially of
the cylindric shape and abuttin~ against each other to close said
cylindric shape;
5 (b) a col1l1e,,li~g means fixedlv holding the abutment sides in abutment;
(c) a plurality of ~qenerally axially elongated ribs integral with the sheet
section, and protruding from said first generally cylindric surface;
(d) a plurality of peri~.lle, "y elongated slots provided in the sheet section,
each pel~ elal slot definin~ a passage through the sheet section from
the first surface to the second surface thereof;
(e) said peripheral slots being discontinued at said abutment sides.
In another aspect, but still defining the invention in general terms, a
method is provided for producing a cylindric screen having a plurality of
generally peripherally oriented, closely spaced apart screening slots each
extending generally the entire periphery of the cylinder, said method comprisingthe steps of:
(a) providin~ an integral, flat, generally rectangular sheet of metallic mâterial
having a first abutment side edge, an opposed, second side edge, a first
end edge, and a second end edge, a first face and an opposed, second
face;
(b) providing, in said first face a plurality of generally equidistantly spaced
apart channels extending in a general direction from said first end edge
to said second end edge and leaving a rib between each pair of said
channels, said ribs likewise extendin~ in a general direction from said
first end edge to said second end edge;
(c) providing, in said second surface, a plurality of generally equidistantly
spaced apart ~rooves extending in the general direction from said first
side edge to said second side edge, each said groove having a ~qenerally
V-shaped cross-section widening in the direction from said first surface
to said second surface, thus defining a narrow bottom sectio,1 and
divergent side wall sections, the maximum width of each second groove
being only a fraction of that of each of the channel;
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(d) providing a slot in the narrow bottom portion of each ~roove to thus
make a passa~e from the respective narrow bottom section to the first
surface;
(e) each slot having the width which is only a fraction of said maximum
width of the respective groove;
(f) rolling said sheet into a cylindric shape wherein said side edges are
~enerally in abutment with each other and said end ed~es are opposed
axial ends of the cylindric shape;
(g) fixedly securing the side edges to each other to enclose said cylindric
1 0 shape.
Brief Des~ ,lio~ of the Drawin~s
The invention will be described by way of preferred embodiments, with
referencetotheacco"".a"yingdia~,d"""dlic,simplified, not-to-scaledrawings,
wherein:
~5 Figure 1 is a simplified perspective view of an embodiment screen
accordin~ to the present invention designed for use in ~ iolls
wherein the accepts flow from inside of the screen out, while the
rejects stay inside the cylinder and are removed from the
respective pressurized screen;~0 Figure 2 is a partial, did~ldll,,,,d~ic section ll-ll of Fig. 1;
Figure 3 is a partial, did~,d"""alic section taken on line lll-lll of Fig. 2;
Fi~ure 4A is a partial sectional view similar to that of Fig. 2 but showing
the abutment of the sides of the screen sheet enclosing the
cylindric shape;~5 Fi~ure 4B is a view similar to that of Fig. 4A but showin~ an alternative
structure of the abutting sides closing the cylindric shape of the
screen;
Figures 5 - 9 are diay,a"ll"d~ic rep,~se~ld~ioils of the steps of the preferred
way of the manufacture of the screen of the present invention;~0 Figures 10 - 13 are diagrammatic partial and simplified rep,~se~lLd~io~ls
showin~ some of possible modifications of the shape of the ribs
integral with the screen of the present invention;
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Figure 14 is a partial cross-sectional view similar to that of Fi~. 2 and
showing the principle of an alternative embodiment of the screen
basket of the present invention;
Figure 15 is a view similar to that of Fig. 14 and showing yet another
e",bc ' "e"L of the screen basket in accor.la~lce with the present
invention.
Detailed D~ ;orl of the Preferred r ' ~ a
The reference numbers of the crJ"~pol ' ~9 portions of the sGreen
basket are de ~iullalt:d with the same reference numbers, regardless whether
10 the plate is in a flat or rol~ed condition and regardless of the instant stage of
production. Also, certain parts of the structure which are functional
counterparts of each other, are referred to with the same digits, the distinction
being made by index letters. It will also be appreciated that Figure 1 is intended
merely as a general ~ ,e~ld~ion of the overall arrangement of the screen
15 basket of the invention with certain known structural features of the screen
baskets (e.g. the securement of end flanges to the basket, the weld holding the
reinforcement ring, actual density of the passage grooves) being omitted or
reduced in number for simplicity.
Referring particularly to Figure 1 and 9, it will be seen that a cylindric
20 screen basket is provided which can be used in a pressure screening device.
The cylindric screen is formed from a single metallic sheet section and is
pl ~r~rdbly made from stainless steel. Figures 1 and 9 show the sheet section
in its cylindric form but in the remaining figures it is shown in a straight,
generally planar configuration for the sake of c~arity. The sheet section 10,
25 which is flat in Fig. 8 but annular in Figs. 1 and 9, has a first surface 11 which
is cylindric in Figures 1 and 9 but in the original shape (Figs. 5 - 8~ it is
generally planar. The opposed face or surface 12 of the sheet section 10
forms, upon rolling as will be described, the exterior of the cylinder (see Figures
1 and 9) but is planar in the remaining figures. The sheet 10 is of a
30 rectangular configuration which is limited by a first end 13, also referred to as
"first axial end 13", and a second axial end 14. The opposed sides 15, 16 of
the sheet 10 are referred to as "first and second abutment side". This is due
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to the fact that the sides 15 16 abut against each other when the plate is
rolled. Refer to Figure 9.
Reference may now be had to Figure 4A where the engagement of the
abutment sides 15, 16 is shown in greater detail. The figure shows that there
5 is a bevel 28 provided in the abutment side 15 and a similar bevel 29 is
provided in the abutment side 16. The abutment sides 15, 16 are conl1e~ l~d
by colllle. li"g means which, in the en hQ ~ ~e~ IL shown, is an axially elon~ated
weld 17. The weld 17 thus holds the abutment sides 15, 16 in abutment.
The state i"""edidt~ly before the clamping of welding of the abutting sides 15
10 and 16 is d;d~ldlllllldli 'y indicated in Figure 9.
Figure 4B shows diayldlllllldLic 'y another embodiment where the
arrangement of the abutment side 15a 16a is different. Here the abutment
sides form each the end of a half-rib 18h with the app,~,p,idl~ bevels being
provided for radially outer and radially inner welds 170 1 7i which are inte~ral15 with the machined sheet of the screen. This provides a simplified dl I dl ,~~t:",en~
of the abutment joint.
The sheet section 10 comprises a number of elongated ribs 18. It
should be noted that only two ribs 18 are shown in Figures 6-8 it being
understood ~see for instance Figure 9 or Figure 1 ) that the number is larcJer
20 depending upon the actual size of the screen and also bearin~ in mind that the
perspective views of Figures 6-8 are merely partial views of the sheet 10. The
ribs 18 are inte~ral with the sheet of 10. This is clearly indicated in Fi~ure 6,
7 and 8 and also in Figure 9. It will be appreciated, of course that the ribs 18could also be secured to the sheet 10 for instance by welding. However the
25 integral structure as shown is preferred. The ribs project from the first face
11.
A plurality of peripheral slots 19 provide each a passage through the
sheet section 10. In other words the slots 19 communicate the first surface
or face section 11 with the second face section 12. Figure 4A shows that the
30 slots 19 are discontinued in a very short section at the abutment sides 15 and
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16. By the same token, it is indicated in Fi~ure 8 that the slots 19 reach into
that part of the axially elongated ribs 18 which is adjacent to the first surface
11.
As best seen in Figure 4A, the joint 17 and the abutment ends are
5 covered by an axially elongated coYer rib 20 which is ~enerally the same in size
as the ribs 18. The rib overlaps both abutment sides 15 and 16 and is secured
to the first surface of the sheet section 10 by a pair of elongated, axially
oriented welds 21, 22. The cylindric screen may be provided with a plurality
of peripheral reinforcing rings of which only one, ring 23, is did~;~ldlllll 'ly10 shown in Figure 1. The peripheral ring 23 is fixedly secured, prt:rt:,dbl,~ by
welding, to the second surface 12. As mentioned above, a number of ribs 23
can be provided such that they envelope the second surface 12 of the annular
sheet section 10. It is shown in Figure 1 and in Figures 7 and 8, that the
peripheral slots 19 are provided in what is referred to as annular slotted regions
15 30 which leave between ll,e",~lves a solid region 31. The peli~ ldl rin~ 23
shown in Figure 1 is shown as being disposed in such solid region 31. The
number of the regions 31 (and thus of the rings 23) is optional.
Turning now to the , t:,a, t::,er,ld~ion of Figure 3, the shape of the
peripheral slots will be described in greater detail. Each slot is comprised of a
20 wide section 24 which displays a generally U or V-shaped cross-sectional
configuration. The cross-section of the wide section 24 widens toward and is
open at the second surface 12. When viewed in cross-sectional view of Figure
3, it defines a concavely rounded bottom portion 25 which coincides with the
discharge end of a narrow slot section 26 which is open both at the bottom 25
25 and at the first surface 11. It is clearly shown in Figure 3 that the narrow slot
section 26 partly penetrates into the respective rib 18 as also indicated in
Figure 8.
The preferred way of manufacturing the cylindric screen of the present
invention will now be described with reference to Figures 5-9, it being
30 emphasized again that Figures 5-8 are mere diagrammatic partial views of a
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rectan~qular sheet from which the screen or at least the substantial portions
thereof are manufactured.
In the first step, an integral, flat, generally rectangular sheet 10 is
provided which has the abutment side edges 15 and 16 and first and second
5 end cdges 13 and 14 as described. Typically, the sheet is made of stainless
steel.
In the second stage of the preferred way of manufacturing the screen,
wide channels are machined in the first surface 11 leaving the longitudinal ribs18. The channels between adjacent ribs 18 are designated with reference
10 number 27 in Figure 6. They are also marked in Fi~qure 9 and 4B.
In the next step, the second surface 12 is provided with a plurality of
~enerally equidistantly spaced ~rooves and these are in effect the wide
sections 24 of the slots as mentioned above. These grooves 24 are located
in slotted regions 30 which, upon rolling of the sheet, become the annular
15 slotted regions 30. The grooves 24 are generally equidistantly spaced within
each slotted region 30. The shape of the grooves 24 is shown in and has been
described with reference to Figure 3.
Typically, the width of the channels 27 is about 40 mm, the usual ran~e
being about 10 mm to about 100 mm depending upon the particular application
20 of the pressure screen.
When the ~rooves 24 are made, the correspondin~q narrow slots 26 are
machined in each ~roove 24 whereby each respective groove 24 and slot 26
combine to produce one peripheral slot as mentioned above. With reference
to Figure 4A, it is pointed out a~qain that, in the embodiment shown, each slot
25 19 circumscribes virtually the entire periphery of the cylindric screen basket
with the exception of the abutment side sections 15, 16 where the slot is
preferably discontinued.
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lt can be seen from the ,~ ,e"Ldlion of FiDure 3 that the slot 26 has
the width which presents a mere fraction of the width of ~roove 24.
Depending on application, the width of the slot 26 is d,upru~ ily 0.1 mm to
1.0 mm, while the maximum width of the groove 24 is typically about 1.5 mm.
5 Fi~ure 8 shows the state of the sheet with the slots machined.
The abutment sides 15 and 16 can be provided at this point or at any
stage during the manufacture, with the bevels 28, 29 intended to provide
space for the lon~oitudinal weld 17 as is well known in the art.
Upon rollin~ of the sheet of Fi~ure 8 çienerally in the direction of arrows
10 R, and R2, to arrive the configuration of Fiçiure 9. Then, the abutment sides 15
and 16 are firmly en~aged one a~ainst the other and the longitudinal weld 17
permanently joins and encloses the cylindric shape of the screen.
Subsequently, the cover rib 20 is applied over the abutment sides 15, 16 by
weldin~ same to the first face 11 (Fi~qure 4A).
It is obvious from the above that the first surface or first facè 11 is the
inflow surface of the peripheral slots 19 while the widened portion 24 presents
the dischar~qe end thereof. The ribs 18 are designed to cooperate with rotatin~
hydrofoils F (Fi~s. 1- - 13~ of the associated pressure screen in order to
~enerate pulsations of the stock being screened as is well known in the art. In
20 the embodiment shown in Figures 1 - 9, the ribs 18 are of a rectançiular shape.
Fii~ures 10 - 13 indicate that the cross-sectional shape is optional and
may assume other configurations. For example, it may be of a half-moon
shaped cross-section (Fig. 10) resulting in a semi-cylindrical rib 1 8a. Accordin~
to another alternative shown in Fig. 11, the ribs may be of an irregular
25 trapezoid cross-section, where the leading side 32b (as viewed in the direction
33 of the motion of the hydrofoil F of the screen) of the ribs 1 8b is at an acute
angle to the bottom of the respective channel 27b, while the trailing side 34b
of the trapezoid is perpendicular to the bottom of the channel 27b. In Fi~. 12
the trapezoidal contour of the ribs 1 8c is regular, with each of the leadin~ sides
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32c and trailing sides 34c being at an acute angle to the bottom of the channel
27c. Fig. 13 shows a modification of the rectangular shape, where a beYel
35d, 36d is provided between each leading and trailing side 32d, 34d and the
top 37d of the respective rib.
Those skilled in the art will readily app(~,.idlt: that the inventive concept
can be realized by other e",bodi",e"ls of the screen than those disclosed
above. Two of many examples of such e"~c 'il,1e"ls, are shown in the
adcco""~a"ying drawings of Figs. 14 and 15.
Referring now to the dia~ldlllllldlic sectional view of Fig. 14 and
co"~pa,i,1~samewiththelt:plese"LdliunofFig.2,itisobviousthat,ifdesired,
the screen plate may be produced with inte~ral ribs of various cross ~ liunal
configurations as discussed above with reference to Fi~s. 10 - 13. As in the
preceding case, there is a number of channels 41 each between a pair of
adjacent ribs 40. There is the widened groove portion 42 associated with each
screening slot 43. The width of the screening slots 43 ~enerally Gorresponds
to the measurements Illerlliul1ed in connection with slots 26 above. In the
embodiment of Fig. 14, however, the slots are machined or otherwise provided
such that they do not pass through the ribs 40. Instead, each narrow slot 43
1~111 lil IdLC:S at the respective rib 40 and the next part of the same peripheral slot
continues only after such rib 40. The orie,lLdtion of the slots 43 and the
grooves 42 is peripheral and the widened grooves 42 at the discharge side of
the screen are each continuous from one end portion to the other as in the firstembodiment described.
In the embodiment of Fig. 15 another modification is shown where both
the narrow screening slot 43 and the associated widened part 42 of each
peripheral groove only extend from one rib 40 to one side of the adjacent rib
40, then, from the other side of that rib to the next rib and so on, about the
periphery of the screen. This embodiment provides a strongly reinforced
version of a screen with peripheral grooves and slots which may be desired
under particularly rough operating conditions where pressure impacts during
the operation of the screen are very high.
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Other aspects of the last two a",bodi",e"~:., such as the ",a( ll I lg
sequence, connectin~ the abutment sides of the screen plates into a cylindric
shape, securement of the outer ,~i"ru,r~r-",e"~ ring etc. are the same as in thefirst embodiment and therefore are not described in detail.
Other embodiments may differ from the el l ,l,odi" ,~"l~ disclosed withûut
departin~ from the present invention 8S set forth in the accrj,,,uall~in~ claims.
