US3082874A

US3082874A - Stock screen

Info

Publication number: US3082874A
Application number: US812645A
Authority: US
Inventors: Edgar J Justus
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1959-05-12
Filing date: 1959-05-12
Publication date: 1963-03-26
Anticipated expiration: 1980-03-26
Also published as: FR1246630A

Description

March 26, 1963 E. J. JUSTUS 3,032,874

STOCK SCREEN Filed May 12, 1959 3 Sheets-Sheet 1 26,? 4/ (/ucrus March 26, 1963 E. J. JUSTUS 3,082,374

STOCK SCREEN Filed May 12, 1959 3 Sheets-Sheet 2 137F211? Ur [name d Juan/.5

March 26, 1963 E. J. JUSTUS 3,0

STOCK SCREEN Filed May 12, 1959 3 Sheets-Sheet 3 I 271 2.27 fur 11642 d z/usrus 3,ti2,874 STOQK SCREEN Edgar .1. Justus, Beloit, Wis assignor to lieloit Iron Works, Beloit, Wis, a corporation of Wisconsin Filed May 12, 1959, Ser- No. 812,645 6 Claims. (Cl. 210-333) This invention relates to apparatus for screening a slurry of fibrous material in liquid suspension such as paper making stock and the like. More particularly, this invention relates to such apparatus wherein the screening area available in a given amount of space is greatly increased and wherein cleaning of the screen is accomplished by the provision of a uniformly increased pressure impulse on an entire screen to avoid bending thereof.

Vertical cylindrical type stock screening apparatus for the final screening of paper stock before it is delivered to the paper making machine has been developed and represents a large advance over the formerly used open type flat screens. Known devices of this type have commonly been constructed with a single large cylindrical screen through which the stock is pumped or, in some cases, with double concentric cylindrical screens. These screens may, for example, be kept clean by the operation of rotating foil in the manner described in U.S. Patent No. 2,835,173, issued to I. H. Martindale on May 20, 1958.

Certain diiiiculties, however, arise from the cleaning action in such a foil cleaned cylindrical screen. As shown in the above Martindale patent, the cleaning is the result of a pressure wave generated by the rotating foil which progresses around the cylindrical screen. This results in a slight localized progressively moving distortion of the screen material which is thin. This flexing of a particular part of the screen is repeated with the passage of each foil. This frequently leads to the early failure of screen material and requires limiting the pressure effect of the foils.

It is then an object of this invention to provide an improved stock screening apparatus which overcomes the above-noted difiiculties of the prior art.

It is a further object of this invention to provide stock screening apparatus having a greatly increased screening area in the equivalent space than has heretofore been available.

It is a still further object of this invention to provide apparatus for screening a slurry of fibrous material in liquid suspension wherein the ratio of screening area to the total space occupied by the apparatus is greater than has heretofore been available.

It is a further object of this invention to provide apparatus for screening a slurry of fibrous material in liquid suspension wherein means are provided to clean a screen member without flexing or deforming it by applying a uniformly increased pressure impulse to said screen member.

Other objects, features, and advantages of the present invention will be more fully apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawings in which like reference characters refer to like parts throughout and wherein:

FIGURE 1 is a front elevational view partially broken away in order to show certain features of the present apparatus in a central sectional view;

FIGURE 2 is a sectional view taken on the line 11-11 of FIG. 1 and showing -the layout plan of the screening apparatus of the present invention;

FIGURES 3 and 4 are enlarged detail views showing alternate possible arrangements of the screens and chambers shown in FIGURE 2.

Turning now to the drawings and in particular to FIG- URES 1 and 2 thereof wherein an exemplary embodiment saaasti Patented Mar. 26, 1953 of the invention is illustrated, -it will be seen that the screening surface is provided by the fifteen cylindrical tubes 16 of screening material each defining within the tube a secondary supply chamber ltla with each of the secondary supply chambers 10a being individually, separately and directly connected to a central primary or main supply chamber 12. As shown, the secondary supply chambers 10a defined by the tubular screens 10 are positioned angularly about the periphery of the central or main supply chamber 12. Furthermore, since each of the tubular screen members 10 has the same diameter and is positioned the same distance from the circumference of the central cylindrical chamber, it follows that the entire screen assembly can be positioned in a cross-sectional area or space equivalent to that which would be occupied by a single cylindrical screen having a diameter such that when positioned concentrically with the central primary supply chamber 12 it would be tangent to the outer edges of all of the tubular screen members Id. In the particular exemplary arrangement shown in the drawings and best seen in FIGURE 2, the circumference or peripheral length of such an equivalent single cylindrical conventional screen would be 188 inches whereas the sum of the peripheral lengths of the fifteen individual screens shown in FIGURE 2 is 450 inches. Since the vertical axial lengths of the tubes 10 shown in FIGURES 1 and 2 can easily be made equal to the vertical length or height of the above noted conventional single cylinder, it follows that the arrangement shown in FIGURE 2 can readily provide a total screening area which is substantially more than twice as great as the screen-area which could be provided in the same total space by a conventional stock screening apparatus using a single cylindrical screen. Depending upon the screening area requirements of any particular application the alternative tubular screen arrangement shown in FIGURES 3 and 4 may provide more or less screening area in the same equivalent space. Turning now to a consideration of the detailed construction of the apparatus shown in FIGURES 1 and 2, it will be noted that a base member 24 serves as a housing for a drive unit 17 and also serves to support three

sections

25, 26, and 27 which are assembled together to form a housing for the stock screening apparatus. The section 25 has an inlet 28 formed therein. Stock to be screened is admitted through the inlet 28 into the base entrance chamber 11 formed as a continuation of the inlet 23 and then flows upwardly into the central main or primary supply chamber 12. The stock admitted through the inlet 28 is of course intended to be received under normal flow pressure from a pump or other similar means. A flange 28a may be provided at the inlet 28 for connection to any suitable supply conduit.

- The inlet chamber 11 is formed within the vertical height enclosed by the two

lowermost housing sections

25 and 26. The screened stock final outlet ring 19 is formed in the section 26. Stock after having passed through the screening tubes .10 in a manner to be described in detail below passes through the outer annulus 18 formed between the tubes 10 and the housing member 27 and flows in a direct continuation of this annulus to the lower outlet ring 19 formed by housing sections 26 and thence to the outlet conduit 1% having flange 19b to which any suitable conduit means may be attached for conveying stock to the paper machine. The portion of the stock which will not pass through the screens lti and is thus rejected drops down through the reject port 20 at the base of each tube into a reject manifold 21 which is another annular conduit formed as shown inside the housing section 26 and which leads to the reject outlet 22.

Mounted within the primary central supply chamber 12 is a foilrotor assembly including a plurality of genorally vertically extending foils 16 which are mounted to extend vertically upwardly from four ribbed arms =13 disposed generally at 96 angles to each other. The ribbed arms 13 are integrally attached to a vertical shaft 17a which may be driven by the motor or drive assembly 17 in any convenient known manner. 'An annular band or ring 16a joins the tops of the foil members together in order to lend rigidity to the spider and foil assembly. A similar band 16b joins the bottoms of the foil members 16.

Upstanding from the interior of the lower housing member 25 is a wall section 29 which extends upwardly from the wall of the inlet 28 and which forms one wall of the inlet chamber 11. Integral with and extending horizontally from the wall section 29 is an annular wall section 30 which forms the base of the secondary supply chambers generally defined by the screens 1% and in which are supported as by screw threading or any other convenient means a shaft 31 extending vertically upward to support a circular top member 32 from which the tubular cylindrical screen members extend downwardly to the base 30 as shown. The member 33 which defines the separate passageway to each of the secondary supply chambers is also supported between the lower base wall and the upper circular wall member or top 32. The wall section 33 is at its base and top an annular member which extends completely around and defines the side or vertical wall of the central primary supply chamber 12. Supported from the top of member 33 is a dished dome 23 which forms the top wall of the central supply chamber '12. Although the dished dome is shown as being independently supported in the preferred embodiment, it will of course be understood that the shaft 17a could be journalled in the central portion of the dished dome 23 if so desired.

As noted above, stock 'to be screened is admitted at the inlet 28 into the base entrance chamber 11 and flows upwardly into the central chamber 12. The ribs 13 on the foil rotor create suflicient turbulence to prevent the separation of the stock. Vanes 14 which depend from the dished dome member 23 as shown, prevent the rotation of the entire mass of stock flowing. These vanes 14 which are, of course, rigidly fixed in position also assists in the distribution of stock flow into and through the slot 15 as the foil rotor rotates and carries the foil 16 between vanes 14 and the passages 15 which connect the central primary chamber =12 with each of the individual secondary supply chambers 16a disposed around the pe riphery of the primary supply chamber 12. The vanes 14, thus, prevent the rotation of the entire mass of stock while at the same time assisting in the distribution of stock flow into and through the passages '15.

Foils 16 are rotated through the body of stock in the central supply chamber 12 at a suitable speed usually from 50450 rpm. by means of the drive '17 turning the shaft 17a. The passage of the foil 16 in front of the inlet to each of the passages 15 creates a momentary wave of pressure increase in the passage 15 and its assoc ated secondary supply chamber 19a. This wave of increased pressure is followed by a reduction in pressure after the foil 16 has passed the inlet to passage 15. In the present apparatus the body of stock in the central supply chamber 12 is prevented from rotating by the fixed vanes 14 which results in a pressure wave of greater magnitude being generated by the foil 16 than could be generated if the vanes 14 were not used. Furthermore, the wave of pressure increase generated by the vane 16 as it passes the relatively restricted inlet to passage 15 is uniform in e the passage 15 and in the entire volume of the secondary secondary supply chambers and into the reject manifold 21 which leads to the reject outlet 22.

The screening apparatus is intended, of course, for final cleaning of stock before delivery to the paper machine. For heavy duty service, a trap may be provided upstream from the inlet chamber or built into the flow chamber 111.

A number of different arrangements of the vanes 14 and the foils 16 are possible some of which are better adapted to a given type of stock or a given application than are the others. Furthermore, the cover plate 23 may be rearranged as required in order to improve the flow conditions for any particular type of stock.

Also, as may be seen in FIGURES 3 and 4, a number of different arrangements of the secondary supply chambers about the periphery of the central supply chamber 12 are possible. In FlGURE 3, parts corresponding to those discussed above in connection with FIGURES l and 2 are indicated by a like reference character to which a single prime has been attached whereas in FIGURE 4 the corresponding parts are indicated by a like reference character towhich a double prime'has been attached. In FIGURES, it will be noted that the secondary supply chamber iiia formed by thecylindrical screens it) are positioned at the end of a passage 15a which is longer than the corresponding passage 15 in FIGURE 2. On the other hand, every other or alternate secondary chambers such as the secondary supply chamber 10b is positioned at the end of a passage 15b which is considerably shorter than the assage 15 shown in FIGURE 2. This, in effect, results in staggering the centers of a the secondary chambers and hence in staggering the radial position of the posts such as the center support post 31a and 3115 as shown in FIGURE 3. This radially staggered relationship of alternate secondary supply chambers, of course permits a greater number of charnbers of the same diameter to be positioned around the periphery of a given central supply chamber 12 and thereby increases the total screening area which can be obtained.

In FIGURE 4, the arrangement is very much like that shown in FIGURE 2 except that the passages 150" are not exactly radially disposed as are the passages 15 in FIGURE 2, The acute angle made by the axes of the passages 15c with the path of travel of the foils 16 tends to give enhanced pressure variation characteristics in the operation of the apparatus.

While a particular exemplary preferred embodiment of the invention has been described in detail above, it

. will be understood that modifications and variations the desired cleaning action without the hitherto unavoidable bending effect upon the. screen member itself,

therein may be efiFected without departing from the true spirit and scope of the novel concepts of thepresent invention as'defined by the following claims.

"I claim as my invention:

i1. A mechanism for screening a slurry comprising: an annular rigid imperforate housing having a slurry inlet therein, i r a plurality of circumferentially'spaced outlet passages leading from said housing, i a plurality of circumferentially spaced screening chambers substantially larger thansaid passages and positioned radially ou'twardly of the passages and open thereto, said chambers having enclosing screening wall forprovidinga large screening surface for each i chamber,

' each of said screening walls having a perforate screening area largerthan the cross sectional area of the passage leading thereto,

and means creating intermittent pressure waves in the imperforate housing to be transmitted to the chambers through said passages.

2. A mechanism for screening a slurry comprising,

an annular rigid imperforate housing having a slurry inlet,

a plurality of circumferentially spaced outlet passages leading from said housing,

a plurality of circumferentially spaced screening chambers substantially larger than said passages and positioned radially outwardly of the passages and open thereto, said chambers having enclosing screening walls for providing a large screening surface for each chamber,

each of said screening walls having a perforate screening area larger than the cross sectional area. of the passage leading thereto,

said screening walls being cylindrically shaped and having a radial inlet opening communicating with the passage leading thereto,

means the ends of the cylindrical screening wall with a discharge opening in one of said ends,

and means creating intermittent pressure waves in the perforate housing to be transmitted to the chambers through said passages.

3. A mechanism for screening a slurry comprising,

an annular rigid imperforate housing having a slurry inlet,

each of said screening walls having a perforate screening area larger than the cross sectional area of the passage leading thereto,

and a foil member within the housing rotatable successively past said passages creating intermittent pressure waves in the imperforate housing to be transmitted to the chambers through said passages.

4. A mechanism for screening a slurry comprising,

an annular rigid imperforate housing having a slurry inlet,

a foil member within the housing rotatable succesively past said passages creating intermittent pressure waves in the imperforate housing to be transmitted to the chambers through said passages,

and stationary vanes radially inwardly of the foil memher preventing rotation of the entire contents within said housing.

5. A mechanism for screening a slurry comprising,

an annular rigid imperforate housing having a slurry inlet,

said outlet passages leading radially outwardly from the housing and arranged so that alternate passages are shorter than intermediate passages and the screening chambers for the longer passages are radially outside the screening chambers for the shorter passages so that larger screening chambers may be used,

6. A mechanism for screening a slurry comprising,

an annular rigid imperforate housing having a slurry inlet,

a plurality of circumferenti-ally spaced screening chambers substantially larger than said passages and positioned radially outwardly of the passages and open thereto, said chambers having enclosing screening walls for providing a large screening surface for each chamber,

and a foil member within the housing rotatable successively past said passages creating intermittent pressure waves in the imperforate housing to be transmitted to the chambers through said passages,

said passages extending radially outwardly at an acute angle toward the path of travel of said foil.

References Cited in the file of this patent UNITED STATES PATENTS 420,136 Willis Jan. 28, 1890 591,645 Baker et al. Oct. 12, 1897 1,926,546 Lampen Sept. 12, 1933 2,066,479 Maclsaac Jan. 5, 1937 2,394,076 Kisch Feb. 5, 1946 2,399,994 Feagin May 7, 1946 2,835,173 Martindale May 20, 1958 2,975,899 Cannon et al. Mar. 21, 1961 FOREIGN PATENTS 122,981 Germany Aug. 12, 1901 170,076 Switzerland Sept. 17, 1934

Claims

2. A MECHANISM FOR SCREENING A SLURRY COMPRISING, AN ANNULAR RIGID IMPERFORATE HOUSING HAVING A SLURRY INLET, A PLURALITY OF CIRCUMFERENTIALLY SPACED OUTLET PASSAGES LEADING FROM SAID HOUSING, A PLURALITY OF CIRCUMFERENTIALLY SPACED SCREENING CHAMBERS SUBSTANTIALLY LARGER THAN SAID PASSAGES AND POSITIONED RADIALLY OUTWARDLY OF THE PASSAGES AND OPEN THERETO, SAID CHAMBERS HAVING ENCLOSING SCREENING WALLS FOR PROVIDING A LARGE SCREENING SURFACE FOR EACH CHAMBER, EACH OF SAID SCREENING WALLS HAVING A PERFORATE SCREENING AREA LARGER THAN THE CROSS SECTIONAL AREA OF THE PASSAGE LEADING THERETO, SAID SCREENING WALLS BEING CYLINDRICALLY SHAPED AND HAVING A RADIAL INLET OPENING COMMUNICATING WITH THE PASSAGE LEADING THERETO, MEANS THE ENDS OF THE CYLINDRICAL SCREENING WALL WITH A DISCHARGE OPENING IN ONE OF SAID ENDS, AND MEANS CREATING INTERMITTENT PRESSURE WAVES IN THE PERFORATE HOUSING TO BE TRANSMITTED TO THE CHAMBERS THROUGH SAID PASSAGES.