US2364171A - Pulp screen - Google Patents

Description

Dec. 5, 1944. s. A, STAGE 2,364,171

PULP SCREEN Filed July 8, 1,940

Patented Dec. 5, 1944 UNITED., STATES PATENTE `OfllTlCIiI i PULP SCREEN Stephen A. Staege. llamiltomnhio, assignur to The Black-Clawson Company, Hamilton, Ohio, a corporation of Ohio Application July 8, 1940, Serial No. 344,332 16 Claims. (Cl. 9234) This invention relates to screening apparatus` and to the removal of rejected material therefrom.`

One object of the invention is the provision of ascreening apparatus for paper pulp, adapted to effectively mix the pulp being screened with an "added stream of water or pulp. Another object is the provision of screening apparatus having means for automatically controlling the disposal or withdrawal of the tailings or rejects in accordance with the amount of tailings or rejects present.

` Another object ofthe invention is sion, in a screening machine for paper pulp, of

a conduit communicating with a rejectcollecting space on one side of the screening surface `,of the machine, and a rotary reversible valve which controls the flow of the rejected material.

"through the conduit.

Other objects and advantages of the invention will be apparent from the following description, the appendedl claims, and the accompany- Xing drawing.

In the drawing,

. Fig. 1 is a top plan view of a screening appa- Y ratus embodying the present invention;

Fig. 2 is a side elevation of the same, with a portion of the screen and the reject valve shown in section; and

Fig. 3 is a diagrammatic showing of the electrical connections of the valve operating motor. Referring more particularly to thedrawing by reference numerals, like partsbeing designated by the same numerals in the several views, the invention, in its preferred form has been shown embodied in a screening apparatus for screeningjmaterial such as paper pulp. The screening t apparatus, as shown, comprises a container including a casing wall I Il having a top cover through the discharge passage I5.

Passage of the pulp through thescreening surface I4 is greatly facilitated by a large number of scraping blades I6 having a construction as more fully disclosed in my prior application Serial No. 285,362, ledJuly 19, 1939, which has now issued` as Patent No. 2,347,716. These `blades extend along the inner surface of the screen and are carried yildingly by springs Il mounted on carrying rings I8 lof a rotatable spiderr I9 which is connected to a shaft 20 operated from a motor 2l `through suitable gear- `ing `in the gear box 22.l When a large number of such blades are used rapidly succeeding passes of the blades over each hole will be secured,

without the necessity of such high operating i speeds as will setup considerable and disturbing centrifugal forces or undue agitation of the body of stock inside the screen. By avoiding such undue agitationI andpreventing unduly high cenl trifugal forces, the main body of stock within the screen is maintained comparatively quiescent, even when large volumes of stock are being passed through the screen, and consequently heavy impurities can settle by gravity to the bottom of the screen and not be thrown outwardly by the centrifugal force to passthrough the holes ofthe screen along with the screened stock. And by using a sulciently large number of blades. passing over the holes at a comparatively loW rate of travel, the blades nevertheless will operate along the supplyside of the screen to give such rapid succession of gentle cleaning actions `that the stock will be prevented from matting to plug up or clog the holes and also from matting or collecting in advance of the blades to give a maintained accumulation which will produce an objectionable matting of the fibers. In operation the satisfactory results of this invention are attained when the blades are operated at such low angular velocity as toproduce centrifugal forces which are negligible with respect `to the discharge of heavy impurities through the screen and yet are moved across the screen and the holes thereof and through the body of stock adjacent the screen at such rate `that the rapid succession` of movements gives gentle cleaning actions whereby the fibers are prevented from accumulating and mattingover the holes to plug or clog them up and are prevented from maintained accumulation in front of the respective blades to give an undesirable matting over of the fibers.

The pulp or` pulped stock` being screened in this machine will contain in suspension fibrous material sufficiently fine to pass through the openings of the screen, and also usable fibrous material or pulp which has not been sufficiently separated so that it is iine enough to pass through such openings and this larger or less disintegrated fibrous material or pulp which is ol such size that it will not pass through the openings of the screen is rejected by the screen and tends to remain in suspension in the space on the inlet or supply side of the screen. In addition, the stock or pulp being screened as it passes to the paper making ymachine still contains, at times, some non-fibrous or unusable heavy materials such as particles of metal, sand, and the like which should beremoved and nally rejected from the system so that they will not contaminate the screened pulp or stock which is passed to the paper making machine. Herein the term rejects is used broadly to cover material which does not pass through the screen and,

as is clear, the larger masses of brous material which require further treatment are separated or segregated so as to avoid objectionable variations in consistency which would affect the voperation of the screen, and so that they maybe returned for further treatment or refining to make them available to be returned to the screen and for use on the paper machine; whereas the sand and grit and other dirt which is also removed is collected or segregated separately and is discharged or finally rejected from the system. The rate of flow through the screen is dependent upon the pressurel of the pulp supplied to theinlet pipe I2, as the blades keepv the screen openings from clogging.

At one side of the screening surface, opposite to the outlet passage I5, is an auxiliary supply passage 23 in free communication with the space surrounding the screening surface, and water or additional pulp thatkhas previously been screened may be supplied through this passage 22 under suitable pressure to the discharge side of the screening apparatus. The material added through the auxiliary inlet 23 thoroughly mixes with the screened pulp issuing through the perforations in the screening surface as the added material ilows around opposite sides of the screening surface.V The screenedpulp passing through the discharge passage I will thus be of a substantially uniform consistency, with the bers in a thoroughly dispersed condition and free of any massing or collection of iiber groups.

Any lighter impurities, foam, etc.,` that may tend to collect at the top of the screen, at its inlet side, flow up through the upwardly extending pipe 24 which extends high enough so that these impurities may be retained at a suitable.

level which permits the withdrawal of gas or air, through the discharge opening at or near the top of pipe 24. The heavy impurities that settle down, due to gravity effect, in the lower portion of the inlet chamber I3 may be periodically withdrawn through a conduit 25 which extends downwardly from the lower wall 26 of the screening chamber.

The screening apparatus is so arranged as to provide an eiective control of the rate at which reject material is removed from the supply side of the screen. The rejects, that include heavy matter that settles rapidly to the bottom of the screening chamber and the larger pieces of fibrous material that will not pass through 'the perforations in the screening surface, accumulate in the space just above the lower wall 26 of the screening machine and are slowly swept around until they enter the top of conduit 25.' This conduit has a downwardly projecting extension 29 in which there are two shut-oli valves 30 and 3I, suitably spaced apartso that any sand', and bits of metal or otherfmatter*substantially heavier than water, together with the heavier or larger brous pieces may be trappedor segregated` `between the two valves, and.v occasionally discharged by opening the lower valve 3`I `.when the upper valve 30 is closed, and then closingv the lower valve 3| and opening the upper Valve 3D* to collect additional heavy material which should be wasted. These valves 30 and 3| may beman ually controlled by the operator,` as occasion mayl require, dependent upon the proportion of .fors eign matter in the pulp being treated;

Extending laterally from the pipe extension 29.' is a branch passage 33through which reject ma-A full lines in Fig. 2 and then place the standpipe"l 31 in' communication with a discharge pipe 4'Il`as indicated in dotted lines. valve 38 arranged between valve 35 and the lower end of the standpipe 31 may be openedto any desired extent to provide desired throttling action and give some suitable rate of flow of material.

into the pipe 31. The upper end ofthe pipe31 is closed against the flow of fluid therethrough'by a plate 39, and the pipe is of considerable heightA so as to form a collecting and reservoir chamberl in which the reject material flowing from the passage 3,3 may betrapped under such pressure as exists on the supply side of the screening surface. If the pressure on the supply side of the screening surface is increased, it will be lapparent that more reject material will flow up into the standpipe 31 when thev passage 36 is in thev position shown in 2 of the drawing. .If the pressure existing on` the supply side of the screen--A ing surface is less thanl some normal value, thenv a correspondingly smaller amount of material i will ilow up into thestandpipe when placed inl communication with the passage 33; Theprese sure on the supply side of the screening surface increases when the proportion of reject material* present increases, this increase in pressure being due to the increase in the consistency of the stock on the supply side of the screening surface and the reduced rate of flow of material through the screen on account of this increase in consistency,

f as the supply of stock to the screen is maintained.

The rate of movement ol the rejectedmaterial. into the standpipe 3l, when communication is` established to that pipe, will thus accord auto matically with the requirementsvfor reject removal.

After placing the branch passage 33'in communication with the bottom. of the standpipel 3l,

the valve 35 is turned so as to interrupt communication between these parts and establish communication from the lower end of the standpipe to the discharge pipe rlill. through the pipe 40 is composed largely of usable fibrous pieces too large to pass through the screen perforations, together with a quantity of smaller fibers and with only a comparatively small proportieriv of heavy extraneous matter, sincethe heavy particles settle down through the exten.- sion pipe 29 and are discharged through the lower end of that pipe. The fibrous materialswithdrawn through the pipe 4U may therefore be This branch pasi A manually operable The material rejected i `itself is carried sible.

fibers saved.; l l

The valve 35 is periodically operated by means of anelectric motor 43, carried on the base 44` whichfserves asa` supportlfor the motor 2|' and as a support for the frainel44" onwhich the screen n Motor 43is a reversible motor, as indicated in Fig. 3l,` having `a reversing mechanism switch `4l which changes the phase relation of two phases of the three-phase supply by selectivelyxenergiz-` ing the relay coils 41a and 41o, These coils control the sets oi switches 4l and 4l" respectively sothatpne set is closed and the other opened.`

The motor driven shaft t6 is provided with` limiting mechanism suchas a. cam 48 of any `suitable The motor.43,has a `speed re-` :matically and the motor started again. The

rate of withdrawal of the rejects from the screening machine is thus automatically controlled in i accordance with thelamount of tailings or rejects characterby means of *which the switch 4'l"`is` reversed automatically after a predetermined part of a revolution of` the shaft 45. The con struction is'such that the shaft 46 turns through a predetermined partol` a revolutionand then automatically reverses its` direction of rotation,

the `speed of operation of theshaftlbeingsuch as to place` thel branch passage 33` in `communication with the standpipe` SIseveral times per` `minute. Since the valve member 35 operates would gradually accumulate between the movable valve memberzandits enclosing wallr to such an extent as to place an extremely large` drag on the movements of the v alvemember and nally produce such a packing of the .bers as to jam the valve and make continued movement impos- This objection however is avoidedin accordance with the present construction.

n Thereversible electriomotor 43 remains ener-- gized continuously during normal operation if the pulp supplied` to `the screening apparatus contains a comparatively largeproportion` of `mato,beinaccordancelwith the actual requirements under diflerent conditions o f use.

A time switch is preferably provided for use in limitingthe operation of therrcject valve when the `screen is used onvery clean stock.` In such case; where the amount of rejects is exceedingly smallythe` time yswitch may be set so that the motor will only operate'a part ol a minute out n of every fteen minute or other suitable period. Sincethere is no direct through path from the screen through which the rejects can pass, the

` time switch` canzinterrupt the operation of the timeiswitch, the screen can handle stock at very l valve and it is immaterial where the valve stops, since thestock and'water from the screen cannot be discharged directly to the outside. The time switch as well as the pressure switch can therefore` be used together to interrupt` the valve operation andthus save pulp when the amount of rejects present is exceedingly small. With the n low pressure or without constantly `adjusting ofthe screening surface decreases below some predeterminedsvalue. takes` place when thereis only a comparatively This decrease in pressure small proportion of material tombe rejected from-.xv n

position by spring 50.. The space atjonefside of the diaphragrnlll` communicates, through a pipe 56, with the supply sideof the screen, the pipe 55 connecting; as shown, to the conduit 25. When the pressure on the supply side `of the screen is` slightly below some normal value the contact memberi53 `will .be moved away from the contact points 52 and` thecircuit to the motor will be` broken, since both switch controlling relay coils 41 willbedeenergized. The -withdrawal of the rejected, material through thelbranch passage 33V willtherefore cease until sufficient material to be rejected collects inthe screen. and causes an` increase in pressure, whereupon the contact53.` will befmovedto contact closing position auto-l the pressure switch for different pressures. This time switch, as shown, includes contacts 58conl. l nectedinlseries with the contacts 52 and adapted to be closed bythe contact plate 59 which is operatdperiodically by projections 69 cna rotatableplate `6l. This plate 6I lis rotated slowly by a suitable time clock or constant speed motor 62. The startingiandxstoppingof the motor 62 is of course under the control of the operator.

While the form `of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this preciseform of apparatus, and that changes may be made therein without departing from the scope of the invention which is dened in the appended claims.

Whatis claimed is`: Y

1., In a screening machine for paper pulp, in combination, a` container having a. screening surface and a reject collecting space on one side of the screening surface, a reject discharge pas- `sage connected to said reject collecting space, means forreceiving a limited quantity of the rejected-material, a valve in said passage operable to one position to` establish communication between Asaidpassage and said receiving means providing forlthe ow of rejected material thcreinto,` and valve drive means operable to periodically shift said valve to another position in` which said passage is closed `and said` limited quantity of rejected material, is discharged` from said receivingmeans. n

2. In a screening machine for `paper pulp, in

combination` a container having a screening s through the conduit, a branch passage projecting from` said conduit ahead of said control surface and a reject collecting space on one side v of the screening surface, a conduit extending downwardly from the reject collecting space, control means adjacent the lower end of the conduit operable to periodically pass limited quantities of heavy rejected material downwardly through the conduit, a branch passage projecting from said conduit ahead of said control means, a valve in said branch passage, automatic means i'or periodically operating said valve to discharge rejected material from said passage. and means associated with said valve to limit flow therethrough to a measured quantity each time the valve opens.

4. In a screening machine for paper pulp, in combination, a container having a screening surface and a reject collecting space on the supply side of the screening surface, a reject discharge passage connected to said space, a valve in said passage operable to control ilow oi' rejected mav terial therethrough, a standpipe communicating with said valve to receive material from said passage, said valve having means for placing the conduit in communication with said standpipe and having additional means for thereafter segregating the standpipe from the passage and opening the standpipe to discharge.

5. In a screening machine for paper pulp, in combination, a closed container for receiving paper pulp under pressure and having a screening surface and a reject collecting space on the supply side of Athe screening surface, a reject discharge passage connected to said reject collecting space, a reservoir chamber connected to said passage and extending upwardly'and having ah upper end closed against free ow of fluid therethrough, and valve means operable to one position to establish communication between a. low portion of the reservoir chamber and said passage providing for flow of a quantity of rejected material into said chamber dependent upon the pressure in said reject collecting space, said valve means being operable to another position to segregate said reservoir chamber from the passage and to open said reservoir chamber to discharge.

6. In a screening machine for paper pulp, in combination, a closed container for receiving paper pulp under pressure and having a screening surface and a reject collecting space on the supply side of the screening surface, a reject discharge passage connected to said reject collecting space, a compression chamber connected to said passage for receiving and segregating a limited quantity of the rejects from said conduit `under the pressure prevailing at the screen intake, and means for periodically placing said compression chamber alternately into communication with said passage and with a discharge opening.

7. In a screening machine of the character described, in combination, a closed container adapted to receive material to be screened under pressure, said container having a screening surface and a reject collecting space on the supply side of the screening surface, a reject discharge passage connected to said reject collecting space, an automatically operable valve for controlling flow through said passage for periodically discharging rejects from said conduit, means associated with said valve to limit the ilow therethrough to a measured quantity each time the valve opens, drive means operating said valve to close and open the passage for the passage of rejected'material therethrough, and means responsive to the pressure of the material on the supply side of the screening surface for controlling the operation of said drive means.

8. In a screening machine, in combination, a container having a screening surface and a reject collecting space on one side of said screening surface, a compression chamber connected to said reject collecting space for segregating a quantity of rejects from said space under the pressure prevailing within the container, valve means for periodically placing said compression lll chamber alternately into communication with said space and with a discharge opening, and pressure responsive means operable in accordance with the pressure on the inlet side of said screening surface for controlling the operation of said valve. f

9. In a screening machine, incombination, a container having a screening surface and a reject collecting space on one side of said`screening surface, a compression chamberconnected to said reject collecting space for segregating a limited quantity of rejects from said space under the pressure prevailing at the screen inlet, valve means for periodically placing said compression chamber alternately into communication with said space and with a. discharge opening, and time controlled means for automatically controlling the operation of said valve.

10. In a screening machine for paper pulp, in combination, a closed container adapted to receive paper pulp under pressure, said container having a screening surface and a reject collecting space at the bottom of the container on the supply side of the screening surface, a conduit extending downwardly from said space, means adjacent the lower end of said conduit for segregating and discharging measured quantities of nally rejected material, a branch passage extending laterally from said conduit ahead of said last-mentioned means, an oscillatory valve in said passage, a standpipe projecting upwardly from said valve for receiving, a quantity of rejected material from said conduit dependent upon the pressure on the supply side of the screening surface. said branch passage having a discharge opening, said valve being'operable to successively place said standpipe in communication with said passage and with said discharge opening,ra reversible motor for operating said valve in reverse directions and providing continued valve movements while the motor is energized, and pressure'responsive means subject to the pressure on the supply side of the screen for automatically deenergizing the motor when the pressure on the supplyv side of the screen is below a predetermined limit.

11. A screening machine for paper pulp stock to be Supplied to a paper making machine comprising a screen casing, an annular screening surface within said casing, means for supplying pulp to the inside of the screening surface, the space between the screening surface and the casing dening an annular discharge chamber for pulp iiowing through the screen, said casing hav ing an outlet opening at one side of the screening surface and having an auxiliary supply passage fr the supply of screened pulp and water leading into the discharge chamber at the other side of the screening surface so that the annular screening surface is between the auxiliary supply passage and said outlet opening with resultant mixing of the auxiliary supply with the pulp flowing through said screen.

l2. A screening machine for paper pulp comprising a screen casing, an annular screening surface within said casing, means for supplying pulp to the inside of the screening surface, the space between the screening surface and the casing defining an annular discharge chamber for pulp owing through the screen, said casing having an outlet opening at one side of the screening surface and having an auxiliary supply passage for the supply of screened pulp and water leading into the discharge chamber at the other side of the screening surface with resultant mixing of the auxiliary supply with the pulp iiowing through said screen, a reject removal passage connected to the space on the supply side of the screening surface, and means within said passage for periodically discharging rejected material through said pipe.

13. In a screening machine of the character described, in combination, a closed container adapted to receive material to be screened under pressure, said container having a stationary screening surface and a reject collecting space connected to the supply side of the screening surface, valve means for controlling said reject collecting space and for periodically discharging rejects fromsaid collecting space, drive means operating said valve means to open and close the same to control the iiow of rejects therethrough to and from said reject collecting space, and means automatically operable when the pressure of the material on the supply side of the screen exceeds a predetermined value for starting said drive means.

14. In a screening machine of the character described, in combination, a closed container adapted to receive material to be screened under pressure, said container having a stationary screening surface, means for supplying material to be screened to one side of said screening surface, means for discharging fibrous material passing ireely through said screen, a discharge passage connected to the space on the supply side of said screen for receiving dirt and pulp material of size too great to pass through said screen, means for segregating and finally discharging from the system said dirt, and means connected to said discharge passage and responsive to an increase in the pressure conditions on the supply side of said screen for cyclica'lly discharging the rejected fibrous material, said latter means being operable to vary the timing of said discharge cycles to maintain the pressure on the supply side of said screen Within predetermined limits. 4

l5. In a screening machine of the character described, in combination, a closed container adapted to receive material to be screened, a screen within said container, means for segregating and withdrawing brous material of size too large to pass through said screen, and means for controlling the discharge of said segregated material comprising a reversible valve, means for receiving a predetermined limited quantity of said segregated material under control of said valve, and means for reversing the operation of said valve so that the reverse movement of the valve will discharge said segregated material from said receiving means and overcome any tendency of brous material to accumulate under pressurebetween the surface of the valve and the valve casing, whereby to prevent such accumulation as will materially interfere with or stall the operating of said valve.

16. In a screening machine for paper pulp, in combination, a screen chamber having a screening surface adapted to operate under pressure and a. reject collecting space on one side of the screening surface, a reject discharge passage connected to said reject collecting space, a closed receiving chamber for receiving a limited quantity of the rejected material, valve means in said` reject discharge passage operable to one position for establishing a flow between said reject collecting space and said receiving chamber of said limited quantity of reject material under the pressure diierential existing between said 4 screen chamber and said receiving chamber, said STEPHEN A. STAEGE.

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