US2347716A - Apparatus for screening paper stock - Google Patents

Description

May 2, 1944 s. A. sTAEGE 2,347,716

APPARATUS FOR SCREENING PAPER STOCK i Filed July 19. 1959 2 Sheets-Sheet l May 2, 1944- s. A. srAEGE 2,347,716

APPARATUS POR SCREENING PAPER STOCK Filed July 19, 1939 2 Sheets-Sheet 2` 'Patented May 2, 19,44

Stephen A. Staege,

Hamilton, Ohio, assignor to The Black-Clawso'n Company, Hamilton, Ohio,

a corporation of Ohio Application July 12, 1939, Serial No. 285,362 'l Claims. (Cl. S32-34) This invention relates to screens for screening paper stock, and the like.

One object of the invention is the provision of apparatus for screeningv paper stock and the like and providing supply and discharge chambers on opposite sides of a cylindrical screening surface, and incorporating a rotatable series of bladesv which operate in contact with the supply side oi the screen at a comparatively slow speed of rota. tion to scrape the fibers gently from the scree i and keep the screen openings clean, the blades being comparatively large in number to provide Aa very rapid succession of scraping actions for the screen holes. I

Another object of the invention is the provision of apparatus for screening paper stock or the like,

providing supply and discharge chambers respectively on the inner and outer sides of a vertical cylindrical screening surface within which is a rotatable series of scraping blades which in normal operation have a maintained scraping contact with the supply side of the screening surface, the blades being comparatively large in number but operating at a comparatively slow rotational speed to provide a very rapid succession of cleaning actions on the perforations of the screen without creating a large centrifugal force on the fluid in the supply chamber.

Another object of the invention is the provision of an apparatus of large capacity for screening paper stock and the like, so arranged as to provide a comparatively slow movement of the stock towards a stationary cylindrica1 screen by reason of a pressure head on the supply side of the screen, the screen having a comparatively large number of cleaning blades which move at a low rate of `speedin contact with the supply side of the screen and` provide a very rapid succession of' gentle cleaning actions on the .screen perforations which keep the screen free of any accumulation or matting of the bers.

Another object of the invention is the provision of the blades with the supply side of the screening surface during normal operation.

Another object of the invention resides inthe method of screening paper-stock and the like in which the stock is supplied to a screen, under a pressure head, the supply side of the screen being cleaned by a very rapid succession of comparay tively slow speed scraping actions which clean the fibers from the screen openings and produce only a negligible centrifugal force outwardly towards the screen surface.

Other objects and advantages of the invention will be apparent from the following description and claims, taken in connection with the accompanying drawings, in which:

Fig. 1 is a vertical sectional view of a screening apparatus embodying the present invention, the section being taken on the line I-I of Fig. 2;

Fig. 2 is a horizontal sectional view through the screening apparatus on the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary section on the line`3-3 of Fig. 1;

Fig.` 4 is a fragmentary section on the line I--I of Fig. 1;

Fig. 5 is a side elevation of the screening appa ratus, shown on a small scale;

Fig. 6 is a perspective view of a tool for retracting the scraping blades from the screen; and

Fig. 7 is a sectional view showing the operation of the retracting tool.

Referring morelparticularly to the drawings, in which like reference numerals designate like parts in the several views, the screening apparatus. shown as a-preferred embodiment of the present invention, comprises a cylindrical shell or housing Ill of sheet metal suitably supported at its lower end on the base structure II. lThe lower wall of the housing is formed by a horizontal annular bottom plate I2 bolted or otherwise secured to peripheral flanges I3 which are welded to the shell I0 and to the base structure I I respectively. The

. central portion of plate I2 carries an upwardly of--a screening apparatus of the charactenmerr;

tioned having. moyision for removinm'the lighteif- 4 impurities and the heavierimpurities by gravity action which are passed to collecting chambers provided at opposite ends of the screening apparatus and both in communication with only the lperipheral portions of the supply chamber.

Another'k object of the invention is the provision of a screening apparatus of the character mentioned and having a large number of slowly rotatable screen cleaning blades supported in such a manner as to insure a maintained yielding contact tapering blockv Il enclosing an upwardly extending 4 rotatable shaft I5." f

Secured to the upper sldesof the plate I2, as by means of welding, is a ring I6 which i's grooved to receive4 and support a vertically extending cylindrical screen I8. The latter is provided with screening holes which are preferably from about .02 to .08 inch or more in diameter, the larger holes being employed for screening stock to be made into paperboard and the smaller h'oles for stock used in themanufacture of high-grade l paper. These holes are so spaced that thel total open area is from 20% to 50% of the perforated area of the screen.

The screen I8 is preferably adapted for ready removalin an upward direction from ring I6, being held in the groove of the ring by a cover plate I9 having a ring 20 of rubber which yieldingly pressesl against the top of the screen when the cover plate is secured in its normal position, indicated in Fig. 1. The screen is preferably a curved metal plate secured at its adjacent ends by a metal connection strip 2| which extends vertically overlappping the abutting ends of the screen, and welded thereto. The lower end of this strip ts in a vertical groove in the ring I6 so that rotational movement of the screen is prevented.

Paper stock or the like is supplied to the screen through a stock supply pipe 22 which extends to the supply chamber 23 of the screening apparatus, the pipe 22 extending to'a supply vat in which the level is sufficiently high so that the stock may be supplied with a head of from 30 to 60 inches or more to the supply chamber 23, or the stock may be supplied from a pump operating to create a pressure equivalent to such pressure head. An upper portion of the supply chamber 23 is partly defined by a wall 24 carried by the cover plate I9 and providing a continuation of the stock supply passage, this wall 24 extending downwardly to ay level somewhat below the top of the screen. A series of quickly operable fastening clamps 25 serves to hold the cover in position.

'I'he discharge chamber 26 which receives the screened stock that has passed through the openings in the screen extends Aannularly, as shown, on the outer side of the screening surface and at one side'is provided with an inwardly flaring discharge passage 21 having connection to a discharge pipe 28 which preferably extends upwardly to a point above the top of the screen surface as indicated in Fig.` 5, or to a. receiving vat the level of which is preferably above the level of the top of the screening surface. The horizontal spacing between the screen and the housing I0 may be greater adjacent the discharge passage 2'I and considerably reduced at the side opposite by positioning the housing eccentrically with respect to the screen so that the velocity of the stock fiow through the chamber 25 may be ,substantially equalized at all points, although, as shown, the housing and the screen are arranged coaxially.

The rotatable shaft l5, which is rotatably mounted within a suitable -bearing housing 29 bolted to the bottom plate I2, is detachably connected to a hub 30, having several radially extending arms 3I. The outer ends of these arms are attached to an annular ring 32 and vertical struts 33 extending' upwardly from ring 32 form supports for additional rings 34 and 35, these parts being welded together and providing a skeleton structure which is rotatable with the shaft. This structure carries a series of screen cleaning blades 3B having forwardly inclined scraping portions which operate in contact with the supply side of the screening surface, moving at a comparatively slow rate of speed so as not to create any considerable V,centrifugal force on the stock in the supply chamber. When a large number of such blades are used rapidly succeeding passes ofthe blades over each hole will be secured, without the necessity of such high operating speeds as will set up considerable and disturbing centrifugal forces or undue agitation of the body of stock 1nside the screen. By avoiding such undue agitation and preventing unduly high centrifugal 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 censequently heavy impurities can settle by gravity to the bottom of the screen and not be thrown outwardly by the centrifugal force to pass through the holes of the screen along with the screened stock. And by using a sufficiently large number of blades, passing over the holes at a comparatively low rate of travel, the blades nevertheless will operate .along the supply side 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 velocit;r as to produce 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 wherebyfthe fibers are prevented from accumulating and matting over the holes to plug or clog them up and are prevented from malntained accumulationin front of the respective blades to give an undesirable matting over of the fibers.

In the embodiment of the invention as herein illustrated, in which a two foot diameter screen is used, the blades, as illustrated for example in Fig. 2, are spaced about two inches apart around the supply side of the screening surface, and 36 such blades are illustrated. With such a construction a rapid succession of gentle cleaning actions may be secured so that such accumulation or matting of the stock is prevented, and at the same time with speeds of rotation which are suiciently low to prevent objectionable centrifugal forces as stated. With the numbe'rof blades and the dimensions stated, and using stock of such consistency as is ordinarily screened in a paper millgenerally, stock of a consistency of about l/2%- the gentle cleaning actions referred to can readily and satisfactorily be secured with most stocks when the shaft carrying the blades is rotating at 75 R. P. M. Of course, as is Well understood,` a pulp screen such as herein described is gener-J ally utilized for screening thenally prepared stock, before it goes to the paper making machine, and such stock will va'ry widely in its characteristics depending upon whether the flbers are derived from wood or rags, whether they have been separated by one or another of the several chemical cooks used or are so-called groundwood, and the extent to which they have been cut and brillated and hydrated during the Apreparatory action in the beaters, joi dans, etc. A so-called slow stock of a given consistency would respond somewhat differently from a free stock, an'd as is well known in the industry comparatively small percentage variations of ber content or consistency may cause great differences in operatscrape oi any fibers v ments stated that the speed should be slow enough to prevent objectionable centrifugal force which would interfere with the gravity separation-of heavymaterial such as particles of metal and the like and yet to give su-fcient relative movement of the blades with respect to the stock and over the holes to prevent the fibers from maintained accumulation or matting in advance of the blades and over the holes. Satisfactory results have been attained with 36 blades in the machines of the dimensions stated, operating as low as 50 R. P. M. with some stocks, satisfactory results have been attained with most stocks operating at, 75 R.. P. M., but with some stocks the speed should be increased to meet the conditions of causing negligible centrifugal force and yet causing the gentle cleaning actions which will prevent the main-A tained accumulation or matting of the fibers be tween the scraper blades and over the holes.

With the blades so operated as to cause 30 to 40 passes over each hole per second the actual accumulation of a mat within the hole itself has been found satisfactorily prevented in all commercial operations, and the proper gentle washing action which prevents any accumulation or matting of fibers in advance of the blades may be maintained with comparatively slow rates of travel of the blades as attained by a low R. P. M. of the order stated, tisfactory results being secured in actual practice with the construction described with rotational speeds ofthe order of one and two turns per second. The large number of blades also provides a well distributed outward pressure on the screen contributing to the internal fluid pressure on the screen to maintain it in a truly circular form and permitting an unusually large open area as compared to the total plate area. D

Each blade is preferably a stainless steel strip about az of an inch in thickness, arranged vertically, and having a length substantially equal to the height of the perforated part of the screen. The scraping portions of the blades are forwardly inclined in the direction of rotation and in an outward direction, preferably at a small acute angle of about as shown. The straight scraping edges 39 of the blades operatev in contact with the screen I8, since the blades are yieldingly carried by flexible steel strips 40, to which they are welded. The inner ends of each of the strips 40 is formed to provide an eye Il. The eyes of the strip are mounted loosely on the pins 42 which are fixed on the rings 32, 34 and 35, while-other pins 43 which also project from the rings 32, 3l and 35 are so positioned as to maintain a tension in the strips 40, and hold the scraping edges of the blades against the screen. Thev strips extend outwardly and rearwardly of the direction of rotation at a small acute angle to the screen, preferably of the order of about 15, so that any blade may yield backwardly and inwardly if it encounters an obstruction that might be lodged in one of the screen openings, without applying an excessive or-destructive force on theblade. In normal operation the forwardly inclined scraping portions of the blades operate with a main'- tained yielding contact with the screen and quietly tending to accumulate on the screen.

The discharge side of the screen is preferably maintained completely submerged by having the pipe 23 extend up to a point above the top of the screen. The stock which enters chamber flows down into the space screen and as the rotating blades move within the through cumiilation or matting of fibers.

the supply the stock flowing outwardly in the screen to pass through the holes Ithese vblades cut across the streams of stock which are flowing radially outward through the holes -and tend to change the radial direction of movement and also tend to carry the stock within the zone of the blades in a rotational direction. The resultant is the gentle cleaning action referred to with any tendency to` accumulation of fibers over the holes being prevented by the rapidly succeeding scraping actions of the blades and the gentle washing action which results from the relative movement of the blades with respect to the stock causing such gentle cleaning that no maintained accumulation of fibers ahead of the blades occurs. Of course, it is physically impossible to avoid the creation of some centrifugal force as the blades move around inside the screen, but at the slow rate of angular travel which has been found to give the satisfactory gentle cleaning and non-mat forming action referred to, the centrifugal forces created are so slight with respect to the large body of stock within the screen and the rotation of the whole mass of stock, because of the skeleton formation of the revolvingblade structure, is so gentle that whatever of centrifugal forces result are negligible with respect to the gravity separation of heavy impurities within the body of the stock. This condition has been satisfactorily attained while still providing such movement of the blades to cut through the radially flowing streams of stock and such relative movement of the blades with respect to'the zone of stock adjacent the screen that the accumulation or matting of fibers over the holes or around the screen and in advance of the blades is prevented. Thus even though the outer portions of the cylindrical body of stock within the screen may move around at a very slow rate of speed along the inner side of the screening surface by the rotational action of the scraping blades there is no objectionable centrifugal force' created, and only the gentle cleaning action which maintains the holes and the surface of the screen and the blades-washed free from any maintained ac- Due to the small radial extent of the blades the inner portions of the cylindrical body of stock will have merely a downward and outward movement. As

the stock fibers approach the openings in the screen, they will move at a comparatively slow speed, their speed of movement however increasing as they enter the openings in the screen so that the stock fibers tend to go through the screen openings aligned with the direction of ow and parallel to one another. Any heavier impurities such as sand or other heavy particles present inthe stockv settle downwardly by gravity action instead of passing through the screen,A and since the speed of rotation of the peripheral portions of the stock in the screen is very small, the heavier impurities will not be thrown out forcibly against the screen surface and may settle rapidly to a point below the screen and thus enter the collecting chamber 45 in which the heavier rejects accumulate, and from which they may be periodically or continuously withdrawn at a suitable rate,

.as by means of a conveyor which operates in a depending to some extent upon the individual design as to diameter and speed of rotation.

The lighter impurities as well as air present 4 In accordance with the present invention, the, l5

power required for rotating the screen scraping blades is only about 3 to 4 H. P. in a screen having an unusually great screening capacity andv capable of screening stock having a consistency of only a very small fraction of one per cent or up to 3% or more. The i-low of stock through the screen is continuous as distinguished from a back and forth pulsating movement, the continuous flow being under a very substantial head so that the stock passes freely through the perforations in the screen which are continuously kept clean. Since the open area of the screen is from to 50% of the total screen area and since the holes' are cleaned a great many times per second, the consistency of the stock on the discharge side of the screen will be substantially the same as that on the supply side of the screen and the same as the stock coming through the supply pipe. Furthermore with a comparatively slow speed of rotation of the blades, the stock supplied to the screening apparatuswill not be beaten or pulped to any appreciable degree. the action of the screening blades being essentially a cleaning or scraping action. In view of the comparatively large rate of flow through the screen, only a very small fractional part of the stock bers will be actually engaged by the scraping edges of. the blades.

Rotational movements of theshaft I5 are imparted by means of a power driven shaft 52 operatingI speed reduction gearing in the housing 29. As shown the shaft 52 is provided with a bevel pinion 53 which meshes with a bevel gear 54 provided on the lower end of the shaft I5.

The shaft is rotatably supported by antifriction bearings 56 and 51 which serve to locate the shaft I5 against axial movement. Above the bearingf51 is aspace -58 provided by the upper portion of. the stationary bearing housing and the lower part of the conical block I4, this space forming a discharge path communicating vwith discharge passages 59 to relieve any water or stock that might ,leak past, the sealing washers 60 of suitable water packing material arranged in-the conical block I4. An overhanging shell 6I ixed on the shaft projects over the stationary.

ring 62 which projects upwardly from the top wall of the housing and prevents any leakage liqvuid that finds its way into the space 58 from leaking into the roller bearing of the drive unit.

The interior of the screening apparatus is readily accessible for cleaning purposes, since the cover plate I9 may be readily removed from the top of the shell II) and the scraping blades are then accessible for inspection or replacement. The cover I9, as shown is integrally or rigidlyconnected to the pipes 22 and 50 which curve upwardly and oppositely so as to extend coaxially. The coaxially extending portions of these pipes spectively and are normally secured thereto by readily removable bolts or clamps 66, which. when loosened, permit the cover I9 to be swungupwardly, provided the quick acting clamp or bolts 25 which normally hold the cover I9 in place are rst removed. When the cover is raised the screen I8 may be readily pulled upwardly for lnspection or replacement or both the inner and outer sides of the screen may be cleaned without withdrawing it. To withdraw or. vreplace the screen quite readily, the blades 36 are pulled inwardly free of contact with the screen, preferably by means of a special tool which permits all of the blades to be pulled in at the same time. This tool designated 59' and shown in part in Figs. 6 and 'I comprises a disk 69 somewhat smaller in diameter than the screen, and having a series of depending rods rigid therewith and corresponding in number and spacing to the blade arrangement. With the rods engaged with all of the spring strips 40, a small rotational movement of the disk 69 will simultaneously force all of the blades inwardly by flexing the strips 49,'until the rods seat in the curved portions III of the blades.

The blades will then be in such a position that the disk 69 will remain in this position and the screen may be lifted out or applied with ease. After removing the screen the tool is removed and the blades themselves, together with their respective spring strips 40, can be removed by merely withdrawing them upwardly.

While the method herein described, and thel form of apparatus for carrying this method into effect, constitute apreferred embodiment of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the inventionwhich is defined in the appended claims.

What is claimed is:

1. A screen of the character described for screening brous material comprising a nxed vertically extending cylindrical screening surface, means providing supply and discharge chambers respectively on the inner and outer sides of said screening surface, means for supplying material to the top of said supply chamber, a rotor operable in the supply chamber and having an annular series of blades provided with screen cleaning portions inclined forwardly toward the screening surface inthe direction of rotation and having a maintained scraping engagement with the screening surface in normal operation, means for rotating said rotor at 'a comparatively slow rate of speed, the blades being of e. comparatively large number with a plurality of blades in each quadrant of the rotor so that each opening in the screen is cleaned'by the scraping action of the blades up to 30 to45 times per second although the centrifugal force on the material being screened at the screening surface is substantially negligible, means for withdrawing heavy matter settling in the supply chamber from the bottom of the supply chamber, and means for maintaining the discharge chamber completely lled with screened material.

2. A screen of the character described for screening brous material comprising a vertical cylindrical screening surface, means providing supply and discharge chambers respectively on the inner and outer sides of said screening surface, means for supplying iluid to the top of the supply chamber, a rotor operable within the are rotatably lcarried in flanges `64 and 65 re- 75 Screening SurfaCe and having an annular series of blades provided with screen contacting prtions that are inclined forwardly toward the screening surface in the direction of rotation,

said blades each having a yielding connection to y the rotor at a point substantially ahead of a radial plane through the point of engagement of the blade with the screen, and means for imparting a slow rotation to said rotor, the blades being of a comparatively large number with a plurality of blades in each quadrant of the rotor so that each opening in the screening surface is cleaned by the scraping action of the blades at'a rate up to 30 to 45 times per second although the centrifugal force on the material being screened at the screening surface is substantially negligible. 3. A screen of the character described for screening brous material in liquid suspension comprising a vertical cylindrical screening surface, means providing supply and discharge chambers respectively on the inner and outer sides oi.'l said screening surface, an annular series of blades provided within the screening surface, said blades having a shortfradial extent compared with the radial thickness of the liquid in the supply chamber and having forwardly inclined screen contacting portions, means supporting said blades for yielding outward movement of their screen contacting portions so that the blades have a maintained contact with the screen surface in normal operation, and means for slowly rotating said blades to avoid creating any substantial centrifugal force on the material being screened at the screening surface, the blades being of a comparatively large number with a plurality of blades in each quadrant of the screen so that each opening in the screening surface is cleaned by the blades up to 30 to 45 times per second.

4. A screen of the character described for ,screening fibrous material in.. liquid suspension comprising a vertically extended cylindrical screening surface, means providing a supply chamber on the inside of said screening surface and a discharge chamber on the outside thereof, a rotor operable in said supply chamber having an annular series of blades, means for mounting said series of blades on said rotor providing for maintained scraping engagement thereof with said screening surface in normal operation, and means for driving said rotor at a comparatively slow rate of speed of about '75 R. P. M. to maintain the centrifugal force on said fibrous material insufficient to prevent gravity separation of heavy impurities and to maintain movement of said blades over said screening surface in rapid succession to provide a washing action preventing 1 the matting or accumulation of the nbrous material over thep surface of the screen and upon the leading surfaces of the blades.

5. A screen of the character described for screening brous material in liquid suspension comprising a vertically extended cylindrical screening surface, means providing a supply.

chamber on the inside of said screening surface and a discharge chamber on the outside thereof, a rotor operable in said supply chamber having an annular series of blades, means for mounting said series of blades on said rotor providing for maintained scraping engagement thereof with said screening surface in normal operation, and means for driving said rotor at a comparatively slow peripheral speed of about 500 feet per minute to maintain the centrifugal force on said fibrous material insuiiicient to prevent gravity separation of heavy impurities andto maintain movement of said blades over said screening surface in rapid succession to provide a Washing action preventing'the matting or accumulation of the fibrous material over the surface of the screen and upon the leading surfaces of the blades.

6. A screen of the character described for screening brous material in liquid suspension comprising a vertically extending cylindrical screening surface, means providing a supply chamber on the inside of said screening surface and a discharge chamber on the outside thereof, a rotor operable in said supply chamber having an annular series of blades including. a plurality of blades in each quadrant thereof, means for mounting said series of blades on said rotor providing for maintained scraping engagement thereof with said screening surface in normal operation, and means for driving said rotor at a comparatively slow rate of speed of about R. P. M. to maintain the centrifugal force on said brous material insuicient to prevent gravity separation of heavy impurities, and to maintain movement of said blades over said screening surface in rapid succession to provide a washing action preventing the matting or accumulation of the fibrous material over the surface of the screen and upon the leading surfaces of the blades.

7. A screen of the character described for screeningdibrous material in liquid suspension comprising a vertically extended cylindrical screening surface, means providing a supply chamber on the inside of said screening surface and a discharge chamber on the outside thereof, a rotor operable in said supply chamber having an annular series of blades including a plurality of blades in each quadrant thereof, means for mounting said series of blades on said rotor providing Afor maintained scraping engagement thereof with said screening surface in normal operation, and means for driving said rotor at a comparatiyely slow rate of speed of about '75 R. P. M. to maintain the centrifugal force on said flbrous material insumcient toprevent gravity separation of heavy impurities and to maintain movement of said blades over said screening surface in rapid succession at a rate up to 30 to 45 passes per second to provide a washing action preventing the matting or accumulation of the fibrous material over the surface of the screen or upon the leading surfaces of the blades.

j STEPHEN A. STAEGE.

Images