US1978443A - Screening pulp - Google Patents

Description

E. J. TRIMBEY SCREENING PULP Oct. 30, 1934.

Filed April 13, 1933 3 Sheets-Sheet 1 INVE TOR Y J M,M

ATTORN EY5 oct ao, 1934. E J, RIMBEY 1,978,443

v SGREEJNING'PULP Filed April 13, 1935 3 Sheets-Sheet 2 ATTORNEYS 3 Sheets-Sheet 5 Filed April 15, 1935 I INVENT R ATTORNEYS Patented Get. 30, 1934 PATENT OFFICE 1,978,443 1 SCREENING PULP Edward James Trimbey, Glens Falls, N. Y. Application April 13, 1933, Serial No. 665,893

19 Claims.

This invention relates to the screening of fibres used in the manufacture of pulp and paper and has for its general object the provision of improvements in that art. More specifically it is my object to make certain improvements in the pulp screen of my U. S. Patent No. 1,856,176.

In my earlier patent I have illustrated and described a pulp screen which is operated as follows: The unscreened pulp is brought to a high rotative velocity in a stationary cylindrical screen chamber by means of a rotor before it comes into contact with the stationary screen plates. By

gradually building up a high rotative velocity in the dilute liquid pulp mass before the fibres come into contact with the screening surface, the slivers or fibres tend to straighten out with their axes parallel to the direction of flow which is a circular path determined by the cylindrical body of the screen. Being at a high rotative speed the centrifugal force thus developed causes the liquid and the desirable short pulp fibres-to pass through the screen perforations while the coarser particles continue to revolve'at this same velocity, being carried around by the rotor and moved to the rejection outlet by means of inclined elements on the periphery of the rotor. If the fibres or slivers are allowed to approach the screen head-on many which should be rejected pass through, and furthermore, if round holes are used many slivers attempting to pass through head-on will become wedged in the holes and soon clog the screen.

When using any type" of pulp screen some means must be provided for continuously freeing the screen plates from the slivers and good fibres on that side of the screen toward which the pulp flow is directed. In the screen of my earlier Patent No. 1,856,176 this freeing of the screen'plates is effected by the revolving rotor ele- 40 ments which revolve at a high speed within the screen chamber and adjacent the plates thereby creating regions of diminished pressure in their wakes which cause a momentary inwardor backward flow of the screened pulp whichfills the casing surrounding the screen and submerges speeds of rotation and more power are required to perform the second function than would be necessary to perform the first only. The regions of diminished pressure which follow the rapidly revolving rotor elements are probably of very limited extent so that at noone time is the entire screening area of the screen subjected to a reversal of pressure. Under these circumstances a high rotor speed seems necessary to create low pressure areas having sufficient pull efiectively to loosen the adhering fibres. Thus if the speed is materially reduced, the fibres will still approach the screen plates with their axes parallel to the line of flow, but in a very short time the screen plates become clogged with fibres and further screening becomes impossible. I havealso discovered that the high rotor speeds necessary for keeping the screen plates open have a: tendency to hair-pin some of the longer fibres, that is to bend and force them sidewise throu'ghthe screen openings, and also to break up knots and .slivers into smaller undesirable particles which may find their way into the screened pulp.

According to the present invention I utilize the rotor to perform its first function only; that is, to align the pulp fibres and bring them smoothly to the screen plates with their axes parallel thereto, .and provide other means for freeing the plates from accumulatedfibres and slivers. This other means creates a pulsating pressure in thescreened pulp surrounding and submerging the screen plates which causes a pulthe screen. I have discovered that such a diaphragm can be operated to free the screen plates satisfactorily and much more economically than by speeding up the rotor beyond those speeds necessary foraligning the fibres.

In the accompanying drawings I have illustrated a preferred embodiment of my invention. In these drawings Figure 1 is an end elevation with parts shown in section, (taken along line 1-1 of Figure 2) of a pulp screen constructed in accordance with the present invention; Figure 2 is a horizontal section taken along line 2--2 of Figure 1; Figure 3 is a side elevation of the screen of Figure 1 viewed from the right; Figure 4 is an end view similar to Figure l but on a smaller scale showing the screened pulp and tailings discharge connections and the inlet for the water used for washing the rejected fibres; Figure 5 is a detail section of the view of the tailings discharge taken along line 55 of Figure 1; and Figure 6 is another detail sectional view taken along line 6-6 of Figure 3.

The outer casing or shell of this screen comprises two circular end castings 1 and 2 connected together by a base casting 3, an outlet casting 4, and two removable diaphragm frames 5 and 6, to be described presently. Within this casing is mounted a stationary cylindrical screen '7 made up of arcuate screen plates 8 mounted in a frame 9 and supported by the end castings 1 and 2. Within this screen is mounted a shaft 10 extending axially through the screen chamber, journaled in one end in a bearing 11 carried by the casting 2, and at the other end in a bearing 12 carried by a pulp inlet elbow 13 mounted upon the casting 1. On this shaft 10 is mounted a rotor 14.

Built into end casting 1 at the pulp inlet is a group of curved stationary vanes 15 so designed that at the point where the inlet elbow is connected the plane of each vane passes through the axis of the shaft 10, while at their inner ends the plane of each of these vanes is approximately at right angles to the shaft. The purpose of these vanes is to change the stream lines or direction of flow so that the pulp will enter the body of the screen with its longitudinal motion converted into'a rotary motion, moving in the same direction as the rotor 14. The potential energy of the entering pulp will thus be conserved and correspondingly less power will be required to operate the screen. The rotor 14 has cast integrally with it and on the inlet side, a number of curved pump blades 16, these blades serving to accelerate the rotative velocity given to the pulp body of the screen by the vanes 15 and to bring it up to its maximum velocity by the time it reaches the screen plate 8, smoothly and without undue agitation or disturbance of the stream line. On the opposite side of the rotor 14 is a pair of warped blades 1'7 which tend to keep the revolving wall of stock in rotation, thus insuring that the fibres approach the screen plates with their axes parallel thereto, and which also move the slivers toward the tailings outlet pipe 18, through which they pass after being scooped out by the inclined lip or skimmer 19. The energy due to the rotative velocity of the tailings is enough to elevate them to a tailings box 22 whence they may flow by gravity to a second screen. Thinning water may be added through water connection 20 and directed against an annular plate 21 carried by the rotor and flung against the screen plates, thus assisting in the further separation of any good fibres which may have been carried nearly to the re- 'jection outlet.

In order to continuously free the screen plates 8 from accumulated fibres and slivers which at low rotor speeds would otherwise clog the openings in those plates, I have provided a pair of oscillating diaphragms which I shall now describe. Thetwo arcuate brass frames 5 and 6, which together extend more than one-half of the circumference of the screen casing are bolted upon the end castings by means of swing bolts '23 and form a part of the casing, as described previously. On eachof these frames is mounted a rubber diaphragm 24, each diaphragm being clamped to its respective frame by means of brass bars 25. These rubber diaphragms are held in arcuate formby'meansof curved brass plates 26 mounted, one on either face thereof, and extending within a few inches of the frames 5 and 6.

Oscillation of these diaphragms is effected by eccentrics which I shall now describe. (Both diaphragms operate alike so that the description of one of these eccentrics will suffice.) Bolted on the sides of frames 5 and 6 and on the cen ter line of each diaphragm are bearing stands 2'7 and 28 respectively, these bearing stands carrying bearings 29 and 30 in which a shaft 31 is journaled. Keyed to this shaft 31 are a pair of eccentrics 32 each comprising two members 33 and 34 keyed together at 35. The relative position of these members determines the total eccentricity which may be varied by turning them relatively to each other, and inserting the key 35 in another of the plurality of keyways provided for it, as illustrated in Figure 1. These eccentrics are connected by means of a pair of connecting arms 36 with a shaft 37 mounted in brackets 38 bolted to the diaphragm. Thus rotation of shaft 31 causes oscillation of the diaphragm.

Shaft 31 is driven by means of a motor 39 mounted on a bracket 40 bolted to adjoining flanges on the frames 5 and 6. This motor has two sprocket wheels 41 each of which drives a sprocket 42 on one of the eccentric shafts 31. I employ chain drives for these eccentrics in order to insure that the diaphragms pulsate in synchronism.

The unscreened pulp enters the screen through inlet elbow 13, passes vanes 15 and into the screen chamber where it is picked up by the rotor 14 and moved outward toward the stationary screen plates 8, the fibres approaching the screen with their axes parallel to it. The screenable fibres pass through the screen plates and into the space between the screen plates and the outer casing of the machine, whence the screened pulp leaves the machine through the outlet opening in casting 4 and passes into a discharge pipe 43 and thence into a header 44, as illustrated in Figure 4. The pulp in the screen is always under a head suflicient to keep the annular space between the screen plates and the outer shell completely filled with screened pulp at all times. Throughout the screening operation the dia phragms 24 are continuously reciprocated result- Y :mg in a pulsating pressure within the machine 'which forces a slight amount of screened pulp back throughout the entire screening area of the screen plates at regular and rapidly recurring intervals, thus freeing those plates of any adhering fibres or slivers. I have operated successfully at four hundred reciprocations of the diaphragms per minute and with a total travel of from one-quarter to three quarters of an inch.

In order to effect the same freeing of the screen by a rapid rotationof the rotor it would be necessary to rotate the rotor a suflicient number of RP. M. to establish a peripheral speed of about two thousand lineal feet per minute or more.

When oscillating diaphragms are employed to expensive round hole screen plates, and in additi'onybecau's'e of lower rotor speeds, requires. even less power with less vibration and wear and tear, minimizeshair-pinning of long fibres, and does not tend to break up large knots and slivers into smaller undesirable particles which might later findtheir Way through the screen perforations.

I claim:

1." The method of screening paper pulp. which comprises imparting a rotary movement to the pulp within a cylindrical screen chamber, pass ingthe pulp through the screenby centrifugal force, and at intervals reversing the flow simultaneously throughout the entire screening surface of the screen to free it of accumulated fibres.

2. The method of screening paper. pulp which comprises: imparting a rotary movement, to the pulp within a cylindrical screen chamber, passing the'pulp through the screen by centrifugal force, and causing a pulsating backflow of screened pulp simultaneously throughout'the entire screening surface of the accumulated fibres.

3. The method of screening paper pulp which comprises imparting a rotary movement to the pulp within a cylindrical screen chamber, passing the pulp through'the screen by centrifugal" force, maintaining the screen submerged in screened pulp, and fluctuating the pressure in the screened pulp to effect a-slight pulsating backfiow of screened pulp simultaneously throughout the entire screening surface of the screen and thereby keep it free of accumulated fibres.

4. The method of screening paper pulp which comprises causing the fibres to approach the screen with their axes parallel thereto so that fibres substantially longer than the diameter of the screen openings are rejected, and at intervals reversing the flow simultaneously throughout the entire screening surface of the screen to free it of accumulated fibres.

5. The method of screening paper pulp which comprises causing the pulp to fiow in a direction substantially parallel to the screen before it reaches the screen, thus alining the fibres parallel to the screen, then forcing the pulp through the screen whereby all fibres substantially longer than the diameter of the screen openings are rejected and at frequent intervals reversing the fiow simultaneously throughout the entire screening surface of the screen to free it of accumulated fibres.

6. The method of screening paper pulp which comprises imparting a rotary movement to the pulp within a cylindrical screen chamber so that when the fibres reach the screen they are moving substantially parallel to the screen surface, passing them through the screen centrifugally, and at rapidly recurring intervals reversing the fiow simultaneously throughout the entire screening surface of the screen to free it of accumulated fibres.

'7. The method of screening paper pulp which comprises imparting a rotary movement to the pulp within a cylindrical screen chamber so that when the fibres reach the screen they are moving substantially parallel to the screen surface, passing them through the screen centrifugally, maintaining the screen submerged in screened pulp, and fluctuating the pressure in the screened pulp to effect a slight pulsating backflow of screened pulp simultaneously throughout the entire screening surface of the screen and thereby keep it free of accumulated fibres.

8. The method of screening paper pulp which screen to free it of comprises continuously introducing the pulp at the center of a rotating mass of pulp in a stathe screen centrifugally,maintainingthe' screen submerged in screened pulp, and fluctuating the pressure in the screened pulp to effect a slight pulsating backflow of screened pulp simultaneously throughout the entire screening surface of thescreen and thereby keep it free of accumulated fibres.

9. Apparatus for screening paper pulp comprising a screen, means for passing pulp through the. screen by centrifugal force, and means operating at intervals for simultaneously reversing the flow throughout the entire screening surface of the screen to free it of accumulated fibres.

10. Apparatus for screening paper pulp comprising a cylindrical. screen, a casing enclosing but spaced from the screen, means for feedmounted in the casing for causing a pulsating backflow of screened pulp throughout the entire screening surface of the screen to free it of accumulated fibres.

11. Apparatus for screening paper pulp comprising a stationary cylindrical screen, a casing enclosing but spaced from the screen, means for feeding pulp to the interior of'the screen, means for imparting rotation to the pulp within the screen, means for maintaining the space between the screen and the casing filled with screened pulp, and means for fluctuating the pressure in the screened pulp to effect a slight, pulsating backflow of screened pulp throughout the entire screening surface of the screen to keep it free of accumulated fibres.

12. Apparatus for screening paper pulp comprising a screen plate having round holes, means for passing pulp through the screen plate and means operating at intervals for simultaneously forcing screened pulp back throughout the entire screening surface of the screen to free it of accumulated fibres.

13. Apparatus for screening paper pulp comprising a cylindrical screen chamber made up of plates having round holes, a casing enclosing but spaced from the screen plates, means for feeding pulp to the interior of the screen chamber, means for rotating the pulp within the screen chamber, means for maintaining the space between the screen plates and the casing filled with screened pulp and means for reversing at intervals the flow throughout the entire screening surface of the screen to free it of accumulated fibres.

14. Apparatus for screening paper pulp comprising a screen, means for passing pulp through the screen by centrifugal force, and a pulsating diaphragm for causing a slight backflow of screened pulp through the screen to free it of accumulated fibres.

15. Apparatus for screening paper pulp comprising a cylindrical screen, a casing enclosing but spaced from the screen, means for feeding pulp to the interior of the screen, means for passing pulp through the screen, means for maintaining the space between the screen and the casing full of screened pulp and apulsating diaphragm mounted in the casing for causing a backflow of screened pulp throughthe screen to free it of accumulated fibres.

16. Apparatus for screening paper pulp comprising a stationary cylindrical screen, a casing enclosing but spaced from the screen, means for feeding pulp tothe interior of the screen, means for imparting rotation tothe pulp Within the screen, means for maintaining the space between the screen and the casing filled with screened pulp, a flexible diaphragm forming part of the casing wall and means for flexing the diaphragm to induce a backflow of screened pulp through the screen to free it of accumulated fibres.

17. Apparatus for screening paper pulp comprising a stationary cylindrical screen, a casing enclosing but spaced from the screen, means for feeding pulp to the interior of the screen, a rotor within the screen for imparting rotation to the pulp and bringing it to the screen with its fibres parallel to the screen, means for maintaining the.

space between the screen and the casing filled with screened pulp, a plurality of flexible diaphragms forming part of the casing Wall, and means for repeatedly and synchronously flexing the diaphragms to force some screened pulp back through the screen to free it of acoumulatedlfibres.

18. A pulp screen comprising the combination of acylindrical screen chamber defined by cylindrical screen plates, an outer casing concentric with. the screen plates and defining an annular space therebetween, a rotor within the chamber, elements carriedby the rotor adjacent the screen plates and extending along substantially the length of the plates, a pulp inlet co-axial with the rotor, an outlet for rejected fibres at one end of the screen chamber, an outlet for screened pulp in the outer casing, means for maintaining the annular space between the casing and the screen plates filled with screened pulp, a flexible diaphragm in the casing wall and means for vibrating the diaphragm to force slight amounts of screened pulp back through the screen plates at regular and rapidly recurring intervals thus freeing those plates of any adhering fibres or slivers.

19. A pulpscreen comprising the combination of a cylindrical screen chamber, a rotor for rotating the pulp within the chamber, an inlet for the pulp co-axial-with the rotor, curved vanes within the inlet for converting the rectilinear motion of the incoming pulp into rotary motion, an outer casing concentric with the screen chamber and defining an annular space therebetween, means for maintaining said annular space filled with screened pulp and a pulsating diaphragm mounted in the casing for causing a backfiow of screened pulp through the screen to free it of accumulated fibres.

EDWARD JAMES TRIMBEY.

Images