US3664501A

US3664501A - Pulp screening machine

Info

Publication number: US3664501A
Application number: US3963A
Authority: US
Inventors: Ben Cowan
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-11-21
Filing date: 1970-01-19
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23
Also published as: CA887765A; SE365832B

Abstract

A pulp screening machine of the rotary type for either horizontal or vertical installation of either the open or pressure type in which the screen is made in sectors, joined together and one end place and a sector shaped screen supporting keeper plate and removed whereby the sectors of the screen plate can be removed axially of the machine without disturbing the screen housing in the line or the mounting of the impeller in the machine.

Description

United States Patent Cowan 1541 PULP SCREENING MACHINE Ben Cowan, 5460 Connaught Avenue, Montreal 29, Quebec, Canada 221 Filed: Jan. 19, 1970 211 Appl. No.: 3,963

[72] Inventor:

[30] Foreign Application Priority Data Nov. 21, 1969 Canada ..068114 [52] (1.8. CI ..209/273, 209/407, 210/232, 210/415 [51 Int. Cl ..B07b l/20 [58] Field of Search... ..209/407, 273, 270, 232, 415, 209/452, 211, 370, 372; 210/403, 394, 210-215 [56] References Cited UNITED STATES PATENTS 3,508,651 4/1970 Hooper ..209/273X 51 May 23, 1972 3,057,476 10/ l 962 Gilbert ..209/21 1 FOREIGN PATENTS OR APPLICATIONS 767,207 2/1952 Germany ..209/407 Primary ExaminerFrank W. Lutter Assistant ExaminerWilliam Cuchlinski, Jr. Attorney-Fetherstonhaugh and Co.

[57] ABSTRACT A pulp screening machine of the rotary type for either horizontal or vertical installation of either the open or pressure type in which the screen is made in sectors, joined together and one end place and a sector shaped screen supporting keeper plate and removed whereby the sectors of the screen plate can be removed axially of the machine without disturbing the screen housing in the line or the mounting of the impeller in the machine.

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3 IINVENT Ben COWA PATENT AGENTS PULP SCREENING MACHINE The invention relates to pulp screens of the rotary type, both open and pressure type, and particularly to means whereby the annular screen can be quickly and efliciently removed from its housing without disturbing the screen housing in the line or the impeller and impeller mounting.

The invention is applicable to either open type gravity operated screens or to pressure type screens, either horizontal or vertically operated, but is of particular advantage in pressure type screens where the housing is formed from a continuous cylindrical tube accessible only from the ends.

Paper pulp screens can be classified into two general designs, open (unpressurized screens), and pressure screens.

The open screens are normally fed with pulp under low pressures (6 to feet of head) and discharge both accepted pulp and rejects at atmospheric pressure. The interior of the screen normally operates at atmospheric pressure. The unpressurized screen is generally more selective and more efficient. It produces cleaner accepted pulp, and the quality and quantity of the rejected material can be closely controlled and adjusted.

The pressure screen operates at all times under a positive pressure in the screen interior which may be of the order of 4 to psi. Both accepts and rejects are discharged under pressure. The essential requirement is to avoid contact with air during the screening process and this avoids the generation of foam in the liquid medium. The rejects are difficult to control in quality, and there is a minimum quantity of rejects flow necessary to maintain operation. For this reason the pressurized screen is not as efficient in the removal of unacceptable material as the open screen.

The open screen is generally built with the screen axis horizontal, and a fairly light frame with removable sections for screen plate screening. The pressure screen is generally built with the screen axis vertical, and a heavy body to withstand the internal pressure. The screen plates are less accessible and more difficult to change.

In summary the open screen is more efficient and flexible in operation, easier to maintain, and cheaper in construction than the pressure screen. The pressure screen is a unit in a straight line flow system, is simpler to install, and does not generate foam.

The Multiple Screen of the present application is a design intended to combine both applications, open or pressure, in a single unit. It uses a cylindrical body for pressure resistance. The screen plate assembly is a standard three-section assembly used for all Cowan screens. Any standard Cowan screen rotor can be installed in the screen which will allow operation as an open screen with the K-X design of Cowan Rotor, or as a pressure screen with the P-S or V type rotor. The assembly may also be set horizontal or vertical if required.

For maintenance and accessibility the front bearing is supported in a hollow beam submerged in the inlet chamber. This beam is open at both ends to atmosphere, so that no liquid can enter the bearing through the packing gland. Any leakage of the packing gland is immediately apparent by the discharge at the open end of the support beam.

The end cover of the screen, at the inlet, can be removed for servicing and washing out the screen. To change screen plates, the top section of keeper plate only is removed, and the four small bolted covers on the housing body of the screen which give access to the handholes. The screen plate sections are then unbolted and a 120 section of plate removed through the opening caused by the removal of the top keeper plate. The other two sections of screen are then pushed up to the top, and removed in the same way. The screen frame is re-assembled in reverse order.

If it is desired only to wash down the screen plate, the inside is accessible through the feed opening without removing the keeper plate. The outside can be inspected and cleaned if necessary through the handholes.

The object of the invention is to provide means whereby screen plates in a pulp screening machine can be withdrawn from a sealed housing without dismantling the housing or the impeller mounted within the housing.

A further object of the invention as used in pressure screening of pulp, is to provide means whereby the screen plates can be removed from their housing without taking the machine out of the line.

A still further object of the invention is to provide means whereby sectors of the annular screen plate can be removed individually from the screen housing with a minimum of disturbance of the screen end plates.

These and other objects of the invention will be apparent from the following detailed description and the accompanying drawings, in which:

FIG. 1 is a longitudinal vertical section of a horizontal pres sure type screen showing typical elements of the present invention.

FIG. 2 is a view similar to FIG. 1 except that one external end 'plate and a portion of an adjacent internal end plate have been removed, and showing a sector of screen plate partially withdrawn from the screen housing.

FIG. 3 is a partial transverse section of one end of the screen housing showing the inner bearing support beam.

FIG. 4 is a vertical section taken on the line 4-4 of FIG. 1.

FIG. 5 is a vertical section taken on the line 5-5 of FIG. 1.

FIG. 6 is a vertical section taken on the line 6-6 of FIG. 1.

FIG. 7 is an enlarged detail of a screen end support.

Referring to the drawings, the pulp screen 5 illustrated is typical of a horizontal type pressure screen. However, the invention is not limited in scope to horizontal pressure screens but could equally well be adapted to vertical pressure screens, or to horizontal and vertical gravity type screens.

The impeller 6 is of simple and well known type consisting of a shaft 7, blades 8 radiating outwards from the shaft, and baffle plates 9. The impeller 6 could be of the type having a conical core, and the blades 8 could also be of the double wall type providing wash water passages, directing the wash water close to the inner surface of the screen plates.

The screen 5 is provided with a cylindrical housing 10 preferably of a type to withstand high internal pressure and be more or less retained permanently in the pulp stock line, the housing being divided longitudinally by the annular plate or partition 1 l to form a stock inlet chamber 12 and of a screening chamber 13.

A keeper plate 14 is bolted to the annular plate 11 by the bolts 15, and is made in two sectors, an upper sector 14a and a lower sector 14b. The abutting edges 16 of the upper and

lower sectors

14a and 14b are disposed at an angle of approximately 20 above a horizontal plane normal to the longitudinal axis of the screen 5. The keeper plate 14 is provided with an axial bore or opening 17 coincident with the axis of the impeller shaft 7, whereby stock from the stock inlet chamber 1 is passed into the screening chamber 13.

A removable outer end wall plate or cover 18 seals the stock inlet chamber 12 while a flanged pipe connection 19 at the upper end of the chamber 12 connects with a source of pulp, not shown, which may be gravity feed or pressure feed to the interior of the housing.

An end plate 20 seals off the end of the screening chamber 13, opposite from the stock inlet chamber 12.

The annular screen 21 extends the full length of the screening chamber 13 and is provided with end bearing rings 22 fitting over the support rings 23 on the end plate 20 and over the support rings 24 on the

keeper plate sectors

14a and 14b, thus allowing the screen to be manually rotated in the housing 10. The contacting surfaces between the rings 22 and the

rings

23 and 24 are slightly angled to reduce end play of the screen 21 between the

end plates

14 and 20, as shown in detail in FIG. 1.

The annular screen 21 is made in three arcuate sectors or

segments

21a, 21b and 210 and are joined together at their abutting edges by pairs of longitudinally disposed angle irons 25 by means of bolts or other suitable fastening means.

Radially opposite each of the two upper abutting pairs of angle irons 25, there is provided a pair of handholes 26 for ready access to the fastening means securing the

screen sectors

21a, 21b or 210 together. These handholes 26 are closed and sealed by the cover plates 27.

The impeller shaft 7 is provided with an outer bearing 28 mounted on the outer facing surface of the end plate and is provided with a drive pulley 29. The shaft 7 is hollow and is provided with a wash water inlet connection 30. A series of apertures 31 through the wall of the hollow portion of the shaft 7 permits the wash water to be injected into the space between the blades 8 of the impeller 6.

The end of the shaft 7, opposite from the wash water connection terminates in a stub shaft 32 which is, in turn supported in the bearing 33. The bearing 33 is mounted within a housing 34 which, in turn is supported in a hollow beam 35 disposed in a horizontal plane normal to the axis of the impeller shaft 7. The end portions 36 of the beam 35 are secured to the wall 37 of the stock inlet chamber 12 in line with the o enings 38 in the wall 37. A cover plate 39 seals the bearing 33 from entry of fluid from the interior of the screen. A stuffing box 33a prevents fluid in the inlet chamber 12 from entry to the bearing 33.

Any leakage of fluid carrying the pulp which may penetrate into the bearing 33 will be carried along the interior of the hollow beam 34 and will be discharged to atmosphere through the open ends 38.

The discharge of the screened pulp from the screening chamber 13 is through the discharge outlet 40, while heavy rejects are discharged from the interior of the screen plate 21 through the opening 41.

A clean out opening 42 is provided at the bottom of the inlet chamber 12. This opening 42 may be closed by the removable plate 43 or by a suitable valve connection.

In order to remove the screen plate 21 from the machine for cleaning, repair or replacement, from the otherwise permanently sealed screening chamber 13, as defined by the cylindrical housing 10, the end wall 18 is first removed. The upper sector 14a of the keeper plate 14 is then removed to expose the upper portions 2lb and 210 of the screen plate 21.

On removal of the cover plates 27 at the handholes 26, access is obtained to the fastening means at the angle irons 25 of the screen sectors.

The screen sectors, when unsecured from each other, can be rotated on their support rings 23 and 24 to bring first one sector 21a and

successive sectors

21b and 21c opposite the enlarged sector opening created by removal of the upper sector 14a ofthe keeper plate 14.

As the sectors of the screen plate 21 are of three equal sectors of 120 and the opening created by removal of the upper sector 14a of the keeper plate 14 is approximately 140, the individual sectors of the screen plate can be withdrawn with ease past the impeller and bearing 33 and its supporting beam 34. The upper edges 14c of the lower keeper plate 1412 form a support for the screen plate sectors as they are being withdrawn.

It will therefore, be apparent that the screen plate 21 can be removed from its housing without having to remove the machine from the pulp line, or in any way interfering with the impeller and its mounting within the housing. It will also be apparent that a thorough cleaning of the interior of the housing, including the impeller can be accomplished when the screen is removed as above described.

In addition, with the screen 21 removed as above described it is a simple matter to remove the complete impeller assembly, if desired, merely by disconnecting the end plate 20 from the housing 10, again, without taking the machine out of the pulp line.

The above procedure is reversed when either the impeller or the screen are to be reinserted into the housing.

Up to now the open type of screen has not been well adapted for use in pressure application because of the necessity for screen rem oval makes it difiicult to design a housing body which Wlll withstand high internal pressures. The present design, as above described, of an uninterrupted cylinder with easy screen removal, makes it feasible to use the same design of housing for both open and pressure screens.

The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows:

ll. In a pulp screening apparatus, the combination of a sta tionary housing having a partition which separates the housing into a pulp screening chamber and a pulp inlet chamber at one end of said screening chamber, said inlet chamber having a removable cover opposite said partition, an impeller rotatably mounted in said housing, an annular screen disposed in the screening chamber and surrounding said impeller, a keeper plate secured to said partition and provided with a central opening which is coaxial with said impeller and communicates said inlet chamber with the interior of the screen in the screening chamber, said keeper plate including a keeper plate sector which is removable from said partition to provide an access passage additional to said central opening, said annular screen consisting of a plurality of segments separably connected together, and means mounting said screen for manual rotation in the screening chamber so that the individual screen segments may be successively brought into alignment with said removable keeper plate sector, whereby upon removal of said cover and of said keeper plate sector and upon separation of the screen segments the segments may be individually and successively removed from the screening chamber through said access passage and through the inlet chamber while leaving the impeller in place.

2. Pulp screening apparatus as set forth in claim 1 which is further characterized in that said annular screen consists of three segments each spanning an arc of said removable keeper plate sector having an arc span greater than 120.

3. Pulp screening apparatus as set forth in claim 1 which is further characterized in that the portion of said keeper plate other than said removable keeper plate sector is also remova ble from said partition.

4. Pulp screening apparatus as set forth in claim 1 in which said impeller includes a shaft, said shaft being supported in bearings, one of said bearings being located within said pulp inlet chamber.

5. Pulp screening apparatus as set forth in claim 4 in which the support for the bearing within the pulp inlet chamber includes a hollow beam disposed transversely within the inlet chamber and the ends of the beam are open to atmosphere externally of said inlet chamber.

6. Pulp screening apparatus as set forth in claim 5 in which said bearing within the inlet chamber includes a stuffing box about the impeller shaft and leakage through said stuffing box is drained to atmosphere through said hollow beam.

7. Pulp screening apparatus as set forth in claim 1 wherein said screening chamber has an end wall axially opposite said partition and wherein said screen mounting means comprise a pair of rings provided on said end wall and on said keeper plate concentrically with said impeller, end portions of said annular screen being rotatably supported by said rings.

8. Pulp screening apparatus as set forth in claim 7 wherein said mounting means also include axially projecting flanges provided at the ends of said screen, said flanges being rotatably seated on said rings.

Claims

1. In a pulp screening apparatus, the combination of a stationary housing having a partition which separates the housing into a pulp screening chamber and a pulp inlet chamber at one end of said screening chamber, said inlet chamber having a removable cover opposite said partition, an impeller rotatably mounted in said housing, an annular screen disposed in the screening chamber and surrounding said impeller, a keeper plate secured to said partition and provided with a central opening which is coaxial with said impeller and communicates said inlet chamber with the interior of the screen in the screening chamber, said keeper plate including a keeper plate sector which is removable from said partition to provide an access passage additional to said central opening, said annular screen consisting of a plurality of segments separably connected together, and means mounting said screen for manual rotation in the screening chamber so that the individual screen segments may be successively brought into alignment with said removable keeper plate sector, whereby upon removal of said cover and of said keeper plate sector and upon separation of the screen segments the segments may be individually and successively removed from the screening chamber through said access passage and through the inlet chamber while leaving the impeller in place.

2. Pulp screening apparatus as set forth in claim 1 which is further characterized in that said annular screen consists of three segments each spanning an arc of 120*, said removable keeper plate sector having an arc span greater than 120*.

3. Pulp screening apparatus as set forth in claim 1 which is further characterized in that the portion of said keeper plate other than said removable keeper plate sector is also removable from said partition.