US3376976A - Screen - Google Patents

Description

A ril 9, 1968 E. o. L. WALLEN 3,376,976 scmmn v Filed Oct. 18, 1965 4 Sheets-Sheet l April 9, 1968 E. o. L. WALLEN 3,376,976

SCREEN Filed Oct. 18, 1965 4 Sheets-Sheet 3 United States Patent 3,376,976 SCREEN Emil Olof Lennart Walln, Stockholm, Sweden, assignor to Grubbens & Co. Aktieholag, Stockholm, Sweden, a Swedish joint-stock company Filed Oct. 18, 1965, Ser. No. 497,023 Claims priority, application Sweden, Oct. 19, 1964, 12,570/64; Dec. 30, 1964, 15,870/64 Claims. (Cl. 209-273) ABSTRACT OF THE DISCLOSURE A screening device having a chamber which is divided by a screen into an inlet reject compartment and an accept compartment, with one or more appropriate inlets and outlets for the material to be screened, and having oscillatable diaphragms on both sides of the screen, one face of at least one diaphragm lying in the path of the flow of the material. A pressure medium is in pressure contact with the other face of the diaphragm and means are provided to oscillate the diaphragms, whereby pulsations of the diaphragms and the pressure medium are transmitted to the material to be screened.

This invention relates to a screen having at least one screening surface which divides the screen chamber into at least one compartment to which the material is to be screened is supplied and from which the reject is withdrawn, here called the inlet reject compartment, and at least one compartment from which the accept is withdrawn, here called the accept compartment. This screen is also provided with inlet means for material to be screened and outlet means for withdrawal or reject and accept.

The present screen is especially intended for classification, screening and/or thickening of fibrous materials, particularly pulp (cellulose pulp). The material, however, can be any solid material whatsoever that is suspended in a vehicle, particularly a liquid vehicle, such as water.

In prior screens wherein the screening surface is enclosed in a chamber, no oscillations are generallyprovided in the material to be screened; in those cases where oscillations are provided they are extremely limited and cause only a slight portion of the quantity of the material to be screened, of the accept and of the reject enclosed in the chamber to oscillate or vibrate.

In comparison with these known screens, it has now been found that the screen according to the invention provides the following advantages:'

(1) Far higher capacity per sq. metre screen area (or per hole) e.g. in order of 23 times higher.

(2) The material to be screened can have a much higher concentration, e.g. 50-100% more than in known screens.

(3) No moving parts rest against the surface of the screen, thus avoiding the need for an exactly circular screen or a thick screen plate.

(4) Clogging (formation of a fibre mat over the entire surface of the screen) is no longer a problem. If clogging should nevertheless occur in the screen according to the invention, all that is necessary is to stop thesupply pump or to close the inlet valve for a few seconds, during which time the screen is freed from clogging or fibre mat and becomes operable again.

(5) Low power consumption per ton of pulp, about half of that with known closed screens.

(6) Low production cost.

The screen according to the invention comprises at least one means for producing oscillations in the entire mass of material, in the screening chamber, rejectand Patented Apr. 9, 1968 accept to be screened. The screening chamber can be closed or open in at least either of the inlet reject compartment and the accept compartment. The means for producing oscillation is preferably a diaphragm which generally constitutes a part of or a whole wall of the chamber, of the inlet reject compartment, or of the accept compartment respectively. The said means may, however, also consist of a means lying within or outside the respective compartment, e.g. a piston pump, in which case the impulse can be transmitted to the material in the chamber through pipes containing a pressure medium.

The shape of the screening surface is not critical; it can be fiat, but can also constitute a jacket surface, eg a prismatic surface, such as a prism having a circular, polgonal or elliptical cross section. It is also possible to arrange more than one screening surface in the same screening chamber.

According to the invention it is desirable to have as long a path as possible for the material to be screened along the screening surface in the direction from the inlet of the material to be screened to the rejwt outlet in order to attain the maximum possible efiiciency. The screening surface is preferably covered on both sides with material, i.e. material to be screened and reject and accept respectively, in order to attain as high a capacity as possible. In the case where the screen is closed, it is preferably full of material to be screened, reject and accept, both the incoming material (material to be screned) and accept suitably being under pressure. In the case where the screen is open, it is suitable that theincoming material (the material to be screened) is under pressure, the inlet reject compartment preferably being closed. Alternatively it is also possible that the accept compartment instead is a closed chamber.-

The material to be screened is suitably introduced in such a manner that coarse foreign particles such as stones, pieces of iron, etc., are removed from the screening surface by centrifugal force or the like. To this end, the screening surface in one embodiment is a jacket surface, particularly a cylindrical surface, the inlet being arranged tangentially in relation to the screening surface; the screening surface is then preferably arranged substantially vertical. In this embodiment it is suitable to arrange the reject outlet at one of the base surfaces (the flat surfaces of the cylinder, etc.) of the screen, generally the lower one.

The means for producing oscillations are located both in the inlet compartment and in the accept compartment of the screen. When these means consist of diaphragms, every said diaphragm may be, for example, a rather stiff, resilient diaphragm, as of thin, stainless steel, possibly corrugated, which is oscillated in a suitable manner known per se. The diaphragm can be made to oscillate (vibrate) synchronously or variably by electronic means, mechanically or in some other suitable way. The diaphragm can also consist of a rubber diaphragm or the like; in these latter diaphragms the oscillating frequency is normally lower, e.g., 1-50 c./s., as compared with up to 20,000 c./s. for stiffer diaphragms. It is of course not necessary, but suitable, that the diaphragm in the inlet reject compartment as well as in the accept compartment be of the same kind.

The oscillation amplitude at periodicities of up to 50 c./s. is preferably of such magnitude that the speed of return flow through the screen holes under at least a part of the return flow period is about twice as fast as the speed through the holes which is calculated from the amount of accept.

The oscillation pulses need not be symmetrical; the pulse for application of pressure to ingoing material can preferably have a longer duration than the pulse for flushing away of reject.

The static pressure on either side of a softer diaphragm, such as a rubber diaphragm, should preferably be the same or practically the same; this can be ensured by, for instance, drilling small holes in the diaphragm. The dia phragm is generally oscillated by means of a pressure medium.

The screen itself can be elastic and is then intended to oscillate in pace with the pulses; it can possibly be supported by a rigid network or the like in order that the pulse shall be buttedly interrupted in one direction, whereas the pulse is free in the other direction. Normally, however, the screen is of rigid material, such as metal plate. The screen can also be moving, e.g., in the case of cylindrical screen rotating.

The holes in the screen can be of any shape. The said holes can thus be round and cylindrical or consist of slits or have any other known cross-section. They can also be entirely or partly conical.

The invention is described more in detail with reference to the accompanying drawing, in which FIG. 1 is a schematic view of a fiat screen according to the invention. FIG. 2 is also a schematic view of another flat screen according to the invention. FIG. 3 is a view of a screen according to the invention having a cylindrical screening surface. FIG. 4 is a schematic plan view of an open fiat screen according to the invention in which the material to be screened is supplied through a pipe or an open channel. FIG. 5 is a schematic vertical view of an open screen according to the invention having a cylindrical screening surface. Finally, FIG. 6 is a vertical view showing a cross section of an open screen according to the invention in which the screening surface is cylindrical and horizontal.

The screen in one of its simplest forms is shown in FIG. 1, wherein the closed chamber is confined by upper walls 2, bottom wall 3 and side walls 4. An inlet for material to be screened is shown at 5 and an outlet for reject at 6 and for accept at 7. A means for producing oscillations is shown at 8 in the form of a piston pump. A screening surface is shown at 9. If desired, the means 8 for producing oscillations can be replaced by, for example, a diaphragm, which can comprise a part of or a whole wall, e.g., wall 3. The screen can be oriented in any manner; thus, for example, the inlet 5 and the reject outlet 6 can be located under the screening surface or the screening surface 9 can be vertical.

In one embodiment more than one screening surface can be arranged; this is shown in a simple form in FIG. 2. The screening surfaces are shown as flat screens at 10 and 11, the said screening surfaces being enclosed in the chamber 12. This chamber is provided with inlet pipes 13 for the material to be screened and outlet pipes 14 for reject and an outlet pipe 15 for accept. The device shown is also provided with two means 16 for producing oscillations, the said oscillations being transmitted to the material to be screened, both reject and accept, by means of the diaphragms 17. Any of this means 16 with its appurtenant diaphragm 17 can be excluded, if desired, and the said means can naturally be designed in some other manner.

In FIG. 3 is shown yet another embodiment of the invention. In this embodiment the screening surface 20 is cylindrical and the material to be screened is introduced through an inlet line 21, which in this case introduces the material to be screened tangentially to the screening surface 20. Inside the screen 20 is a diaphragm 22, which by means of impulse-emitting means 23, 24 provides oscillations in the material to be screened. Thus, there are shown a resilient diaphragm 23 and a magnetic vibrator 24. Via a pressure medium 25 oscillations are also transmitted from these impulse-emitting means 23, 24 to a diaphragm 26 which surrounds the screen. The space 22a is also filled with a fluid pressure medium responsive to the oscillations of the diaphragm 23. For the reject there is an outlet line 27 and for the accept an outlet line 28. On account of the tangential input of the material to be screened through the line 28, heavy foreign particles, such as stones, iron objects, etc., are separated by centrifugal force. If the material to be screened is excessively thickened towards the reject outlet, it is possible to arrange at the lower part of the screening surface a supply of vehicle, i.e., normally water. This can naturally also be done in other embodiments of the screen according to the invention. In the embodiment according to FIG. 3 the screen may possibly also be rotatable. Of course, it is also possible to use a screening surface the shape of which is other than cylindrical, e.g., in the shape of a barrel or of an hour-glass.

Tests have been carried out with a cylindrical screen according to the embodiment illustrated in FIG. 3; the diameter of the screening surface was 150 mm. and the screening surface contained 15,100 punched holes with a diameter of 1.5 mm. The tested pulp consisted of slushed magazines being comparable with groundwood pulp; however, the tested pulp contained about 10% reject in the form of unslushed pieces of paper, etc. (paper pieces not being entirely disintegrated in the pulper). This high content of reject was desirable in order to test clogging of the screen. The discharge through the screen was increased to considerably more than 600 litres per minute and the inlet concentration was increased to 2.5% without any clogging occurring during the several hours over which the test extended. The reject outlet was opened intermittently every 515 minutes.

The said test was repeated with long-fibre kraft wrapping paper. The slushed pulp was pumped directly to the screen and had a concentration of about 1.6%. In this case, also, no clogging occurred during a flow through the screen of considerably more than 600 litres per minute.

The open screen in a simple form is shown in FIG. 4 where the material to be screened is supplied through a duct or open channel 101 and the reject is withdrawn at 102. The accept is withdrawn at 103. Means for producing oscillations are shown at 104 and 105 and are shown in the form of diaphragms which are oscillated to and fro in a mechanical way, for example. The screen is divided into an inlet reject compartment 106 and an accept compartment -107 by means of a screening surface 108. In this embodiment the screening surface is substantially vertical.

In FIG. 5 there is shown an embodiment of the invention in which the screening surface is cylindrical. The material to be screened is admitted through a duct or channel 121, which in this case introduces the material tangentially towards the vertical cylindrical screening surface 120. The screening surface 120 divides the screen into an inlet reject compartment 122 and an accept compartment 123. In this case with confined supply conduit there is maintained a liquid level 124 in the inlet reject compartment. This compartment can, if desired, be completely confined, and the material to be screened in the compartment 122 can be under pressure. In the accept compartment 123 a liquid level 125 is maintained. The accept is withdrawn through a conduit 126. In the accept compartment 123 there is a diaphragm 127 which produces oscillations in the mass of material to be screened, reject and accept. The inlet reject compartment is also provided with a diaphragm 128 for producing oscillations. The oscillations of the diaphragms 127 and 128 are produced by means of a resilient diaphragm 129 or the like. The oscillations are transmitted by means of a pressure medium within the spaces 127a, 128a, 129a. For the reject there is an outlet conduit 130. By the tangential supply of the material through the conduit 121 coarse foreign particles, such as stones, scrap and the like, are separated by centrifugal action. These particles are taken out through 131. If the material to be screened should be thickened too much inthe reject compartment, it is possible to arrange a supply of vehicle, i.e. normally water, at the lower part of the screening surface. This can naturally be done also in other embodiments of the present invention. In the embodiment according to FIG. 6 the screen may possibly also be rotatable. It is, of course, also possible to use a screen the shape of which is other than cylindrical, e.g. one in the shape of a barrel or of an hour-glass or one having a polygonal or elliptical cross sectin.

In the embodiment shown in FIG. 6- the screening surface is cylindrical and horizontal. Within the screening surface there is a diaphragm 141 for producing oscillations and in the vessel 142 surrounding the screening surface 140 there is located a diaphragm -143 for pro-ducing oscillations. The vessel 142 is open. This device is analogous to the device shown in FIG. and is, of course, also provided with conduits, and channels respectively, for supply of material to be screened and for removal of reject, and accept respectively.

What I claim is:

1. A screening apparatus for screening fluent material comprising an enclosure having a screening chamber therein, a screen within said chamber dividing said chamber into an accept compartment and a reject compartment, an inlet for said chamber arranged to direct the inlet flow towards the screen, at least one outlet for each separate compartment, an oscillatable diaphragm for each compartment, one on each side of said screen, the fluent material being adapted to pass between said screen and said diaphragms, a chamber adjacent each diaphragm for receiving a pressure medium, said diaphragms adapted to be pulsated by said pressure medium in contact therewith, means for causing pulsations in said pressure medium, the pulsations thereof being transmitted to said diaphragms and said fluent material through said pressure medium.

2. A screening apparatus according to claim 1, in which said means for causing pulsations comprises a third diaphragm and a vibrating means therefor in contact with said pressure medium.

3. A screening apparatus according to claim 2 in which said third diaphragm is angularly disposed with respect to said two other diaphragms.

4. A screening apparatus according to claim 1 in which said diaphragms are oscillated at the same rate and synchronously in the same oscillation direction.

5. A screening apparatus according to claim 1 in which the screen, diaphragms and chamber walls each comprise a surface of revolution.

References Cited UNITED STATES PATENTS 806,641 12/1905 Chapman 209-273 815,421 3/1906 Goodrick 209-273 1,399,653 12/1921 Pope 209-270 1,694,622. 12/1928 Lindquist 209-270 1,990,288 2/1935 Knight 209-273 2,358,970 9/1944 Gray 209-273 2,368,291 1/ 1945 Dustan 209-273 2,480,119 8/1949 Cram 209-273 2,593,202 4/1952 Schenk 209-270 2,607,490 8/1952 Newton 209-270 2,988,223 6/1961 Janson 209-250 3,255,883 6/1966 Nelson et al. 209-273 HARRY B. THORNTON, Primary Examiner.

TIM R. MILES, Examiner.

Images