IL33778A - Method and apparatus for the continuous formation of webs from particles suspended in a liquid - Google Patents

Description

METHOD APPARATUS FOR THE OP WEBS FROM PARTICLES SUSPENDED IE A LIQUID 31975 The continuous formation of from particles such as paper or textile fibres suspended in a liquid is as a rule if the concentration of the particles suspended is by a method in which the suspension is supplied to a feed box one wall of which is formed by an endless sieve moving at a constant on which the particles are deposited by continuous The rate of feed of the suspension is directly dependent on the filtering resistance of the sieve and of the cake formed and on the driving force or filtering Where this method is used industrially for the formation pf continuous webs of solid particles more or less strict requirements are apt to exist as the uniformity of or thickness of the the arrangement of the particles and their more or less regular since certain uses require the preferential orientation of the particles in the direction in which the production of the web while other uses necessitate an isotropic disposition of the the arrangement of the particles through the thickness of the especially with a view to avoiding a difference of or structure between the two sides of the the retention of fine elements contained in the other specific properties such for the body between the thickness and unit the the ratio between the transverse and longitudinal the ratio between the breaking strength and tearing the bursting and the The control of the parameters determining the properties of the web produced depends mainly on the control of the filtering conditions oyer the entire surface formation of the In particular it is as a rule desirable that it shall be possible to regulate distribution of the rate of tion over the length of the filter and to increase or reduce at will the of the filter Too high a local rate of at a may have consequence to entrain too large a proportion of the fine particles with the filtrate or to too much the porosity of the to produce Too low a local filtering rate is liable to lower too much the cohesion of the particles deposited on the surface or too much to clog the A faulty distribution of the filterin rates over the length of the filtering zone may produce a faulty local relative speed the sieve and the which would lead to a possibly undesirable orientation of the long particleB owing to a combing In many the simultaneous compliance with these various requirements may justify the desire to make the filtering rate uniform over the entire surface on which the web is being to create conditions which very closely approach such and can be regulated by Now i is known that the resistance increases with the uni weight of the deposited filterin increases along the filtering in order to make the filtering rate In the case of incompressible particles the rate of increase of the driving required achieving a uniform rate of filtration may be Against where the filtering layer formed by particles is whioh is the rule with it may be in order to achieve a rate to increase the driving or filtering force along the zone of filter formation accordance with the formulai Hs Ho where Ho is the driving or filtering force at starting point of the filtering is the driving or orce at the distance that starting pointj is a constant depending on the a is an exponent equal to or greater than the present inventio concerns a process for the continuous formation of webs by the filtration of particles suspended in a which is mainly characterized in that the suspension made flow downwards over a moving sieve sloping down i its moving The slope of the sieve in the moving direction is preferably constant in the case of incompressible In work with compressible particles the slope of the sieve In this manner the gradual increase of natural hydrostatic head of the or filtering along the sieve should correspond to the above formula with an exponent o in the case of incompressible and greater than 1 in the case of compressible with a view to achieving a rate of filtration in accordance with that formula oyer the entire surface of cake a uniform rate of The invention also concerns an apparatus for carrying out aforesaid which comprises a conduit for supplying the suspension to a feed box in which the suspension has a a zone including a conduit sloping downwards the bottom of the feed and having two side a transverse top wall and a bottom wall by a downwards proceeding stretch of a movable endless downwards proceeding supports for this sieve so disposed as to to the sieve the form required for a predetermined rate of variation of the filtering a vat for receiving the liquid passing through the the upper wall of the conduit having a so coordinated to that of the filtering bottom wall that the of the conduit decreases the a d means defining an outlet for the web from the following suspension should flow along the entire sieve at a controlled speed relative to the moving of the this purpose the top wall of the conduit above the sieve is so that the rate of decrease of the of the conduit in the direction of flour corresponds to a predetermined one that produces a constant rate of flow of the Above the surface of the suspension or the filtering surface the or pressure may be made in such manner that the effective magnitude of the hydrostatic pressure can be modified along the entire filtering without change of level of the free surface of the suspension in the feed The shape of the may also be variable with a view to adapting the machine to particular working in accordance with the invention disclosed in the Israeli Patent the or pressure the suspension may be made variable so as to make it possible to regulate directly the output a tight restricted passage for the delivery of the The increased or reduoed pressure beneath the filtering surface is then so adjusted that the differential filtering pressure between both sides o the filtering surface is Some embodiments of the invention are b way example the annexed drawings in 1 is a vertical section of machine provided with a filtering apparatus accordance with the 2 shows similarly another embodiment of invention in which the free ee of the suspension is subjected to a regulable increased or reduced shows similarly an embodiment of the invention in which the bottom surface of the filtering conduit is subjected to a regulable reduced 4 shows similarly a modification of the of 5 shows similarly a modification of the embodiment of 1 in which regulable Increased or reduced pressure is applied free surface of the suspension and beneath the filtering The filtering apparatus according to the invention shown in 1 comprises a conduit through which the suspension is supplied from the place where it is to a chamber 2 in which the flow of the suspension assumes the full width of the while a manifold constituted by a plurality of tubes distributes suspension uniformly over of the feed box e elements 2 and 5 well as the adjacent part of the box 4 have an upward slope the direction of I the feed box the suspension has a free surface Downstream of the latter the suspension descends again through a conduit 6 whose bottom 7 is constituted by one stretch of a endless sieve 8 moving with constant The bottom 7 by means of a series of transverse bars of turnable 9 in such a manner that the hydrostatic head increases at the desired rate along the entire filtering in such a manner that the rate filtration becomes completely uniform over the entire filtering This complete of the rate of filtration can be achieved in that the free surface 5 of the suspension is kept at such a level that the lowest hydrostatic head existing at the upper end 20 of the filtering zone is appropriate for the cake resistance required for a given desired rate of By way of to which the invention ia not 1 shows the top wall 10 of the channel is also the front wall of the feed shaped in such a manner that the rate of flow of the suspension in a direction perpendicular to the filter is at all points constant and correlated to the moving speed of endleas sieve The downstream end of the conduit 6 is narrowed into a orifice by a roller An endless belt 12 which runs over several among them the roller squeezes the web 13 formed by the deposited particles against the endless sieve 8 in the delivery She lower surface of the endless sieve 9 in the filtering zone 7 is free above a vat 14 which receives the filtering liquid and has at its bottom a drain The upper par of the filtering sieve may protected by a flexible shield Preferably the position is adjustable so that the starting point 20 of the filtering zone can be and accordingly the length of the filtering zone be in order to adapt filtering zone different cake resistances depending on the product to be In embodiment of the feed box covered at the top by a lid 15 disposed at some distance above the free surface of the This makes it possible to generate in the space above the surface 5 a state of increased or reduced pressure through a conduit by means of a device whereby the e of the sieve can be varied without requiring a variation of the level of the surface The rate of delivery of the web can be regulated to the desired magnitude by the adjustment of the distance of the roller 11 from the In the embodiment of the filtering stretch 7 of the endless sieve 8 forms the top wall of a closed vat p which elevated or reduced pressure can be set through a conduit by means of an apparatus 24 with a view to modifying at will the effective magnitude of the hydrostatic head the without requiring a change of level of the free A simplified embodi of the present particularly suitable use with particles and filtration from a viscous under which conditions resistance increases as a linear function of the thickness of the is illustrated in It comprises a straight filtering plate 19 sloping downwards at an appropriate over which the endless sieve embodiment of 5 shows the application of the present invention to the invention disclosed in the Israeli Specification In this embodiment the free surface 5 is subjected to elevated or reduced a pressure through a conduit 17 by means of an appratus and an elevated or reduced pressure beneath the sieve is set up i the closed vat through a conduit 23 by means of an apparatus which latter elevated or reduced pressure is correlated to the elevated or reduced pressure above the surface 5 by means of a differential regulator connected to feelers in order to produce the desired filtering In this manner the rate of output can be regulated directly by variation the pressure above the level while the magnitude of the filtering pressure o pressures above and beneath the is regulated by the differential regulator 25 which regulates the pressure in the vat 16 as Under these conditions it is possible to do away with the tightened narrow delivery orifice for the web at the outlet end of the conduit 6 in the other is defined by the roller and to replace the roller by a tiltable flap 26 disposed at a distance above the The level of the surface 5 in the feed box can be kept constant by means a regulator 27 having two feelers 32 which actuate a valve 28 controlling the supply of suspension to the feed The machine can be adapted to suspensions of various compositions by modification of the shape of the filter 7 of 3 and can be effected by variatio of the positio of the bars or rollers 9 in with a displacement of the roller 29 serving for tensioning the sieve Further modifications of the embodiment here illustrated may for the following the roller 11 the outlet end of the conduit which determines the tightened outlet slot for the may be either smooth and or a perforated hollow or a solid Or perforated lined with a felt or a solid or perforated cylinder wrapped in a permeable fabric or sieve and in each case where the roller is perforated it may be connected to one or several suction The walls of the conduit in the aone be made for allowing variations of the width of the web to be insufficientOCRQuality

Claims (1)

1. A process for the continuous formation of webs b the filtration of particles suspended in a liquid, wherein the suspension is made to flow downwards over a moving , sieve sloping down in its moving direction^ 2. A process according to Claim 1, wherein the slope of the sieve is constant, 3· A process according to Claim 1 wherein the .lope of the sieve increases gradually in the direction of flow* 4i A process according to Claim 1, 2 or 3, wherein the pressure above the sieve is varied in accordance with specific roquireaents of the operational conditions. 5. A process according to any of the preceding Claims, wherein a uniform rate of filtration is produced over the entire iltering ssone in that the foria of the sieve in the filtering zone is so shaped that the thickness of the suspension oh the filter i determined by the formula Hs as Ho + sa wherei Ho is the driving or filtering force at the starting point of the filtering gone; Hs is the driving o filtering force at tho distance (s) from that starting point; £ is a constant depending on the filtering parameters} « is h exponent equal to or greater than 1. 6. A process according to Claim 5» applied to the case of suspensions of incompressible particles, wherein a « 1. 7. A process according to Glaim 5, applied to the case of suspensions of compressible particles, wherein 1. 8. An apparatus for carrying out the process according to any of Claims 1 to 7, comprising a conduit for supplying the suspension to feed box in which the suspension has a free surface; a web-forming zone including a conduit sloping downwards from the bottom of the feed box and having two side walls, a transverse top wall and a bottom wall formed by a downwards proceeding stretch of a movable endless sieve, downwards proceeding supports for this sieve so disposed as to impart to the sieve th form required for a predetermined rate of variation of the filtering pressure; a vat for receiving the liquid passing through the sieve; the upper wall of the conduit having a form so coordinated to that of the filtering bottom wall that the cross-section of the conduit decreases in the downstream direction until; and means defining an outlet for the web from the filtering zone. 9i An apparatus according to Claim 8, wherein the delivery outlet for the web is defined by a roller defining with the sieve a slot-like orifice. 10. An apparatus according to Claim 8, wherein the delivery outlet for the ¾reb is defined by a tlltable flap. 11. An apparatus according to Claims 8, 9 or 10, xfherein the conduit is closed at the top by a wall so shaped that the cross-section of the conduit decreases in the direction of flow of the suspension in such a manner that the rate of flow remains constant. 12* · An apparatus according to any of Claim 8, 9 or 10, wherein the conduit is closed at the top by a wall which can be adjusted so as to vary the rate of flow of the suspension, 13*; An apparatus according to any of Claims 8 to 12, wherein the feed box is closed by a lid and means are provided for setting up a. state o superatmospherie or sub-atmospheric pressure in the feed box above the free surface Of the suspension* 14. An apparatus according to any of Claims Θ to 13, wherein the stretch of the sieve in the filtering zone is straight, 15* An apparatus according to any of Claims 8 to 13, coiaprising means for varying the shape of the stretch of the sieve in the filtering zone., PARTNERS RO/ZS