US2631733A

US2631733A - Method and apparatus for the continuous screening of fluids

Info

Publication number: US2631733A
Application number: US778800A
Authority: US
Inventors: Carl H Rowe; Elmer R Mokros
Original assignee: K C M Co
Current assignee: K C M Co; K-C-M Co
Priority date: 1947-10-09
Filing date: 1947-10-09
Publication date: 1953-03-17
Anticipated expiration: 1970-03-17

Description

c. H. ROWE ETAL 2,631,733 METHOD AND APPARATUS FOR THE CONTINUOUS V SCREENING 0F FLUIDS March 17, 1953 3 Sheets-Sheet l 7 Filed 001.. 9, 1947 8 5 r a 0 r 5 V M Te rm 5 c. H. ROWE ET AL 2,631,733 METHOD AND APPARATUS FOR THE CONTINUOUS SCREENING 0F FLUIDS March 17, 1953 5 Sheets-Sheet 2 Filed Oct. 9, 1947 Carl f1 Razz/6 flmrzeflfohws, F 4 fln MM jam,

mi km March 17, 1953 c. H. ROWE ET AL METHOD AND APPAR ATUS FOR THE CONTINUOUS SCREENING OF FLUIDS 5 Sheets-Sheet 5 Filed 001;. 9, 1947 Elmer/1 .2110

Big/s.

Patented Mar. 17, 1953 UNITED STATES PAZI'SEJNT OFFICE METHOD AND APPARATUS :FO-R .THE

. CONTINUOUS SGREENING.OF .FLUIDIS Application October 9, 1947 Serial No; 778,800

9 Claims.

"'llhepresent invention relates generally to an improved method and apparatus for continuously screening suspended particles from-fluid andsemi-fiuid materials, and in particular to animproved method and apparatus for continuously screening oversized materials from viscoussuspensions such as the suspensions used in-coa-tingpaper and the like.

Inthemanufacture of coated paper, inorder to obtain a finished sheet having the requisite bright, smooth surface, it has been found necessary to coat the surface of the base sheet with viscous coating mixtures having certain highly specialized characteristics. As one step'in production of satisfactory coating mixtures for this purpose, it has been found desirable to screen the; mixture prior to its application to the paper sheet, and the provision of efficient screening apparatus for this purpose has presented a seriousproblem to the art. These coating mixtures usually comprise a mixture of an adhesive, china clay, and a bright mineral, such as calcium carbonate or satin white. The coatin mixtures in current use have a viscosity of the order of several hundred centipoises. .In vthe screening operation, in additionto removing all foreign material such as grit, dirt, fibers, etc., all particles which are over a certain critical size should-be removed. Usuallyit is considered necessary to remove all particles having vacrosss'ectional dimension greater than about .003 inch, and it isjdesirable to remove thosehaving a cross-sectional dimension over .001 inch. If. this is done, the-surface of theffinished paper can'be formed free from surface defects and with the requisitetover-all smoothness.

'I-leretQf-ore, the usual method for screening such c'oatingshas been to pass them through either a cartridge type filter or through a vibrating screen. Neither method is wholly satisfactory or wholly effective because the viscous character of the coating material being screened so reduces the rateof flow of the material that that the screening mechanisms become uneconomically large if complete screening of the smaller size particles is to be effected. The flow rates and capacities of the present screening equipment can be increased by either-reducin hssolids contentof the co ting material, which is und irable, or by increasin the size'of the openings inthe fil erorscreen, but this is also unde irable. ,If the solidscontentof the coating is greatly reduced. a poor-surfaced paper resul s, W hneither thedesired opaci y and printability nor a bright appearance. When the 2 screen capacity-is increased by enlarging'the openings above theestablishedcritical sizes; objectionable materials inherent in the coatings are allowed to pass through the screen with sim ilar impairment of the coated surface.

The principal object of the present inven-- tion, therefore, is to provide an improved, economically practical apparatus and methodwhich will effectr-apid and efficient screening of fine particles from fluid or semi-fluid materials of this character. A -particularobject is to provide apparatus adapted for the continuous screening of paper coatings wherein particles having a maximum cross-sectional dimension of .003 inch or less can be screened from the coating mixtures at very high rates of flow. Other objects and advantages of the invention will be clear upon reference to the following description and the accompanying drawings of one embodiment of the invention.

In the drawings:

Fig. 1 is a side elevational view of a continuous belt screen, in accordance with the invention;

Fig. 2' is an-end elevational view of the apparatusillustrated in Fig. 1;

Fig. 3 is-a diagrammatic, elevational view of the drivearrangement employed'in'the apparatus illustrated;

.Fig. '4 .is a side elevational view, partially in section, of a beltwipe adapted for use with the apparatus of Fig. 1;

Fig. 5 is an enlarged, cross-sectional view of the wiping blade and supporting tube which is apart of the belt wipe illustrated in Fig. 4;

Fig.6 is a sectional view'of a ro-ll wipe adapted toremove materials from the belt rolls in the-apparatus illustrated;

Fig. '7 is a sectional view .of the rejection pan of the apparatus of'the present invention; and

Fig. 8 is a sectional View of the air, jet manifold which is provided for continuously cleaning the screen inthe apparatus illustrated.

Generally stated, the screening process of the invention includes providing a pool of unscreened material at the nip formed between an arcuate. surface and ascreen having the desired dimensions while producing relative movement between the screen and the surface so as to cause the material being screened to pass through the screen; Mean for wiping'the surface ofth-e screen may be provided along the line of contact of the screen and the surface to facilitate the removal of the "screened material. This means may comprise a'doctor blade or a'wipe.

Various cleaning and recycling means may also :be incorporated into the apparatus, so that close control of the size and purity of the screened particles can be maintained at all times. It will be apparent that various structures can be used to accomplish the method of the invention. These include: the continuous belt screen and roll combination, illustrated in the drawings, a vibrating screen and a stationary or rotating surface, a stationary screen and a reciprocating, rotating, or rocking surface, or a reciprocating screen and a reciprocating, rotating, or rocking surface.

The embodiment of the invention illustrated in the drawings, is especially adapted to the screening of paper coatings and like viscous materials which must be delivered in large volumes. For convenience, the usable material which passes through the screen will be hereinafter termed the accepted material, and the oversize material which does not pass through the'screen will be termed the rejected material.

The apparatus generally includes a frame 1 I, a plurality of rolls i2, 33, Hi, and i5 which are supported on the frame ii for rotatable movement, an endless screen ll disposed about the rolls as a belt, means for rotating the rolls at predetermined speeds, and means for introducing a pool of the material to be screened into one or more of the nips formed between the rolls i2, l3, and M and the screen 1?. Means are also provided for removing accepted material from the screen H and for conducting away the rejected material. To overcome any tendency of the material being screened to clog the screen openings during operation, means are provided for continuously cleanin the screen H.

The main frame I i comprises a plurality of vertically extending supporting columns l9 which are connected by suitable horizontally extending members 2!. The various elements of the frame .Il may, as illustrated, be fabricated from pipe members or they may be of any convenient structural shape. A pen 23, conveniently fabricated from sheet metal, is supported in the frame ll under the apparatus, andserves to catch the accepted material which passes through the screen [1. The pan 23 slopes downwardly to a low point at one side of the apparatus, where it is connected to a suitable conduit 25 which is adapted to conduct the screened coatings to the coating rolls or press. In the apparatus illustrated, there is no provision for a cabinet or outer shell around the apparatus, but it will be understood that when certain types of materials are being screened a shell should be provided to prevent the material from splashing onto surrounding working spaces. The provision of a cabinet or shell also makes possible the maintenance of a high humidity about the screen so that the material being screened will not dry out.

The rolls l2, l3, and I d are horizontally disposed and'extend transversely across the frame i l. The rolls are journaled for rotatable movement into bearings 520., i361, and Ma, respectively, on the main frame l i. In the apparatus illustrated, three active screening roll are shown, rolls 5?, l3, and I4; the number of active screening rolls is limited only by the length of the screen belt I1, and additional rolls may be used to increase the capacity of the apparatus.

The screen if is a continuous, woven, wire belt which is disposed about the rolls, and is adapted to travel with them. The screen 57 may be of any desired mesh, having regard to the dimensions of the particles to be screened, but it should be so fabricated that the bond between the butt ends of the screening wire used is smooth, so as to ofier no projections which will interfere with the operation of the apparatus. Good screening has been obtained on a commercial embodiment of the apparatus with only a very small amount of screen wrap on its associated roll. However, the more wrap that can be obtained the better the screening action. While the apparatus herein illustrated employs a flexible wire screen to effect the size separation other equivalent screening mediums can be used, as for example a plastic screen, a perforated sheet, a cloth screen, or the like.

In the removal of particles which have crosssectional dimensions over .003 inch, we prefer to use mesh screen which has wires .00225 inch in diameter and screen openings .004 inch by .004 inch.

In the apparatus illustrated, the screen I! is driven by the drive roll 63, which is the righthand screening roll in Fig. 1. The screening roll I2 on the lefthand end of the apparatus (Fig. 1) serves as a take-up roll !2, in order that the tension-of the screen can be adjusted. To accomplish'this function, the bearings i2a for the take-up roll i2 are supported upon vertically extending members 2'3, which are pivoted to brackets 29 on the main frame I l byhorizontally disposed, transversely extending, pins 3|. The other ends of the pivoted members 2? are connected to brackets 33 on the main frame i! by threaded members 35 which are operable, upon rotation, to move the bearings In and their associated roll I2 inwardly or outwardly in relation to the main frame H. The threaded members 35 are provided with a hand wheel 3? for adjustment, and are protected from splashing liquid by a conventional rubber bellows 39.

The apparatus is driven by an electric motor 4 I which is supported on a bracket -43 on the main frame H. The motor 44 is connected to a chain drive, variable speed reducing unit 45 by means of a chain belt ll (Fig. 3). The output shaft Q8 of the reducing unit 45 is operatively connected to the drive roll shaft extension I312 by a suitable chain belt 49. Drive roll i 3 is adapted to be driven at a rate which will move the screen over a range of from about 60 to linear feet per minute. The take-up roll I! rotates freely in its bearings l2a, and is driven by the screen belt 1?.

The roll l4 on the lower run of the belt is termed the intermediate roll, and its shaft [4b is adapted to be driven directly from the output shaft :38 of the reducing unit 45, which provides power for the drive roll 53. The intermediate roll M may be driven at either the same peripheral speed as the screen belt :1, or as in the illustrated apparatus, it may be driven at a higher peripheral speed with resultant increase in the capacity of the apparatus. In the illustrated apparatu the relative speeds of the intermediate and drive rolls may be in any desired ratio, the range of peripheral speed for the intermediate roll being from 100 to 300 feet per minute for drive roll speeds within the range of 60 to 180 feet per minute as specified above.

The guide roll I 5 engages the upper run of the screen belt H, and this roll is similar to the conventional felt guide rolls Whichare used on papermaking machines. The function of the guide roll I5 is to prevent side-play of the screen belt IT; and to accomplish this, it co-acts a palm and escapement control mechanism Similar to that used in the conventional felt guide.

linkage 5| .so as tocause one of the bowls 15.5.

depending upon the movement. of -the;-screen IT, to. engage one, side of z the; ratchet wheel :51. One side :of the ratchet wheel 15.! has teeth which effect clockwise :movement, and :the rot-her .side has teeth. which :effect countersclockwise-movement'. The rotation of Sthe; ratchet wheel 512011 the threaded member 59- .in response to. .movemerit of one of the :pawls55, thus :eiiectssiideable, longitudinal movement of the bearingon :one end of the guide roll I5 relative to theframe II and this, in turn, re-aligns the screen belt 11 and disengages the pawl and ratchet-wheel.

For delivering the coating material to the screen, distributing manifolds 6.3, 63a, and 63?), are provided adjacent thenips formed between the belt screen I1 and the surfaces of the -takeup roll I2, the intermediate-roll. I4, andtthe drive roll I3. The manifolds furnish a constantsupply of material to the screening nips. The-manifolds comprise horizontally extending pipelines which are drilled with suitable holesand which are supported in fixed relationship :to their associated roll, or they may comprise slotted troughs which are shaped to provide *the required flow of material. The -manifolds 63a and 63b are supported at each endon thefra-m H and the manifold 6.3 is supported on a;pair of brackets 66 which are=attached to the vertically extending members 27 which form-a part of the take-up roll sup-porting "andpositioning means. The manifoldsareisupplied with material through suitablepipelines -65, and theflow of material is regulated by means of valves (not shown) so that the material being s-creeneddoes not run over the edges of the screen Il'into the pan 23 which receives the acoepted coatin materials.

Screen or belt wipes t1, Bla, and etc (Figs. 4 and 5) are provided adjacent each of the screening rolls, as illustrated in Fig. 1, for-removing continuously accepted material from the screen. These wipes are each supported from the main frame I I' by a transversely extending rod-.or tube member 69. Eachof the rod or tubes 69 is journaled into suitable bearings-ion the frame I I for rotatable movement. A clamp- .ing arrangement ll which is adaptedtovhold a wiping blade 13 madefromrubber or an material which does not introduce excessive wire wear, is connected by web sections I5 to-each of the tubes $9. The clampingarrangement is provided with a series of clamping bolts 11 so forces the Wiping blade 13 against theiscreen I1. :(rjig. .4).. Each of the scr n "wipes 11wsitioned adjacent one of the screening. rolls 1.2. 1:3, and 14,550 that the blades 13 engage the screen .belt ;I-'i along the line of contact of the screen .belt .zI'I and the surface ,of the adjacent roll, thereby permitting maximum pressur to beapplied to the screen I? without possibility of injury to thescreen.

Roll wipes 81 and 8.1a are provided on the upwardly moving side of theitake-up roll-I2 and the intermediate roll l4 (Fig. 1).. Each ofthe roll .Wipesis of the edge type andz prises a wiping bladefiii which is fabricated from rubber orzthe like, and which is held in place by ,a clampingmemberel and a plurality of machine screws :93. The clamping member-9| of the roll wipeafi'l is rigidly attached to the manifold 63 by means of ,a pairof clamping rings 19%. The

clamping memberqlll oi theroll wipe 61a. isattached to a tube- 95 which is iournaled ,into suitable bearings (not-shown) on the frame l-I, as illustrated'in .Fig. 6, in:the same manner as the tubes 69 which support the screen-wipes r61. Gounterweight arms-'9'! are attached to the tub 95 for the-roll-wipe fi'i-a 'by meansof set screws .99 (Fig. 6),. The counterweight arms 9-! are provided with a weight 10!, which may be adjustablyysecured to the arm 91. By varying the position of the-weights IN, the pressure "of the blade 89.0n the surface of the roll it maybe increased and the cleaning action facilitated. The roll wine 8? is heldiin fixed relation to the roll :82 by the manifold 63.

:A save-all pan m3 is supported -on-the-f-rame -'I'l:a position adjacent the point where the screen belt I"! movesraway from the drive roll .I3 (Fig. '7), at which point the screen-belt I1, is washed, aswill vbe hereinafter described. Th save-all pan Ill? .is fabricated from sheet m,etal,.and;is

supported from a transversely extending tube member I95 which is journaled for rotatable movement in-pedes tal bearings I01 at each side of thermainframel I. The tube I0 5;i-s provided with a plurality of s1otsI09on each ofits-sides withinthe pan, so as to allow material flowing intoithep-anJIM to run out the end of the'tube lflfiaintoa disposal pipe. I II On the.- forwardedge otthepan-IBB, .end'wipes II3 are provided for retainingmaterial 'fromfiowing lengthwiseof the '1.O11.|.3,..3.-I1di13h659 co-act with a doctonblade II :5 whichefiects removalof material from the roll I;3 The. entire; pan: assembly is counter-weighted ina suitable manner suchxas'by: the armsi I I;'I and weights I I9, illustrated.

-A- plur.al ity of water ,ietstZIare provided-for washingandgoleaning the screen II. Theseexwtend'transversely across :the ,belt screen I! ,inxa

position iadiacent the location .of. the doctor blade: H5. The water jets I ZI aresupplied'from -a.:suitable pipeline I23. At the upper endof the save-all pan L03, :an air doctor 'fl 2'5'is provided, which efrects the drying of the screenI'I after it -iswashed'f-ree-cf adhering materials by the water jets I2I. This air-doctor I25 prevents dilution of; the coating materials being screen-ed by wash water which might otherwise adhere to the screen H. The air. doctor l'2f5 comprises a transversely extending tube member IZ I in which is milledalongitudinallyextending slot. [29 {Fig 8). Longitudinal stifiening members I'3I. areattache'd to the vtubeIZ'I adjacent the slot inthe tube,. and these are provided with orifice plates I33 vwhichareadjustably bolted to the stiffening members I 3 I- so--that the intensityof the 3,i1ib1a$t may be varied. The tube I2! is connected to a suitable source of pressure air by a conduit I35.

In one commercial embodiment of the invention adapted to screen paper coatings, a 160 mesh screen, as before described, having a width of 50 inches is disposed about three active screening rolls, a drive roll, a take-up roll, and an intermediate roll. The take-up roll and the drive roll are 18 inches in diameter and the intermediate roll is 12 inches in diameter.

During operation, the drive roll I3 is rotated at between about 13 and 38 R. P. M., by the motor 4|. The coating material which is to be screened is pumped through the

manifolds

63, 63a, and 63b. The coating first flows onto the take-up roll t2, where it rotates with the roll until it is forced through the screen I! by the pressure exerted at the nip formed between the roll surface and the screen IT. The rejected or o ersize-d materials follow around the roll I2 and are wiped off by the roll wipe 87 provided below the take-up roll manifold. The accepted material is removed from the belt I! by the belt wipe '61 as at I31, and falls into the pan '23 from which it is continuously withdrawn through the conduit 25.

The rejected material from the take-up roll I2 falls back to the screen I! and joins the unscreened material which flows onto the screen I I from the press roll manifold 53a. The accepted material on the screen I! at this point is forced through the screen I! by the pressure exerted by the belt screen I! at the roll M, and is removed by the screen wipe B'Ia. The rejected material follows the roll I4 around until it is scraped from the roll by the edge wipe illustrated at 81a. The accepted material falls into the pan 23 and flows out through the conduit 25.

The rejected material from the roll I4 also falls back onto the screen H, where it joins the unscreened material flowing onto the belt from the 4 manifold at 63b. This material is screened at the nip between the screen belt and the drive roll I3, and the accepted material is removed from the belt by the belt wipe 61b and falls into the pan 23. The rejected material from all three rolls then follows around the drive roll I3 until it is removed by the doctor blade H5, aided by the spaced water jets I2 I. The cleaned screen I! then passes through the air jet cleaner I125, which removes any water that may adhere to the screen. If the screen belt i=1 develops side-movement at any time it is automatically re-aligned by means of the palm and escapement mechanism of the uide roll I5.

The installation and the renewal of the screen I belts of the apparatus is facilitated by the inclusion of a pair of removable spacer blocks It! in the frame II of the machine. The blocks I31 are located on one side of the frame in a position adjacent the lower run of the screen belt II. When it is desired to remove or install a screen belt, the blocks I 37 are removed and the screen belt is pulled outwardly over the ends of the rolls, and a new screen is inserted in its place.

The operation of continuous screenin apparatus in accordance with the invention is typified by extremely high rates of flow and unusually accurate particle size separation. In a particular run of the commercial embodiment of the invention which has been described, the screen was operated at 120 linear feet per minute and the intermediate roll was opera-ted at a peripheral speed of about 200 feet per minute. A typical papercoat-ing being screened had a viscosity of about 100 to 200 centipoises and had a solids content of about 63 percent. During the run the coating mixture was screened at a rate of 85 gal. per minute and about 90 percent of the oversized material (cross sectional dimensions over .003 inch) was removed from the coating mixture, and only 0.4 percent of the acceptable material flowed out with the rejected or over-sized material.

The over-all capacity of the apparatus can be greatly increased if the intermediate roll I4 is operated at a peripheral speed that is greater than the linear speed of the screen belt H, as before described. The difference between the speeds may be relatively large, provided the proportion of the oversized material is not excessive and the character of the material being screened is not such as to cause undue wear on the screen. A plurality of intermediate rolls may also be provided when it is desired to greatly increase the capacity of the existing apparatus, or when space requirements render it impractical to add more separate units of equipment.

The apparatus and method of the invention provide for the economical and eflicient screening of liquid materials, and especially viscous materials, containing particles of difiering cross sectional dimensions. The positive force which is applied to the material when it is engaged in the nip between the roll surface and the screen makes possible the rapid and efficient screening of viscous fluids such as paper coatings, and even permits the screening of pasty, semi-fluids such as paint pigments, printers ink, toothpaste, and the like.

The arrangement of the rolls is not extremely critical, but we have found that the particular arrangement illustrated, which subjects the larger portion of the rejected material to more than one screening operation, is very eifective for screening paper coatings. The rescreening of a major portion of the rejected material at subsequent nips maintains the percentage of acceptable coating material flowing out with the finally rejected material at a minimum.

The features of our invention that are believed to be new are expressly set forth in the appended claims.

We claim:

1. In apparatus for screening fluid materials, a roll, a wire belt screen supported for movement in contact with a portion of said roll, said screen contacting said roll along a line which extends across the entire width of said screen, means for moving said belt screen at a predetermined linear speed, means for tensioning said belt screen, means for rotating said roll, means for introducing the material to be screened into the nip formed between the surface of said roll and said belt screen, whereby the movement of said belt screen and said roll forces acceptable material of a size determined by the openings of said screen through said belt screen, a first wiping blade extending across said belt screen for removing acceptable material from said belt screen, said first wiping blade being in contact with said belt screen in a region where said belt screen is disposed about said roll, and a second wiping blade disposed in contact with the surface of said roll for removing material adhering to said roll.

2. In apparatus for screening fluid materials, a roll, a flexible wire belt screen supported for movement in contact with a portion of said roll, said screen contacting said roll along a line which extends across the entire width of said screen,

9 means for moving said belt screen at'a predetermined linear speed, means for-'ten'sioning said belt screen, means for driving said roll at a peripheral speed at least as great as the linear speed of said beltscreen, means for introducing the material to-be screened into the nipiormed between the surface of said roll and said-belt screen, whereby the movement of said belt screen and said roll forces acceptable material of a size determined by the openings of saidscreen through said belt screen, a first wiping blade extending across said belt screen for removing acceptable material from said beltscreen, said first wiping blade being inc'cntact with said belt screen in a region where said belt screen is disposed about saidrell, and-a second-wiping blade disposed in contact with the surface of said roll for removing material adhering to said roll, and means for cleaning the belt screen after each contact with said roll including a jet of fluidwhichis directed through the openings of said belt screen.

3. Apparatus for screening fluid materials comprising a frame, 'a plurality of horizontally extending, transversely disposed rolls rotatably supported on said frame, a flexible; endless screen disposed about said rolls as a belt, driving means, means connecting at least one" of said rolls to said driving means for effecting movement of said screen; meansfor tensio'ning said screen about said rolls, means forforming a pool'of the material being. screened in' the nip formed between said" screen and the surface of one of said rolls, a first wiping blade for removing material which passes through said screen, and means for removing the material retained on said one roll upon each revolution thereof, including a secondwiping blade engaged against said roll in such a position that the material removed from said rollialls back upon said screen and is carried between said screen and another of said rolls.

4. Apparatus for screening fluid materials comprising a frame, a plurality of horizontally extending, transversely disposed, generally parallel rolls rotatably supported on said frame, a flexible endless screen disposed about said rolls as a belt, having an upper and a lower run, rotatable means for driving at least one of said rolls, and one of said rolls being adjustable so as to tension said screen, means for forming a pool of the material being screened in the nip formed between said screen and the surface of at least one of said rolls, at least one transversely extending wiping blade contacting the lower run of said screen for removing material which passes through said screen, another wiping blade which engages the surface of the one of the plurali-ty of rolls adjacent the beginning of the upper run of said belt screen, the material removed by said last mentioned wiping blade b ing the over-sized portion of the material being screened, and means for conducting said oversized portion away from said last mentioned wiping blade.

5. Apparatus of the class described comprising a flexible, endless screen, means including a pair or" spaced-apart, transversely extending, generally parallel rolls for supporting said screen as a belt, one of said support rolls being adjustable so as to adjust the tension in said belt screen, at least one intermediate roll, means for supporting said intermediate roll in contact with said belt screen, means for driving one of said support rolls to effect linear movement of said 10 screen, meansfor driving-said intermediate roll with a surface speed at least equal to the linear speedof said screen, material inlets adjacent the nips formed between'said screen and said-supporting rolls and said intermediate roll a first wiping blade engaged against said screen at a position on eachof said rolls for removing the material which passes through-said screen-fromthe surface of said screen, means for cellecting the material-passing through said screen, and a second wiping blade engaged against the surface or one of said rolls and means for conducting the material collected by said second wiping biade away fromthe apparatus.

6. Apparatus of the classcescribed comprising aflexible, endless screen,-means-including a pair of spaced-apart, horizontally disposed, transversely extending, generally parallel rolls for supporting said screen a belt,-one of said support'rolls being adjustable so as to adjust the tension in saidscreeinatleast one intermediate roll, means for supportingsaid intermediate roll in-eontact with said screen, means for driving one of said support rolls to effect linear movement of" said screen, means for driving said intermediate roll with a surface speed greater thanthe l near speed of said screen-material inletsadiacent the nips formed betweenv said screen and said supporting rollsand said intermediate roll, wiping means engagedagainst said screen atea'ch of said rolls for removing acceptedmaterial from said belt screen, saidw-iping means being located over the area of contact between said rolls nd said screen,-means-for collecting said accepted material, and means-for continuously wiping the surfaces of said supporting rolls and said intermediate roll whereby material retained by said screen is removed from said apparatus.

7. Apparatus ofthe classdescribed comprising a flexible, endless'screen, meansincluding a pair of spaced-apart, horizontally disposed, transversely extending, generally parallel rolls for supporting said screen as a belt, one of said support rolls being adjustable so as to adjust the tension in said screen, at least one press roll, means for rotatably supporting said press roll in contact with said screen, means for driving one of said support rolls to effect linear movement of said screen, means for driving said intermediate roll with a peripheral speed greater than the linear speed of said screen, material inlets adjacent the nips formed between said screen and said supporting rolls and said intermediate roll, wiping blades engaged against said screen at a position on each of said rolls for removing accepted material from said screen, means for collecting said accepted material, means for continuously wiping the surfaces of said supporting rolls and said intermediate roll whereby said material retained by said screen is removed from said apparatus, and means for cleaning said screen after each cycle of said apparatus inc-luding washing means extending transversely across said screen and drying means which includes an air blast directed on said screen at a point spaced from said washing means.

8. Apparatus for screening fluid materials comprising a frame, a pair of horizontally extending, transversely disposed, generally parallel rolls rotatably supported on said frame, a flexible endless screen disposed about said rolls as a belt having an upper and a lower run, rotatable means for driving at least one of said rolls, and one of said rolls being adjustable to tension said screen into driving engagement with said pair of rolls, means for forming a pool of the material being screened in the nips formed between said screen and the surfaces of said rolls whereby said material will be moved between said screen and said roll surfaces, a pair of wiping blades contacting said screen, one of said blades being disposed adjacent each of said rolls for removing material which passes through aid screen from the surface of said screen, and a second pair of wiping blades, each of said second pair of wiping blades engaging the surfaces of one of said rolls, and means associated with the wiping blade engaged against the surface of the roll which i adjacent the beginning of the upper run of said screen, for removing from the apparatus the material wiped from that roll, the wiping blade associated with the other of said rolls being positioned to deposit the material removed from the surface of that roll upon the lower run of said belt so that the material passes through the nip between said screen and the other of said rolls.

9. Apparatus for screening fluid materials comprising a frame, a pair of horizontally extending, transversely disposed, generally arallel rolls rotatably supported on said frame, a flexible endless screen disposed about said roll as a belt having an upper and, a lower run, rotatable means for driving at least one of said rolls, and one of said rolls being adjustable to tension said screen into driving engagement with said pair of rolls, means for forming a pool of the material being screened in th nip formed between said screen and the surfaces of said rolls whereby said material will be moved between said screen and said r011 surfaces, a pair of wiping blades contacting said screen, one of said blades being disposed adjacent each of said rolls for removing material which passes through said screen from the surface of said screen, and a second pair of wiping blades, each of said second pair of wiping blades engaging the surfaces of one of said rolls, means associated with the wiping blade engaged against the surface of the roll which is adjacent the beginning of the upper run of said screen for removing from the apparatus the material wiped from that roll, the wiping blade associated with the other of said rolls being positioned to deposit the material removed from the surface of that roll upon the lower run of said belt so that the material passes through the nip between said screen and the other of said rolls, and means for cleaning said screen after each cycle of said apparatus, said cleaning means being located along the upper run of said screen and including a washing means which extends transversely across said screen and drying means which includes an air blast directed against said screen at a point spaced from said washing means.

CARL H. ROWE.

ELMER R. MOKROS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 392,606 Heywood Nov. 13, 1888 514,300 Birch Feb. 6, 1894 582,519 Birch May 11, 1897 1,301,532 Allen Apr. 22, 1919 1,638,975 Antoine Aug. 16, 1927 1,691,950 Wright et a1 Nov. 20, 1928 1,883,526 Bryan Oct. 18, 1932 2,097,529 Nordell Nov. 2, 1937 2,278,525 Rich et a1 Apr. 7, 1942 FOREIGN PATENTS Number Country Date 85,043 Germany Jan. 27, 1896 296,625 Germany Feb. 19, 1917 29,375 Great Britain Oct. 3, 1930 305,359 Germany May 3, 1918