US2056310A - Screen - Google Patents

Description

. E. PALMER SCREEN 4oct. a, 1936.

Filed April- 26', '1955 2 Sheets-Sheet l Qct. 6, .1936.

F. E.` PALMER SCREEN 2 Sheets-Sheet 2 UNITED STATES SCREEN Frederick E. Palmer,

Sherbrooke, Quebec, Canada, assigner to Sherbrooke Machineries Limited, Sherbrooke, Quebec, Canada, a corporation of Canada Application April 26, 1935, Serial No. 18,324

'10 Claims. (Cl. {l2-34)` Y This invention relates to screens and more particularly, though not exclusively, to screens intended for screening pulp in paper manufacture where the diluted stock is fed to a screen drum, usually the interior thereof, and there acted on by movable devices, such, for example, as impeller blades, the finer bersbeing thereby passed through the meshesY of the screen, while the coarser particles or tailings are discharged from the edge thereof.

The object of the invention is to improve the eiiiciency of such screens, both in respect to the effectiveness of the screening operation and the consumption of power, and more particularly in screens of the type shown in Patents No. 1,172,239 to I-Iaug and No. 1,714,047 to Reed and Spafford. In this type of screen the diluted stock is fed through the end of the machine to the inner part of the screening chamber by a feeding conduit or conduits projecting into the chamber and is then picked up by impeller blades which force the stock outwardly against the screen.

In such screens as heretofore constructed, the feeding head or pressure on the stock has been relied on to force the stock radially outward from the feeding conduit; The jets of stock thus entering the chamber are struck more or less broadside bythe impeller blades and are thereby forced outwardly toward and around the interior of the screen. The impact of the moving impeller vane on the outwardly moving stock takes place where the linear velocity of the vane is relatively high and results in an unusually violent reaction between the impeller and the stock which absorbs driving power. Such impact also creates more or less turbulence in the resulting movement of the stock. Under the vimpact of the impeller vanes,

the stock is forced away from the blade but the movements which it assumes and the angles under which it impinges against the screening surface are irregular, varying, uncontrollable and more or less ineffective for quick and efficient screening.

The present invention has among other objects the provisions for so delivering the stock into the screening chamber and against the screen that a smooth' but forceful delivery of the stock into the screening chamber is accomplished without unnecessary consumption of power or turbulence of the stock, delivery being maintained against the screen at effective angles and under such conditions that a quicker and more effective screening action is secured.

These and other objects of the invention will be best understood by reference to the following description when taken in connection with the accompanying illustration of one specific embodiment thereof, while its scope will be more particularly pointed out in the appended claims.

In the drawings:

Fig. l is an elevation, principally in central longitudinal section, showing the principal working parts of the screen embodying one form of the invention;

Fig. 2 is a central sectional elevation taken on the line 2-2 through the screen shown in Fig. l,- the impeller parts and screening vanes however being shown in end elevation;

Fig. 3 is a fragmentary side elevation of the spider, showing the three vanes appearing at the left-hand side of Fig. 2;

Fig. Il is a cross-sectional elevation showing one of the diffuser elements; and Fig. 5 is a cross sectional elevation through a screening vane on the line 5-5 in Fig. 3.

Referring to the drawings (Figs. 1 and 2) and tothe embodiment of the invention which is there disclosed for illustrative purposesthe screen comprises opposite end members or casings Il having feet I3 on which the screen is supported. yThe end members have end anges l5 to which is secured the outer cylindrical casing Il which may be formed of detachable sectional portions which may be removable for purposes of inspection or repair of the screen drum and other interior parts.

Within the outer casing l1 there is provided a perforated or foraminous screen plate I9 in the form of a drum of any tionv secured at its endsto the inwardly projecting flange rings 2l which are secured to the end members. The space within the screen drum constitutes the `screening chamber to which the diluted stock is fed. The annular space between the drum and the outer casing constitutes the screened-stock chamber, the latter having an outlet 23 through which the finer screened stock is discharged after having passed through the screen and into the screened-stock chamber.

The diluted stock is fed to the apparatus from any desired source of supply and under a head sufficient to maintain a steady supply to the screening chamber through the supply conduit 25 (Fig. 2) to the stock supply compartment 2l locatedvon top of the outer casing Il, and is thence carried into the opposite ends of the screening chamberthrough branched supply conduits 29 (Fig. 1) which turn downwardly at the outside of each opposite end casing Il.

The stock supply passages, the tailings discharge passages and the impelling devices on opposite sides of the central plane of the screen are of substantially similar construction and the parts on one side only .of the'screen need to be described in detail.

At each end of the screen the stock passes through the downwardly directed feed conduit 2,9 into the top of an annular feed drumjl, there being one such drum. at each end of the machine suitable lor usual construcentirely encircling the impeller shaft bearings 33.

The feed drum has an annular discharge opening which faces the annular mouth of the stationary feed conduit 35 extending inwardly within the screening chamber. The feed conduit is in the form of an annular truncated conical chamber symmetrically positioned. about the axis of the screen and formed by the inner and outer walls 31 and 39, respectively, which taper toward the axis of the screen. Y Y

Facing the annular discharge rnouth of each feed conduit and in closely tting and working relation thereto is an annular mouth 4| of a rotary, centrifugal, stock-ejecting impeller 43. The latter is mounted on the hub 45 keyed or otherwise secured to the impeller shaft 41 which is rotatable in the bearings 33 and driven through the pulley 49 from any external source of power.

The hub 45 carries the disk-like spider 5I positioned midway the length of the screening chamber and sub-dividing the impeller into two similar impelling chambers, the mouth of one chamber registering with the annular mouth of one feed conduit and the opposite mouth of the other with the annular mouth of the opposite feed conduit. The centrifugal impeller 43 is provided with curved impelling vanes 53 (herein six in number) forming with the impeller walls passages which receive Vthe stock directly and laterally from the mouth of the feed conduit but which curve outwardly so as to eject the stock forcibly into the screening chamber. These passages and vanes are duplicated on opposite sides of the spider 5l. On the impeller shaft between the conduit wall 31 and the impeller hub there is threaded a bushing 55 (Fig. 1) which acts both to fix the hub longitudinally of the shaft and as a bearing and stuing box to prevent the escape of the stock at the joint between the hub and conduit.

The result is that the stock, While fed continuously in a lateral direction into the annular mouth of the impeller, is picked up by the impeller vanes relatively close to the axis .of the screen, where their linear velocity is relatively low, and the stock has imparted to it a movement changing .from an axial to a radial direction. This movement at first is relatively gentle but is quickly accelerated so that on reaching the outer edges of the vanes the stock has acquired a high centrifugal velocity and pressure and is forcibly ejected through the screening chamber toward the screening surface. This action, however, is accomplished through a smooth, accelerated but unbroken movement of the stock from the time it leaves the feed conduit until ejected into the chamber, avoiding shocks and impacts between the stock and the impeller and the unnecessary consumption of power resulting therefrom.

Bolted to one side of the periphery of the spider by means of end flanges 51 there is arranged a series (herein twelve) of equally spaced, laterally extending, screening vanes or blades 59, a series of similar and correspondingly positioned vanes being carried at the opposite side of the spider. The outer edges of these vanes have a path of movement in close proximity to the screening surface. The assembled vane structure is stiffened by means of annular rings 6| bolted to. the back wall Yof each vane.

Each vane (as shown in Fig. 3) longitudinally the screen is inclined with relation to the direction of rotation (which is indicated by the arrow in Fig. 2) backward from the spider support to its outer end. Transversely the screen.

the leading face of each blade is also inclined backwardly and outwardly with reference to the direction of rotation, and its face from one end to the other has a distinctly concave shape, as will be seen from a cross-section shown in Fig. 5.

f Each vane, as will be seen in Fig. 1, narrows somewhat from the point of its attachment to the spider toward its outer end, being gradually tapered on its inner edge and more abruptly on its outer edge. The backward inclination of the concave face also increases from the inner to the outer end so that the stock near the outer end is Inet by the vane at a somewhat iiatter angle, increasing the effectiveness of the vane thereat for the purpose of acting on the coarse fibers which have been removed from the region of delivery by the centrifugal impeller.

For the purpose hereinafter explained, there are providedbetween certain of the screening vanes, and also bolted to the peripheral edge of the spider, stock diffusing members in the form of blocks 63 presenting an outwardly curved or concaved face 65 by which the outwardly moving stock encountering the `same is diffused longitudinally in the direction of the end of the screen over the screening surface and in front of the next succeeding screening vane. The end of each such block fits snugly against the concaved front face of the adjoining and succeeding vane 59 and extends a substantial part of the distance intervening between the next preceding vane. Three such diffusing members are shown in the drawings equally spaced at each side of the spider, one between each four pairs of vanes, those on one side being staggered or alternating with those on the other. Any desired number of the vanes, however, may be equipped with such diffusing members.

At and beyond each opposite end of the screen drum, the casing Il is shaped to provide an annular tailings chamber 61 (Fig. l), presenting an annular pocket of substantial capacity and of a diameter greater than that ofthe screen drum. The tailings chamber extends entirely around the screen and presents an annular mouth opening into the screening chamber, into which mouth the coarser particles of tailings are nally entered during the screening operation. Gravitating down these are finally discharged into the reclaiming system through the tailings outlet 69 opening into the tailings chamber at the bottom of the casing.

Located at the mouth of such tailings outlet 69 is a circular shower pipe 1| which is adapted to emit a distributed series of water sprays across the endsof the rotating screening vanes and in the general direction indicated in Fig. 1. This tends to dilute and force back the tailings into the screening chamber and away from the tailings chamber. The amount of tailings passing into the tailings chamber and against the water spray may be regulated by adjusting the flow of water through the shower pipe 1|.

Near the lower part of the tailings chamber there is also provided a second shower pipe 13 (shown in Fig. 2) entering the tailings chamber and so arranged as to emit a shower spray into Y and up the sides of the tailings chamber to assist stock and coarse or foreign substances tending to accumulate in the bottom of the annula-r feed drum 3l may be removed and by-passed through the tailings outlet 69 through the passage 'l'l by means of the valve 19. l

The operation-of the screenvis as follows: As already stated, the stock passing through the annular feed conduit is picked up by the centrifugal impeller, its movement accelerated, and is forcibly ejected from the discharging periphery of the impeller toward the screening surface. The action of the centrifugal impeller is to throw the major part of the stock outwardly in a general tangential direction and in a path which, vie-wed transversely the screen as in Fig. 2, may be generally indicated bythe dotted arrow lines a. Viewed lengthwise the screen, however,'its path is in a direction (as indicated by the dotted arrow lines b in Fig. l) where it is adapted to be met by the broad concave face of a Screening vane 549 in and about the central region of the screening chamber.

It will be seen that a Xed relative position is maintained between the impeller vanes and the screening vanes during rotation of the impeller.

This position is such that vthe stock thrown for cibly toward the screen (in the path indicated by the arrows min Fig. 2 and at a somewhat acute angle relatively to the Vscreening surface) is im-v mediately struck and picked up while in motion4 by the concave face of the succeeding screening vane, there being six such vanes which thus cooperate, respectively, with the six vanes of the centrifugal impeller. These six vanes 59', for purposes of distinction, will be termed the impact screening'vanes and in Figs. 2 and 3 are marked 59a. With the momentum added by the impact against the vane to the momentum initiated by the centrifugal impeller, the stock thus encountcred by vane 59a is forcibly deflected against the screening surface and caused to impinge thereat at a less acute and more effective screening angle and in a direction closely approximating a radial direction.

This promptly effects in the first instance a substantial and effective separation of the ner stock and free water, leaving a large proportion of oversize coarse fibers which are then separated and removed from the remnant of finer fibers by the subsequent screening action of 'the' vanes. Due to the backward lengthwise inclination of the impeller blades, this unscreenedV stock' is forced outwardly toward the tailings chamber 61 but is continually subject to dilution by shower water from the annular shower pipe 1l. This continued action effects the separation and passage through the screen of the remaining nner particles as they are carried around by the screening vanes.

The coarse unscreened stock in its movement outwardly alongvthe blades toward the tailings chamber is more or less agitatedk as well as diluted by the showerwater and Yis thrown forcibly against the screening surface. Due to the somewhat more pronounced angle of the outer ends of. the concave screening vanes with'relation to the screening surface, such action becomes more forcible toward the ends of the vanes as the proportion of coarserA tailings increases.

By repetitions of this action the'coarser particles or tailings are worked to the outer edges of the screen and finally` pass into the tailings chamber, from which they are vultimately Ydischarged through the tailings outlet 69.

'Ihe major part of the stock delivered bythe impeller is thus given at the outset a highly effective screening action, removing the major part of the finer particles near the center of the screen and leaving a minimum number of the ner particles to be subsequently separated as the tailings are worked toward the Itailings chamber. y

In the rotation of. the impeller a certain minor portion of the stock will leave the periphery of the impeller in a path which is more nearly radial than tangential and which may be generally represented by the dotted arrow lines `c in Fig. 2 and d in Fig. l. To take care of this minor portion there are provided the vanes (identie'dfas 59h in Fig. 2) which are intermediate the vanes 59e positioned to act on the longitudinally deliveredstock and heretofore referred to as the irnpact screening vanes. A proportion of the finer part of this stock will pass radially outward through the screening surface. The unscreened portion of this stock is picked up by the next succeeding vane 59h. At the same time it is forced outwardly away from the center of. the screen by the action of the diffusing member'tB, the separation of the coarser from the remaining finer particles of stock and the ultimate delivery of the tailings Vinto the tailings chamber taking effect substantially as heretofore described in connection with the action of the impact screening vanes.

While I have herein shown and described fo-r purposes of illustration one specific embodiment of my invention, it will be understood that extensive changesl in and variations from the form, details and arrangement of parts may be made, all without departing from the spirit and essence of the invention as expressed by the following claims.

1. In a machine of the character described, the combination with a screen drum having a tailings discharge at an end of the interior thereof, of a rotary vaned impeller positioned within said drum, means for feeding stock to said impeller to be ejected forcibly toward the screening surface of the drum, means for acting on the stock thus ejected comprising a series of screening vanes extending longitudinally of the drum adjacent the screening surface thereof, between the latter and the impeller and spaced from the discharging periphery of theimpeller, said vanes being rotatable with said impeller and having the leading faces inclined outwardly and backwardly with relation to the direction of rotation and movable in a path to intersect the path of the stock ejected from said impeller and deflect the same toward the screening surface, said vanes being furthermore inclined longitudinally toward the tailings discharge away from the direction of rotation, and'means for rotating said impeller and said vanes.

2. In a machine of the character described, the combination with a screen drum, of a rotary, centrifugal, vaned impeller positioned within said drum, means for feeding stock to said impeller to be ejected forcibly and tangentially outward toward the screening surface of said drum, and means for acting on the stock thus ejected comprising a series of screening vanes extending 1ongitudina-lly of the drum adjacent the screening surface thereof, between the latter and the impeller and spaced from the discharging periphery of the impeller, said vanes being rotatable with said impeller and in a relationship thereto to intercept the vstock ejected tangentially from the impeller,`and said vanes having a concave leading face inclined outwardly and rearwardly with relation to the direction of rotation to deflect the stock at a less acute angle against the screening surface, and means for rotating said impeller and said vanes.

3. In a machine of the character described, the combination with a screen drum having a tailings discharge at an end of the interior thereof, of means for entering and delivering stock within said drum, and means for acting on said stock comprising a series of vanes rotatable in a path adjacent the screening surface of said drum, the leading faces of said vanes being inclined outwardly and backwardly to the direction of rotation and having an increasing inclination toward the tailings discharge.

4. In a machine of the character described, the combination with a screen drum, of a rotary, centrifugal, vaned impeller positioned within said drum, means for feeding stock to said impeller to be ejected forcibly outward toward the screening surface of said drum, and means for acting on the stock thus ejected comprising a series of screening vanes equal in number to the number of vanes of the impeller, said vanes extending longitudinally of the drum adjacent the screening surface thereof, between the latter and the impeller and spaced from the discharge periphery of the impeller, said series of vanes being rotatable with the impeller and in a relationship thereto to intercept stock ejected tangentially from the impeller and deflect the same against the screening surface, and a second series of similarly arranged vanes each positioned intermediate successive vanes of the first series.

5. In a machine of the character described, the combination with a screen drum, of a rotary, centrifugal, vaned impeller positioned within said drum, means for feeding stock to said impeller to be ejected forcibly outward toward the screening surface of said drum, means for acting on the stock thus ejected comprising a series of screening vanes equal in number to the number of vanes of the impeller, said vanes extending longitudinally of the drum adjacent the screening surface thereof, between the latter and the impeller and spaced from Vthe discharge periphery of the imn peller, said series of vanes being rotatable with the impeller and in a relationship thereto to intercept stock tangentially from the impeller and deflect the same against the screening surface, a second series of similarly arranged vanes each positioned intermediate successive vanes of therst series, and stock diffusing members rotatable with said vanes for receiving stock passing outwardly from said impeller and diverting it toward the tailings discharge end of the kScreen drum.

6. In a machine of the cliarticterdescribed, the;

combination with a screen drum having a tail.- ings discharge at an end thereof, of a rotatable vane supporting member, a series of screening vanes supported near the periphery of said member extending longitudinally of the drum and having a path of movement adjacent the screening surface thereof, and stock diffusing members also carried by said vane supporting member between the vanes thereof and presenting a defiecting surface to stock passing outwardly toward the screening surface tending to direct the same toward the tailings discharge.

7. In a machine of the character describ ed, the combination with a horizontally arranged screen drum having a tailings discharge at an end thereof. of a centrifugal impeller within said drum,

means for entering stock to said impeller to be forcibly ejected therefrom toward the screening surface of the drum, a rotatable vane supporting member, a Series of screening vanes Acarried thereby extending longitudinally of the drum adjacent the screening surface thereof, said vanes being between said impeller and said screening surface and adapted to intersect the path of stock ejected from said impeller, and stock diffusing members carried by said vane support, between successive vanes thereof and shaped to deflect stock passing outwardly from the impeller toward the tailings discharge.

8. In a machine of the character described, the combination with a horizontal screen drum, of means for entering the stock through the end of the drum comprising a coaxially-arranged, annular, feed conduit terminating in an annular delivery mouth closely adjacent the axis of the drum, a rotatable, centrifugal impeller positioned coaxially within the drum and having an annular inlet mouth registering with and in close Working relation to the opposed annular mouth of the feed conduit and having a series of curved impeller vanes terminating in portions curved away from the direction of rotation of said vanes, the latter being adapted to engage the entering stock Where its linear velocity is relatively slight and impart to it a smooth, accelerated but unbroken movement changing from an axial to a radial direction and to discharge it forcibly outward toward the screening surface and tangentially from the ends of said vanes, and Vrotatable screening vanes rotatable in the same direction with said impeller but traveling in an orbit outside of and spaced from that of the impeller vanes and adjacent the screening surface, said screening vanes being adapted to engage the stock discharge from said impeller vanes.

9. In a machine of the character described, the combination with a horizontal screen drum having an interior screening chamber, of means for entering the stock through the end of the drum, a rotatable, centrifugal impeller in said chamber adapted to receive the stock and having a series of curved impeller vanes terminating in portions curved away from the direction of rotation and adapted to eject the stock outwardly and tangentially toward the screening surface of the drum, and screening vanes rotatable in the same direction with said impeller but traveling in an orbit outside of and spaced from that of the im.- peller vanes and adjacent the screening surface, said V,screening vanes having concaved leading faces adapted to intercept the moving stock ejected by said impeller. i

l0. In a machine of the character described, the combination with a horizontal screen drum having a screening chamber, of means for entering the stock through the end of the drum, a centrifugal, vaned impeller coaxially arranged in said chamber adapted to receive the stock and eject the same outwardly toward the screening surface of the drum and in a generally tangential direction to the impeller, and a series of screening vanes rotating in the same direction with said impeller but traveling in an orbit outside of but spaced from that of the impeller vanes and adjacent the screening surface, said vanes being positioned to engage said tangentlally ejected stock while in motion, thereby to add momentum to the momentum of the moving stock and to direct it against the screening surface at a more effective screening angle..

FREDERICK E. PALMER.

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