US2994562A - Rotary screw pumping of thick fibrous liquid suspensions - Google Patents

Description

1961 A. A. ZALlS 2,994,562

ROTARY SCREW PUMPING OF THICK FIBROUS LIQUID SUSPENSIONS Filed Feb. 5, 1959 2 Sheets- 51188; l

fizz/anim- G Awe/IA Zalzs United States Patent 2,994,562 ROTARY SCREW PUMPING 0F THICK FIBROUS LIQUID SUSPENSIONS Albert A. Zalis, Warren, Mass., assignor to Warren Pumps, Inc., Warren, Mass, a corporation of Massachusetts Filed Feb. 5, 1959, Ser. No. 791,392 3 Claims. (Cl. 30214) This invention relates to positive displacement-pumping, by rotary screw pumps, of various liquid suspensions which, because of their thick high density fibrous content, have heretofore been very 'ditficult, if not impossible, to handle and circulate by conventional liquid pumping equipment.

Rotary screw pumps are self-priming, rarely become air-bound and have excellent suction-lift capabilities. Because of their capacity to produce a constant pulseless liquid flow, screw pumps are extensively used in numerous industries for the heavy duty circulation and transfer of liquid and semi-liquid materials that vary in viscosity over a very wide range. Examples of such are all grades of diesel and fuel oils, lubricating oils and greases, gashouse tars and asphalts, paints and varnishes, soaps, molasses and the like.

In the pulp and paper industry, practically all of the materials that are required to be circulated and/ or transported are in some form of aqueous suspension, such as to permit of their being pumped from place to place. Heretofore, in this industry, many of these large-scale pumping services have been supplied by centrifugal pumps of various types and sizes. But centrifugal pumps can be used effectively only with pulp and paper stocks or slurries of relatively low consistency; they cannot cope with suspensions in which the fibrous content is greater, say, than to 6 percent.

More particularly, no centrifugal pump, nor any other pump, has heretofore been able to handle these high density fibrous pulp suspensions when much of their fibrous content instead of being dispersed, is concentrated in the form of closely matted large area slabs or pieces of lap pulp. This condition, usually encountered in the transfer of thick suspensions of pulp stocks or slurries to storage chests and the like, has heretofore necessitated the use of expensive equipment for the continuous bulk progression of such concentrated lap pulp suspensions, either by gravity or by conveyors, or by both of these means.

My invention, as hereinafter described, incorporates, in screw pumps of ordinary construction, a very simple and effective means to adapt them to the handling and circulation of all such fibrous suspensions regardless of their consistency and/ or of the size of their matted fibrous lap pulp concentrations. In particular, my invention provides, for rotary screw pumps, a novel fluid intake construction, wherein all such matted fibrous lap pulp concentrations are effectively reduced, in the absence of fibre damage or severance, to pumpable size, such as to pass, without danger of clogging or blocking, through the screw pumps usual helical passages.

Other and further objects and advantages of my invention will become apparent from the following detailed description thereof, taken in connection with the accompanying illustrative drawings, in which FIG. 1 is a top plan view, partly in horizontal section showing the application of my invention to a conventional twin screw pump.

FIG. 2 is a vertical sectional view, substantially on the line 22 of FIG. 1, of my improved twin screw pump construction.

Patented Aug. 1, 1961 FIG. 3 is a transverse vertical sectional view, substantially on line 3-3 of FIG. 2, of the pumping screws.

FIG. 4 is a fragmentary larger scale cross-sectional View, substantially on line 4-4 of FIG. 2, showing the novel fluid intake construction for the illustrated twin screw pump.

FIG. 5 is a large scale perspective view of one of the active elements of said fluid intake construction.

Referring first to FIGS. 1, 2 and 3, the illustrated screw pump has a hollow open-ended casing 1, mounted on a suitable base 2. Near one end, said casing 1 is shown with an upwardly-opening fluid intake chamber 3 of relatively large cross-sectional area. As best shown by FIG. 4, this intake chamber 3 provides, for the entering fluids containment, a pair of opposite downwardly-convergent side walls 3a, 311, connected at their lower ends by a bottom wall 3b. Near its other end, said casing 1 has a laterally-opening fluid discharge portion '4.

Between said intake and discharge portions 3 and 4, the hollow casing 1 is of the uniform cross-section illustrated by FIG. 3, such as to provide, for reception of the pumps two screws, a pair of parallel side-by- side interior bores 5, 5 in the usual slightly overlapping relation. These overlapping bores 5, 5 at their opposite ends, open into the casings intake and discharge portions 3 and 4 respectively. Passing concentrically through the bores 5, 5 are the pumps two screw-carrying shafts or rotors 6, 6. These rotors 6, 6 extend across the pumps intake chamber 3, and are here shown as having their proximate ends journalled in suitable bearings 7, 7 provided by a plate 8 attached to the pump casing 1 and serving to close the end thereof that provides the pump intake 3.

At their other ends, the screw-carrying shafts or rotors 6, 6 are journalled in suitable bearings 9, 9, provided as here shown by a gear housing 10 which is attached to the pump casing and serves to close at the end adjacent to the pumps discharge 4. Within the housing 10, said shafts or rotors =6, 6 carry the usual intermeshing gears 11, 11, by which rotation, as imparted to an extension 6' of one such shaft is transmitted at the same speed, but in opposite direction, to the other shaft or rotor.

Keyed, pinned or otherwise suitably secured to rotors or shafts 6, 6 are sleeves or hubs 12, 12 which provide, within the bores 5, 5 the pumps two intermeshing screws. These in each case take the usual form of a continuous external helical rib 13 on each hub 12, that meshes with the oppositely-rotating external helical rib 13 of the other hub 12. The outer peripheral surfaces 14, 14 of these helical ribs 13, 13 have ample and adequate clearance with their respective bores 5, 5. Preferably, both side or flank surfaces 15, 15 of each rib 13 are concave in cross-section, as best shown at .16, 16 in FIG. 3.

Intermeshing pumping screws of this general construction are Well known in the art. Also well known is their capacity, when rotated oppositely, to obtain a constant pulseless pumping flow, axially through their bores 5, 5, of all kinds of liquids and/or liquid suspensions of fibrous material that are supplied to the intake chamber 3. No serious detriment to this steady pumping action arises from the presence of considerable amounts of entrained air or other gases in the pumped liquids, or from air or other gases entrapped in the fibrous content of thick liquid suspensions. Nor is this steady pumping action adversely affected in any way by matted accumulations or concentrations of fibrous pulp material, unless same are of such lange size as to clog or block the relatively wide and deep helical grooves or channels 17, 17 of the pumps intermeshing screws.

My invention eliminates the possibility of any such clogging or blocking of these helical grooves or channels a generally helical path on the sleeves outer surface. 7

This helical path preferably has a somewhat greater lead or pitch than that of the associated rotors pumping screw.

The leading end'of each projection 19, in the direction of its rotors rotation, is a generally rectangular shoulder or surface 20, that rises substantially at right angles from the cylindrical surface of the sleeve 18. From the side edges and the top or outer edge of each shoulder 20, the sides or flanks 21, 21 and the outer surface 22 of each projection 19 extend back helically on the sleeve 18, and at the same time slope or taper inwardly, very gradually, such as to merge with the sleeves cylindrical surface substantially at the base of the shoulder 20 of the next projection 19' of the helical series. As shown in FIGS.

4 and 5, the angular spacing of the successive shoulders 20, 20 of this helical series is preferably of the order of 120.

These elongated helical projections 19, 19 of the respective oppositely rotating sleeves 18, 18 are not of sufiicient height, even at their shoulders 20, 20, for their paths to overlap, or for the projections of one sleeve to mesh with those of the other sleeve. In other words, there is a very appreciable clearance between the two sets of projections 19, 19. Also there is a very appreciable spacing or clearance between said projections 19, 19, and the side and bottom walls of the intake chamber 3. But the constant rotation of the two sets of projections 19, 19, creates a very desirable turbulence in any thick fibrous suspension that is supplied or delivered to the screw-pumps intake chamber 3. In addition, the relatively large pitch or lead of their side surfaces 21, 21 urges the material at all times in the direction of the pumping screws, and prevents its suspended fibrous content from settling against the bottom and sides of the intake chamber 3.

Moreover, the sharp leading shoulders 20, 20 of these rotating helical projections 19, 19 are exceedingly efiective in breaking up, and reducing to pumpable size, all of the matted accumulations and concentrations of fibrous material that the intake chamber receives. Especially is this the case with large pieces or slabs or lap pulp, sometimes a square foot or more in area, which, but for the constant and rapid breaking-up action of these rotating shouldered elements, would block the intake of the pump. It is to be noted that this breaking-up and size-reducing action is in no case a shearing action, such as would damage the fibres of these liquid-borne materials.

This is because these adjacent sets of discontinuous helically-disposed ribs 19, 19 move through circular paths which, even at the maximum diameters of said ribs, are appreciably spaced, not only from each other, as shown by FIG. 1, but also, as shown by FIG. 4, from the proximate side and bottom wall surfaces of the intake chamber 3. This spacing of the respective sets of ribs from each other, and also from the intake chamber walls, inhibits any pumping action, as well as any fibre-shearing action, in the intake chamber 3, from the constant rotagion therein of these sets of discontinuous helical ribs 19, 19.

It will be clear from the foregoing that my invention provides a screw pump that is particularly effective in the pulp and paper industry for the handling of all thick fibrous suspensions of high consistencies. For this reason, it is highly useful in pulp washing installations and also in pulp bleaching, especially with all so-called highdensity bleachers.

I claim:

1. For rotary screw pumping of thick fibrous suspensions, containing matted concentrations of the fibrous content, a multi-screw pump providing a casing having parallel overlapping bores, oppositely rotating rotors extending axially of said bores and providing continuous helical intermeshing pumping ribs within said bores, an intake chamber for said pump communicating with said bores, and across which said rotors are extended, said intake chamber having side and bottom walls for containment of the entering fibrous suspension, and a set of discontinuous rib-like projections on each rotor within said intake chamber, for agitating said suspension, and for breaking up its matted fibrous concentrations, the projections of each set at their respective maximum diameters being appreciably spaced from those of each other set, and also appreciably spaced from the nearest side and bottom walls of said intake chamber, whereby to exert no pumping action in said chamber on the entering fibrous suspension, and no shearing action in said chamber on the fibrous content of said suspension.

2. A multi-screw pump as claimed in claim 1, in which the rotor projections within the pumps inlet chamber are angularly spaced on the respective rotors in substantially helical arrangement, such as to urge the entering fibrous suspension toward the bores that contain said intermeshing pumping ribs.

3. A multi-screw pump as claimed inclaim 2, in which said rotor projections within the pumps inlet chamber have leading surfaces in the form of substantially radial shoulders, from which the height of each projection gradually decreases.

References Cited in the file of this patent UNITED STATES PATENTS 2,231,357 Burghauser Feb. 11, 1941 2,592,476 Sennet Apr. 8, 1952 2,745,643 Kleinlein May 15, 1956

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