US3000503A - Spiral classifier - Google Patents

Description

Sept. 19, 1961 Filed July 9, 1958 W. H. RECK SPIRAL CLASSIFIER 5 Sheets-Sheet 1 IN VENTOR gMwyw ATTORNEYJ Sept. 19, 1961 w.'|-|. RECK SPIRAL CLASSIFIER 5 Sheets-Sheet 2 Filed July 9, 1958 INVENTOR #Qzmm @aa ATTORNEYS Sept. 19, 1961 w. H. RECK 3,000,503

SPIRAL CLASSIFIER Filed July 9, 1958 3 Sheets-Sheet 5 INVENTOR Izzy/2m @(A ATTORNEY:

3,000,503 SPIRAL CLASSIFIER William H. Reck, Palo Alto, Calif., assignor to Western Machinery Company, San Francisco, Calif., 21 corporation of Utah Filed July 9, 1958, Ser. No. 747,459 22 Claims. (Cl. 209-464) This invention relates to improvements in spiral classifiers for wet separations and is more particularly concerned with an improved apparatus for classifying, desliming, dewaterin-g, Washing and sizing of ore and pulp. The apparatus exemplified in the present application particularly provides for classifying the sands (loose granular material resulting from the disintegration of ore or rock) and slimes in wet crushed pulp (pulverized ore or rock mixed with water or other liquid).

This application is a continuation-in-part of my copending application Serial Number 489,535 filed February 21, 1955, and now abandoned.

In recent years, industries have recognized the advantages of employing special classifiers in the operation of wet separation. In such a process, pulp to be classified, washed sized, deslimed and dewatered is introduced into the lower end of an inclined trough or tank partially filled with liquid to form a settling pool at the base of the incline. The coarser and heavier particles otherwise referred to as sands, which settle to the lower portion of the pool are continuously removed by a screw conveyor and are conveyed upwardly along the inclined trough. As the sands are removed from the setting pool, they are subjected to a mixing and turning action to expel slime and liquid entrained in the solid mass being conveyed up the incline. The slimes and liquid expelled drain off downwardly into the pool and are carried off by an overflow. The deslimed and dewatered sands are discharged by the conveyor at the upper end of the trough. The present invention is concerned with such types of operations.

Among the factors involved in the device and methods for removing the settled sands in the classifier operation is the necessity for ample sand raking capacity which is a direct function of the conveyor capacity in relation to the specific product being raked by the screw conveyor. The raking capacity for optimum results is required to be balanced with the size of the settling pool and is more readily achieved by classifiers of shorter overall lengths. The length of the apparatus in turn may be shortened by improving the drainage characteristics of the sand being conveyed to the discharge. In addition, the discharge sand is required to contain no free moisture and should be sufficiently dry to facilitate transportation on conveyor belts, thus further calling for improved drainage characteristics of the classifying apparatus.

Thus, one of the primary requisites of a Wet separation operation is to provide for efficient dewatering and desliming of the sand and hence for proper drainage of the expelled slime and liquid back to the settling zone. To this end, it has been found that by providing for a beach area under the screw conveyor on the inclined bottom deck of the trough near the sand discharge outlet, the discharged sand contains substantially less moisture and is accordingly drier and of improved quality to facilitate ease of handling in subsequent operations. This beach area consists of a bed of sand immediately below the outlet which'is deeper than the bed of sand built up under the remaining length of the conveyor. The deeper bed functions to provide a more efficient drainage and owing to its characteristics has the effect of a beach. The drainage bed is established, according to this invention, essentially by reducing the diameter of several flights of the screw conveyor at the upper or discharge end of the trough.

nited States Extent 1 ice 2 from the beach effect is to retain a uniform predetermined depth of the beach and to prevent crumpling or disintegration of the bed once formed particularly in the area immediately adjacent to the sand outlet formed in the bottom of the trough.

Several attempts have been made in the past to achieve improved drainage of spiral or screw conveyor classifying apparatus for wet separations. To this end, an example of the patented prior art is disclosed in the German patent, Number 74,802 issued July 28, 1893, to Carl Friedrick Bauer for a sand washing machine. In the Bauer apparatus, a screw conveyor is rotatably mounted in an inclined trough to convey sand from a pool of liquid at the lower end of the trough to the upper end thereof whence it is laterally discharged. Portions of several of the flights of upper end of the screw conveyor are removed to interrupt the continuous movement of the sand and thereby to form intermittently moved heaps of sand under the conveyor so as to allow time for the entrained water to drain from this excess accumulation. The interruption in the continuous movement of sand to facilitate drainage, however, does not form a drainage bed or beach and the accumulated sand is carried away as the fully extended portion of the spiral flight sweeps across the bottom of the trough in completing a revolution of the conveyor. Moreover, the excess sand that does accumulate is allowed to slope off at its upper end and is not retained to prevent crumbling or disintegration of the drainage bed once formed.

Thus, with the present invention, a permanent drainage bed is provided at the upper end of the classified trough to facilitate continuous drainage of the slimes and liquid expelled from the sands being discharged from the classifier. This bed is formed by reducing the diameters of several of the flights of the spiral conveyor at its discharge end. A permanent beach, therefore, is effectively established and, depending upon Whether the reduced diameter flights are of equal diameter or are of progressively reduced diameters, the beach will either be of the simplex type or multiple type.

Further, in accordance with the present invention, a novel retaining device is incorporated into the classifier apparatus to assist in the formation of a drainage bed of proper depth to facilitate adequate drainage of the slime and liquid expelled from the sand being discharged and more particularly to preserve and retain the uniformity of the bed depth by preventing crumbling and disintegration thereof.

Accordingly, with the foregoing purposes and considerations in mind, it is the primary object of this invention to provide a novel spiral classifier promoting improved drainage characteristics for the material being classified.

It is a further object of this invention to provide for an improved spiral conveyor embodying an economical, simplified and efiicient form of means for drying coarse discharge particles of sand.

It is further the object of this invention to provide a novel spiral classifier which will establish and maintain a beach area adjacent the classified material discharge, either of the single or multiple type.

It is further the object of this invention to provide a novel spiral classifier having improved drainage characteristics to facilitate a reduction in the length of the apparatus normally required and to permit a raising of the classified material discharge elevation to required operating levels for closed communication with grinding mills and the like.

It is a further object of this invention to provide for an improved spiral classifier which will establish and retain a drainage bed of predetermined depth adjacent the sand discharge.

It is a further object of this invention to provide for an improved spiral classifier having a screw conveyor mounted in an inclined trough and including drainage bed retention means in which the spacing between the screw conveyor and the portion of the bottom deck of the trough adjacent the classified material outlet is substantially greater than the spacing between the remainder of the deck and the conveyor whereby a deeper bed of sand of uniform predetermined depth is established and retained.

It is further the object of this invention to provide for a novel spiral classifier for establishing a drainage bed adjacent to the classified material outlet and having a bed retaining wall to assist in the formation of the bed and to prevent disintegration and crumbling of the bed once formed.

Further objects of the invention will presently appear as the description proceeds in connection with the appended claims and the annexed drawings wherein:

FIGURE 1 is a side elevation illustrating one embodiment of the spiral classifier apparatus with the side wall of the classifier trough partially broken away;

FIGURE 2 is a side elevation illustrating a further embodiment of the spiral classifier apparatus with the side wall of the trough completely removed showing the spiral conveyor with a ribbon spiral having a variable pitch at the overflow end and with the last two flights at the discharge end being reduced in diameter to form a simplex beach;

FIGURE 3 is a side elevation of a further embodiment of the invention with the side trough wall removed similar to FIGURE 2 where the last two flights are of progressively smaller diameter than each preceding flight for forming a multiple beach;

FIGURE 4 is a section substantially along line 4-4 of FIGURE 1 illustrating one embodiment of the drainage bed retaining wall;

FIGURE 5 is a view similar to FIGURE 4 where a further embodiment of the drainage bed retaining wall is illustrated; and

FIGURE 6 is an enlarged fragmental side elevation illustrating the upper discharge end of a further embodiment of the spiral classifier apparatus with the side wall of the trough removed.

Referring now to the drawings and more particularly to FIGURES l3, a spiral classifier apparatus is there illustrated which is generally designated at 10 and comprises an elongated trough 12 suitably supported as by beams or standards (not shown) with its bottom drainage deck 14 in an inclined position. The trough 12 is formed with side walls 16 and 18 joined to the drainage deck 14 as by welding or other suitable means and end walls 20 and 22 respectively at the lower overflow end and the upper discharge end of the trough.

The lower end of the trough 12 defines a settling zone for the unclassified pulp which is fed into the trough through a rectangular inlet 23 formed in the side wall 16 above the settling zone liquid level which is indicated by the dotted line 24. This liquid level is maintained by the overflow of excess liquid in the trough over a weir 26 formed at the top of end wall 20. The fines in the liquid overflowing the weir 26 may be discharged into a suitable receptacle (not shown) from which it may be conducted for subsequent treatment.

Classified settling sands fed into the settling zone of trough 12 are moved along the inclined bottom drainage deck 14 to an elevated discharge lip 28 by an axially fixed rotatable advanced pitched spiral conveyor designated generally by the reference numeral 30 and which is mounted in spaced relation-to the drainage deck 14. This spiral conveyor 30 comprises a rigid tubular shaft 32 suitably journalled in the trough 12 and mounted for rotation about an axis substantially parallel with the.

drainage deck 14. The shaft 32 is driven by a prime mover (not shown) and a suitable gear drive (not shown) or other power transmission connection. The spiral conveyors shown in FIGURES l, 2 and 3 are what are known in the art as vari-pitch due to the variable pitches of the helical turns of the ribbons at the pool end. These helical turns are double spirals having two ribbons, spaced diametrically, to form the spiral helix. The pitch of the helix angle in the settling pool zone of the trough 12 increases with each half turn up to the approximate region of the inlet 23. Thereafter, with the exception of the last three flights, the pitch of each flight is uniform.

Referring to FIGURE 2, the third flight 34, from the discharge end of the spiral helix, is reduced slightly from its predecessor. The last two flights 36 and 38 have substantially increased pitches and are substantially equally reduced in diameter with respect to flight 34-. This reduction in diameter between flights 34 and 36 is accomplished in one full turn of the helix. This means that the last two flights 36 and 38 of each ribbon have a greater peripheral clearance, with respect to the bottom drainage deck 14 of the trough 12 than any of the outer flights in the spiral assembly.

Referring now to FIGURE 3, the structure shown therein is substantially identical with that shown in FIG- URE 2 and described in connection therewith, with the exception of the last two flights 40 and 42. Flight 4% is of reduced diameter with respect to its predecessor 44, which is the diameter for the remainder of the spiral assembly, and flight 42 is still further reduced in diameter, being less than its predecessor, flight ii). The reduction in diameter for the flight 40 is accomplished in one-half turn and the further reduction required for flight 42 is also accomplished in one-half turn.

Referring now to FIGURES 1 and 4, a retaining wall is there illustrated at 46 comprising a plate of predetermined height joined to the drainage deck by welding or other suitable means immediately adjacent to the discharge lip 28. This retaining wall extends transversely across the trough and joins to the side walls 16 and 18.

Referring to FIGURE 5, the alternative retaining wall 48 illustrated therein is substantially identical with that shown in FIGURE 4 and described in connection therewith, with the exception of the end portions of the plate. With continued reference to FIGURE 5, the retaining wall 48 is provided with inclined end portions which slope upwardly from points on the plate equidistant from the center thereof.

In operation of the apparatus illustrated in FIGURES 13, the settled sands in the pool are constantly and continuously moved up along the drainage deck 14, of the trough 12 by the conveyor 30. The rotation of the spiral conveyor further causes the sand to be turned, mixed, squeezed and packed to expel entrained liquid and slime. As the spiral 30 turns, the sands are normally carried to one side of the classifier trough in the direction of the rotation of the spiral. The center line areas of the trough bottom are therefore unobstructed and serve as a free drainage channel for the back drainage of the slimes and liquid.

Since the entire periphery of the conveyor 30 is in predetermined spaced relationship to the drainage deck 14 and the diameters of the spiral flights are substantially equal, with the exception of the last two flights, a bed of sand indicated at 52 will be formed by accumulations of conveyed material and will uniformly extend substantially from the settling pool to the spiral flights of reduced diameter at the upper end of the trough 12. With the present invention, a second deeper bed of predetermined depth will be built up under the reduced diameter flights for the balance of the length of the spiral and is indicated at 54 in FIGURE 1, 56 in FIGURE 2 and 58 in FIGURE 3. Each of these beds, 54, 56 and 58, is disposed between the bed 52 of lesser depth and the discharge lip 28 and forms a beach to facilitate improved drainage of liquid and slime expelled from the sands being conveyed from the settling pool.

Referring particularly to FIGURE 2, thebeach defined by the drainage bed 56 is formed by the last two flights, 36 and 38, of the spiral assembly 30 which are of equal reduced diameters. This drainage bed 56 formed thereby defines a simplex beach of substantially uniform depth. In contrast, with reference to FIGURE 3, the beach defined by the drainage bed 58 is formed by flights 40 and 42 which are of progressively reduced diameters. Hence, a multiple or stepped beach indicated at 56 is formed by these last two flights of the spiral conveyor and consequently acquires a greater depth adjacent the outlet. The increased pitch of the last two flights, 36 and 38 in FIGURE 2, and 40 and 42 in FIG- URE 3, give a greatly increased loading capacity at the outlet, while at the same time maintaining the beach characteristics on the sand deck. It has been found by test that this greatly improves the sand drainage immediately prior to delivery at the outlet end and virtually assures the elimination of all free moisture and slime prior to delivery.

In discharging the sands from the trough, the material passing over the drainage bed 56 and 58 of FIGURES 2 and 3 respectively and through the outlet, tends to cause the bed once formed to disintegrate and to crumble particularly at the discharge lip 28. Thus, the bed is being constantly reformed as portions are carried oif with the discharge material. Consequently, the maximum drainage effect of the bed is not realized.

Accordingly, with the preferred form of the present invention, a transversely extending retaining wall is provided adjacent the discharge lip 28 to assist in forming the bed and to preserve or retain the depth of the bed once formed. This retaining wall acts to prevent disintegration and crumbling of the drainage bed during the course of operation of the apparatus. The retaining wall 46 (FIG- URE 4) establishes a uniform bed level across the trough at the discharge lip while the retaining wall 48 of FIG- URE 5 facilitates the establishment of greater bed depths adjacent the side walls 16 and 18 of the trough 12 to provide for increased drainage capacity.

Referring to FIGURE 1, the drainage bed 54 established by the retaining wall 36 and the spiral conveyor 30 insures a full bed depth immediately adjacent to the discharge lip 28 in contrast with slope established in beds 56 and 58 of FIGURES 2 and 3 respectively. The spiral conveyor 30 illustrated in the embodiment of FIGURE 1 is the same as that illustrated in FIGURE 2 wherein the flights 36 and 38 are equally reduced in diameter. It is understood, however, that it is within the scope of this invention to alternatively employ the spiral conveyor of FIGURE 3 to form a stepped or multiple beach in conjunction with either the retaining wall 48 or 46. Thus, referring to FIGURE 6, the multiple beach 60 established by the spiral flights 40 and 42 of progressively reduced diameter is formed with an inclined surface having its greatest depth adjacent to the retaining wall 46. The inclination of the drainage bed 60 offers greater resistance to the forward movement of the sand being raked by the conveyor. The pressure, therefore, exerted on the sand being raked as it passes over the bed is consequently increased to facilitate an additional squeezing action for expelling entrained slime and liquid from the sand before it is discharged.

In the elimination of the last vestiges of free moisture from the sand adjacent the outlet, the beach established in this manner provides excellent drainage to the channels established earlier in the spiral rotation and convey- Because of the effectiveness of the drainage and the action induced by the beach areas, it has been found possible to construct the spiral assemblies for the classifier in shorter lengths, which not only results in a lower manufacturing cost, but substantially economy in space and operation, both of which are important.

The beach established by the multiple reduction of diameters, illustrated in FIGURE 3, permits satisfactory and efficient operation at steep slopes to achieve the desired head room for installation in closed grinding circuits. The advantages secured by the beach-type spiral classifiers described herein make them most desirable for use with closed circuit grinding operatons as they meet both the requirements of an elevated sand discharge and minimum head room and floor requirements.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a spiral classifier for wet separations, an upwardly inclined trough, a substantially continuous spiral assembly mounted for rotation in said trough about an axis substantially parallel to the deck of said trough and having the last two flights thereof at the discharge end of said trough of reduced diameter, providing greater clearance between the deck of said trough and the perimeter of the said spiral assembly.

2. In a spiral classifier for wet separations, an upwardly inclined trough, a spiral assembly mounted for rotation in said trough about an axis substantially parallel to the bottom of said trough and having substantially continuous ribbon spirals of substantially uniform diameter but where the last two flights at the discharge end are of reduced diameter with the last flight being of still smaller diameter than the next to last flight.

3. In a spiral classifier for wet separations, an upwardly inclined trough, a spiral assembly mounted for rotation in said trough about an axis substantailly parallel to the deck of said trough and having a plurality of substantially continuous ribbons, the last two flights at the discharge end of said trough being of increased pitch and reduced diameter providing greater clearance between the deck of said trough and the perimeter of the said ribbons of the spiral assembly.

4. In a spiral classifier for wet separations, an upwardly inclined trough, a spiral assembly mounted for rotation in said trough about an axis substantially parallel to the bottom of said trough and comprising a plurality of substantially continuous helical ribbons having the last two flights at the upper discharge end of said trough of greater pitch and smaller diameter than the other flights thereof and where the reduction in diameter is accomplished in one full turn of the helix.

5. In a spiral classifier for Wet separations, an upwardly inclined trough, a spiral assembly mounted for rotation in said trough about an axis substantially parallel to the bottom of said trough and comprising a plurality of substantially continuous helical ribbons having the last two flights at the upper discharge end of said trough of greater pitch and progressively smaller diameter than the other flights thereof and where the progressive reduction in diameter between said flights is accomplished in one half turn of the helix.

6. A spiral classifier for wet separations comprising an upwardly inclined trough having an outlet adjacent the upper end thereof, a screw conveyor mounted for rotation in said trough for conveying material upwardly along said trough to said outlet, the spacing between the periphery of said screw conveyor and the bottom of said trough being greater at the upper end region of said trough adjacent said outlet than along the region of said trough below said upper end region to permit accumulation of a predetermined amount of the conveyed material in the bottom of said trough at said upper end region to form a drainage bed at said upper end region at least one flight of said conveyor at said trough upper end region being of lesser diameter than the remainder of the flights thereof.

7. A spiral classifier for wet separations comprising an upwardly inclined trough having an outlet adjacent the upper end thereof, a screw conveyor mounted for rotation in said trough for conveying material upwardly along said trough to said outlet, the spacing between the periphery of said screw conveyor and the bottom of said trough being greater at the upper end region of said trough adjacent said outlet along the region of said trough below said upper end region to permit accumulation of a predetermined amount of the conveyed material in the bottom of said trough at said upper end region to form a drainage bed at the upper end region, the spacing between the bottom of said trough and the axis of rotation of said conveyor being substantially uniform along the length of said trough and a plurality of flights of said conveyor at said trough upper end region being of lesser diameter than the remainder of the flights thereof.

8. The classifier defined in claim 7 wherein said plurality of flights are of progressively decreasing diameter toward said trough outlet.

9. The classifier defined in claim 7 wherein at least two of said plurality of flights are of uniform diameter.

10. In a spiral classifier for wet separations, a trough having an inclined drainage deck extending upwardly from a settling zone and defining an outlet adjacent the upper end of said drainage deck, a rotatable screw conveyor mounted in said trough in spaced relation to said drainage deck for conveying material from said settling zone upwardly along said drainage deck to said outlet, the spacing between the periphery of said screw conveyor and said drainage deck being greater adjacent said outlet than the spacing along the remaining portion of said drainage deck for forming a drainage bed comprising an accumulation of conveyed material of predetermined depth on said drainage deck adjacent said outlet, and means between said drainage bed and said outlet for retaining and assisting in the establishment of said bed, said last named means comprising a retaining wall of predetermined height joined to said drainage deck transversely of the axis of said screw conveyor and immediately adjacent said outlet at the upper end of said drainage bed, said conveyor being mounted about an axis substantially parallel to said drainage deck and comprising a plurality of first adjacent flights of substantially equal diameter to provide for a substantially uniform clearance between said first flights and said drainage deck and a plurality of second adjacent flights at the outlet end of said trough of lesser diameter than said first flights.

11. The-classifier defined in claim 10 wherein said second flights are of uniform diameter.

12. The classifier defined in claim 10 wherein said second flights are of progressively decreasing diameter toward said trough outlet.

13. The classifier defined in claim 11 wherein said first and second flights comprise continuous helical ribbons wherein the reduction of diameter between said first and second flights is accomplished in one full turn of the helix.

14. The classifier defined in claim 12 wherein said first and second flights comprise continuous helical ribbons wherein the reduction in diameter between said flights is accomplished in one half turn of the helix.

15. The classifier defined in claim 10 wherein the pitch of said second flights is greater than the pitch for said first flights.

16. In a spiral classifier for wet separations, a trough having an upwardly inclined bottom deck and defining an outlet adjacent the upper end of said deck; a rotatably advanced pitched screw conveyor mounted about an axis substantially parallel with said deck for conveying material from a settling pool located at the lower end ofsaid deck upwardly along said deck to said outlet and comprising means for forming a permanent drainage bed of uniform depth under said conveyor comprising accumulations of said conveyed material extending from said settling pool at the lower end of said deck to a predetermined distance from said outlet and means for forming a deeper permanent drainage bed of conveyed material on said deck between said uniform bed and said outlet for draining liquid in the conveyed material down said inclined deck to said settling pool; and means extending transversely of the axis of said conveyor between said deeper bed and said outlet for retaining and further assisting in the formation of said deeper bed.

17. The classifier defined in claim 16 wherein said bed retaining and formation means comprises a baflle plate of predetermined height extending transversely across said deck immediately adjacent to said outlet at the upper end of said bed.

18. The classifier defined in claim 16 wherein said uniform bed forming means and said deeper bed forming means comprise spiral flights having a plurality of turns of reduced diameter at the discharge end thereof.

19. The method of classifying material by wet separation comprising the steps of introducing the material into a pool of liquid, permitting the heavier particles of such material to settle to the lower portion of said pool, providing a first inclined drainage bed extending above the liquid level in said pool toward an outlet for dried particle discharge and extending downwardly into said pool, providing a second permanent drainage bed with said particles of predetermined depth greater than that of said first bed intermediate said outlet and said first bed and extending from a point adjacent said outlet and terminating at a predetermined distance above the liquid level of said pool so as to form a beach area with respect to said first bed, continuously removing the particles collected in the lower portion of said pool, conveying the particles over said beds to said outlet, subjecting the particles as they are conveyed to a mixing and squeezing action to expel slime and liquid entrained therein, continuously draining the expelled slime and liquid back to said pool through said first and second beds to thereby assure elimination of moisture and slime from said particles, and discharging the deslimed and dewatered particles through said outlet.

20. The method as defined in claim 19 wherein said second bed is formed with an upper exposed surface substantially parallel with the upper surface of said first bed.

21. The method as defined in claim 19 wherein said second bed is formed with an upper exposed surface that is gradually inclined upwardly in the direction of which the particles are conveyed and with respect to the upper surface of said first bed, and squeezing the particles continuously removed from said pool against the inclined surface of said second bed to further facilitate the removal of entrained slime and liquid in said particles prior to discharge thereof through said outlet.

22. A spiral classifier for wet separations comprising an upwardly inclined trough having an outlet adjacent the upper end thereof, a screw conveyor mounted for rotation in said trough for conveying material upwardly along said trough to said outlet, the spacing between the periphery of said conveyor and the bottom of said trough being uniform below the upper end region of said trough adjacent said outlet and being greater than said uniform spacing at said upper end region to permit accumulation of a predetermined depth of the conveyed material in the bottom of said trough at said upper end region to form a drainage bed at said upper end region.

References Cited in the file of this patent UNITED STATES PATENTS 992,629 Akins May 16, 1911 2,428,789 Dickson Oct. 14, 1947 FOREIGN PATENTS 74,802 Germany July 28, 1893 212,551 Germany Aug. 4, 1909

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