US2416499A - Vibratory rotary screen - Google Patents

Description

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Patented Feb. 25, 1947` VIBRAToRY ROTARY SCREEN Walter E. Saxe, Alhambra, Calif., assigner to The Conveyor Company, Los Angeles, Calif., a corporation of California Application December 7, 1942, Serial No. 468,312

(Cl. 209-287) f 2 Claims.

My invention relates to apparatus for classifying comminuted materials, particularly devices for separating relatively fine particles from coarser particles, and is directed to an improved form of rotary screen and an improved method of operating a rotary screen.

In apparatus to which my invention pertains, material is introduced in one end of a rotating screen having arcuate walls, for example, a screen having the conguration of a cylinder or truncated cone, the iiner particles passing radially outward through the mesh of the screen and the coarser particles being discharged from the opposite end of the screen. Vibration of the screen While it is rotating about its, longitudinal axis not only favors the movement of the finer particles through the mesh of the screen, but also raises the maximum speed at which the screen may be rotated withoutl centrifugal force preventing the material from traveling longitudinally of the screen.

One object of my invention is to Vibratea rotating screen substantially uniformly throughout the length of the screen.- More specifically, I propose to rotate an arcuate screen about a longitudinal axis and simultaneously to revolve the screen bodily about a second and parallel axis, thereby causing the rst axis to move in a substantially cylindrical path.

Vibration of a rotating screen is, in the usual construction, distributed throughout the whole of the apparatus with consequent undesirable effects, wear on bearings being particularly noticeable. One of the objects of my invention is to provide means for counter-balancing the vibratory movement of a rotary screen. More particularly, it is my .object to provide for neutralizing the vibratory effect involved by mounting the screen eccentrically on a rotary means that is counterbalanced with respect to the eccentricity of the screen mounting so that the moment of inertia of the counterbalanoed rotary means about its axis of rotation will substantially equal the moment of inertia of the screen and its load of materials with respect to the same axis.

Another object of my invention is not only to vibrate a rotary screen but also to rotate the screen at alternate speeds. In the preferred form of my invention, one of these speeds is below and the other is above the critical speed at which centrifugal force pressing the material outward against the peripheral wall of the screen suspends movement of the material longitudinally of the screen.

Another object of my invention is to provide means limiting the depth of the material moving longitudinally of the rotary screen, this object being accomplished by providing an outer helical blade to convey material from the inlet end of the screen to the outlet end in combination with an inner helical blade of opposite disposition to move excess material in the opposite direction.

A further object of my invention is to provide -a rota-ry screen characterized by features recited above vthat is compact and is arranged as a readily portable unit.

While my invention may be utilized in various arts for the separation of materials, I elect for the purposes of this disclosure to describe an embcdiment ',designedprmarily for screening mud employed in rotary drilling of Wells. The mud is circulated by a slush pump in a continuous cycle through the well from a mud pit atthe surface. In the recycling of the mud` the screening device hereinafter described may be employed on the inlet side of the slush pump to remove from the mud fragments of rock and other foreign matter brought to the surface by the mud.

Other objects of my invention relate to the construction of the rotary screen per se. One of these objects is to minimize the tendency` of a sheet of screen material to be cut by the frame on which it is mounted. Another object of my invention is to provide a method of mounting rela.- tively fragile screen material on a frame under tension not to exceed a predetermined maximum stress, such maximum being under the breaking point of the screen material.

The above and other objects and advantages of my invention will be apparent from the description to follow, taken with the accompanying drawings.

In the drawings:

Fig. 1 is a longitudinal section through the housing of my apparatus showing the rotary screen partly in section;

Fig. 2 is an end view of my apparatus with the end of the housing broken away to show the interior mechanism;

Fig. 3 is a similar view from the opposite end of the apparatus;

Fig. 4 is a diagrammatic representation of the rotary means for vibrating the rotary screen in a counterbalanced manner;

Fig. 5 is an enlarged section through the wail of the rotary screen member takenalong the line 5 5 of Fig. l., indicating the manner in which the sheet of screen material is assembled to the screen frame;

Fig. 6 is a schematic view .to show how a pair Fig. 7 is a diagrammatic representation of means associated with the electricaLcircuits of the screen motor to provide for alternating speeds f screen rotation.

The screening mechanism is encased by a housf ing generally designated Ill and is preferably designed as a compact portable unit. I nd it con- `venient to provide the housing with a pair oi' brackets I I by means of which the screening unit jmay be suspended from a longitudinal rod I2 extending between a pair of spaced timber frames I3, the rod being anchored to the frames by U- bolts I4. By utilizing the brackets/II, a crane 1may be employed to lift the unit in a convenient lmanner.

The housing comprises a top wall I1, a pair of arcuate side plates I8 on one side, a pair of ar- `cuate side plates I9 on the opposite side, a front wall 20, and a rear wall 2| having vent ports 22 protected by hoods 23. The housing is built laround a frame that includes a pair of longitudinal side channels 25, a longitudinal bottom and the top plate of the'housing.

Within the housing, a hollow rotary screen Ymember. generally designated 33, is supported by a shaft 34 journaled in a front' bearing 35 and a rear bearing 36, the bearings being supported respectively by cross channels 31 and 38 interconnecting the side channels of the frame. Material is introduced into the front end of the rotary screen member,33 either through a chute 40 extending downwardly from the top of the housingand having an inclined feed spout 4I, or through a second feed chute 42 entering the housingthrough the front wall 20 at a relatively slight inclination. When dry materials arebeing screened, the vertical chute 40 is employed, but if the material is wet enough to flow, the lower chute -42 is employed. The fine material that passes through the mesh of the rotary screen `oi. eccentric gears may be incorporated in my` `apparatus to provide for alternating speeds of 3 screen rotation; and

the drawings the screen has the conguration of a true cylinder. l,

i Perforate screen material is mounted on a cylindrical frame, generally designated 53, which may comprise a spiral band 54 with the various revolutions of the spiral band interconnected by spaced longitudinal bands 55. The ends of the frame are provided by ring members 56 reinforced by radial flanges 51, the ring member at the front end carrying an erid wall v58 of frustoconical configuration extending around the discharge ends of the feed spout 4I and the feed chute 42. The cylindrical frame 53 may be readily fabricated by cutting metal out of a metal cylinder in the pattern indicated' and by welding angle-iron rings to the two ends of the apertured cylinder. Preferably, the various bands comprising the cylindrical frame 53 are provided on their outer surfaces with coatings or layers 60 of rubber or other suitable material, as best shown in Fig. 5,.

For the purpose of holding screen material on i the cylindrical frame 53, I provide in the preferred form of Vmy invention an outer cylindrical frame assembly, generally designated 62, that is complementary to the frame 53 and includes spiral band members 54a to overlie the spiral band. 54 of the frame 53, and longitudinal band members 55a to overlie the corresponding longitudinal band members 55 of the frame 53. The inner surfaces of the various bands in this outer assembly 62 may be provided with layers 63 of rubber or other suitable material.

The outer frame assembly 62 is divided into a number of releasably interconnected sections, for example, three sections as indicated in Fig. 3.

, Along each longitudinal edge of each section is an angle-iron 64 apertured to receive a series of bolts 65 for interconnecting the various sections. At each juncture between two sections of the outer cylindrical assembly 62, there is a longitudinal rib 61 provided by welding a bar to the inner cylindrical frame 53, the bar being provided with slots 68 in its outer edge to clear the bolts member 33 is received by a hopper 44 having a discharge port 45 through the bottom channel 26, the hopper being of sheet metal with its upper rim reinforced by an angle 46. The coarse material passing out of the rear end of the rotary screen 33 drops into a chute 41 leading to a discharge port 43 in the bottom channel 26.

1 Since it may be desirable to add water or to subject the material to water'treatment during the screening operation, I provide a pair of spray pipes 5I) extending longitudinally along the upper side of the rotary member 33, the two pipes being fed from a common supply pipe 5I, the pipes 50 being perforated to discharge a plurality of streams downward against the rotary screen member in a well known manner. K

I 'I'he rotary screen member 33 may be of any hollow configuration providing arcuate walls and adapted to cause material to travel along the walls from one end of the rotary screen to the other. For example, the rotary screen member may be cylindroidal or conical in configuration.

'In the preferred form of my invention shown in The perforate screen material 10, preferably wire cloth, is clamped against the inner cylindrical frame 53 by the outer cylindrical assembly 62, there being one sheet of the screen material coextensive with each section of the outer frame assembly 62. Each longitudinal edge of each of the screen sheets is attached as by soldering to a longitudinal strip 1| of suitable metal, the strip being bent to an angle to provide a longitudinal flange 12 against which the corresponding angle 64 of the outer frame assembly normally abuts.

The mounting of relatively fragile wire cloth on a screen frame usually requires such care that it is not a matter for an unskilled mechanic. By virtue of my construction, however, no great skill i is required. The layers `of rubber 6U and 63 pronormal operatiorrof the apparatus.

tect the screen material from all sharp edges.

while the rotary screen is being assembled as well as when the screen is subject to vibration in the There are no bolt holes to weaken the screen.

A feature of my construction is that not only does it simplify the task of assembling wire cloth to the screen frame, but also may be .designed to limit the tension placed on the screen to a prel determined maximum well under the breaking ploy 16 gauge soft copper for the longitudinal edge strips 1|, since 16 gauge soft copper formed to an angle, as indicated in Fig. 5, will yield to deformation of the angle by a force acting on the flange 12 before it will engender sufficient tension to break the wire cloth, but, on the other hand,

will resist such deformation to a sulicient extent to place the wire cloth under the desired tension. Up to the yielding point of the copper angle, I may control the tension applied to the wire cloth when the bolts 65 are tightened by simply regulating the dimension of the wire cloth with respect to the arcuate dimension of the corresponding section of the outer cylindrical frame assembly 62. In all cases, the sheet of wire cloth will be somewhat *shorter than the arcuate extent of the corresponding outer frame section so that the wire cloth is placed under tension as the outer frame section is moved into clamped position a'fainst the inner cylindrical frame 53. If the relative length of a particular sheet of wire cloth is so short as to tend to engender excessive stress when the rotary screen is assembled, the assembling process will result in the bend in the copper strip being slightly ironed out, the yielding of the material causing the flanges 12 to swing outward, for example, to the dotted positions indicated at 12a in Fig. 5.

To cause material to be transported through the apparatus in a controlled manner as the screen member 33 rotates. I may provide a helical blade '|4 which follows and is welded to the spiral band 54 of the inner cylindrical frame 53. As viewed axially, this helical blade is annular in configuration, the width of the blade corresponding to the maximum depth of material desirable in the screen. To prevent material from exceeding that maximum depth, I may provide a second helical blade 15 inside the rst helical blade and opposite'ly disposed relative thereto for movement of material in the reverse direction. By virtue of this arrangement, the outer helical blade 14 will serve as a screw to move material from the front end of the rotary screen to the rear end thereof, but material extending above the width of the outer helical blade will be engaged by the inner helical blade 15 which will act as a screw to move such excess material toward the inlet end of the screen, It will be apparent that any temporary excess of material at the inlet end of the screen will tend to be distributeduniformly toward the discharge end of the screen.

The inner helical blade 15 is mounted on a hollow member or shaft such as a tube 16 extending axially through the rotary screen'. By interconnecting the two helical blades at their intersection points with suitable pieces of metal 18 welded thereto, I may use the two blades to support the whole of the rotary screen member 33 on the tube 16.

The axial tube 16 through the rotary screen is supported in turn by a pair of roller bearings 80 embracing cylindrical portions 8| of the shaft 34, which cylindrical portions are in alignment with each other but are eccentric to the axis of the two shaft bearings 35 and '36. As 'the result of such eccentricity, rotation of the shaft 34 will cause the rotary screen member 33 to move in a relatively small orbit, the axis of the rotary screen member describing a cylindrical path, the orbital movement being uniform from one end to the other of the screen. I contemplate having this orbital movement occur at a rate to vibrate material in the rotary screen member. For example, in one embodiment of my invention the shaft is operated at 1350 R. P. M.

` Since such vibration tends to have an undesirable effect on the shaft bearings 35 and 36,' as well as on other parts of the apparatus, I provide means to compensate for the orbital movement of the rotary screen member with respect to the axis of the two bearings 35 and 36. Such compensating means may be any form of counterbalance associated with the shaft 34. In the preferred form of my invention, I find it desirable, for the sake of compactness and for other reasons, to place the counterbalancing means within the axial tube 'I6 of the rotary screen member. This end may be accomplished by simply forming the shaft 34 with an integral counterbalancing portion 82 intermediate the two portions 8| that carry the screen bearings 80, the eccentricity of the counterbalancing portion 82 of the shaft being diametrically opposite from the eccentricity of the cylindrical portions 8| of the shaft with respect to the axis of the two bearings 35 and 36.

The desired relationship may be understoodby referring to Fig. 4 in which the inner circle 84 with its central axis 85 represents the portions of the shaft 34 journaled in the bearings 35 and 36. The tube 16 of the rotaryscreen member together with the two bearings are represented, by the circle 86 having its center 81 to one side of the axis 85.- The counterbalancing portion of the shaft represented by the circle 88 has its center 89 spaced from the axis 85 dlametrically opposite from the center 81. It is contemplated that the masses involved with respect to their radial distances from the axis will be such as to provide substantially rotational balance, i. e.y that the moment of inertia of the counterbalancing portion 82 with respect to the axis of the bearingsv 35 and 36 will substantially equal the moment of inertia of the rotary screen member 33 together with its normal operating load of material about the same axis.

A motor 90 for operating the moving parts of my apparatus may be'mounted on a vertical frame comprising two vertical channels 92, a bottom channel 93, and a pair of top angles 94. A motor shaft carries two sheaves, a larger sheave 96 to drive the shaft '34, and a smaller sheave 91 to drive the rotary screen member 33. The larger sheave 96 is operatively connected by a suitable belt 98 with a sheave 99 keyed to the shaft 34. The smaller sheave 91 of the motor is operatively connected by a belt |00 with an idler sheave |02, and with a relatively large sheave 03 in the lower part of the housing. The

idler sheave |02 is mounted on a shaft |04 jour-"M" naled in a pair of bearings |05 supported by corresponding brackets |06, the bearings being adjustable along the brackets to provide for adjustable tensioning of the belt |00. The large sheave |03 is keyed to a countershaft |08 journaled in spaced bearings |09 and ||0, the bearing |09 be-` ing mounted on an angle-iron ||I supported by the two angles 29 and the bearing ||0 being supported on an angle-iron ||2 interconnecting the motor supporting channels 92. Keyed to the countershaft |08 is a small double-grooved sheave I4 that is connected by a Dair of belts ||5 with a larger double-grooved sheave ||6 that is keyed to the axial tube 16 of the rotary screen member. The speed reduction accomplished by the several ratios between the motor and the axial tube 16 preferably is such that while the motor revolves the shaft 34 at 1350 R. P. M., it simultaneously revolves the rotary screen at approximately 44 R. P. M.

` In one form of my invention, I provide for alternating the operation of the rotary screen member between two speeds. One of these speeds will, of course, be sumciently low to permit the outer helical blade 14 to convey material through the rotary screen member, and the other speed may be sufficiently high to cause centrifugal force to predominate suliciently to hold the mass of material against the inner Wall of the rotary screen member. The alternations in speed may be relatively rapid to promote agitation of material in the screeny or either speed may be prolonged.- In some processes sustained periods of predominating centrifugal pressure may be desired.

` The manner in which the preferred form of my invention previously described may be modified to provide for alternating speeds of rotation is suggested by Fig. 6. In this ligure the previously described sheave |03 driven by the belt |00 is on a countershaft |08a. Instead of placing the double-grooved sheave ||4 on the same countershaft, I mount it on a. second countershaft ||9 and connect the two countershafts ||8a and ||9 by a pair of eccentric gears |20. This arrangement will provide relatively rapid alternations in the speed of the rotary screen member with conv sequent agitation of the material in the screen.

i Slower speed alternatlons and more prolonged speed intervals may b'e` provided by a mechanical switching arrangement constructed as indicated by Fig. 7. The motor 90a, in this case an induction motor, is energized by wires |23' through a switch having three blades |24. In one position of the switch blades, eight poles of the motor stator |25 are energized through wires |26, whereas in the alternate position of the switch blades |24 a lower number of poles, say six poles of the stator, are energized through wires |21. Through an operative connection indicated by the dotted line |30, the motor actuates a worm |3| that meshes with a worm gear |32. The Worm gear |32 by means of a crank |33 reciprocates a rocker arm |35 that is pivoted at |36. The lower end of the rocker arm |35 is connected by a suitable spring |31 to the end of a lever |38 that is pivoted at |39 to swing between two fixed stops |40 and |4I. By virtue of the relationship indicated, the lever |38 moves from one of vthe stops to the other with a snap action whenever the spring |31 is carried across the lever by the rocker arm |35. As the result of incorporating a control of the character described in my apparatus, the motor will operate alternately at two speeds for relatively prolonged periods.

The forms of my invention described in specic detail for the purpose of this disclosure will suggest to those skilled in the art various changes and modifications that do not depart from the spirit of my conception; I reserve the right to all such changes and modifications that properly come within the scope of my appended claims.

In my appended claims, the verb to rotate is employed in the sense of a body so moving that v the various parts of the body describe equal arcs in equal periods of time about a common axis, whereas the verb to vibrate is used in the sense of bodily movement in an orbit.

I claim as my invention:

1. A machine of the character described, having: a hollow screen; means to rotate the screen about a longitudinal axis; means to simultaneously vibrate the screen; a helical blade disposed in the screen to form in conjunction with the inner surface thereof means to convey material through the screen, said blade being annular; and a second oppositely disposed helical blade mounted inside the first helical blade to move in the opposite direction through the screen material exceeding the depth of said iirst blade.

2. A combination as in claim 1 in which means is provided to counterbalance the vibration of the screen.

WALTER E. SAXE.

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

UNITED STATES PATENTS Number Name Date 11,637 Akins Sept. 5, 1854 567,569 Maish Sept. 8, 1896 2,027,375 Fraser Jan. 14, 1936 335,155 Smith Feb. .2, 1886 404,345 Cornwall May 28, 1889 2,271,900 Mowbray Feb. 3, 1942 1,733,604 Johnson Oct. 29, 1929 1,620,865 Blackden Mar. 15, 1927A 1,455,907 Daman May 22, 1923 2,311,814 Behnke Feb. 23, 1943 975,178 Thomas Nov. 8, 1910 508,282 Clancy Nov. 7, 1893 FOREIGN PATENTS Number Country Date 625,745` German Feb. 15, 1936 61,649 German May 9, 1892; 213,790

British Apr. 10, 1924

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