US3087617A - Screener - Google Patents

Description

April 1963 A. R. FORSBERG 3,087,617

SCREENER Filed March 2, 1960 3 Sheets-Sheet 1 April 30, 1963 A. R. FORSBERG 3,087,617

SCREENER Filed March 2, 1960 3 Sheets-Sheet 2 flTTOR/VEYS 4271/02 1?. FORSBERG April 30, 1963" A. R. FORSBERG SCREENER s Sheets-Sheet 5 Filed March 2, 1960 Afro/P215);

United States Patent 3,tl87,617 SCREENER Arthur R. Forsberg, Thief River Falls, Minn. Filed Mar. 2, 1960, Ser. No. 12,363 Claims. (Cl. 209-319) This invention relates to screening machines and in particular to those of the vibrating screen variety and more particularly to those of the type which are moved or rocked in a circular or gyratory path to impart positive rocking shifting movement to all parts of the screening surface.

In most of the screening devices of this type, the screening machines and their supporting structures are subjected to unbalancing destructive vibratory shock which shortens the life of the machine and renders the same very noisy in operation, particularly when they are operated at high speeds which they normally must operate at to obtain the efiiciency of screening desired. Because of this vibratory movement and destructive unbalancing shock, it has previously been impossible in the past to mount the charging hoppers and the discharge funnels or spouts in compact communicating relationship with the screening box itself. In the screening machines previously and presently available the screens tend to flex in the center due to their continuous circular motion at a high rate of speed which causes lost motion in the flexed portion of the screen. Also, in prior art devices, the center of the screen is conventionally higher than the sides thereof and the material being screened therefor tends to run heavier in the sides than in the center causing an uneven flow and screening of material as it passes through the screening devices.

Therefore, an important object of my invention is a novel screening machine in which the screening box or shoe is independently mounted and gyrated and which has the feed hopper and discharge spout mounted immediately adjacent thereto in flow communication therewith without being subjected to the gyratory movement of the screening box or to any substantial vibratory movement resulting therefrom.

Still another object is a screening machine of the class described having novel means for positively moving or rocking the screening box in a circular or gyratory path and which is balanced in such fashion that the destructive unbalancing vibratory shock normally associated with prior are devices is eliminated to provide a banced drive to reduce the noise of operation and add to the life of the machine thereby providing a substantially noiseless vibrationless screener.

Still another object is a screening device of the class described having novel means for removably and releasably supporting and clamping the screens in place to pre vent bending and bowing and flexing thereof during use and also permitting easy removal of the screens for cleaning, repairing or replacing thereof.

Still another object is a screening machine of the class described employing novel screen bracing means which render the screens perfectly flat during use enabling a uniform flow of material across the entire width of the screen.

Still another object is a screening machine of the class described employing novel screen clamping and supporting means which permit all of the screens to be clamped simultaneously by operation or actuation of a single locking mechanism.

Still another object is a screening machine of the class described having a novel screen supporting and bracing means which prevents lost motion in the center of the screen when the screening shoe or box is gyrated through a generally circular movement about a generally horizontal transverse axis.

3,087,617. Patented Apr. 30, 1963 "ice Still another object is a screening machine of the class described in which the screening box, feed hopper and discharge spout are compactly mounted on a common frame in direct flow communication with one another and in which the screening box is gyrated without any vibratory motion being transferred to the hopper and the discharge spout.

Still another object is a screening machine for all types of screenable material having high capacity and adapted to prevent blinding or clogging of the machine and which eliminates the need for screen blinding brushes which are frequently required on many of the presently and previously available screening devices and those of the prior art and which is so designed as to reduce maintenance to a minimum.

Still another object is a screening machine of the class described having a feed hopper with both positive control for bin feed operation and spring loaded control for mill stream operation.

Still another object is a screening machine of the class described which features bridge type construction employing light weight material and bridge type bracing providing tremendous strength with light weight to achieve a substantially vibrationless, noiseless machine.

Another object is a screening machine of the class described which is readily disassembled and in which the screening box may be completely removed from the supporting frame to enable said box to be tipped or tilted so as to be passed through narrow doorways and the like and for convenience in transportation thereof.

These and other objects and advantages of my invention will more fully appear from the following description made in connection with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views, and in which:

FIG. 1 is a perspective view of the assembled screening machine of my invention;

FIG. 2 is a side elevational View;

FIG. 3 is a front elevational view with portions thereof in broken section;

FIG. 4 is a vertical longitudinal sectional view of the screening box;

FIG. 5 is a vertical transverse sectional view taken on the line 55 of FIG. 2;

FIG. 6 is a detail side elevational view of the eccentric and counterweight therefor;

FIG. 7 is a detail sectional view on an enlarged scale taken on the line 7-7 of FIG. 5; and

FIG. 8 is a detail sectional view on an enlarged scale taken on the same line as FIG. 7 and showing an alternate form of the invention.

Reference is now made to the accompanying drawings for a more detailed description of a preferred embodiment of my invention illustrated therein. As best illustrated in FIGS. 1 and 2, the composite screening machine of my invention includes a screening box B, a feed hopper H and a multiple discharge manifold or spout S, all of which are mounted on and supported by a common main frame F, the side members of which are detachably connected to the cross members thereof by the bolts 9 for facilitating the assembly and disassembly thereof and complete removal from the screening box when desired.

Considering first the screening box B, it comprises a suitable shell or housing 10 made of light weight sheet steel which is reinforced by suitable transverse ribbing or channels 11 secured to the top of the housing and by vertically disposed reinforcing members or channels 12 disposed vertically on the sides of the housing. The housing is yieldingly and resiliently suspended in inclined fashion from front to back from the frame F by means of suitably tensioned helically coiled shock absorbers or springs 13 disposed adjacent the four corners of the housing and interconnecting the housing with the frame. The lower ends of the springs 13 are connected With the screening box by means of suitable mounting brackets 13a secured to the outsideof the shell 10. The upper ends of the springs 13 are adjustably suspended from the frame F by means of a vertically disposed draw bolt 13b connected to the upper end of the spring, the draw bolt in turn being supported by a horizontal anchoring member 130 secured to the frame F and having an aperture in the outer end thereof for receiving the draw bolt 13b. The tension in the springs may be adjusted by vertically adjusting the draw bolt 13b.

The housing has enclosed therein a plurality of horizontally disposed screens 14, and 16, the screens being of increasingly finer mesh as they proceed from top to bottom, the topmost screen 14 being of coarser mesh than the next succeeding screen 15 and the bottommost screen 16 being of the finest mesh of all. Each of the screens are provided with inwardly turned hook means or strips 1 7 on the sides thereof which are adapted to be removably engaged by the downwardly extending clamps 18 provided on the inner sides of the housing to removably secure and mount the screens inside the housing or box. The clamps 18 are resilient in nature and are each provided with a suitable transverse draw bolts 19 which extend through the sides of the housing 10 and are threadedly engaged by the T-handles 20 which extend outwardly from the sides of the housing 10. By turning the T-handles, the draw bolts are thereby pulled against the clamps 18 which in turn press against the hook strips 17 with which they are engaged to stretch the screens and securely tighten the screens and hold them taut.

The bottom screen 16 rests on and is supported by a plurality of longitudinal extending transversely spaced apart channel supporting members 21 (three are shown) which are secured to the bottom or floor of the housing 10. It will be noted that the channels 21 and the remainder of the screen supporting members hereinafter to be described are preferably equi-spaced transversely or laterally from each other and from the sides of the housing 10 so that the lateral unsupported span of the screens between adjacent supporting members is substantially the same. A spacing and clamping unit indicated generally by the letter X rests on the top of the bottom screen 16 and extends vertically between the screen 16 and the middle screen 15 immediately thereabove. The supporting and bracing unit X includes three transversely spaced sub-units each of which consist of a pair of vertically aligned longitudinally extending clamping and supporting rods 22 which are rigidly interconnected to one another by suitable vertical bracing members 23, the sub-units in turn being laterally interconnected to one another and suitably braced by means of suitable horizontal transverse bracing members 24. Thus, the lower rods 22 are adapted to rest upon the top of the bottom screen 16 while the top rods 22 are adapted to engage the under surface of the middle screen 15 which rests thereupon and is supported thereby. The supporting and bracing unit X is in turn tightened and braced to prevent vibration and shifting thereof during the vibrating movement of the housing 10 by means of suitable tensioning cables 25 connected to the vertical bracing of the side sub-units and extending to and connecting with threaded adjustment draw bolts 26 disposed in the sides of the housing 10.

A bracing and supporting unit Y similar to the previously described supporting and bracing unit X is disposed between the middle screen 15 and the top screen 14 and includes sub-units consisting of the longitudinally extending vertically spaced apart pairs of screen engaging and clamping rods 27 which are interconnected by suitable vertical bracing 28 and horizontal transverse bracing members 29, the.unit Y also being braced against shifting movement with respect to the housing by means of tensioning cables 25 and tensioning bolts 26 extending between the sides of the housing and the side sub-units of unit Y. Thus, the lower rods 27 rest upon the top of the intermediate screen 15 in direct opposition to the rods 22 engaging the opposite side of the screen while the upper rods 27 engage and support the lower face of the top screen 14 to support the same.

A hold down or clamping unit Z is disposed atop the top screen 14 and intermediate said screen and the roof of the housing 10. This unit includes longitudinally disposed transversely spaced apart clamping rods 30 which rest upon the top of the screen 14 directly opposite the rods 27, which rods have mounted thereatop and rigidly secured thereto longitudinally spaced apart pairs of longitudinally disposed bowed or inverted V-shaped bracing members 31 interconnected by transverse rods 31a each of the bows 31 having an upstanding guide arm 32 extending upwardly from the mid-portion thereof, the upper end portion of which protrudes through an opening in the top of the housing 10. Each of the upstanding arms 32 carries thereon a helical coiled spring 33 freely wound thereabout and longitudinally compressible thereabout. The upper ends of the springs 33 having bearing thereagainst suitable pressure applying collars 34 which are freely slidable on the arms 32 and are adapted to be actuated for axial movement thereon by pivotal interconnection with the outer end of the lower lever arm 35 of the multiple bell cranks indicated generally by the numeral C which bell cranks also include the transversely disposed pivotally mounted lever supporting sleeve 36 which is journalled in and rotatably supported by the pairs of vertically spaced apart mounting flanges 37 found at each side of the housing 10. Each of the sleeves 36 are provided with the upper lever arms 38 of the bell cranks, the front and back lever arms 38 on the same side of the housing on each of the sleeves 36 being actuatingly interconnected for simultaneous movement by means of a handle bar link 39 which is pivotally connected at each end to said front and back lever arms 38.

The handle bars are actuated and the bell cranks rotated by means of a toggle unit on each side of the housing which includes a toggle handle 40 which is pivotally mounted to a vertical upstanding flange 41 carried by the top of the housing and mounted on a bearing 42 carried by the flange 41, the lower end of the handle 40 being pivotally connected to the other half of the toggle unit consisting of the link or lever 43 which is pivotally con nected to the toggle handle 40 at one end and pivotally connected to the back upper lever arms 38 of the bell cranks. Thus, by moving the handles 40 forwardly to the locked hold down position shown in the drawings, the bell cranks are caused to rotate in the opposite or clockwise direction thereby causing the collars 34 to press downwardly against the springs 33 which are compressed thereby and apply uniform pressure downwardly through the bowed braces 31 to the clamping rods 30 which in turn press downwardly to apply uniform pressure to the supporting and bracing units X and Y disposed therebelow, thereby securely clamping the screens between their respective directly opposed clamping rods and maintaining them in a perfectly flat unfiexible condition, thereby preventing flexing of the screens and lost motion during vibration or rocking of the screening box and permitting uniform How of material through the entire width of each of the screens. Thus, when the toggle is in locked condition, the top screen 14 is securely clamped between the clamping rods 27 and 39, the intermediate screen 15 is clamped between the clamping rods 27 and 22 and the bottom screen 16 is clamped between the rods 22 and the bottom channel supports 21.

It will be noted that the channels 21 and the rods 22, 27 and 30 are in vertical alignment with one another to enable the uniform application of vertical downward pressure therebetween by means of the hold down unit and bell crank mechanism previously described.

It can be seen that the screens 14, 15 and 16 are firmly braced and supported by the channel 21 and bracing units X and Y and hold down unit Z to keep them perfectly flat during use and prevent bowing and flexing thereof by means of the light weight but very sturdy and strong bracing and support previously above described. Thus, this arrangement not only provides maximum strength with a minimum of weight but also provides the support and strength necessary to prevent the bending and flexing of the screen and Without interfering with and positively promoting the uniform flow of material along the width of the screens. In addition, the clamping and supporting mechanism is easily operable as can be seen from either side of the machine by simple actuation of either of the toggle handles it), and the hold down arrangement also permits the screens to be releasably and securely clamped in position so that they may be unclamped and easily removed for cleaning, repairing and/or replacing when necessary.

To positively move or rock the housing through a circular or gyratory path, I provide a rotatable shaft 44 which extends through the entire body of the screening shoe, the ends thereof being carried in ball bearings 45 secured directly to the frame. Ball bearings 46 are also provided which are secured directly to the sides of the shoe or housing 10 for mounting the screening box on the shaft. These bearings 46 enclose and are engaged by eccentrics 47 carried by the rotatable shaft 44. The shaft 44 represents the only direct positive connection between the shoe or box B and the frame F of the machine. The shaft 44 also carries a cup-shaped fly wheel 48 which is secured thereto for simultaneous rotary movement therewith, which fly wheel 48 is provided with a balance weight or counterweight 49 installed on the inner thereof in direct radial alignment With the bearing unit and the shoe and its eccentric, which weight is 180 out of phase or timed 180 from eccentric in the shoe bearing. Therefore, While the shoe is exerting centrifugal force in one direction, the counterweight is exerting an equal centrifugal force in the directly opposite direction. Due to the fact that the counterweight 49 is centered directly in line with the bearings 46 on the shoe :and the eccentrics 47, these centrifugal forces or stresses are applied to the shaft at the same point and thereby eliminates shaft whip and vibration from the frame and the box which is so prevalent in prior art devices and permits only positive balanced gyratory movement of the box B. The counterweight thus enables -the shaft and screening box to maintain positive balance at all times and results in a substantially vibrationless and noiseless machine.

The shaft 44 is driven through any suitable transmission means such as the drive pulley 57 and drive belt 58 by means of a conventional motor M which is capable of rotating high speeds on the order of 1500 to 2000- rpm. Thus, due to the counterweight and counterbalance provided by the counterweight 49 the shaft Whip associated with conventional types of screeners is thereby eliminated as well as vibration of the frame F. Therefore, due to the vibrationless frame F, it becomes possible to connect the feed hopper 1-1 and discharge spout S directly to the frame in direct flow communication with the screening box 13 without having any substantial vibratory movement imparted thereto.

The hopper H shown is a funnel type hopper carried on the frame F by means of the outwardly extending portion 50 thereof. The lower discharge end of the funnel or hopper H is provided with a feed chute 51 which disconnectedly overlaps the outer end of another feed plate chute 52 connected in flow communication with the interior of the screening machine. The feed pipe delivering the prodnot or material to be screened to the inlet mouth 59 of the hopper should preferably be positioned to deliver the material into the hopper from directly above or from front or rear to accomplish uniform feeding of the screening box, since feeding from the side will cause uneven feeding thereof. The feed hopper is provided with positive control for bin feed operation. When operating on mill stream, connecting links on each side of the hopper are replaced with suitable adjustably tensioned springs which are hooked to the feed plate and adjusted to maintain enough product or material in the hopper to feed full width.

The multiple discharge spout S on the other or forward end of the machine is removably mounted on the front end of the frame F and in overlapping disconnected relation with the forward ends of the screen-s to enable the various screening products to be separately removed and disposed of. Thus, the multiple discharge spout S includes individual spouts 53, 54 and which are in independent flow communication with their respective screens, the outermost spout 53 handling the scalpings from the top screen 14, the middle screen 15 communicates with the middle or main screen outlet 54 to remove the product passing over the screen 15 and the third spout 55 is adapted to discharge the product passing over the bottom screen 16. A discharge spout 56 is carried by the front end of the screening box and provides an outlet for the dirt and other material which collects on the bottom or floor 10a of the screening box.

The screens hereinbefore described are substantially non-blinding in the screening of dry granular materials. However, there are some types of ground oily-base products or materials which are subject to packing which are normally practically impossible to properly screen since the conventional brushing merely causes the oily product to mat the screen. Therefore, as an important part of this invention, I have developed means for preventing blinding of the screens by these oily materials, which means are best seen in FIGS. 5, 7 and 8. The novel means devised comprises laying one or more objects such as the metal chains 60 on top of and lengthwise of the screens 14, 15 and 16, which chains are anchored in any suitable fashion and are allowed to vibrate on top of the screens as they are gyrated, the vibration imparted to the screens by the chains preventing blinding by these oily materials. Rubber covered chains may be substituted for the regular metallic ones where desired.

FIG. 8 illustrates a modification or alternate form of non-blinding means which consists of a series of rubber balls 61 interconnected with one another by flexible cord or cable means 62 to form an elongate flexible vibration imparting medium anchored to the housing in any suitable fashion and adapted to rest atop :the screens in place of the chains 69, and repeatedly jar the screens during the gyration thereof to vibrate same and prevent blinding. Round bristle brushes may be substituted for the rubber balls 61 where desired. These chains or their equivalents may be adapted for detachable connection to the screener and applied only when these oily materials and those subject to packing are to be handled thereby, if desired.

From the foregoing description, the advantages of my invention are readily apparent. The entire screening mechanism, including the screening box, hopper, discharge spout and frame are compactly united as a high capacity non-blinding unit which may be readily installed in a minimum amount of space close to the source of material to be screened. Because the unit is substantially noiseless and vibrationless, due to the resilient yielding suspension of the screening box from the frame and balanced positive vibrationless gyratory movement thereof provided by the counterbalance eccentric drive shaft, the entire unit may be permitted to rest freely on any suit-able supporting surface without bolting or otherwise permanently securing the unit thereto to enable the entire unit to be readily transported or moved from place to place as desired, which is facilitated by the strong but light weight construction provided. The noiseless vibrationless features are particularly attractive for obvious reasons. The easy-to-operate hold down arrangement for removably clamping the screens in place within the screening box enables the screens to be readily removed and replaced from either end of the box and also enables the screens to be maintained in a perfectly flat condition during use to permit uniform flow of material across the entire width of the screens and to prevent flexing of the screens and lost motion. The operation thereof is simplicity itself, requiring only two adjustments, that of the rate of the feed of the material and the speed of the motor, and maintenance is reduced to a minimum, since only the shaft, belt and four bearings bear watching and periodic maintenance.

The novel, free floating nature of the screen clamping or hold down units, together with the ease with which the screens may be slid into and out of the screening box and the quickly releasable feature of the locking or clamping mechanism are novel features which are not available on prior art devices and materially add to the efficiency, usefulnes s and overall desirability for this type of screening device.

Thus, briefly, the screening machine herein disclosed and described has the following outstanding features which are distinct from and not available on other similar devices. These features are:

(1) The novel screen hold down system and the simple yet eflicient means of operating same;

(2) The shaft counter balancing system employing a cup-shaped fly-wheel with the counterweight disposed in direct radial alignment with the bearing unit and eccentric on the shoe;

(3) The light weight bridge-type construction;

(4) The ability to completely disassemble the machine and completely remove the frame from the screening box to permit the equipment to pass through narrow openings such as doorways and for ease in moving and transportation; and

(5) The non-blinding chains or their equivalents for vibrating the screens while they are being gyrated.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the various parts without departing from the scope of my invention.

What I claim is:

1. In a screening machine, a screening box having a plurality of removable horizontally disposed vertically spaced screens, means for connecting said screens to the sides of said box, means for drawing said screen's towards the sides of said box to stretch said screens and maintain them in a taut condition, and means for supporting the medial portions of said screens to prevent flexing thereof and permit uniform flow of material across substantially the entire width thereof, said means including a longitudinally disposed elongate member having the bottom screen resting thereon, spacing units interposed between adjacent pairs of screens, each unit including elongate longitudinally disposed vertically spaced and interconnected clamping members adapted to engage and press against the opposing sides of said adjacent screens, a hold down unit disposed above the top screen and including an elongated longitudinally disposed clamping member resting on the upper surface of said top screen, all of said members being in substantial vertical alignment with one another from the top to the bottom of said box, and means for applying downward pressure against the hold down unit and its clamping member to press the vertically aligned members together and securely clamp the screens therebetween to prevent flexing thereof during use.

2. The structure set forth in claim 1, including bracing means interconnecting said spacing units and said box and preventing lateral movement of said units.

3. The structure set forth in claim 2, wherein said means for applying pressure against said hold down unit includes lever means pivotally mounted on said box, resilient means interconnecting said lever and said hold down unit, and means for actuating said lever causing said lever to compress said resilient means and apply downward clamping pressure to said hold down unit and said clamping members.

4. The structure set forth in claim 1, including a boxsupporting frame, means yieldingly and resiliently suspending the box from said frame, and means carried by said frame and cooperatively engaged with said box for continuously gyrating said box about a transverse horizontal axis to provide positive balanced gyratory screening movement thereto.

5. In a screening machine, a screening box having a plurality of removable horizontally disposed vertically spaced screens, means for connecting said screens to the sides of said box, means for drawing said screens towards the sides of said box to stretch said screens and maintain them in a taut condition, and means for supporting the medial portion of said screens to prevent flexing thereof and permit uniform flow of material across substantially the entire width thereof, said means including a longitudinally disposed elongate member having the bottom screen resting thereon, spacing units interposed between adjacent pairs of screens, each unit including elongate longitudinally disposed vertically spaced and interconnected clamping members adapted to engage and press against the opposing faces of said adjacent screens, a hold down unit disposed above the top screen and including an elongate longitudinally disposed clamping member resting on the upper surface of said top screen, all of said members being in substantial vertical alignment with one another from the top to the bottom of said box, and means for applying downward pressure against the hold down unit and its clamping member to press the vertically aligned members together and securely, clamp the screens therebetween to prevent flexing thereof during use, said last named means including a generally upwardly extending guide arm carried by said hold down unit, a spring coiled about said arm, the lower end of which is adapted to bear against said hold down unit, a spring-compressing element slidably mounted on said arm and adapted to bear against the upper end of said spring, a bell type lever pivotally mounted on said box, one lever arm of said bell crank being pivotally connected to said spring compressing element to reciprocate the same towards and away from said spring, and toggle means including an operating handle comprising one lever arm of the toggle interconnected with the other lever arm of the bell crank and adapted to actuate same to selectively apply and release downward clamping pressure against the hold down unit through the spring and compressing element cooperatively interconnected therewith.

6. Screening apparatus comprising in combination a screening unit including a screening box, a drive shaft extending transversely of said box and supporting same and freely rotatable relative thereto, eccentric means mounted on said shaft and cooperatively engaged with said box for gyrating said box about the axis of rotation of said shaft in response to the rotation thereof, and structure for supporting said unit comprising integral side frames and cross members extending between and interconnecting said side frames, bearing means carried by each of said side frames for receiving the outer ends of said drive shaft whereby the screening unit is mounted on said supporting structure between the sides thereof, said drive shaft being adapted for ready disengagement from said bearings and the side frames being readily disconnectible from said cross members whereby said side frames and the bearings carried thereby can be quickly detached from supporting engagement with said screening unit to permit transportation of said unit independently of said side frames.

7. A substantially vibrationless screening apparatus comprising in combination a screening unit consisting of a screening box, a plurality of generally horizontally disposed, vertically spaced apart screens mounted within said box, means for drawing the screens towards the sides of said box to stretch said screens and maintain them in taut condition, releasable clamping means adapted to grasp the screens intermediate the sides thereof and pre vent flexing thereof during use, a rotatable shaft extending through said box transversely thereof and freely rotatable relative thereto, eccentric means mounted on said shaft for rotation therewith and cooperatively engaged with said box and gyrating said box about the axis of rotation of said shaft, counterweight means mounted on said shaft in radial alignment with said eccentric and adapted to exert a force equal and directly opposite to that effected by said eccentric to prevent vibration of said shaft, supporting structure for said screening unit including integral side frames, second bearing means carried by said side frames adapted to receive and support the outer ends of said drive shaft on said frames, cross members disposed adjacent the feed and discharge ends of said box and extending between and interconnecting said side frames, spring means resiliently suspending said box from said structure, hopper means mounted on the cross member adjacent the feed end of the box in disconnected flow communication with the feed end of said box, spout means mounted on the cross member adjacent the discharge end of the box in disconnected flow communication with the discharge end thereof, said shaft being quickly disengageable from said second bearing means and said side frames being adapted for quick disengagement from said cross members whereby the side frames and second bearing means can be quickly removed from supporting engagement with said screening unit and whereby said screening unit can be readily transported as an entirety independently of said side frames.

8. In a screening machine including a screening box and a supporting frame for said box, means for gyrating said box including a rotatable shaft carried by said box, bearing means carried by said 'box, and eccentric means cooperatively engaged with said shaft for rotation therewith and rotatable within said bearing means to provide said gy-ratory movement to said box in response to the rotation of said shaft, a cup-shaped fly wheel mounted on said shaft and rotatable therewith, said fly Wheel substantially enclosing said eccentric means, and counterweight means mounted on the peripheral rim of said fly wheel in direct radial alignment with said eccentric means and adapted to exert a force equal and diametrically opposite to that exerted by said eccentric means to eliminate whipping of said shaft.

9. In screening apparatus, a screening box and means for shaking same, said screening box including a plurality of generally horizontally disposed vertically spaced screens, and means for engaging and holding the medial portions of said screens against flexing movement, said last named means including means underlying and supporting a portion of the lowermost of said screens intermediate the sides thereof, spacing means interposed and extending between adjacent pairs of screens and engaging same to maintain them a uniform distance apart, hold down means resting on the top of the uppermost of said screens, said supporting, spacing and hold down means being vertically aligned and adapted to cooperate with each other to sandwich and clamp the screens therebetween and hold them rigid, and means for squeezing said supporting, spacing and hold down means together simultaneously to accomplish the aforementioned clamping of said screens.

10. In screening apparatus including an elongate screening box, a plurality of generally horizontal screen means mounted in said box, and means for gyrating said box about a transverse horizontal axis, means :for releasably anchoring the side marginal edge portions of said screen means to said box, and releasable clamping means anchored to said box, said clamping means including elongate vertically aligned -clamping members disposed longitudinally of said box and adapted to engage opposite sides of the medial portion of said screen means intermediate the marginal edge portions thereof and hold said screen means and prevent flexing thereof during gyration of said box, the opposing clamping members being capable of relative vertical opening and closing movement therebetween for each screen, said clamping means including means to cause simultaneous opening and closing movement of all of said clamping members.

References Cited in the file of this patent UNITED STATES PATENTS 440,301 Boorrnan Nov. 11, 1890 620,048 Oyer Feb. 21, 1899 1,534,416 Schuler Apr. 21, 1925 1,693,940 Robins Apr. 12, 1927 1,713,143 Overstrom May 14, 1929 1,899,209 Petit Feb. 28, 1933 2,004,965 Wetlaufer June 18, 1935 2,053,895 Burmeister Sept. 8, 1936 2,194,721 Piper Mar. 26, 1940 2,238,711 Soldan Apr. 15, 1941 2,246,483 Dillon June 17, 1941 2,358,453 Gilson Sept. 19, 1944 2,477,123 Gil-son July 26, 1949 2,500,965 Symons Mar. 21, 1950 2,787,277 Barry Apr. 21, 1957 2,874,841 Peterson Feb. 24, 1959 2,899,059 Schroth Aug. 11, 1959 2,964,186 Ferara Dec. 13, 1960

Claims (1)

10. IN SCREENING APPARATUS INCLUDING AN ELONGATE SCREENING BOX, A PLURALITY OF GENERALLY HORIZONTAL SCREEN MEANS MOUNTED IN SAID BOX, AND MEANS FOR GYRATING SAID BOX ABOUT A TRANSVERSE HORIZONTAL AXIS, MEANS FOR RELEASABLY ANCHORING THE SIDE MARGINAL EDGE PORTIONS OF SAID SCREEN MEANS TO SAID BOX, AND RELEASABLE CLAMPING MEANS ANCHORED TO SAID BOX, SAID CLAMPING MEANS INCLUDING ELONGATE VERTICALLY ALIGNED CLAMPING MEMBERS DISPOSED LONGITUDINALLY OF SAID BOX AND ADAPTED TO ENGAGE OPPOSITE SIDES OF THE MEDIAL PORTION OF SAID SCREEN MEANS INTEMEDIATE THE MARGINAL EDGE PORTIONS THEREOF AND HOLD SAID SCREEN MEANS AND PREVENT FLEXING THEREOF DURING GYRATION OF SAID BOX, THE OPPOSING CLAMPING MEMBERS BEING CAPABLE OF RELATIVE VERTICAL OPENING AND CLOSING MOVEMENT THEREBETWEEN FOR EACH SCREEN, SAID CLAMPING MEANS INCLUDING MEANS TO CAUSE SIMULTANEOUS OPENING AND CLOSING MOVEMENT OF ALL OF SAID CLAMPING MEMBERS.

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