US3491881A

US3491881A - Vibrating screen

Info

Publication number: US3491881A
Application number: US713532A
Authority: US
Inventors: Clyde W Winquist
Original assignee: Nordberg Manufacturing Co
Current assignee: Nordberg Manufacturing Co
Priority date: 1968-03-15
Filing date: 1968-03-15
Publication date: 1970-01-27
Anticipated expiration: 1987-01-27

Description

C. w. WINQUIST VIBRATING SCREEN Jan. 27, 1970 6 Sheets-Sheet l Filed March l5, 1968 Jan. 27, 197i) c. w. wlNQulsT 3,491,881

' VIBRATING SCREEN Y Filed March l5, 1968 6 Sheets-Sheet 2 l Jian/yf.

Jan. 27, 1970 c.`w. wlNQulsT 3,491,881

VIBRATING SCREEN 6 Sheets-Sheet 5 Filed March l5, 1968 C. W. WINQUIST VIBRATING SCREEN 6- Sheets-Sheet 5 ".Lm.27,1970 i .jwws'nNQuls-fr 3,491,831

VIBRATING SCREEN Filed Marchas, 1968 e sheets-sheet e United States Patent O 3,491,881 VIBRAIING SCREEN Clyde W. Winquist, New Berlin, Wis., assignor to Nordberg Manufacturing Company, Milwaukee, Wis., a corporation of Wisconsin Filed Mar. 15, 1968, Ser. No. 713,532 Int. Cl. B07b 1/30 U.S. Cl. 209-326 7 Claims ABSTRACT OF THE DISCLOSURE A vibrating screen for classifying materials according to size and having a vibrator frame, base or overhead structure for yieldingly supporting the vibrator frame, a vibrator assembly, drive means for the vibrator assembly, and one or more inclined screen decks formed in part by a plurality of unitized support trays. A circulating oil lubrication system for the vibrator assembly bearings is provided.

Summary of the invention This invention relates to vibrating screens and more particularly to an improved vibrating screen for classifying materials according to size.

One object of this invention is an improved vibrating screen having a vibrator frame, a vibrator assembly supported by the vibrator frame, support means for yieldingly supporting the vibrator frame, means for driving the vibrator assembly, and at least one inclined screen deck.

Another object of this invention is to provide a vibrating screen as above in which each screen deck is formed by a plurality of easily removable and replaceable unitized support trays.

Another object is a vibrating screen having a base frame or overhead suspension means.

Another object of this invention is a bearing oil lubrication system which prohibits oil from entering the counterweight portion of the shaft casing and insures an axial ow of oil through each bearing.

Another object of this invention is a vibrator having a counterweight shaft adapted to removably receive a varying number of substantially similar counterweights to enable the amplitude of the circular throw of the vibrating screen to be readily varied.

Another object of this invention is a vibrating screen structure that enables economical manufacture of a wide variety of vibrating screen sizes having a variety of circular throw amplitudes and screen deck inclinations.

Other objects and advantages of the invention will become apparent upon reading the following description of the invention.

Brief description of the drawings The invention is illustrated more or less diagrammatically in the accompanying drawings wherein:

FIGURE 1 is the side elevational view showing one embodiment of the improved vibrating screen of this invention;

FIGURE 2 is a top plan view of the vibrating screen of FIGURE l with portions cut away;

FIGURE 3 is a partial cross-sectional View to an enlarged scale taken along line 3-3 of FIGURE 1;

FIGURE 4 is a partial cross-sectional view to an enlarged scale taken along line 4-4 of FIGURE 2;

FIGURE 5 is an end view of the counterweight sheave mounting eccentric brushing;

3,491,881 Patented Jan. 27, 1970 ICC FIGURE 6 is a cross-sectional view taken along line 6*6 of FIGURE 5;

FIGURE 7 is a top plan view of a typical screen deck used in the improved vibrating screen of FIGURE 1;

FIGURE 8 is a cross-sectional view taken along line 8 8 of FIGURE 7;

FIGURE 9 shows a partial side elevational view of another embodiment of the vibrating screen of this invention;

FIGURE 10 is a cross-sectional view to an enlarged scale taken along line 10-10 of FIGURE 9;

FIGURE 11 is an enlarged partial cross-sectional view similar to FIGURE 3 showing still another variation for this invention.

Description of the preferred embodiments Like reference numerals will be used to refer to like parts throughout the following description of the drawmgs.

Referring now to FIGURES 1 and 2, one embodiment of the vibrating screen of this invention has been shown at 10 as including a suitable base frame 12, a vibrator frame assembly 14, vibrator frame suspension means 16, means 18 for inducing generally circular oscillatory motion to the vibrator frame 14, a top screening deck 20, a middle screening deck 22, and a bottom screening deck 24.

The base frame 12 comprises two spaced, parallel ground-engaging Ibeams 26 having respectively an infeed base pedestal 28 extending vertically therefrom at a point adjacent one end and a discharge end base pedestal 30 extending vertically therefrom at a point adjacent the other end. The

base pedestals

28 and 30 are preferably removably secured to the ground engaging members 26 by suitable fasteners. Suitable feed-end cross ties 32, a.

discharge end cross tie 34, and base support angles 36 may be employed to enhance the rigidity of the base frame 12. Like the

pedestals

28 and 30, it is preferred that the feed-end cross ties 32, the discharge end cross tie 34, and the base support angles 36 be removably secured in position using suitable fasteners.

The vibrator frame assembly 14 has been shown as comprising a pair of spaced parallel side plates 38 secured together by suitable transverse structural members such as feed-end beams 40, discharge spouts 42 and suitable tubular members 44. Each tubular member 44 has ends 46 and 47 projecting outwardly through each side plate 38.

As best shown in FIGURES 1 and 3, the vibrator frame suspension means 16 includes four vertically extending helical compression springs 48. Each spring 48 is mounted respectively atop one of the

pedestals

28, 30 by telescoping its lower end over a suitable tubular guide sleeve 49 extending vertically from each pedestal. A bracket 50, adapted to be secured to one of the projecting ends 46, 47 of the tubular members 44, is suitably mounted atop each spring 48. In this instance, the bracket S0 is formed as a split collar 51 adapted to receive and clamp around the projecting ends 46, 47 of tubular members 44. The collar 51 is mounted upon a plate 52 which rests on the spring 48 and carries a tubular sleeve 53 which telescopes Within the upper end of spring 48.

The means 18 for inducing generally circular oscillatory motion to the vibrating frame comprise a vibrator 54 and drive means 56.

As best shown in FIGURES 2 and 4, the vibrator 54 includes a counterweight or eccentric shaft 57 extending transversely between the side plates 38 and suitably supported by bearings 58 adjacent each end. Since both ends of the vibrator assembly 54 are identical, only one end has been shown in FIGURE 4 and will be hereinafter described. The counterweight shaft 57 is housed within a casing 60 having a flanged portion 62 at each end which terminates in a radial flange 64 and an axially disposed annular boss 66. As shown in FIGURE 4, the casing 60 is mounted transversely between the side plates 38 with the annular boss 66 piloted within an aperture 65 formed in the side plate 38 and the radial flange 64 abutting the inner surface of side plate 38. Each bearing 58 is suitably retained within an annular bearing housing 68 which telescopes within the flanged portion 62 of casing 60 and has a radially extending flanged portion 70. A side plate shim 72 formed with an aperture 74 adapted to allow passage of the bearing housing 68 therethrough is positioned between the side plate 38 and the flange 70 of the bearing housing 68. The side plate shim 72 may vary in size and thickness depending on the use of the vibrator and the thickness of the side plate 38 and, as best shown in FIG- URE l, it is suitably secured to the side plate by a plurality of fasteners 76. The bearing housing 68 and shaft casing 60 are secured to the side plate 38 and side plate shim 72 combination by pulling up the flanges 64 and 70 therearound using a plurality of bearing bolts 78 as shown in FIGURE 4. The bearings 58 and counterweight shaft 57 are secured against axial displacement in a conventional manner using a suitable threaded member 80 pulled up against the inner race of the bearing 58. An annular bearing closure member 82 is secured to the bearing housing 68 and a suitable rotating bearing seal member 84 carried by the counterweight shaft 57 may be employed to seal each bearing 58.

Further sealing may be effected by providing an O-ring 86 between the end of the shaft casing and the bearing housing and an O-ring 88 to prevent leakage along the counterweight shaft 57.

As best shown in FIGURE 2, the counterweight shaft 57 is adapted to mount five counterweights 89. Each counterweight 89 is formed with a central channel 90 adapted to receive the counterweight shaft 57 therein. -Each counterweight 89 is formed with two radially extending apertures 92 and is attached to the counterweight shaft 57 by suitable fasteners 94 extending therethrough. Although five counterweights 89 have been shown, it should be understood that any number of counterweights may be used so long as they are symmetrically applied about the longitudinal centerline of the screen.

Attached to each end of the counterweight shaft 57 is a suitable sheave 96 and bushing 98.

The sheaves 96 are adapted to receive sheave counterweights 102 in varying numbers as shown in FIGURES 1 and 4. As will be understood by those skilled in the art, the circular throw of the vibrator screen is determined, in part, by the amount of weight positioned eccentrically to the rotating counterweight shaft 57 and, accordingly, by varying the arrangement and number of counterweights 89 and the number and arrangement of sheave counterweights 102, the circular throw of the improved vibrator screen of this invention may be varied. In addition, it should be pointed out that the shaft 57 may be any crosssectional shape such as square or round with the counterweights 89 adapted to be secured to the shaft.

The eccentric bushing 98 is best shown in FIGURES 5 and 6 as having a cylindrical bore 104 and a tapered or truncated conical outer axial surface 106 formed eccentrically to the cylindrical bore 104. As will be hereinafter understood, the amount of eccentricity between

surface

104 and 106 is selected such that when the sheave 96 is mounted as shown in FIGURE 4, and shaft 57 is rotated, causing a circular displacement of the vibrator frame assembly 14, the sheave 96 will appear to be rotating about a stationary axis.

The eccentric bushing 98 is formed with a radial flange 108, an axial keyway slot 110, and is split as at 112. The

sheave 96 is formed with a tapered mounting bore 113 and an axial keyway slot 114 adapted to receive respectively the bushing 98 and a-key 115. The key 115 extends into the shaft 57 to rotationally secure the sheave 96 and bushing 9S to the shaft 57. In order to axially retain the sheave 96 and bushing 98 on the shaft 57, the flange 108 is urged toward the hub of the sheave 96 using suitable bolts 116 thereby camming the split bushing 98 into tight gripping engagement with the end of counterweight shaft As best shown in FIGURE 4, the shaft casing includes a radially inwardly projecting flange 118 to which a suitable annular sealing element 119 is secured. Each flange 118 and sealing element 119 is positioned so as to form a chamber 120 enclosing the counterweights 89. The sealing elements 119 are adapted to substantially prevent lubrieating oil from entering the counterweight chamber 120.

An oil reservoir chamber 121 is formed below the shaft casing 60 by suitable side and tbottom closure members 122 and 123 respectively. As shown in FIGURE 4, the oil reservo-ir chamber 121 extends between the flanged portions 62 of the casing 60.

A crescent or otherwise suitably shaped member 124 is secured to the bearing housing 68 in a position forming a well 126 between the sealing element 119 and the bearing housing 68.

The oil reservoir 121 communicates with the well 126 through a passage formed in the casing 60. The outboard side of each bearing 58 communicates with the oil reservoir 121 through a radial passage 127 and an axial passage 128 formed in the bearing closure member 82; an axial passage 130, and a radial passage 132 formed in the bearing housing y68; passages 134 and 136 formed in the flanged portion 62 of shaft casing 60; and a tube or pip-e 138 communicating with passage 136 and extending to a point just short of the longitudinal axis of the vibrating screen. The tube 138 may be suitably supported at its outward end by a clamp 140.

As shown in FIGURE 4, oil is added until the level of oil in well 126 is slightly below the upper edge of dam 124 and slightly above the upper end of radial passage 127. The height of the dam 124 may be varied to regulate the amount of oil required in each bearing 58.

In order to effect a positive axial flow of oil axially outwardly through each bearing 58, an oil flinger 142 is secured to the shaft 57 so as to extend into the well 126. The flinger 142 is formed as a radially extending disk having a peripheral rim or turned-up flange 144 extending toward its respective bearing 58. As the counterweight shaft 57 is rotated, the oil flinger 142 gathers oil from well 126 and throws it radially outwardly where the rim 144 directs or deflects it toward the bearing 58 and bearing housing 68. The oil then gravity flows into the bearing 58 thereby creating an axial flow of oil through the bearing 58.

In addition, it should be pointed out that the lubrication system is designed to be interchangeable between oil and grease. When the system is altered for lubrication by grease dam 124 may be raised to engage shaft 57 forming an annular seal to prevent grease from transferring to the counterweights 89. As shown in FIGURE 4, lubrication grease may be added to the system through ports 129 and 131 sealed respectively by

plugs

133 and 135.

The vibrator drive means 56 is best shown in FIG- URES l and 2 as comprising a drive motor 150 suitably secured to a motor base plate 152 having one side hingeably or pivotably connected as at 154 to a suitable motor base frame 156. The motor base frame is suitably secured to the Ibeam 26 or any other suitable supporting structure such as building beams or a concrete pier by a suitable bracket 157. A drive sheave 158y is placed in driving connection with the drive motor and one or more suitable drive belts 160 are placed in driving connection between the counterweight shaft sheave 96 and the drive sheave 158 thereby forming a driving connection between the motor 150 and the counterweight shaft 57.

The drive belts 160 are tensioned by a spring 162 telescoped or threaded on an eye bolt 164 having its lower end pivotably attached to the base frame 156 as at 166. The motor base plate 152 is formed with an angled platform 168 having an aperture therethrough adapted to receive the eye bolt 164. The spring 162 is then positioned between the platform 168 and suitable fasteners 170 at the free end of eye bolt 164.

Although the improved vibrator screen of the invention has been shown as having three screening decks 20, 22 and 24, it should be understood that more or less than three decks may be used. A typical screening deck has been shown in FIGURES 7 and 8 as comprising a plurality of unitized support trays 172 abutted end to end and a woven wire screen cloth 174 stretched over the support trays by suitable tension plates 176. The relatively short tension plates 1716 provide a more uniform tensioning than would be possible with the use of one or two longer plates.

As shown in FIGURE 8, the tension plates 176 are bolted through the side plates 38 by fasteners 178 which provide for quick cloth changing. A special hardened carriage bolt may be used as the fastener with an extra length nut 182 to hold the cloth in adequate tension and to facilitate wrenching for quicker cloth change. The bolt sleeves 180 may be made from ductile iron and nest in holes in the side plates 38 to provide pivots for tensioning over a wide range of cloth wire diameter without distorting the tension bolts. In addition a clamp strip 184 may be used to clamp the woven wire screen cloth 174 to the support trays along the longitudinal axis of the vibrator screen.

Each support tray 172 is formed using two spaced generally parallel cross or transverse channels 190 secured as by welding at their ends by two spaced, generally parallel side channels 192. Transverse rib members 194 are suitably secured as by 'welding between the side channels 192 at points intermediate the cross channels 190. A plurality of support bars 196 and a central tubular member 197 are suitably secured as by welding between cross channels 190 to form a grid-like structure as shown in FIGURES 7 and 8. The upper edge of the support bars 196 extend above the upper edge of the rib members 194 and cross channels 190. Suitable buffer strips 198 adapted to have the woven wire screen cloth 174 stretched taut thereover extend along and are suitably secured to the upper edge of the support bars 196.

Each support tray 172 is secured between the side plates 38 by suitable fasteners 200 which engage the side channels 192. Shims 202 may be provided between the side channels 192 and the side plates 38 if required.

As best shown in FIGURES 1 and 3, each

base pedestal

28, 30 is formed using an I-beam having side flanges 210 connected by a central web 212. Adjacent the upper end of each pedestal a friction check support plate 214 is Welded or otherwise suitably secured between the flanges 210. A tubular sleeve 216 is welded or otherwise suitably secured between the web 212 and the support plate 214 in a position in which the central axis of the sleeve 216 is generally perpendicular to the side plate 38.

A friction check block 218 having a portion 220 adapted to frictionally engage the side plate 38 and a backer plate 222 having a tubular sleeve 224 extending axially therefrom is positioned with the sleeve 216. The brake material 220 is preferably an asbestos fabric having a static coefficient of friction not less than 0.4 on painted steel under a load of 1,400 pounds. It should be understood, however, that other suitable materials may be used. Each friction check block 218 is yieldingly urged against one of the side plates 38 by a spring 226 housed within the sleeve 216 and compressed s0 as to apply the proper loading against the side plate 38 by a friction check cover plate 228 having a tubular sleeve 230 extending within the spring 226. The friction check cover 228 is secured to the web 212 of each

pedestal

28, 30 by suitable fasteners 232. It should be noted that by varying the amount by which the friction check cover 228 is pulled up by fasteners 232, the force of frictional engagement of the brake material 220 against the side plate 38 may be varied.

Referring now to FIGURES 9 and l0, a further embodiment of the improved vibrating screen of this invention has been shown in which overhead suspension means as at 240 are employed in place of the base frame 12. A wire rope 242 is secured to a plate 244 which rests atop a suitable compression spring 246. The lower end of each spring 246 is supported by any suitable stationary structure. Ihe lower end of each wire rope 242 is formed into a loop 248 in any suitable manner as by using clamps 250. An annular thimble 251 having an arcuate peripheral groove 252 is suitably secured to each projecting end 46 of the tubular members 44. Each wire rope loop 248 is positioned around one thimble 251, as shown in FIGURES 9 and 10, with the rope engaging the arcuate groove 252.

When using the overhead suspension means 240, it is preferred that belt drive tensioning means shown generally at 253 be utilized to insure that thedrive belts are properly tensioned. As shown in FIGURE 9, the belt drive tensioning means 253 includes a horizontally disposed tension spring 254 secured at one end 256 to the vibrator frame 14 and at the other end 258 to any suitable stationary structure.

FIGURE l1 discloses additional variations in interchangeable parts for this invention. For instance, this ligure shows another means for suspending the vibrator frame including four vertically supported airmounts 320. Each airmount is located respectively atop one of the

pedestals

28, 30 which as shown and previously described may vary in size and/or height. A bracket 50 adapted to be secured to one of the projecting ends 46, 47 of the tubular members 44 is suitably mounted atop each airmount 320. In this instance, the bracket 50 is formed as a split collar 51 similar to the collar shown in FIGURE 3. The collar 51 is mounted upon a plate 322 which rests on the airmount 320 and the airmount is secured to the pedestal 30 by appropriate fasteners shown at 324.

`In addition airmounts 330 may be employed to yieldingly urge the friction check blocks 318 against the side plates 38. As shown in FIGURE 11 the airmount 330 is housed within a sleeve 332 and compressed so as to apply the proper loading against the side plate 38 by a friction check cover plate 334. The friction check cover plate 334 is preferably secured to the pedestal 30 as by welding. Suitable fasteners 336 secure the airmount 330 to the cover plate 334 and an air valve shown at 338 releases air from the airmount 330.

FIGURE ll also shows another form for attaching the projecting ends 46, 47 of tubular members 44 to the side plates 38. In FIGURE l1 the projecting end 46 is secured to the side plate by the bolted assembly 340. An inner ring 342 is welded to the tubular member 44 while a split outer ring 344 is clamped to the tubular member by bolts 346. A plurality of bolts 348 extending substantially parallel with the tubular member 44 may be employed to secure the inner and outer -rings to the side plate 38.

The use, operation andfunction of the improved vibrating screen of this invention are as follows:

The material to be screened is delivered to the elevated feed end of the top screen deck 20, flows down the top screen deck, and is discharged from spout 42. As the material flows from the feed end to the discharge end, particles smaller than the openings in the top deck screen cloth 174 pass through to the middle screen deck 22. In the same manner, particles smaller than the openings in the middle deck 22 pass through to the bottom deck 24, all other particles being discharged from the middle screen deck spout 42.

The vibrator assembly S4 and drive means 56 cause the vibrator frame assembly 14 and hence the decks 20, 22, and 24 to move in a generally circular vibratory or oscillatory motion which hastens the screening process. The amplitude of this circular vibratory or oscillatory motion may be readily varied by changing the number and arrangement of counterweights 89 and 102.

Each screen deck 20, 22 and 24 is formed in part by a plurality of support trays 172 which are sized so that they may be easily manipulated. Accordingly, should a support tray 172 become damaged or worn, it may be readily replaced without disturbing the surrounding structure. Further, such construction facilitates the economic manufacture of various sized vibratory screens.

The vibrator assembly may be provided with either an oil or grease lubrication system. In an oil lubrication system a positive flow of oil is established axially outwardly through each shaft bearing 58. Oil in well 126 is collected by the finger 142 as it passes therethrough. The oil is then thrown onto the bearing 58 and bearing housing 68 and runs into bearing 58 axially outwardly of darn member 124, thereby creating a pressure head relative to the oil level in well 126. Accordingly, oil flows axially outwardly through each bearing 58, through passages 127, 128, 130, 132, 134, and 136, through tube 138, into reservoir 121, and is returned to well 126 through passage 125.

It has been found that if the counterweights 89 move through the lubricating oil, the oil may become excessively heated. Accordingly, sealing members 119 are provided to form a generally oil-tight counterweight chamber 120.

The shims 72 may be utilized to provide a thickened bearing wall for vibrator assembly mounting fasteners 78 while enabling the use of relatively thin side plates 38.

Each counterweight shaft sheave 96 is secured to one end of the counterweight shaft 57 by an eccentric bushing 98, key 115, and fasteners 116. The eccentric bushing is adapted to mount the counterweight shaft sheave 96 such that it will appear to be rotating about a stationary axis thereby enabling the vibrator assembly to be driven by a generally stationary drive motor 150.

The construction of the vibrator frame is such that it may be supported by the projecting tube ends 46, 47 using either the base frame 12 or the overhead suspension means 240. The base frame 12 is of a non-welded, bolted construction which enables it to be easily varied. For example to change the inclination of the frame 14 and screen decks 20, 22, and 24, variously

sized pedestals

28, 30 may be used.

I claim:

1. A vibratory screen adapted to classify materials by size, said screen including, in combination:

a vibratory frame comprising spaced generally parallel side plates, structural members extending between said side plates, and two spaced parallel tubes extending transversely between said side plates and projecting outwardly therefrom;

means for inducing generally circular oscillatory motion to said vibratory frame, said means including, a counterweight shaft adapted for rotation and having at least one counterweight eccentrically secured thereto and drive means for rotatably driving said counterweight shaft;

a tubular casing extending between said side plates and enclosing said counterweight shaft, each end of said casing terminating in an axially disposed annular boss and a radial flange, said tubular casing having said radial anges respectively abutting said side plates and said axial bosses respectively piloted within apertures formed in said side plates, closure means carried by said tubular casing forming a counterweight chamber therein enclosing said counterweights and adapted to prevent lubricating oil from entering said chamber;

an annular bearing housing telescoped within each end of said tubular casing;

a lbearing within each said bearing housing rotatably supporting said counterweight shaft;

means forming an oil reservoir chamber underlying said shaft casing;

conduit means communicating each side of each said bearing with said reservoir; and

means carried by said counterweight shaft adjacent each end thereof for establishing an axial flow of oil through each said bearing;

at least one screen deck extending between said side plates, each said screen deck forming a plurality of support trays including a cover screen cloth stretched over and supported by said tray; and

means for yieldably supporting said vibratory frame by said projecting tube ends in a position in which each said screen deck is inclined.

2. The vibratory screen of claim 1 further characterized in that said means for establishing an axial flow of oil through said bearings comprise a radial disc terminating in a peripheral rim extending toward its respective bearing, each said disc being axially closely spaced from its respective bearing and secured to said counterweight shaft for rotation therewith.

3. The vibratory screen of claim 1 further characterized in that each said counterweight is substantially identical and is adapted to be removably secured to said counterweight shaft in varying numbers to thereby readily enable the circular throw of the vibratory screen to be varied.

4. The vibratory screen of claim 1 further characterized in that said means for yieldably supporting said vibratory frame comprises a base frame including: generally parallel, horizontally extending, spaced members; two vertically extending pedestals removably secured to each said horizontal member; a helical compression spring extending vertically from each said pedestal; means supported by each said vertical spring for attachment to one of said projecting tube ends; and cross-tie members removably secured between said horizontal members and respective ones of said pedestals to thereby form a readily variable unitary supporting structure.

5. The vibratory screen of claim 4 further characterized by and including dampening means comprising at least one friction check assembly carried by one pedestal, each said friction check assembly including a friction check block formed of heat resistant brake material, yielding means adapted to urge said friction check block into en- 50 gagement with one of said side plates and means to vary the urging force of said yielding means.

6. The vibratory screen of claim 1 further characterized in that said means for yieldingly supporting said vibratory frame comprises:

an annular thimble secured around each said projecting tube end, each said thimble having an arcuate peripheral groove formed therearound. and

a rope for each said projecting tube end, each said rope being yieldingly suspended from overhead supporting structure, a loop formed adjacent the lower end of each said rope, with each said loop supportingly engaging one of said thimble peripheral grooves.

7. The vibratory screen of claim 1 further characterized in that said drive means for said counterweight shaft comprises:

a drive motor, a drive sheave adapted to be driven by said motor, a counterweight shaft sheave, means for mounting said counterweight shaft sheave on said counterweight shaft so that the central axis of said counterweight shaft sheave and the rotational axis of said counterweight shaft are displaced by an amount generally equal to the radial throw of said vibratory screen and so that said counterweight shaft sheave central axis remains generally fixed in position relative to said drive sheave, and

drive connection means between said drive sheave and said counterweight shaft sheave.

References Cited UNITED STATES PATENTS Robins 209-326 Burmeister 209-415 X Lincoln 74-61 De Kanski.

Parks 209-326 Rhoads 184-11 10 2,599,496 6/ 1952 Soldan 209-366.5 X 2,728,614 12/1955 Rink 2019-367 X 2,828,014 3/1958 Wantling 209-326 2,316,725 4/ 1943 Symons 209-329 5 FOREIGN PATENTS 62,629 3/ 1949 Netherlands.

HARRY B. THORNTON, Primary Examiner 10 R. HALPER, Assistant Examiner U.S. Cl. X.R.