US3834534A

US3834534A - Variable mode vibratory screen

Info

Publication number: US3834534A
Application number: US00209629A
Authority: US
Inventors: T Peterson; R Crosser
Original assignee: Kennecott Copper Corp
Current assignee: Kennecott Utah Copper LLC; Kennecott Corp
Priority date: 1971-12-20
Filing date: 1971-12-20
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10

Abstract

A variable mode vibratory screen for screening and conveying particulate matter and for varying the mode of vibration during the screening operation preferably includes a frame, screen cloth mounted on the frame, and springing means attached to the frame for resiliently supporting the frame on a load-bearing surface. Means for imparting vibratory motion to the screen is mounted on the frame, preferably on a longitudinal structural member extending the length of the underside of the frame. Control means connected to the vibratory means varies the vibratory mode of the screen during operation. The mode can be varied between high frequency, low amplitude vibration and high amplitude, low frequency vibration to effect optimum screening efficiency and high acceleration of the particulate matter across the surface of the screen. The vibrational modes can be varied, for example, by automatic sequencing through a preselected series of modes, or by a sensing device which senses any lessening of the amplitude of vibration caused by the build-up of particulate matter on the screen and signals a control mechanism to change the vibrational mode.

Description

United States Patent Peterson et al.

[ 1 Sept. 10, 1974 VARIABLE MODE VIBRATORY SCREEN Utah [73] Assignee: Kennecot Copper Corporation, New

York, NY.

[22] Filed: Dec. 20, 1971 21 Appl. No.2 209,629

[52] US. Cl 209/326, 209/365 R, 209/379, 198/220 DD [51] Int. Cl B07b 1/28, 1307b l/42 [58] Field of Search 204/365 R, 365 A, 365 B, 204/367, 326, 325, 329, 368; 74/61; 198/220 DD, 379, 363, 364

585,233 10/1959 Canada ..l98/220DD Primary Examiner-Robert Halper Attorney, Agent, or Firm-Philip A. Mallinckrodt [5 7] ABSTRACT A variable mode vibratory screen for screening and conveying particulate matter and for varying the mode of vibration during the screening operation preferably includes a frame, screen cloth mounted on the frame, and springing means attached to the frame for resiliently supporting the frame on a load-bearing surface. Means for imparting vibratory motion to the screen is mounted on the frame, preferably on a longitudinal structural member extending the length of the underside of the frame. Control means connected to the vibratory means varies the vibratory mode of the screen during operation. The mode can be varied between high frequency, low amplitude vibration and high amplitude, low frequency vibration to effect optimum screening efficiency and high acceleration of the particulate matter across the surface of the screen. The vibrational modes can be varied, for example, by automatic sequencing through a preselected series of modes, or by a sensing device which senses any lessening of the amplitude of vibration caused by the buildup of particulate matter on the screen and signals a control mechanism to change the vibrational mode.

6 Claims, 5 Drawing Figures PAIENIEU SEN 01914 SHEEI 2 (IF 3 IDNVENTORS THOMAS PETERSON PATENTEDSEP 1 01914 SHEEI 3 OF 3 INVENTORS THOMAS D. PETERSON RALPH W. CROSSER, Jr.

VARIABLE MODE VIBRATORY SCREEN BACKGROUND OF THE INVENTION 1. Field This invention relates to vibratory screens for screening particulate materials.

2. State of the Art Vibratory screens have long been used for sizing particulate matter. Such screens commonly have a double function, i.e., passing the smaller particulate matter through the screen apertures and moving the larger particulate matter across the surface of the screen. Maximum screening efficiently is obtained by using a vibrational mode in which the vibration has a high frequency and a low amplitude. In this mode the material tends to remain in place on the screen while the smaller sized particles pass through the screen apertures. However, the screen apertures are also subject to plugging by reason of the larger particles becoming impacted or wedged in the apertures. The low amplitude of the screens vertical vibratory motion is insufficient to eject the wedged particles and efiiciency of the screen becomes severely reduced.

When the vibrational mode is of high amplitude and low frequency, the particulate material on the screen tends to move rapidly across the screen surface rather than to remain in place for efficient screening. This mode, however, has the advantage of forcing impacted particulate material out of the apertures, and thereby cleans the screen in addition to moving the material across the screen.

I-Ieretofore, vibratory screens have generally been constructed to operate in a single vibratory mode located somewhere between the high amplitude, low frequency mode and the high frequency, low amplitude mode. Such an intermediate mode couples reduced screening capability with inefficient movement of material across the screen. These vibratory screens have not been able to achieve either optimum screening efficiency or high acceleration of non-screened material across the screen and, consequently, are less than satisfactory.

Other vibratory screens have been proposed which have the capability of being operated in more than one mode, but the mode can be changed only by manually adjusting the vibrational source after stopping the screen. Such adjustments require major expenditures of time and efiort and still do not overcome the problems inherent in single mode screens.

OBJECTIVES It was an objective in the making of this invention to provide vibratory screen apparatus capable of varying the vibratory modes of the screen during operation in order to effect optimum screening efficiency, high acceleration of material across the screen, and unplugging of screen apertures that may become plugged during the screening operation.

SUMMARY OF THE INVENTION In accordance with the invention, a vibratory screen for screening and conveying particulate matter has controlled vibratory means for varying the mode of vibration of the screen during the screening operation. The screen advantageously comprises a frame with screen cloth mounted thereon and springing means attached to the frame which is adapted to resiliently support the frame and screen cloth on a load-bearing surface. Preferably. the frame is constructed for positioning at an acute angle with the horizontal for facilitating the movement of particulate matter downwardly across the screen. Means for imparting vibratory motion to the screen, for example a pneumatic or hydraulic vibratory motor, is mounted on the frame; Such vibratory means is preferably slideably mounted on a longitudinal support beam secured to the frame and extending from end to end thereof under the screen cloth.

Control means for varying the mode of vibration imparted to the screen during operation is connected to the vibratory motor. The mode can be varied as necessary to achieve the objectives of the invention between a high amplitude, low frequency mode and a high frequency, low amplitude mode. The control means can be automated to provide for automatic sequencing through a pre-selected series of vibrational modes. Alternatively, a sensing device can be attached to the screen to detect any decrease in the motion of the screen caused by overloading or plugging of screen apertures. The sensing device is capable of transmitting a variable signal to the control means which responds by initiating a new mode to correct the condition actuating the sensor.

THE DRAWING The best mode presently contemplated of carrying out the invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a perspective view of the vibratory screen mounted at an angle with the horizontal;

FIG. 2, a side elevational view of the screen;

FIG. 3, a longitudinal vertical section taken along 33 of FIG. 2;

FIG. 4, a similar view taken along line 4-4 of FIG. I; and

FIG. 5, a schematic diagram of a vibratory power source and control system therefor. I

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT As shown in detail in FIGS. 1, 2, and 4, the illustrated vibratory screen has a frame 10, which is of rectangular configuration in this embodiment, but can be of any appropriate shape or form. Frame 10 is constructed of steel box-type beams l1, 12, 13, 14 secured together at the four corners thereof by welding, bolting, or other appropriate means. An elongate steel beam 15 extends from the midpoint of beam 12 to the midpoint of beam 14 and is firmly secured at each end to frame 10 for strengthening the frame.

Frame 10 is disposed at an acute angle with the horizontal, here 45 degrees, for facilitating the flow of particulate material across the screen cloth and into a hopper or receptacle 18 disposed below the lower end of the screen. Particulate material can be prevented from falling off the lateral sides of screen cloth 16 during its journey across the screen by securing

retaining boards

19 and 19a, respectively, to frame sides 11 and 13 so they extend above the upper surface of the screen cloth. Particulate material passing through screen cloth 16 falls into a receptacle 20 disposed beneath the screen. The means 21 for imparting vibratory motion to the screen in this embodiment is a rotatable eccentric and motor drive of conventional type, here indicated generally at 21a, mounted in a housing 22 which is slideably secured to the underside of elongate beam 15 by means of a steel plate 23 bolted to a retainer clip 24 with four adjustable nuts and bolts 25. Although vibratory means 21 may be fixedly attached to frame in any suitable manner, it is preferred to mount such means for sliding along beam so as to be able to adjust its position to any point along the length of such beam. If greater vibrational motion is desired at one end of the screen than at the other, the vibratory means 21 can be secured nearer that end of frame It). For example, if an overload of material occurs at the upper end of the screen, resulting in significant plugging of screen cloth 16, the vibratory means can be moved to such upper end to provide localized intensive vibration. Vibratory drive 21a can be powered by any conventional means, such as compressed air, hydraulic fluid, or electricity.

As shown in FIGS. 1, 2, and 4, frame 10 is resiliently supported by four vertically mounted

coil spring assemblies

26, 27, 28, and 29, with their upper ends respectively mounted at or near the four corners of the frame. The lower ends of

such spring assemblies

26, 27, 28, 29

are secured to a load-bearing surface, which in this embodiment is provided by T-

beams

30, 31 disposed at an acute angle with the horizontal and supported in some suitable manner (not shown).

As depicted in detail in FIG. 3, each spring assembly in this embodiment includes a coil spring 32 secured at its upper end to the underside of an upper mounting block 33 by means of a lower plate 34 positioned below the upper coil 35 of spring 32. Upper coil 35 and block 33 are positioned between lower plate 34 and a corresponding upper plate 36 disposed on the upper surface of block 33. Lower plate 34 and upper plate 36 are secured together by a pair of

bolts

37 and 38. Upper mounting block 33 is secured to frame 10 by a spring housing 39 which is fixedly attached to a side beam of frame 10. The upper surface of mounting block 33 is secured to the interior of spring housing 39 by means of a relatively large bolt 40 having a washer 41 and an adjusting nut 42. Coil spring 32 and mounting block 33 can be conveniently removed from housing 39 by simply loosening nut 42 on bolt 40 and sliding the spring and block out of housing 39.

At the lower end of spring assembly 29, the lower coil 32a of spring 32 is secured to lower mounting block 44 by

bolts

45 and 46, which extend from a securing plate 47 disposed against the upper surface of coil 32a downwardly into block 44. Block 44 is secured at its lower end to the upper surface of mounting box 48 by bolts 49. Mounting box 48 is secured by welding or other appropriate means to the broad upper surface of T-beam 31.

The vibrational mode of vibratory drive 21a can be varied by a control mechanism 50, a specific embodiment of which is illustrated in FIG. 5 utilizing compressed air or hydraulic fluid. The powering medium, for example compressed air, is fed to the vibratory drive 21a through conduit 52. The air exhausts from vibratory drive 21a through line 53, which branches into two or

more conduits

54 and 55.

Conduits

54, 55 lead through

solenoid valves

56 and 57, respectively, to conduits 58 and 59, which are connected in turn to respective conventional

back pressure regulators

60 and 61. These regulators vary the amount of compressed air which is released to the atmosphere, thereby changing the frequency of vibration, or vibratory mode, imparted by vibratory drive.

Other means of controlling the operation of the vibrator, for example valves controlling the amount of compressed air reaching the vibrator or the like, are also employable. Valves S6 and 57 are controlled by a sequence of four electrical timers, Tl, T-2, T-3, and T-4. These timers are, in turn, controlled by selector switches S-1 and 5-2, which may be set so that operation of the

valves

56 and 57 can be manually controlled when desired, although operation of these valves is advantageously controlled by an automated sequencing of preselected vibrational modes.

Switch 5-] is a single pole, three position switch having positions A (Automatic), 0 (Off), and H (Hand, i.e. manual control). Switch 8-2 is a single pole, two position switch connected to control valve 56 from position No. l and connected to control valve 57 from position No. 2, thus providing manual control of these two valves.

Switch S-1 is connected through electrical head 62 to a conventional 110 volt power source. When in its A position providing for automated operation, current flows through line 63 and the normally closed contact 64 of timer T4 to timer Tl, which will start its timing operations. When the time set for timer T--1 has elapsed, which is the amount of time desired for a preselected vibrational mode, contact 65 in timer T-1 closes and power flows through line 66 and the normally closed contact 67 of timer T-2 to line 68. Line 68 is connected to valve 56 and transmits power for opening such valve to begin operation of a second preselected vibrational mode. At the same time, timer T-2 begins operating. When the time set for timer T-2 has elapsed, normally closed contact 67 opens to thereby cause closing of valve 56; also, the normally open contact 69 closes to permit power to flow from line 63 through contact 69 to line 70-. Since line 70 is connected with timer T-3, such timer also begins operating. When the time set for timer T-3 has elapsed, a normally open contact 71 is closed to permit power to flow into line 72 opening valve 57. Power also flows into line 73, which causes timer T-4 to begin operating. When the time set for timer T-4 has elapsed, normally closed contact 64 opens momentarily, thereby interrupting power to all the timer circuits. Valve 57 closes to stop the second vibrational mode, and vibratory drive 210 reverts to the original mode as the sequence begins again. An electrical line 73 connects all timers, valves, and switches to the power source to complete the circuit.

Valves

56 and 57 can be operated in any desired sequence by placing switch 5-1 in the manual position to activate manually operated switch S2. Depending upon whether switch 8-2 is thrown to position No. 1 or position No. 2, it opens either valve 56 or valve 57 through

electrical lines

74 or 75 which connect, respectively, to electrical lines 68 and 72.

Additional valves and pressure regulators or their equivalents can be provided to supply a variety of vibrational modes. Thus, the six fundamental modes and any combination thereof can be provided for so that vibratory modes can be selected enabling the screen to perform precisely as desired with respect to the particulate matter on the screen.

An alternative control system for changing the vibrational modes, employing one or more sensors 76 attached to the screen can be provided in well known manner. Typical placements of a sensor 76 is shown in FIG. 1 on the side of frame 10, but it can be placed on screen cloth 16 if desired. The sensor may be of any suitable type for detecting changes in screen acceleration caused by the presence of excess particulate material on portions of the screen. Upon detecting such a motion change, the sensor sends a variable signal to a control mechanism, such as described and shown in connection with FIG. 5, which responds to the signal by selecting an appropriate vibratory mode to correct the condition, e.g. unplugging the screen and moving the particulate material build-up along the screen. The sensor again detects the change in acceleration of material caused by the removal of the build-up of material, and sends a signal to the control mechanism for a return to the more efficient screening mode.

It is possible simultaneously to vibrate the screen in more than one mode. This can be accomplished by mounting two vibratory means 21 on the support beam 15. One such means may be made to vibrate the screen in its natural frequency, while the other vibrates the screen in a different mode. An application of this dual vibratory system can be used for classifying extremely sticky material, where high frequency vibration of the screen prevents the material from adhering to it while vibration at natural frequency, with its associated high acceleration and displacement, moves the material along the surface.

An advantage of the use of a direct-drive motor, such as has been indicated heretofore, with vibration applied directly to the screen frame lies in the fact that the direct drive incorporates no bolts, gear reductions, cams or other high-wear items. Only the air, hydraulic, electrical or other power source leads need move relative to the screen. There are no belt tensioning problems, no drive alignment problems, nor mechanical wear points.

The sensor 76 for detecting screen acceleration changes may be any conventional sensing device for determining changes in motion. A preferred device for this purpose is an accelerometer, which is readily available commercially from several manufacturers.

Whereas this invention is illustrated and described herein with respect to certain preferred forms, it is to be understood that many variations are possible without departing from the inventive concepts particularly pointed out in the claims.

We claim:

1. Apparatus for screening and conveying particulate matter, comprising a screen cloth; a supporting frame for the screen cloth; an elongate structural member attached to the underside of said frame and extending from end to end thereof; springing means adapted to resiliently support said frame and said screen cloth on a load-bearing surface, for both sizing and conveying purposes; vibratory means slideably mounted on the elongate structural member for imparting vibratory motion to said frame and said screen cloth; and control means for the vibratory means adapted to vary the mode of vibration imparted to said frame and said screen cloth between a high amplitude, low frequency vibration and a high frequency, low amplitude vibration.

2. Apparatus as set forth in claim 1, wherein the vibratory means is mounted on the screen.

3. Apparatus as set forth in claim 1, wherein the springing means comprises a plurality of springs individually mounted on the frame.

4. Apparatus as set forth in claim 1, wherein the vibratory means is driven by compressed air.

5. Apparatus as set forth in claim 1, wherein the vibratory means is driven by hydraulic fluid.

6. Apparatus for screening and conveying particulate matter, comprising a sizing screen; springing means adapted to resiliently support the screen on a loadbearing surface for both sizing and conveying purposes; means for imparting vibratory motion to the screen; and control means for the vibratory means adapted to vary the mode of vibration imparted to the screen between a high amplitude, low frequency vibration and a high-frequency, low amplitude vibration; and sensing means attached to the screen, said sensing means being adapted to actuate the control means for the vibratory means to change the mode of vibration by sensing plugging of the screen apertures by particulate matter on the screen.

Claims

6. Apparatus for screening and conveying particulate matter, comprising a sizing screen; springing means adapted to resiliently support the screen on a load-bearing surface for both sizing and conveying purposes; means for imparting vibratory motion to the screen; and control means for the vibratory means adapted to vary the mode of vibration imparted to the screen between a high amplitude, low frequency vibration and a high-frequency, low amplitude vibration; and sensing means attached to the screen, said sensing means being adapted to actuate the control means for the vibratory means to change the mode of vibration by sensing plugging of the screen apertures by particulate matter on the screen.