US3123552A

US3123552A - Snusber for vibsating screens

Info

Publication number: US3123552A
Authority: US
Publication date: 1964-03-03
Anticipated expiration: 1981-03-03

Description

March 3, 1964 w, ow 3,123,552

I SNUBBER F OR VIBRATING SCREENS Filed March 20. 1961 GJEORG'E Milan 254 INVENTOR.

Arron/viva United States Patent 3,123,552 SNUBEER FQR VKERA'HNG SCREENS George W. Lowry, Pasadena, Calif., assignor to Overstrum & Sons, End, Alhambra, Calif., a corporation of California Filed Mar. 20, 1%1, Ser. No. 96,929 Claims. (ill. 269-326) The present invention relates generally to vibrating screens, and more especially to snubbing devices which limit the movement of the screens when they are vibrated at or near resonant speeds.

The vibrating screen consists generally of a screen box which is resiliently supported by a suitable arrangement of springs upon a stationary base or frame. The box is given a vibrating motion while the base remains stationary. A screen of this character is used to separate dry particles by size, the fine particles generally passing through the screen while the over-size particles are delivered at the discharge end of the screen box. The vibrating motion is very rapid and ordinarily is in a vertical plane. The motion of the screen box is not limited to a reciprocating motion but varies from a circular motion to a more or less elliptical one at different points on the screen box.

When vibrating at normal operating speeds, the movement of the screen box with respect to the stationary frame is relatively limited. While the exact amplitude may be varied or controlled by design to best handle materials of a desired size, the amplitude of motion is normally a small fraction of an inch. The speed of vibration is relatively high, being usually in the range of 1200 to 1800 rpm. As the screen starts and stops its. speed rises from zero to a normal operating, speed within the range just given-and then slowly decreases from the operating speed hack to zero. Within this total range of speeds, the screen box will normally pass through at least one resonant speed or a harmonic thereof. Since a high degree of resonance is obtained at any commonly encountered harmonic above or below the true resonant speed, the term resonant speed as used herein is intended to be broad enough to include such harmonics.

As the screen box is vibrated at a speed which approaches or passes through a resonant speed, the amplitude of motion is very greatly increased and may reach a magntiucle several times greater than the normal amplitude of'movement. This increased amplitude of motion produces a wild, bucking motion of the screen box which is very detrimental to the equipment and can even wreck the screen if sufficiently violent and uncontrolled.

Thus it becomes a general object of my invention to provide snubber means for use with a shaking or vibrating screen which restrains the amplitude of movement of the screen box at vibrational speeds at or near resonant speeds, thus eliminating excessive movement of the screen box.

It is a further object of the invention to provide mean-s for absorbing the energy of the moving screen box when the amplitude of movement of the box is'excessive, but without placing any load upon or otherwise affecting the operation of the screen box at normal operating speeds of vibration;

A further object of the invention is to provide an energy absorbing snubber which may be added to,- or incorporated in the design of, screens already known and which is itself simple in design and reliable in operation.

These objects of my invention are achieved in a vibrating screen having a stationary frame member and a relatively movable member on the screen box by providing snubber means comprising a resilient energy absorber mounted on one of said members and a rigid bumper mounted'on the other of said members. The absorber ice and bumper are spaced apart by a distance greater than the normal relative movement of the absorber and bumper at the usual operating speeds but less than such relative movement at a resonant speed of the screen box. Consequently the snubber means is inoperative at normal operating speeds of the screen but becomes operational at or near resonant speeds when relative motion is greater.

In a preferred form the absorber and bumper have mutually engaging surfaces which are inclined to the direction of motion of the screen box, which is normally in a vertical plane. As a result there is frictional engagement of these two surfaces as they move one over the other. The friction assists in absorbing and wasting the excess energy of the screen box; also a portion of the energy absorbed by the device is used up in deforming the resilient energy absorber. In this Way the energy in the screen box producing an excessive amplitude of movement is absorbed and the movement of the screen box is maintained within desired limits.

How the above objects and advantages of my invention, as well as others not specifically mentioned therein, are attained will be more readily understood by reference to the following description and to the annexed drawing, in which:

FIG. 1 is a side elevation of a typical screen to which the present invention has been app-lied.

FIG. 2 is an end view of the screen of PEG. 1 as viewed from the right thereof.

FIG. 3 is an enlarged fragmentary side elevation showing the snubber and portions of the screen box and stationary frame.

FIG. 4 is an elevation and vertical section of the snubber as viewed from the right in FIG. 3.

FIG. 5 is a view similar to FIG. 4 showing how the parts may be reversed in position.

FIG. 6 is an elevation of a variational form of the invention.

Referring now to the drawing, and more especially to FIGS. 1 and 2 there is shown a vibrating or shaking screen which comprises a stationary base or frame indicated generally at 10. On this frame is mounted the vibrating screen box 12 by means of four spiral springs 14. These springs provide a yielding, resilient support for thescreen box which permits it to move freely, within limits, with respect to the stationary frame 19 on which the screen box is mounted.

Vibratory motion is imparted to the screen box by a pair of unbalanced fiy wheels 15 which are mounted on the ends of a shaft extending transversely across and above the screen box, the shaft being journaled in bearings which are attached to the screen box. The fiy wheels are rotated by means of belt 16 passing over pulley 17 on the end of the rotating shaft.

Materials to be screened are fed to the screen box at the upper end thereof by any suitable means, not illustrated. The lines pass by gravity through the bottom of the screen box and the oversize particles are discharged at the lower end.

The vibrating screen so far described is of a well known type and accordingly it is not considered necessary to describe it in further detail. It will also be understood that the invention is not necessarily limited to the vibrating screen having exactly the features of construction herein illustrated and described since in a broad sense the invention may be applied to any other vibrating screen in which it is desired to control or eliminate excessive amplitude of motion.

Turningnow to FIGS. 3 and 4, there is shown therein a typical embodiment of the snubbing means constituting my invention. On the angle as, which is a part of stationary frame it), there is a mounted angle bracket 21. The angle bracket may be attached to the top face of 3:5 angle 2t) in any suitable way, as by welding, bolts or otherwise. To the inner vertical face of bracket 21 there is attached the energy absorber 22 of my improved snubber, such absorber being attached to the bracket preferably by bolts 25 or other means which permit easy replacement o the energy absorber member. Energy absorber is made of a yielding, resilient material such as rubber or neoprene or the like that is necessarily comparatively firm and hard in order to resist the loads imposed upon it and not to be deformed excessively thereby. The outer surface of the energy absorber indicated at Z-la is arcuate, preferably being semi-cylindrical in shape, for reasons which wi l be explained. In order to allow greater deformation of the energy absorber while maintaining a desired degree of stiffness or hardness and to dissipate internal heat, it is preferably that the absorber be provided with a central opening as at 24.

The other active portion of the snubber is the bumper means which is mounted on th outside face of side plate 25 of screen box 12. The bumper means comprises a backing plate 2. on which is mounted a pair of rigid bumpers 2'7 whic may conveniently be formed by short right angular sections. These angular sections 27 are turned with both legs in contact with backing plate 26 and are attached thereto in a suitable manner, as by welding.

The bumpers 2"? each have an outer face 27a which is inclined with respect to the direction of motion of screen box 12, such motion being in a vertical plane; and these inclined faces are adapted to engage the energy absorber 22 on the outer arcuate surface thereof. Since the two faces 2% alternately engage the energy absorber, they are preferably equally and oppositely inclined with respect to the vertical and are placed on opposite sides of energy absorber so that one of these faces strikes against the arcuate surface of the absorber at the end of the upward and the downward strokes respectively of the screen box.

The surface 21a of the energy absorber is inclined to the direction of relative motion of the screen box, assuming to be vertical in this case, at the area of contact with the rigid bumpers. This is true since the tangent to the absorber surface at the point of initial contact with the bumper is approximately parallel to the contacting surface 27a; and, in any event, when the absorber has been deformed by movement of the bumper, the area on the absorber in contact with the bumper is parallel to and extends over a substantial portion of the area of bumper surface 27a.

The snubbers are preferably applied to the screen in pairs, one snubber of each pair being located at each of two opposite sides of the screen box as may be seen in FIG. 2. FIG. 1 shows two bumpers at one side of the screen box and accordingly there are two others directly opposite on the other side of the screen box, or a total of four. Since the bumpers engage an energy absorber over inclined surfaces, the forces at one bumper have horizontal components which alone would tend to shift the screen box laterally, However, by locating the snubbers one at each of two opposite sides of the screen box the horizontal components of the forces produced by a pair of snubbers are opposite and eutralize each other since they are substantially equal. The result is that there is no lateral movement of the screen box because of the snubbing action and the arrangement provides lateral stability to the screen box during the snubbing periods at or near resonant speeds.

Under normal operating conditions, the normal vertical movement of the screen box 12 may be as small as of an inch or as large as of an inch. The magnitude of this movement is generally determined by the type and size of particles being screened and is relatively content for any given installation. The total amplitude of movement at a normal operating speed is indicated in FIG. 4 as being 2D, D being the relative displacement in either direction of the screen box from the rest position shown in the figure.

The vertical spacing between the absorber 22 and each of the bumpers 2'? is indicated at S. This spacing S is greater than the normal relative displacement D from a rest position of the bumpers and the absorber at ordinary vibrating speeds of the screen. This spacing is related to the dispacement D since we are here concerned p imarily with the movement of the absorber and the bumper towards each other during one-half of each cycle of movement.

The vertical spacing S between the absorber and each bumper may, for example, equal two to three times the relative displacement D of the absorber and bumper from a rest position occurring at normal operating speeds. This spacing insures that the components of the snubber do not come into contact at normal operating speeds but become effective to limit the amplitude of movement shortly after the amplitude begins to lengthen from its normal operating length. This vertical spacing is also sufficient to insure that the bumper means restrains the screen box when it approaches and passes through a resonant speed when if uncontrolled it may have a throw of five or more times the amplitude of ordinary movement.

Control of excess or bucking motion of the screen box at or near a resonant speed is effected by absorbing at the end of each stroke some of the excess energy which produces the greater amplitude of motion. This energy is absorbed in two ways. First, by ordinary deformation of the energy absorber 22 as one of the bumpers 27 strikes against it and deforms it. Second, energy is absorbed by friction created by the bumper surface 27a moving over the arcuate surface 21a of the energy absorber. In both of these cases the energy absorbed appears as heat but is quickly dissipated to the atmosphere, and none of the heat is transferred to springs 14 or other portions of the supporting structure.

FIG. 4- illustrates a preferred embodiment of the snubber in which the resilient energy absorber is mounted on the stationary member 21 of the frame while the two bumpers 27 are mounted on the screen box plate 25. This arrangement is preferred for various reasons; but it is entirely satisfactory to reverse the parts as shown in FIG. 5. When reversed, the energy absorbing member 22 is mounted on the screen box plate 25 while the two bumpers 27 are then mounted on the stationary member 21 constituting part of the frame.

A further variation of the snubber arrangement illustrated in FIG. 4 may be effected as shown in FIG. 6. Instead of using a single energy absorber, satisfactory results may be obtained by using two such resilient absorbers but this arrangement requires only a single bumper. Referring to FIG. 6, it will be seen that a single bumper 30 is mounted upon backing plate 31 which is attached to the side plate 25 of the screen box. As in the earlier arrangement, bumper Elli has a pair of oppositely inclined faces 3th: and 30b against which the resilient energy absorber makes contact.

The resilient energy absorber is now divided in two blocks 33' which are mounted upon an angle 34 supported by bracket 35 on the angle 2th forming a portion of the stationary frame 10. Although the mutually engaging faces of the energy absorber and the bumper in this form of snubber means are planar, they are still inclined to the direction of movement of the screen box and the vertical spacing 5 between them is determined in the same manner as previously described.

From the foregoing description it will be seen that various changes in the detailed design and arrangement of the parts of the snubber means constituting my invention may be made by persons skilled in the art without departing from the spirit and scope of my invention Accordingly it is to be understood that the foregoing description is considered to be illustrative of, rather than limitated upon, the invention as defined by the appended claims.

I claim: 1. In a vibrating screen, the combination comprising: a stationary frame including a frame member; a screen box including a screen box member; resilient means mounting the screen box on the frame for limited relative movement in a first plane and also transversely thereto; drive means vibrating the screen box relative to the frame in said first plane; and snubber means at each of two opposed positions spaced apart transversely of the first plane, each snubber means including a resilient energy absorber on one of said members and rigid bumper means on the other of said members; said absorber and said bumper means comprising a pair of elements mounted on one of said members and a single element mounted on the other of said members at a position between and aligned with the pair of elements in the direction of said relative movement in said plane; the spacing between successive ones of said elements in the direction of the relative movement in said plane being greater than the normal relative movement between said absorber and said bumper means at ordinary operating speeds of the screen box but less than the relative movement between said absorber and said bumper means at a resonant speed of the screen box; each absorber and bumper means having mutually engaging surfaces inclined to the direction of relative movement of the absorber and bumper means whereby engagement of the absorber with the associated bumper means produces a thrust transversely of the plane and the thrusts produced at said two positions are oppositely directed and substantially neutralize one another.

2. In a vibrating screen the combination as in claim 1 in which the absorber is mounted on the frame member and the bumper is on the screen box member.

3. In a vibrating screen, the combination as in claim 1 in which the absorber is on the screen box member and the bumper is on the frame member.

4. In a vibrating screen, the combination as in claim 1 in which the absorber is a body of comparatively stiff rubber having an arcuate external surface, and the bumper has a pair of equally and oppositely inclined surfaces alternately engageable with the arcuate surface of the absorber.

5. In a vibrating screen the combination as in claim 1 in which each snubber comprises a pair of spaced rigid bumpers with oppositely inclined surfaces mounted one at each of opposite sides of the resilient energy absorber.

References Cited in the file of this patent UNITED STATES PATENTS 2,314,505 McIntyre Mar. 23, 1943 2,321,166 Symons June 8, 1943 2,328,378 Dudley Aug. 31, 1943 2,571,784 Tellock Oct. 16, 1951 2,701,061 Kluge Feb. 1, 1955 2,701,727 Linn Feb. 8, 1955 2,761,696 Brown Sept. 4, 1956 2,828,014 Wantling Mar. 25, 1958

Claims

1. IN A VIBRATING SCREEN, THE COMBINATION COMPRISING: A STATIONARY FRAME INCLUDING A FRAME MEMBER; A SCREEN BOX INCLUDING A SCREEN BOX MEMBER; RESILIENT MEANS MOUNTING THE SCREEN BOX ON THE FRAME FOR LIMITED RELATIVE MOVEMENT IN A FIRST PLANE AND ALSO TRANSVERSELY THERETO; DRIVE MEANS VIBRATING THE SCREEN BOX RELATIVE TO THE FRAME IN SAID FIRST PLANE; AND SNUBBER MEANS AT EACH OF TWO OPPOSED POSITIONS SPACED APART TRANSVERSELY OF THE FIRST PLANE, EACH SNUBBER MEANS INCLUDING A RESILIENT ENERGY ABSORBER ON ONE OF SAID MEMBERS AND RIGID BUMBER MEANS ON THE OTHER OF SAID MEMBERS; SAID ABSORBER AND SAID BUMPER MEANS COMPRISING A PAIR OF ELEMENTS MOUNTED ON ONE OF SAID MEMBERS AND A SINGLE ELEMENT MOUNTED ON THE OTHER OF SAID MEMBERS AT A POSITION BETWEEN AND ALIGNED WITH THE PAIR OF ELEMENTS IN THE DIRECTION OF SAID RELATIVE MOVEMENT IN SAID PLANE; THE SPACING BETWEEN SUCCESSIVE ONES OF SAID ELEMENTS IN THE DIRECTION OF THE RELATIVE MOVEMENT IN SAID PLANE BEING GREATER THAN THE NORMAL RELATIVE MOVEMENT BETWEEN SAID ABSORBER AND SAID BUMPER MEANS AT ORDINARY OPERATING SPEEDS OF THE SCREEN BOX BUT LESS THAN THE RELATIVE MOVEMENT SAID ABSORBER AND SAID BUMPER MEANS AT A RESONANT SPEED OF THE SCREEN BOX; EACH ABSORBER AND BUMPER MEANS HAVING MUTUALLY ENGAGING SURFACES INCLINED TO THE DIRECTION OF RELATIVE MOVEMENT OF THE ABSORBER AND BUMPER MEANS WHEREBY ENGAGEMENT OF THE ABSORBER WITH THE ASSOCIATED BUMPER MEANS PRODUCES A THRUST TRANSVERSELY OF THE PLANE AND THE THRUSTS PRODUCED AT SAID TWO POSITIONS ARE OPPOSITELY DIRECTED AND SUBSTANTIALLY NEUTRALIZE ONE ANOTHER.