US2372791A - Screen - Google Patents

Description

A. L. MUNRO April 3, 1945.

S GREEN Filed Jan. 10, 1944 3 Sheets-Sheet l INVENTOR. 7 A 7" ro/eA/z's d A. L. MUNRO April 3, 1945.

SCREEN Filed Jan. 10, 1944 3 Sheets-Sheet 2 Egg==========Q April 3, 1945. L MUNRO 2,372,791

SCREEN Filed Jan. 10, 1944 3 Sheets-Sheet 3 IN V EN TOR.

I Patented Apr. 3, 1945 SCREEN Alexander L. Munro, Milwaukee, Wis., assignor to Smith Engineering Works, Milwaukee, Wis., a corporation of Wisconsin Application January 10, 1944, Serial No. 517,664

6 Claims.

This invention relates generally to improvements in the art of imparting motion to vibratory bodies, and relates more specifically to improvements in the construction and operation of mechanisms for eifecting smooth starting and stopping of gyratory and reciprocable screens or the like.

The principal object of my present invention is to provide new and useful mechanism for imparting gradually increasing and diminishing steady vibration to and from movably suspended bodies such as separating screens, without undesirable shock or other disturbance.

In prior vibratory screens of the type wherein a screening unit comprising one or more screen decks is resiliently mounted upon a support and is vibratedzby means of one or more revolving unbalanced weigh-ts carried by a rapidly rotating shaft disposed transversely of the unit, considerable difficultyl 1 as been encountered whenever the speed ofihe shaft was caused to pass through the .critical vibrating frequency of.-the loaded resilient supports during starting and stopping of the screens. As the shaft speed approaches and passes through this critical vibration frequency of the resilient supports, violent oscillation and bouncing of the screening unit often results, and these disturbances may be so violent as to seriously damage the supporting structure. The annoyance has been found to exist in screens wherein the vibrating or gyrating mechanism is carried solely by the vibratory unit, and also in screens of the type having fixed bearings for the weight supporting shaft; and is also encountered when utilizing springs, rubber blocks, or other types of supports having critical vibratory frequencies. I have discovered that the annoying disturbances can be eliminated by causing the weights which normally vibrate or gyrate the screen unit, to assume an approximately balanced position until after the supporting shaft speed has passed through the critical vibrating frequency of the resilient supports, and by preventing these weights from assuming normally unbalanced condition until after the danger zone has been passed during starting and stopping.

It is therefore a more specific object of the present invention to provide improved instrumentalities for most effectively eliminating such undesirable disturbances when stopping and starting rapidly gyrating or vibrating freely movably suspended bodies such as reciprocating screens or the like.

Another specific object of my invention is to provide-simple and automatically functioning mechanism for effecting smooth and rapid acceleration and deceleration of a gyrating unit for vibratory screen bodies or the like, which are normally operable at relatively high speed.

A further specific object of this invention is to provide an improved high speed vibrating unit for reciprocating separating screens, wherein revolving eccentric weights are movably suspended so as to vary the effects of centrifugal force resulting from revolution thereof at different speeds, in order to control the degree of vibration of the screens with which the weights cooperate.

Still another specific object of the invention is to provide an improved gyrating assemblage adapted for direct mounting upon a movable body such as a vibratory screen normally operable at high speed, and which will permit smooth starting and stopping of the screen in a safe and most efficient manner.

An additional specific object of my invention is to provide a simple and durable separating screen for mixed granular materials, which may be manufactured at moderate cost and which may also be utilized for diverse purposes without undesirably aifecting the screen supporting structure.

These and other specific objects and advantages of the invention will be clearly apparent from the following detailed description.

A clear conception of typical embodiments of the invention, and of the construction and operation of a separating screen built in accordance with the improvement, may be had by referring to the drawings accompanying and forming a part of this specification wherein like reference characters designate the same or similar parts in the various views.

Fig. 1 is a top view of a typical vibratory screen assemblage embodying the improvement, and adapted to be driven by an electric motor through a flexible endless belt drive;

Fig. 2 is a, side elevation of the screen assembly shown in Fig. 1;

Fig. 3 is an end elevation of the screen assemblage of Figs. 1 and 2 looking toward the lower discharge ends of the screen decks;

Fig. 4 is an opposite end elevation of the same typical double deck screen assembly;

Fig. 5 is an enlarged side elevation of one type of movable weight assemblage showing the two weights thereof in neutral position in solid and dotted lines, and in unbalanced active position in dot-and-dash lines;

Fig. 6 is a similarly enlarged fragmentary central vertical section through the assemblage of Fig. 5, taken along the line 66;

Fig. 'l is a likewise enlarged central horizontal section through the same assemblage, taken along the line (-1;

Fig. 8 is a similar side elevation of another type of movable weight assembly, showing the weights in neutral position in solid lines, and in active position in dot-and-dash lines;

Fig, 9 is a central vertical section through the assemblage of Fig. 8; and

Fig. 10 is a transverse section through the same assemblage, taken along the line ill-l of Fig. 8.

While the invention has been shown and described herein as having been applied to a double deck electric motor driven gyratory or vibratory screening system, it is not my desire or intention to thereby unnecessarily limit or restrict the utility or field of application of the several improved features, and some of the improved details of vibratory screen structure shown and described but not claimed herein, constitute no part of my present invention.

Referring generally to Figs. 1 to 4 inclusive, the improved gyratory screen assembly shown therein, comprises in general a freely movably supported body consisting of an approximately rectangular main frame 9 and a pair of superimposed inclined coarse and fine screen decks III, II respectively secured thereto; a fixed approximately rectangular supporting frame or member i2 upon which the main frame 9 is movably suspended by means of two widely separated resilient members or springs i3 at the feed end and a pair of closely adjacent resilient members or springs ll at the discharge end, which cooperate to provide a resilient three point suspension for the movable body; a sturdy transverse shaft l5 jour nailed for rotation in bearings i1 secured to the opposite side walls of the main frame 3 and bein carried solely by the movable body; a weighted rotor l6 attached to each end portion of the shaft l5 adjacent to a bearing l'l; an electric motor I! mounted upon the fixed frame member l2 above the screen decks l0, II; and a multiple V-belt drive for the gyrating unit, consisting of a driving pulley I9 secured to the motor shaft 20, a driven pulley 2| secured to the gyrator shaft l5, and several resilient V-belts 22 coacting with grooves in the pulleys l9, 2|.

The main frame 3 and frame member i2 may be durably constructed of sheet metal and structural steel, and the resilient suspension members or springs l3. H for the movable body, may be of the helical compression type and permit free gyration or vibration of the main frame 3 and screen decks l0, ll without imparting such motion to the fixed member l2. The lower extremity of each of the widely separated springs l3 at the feed or head end of the assemblage, rests upon an inwardly projecting bracket 23 rigidly secured to the fixed member l2, and the movable frame 9 is provided with rigid outwardly extending ears 24 which coact with the upper extremities of the springs I3 as shown in Fig. 4. The lower ends both of the adjoining springs H at the discharge or tail end of the assembly. rest upon a common transverse plate 25 which is rigidly attached to the supporting member l2 by adjustable bolts and brackets 26. while another common plate 21 secured to the main frame 3 coacts with the upper ends of these springs M as indicated in Fig. 3. This resilient support or spring arrangement obviously provides a flexible threepoint adjustable suspension for the freely movable body, and rubber supports may obviously be used instead of springs; and while only two Screen decks i0, H are shown, there may be any desired number of these decks.

The sturdy transverse weight supporting shaft l5 which is carried solely by the movable body, has all external surfaces thereof formed concentrio with its central longitudinal axis; and the supporting or journal bearings I! at the opposite sides of the screen decks ll, l2 in which the shaft i5 is rotatably mounted, are also disposed concentric with respect to this shaft axis. The gyrating rotors 16 which are secured to the shaft l5 outwardly of each of the bearings H,

are of like but improved construction and are adapted to normally gyrate the movable body comprising the frame 9, screen decks III, II, and the load carried by these decks, about a normally fixed axis of gyration which is disposed parallel to but eccentrically of the central shaft axis, so that when the shaft I5 is being rotated at normal speed. the movable body will gyrate about the. fixed axis of gyration in a direction perpendicular to the shaft axis and will thus vibrate the screen decks III, II.

One improved construction of gyrating rotors I6 is shown in detail in Figs. 5 to 7 inclusive, and each of these assemblages comprises a disk 23 provided with a cylindrical peripheral guard rim 29 and with a rigid control hub 30 firmly attached to the shaft i5 by means of a key 3|; 0. pair of similar pendulum weights 32 swingably suspended on opposite sides of the disk 23 by means of a p vot pin 33 secured to the hub 30 as by a set screw 34; and a tension spring 35 connecting an intermediate portion of each weight 32 with the rim 29 so as to resiliently restrain the outward swinging motion of the weights. The movable weights 32 are preferably located as near as possible to each other, and are simultaneously swingable in opposite directions about the pivot pin 33; and when the weights 32 are disposed as shown in solid lines in Fig. 5, their centers of gravity are located on substantially oppos te sides of the central axis of the shaft l5 so that the unbalanced actlon of the weights 32 is neutralized and each rotor I6 is substantially balanced. This counter-balanced or neutral condition of the weights 32 prevails when the shaft I5 is at rest or rotating slowly. but when the shaft is rotated above a certain speed beyond the critical vibrating frequency of the springs I 3, I I, both weights 32 of each rotor I6 are automatically swung outwardly about their suspension pivot pins 33 by centrifugal force. When the shaft I5 is rotating at normal speed, all of the weights 32 will be disposed in similar outermost positions relative to their pivotal supports, as indicated in dot-anddash lines in Fig. 5.

Another construction of improved gyrating rotor I6 is shown in detail in Figs. 8 to 10 inclusive, and each of the modified assemblages comprises a disk 28' provided with a cylindrical peripheral guard rim 29 and with a central rigid hub 30 firmly attached to the shaft l5 by means of a key 3|; a pair of similar pendulum weights 32' swingably suspended on the same side of the disk 23 upon a pivot pin 35 secured to the hub 30; and a tension spring 35 connecting an intermediate portion of each weight 32' with the rim 29 so as to resiliently restrain the outward swinging motion of the weights. The movable weights 32' are simultaneously swingable in opposite directions about the pivot pin 33; and when these weights are disposed as shown in solid lines in Fig. 8, their centers of gravity are located on substantially opposite sides of the central axis of the shaft I! so that the unbalanced action of the weights 32' is neutralized and each rotor i6 is approximately balanced. This counter-balanced or neutral condition of the weights 32' prevails when the shaft I is at rest or rotating slowly, but when the shaft I5 is rotated above the critical or dangerous speed, both weights 32' of each rotor l6 will be swung about the pivot pins 33 by centrifugal force. When the shaft I5 is rotating at normal speed, the two weights 32' of each rotor "5' will be disposed in abutting position as shown in dot-and-dash lines in Fig. 8, and the centers of gravity of all of the abutting weight assemblages should then be located on the same side of the shaft l5.

This eccentric or unbalanced condition of the weights 32, 32' while revolving at relatively high speed, causes the shaft l5 and the frame 9 and screen decks Ill, II which are freely movably suspended and support the shaft l5, to gyrate about the fixed axis of gyration located eccentrically of the shaft axis and between this shaft axis and the center line of gravity of the weights 32, thereby rapidly vibrating the screens. The tension springs 35 constantly resiliently restrain the outwardswinging motion of the weights 32. 32' and tend to automatically return their respective weights to neutral or inactive position when the speed of rotation of the shaft I5 is reduced and before the shaft speed again reaches the critical vibrating frequency of the springs I 3, I4, thereby eliminating bouncing of the screen unit both when starting and stopping the machine.

Because of the fact that the movable body including the frame 9, screen decks I0. II and shaft I5, is gyratable about an axis of gyration which is eccentric to the central shaft axis. it may be desirable to form the driven pulley 2| of the belt drive with its central bore concentric relative to the shaft axis and its peripheral rim concentric with the normal axis of gyration, so that the pulley face will revolve about the latter axis as a center during normal operation of the vibratory screen. Such formation of the pulley 21 will eliminate undesirable whipping of the belts 22 during normal operation of the assemblage, but this special construction of the pulley is not essential. If the driven pulley 2| is thus formed with an eccentric bore and face, it may be desirable to provide means such as an adjustable tension spring 36 shown in Figs. 1 to 4 inclusive, for maintaining proper tension on the belts 22 at all times; and in order to eliminate objectionable side sway of the vibrating screen body, a flexible transverse cable 3! connecting th medial portion of the head end of the frame 9 with the opposite sides of the fixed supporting member l2, may also be provided, but these refinements are not a part of the present improvement.

While the normal operation and functioning of my improved gyratory or vibratory screen assemblage should be apparent from the foregoing detailed description, a short rsum thereof will be given. When the screen is at rest, the shaft l5 and rotor l6, l6 are also at rest, and the weights 32, 32' of the several rotors IE will be in counter-balanced or neutral position as shown in solid lines in Figs. 5 and 8. In order to vibrate the screen decks II), II it is only necessary to start the motor I8 thus imparting rotary motion to the shaft l5 through the pulleys l9, 2| and belts 22. As the speed of rotation of the shaft increases, all of the weights gradually swing outwardly about the alined pins 38 of the two rotors l6, thereby simultaneousl unbalancing both rotors to like and increasing extent, and causing the shaft l5, frame ,9 and screen decks "I, H to gyrate about the normal axis of gyration disposed eccentrically of the main shaft axis. This axis of gyration will gradually move farther away from the central shaft axis until maximum or normal speed is attained whereupon the position of the axis of gyration will becom fixed and the weights 32, 32' will all assume the positions shown in dot-and-dash lines in Figs. 5 and 8 with their centers of gravity farthest away from the shaft axis. The tension springs 35 will obviouslyprevent sudden displacement of the weights and will thus produce gradual transition of the movable body from a condition of rest to the condition of maximum gyration or vibration; and the improved assemblage has been found to eliminate all objectionable disturbances when starting and stopping a resiliently supported vibratory body such as a screen assemblage.

From the foregoing detailed description of the construction and operation of my improved screen, it will be apparent that the present invention provides a body gyrating system which besidesbeing simple in construction and efflcient in normal operation, is also adapted to be rapidly ac celerated or decelerated without introducing undesirable bouncing or violent shaking durin starting and stopping. The improved rotor structure with their resiliently restrained movable weights, function to automatically vary the magnitude of the radius of gyration of the movable body in accordance with variation in the speed of vibration, and insure gradual transition of the shaft speed through the zone of critical vibration frequency of the resilient supports, regardless of the rate of changes of the shaft speeds. This improved formation of the rotors also permits the main shaft l5 and bearings I1 to be formed with concentric surfaces throughout, thereby greatly facilitating manufacture of these parts, and the rotor assemblages are obviously relatively simple and compact but durable and safe in structure. The improvement may be advantageously applied to various types of vibratory screens and has proven highly satisfactory; and the movable weights will entirely eliminate objectionable disturbances heretofore encountered in the operation of vibratory or gyratory screen assemblages both of the type wherein the gyrating rotor unit is carried by the freely movably suspended screen frame and decks, and wherein the weight supporting shaft is mounted in fixed bearings. The improved mechanism by virtue of the fact that it eliminates objectionable bouncing and other violent disturbances, also protects the foundat on or supporting structure and thus prolongs the lif of the entire installation.

It should be understood that it is not desired to limit this invention to the exact details of construction or to the precise mode of operation and use, herein shown and described, for various modifications within the scope of the appended claims may occur to persons skilled in the art.

I claim:

1. For use on a vibrating assemblage having a shaft rotatably journalled thereon for normal relatively high speed rotation, balancing means consisting of weights having a common pivotal axis disposed eccentrically of the shaft axis and being in approximately relatively balanced position with respect to each other at low peeds, but being movable independently of each other to similar positions in relation to the common pivotal axis of the weights at normal speed.

2. For use on a vibratory assemblage having a high speed rotary shaft associated therewith, balancing means comprising weight suspended from a common eccentric pivot carried by the shaft, said weights being in relatively balanced position at low shaft speeds, but being movable independently of each other by centrifugal force to similar unbalanced positions at normal shaft speed so as to produce vibration of the assemblage.

3. A vibratory assemblage, comprising, a freely movably supported body, and a pair of weights carried by said body and being revolvable about an axis togyrate the body, said weights being pivotally suspended to swing about a common axis disposed eccentrically of said axi of revolution thereof, and being swingable about said eccentric axis independently of each other.

4. A vibratory assemblage, comprising, a freely movably supported body, and a pair of weights carried by said body and being revolvable about an axis to gyrate the body, said weights bein pivotally suspended to swing about a common axis disposed eccentrically of said axi of revolution thereof, and being swingable about said eccentric axis independently of each other from positions on opposite sides of the common plane of said axes at low speed to overlapping position at maximum speed.

5. A vibratory assemblage, comprising, a freely movably supported body having a shaft journalled for rotation thereon, and a pair of weights carried by and being revolvabl'e by said shaft, said weights being swingable independently of each other about a common axis disposed eccentriczailly of the axis of rotation of said shaft.

6. A vibratory assemblage, comprising, a freely movable body having a shaft joumalled thereon and extending transversely thereacross, and a pair of weights carried by each end of said shaft and being revoivable thereby, the weights of each pair being swingable independently of each other about an axis common to both pairs and disposed eccentrically of the axi of rotation of said shaft.

ALEXANDER L. MUNRO.

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