US2286770A

US2286770A - Throwout mechanism for screens

Info

Publication number: US2286770A
Application number: US288275A
Authority: US
Inventors: Loren G Symons
Original assignee: Nordberg Manufacturing Co
Current assignee: Nordberg Manufacturing Co
Priority date: 1939-08-04
Filing date: 1939-08-04
Publication date: 1942-06-16
Anticipated expiration: 1959-06-16

Description

June 16,4 1942. L, G, sYMQNs 2,286,770

THRowouT MECHANISM Fon scREENs Filed Aug. 4, 1959 :s sheets-sheet 1 Zara/2 fy/feoms' R.. uw

June 16, 1942. l.. G. sYMoNs.

THROWOUT MECHAISM FOR SCREENS 3 Sheets-Sheet 2 yFiled Aug. 4. 1939 Patented .lune 16, 1942 2,286,770 THROWOUT MECHANESM FOR SCREENS Appncation August 4, iesa'seriai No. 283,275

' 28 claims. (ci. zoe-367) My invention relates to an improvement in screen, or material separating devices, and has for one purpose the provision of means for vibrating such a screen. 1

Another purpose is the prevention of screen opping or screen vibration oi undue amplitude during the starting and stopping of the screen. l

Another purpose is the provision of improved means for rendering the vibrating means operative at the normal speed of rotation of said vibrating means, while avoiding undesired vibration at the lowered speeds of rotation.

Another purpose is, broadly, the provision of an improved vibrating means which may be applicable, not merely to screens, but to a variety of objects or situations Where vibration is desired.

Another purpose is the provision of means for readily adjusting the rate and amplitude of vibration of a vibrating screen or other member to which it is applied.'

Other purposes will appear from time to time in the course of the specification and claims.

The present application is a continuation in part of my application Serial No. 140,795, led on May 5, 1937, which in turn is a division of my application Serial No. 26,233, led on June 12, 1935, issued as Patent No. 2,085,774 on July 6, 1937.

I illustrate my invention more or less diagrammatically in the accompanying drawings wherein:

Fig. 1 is a longitudinal section through a unit made in accordance with my invention, such section extending transversely across a screen to which my vibrating unit is applied;

Fig. 2 is a section on the line 2 2 of Fig. 1;

Fig. 3 is a section similar to Fig. 2, with parts in a diierent position and some parts omitted;

Fig. 4 is a plan view of the central part of the structure shown in Fig. 1, with the cover member removed;

Fig. 5 is a section on the line 5-5 oi Fig. 1;

Fig. 6 is a section similar to Fig. 1 through a variant form of the device; f Fig. 7 is a section on the line I-l of Fig. 6; and Y Fig. 8 is a section on the line v8-,8 of Fig.

Like parts are indicated by like symbols throughoutvthe specification and drawings.

Since my throwout mechanism may be applied to a wide variety of screens, and also to other mechanisms, I have not illustrated the screens in detail, but have merely indicated the parts of the screen or screen structure and screen base to which the throwout mechanism of my invention may be applied.

Referring to the drawings, and referring first to the form of Figs. 1 and following, I illustrates a member which may form part of a fixed supporting screen frame. 2 indicates one side of the screen frame or deck proper, it being understood that another side thereof is located at the other end of the throwout member, which is diagrammatically indicated iny Fig. 2. 'Ihe screen frame as a whole is mounted in any suitable and vibratable manner upon any suitable base or xed frame portion, which may form part of or also support the above mentioned frame portion I. 3, 3 indicate pairs of channel members jointed edge to edge to form transverse frame members or supports extending between the opposite side members 2 of the screen frame or deck. l Y l Mounted between the` members 3 are'bearing assemblies including an outer vhousing or annulus 4, provided with brackets 5 and secured to the members 3. locked together in relationV to the transverse members 3 by any suitable boltsA 5. It will be understood that two such bearing assemblies are employed, one adjacent each of the side frame members 2. 'Ifhe bearing assemblies include outer races 1, rollers 8 and inner races 9. Mounted withinl the bearing assemblies is a yshait element having end portions I0, II. These portions are connected by an intermediate rectangular shaped member I 2, shown in section in Figs. 2 and 3. Such rectangular portion has outwardly extending -anges I3, extending outwardly from each side thereof. The member II has a portion of reduced diameter I4, upon which is mounted, by means of a key I5a and securing member Illb, a ,sleeve I5, carrying al labyrinth member I6, interpenetrating with a corresponding labyrinth portion `Il, of the bearing assembly,whereby the penetration of dust is prevented. The piece I5 also carries lugs I8, which formpart of a flexible connection generally indicated as IS, the details of which do not of themselves form part of the present invention. i

2D is a drive shaft also secured to the said flexible connection,l it being also connected at its opposite end to a second flexible structure generally indicated as 2|, which in turn is mounted upon a shaft 22 having reduced portions 23, mounted in a ball bearing assembly 24, shown as secured to the frame member I.

25 is any suitable drive pulley mounted on a The bearing assembly is reduced outer end portion 26 of the said shaft structure 22. It will be understood that from any suitable power source, through the pulley 25, the shaft 22 may be rotated, and in turn through the flexible connection 2| rotates the shaft 26. The shaft 28 in turn, through the flexible connection I9, rotates the shaft structure above described, including the rectangular portion l2. A plurality of exible connections provides a continuing drive of the vibration of the screen structure of which the side frame members 2 form a part. In other words, the screen may be continuously rotated through a fixed drive through the flexible connection above described. Said flexible connection as such does not form part of the present invention and is therefore not described in detail.

Note that the shaft portion I2 also carries

dust protectors

28, 29, having labyrinth portions interpenetrating with corresponding labyrinth portions of the members 4, whereby the access of dust is prevented.

Mounted at each end of the rectangular portion l2 are guides or keys generally indicated as 3l), 3|. Guided upon such keys is a weight structure generally indicated as 32, having a generally arcuate exterior surface 33, and provided at either end with a slot 34 to receive the key structures 38, 3|. The weight 32 is normally held in the position in which it is shown in Fig. 2 by a coil spring 35, which is compressed between one wall of the rectangular portion I2 and a head 38. Said head 3B is screw-threadediy adjustable upon the screw-threaded portion of a bolt 31, the bolt in turn passing through the weight 32 and being provided with ahead 38, countersunk therein and yconforming to the generally arcuate exterior, as at 38. The bolt 31 passes through suitable apertures in the rectangular portion l2, as indicated in Figs. 1, 2 and 3. For ready adjustment, the member 36 is provided with generally radial slots 48, which are adapted to receive an appropriate tool for rotating the member 36 in relation to the screw 31.

4| is a shock-absorbing washer, which may be of compressible material, such as rubber or the like. It may be bolted or riveted as at 42 to the lower face of the member 36. 43 is a snubber spring also interposed between the lower wall of the rectangular portion l2 and the head 36. The parts are normally disengaged, as shown in Figs. l and 2, but are engaged when the parts are in the position shown in Fig. 3. I illustrate the snubber spring 43 as engaging the lower collar 48, which is shown as forming part of the member 35.

45 is another shock-absorbing washer of yielding material, which is mounted on the weight 32 and is effective to cushion the return of the weight against the outer side of the lower wall of the rectangular portion I2, referring to Fig. l.

l Referring to the form of Figs. 6, 7 and 8, I illustrate a variant form of vibrator or rotor.

I illustrate a bearingsleeve 58 which is provided at yopposite sides with at webs 5|, to which may be bolted springs 52, 53, respectively, on opposite sides of the axis of rotation of the rotor. These springs, formed, for example, of thin laminae, may be bolted in position as by the employment of clamping plates 54, bolts and nuts 56.

The other ends of the springs 52 and 53 are secured in any suitable manner to a screen frame or deck, which may be similar to the screen frame 2 of Fig. 1. i

The rotor itself includes the shaft 66 provided with any suitable pulley 6| about which may pass the belt 62 to any suitable motor or power source. 64 indicates an inner ball race about the shaft 66 and 65 an outer ball race within the member 58. indicates any suitable balls or rollers whereby the shaft Sil is permitted to rotate freely with a minimum of friction within the sleeve 58. 61 is one member of any suitable dust excluding labyrinth or seal and 63 the opposite member. It will be understood that the member 61 rotates with the shaft whereas 58 is fixed in relation to or forms part of the member 56. It will be realized that any other suitable means for excluding dust or confining lubricant may be employed. 89 is an inner end plate associated with the end member 18 to which the cylindrical housing portion 1| may be secured in any suitable manner, for example, by welding. The result is a tightly closed housing with no room for access of dust. It will be understood that whereas I have described but one end of the vibrating mechanism, both ends may be identically formed.

Rotating with and as a part of the shaft 6|) is the square central portion 15 which extends substantially throughout the length of the housing 1|. Secured to it is a shorter fixed member 16, herein shown as spaced centrally of the square central portion and having outwardly extending shoulders 11 which may be apertured as at 18 to permit the passage therethrough of limit bolts 19 the length of which may be adjusted as by nuts 80, tting in pockets 8| in the outer face of the member 16. The bolts 19 are provided with limit heads 82. 83 indicate compression springs surrounding the bolts 18 and compressed between the heads 82 and the bottom surface 84 of pockets or apertures 85 formed in side members 85. The side members 86, of which two are shown, are connected to the

cross members

81 and 83. It will be understood that the

members

86, 81 and 88 may be integral or secured together by the pins with heads 9| and adjustable nuts 92 so that they move as a unit. The side members 86 and the cross member 81 extend substantially throughout the length of the housing 1|, whereas the smaller cross members 88 may be secured at either end of the members 86, as illustrated in Figs `6 and 8. The cross members 88 are preferably spaced from the members 86 by spacing bars 89 of predetermined thickness, which determine the clearance 86a between the square shaft 15 and the cross bars 88. It will be understood that the strength of the springs 88 is such that when the rotor is at rest the parts are normally in the position in which they are shown in Figs. '1 and 8. When the motor is driving the rotor through the pulleys 6l and when a predetermined speed of rotation is reached, then the centrifugal tendency of the member 81, with its attached members 86, over.. comes the force of the springs 83 and moves outwardly from the center of rotation of the shaft 68. The parts are so proportioned that when the springs 83 hold the parts in the position of Fig. 8 the rotor is in dynamic balance and will rotate without causing any vibration. When the speed increases suiciently to cause the

members

86, 81, 68 and 88 to move centrifugally outwardly from the axis of rotation of the rotor, the member then becomes unbalanced, and, in response to its rotation, vibrates and causes a vibration of all attached parts including the screen deck. The clearance 88a obtained by the Spacing members 89, limits the distance the members 8B, 81 can move outwardly from the axis of the rotor 15.

The rate of rotation necessary to cause this unbalance may be determined, controlled and adjusted by setting the nuts 80 in order to increase or diminish the compression on the springs 83.

It will be understood that the spacing members 89 may be replaced by similar spacing members of more'or less thickness in order to vary the clearance 89a which defines the possible movement of the member 81, away from the center of rotation of the shaft 60 and away from the opposite xed member 1'6. Thus I can, by setting the springs 83, limit or control the speed oi rotation necessary to cause unbalance, and by varying the thickness of the spacing members 89 I can limit the possible maximum unbalance permitted.

It will be realized that whereas I have described and shown a practical and operative device, nevertheless many changes might be made in the size, shape, number and disposition of parts without departing from the spirit of my invention. I therefore wish my description and k showing to be taken as in a broad sense illustrative and diagrammatic rather than as limiting me to my specific showing.

For example, whereas the central portion of the rotor is shown as generally rectangular in form and shaped to form a central depression or channel, it will be understood, of course, that its form may be widely varied.

The use and operation of my invention are as follows:

In employing a screen of the type shown herein I nd that in rotating an unbalanced member the initial rotation at relatively low speed causes a wide amplitude vibration or opping of the vibratory member and of the screen, which is highly disadvantageous. The constraint on the screen caused by this iiopping makes trouble both in starting and in stopping. In a screen of this type I nd it advantageous to provide means for vibrating the screen which stay reasonably close to dynamic balance until a predetermined speed of rotation is reached. Then the resistance of the

springs

83 or 35 is more or less gradually overcome and the previously balanced rotor becomes an unbalanced rotor. But it does not become unbalanced until after the dangerous low speed rate of rotation is passed. When it comes up to full speed it serves its function as an unbalanced vibrating member with no racking of or damage to the screen and with no excess pounding or vibration. On the other hand, when the screen is stopped, the heretofore unbalanced rotor becomes a balanced rotor be- `fore the speed of rotation has dropped to a point Where the damaging fiopping takes place.

Referring to the form of Figs, 1 to 5, it will be observed that when the parts are at rest, as shown in Figs. 1 and 2, the weight 32 is urged by the spring 35 against the lower wall of the reotangular portion I2, referring to Figs. 1 and 2, the actual engagement being against the cushioning pad or washer 45. The weight structure is guided ateach end by the

keying connections

3D, 34 and 3l, 34. When rotation is begun, and until the speed of rotation reaches a predetermined minimum, the spring 35 is of sufficient strength to hold the parts in the position shown in Figs. 1 and 2.

In actual practice, in the structure actually employed, when at rest the center of gravity of the weight is slightly eccentric of the center of gravity of the unit, but not enough to cause undue vibration and overthrow in starting and stopping. As soon as the unit attains a speed above the dangerous surge vibration point, or approximately 300 or 400 R. P. M., the centrifugal force of the weight overcomes the force of the spring 35, and the weight moves out into the Y position in which it is shown in Fig. 3, compressing the spring 35. When the weight moves outwardly along its keyways, tol its limit position, any shock is snubbed by the engagement of the spring 43 with the collar or offset 44. The washer 4I is a further cushioning or shock-preventing factor. During the time that the screen is running this position is maintained, and the weight is rotated by slides or key connections 30, 3i, which interpenetrate with it, and is held in place by the large head or nut 36.

The spring 43 is useful as a snubber, since, when the weight 32 starts out, under centrifugal force, it moves very rapidly, and the spring prevents any banging against the face of the nut or possible damage to the bearings. When the Weight moves back into place as the screen slows down, the washer i5 is eiective to prevent chattering.

In the operation of the device it Will be understood that the

movable weight

32 or 81 is'normally held in the position shown in Figs. 2 or 8, until va predetermined speed of rotation is reached. When in such position any variation between the center of gravity of the rotor and its axis of rotation is so slight as not to cause any undesired amplitude of vibration or flopping. When the critical point is passed, the movable weight moves centrifugally quite sharply outwardly until i t reaches the outer limit of its possible movement, Thus, when the device is running at a low speed and up to a predetermined threshold, the weight is held in the position shown in Fig. 1. Quite suddenly, after a predetermined threshold of speed is passed, the

movable weight

32 or 81 moves sharply out to its outer limit, and the rotor then operates as an unbalanced and vibration-causing member. The snubbing or cushioning means shown, for eX- ample, in Fig. 3 and including the spring 43 prevent any shock or damage, which effect is assisted by the compressible washer III. When the speed of rotation again drops past a predetermined threshold, the spring 35 is effective sharply to draw the weight back into initial position, preventing any flopping or damaging vibration. When drawn to this position, the compressible washer is eiTective to cushion the shock and to prevent the chattering which would vensue from a metal to metal contact.

Note that the boxes or bearing assemblies 4 are fastened through the channel beams 3 to the deck that is to be vibrated and which includes the side frame elements 2. The driving mechanism, including the shaft 22 and the pulley 25 being mounted on the xed frame portion I, does not vibrate, and any suitable V-belt drive can be 'taken ofi from the pulley 25 in any desired direction. The above described flexible connections or couplings, generally indicated as I9 and 2I, with the intervening shaft 20, transmit the rotation from the drive proper to the vibrating unit, and at the same time absorb the vibration of the unit and prevent its transmission to the base member I or to the floor of the building` It may be important to vary or control the amplitude of vibration. This can be done by the rotation of the single nut or head 56. As the nut is tightened down on the bolt 31, the distance the weight will throw out willv be lessened, and any rate of vibration within a wide range can be had by simply turning the nut 36 one way or another with any suitable tool. Preferably a special tool is provided, conforming to the radial slots of the nut.

In order to prevent dust, Imay enclose or shield the unit as aA whole by the provision of upper and lower plates fil, shown as outwardly bowed and as secured to the transverse channel frame members 3, which may, of course, be readily removable for access to the vibrating structure.

The roller bearings may readily be supplied with grease by any suitable conventional grease ttings, indicated at 48.

Referring to the form of Figs. 6, 7 and 3, the operation is essentially similar, but the details vary. The throwout mechanism is illustrated, for example, in Figs. 6 and 8, as employed on the transversely extending leaf springs 52, "ii, this particular unit being illustrated as yieldingly mounted upon lthe screen member proper. It will'be understood, however, that this type or" mounting is merely illustrative, and that the unit shown may be applied directly to the screen frame or deck, as is the form of Figs. l and following.

I claim:

l'. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck, and

means for rotating it, said rotor including a cen- I tral portion, a weight mounted on said rotor and longitudinally extending along said rotor, and partially surrounding said central portion, yielding means tending normally to hold said weight in xed position against the exterior of said central portion until a predetermined speed of rotation of the rotor is attained, means for guiding said weight in a generally radial path, means for limiting the outward movement of said weight in relation to said rotor, in response to centrifugal action, and yielding snubbing means eiiective at the outward limit of movement of the weight, and adapted to cushion the movement of the weight at the end of its outward excursion.

2. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on the screen deck, and means for rotating it, a bearing connection between each end of said rotor and opposite portions of said screen deck, said rotor including a central portion intermediate said bearing connections, a weight mounted on` said central portion and extending longitudinally therealong, yielding means tending normally to hold said weight at a fixed inward position in relation to said central portion until a predetermined speed of rotation of the rotor is obtained, means for guiding the weight for outward movement, and means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action, said limiting means including a bolt passing through said central portion and secured to said weight, and a head for said bolt adapted to engage said central portion when said weight moves centrifugally outwardly a predetermined distance.

3. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on the screen deck, and

means for rotating it, a bearing connectionbetween each end of said rotor and opposite portions of said screen deck, said rotor including a central portion intermediate said bearing connections, a weight mounted on said central portion and extending longitudinally therealong, yielding means tending normally to hold said weight at a Xed inward position in relation to said central portion until a predetermined speed of rotation of the rotor is obtained, means for guiding the weight for outward movement, and means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action, said limiting means including a bolt passing through said central portion and secured to said weight, and a head for said bolt adapted to engage said central portion when said weight moves centriiugally outwardly a predetermined distance, and snubbing means adapted toV Cushion the outward movement of said weight.

4. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on the screen deck, and means for rotating it, a bearing connection between each end of said rotor and opposite' portions of said screen deck,said rotor including a central portion intermediate said bearing connections, a weight mounted on said central portion, yielding means tending normally to hold said weight at a xed inward position in relation to said central portion until a predetermined speed of rotation of the rotor is obtained, means for guiding the weight for outward movement, and means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action, said guiding means including interpenetrating sliding connections on weight and rotor located at each end of said weight, said limiting means including a single bolt passing' through said central portion and secured to said weight and located intermediate said sliding connections, and a head for said bolt adapted to engage said central portion when said weight moves centrifugally outwardly a predetermined distance.

5. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means tending normally to hold said weight in Xed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, and snubbing means effective to cushion the shock of the stoppage of the weight at its outward limit of movement.

6. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means tending normally to hold said weight in fixed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, and snubbing means effective to cushion the shock of the stoppage of the weight at its outward limit of movement, said snubbing means including a coil spring and an abutment therefor.

'7. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means tending normally to .hold said weight in fixed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, and snubbing means elective to cushion the shock of the stoppage of the weight at its outward limit of movement, said snubbing means including a pad of shock absorbent material interposed between the Said limiting means and said weight when said weight moves to its outward limit of movement.

8. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means tending normally to hold said weight in fixed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, snubbing means effective to cushion the shock of the stoppage of the weight at its outward limit of movement, said snubbing means including a pad of shock absorbent material interposed between the said limiting means and said weight when said weight moves to its outward limit of movement, and additional snubbing means, including a spring adapted to be compressed between the weight and the movement limiting means at the outward limit of movement of the weight.

9. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means tending normally to hold said weight in xed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, snubbing means effective to cushion the shock of the stoppage of the weight at its outward limit of movement, and additional means adapted to cushion the shock of the return of the weight toward its initial position in relation to the rotor.

l0. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, yielding means, including a coil spring, tending normally to hold said weight in fixed position in relation to said rotor until a predetermined speed of rotation of the rotor is obtained, means for limiting the outward movement of the weight in relation to said rotor, and snubbing means elective to cushion the shock of the stoppage of the weight at its outward limit of movement, said snubbing means including a coil spring and an abutment therefor, said last mentioned coil spring being concentric with said rst mentioned coil spring.

11. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a single weight mounted on said rotor, including a member substantially surrounding said rotor and extending longitudinally therealong, for a distance substantially greater than the diameter of the rotor and located substantially midway between the ends of the rotor, means for guiding said weight for generally radial movement in relation to said rotor, including sliding track connections between said weight and said rotor` at each end of the weight, yielding means tending normally to hold said weight in xed position around said rotor until a predetermined speed of rotation of the rotor is obtained, including a 'coil spring partially housed within said rotor, and means for limiting the outward movement of the weight in relation to said rotor.

12. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor `rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, including a member substantially surrounding said rotor and extending longitudinally therealong, means for .guiding said weight for generally radial movement in relation to said rotor, including sliding track connections between said weight and said rotor, yielding means tending normally to hold said weight in xed position around said rotor until a predetermined speed of rotation of the rotor is obtained, including a coil spring partially housed within said rotor, and means for limiting the outward movement of the weight in relation to said rotor, including a bolt passing through said rotor and secured at one end to the weight, and a head on the opposite end of said bolt adapted to engage the rotor when the weight is moved to extended position, said coil spring surrounding said bolt.

13. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight mounted on said rotor, ,including a member substantially surrounding said'rotor and extending longitudinally therealong, means for guiding said weight for generally radial movement in relation to said rotor, including sliding track connections between said Weight and said rotor, yielding means tending normally to hold said weight in xed position around said rotor until a predetermined speed of rotation of the rotor is obtained, including a coil spring partially housed within said rotor, means for limiting the outward movement of the weight in relation to said rotor, including a bolt passing through said rotor and secured at one end to the weight, a head on the opposite end of said bolt adapted to engage the rotor when theV weight is moved to extended position, said coil spring surrounding said bolt, and means for cushioning the outward movement of said weight, including a second coil spring concentricwith the first and adapted to be compressed between said weight and said head when the weight moves outwardly toward extended position.

14. In a vibrating unit for screens and the like, and in combination with a screen deck and side frame 4means therefor, a rotor rotatably mounted on said screen deck and lying between top and bottom of said side frame means, and means for rotating it, a weight mounted on said rotor, said weight being of a length substantially greater than the diameter of the rotor and being located substantially midway between they ends of the rotor and extending longitudinally along the axis of the rotor in general parallelism with said axis, means for guiding said weight for generally radial movement in relation to the rotor and for holding it at all positions in parallelism with the axis of the rotor', yielding means tending normally to hold said weight in xedposition'in relation to said rotor until a predetermined speed of rotation of therotor is reached, the rotor,

when the weight is in such initial iixed position, being in substantial balance,` and means for limiting the outward movement of the weight in relation to the rotor to a range of movement lying within the vertical extension of the side frame means of the screen deck.

15. In a Vibrating unit for screens and the like, and in combination with a screen deck and side frame means therefor, a rotor rotatably mounted on said screen deck and lying between top and bottom of said side frame means, and means for rotating it, a weight mounted on said rotor, said weight being of a'length substantially greater than the diameter of the rotor and being located substantially midway between the ends of the rotor and extending longitudinally along the axis of the rotor in general parallelism with said axis, means for guiding said weight for generally radial movement in relation to the rotor,

yielding means tending normally to hold said weight in xed position in relation to said rotor until a predetermined speed of rotation of the rotor is reached, the rotor, when the weight is in such initial xed position, being in substantial balance, and means for limiting the outward' movement of Ythe weight in relation to the rotor to a range of movement lying within the vertical extension of the side frame means of the screen deck.

16. In combination, a screen deck including a pair of longitudinally extending generally lparallel side frame members, a rotor extending transversely between said frame members .and lying in the general horizontal plane thereof, means for rotating the rotor, a weight mounted on the rotor substantially midway between the ends of the rotor, and means for guiding it for generally radial movement in relation to the rotor, yielding means tending normally to hold the weight in xed position in relation to the rotor until a predetermined speed of rotation of the rotor is reached, and means for limiting the outward movement of the weight in relation to the rotor to a range of movement lying generally between top and bottom of said side frame members.

17.*In combination, a screen deck including a pair of longitudinally extending generally parallel side frame members, a rotor extending transversely between said frame members and lying in the general horizontal plane thereof, means "for rotating the rotor, a weight mounted on the rotor substantially midway .between the ends of the rotor, and means for guiding it for generally radial movement in relation to the rotor, yielding means tending normally to hold the weight in Vxed position in relation to the rotor until a .predetermined speed ofrotation Aof Vthe rotor is reached, `and means'for limiting the outward movement of the weight in relation to the rotor to a range of movement lying generally between top and lbottom of said side frame members, and snubbing cushioning means effective to cushion the shock of the stoppage of the weight at the outward limit of its movement.

18. In a vibrating unit for screens Yand the like, and in combination with a screen deck, a rotor rotatably supported on said screen deck and means for rotating it, a weight `mounted on said rotor substantially between the ends 4thereof and extending longitudinally therealong in general parallelism with the axis of rotation of the rotor. for a distance substantially greater than Vthe diameter of the rotor, yielding means tending normally to hold saiclweight in iixed position in relation to said rotor until a predetermined speed of rotation of said rotor is reached, and means -for limiting-the outward movement of the weight like, and in combination with a screen deck, a

rotor rotatably supported on `said screen deck and means for rotating it, a weightmounted on said rotor substantially-between the endsthereof and extending longitudinally therealong in general parallelism with -the laxis of rotation of the rotor'for a distance substantially greater than the diameter of the rotor, means Vfor limiting the outward movement of the weight in relation to the rotor, including a single, `headed limit member located-intermediate the ends Vof said weight, and yielding means tending normally to hold said weight infixed position in relation to said rotor, including a coil spring surrounding said headed member yand interposed between said weight and rotor.

20. In a vibratory screen,-a base, a Screen deck vibratably mounted on said base, said screen deck including side frame members, a drive shaft mounted on said'base in Yhorirontal alignment with said side frame members, a rotor mounted on said deck and-extending transversely between said side frame members, `in general alignment with said drive shaft, one of said side framemembers being apertured in alignment therewith, and a exible driving -connection extending through said aperture and in flexible relationship-with said rotor and said drive shaftVanda Aweight mounted on said rotor and extending along said rotorior a distance substantially exceeding the diameter ofthe rotor, and being located substantially midwaybetween the ends of the rotor, means for guiding itlfor generally radial movement in relation to said rotor, Ymeans for limiting said movement, and Vmeans for normally holding Ait Iinan initial fixed position in relation to said the rotor is reached.

2l. In a vibrating unit for screensand the like, and in combination with a screen-deck, a rotor rotatably mounted on said screen deck for rotation about a horizontal axis at right angles to the path Vof material across the deck, said rotor including a central portion intermediate the sides of the screenV deck, a Weight mounted on said rotor and partially surrounding said central portionat all positions-of the weight, and extending longitudinally along said central portion for a distance-substantially greater'than the diameter of said central portion, said Yweight being channeled'alcng one side toreceive said central -portion, yielding means tendingY normally to hold said weight inixedvinner Yposition in relation to said central porti-en until a predetermined speed of rotation of the rotoris reached, the weight and the rest of the rotor, when the weight isV in such initial position, being substantially Vin balance, means for guiding -said lweight in a generally radial path outwardly V-from the axis of rotation of the rotor while maintainingY the weight parallel with the axis ofthe rotor, and'means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action to a distance substantially less than the diameter cf the rotor.

22. In a vibrating unit for screensand the like,

rotatably mounted on said screen deck for rotation about a horizontal axis at right angles to the path of material across the deck, said rotor including a central portion intermediate the sides of the screen deck, a weight mounted on said rotor and partially surrounding said central por tion at all positions of the weight, and extending longitudinally along said central portion for a distance substantially greater than the diameter of said central portion, said weight being channeled along one side to receive said central portion, yielding means tending normally to hold said weight in iixed inner position in relation to said central portion until a predetermined speed of rotation of the rotor is reached, the weight and the rest of the rotor, when the weight is in such initial position, being substantially in balance, means for guiding said weight in a generally radial path outwardly from the axis of rotation of the rotor while maintaining the weight parallel with the axis of the rotor, and means for limiting the outward movement, of the weight in relation to the rotor in response to centrifugal action.

23. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably mounted on said screen deck for rotation about a horizontal axis at right angles to the path oi material across the deck, said rotor including a central portion extending along and surrounding the axis of rotation of the rotor, a single weight mounted on said rotor substantially midway intermediate the ends of the rotor and extending longitudinally along said central portion cf the rotor for a distance substantially greater than the diameter of said central portion,

yielding means tending normally to hold said f' weight in xed inner position in relation to said central portion until a predetermined speed of rotation of the rotor is reached, the weight and the rest of the rotor, when the weight is in such initial position, being substantially in balance,

and means for guiding said weight in a generally radial path outwardly from the axis of rotation of the rotor while maintaining the weight parallel with the axis of the rotor, and means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action, including a single limit member extending from said weight through said rotor and having a limit element at the outer end thereof.

24. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably mounted on said screen deck for rotation about a horizontal axis at right angles to the path oi material across the deck, said rotor including a central portion extending along and surrounding the axis of rotation of the rotor, a single weight mounted on said rotor substantially midway intermediate the ends of the rotor and extending longitudinally along said central portion of the rotor for a distance substantially greater than the diameter of said central portion, yielding means tending normally to hold said weight in fixed inner position in relation to said central portion until a predetermined speed of rotation of the rotor is reached, the weight and the rest of the rotor, when the weight is in such initial position, being substantially in balance, and means for guiding said weight in a generally radial path outwardly from the axis of rotation of the rotor while maintaining the weight parallel with the axis of the rotor, and means for limiting the outward movement of the weightvin relation to the rotor in response to centrifugal action, including a single limit member extending from said weight through said rotor and having a limit element adjustably mounted at the outer end thereof.

25. In a vibrating unit for screens and the like, and in combination with a screen deck, a rotor rotatably mounted on said screen deck for rotation about a horizontal axisat right angles to the path of material across the deck, said rotor including a central portion extending along and surrounding the axis of rotation of the rotor, a single weight mounted on said rotor substantially midway intermediate the ends of the rotg1 and extending longitudinally along said central portion of the rotor for a distance substantially greater than the diameter of said central portion, means for l guiding said weight in a generally radial path outwardly from the axis of rotation of the rotor while maintaining the weight parallel with the axis of the rotor, and means for limiting the outward movement of the weight in relation to the rotor in response to centrifugal action, including a single limit member extending from said weight through said rotor and having a limit element at the outer end thereof, a coil spring surrounding said limit member and adapted normally to hold said weight fixed in inner position in relation to said central portion until a predetermined speed of rotation of the rotor is reached, and an additional snubber spring surrounding said limit member and adapted to cushion the outward movement lof the weight when it moves centrifugally outwardly from the rotor.

26. In combination, a screen deck including a pair of longitudinally extending generally parallel side frame members, a rotor extending transversely between said frame members and lying in the general horizontal plane thereof, means for rotating the rotor, a weight mounted on the rotor substantially midway between the ends of the rotor, and means for guiding it for generally radial movement in relation te the rotor, yielding means tending normally to hold the weight in xed position in relation to the rotor until a predetermined speed of rotation of the rotor is reached, and means for limiting the outward movement of the weight in relation to the rotor to a range of movement lying generally between top and bottom of said side frame members, said weight including a hollow portion adapted to surround said rotor on three sides when said weight is in withdrawn position adjacent the axis of rotation of the rotor.

27. In combination, a screen deck including a pair of longitudinally extending generally parallel side frame members, a rotor extending transversely between said frame members and lying in the general horizontal `plane thereof, means for rotating the rotor, a weight mounted on the rotor substantially midway between the ends of the rotor, and means for guiding it for generally radial movement in relation to the rotor, yielding means tending normally to hold the weight in fixed position in relation to the rotor until a predetermined speed of rotation of the rotor is reached, and means for limiting the outward movement of the weight in relation to the rotor to a range of movement lying generally between top and bottom of said side frame members, said rotor having end extensions, fixed bearing shells surrounding said end extensions, roller bearings located between said end extensions and the inner faces of said iixed shells, and sealing means between said rotor and said shells located at each side of said roller bearings.

28. In combination, a screen deck including a pair of longitudinally extending generally parallel side frame members, a rotor extending transversely between said frame members and lying in the general horizontal plane thereof, means for rotating the rotor, a weight mounted on the rotor substantially midway between the ends of the rotor, and means for guiding it for generally radial movement in relation to the rotor, yielding means tending normally to hold the weight in iixed position in relation t0 the rotor until a predetermined speed of rotation of the rotor is reached, and means for limiting the outward movement of the weight in relation to the rotor to a range of movement lying generally between top and bottom of said side frame members, and a generally tubular housing extending in parallelism with the rotor, and surrounding it, the walls of said housing closely approaching the path described by the parts of the rotor most remote from the axis of rotation, at their most extended position, the whole housing lying generally between the tops and bottoms of said frame members.

LOREN G. SYMONS.