US2204379A - Vibrating screen structure - Google Patents

Description

June 11, 1940. A, VER RQM 2,204,379.

VIBRATING SCREEN STRUCTURE Filed Dec. 20, 1935 2 Sheets-Sheet 1 ATTORNEYS.

June 11, 1940. V G. A. OVERSTROM vmmme SCREEN STRUCTURE 2 Sheets-Sheet 2 Filed Dec. 20, 1935 A TTORNE YS.

mama June 11,1940 i i I H i 2 UNITED STATES PATENT OFFICE I 2,204,319 1 VIBRATING some: smoo'rom: Gustave A. ovum-om, Big sin, Calif.

I Application December 20, 1935, Serial No. 55,348

7 Claims. (01. 209-326) This invention relates to vibrating screen initial screening action to which they are substructures, and more particularly to structures jected, butarealso quickly removed thereby enof such nature that the particles of material to abling the smaller or undersized particles to be be treated are initially subjected to a more or subjected to a more efficient screening action,

having a predominant component, more or less tofore. vertical, which, as the particles progress along A further object is to provide a screen structhe screen, is gradually transformed into a ture in the. operation of which piling up of the vibratory movement having a predominant more material to be screened is avoided at thearea 10 or less horizontal or progressing feeding moveon the screen surface upon which the material 10 ment in the direction of travel of the particles. is initially deposited.

The object of the invention is to provide a Afurther object is toprovide a screen structure screen structure of such nature that the material in which the screening element is yieldingly supto be treated is quickly and rapidly stratified ported and is vibrated, the means for vibrating over the screen surface when first supplied therethe same being so relatively arranged with re- 15 to so as to effect a rapidinitial separation of the spect to the yielding supports of the screen elelarger and smaller particles, while at the same 'ment as to secure a desirable coordination of the time gradually transforming the screening action forces created by the vibrating means and the into a progressing or feeding action as the partiyielding supports, when in operation, which co- :0 cles of material travel along the screening surordination accomplishes the progressive diminuso face. v tion of the impact force of the particles upon A further object is to provide a screen structhe screen surface, and the progressive movement ture of such nature that the material to be which secures the feed of the material along the treated is subjected to a conjoint effect of forces screen surface remains substantially constant. which control and modify each other, as the A further object is to provide a screening apg5 screening action proceeds, thereby enabling me paratus in which excessive movements of the to accomplish an efficient screening of the mascreen box and screening elements carried there.- terial in a shorter period of time and at a less by, when the apparatus is being started or speed of operation than has heretofore been stopped, s reduced to a minimum. These move- A further object is to provide a more steady, bronco action are injurious to the structure constant, and continuous progression or travel and especially to the screen elements and spring of the material over and alonglthe surface of the .supports.

screening element, and to reduce or avoid un- Other objects of the invention will appear 3:; necessary or undesirable back travel or movemore fully hereinafter. ment of the material at any point of the screen- The invention consists substantially in the ing surface, thereby securing a more uniform-and construction, combination, location, relative arcoordinated continuity of screening action rangement of parts, and method of operation, all throughout the entire area of the screen element. as will be more fully hereinafter set forth, as

less violent vibratory or screening movement and at a more rapid progressive speed than here-' 6 possible. ments, sometimes referred to in the field as 30 1 A further object is to provide'a. screen struc illustrated in the accompanying drawings, and 40 ture in which undesirable and excessive tilting finally pointed out in the appended claims. action of the screen element when in operation Referring to theaccompanying drawings and is avoided or reducedto a minimum, and whereto the various views and reference signs appearin the screen element can be mounted with a ing thereon:

less degree of tilt, when desired, than has here- Fig. 1 is a view in top plan of a screen structofore been possible, thereby enabling me to emture embodying the principles of my invention. ploy screen elements of shorter dimension in the Figs. 2 and 3 are, respectively, views in side direction of feed of the material under treatand end elevation of the structure shown in ment, and to avoid or reduce the wrecking and Fig. 1. r pounding action which is often developed in Fig. 4 is a diagrammatic view illustrating the.

screen structures heretofore used. action when in'operation of the structure shown A further object is to provide a screen strucin Figs. 1, 2 and 3. ture in which the over-size particles of material Figs. 5, 6 and 7 are, respectively, broken views under treatment are not only separated from in top plan, side and end elevation, of a screen 5 the smaller size particles at substantially the structure which'I will refer to as a suspended 5 invention.

Figs. 8 and 9 are diagrammatic views illustrating the action when in operation of the screen structure shown in Figs. 5, 6 and '7.

In the screening art the construction of the screen must necessarily vary in many of its details according to the particular conditions and problems encountered in the use thereof in the various industries. For example, various characters,'size, weight, nature and-conditions of materials to be handled; various capacities or outputs per unit of time to be effected; various speeds of operation necessary to attain the most efficient screening action; various methods employed in connection with the screening operations; various other practical conditions encountered such as cost of installation, cost of repair, cost of operation, and character of available power for operation: All these factors require more or less modification of details of structure and arrangement and accessory parts, according to the particular field of use the apparatus is to serve, to enable it to accomplish most efficiently its best results and attain its maximum advantages. I have therefore illustrated various forms of embodiment of my invention, but in its broadest and most generic principles I do not wish to be limited or restricted to any particular or specific form. I also wish it to be understood that the generic principles of my invention may be employed in various other specific forms of struc-' ture and details, of which those shown are illustrative.

I have found that in practically all forms of mechanically driven vibratory screening structures at present in use forces are developed in the screen element, when in operation, which ex ert a retarding action on-the forward progression or feed movement of the material over and along the surface of the screen, and hence a delay in the separation and elimination of the oversize portions of the material being treated. In other words what I shall call a back-lash action is exerted upon the material particles. This backlash or retarding action is exceedingly detrimental to efficient screening. It not only tends to clog the meshes of the screen element, thereby preventing the free passage therethrough of the smaller and finer particles of material, but it also tends to cause material to pile up on the screen all along its length in its discharging dimension, thereby creating unbalancing weight conditions on the screen element, and a failure to secure and maintain uniform screening action. I have discovered that this back-lash or retarding action is due to the fact that in screen structures at present in use the screen element is subjected to forces which not only tend to move or vibrate it in a combined uniform vertical and horizontal direction at every point in its surface, thereby causing every such point to travel in a more or less oval path, or pathshaving uniform vertical and horizontal components, but also to forces which cause the screen element at the same time to simultaneously tip vertically about a horizontal axis located somewhere within its length, depending upon the location of the point of connection of the vibrating means to the screen box. In other words, during the tendency of the screen element to move in generally oval paths, there is developed also a tendency for one end of that element to move upwardly while the other end moves downwardly.

It is among the important objects and purposes t p and which embodies the principles oi my of my present invention to provide means and a method to eliminate this back-lash or retarding action, and I accomplish this result, in the broader scope of my invention, by providing a screen structure, in one or another physical form of various practical embodiments of the idea, in which, in operation, the vertical component of the vibratory or oval movement of the screen element predominates at the point where the material to be treated is first delivered onto the screen surface, but which wanes progressively towards the discharge end of the screen, while at the same time the horizontal component of said movement remains substantially the same throughout the feed of the material towards the discharge end of the screen. a

In Figs. 1, 2 and 3 I have shown a screen strucslightly endwise or in the direction of the line of feed of the material thereover while being screened. The frame side members 3 are connected together at their opposite ends by means of a cross strut 5. Interposed between the cross strut 5 and the screen box 2 are one or more springs 6, shown in this instance as coil springs, upon which rests the adjacent end of the screen box. Where the screen box is to occupy an inclined position, which is acommon practice in screen structures, the yielding legs 4 support the lower end of the box 2, while the coil springs 6 support its upper end. A short rod I is pivotally connected at one end to the screen box 2 and extends through a hole in the cross strut 5. A

, spring 8 is mounted on the free end of rod 1 and is held between the cross strut 5 and a nut adjustably mounted on the end of rod 1. By this means the tension of spring 8 may be adjustably varied.

The screen box is vibrated by means of an unbalanced pulley 9 which may be of well known structure and mode of operation in the screening art, and hence need not be here described in detail. This vibrating pulley device is mounted upon and carried by the screen box as is also common practice.

In the arrangement shown the spring 8 acts upon the screen box in opposition to the action of the box supporting springs 6, and, in addition, the spring 8 is of less tension than that of the springs 6. It will also be seen that the box supporting springs 6 and I, are disposed in angular relation with respect to each other as well as with respect to the screen element and box, the angular relation of the springs 6 and 4 being on lines which intersect each other at some point above the screen box.

It will be seen that the tension which the springs 6 exert on the screen box is more or less in opposition to that which the spring or yielding legs 4 exert on said box. It will also be seen that any endwise movement of the screen box in the direction of progression of the material over and along the screen surface is in opposition to the tension which the legs 4 exert on the box, and that by reason of the action of springs l the discharge end of the. screen box or screen element is constrained to move sub.-

horizontal ,line.

in an are about the point of attachment of said legs to the sill members 3 of the supporting framework, and onlyto a limited degree of throw. But this arcuate movement is of such a slight curvature that its arc curvature maybe disregarded'for all practical purposes, and that the movement of the screenbox at its discharge I end may be properly said to be in a substantially straight lineand in the direction of progression of the material towards said discharge end. It will also be noted that by this arran ement the discharge end of the screen box is held against any substantial or appreciable vertical movement. In other words the discharge end of the screen box is so held and constrained in its movements by the legs 4 that the efiect of the vertical component of the vibrating forces, which produces the material agitating or screening movement of the vibrating devices, has practically or substantially disappeared, while the effect of the horizontal component of said forces, which is the material progressing or feed movement,

remains the same as at the beginning of the vibrating movement. "n the-other hand, the opposite end of .the screen box is influenced by the combined action of the vibrating means and the supporting springs 6, to move in a more or less predominating vertical direction. The resuit is that at the upper end of the screen box the effect of the vertical component of the vibrating forces is at its maximum. But, due to the combined action and cooperation of the spring tensions as the operation proceeds. the vertical component or screening movement decreases progressively as the horizontal or feedreti'cal axis of the unbalanced pulley, and b, b,-

' b 11 represents thetheoretical throw or range modified by the combined action of the springs" 6 and 4, during one complete revolution of the unbalanced pulley. It will be understood, that the oval b, represents the movement of the screen element at one spot or point in said transverse line, and that the same movement takes place at all points in said transverse line, at each complete revolution of the unbalanced pulley. Inspection of the oval graph b, reveals that its upper portion, although representing the movement due to one-half of a revolutionof the pulley, is more extensive and has a greater vertically inclined dimension than the lower portion of said graph, although said lower portion is produced also in one half of a revolution of the pulley and in the same length of time. This means that in the region of the upper end of the screen element where the material to be treated first reaches the surface of the screen element. the material receives a sharp and a somewhat substantially retards the screening action.

screening action being exerted thereon.

prolonged upward throw. This is a most desirable characteristicof the screening operation as it accomplishes a quick stratification of the material and separation of the oversized particles from the smaller particles, while at the same time, preventing the clogging up of the meshes of the screen element in the area which initially receives the material. It will also be seen that while the material is receiving this first sharp prolonged upwardly directed force it is subjected -to a horizontal impetus tending to displace the material in a feeding or progressing direction downwardly along and towards the discharge end of the screen element. Inspection of the graphs b, b, b, reveals that as the material feeds or progresses towards the discharge end of the screenelement, the sharpness of the upward throw. progressively wanes or diminishes while the horizontal feeding or progressing impetus remains 'fairly constant, as the material approaches the discharge end of the screen eleresult, and an apparatus which possesses these characteristics enables me to secure the advantages and benefits B seek in such apparatus. I have found in practice that not only is a better and more efficient screening action secured, but that result is attained in a shorter space of time. and at a very substantially slower speed of the vibrating means employed. For example, I have found that a speed of rotation of the unbalanced pulley type of vibrating means can be reduced to one thousand or eleven hundred revoluations per unit of time, whereas heretofore it has required a speed of some eighteenhundred or more revolutions. This result enormously reduces the wear and tear on the apparatus itself as well as the wrecking and pounding vibrations set up in the framework and settingof the apparatus. I have found also that by reducing the wear and tear on the apparatus itself a very substantial saving is effected in avoidingv breakdowns and breakage of the apparatus, and a longrn life of active and continuous operation is secured. I have also found thatv I am enabled to employ a very much shorter 'screen element in the direction of the feed of the material, thereby greatly reducing the cost of the apparatus and of the supporting framework therefor. I have also found in the practical u e of the apparatus that back-lash or reverse movements of the material is entirely avoided, which is a most important characteristic of the apparatus. as such back-lash or reverse travel of the material, which is present in many. types and forms of screening apparatus heretofore in use, very It has been endeavored to overcome this trouble by giving the screen element a greater degree of vertical tilt in its setting so as to enable gravity to act upon the material, especially the oversized particles thereof, and cause the same to be eliminated. But any. excessive tilting of the screen element produces undesirable movements of the material particles on or along the surface of the screen element without any This causes ineflicient screening of the material. I

have'found that in the practical operation of a screening apparatus embodying the principles above'set forth, I am enabled to employ a screen element set in only a slightly tilted position, or even in a horizontal position without impairment of its efilciency due to the action of gravity. Sometimes this becomes an important factor where the space available for the installation of the apparatus is limited and will not permit any great amount of tilting of the screen box.

I have also found that in some special uses of screening apparatus, for instance, in the handling of wet material, such as in oil well mud, sewerage,

and other similar purposes water jets are fre-,

quently employed to eliminate any excessive accumulations of material at one point or another of the screen element surface. The use of water jets in this manner, while being an expedient heretofore extensively employed in the use of screening apparatus, inevitably causes some loss of valuable quantities of particles of the material to be recovered, by being carried away by the water 'jets, but such water jets dilute the mud particles to be recovered. This is most undesirable. eration and dilutions of such methods are entirely avoided in the use of screening apparatus embodying my invention.

I ascribe the attainment of the advantages and benefits referred to, in the use of apparatus embodying my invention, to the fact that the discharge end of the screen element is yieldingly supported in such manner as to permit only an inappreciable vertical throw to be imparted to the material without any substantial variation in the horizontal or feeding movements imparted thereto, while the material receiving end of thescreen element is yieldingly supported in such manner as to permit a greatly predominating vertical throw or impulse to be applied to the material, and to the coordination of the actions exerted which permits the predominating vertical throw to be gradually and progressively eliminated as the screening actions progress along the feeding length of the screen element.

While in Figs. 1, 2 and 3, the screen box is shown supported in raised position above its supporting framework, the same advantageous results and benefits can be realized in a structure in which the screen box is-suspended beneath its supporting frame. Such a structure and arrangement is shown in Figs. 5, 6' and '7, wherein the screen box I is suspended beneath the sill members H, by means of yielding or resilient legs 12, which are securely bolted or otherwise fastened at their upper ends to the sill members H, and depending from said sills, are attached at their lower ends to the screen box III, at points adjacent the delivery end of the screen element. The material receiving end of the screen box is yieldingly supported by means of springs l3,

carried by rods H which extend through openings in a cross piece l of the base frame and are pivotally attached to the screen box. Interposed between the screen box and the cross piece l5 are one or more springs ii of relatively less tension than the springs l3, and the tension of which is arranged to act upon the screen box in opposition to that of the springs l3. This arrangement, as in the form shown in Figs. 1, 2 and 3, secures a smooth uniform action of the apparatus. The unbalanced pulley l1, Figs. 5 and 6, as in the case of Figs. 1 and 2, is mounted upon and carried by the screen box and, when rotated, imparts vibratory movements thereto.

It will be seen that the relative angles of inclination of the legs I! and springs l3 correspond The losses and inefficiency in op-- to like characteristics of the structure shown in Figs. 1, 2 and 3.

The mode of operation as well as the practical advantages and benefits attained in the arrangement shown in Figs. 1, 2 and 3 are also realized in ,the form shown in Figs. 5, 6 and 7.

In the diagrammatic views of Figs. 8 and 9, I have shown graphically the nature of the move-.- ments imparted to the screen element along its length in. feeding direction, in the case of the .suspended arrangement of screen box shown in Figs. 5, 6 and 7. The difference between Figs. 8 and 9 is that Fig. 8 illustrates the action when the material supply end of the screen box is permitted a freer vertical movement; that is when that end of the box is supported bya comparatively weak spring, whereas, Fig. 9 illustrates the action when the supporting resistance of the spring supports at the material supply end of the screen box, is increased.

In these diagrams the ovate graphs e illustrate graphically the exact movements of the screen element when in operation from the material supply end to the discharge end thereof. Here, again, it Will be observed that the vertical movements at the material supply end predominate, in both instances, over the horizontal or feed progressing movements, but they progressively decrease in the material feeding direction until they substantially disappear at the discharge end of the screen box, while the horizontal or feed progessing movements remain substantially constant.

In both Figs. 8 and 9 I have shown what would happen if the length of the screen element in material feeding direction should be unduly extended beyond the position of the supporting legs for the discharge end of the screen box. The line d, in each figure will represent the yielding or resilient supporting legs l2 of Figs, 5, 6 and 7. When it is attempted to carry the screening action beyond the point of attachment of the legs to the screen box it will be seen that the ovate graphs e, disclose an increase in the vertical movement, the increase growing greater and greater the farther beyond the spring supporting legs the screening operation is carried, see Fig. 8.

A comparison of the diagram of Figs. 8 and 9, shows the importance of adjustability of the tension of the springs which support the material receiving end of the screen box, in that when the tension resistance is increased (see Fig. 9), a more rapid elimination of the vertical throw is accomplished. I therefore prefer to. provide for the suitable adjustment of the supporting springs for the material receiving end of the screen box, thereby enabling the apparatus to be adjusted to the requirements of use to be encountered.

It will be seen that in the various forms of embodiment of my invention the screen box. at its material receiving end, is subjected to a combined vertical screening and horizontal feeding movement in which the vertical screening movements greatly-predominate over the horizontal feeding movements. This action is attained in each instance by supporting that end of the screen box upon springs, or spring tensions, which are applied in a line in angular or inclined relation to the screen element. The discharge end of the screen box is yieldingly supported but constrained against substantial vertical vibration while permitted a limited endwise or material feeding movement, the line of yielding support being inclined vertically in opposite direction with respect to that at the head end of the screen box. The result is that the screening movements, while greatest at the head or material receiving end of the screen box, gradually diminish as the feed of the material proresses towards the discharge end of the box, while the material feeding movements remain substantially constant throughout. I am enabled to secure this result by reason of the combined and conjoint action of the various features of vibrating means, and spring mountings, and the inclined relation of the linesof movements of the respective ends of the screen box.

In practice I prefer to mount the vibrating means upon the screen box at a point adjacent the area upon which the material to be treated is delivered to the screening element, and I also prefer. to arrange the vibrating means adjacent the inclined line of movement of the box permitted by the spring support at that end of the box.

From the foregoing description it will be seen that I secure a very speedy separation and removal of the various portions or particles of material under treatment, and amost eiiicient screening action for the more valuable portions or particles of the material. I am also enabled to eliminate or greatly reduce the transmission of pounding and disintegrating action to the supporting structure and framework of the apparatus. I am also enabled to secure more eillcient screening action at a greatly reduced speed of operation, and I am enabled to secure these substantial benefits and advantages by lighter and less costly structures, and with less wear and tear than heretofore.

While I have shown various forms of embodiment of my invention it is to be understood that, in its broadest scope my invention is not to be limited or restricted to the specific details of structure in any of its illustrated embodiments.

But having set forth and described my invention in various forms, what I claim as new and useful, and of my own invention is:

1. A vibrating screen structure including a screen box having a screen cloth therein, a support, a pair of transversely flexible leaf spring supporting legs secured to the support and attached to the screen box near its discharge end, the longitudinal axes of said legs being inclined upwardly and towards the feed end of the box,

a pair of longitudinally flexible resilient members interposed between the support and the box near the feed end, said members being resilient along lines inclined upwardly and towards the discharge end of the box, said supporting legs and resilient members forming the sole support for the box and a rotatable unbalanced vibration imparting member mounted solely on the screen box, said unbalanced member vibrating the screen box in a substantially oval path in a vertical plane at the feed end.

2. A vibrating screen structure including a screen box having a screen cloth therein, a support, a pair of flexible-leaf spring supporting legs secured at one end to the support and attached at the other end to the screen box near its discharge end, the longitudinal axes of said legs being inclined upwardly and at an angle towards the feed end of the box, a pair of longitudinally compressible resilient members interposed between the support and the box near the feed end, said members being resilient along lines inclined upwardly and at an angle towards the discharge end of the box, said supporting legs and compressible members forming "spring supports and coiled springs forming the sole support for the box, a rotatable unbalanced means mounted solely on the box to vibrate it, the longitudinal axes of the leaf spring supports and the coiled springs being respectively inclined upwardly and toward each other, whereby the downward vertical components of the centrifugal force of the unbalanced means coacting with the coiled springs move the box toward the discharge end against -the -resistance of the leaf spring supports.

4. A vibrating screen structure including a screen box having a screen cloth therein, a sup port, a pair of flexible leaf spring supporting legs secured at oneend to the support and attached at the other endto the screen box near its discharge end, the longitudinal axes of said legs being inclined upwardly toward the feed end of the box, a pair of longitudinally compressible resilient members interposed between the support and the box near the feed end, said members being resilient along lines inclined upwardly and toward the discharge'end of the box, said supporting legs and compressible members forming the sole support for the box, and a rotatable unbalanced means mounted solely on the box to vibrate it, whereby the downward vertical components of the centrifugal force of the unbalanced means coacting with the said resilient members move the box toward the discharge end to counteract the tendency of the screen box to move toward the feed end due to the inclination of'the flexible supporting legs.

5. In a screen structure a supporting base, a

screen box having a screen cloth therein, leaf spring supports having transverse flexibility for the discharge end of the screen box, means for securing each of said supports at one end to the base and at the other end to the screen box at the discharge end, coiled springs interposed between the screen box and the base at the feed end of the box, said leaf spring supports and coiled springs forming the sole support for the box, a rotatable unbalanced means mounted solely on the screen box to vibrate it, the longitudinal axes of the leaf spring supports and the coiled springs on the respective sides of the screen box being inclined upwardly toward each other so as to intersect, and means for adjusting the tension on the coiled" springs at the feed end of the box to lengthen or shorten the vertical movement of the box at that end.

6. A vibrating screen structure including a screen box having a screen cloth therein, a support, a pair of flexible leaf spring supporting legs secured to the support and attached to the screen box near its discharge end, the longitudinal axes of said legs being inclined upwardly and towards the feed end of the box. a pair of longitudinally flexible resilient members interposed between the support and the box near the feed end, said members being resilient along lines inclined upwardly and towards the discharge end of the box and exerting pressure in said direction, said supporting legs and resilient members iorming the sole support for the box, and a rotatable unbalanced vibration imparting member mounted solely on the screen box, the axes of 5 the supporting legs and the lines of longitudinal flexibility of the resilient members on the same side of the box intersecting at an angle so that said unbalanced member when rotated produces vertical and horizontal components or centrifugal 10 force during the last half of the downward revolution thereof which cooperate to move the screen box toward its discharge end.

7. In a screen structure, a supporting base, a screen box having a screen cloth therein, leaf is spring supports for the discharge end of the screen box having transverse flexibility, means for rigidly securing each of said supports at one end to the base and at the other end to the screen box at the discharge end, coiled springs interposed between the screen box and the base at the feed end of the box, said leaf springsupports and coiled springs iormlng the sole support for the box, a rotatable unbalanced means mounted solely on the box to vibrate it, the lonlast half of the downward revolution thereof' cooperate to move the screen box towards its discharge end, and means for varying the initial compression of said coiled springs.

' GUSTAVE A. OVERSTROM.

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