Patent Publication Number: US-6220447-B1

Title: Variable frequency screening apparatus

Description:
This application is a continuation of application Ser. No. 08/720,362 filed Sep. 27, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a powered screening apparatus, and more particularly, to a variable frequency screening apparatus used to separate and sort multiple size solids and particulates. 
     Vibrating screen arrangements have been used for many years in gravel and rock quarrying for sizing rock product and/or for removing undesirable material from the eventual finished product. Generally, the arrangements comprise a working member supported on a frame and an exciter arranged to impart vibrating motion to the member. The working member is fitted with a screen deck with a conventionally rigid aperture element which may be made up of a plurality of screening panels. 
     Despite the fact that the working member is vibrated in use, blinding of the apertures in the screening material occurs. When blinding occurs, separation of particulates becomes less uniform and less efficient. It is, therefore, an object of this invention to reduce blinding and improve efficiency. 
     Vibrating screen decks have been used widely in the past for separating particulates of various sizes and composition. Such screening decks typically comprise a rectangular frame suspended in operation with screen cloth mounted within the frame from which the materials are separated. The frame and screen in such decks are suspended at an angle. The entire frame is vibrated, thus imparting vibration to the machine which in turn causes the solids to move down the screen. As materials move down the vibrating screen, the solids of smaller mesh size pass through the screen with larger solids discharged from the lower end of the screen. 
     One disadvantage of such prior screening devices is imparting vibration to the entire system without a corresponding reduction in the blinding. Decks of this size can typically employ motors of forty horsepower (40 h.p.) or more. Another disadvantage of such prior decks is the susceptibility of frequent maintenance because the vibration is imparted to the entire deck for sustained lengths of time thus causing stress on joints of various fitted parts. Accordingly, it is an object of this invention to reduce stress on the joints of the various fitted parts. 
     Other screening apparatus have been developed which attempt to reduce a substantial energy requirement in such devices. In these apparatus, a plurality of small vibrator motors have been employed which are coupled to tappet shafts extending beneath the screen material at various locations spaced along the length of the screen. The tappet shafts are coupled by relatively complex linkages to a vibrator motor on the exterior of the frame deck. A plurality of tappet shafts or arms are positioned on the shaft which move eccentrically to strike the screen from beneath. The particular tappet arrangements in such decks necessitate relatively complex linkages and cause localized tapping of the screen both of which result in concentrated wear. Such power screening decks require frequent adjustment to keep the screen in contact with the tappets. Such prior screening decks are also susceptible to frequent blinding. It is, therefore, an object of this invention to eliminate the complex linkages, reduce frequent necessity for adjustment and increase the efficiency of the screening deck. 
     Yet another disadvantage of such prior screening devices is the inability to independently adjust the frequency with which various tappets spaced beneath the screen strike the screen. With other devices, the frequency with which tappets strike the screen is uniform. This uniform frequency causes a constant motion to the screening surface which in turn exacerbates blinding. It is, therefore, an object of this invention to permit the relative frequency that the tappets strike the screen to be selectively adjusted to vary the screen vibration which in turn reduces blinding and improves screening efficiency. 
     SUMMARY OF THE INVENTION 
     According to the invention, a screening arrangement defining a feed end and a discharge end comprises a pair of elongated side members extending between the feed end and a discharge end, a pair of support members each attached to opposing elongated side frame members, at least one screen deck comprised of a flexible material extended between and secured to the screen support members, a first striking frame arm shaft rotatably attached to opposing sides of said elongated side members, a second striking frame arm shaft rotatably mounted to said elongated side members and spaced from said first striking frame shaft, a pair of striking frames mounted to each striking frame shaft which alternately strike the under side of the screen material as each striking frame shaft pivots, means to selectively pivot each striking frame shaft such that said striking frames on each shaft to strike the screen material, a striking frame arm attached at one of its ends to one end of said shaft, and a connecting arm rotatably attached at its ends to and between the opposing ends of each striking frame arm. The screen apparatus may be held or supported at an angle with the discharge end lower than the feed end, thus permitting the screen material to form a downward slope which in turn permits particulates which do not fall through the screening material to discharge through the lower end or discharge end. 
     These and other objects, features and advantages of the present apparatus will be clearly understood to those skilled in the arts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the preferred embodiment of the variable frequency screening apparatus showing the components of the apparatus; 
     FIG. 2 is an end elevation view of the variable frequency screening apparatus as viewed substantially along the line  22  of FIG. 1 showing the striking frame in contact with the screening material; 
     FIG. 3 is a top view of the variable frequency screening apparatus showing the components of the apparatus. 
     FIG. 4 is a cross-sectional and elevational view of the variable frequency screening apparatus showing first striking frames in contact with the screening material; and 
     FIG. 5 is a side elevational view of the variable frequency screening apparatus showing second striking frames in contact with the screening material and the first striking frames withdrawn from the screening materials. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An overall view of the powered screening apparatus is shown in FIG.  3 . 
     The screen apparatus  10  comprises a generally rigid frame  12 , having a pair of longitudinally extended elongated side members  14  such as channel beams as shown in FIGS. 2 and 3. The elongated frame members  14  are held apart and spaced in generally parallel relationship to each other by transverse members  16  as shown in FIG.  3 . These transverse members  16  also provide support for the screening material  18 . 
     Screening material  18  is contained within the frame  12 . Solids and particulates pass over the screening material  18  to be separated. Transverse members  16  are attached conventionally such as by welding to opposing sides members  14 . 
     At least one pair of striking frame shafts  20  are spaced generally parallel to transverse member  16  and beneath screening material  18 . Striking frame shafts  20  are pivotally attached to frame members  14 . A rigid shelf member  22  is provided outboard of frame members  14 . A conventional bearing  24  is attached to shelf  22  on opposing sides of frame members  14 . Bearings  24  are arranged to carry striking frame shafts such that striking frame shafts  20  are essentially perpendicular to the inboard portion of frame members  14  and beneath screen material  18 . 
     A first striking frame  26  is attached to each striking frame shaft  20  essentially along its length beneath the screening material  18 . A second striking frame  28  is attached to striking frame shaft  20  essentially parallel to striking frame shaft  20  and essentially parallel to first striking frame  26 . The second striking frame  28  is mounted beneath screening material  18 . First striking frame  26  and second striking frame  28  are attached conventionally to striking frame shafts  20  as by welding. Said first and second striking frames may be selectively distanced from said shaft by elongating or shortening striking frame arm  27  and arm  29  on said first and second striking frames. 
     A means for imparting motion and vibration to the screening material is generally shown at  30 . A striking shaft arm  32  is attached at each end  31  of striking frame shaft  20  outboard of frame members  14 . Connecting arms  34  are connected at end  36  of the striking shaft arms. Each end  36  of each connecting arm  34  is rotatably attached to end  36  of each striking shaft arm  32 . An eccentric shaft arm  38  is connected at one end  40  to a link  41 . The other portion of link  41  is attached to striking shaft arm  32  near the end  36  of striking shaft arm. The opposite end  42  of eccentric arm  38  is attached to one end of eccentric shaft  44 . A sheave  46  is attached to eccentric shaft  44 . A second sheave  48  is attached to shaft  50  of a conventional electric motor  52 . Sheaves  46  and  48  are aligned such that drive belt  54  permits sheave  48  to drive sheave  46 . Eccentric shaft  44  is rotatably attached through bearing  56  and is attached outboard to frame member  14 . 
     An important feature of the present invention is controlling the frequency and amplitude of the individual striking frames thus varying the screen vibration over the length of the screen during operation. Various materials separate better by imparting different frequencies and amplitudes of vibration to the screen material. Accordingly, the ability to control the frequency and amplitude of each striking frame at different locations along the screen is a desired quality of the present invention. To this end, the length of the striking frame arm  27  and the length of the striking shaft arm  32  may be selected to achieve the desired amplitude at each location along the screen. 
     Vibration control circuits for motor  52  have not been shown because they are within the selection of one skilled in the art from a wide range of speed controls which have been employed for other purposes. It will be recognized by those skilled in the art that varying the speed of motor  52  will provide additional control of the frequency of the vibration imparted to screen material  18 . 
     The operation of the variable frequency screening apparatus according to the invention is as follows: 
     The bulk material is loaded at the feed end  56  onto the stop of screening surface  18 . As a result of the vibrations imparted to the screening material, the bulk material moves down along the screening material  18 . As the material moves along the screening material  18 , smaller particles drop through the apertures in the screening material  18 . 
     The vibration is imparted to the screening material by activating motor  52 . As first striking frame  26  strikes the under surface of screening material  18 , the second striking frame  28  rotates away from and out of contact with the under surface of screening material  18 . This motion is illustrated in FIG.  4 . As striking frame  26  rotates downward away from the under side of the screening material  18 , second striking frame  28  rotates upward and strikes the under side of screening material  18 . This motion is illustrated in FIG.  5 . The alternating or oscillating of first striking frame  26  and second striking frame  28  at various frequencies causes a flexing of screen material  18  thus eliminating blinding of the screening material. 
     Although the invention is described and illustrated with Preference to a specific embodiment thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment, but is capable of numerous modifications within the scope of the intended claims.