S&F Ref: P058756 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address IFE Aufbereitungstechnik GmbH, of Patertal 20, A-3340, of Applicant: Waidhofen/Ybbs, Austria Actual Inventor(s): Christian Karl Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Flip-flow screen The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(70704951) FLIP-FLOW SCREEN The invention relates to a flip-flow screen according to the preamble of Claim 1 and DE 34 11 719. This patent discloses a flip-flow screen with a screening surface which runs at an incline relative to vertical, wherein every second crossbar is moved in an approximately back and forth linear motion in order to tension and compress the bendable or elastic screening elements adjacent thereto in alternating fashion so that plugging can be prevented and so that the screened material can flow. This back and forth motion, which is in fact a motion along a section of a circular arc, is achieved by attaching the moving crossbars to pendulums mounted above the screen bed, the pendulums having a mass below the screen bed so that they oscillate when the screen casing oscillates and thereby bring about the intended motion of the crossbars. However, due to its complicated design, the asymmetric position relative to the inclined screen, the limited incline position associated therewith and the tendency for dirt to build up, this design has not found much favour. An improvement of the above patent is described in EP 197 191, wherein the moving crossbars are mounted such that they can move normal to the plane of the screen, held in the rest position by springs at a specified position, and are set into approximately linear motion through the motion of the screen casing. This causes the tensioning and compressing of the screen bed to always occur simultaneously in both screening fields symmetric with respect to the moving crossbars, which is not beneficial to the movement of the screened material. Moving the crossbars normal relative to the plane of the screen results in extremely minimal cleaning in the screen bed, presumably since there is no actual compression since the movement of the moving crossbar does not permit it. This device has not proven to be effective in practice and is not in use. An extremely complex screening machine is known from EP 1 228 814 in which the level of complexity was accepted so that the machine could be designed to be fully enclosed. In this screening machine, the screen bed is disposed on longitudinal bars that run along the slope line, the bars in turn being mounted tiltably on crossbars, wherein the crossbars are -2 held by spring elements in the rest position. The machine is driven eccentrically on the frame, the axis of rotation of the eccentric drive lying parallel to the lateral supports; nevertheless, because eccentric masses are provided in the bearings of the longitudinal supports, these supports execute the tilting motion provided, thereby effecting the elongation and compression of the screen bed from side wall to side wall. What is interesting is that in principal each longitudinal support is designed to be tiltable and that additional immovable auxiliary supports are provided in only one embodiment, which is not described in more detail. This device is extremely complicated and also fragile, and this complexity is probably only justifiable for some screening processes because of the ability to enclose such a screening device. Thus, the goal of the invention is to provide a simple and robust flip-flow screening machine which can also be easily tailored to different screening situations in at least one embodiment. According to the invention, these goals are achieved by the features indicated in the characterizing portion of Claim 1. In other words, the moving crossbars are held pivotably in the frame and are brought to a spring-supported rest position, the pivot axis and the centre of gravity do not coincide (more precisely: the instantaneous pivot axis main axis of inertia), this condition being achievable through appropriate geometry. This results in a system which can be vibrated without the need for the moving crossbars to have their own drives. In one embodiment, the crossbars have at least one radial arm on which an eccentric mass is provided. Preferably, the arm is provided at one of the ends of the crossbars located outside the frame. What is particularly preferred is to provide such eccentric masses on both sides symmetric relative to the centre plane of the screen. If the frame of such a screen is now made to vibrate, whether in linear oscillations or circular oscillations, every crossbar forms an elastic dual-mass system together with the frame as a result of the mounting and eccentric mass of the crossbar. The tilting motion of the moving crossbars induced thereby result in the tensioning and compression motion as is common in conventional dual-frame systems. This tilting motion is enhanced by -3 correctly selecting the spring characteristics such that the natural frequency of the moving crossbar system is near to the drive frequency of the screening machine. The moving crossbars can be mounted either in conventional shaft bearings (friction bearings or rolling bearings) and the rest position can be secured through torsion springs, for example, or else mounting can be achieved in rubber bearings or the like, which apply a restoring force and provide resiliency in the screening direction and normal thereto, which reduces impact loads to the frame and the crossbar. The invention is explained in more detail below with the aid of the drawing. Shown on Fig. 1 is a perspective side view of a screen designed according to the invention with a side wall, part of which is cut away, and on Fig. 2 the end of a crossbar together with bearing in a perspective view. Fig. I shows a flip-flow screen designed according to the invention in a horizontal configuration. A screen bed 3 is fastened to the upper ends of moving crossbars I and fixed crossbars 12, which are disposed in a frame 13 at the side panels 8 thereof in alternating fashion. The frame 13 and with it the screening surface are placed at an appropriate inclined position during operation, with bars 1, 12 running horizontally. Fig. 2 shows the end of a crossbar I of a flip-flow screening machine according to the invention. At the upper edge of the crossbar 1 is a fitted screen bed 2 fastened thereto, which can be achieved through screw attachment, insertion into corresponding notches in the crossbar 1 or through other fastening means known in the prior art. Usually, the screen bed 2 comprises individual elements that reach from crossbar to crossbar, as is indicated by the solid line 3 near crossbar 1. Crossbar I is mounted in side panel 8 of the screen frame such that it rotates eccentrically using a pivot bearing 7, in other words the centre of gravity 6 (and thus each of the main axes of inertia of the crossbars, the only meaningful axis being the one that runs practically parallel to the pivot axis 5) of the crossbar is at a distance from the pivot axis 5. Further, the distance of the centre of gravity 6 from the pivot axis 5 can be changed by attaching additional masses 11, thus allowing the natural frequency of the crossbar I to be changed.
-4 The additional masses 11 can be attached directly to the crossbar I or can be attached to another point of the system using a lever 10. External attachment is preferred here, and usually is, because of the better accessibility. As indicated in the figure, the eccentric mass 11 is not designed as a single piece, but consists of a plurality of individual discs, which enables the magnitude of this mass to be easily and quickly changed, thereby allowing adjustment according to the respective circumstances. It is also not necessary for the eccentric mass to have the cylindrical shape as shown, and the lever arm, the distance between the centre of gravity of the eccentric mass 10 and the pivot axis 5 can be designed to be adjustable. Another embodiment of the eccentric shifting can also be realized using brackets 4, levers or in another suitable way. Another embodiment option is a central attachment of the crossbar 1 to the pivot axis 5, whereby the centre of gravity 6 of the pivot axis is shifted by attaching additional masses 11 at a distance to the pivot axis 5. It is obvious that when the crossbar 1 is pivoted about axis 5, as indicated by double arrow 9, the upper area of the crossbar where it is connected to the screen bed 2 executes essentially linear back and forth motions, whereupon the screen bed 2 is compressed and tensioned to the right and to the left of the crossbar 1 in alternating fashion. More precisely, the crossbar I executes an arcing motion about a pivot axis that is fixed to the frame in the case of a fixed mounting; when the mounting is through rubber blocks or the like, only an approximately circular motion is made. For this reason, mention was made above of the "instantaneous pivot axis", but in reality all of these instantaneous pivot axes are at most only a few millimetres away from one another corresponding to the maximum linear deflection of the rubber bearings in a plane parallel to side panel 8. Side panel 8 of the screening device is made to oscillate appropriately, for which a wide variety of known devices exist in the prior art. If the oscillation is linear, it can be made parallel or at an incline relative to the plane of the screen bed 2, but a circular or elliptical oscillation can also be made using eccentric or crank shafts, etc. relative to the foundation. The mass in its entirety, which is solidly connected to side panel 8 (and rigidly if technically feasible), forms a two-mass oscillating system completely independent of the type of oscillation and of the way in which the oscillation is introduced to the screening -5 device, and thereby to side panel 8. This system consists of the mounting in the pivot bearing 7, which is able to pivot about axis 5, and the eccentric mass 11. The crossbar system is made to oscillate in its entirety, and therewith crossbar 1, bracket 4, pivot bearing 7, radial arm 10 and eccentric mass 11, as well as a corresponding arm and eccentric mass on the opposite side, if necessary. The alternating tensioning and compression of the screen bed 2 desired is achieved through this oscillation and the back and forth motion of crossbar 1 about axis 5 induced thereby. As mentioned above already, the mounting of crossbar 1 in side panel 8 does not have to occur through a classical pivot bearing, but can also be accomplished through mounting in rubber blocks, for example. In the process, the rubber blocks execute both the restoring force or restoring moment in the rotational sense about pivot axis 5, in addition to providing a certain degree of resiliency in both the vertical and the horizontal direction (in the same sense as the resiliency in the direction normal to axis 5 and parallel to the screening plane 2 and both normal to axis 5 as well as to the screening plane 2 and along axis 5); this makes anisotropic spring characteristics possible by appropriately selecting the geometry and composition of the rubber bearings. Possible materials for such crossbars and eccentric masses include all materials known in screen design, and one trained in the art and with knowledge of the invention would find it straightforward to appropriately select and dimension one. The other components are in accordance with the prior art, including the foundation supports and the drive, and therefore require no further explanation here. As a whole, the advantage compared to the prior art is in the compact design and the complete elimination of a second frame, which would have been connected to the moving crossbars and which as a whole oscillates relative to side panel 8. The screening device is extremely reduced in mass and volume, and it is furthermore possible to get by using only one drive-if necessary one drive per side panel-for the entire screen and it is easily possible to successfully tailor the process to the respective screening conditions since the eccentric masses are easily accessible.
-6 The invention is not limited to the exemplary embodiment illustrated and discussed, but can be modified in various ways. For example, it is not necessary for the radial arm 10 and the brackets 4 to point in the same direction. This can be done differently than what is shown, in particular for screen beds 2 that are placed at very steep angles. The radial arms can also be disposed inside the screening frame, and thus "in back of' the side panel 8, in particular for this opposite arrangement, which in particular facilitates the ability to enclose the machine, albeit with the increased difficulty in changing the dynamic eccentricity because work must be done underneath the screen bed and inside the frame. Finally, if no value is placed on the ease of changing the dynamic eccentricity, this can also be effected by correspondingly designing the crossbar 1, with the centre of gravity outside the pivot axis. What is important is that the rest position of the crossbar is safeguarded through a spring force, the upper area being correctly positioned at that point.