BACKGROUND TO THE INVENTION

THIS invention relates to a screen assembly of the type which can be used to screen crushed rock and the like under the influence of vibratory agitation.

Screens of the aforementioned type are used extensively in the mining industry and are notable for being particularly robust and large. Generally the screen will comprise a rectangular frame on which a screen surface is mounted and the frame will be vibrated in order to impart the necessary vibratory motion to the screen surface.

One of the problems associated with the aforementioned type of screen arises on account of the large size of the equipment. Where the screen needs to be replaced this can generally only be done with the aid of a large crane which must be brought into position in order to lift the screen from its foundations. Handling and repair of the screen is thus a logistical operational problem and replacement of such screens can lead to considerably down time for the operation in which the screen is being used.

It often occurs that certain areas of the screen surface tend to wear faster than others. However, where this occurs, and if the screen surface cannot be repaired in-situ, the entire screen equipment needs to be removed and repaired leading to the aforementioned lengthy downtime. In-situ repair of such screens is also difficult on account of the generally hazardous and confined working environment. Accordingly, the general maintenance and repair of such screens tends to cause significant problems to the operating personnel and adds considerably to the , cost of running the operation in which the screen is installed.

SUMMARY OF THE INVENTION

According to the invention there is provided a screen assembly comprising:

a support frame adapted to be mounted to a suitable support foundation;

a plurality of screen elements resiliently mounted to the support frame in generally edge to edge relationship so as to define a generally planar screen surface; and

vibration means connected to each of the screen elements to individually vibrate each of the screen elements.

Preferably the support frame is of generally rectangular configuration having a feed end and a discharge end and the individual screen elements are similarly configured in a rectangular configuration and arranged in a series of banks of screen elements, each bank comprising a plurality of side by side screen elements extending transversely across the width of the screen assembly The screen surface will preferably be made up of a series of banks of screen elements, each bank of screen elements having a feed end and a discharge end. The discharge end of one bank of screen elements preferable overlaps the feed end of its adjacent bank of screen elements.

The individual screen elements are preferably mounted on suspension means to the support frame. The suspension means may include first and second suspension elements mounted below the feed and discharge ends respectively of the screen elements. The suspension elements may each comprise one or

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more suspension arms which are pivotable relative to resilient mounts by means of which the suspension arms are connected to the support frame. The suspension arms may comprise "Rosta" mount type suspension devices. The individual screen elements may include a planar, non-pervious strip adjacent either the feed or discharge end thereof which will overlie the suspension element there below to limit the discharge of screened material onto the suspension elements.

The vibration means may comprise a pair of eccentrically weighted shafts which are connected to each of the screen elements via brackets. Preferably each bank of suspension elements will be vibrated by means of its own pair of eccentrically weighted shafts. Each screen element may include a pair of eccentric weights rotationally mounted on the connection brackets, the weights of adjacent screen elements being connected together by common shafts for each bank of screen elements. A suitable drive arrangement will be provided for driving the shafts of the respective banks of screen elements.

The connection brackets are preferably angled forwardly and the arrangements of the weights are such that the maximum amplitude of the vibrations will be in a forward direction thereby providing a forward impetus to material to be screened by the screen elements. The material on the screen elements will thus tend to move from the feed end to the discharge end of the screen elements as a consequence of the direction of vibration of the screen elements by the vibration means.

An embodiment of the invention is described in detail in the following passages of the specification which refer to the accompanying drawings. The drawings, however, are merely illustrative of how the invention might

be put into effect, so that the specific form and arrangement of the various features shown is not to be understood as limiting on the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a plan view of a screen assembly according to the invention;

Figure 2 shows a cross-sectional view of the screen assembly shown in

Figure 1 along line 2-2 depicted in Figure 1 ;

Figure 3 shows a detailed side view of a screen element for use in the screen assembly depicted in Figures 1 and 2;

Figure 4 shows an enlarged detailed side view of the discharge end of a screen element;

Figure 5 shows a detailed side view of the feed end of a screen element;

Figure 6 shows a detailed perspective view of a second embodiment of a screen element according to the invention;

Figure 7 shows a perspective view of a support frame having screen elements of the type depicted in Figure 6 mounted thereto; and

Figure 8 shows a similar view to that of Figure 7 but with only a single screen element mounted to the support frame.

DETAILED DESCRIPTION

A screen assembly 10 as shown in the drawings is a generally rectangular configuration and has a side wall 12 for containment of material to be screened (not shown). The screen assembly 10 has a feed end 14 onto which the material to be screened will be fed and a discharge end 16 from which material which has not passed through the screen during the screening process will discharge. The screen assembly 10 has a screen surface 18 which is comprised of a plurality of screen elements 20, the screen elements 20 being arranged side by side in banks 22.

The individual screen elements 20 will be movable relative to each other and for this purpose are individually mounted to a support frame indicated at numeral 24 in Figure 2 of the drawings. The individual screen elements 20 are each mounted via suspension means to the support frame 24 in a manner as will be described in more detail here below.

The individual screen elements are vibrated by vibration means 26. Each bank 22 has a drive motor 28 associated therewith and that drive motor 28 will drive a pair of shafts numbered 30 and 32 which will provide the drive force for vibratory arrangements associated with each of the respective screen elements. The vibratory arrangements will be described in more detail here below.

As will be clear from Figure 1 of the drawings, the screen surface 18 is basically continuous with the individual screen element in each bank 22 being spaced relatively close to each other in a side by side relationship. Each screen element 20 has a feed end 34 and a discharge end 36 with the discharge end of one screen element overlying the feed end 34 of the screen element adjacent thereto in the direction of the general travel of the screen assembly 10. The arrangement is best seen in Figure 2 of the drawings in which the direction of travel of the material being screened is depicted by arrow 38.

Each screen element 20 is comprised of a screen panel 40 which is supported by a plurality of cross bars 42 which in turn span between carrier beams 44 which run length wise of the screen elements, that is, extend between the feed end 34 and the discharge end 36 of the screen elements.

Each screen element is mounted, front and back, by suspension means to the frame 24. The suspension means comprises a first suspension element 46 located below the feed end 34 of the screen element and a second suspension element 48 located below the discharge end 36 of the screen element. This arrangement is best seen in Figures 5 and 6 of the drawings. The first and second suspension elements comprise "Rosta" mounts which a two arm suspension arrangements manufactured by Rosta- Werk AG of Switzerland. This type of suspension arrangement is well known in this type of industry and need not be described herein in any great detail. Basically Rosta mount suspension elements comprise a pair of arms 50, each end of which is mounted via a square rubber bush into a mounting bracket, and rotation of the arm in relation to mounting bracket is resisted by the square rubber bush. Each suspension element 46 and 48 comprises a pair of arms and four rubber

bushes as shown in the drawings.

As previously mentioned, the discharge end 36 of each screen element overlies the feed end 34 of the element which is adjacent thereto in the direction of material feed 38. A gap 54 is thus defined at this overlap. A seal 56 is located in this gap so as to prevent material to be screened passing through the gap 54 and into the area below the screen surface without being screened. The seal 56 has a resilient seal so that vibration movement between adjacent screen elements will not damage the seal. In a preferred form of the invention the seal 56 is comprised of an angle bracket 58 which is mounted via a single Rosta mount 60 to the leading end 34 of the lower screen element. The angle bracket 58 has an elastomeric lip 62 which will engage against the underside 64 of the upper screen element should these components come into contact with each other. Any hard impact between the two screen elements will tend to rotate the angle bracket 58 against the action of the Rosta mount 60.

The trailing end of each screen element has an impervious strip 64 fitted thereto to prevent screen material falling onto the suspension arrangements. This impervious strip 64 is preferably formed from a polymeric, resilient material and serves to lead material to be screened from the discharge end of one screen element onto the feed end of the adjacent screen element.

The vibration arrangement for the screen elements is substantially conventional for screen assemblies of this type except that in this case each screen element is individually vibrated. As shown in Figures 3 and 4, each screen element has an upstanding bracket 66 mounted thereto which leans forwardly at angle α which is approximately equal to 45°. The shafts 30

and 32 pass through the bracket 66 as shown and eccentric weights 68 and 70 are fitted respectively to the shafts 30 and 32. The shafts 30 and 32 will rotate in synchronisation so that the eccentricity of the weights counteract the amplitude of the vibrations in certain positions of rotation and amplify the vibrations in other positions of rotation. The principle of vibrating screens using a pair of synchronised weights to move material towards the discharge end of the screen assembly is known and need not be described in greater detail herein. It suffices to say that the vibration will have the effect of moving material to be screened from the feed end to the discharge end of each individual screen element. As shown in Figure 4 it is preferred that each screen element 20 has a pair of brackets 66 on opposite sides of which two sets of eccentric weights are mounted as shown. The brackets are connected together by means of spacer tubes 72 through which the shafts 30 and 32 pass. It is envisaged that the weights will provide approximately 1800 kgf total force on the screen elements but clearly for different configurations and arrangements of screen, different vibratory characteristics are envisaged.

As shown in Figures 6 to 8, a screen element 110 comprises a pair of parallel main carrier beams 112 which support a plurality of cross bars 114. Screen panels 1 16 are, in turn, supported on the cross bars 1 14. The panels 116 may comprise interconnected polyurethane or polyethylene panels.

A pair of mounting brackets 1 18 are mounted to the beams 1 12 and these brackets 118 carry a pair of vibratory motors 120 for vibrating the screen element. Each of the motors 120 has a pair of eccentric weights 122 fitted thereto so as to be rotatable with the motor, the effect of the rotation of the weights being to impart a vibratory motion to the screen element 1 10. The

motors 120 are fitted to U-shaped support brackets 126 which are mounted to the mounting brackets 1 18. It will be noted that the support brackets 126 are mounted peφendicular to each other. The motors 120 and support brackets 126 are basically identical to each other so that replacement spares for the screen element are interchangeable with each other.

The screen element 1 10 has a resilient back flange 128 formed of a polyethylene material, the resilience being adapted to accommodate vibration of the screen element, particularly where the motors are starting up or slowing down. The screen element is mounted on suspension means 130 which is of the type described in more detail with reference to Figure 5.

The screen element 1 10 shown in Figure 6 of the drawings may be mounted within a support frame on its own or it may be mounted in banks as described above. As shown in Figures 7 and 8 of the drawings, where the screen elements 110 are mounted in banks the screen assembly will include side walls 132 and downwardly extending chutes 134 which lead to outlets 136 through which the screen material will pass. The material which does not pass through the screen will pass through the end chute 138. The motors 120 of adjacent screen elements will be connected together by shafts 140 which will serve to keep the banks of screen elements vibrating together so that individual screen elements vibrate in synchronisation with each other. The shafts 140 may have protective sleeves 142 fitted between the adjacent motors.

The advantage of the screen element described with reference to Figures 6 to 8 is that it is an entirely self-contained unit. Thus, the screen element will operate effectively whether it is used on its own, or as part of a bank of screen elements. The operator of a screening plant can therefore keep in stock one or more screen elements 1 10 and in the event of a screen element

requiring maintenance or replacement a replacement screen element will be readily available from stock. Thus, the operation in which the screen element is used will be interrupted for only a relatively short period of time, that is, the time it takes to lift out the malfunctioning screen element and replace it with a spare unit. Generally an overhead travelling crane will permanently be mounted above the screen assembly for lifting out the screen elements as and when required.

From the aforegoing it will be appreciated that repairing of the individual screen elements will be relatively easy to achieve. Any defective or broken screen element can be individually replaced by simply disconnecting that screen element from its suspension means and removing the vibratory shafts therefrom to enable it to be lifted away from the remaining portion of the screen. Since each individual screen element can be replaced separately from the others, it is not necessary to remove the entire screen assembly from its location in order to repair it and therefore it is envisaged that interruption to the operation in which the screen element is an integral part will be minimised. Also, the lifting arrangement required to lift the individual screen elements will be significantly lighter than would be the case if the entire screen assembly had to be removed for repair and maintenance. It is envisaged that significant overall savings will be achieved using a modular screen assembly of the type described herein over prior arrangements where this individual replacement was not possible.