GB2351247A

GB2351247A - Mobile screening apparatus

Info

Publication number: GB2351247A
Application number: GB9914498A
Authority: GB
Inventors: Anthony Devlin; Richard Patrick Byrne; Gordon Hugh Dunn
Original assignee: Finlay Hydrascreens Omagh Ltd
Current assignee: Finlay Hydrascreens Omagh Ltd
Priority date: 1999-06-22
Filing date: 1999-06-22
Publication date: 2000-12-27
Anticipated expiration: 2019-06-22
Also published as: GB2351247B; GB9914498D0

Abstract

Mobile screening apparatus 1 comprises a support frame 3 carrying a hopper assembly 4 and a reject grid 41 over a hopper 42, conveyor means 5 extending longitudinally of the support frame beneath the hopper assembly for receiving material passed through the hopper and conveying it to a screening device 6 adapted to screen passed material into at least two fractions of different coarseness and to pass each such fraction to a separate discharge means 7 for discharge from the apparatus. The conveyor means includes a main conveyor 52 having a support boom 521 formed by an upwardly inclined proximal section 522 and 523 joined to a distal section at a pivot joint 525. The distal section of the main conveyor support boom and the screening device are each pivotally mounted 601 with respect to the support frame, and means 602 is provided for raising and lowering the screening device and distal conveyor section between a working position in which the distal conveyor section forms an upwardly extending extension of the proximal conveyor section and the screening device is arranged to discharge at least one oversize fraction of screened material onto the inboard end 721 of a side discharge conveyor 72, and a transport position which is of reduced height.

Description

2351247 MOBILE SCREENING APPARATUS.

This invention relates to mobile screening apparatus of the type which includes a support frame carrying a hopper assembly comprising a reject grid over a hopper, conveyor means extending longitudinally of the support frame beneath said hopper assembly for receiving material passed through the hopper and conveying it to a screening device adapted to screen passed material into at least two fractions of different coarseness and to pass each such fraction to a separate discharge means for discharge from the apparatus.

The conveyor means typically comprises an upwardly inclined conveyor which is arranged to discharge material to be screened to the upper end of a longitudinally inclined screening device. In order not to increase the overall length of the apparatus too much, the screening device is located in a space beneath the upwardly inclined conveyor feeding it. The screening device may incorporate one screen for separating the material into fine and coarse fractions, or two screens for separating the material into fine, medium and coarse fractions as desired. It would be possible to incorporate more screens, but spatial constraints make discharge of four or more fractions difficult and demand for such a machine is low. The size of the screen or screens may be adapted for specific tasks such as the screening of sand and gravel or coarse aggregates from the mining, quarrying or demolition industries, for top-soil screening and for coal processing.

It will be apparent that for many industrial purposes it is desirable to increase the throughput capacity of such screening apparatus. There are various known ways of increasing throughput capacity, for example by making use of an inclined screen and/or a vibrating screen, but ultimately, 2 the only way of increasing the throughput is to make the apparatus bigger, that is to say, to make the screening device wider and longer. Since the screening device and the conveyor feeding it are inclined, making them longer would also entail making them taller, and this is where the problem 5 lies.

It will be apparent that the requirement for the presence of a screening apparatus at any given site may be shorter than the working life of the apparatus: indeed for top-soil and demolition screening operations, the presence of the apparatus may only be required for a few weeks or even a few days. Thus there is a requirement that the screening apparatus should be mobile so that it can be transported from site to site; this generally has to be done by road. The presence of bridges over roads imposes a maximum allowable height on such apparatus.

It is an object of the present invention to provide a mobile screening apparatus which affords a favourable compromise as between its height and its throughput capacity.

According to the present invention, there is provided mobile screening apparatus which comprises a support frame carrying a hopper assembly comprising a reject grid over a hopper, conveyor means extending longitudinally of the support frame beneath said hopper assembly for receiving material passed through the hopper and conveying it to a screening device adapted to screen passed material into at least two fractions of different coarseness and to pass each such fraction to a separate discharge means for discharge from the apparatus, wherein said conveyor means includes a main conveyor having a support boom formed by an upwardly inclined proximal section joined to a distal section at a pivot joint, wherein the distal section of the main conveyor support boom 3 and the screening device are each pivotally mounted with respect to the support frame, and wherein means is provided for raising and lowering the screening device and distal conveyor section between (a) a working position in which the distal conveyor section forms an upwardly extending extension of the proximal conveyor section and the screening device is arranged to discharge at least one oversize fraction of screened material onto the inboard end of a side discharge conveyor, and (b) a transport position which is of reduced height.

Since the screening device and its overhead conveyor can be folded down for transport, a favourable compromise is reached between total height in the transport configuration and height and length and thus throughput capacity in the working configuration.

The extent of such favourability is promoted by increasing the extent to which the main conveyor and screening device can be folded down, though no further advantage is to be gained by folding down beyond the horizontal when their height would be determined by the height of the conveyor pivot axle. It is accordingly preferred that the distal conveyor section and the screening device extend generally horizontally in the transport position.

There is no advantage to be gained in terms of headroom clearance by reducing the height of the main conveyor and screening device below the height of the hopper assembly, and hopper capacity is increased by making it as tall as possible. It is therefore advantageous for the hopper assembly and the main conveyor to be of substantially the same height when the apparatus is in the transport configuration.

4 Efficiency is promoted when, as is preferred, the reject grid of the hopper assembly is lowerable from an inclined working position to a transport position in which the hopper assembly is of reduced height.

Apparatus according to the invention also preferably has one or more of 5 the following optional features and advantages associated therewith:

The means for raising and lowering the screening device and distal conveyor section includes at least one fluid operated ram; this is convenient and facilitates setting up of the apparatus on arrival on site and its striking preparatory to transport to a next site; At least one extensible support leg extends between an end portion of the support frame and a distal portion of the screening device and/or of the distal conveyor section for supporting them in the working position; this promotes the structural efficiency of the machine; The or each said support leg is extensible by a fluid-operated ram; this is a simple and convenient way of controlling and powering raising and lowering of the screening device and main conveyor; Means is provided for locking the or each said extensible support leg at a selected one of a plurality of extensions; this allows the screening device and the main conveyor to be held in a stable manner at a selected one of a plurality of inclinations to the horizontal; A longitudinal discharge conveyor is provided beneath the screening device for receiving a fine fraction of screened material and discharging it to one end of the apparatus; this promotes narrowness of the apparatus and thus its ease of transport from site to site; it is alternatively of advantage in increasing the number of possible discharge conveyors, The fines discharge conveyor is connected to the screening device and/or main conveyor for raising and lowering therewith; this is a convenient way of raising the discharge end of the fines discharge conveyor which allows it to discharge material to form a taller and thus larger stockpile or directly into a truck or wagon of larger size than would otherwise be possible; The fines discharge conveyor may be connected to the screening device by means of one or more extensible connector struts; The or each extensible connector strut may be extensible under fluid ram control; this has the advantage of allowing a degree of independent variation of the inclination of the fines discharge conveyor; The fines discharge conveyor includes an outboard end section which is pivotally connected to an inboard section so that the outboard section may be folded upwardly into a transport position thereby to shorten the apparatus without substantially increasing its height; The screening device includes two screens for screening material into fine, medium and coarse size fractions and is, in the working position, adapted to pass the medium and coarse fractions to the inboard ends of two different respective side discharge conveyors; The two different respective side discharge conveyors are arranged to discharge material to opposite sides of the apparatus; this is most convenient for allowing large stockpiles to be built up and/or for allowing truck access to positions beneath either or both of such side discharge conveyors; A chute is provided for guiding the coarse fraction over the inboard end of the medium fraction discharge conveyor for discharge onto the inboard end of the coarse fraction discharge conveyor, this is a convenient way of maintaining separation of those fractions after screening; The or each side discharge conveyor has an outboard section which is movable from a working position, to a transport position in which that 6 outboard section is folded inwardly and downwardly so that it extends longitudinally of the apparatus with the conveying surface being generally vertical, and back; this allows the width of the apparatus to be kept within limits for road transportation while at the same time allowing the side 5 discharge conveyors to be longer so their discharge ends are higher; Said hopper assembly includes at least one screen; this allows rejection of a second oversize fraction of material; such second oversize fraction may be discharged to the same side of the apparatus as the fraction rejected by the reject grid, or to a different side; either or both of those fractions could be discharged to ground, to a further conveyor, for example to some other machinery, for example to a crusher; Said hopper assembly includes sprung mounts carrying said reject grid and means is provided for vibrating such grid; this promotes throughput and militates against jamming; The conveyor means includes a longitudinal hopper conveyor located beneath the hopper for receiving material passing through the hopper and passing in to the proximal end of the main conveyor; the screening device has to be inclined quite steeply for example in the range 20' to 30' in order to promote a high throughput, and this has a determining effect on the inclination of the main conveyor; a conveyor section beneath the hopper does not need to be so steeply inclined as the main conveyor; such an arrangement promotes height-wise compactness at the hopper end of the apparatus; The support frame carries a hydraulic pump for driving the conveyor means; this is a simple and convenient way of carrying power to the conveyors The or at least one screen of the screening device is carried by a screenbox mounted to a screen subframe by sprung mounts and means is 7 provided for vibrating such screenbox; this promotes a high throughput for a given size and shape of screen, and it militates against jamming; The apparatus as a whole may be supported and arranged for transport in various ways. In some preferred embodiments of the invention, a read end of the support frame is itself supported by a wheeled subframe assembly, for example a twin axle unit while its other end is arranged for support by legs when in the working configuration, and for coupling to and support by a road tractor unit for transport from site to site.

The invention is of particular advantage in embodiments in which the support frame is carried by a tracked bogie. Embodiments of the invention whose main frames are supported by tracks are much easier to move about on site than are embodiments whose main frames are supported by legs in the working configuration: the apparatus can be moved on those tracks from one position on site to another, for example at about walking speed. A leg-supported wheeled apparatus requires to be hitched to a tractor unit and then moved. But for transportation from site to site, a tracked apparatus requires to be loaded onto a transporter such as a "low-loader", and this of course will add to the height of the apparatus above ground level. It is thus of particular importance to achieve a height saving in such embodiments.

Preferably, the support frame carries hydraulic means for driving the tracks of the bogie whereby the apparatus is a self-propelled apparatus.

Different hydraulic circuits are advantageously provided which are so arranged that power cannot be applied to the conveyors while power is being applied to the tracks; this has advantages in safety.

8 Preferred embodiments of the invention will now be described in greater detail with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a side elevation of a screening apparatus loaded onto a trailer for transport from one site to another, and Figure 2 is a corresponding view of the same apparatus set up in its working configuration, and Figure 3 is a side elevation of a second embodiment of screening apparatus set up in its working configuration.

In the drawings, Figure 1 is a side elevation of a screening apparatus 1 loaded onto a trailer 2 for transport from one site to another, and Figure 2 is a corresponding view of the same apparatus 1 set up in its working configuration. Figure 3 is a side elevation of a second embodiment of screening apparatus set up in its working configuration in which similar integers are given like reference numerals.

The mobile screening apparatus 1 comprises a support frame 3 carrying a hopper assembly 4 comprising a reject grid 41 over a hopper 42. Conveyor means 5 includes a hopper conveyor 51 and a main conveyor 52 which extend longitudinally of the support frame 3. The hopper conveyor 51 extends beneath the hopper assembly for receiving material passed through the hopper 42 and conveying it to the main conveyor 52 and thence to a screening device 6 adapted to screen passed material into at least two fractions of different coarseness and to pass each such fraction to a separate discharge means 7 for discharge from the apparatus.

In the illustrated apparatus there are three separate discharge conveyors 71, 72, 73.

9 As mentioned, the conveyor means 5 includes a longitudinal hopper conveyor 51 located beneath the hopper 42 for receiving material passing through the hopper 42 and passing in to the proximal end 522 of the main conveyor 52. The screening device 6 has to be inclined quite steeply, for example in the range 20' to 30' in order to promote a high throughput, and this has a determining effect on the inclination of the main conveyor 52; a conveyor section 51 beneath the hopper 42 does not need to be so steeply inclined as the main conveyor 52. The use of a separate conveyor section 51 beneath the hopper allows that section to have a much less steep inclination, and this promotes height-wise compactness at the hopper end of the apparatus; The main conveyor 52 has a support boom 521 formed by an upwardly inclined proximal section, itself formed in two parts 522, 523 joined to a distal section 524 at a pivot joint 525. The distal section 524 of the main conveyor support boom 521 and the screening device 6 are pivotally mounted 601 with respect to the support frame, and means 602 is provided for raising and lowering the screening device 6 and conveyor distal section 524 between (a) a working position as shown in Figure 2, in which the distal 20 conveyor section 524 forms an upwardly extending extension of the proximal conveyor section 522, 523 and the screening device 6 is arranged to discharge at least one oversize fraction of screened material onto the inboard end 721 of a side discharge conveyor 72, and (b) a transport position as shown in Figure 1, which is of reduced height.

Since the screening device 6 and its overhead main conveyor 52 can be folded down for transport, a favourable compromise is reached between total height in the transport configuration (Figure 1) and height and length and thus, for a given width, throughput capacity, in the working configuration (Figure 2).

The extent of such favourability is promoted by increasing the extent to which the main conveyor and screening device can be folded down, though no further advantage is to be gained by folding down beyond the horizontal when their height would be determined by the height of the conveyor pivot axle. It is accordingly preferred that the distal conveyor section 521 and the screening device 6 extend generally horizontally in the transport position, as shown in Figure 1.

There is no advantage to be gained in terms of headroom clearance by reducing the height of the main conveyor 5 and screening device 6 below the height of the hopper assembly 4, and hopper capacity is increased by making it as tall as possible. It is therefore advantageous for the hopper assembly 4 and the main conveyor 5 to be of substantially the same height when the apparatus is in the transport configuration, again as shown in Figure 1.

Efficiency is promoted when, as is preferred, the reject grid 41 of the hopper assembly 4 is lowerable from an inclined working position as shown in Figure 2 to a transport position in which the hopper assembly is of reduced height as shown in Figure 1. It may be useful to have the grid arranged for setting at a number of intermediate inclinations. Grid 41 may for example be pivotable about axle 411 under control of gearing 412 actuatable by hydraulic pump 8.

The hopper assembly 4 may include a screen 43 in order to allow 25 rejection of a second oversize fraction of material; such second oversize fraction may be discharged to the same side of the apparatus as the 11 fraction rejected by the reject grid, or to a different side, that is, to the opposite side or to the back; either or both of those fractions could be discharged to ground, or to a further conveyor, for example leading to some other machinery, such as a crusher, or otherwise.

The hopper assembly 4 may also include sprung mounts carrying the reject grid 41 and means for vibrating such grid in order to promote throughput and militate against jamming An extensible support leg 9 extends between an end pivot 31 of the support frame 3 and a distal portion 611 of a subframe 61 of the screening device for supporting that and the distal conveyor section 521 in the working position as shown in Figure 1.

The means for raising and lowering the screening device and distal conveyor section include fluid operated rams (not shown) which are located alongside extensible support legs 9 and which operate to control the lengths of those legs Means is provided for locking the or each said extensible support leg 9 at a selected one of a plurality of extensions; this allows the screening device and the main conveyor to be held in a stable manner at a selected one of a plurality of inclinations to the horizontal. This is conveniently done by drilling the telescoping sections of those legs at intervals and provided pins (not shown) to interengage with those holes and thus lock the lengths of the legs.

The outboard end of the distal end section 521 of the main conveyor 52 is supported at each side by a strut 62 of fixed length extending between a lug 621 on the conveyor and a lug 622 on the screen subframe 61. At its 12 inboard end, the distal end section 521 of the main conveyor 52 is supported at each side by a telescopic strut 63 extending between a lug 631 on the conveyor and a lug 632 on the screen subframe 61.

A longitudinal discharge conveyor 71 is provided beneath the screening device 6 for receiving a fine fraction of screened material and discharging it to one end of the apparatus; this promotes narrowness of the apparatus and thus its ease of transport from site to site; it also allows the number of discharge conveyors to be conveniently increased to three.

The fines discharge conveyor 71 is connected to the subframe 61 of the screening device 6 for raising and lowering therewith; this is a convenient way of raising the discharge end 710 of the fines discharge conveyor 71 which allows it to discharge material to form a taller and thus larger stockpile or to discharge directly into a truck or wagon of larger size than would otherwise be possible.

The fines discharge conveyor may be connected to the screening device by means of one or more extensible connector struts such as 711, and the or each extensible connector strut 711 may be constituted by a fluid ram or be extensible under fluid ram control; this has the advantage of allowing a degree of independent variation of the inclination of the fines discharge conveyor 71.

The fines discharge conveyor includes an outboard end section 710 which is pivotally connected to an inboard section so that the outboard section 710 may be folded upwardly into a transport position as shown in Figure 1 thereby to shorten the apparatus without substantially increasing its height. Such pivotal movement may be controlled by fluid operated ram 713.

13 The screening device includes two screens 612, 613 for screening material into fine, medium and coarse size fractions and is, in the working position as shown in Figure 2, adapted to pass the medium and coarse fractions to the inboard ends 721, 731 of two different respective side discharge conveyors 72, 73.

The two different respective side discharge conveyors 72, 73 are arranged to discharge material to opposite sides of the apparatus; this is most convenient for allowing large stockpiles to be built up andlor for allowing truck access to positions beneath either or both of such side discharge conveyors; A chute 614 is provided for guiding the coarse fraction over the inboard end 721 of the medium fraction discharge conveyor 72 for discharge onto the inboard end 731 of the coarse fraction discharge conveyor 73. This is a convenient way of maintaining separation of those fractions after screening. The chute 614 is suitably pivotally mounted.

As shown in Figure 3, the or each side discharge conveyor 72, 73 suitably has an outboard section 722 which is movable from a working position, to a transport position in which that outboard section 722 is folded inwardly and downwardly so that it extends longitudinally of the apparatus with the conveying surface being generally vertical; this allows the width of the apparatus to be kept within limits for road transportation while at the same time allowing the side discharge conveyors to be longer so their discharge ends are higher. In the arrangement shown in Figure 3, the outboard boom section 722 is connected to the apparatus main frame 3 in the neighbourhood of its inboard end 721 by a pivot joint 723 whose axis is arranged at such an angle that as the boom 722 moves from its sideways discharge position to its longitudinal transport position, that boom section 14 also rotates through about 90'. This allows the width of the apparatus to be effectively minimised for transport.

If desired additional support may be provided to the outboard boom section 722 by a pair of support legs extending between a crosstree 724 on the boom and attachment points 725, 726 on the apparatus main frame 3 below and to either side of the pivot joint 723.

The support frame carries at least one hydraulic pump for driving the conveyor means; this is a simple and convenient way of carrying power to the feed conveyors 5 and the discharge conveyors 7.

The or at least one screen 612, 613 of the screening device is carried by a screenbox 615 mounted at 618 to a screen subframe 61 by sprung mounts 616 and means 617 is provided for vibrating such screenbox 615; this promotes a high throughput for a given size and shape of screen, and it militates against jamming; The apparatus as a whole may be supported and arranged for transport in various ways. In some preferred embodiments of the invention, a read end of the support frame is itself supported by a wheeled subframe assembly, for example a twin axle unit while its other end is arranged for support by legs when in the working configuration, and for coupling to and support by a road tractor unit for transport from site to site.

The invention is of particular advantage in embodiments in which the support frame is carried by a tracked bogie 10 as illustrated.

Embodiments of the invention whose main frames are supported by tracks are much easier to move about on site than are embodiments whose main frames are supported by legs in the working configuration: the apparatus can be moved on those tracks from one position on site to another, for example at about walking speed. A leg-supported wheeled apparatus requires to be hitched to a tractor unit and then moved. But for transportation from site to site, a tracked apparatus requires to be loaded onto a transporter such as a "low-loader" 11. as shown in Figure 1, and this of course will add to the height of the apparatus above ground level. It is thus of particular importance to achieve a height saving in such embodiments.

Preferably, the support frame carries hydraulic means for driving the 10 tracks of the bogie whereby the apparatus is a self-propelled apparatus.

16

Claims

1 Mobile screening apparatus which comprises a support frame carrying a hopper assembly comprising a reject grid over a hopper, conveyor means extending longitudinally of the support frame beneath said hopper assembly for receiving material passed through the hopper and conveying it to a screening device adapted to screen passed material into at least two fractions of different coarseness and to pass each such fraction to a separate discharge means for discharge from the apparatus, wherein said conveyor means includes a main conveyor having a support boom formed by an upwardly inclined proximal section joined to a distal section at a pivot joint, wherein the distal section of the main conveyor support boom and the screening device are each pivotally mounted with respect to the support frame, and wherein means is provided for raising and lowering the screening device and distal conveyor section between (a) a working position in which the distal conveyor section forms an upwardly extending extension of the proximal conveyor section and the screening device is arranged to discharge at least one oversize fraction of screened material onto the inboard end of a side discharge conveyor, and (b) a transport position which is of reduced height.

2. Mobile screening apparatus according to claim 1, wherein in the transport position, the distal conveyor section and the screening device extend generally horizontally.

17

3. Mobile screening apparatus according to claim 1 or 2, wherein when the apparatus is in the transport condition, the hopper assembly and main conveyor are of substantially the same height.

4. Mobile screening apparatus according to any preceding claim wherein the reject grid of the hopper assembly is lowerable from an inclined working position to a transport position in which the hopper assembly is of reduced height.

5. Mobile screening apparatus according to any preceding claim wherein the means for raising and lowering the screening device and 10 distal conveyor section includes at least one fluid operated ram.

6. Mobile screening apparatus according to any preceding claim wherein at least one extensible support leg extends between an end portion of the support frame and a distal portion of the screening device and/or of the distal conveyor section for supporting them in the working position.

7. Mobile screening apparatus according to claim 6, wherein the or each said support leg is extensible by a fluid-operated ram.

8. Mobile screening apparatus according to claim 6 or 7, wherein means is provided for locking the or each said extensible support leg at a selected one of a plurality of extensions.

1

9. Mobile screening apparatus according to any preceding claim wherein a longitudinal discharge conveyor is provided beneath the screening device for receiving a fine fraction of screened material and discharging it to one end of the apparatus.

18

10. Mobile screening apparatus according to claim 9, wherein such fines discharge conveyor is connected to the screening device for raising and lowering therewith.

11. Mobile screening apparatus according to claim 9 or 10, wherein the fines discharge conveyor is connected to the screening device by means of one or more extensible connector struts.

12. Mobile screening apparatus according to claim 11, wherein the or each extensible connector strut is extensible under fluid ram control.

13. Mobile screening apparatus according to any of claims 9 to 12, wherein the fines discharge conveyor includes an outboard end section which is pivotally connected to an inboard section so that the outboard section may be folded upwardly into a transport position thereby to shorten the apparatus without substantially increasing its height.

14. Mobile screening apparatus according to any preceding claim wherein the screening device includes two screens for screening material into fine, medium and coarse size fractions and is, in the working position, adapted to pass the medium and coarse fractions to the inboard ends of two different respective side discharge conveyors.

15. Mobile screening apparatus according to claim 14, wherein the two different respective side discharge conveyors are arranged to discharge material to opposite sides of the apparatus.

19

16. Mobile screening apparatus according to claim 14 or 15, wherein a chute is provided for guiding the coarse fraction over the inboard end of the medium fraction discharge conveyor for discharge onto the inboard end of the coarse fraction discharge conveyor.

17. Mobile screening apparatus according to any preceding claim wherein the or each side discharge conveyor has an outboard section which is movable from a working position, to a transport position in which that outboard section is folded inwardly and downwardly so that it extends longitudinally of the apparatus with the conveying surface being generally vertical, and back.

18. Mobile screening apparatus according to any preceding claim wherein said hopper assembly includes at least one screen.

19. Mobile screening apparatus according to any preceding claim wherein said hopper assembly includes sprung mounts carrying said reject grid and means is provided for vibrating such grid.

20. Mobile screening apparatus according to any preceding claim wherein the conveyor means includes a longitudinal hopper conveyor located beneath the hopper for receiving material passing through the hopper and passing in to the proximal end of the main conveyor.

21. Mobile screening apparatus according to any preceding claim wherein the support frame carries a hydraulic pump for driving the conveyor means.

22. Mobile screening apparatus according to any preceding claim wherein the or at least one screen of the screening device is carried by a screenbox mounted to a screen subframe by sprung mounts and means is provided for vibrating such screenbox.

23. Mobile screening apparatus according to any preceding claim wherein the support frame is carried by a tracked bogie.

24. Mobile screening apparatus according to claim 23, wherein the support frame carries hydraulic means for driving the tracks of the bogie whereby the apparatus is a self-propelled apparatus.

25. Mobile screening apparatus according to claims 22 and 24, wherein different hydraulic circuits are provided which are so arranged that power cannot be applied to the conveyors while power is being applied to the tracks.

26. Mobile screening apparatus substantially as herein described with reference to the accompanying drawings.