This invention relates to conveying and screening apparatus for size classifying discrete material into different grades. The apparatus is of a type having an elongate elevator normally inclined from a loading end towards a discharge end whereat a screen box is provided in a normally declined position, length-adjustable stay means being provided to adjust the angle of declination. The elevator has a suppoπ structure with an endless conveyor arranged around two spaced transverse rollers provided on the structure. The screen box has an upstanding surround within which one or more vertically-spaced stations have been provided, the or each to horizontally carry an elongate screening surface. The screen box is adapted for pivotal support relative to the structure such that the delivery end of the conveyor is above the upper end of the screen box. That part of the surround at the discharge end of the screen box is of restricted height relative to the remainder of the surround, the height being restricted and determined by the position of the or the lowest screening surface. Such an apparatus is referred to hereinafter as "a conveying and screening apparatus of the type stated". In one form, the elevator is mobile and has ground-engaging wheels to enable the apparatus to be manoeuvred on site and, when provided with coupling means at its loading end, to be coupled to a tractor unit and transported to or between sites where screening of material is required. Length-adjustable means is provided to raise or lower the support structure relative to the region of the wheel mounting(s), the structure pivoting about the under surface of the loading end thereof.

A disadvantage exists in transporting, on public roads, such apparatus due to its length and heretofore this has been overcome by demounting the screen box, or articulating the screen box about the discharge end of the elevator by using other

equipment to tuck, it under said discharge end. The procedure is time-consuming and labour intensive. With increasing costs of such equipment to buy or lease, the desirability to move equipment from site to site increases to maximise the usage of the apparatus. Another disadvantage that exists is in the operations of maintenance and replacement of screening surface(s) in the screen box since at the lowest angle of inclination of the elevator the screen box is still some distance off the ground. These operations require to be performed by personnel standing on platforms or staging provided around the screen box for such purpose. These operations are of necessity time-consuming. An object of the present invention is to obviate or mitigate these disadvantages.

Accordingly, the present invention is a conveying and screening apparatus of the type stated, in which the structure has rail means provided extending towards the discharge end of the elevator, a sub-structure being provided having wheel arrangements whose wheels engage and track the rail means, the screen box being pivotally supported on said sub-structure, and means to move the sub-structure along the rail means whereby the screen box is movable between an in-use position extending from the discharge end of the conveyor and an out-of-use position withdrawn below the structure.

Preferably, the rail means are two C-shaped rails spaced apart and oppositely open side facing with the wheel arrangements being two bogies each having two spaced apart wheels, corresponding wheels being arranged in tandem with the corresponding wheels of each bogie running along a respective rail. The corresponding wheels of each arrangement are preferably mounted on a substantially triangular plate, the two plates being secured together by a transom to form the sub-structure. Locking means are preferably provided to secure the sub-structure to each rail in any of at least two positions, namely an in-use position and an out-of-use position of the screen box. Each locking means is desirably a bolt provided in a housing, the bolt

being spring-biased outwardly to engage in a hole provided in a lug, one lug being provided at each of the two positions. Each lug beneficially has a ramp to be engaged by the outer end of a respective bolt to slide therealong and be urged into its housing to be released to engage the respective hole on alignment therewith. The inner end of each bolt extends out from the housing and desirably has an eye for engagement by a flexible element, such as a cord or a chain, to release the bolt from its engagement with the hole.

Preferably also, the moving means includes a length of chain anchored at both ends adjacent to both ends of the rails respectively, the chain between its ends being entrained around two sprocket wheels mounted on a bracket secured to the sub¬ structure, a first wheel being secured to a hydraulic motor for driven motion and the second wheel being mounted to act as a jockey wheel to maintain the chain in contact with the sprockets of the first wheel, whereby on actuation of the motor the wheels move along the chain with consequent movement of the sub-structure and screen box along the rails.

.An embodiment of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which: -

Fig. 1 is a side elevation of a conveying and screening apparatus according to the present invention being shown mounted at its loading end on a material-feeding hopper having an inclined over-sized material reject grid, the hopper being coupled to a tractor unit, a screen box being shown in an out-of-use position with stay means retracted;

Fig. 2 is a side elevation of the apparatus and hopper as shown in Fig. 1 with the hopper decoupled and free-standing, and the stay means being extended; Fig. 3 is a side elevation of the apparatus and hopper as shown in Fig. 2 and with the screen box moved to an in-use position;

Fig. 4 is a side elevation to an enlarged scale of a discharge end of an elevator of the apparatus with the screen box in an in-use position;

Fig. 5 is a side elevation, to the same scale as Fig. 4, of the discharge end of the elevator with the screen box in an intermediate position; and Fig. 6 is a sectional view of a locking detail.

Referring to the drawings, the conveying and screening apparatus is of a type stated having an elongate elevator 10 normally inclined from a loading end towards a discharge end whereat a screen box 12 is provided in a normally declined position. Length-adjustable stay means are provided to adjust the angle of declination. The stay means are two telescopic stays 14. one part 14A of each having one aperture 15 and the other part 14B of each having a series of apertures 16 to be aligned, one at a time, with the aperture 15. Each stay 14 is adjusted telescopically by a ram and cylinder arrangement 18 (Fig. 5). The elevator 10 has a support structure 20 with an endless belt conveyor 22 arranged around two spaced transverse rollers 24 provided on the structure 20. Two lateral sides 23 are provided one to mask each longitudinal side of the conveyor 22. The screen box 12 has an upstanding surround 26 within which one or more vertically-spaced stations (not shown) have been provided, the or each to horizontally carry an elongate screening surface (not shown). The screen box 12 is adapted at 28 for pivotal support relative to the structure 20 such that the delivery end of the conveyor 22 is above the upper end of the screen box 12. That part of the surround 26 at the discharge end of the screen box 12 is of restricted height relative to the remainder of the surround 26, the height being restricted and determined by the position of the or the lowest screening surface.

In the embodiment illustrated, the elevator 10 is mobile and has ground- engaging wheels 30 to enable the apparatus to be manoeuvred on site and, when provided with coupling means at its loading end, to be coupled to a tractor unit and transported to or between sites where screening of material is required. Length-

adjustable stay means 32 is provided to raise or lower the support structure 20 relative to the region of the wheel mounting(s), the structure 20 pivoting about the under surface of the loading end thereof.

The structure 20 has rail means provided extending towards the discharge end of the elevator 10. A sub-structure 34 is provided having wheel arrangements whose wheels 36 engage and track the rail means. The screen box 12 is pivotally supported on said sub-structure 34.

The rail means are two C-shaped rails 38 spaced apart and oppositely open side facing with the wheel arrangements being two bogies each having two spaced apart wheels 36, corresponding wheels being arranged in tandem with the corresponding wheels 36 of each bogie running along a respective rail 38. The corresponding wheels 36 of each arrangement are mounted on a substantially triangular plate 40. The plates 40 are secured together by a transom 42 to form the sub-structure 34.

Locking means are provided to secure the sub-structure 34 to each rail 38 in any of three positions, namely an in-use position and an out-of-use position and an intermediate position of the screen box 12. Each locking means (Fig. 6) is a bolt 44 provided in a housing 46, the bolt 44 being spring-biased outwardly by a coil spring 51 to engage in a hole 50 provided in a lug 48, one lug 48 being provided at each of the three positions. Each lug 48 has a ramp 52 to be engaged by the outer end of a respective bolt 44 to slide therealong and be urged into its housing 46 against its spring 51 which is compressed, the bolt 44 to be released to engage the respective hole 50 on alignment therewith. The inner end of each bolt 44 extends out from the housing 46 and has an eye 54 for engagement by a flexible element (not shown), such as a cord or a chain to release the bolt 44 from its engagement with the hole 50. Each bolt 44 passes through a complementarily shaped aperture in a top wall of the housing 46. The bolt 44 has a diametrical key on its shank to restrict extension through the aperture and against which the coil spring 51 can abut, a similarly shaped aperture with keyhole being

provided in the bottom wall with a further radial key being provided on the shank such that on movement against the biasing (using the eye and flexible element) the bolt 44 can be rotated whereby the radial key being out-of-alignment will hold the bolt 50 in a withdrawn state until released. Means to move the sub- structure 34 along the rail means is provided whereby the screen box 12 is movable between an in-use position extending from the discharge end of the conveyor 22 and 'an out-of-use position withdrawn below the structure 20 as shown in Figs.3 and 2 respectively. The moving means includes a length of chain 56 anchored at 58 to both ends adjacent to both ends of the rails 38 respectively, the chain 56 between its ends being entrained around two sprocket wheels 60,62 mounted on a bracket 64 secured to the sub-structure 34. A first wheel 60 is secured to a hydraulic motor (not shown) for driven motion and the second wheel 62 is mounted to act as a jockey wheel to maintain the chain 56 in contact with the sprockets of the first wheel 60, whereby on actuation of the motor the wheel 60 moves along the chain 56 with consequent movement of the sub-structure 34 and screen box 12 along the rails 38.

In use, the present invention is shown mounted at its loading end on a material- feeding hopper 66 having an inclined over-sized material reject grid 68. The hopper 66 is coupled to a tractor unit 70 for transportation (Fig. 1). When on site, the unit 70 is decoupled from the hopper 66 which is then adapted to be free-standing. Discrete material is fed onto the reject grid 68 to separate oversize material therefrom with the residue material passing therethrough and fed into the hopper 66 and onto the conveyor 22. With the screen box 12 moved to an in-use position, the bolt conveyor 22 activated, and the stays 14 extended to give the required angle of declination for the screen box 12, the material is fed up the conveyor and delivered to the screen box to be size classified into the required grades. At the required length of the stays 14, the parts 14A, 14B are pinned together and at the different positions of the

sub-structure 34 along the rails 38, the bolts 44 are locked in position, in all cases to prevent movement from the selected position

An advantage of the present invention is that the screen box can be withdrawn under and extended from the discharge end of the elevator without the requirement of using other equipment and thus these operations are not as time-consuming and labour intensive as heretofore. Further in the operations of maintenance and replacement of screening surface(s) in the screen box, the screen box can be lowered to near ground level by retracting the stay means 32 thereby mitigating the requirement of manufacturers having to provide personnel platforms or staging around the screen box for such purpose.

In a modification, the bolt 44 may be operated by a ram and cylinder arrangement which is either hydraulically or pneumatically powered rather than by manual operation.

Variations and modifications can be made to the invention without departing

from the scope of the invention described above and as claimed hereinafter.