GB2077144A - Screening apparatus - Google Patents

Abstract

A rotatable circular screening deck comprises a plurality of elongated screening elements (2) radiating from a rotatably mounted hub (3), the screening elements defining longitudinally extending separating edges (5) for separating undersize and oversize material being treated. Each separating edge is constituted by a relatively uppermost margin of the associated screening element. <IMAGE>

Description

SPECIFICATION Screening apparatus This invention relates to sizing screens for particulate material of different sizes.

In particular, although not exclusively, the present invention relates to sizing screens for screening small size particles, for example, particles less than twenty-five millimeters.

The present invention is particularly, although not exclusively, related to sizing screens of the kind described and claimed in our prior British patent specification Serial No.

1 307 290. Claim 1 of the prior specification defines a sizing screen comprising a circular screen surface consisting of a plurality of elongated members projecting from a hub and mounted for rotation about a generally vertical axis, drive means for rotating the surface, means for feeding material onto the surface, first collection means positioned adjacent to the outer periphery of the surface for collecting oversize material, and second collection means positioned below the surface for collecting undersize material. The elongated members projecting from the hub were of substantially circular cross-section.

An object of the present invention is to provide improved screening apparatus.

According to the present invention screening apparatus for particulate material of different sizes provides a movable screening deck comprising a plurality of elongated screening elements adapted to define screen apertures through which, during treatment of the particulate material, undersize material passes as oversize material flows over the screening deck, at least a number of the elongated screening elements defining longitudinally extending separating edges for separating undersize and oversize material being treated, each separating edge being constituted by a relatively uppermost margin of the associated screening element.

Preferably, the relatively uppermost margin of each screening element defines a generally horizontal uppermost screen surface.

Preferably, each screening edge is formed by the intersection of the associated generally horizontal uppermost screen surface with a downwardly inclined surface.

Advantageously, each screening element has a cross-section of generally parallelogram form.

Preferably, the movable screening deck is generally circular the plurality of elongated screening elements radiating from a hub mounted for rotation about a generally vertical axis.

Preferably, drive means are provided for rotating the hub.

Advantageously, first and second collection means are provided for the treated undersize and oversize particulate material, respectively.

Conveniently, feed means are provided for feeding untreated particulate material onto the screening deck.

Preferably, means are provided for selectively varying the rotational speed of the screening deck.

By way of example only, one embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an incomplete diagrammatic plan of screening apparatus constructed in accordance with the present invention; and Figure 2 is a cross-sectional view taken along line ll-ll of Fig. 1 and drawn on an enlarged scale.

Fig. 1 of the drawings shows an incomplete plan of a generally horizontal rotatable screening deck 1 comprising a plurality of elongated screening elements 2 radiating out from all around a hub 3 mounted for rotation about a generally vertical axis 4. In Fig. 1 only a number of elements 2 are shown. The hub is driven by drive means (not shown), for example, an electric drive motor and gearing. Typical examples of suitable drive means for the screening deck are disclosed in our British patent specifications Serial Nos. 1 307 290, 2 005 1 57 and 2 030 475. The drive means may include control means for selectively varying the rotational speed of the screen deck.

Feed means (not shown) are provided for feeding untreated particulate material onto the uppermost surface of the rotating screening deck. Typical examples of suitable feed means are disclosed in our British patent specifications Serial Nos. 1 307 290 and 2005 157.

Each of the elongated screening elements has a cross-section of generally parallelogram form (see Fig. 2) such that each element defines a leading, forwardly directed, longitudinally extending separating edge 5 extending substantially the length of the associated screening element. In operation as the screening deck is rotated and untreated particulate material is fed onto and passes over the screening deck, the longitudinal separating edge 5 defined by each screening element tends to separate or divide the undersize particulate material, from the oversize particulate material, each separating edge being constituted by a relatively uppermost margin of the associated screening element. As seen in Fig.

2 the relatively uppermost margin of each screening element defines a generally horizontal uppermost screen surface 6 with the longitudinal separating edge 5 formed by the intersection of the associated generally horizontal uppermost screen surface 6 with a downwardly inclined surface 7. Two adjacent screening elements defining a screen aperture 8 through which undersize particulate material passes.

From Fig. 2 it will be appreciated that as the screening deck is rotated at relatively high speed and the elongated screening elements are moved in the direction indicated by arrow Y the cross-sectional form of the elements is such that an air flow is induced by the screening movement of the elements, the induced air flow which is indicated by arrows x in Fig.

2 tending to urge undersize particulate material to pass through the defined screen apertures 8. As seen in Fig. 2 the previously mentioned leading downwardly inclined surfaces 7 co-operate with trailing downwardly inclined surfaces 9 on adjacent screening elements to define downwardly inclined passages 10, the associated two surfaces 7 and 9 defining opposed faces of the passages.

Undersize material separated from oversize material by the action of the separating edges 5 passes along the passages 10 to be discharged through passage outlets 11 towards undersize material collection means (not shown). In one example of screening apparatus the undersize material falls into a discharge hopper. Typical undersize collection means are disclosed in our British patent specifications Serial Nos. 1 307 290, 2 005 157 and 2 030 475.

As the particulate material is being treated the induced downward air flow tends to carry very small particles, for example airborne particles, through the screen passages 10 towards the undersize material collection means.

Oversize particulate material flows over the screening deck to be discharged radially from the screening deck under the action of centrifugal force. Oversize material collection means are arranged around the perimeter of the circular screening deck to receive treated material flung off the relatively rapidly revolving screening deck. Typical examples of suitable oversize material collection means are disclosed in our British patent specifications Serial Nos. 1 307 290, 2 005 157 and 2030 475.

From the above description it will be seen that the present invention tends to provide more efficient screening apparatus.

In other embodiments of the invention only a number of the screening elements have a cross-section generally in the form of a parallelogram.

In still other embodiments of the invention the surfaces 7 and/or 9 are curved.

In further embodiments the elements are of generally triangular form.

Claims (10)

1. Screening apparatus for particulate material of different sizes providing a movable screening deck comprising a plurality of elongated screening elements adapted to define screen apertures through which, during treatment of the particulate material, undersize material passes as oversize material flows over the screening deck, at least a number of the elongated screening elements defining longitudinally extending separating edges for separating undersize and oversize material being treated, each separating edge being constituted by a relatively uppermost margin of the associated screening element.

2. Apparatus as claimed in claim 1, in which the relatively uppermost margin of each screening element defines a generally horizontal uppermost screen surface.

3. Apparatus as claimed in claim 2, in which each screening edge is formed by the intersection of the associated generally horizontal uppermost screen surface with a downwardly inclined surface.

4. Apparatus as claimed in claim 3, in which each screening element has a crosssection of generally parallelogram form.

5. Apparatus as claimed in any one of the preceding claims, in which the movable screening deck is generally circular, the plurality of elongated screening elements radiating from a hub mounted for rotation about a generally vertical axis.

6. Apparatus as claimed in claim 5, in which drive means are provided for rotating the hub.

7. Apparatus as claimed in any one of the preceding claims, in which first and second collection means are provided for the treated undersize and oversize particulate material, respectively.

8. Apparatus as claimed in any one of the preceding claims, in which feed means are provided for feeding untreated particular material onto the screening deck.

9. Apparatus as claimed in any one of the preceding claims, in which means are provided for selectively varying the rotational speed of the screening deck.

10. Screening apparatus for particulate material of different sizes substantially as described herein and substantially as shown in the accompanying drawings.