GB2089685A - Screening apparatus - Google Patents

Abstract

Screening apparatus comprising a tubular frusto conical or cylindrical screen having an inlet for particulate material to be screened, an outlet for coarser material and perforate walls formed by perforate elastomeric screening members supported on a frame formed by end rings 12, 13 and struts 14, 15 and 16 through which finer particulate material passes in use. <IMAGE>

Description

SPECIFICATION Screening apparatus This invention relates to screening apparatus employing at least one tubular screening member.

Screening apparatus comprising tubular screening members is widely used by the coal mining, quarrying and sand and gravel industries to grade particulate material. Such apparatus generally comprises a tubular perforate screening member attached at one end to a face plate having a central opening through which the particulate material is introduced. Th face plate and the tubular member rotate together and the fine particulate material falls through the perforate walls of the tubular member whilst the coarser material gradually moves along the length of the tubular member and eventually exits from the end remote from the face plate.

The perforate walls of the tubular member are generally formed by rigid perforate steel members of arcuate cross section wbhich are located on a frame and bolted together to form a cylindrical wall.

These steel members typically require a crane or hoist far their installation or removal. Because they are rigid, they have bulky articles to store and to transport.

The present invention provides screening apparatus comprising a tubular screening member having an inlet for particulate material to be screened, an outlet for coarser material and perforate walls for allowing the passage of finer material, and comprising a frame, supporting one or more perforate screening members of elastomeric material.

Preferably the or each said perforate screening member is tensioned in the direction circumferential of the tubular member.

In order to achieve this, it may be that the frame is of fixed size and the or each said perforate screening member has a pair of longitudinally extending free edges and the said perforate screening member or members are tensioned by drawing free edges arranged adjacent one another together.

Alternatively, it may be that the frame is expandable to tension the or each perforate screening member.

Preferably there are a plurality of the said perforate screening members each being a perforate elastomeric sheet, the sheets being joined edge to edge to cover the frame.

One suitable method for joining sheets edge to edge is to provide on each such edge a flange extending from the sheet surface and to join the flanges of adjacent edges face to face. This may be done by bolts or rivets or other conventional fastening means. Drawing the flanges together, e.g. by bolts may provide a ready means of tensioning the perforate screening members on the frame.

Preferably the tubular screening member is generally circular in cross-section. It may be desirable that the tubular member taper, usually from an inlet end to an outlet end.

The screening apparatus of the invention may comprise a plurality of interfitted tubular screening members. which are Preferably coaxial. Generally, the perforations in the more outer tubular screening members will be smaller than those of a more inner tubular screening member.

Suitable elastomeric materials include polypropylene, synthetic and natural rubbers generally including elastomeric polyurethane, and polybutadienes.

Preferably the elastomeric material should have good abrasion resistance. Elastomeric materials are available which are considerably superior to steel as regards abrasion resistance.

The elastomeric material may be a laminate of different elastomers chosen for particular attributes.

For instance a laminate may comprise a layer of rubber chosen for its high abrasion resistance and a layer of polypropylene chosen to provide a high degree of rigidity when the composition is tensioned.

The invention will be illustrated by the following description of a preferred embodiment with reference to and as illustrated in the accompanying drawing in which Figure 1 shows an elastomeric, perforate sheet member.

Figure 2 is a plan view of a frame of a tubular perforate member of a screening apparatus of the invention; and Figure 3 is an end view of the frame of Figure 2 fitted with sheets as shown in Figure 1.

The perforate sheet 1 shown in Figure 1 (one corner only of the whole sheet is shown), is of elastomeric material and has a regular array of square perforations 2 penetrating the whole thickness of the sheet. Naturally, the perforations may be of any desired shape instead of square, e.g. circular.

The whole sheet is of trapeziform shape having longer and shorter parallel edges 3 and a pair of longitudinal edges 4. Along each longitudinal edge 4 (only one is shown) there is provided a metal backing plate 5 on one side of the sheet and an angle 6 on the other. These are connected through the sheet 1 by bolts or rivets or other fastening means (not shown). The angle 6 provides an upstanding flange 7 provided with spaces holes 8 for receiving tension bolts.

Figure 2 shows a tubular frame 9 which is bolted to a rotatable face plate 10 by bolts extending through an annuiarflange 11.

The tubular frame comprises smaller and larger end rings, 12 and 13 respectively. The end rings are joined by longitudinal struts 14, 15 and 16. Afurther strut lies directly behind strut 14 in the drawing. The struts are equally spaced about the periphery of the end rings. More than four struts could of course be employed.

A strengthening hoop 17 is provided within the struts midway between the end rings. Further such strengthening hoops could be provided.

The larger end ring 13 bears the annular flange 11 through which the whole frame is bolted to the face plate 10. Face plate 10 has a central aperture through which particulate material may be introduced.

As shown in Figure 3, a number of sheets 1 may be arranged over the frame 9 with their flanges 7 arranged face to face. The size of the sheets is chosen such that the flanges 7 will not all meet face to face without the sheets being stretched around the frame. Bolts extending through the holes 8 may then be used to draw the flanges 7 together, stretching the sheets to the desired extent.

In Figure 3, three sheets 1 are shown. A greater or a lesser number may be employed. Only one sheet may be employed if desired but the replacement of locally damaged parts of the perforate wall framed by the sheets may be possible if several sheets are used.

Similarly, the sheets may be long enough to extend over the entire length of the frame or else two or more sheets may be required to cover the whole length.

In the embodiment shown, the tubular screening member formed by the frame 9 and the sheets 1 is frusto-conical. It need not however be of tapering cross section and may for instance be a right circular cylinder.

Two or more tubular screening members arranged coaxially may be bolted to the face plate 10 and progressive grading of particulate material may thereby be obtained.

The frame may be of metal as is conventionally the case. In order to improve the resistance to abrasion of the frame parts they may be coated with an anti-abrasive coating material such as a synthetic or natural rubber. The same may be done to protect other parts such as the face plate which are in contact with the particulate material when the screening apparatus is in use.

Advantages of the rotary screening machine described over the conventional rotary screening machines employing steel screens are that the flexible elastomeric screens are much lighter than the steel screens, can have better abrasion resistance, and are quieter in operation. Replacement of damaged parts of the perforate wall is easierthan in the case of steel screens and the flexible sheets of perforate elastomer may be rolled up for easy storage and transport. Further, when there are several coaxial layers of screen material outer layers may be partially released and peeled backto give access to inner layers thus avoiding complete removal of the outer layers.

Claims (8)

1. Screening apparatus comprising a tubular screening member having an inletfor particulate material to be screened, an outlet for coarser material and perforate walls for allowing the passage of finer material, and comprising a frame, supporting one or more perforate screening members of elastomeric material.

2. Apparatus as claimed in claim 1 wherein the or each said perforate screening member is tensioned in the direction circumferential of the tubular member.

3. Apparatus as claimed in claim 2 wherein the frame is of fixed size and the or each said perforate screening member has a pair of longitudinally extending free edges and the said perforate screening member or members are tensioned by drawing free edges arranged adjacent one another together.

4. Apparatus as claimed in claim 2 wherein the frame is expandable to tension the or each perforate screening member.

5. Apparatus as claimed in claim 4 or 5 wherein there are a plurality of the said perforate screening members each being a perforate elastomeric sheet, the sheets being joined edge to edge to cover the frame.

6. Apparatus as claimed in any preceding claim wherein the tubular screening member is of generally circular cross section.

7. Apparatus as claimed in any preceding claim comprising a plurality of interfitted tubular screening members.

8. Screening apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.