GB1604423A

GB1604423A - Screens

Info

Publication number: GB1604423A
Application number: GB2443777A
Authority: GB
Original assignee: Trelleborg Ltd
Current assignee: Trelleborg Ltd
Priority date: 1978-05-22
Filing date: 1978-05-22
Publication date: 1981-12-09

Description

(54) IMPROVEMENTS IN SCREENS (71) We, TRELLEBORG LIMITED (formerly known as Trelleborg Rubber Limited, of 90 Somers Road, Rugby, Warwickshire, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to screening of particulate materials, and more especially relates to a screen built from a plurality of like components and suitable to dewater a slurry of differently sized particles, while separating the finer particles from the coarser.

It is known to form a screen either from a plurality of inter-woven or attached strands of material or by perforating a continuous sheet of the material. In use any screen is abraded by the particles of material impinging upon it, especially when these are more or less sharp mineral particles suspended in a slurry of water and thus capable of individual rapid movement. This abrasion in use has the effect both of increasing the size of the orifices (so that the material passing through is not accurately graded) and of abrading away the surface of the screen so that the overall mechanical strength is diminished. In the case where the screen comprises interlaced strands of material, there is also the danger that the strands will become mutually displaced leading to changes in dimension of the orifices defined between them.

It is also known to provide a screen of such material basically made of metal but to clad it with an abrasion-resistant surface for example of polyurethane rubber. This, however, will eventually wear in the same way as the purely metal screens.

All of the designs discussed above suffer from the same disadvantage that when wear has taken place the whole screen must be removed and replaced. Typically, however, a screen does not wear uniformly and parts of its surface may be relatively unabraded while other parts are abraded beyond their useful life.

To overcome this disadvantage the present invention provides a screen for the separation of particulate material in which the screen surface comprises (i) a plurality of identical strips or laths, each lath tapering in cross-section from an upper edge to a lower edge and having (a) two fixing bosses, one at or towards one end and one intermediate the ends, each such fixing boss possessing a through hole and (b) unapertured spacing bosses, one located between the two fixing bosses and one at or towards the other end of the lath, all the bosses of each lath projecting from the same lath surface and to the same extent, the laths being parallel with their projecting bosses facing in the same direction and fixing boss holes in alignment, and (ii) a plurality of clamping bolts or rods each passing through aligned holes in adjacent laths whereby the laths are clamped together, spaced by the bosses, to define elongate orifices between them.

Preferably, moreover the lath is from 2 to 10 times as wide as its maximum thickness, a preferred range being from 3 to 6 times as wide. It is generally considered advisable for the wider edge of each lath to be between 2 and 3 times as thick as the narrower edge.

Since the various laths are aligned with their wider edges in a single flat or curved surface and spaced apart to define the elongate screen orifices, any particle which passes through the orifices will not be trapped between the adjacent surfaces of the lath further down the screen.

These laths may be from 100 to 1000 mm long, but are preferably from 150 to 600 mm long and are most preferably presented in modules e.g. of 200 or 400 mm. The projecton of the bosses from the lath may be from 0.1 to 5 mm but is preferably between 0.2 to 3 mm. It is envisaged to provide pluralities of otherwise identical laths with projections of different sizes whereby screens can be built up of any desired gap between laths. Generally the projections of different types of lath will rise in steps of 0.2 of a millimetre but it is possible that smaller steps could be provided.

The laths may be from 5 to 25 mm wide but are preferably between 10 and 15 mm wide, being typically 3 to 4 mm thick at one edge and I or 2 mm thick at the other edge.

It is important to appreciate with the present invention that the grid or screen structure should be robust and heavy in nature since it is generally used as part of a vibratory framework. Clearly, a screen which is robust in construction can present fewer orifices per unit area than a screen which is of flimsy construction. In the screen of the present invention between 50 and 75% of the total area of the gaps between the laths is available for uninterrupted passage of material, the remaining proportion being obstructed to some extent by the spacing bosses and fixing bosses passing transversely across the screen in relation to the lath direction.

Obstruction by these bosses can be minimised if the upper surface of the bosses is other than flat. Clearly, it is most convenient to make the bosses circular in appearance so that particles which pass between the laths and land on this circular boss surface can slide off to one side or the other without accumulation. In this regard it is preferred if the upper surface of the bosses does not reach above one quarter or below one half of the distance between the upper and lower edges from the upper edge of the laths. This then provides a useful indication of unacceptable wear since if the laths wear away until the bosses are exposed the tapering cross-section will by that point be providing too great a spacing for the purpose required.

To facilitate lengthwise build-up of adjacent laths, it is possible to provide a halfjoint at each end whereby the two halves of the half joints of endwise abutting laths overlap and provide a continuous lath structure of uniform thickness across the screen.

The screens according to the invention can be built up as flat vibratory screens, but it is also envisaged to provide curved laths so that a curved screen can be built up between suitable side plates which the bolts or rods are either screwed or welded.

The invention will be further described with reference to the accompanying drawings, in which: FIGURE 1 shows diagrammatically a perspective view of a single lath: and FIGURE 2 shows in fragmentary form the assembly of a plurality of such laths to form a screen surface.

In Figure 1 a lath of hard polyurethane rubber generally indicated at 1 has at each end a half joint 2 so that a plurality of such laths can be joined end to end with the inner faces of their halfjoints contacting. The lath is tapered in cross-section, and is smooth on one face (not shown) but has projecting spacing and fixing bosses 3 and 4 respectively on the other face. The extent of projection of all bosses is identical. Each fixing boss has a through hole 5.

Figure 2 shows in fragmentary form the assembly of three laths 1 with the fixing bosses 4 aligned and a bolt 6 passing through the holes 5. Adjacent laths are spaced apart by the degree of projection of the spacing bosses 3 and fixing bosses 4. When the screen is viewed from above, there will be clear apertures between the laths in those zones marked A, but the apertures will be obscured in the zones F (where the fixing bosses extend across the screen) or S, where the spacing bosses extend across the screen. The appearance of the fixing bosses and spacing bosses when they are aligned and the screen is held together is that of a solid reinforcing bar of the polyurethane rubber, so that the whole screen presents a heavy-duty robust aspect.

The total area A, as shown on Figure 2 is typically about two thirds of the overall visible screen area; needless of say, half or thereabouts of the area A is traversed by the laths themselves. Thereby the ratio of aperture to material is about one third. As outlined above, the bosses are circular in cross-section whereby any particle of material which passes below the upper edge of the screen and impinges on the boss slides off the one side or the other without being trapped.

The bosses could be of any upper surface shape which facilitates this, such as triangular or diamond shape, but it is clearly more each to make them circular in this way.

WHAT WE CLAIM IS: 1. A screen for the separation of particulate material in which the screen surface comprises (i) a plurality of identical strips or laths, each lath tapering in cross-section from an upper edge to a lower edge and having (a) two fixing bosses, one at or towards one end and one intermediate the ends, each such fixing boss possessing a through hole and (b) unapertured spacing bosses, one located between the two fixing bosses and one at or towards the other end of the lath, all the bosses of each lath projecting from the same lath surface and to the same extent, the laths being parallel with their projecting bosses facing in the same direction and fixing boss holes in alignment, and (li) a plurality of clamping bolts or rods each passing through aligned holes in adjacent laths whereby the laths are clamped together, spaced by the bosses, to define elongate orifices between them.

2. A screen as claimed in claim 1,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mm. It is envisaged to provide pluralities of otherwise identical laths with projections of different sizes whereby screens can be built up of any desired gap between laths. Generally the projections of different types of lath will rise in steps of 0.2 of a millimetre but it is possible that smaller steps could be provided. The laths may be from 5 to 25 mm wide but are preferably between 10 and 15 mm wide, being typically 3 to 4 mm thick at one edge and I or 2 mm thick at the other edge. It is important to appreciate with the present invention that the grid or screen structure should be robust and heavy in nature since it is generally used as part of a vibratory framework. Clearly, a screen which is robust in construction can present fewer orifices per unit area than a screen which is of flimsy construction. In the screen of the present invention between 50 and 75% of the total area of the gaps between the laths is available for uninterrupted passage of material, the remaining proportion being obstructed to some extent by the spacing bosses and fixing bosses passing transversely across the screen in relation to the lath direction. Obstruction by these bosses can be minimised if the upper surface of the bosses is other than flat. Clearly, it is most convenient to make the bosses circular in appearance so that particles which pass between the laths and land on this circular boss surface can slide off to one side or the other without accumulation. In this regard it is preferred if the upper surface of the bosses does not reach above one quarter or below one half of the distance between the upper and lower edges from the upper edge of the laths. This then provides a useful indication of unacceptable wear since if the laths wear away until the bosses are exposed the tapering cross-section will by that point be providing too great a spacing for the purpose required. To facilitate lengthwise build-up of adjacent laths, it is possible to provide a halfjoint at each end whereby the two halves of the half joints of endwise abutting laths overlap and provide a continuous lath structure of uniform thickness across the screen. The screens according to the invention can be built up as flat vibratory screens, but it is also envisaged to provide curved laths so that a curved screen can be built up between suitable side plates which the bolts or rods are either screwed or welded. The invention will be further described with reference to the accompanying drawings, in which: FIGURE 1 shows diagrammatically a perspective view of a single lath: and FIGURE 2 shows in fragmentary form the assembly of a plurality of such laths to form a screen surface. In Figure 1 a lath of hard polyurethane rubber generally indicated at 1 has at each end a half joint 2 so that a plurality of such laths can be joined end to end with the inner faces of their halfjoints contacting. The lath is tapered in cross-section, and is smooth on one face (not shown) but has projecting spacing and fixing bosses 3 and 4 respectively on the other face. The extent of projection of all bosses is identical. Each fixing boss has a through hole 5. Figure 2 shows in fragmentary form the assembly of three laths 1 with the fixing bosses 4 aligned and a bolt 6 passing through the holes 5. Adjacent laths are spaced apart by the degree of projection of the spacing bosses 3 and fixing bosses 4. When the screen is viewed from above, there will be clear apertures between the laths in those zones marked A, but the apertures will be obscured in the zones F (where the fixing bosses extend across the screen) or S, where the spacing bosses extend across the screen. The appearance of the fixing bosses and spacing bosses when they are aligned and the screen is held together is that of a solid reinforcing bar of the polyurethane rubber, so that the whole screen presents a heavy-duty robust aspect. The total area A, as shown on Figure 2 is typically about two thirds of the overall visible screen area; needless of say, half or thereabouts of the area A is traversed by the laths themselves. Thereby the ratio of aperture to material is about one third. As outlined above, the bosses are circular in cross-section whereby any particle of material which passes below the upper edge of the screen and impinges on the boss slides off the one side or the other without being trapped. The bosses could be of any upper surface shape which facilitates this, such as triangular or diamond shape, but it is clearly more each to make them circular in this way. WHAT WE CLAIM IS:

1. A screen for the separation of particulate material in which the screen surface comprises (i) a plurality of identical strips or laths, each lath tapering in cross-section from an upper edge to a lower edge and having (a) two fixing bosses, one at or towards one end and one intermediate the ends, each such fixing boss possessing a through hole and (b) unapertured spacing bosses, one located between the two fixing bosses and one at or towards the other end of the lath, all the bosses of each lath projecting from the same lath surface and to the same extent, the laths being parallel with their projecting bosses facing in the same direction and fixing boss holes in alignment, and (li) a plurality of clamping bolts or rods each passing through aligned holes in adjacent laths whereby the laths are clamped together, spaced by the bosses, to define elongate orifices between them.

2. A screen as claimed in claim 1,

wherein each lath is from 2 to 10 times as wide as its maximum thickness.

3. A screen as claimed in any one of the preceding claims, wherein the wider edge of each lath is between 2 and 3 times as thick as the narrow edge.

4. A screen as claimed in ay one of the preceding claims, in which each lath is 100 to 1,000 mm long, 5 to 25 mm wide, 3 to 4 mm thick at one edge and 1 or 2 mm thick at the other edge; and in which the bosses project 0.1 to 5 mm.

5. A screen as claimed in claim 4, in which each lath is 150--600 mm long, and the bosses project 0.2 to 3 mm.

6. A screen as claimed in any one of the preceding claims, wherein from 50 to 75% of the total area between adjacent laths is available for uninterupted passage of mate rial.

7. A screen as claimed in any one of the preceding claims, wherein the bosses are circular in cross-section.

8. A screen as claimed in any one of the preceding claims, wherein the upper surfaces of the bosses lie between one quarter and one half of the distance between the upper and lower edges of the laths from the upper edges.

9. A screen as claimed in any one of the preceding claims, wherein each lath has a halfjoint at each end and the two halves of the halfjoints of end-wise abutting laths overlap and provide a continuous lath structure of uniform thickness across the screen.

10. A screen as claimed in any one of the preceding claims, with a flat surface.

11. A screen as claimed in any one of the preceding claims, with a curved surface.

12. A screen as claimed in claim 1 and substantially as herein described with reference to, and as illustrated in Figure 2 of the accompanying drawings.