WO2007096607A1

WO2007096607A1 - Materials screen

Info

Publication number: WO2007096607A1
Application number: PCT/GB2007/000596
Authority: WO
Inventors: Brian Mackenzie
Original assignee: Brian Mackenzie
Priority date: 2006-02-21
Filing date: 2007-02-21
Publication date: 2007-08-30
Also published as: GB2435227A; GB0603404D0; EP1991368A1

Abstract

A materials screen (10) for materials such as aggregates defines a plurality of apertures (12) and is formed of a first, relatively soft layer (14) and a second, relatively hard layer (16).

Description

Materials Screen

The present invention relates to materials screens, particularly but not exclusively materials screens for screening material such as aggregates.

In this specification the term "screen" refers to sieve-, riddle- or filter- type apparatus which is used to separate larger size fractions of particulate material from smaller size fractions. Typically a screen defines a plurality of apertures through which the smaller particles pass, while the larger particles are retained on or pass over the screen. The operation of separating the larger particles from the smaller particles using such a screen is thus termed "screening".

The screening of fine materials has always been problematic owing to the tendency of such material to block up the apertures of a screen (pegging) and/or form a continuous blanket over the surface of the screen (blinding). In both cases the efficiency of the screening process is adversely affected, as the open area of the screen is reduced. These problems are exacerbated if the material being screened has a high moisture content. Fine particles may then build up on the surface of the screen and agglomerate, forming large and heavy lumps which further reduce efficiency and can damage the screen itself.

In high volume environments such as quarries, screens are typically used in vibratory screening apparatus. The materials being screened are abrasive, and thus the environment is arduous, leading to high rates of wear, and the frequent necessity for the maintenance and replacement of screens.

Conventionally, such screens are formed of resiliently deformable material such as rubber or polyurethane which has a high resistance to abrasion. The deformation of the material under vibration helps to prevent build up of fine material. In one conventional example, a screen comprises a rubber membrane which is relatively thin to minimise the possibility of material pegging within the screen. However such screens are relatively fragile and often fail as a result of mechanical damage from the passage of lumps of material or metal. Such screens also require support members which may be fitted to the screens before installation. The support members reduce the efficiency of the screens and make installation of the screens difficult in the confined space typically available within the vibratory apparatus.

According to a first aspect of the present invention, there is provided a materials screen for material such as aggregates, the screen defining a plurality of apertures and being formed of a first, relatively soft layer and a second relatively hard layer.

Preferably, each aperture extends through both layers. Preferably each aperture is larger in cross section plan area in the second layer than in the first layer. Preferably each aperture has a minimum cross section plan area. Preferably the minimum cross section plan area is located in the first layer, and may be located towards the outer surface of the first layer. Preferably the aperture cross section plan area increases from the minimum cross section plan area towards the outer surface of the second layer.

Preferably in use, the first layer is the upper layer, and the second layer is the lower layer.

Preferably the screen includes a plurality of elongate reinforcement members. Preferably the reinforcement members are located in the second layer.

Preferably, the apertures interrupt a proportion of the reinforcement members. Preferably the screen includes a first area, or a plurality of first areas, having apertures. Preferably in the or each first area, substantially all the reinforcement members are interrupted. Preferably the screen includes a second area or a plurality of second areas without apertures. Preferably, in the second areas the reinforcement members are not interrupted.

Preferably the apertures are arranged in rows, and alternate rows may be offset to ensure all the reinforcement members are interrupted. Preferably the apertures are regularly spaced along the rows. Preferably, the rows extend along the length of the screen.

Preferably, in the or each first area, the screen comprises spaced transverse members, and may comprise spaced longitudinal members, which may together define the apertures. Preferably, at least one reinforcement member passes through each of the transverse members.

Preferably the reinforcement members are spaced apart, and may be parallel with each other, and may be aligned in a direction substantially at 90° to the direction of the rows.

Preferably the or each second area includes one or more transverse areas, which may extend transversely across the width of the screen. Preferably the or each second area includes one or more longitudinal areas, which may extend longitudinally along the length of the screen.

Preferably the apertures are formed by punching. Preferably the screen is formed of a resiliently deformable material, which may be a rubber material, and may be formed integrally by hot vulcanising.

Preferably the reinforcement members may be in the form of cords, which may be formed of plastics material. According to a second aspect of the present invention, there is provided a method of manufacture of a screen for material such as aggregates, the method including the steps of forming a screen of a first, relatively soft layer and a second relatively hard layer, and forming a plurality of apertures through the screen.

Preferably, the screen includes any of the features described above in any of the preceding paragraphs.

According to a third aspect of the present invention, there is provided a materials screen for material such as aggregates, the screen defining a plurality of apertures and including a plurality of elongate reinforcement members, the apertures interrupting a proportion of the reinforcement members.

Preferably, the screen includes any of the features described above in any of the said preceding paragraphs.

According to a fourth aspect of the present invention, there is provided a method of manufacture of a screen, the method including the steps of forming a screen including a plurality of elongate reinforcement members, and then forming a plurality of apertures extending through the screen, the apertures interrupting a proportion of the reinforcement members.

According to a fifth aspect of the present invention, there is provided a materials screen for material such as aggregates, the screen defining a plurality of apertures, the screen including a first area having apertures and a second area without apertures. Preferably, the screen includes any of the features described above in any of the said preceding paragraphs.

According to a sixth aspect of the present invention, there is provided a method of manufacture of a screen, the method including the step of forming a plurality of apertures through the screen, the screen including a first area having apertures and a second area without apertures.

According to a seventh aspect of the invention, there is provided a modular screen assembly, the assembly including a screen as described above in any of the said preceding paragraphs.

According to an eighth aspect of the invention, there is provided screening apparatus, the screening apparatus including a screen as described above in any of the said preceding paragraphs.

According to a ninth aspect of the invention, there is provided a method of screening material, the method including the use of a screen as described above in any of the said preceding paragraphs.

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-

Fig. 1 is a plan view of a materials screen;

Fig. 2 is a part cross sectional view from one side of the materials screen of Fig. 1 ; Figs. 3A and 3B are cross sectional views from another side of the materials screen of Figs. 1 and 2, showing the formation of an aperture;

Fig. 4 is a plan cross sectional view of an enlarged part of the materials screen of Fig. 1 as indicated by the reference label IV in Fig. 1 ;

Fig. 5 is a still further enlarged view of part of the screen of Fig. 1 in plan cross section; and

Fig. 6 is a schematic view of a modular screen assembly.

Figs. 1 and 2 shows a material screen 10, the materials screen 10 being formed of a first, relatively soft layer 14 and a second, relatively hard layer 16. The second layer 16 includes a plurality of reinforcement members 18. The reinforcement members 18 are substantially aligned in parallel and regularly spaced apart, and run transversely across the screen 10.

The material screen 10 is formed integrally by hot vulcanising, the first and second layers 14, 16 being formed together in the vulcanising process into a single member with the reinforcement members 18 passing therethrough.

A plurality of apertures 12 are then formed by punching through the screen 10 as shown in Figs. 3A and 3B. The apertures 12 are formed by a punch tool 30 which punches through the reinforcement members 18 to interrupt the reinforcement members 18, the punch tool 30 moving from the second layer 16 to the first layer 14 as indicated by arrow B in Fig. 3A. The apertures 12 thus formed generally widen from the first layer 14 through the second layer 16, so that each aperture 12 is larger in cross section plan area in the second layer 16 than in the first layer 14. A minimum cross sectional area 34 of each aperture 12 is located towards the upper surface 38 in use of the materials screen 10, which is the outer surface of the first layer 14. Thus, each aperture 12 substantially increases in size from the upper surface 38 of the screen 10 to a lower surface 48. Each aperture 12 includes a relatively small flared inlet section 60 in which the aperture 12 reduces in plan area from the upper surface 38 to the minimum cross sectional area 34. 5

Each of the layers 14, 16 is formed of a resiliently deformable material, such as rubber or polyurethane. The upper layer 14 could be formed of a material having a Shore hardness of between 30 and 50. More preferably, the Shore hardness of the material forming the upper layer 14 is in the region I O of 35 to 45, and optimally is approximately 40. The upper layer could be formed of a synthetic rubber having a high proportion of natural rubber, preferably of more than 90% natural rubber.

The material forming the lower layer 16 could have a Shore hardness 15 of between 60 and 70, and optimally is approximately 65.

The reinforcement members 18 could be formed of any suitable material. In one example, the reinforcement members 18 are in the form of cords, which could be formed of a plastics material such as polyester and 0 could be arranged to provide an unpunched material tensile strength of between 180 and 200 KN/m per ply of cords.

As shown in Fig. 1 , the screen 10 includes a plurality of first areas 20 in which apertures 12 are formed, and a plurality of second areas 22 which are 5 unpunched and therefore without apertures. The second areas 22 include a border area 28, which extends around the perimeter of the material screen 10, a plurality of transverse areas 24 which extend transversely across the width of the screen 10 and a plurality of longitudinal areas 26, which extend longitudinally along the length of the screen 10. 0

Figs. 4 and 5 show the arrangement of the apertures 12 in enlarged detail as plan cross sectional views so that the reinforcement members 18 are visible. Within each first area 20, the apertures 12 are arranged in rows 62A, 62B running longitudinally, the apertures 12 being regularly spaced along each row 62A, 62B. Each alternate row, e.g. 62A, is offset longitudinally from its neighbouring rows e.g. 62B. In the example shown in Figs. 4 and 5, the amount of offset between neighbouring rows 62A, 62B is approximately half of the spacing 46 between apertures 12. The offset spacing is also substantially equal to the spacing 40 between the reinforcement members 18, and the apertures 12 are arranged to correspond with the spacing of the reinforcement members 18 so that all of the reinforcement members 18 of the first areas 20 are interrupted by the alternate rows 62A, 62B of the apertures 12.

Within the first areas 20, the materials screen 10 is formed of transverse members 34 and longitudinal members 36.The aforesaid spacing 40 of the reinforcement members 18 and the spacing 46 of the apertures 12 results in one reinforcement member 18 passing through each of the transverse members 34, so that each of the transverse members 34 is reinforced by one of the reinforcement members 18.

The arrangement of the apertures 12 and the reinforcement members

18 shown in Figs. 4 and 5 is merely one example. Other arrangements are possible. The apertures might not be arranged in rows. The amount of offset between neighbouring rows could be different, and could be different to the spacing 40 of the reinforcement members 18. In one example, the spacing 40 between the reinforcement members 18 could be relatively small, so that a plurality of reinforcement members 18 pass through each of the transverse members 34.

As shown in Fig. 4, in the transverse areas 24 of the second areas 22, the reinforcement members 18 extend without interruption across the whole width of the materials screen 10. The reinforcement members 18 are aligned in a direction substantially at 90° to the direction of the rows 62. In use, the materials screen 10 is fitted onto a frame (not shown) within a vibratory screening machine. In operation, the screen 10 is vibrated, and a particulate material to be screened such as aggregate is fed over and along 5 the length of the screen 10 in a direction indicated by arrow A in Fig. 1. The frame of the machine provides support generally around and beneath the border areas 28 of the screen 10, and also beneath the longitudinal areas 26. The screen 10 is fixed to the frame in such a way that tension is applied to the longitudinal edges 29 of the screen 10 as indicated by arrows C to tension the

I O screen 10 transversely through the transverse areas 24 and hold the screen 10 onto the frame. Thus, as the screen 10 is vibrated, the frame supports the border areas 28 and the longitudinal areas 26, and the transverse areas 24 are in tension, so that the vibration force is directed to the unsupported, punched first areas 20.

15

As the material passes over the screen, particles will pass through the apertures 12 depending on the size and shape of the apertures 12 relative to the particles. The arrangement of the unsupported first aperture areas 20 optimises the efficiency of the vibratory screening process, permitting higher 0 throughputs of material, since all of the apertures 12 are open and not blocked by supports. The flexing of the first areas 20 during vibration also improves resistance to pegging and blinding.

The interruption of all of the reinforcement members 18 in the first 5 areas 20 increases the flexibility of the first areas 20, thus permitting more efficient operation.

The vibration characteristics of the first areas 20 depend on a number of factors, including the size of the first areas 20, the frequency and amplitude 0 of vibration, and the type and condition of the material being screened. It has been found that by varying the size of the first areas 20 to suit the material being screened, the vibration characteristics can be altered and improvements in operating efficiency can be achieved. Thus the materials screen 10 can be "tuned" to optimise the efficiency of screening of a particular material.

The shape of the aperture 12 as shown in Fig. 3B substantially prevents pegging or blocking of the apertures since the position of the minimum cross sectional area 32 is substantially at or towards the upper surface 38 of the screen 10, and the aperture 12 increases in size from the minimum cross sectional area 32 downwardly to the lower surface 48. The lower layer 16 thus does not specifically contribute to the separation of the material, but provides support for the upper layer 14. The small flared section 60 is not in practice deep enough to cause pegging, and in fact has been found to aid the movement of particles into the apertures 12, thereby improving efficiency.

In use, the transverse members 34 within the first areas 20 extend across the direction of motion of the material as indicated by arrow A in Fig. 4, and thus are particularly subject to wear. The reinforcement of each transverse member 34 with at least one reinforcement member 18 thus strengthens the screen 10 at its most vulnerable points, increasing the operating life of the screen 10, but because the interrupted reinforcement members 18 are relatively short in length, the vibration characteristics are not substantially impeded. Furthermore, the lamination of the relatively soft upper layer 14 with the relatively hard lower layer 16 and the forming of the apertures 12 through both layers 14, 16 ensures that each aperture 12 is defined by two layers of material, the second lower, harder layer 16 providing reinforcement, strength and rigidity, and the softer upper first layer 14 providing resilience and wear and abrasion resistance.

In one example, each of the layers 14, 16 are approximately 2.5mm in thickness, and the materials screen 10 has an overall thickness of between 4 and 5mm. The screen 10 could be of any suitable size. In one example, the screen 10 could be up to approximately 3000mm wide and 1600mm long, with border areas 28 extending inwardly 50mm from each edge of the screen 10. Each of the first areas 20 could be approximately 100 - 150mm in length and having a width which is dependent on the position of the frame longitudinal 5 supports, but could be between 200 and 500mm. The apertures 12 defined within the first areas could be between 2 and 15mm in width and length depending on the material to be screened, and could be rectangular, with longer sides extending along the length of the screen 10. In the second areas 22, the width of the longitudinal areas 26 could be approximately 40mm, and I 0 the width of the transverse areas 24 could be 20mm.

The transverse areas 24 act as integral tension bands, reducing or removing the requirement for additional separate support members or separate tension bands, resulting in an economical screen which can be fitted 15 relatively easily in the cramped spaces available within a vibratory screening machine. The transverse areas 24 cannot de-bond during operation. The screen of the invention is relatively strong, relatively cheap to manufacture, and with improved operating efficiency and improved operational life.

0 Fig. 6 shows in schematic form a modular screen assembly 70, which includes a plurality of screens 10, each screen 10 being substantially the same as the materials screen 10 described previously. Each materials screen 10 includes a plurality of first punched areas 20 and second unpunched areas 22. The second unpunched areas include transverse areas 24 and 5 longitudinal areas 26.

The screen assembly 70 could include a support frame (not shown) for supporting each of the screens 10, and the screens 10 could be modular in that they are of a standardised size to permit interchangeability, and the 0 assembly could be arranged to permit easy replacement of the screens 10 on the frame. Various other modifications could be made without departing from the scope of the invention. The screen 10 could be of any suitable size and shape, and could be formed of any suitable material. The first areas 20 and second areas 22 could be of any suitable size and shape. The apertures 12 5 could be formed in any suitable way, and could be of any suitable size and shape. The materials screen could be for use in any suitable screening apparatus, and could be used for screening any suitable material.

Any of the features described could be used singly or in any suitable I O combination.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any 15 patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A materials screen for material such as aggregates, the screen defining a plurality of apertures and being formed of a first, relatively soft layer and a second relatively hard layer.

2. A screen according to claim 1 , in which each aperture extends through both layers.

3. A screen according to claim 2, in which each aperture is larger in cross section plan area in the second layer than in the first layer.

4. A screen according to claims 2 or 3, in which each aperture has a minimum cross section plan area which is located in the first layer.

5. A screen according to claim 4, in which the minimum cross section plan area is located towards the outer surface of the first layer.

6. A screen according to claims 4 or 5, in which the aperture cross section plan area increases from the minimum cross section plan area towards the outer surface of the second layer.

7. A screen according to any of the preceding claims, in which the first layer is the in use upper layer, and the second layer is the in use lower layer.

8. A screen according to any of the preceding claims, in which the screen includes a plurality of elongate reinforcement members.

9. A screen according to claim 8, in which the reinforcement members are located in the second layer.

10. A screen according to claims 8 or 9, in which the apertures interrupt a proportion of the reinforcement members.

11. A screen according to any of the preceding claims, in which the screen includes a first area, or a plurality of first areas, having apertures.

12. A screen according to claim 11 when dependent on claim 10, in which in the or each first area, substantially all the reinforcement members are interrupted.

13. A screen according to any of the preceding claims, in which the screen includes a second area, or a plurality of second areas, without apertures.

14. A screen according to claim 13, in which in the second areas the reinforcement members are not interrupted.

15. A screen according to any of the preceding claims, in which the apertures are arranged in rows.

16. A screen according to claim 15 when dependent on claim 10 or any claim dependent thereon, in which alternate rows are offset to ensure all the reinforcement members are interrupted.

17. A screen according to claims 15 or 16, in which the apertures are regularly spaced along the rows.

18. A screen according to any of claims 15 to 17, in which the rows extend along the length of the screen.

19. A screen according to claim 11 or any claim dependent thereon, in which in the or each first area, the screen comprises spaced transverse members, and spaced longitudinal members, which together define the apertures.

20. A screen according to claim 19 when dependent on claim 8, in which at least one reinforcement member passes through each of the transverse members.

21. A screen according to claim 8 or any claim dependent thereon, in which the reinforcement members are spaced apart, and parallel with each other.

22. A screen according to claim 21 when dependent on claim 15 or any claim dependent thereon, in which the reinforcement members are aligned in a direction substantially at 90° to the direction of the rows.

23. A screen according to claim 13 or any claim dependent thereon, in which the or each second area includes one or more transverse areas, which extend transversely across the width of the screen.

24. A screen according to claim 13 or any claim dependent thereon, in which the or each second area includes one or more longitudinal areas, which extend longitudinally along the length of the screen.

25. A screen according to any of the preceding claims, in which the apertures are formed by punching.

26. A screen according to any of the preceding claims, in which the screen is formed of a resiliently deformable material.

27. A screen according to claim 26, in which the screen is formed of a rubber material.

28. A screen according to claim 27, in which the screen is formed integrally by hot vulcanising.

29. A screen according to claim 8 or any claim dependent thereon, the reinforcement members are in the form of cords.

30. A screen according to claim 29, in which the cords are formed of plastics material.

31. A method of manufacture of a screen for material such as aggregates, the method including the steps of forming a screen of a first, relatively soft layer and a second relatively hard layer, and forming a plurality of apertures through the screen.

32. A method according claim 31 , in which the screen is according to any of the claims 1 to 30.

33. A materials screen for material such as aggregates, the screen defining a plurality of apertures and including a plurality of elongate reinforcement members, the apertures interrupting a proportion of the reinforcement members.

34. A screen according to claim 33, in which the screen is according to any of claims 1 to 30.

35. A method of manufacture of a screen, the method including the steps of forming a screen including a plurality of elongate reinforcement members, and then forming a plurality of apertures extending through the screen, the apertures interrupting a proportion of the reinforcement members.

36. A method according to claim 35, in which the screen is according to claims 33 or 34.

37. A materials screen for material such as aggregates, the screen defining a plurality of apertures, the screen including a first area having apertures and a second area without apertures.

38. A screen according to claim 37, in which the screen is according to any of claims 1 to 30.

39. A method of manufacture of a screen, the method including the step of forming a plurality of apertures through the screen, the screen including a first area having apertures and a second area without apertures.

40. A method according to claim 39, in which the screen is according to claims 37 or 38.

41. A modular screen assembly, the assembly including a screen according to any of claims 1 to 30, or 33 or 34, or 37 or 38.

42. Screening apparatus, the screening apparatus including a screen according to any of claims 1 to 30, or 33 or 34, or 37 or 38.

43. A method of screening material, the method including the use of a screen according to any of claims 1 to 30, or 33 or 34, or 37 or 38.

44. A materials screen substantially as hereinbefore described and with reference to the accompanying drawings.

45. A method of manufacture of a screen substantially as hereinbefore described and with reference to the accompanying drawings.

46. A screen assembly substantially as hereinbefore described and with reference to the accompanying drawings.

47. Screening apparatus substantially as hereinbefore described and with reference to the accompanying drawings.

48. A method of screening material substantially as hereinbefore described and with reference to the accompanying drawings.

49. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.