GB2356364A

GB2356364A - A screenbox

Info

Publication number: GB2356364A
Application number: GB0025524A
Authority: GB
Inventors: Neill Suitor; Daniel James Mccusker
Original assignee: Powerscreen International Distribution Ltd
Current assignee: Powerscreen International Distribution Ltd
Priority date: 1999-10-28
Filing date: 2000-10-18
Publication date: 2001-05-23
Also published as: GB0025524D0; GB9925417D0; DE10053845A1

Abstract

A screenbox 1 comprises at least a first screen (2, fig 4a) having a first section 21 which is side-tensioned using anchorage points 26 at the sides of the screenbox and a second section (22, fig 4a) which is end-tensioned between cross members 34, 39. The side-tensioned first screen section 21 is located at the load end 11 of the screenbox, and may be cambered about an axis which is longitudinal of the screenbox. It is typically a third of the length of the second first screen section (22). The screenbox also comprises a vibratable screening means, wherein the screenbox is mounted to a subframe via resilient suspension units 51, 52 in such manner that its dead weight is supported, and wherein means 7, 76 are provided for transmitting vibrational forces to the screenbox 1, the transmission means being substantially unloaded in the absence of such vibration and in the absence of material being screened.

Description

2356364 IMPROVEMENTS RELATING TO SCREENBOXES This invention relates to

screenboxes.

Screenboxes are used inter alia at quarries, landfill sites, coal, sand and gravel pits, construction sites and elsewhere for the screening of various materials including solid waste, crushed rock, coal, sand, gravel, demolition 5 rubble, clay, peat, compost, slurry, ash, and mineral ores.

In a typical screening system using such a screenbox, the material to be screened is first fed to a hopper above an inclined reject grid formed from hardened steel bars which rejects grossly oversized material. That grossly oversized material is usually allowed to fall to ground. Material falling through the reject grid passes to a conveyor, optionally via a scalping grid, and is then conveyed upwardly and discharged onto the load or upper end of an inclined screenbox which may be located downwardly inclined either back beneath the conveyor, or as an outward extension of the conveyor. The screenbox will contain one or more screens for dividing the material into two or more size fractions. The material is then passed to stockpiles, transporters (possibly comprising further conveyors) or other processing apparatus.

A screenbox of a high throughput machine may typically have a nominal size of 1.5 x 3.0 m, and to assist in handling of the screens, which need replacement from time to time as they wear out or become damaged, and to assist in their securing in the screenbox, it is known to make the screens in two sections, each 1.5 x 1.5 m. Such screen sections are fixed to cross beams at the centre of the screenbox and are held tensioned by a movable beam at each end of the screenbox.

Such an arrangement has been used successfully for many years, but we have now appreciated that the conventional arrangement has certain 2 disadvantages, and it is accordingly an object of the present invention to provide a new and improved screenbox.

According to the present invention, there is provided a screenbox comprising a screen (hereinafter called "first screen") having a first section 5 which is side-tensioned and a second section which is endtensioned.

Such an arrangement is new and it allows a certain versatility in the arrangement of the screen sections of the screen, specific aspects of screen construction having their own particular advantages.

It is particularly preferred that said side-tensioned first screen section is located at the load end of the screenbox, since it is in this configuration that the advantages afforded by the present invention are most apparent.

In embodiments of the invention in which said screenbox includes more than one said screen, it is also particularly preferred that said first screen is the top screen of the screenbox, since it is in this configuration too that the advantages afforded by the present invention are most apparent.

Preferably, said first, side-tensioned first screen section is cambered about an axis which is longitudinal of the screenbox. Such an arrangement is simplified by side-tensioning the screen section as opposed to endtensioning it, and it has the advantage that as material falls onto such a cambered screen section, that material tends to be shed towards either side of the screenbox. Since there is a tendency for material to be deposited onto a central region of that screen section, this promotes an even distribution of material across the width of the screen leading to increased screening efficiency.

In preferred embodiments of the invention, the first section of the first screen is shorter (measured longitudinally of the screenbox) than the second 3 first screen section. We have noted that the principal cause of damage to or wear of the screen or screens of the screenbox is due to the impact of material to be screened as it falls from a conveyor onto the screen. Thus it is the load end of the first screen which is most affected. The adoption of this particular combination of preferred optional features affords'advantages of economy in that the first section of the screen may be replaced independently of the second, and, since it is shorter than the second screen section (for a given size of screenbox), and thus shorter than previously known screen sections, it will be lighter in weight and less expensive. It is suitable for the side-tensioned screen section to be less than one third of the total length of the first screen, and in a particular preferred embodiment, it has a length of about one quarter of the top total screen length. The greatest proportion of impact damage is caused in that quarter length of the screen, and the adoption of this combination of features therefore promotes maintenance efficiency.

In order to limit strains on the first screen and consequent sag, it is preferred that said first screen is supported by cross members attached to screen sides.

Advantageously, said first screen is supported by a cross members including a welded grid which is adapted to support said first section of the first screen and comprises at least one medial cross member and at least one medial longitudinal screenbox frame member. The use of such a welded grid is of great value in prolonging the working life of that first section of the first screen. Furthermore, the or each cross member of that grid may be curved to impart a camber to the screen section as is preferred In the most preferred embodiments of the invention, the screenbox is resiliently mounted on a sub-frame and means are provided for vibrating such screenbox. Vibrating screens are well known per se, and have the 4 advantage, as compared with non-vibrating screens, of a greatly increased maximum throughput (tonnes/hour) for a given size of screen.

Preferably, the screenbox is mounted to the subframe in such manner that its dead weight is supported by resilient suspension members and means for transmitting vibrational forces to the screenbox are substantially unloaded in the absence of such vibration and in the absence of material being screened. This permits the vibration transmitting elements to be of lighter construction than would otherwise be possible, with consequent savings in weight, materials and cost, and simplifies the damping of reaction vibrations imparted to the subframe and to the remainder of the apparatus.

Indeed, this feature is of particular practical importance independently of the presence of a side-tensioned first screen section, and it is itself believed to be novel. Accordingly, in its second aspect the present invention provides a screenbox for vibratable screening means, which screenbox is mounted to a subframe via resilient suspension units in such manner that its dead weight is supported, and wherein means are provided for transmitting vibrational forces to the screenbox which transmission means are substantially unloaded in the absence of such vibration and in the absence of material being screened.

In the most preferred embodiments of the invention, the screenbox comprises screen sides joined together by cross members which are bolted to the screen sides. Such cross members are useful for supporting sections of screens during operation of the screenbox. It is known to provide cross members which are welded to screen sides. Bolting, especially huckbolting as is particularly preferred, offers certain advantages over welding. When a screenbox is manufactured by welding cross members between a pair of screen sides, certain stresses are inevitably set up in the skeleton of the screenbox. The constant vibration to which the screenbox is subjected in use exacerbates these stresses with the result that the screenbox undergoes fatigue failure and cracks are formed. The use of bolts for fastening the screenbox together alleviates this disadvantage.

This feature too is considered to be of great practical importance, and in its third aspect, the present invention provides a screenbox mounted on a subframe via resilient suspension units wherein means are provided for transmitting vibrational forces to the screenbox and wherein the screenbox comprises screen sides joined together by cross members which are bolted to the screen sides.

Preferably, means for transmitting vibrational forces to said screenbox comprises an eccentric shaft extending across the subframe and the screenbox, and means for driving such shaft in rotation. This can provide a very simple and robust means for transmitting the required vibrational forces.

Such shaft advantageously carries a counterbalancing asymmetrical flywheel at each side of the screenbox. This helps to reduce vibrational reaction forces passed to the sub-frame and thence to the remainder of the apparatus.

Preferably, the vibration transmitting means is resiliently mounted to the 20 subframe. This too can help reduce vibration of the subframe.

Advantageously, the vibration transmitting shaft is carried by a bearing which is resiliently mounted to the subframe via elastomeric blocks. The use of such elastomeric blocks promotes damping of vibrations passing to the subframe.

A screenbox. according to the invention is intended to be used mounted so as to be downwardly inclined from its load end to its discharge end. In this 6 way, material being screened can naturally gravitate through the screenbox.

Advantageously, means is provided for varying the angle of such inclination. The inclination can thus be adjusted as desired for the optimum throughput of different grades or types of material which it isdesired to screen In such embodiments of the invention, it is preferable that each side of the screenbox carries suspension mountings respectively located towards its load and discharge ends, each such mounting being arranged to support the screenbox against working movement along a working axis which is inclined with respect to a notional line joining the suspension mountings at that respective side of the screenbox, and the acute angle between that notional line and the discharge-end working axis is smaller than the acute angle between that line and the load-end working axis. This promotes a proper support of the dead weight of the screenbox by suspension units bearing on such suspension mountings.

Preferably, the screenbox is tiltable between a first angle of inclination at which the working axes of the load-end units are substantially vertical and a second angle of inclination at which the working axes of the discharge-end units are substantially vertical.

Advantageously, said screenbox is a multi-deck screenbox and at least one lower screen is located beneath the first screen thereof This permits the screening of material fed to the screenbox into at least three different size fractions. The lower screen may be made in the same way as the first screen if desired, or it may be wholly end-tensioned.

A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which:

7 Figure 1 is a perspective view from one side, above, and the discharge end, of a screenbox in accordance with the invention, the screen box being mounted on a subframe; Figure 2 is a perspective view from above, the discharge end, and one side, of the screenbox of Figure 1; Figure 3 is a perspective view from below, the load end, and the other side, of the screenbox of Figure 1; Figures 4a and 4b are side elevations of that other side, of the screenbox of Figure 1; and Figure 5 is section on the line V-V of Figure 4a, also showing the subframe.

In the drawings, a screenbox I comprises a first screen 2 having a first section 21 which is side-tensioned and a second section 22 which is end tensioned. The screen sections are shown in Figures 4a and 4b.

The embodiment of screenbox illustrated is a multi-deck screenbox and a lower screen 23 is located beneath the first screen 21, 22. This permits the screening of material fed to the screenbox into at least three different size fractions. The lower screen 23 may be made in the same way as the first screen if desired, or it may be wholly end-tensioned as either a single screen section or a two section screen 24, 25 as shown.

The side-tensioned first screen section 21 is located at the load end I I of the screenbox 1, since it is in this configuration that the advantages afforded by the present invention are most apparent. Side tensioning is suitably effected by anchoring the side ends of t1fe first screen section 21 at 25 anchorage points 26.

The side-tensioned first screen section 21 is shorter (measured longitudinally of the screenbox 1) than the second first screen section 22. The principal cause. of damage to or wear of the first screen of a screenbox is due to the impact of material to be screened as it falls from a conveyor onto the first screen. Thus it is the load end of the first screen which is most affected. Using a short first screen section at the load end affords advantages of economy because that first section of the screen may be replaced independently of the second, and (for a given size of screenbox) since it is shorter than the second, and thus shorter than previously known screen sections, it will be lighter in weight and less expensive. It is suitable for the side-tensioned screen section to be about one quarter of the top total screen length, since it is in that first quarter where the greatest proportion of impact damage is caused.

In order to limit strains on the first screen sections 21, 22 and consequent sag, they are supported by cross members 31 to 39 attached to screen sides 4. The load end section 24 of the bottom screen 23 is carried by cross members 40 to 43, and the discharge end section 25 of the bottom screen 23 is supported by cross members 44 to 47.

Apart from the fact that these cross members are bolted to the screen sides, the arrangement of the bottom screen shown in Fig. 4a is conventional. The bottom screen load end section 24 is end-tensioned between cross members 40 and 43 while the bottom screen discharge end section 25 is end-tensioned between cross members 44 and 47. Those screen sections are respectively supported by intermediate cross members 41, 42 and 45, 46.

Those intermediate cross members are located above the planes containing their respective end-tensioning members so that the two screen sections are each held tensioned in a camber about a transverse axis. This ensures that the screen sections are held taut and properly supported for a long working life and efficient screening. The discharge end section 22 of the f-irst 9 screen 2 is likewise held end-tensioned between cross members 34 and 39 over intermediate cross members 35 to 38, these also being arranged so that the discharge end section 22 of the first screen 2 is held tensioned in a camber about a transverse axis.

Cross members 31 to 33 are welded into a grid 3 which is adapted to support the first, side-tensioned first screen section 21. The grid 3 comprises at least one medial cross member 32 and at least one medial longitudinal screenbox frame member 30. The use of such a welded grid is of great value in prolonging the working life of that first section of the first screen. The cross members 31 to 33 of that grid 3 have curved upper edges to impart a camber to the first screen section 21 as it is tensioned at the sides of the screenbox.

The side-tensioned first screen section 21 is thus cambered about an axis which is longitudinal of the screenbox 1. Such an arrangement is made possible by side-tensioning the screen section as opposed to endtensioning it, and it has the advantage that as material falls onto such a cambered screen section, that material tends to be shed towards either side of the screenbox which naturally promotes an even distribution of material across the full width of the screen leading to increased efficiency.

The screenbox 1 is resiliently mounted by means of four suspension units 5 on a sub-frame 6 and means 7 are provided for vibrating such screenbox. Vibrating screens are well known per se, and have the advantage, as compared with non-vibrating screens, of a greatly increased maximum throughput (tonnes/hour) for a given size of screen.

In the embodiment illustrated, the screenbox I is mounted to the subfrarne 6 in such manner that its dead weight is supported by the resilient suspension units 5 and the means 6 for transmitting vibrational forces to the screenbox are substantially unloaded in the absence of such vibration and in the absence of material being screened. This permits the vibration transmitting elements to be of lighter construction than would otherwise be possible, with consequent savings in weight, materials and cost, and simplifies the damping of reaction vibrations imparted to the subframe 'and to the remainder of the apparatus.

Indeed, this feature forms the second aspect the present invention which provides a screenbox 1 for vibratable screening means, which screenbox I is mounted to a subframe 6 via resilient suspension units 5 in such manner that its dead weight is supported, and wherein means 7 are provided for transmitting vibrational forces to the screenbox I which transmission means are substantially unloaded in the absence of such vibration and in the absence of material being screened.

The means 7 for transmitting vibrational forces to said screenbox comprises a shaft 71 extending across the subframe 6 and the screenbox 1, carried by bearings 72, 73 respectively mounted on the subframe 6 and the screen sides 4. The bearings 72 carrying the shaft 71 are resiliently mounted to the subframe 6 by means of elastomeric blocks 74 in order to reduce the transmission of vibrations to the subframe. A pulley 75 is provided for driving the shaft 71 in rotation.

The shaft 71 is eccentric so that the axis at the bearings 73 on the screenbox are offset by a few millimetres from the axis at the bearings 72 on the subframe. An offset of 3mm will give an amplitude of vibration of 6mm and this is found suitable for most purposes. The shaft carries a counterbalancing asymmetrical flywheel 76 at each side of the screenbox 1 in order to reduce vibrational reaction forces passed to the sub-frame 2 and thence to the remainder of the apparatus. Within the screenbox, the eccentric shaft 71 is enclosed within a housing 77 to protect it from the I I material being screened. The housing 77 is bolted to the screen sides 4.

In the illustrated embodiment of the invention, the screenbox I comprises screen sides 4 joined together by cross members 31 to 39 and 40 to 47 which are huck-bolted to the screen sides.

Thus, the present invention provides a screenbox I mounted on a subframe 6 via resilient suspension units 5 wherein means 7 are provided for transmitting vibrational forces to the screenbox 1 and wherein the screenbox 1 comprises screen sides 4 joined together by cross members 31 to 47 which are bolted to the screen sides 4.

A screenbox according to the invention is intended to be used mounted so as to be downwardly inclined from its load end I I to its discharge end 12. In this way, material being screened can naturally gravitate through the screenbox.

Means (not shown) which is known per se is provided for varying the angle of such inclination. The inclination can thus be adjusted as desired for the optimum throughput of different grades or types of material which it is desired to screen Each side of the screenbox carries suspension units carried by suspension mountings 51, 52 respectively located towards the load and discharge ends 11, 12, each such mounting being arranged to support the screenbox I against working movement along a working axis 53, 54 which is inclined with respect to a notional line 55 joining the suspension mountings 51, 52 at that respective side of the screenbox. The acute angle a between that notional line 55 and the discharge-end working axis 54 is smaller than the acute angle B between that line 55 and the load-end working axis 53. This promotes a proper support of the dead weight of the screenbox I by suspension units bearing on such suspension mountings, and is particularly 12 advantageous when the screenbox 1 is of variable inclination.

For example, the screenbox may be tiltable between a first angle of inclination at which the working axes 53 of the load-end suspension mountings 51 are substantially vertical and a second angle of inclination at which the working axes 54 of the discharge-end suspension mountings 52 are substantially vertical.

As shown in Figure 4b, the inclination of the load end section 24 of the lower screen 23 may be varied e.g. by 3' by raising the load end of that section. It is sometimes desirable to increase the slope of the load end section of a screen, whether for promoting slicing of material when that section is constituted as a speedharp rAther than a mesh screen, or simply for moving material on more quickly while the second section is less steeply inclined to allow a better gradation of screened material.

Claims

13 CLAIMS

I A screenbox comprising a screen (hereinafter called "first screen") having a first section which is side-tensioned and a second section which is end-tensioned.

2. A screenbox according to Claim 1, wherein said first, side-tensioned 5 first screen section is located at the load end of the screenbox.

3. A screenbox according to Claim 1 or 2, wherein said first, sidetensioned first screen section is cambered about an axis which is longitudinal of the screenbox.

4. A screenbox according to any preceding claim wherein the first 10 section of the first screen is shorter than the second first screen section.

5. A screenbox according to Claim 4, wherein the first section of the first screen is less than one third the total length of the first screen.

6. A screenbox according to any preceding claim, wherein said first screen is supported by cross members attached to screen sides.

7. A screenbox according to Claim 6, wherein said first screen is supported by a cross members including a welded grid which is adapted to support said first section of the first screen and comprises at least one medial cross member and at least one medial longitudinal screenbox frame member.

8. A screenbox according to any preceding claim, wherein such screenbox is resiliently mounted on a sub-frame dnd means are provided for vibrating such screenbox.

14

9. A screenbox according to Claim 8, wherein the screenbox is mounted to the subframe in such manner that its dead weight is supported by resilient suspension members and wherein means for transmitting vibrational forces to the screenbox are substantially unloaded in the absence of such vibration and in the absence of material being screened.

10. A screenbox for vibratable screening means, which screenbox is mounted to a subframe via resilient suspension units in such manner that its dead weight is supported, and wherein means are provided for transmitting vibrational forces to the screenbox which transmission means are substantially unloaded in the absence of such vibration and in the absence of material being screened.

11. A screenbox according to any of Claims 8 to 10, which screenbox comprises screen sides joined together by cross members which are bolted to the screen sides.

12. A screenbox mounted on a subframe via resilient suspension units wherein means are provided for transmitting vibrational forces to the screenbox and wherein the screenbox comprises screen sides joined together by cross members which are bolted to the screen sides.

13. A screenbox according to any of Claims 8 to 12, wherein means for transmitting vibrational forces to said screenbox comprises an eccentric shaft extending across the subframe and the screenbox, and means for driving such shaft in rotation.

14. A screenbox according to claim 13, wherein such shaft carries a counterbalancing asymmetrical flywheel at each side of the screenbox.

15. A screenbox according to any of Claims 8 to 14, wherein the vibration transmitting means is resiliently mounted to the subframe.

16. A screenbox according to Claim 15, wherein the vibration transmitting shaft is carried by a bearing which is resiliently mounted to the subframe via elastomeric blocks.

17. A screenbox according to any preceding claim, mounted -so as to be 5 downwardly inclined from a load end to a discharge end.

18. A screenbox according to Claim 17, wherein means is provided for varying the angle of such inclination.

19. A screenbox according to any of Claims 8 to 16, and to either of Claims 17 and 18, wherein each side of the screenbox carries suspension mountings respectively located towards its load and discharge ends, each such mounting being arranged to support the screenbox against working movement along a working axis which is inclined with respect to a notional line joining the suspension mountings at that respective side of the screenbox, and wherein the acute angle between the notional line and the discharge-end working axis is smaller than the acute angle between that line and the load-end working axis.

20. A screenbox according to Claims 18 and 19, wherein the screenbox is tiltable between a first angle of inclination at which the working axes of the load-end units are substantially vertical and a second angle of inclination at which the working axes of the discharge-end units are substantially vertical.

21. A screenbox according to any preceding claim, wherein said screenbox is a multi-deck screenbox and at least one lower screen is located beneath the first screen thereof

22. A screenbox substantially as herein described with reference to the accompanying diagrammatic drawings.