SCREENING MACHINE FOR SCREENING MATERIAL ACCORDING TO SIZE

Abstract

A circle throw screening machine for screening particulate material according to size is described. The machine comprises a housing (2) having a longitudinal aspect, an upper perforated deck (7), a frame (3) configured for mounting the housing, and a suspension system (4) for mounting the housing to the frame and configured to allow vibration of the housing relative to the frame. Three rotatable unbalanced drive shafts (5) are coupled to the housing (2) and configured to vibrate the housing in response to rotation of the drive shafts, wherein the three rotatable unbalanced drive shafts are equally spaced along the longitudinal aspect of the housing. A drive mechanism (6) is coupled to the unbalanced drive shafts (5) and configured to effect synchronous rotation of the three drive shafts in the same direction. The machine can achieve high acceleration of 6.4G and 9.7G through the use of two or three parallel shafts respectively (NB. 2 shafts is suffice for a G of 6.4 and 3 shaft is suffice for 9.7G) distanced from each other by a distance of about one quarter of the length of the deck, configured for synchronous rotation.

Claims

1. A circle throw screening machine for screening particulate material according to size, the machine comprising: a housing (2) having a longitudinal aspect, an upper perforated deck (7) and a lower deck disposed underneath the perforated upper deck; a frame (3) configured for mounting the housing; a suspension system (4) for mounting the housing to the frame and configured to allow isolation of the housing relative to the frame; three rotatable unbalanced drive shafts (5) coupled to the housing (2) and configured to vibrate the housing in response to rotation of the drive shafts; and a drive mechanism (6) coupled to the unbalanced drive shafts (5) and configured to effect synchronous rotation of the three drive shafts in the same direction. wherein the three rotatable unbalanced drive shafts are equally spaced along a longitudinal aspect of the upper perforated deck (7).

2. A circle throw screening machine according to claim 1 in which the drive mechanism is configured to subject the particles to a G-force at or above 9.7G.

3. A circle throw screening machine according to claim 1 or 2 in which the drive mechanism is actuated to effect synchronous rotation of the three drive shafts at a rotational speed sufficient to effect three rotations of each shaft per particle throw time.

4. A circle throw screening machine according to any preceding claim in which the drive mechanism (6) comprises a single motor (23) configured for synchronous rotation of the three drive shafts.

5. A circle throw screening machine according to claim 4 wherein the single motor (23) is operatively coupled to a first of the drive shafts for rotation thereof.

6. A circle throw screening machine according to any preceding claim wherein the drive mechanism (6) comprises three external drive shafts (22), each of which is coupled to an unbalanced drive shaft by a constant velocity joint.

7. A circle throw screening machine according to claim 6 in which the external drive shafts (22) include a central external drive shaft (22A) and two side external drive shafts (22B, 22C), wherein the central external drive shaft is operatively connected to the motor (23) by a drive belt (24) and each of the side external drive shafts are operatively connected to the central external drive shafts by a timing belt (25).

8. A circle throw screening machine according to any preceding claim in which each drive shaft is mounted to the sidewalls (10) of the housing (2) in a manner that allows rotation of the unbalanced drive shafts (5) relative to the housing and translation of vibrational movement of the shafts (5) to the housing.

9. A circle throw screening machine according to any preceding claim in which an unbalanced weight (20) is disposed on each end of each of the unbalanced drive shafts (5).

10. A circle throw screening machine according to any preceding claim including a plurality of lower decks including at least one perforated lower deck (8).

11. A circle throw screening machine according to any preceding claim, in which the three unbalanced drive shafts extend laterally across the deck orthogonal to the longitudinal aspect of the deck.

12. A circle throw screening machine according to any preceding claim, in which the drive shafts (5) are parallel to each other and orthogonal to the longitudinal aspect of the housing.

13. A circle throw screening machine according to any preceding claim, in which the upper perforated deck (7) has a mesh size of between 0.025 mm and 1 mm.

14. A circle throw screening machine according to any preceding claim, in which the upper perforated deck (7) has a mesh size of between 2 mm and 50 mm.

15. A process for screening a particulate material that employs a circle throw screening machine according to any of claims 1 to 14, the process comprising the steps of delivering material to be screened to a top end of the upper perforated deck (7), actuating the drive mechanism (6) to effect synchronous rotation of the three unbalanced drive shafts (5) and effect vibrational movement of the housing (2), whereby the vibrational movement of the housing moves some of the material along the inclined upper perforated deck (7) and simultaneously separates the material into a first fraction of material which is delivered to a lower deck and a second fraction of material that is delivered to a bottom end of the upper perforated deck.

16. A process according to claim 15 in which the drive mechanism is actuated to subject the particles on the deck to a G-force at or above 9.7G.

17. A process according to claim 15 or 16 in which the drive mechanism is actuated to effect synchronous rotation of the three drive shafts (5) at a rotational speed sufficient to effect three rotations of each shaft per particle throw time.

18. A process according to any of claims 15 to 17 in which the particulate material is building material.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0045] FIG. 1A is a perspective view of the MST circle throw screening machine of the invention; (As previously discussed

[0046] FIG. 1B is a side view of the circle throw screening machine of FIG. 1;

[0047] FIG. 1C is an exploded detailed view of part of the circle throw screening machine of FIG. 1A;

[0048] FIG. 2 is a perspective view of the housing forming part of an SST screening machine of the invention shown without the upper and lower perforated screens to illustrate the internal configuration of the housing;

[0049] FIG. 3 is a side elevational view of the housing of FIG. 2;

[0050] FIG. 4 is a top plan view of the housing of FIG. 2;

[0051] FIG. 5 is a sectional view through the housing taken along the lines V-V of FIG. 2;

[0052] FIG. 6 is a top view of the elevational side view of FIG. 3.

[0053] FIG. 7 is a detail of from FIG. 5 showing a support system for the upper and lower perforated deck; and

[0054] FIG. 8 is a perspective view of a drive mechanism for the three rotatable unbalanced drive shafts forming part of the MST and SST circle throw screening machines of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0055] Referring to the drawings, and initially to FIG. 1, there is illustrated a circle throw screening machine of the invention indicated generally by the reference numeral 1. The machine illustrated is referred to as a MST circle throw screening machine and is used for fine, micron-sized, screening applications including defillerisation of sand and mud dewatering. The MST machine 1 comprises a housing 2, a frame 3, a Rosta suspension system 4 (FIG. 1c) coupling the housing 2 to the frame 3, three rotatable unbalanced drive shafts 5, and a drive mechanism 6 for driving the drive shafts 5. The frame 3 is configured to position the housing 2 in an inclined orientation, inclined at 8-14 degrees to the horizontal, although inclined mounting is not essential. The housing has an upper deck 7 comprising four perforated screen sections which abut end-to-end to form a screening deck bolted on to the support frame and having a screening length of 4 m and a screening aperture between 0.075 mm and 0.1 mm. The drive shafts 5 are disposed beneath, and equally spaced along, the deck 7.

[0056] Referring specifically to FIG. 1C, the degree of inclination of the housing with respect to the frame can be adjusted between 8, 10, 12 and 14 degrees by moving the position of the handle 26 in the slotted bracket 27.

[0057] In more detail, and referring to FIGS. 2 to 7, the circle throw screening machine of the invention will be described in more detail with reference to a second embodiment of the machine referred to as a SST circle throw screening machine. This machine is substantially similar to the MST machine described with reference to FIG. 1 with the exception that the upper deck 7 is formed from five sections which abut end-to-end to form a screening deck 5.6 m in length and having a screening aperture between 2 mm and 50 mm, and the SST machine has a lower deck 8 disposed beneath the three drive shafts 5. The SST machine is used for coarse screening applications including gypsum, rocks, stones, harbour mud and the like.

[0058] Referring to FIGS. 2 to 6, the housing 2 is coupled to the frame 3 by helical springs 12 (which comprise the suspension system) disposed at the foot of pillars 11 on each side of the housing. The purpose of the springs is to allow the housing to vibrate relative to the frame during rotation of the unbalanced drive shafts.

[0059] The housing 2 has opposed side walls 10, between the pillars and springs on both sides is a double plate on each side which is 6 mm thicker than the rest of the machine sidewall width of 8 mm, with the pillars 11 mounted to the side walls 10. The upper deck 7 comprises five cross-struts 14 mounted between the side walls and in addition three longitudinal struts 15 mounted to each end of the housing (the screens are removed for illustration purposes). The lower deck 8 comprises six cross-struts 16 mounted between the side walls and three longitudinal struts 17 mounted to each end of the housing (the screens are removed for illustration purposes).

[0060] Referring specifically to FIGS. 2 and 4, each unbalanced drive shaft 5 is mounted between the side walls 10 for rotation relative to the housing. Spherical roller bearings (not shown) designed for supporting an oscillating load are provided to carry the drive shafts and translate vibration of the shaft into vibration of the housing. An unbalanced weight 20 is provided at each end of the drive shafts 5, external to the side walls of the housing, for rotation with the drive shaft. As is evident from FIG. 2, the unbalanced drive shafts run substantially orthogonal to the longitudinal aspect of the housing, and are equally spaced along and below the deck 7 in the MST machine, and along and between the decks 7 and 8 in the SST machine). During use, rotation of the shafts and unbalanced weights cause the shafts to vibrate, and the vibration is passed to the housing which in turn causes the upper deck to vibrate and effect a screening action on particulate material disposed on the upper deck 7 in the MST machine and on both decks 7, 8 in the SST machine.

[0061] The housing 2 includes a cross-tensioning support system for the upper deck 7 (on SST only) which is indicated by the reference numeral A in FIG. 5 and shown in an exploded view in FIG. 7. The support system comprises an elongated L-shaped corner support 18 mounted on each sidewall of the housing, and formed in five sections corresponding to the five sections of the upper deck, and an elongated tensioning plate 19 mounted on each sidewall of the housing above the corner support 18. The upper screen sections are mounted to the housing, and tensioned, between the corner supports 18 and tensioning plates 19.

[0062] Referring now to FIG. 8, the drive mechanism 6 for both the MST and SST machines is illustrated and comprises a motor 23 having a motor drive shaft 21, three external drive shafts namely a central external drive shaft 22A, and side external drive shafts 22B and 22C. Each of the external drive shafts 22A, 22B and 22C are coupled to the unbalanced drive shafts of the housing by CV joints (not shown). The motor drive shaft 21 is operatively coupled to the central external drive shaft 22A by a drive belt 24, and the side external drive shafts 22B, 22C are coupled to the central external drive shaft 22A by timing belts 25. This arrangement provides for the three unbalanced shafts of the housing being driven by a single variable speed motor and rotating in the same direction of rotation and at the same speed, and obviated the need for multiple motors and motor-speed synchronisation software.

[0063] In use, the motor is started causing the three unbalanced drive shafts to rotate which in turn causes the upper deck to vibrate. Particulate material is delivered to the uppermost end of the upper deck, typically by means of an inlet hopper (see inlet hopper 40 in FIG. 1A). Upon delivery to the deck, the vibration of the deck causes the particles on the deck to lift-off with a vertical acceleration Kv and then land back on the deck with an impact that causes the particles to pass through the perforated deck. With the machine of the present invention, the rotational speed of the unbalanced shafts can be set such that the mechanical acceleration of the screen particles is 9.7 G, without causing the deck to buckle or break. The particles which pass through the upper perforated screen pass on to the lower (non-perforated) deck, which also vibrates, causing the particles to move along the deck to a lower end of the deck where they pass on to a conveyor for storage or for further processing. The particulate material which remains on the upper deck is moved towards the lower end of the deck by the incline and vibration, where it is delivered to an adjacent conveyor for further processing or re-circulation through the screening machine for further screening. In this embodiment, the machine screens particulate material to provide two fractions, a coarse fraction which remains on the upper deck and a less coarse fraction that passes through the upper deck on to the lower deck.

[0064] The embodiment of the machine described above has a non-perforated lower deck, which collects the finer fraction of particulate material and passes to a collection hopper or conveyor (or the like). In this embodiment, the screening machine produces three fractions of material, a coarse fraction which remains on the upper deck, a less coarse fraction which remains on the (lower) deck. When referring to the SST it has 3 fractions as mentioned. The MST has only 2 fractions material; the top deck (overs) and the material which falls through this onto the conveyor (fines).

[0065] The embodiment of the machine of the invention described above is fitted with a cross tension system, slightly arched over bucker-up strips and tightened on both sides (SST only). However, in another embodiment, the machine is fitted with flat rectangular prefabricated screening panels, bolted straight on to the support frame (MST only). Both systems are very coarse and are capable of resisting a G-force (approaching) 100 on the machine.

[0066] The invention is not limited to the embodiment hereinbefore described which may be varied in construction and details without departing from the spirit of the invention.