VIBRATORY SCREENING APPARATUS

Abstract: There is disclosed a vibratory screening apparatus (10, 10a) comprising a frame having a pair of opposed screen frame sides (11, 11a), a screen deck (13, 13a) mounted on the frame sides (11), and a shaft-driven vibratory mechanism coupled with the screen deck (13) to impart vibration energy thereto to assist the screening operation, the mechanism comprising: a pair of stubshafts (14) or projecting shaft ends (14b) associated one with each of the frame sides (11); a respective pair of bearing housings (15, 16; 15a, 16a) supporting each stubshaft (14) or shaft end (14b) and mounted on the respective frame sides (11, 11a) and spaced apart from each other; a respective counterweight (17, 17a) mounted on each stubshaft (14) or shaft end (14b) in the space between the housings (15, 16; 15a, 16a) of each pair, with the counterweight being rotatable with the stubshaft (14) or shaft end (14b) in order to apply vibration energy to the stubshaft and therefrom to the screen deck (13) via the bearing housings (15, 16; 15a, 16a) and the frame sides (11); and drive means (20, 20a) arranged to drive the vibratory mechanism. In one embodiment a drive motor (20) is coupled with each stubshaft (14) and arranged to apply synchronous drive to each stubshaft. In a second embodiment, a single shaft (14a) extends between the frame side (11a) and a single drive motor (20a) is coupled with one shaft end (14b). In both embodiments, the spaced bearing housings (15, 16; 15a, 16a) supporting each shaft end (14, 14b) with the counterweight (17, 17a) in the space between the housings provide vibrational energy to operate the screen but in a way which reduces the tendency of the drive shaft to oscillate excessively.

Description: VIBRATORY SCREENING APPARATUS This invention relates to a vibratory screening apparatus comprising a frame, at least one screen mounted on the frame, and a shaft-driven vibrating mechanism coupled with the screen in order to impart vibration thereto so as to assist the screening action. The invention has been developed primarily in connection with a screening apparatus for use in separating crushed stone, aggregate and the like into portions of different sizes, and seeks to provide an improved design of vibrating mechanism to apply vibration energy to the screen. It should be understood that a single screen e.g. a mesh screen comprises a minimum provision of screening in an apparatus according to the invention, though preferred embodiments will usually have more than one screen mesh or "deck", and may also have sets of vibratory grid bars. In one known design of vibratory screening apparatus, a shaft-driven vibrating mechanism comprises a single shaft which extends horizontally through the screen frame between opposed frame sides in the space between two screen decks, and in which each end region of the shaft is mounted on the respective screen side via a bearing housing which is secured to the frame side, and a counterweight is mounted on each free end of the shaft which projects outwardly of the respective bearing housing. Each counterweight comprises an off-set mass, and rotation of the shaft results in application of centrifugal force to the shaft via the counterweights which imparts required vibration energy to the screens of the apparatus. In this known apparatus, substantial bending moments are applied to the shaft by the counterweights, both by reason of the counterweights being mounted on the outwardly projecting ends of the shafts, and also because of the considerable overall length of the shaft which is required to extend throughout the width of the apparatus between the opposed screen frame sides. This causes the mid-region of the shaft to undergo substantial deflection which is undesirable, in that the shaft diameter will have to be of a sufficient size to withstand this applied bending load, and also there will be feedback to the mountings of the bearing housings on the frame sides which will also have to be suitably robust to bear these loads. The invention therefore seeks to provide a design of shaft-driven vibratory mechanism which is an improvement over this known apparatus, while still providing an efficient transfer of vibration energy to the screening elements of the apparatus. According to a first aspect of the invention there is provided a vibratory screening apparatus which comprises a frame having a pair of opposed screen frame sides, at least one screen mounted on said frame sides, and a shaft-driven vibratory mechanism coupled with the screen in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a pair of stubshafts, associated one with each of said frame sides; a respective pair of bearing housings supporting each stubshaft, said housings being mounted on the respective frame side and being spaced apart from each other; a respective counterweight mounted on each stubshaft in the space between the housings, said counterweight being rotatable with the stubshaft in order to apply vibration energy to the stubshaft and therefrom to the screen via the bearing housings and the frame sides; and, drive means coupled with each stubshaft to apply rotary motion thereto. Apparatus according to the first aspect of the invention therefore is able to provide efficient transfer of vibration energy to the screen, but by reason of the short length of the stubshafts and the mounting of each stubshaft on each frame side via a pair of spaced bearing housings, the bending loads applied to each stubshaft by each counterweight are reduced as compared with the known arrangement of a single long shaft (and can easily be borne by the housings), and with consequent reduction in deflection applied to each shaft. Preferably, the drive means coupled with each stubshaft comprises a drive motor coupled with the outward free end of each stubshaft, and desirably the shafts are driven in "" synchronism with each other, so that the same pattern of vibrations are applied to the screen at each side thereof. In a preferred embodiment, each motor is a hydraulic motor, one of which will be driven in clockwise rotation, and the other of which will be driven in anti-clockwise rotation. Preferably, the motors comprise gear-type motors which are arranged in parallel to a common pumped supply from one or more pumps, and are therefore able to self-regulate the operation of the motors so as to apply vibration energy to each of the two opposed side frames of the screen with such vibration energy being in phase. However, as an alternative to ύse-of-hydraulic motors arranged in parallel, synchronous electric motors may be provided. According to a second aspect of the invention there is provided a vibratory screening apparatus which comprises a frame having a pair of opposed screen frame sides, at least one screen mounted on said frame sides, and a shaft-driven vibratory mechanism coupled with the screen in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a pair of stubshafts, associated one with each of said frame sides; bearing housings supporting the stubshafts and mounted on the frame sides; a respective counterweight mounted on each stubshaft and being rotatable therewith in order to apply vibration energy to the stubshaft and therefrom to the screen via the bearing housings; and, drive motors coupled with each stubshaft and arranged to apply synchronous rotary motion to each stubshaft. In a preferred arrangement, the screening apparatus will have more than one "screen". Typically, each "screen" will comprise a screen mesh or "deck", arranged one above the other, so as to screen consecutively smaller size fractions of the material supplied to the top deck. The apparatus may also include vibratory screen bars. The motors may be driven "^" at speeds of the order of 1,000 rpm, and typical path of oscillation imparted to the screen may be about 5 mm i.e. a "throw" of about 5 mm. Suitable resilient dampers will be arranged to absorb the vibration energy imparted to the screen or screens. However, while the first and second aspects of the invention, and preferred features thereof, comprise one solution to the problems referred to of the known single shaft-driven vibrating mechanism, in a third aspect of the invention an improved mounting of a single shaft to drive the vibrating mechanism provides a further solution to the problems of the known arrangement. ~ - ~ " ~~~ Accordingly, in a third aspect of the invention there is provided a vibratory screening apparatus which comprises a frame having a pair of opposed screen frame sides, at least one screen mounted on said frame sides, and a shaft-driven vibratory mechanism coupled with the screen in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a shaft extending between the frame sides, and having end portions projecting outwardly of each frame side; a respective pair of bearing housings supporting each shaft end portion, said housings being mounted on the respective frame side and being spaced apart from each other; a respective counterweight mounted on each shaft end portion in the space between the housings, said counterweight being rotatable with the shaft in order to apply vibration energy to the shaft and therefrom to the screen via the bearing housings and the frame sides; and, drive means coupled with the shaft to apply rotary motion thereto. Apparatus according to the third aspect of the invention therefore is able to provide efficient transfer of vibration energy to the screen, and the provision of a pair of spaced bearing housings mounting each shaft end portion, with a respective counterweight mounted therebetween, enables the bending loads applied to the shaft to be reduced as compared with the known arrangement, and with consequent reduction in deflection applied to the shaft. Preferably, the screening apparatus is a multi-deck screen, and the shaft extends between the two frame sides in the space between a pair of upper and lower screen decks. The drive means coupled with the shaft may comprise a drive motor coupled with one of the outward free ends of the shaft, and the motor may comprise a hydraulic motor, or an electric motor. Since a single shaft is employed to apply the vibration energy to the screen deck(s), by reason of the rigid mounting assembly of a pair of bearing housings mounting each "ojecting end of the shaft, the shaft can be driven at high speed of rotation without generating any undue deflection or "whip" in the shaft in its mid-region. A typical path of oscillation imparted to the or each screen deck may be about 5mm i.e. "throw" of about 5mm under the application of the vibration energy to the screen deck(s) by the shaft driven vibrating mechanism. Suitable resilient ^ dampers may be arranged between the subframe and the assembly of frame sides, bearing housings, drive shaft and screen decks, to absorb the vibration energy imparted to the screen deck(s). Preferred embodiments of vibratory screening apparatus according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front elevation of a first embodiment of vibratory screening apparatus according to the invention; Figure 2 is a side elevation of the apparatus shown in Figure 1 ; Figure 3 is a schematic illustration of a pumped hydraulic circuit for operating hydraulic motors which drive the vibratory screening apparatus; and, Figure 4 is a view, similar to Figure 1 , of a second embodiment of vibratory screening apparatus according to the invention. Referring now to Figures 1 to 3 of the drawings, there is shown one preferred embodiment of vibratory screening apparatus of a type suitable for use in a quarry installation, in order to separate out different size portions of material to be screened, such as crushed stone, aggregate and the like. The illustrated embodiment is a multi-deck arrangement of a number of screen meshes arranged one above the other, which is a preferred arrangement. However, a minimum provision of a vibratory screening apparatus according to the invention will be provision of a single screen. The apparatus is designated generally by reference 10 and comprises a frame having a pair of opposed screen frame sides 11, and at least one screen which is mounted on the frame sides 11. ~ In the illustrated embodiment, a multi-deck arrangement of screens mounted on frame sides 11 is designated generally by reference 12, and individual screen meshes thereof are designated by reference 13. A shaft-driven vibratory mechanism is coupled with the screen deck 12 in order to impart vibration energy thereto so as to assist the screening operation. The shaft-driven vibratory mechanism comprises a pair of stubshafts 14, associated one with each of the frame sides 11. Each stubshaft 14 is supported by a respective pair of bearing housings, comprising an inboard housing 15 and outboard housing 16. The inboard housings 15 may comprise so-called "plummer block housings", and the outboard housings 16 incorporate spherical roller bearings. It will be noted from Figure 1 that the housings 15 and 16 of each pair are spaced apart from each other, and a respective counterweight 17 is mounted on each stubshaft 14 in the space between housings—15 and 16, and is keyed to the stubshaft so as to be rotatable therewith. Therefore, upon application of drive to each stubshaft 14, the respective counterweight 17 is driven in rotation, and by virtue of being an off-set mass, this applies centrifugal force to the stubshaft. This applies vibration energy to the stubshaft, which is transmitted to screen 12 via the bearing housings 15 and 16 and ~ the frame sides 11. As can be seen in Figures 1 and 2, each of the housings 15 and 16 is rigidly secured to a short length of box-shaped support beam 18 which extends between upright support beams 19 at each side frame 11, and which form part of a rigid side frame support structure. Drive means is coupled with each stubshaft 14 to apply rotation thereto, and in the illustrated embodiment comprises a respective hydraulic motor 20 which is arranged to drive the respective stubshaft 14 in synchronism, with one of the motors applying clockwise rotation and the other applying anti-clockwise rotation. Typically, shafts 14 may be driven at speeds of the order of 1,000 rpm, and by virtue of the way in which the screen 12 is mounted in the side frames 11 of the apparatus, typical paths of oscillation imparted to the screen are about 5 mm i.e. a "throw" of 5 mm. Suitable resilient dampers are arranged to absorb the vibration imparted to the components of the screen. The illustrated embodiment has been found to provide for efficient transfer of vibration energy to the components of the screen, but in a way which does not apply unduly large bending loads to each stubshaft. This is achieved by virtue of the relatively short lengths of each stubshaft, and the mounting of each stubshaft between a pair of spaced bearing housings, and with the counterweight being arranged on each stubshaft in the space between the two housings. This avoids the substantial bending stresses generated in an existing design of long shaft extending throughout the width of the apparatus, and which is supported at each shaft end by a single bearing housing, and with the counterweight arranged on the projecting end of the long shaft. This also avoids the problems of undue deflection which takes place in the mid-region of the long shaft in the existing arrangement. Figure 3 shows schematically a hydraulic circuit which drives the motors 20, from which it-can be seen that the motors 20 are arranged in parallel to a pumped supply from one or more pumps 21. The motors 20 is this arrangement are gear-type hydraulic motors, and the arrangement is such that the motors operate in synchronism with each other, and if there should be any tendency for one shaft 14 and its counterweight 17 to get out of phase with the other shaft and its counterweight, the system self-adjusts or self- compensates (by feedback from the motors) rapidly to get them back in phase. It has been observed that, even if the shafts should be out of phase on start-up, the system rapidly "tunes" itself and gets the counterweights in phase with each other. This is particularly advantageous, as it provides uniform application of vibration energy to each side frame and then to the screen(s). It should be understood that a hydraulic circuit and hydraulic motors are merely one preferred way of providing a self-regulating uniform application of vibration energy to each side of the screen frame i.e. patterns of vibration energy to each side which are in phase with each other. Other drive systems may be provided, including use of synchronous electric motors coupled with the stubshafts 14. Referring now to Figure 4 of the drawings, there is shown a second preferred embodiment of vibratory screening apparatus of a type suitable for use in a quarry installation, in order to separate out different size portions of material to be screened, such as crushed stone, aggregate and the like. The illustrated embodiment is a multi-deck arrangement of a number of screen meshes arranged one above the other, which is a preferred arrangement. However, a minimum provision of a vibratory screening apparatus according to the invention will be provision of a single screen. The apparatus is generally similar to the apparatus described above with reference to Figures 1 to 3, and corresponding parts are given the same references with the ~» addition of the letter a. The apparatus is designated generally by reference 1Oa and comprises a frame having a pair of opposed screen frame sides 11a and at least one screen which is mounted on the frame sides 11a. In the illustrated embodiment, a multi-deck arrangement of screens mounted on frame sides 11a is designated generally by reference 12a and individual screen meshes thereof are designated by reference 13a. A shaft-driven vibratory mechanism is coupled with the screen deck 12a in order to impart vibration energy thereto so as to assist the screening operation, and comprises a single shaft 14a extending between the two frame sides 11a, and having end portions 14b projecting outwardly of each frame side 11a. Each shaft end 14b is supported by a respective pair of bearing housings, comprising an inboard housing 15a and an outboard housing 16a. The inboard housings 15a may comprise so-called "plummer block housings", and the outboard housings 16a incorporate spherical roller bearings. It will be noted from figure 4 that the housings 15a and 16a of each pair are spaced apart from each other, and a respective counterweight 17a is mounted on each shaft end portion 14b in the space between housings 15a and 16a, and is keyed to the shaft 14a to be rotatable therewith. Therefore, upon application of drive to the shaft 14a, the counterweights 17a are driven in rotation, and by virtue of being off-set masses, this applies centrifugal force to the shaft 14a. This applies vibration energy to the shaft, which is transmitted to the screen 12a via the bearing housings 15a and 16a and the frame sides 11a. Each of the housings 15a and 16a is rigidly secured to a short length of box-shaped support beam 19a which extends between upright support beams (see reference 20 at each frame side 11, as shown in Figure 2), and which form part of a rigid side frame support structure. Drive means is coupled with the shaft 14a to apply rotation thereto, and in the illustrated embodiment comprises a hydraulic or electric motor 20a coupled with one of the free projecting ends 14b of the shaft 14a (the right hand end in Figure 4), and which can drive the shaft 14a in high speed rotation to apply vibration energy to the screen deck 12a. The shaft 14a may be driven at speeds of the order of 1,000 rpm, or even higher speed if required, and by virtue of the way in which the screen 12a is mounted in the side frames 11a of the apparatus, typical paths of oscillation imparted to the screen are about 5mm i.e. a "throw" of 5mm, or even larger if required. Suitable resilient dampers are arranged to absorb the vibration imparted to the components of the screen. The illustrated embodiment provides efficient transfer of vibration energy to the components of the screen, but in a way which does not apply unduly large bending loads to the shaft, and which is achieved by virtue of the support of each projecting end (14b) of the shaft by a pair of spaced bearing housings 15 and 16, and with the counterweight 17a arranged on each end portion between the two housings. This avoids the problems of undue deflection taking place in—the mid- region of the shaft, even in the case of fairly high speed rotation. In a preferred arrangement, shaft 14a is hollow to reduce its weight and rotational inertia while still providing sufficient strength to withstand applied torsional and bending loads. The hollow shaft may be of circular or other suitable cross-section to reduce the weight and rotational inertia while still retaining sufficient strength.

Claims: CLAIMS 1. A vibratory screening apparatus (10) which comprises a frame having a pair of opposed screen frame sides (11), at least one screen (13) mounted on said frame sides (11), and a shaft-driven vibratory mechanism coupled with the screen (13) in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a pair of stubshafts (14) associated one with each of said frame sides (11); a respective pair of bearing housings (15, 16) supporting each stubshaft (14), said housings being mounted on the respective frame side (11) and being spaced apart from each other; a respective counterweight (17) mounted on each stubshaft (14) in the space between the housings (15, 16), said counterweight being rotatable with the stubshaft (14) in order to apply vibration energy to the stubshaft and therefrom to the screen (13) via the bearing housings (15, 16) and the frame sides (11); and, drive means (20) coupled with each stubshaft (14) to apply rotary motion thereto. 2. Apparatus according to Claim 1 , in which the drive means coupled with each stubshaft (14) comprises a drive motor (20) coupled with the outward free end of each stubshaft, and the two motors being arranged to drive the stubshafts (14) in synchronism with each other, so that the same pattern of vibrations are applied to the screen (13) at each side thereof. 3. Apparatus according to Claim 2 , in which each motor (20) is a hydraulic motor, and the two motors are arranged in parallel to a common source (21) of pumped fluid. 4. Apparatus according to any one of Claims 1 to 3, in which the screen (13) forms part of a multi-deck screen (12), and each side frame (11) supports the multi-deck screen (12) and includes support beams (18) on which said housings (15, 16) are mounted. 5. A vibratory screening apparatus (10) which comprises a frame having a pair of opposed screen frame sides (11), at least one screen (13) mounted on said frame sides (11), and a shaft-driven vibratory mechanism coupled with the screen (13) in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a pair of stubshafts (14), associated one with each of said frame sides (11); bearing housings (15, 16) supporting the stubshafts (14) and mounted on the frame sides (11); a respective counterweight (17) mounted on each stubshaft (14) and being rotatable therewith in order to apply vibration energy to the stubshaft and therefrom to the screen (13) via the bearing housings (15, 16); and, drive motors (20) coupled with each stubshaft (14) and arranged to apply synchronous rotary motion to each stubshaft. 6. Apparatus according to Claim 5, in which the motors (20) comprise hydraulic motors arranged in parallel to a common pumped supply source (21). 7. Apparatus according to Claim 5, in which the motors (20) comprise synchronous electric motors. 8. Apparatus according to any one of Claims 5 to 7, in which each stubshaft (14) is supported by a respective pair of bearing housings (15, 16) which are spaced apart from each other, and which are mounted on support beams (18) which form part of the side frame support structure (11) of the screen (13). 9. A vibratory screening apparatus which comprises a frame having a pair of opposed screen frame sides (11a), at least one screen (13a) mounted on said frame sides (11a), and a shaft-driven vibratory mechanism coupled with the screen (13a) in order to impart vibration energy thereto so as to assist the screening operation, said mechanism comprising: a shaft (14a) extending between the frame sides (11a), and having end portions (14b) projecting outwardly of each frame side (11a); a respective pair of bearing housings (15a, 16a) supporting each shaft end portion (14b), said housings being mounted on the respective frame side (11a) and being spaced apart from each other; a respective counterweight (17a) mounted on each shaft end portion (14b) in the space between the housings (15a, 16a), said counterweight (17a) being -rotatable with the shaft (14a) in order to apply vibration energy to the shaft and therefrom to the screen (13a) via the bearing housings (15a, 16a) and the frame sides (11a); and drive means (20a) coupled with the shaft (14a) to apply rotary motion thereto. 10. Apparatus according to Claim 9, in which the screening apparatus is a multi-deck screen, and the shaft (14a) extends between the two frame sides (11a) in the space between a pair of upper and lower screen decks. 11. Apparatus according to Claim 9 or 10, in which the drive means coupled with the shaft (14a) comprises a drive motor (20a) coupled with one of the outward free ends of the shaft. 12. Apparatus according to Claim 11, in which the motor (20a) comprises a hydraulic motor, or an electric motor. 13. Apparatus according to any one of Claims 9 to 12, in which the shaft (14a) is a hollow shaft.

Inventors: DOUGLAS PATRICK JOSEPH, DOUGLAS, PATRICK, JOSEPH
Applicants: DOUGLAS PATRICK J, DOUGLAS, PATRICK, JOSEPH
Application year: 1993
Main classification: B07B1
IPC codes: B07B1