VIBRATING SCREENING DEVICE

Abstract: Vibrating screening device with a screenbox (1) with screening means (13-16) and a rotating screen excenter shaft (2), which, when rotated, is arranged to transfer a vibrating movement to said screenbox (1) through two outer screenbox bearings (5) in which the screen excenter shaft is rotary journalled, said outer screenbox bearings being arranged at opposite sides of said screenbox for transferring to said screenbox a vibration producing force, characterized in that said screen excenter shaft is also journalled in at least one support bearing (6) arranged between said outer screenbox bearings (5).

Description: Vibrating Screening .Device Vibrating screening devices (vibrating sieving devices) driven by one or more excenter shaft or shafts are known. Such a screening device normally comprises a screenbox of usually rectangular shape provided with one or more screen decks. Two main types of such devices are devices in which the excenter shaft is at its ends joumalled in bearings which are rigidly connected to a fixed frame or a foundation construction so that said outer bearings are maintained in a fixed position whereas an excentric part of the shaft performs an excentric, vibrating motion which is transferred to the screenbox. Another type of vibrating screening devices is provided with an excenter shaft which at one or both of its ends is provided with a heavy mass so that when the shaft is rotated said mass and the screenbox both perform vibrating motions around a centre of motion. Both said types of devices are comprised by this invention. Usually said excenter shaft is driven with an electric motor or other type of motor which may be connected directly to the screen shaft or connected to said shaft through a rope gear or some other type of well known trans¬ mission device. It is often difficult to increase the rotation speed and the vibration frequency of previously known vibrating screening devices above a certain limit since above said limit the device is subjected to severe self-oscillation effects which disturb the funtion and increase the wear of bearings etc. According to the invention it is possible to avoid said difficulties by using a vibrating screening device with a screenbox with screening means (such as wire net, bars, metal sheets with openings etc.) and a rotating screen excenter shaft, which, when rotated, is arranged to transfer a vibrating movement to said screenbox through two or more outer screenbox bearings in which the screen excenter shaft is rotary joumalled, said outer screenbox bearings being arranged at opposite sides of said screen box for transferring to said screenbox a vibration producing force, said device being characterized in that said screen excenter shaft is also jou alled in at least one support bearing between said outer screenbox bearings. Said support bearing or support bearings are preferably arranged to be supported by the screenbox, e.g. by being arranged in a screen excenter shaft tube which surrounds the excenter shaft and protects the shaft against the material being screened. Preferably said shaft tube is divided into two parts of essentially equal length with a bearing housing arranged between said two tube parts for holding and supporting the support bearing essentially half-way between the outer screenbox bearings, said tube extending between said two outer screenbox bearings and preferably being secured to the housings used for said bearings or to the screenbox walls close to said bearings. If more than one support bearing is used, said bearings are preferably arranged with equally large interspaces along the distance between the two outer screenbox bearings, and the shaft tube is then preferably divided into a corresponding number of parts with a support bearing housing arranged between each two of its said parts, e.g. if two support bearings are used, the tube is preferably divided into three parts, etc. It is, however, also possible to use one unitary tube which is not divided into parts and arrange the support bearing or bearings within said tube with suitable means, but usually the radial gap between the shaft and the tube is too narrow to permit the arrangement of bearings therebetween without a special housing. The support bearings preferably consist of ball-bearings or roller-bearings such as needle bearings, but it is also possible to use a sliding bearing, preferably oil lubricated. The main purpose of the support bearings is to prevent self-oscillation of the shaft and it is .therefore possible to use a bearing with substantially smaller load-supporting capacity than the outer screenbox bearings, which normally are intended to support the main part of the static and dynamic weight of the screenbox and the materials thereon. According to a preferred embodiment the screenbox is provided with one or more intermediate wall or walls extending preferably substantially perpendicular to the excenter screen shaft and substantially parallel to outer side walls of said box. Said intermediate wall or intermediate walls preferably divide the distance between said outer screenbox walls into two or more parts of equal length, i.e. if one intermediate wall is used it is arranged substantially in the middle of the box. The intermediate walls extend to substantially the same height as the outer side walls and preferably extend through all screen decks in the box dividing said screen decks into two or more parts, depending upon the number of intermediate walls. Said intermediate wall or intermediate walls are preferably rigidly arranged in the screenbox and form load-supporting part thereof.- The screening means which form the screen decks thus extend in the direction of the shaft between an outer wall and the intermediate wall or between two intermediate walls resp. This is an advantage since it is easy to arrange and exchange said more narrow screening means than a screening means extending the entire distance between the outer screenbox walls. Furthermore,screening means with different screen openings can be used in the screen decks on each side of an intermediate wall which makes the screening device more flexible in use. Furthermore, the support bearing or support bearings are preferably supported by said intermediate wall or intermediate walls e.g. by securing the support bearing housing to said intermediate wall. Preferably the shaft tube parts are also secured to the intermediate wall and the outer side walls of the box e.g. by being provided with flanges welded to said tube part and e.g. fastened with bolts to said walls. The intermediate wall or intermediate walls also in the lengthwise direction have essentially the same extension as the outer side walls of the screenbox i.e. extend from the inlet end of the box to the outlet end. The number of screen decks may be 1, 2, 3, 4, 5, 6 or more arranged on top of each other in a per se well known manner with the size of the openings decreasing in the downward direction. It is normally desired that the gap between the shaft and the shaft tube is as small as possible, and said gap may under resting condition be selected to e.g. at most 15 mm, at most 10 mm, at most 6 mm, at most 4 mm or at most 2 mm. The invention is in the following explained with reference to the accompanying figures. Figure 1 is a schematic view of the screenbox. Figure 2 is a similar view of the screenbox with the screen decks removed. Figure 3 is a schematic section through the box and the shaft. Figure 4 is a schematic view of a shaft tube part. The device shown on the figures comprises a screenbox 1 of substantially rectangular shape provided with an excenter shaft axis schematically indicated with a line 2 on figure 1 and shown in greater detail on the other figures. Said shaft extends substantially perpendicular to the outer side walls 11, 12 of the box 1. The longitudinal extension of the box from the inlet end to the outlet end 24 is 2300 mm and the breadth between the side walls 11, 12 is 1400 mm. The shaft 2 rests on outer bearings 3 which are supported on a fixed frame 19 suitably connected to a foundation construction. The shaft also comprises an excentric part 4 extending between two outer screenbox bearings 5, arranged in housings fastened to the screenbox for transferring a vibrating motion to the said box when the shaft is rotated. The shaft is also joumalled in a support bearing 6 arranged in the centre between the bearings 5 and held in a support bearing housing.- The box is also provided with an intermediate wall 9 arranged substantially centrally between the side walls 11, 12 and with substantially the same extension in the lengthhwise and vertical directions. There are two screen decks formed by screening means 13. 14 and 15, 16 resp. shown on the figure as wire nets. The screenbox is also provided with screen springs 21 arranged at each corner of the box which contribute to support the weight of the box and maintain the box in a desired position, usually with the screen decks sloping in relation to the horizontal plane, e.g. in an angle of 10-75° preferably 20-60°, in a per se known manner. The shaft is also provided with a rope wheel 20, for driving the shaft with ropes and e.g. an electric motor. Furthermore, the shaft is provided with balancing weights 22, which balance the excentric part 4 of the shaft. The support bearing 6 is connected to the intermediate wall 9 through a bearing housing 23 formed in flanges arranged on shaft tube parts 25, arranged on each side of the intermediate wall and extending between the outer walls and said intermediate wall. Said flanges are preferably machined with sufficient precision to form a straight tube from said tube part 25 with a deflection smaller than the desired gap between the shaft and the tube when fastened with e.g. bolts through the end flanges of said tube parts. The support bearing 6 may be arranged to support a substantial part of the dynamic and static loads exerted on the screenbox but is preferably arranged to be subjected to only a minor part of said load, e.g. to at most 10 %, at most 20 %, at most 50 % or at most 75 % of the load exerted on each of the outer screenbox bearings 5. Thus already a small bearing exerting only a small force on the shaft is sufficient to prevent violent self-vibrations of the shaft and displace the critical speed of rotation to a substantially higher level e.g. from about 700 rpm or above to about 1500 rpm or above so that the speed of rotation and the vibration frequency can be increased to a level close to said higher value. An advantage of the invention is also that the deflection of- the shaft within the box caused by the rotation and the forces exerted on the shaft thereby can be decreased substantially, which means that the gap between the shaft and the surrounding shaft tube can be decreased in a corresponding degree since, obviously, said gap must be made large enought to prevent the shaft, when deflected, comes into contact with the inner side of the shaft tube. This is important, especially when the shaft with the tube is arranged between screen decks since the shaft and tube form an obstacle to the flow of the screened material on the deck below. In the device shown on the figures with a shaft with an outer diameter of 75 mm and a diameter of 85 mm of the excentric . part 4 the self-vibration frequency could be increased from 873 rpm to a frequency of 1773 rpm with the support bearing shown on the figures. The dimensions of the devices according to the invention may vary within broad limits. Special advantages may, however, be achieved e.g. when the extention of the screen excenter shaft between the outer bearings 3 amounts to at least 750 mm, optionally at least 1000, at least 1250 mm or at least 1500 mm. The diameter of the shaft may also vary within broad limits. Non-restricting values are e.g. for the outer part or the excentic part of the shaft at least 50 mm, at least 60 mm or at least 70 mm, and the diameter may extend up to 150 mm or more. The distance between the outer screenbox bearings and the support bearing and between support bearings resp. may also vary within broad limits. Non-restricting values are e.g. from 200 mm, from 300 mm or from 400 mm, and as suitable upper ranges one may mention e.g. up to 300 mm, up to 500 mm, up to 750 mm or up to 1000 mm or above. The distsance between the outer screenbox side walls and the intermediate wall and between the intermediate walls resp. may also vary within broad ranges, e.g. from at least 200, at least 300, at least 400 or at least 500 mm and suitable upward limits are e.g. at most 1000 mm or above, at most 800 mm, at most 600 mm or at most 500 mm. The frequency of rotation of the shaft may also vary within broad ranges, e.g. without " restricting the invention, from at least 500, at least 700 or at least 900 rpm, and examples of suitable upper limits are e.g. up to 2000, up to 1750, up to 1500 or up to 1200 rpm depending upon the circumstances. The construction may also be arranged to permit a maximum deflection of the shaft when rotated at the operation rpm within broad ranges, e.g. at most 10 mm, at most 8 mm, at most 6 mm, at most 4 mm or at most 2 mm or below. The screen openings may also vary within broad ranges e.g. between 0.5 and 150 mm in diameter but also larger and smaller screen openings can be used. The screen material may also vary, and may consist of inorganic or organic materials, such ' as gravel, sand, ore, vegetables, grains, etc. Figure 5 shows schematically a section through a screen box two intermediate walls 9 and two support bearings 6 arranged in housings 23 as explained with reference to figures 1-4. Equivalente parts on figures 1-5 are shown with identical reference numerals. The device according to figure 5 is provided with heavy masses 26 at each end of the shaft 2 mounted excentrically in relation to the shaft and the device is intended to vibrate in a free motion around a center of motion , i.e. the shaft 2 is not jounalled in fixed outer bearings 3 as the device on figures 1-4.

Claims: CLAIMS 1. Vibrating screening device with a screenbox (1) with screening means (13-16) and a rotating screen excenter shaft (2), which, when rotated, is arranged to transfer a vibrating movement to said screenbox (1) through two outer screenbox bearings (5) in which the screen excenter shaft is rotary joumalled, said outer screenbox bearings being arranged at opposite sides of said screenbox for transferring to said screenbox a vibration producing force, c h a r a c t¬ e r i z e d in that said screen excenter shaft is also joumalled in at least one support bearing (6) arranged between said outer screenbox bearings (5). 2. Vibrating screening device according to claim 1, c h a r¬ a c t e r i z e d in that said screen excenter shaft (2) is also joumalled in at least two outer screen excenter shaft bearings (3), which are not connected to the screenbox (1) and arranged excentrically in relation to said screenbox bearings (5), said outer screen excenter shaft bearings (3) preferably being connected to a fixed or heavy support or foundation construction (19). 3. Vibrating screening device according to claim 1,- c h a r a c t e r i z e d in that said screen excenter shaft (2) is provided with at least one excentric mass means of a relatively large weight which is arranged on a part of said screen excenter shaft which extends beyond that part (4) of the screen shaft (2) which extends between the outer screenbox bearings (5) at one side of said part (4) of the shaft or at both sides thereof, wherein the vibrating motion of said screenbox (1) is achieved as a preferably free or spring-loaded movement in relation to said excentric mass means. 4. A vibrating screening device according to any of the preceding claims, c h a r a c t e r i z e d in that at least one support bearing (6) which supports the excenter shaft is arranged at the critical point or critical points (point or points with the largest deflection of the shaft when rotated in the absence of said support bearing (6)) of that part (4) of the screen excenter shaft which extends between said outer screenbox bearings, or is arranged at a distance from the centre point between said outer screenbox bearings (5), or at sub-dividing points dividing said distance between said outer screenbox bearings (5) into 3, 4, 5 etc. parts of substantially equal length, or at a distance from said centre point or sub-dividing point or from said critical point which amounts to at most 25 %, preferably at most 10 % or at most 5% of the distance between said outer screenbox bearings (5). 5. Vibrating screening device according to any of the preceding claims, c h a r a c t e r i z ed in that it is provided with at least two screen decks (7, 8), preferably with the screen excenter shaft (2) arranged between said screen decks. 6. Vibrating screening device according to any of the preceding claims, c h a r a c t e r i z e d in that said screenbox (1) is provided with at least one longitudinal intermediate wall (9), which is preferably parallel to the side walls of the screenbox and perpendicular to said screen excenter shaft (2), said support bearing (6) optionally being fastened to said intermediate wall. 7. Vibrating screening device according to any of the preceding claims, c h a r a c t e r i z e d in that the part (4) of the screen excenter shaft (2) which is arranged within said screenbox (1) is arranged in a screen excenter shaft tube (10) which preferably protects the screen shaft against contact with the material being screened, said shaft tube (10) preferably being connected to the side walls (11, 12) of the screenbox which extend substantially in a cross direction to the direction of said screen excenter shaft, and optionally connected to said intermediate wall or walls (9) if such are used, especially for acting as a stiffening means cooperating with the screenbox walls. * 8. Vibrating screening device according to any of the preceding claims comprising at least one intermediate wall (9) c h a r a c t e r i z e d in that the screen deck or screen decks are sub-divided into screen deck elements (13, 14, 15, 16) which extend in the direction of the screen excenter shaft betweeen an outer wall and an intermediate wall of the screenbox or between two intermediate walls of the screenbox, said screen elements preferably being arranged detachable in the screenbox and preferably with means (14) for adjusting a tensioning force between the outlet end or front end (18) of the screenbox and the opposite rear end (19) of the screenbox. 9. Vibrating screening device according to any of the preceding claims characterized in that the screen excenter shaft tube (10) is divided into at least two preferably detachably joined shaft tube parts, preferably of essentially equal length, said support bearing or support bearings (6) being arranged at the joint or joints between said shaft tube parts for supporting the screen excenter shaft against the shaft tube (10) through said support bearings (6).

Inventors: ERIKSSON JAN ERIK, ERIKSSON, JAN, ERIK
Applicants: DOUGLAS PATRICK J, ERIKSSON JAN ERIK, DOUGLAS, PATRICK, J., ERIKSSON, JAN, ERIK
Application year: 1986
Main classification: B07B1
IPC codes: B07B1