EP0085458B1

EP0085458B1 - Sieving device

Info

Publication number: EP0085458B1
Application number: EP83200109A
Authority: EP
Inventors: Theodorus Jacobus Heesen
Original assignee: Heesen Theodorus Jacobus
Current assignee: Machinefabriek A Wijnveen BV
Priority date: 1982-02-02
Filing date: 1983-01-25
Publication date: 1987-04-29
Also published as: ATE26806T1; NL8200375A; EP0085458A1; JPS58133877A; JPH0114828B2; NL177572C; DE3371180D1; NL177572B

Abstract

The invention is relating to a sieving device comprising a pervious sieve surface (22) adapted to rotate about an upwardly rotary axis, whereby the sieve surface (22) has a curved sectional area in a manner such that parts of the sieve surface located near the rotary axis and near the outer periphery are at a higher level than the parts of the sieve surface located there between.

Description

The invention relates to a sieving device comprising a rotary pervious sieve surface rotatable about an upwardly extending axis of rotation whereby the sieve surface has a sectional area in a manner such that outer parts of the sieve surface located near the outer periphery are at a higher level than parts of the sieve surface located between said outer parts and said axis of rotation.
Such a sieving device is known from NL-A-7605572. In this known sieving device the sieve surface forms part of the outer surface of a cone, in which the part nearest the rotary axis is at the lower level and the part of the sieve surface furthest remote from the rotary axis at the higher level. During operation the material to be sieved has to move outwardly along the sieve surface, the fine particles to be separated have to fall down through the sieve surface and the coarse particles have to be ejected from the outer periphery of the sieve surface.
In this known construction the velocity of the material to be sieved increases according as the material gets further away from the rotary axis, whilst also the size of the sieve surface increases quadratically with the distance from the rotary axis.
When the speed of rotation is chosed low, the speed of movement of the material to be sieved towards the outer periphery of the sieve is proportionally low near the rotary axis so that comparatively only a small amount of material can be processed per unit time. However, when the speed of rotation of the sieve is raised, the product will pass through the major part of the sieve surface at a distance from the rotary axis with such a velocity that an effective sieving is out of the question.
A further disadvantage of this known sieving device is that particles can easily stick in the perforations of the sieve surface from which they can no longer part, since on the contrary due to the effect of the centrifugal force or force of gravity they clamp tight in the perforations.
The invention has for its object to provide a sieving device of the kind set forth by which the disadvantages inherent to the known sieving device can be avoided.
According the invention this can be achieved in that the sieve surface is curved in a manner that parts of the sieve surface located near the axis of rotation and said outer parts are situated at a higher level than parts of the sieve surface located there between, whereby during rotation of the sieve surface with the normal operational speed the displacement of the material to be sieved by the action of the centrifugal force and the component of the force of gravity extending parallel to the sieve surface takes place with at least substantially constant speed in a radial direction outwards from the middle of the sieve surface.
It is noted that from DE-C-71863 there is known a device having a sieve member rotatable about two parallel axes of rotation, however said device has a flat sieve surface extending perpendicular to said axes of rotation.
Further DE-C-862996 shows a sieving device with a curved sieve surface, however said sieve surface is not rotated during use.
The invention will be described more fully hereinafter with reference to the accompanying Figures.

Fig. 1 is a schematic cross-sectional view of an embodiment of a sieving device in accordance with the invention.
Figs. 2 to 4 show different embodiments of shafts with the aid of which the sieve surface can be supported.

The sieving device shown in Fig. 1 comprises a circular-section housing 1, the lower part of which is tapering in downward direction. In the housing 1 is arranged a supporting assembly 2 as well as a stationary, continuous gutter 3. With the gutter communicates the top end of an outlet pipe 4, which extends beyond the housing 1.
To the frame 2 is secured a housing 5, in which a vertical shaft 6 is journalled with the aid of bearings 7. The lower end of the shaft 6 is provided with a gear wheel 8, which is coupled with the aid of a toothed rope 9 with a toothed wheel 10 fastened to the shaft of a motor 11 supported by the supporting frame 2. The shaft 6 is integral with a shaft 12 extending above the shaft 6, on which shaft 12 a hood 13 is rotatably journalled with the aid of bearings 14. The hood 13 is integral with a toothed wheel 15, which is coupled with the aid of a toothed belt 16 with a toothed wheel 17 fastened to the output shaft of an electric motor 18, which is also secured to the supporting frame 2.
To the hood 13 is fastened a plate 19 forming part of a conical surface and being downwardly and outwardly inclined away from the hood 13. The lower rim of the conical plate 19 is secured by means of a few strips 20 to a continuous sheath 21. Between the top rim of the sheath 21 and the hood 13 is provided a sieve surface 22. From Fig. 1 it will be apparent that this sieve surface is curved so that the rim of this annular sieve surface fastened to the hood 13 and the circumferential rim of this sieve surface 22 fastened to the top rim of the sheath 21 are located at a higher level than the part of the sieve surface in between the former.
On the top side the housing has a central inlet port 23 for the introduction of the material to be sieved.
Potential dispositions of the shafts 6 and 12 forming one unit are shown in detail in Figs. 2, 3 and 4.
Fig. 2 shows that the centre lines of the shafts 6 and 12 may be parallel to one another and be spaced from one another by a distance e. Preferably said distance e is, for example, 2 mms.
As an alternative the centre lines of the two shafts may be at an angle a to one another, said angle a preferably being 35°. The centre line of the shaft 12 may intersect the centre line of the shaft 6 in the plane in which the two shafts join one another as is shown in Fig. 3 or in this plane the shafts may again be spaced apart by a distance e as shown in Fig. 4.
In operation material will be fed through the inlet port 23 and arrive at the sieve surface. With the aid of the motor 18 the sieve surface is rotated about the rotary axis of the shaft 12 so that the material striking the sieve surface is subjected to a centrifugal force and will move outwardly along said sieve surface. The fine particles of the material. can pass through the perforations of the sieve surface and be guided or not guided by the conical plate 19 to the gutter 3. With the aid of the strips 20 this material is displaced towards the opening where the pipe 4 adjoins the gutter 3 so that the fine material can be conducted away through the pipe. The coarse particles of the material are displaced outwardly along the sieve surface 22, be ejected across the outer rim of the sieve surface and be conducted away through a delivery port 24 in the underside of the housing 1.
Since initially the supplied material moves along a downwardly inclined part of the sieve surface 22, the movement of this material is further accelerated by the action of the resolved component of gravity extending parallel to the sieve surface. This component of gravity thus supports the centrifugal force which brings about an outward displacement of the material.
After having passed beyond the lowermost point of the sieve surface, designated by A, the material moving along the sieve surface has to move upwards towards the outer rim of the sieve surface. During this upward movement the component of the force of gravity extending parallel to the sieve surface will counteract the centrifugal force. Therefore, by a suitable design of the curved sieve surface 22a most effective displacement of the material along the sieve surface can be ensured, preferably in a manner such that the velocity with which the particles of the material move outwards away from the centre line of the sieve surface remains at least substantially constant, viewed in a horizontal direction.
In the preferred embodiment of the invention described and illustrated herein the sieve surface rotates not only about the rotary axis formed by the centre line of the shaft 12, but also the shaft 6 carrying the shaft 12 is rotated with the aid of the electric motor 11. When the shafts are disposed as is shown in Fig. 2, the sieve surface will perform a swinging movement in a horizontal sense, the amplitude of the sieve surface being equal to twice the distance e between the centre lines of the two shafts. Preferably the speed of rotation of the shaft 6 appreciably exceeds that of the sieve surface about the shaft 12 so that the sieve surface will perform a strong rocking movement, which will counteract obturation of the pores of the sieve surface.
When the shafts are disposed as is shown in Figs. 3 and 4, the sieve surface will, in addition, perform a tilting movement about an imaginary tilting axis at right angles to the centre line of the shaft 6. It will be obvious that as a result the sieve surface will perform upward and downward movements during operation, the deflection of the sieve surface increasing with a growing distance from the rotary axis. This will intensify the sieving effect and contribute to avoidance of clogging of the sieve surface.
The figures used in the claims are only meant to explain more clearly the intention of the invention and are not supposed to be any restriction concerning the interpretation of the invention.

Claims

1. A sieving device comprising a rotary pervious sieve surface (22) rotatable about an upwardly extending axis of rotation (12) whereby the sieve surface has a sectional area in a manner such that outer parts of the sieve surface located near the outer periphery are at a higher level than parts of the sieve surface located between said outer parts and said axis of rotation (12) characterized in that the sieve surface is curved in a manner that parts of the sieve surface (22) located near the axis of rotation and said outer parts are situated at a higher level than parts of the sieve surface located there between, whereby during rotation of the sieve surface with the normal operational speed the displacement of the material to be sieved by the action of the centrifugal force and the component of the force of gravity extending parallel to the sieve takes place with at least substantially constant speed in a radial direction outwards from the middle of the sieve surface.

2. A sieving device as claimed in claim 1 characterized in that the sieve surface (22) is adapted to rotate about two at least substantially parallel axes of rotation (6, 8).

3. A sieving device as claimed in claim 1 or 2 characterized in that means (12, a) are provided with the aid of which a tilting movement about a pivotal axis extending transversely of the axis of rotation (6) of the sieve surface (22) can be imparted to the sieve surface.

4. A sieving device as claimed in any one of the preceding claims characterized in that the sieve surface (22) is rotatably mounted on a shaft (12) supporting the sieve surface and is coupled with a driving source (18), whilst the shaft (12) supporting the sieve surface (22) is fastened to a second shaft (6) which is also coupled with a driving source (11).

5. A sieving device as claimed in claim 4 characterized in that the interconnected shafts (6, 12) extend parallel to one another.

6. A sieving device as claimed in claim 4 characterized in that the interconnected shafts (6, 12) are at an angle (a), to one another.