GB2069359A - Screen for Vibrating Centrifugal Separation Machines - Google Patents

Abstract

The screen is made in the form of a solid of revolution and comprises a sifting part 2 and a non-sifting part 1. The generatrix of the sifting part 2 has a stepped shape, each step 4 forming a solid of revolution in the form of a hollow conic frustum whose major base faces opposite to the movement of the layer of the loose material 7 under treatment. <IMAGE>

Description

SPECIFICATION Screen for Vibrating Centrifugal Separation Machines The present invention relates to devices for separating various loose materials and has particular reference to screens for vibrating centrifugal separation machines.

It can be used for separating seeds and various grain materials in agriculture and the food industry and for separating various loose mineral materials in the mining, chemical and other industries.

The essence of the invention resides in providing a screen for vibrating centrifugal separation machines, which screen is made in the form of a solid of revolution and has a sifting part designed for sifting loose material and anon- sifting part serving for attaching the seeve to the mounting elements of the machine, wherein according to the invention, the generatrix of the surface of the sifting part of the screen is of stepped form.

The resultant shape of the screen surface makes it possible to substantially augment the loosening of the layer of the material under treatment, thereby increasing the rate of movement of small particles from inside the layer towards the screen surface. A further advantage of said shape of the screen surface is that it adds to the rigidity of the screen wall.

It is desirable that each step of the generatrix be shaped so that its revolution produces a hollow frustum of a cone whose major base faces opposite to the movement of the material under treatment. This constructional arrangement provides for increasing the rate of sifting the particles of loose material through the screen apertures.

Now the invention will be described in detail with reference to the accompanying drawings in which: Figure 1 is a general view of the screen constructed according to the present invention for use in vibrating centrifugal separation machines.

Figure 2 is a longitudinal sectional view of the screen constructed according to the present invention for use in vibrating centrifugal separation machines.

Figure 3 is a fragmentary longitudinal sectional view of the perforated portion of the screen constituting the present invention and of the layer of loose material on the surface thereof.

Figure 4 is a fragmentary longitudinal sectional view of the perforated portion of a prior-art screen and of the layer of loose material on the surface thereof.

The screen for vibrating centrifugal separation machines which constitutes the present invention comprises a non-sifting part 1 (Figure 1) designed for attaching the screen to the mounting elements of the machine involved and a sifting part 2 designed for sifting loose material. The generatrix 3 (Figure 2) of the surface of the screen sifting part 2 (Figure 1) has a stepped shape. Each step 4 (Figure 3) of the generatrix 3 (Figure 2) has pitch "I" and height "h". The portions of the screen surface corresponding to each step 4 (Figure 3) of the generatrix 3 (Figure 2) have smooth junctions curved in a cross section to the radius "r". The pitch "I" is several times greater than the height "h".

rr .

The shape and size of holes 5 (Figure 1) in the wall of the screen sifting part 2 depend on the screen application. The holes 5 may be round, rectangular, square, triangular, oval etc.

The non-sifting part 1 and the sifting part 2 can be made of identical or different materials, for example, of steel, or of steel and plastics, etc.

For use in a vibrating centrifugal separation machine, the screen is attached to the mounting elements 6 (Figure 2) of the machine rotor by any method known in the art and is simultaneously rotated and reciprocated by the method appropriate to the design of the machine involved.

For example, in a machine with a vertical rotor the screen is simultaneously rotated about its axis and reciprocated along the axis. The loose material is fed at the screen top onto the screen inner surface. Coming into contact with the screen surface, the material assumes a rotary motion which gives rise to centrifugal forces and the latter cause the material to form an annular layer 7 (Figure 2) on the screen surface. The oscillating movement of the screen sets up inertia forces which impart pulsating relative velocity to the material layer 7 due to which the material moves downwards on the screen surface at the average veldcity V,.

Moving from step to ste, the material layer 7 becomes substantially deformed, which augments the loosening of the material and sharply increases the rate of movement of small particles from inside the layer 7 towards the surface of the screen. Then said particles are sifted through the holes 5 and collected in the machine to produce a separate fraction. This way of loosening the material layer substantially increases the working capacity of the screen.

The centrifugal forces of the material layer 7 exert a comparatively heavy radial pressure onto the screen wall. However, the stepped construction of the screen wall substantially increases the radial rigidity thereof and thereby considerably increases the screen strength and longevity.

For convenience in use, the screen constituting the present invention can be divided into several parts along the generatrix 3 (Figure 2) in such a manner that putting said parts together will form a surface of revolution.

The efficiency of screen performance is largely dependent on the shape of the steps 4 (Figure 3) and the orientation thereof in relation to the direction of movement of the material layer 7. The steps 4 must be shaped and orientated so that the major base of the hollow conic frustum produced by their revolution faces opposite to the movement of the material layer 7. This condition provides for the required reduction of the relative velocity of the particles in direct contact with the screen surface when increase takes place, for example, in the frequency of screen vibration, due to which small particles have more possibility of getting into the holes and thereby the rate of their sifting is increased substantially.

This is attributed to the fact that when a particle "m" (Figure 3) of loose material moves specifically under the action, of its weight "P" directly on the screen surface, it travels not only along the screen axis, but also some distance towards the axis. During such movement the particle meets additional resistance from the centrifugal inertia force component directed along the step, due to which the relative velocity V0 of the particle becomes considerably less than the average velocity V, of the material layer. Under these conditions the particle "m" gets into the holes and passes there through much more frequently than in the case of the prior-art screen, all the rest of the conditions being equal.In the prior-art screen made, for example, in the form of a vertical hollow cylinder, the particle "m" (Figure 4) moves on the screen surface along the screen axis specifically under the action of its weight "P".

In this screen the centrifugal force is normal to the generatrix of its surface. Therefore, with all the rest of the conditions equal, the particle "m" moves in the prior-art screen at a relative velocity V'O which is greater than V0 (Figure 3). The velocity V'O (Figure 4) of the particle "m" differs insignificantly from the average velocity V1, of the material layer which adversely affects both the loosening of the material layer and the rate of particle sifting.

With the generatrix of the surface of the screen sifting part 2 (Figure 1) comprising the steps 4 (Figure 3) according to the invention, the velocity of the particles on the surface of the layer 7 (Figure 3) can be several times greater than the velocity of the particles "m" on the screen surface inasmuch as the upper portions of the layer 7 move over the projections of the steps 4 and the latter restrict their motion to a smaller extent. This condition boosts the loosening of the layer 7 and promotes further increase in the working capacity of the screen.

For convenience in manufacture and standardization of the screen consistuting the present invention, it is desirable that parameters "h" and "I" be the same for all the steps 4 (Figure 3) of the generatrix 3 (Figure 2).

The screen for vibrating centrifugal separation machines which constitutes the present invention has the advantage that in virtue of the stepped separating surface it effects more intensive loosening of the layer of the material under treatment and at the same time possesses a higher rigidity.

Another advantage is that more intensive sifting of the material is achieved by virtue of shaping the screen steps in accordance with the invention. These features substantially increase the working capacity and longevity of the screen.

It is the greatest advantage of the screen constructed according to the invention that it provides for more thorough and intensive sifting of loose materials.

As compared with the screen known in the prior art, the use of the screen according to the invention in vibrating centrifugal separation machines, for example, for cleaning and/or grading seeds and various grain materials increases the working capacity of the machines involved by 25 to 30 percent without any substantial additional expenses.

Claims (5)

Claims 1. A screen for vibrating centrifugal separation machines, which screen is made in the form of a solid of revolution and comprises two parts, one of which serves the purpose of attaching the whole screen to the mounting elements of said machines and the other has holes and is designed for separating the material under treatment, the generatrix of the surface of said part having a stepped shape which substantially improves the separating properties of said screen in using same in said vibrating centrifugal separation machines. 2. A screen for vibrating centrifugal separation machines as claimed in Claim 1, wherein each step of said generatrix forms, by revolution thereof, a hollow frustum of a cone with a major base and a minor base, said major base facing opposite to the direction of movement of the material under treatment. 3. A screen for vibrating centrifugal separation machines, substantially as described herein with reference to the accompanying drawings. New claims or amendments to claims filed on 17 Oct. 1980. Superseded claims 1-3 New or Amended Claims:-

1. A screen for vibrating centrifugal separation machines, made in form of a solid of revolution and comprising two parts one of which serves for attaching the whole screen to the mounting elements of said machine and the other has a plurality of holes and is intended for separating the material being processed, said other part consisting of several identical axial hollow truncated cones interconnected with one another at their major bases.

2. A screen for vibrating centrifugal separation machines as claimed in claim 1, wherein each of said truncated cones has its major base facing against the movement of the material being separated.

3. A screen for vibrating centrifugal separation machines as claimed in claims 1 and 2, wherein the height of each of said truncated cones is several times the difference between the diameters of its major and minor bases.

4. A screen for vibrating centrifugal separation machines as claimed in claims 1, 2 and 3, which is disjoined into several parts along the generating line of the surface of each of said truncated cones.

5. A screen for vibrating centrifugal separation machines, substantially as hereinabove described with reference to the accompanying drawings.