EP0641264B1 - Quality-control sieve and method of using it - Google Patents

Abstract

PCT No. PCT/CH94/00053 Sec. 371 Date Mar. 1, 1995 Sec. 102(e) Date Mar. 1, 1995 PCT Filed Mar. 11, 1994 PCT Pub. No. WO94/20228 PCT Pub. Date Sep. 15, 1994The novel invention proposes a final screen which is very reliable in operation and which is suitable more particularly also for building into a pneumatic conveying line. In a first section the material is distributed uniformly over the entire peripheral surface of the screen shell. The subsequent section is used for completing screening and separating the coarse material out through an outlet. A centrifuging rotor with helically arranged elastomeric cleaning lobes projecting from the centrifuging bars provide a high throughput and particularly damage-obviating discharge of even relatively large foreign bodies.

Description

Technical field

The invention relates to a control screen, in particular with a pneumatic material feed, a screen housing, a cylindrical screen jacket with a centrifugal rotor rotating therein, an outlet for the screen rejection and an outlet for the screen diarrhea.

State of the art

Apart from breakdowns, mill companies today deliver finished products, the purity of which is almost absolute with regard to third-party stocking. The product already goes through a large number of sieving stages during the regrind extraction. Control screenings at the customer now, contrary to expectations, show a disturbing stocking or disturbing foreign components. This therefore requires another control screening before the further processing of flour and semolina-like goods. Such an entrance control sieve with the buyers of food or feed or mill products has very specific requirements. In principle, only a few grams of impurities need to be sifted out of relatively large quantities, for example from 8000 kg of flour per hour. The control screening should be particularly reliable before further processing. It is often necessary to choose where to place the screening machine on the conveyor route. The control sieve can be installed within a pneumatic transport, for example, which is already present, but it is required that a corresponding sieving device does not result in great resistance, which would increase the force required for the pneumatic transport. It has here, based on the proposal of old German patent specification No. 867 193, a separate genre of the so-called "screening machines in compressed air delivery" developed. This old publication proposed to arrange a beater mechanism with a high rotational speed within a cylindrical sieve jacket and to further convey the flour freed from the shells via an annular cylindrical channel with the air flow. The accent of this facility, however, lies in its function as a bran spinner, which is a typical aggregate in mill processing technology. In DE-OS No. 2 121 726, the device mentioned was further developed with a view to the actual function of the control screening of large quantities of flour, which for example have to be reloaded into silos by a transport vehicle. It is proposed to arrange the screening device at the end of a pneumatic delivery line. Instead of the traditional beater mechanism for bran centrifuges, a rotor with longitudinal blades is selected and the material to be screened is guided against the screen jacket by a disc.

In a further development of the control screening device according to DE-OS No. 2 338 909, it is proposed to mount the rotor which throws the screenings outwards only on one side. The feeding pneumatic conveying line can be extended in the axial direction from the machine side opposite the drive to the middle of the sieve cylinder interior. The disadvantages here were unfavorable flow conditions for the good-air mixture and a concept which, because of the one-sided bearing, is only suitable for mechanical engineering for smaller units. Access to the sieve is difficult.

DE-AS 1 255 461 further describes a sieve drum which can have a cutting disc in the form of a worm thread on the rotor. However, such an arrangement is unsuitable for a pneumatic supply of goods. GB-A 18054 in turn describes a device for sorting, cleaning and polishing peas, beans, corn, seeds and the like. Like., Which has a sieve housing with a sieve jacket with a centrifugal rotor rotating therein, the centrifugal rotor having centrifugal strips which extend essentially over the length of the sieve jacket. The centrifugal strips have radially projecting tabs made of elastic material. However, such a device is unsuitable for the control screening of flour or a pneumatic material feed.

Presentation of the invention

The object of the invention was now to avoid the disadvantages of the known solutions, in particular to achieve a high throughput with the greatest possible security for the control screening. In the case of pneumatic transport, there should only be a slight loss of pressure.

The solution according to the invention is characterized in that the centrifugal rotor has a plurality of centrifugal strips, which extend essentially over the entire length of the screen jacket, with radially projecting conveying or cleaning tabs, which are preferably made of rubber-elastic material, and work in the vicinity of the screen jacket or the Lightly touch the inner surface of the sieve jacket, the conveyor or cleaning tabs being arranged on the same centrifugal bar with a longitudinal spacing and a staggered arrangement to the following centrifugal bar.

The invention allows a number of particularly advantageous configurations. Experience in the prior art assumed that the best sieving effect can be maintained in the long run by attaching effective brush elements to the centrifugal strips over the entire inner sieving surface; so that, to a certain extent, the sieve is constantly brushed. A sieve opening is deliberately chosen through which all flour can pass. Exactly through the relatively large sieve openings, however, tired bristles (D <0.3 mm) can penetrate the brush cleaning element and undesirably reach e.g. in the food. An optimal sieving effect was achieved when the centrifugal strips have several, radially protruding, rubber-elastic conveying or cleaning tabs. Corresponding bristle parts no longer occur with the elastic conveyor or cleaning rags. Rather, the tests have shown that those that were already in the estate are even read out. It is also proposed that the cleaning cloth on the same fling bar are arranged at a longitudinal distance from one another, preferably with a staggered arrangement to the next following flap bar to form a helical conveying component over the length of the screen jacket. The resulting swirl-like movement of the material supports the sieving, and at the same time ensures that the coarse material is conveyed quickly and foreign bodies are discharged to the outlet. The elastic cleaning rags touch the inner surface of the sieve (work surface) for flour or semolina-like products, for example, and keep it clean. Solid coarse parts such as screws, pins or the like cannot get caught between the blow bars and the sieve jacket due to the elastic design and a preferably trapezoidal shape. Even when the friction force increases slightly, the flap deforms and allows the part to pass. This means that there is no greater friction (heat) on the sieve. Gentle discharge is made possible, so that there is no damage to the sieve. Tests were carried out with a variety of different foreign bodies (coarse parts) under the most extreme conditions. Neither air nor product, but only foreign parts were fed into the machine. There was no damage to the mesh or to foreign parts themselves.

However, the expected performance could also be achieved with pneumatic material feed, and a low pressure loss in the order of 30 to 50 mm ws (water column) was found. Tests have confirmed that the material to be screened is not simply guided into the space of the screen cylinder, but can at the same time be optimally distributed within a first section of the screen jacket by an entry distributor. The majority of the flour passes through the screen jacket in the first third, provided that the centrifugal bars are already fully effective in this section. The feed distributor is designed as a driven feed slug and can be a feed screw, preferably one or two or more threads. If the feed distributor actually acts like a spreader plate, the worm housing can be designed to be rotatable, with inlet connections for the pneumatic material feed opening radially or tangentially to the axis of rotation of the centrifugal rotor. With a large number of dispositions with regard to the position and direction of the pneumatic conveying line, this makes it easy to connect to any point on the circumference with the smallest possible number of pipe bends. With purely mechanical feeding, the connection can be freely selected at least within an upper angle of 90 °. Due to the mechanically forced uniform distribution effect by the feed distributor, the special direction of the material feed no longer has any influence on the product loading on the sieve. It has been shown that the rotor can be driven at low speed, preferably at less than 500 rpm. As a result, the service life of the control screen device, in particular the service life of the screen jacket and the cleaning cloth, can be increased. A further displacement body can be arranged between the distribution section and the outlet for the screen repulsion, the outlet in the form of an annular gap for the screen repulsion preferably being formed by a rubber-elastic disk. Furthermore, it is also possible for the centrifugal rotor to have a stepped or conically widening displacement body or at least 2 corresponding baffle plates between the distribution section and the outlet.

The invention further relates to the use of the control sieve device for the control sieving of flour-like goods.

Brief description of the invention

die Figur 1

ein Kontrollsieb im Querschnitt;

die Figur 2

schematisch die Anordnung von Reinigungslappen mit 4 direkt hintereinander dargestellen Schleuderleisten;

die Figur 3

eine Ansicht III der Figur 2;

die Figur 4

einen Schnit IV-IV der Figur 2 in grösserem Maßstab;

die Figur 5

schematisch eine pneumatische Druckförderanlage mit Kontroll-Siebung;

Show it:

the figure 1

a control screen in cross section;

the figure 2

schematically the arrangement of cleaning rags with 4 centrifugal strips shown directly one behind the other;

the figure 3

a view III of Figure 2;

the figure 4

a section IV-IV of Figure 2 on a larger scale;

the figure 5

schematically a pneumatic pressure conveyor with control screening;

Ways of Carrying Out the Invention

In the following, reference is now made to FIG. A pneumatic material feed 1 is connected via an elbow piece 2 to a connection piece 3 of a rotatable screw housing 4 of an entry screw 5. The feed screw 5 is fixedly connected to a shaft 6 of a centrifugal rotor 7 which can be driven via a pulley 8. The housing 4 can be rotated about the axis 9 of the centrifugal rotor 7 and arranged in any rotational position, for example screwed onto a sieve housing 16 via clamping rings 10. The scrubbing rotor 7 is surrounded over the entire length by a screen jacket 11, so that the cleaned material can only pass through the meshes of the screen jacket 11. Coarser parts that have to be screened are removed at the opposite end through an outlet 12. The outlet 12 is delimited by the screen jacket 11 and by a rubber-elastic plate 13, which has a slightly smaller diameter than the screen jacket 11 and forms a gap 14. A coarse material box 15 can preferably be pivoted away about a vertical axis, for checking the screen jacket or for service work. The screen housing 16 and a collecting container 17 and feed 18 and end flap 19 are pressure-resistant as required educated. The lower part of the machine housing is equipped as a collecting funnel 20, on which a delivery pipe 21 (outlet) is arranged for the pneumatic further transport of the sieved material.

The centrifugal rotor 7 has four centrifugal strips 22 which extend essentially over the entire length L of the screen jacket 11, these being arranged offset by 90 ° each. The centrifugal strips have the primary function of keeping the material in a strong circular motion so that the material is always driven to the screen jacket 11 by the corresponding centrifugal force. On the centrifugal rotor 7, two baffle plates 24 and 25 are also arranged, which are intended to prevent the material from being moved too directly. The two baffle plates 24 and 25 simultaneously divide the inner screen space into three parts, a first section A preferably being less than 1/3 of the length and the remaining section B correspondingly being more than 2/3 of the length. Section A simultaneously forms the distribution table section in which the material is distributed uniformly over the entire circumference of the screen jacket 11 by the rotary movement of the feed screw 5. An additional distribution effect is achieved in that the centrifugal strips 22 also extend over this section by a dimension As ''. The stringer bars 22 are rigidly connected to the shaft 6 by an arm cross 26. A large number of conveyor or cleaning tabs 23 are fixedly attached to the centrifugal strips 22, which protrude radially, are more or less rubber-elastic and lightly touch the screen jacket 11 for all non-abrasive goods.

The cleaning rags 23 are shown on a larger scale in FIGS. 2, 3 and 4. The conveyor or wiping cleaning tabs 23 are, as can be seen from FIG. 4, attached to the centrifugal bars 22 by a clamping bar 27 and can bend backwards when a large foreign body enters (23 '), so that the latter is not jammed, such as this can happen with rigid strips. In Figure 3, the four flinger 22 are shown schematically lined up. The conveying or cleaning tabs are offset by a dimension X, the dimension X also corresponding approximately to the length of an individual cleaning tab 23 in the example. The individual cleaning rag is preferably given a trapezoidal shape, so that over the entire length of an individual fling bar 22 a sawtooth shape is formed (Figure 2). The offset arrangement produces a conveying effect as indicated by the arrows 28 (FIG. 3). This creates a swirl effect in the interior of the screen jacket especially for the coarse material, towards the outlet, at the end of the screen jacket. It is particularly important that the centrifugal strips 22 and the cleaning tabs 23 are also fully effective in the distribution section A. In this area, therefore, due to the unequal length of the cleaning tabs 23a, 23b, 23c and 23d, without displacement, only a minimal conveying effect, but intensive distribution and sieve support is desired.

FIG. 5 shows an example of a pneumatic pressure delivery system with a built-in control screen 30. A blower 31 supplies the required compressed air, which can be adjusted in pressure via a pressure control valve 37. The material is fed into the pressure delivery line 1 via a rotary lock 32. Dash-dotted lines indicate that the delivery line can also be laid according to line 1 ', which is feasible by turning the screw housing 4 according to arrow 33. The pneumatic tube 21 for the screened material is conveyed with the same conveying air into a trimelle 34 or, for example, into a container from which the air is discharged via a filter 35 and a fan 36 and the material can be fed for further processing.

Claims (6)

1. Quality-control sieve, in particular with a pneumatic material supply means (1), a sieve housing (16), a cylindrical mesh (11) with a centrifugal rotor (7) revolving therein, an outlet (12) for material rejected by the sieve and an outlet (21) for the undersize, wherein the centrifugal rotor (7) has several rotor bars (22) extending substantially over the entire length of the mesh (11) with radially projecting conveying and cleaning fins (23) which are preferably formed from elastic material and operate in the vicinity of the mesh, characterised in that the conveying and cleaning fins (23) are arranged on the same rotor bar (22) with longitudinal spacing from one another, with an offset arrangement from the next rotor bar (22) for forming a helical conveying component from the inlet into the mesh (11) to the outlet (12) for material rejected by the sieve.
2. Quality-control sieve according to claim 1, characterised in that the conveying and cleaning fins (23) consist of an elastomeric material and easily contact the internal surface of the mesh (11).
3. Quality-control sieve according to claim 1, characterised in that the material supply means (1) is designed as a rotatable housing (4) with an inlet nozzle (3) opening radially or tangentially to the axis of rotation of the centrifugal rotor (7).
4. Quality-control sieve according to one of claims 1 to 3, characterised in that a distribution section (A) is formed within the mesh (11), for example in the first third, for the mechanical uniform distribution of the material at the inlet into the mesh (11) directly over the entire circumference of the sieve.
5. Quality-control sieve according to claim 4, characterised in that the distribution section (A) is limited by a co-revolving baffle plate (24) and the outlet (12) for material rejected by the sieve is formed by an elastic disk (13).
6. Use of the quality-control sieve according to claims 1 to 5 for the quality-control sieving of flour-like materials.

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