WO2010043712A1

WO2010043712A1 - Screening machine

Info

Publication number: WO2010043712A1
Application number: PCT/EP2009/063608
Authority: WO
Inventors: Andreas Meile; Christoph Kaufmann
Original assignee: Bühler AG
Priority date: 2008-10-16
Filing date: 2009-10-16
Publication date: 2010-04-22
Also published as: EP2340130A1; CN102186606A; JP2012505741A; EP2340130B1; JP5743892B2; CN102186606B

Abstract

The invention relates to a screen for a screening machine for screening a product into two fractions. To avoid detrimental effects to the quality of the product due to damage at the screen mesh of a screen (9), the screen is provided with a metal layer, in particular in the manner of a conduction path, wherein the electrical resistance of said layer is measured and wherein changes in the resistance indicate damages.

Description

screening machine

The invention relates to a sieve for a screening machine for screening a product in at least two fractions.

Sieving machines and sieves, in particular for separating mealy products or for cleaning bran, are known per se. Depending on the type of sieve, a finer fraction can penetrate the sieve cloth (sieve passage), while the coarser fraction is discharged as a sieve shake. As a mesh fabric plastic mesh or metal wire mesh for flour sifting are used.

Particularly in the case of flour sifting, an admixture of coarse particles into the diarrhea product should be avoided, so that wear-related cracks or breaks in screen fabrics, in particular made of plastics, must be recognized early. In the simplest form, this is done by constant manual checks.

Already in DE-OS-1648368 a method for non-contact and non-destructive measurement of Siebabriebes has been proposed. For this purpose, a radiation should be directed to the mesh and the reflective portion should be measured. The measured value should be a function of the remaining thickness of the screen or the absolute abrasion of the wire mesh wires, i. H. in particular be metal wires. When a limit value is reached, a signal should be triggered indicating the required screen change.

In a screening device according to DE-A-4324066, a screen fabric of plastic fibers on additional electrically conductive threads, in particular carbon fibers in one direction, which are laterally spaced from each other and with the sieve in axial Direction are curious. Conductivity measurements should reliably enable error monitoring (eg screen breakage). The electrically conductive fibers form an electrode arrangement whose conductivity changes when at least one thread breaks, which is used as a detection signal. Damage to the plastic fibers, in particular longitudinal cracks, may not be detectable at all or too late. It is further proposed to be able to use other physical variables analogously.

It is known from DE-U-6751332 and DE-OS 2326306 to completely surround woven plastics materials with metallic layers, in particular of silver or copper, in order to increase the strength and rigidity of these fabrics. The layer thicknesses are about 20-100μm. DE-C-3227020 discloses the sticking of insulated wire threads on a wire, DE-A-2443548 the incorporation of electrical control threads in fabric panels. It is stated in DE-A-4324066 that such threads can lead to a hardening and thus increased susceptibility to breakage of the tissue.

The invention has for its object to provide a sieve for a screening machine, which allows a simple and safe tektieren detection of cracks or breaks in the sieve (in particular of plastic fibers). The object is achieved by the features of the independent claims.

A sieve according to the invention has a sieve surface made of plastic, preferably of plastic fibers. Plastics are here and below understood to mean materials whose essential constituents consist of such macromolecular organic compounds which are formed synthetically or by modification of natural products. The screen surface may preferably be a screen fabric made of plastic; also a screen surface with through openings that are not formed by a fabric (for example, due to punched holes in a fabric), but can be used according to the invention. The screen surface or the screen fabric here is at least partially provided with an electrically conductive layer, in particular a metallic layer.

The electrical conductivity of metals, which are preferably used as an electrically conductive layer, is usually larger by some orders of magnitude than that of plastics. The electrically conductive layer makes it possible to measure the electrical resistance along this layer continuously or periodically. It has been found that electrical resistance can be used very reliably as a criterion for the quality of the screen, since damage to the screen structure results in a measurable change in the electrical resistance. In this case, damage to the screen structure is understood to mean, in particular, both the formation of cracks and the complete severing of boundaries of the passage openings of the screen, in particular of warp / weft threads, as well as the wear and tear (thickness reduction). Sieve wear as well as incipient destruction by injury or penetration of the sieve fabric (hole, crack or break) can be detected.

As the plastic of the screen fabric, in particular as synthetic fibers of the screen fabric, preferred within the scope of the invention are: o polyamides (PA), in particular o PA6, o PA66; o polyalkylenes, in particular o polyethylene (PE), preferably of high density (HDPE), o polypropylene (PP), o polyethylene / polypropylene copolymers (PE / PP); o Polyester, in particular o polyethylene terephthalate (PET), o polybutylene terephthalate (PBT).

In preferred embodiments, the metal (s) of the electrically conductive layer is / are selected from the group consisting of silver, titanium, chromium, and mixtures thereof. Silver is particularly preferred because of the extraordinarily high conductivity of 61 × 10 5 S / m, since this makes the detectable absolute changes in the conductivity greater.

More preferably, the electrically conductive layer is not over the entire surface of the screen surface, in particular the screen fabric is formed. In particular, a coating is possible only in particularly stressed partial areas.

It has been shown that in resistance measurements on a sieve which is provided substantially flat with the electrically conductive layer, only changes in the order of magnitude of a few V _° result in a wire break depending on the position and size of the damage. Although effects of this magnitude are readily measurable, they can, under certain circumstances, be superimposed by disturbing influences during operation of a screening machine.

Surprisingly and with very particular preference, the invention can be further improved by designing the electrically conductive layer as a conductor track. Conductor tracks are understood here and below to be electrically conductive connection paths between defined points. The resistance measurement is thereby considerably simplified, since with a suitable arrangement the track must only qualitatively between "conductive" and "non-conductive" must be distinguished.

Here, the conductor track is preferably arranged such that it extends substantially at an angle ≠ 0 ° to the boundaries of the screen openings, in particular at an angle ≠ 0 ° to warp threads and / or weft threads of the plastic fabric; "Substantially" here means that in particular in direction reversal areas of, for example, a meandering arranged conductor track in limited subareas, in particular an arrangement along warp and / or weft threads is possible In particular embodiments, the conductor track is designed in such a way that it is in the Essentially at an angle of approximately 30 ° to approximately 60 ° (preferably at an angle of approximately 45 °) to the boundaries of the screen openings, in particular to warp threads and / or weft threads of the plastic fabric In the width of the track, damage can be detected in all directions, in particular longitudinally and / or transversely to the direction of the weft / warp threads The track can in particular be arranged in such a way that damage can be detected if its extent is at least equal to that of the track Mesh size correspond (in particular of at least two i stitches when a thread breaks) in order to avoid major damage to the screen mesh and thus a deterioration of the screening result.

In particularly preferred embodiments, the electrically conductive layer is formed homogeneously, ie in particular with respect to (individually or in combination) of the material, the structure, the thickness, the width. A sieve according to the invention can be designed, in particular, as a round sieve sheath, in which a reel work can be arranged in a rotatable manner.

Suitable methods for producing a sieve described above are known per se. Methods for applying metallic layers to tissue (for example by vapor deposition, sputtering (cathode sputtering) or plasma spraying (PVD)) according to step ii) are known, in particular, from EP 925 196 B1; the disclosure of which is incorporated by reference into the description of the present invention.

A screen according to the invention as described above finds particular use in a screening machine. Another aspect of the invention thus relates to a screening machine comprising a sieve as described above. Screening machines are understood in this context, in particular drum screens and Plansichter.

Another aspect of the invention relates to a method for operating a screening machine, wherein the electrical resistance of the electrically conductive, in particular metallic layer is measured continuously or periodically. The resistance measurement can be carried out with constant current or constant voltage. On the basis of the measured electrical resistance, the quality of the sieve can then be determined.

In a further aspect, the invention also relates to a method of servicing a screening machine, comprising the step of replacing a screen as described above, which has damage or wear, by a screen without damage or wear, in particular as described above. It has also been found that the coating (in particular a full-surface coating) may already be suitable for reducing the wear on the screen fabric.

The sieve is preferably tensioned in the radial direction. Round or drum sieves as well as flat, flat sieves can be detected. In a sieve according to the invention, the sieve surface or the sieve fabric is fastened in particular to a frame, preferably stretched on a frame. The sieve can preferably also be equipped with electrical connections (for example sockets, plugs, or the like) via which the resistance measurement, in particular along the conductor track, is made possible.

It has been shown that influences of the resistance measurement result by environmental and operational influences such as in particular temperature or vibration influences can be easily compensated with routine measures.

The inventive sieve can also be used in building openings of silos or mills, z. B. by clamping on windows to detect damage to these openings can.

The invention will be explained in more detail with reference to embodiments and figures, without the subject of the invention would be limited to these embodiments. Show it :

Fig. 1: a drum screen;

2 shows a metallic fabric coating in a schematic representation; Fig. 3: tissue in schematic representation;

Fig. 4: enlarged detail of Fig. 2;

Fig. 5: measuring arrangement.

A drum screening machine shown in FIG. 1 has a product inlet 1 in a screening jacket 2. Within the screen shell 2, a rotating beater mechanism 3 is arranged, which is driven by a motor 4 with belt transfer 5.

The product is thrown against the screen jacket 2 by the rotating beater mechanism 3. The finer product passes through the screen jacket 2 and enters a diarrhea outlet 6, the coarser product leaves the screening jacket 2 or the drum screening machine through a discharge outlet 7.

When sieving / spinning flour, a product mixture that is difficult to separate is spotted and the screening jacket 2 has a support basket which is surrounded by a screen fabric made of polyester or polyamide threads.

2 shows by way of example the coating of a screen 9 with a conductor track 8 made of silver. The layer thickness of the conductor track is in the nanometer range, in particular in the range of about 20 to 800 nm, preferably from 60 to 650 nm, particularly preferably from 100 to 500 nm.

By arranging the conductor track diagonally to the warp / weft threads of the fabric, damage can be detected according to the structure course of the conductor track 8 by evaluating the resistance measured values in an evaluation electronics. FIG. 3 shows a square fabric of warp threads 10 and weft threads 11 to illustrate a possible fabric structure of a wire 9.

FIG. 4 schematically shows an enlarged section of FIG. 2, whereby the warp and weft threads are also shown. For the coating known methods can be used.

FIG. 5 shows an exemplary experimental setup for measuring a screen (9) coated over the entire surface. On the right side of the diagram, the screen is connected to a voltage source. Ohm's law R = U / I allows the sieve resistance R i5 to be determined on the basis of the applied voltage U and the measured current intensity I. The fully coated sieve has a resistance Rl in the perfect condition. A damaged screen showing a crack, breakage or abrasion shows a resistance R2 ≠ Rl. Interruptions result, for example, in an increase in resistance, whereas local shorts in one

20 decrease in resistance result. It can be seen that the conductor must be arranged in such a way relative to the fabric structure of the screen, that in the method as described above, a continuous conductor track is obtained.

25 Further embodiments of the invention relate to:

(a) a screening machine, with a flat or round screen, the screen comprising a screen of plastic fibers, and the screen being at least partially provided with a metallic layer; b) a screening machine as described in a), wherein the layer is formed like a conductor in the form of a resistance coil;

c) a screening machine as described in a), wherein the layer is homogeneous;

d) a screening machine as described in a), b) or c), wherein the layer consists of silver or titanium;

e) a screening machine as described in a), b) or c), characterized in that the sieve is designed as a round screen jacket, in which a racket mechanism is arranged rotatably;

f) a method for operating a screening machine as described in a), b), c) or d, wherein the electrical resistance of a layer is measured continuously or periodically.

Claims

claims

1. sieve with a sieve surface made of plastic, in particular a sieve fabric made of plastic, characterized in that

5, the screen surface, in particular the screen fabric, is at least partially provided with an electrically conductive, in particular a metallic layer.

2. Screen according to claim 1, characterized in that the lo Siebgewebe is formed of plastic fibers.

3. Screen according to one of claims 1 or 2, characterized in that the plastic of the screen fabric, in particular the plastic fibers of the screen fabric are selected from i5 the group consisting of polyamides (PA), in particular PA6, PA66; Polyalkylenes, in particular polyethylene (PE), preferably of high density (HDPE), polypropylene (PP) and polyethylene / polypropylene copolymers (PE / PP); Polyester, in particular polyethylene terephthalate (PET), polybutylene

20 rephtalate (PBT).

4. Screen according to one of claims 1 to 3, characterized in that the / the metal (s) of the electrically conductive layer is / are selected from the group consisting of

25 silver, titanium, chromium and mixtures thereof.

5. sieve according to one of claims 1 to 4, characterized in that the electrically conductive layer is not over the entire surface of the screen surface, in particular the Siebgewe-

30 be, is formed.

6. Screen according to claim 5, characterized in that the electrically conductive layer is formed as a conductor track.

5 sieve according to claim 6, characterized in that the conductor track extends substantially transversely to the boundaries of the sieve openings.

8. sieve according to claim 6, characterized in that the lo conductor runs substantially transverse to warp threads and weft threads of the plastic fabric.

9. sieve according to one of claims 1 to 8, characterized in that the electrically conductive layer is homogeneous i5.

10. Screen according to one of claims 1 to 9, characterized in that the screen is designed as a round screen jacket (2), in which a racket (3) rotatably arranged

20 is.

11. Sieving machine containing a sieve according to one of claims 1 to 10.

25 12. A method for operating a screening machine according to claim 10, characterized in that the electrical resistance of the electrically conductive, in particular metallic layer is measured continuously or periodically.

13. Method according to claim 12, characterized in that the quality of the sieve is determined on the basis of the measured electrical resistance.

14. A method of servicing a screening machine, comprising the step of replacing a screen according to any one of claims 1 to 10, which has damage or wear, through a screen without damage or wear, in particular according to one of claims 1 to 10.

15. A method of servicing a screening machine, comprising the step of replacing a screen, in particular according to one of claims 1 to 10, which has damage or wear, by a screen without damage or wear, according to one of claims 1 to 10.

16. Use of a sieve according to one of claims 1 to 10 in a screening machine.

17. Use of a sieve according to claim 16 in a screening machine, in particular in exchange for a defective sieve.