WO2014019925A1

WO2014019925A1 - Screen cleaner for plansifter

Info

Publication number: WO2014019925A1
Application number: PCT/EP2013/065682
Authority: WO
Inventors: Daniel LAUBSCHER
Original assignee: Bühler AG
Priority date: 2012-08-02
Filing date: 2013-07-25
Publication date: 2014-02-06

Abstract

Screen cleaner for plansifter, comprising a magnetically detectable material, preferably bound in a plastic; and/or a magnetic material bound in a plastic and/or a magnetic plastic. The magnetic property of the screen cleaner has the effect of improving the capability of detecting and isolating particles (in particular with conventional magnetic separators) that originate from faulty screen cleaners.

Description

SCREEN CLEANER FOR PLANNERS

The invention relates to the field of fractionation of milling products, namely plansifter, in particular screen cleaner for such Plansichter.

Generic screen cleaners for Plansichter as such have long been known, for example, from the documents EP 0 584 302 B1 and DE 10 2006 005 970 A1 known. They are inserted into the sieve boxes of Plansichtern and move due to the movements (eg, shaking, gyros o. The like.) Of Plansichters within the sieve frame or in segments of the sieve frame essentially freely around. Here, cleaning elements of the sieve cleaner stroke from below along the sieve covering and thus clean the sieve. The screen cleaner is typically provided with a wobble in its middle area, so that the extremities of the screen cleaner in addition to the mere horizontal movement within the screen frame also perform tipping and Abkippbewegungen and therefore edit both the Siebbespannung and the bottom of the screen box. Sieve cleaners are usually made of rubber-elastic material, whereby excessive mechanical stress on the sieve covering, by which the sieve covering becomes blind or in extreme cases even tears, is avoided.

It is a fundamental effort in the mill to avoid contaminations of the ground material, especially with metallic impurities from the outset, but in any case reliably read such impurities from the ground material. The use of metal is therefore avoided, at least in (especially free) moving parts where possible, such parts come into contact with the material to be ground. Since a complete waiver of metal parts is not possible in general, so-called magnetic separators are, for example, arranged in conveying lines of the ground material to isolate the metal parts due to magnetic forces from the Mahlgutstrom and retain. Also for generic screen cleaner, the prevailing teaching has consistently been that the use of metal should be avoided if possible. Screen cleaners made of metallic material are therefore not available on the market. For example, it is explicitly pointed out, for example, in EP 0 584 302 B1 that it is very important that the screen cleaner is preferably made of plastic made without metal; the reduction in noise of an operating plan sifter with generic screen cleaners has also been attributed to the use of a non-metallic material. Only for special applications have metallic components of sieve cleaners been described in those partial areas which could come into contact with the material to be ground and the sieve frame / sieve box; Thus, for example, in DE 10 2006 005 970 A1 a screen cleaner with metal caps on the extremities is described, in order to meet the specific requirements in the sighting of particularly abrasive substances, such as, for example, sugar.

European regulations require that, under normal or foreseeable conditions of use, materials and articles intended to come into contact with food do not dispose of ingredients to foods in quantities likely to endanger human health, an unjustifiable change in the product Food or to alter the organoleptic properties of the food (Regulations EC No 1935/2004 and 10/201 1). It is also necessary in case of damage to be able to trace the origin of any contamination of the food. However, in practice, visual inspection of the screen stock is unrealistic due to the high throughput of a typical mill. The automatic color detection and isolation of particles in the screenings, however, would be technically possible, for example. With sorting machines from Sortex Ltd .; However, this requires a relatively high overall equipment cost.

There is therefore a need to further improve the detectability and isolability of particles derived from defective screen cleaners.

It is thus an object of the present invention to obviate the drawbacks of the prior art, in particular to provide screen cleaners with which the detectability and isolability of particles derived from defective screen cleaners is improved.

This object is solved by the subject matters of the independent claims. A first aspect of the present invention relates to a screen cleaner for Plansichter, comprising a magnetically detectable material bound in a plastic. Such embodiments of the invention are particularly easy to implement and therefore presently preferred, as will be explained in detail below.

Alternatively or additionally, a bonded in a plastic magnetic material and / or a magnetic plastic can be used in the invention.

Plastic-bonded magnetic material is known per se. Also, magnetically bound magnetically detectable material as such is known and often referred to as MDP (metal detectable plastic). Such materials are a composite material (a so-called composite material) in which a particulate inorganic material is embedded in a matrix of a plastic material. The screen cleaner can also consist essentially completely of such composite materials, as will be explained below.

As a magnetically detectable material is basically any paramagnetic, ferrimagnetic, antiferromagnetic or - particularly preferred - ferromagnetic material into consideration. Combinations of these materials are, of course, possible and readily ascertainable by those skilled in the art by means of routine experimentation. Particularly preferably, the magnetically detectable material is selected from the group consisting of

- ferromagnetic elements, in particular Fe, Co, Ni, Gd, Dy;

ferromagnetic alloys, in particular FeAlNiCo, SmCoFe, Nd ₂ Fe ₁₄ B, NiFe, preferably Ni ₈₀ Fe ₂ O;

as well as combinations of these materials.

As a particulate inorganic magnetic material in the invention, a magnetic material, in particular a magnetic powder is used; The resulting composite material will then expertly as a plastic-bound magnet designated. This is used in the prior art, especially for the production of complex or specially shaped magnets. Materials suitable for use in the invention are commercially available, for example from ThyssenKrupp.

Magnetic plastics as such are known and can be used in the invention. Here, the magnetic property is no longer based on embedded, particulate magnetic powder, but rather is due to the nature of the polymer chain of the plastic itself.

With all the aforementioned materials, both the composite materials and the magnetic plastics, can be compared to the known from the prior art screen cleaners realize significant advantages. On the one hand, the previous detection of particles that originate from faulty sieve cleaners is based on a mere optical control. As explained, a visual inspection is not practical; an automated, apparative solution, however, requires enormous effort. Due to the magnetically or magnetically detectable property of the sieve cleaner according to the invention, particles originating from these sieve cleaners can be retained on conventional magnetic separators. There is thus not only a detection, but also a separation of the particles. It was not easy to expect that the achievable magnetic or magnetic detectable properties of the screen cleaner under practical conditions in a mill sufficient for this purpose. However, it has surprisingly been found that this is readily and very reliably the case. The technical assumption, the use of metal in particular in freely moving parts should be avoided as far as possible, has proven to be unfounded at least for the applicable in the context of the invention, bound in a plastic magnetic materials or magnetically detectable materials. In particular, for magnetic plastics applies that they even do without any addition of metal and also meet the demands on food safety, as explained in the introduction.

In a particularly preferred embodiment, the screen cleaner has an elastic plastic. Such elastic trained sieve cleaner as such are known from the prior art; The elasticity is determined by a suitable choice realized the plastic material. Typically, thermoplastics are used. Suitable base materials can be obtained, for example, from the companies Evonik, BASF and Bayer.

The elastic plastic has in preferred embodiments

a Shore A hardness according to DIN 53505 (2000-08) in the range from 70 to 95, preferably from 75 to 90;

and or

a Shore D hardness according to DIN 53505 (2000-08) in the range from 25 to 55, preferably from 30 to 45

on. Such elasticities have proven to be a particularly advantageous compromise of necessary rigidity (in order to exert the required forces) as well as advantageous protection of coming into contact with the screen cleaner Siebbespannung and other parts of Plansichters, especially the screen frame and the bottom of the screen box.

When operating a plan sifter, fragments of sieve cleaners may have a size of typically up to 500 mm ³ ; However, in most cases, fragments have a size of <500 mm ³ .

Particularly advantageously, the plastic is selected such that there is an abrasion according to DIN ISO 4649-A (2006-1 1) of <70 mm ³ , preferably of <50 mm ³ , particularly preferably of <30 mm ³ . Although in the context of the invention the detectability and isolability of particles which originate from defective sieve cleaners is improved, the formation of such impurities can be prevented as far as possible from the outset by means of materials suitably selected.

The magnetic material bound in plastic may be a permanent magnet powder, in particular powdered hard ferrite (for example barium or strontium ferrite),

or rare earth magnetic powder, especially neodymium-iron-boron (NdFeB). As plastic, in which the magnetic material or the magnetically detectable material is bound, food grade plastics are used, for the reasons explained in the introduction. It is preferably a thermoplastic polymer, in particular selected from the group consisting of polyacetals, polyethylenes, polyethers, polycarbonates, polyurethanes and mixtures thereof. Most preferably, the polyurethane is a polyether polyurethane elastomer; Suitable polyether polyurethane elastomers are available, for example, from Bayer under the tradenames Texin® and Desmopan® or else from BASF under the trade name Elastogran®.

The magnetic plastic which can be used in the context of the invention is preferably an organic polymer backbone provided with an acceptor molecule. For example, tetracyanoethylene (TCNE) and / or a 7,7,8,8-tetracyanoquinodimethane (TCNQ) can be used as acceptor molecule. As the polymer backbone, a polyaniline can be used. Thus, within the scope of the invention, for example, a polyaniline modified with 7,7,8,8-tetracyanoquinodimethane (TCNQ) is suitable, as described by Zaidi et al. and designated as PANiCNQ (Zaidi et al., Polymer 45 (2004), 5683-5689).

In particularly advantageous embodiments of a sieve cleaner according to the invention, at least one outer layer is dyed in a color which differs in particular from white. This allows the visual inspection of the particles, which were read out of the screenings due to their magnetically or magnetically detectable properties. It can therefore already be made due to the color of the particles an assignment to the place where the faulty sieve cleaner is, eg. An assignment to a particular Plansichter or a certain Plansichtergruppe the mill, if different depending on the location in the mill Sieve cleaner can be used. If it is necessary or desired to replace the defective sieve cleaner, this can be done selectively on account of the simple color assignability: the color of the particle which is read out of the sieve due to its magnetically or magnetically detectable property allows the location of the defective sieve cleaner in the mill. Of course, it is within the scope of the invention also possible that not only an outer layer of the screen cleaner is colored, but that the screen cleaner is substantially completely colored in a particular color different from white. On the one hand, this allows a particularly simple production, for example by injection molding. In addition, a reliable assignability is guaranteed even when internal particles of the sieve cleaner are dissolved out. By "essentially complete" through-coloring of the screen cleaner, it is understood that at least the base material (typically the elastomeric plastic of the base body) is dyed through in particular on the screen cleaner, not in an outer layer or through-colored cleaning aids such as bristles or the like. are of course possible.

Another aspect of the invention relates to a method for producing a screen cleaner as described above, comprising a step of injection molding or compression molding of a

- magnetically detectable material, together with a plastic;

and or

- A magnetic material, together with a plastic, and / or a magnetic plastic.

In particular, in the use of thermoplastics, the production by injection molding is particularly preferred because this allows a particularly cost-effective production in large quantities. The processing preferably takes place in such a way that the magnetically or magnetically detectable material bound in a thermoplastic material is provided in the form of a granulate; Each granule therefore already constitutes a composite material of magnetic powder or metallically magnetically detectable material and plastic matrix, as explained above. This granulate can be processed by conventional per se injection molding method to inventive screen cleaners. In particular, for rare earth magnetic powder such as neodymium-iron-boron (NdFeB), a compression molding method can be used in the invention. Due to the achievable in the molding process, higher degree of filling with magnetic powder, a higher magnetic level (energy product) can be achieved in comparison with moldings produced by injection molding, resulting in even higher Reliability of the magnetic deposition of particles of these moldings reflected.

A further aspect of the invention relates to a set comprising at least two sieve cleaners, wherein at least one respective outer layer of the sieve cleaner is dyed in respectively different colors different from white, preferably in each case substantially all of the sieve cleaners are dyed through in different colors different from white. This allows in addition to the magnetic separation and a simple visual control, as already explained above: It can thus already be made due to the color of the deposited particles an assignment to the place where the defective screen cleaner is, eg. An assignment to a certain plan sifters or a specific plansifter group of the mill, if depending on the location in the mill different colored screen cleaner can be used.

In a further aspect, the invention thus basically relates to the use of a

magnetically detectable material, preferably bound in a plastic;

and or

- In a plastic bonded magnetic material and / or a magnetic plastic;

to improve the detectability and isolability of particles originating from defective sieve cleaners.

Another aspect of the invention relates to a method of separating particles originating from defective screen cleaners from a stream of screened material, wherein the screened product stream is passed through a magnetic separator and the particles are retained on the magnetic separator. Suitable magnetic separators for this purpose are known in the art and available in the market. Magnetic separators are available, for example, as a drum magnetic separator (DFRT from Bühler AG) or a magnetic apparatus (MMUA from Bühler AG). It is advantageous that such magnetic separator are usually installed in mills, which is why for the Separation of particles defective screen cleaner no additional equipment expense must be operated.

The invention will be explained in more detail in an embodiment with reference to a figure, without the subject of the invention would be limited to the embodiment shown. Hereby shows:

Figure 1: Schematic representation of a generic screen cleaner.

Figure 1 shows an example of a generic screen cleaner 1, which may be formed according to the invention; Of course, however, differently shaped screen cleaner can be configured according to the invention. The embodiment shown represents a screen cleaner 1, which rises in its central region with a wobble foot 2 on a bottom plate 3a of the screen box 3b. The screen cleaner 1 is formed in a star-shaped plan view (as shown in EP 0 584 302 B1), which is only partially recognizable in the side view shown here. At one extremity of the star-shaped sieve cleaner 1, a slit and bottom rinsing nose 4 is arranged, by means of which sieve diarrhea is cleared from the bottom plate 3a of the sieve box 3b by lateral slot openings 5. Above the sieve cleaner 1, the sieve covering 8 is arranged, which is fastened on a screen frame 6. The screen frame 6 advantageously has an edge 7 designed in such a way that the extremities of the screen cleaner 1 are abutted and thrown back with the preferably elastic material during operation of the planifter. At the extremities of the sieve cleaner 1 cleaning elements 9 are mounted (possibly in end regions of the extremities) in the direction of Siebbespannung, which are formed in the embodiment as nubs. Of course, however, for example, brush as cleaning elements 9 can be used.

A sieve cleaner 1 according to the invention can now be formed, particularly advantageously, substantially completely from a magnetic material or magnetically detectable material bonded in a plastic; Alternatively, training is also possible from a magnetic plastic, as stated above. If due to the constant mechanical stress of the sieve cleaner by impacts On materials of greater hardness (eg., The bottom plate 3a of the sieve box 3b and in particular the edge 7 of the sieve frame 6) particles of the sieve cleaner 1 should be replaced, they are carried out with the Siebdurchfall through the lateral slot opening 5 and finally in ordinary magnetic separators, which Strainer passes anyway, retained.

In particular, for the matrix material polyether polyurethane with ferromagnetic material finely dispersed therein, or hard ferrite magnetic powder, or rare earth magnetic powder, it has been found that the abrasion of such a material can be almost completely retained on commercially available magnetic separators as described above.

Claims

1 . Screen cleaner for plan sifter, comprising

a magnetically detectable material bound in a plastic;

and or

- A bonded in a plastic magnetic material and / or a magnetic plastic.

2. Strainer cleaner according to claim 1, characterized in that the sieve cleaner has an elastic plastic.

3. Strainer cleaner according to claim 2, characterized in that the elastic plastic

a Shore A hardness according to DIN 53505 (2000-08) in the range from 70 to 95, preferably from 75 to 90; and or

having.

4. sieve cleaner comprises according to one of the preceding claims, characterized in that the plastic abrasion in accordance with DIN ISO 4649-A (2006-1 1) of <70 mm ^3, preferably of <50 mm ^3, more preferably of <30 mm ³ ,

5. sieve cleaner according to one of the preceding claims, characterized in that the magnetically detectable material is selected from the group consisting of paramagnetic materials; ferrimagnetic materials; antiferromagnetic materials; and, more preferably, ferromagnetic materials; as well as combinations of these materials.

6. sieve cleaner according to one of the preceding claims, characterized in that the magnetically detectable material is selected from the group consisting of - ferromagnetic elements, in particular Fe, Co, Ni, Gd, Dy;

as well as combinations of these materials.

7. sieve cleaner according to any one of the preceding claims, characterized in that it is in the bound plastic in magnetic material to permanent magnet powder, in particular powdered hard ferrite, or rare earth magnet powder, in particular NdFeB is.

8. Screen cleaner according to one of the preceding claims, characterized in that it is the plastic in which the magnetically detectable material and / or the magnetic material is bonded, is a thermoplastic polymer, in particular selected from the group consisting of polyacetals; polyethylenes; polyethers; polycarbonates; Polyurethanes and mixtures thereof.

9. sieve cleaner according to claim 8, characterized in that it is the polyurethane is a polyether polyurethane elastomer.

10. Sieve cleaner according to one of the preceding claims, characterized in that it is in the magnetic plastic to one with an acceptor, in particular tetracyanoethylene (TCNE) and / or a 7,7,8,8-tetracyanoquinodimethane (TCNQ), provided , organic polymer backbone, especially a polyaniline.

1 1. Screen cleaner according to one of the preceding claims, characterized in that

- At least an outer layer of the screen cleaner dyed in a particular color of white different color; or

- The screen cleaner is substantially completely colored in a particular color different from white.

12. A method for producing a screen cleaner according to one of the preceding claims, comprising a step of injection molding or compression molding of a

- magnetically detectable material, together with a plastic;

and or

- A magnetic material, together with a plastic, and / or a magnetic plastic.

13. Set comprising at least two sieve cleaner, in particular according to one of claims 1 to 1 1, characterized in that at least one respective outer layer of the sieve cleaner dyed in each case different, in particular of white different colors, preferably in each case substantially all of the sieve cleaner in different, in particular of white different colors are colored.

14. Use

a magnetically detectable material, preferably bound in a plastic;

and or

- A bonded in a plastic magnetic material and / or a magnetic plastic;

15. A method for separating particles that come from defective sieve cleaner, in particular according to one of claims 1 to 1 1, from a Siebgutstrom, characterized in that the Siebgutstrom is passed through a magnetic separator and the particles are retained on the magnetic separator.