Magnetic conveying device

Abstract

The invention relates to a magnetic conveying device for transporting plate-shaped objects (1), comprising a plurality of magnetic holding elements (4) which are arranged one behind the other in the conveying direction (F) and comprising at least one conveyor belt (3) which runs past the magnetic holding elements (4) and which is designed to be at least partly electrically conductive and thus antistatic. The invention is characterized in that the conveyor belt (3) is made of a plastic composite, thereby using at least one thermoplastic into which electrically conductive particles (6) are continuously incorporated.

Description

[0001] Magnetic conveyor system

[0002] Description:

[0003] The invention relates to a magnetic conveyor device for transporting plate-shaped objects, with a plurality of magnetic holding elements arranged one behind the other in the conveying direction, and with at least one conveyor belt running past the magnetic holding elements, which is at least partially electrically conductive and thus antistatic.

[0004] A magnetic conveyor system of the design described above is described in the applicant's EP 2 576 403 B1. As explained therein, such magnetic conveyor systems are typically used for both the suspended and surface-mounted transport of sheet metal as plate-shaped objects. The sheet metal in question may be those that are subsequently processed into housing sheets for, for example, household appliances, stamped parts in the automotive industry, can lids, etc. Accordingly, the plate-shaped objects in question are usually designed to be ferromagnetic or magnetizable so that they can be attached to the passing conveyor belt with the aid of the magnetic holding elements and ejected with precision. For this purpose, switchable electromagnets are used as magnetic holding elements. Permanent magnets can also be used.

[0005] If non-ferromagnetic materials such as glass plates, wood plates, plastic plates, etc. are to be transported with such a magnetic conveyor, it is usually additionally equipped with vacuum holding elements. In this case, one speaks of a so-called combined conveyor, as described in the further prior art according to EP 0 893 372 A1 or DE 10 2005 001 568 A1. As a result of the increasing conveyor speeds today, electrostatic charges are observed, which can be traced back primarily to the friction between the conveyor belt and the magnetic holding elements or vacuum holding elements or between the conveyor belt and a frame holding the said elements. For this reason, within the scope of the generic EP 2 576 403 B1, one works, among other things, in such a way that at least the upper side of the conveyor belt, ieThe side facing away from the plate-shaped objects and facing the magnetic holding elements, with the teeth usually arranged there, has a full-surface antistatic coating. This antistatic coating has an electrical surface resistance below 100 kΩ. In this way, the conveyor belt running past the magnetic holding elements is at least partially electrically conductive and thus antistatic.

[0006] The state of the art has proven effective in that, on the one hand, wear is reduced and, on the other hand, any sparking caused by electrostatic charging no longer occurs. To this end, the known teaching additionally provides that the guide rails connected to the magnetic holding elements also have a metal and / or plastic coating. This has generally proven effective, but still offers room for improvement.

[0007] The additional implementation and equipping of the guide rails with the metal coating requires a special procedure. This also applies to the full-surface and antistatic coating. This is because this is usually designed as a fabric coating, and in particular a plastic fabric coating. This requires that the fabric or plastic fabric in question be placed on the upper side of the conveyor belt. Nowadays, however, there is also demand and requirement for designs that are designed to work fundamentally without additional plastic fabric, or with one that is not located on the surface but rather embedded in the conveyor belt. In this context, there are already examples in the prior art showing how a conveyor belt can generally be designed to be electrically conductive in order to counteract electrostatic charging. Reference is made to DE 102 30 306 A1.However, the known conveyor belt is not intended or designed for interaction with a magnetic conveyor device.

[0008] While longitudinally embedded reinforcements made of steel, for example, are discussed here, these reinforcements are not necessarily suitable or designed to interact with the magnetic holding elements in such a way that the interaction eliminates any sagging or ensures defined guidance of the conveyor belt relative to the magnetic holding elements. The invention aims to remedy this situation.

[0009] The invention is based on the technical problem of further developing such a magnetic conveyor device for transporting plate-shaped objects in such a way that universally designed conveyor belts can be used, and in particular those without surface fabric, with a perfect antistatic design and taking into account cost-effective production.

[0010] To solve this technical problem, a generic magnetic conveyor device for transporting plate-shaped objects is characterized in that the conveyor belt is made of a plastic composite using at least one thermoplastic with electrically conductive particles embedded therein.

[0011] Within the scope of the invention, a conveyor belt or conveyor belt is still used, which is initially and regularly produced by extrusion from a thermoplastic material, in particular a thermoplastic elastomer. Thermoplastic polyurethanes have proven particularly suitable for this purpose. According to the invention, a plastic composite is now used, i.e., the thermoplastic material or thermoplastic elastomer in question together with embedded electrically conductive particles.

[0012] These electrically conductive particles are usually electrically conductive amorphous plastic. This can be easily mixed into the elastomeric plastic or thermoplastic elastomer during production by combining the plastic and the conductive particles in question to form a compound, which is then extruded together into the conveyor belt. In this way, the electrically conductive particles embedded in the thermoplastic are evenly distributed throughout both the length and the thickness of the conveyor belt produced in this way. This is further supported by the fact that the conductive particles are usually added to the plastic granules in powder form. This means that the particle size of the electrically conductive particles is a few micrometers and usually even less than 1 pm.This results in a uniform and consistent mixing of the plastic granules with the individual granules, which generally have particle sizes of 0.1 mm to 1 mm and larger. In contrast, the powdered electrically conductive particles are generally a hundred times smaller, having the previously stated particle size of 1 pm and smaller. This is, of course, only an example.

[0013] The electrically conductive amorphous carbon can be admixed with the thermoplastic elastomer in the form of, for example, carbon black. The addition takes place before extrusion of the plastic composite produced in this way. A grammage of the electrically conductive particles in the plastic granulate has proven particularly advantageous in which the respective conductive particles account for more than 1 wt.% to 20 wt.% in the mixture or plastic composite. In particular, the grammage of the electrically conductive particles - in each case based on the total mixture - is between 2 wt.% and 10 wt.%. A grammage of the conductive particles in the plastic composite, i.e. of the total amount, of 3 wt.% to 5 wt.% is very particularly preferred.

[0014] In this way, on the one hand, consistent electrical conductivity of the conveyor belt is provided, and on the other hand, the conveyor belt can be extruded without any problems. At the same time, any mechanical properties of the conveyor belt with regard to strength, tensile strength, and flexural elasticity are not negatively affected overall. This is especially true if the proportion of conductive particles in the plastic composite is below 10 wt.%. In either case, electrical resistances of less than 100 kO can be observed in this way if the resistance of the conveyor belt used according to the invention is measured between an upper side facing the plate-shaped objects and an upper side facing away from the objects in question and facing the magnetic holding elements.In fact, resistances of only 20 kΩ, and especially even 10 kΩ or less, are usually observed at this point, thus preventing any electrostatic charges from forming. In fact, this prevents both electrostatic charges and any sparking. This represents the main advantage.

[0015] Another special feature to consider is that the conveyor belt can additionally be equipped with a fabric inserted or applied thereto. In principle, multiple fabrics are also conceivable. For example, the conveyor belt can be equipped with such a fabric both on its upper side facing the plate-shaped objects and on its upper side facing away from the plate-shaped objects and facing the magnetic holding elements. The fabric is generally also designed to be electrically conductive. For this purpose, the fabric can be coated, for example, with an adhesion promoter that ensures the required electrical conductivity of the fabric. Such adhesion promoters are generally known and can be used to impregnate the fabric. Reference is made to DE 102 30 306 A1 as an example.

[0016] Alternatively, a coating with a plastic fabric can be applied, as described in the generic EP 2 576 403 B1. The fabric in question is generally provided in the area of ​​the surface facing the plates, or the upper side of the conveyor belt.

[0017] Of particular inventive importance is the fact that the conveyor belt is equipped with steel parts or steel strands running in the conveying direction. The steel cables or steel strands are each designed to be magnetizable. Furthermore, the steel cables or steel strands are located inside the conveyor belt, preferably in the area of ​​the surface or upper side of the conveyor belt facing the magnetic holding elements. In this way, the magnetic field emanating from the magnetic holding elements and generally oriented perpendicular to the conveying direction and thus also to the longitudinal extent of the conveyor belt is amplified in the perpendicular direction in question by the magnetizable steel cables or steel strands embedded in the conveyor belt.In addition, the steel cables or steel strands, which are generally evenly distributed across the width of the conveyor belt, mean that the vertical magnetic field lines in this area extend further than without the steel strands and, on the other hand, have a greater density than in the situation without the steel strands, as will be explained in more detail with reference to the description of the figures.

[0018] As a result, the overall holding force exerted by the magnetic holding elements on the plate-shaped objects is increased, while at the same time, any air gap between the plate-shaped objects and the conveyor belt or a frame guiding the conveyor belt is reduced. At the same time, the steel cables or steel strands ensure that any sagging along the length of the frame is prevented, particularly during suspended transport of the conveyor belt. Furthermore, when the plate-shaped objects are transported in a horizontal position, the guidance of the conveyor belt relative to the frame is improved, thus reducing any wear on the optionally provided guide rails.

[0019] This allows the teeth, usually provided on the upper side of the conveyor belt facing the magnetic holding elements, to engage the associated gears, to be designed to be narrower overall in cross-section than the conveyor belt itself. Typically, two longitudinally continuous rows of teeth are used at this point, spaced apart from each other, as explained in more detail in the description of the figures. In any case, the overall effect achieved is that the magnetic poles of the magnetic holding elements, or the magnetic field lines emanating from the magnetic poles, of the magnetic holding elements extend to the air gap between the magnetic holding elements and the conveyor belt and (far) beyond.

[0020] The result is a magnetic conveyor system for transporting plate-shaped objects that utilizes a simple and particularly effective antistatic conveyor belt or conveyor belt. In addition, the conveyor belt with its embedded steel strands or steel cables, in conjunction with the magnetic holding elements, specifically ensures that the magnetic field lines emanating from the magnetic holding elements and oriented perpendicular to the longitudinal extension of the conveyor belt or the conveying direction, exhibit both a greater density and a greater range compared to a situation in which the steel cables or steel strands are not provided. These are the key advantages.

[0021] The invention is explained in more detail below with reference to a drawing which merely represents an exemplary embodiment; in the drawings:

[0022] Fig. 1 shows the magnetic conveyor device according to the invention in a schematic longitudinal view, partly in section,

[0023] Fig. 2 is a schematic cross-section through the article according to Figure 1 and

[0024] Fig. 3 shows the conveyor belt used in detail. The figures show a magnetic conveyor device which is used to transport plate-shaped objects 1, as can be understood from Fig. 1. For this purpose, the plate-shaped objects 1 are transported in a conveying direction F, for example from one processing station to the next. The conveying direction F corresponds to the longitudinal direction of the magnetic conveyor device and a conveyor belt 3 which runs around a frame 2. In the longitudinal direction of the frame 2 and consequently in the conveying direction F, a plurality of magnetic holding elements 4 are provided, with the aid of which the plate-shaped objects 1 are magnetically attracted and placed on the conveyor belt 3 which runs past the magnetic holding elements 4 in the conveying direction F.

[0025] For this purpose, the magnetic holding elements 4 are typically electromagnets which, according to the exemplary embodiment and not by way of limitation, generate a magnetic field which is oriented perpendicular to the conveying direction F and consequently to the longitudinal extent of the conveyor belt 3, as can be seen from the schematically plotted magnetic field lines 5 in Fig. 2. Here, one can see a north pole S facing the plate-shaped objects 1 and an opposite south pole S with the magnetic field lines 5 forming between them. This generates the magnetic field oriented perpendicular to the conveying direction F or the longitudinal extent of the conveyor belt 3. This is not restrictive and is only an example. In any case, the plate-shaped and magnetizable objects 1 are attracted to the magnetic holding elements 4 and applied to the conveyor belt 3.

[0026] According to the exemplary embodiment, the conveyor belt 3 is at least partially electrically conductive and thus antistatic. This electrical conductivity and the associated antistatic effect of the conveyor belt 3 is realized and implemented within the scope of the invention in that the conveyor belt 3 is made of a plastic composite using at least one thermoplastic with electrically conductive particles 6 embedded throughout it. In fact, these electrically conductive particles 6 can be seen schematically in the sectional view of the conveyor belt 3 in Fig. 3. The conveyor belt 3 is manufactured by a plastic injection molding process in such a way that a thermoplastic elastomer, for example polyurethane, is mixed with the electrically conductive particles 6 in question.For this purpose, the conductive particles 6 are mixed with a corresponding plastic granulate, and the compound produced in this way is extruded or co-extruded, forming the desired plastic composite and thus the conveyor belt 3. This also ensures that the electrically conductive particles 6 are present and embedded throughout the conveyor belt 3. This means that the electrically conductive particles 6 are evenly distributed across the cross-section of the conveyor belt 3, both in terms of the distribution of the conductive particles 6 in the longitudinal direction of the conveyor belt and in the transverse direction, as can be seen from the sectional view in Fig. 3.

[0027] According to the exemplary embodiment, electrically conductive amorphous carbon is used as the electrically conductive particle 6. This is of course only an example. Furthermore, the grammages already referred to in the introduction to the description are used here. A thermoplastic elastomer, for example polyurethane, is used as the thermoplastic. In addition, the conveyor belt 3 can be equipped with one or more applied or inserted fabrics 7. The sectional view in Fig. 3 shows that both a fabric 7 facing the plate-shaped objects 1 and a further fabric 7 provided on the opposite upper side are realized. In principle, one or both fabrics 7 can also be present inside the conveyor belt 3 and here ensure its structural stability. As a rule, however, the fabric 7 is found on one or more sides, if necessary.both upper sides of the conveyor belt 3. In addition, the fabric 7 is also electrically conductive, as explained in detail in the introduction to the description.

[0028] Of essential importance for the invention is the fact that the conveyor belt 3 is equipped with steel cables or steel strands 8 running in the conveying direction F. The steel cables or steel strands 8 are magnetizable. Furthermore, the steel cables or steel strands 8 run continuously in the longitudinal direction of the conveyor belt 3 and thus also in the conveying direction F. Furthermore, it can be seen from Fig. 3 that the steel cables or steel strands 8 are evenly distributed inside the conveyor belt 3. Furthermore, Fig. 3 makes it clear that the steel cables or steel strands 8 are placed inside the conveyor belt 3, specifically in the area of ​​the surface or top side of the conveyor belt 3 facing the magnetic holding elements 4.

[0029] In this way, the overall result is that the magnetic field lines 9 shown in Fig. 3 and generated by the magnetic holding elements 4, on the one hand, extend further in the direction of the plate-shaped objects 1 and, on the other hand, have a greater density than would be the case without the steel strands 8. This can be seen from Fig. 3, in which the magnetic field lines 9 generated by the magnetic holding elements 4 without the additionally provided and reinforcing steel cables or steel strands 8 are shown in dash-dotted lines and represented by 9i. In contrast, the situation with steel cables or steel strands 8 provided is reflected in the course of the solid magnetic field lines 9 with the reference number 92. It can be seen that the additionally provided steel cables or steel strands in the interior of the conveyor belt 3 and in the area of ​​the surface or surface facing the magnetic holding elements 4Top side, the then forming magnetic field lines 92 extend further in the direction of the plate-shaped objects 1, which leads to a correspondingly increased height H2 compared to the situation with the height Hi when steel cables or steel strands 8 are not present. At the same time, it can also be seen that the magnetic field lines 92 have an overall greater density in the area of ​​the plate-shaped objects 1 when steel cables or steel strands 8 are present than in the case where the steel cables or steel strands 8 are not present. This includes the course of the magnetic field lines 9i.

[0030] In this way, it is achieved overall that the magnetic field lines 92 of the magnetic holding elements 4 not only reach up to an air gap between the magnetic holding elements 4 and the conveyor belt 3, but far beyond this air gap, up to the height H2 as shown in Fig. 3. This then leads overall to the plate-shaped and also magnetizable plates 1 being attracted to the conveyor belt 3 with increased adhesive force and at the same time the air gap between the conveyor belt 3 and the magnetic holding elements 4 or the frame 2 is reduced overall.

[0031] Finally, from the illustration in Fig. 1, it can be seen that the magnetic holding elements 4 are not only arranged within the frame 2, but also the frame 2 and consequently the magnetic conveyor device

[0032] is or can be additionally designed with vacuum units 10. With the aid of these vacuum units 10, the plate-shaped objects 1 can be placed on the conveyor belt 3 in addition to the magnetic holding elements 4. This is particularly advantageous if the plate-shaped objects 1 are not themselves magnetizable.

[0033] In principle, the vacuum units 10 can also have a supporting effect and increase the adhesive force exerted on the plate-shaped objects 1.

Claims

Patent claims:

1. Magnetic conveyor device for transporting plate-shaped objects (1), with a plurality of magnetic holding elements (4) arranged one behind the other in the conveying direction (F), and with at least one conveyor belt (3) running past the magnetic holding elements (4), which is at least partially electrically conductive and thus antistatic, characterized in that the conveyor belt (3) is made of a plastic composite using at least one thermoplastic with electrically conductive particles (6) embedded throughout.

2. Device according to claim 1, characterized in that the conductivity particles (6) are electrically conductive amorphous carbon.

3. Device according to claim 1 or 2, characterized in that the conductivity particles (6) are mixed into a plastic granulate in a grammage of more than 1 wt.% to 20 wt.%, in particular 2 wt.% to 10 wt.% and preferably 3 wt.% to 5 wt.%, in each case based on the total mass.

4. Device according to one of claims 1 to 3, characterized in that the thermoplastic material for producing the conveyor belt (3) is designed as a thermoplastic elastomer, for example polyurethane.

5. Device according to one of claims 1 to 4, characterized in that the conveyor belt (3) is equipped with at least one fabric (7) applied or inserted therein.

6. Device according to claim 5, characterized in that the fabric (7) is also electrically conductive.

7. Device according to claim 5 or 6, characterized in that the fabric (7) is arranged in the region of a surface or upper side of the conveyor belt (3) facing the plate-shaped objects (1).

8. Device according to one of claims 1 to 7, characterized in that the conveyor belt (3) has steel cables or steel strands (8) running in the conveying direction (F).

9. Device according to claim 8, characterized in that the steel cables or steel strands (8) are arranged in the interior of the conveyor belt (3), preferably in the region of a surface or upper side facing the magnetic holding elements (4).

10. Device according to claim 9, characterized in that magnetic field lines (9) of the magnetic holding elements (4) extend beyond an air gap between the magnetic holding elements (4) and the conveyor belt (3).

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