EP2322013B1 - Mixing device having induction heating - Google Patents

Abstract

The present invention concerns a mixing device having a preferably rotating container for accommodating material to be mixed, at least one mixing tool arranged in the interior of the container and a heating device for heating the material to be mixed. To provide a mixing device of the kind set forth in the opening part of this specification which permits the fastest possible heating of the material to be mixed, preferably also to temperatures higher than 200° C., it is proposed in accordance with the invention that the container at least partially comprises an electrically conductive material and the heating device has at least one coil which can be excited by an electric alternating field and which is so arranged that eddy currents are produced in the electrically conductive material of the container by the magnetic field change which occurs when the current flow changes.

Description

The present invention relates to a mixing device with a container for receiving mixed material, a mixing tool arranged in the interior of the container and a heating device for heating the mixed material.

The mixing, i. The combination of at least two starting materials with different properties into a mixture of substances is a fundamental operation in mechanical engineering.

With the help of a mixing device the highest possible homogeneity of the new substance should be achieved. In order to achieve the desired homogeneity, mixing devices with a rotating mixing container are used, for example.

In these at least one mixing tool is arranged eccentrically in the interior of the container in the rule. If the container rotates, the mixed material received in the container is transported to the mixing tool and mixed with the aid of the mixing tool. With such mixers materials of any type and consistency can be processed quickly and in high quality.

Experience has shown that a mixer with rotating container mixes without noticeable segregation, since a complete circulation of material is achieved during one revolution of the mixing container.

Since some mixing processes are associated with a chemical reaction, which requires the supply of a certain activation energy, it is already common for some applications to heat the mix during mixing. This is also necessary if a thermal fluid removal should take place superimposed during the mixing process.

In order to allow heating of the mix in the mixer, therefore, some mixing device on a heating jacket, which surrounds the container wall and is in contact therewith. Heat energy can then be supplied to the mixing container via the heating jacket. The heating jacket is depending on the heat transfer medium either as a double jacket for hot water or Thermal oil heating or at higher design pressures for steam heating as a wart jacket or with welded-on half pipes. The known solutions are limited in terms of their maximum wall temperature by the maximum allowable temperature of the heat transfer medium or steam heating by the necessary compressive strength of the double jacket.

Furthermore, it is not possible with these solutions to realize fast heating curves up to very high wall temperatures, since the heating rate is limited by the heat transfer coefficient of the liquid or the vapor phase to the container wall and the pressure losses and thus the flow rate of the heat transfer medium in the heating mantle.

It is therefore against the background of the described prior art, the object of the present invention to provide a mixing device of the type mentioned, which allows the fastest possible heating of the mixed material, preferably also to temperatures greater than 200 ° C.

According to the invention, this object is achieved in that the container consists at least partially of an electrically conductive, preferably metallic material and the heater has at least one stimulable with an alternating electric field coil, which is arranged such that by the resulting change in current flow magnetic field change in the electrically conductive Material of the container eddy currents are generated. These eddy currents ensure heating of the container. This inductive heating of the container allows a targeted and direct heating of the container and thus the mixed material, without first a heat transfer medium must be heated. In addition, the achievable temperature increase is limited only by the performance of the coil and not by the chemical-physical properties of the heat transfer medium.

In a preferred embodiment, at least one stripping device, which is movable relative to the container wall, is provided in the interior of the container in the vicinity of the container wall and / or the container bottom. In the simplest case, the stripping device is static, so that the necessary relative movement is generated only by the rotation of the container.

The stripping device ensures a continuous vertical component of the mixed material flow and prevents buildup or caking on the container wall and / or bottom. In addition, with a concentric emptying opening in the mixing container bottom, the emptying process is accelerated at the end of the mixing time.

In a further, particularly preferred embodiment, the stripping device has a temperature sensor for detecting the temperature of the mixed material. The stripping device has proven to be particularly suitable to receive a temperature sensor to detect the temperature of the mix since the scraper is in direct contact with the mix. Alternatively, the mixing product temperature determination can also be effected via a product-contacting or non-contact temperature sensor introduced separately from the stripping apparatus into the mixing chamber.

In a further preferred embodiment it is provided that at least two separately controllable heating devices are present, wherein preferably both heaters each have at least one excitable with an alternating electric field coil, which is arranged such that by the change in current flow resulting magnetic field change in the electrically conductive material the container eddy currents are generated.

In order to ensure the most uniform possible heating of the mixed material or to adjust the heat output according to the heat flows in the mix, it may be advantageous for some applications if several separately controllable heating devices are provided, for example, one or more of the heaters for heating the container bottom and one or more further heating devices are designed for heating the container wall. In addition, heating device for heating the mixing tool and / or the stripping device could also be provided.

In this case, the power of the heating device designed for heating the container wall can be the same size but also larger or smaller than the output of the heating device designed for heating the container bottom. The power distribution between the wall and the floor preferably corresponds approximately to the area ratio between the preferably cylindrical wall surface to be directly heated and the surface to be heated directly, preferably the annular surface or the circular surface of the container bottom. In a particularly preferred embodiment, the power distribution to the effective heat transfer surface is similar to the mix inside the container. In a vertical mixing mixing vessel, the bottom surface is usually almost completely covered with material. The heat flow thus takes place over the entire heated floor area. In a comparison with the horizontal inclined mixing container with a stationary stripping device depending on the arrangement of the stripping up to about 10-20% of the bottom surface can not be directly applied with product. In the areas that are not directly exposed to product, there is thus a significantly lower heat flow resulting from the heat loss due to radiation and convection at this point. The same applies to the wall surfaces, wherein, in addition, the material filling directly touches only a portion of the heated wall surface in the stationary state, which is stationary relative to the container wall. while the part of the heated wall surface located above it is in contact with the mix to be thrown from the mixer to the wall and is used for heat transfer. For example, with a surface area ratio of 3: 1, a heating power distribution of at least 1: 1, preferably at least 1.5: 1 and very particularly preferably at least 2: 1, is advantageous.

Advantageously, the container is rotationally symmetrical, wherein it is provided in a preferred embodiment that the heating device is arranged to heat the container bottom such that an outer annular portion of the container bottom is not substantially heated by the heater, wherein the annular portion preferably has a width which is greater than 5% and more preferably greater than 10% of the container diameter.

In other words, the stimulable coil is arranged parallel to the container bottom, but not with respect to the described annular portion. This ensures that there is no overheating of the container in the area of the container corner, when at the same time the container wall is heated with a second heater and concentrate the field lines of the two coils in the corner of the container.

Alternatively or in combination, the heating means for heating the container bottom may be arranged so that an inner circular portion of the container bottom is not substantially heated by the heating device, the circular portion preferably having a diameter greater than 30%, more preferably greater than 50% of the container diameter is.

In other words, the stimulable coil is disposed in a plane substantially parallel to the container bottom, however, an inner circular portion and an outer annular portion having no coil windings to ensure that neither container corner nor the center of the container bottom are heated directly. In general, there is a corresponding drive for the container in the center of the container bottom. Since the drive or greases used therein are often sensitive to heat, this area is excluded in the dimensioning of the heater for the container bottom. In a particularly preferred embodiment, the drive region is additionally shielded from the electromagnetic alternating field of the coil.

In an alternative embodiment, alternatively or in combination, a container closure could be inductively heated. Similarly, the heater can be used for heating the container wall may be arranged so that a lower cylinder jacket-shaped portion of the container wall is not substantially heated by the heater, wherein the lower cylinder jacket-shaped portion preferably has a height which is greater than 5%, more preferably greater than 10% of the container wall height. By this arrangement, the excessive heating of the container corner is avoided by field overlay with simultaneous arrangement of a heater on the container bottom.

Furthermore, the heating device for heating the container wall may be arranged such that an upper cylinder jacket-shaped portion of the container wall is not substantially heated by the heater, wherein the upper cylinder jacket-shaped portion preferably has a height which is greater than 10%, more preferably greater than 20% of Container wall height is. Often, the mixing container is not completely filled with mix so that is prevented by the action described that the part of the container wall that is not in contact with the mix is heated directly.

In a further embodiment, the upper cylinder jacket-shaped portion of the container wall can be made of an electrically non-conductive material and / or a material with very low thermal conductivity.

In a further particularly preferred embodiment it is provided that between the container outside on the one hand and stimulable coil of the at least one heater on the other hand an electrically non-conductive, preferably non-metallic insulation element, which is preferably attached to the container outside, is present. The insulation element is best glued to the container outside. This insulating element serves to reduce the heat emission of the container to the environment. This saves energy and reduces the expenses for protection against contact.

The windings of the coil for the heating device associated with the container bottom may for example be arranged in the vicinity of the outside of the container bottom and run spirally around the axis of rotation of the container. This arrangement ensures a uniform heating of the container bottom. Alternatively, the windings may also be arranged only in a circular segment. Since the container rotates relative to the windings, then the entire container bottom is heated. Although this arrangement leads to a less uniform heating of the container bottom, but it can be easily retrofitted to existing mixing devices. Here, the center angle of the circular segment is preferably less than 180 ° and more preferably less than 90 ° and most preferably less than 45 °.

Likewise, the windings of the coil, the heater associated with the container wall can be arranged in the vicinity of the container wall and extend substantially concentrically around the container wall, so that substantially the entire container wall, with the exception of the free upper and lower wall portions, can be heated.

Again, alternatively, the windings may also be arranged only in the region of a container wall section. The rotation of the container ensures that the entire wall can be heated. This arrangement can be retrofitted to existing mixing devices more easily.

In addition to the possibility alone to provide the wall or alone the bottom of the mixing container with a heating element, for example, a substantially L-shaped heating element could be provided, in each of which a coil is arranged in the two L-legs. This L-shaped heating element is arranged with a leg parallel to the container wall and with the other leg parallel to the container bottom.

For some applications, it may be advantageous if at least one temperature sensor is provided for measuring the container bottom temperature, wherein the temperature sensor is preferably an infrared sensor and detects the temperature on the outside of the container bottom.

Furthermore, at least one temperature sensor may be provided for measuring the container wall, wherein here too the temperature sensor is preferably an infrared sensor and detects the temperature on the outside of the container wall. In the case of the use of infrared sensors, the insulation may have recesses, so that with the aid of the infrared sensors, the temperature of the container bottom and / or the container wall can be detected directly.

In principle, it is possible to set the temperature of the container bottom with the aid of the heating device for the container bottom with the aid of the corresponding temperature sensor very accurately. In the same way, the temperature of the container wall can be regulated accordingly. In order to minimize deformations of the container due to the thermal expansion, the control is preferably carried out such that the temperature difference between the container bottom on the one hand and the container wall on the other hand is as small as possible.

Figur 1

eine erste Ausführungsform der Erfindung,

Figur 2

eine zweite Ausführungsform der Erfindung,

Figur 3

eine dritte Ausführungsform der Erfindung und

Figur 4

eine vierte Ausführungsform der Erfindung.

In a preferred embodiment, the stimulable coil is at least partially shielded towards the outside. This shielding is preferably carried out by means of a ferrite shield. Further advantages, features and possible applications of the present invention will become apparent from the following description of preferred embodiments and the accompanying figures. Show it:

FIG. 1

a first embodiment of the invention,

FIG. 2

a second embodiment of the invention,

FIG. 3

a third embodiment of the invention and

FIG. 4

A fourth embodiment of the invention.

In FIG. 1 a first embodiment of the mixer 1 according to the invention is shown. The mixer 1 has a container 2 and a mixing tool 3 arranged in the container 2, which can be driven by means of a motor 4. The mixing tool 3 is arranged asymmetrically in the container 2.

The container 2 is arranged within a housing 7 with a housing cover 6. Also visible is a scraper 5, which is attached to the housing cover 6.

The container 2 is for example made of metallic material and surrounded by an insulating layer 8. In the housing 7 and substantially parallel to the container bottom and the container wall two coils 9 and 10 are arranged, which can be impressed via the leads 11 and 12 of the power supply 13, an AC voltage. In addition, corresponding cooling media for heat dissipation of the power loss in the coil can be transported via the same or separately designed supply lines. The transmitted over the supply AC voltage ensures that eddy currents are generated in the container 2, which in turn lead to heating of the container. Both coils 9, 10 are shielded at least to the outside, preferably also towards the edges by means of a ferrite shield 14. This ferrite shield 14 serves to avoid possible eddy current generation and thus heating outside the container.

The heating device 9 associated with the container wall does not extend over the entire container height. An upper portion of the container wall, which is generally not charged with mix, is not heated. In the same way, the heating device 9 does not extend to the container corner in order to avoid excessive heating of the container in the corner.

The heater 10 for the container bottom is also not executed to the corner. In addition, a circular central area of the container, over which the container is generally driven, is not heated. A first temperature sensor 15 is provided on the scraper 5 in order to determine the temperature of the mixed material. Furthermore, infrared temperature sensors are in the range the container wall and arranged in the region of the container bottom. In order to enable an exact temperature determination, the insulation 8 has corresponding recesses.

In FIG. 2 a second embodiment of the mixing device according to the invention is shown.

This embodiment differs from that in FIG FIG. 1 shown embodiment only in that for heating the container wall two heaters 9 ', 9 "are provided, both of which can be controlled separately from each other via the connections 12', 12" of the power supply 13.

Accordingly, two temperature sensors 17 'and 17 "are also provided for detecting the container wall temperature at two different positions. <br/> <br/> With this arrangement, the heating outputs can be individually adjusted via the height of the wall to the heat output transmitted inside the container.

In FIG. 3 a third embodiment of the mixer according to the invention is shown. It can be seen here that the mixer can be tilted about a horizontal axis. For emptying the mixer, therefore, the housing cover 6 is first tilted out of the container together with the mixing tool 3 and the stripping device 5. Then the container is tilted together with mix to the side, so that the mix is transferred in a provided for this purpose car 18. The L-shaped heater consists in the case shown only of a coil, so that the wall and the bottom of the mixing container are not individually adjustable. A fixed, non-controllable power distribution between wall and floor can be realized for example via a different number of windings of the coil in wall and floor. Also, the corner areas between wall and floor can be substantially excluded from the direct heating, in which the corner area is recessed by the windings accordingly. This represents a particularly cost-effective embodiment of the invention.

In FIG. 4 a fourth embodiment of the invention is shown. Unlike in the FIGS. 1 and 2 In this embodiment, the coils extend around the entire container or over the entire bottom surface. This embodiment produces the most uniform heating of the container 2. For most applications, however, the arrangement according to the embodiments 1 and 2 is sufficient, especially since this can be retrofitted in existing mixing devices.

LIST OF REFERENCE NUMBERS

1

mixer

2

container

3

mixing tool

4

engine

5

scraper

6

housing cover

7

casing

8th

damp course

9, 9 ', 9 "

Coil / heater

10

Coil / heater

11

supply

12, 12 ', 12 "

supply

13

power supply

14

ferrite shield

15

temperature sensor

16

infrared sensor

17, 17 ', 17 "

infrared sensor

18

dare

Claims (15)

1. A mixing device (1) having a preferably rotating container (2) for accommodating material to be mixed, at least one mixing tool (3) arranged in the interior of the container (2) and a heating device (9, 10) for heating the material to be mixed, characterised in that the container (2) at least partially comprises an electrically conductive material and the heating device (9, 10) has at least one coil (9, 10) which can be excited by an electric alternating field and which is so arranged that eddy currents are produced in the electrically conductive material of the container (2) by the magnetic field change which occurs when the current flow changes.
2. A mixing device (1) according to claim 1 characterised in that provided in the interior of the container (2) in the proximity of the container wall and/or the container bottom is at least one preferably static stripping device (5) which is movable relative to the container wall.
3. A mixing device (1) according to claim 1 or claim 2 characterised in that provided in the interior of the container (2) is a temperature sensor (15) for determining the temperature of the material to be mixed, wherein the temperature sensor (15) is preferably arranged at or in the stripping device (5).
4. A mixing device (1) according to one of claims 1 to 3 characterised in that there are provided at least two separately regulatable heating devices (9, 10), wherein preferably both heating devices (9, 10) respectively have at least one coil (9, 10) which can be excited by an electric alternating field and which are so arranged that eddy currents are produced in the electrically conductive material of the container (2) by the magnetic field change which occurs when the current flow changes wherein especially preferred that at least one of the heating devices (10) is designed to heat the container bottom and at least one further heating device (9) is designed to heat the container wall.
5. A mixing device (1) according to claim 4 characterised in that the ratio of the power of the heating device (9) designed to heat the container wall to the power of the heating device (10) designed to heat the container bottom approximately corresponds to the surface area ratio of the heated wall surface and the heated bottom surface and/or that the container (2) is rotationally symmetrical and the heating device (10) for heating the container bottom is so arranged that an outer portion of the container bottom, in the form of a circular ring, is not substantially heated by the heating device (10), wherein the portion in the form of a circular ring is preferably of a width greater than 5 % of the container diameter.
6. A mixing device (1) according to one of claims 4 to 5 characterised in that the container (2) is rotationally symmetrical and the heating device (10) for heating the container bottom is so arranged that an inner circular portion of the container bottom is not substantially heated by the heating device (10), wherein the circular portion is preferably of a diameter greater than 30 %, particularly preferably than 50 % of the container diameter.
7. A mixing device (1) according to one of claims 4 to 6 characterised in that the container (2) is rotationally symmetrical and the heating device (9) for heating the container wall is so arranged that a lower portion of the container wall, in the form of a cylindrical surface, is not substantially heated by the heating device (9), wherein the lower portion in the form of a cylindrical surface is preferably of a height greater than 5 %, particularly preferably greater than 10 %, of the container wall height.
8. A mixing device according to one of claims 4 to 7 characterised in that the container (2) is rotationally symmetrical and the heating device (9) for heating the container wall is so arranged that an upper portion of the container wall, in the form of a cylindrical surface, is not substantially heated by the heating device (9), wherein the upper portion in the form of a cylindrical surface is preferably of a height greater than 10 %, particularly preferably greater than 20 %, of the container wall height.
9. A mixing device (1) according to one of claims 1 to 8 characterised in that the upper portion of the container wall, in the form of a cylindrical surface, is made of an electrically non-conductive material and/or a material of very low thermal conductivity and/or provided between the outside of the container on the one hand and the excitable coil of the at least one heating device (9, 10) is a non-metallic insulating element which is preferably secured to the outside of the container, more specifically best by way of a non-releasable connection.
10. A mixing device (1) according to one of claims 1 to 9 characterised in that an excitable coil is arranged in the proximity of the outside of the container bottom and has a plurality of windings which extend substantially in a spiral around the axis of rotation of the container (2).
11. A mixing device (1) according to one of claims 1 to 10 characterised in that an excitable coil is arranged in the proximity of the outside of the container bottom and has a plurality of windings which extend substantially completely around the container wall.
12. A mixing device (1) according to one of claims 1 to 111 characterised in that there is provided a temperature sensor (16) for measuring the container bottom temperature, wherein the temperature sensor (16) is preferably an infrared sensor.
13. A mixing device (1) according to one of claims 1 to 12 characterised in that there is provided a temperature sensor (17) for measuring the container wall, wherein the temperature sensor (17) is preferably an infrared sensor.
14. A mixing device (1) according to one of claims 1 to 13 characterised in that there is provided a substantially L-shaped heating element having a limb which is preferably substantially in the shape of a cylinder portion, wherein the L-shaped heating element covers less than 180°, particularly preferably less than 90° and best less than 45° of the container wall.
15. A mixing device (1) according to one of claims 1 to 14 characterised in that the excitable coil is at least partially shielded outwardly, preferably by means of a ferrite shielding (14).

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