DEVICE FOR DETERMINING THE TEMPERATURE OF A MIXTURE IN A ROTARY MIXER

Description

[0001] The present invention relates to a device for determining the temperature of the mixture in a rotary mixer.

[0002] Determining the temperature of a mixture allows conclusions to be drawn about its condition and thus whether the desired thoroughness of mixing has been achieved or whether further mixing is necessary. Furthermore, continuously recording the mixture temperature during the mixing process is suitable as an in-process control and can quickly identify undesirable deviations during mixing, as well as segregation processes caused by overmixing.

[0003] The literature on the prior art mainly describes measurement techniques that require direct contact between a sensor and the mixture. DE 1 257 113 A discloses a mixer for fine-grained, powdery, liquid, or pasty materials, comprising an upright, cylindrical, sealable mixing vessel and concentrically arranged, high-speed rotating mixing tools within it. Among other things, it aims to determine the continuously increasing actual temperature of the mixture during the mixing process in a particularly simple and suitable manner. It proposes a deflector for the mixture, designed in cross-section as a body tapering in the direction of rotation of the mixing tools, with supply lines for liquids and / or gases and a thermometer.In one practical embodiment, a thermometer probe is arranged within the deflector, protruding from the deflector near its lower end on the side facing the container wall. The probe runs diagonally downwards at an acute angle to the container wall. It extends forward from the deflector in such a way that the rotating and upwardly pressed mixture strikes the probe tip almost perpendicularly. This prevents the mixture from accumulating in dead zones of the probe and thus forming a heat-insulating layer on the probe surface, which would prevent a virtually instantaneous and accurate thermometer reading. The measuring lead of the remote thermometer is routed through the deflector's cavity.

[0004] DE 10 113 451 A1 discloses a bearing housing for a stirring shaft, to which a stirring disc is preferably attached, with a lance that is connected to the bearing housing at one end and has a temperature sensor at the other end, and a lead-in line for the temperature sensor that is guided at least partially through the bearing housing and extends at least partially through the lance to the temperature sensor. Preferably, the lance is provided with a predetermined breaking point. Here, too, the problem arises that part of the temperature measuring device, in this case the lance, is located in the stirring vessel and is therefore exposed to the risk of excessive mechanical forces.

[0005] DE 10 2008 041 104 A1 discloses a mixing device that consists at least partially of an electrically conductive, preferably metallic, material. A heating device, comprising at least one coil excitable by an alternating electric field, is arranged such that eddy currents are generated in the electrically conductive material of the mixing container by the change in the magnetic field resulting from the altered current flow. This allows the mixing container and the material to be mixed to be heated quickly, as the eddy currents heat the container. In a preferred embodiment, at least one scraper device is provided inside the container near the container wall and / or the container bottom, which is movable relative to the container wall. In the simplest case, the scraper device is static, so that the necessary relative movement is generated solely by rotating the container.According to DE 10 2008 041 104 A1, the temperature of the mixture can now be determined by a temperature sensor integrated into the scraper device, as this device is in direct contact with the mixture. Alternatively, the mixture temperature can also be determined using a product-contacting or non-contacting temperature sensor installed separately from the scraper device in the mixing chamber. In either case, the temperature sensor is located within the mixing vessel.

[0006] Another rotary mixer with a moving pyrometric temperature sensor is known from US5951164 A.

[0007] A disadvantage of the current state of the art is that all temperature sensors are currently positioned inside the mixing vessel. At high rotational speeds, such as those that can occur in rotary mixers, these temperature sensors are subjected to high centrifugal forces, and the electronic connection or wiring can lead to high maintenance costs or the frequent replacement of the sensors. Furthermore, measurement inaccuracies can arise if it is not possible to generate a material flow along the sensor, as baked-on material can act as thermal insulation. A non-contact sensor, where the sensor is nevertheless positioned inside the mixing vessel, would absolutely have to be positioned in such a way as to prevent contamination by the mixture. This would require significant design effort and, depending on the mixer, would also necessitate individual adaptations.

[0008] The task therefore is to provide a device that eliminates the aforementioned disadvantages of the prior art and is particularly suitable for rotary mixers, which exhibit a high mechanical load on all components.

[0009] This problem is solved by a rotary mixer according to claim 1 or by a method according to claim 11, in which a rotary mixer according to claim 1 is used. Advantageous embodiments are described in the respective dependent claims.

[0010] A device for determining the temperature of a mixture in a rotary mixer is presented. The device comprises a housing and a mixing container movable to various rotational positions on a circular path. The mixing container has a base and a side wall for receiving the mixture and is designed as a rotating body with an axis of symmetry arranged obliquely to the plane of the circular path and orthogonally to the base. The mixing container is rotatably mounted about the axis of symmetry. In a resting state, the device contains no mixture, while in an operating state, when the mixing container is filled with mixture, it rotates on the circular path. A non-contact radiation detector is fixedly mounted on the housing and directed towards the circular path. The radiation detector is preferably part of a pyrometer that detects infrared radiation.In principle, other detectors can also be used which allow conclusions to be drawn about the temperature of the mixture based on the reflection of electromagnetic radiation and thus operate without contact.

[0011] The core of the radiation detector is preferably a radiation sensor onto which incident radiation is focused, preferably by a suitable lens. The size of the maximum area detected by the radiation detector as a measurement spot on a measurement object, in this case the mixture, depends proportionally to the distance between the radiation detector and the measurement object. Thus, the greater the distance of the radiation detector, and therefore also of the radiation sensor, from the mixture, the larger the area of ​​the measurement spot.

[0012] Naturally, the radiation detector cannot be oriented arbitrarily. To measure the mixture temperature with sufficient accuracy, it must at least be directed along the circular path on which the mixing container moves during operation. However, it is advantageous if, in the resting state, the measurement spot lies entirely within the half of the soil surface inside the mixture container that is furthest from the plane of the circular path, and if, during operation, at least a portion of the mixture is completely within the radiation detector's beam path in one or more rotational positions.It should be noted that, for example, when at rest, the mix, which is distributed across the entire surface of the bottom of the mixing container, is displaced by centrifugal forces towards the upper edge of the container during rotation (i.e., when the device is in operation), thereby covering parts of the bottom and the adjacent container wall. As a rule, the mixing container rotates in the opposite direction to the container's circular motion to prevent the mix from adhering to the container wall. The mixing container is also usually easily replaceable.

[0013] It is particularly preferred if the distance of the radiation detector from the bottom of the mixing container is selected such that the circular measurement spot on the bottom of the mixing container has a diameter no larger than the radius of the bottom. The measurement spot can thus be positioned entirely in the upper half of the bottom.

[0014] Since even a preferably oriented radiation detector without high-precision timing detects not only the temperature of the mixture but also the surrounding area of ​​the mixing vessel, which contains no mixture, it is advantageous for the radiation detector to be connected to a data processing unit. The data processing unit is advantageously configured to record the data units received from the radiation detector, calculate individual temperature values ​​from these data units, and determine the respective maximum of each individual temperature value within predefined time intervals. It is particularly advantageous if local maxima of a series of temperature values ​​can also be output, so that a distinction can be made between the mixture and potentially other temperature peaks that might be caused, for example, by malfunctions of the rotary mixer.An emergency shutdown or warning device can also be linked to reaching a specific threshold value.

[0015] Finally, it is advantageous and usually essential that the data processing unit is configured to calculate the individual temperature values ​​based on the emissivity of the mixture. Since in many applications only minor differences occur in the material being mixed, resetting the emissivity is only necessary when there is a fundamental change in the mixture.

[0016] In mixing processes requiring a vacuum relative to normal pressure, the radiation detector can be permanently mounted on or inside the housing so that it is located together with the temperature detector in a sealed compartment. This compartment can be sealed to create a uniform vacuum relative to normal pressure, ensuring that both the mixture and the radiation detector are equally affected. This has the advantage that no lid is required between the mixture and the radiation detector, which would also affect the measurement if the lid were transparent. For mixing processes that absolutely require a cover—in practice, usually a lid that seals the mixing container—a germanium disc can be integrated into the lid. This disc is positioned within the radiation detector's beam path in at least one rotational position of the mixing container. Germanium discs can be designed so that they do not interfere with the measurement.

[0017] A method that utilizes the proposed device for temperature determination comprises the following steps: i) Filling the mixing container with the mixture and positioning the mixture in the beam path of the radiation detector, followed by determining the temperature of the mixture at rest as T0 using the data processing unit; ii) bringing the device into operating mode with a rotational speed of the mixing container on a circular path of more than a predetermined number of revolutions per minute (rpm); iii) taking spot measurements of the mixture temperature at regular time intervals; iv) determining the maximum measured mixture temperature after a predetermined number of revolutions. This method also allows for recording how quickly the temperature rises in mixtures with a high friction content, and the rotation speed, or even cooling, can be adjusted accordingly to optimize the mixing process. For this purpose, it is advantageous to determine temperature maxima after a specific number of rotations of the mixing container on its circular path, plot them as a graph, and analyze the data.

[0018] It is important that the temperature measurement using the radiation detector is performed at specific points, so that there is a measurement-free interval between individual measurements. During this measurement-free interval, i.e., the time interval between individual measurements, the mixing container continues to rotate and covers a certain distance depending on its rotational speed, which is usually specified in revolutions per minute (rpm). To achieve good measurement accuracy, it is therefore advantageous if the distance traveled during the time interval is no greater than the radius of the bottom of the mixing container, in order to ensure a high probability that a measurement takes place when the device is in its operating state, in which the measuring point is exclusively measuring the mixing material.The value of the time interval between the point measurements, specified in milliseconds, should therefore preferably not be greater than the quotient of the radius of the ground of the mix pickup and 1 / 60,000th of the rotational speed (rpm) multiplied by the circumference of the circular path.

[0019] The device presented below is explained by way of example using the drawing, without being limited to this example. Legend:

[0020] 1 Device for temperature determination 2 Rotary mixer 3 Housing 4 Radiation detector 5 Radiation sensor 6 Pyrometer 7 Base 8 Side wall 9 Mixing material intake 10 Mixing container 11 Axis of symmetry 12 Base radius 13 Mixing material 14 Circular path 15 Plane of the circular path 16 Main axis of rotation 17 Beam path 18 Measurement spot 19 Lid 20 Germanium disk

[0021] Fig. 1Figure 1 shows a cross-sectional section of a rotary mixer (2) comprising a temperature determination device (1) consisting of a stationary housing (3) and a radiation detector (4) with a radiation sensor (5) as part of a pyrometer (6), as well as a mixing container (10) having a base (7), a side wall (8), and an easily replaceable mixing material receptacle (9). The mixing container (10) is movable about a principal axis of rotation (16) into different rotational positions on a circular path (14) that passes through the intersection of the center of the beam path (17) with the base (7) and is shown here as a point. The mixing container (10) is designed as a solid of revolution whose axis of symmetry (11) is arranged orthogonally to the base (7) and obliquely to the plane (15) of the circular path (14).The radiation detector (4) is arranged on the stationary housing (3) such that the beam path (17) of the pyrometer (6) is directed onto the circular path (14). The device (1) is shown here in its operating state (A), in which the mixing container (10) rotates on the circular path (14) and the material receptacle (9) is filled with material (13), which is displaced towards the upper half of the material receptacle (9) due to the centrifugal forces resulting from the rotation of the mixing container (10) about the main axis of rotation (16). In the rotational position of the mixing container (10) shown, the measuring spot (18) is located entirely on the material (13) and, in the rest state (R) (not shown here), i.e., in the absence of the material (13), would strike the upper half of the bottom (7) of the material receptacle (9). This is possible because the diameter of the circular measurement spot (18) is smaller than the radius of the ground (7).The optional lid (19) is also shown, which closes the mixing container (9) and thus effectively prevents the escape of, for example, finely powdered substances. The beam path (17) is oriented such that, in at least one rotational position of the mixing container (10), it passes completely through the germanium disk (20) integrated into the lid (19).

Claims

1. A rotary mixer (2), comprising: a device (1) for determining a temperature of a mixed material (13) in said rotary mixer (2); a stationary housing (3); a mixing container (10) that can be moved on a circular path (14) into different rotational positions about a main axis of rotation (16), the mixing container having a mixied material receptacle (9) with a bottom (7) and a side wall (8), wherein the mixed material receptacle (9) is in form of a solid of revolution with an axis of symmetry (11) arranged obliquely to a plane (15) of the circular path (14) and orthogonally to the bottom (7); and wherein the mixing container (10) is rotably mounted about the axis of symmetry (11) and wherein the mixing container (10) in an idle state (R) has no mixed material (13) and in an operating state (A) the mixing container (10) filled with mixed material (13) rotates on the circular path (14) characterized in that a non-contact measuring radiation detector (4) is arranged in a stationary manner on the housing (3) and is directed towards the circular path (14).

2. The rotary mixer (2) according to claim 1, characterized in that the radiation detector (4) has a radiation sensor (5) on which incident radiation is focused, and the extent of the maximum area detected by the radiation detector (4) as a measuring spot (18) on the mixed material (13) is proportionally dependent on the distance between the radiation detector (4) and the mixed material (13).

3. The rotary mixer (2) according to one of the preceding claims, characterized in that the measuring spot (18) in the idle state (R) is completely in the upper half of the surface of the bottom (7) within the mixed material receptacle (9) and in the operating state (A) at least part of the mixed material (13) is completely introduced into the beam path (17) of the radiation detector (4) in one or more rotational positions.

4. The rotary mixer (2) according to claim 3, characterized in that the measuring spot (18) is circular and has a diameter that is not larger than the radius of the bottom (7) of the mixed material receptacle (9).

5. The rotary mixer (2) according to one of the preceding claims, characterized in that the radiation detector (4) is connected to a data processing unit.

6. The rotary mixer (2) according to one of the preceding claims, characterized in that the radiation detector (4) is part of a pyrometer (6).

7. The rotary mixer (2) according to one of the preceding claims, characterized in that the data processing unit is set up to record the data units received by the radiation detector (4), to calculate individual temperature values from the data units and to determine the respective maximum of the individual temperature values in predetermined time periods.

8. The rotary mixer (2) according to claim 7, characterized in that the data processing unit is configured to calculate the individual temperature values by specifying the emissivity of the mixed material (13).

9. The rotary mixer (2) according to one of the preceding claims, characterized in that the mixing container (10) has a closable lid (19), in which a germanium disk (20) is installed, which is positioned in at least one rotational position of the mixing container (10) in the beam path (17) of the radiation detector (4) and is so designed that it has no influence on the measurement using the radiation detector (4).

10. The rotary mixer (2) according to one of the preceding claims, characterized in that the mixed material (13) and the radiation detector (4) are arranged in a space which can be sealed in such a way that a uniform negative pressure compared to normal pressure can be generated therein, to which the mixed material (13) and the radiation detector (4) are equally exposed.

11. Method for determining temperature using a rotary mixer (2) according to one of claims 1 to 10, characterized by the following steps: i) filling the mixing container (10) with the mixed material (13) and positioning the mixed material (13) in the beam path (17) of the radiation detector (4) with subsequent determination of the temperature of the mixed material (13) at rest as T0 using the data processing unit; ii) transferring the rotary mixer (2) into the operating state (A) with a speed of rotation of the mixing container (10) on the circular path (14) of more than a predetermined number of revolutions per minute (rpm); iii) selective measurements of the mixed material temperature at regular time intervals; iv) determination of the maximum measured mixed material temperature after a predetermined number of revolutions.

12. Method according to claim 11, characterized by the following additional step: v) Repeated determination of the maximum measured mixed material temperature after a predetermined number of revolutions.

13. Method according to claim 11 or 12, characterized by the recording of the specific temperature maxima as a graph.

14. Method according to one of claims 11 to 13, characterized in that the value of the time interval between the point measurements specified in milliseconds is not greater than the quotient of the radius of the bottom (12) of the mixed material receptacle (9) and a 60,000th of the speed (rpm) multiplied by the circumference of the circular path (14).