DEVICE FOR DETERMINING THE THICKNESS OF AN OBJECT

Description

[0001] The invention relates to a device for determining the thickness of an object, in particular a strip-shaped or plate-shaped object, preferably for use in a hot rolling process, with a frame having an upper and a lower leg, wherein each leg has a sensor for contactless distance measurement to the object, wherein each leg has a structure made up of several layers to reduce the temperature effect on the frame and / or the sensor, wherein a first layer has a base frame element or is formed by such a base frame element, wherein a second layer is formed by a casing surrounding the base frame element and wherein a cooling device having a fan is arranged in the base frame element.

[0002] Such devices are known in practice and exist in various designs. Such frames are designed, for example, as so-called C-shaped frames or measuring frames, which have two legs coupled by a connecting piece, between which an object to be measured or a measurement object is to be inserted for the measurement. In this case, corresponding sensors for measuring a distance are often attached to both legs.

[0003] When measuring the thickness of moving or stationary, strip-shaped or plate-shaped materials, measuring systems are often used in which distance sensors are mounted in a C-shaped measuring frame. A distance sensor above and below the strip-shaped or plate-shaped measuring object measures the distance from the respective sensor to the surface of the object. The thickness of the object can be determined from the known distance between the sensors. The problem here, however, is that the distance between the sensors can change due to external influences such as changes in temperature. When the temperature changes, the frame construction can expand or deform due to the material's own thermal expansion coefficient, which leads to a change in the relative position of the sensors and thus to measurement errors in the thickness measurement.Furthermore, temperatures that occur unevenly - both temporally and spatially - can lead to stresses in the frame construction due to the different temperature expansion, which can also affect the measurement.

[0004] There are various concepts regarding design and material composition that are intended to enable stable measurement values ​​to be delivered with a suitable device, for example, a C-frame, despite temperature changes in the environment and / or target or object. Conventional solutions are generally suitable for applications with relatively stable environmental conditions.

[0005] According to the prior art, for example, DE 20 2014 001 175 U1 discloses a corresponding device for determining the thickness of an object in the form of moving, strip-shaped and plate-shaped materials. This device is preferably used in cold rolling and has the essential features of the preamble of claim 1. According to this prior art, the legs of a C-frame are wrapped with copper tubes through which fluid flows in a closed circuit - without cooling or heating. The aim of this arrangement is to prevent uneven temperature changes in the C-frame. The effect of temperature changes is to be determined and compensated for using strain gauges. In cold rolling, the material is not heated before rolling.Only due to the introduced forming energy does the material heat up slightly as it passes through the rolling mill, whereby this heating depends on ambient conditions and possible cooling.

[0006] This design does not offer a solution for dealing with the heat stress occurring in the hot rolling area, as temperatures of up to 1200°C are reached during hot rolling.

[0007] In the case of significant fluctuations in ambient temperature and thermal radiation, such known solutions have the disadvantage that relatively large amounts of energy are added or removed at specific points through the fluid circuit - in conjunction with heat conduction from the measuring leg to the copper pipe. This gives rise to numerous problems, such as rapid changes in the distance between the sensors caused by localized thermal expansion, while distortion can also occur due to temperature differences between the coolant supply and return lines and the resulting temperature differences on the frame. In the known device, this contradicts the desired inert system, which should be characterized by changes in ambient conditions affecting the distance between the sensors only slowly so that no errors relevant to measurement accuracy occur between two possible calibration or zeroing cycles.

[0008] In C-frames for hot rolling, the connection length between the two sensors – one per material side – along the frame is usually several meters. This connection length consists of the length of the upper and lower legs of the C-frame and the connecting piece between the legs, which essentially defines the measuring distance of the sensors. A uniform temperature change essentially results in a change in length in the area of ​​the connecting piece, whereby this change in length directly influences the thickness measurement. Since the change in length of the legs is approximately identical and perpendicular to the measuring axis, this influence on the thickness measurement can be neglected.

[0009] If there is a lateral offset of the sensors due to different lengths of the upper and lower legs, the measuring points of the sensors are no longer directly opposite each other, which leads to errors in the thickness measurement, especially if the measuring object or object is tilted.

[0010] In practice, different temperature changes within a leg—on the side facing the other leg and on the side facing away from it—have a serious impact. This results in distortion comparable to the distortion of bimetal when heated, which directly results in measurement errors.

[0011] In practice, however, the temperature input to the C-frame is not uniform. This is due, on the one hand, to the high loads caused by heat radiation from the target during hot rolling, with heat radiation from red-hot steel estimated at approximately 170 kW / m², and, on the other hand, to the resulting heat convection that occurs in this environment. Even a frame made of a material with a particularly low coefficient of thermal expansion, such as Invar®, would have far too large a temperature drift to allow for precise thickness measurement.

[0012] Furthermore, a device for determining the thickness of an object is known from JP H07 83635 A. This document shows a radiation protection device for a frame and not a flow guide for a fluid.

[0013] Furthermore, a heat-insulating glass that is permeable to sensor signals is known from CN 104 264 555 A.

[0014] Furthermore, CN 1 958 184 A shows a device for determining the thickness of an object, wherein different cooling systems for a frame are disclosed.

[0015] The present invention is therefore based on the object of specifying a device of the type mentioned at the outset, according to which a reliable measurement of the thickness of an object is possible even in an environment with high temperatures using structurally simple and cost-effective means.

[0016] According to the invention, the above object is achieved by a device having the features of claim 1. The device according to the invention is designed and developed in such a way that the fan can generate an air flow that flows in the space between the base frame element and the casing.

[0017] In this device, the legs are constructed in multiple layers, preferably in multiple stages, to enable a reduction in temperature effects on the frame and / or the sensor at particularly high and / or low temperatures and / or during significant temperature changes during a measurement. Each layer can individually reduce the temperature effects on the frame and / or the sensor, for example, by dissipating heat or protecting against thermal radiation. The device can be used to protect the sensor or multiple sensors from temperature effects caused, for example, by excessively high or very high ambient temperatures.Secondly, to achieve particularly reliable measurements with high accuracy in thickness measurement, it is crucial that the frame is also protected, for example, with a base frame element and, if necessary, connecting pieces between the legs, thus ensuring a connection between the sensors. This is also achieved through the layered structure of the legs. Ultimately, measurement errors arise from the fact that the structure of the device, including the frame and its components, bends due to temperature. Such a multi-layered structure can be implemented cost-effectively.

[0018] In an advantageous embodiment of the device, the base frame element is designed as a hollow body. This first layer forms a secure and stable basic structure for the device.

[0019] In a further advantageous manner, the sensor can be assigned to the base frame element or arranged in the base frame element. In particular, when the sensor is arranged in the base frame element, the base frame element provides shielding of the sensor from external temperature influences.

[0020] A cooling device, which can be designed as an active or passive cooling device, is arranged in the base frame element. The cooling device can be arranged in a connecting piece of the base frame element, for example, in a C-shaped frame configuration. This provides a secure and protected arrangement of the cooling device, while also providing a particularly compact design of the device.

[0021] To ensure a particularly reliable cooling effect, the cooling device can have a cooling register filled with a cooling medium. The cooling register serves to cool and / or temper a cooling fluid, such as ambient air. Particularly in the case of such a cooling device, the base frame element can be permeable to ambient air. In this case, tempered air can be flowed through the base frame element to the sensor by means of the cooling device and the cooling medium in order to achieve a corresponding cooling effect or tempering of the sensor.

[0022] The air flow can be particularly advantageously realized by means of a forward flow from the cooling device to the sensor and a return flow from the sensor to the cooling device. This allows a preferably closed air circuit to be realized.

[0023] In a further advantageous embodiment of the device according to the invention, the second layer can have a substantially closed casing for the first layer or can be formed by such a casing. This second layer enclosing the first layer essentially forms a protective shield for the first layer against external temperature influences. Thermal radiation can be substantially blocked from the first layer by the second layer. Furthermore, the structure comprising a first layer and a second layer enclosing the first layer can form a flow channel for a fluid flow, preferably in conjunction with a cooling device. The return flow or the forward flow, for example to or from a cooling device, can be realized between the casing and the base frame element.A corresponding flow channel can be formed by a gap or space between the first layer and the second layer.

[0024] In a further advantageous manner, the jacket can be constructed from several segments, wherein the individual segments are preferably coupled by means of elastic membranes, which preferably connect the individual segments to one another in an airtight manner and can absorb and compensate for changes in length occurring due to temperature expansion.

[0025] In addition to the first and / or second layer, a further layer can be provided, which has a radiation protection device, preferably a radiation protection plate, for the first or second layer or is formed by such a radiation protection device. Such a further layer can particularly advantageously form a further stage for reducing external temperature influences on the sensor.

[0026] To reliably compensate for or accommodate temperature-related changes in length or expansion of the individual layers, the additional layer can be mounted on the first layer or on the second layer, preferably by means of a guide, in particular a slotted guide, so that it can be moved or displaced relative to the first layer or the second layer. The additional layer can be mounted on the first layer if no second layer is present.

[0027] In a further advantageous manner, the casing and / or the radiation protection device can be formed from a preferably polished and / or shiny metal. This enables particularly reliable reflection of thermal radiation impinging on the casing or the radiation protection device, with a corresponding protective effect for the sensor. Particularly advantageously, a material with a low emissivity can be provided as the material of the casing and / or the radiation protection device. Such a material reflects impinging thermal radiation very efficiently.

[0028] To ensure reliable measurement, the first layer and / or the second layer and / or the further layer can have a passage for sensor signals to and / or from the object, preferably sealed with glass or heat-insulating glass. This ensures that, for example, optical sensor signals can pass unhindered through the implemented layers between the sensor and the object.

[0029] To further reduce temperature effects on the frame and / or the sensor, a space through which a predefined fluid, preferably ambient air, can flow can be formed between the second layer and the further layer to create a fluid layer. Such a fluid layer provides reliable thermal insulation between the respective layers, since ambient air, in particular, has a highly insulating effect. Suitable insulating gases can also be used as the fluid.

[0030] To prevent heat conduction between the layers, the first layer can be coupled to the second layer or the further layer and / or the second layer to the further layer via a point-acting connecting means. Such a connecting means can be implemented by one or more point-acting spacers between the layers, whereby such a point-acting connecting means allows only very low heat conduction between the layers.

[0031] With the device according to the invention, for example, a device with a C-shaped frame can be realized, which is both cost-effective and in which the connection between the two sensors is largely decoupled from the ambient temperature influence and the resulting force effect. Any additional cooling required for the frame and the sensors can be kept to a minimum. In this respect, the device according to the invention implements a concept that minimizes the influence of ambient conditions on the thickness measurement.

[0032] In the following, key aspects of exemplary embodiments of the device according to the invention are summarized for explanation: With the present invention, a multi-stage cooling concept with a preferably closed cooling circuit can be implemented. In the exemplary embodiment of the frame as a C-shaped frame, the cooling concept initially consists of decoupling the C-shaped frame or connecting frame of the sensors from temperature influences from the environment. Various measures can be taken for this purpose to minimize the influence of the ambient temperature, including the temperature input caused by thermal radiation, on the frame construction. The structure of an exemplary embodiment of a C-frame according to the invention is described below from the outside to the inside as an example: In a first stage, a radiation protection plate is attached as the outermost layer, so to speak.It consists of a polished / shiny metal, such as steel or stainless steel, with a low emissivity as a measure of the directed thermal emissivity. Since, according to Kirchhoff's law, the directed thermal emissivity is equal to the absorptivity, a material with a low emissivity or low emissivity reflects incoming thermal radiation very efficiently.

[0033] The radiation shield is suspended from a casing. The connection is designed to compensate for differences in thermal expansion between the materials used, for example, by means of a guide rail.

[0034] In a test device, the temperature of the side of the sheet facing away from the target increases by up to 150°C within less than ten minutes.

[0035] A second stage consists of an air gap between the radiation shield and the underlying jacket. Air has insulating properties and continues to transport heat. The first radiation shield layer—the radiation shield—is not hermetically sealed, so in the second stage, heat is dissipated by convection.

[0036] A third stage consists of the jacket, which in turn is made of polished / shiny metal, for example a steel or stainless steel with low emissivity.

[0037] This jacket encloses a base frame element or the base C-frame in a nearly airtight manner, but is only mechanically connected to it at the base surface – the interface with the linear axis – and in the front area of ​​the measuring legs. At the point where the jacket covers the sensors, the jacket has an opening so that the beam path of the optical sensors is not obstructed. To ensure airtightness, the openings are sealed with heat-insulating glass. The heat-insulating glass is permeable to the optical radiation from the sensors, such as laser radiation, but blocks thermal radiation in the infrared range. This means that the temperature fluctuation on the inside of the jacket or jacket sheet is only about a quarter of that of the radiation protection sheet.

[0038] A fourth stage consists of an air gap between the shell and the base frame element. Within the air gap, air circulates in an active and closed cooling circuit.

[0039] The final stage is the actual base C-frame or base frame element. This contains the sensor mounts at the leg ends and the cooling coil inside the connector. It is designed as a hollow body through which the air from the cooling circuit flows.

[0040] For air guidance, the air enclosed within the casing is circulated by a fan as follows: From the fan, located inside the connector in the base frame element, the air flows through the cooling coil through the legs of the base frame element to the sensors. The cooling coil contains a cooling medium and cooling fins, which ensure efficient heat transfer from the cooling air to the cooling medium. The cooling medium dissipates the heat from the base frame element to the outside, for example, via an external fan. From the sensors, the air flows between the outside of the base frame element and the casing back to the fan. This ensures that temperature fluctuations on the base frame element are virtually eliminated.

[0041] Through the above-mentioned measures, the high ambient temperature occurring outside the thickness measuring system or device is very efficiently reduced step by step to such an extent that moderate temperatures prevail at the base frame element and thus also at the location of the sensors, which firstly lie within the permissible temperature range for the sensors and secondly do not impair the measurement.

[0042] However, the resulting stepped temperature profile in the cross-section of the measuring system or device leads to, for example, the radiation shielding plate having a significantly higher temperature than the casing. Due to the different expansion, this leads to a relative displacement of the radiation shielding plate relative to the casing.

[0043] To avoid mechanical stress, the radiation shield and the jacket are connected at only a few points. These points are designed so that there is no rigid connection. Rather, they are mounted in a floating manner. This design allows for different thermal expansion of the two layers.

[0044] The same applies to the next layer, the casing. The casing is divided into several segments, each of which is hermetically connected with an elastic membrane. The membranes can absorb and compensate for the length changes that occur due to temperature expansion. The connecting segments between the upright and the sensor head are also mounted on a floating support to minimize fluctuations in the force applied to the base frame element.

[0045] The multi-stage cooling concept means that only minimal cooling capacity is required. The majority of the radiant heat is already deflected from the casing by the radiation shield. Furthermore, the back of the shields is cooled by the airflow created by convection.

[0046] Heat conduction from the jacket into the base frame element is virtually eliminated by reducing mechanical connections between the jacket and the base frame element. The jacket is cooled by air cooling in this stage, but little cooling power is required for the jacket, as it can heat up—in practice by up to 40°C—without affecting the thickness measurement. The heat absorption of the base frame element due to thermal radiation from the jacket is low in this temperature range, as both the radiating and absorbing surfaces have a low emissivity factor.

[0047] The air cooled in the cooling register flows directly to the sensors in the interior of the base frame element, so that both the base frame element and the sensors exhibit almost no temperature fluctuation during operation.

[0048] The measures listed above largely eliminate the influence of ambient conditions on the thickness measurement.

[0049] The largest remaining disturbance is the different heating within each leg—on the side facing the other leg and the side facing away from it. Due to the length of the legs, differences in the range of a few 1 / 10 °C are sufficient to generate significant measurement errors. The temperatures at the relevant points are measured, and the effect on the thickness measurement is determined. During operation, the resulting error can be almost completely eliminated by incorporating a correction value.

[0050] There are now various possibilities for advantageously embodying and developing the teaching of the present invention. For this purpose, reference is made, on the one hand, to the dependent claims and, on the other hand, to the following explanation of a preferred embodiment of the device according to the invention with reference to the drawing. In conjunction with the explanation of the preferred embodiment with reference to the drawing, generally preferred embodiments and developments of the teaching are also explained. The drawing shows: Fig. 1 in a side view - A - and in a front view - B - an embodiment of a device according to the invention for determining the thickness of an object, Fig. 2 a cross section, enlarged, through an upper leg of the device according to Fig. 1 , Fig. 3 a cross-section, enlarged, through a lower leg of the device according to Fig. 1 and Fig. 4 in a side view, cut, the device from Fig. 1 .

[0051] Fig. 1 shows, in a side view - A - and a front view - B - an embodiment of a device 1 according to the invention. A C-shaped frame 2 is mounted on a linear axis 3 such that it can be moved traversingly relative to the object 4 to be measured, for example, a steel web 4. Thus, a measuring track is recorded transversely to the direction of movement of the steel web 4. The C-shaped frame 2 consists of an upper leg 5 and a lower leg 6, which are connected to one another via a connecting piece 7. At the outer end of each leg 5, 6 there is an optical distance sensor 8a, 8b, for example a laser profile sensor. The upper sensor 8a measures against the upper side of the steel strip or steel web 4, and the lower sensor 8b measures against the underside of the steel strip or steel web 4.The thickness of the steel strip or steel track 4 can be determined from the two measured values ​​and the known distance between the sensors 8a, 8b.

[0052] Fig. 2 shows a cross-section through the upper leg 5 of the C-frame 2. The sensor 8a is attached to an inner base frame element 9. Cooling air 10 flows through the interior of the base frame element 9, which also flows past the sensors 8a, 8b and cools them. The base frame element 9 is surrounded by a casing 11. This casing is arranged at a distance from the base frame element 9, with only a few point-shaped fastenings (not shown), so that thermal bridges are avoided as much as possible. Cooling air 10 also flows between the casing 11 and the base frame element 9.

[0053] Fig. 3 shows a cross-section through the lower leg 6 of the C-frame 2, wherein the lower leg 6 is additionally provided with a radiation shield 12. This radiation shield 12 is also connected to the casing 11 by spacers 13a, 13b. The spacers 13a, 13b are designed to be floating, so that movements of the radiation shield 12 due to different thermal expansion are not transmitted to the casing 11. The radiation shield 12 is not hermetically sealed, so that the heating of an air layer 19 between the radiation shield 12 and the casing 11 is reduced by convection.

[0054] Fig. 4shows a side view of the C-frame 2. A cooling register 14 is mounted in the connecting piece 7 between the upper leg 5 and the lower leg 6. The cooling register 14 has cooling fins 15 for heat exchange with the cooling air 10. In the cooling register 14, a coolant is used to transport the heat to the outside via a connection 16. With the help of a fan 17 inside the C-frame 2, an air flow 18a, 18b is generated. The air flows from the cooling register 14 inside the base frame element 9, inside the upper leg 5 and lower leg 6, to the sensors 8a, 8b. From there, the cooling air 10 then flows back through the space between the base frame element 9 and the casing 11 to the cooling register 14, where the cooling air 10 releases the absorbed heat. This creates a closed cooling circuit inside the C-frame 2.

[0055] The embodiment of the device according to the invention provides a device for determining the thickness of web-shaped or plate-shaped objects 4, particularly for use in hot rolling. The device consists of a C-frame 2 with an upper leg 5 and a lower leg 6 and a connecting piece 7, wherein an optical sensor 8a, 8b for determining the thickness is arranged on at least one leg 5, 6. To eliminate the temperature influence on the at least one sensor 8a, 8b, the leg 5, 6 of the C-frame 2 supporting the sensor 8a, 8b has a multi-layer construction.

[0056] With regard to further advantageous embodiments of the device according to the invention, reference is made to the general part of the description and to the appended claims in order to avoid repetition.

[0057] Finally, it should be expressly pointed out that the embodiment described above serves only to explain the claimed teaching, but does not limit it to this embodiment. List of reference symbols

[0058] 1Device 2C-shaped frame 3Linear axis 4Object, steel track 5Upper leg 6Lower leg 7Connector 8aSensor 8bSensor 9Base frame element 10Cooling air 11Shroud 12Radiation shield 13aSpacer 13bSpacer 14Cooling register 15Cooling fins 16Connection 17Fan 18aAir flow 18bAir flow 19Air layer

Claims

1. Apparatus (1) for determining the thickness of an object (4), in particular a strip-like or plate-like object (4), preferably for use in a hot-rolling process, having a frame (2) which has an upper member and a lower member (5, 6), wherein each member (5, 6) has a sensor (8a, 8b) for contactless distance measurement with respect to the object (4), wherein each member (5, 6), in order to reduce a temperature effect on the frame (2) and / or the sensor (8a, 8b), has a structure comprising a plurality of layers, wherein a first layer has a base frame element (9) or is formed by such a base frame element (9), wherein a second layer is formed by means of a cover (11) which surrounds the base frame element (9), and wherein a cooling device having a fan (17) is arranged in the base frame element (9), characterised in that, as a result of the fan (17), an air flow (18a, 18b) which flows in the intermediate space between the base frame element (9) and the cover (11) can be produced.

2. Apparatus according to claim 1, characterised in that the base frame element (9) is in the form of a hollow member.

3. Apparatus according to claim 1 or claim 2, characterised in that the sensor (8a, 8b) is associated with the base frame element (9) or is arranged in the base frame element (9).

4. Apparatus according to any one of claims 1 to 3, characterised in that the cooling device is arranged in a connection piece (7) of the base frame element (9).

5. Apparatus according to any one of claims 1 to 4, characterised in that the cooling device has a cooling register (14) which is filled with a cooling medium.

6. Apparatus according to any one of claims 1 to 5, characterised in that ambient air (10) can flow through the base frame element (9).

7. Apparatus according to any one of claims 1 to 6, characterised in that the air flow (18a, 18b) is produced by means of a forward flow (18a, 18b) from the cooling device to the sensor (8a, 8b) and a return flow from the sensor (8a, 8b) back to the cooling device.

8. Apparatus according to any one of claims 1 to 7, characterised in that the second layer has a substantially closed cover (11) for the first layer or is formed by such a cover (11), wherein the return flow or the forward flow is preferably produced between the cover (11) and the base frame element (9).

9. Apparatus according to claim 8, characterised in that the cover (11) is constructed from a plurality of segments, which are preferably coupled by means of resilient membranes.

10. Apparatus according to any one of claims 1 to 9, characterised in that an additional layer has a radiation protection device (12), preferably a radiation protection sheet, for the first or the second layer or is formed by such a radiation protection device.

11. Apparatus according to claim 10, characterised in that the additional layer is supported on the first layer or on the second layer so as to be able to be moved or displaced relative to the first layer or the second layer preferably by means of a guide, in particular a slotted guide.

12. Apparatus according to any one of claims 1 to 11, characterised in that the cover (11) and / or the radiation protection device is formed from a preferably polished and / or shiny metal, preferably having a low degree of emission.

13. Apparatus according to any one of claims 1 to 12, characterised in that the first layer and / or the second layer and / or the additional layer has a passage, which is preferably closed by means of a glass or heat protection glass, for sensor signals to and / or from the object (4).

14. Apparatus according to any one of claims 1 to 13, characterised in that between the second layer and the additional layer an intermediate space through which a predetermined fluid, preferably ambient air (10), can flow is formed in order to produce a fluid layer.

15. Apparatus according to any one of claims 1 to 14, characterised in that the first layer is coupled to the second layer or the additional layer and / or in that the second layer is coupled to the additional layer by way of a locally active connection means.