Heating device and heating method

Abstract

To provide a heating apparatus equipped with a radiation thermometer capable of being automatically controlled using the radiation thermometer and capable of uniformly heating a workpiece in a short time, and a heating method.SOLUTION: A heating apparatus 1 includes an infrared heater 2 that heats a workpiece W, a control unit 5 that controls the output of the infrared heater 2, and a radiation thermometer 4 that measures the surface temperature of the workpiece W, and the infrared heater 2 can arbitrarily change the output between a first output for rapidly raising the temperature of the workpiece W until the surface temperature of the workpiece W reaches a predetermined target temperature, and a second output that emits mid-infrared to far-infrared rays at a lower output than the first output and maintains the surface temperature of the workpiece W until the internal temperature of the workpiece W reaches the target temperature. The second output is controlled by the control unit 5 according to the surface temperature of the workpiece W measured by the radiation thermometer 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heating device and a heating method that can heat an object to the inside uniformly in a short time. [Background technology]

[0002] Conventionally, when infrared light is used to rapidly heat workpieces (heated objects) such as CFRP (carbon fiber reinforced composites) and GFRP (glass fiber reinforced composites), resins, and other materials, the surface of the object heats preferentially, resulting in a temperature difference between the surface and center of the object, making it difficult to heat the entire object uniformly. Furthermore, even when attempting to measure the temperature using a radiation thermometer to control the temperature during heating, the scattered infrared light overlaps with the measurement range (infrared region) of the radiation thermometer, making accurate temperature measurements difficult. In particular, when attempting to rapidly heat thick objects (thick objects) with thicknesses of 2 mm or more, a large temperature difference of several tens of degrees Celsius or more can occur between the surface and center of the object. This temperature difference can lead to quality degradation in processes such as press molding that follow heating. Therefore, thick objects have traditionally been heated slowly over a long period of time to reduce the temperature difference between the surface and center of the sample, which reduces productivity.

[0003] In this context, Patent Document 1 discloses a technology for heating a workpiece so that the temperature difference between the surface and interior of the workpiece is small, by transporting the workpiece on a conveyor in a heating furnace, rapidly raising the surface temperature of the workpiece to a target temperature in a first heating zone upstream, limiting the heating temperature in a soaking zone downstream of the first heating zone to an extent that prevents a sudden drop in the surface temperature of the workpiece, and raising the internal temperature of the workpiece by heat transfer from the surface side to the interior side of the workpiece, and then heating the workpiece so that the surface temperature and internal temperature of the workpiece are within the target temperature range in a second heating zone further downstream, thereby heating the workpiece so that the surface temperature is again raised to the target temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5547940 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the heating method disclosed in Patent Document 1 merely sets the temperature and temperature rise time (conveyor speed) in each heating zone of the heating furnace and then heats the material. Therefore, it is necessary to consider the optimal heating conditions every time the shape of the workpiece or other conditions change, and it must be said that this method is far from automatic control of the heating device. In addition, since it is necessary to arrange heating zones with different temperature ranges side by side from upstream to downstream, the furnace length must be long, and a large heating device is required.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a heating device and a heating method that are capable of automatically controlling the heating temperature using a radiation thermometer and that can heat a workpiece uniformly in a short time. [Means for solving the problem]

[0007] In order to achieve the above object, the invention described in claim 1 is a heating device comprising an infrared heater for heating an object to be heated, a control unit for controlling the output of the infrared heater, and a radiation thermometer for measuring the surface temperature of the object to be heated, wherein the infrared heater: It emits near-infrared light, The output can be freely changed between a first output that heats the object until its surface temperature reaches a predetermined target temperature, and a second output that radiates mid-infrared to far-infrared rays at a lower output than the first output and maintains the surface temperature of the object until its internal temperature reaches the target temperature, and the second output is controlled by a control unit according to the surface temperature of the object measured by a radiation thermometer. The invention as set forth in claim 2 is characterized in that, in the above-mentioned configuration, the radiation thermometer includes a radiation excluding cylinder the inside of which is painted with a material having infrared absorbing properties. The invention as recited in claim 3 is characterized in that, in the above-mentioned configuration, the first output is a maximum output related to the infrared heater. The invention described in claim 4 is a heating method using a heating device equipped with a radiation thermometer described in any one of claims 1 to 3, characterized in that a heating turn is performed in which an infrared heater with a first output heats up the object to be heated until the surface temperature of the object reaches a predetermined target temperature, and a heat retention turn is performed in which an infrared heater with a second output maintains the surface temperature of the object to be heated until the internal temperature of the object reaches the target temperature, and in the heat retention turn, the second output is controlled by a control unit according to the surface temperature of the object to be heated measured by the radiation thermometer. [Effects of the Invention]

[0008] The main effect of the present invention is to provide a heating device and a heating method equipped with a radiation thermometer that can automatically control the heating temperature using a radiation thermometer and can heat a workpiece uniformly in a short time. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are explanatory views showing a heating device of the present invention, in which (a) is a plan view and (b) is a cross-sectional view taken along line AA of (a). [Figure 2] FIG. 1 is an explanatory diagram showing a radiation thermometer of the present invention. [Figure 3] 10 is a graph showing an image of the transition of the output of an infrared heater and the temperature of the surface and cross-section center of a workpiece in a heating process. [Figure 4] 10 is a graph showing the results of a heating test. [Figure 5] 10 is a graph showing the relationship between the difference between the workpiece surface temperature measured using a thermocouple and the workpiece surface temperature measured using a radiation thermometer, and the output of an infrared heater. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a heating device of the present invention, where (a) is a plan view and (b) is a cross-sectional view taken along line AA of (a). As shown in Figures 1(a) and (b), the heating device 1 is equipped with multiple straight tube infrared heaters 2, a movable stage 3 on which a workpiece W such as CFRP to be heated can be loaded and which moves in a predetermined direction within the heating device 1, a radiation thermometer 4 for measuring the surface temperature of the workpiece W, and a control unit 5 for controlling the output of the infrared heaters 2. In this embodiment, the stage 3 moves on two rails R installed along two opposing sides of the heating device 1, and a known movement mechanism is applied as the movement mechanism for the stage 3. The control unit 5 may be connected to each infrared heater 2 individually and control each infrared heater 2 individually, or may be connected to all infrared heaters 2 uniformly. The control unit 5 is also connected to the radiation thermometer 4 and is capable of adjusting the output of the infrared heater 2 according to the temperature measured by the radiation thermometer 4. The output of the infrared heater 2 can be adjusted to any value between 0%, which is the stopped state, and 100%, which is the maximum output. The workpiece W is heated by the heating device 1 to eliminate latent stress, and after heating, is subjected to deformation processing such as press molding, lamination, and other processing.

[0011] As shown in FIG. 1(b), the infrared heaters 2 are arranged in an upper heater unit 2a and a lower heater unit 2b, sandwiching the stage 3 from above and below. Reflection units 6 are provided above the upper heater 2a and below the lower heater 2b to improve heating efficiency. Furthermore, heat insulating materials 7 are provided above and below the reflection units 6 to prevent heat transfer to the outside of the heating device 1. By providing the upper heater 2a and the lower heater 2b, the workpiece W can be heated simultaneously from both the top and bottom sides, so the workpiece W can be heated without causing an extreme temperature difference between the top and bottom surfaces of the workpiece W.

[0012] FIG. 2 is an explanatory diagram showing the radiation thermometer of the present invention. As shown in FIG. 2, the radiation thermometer 4 includes a detector 4a, a lens 4b, and a cylindrical radiation excluding tube 8 having a predetermined length. The radiation thermometer 4 measures the surface temperature of the workpiece W by detecting infrared rays emitted from the surface of the workpiece W via the lens 4b using the detector 4a and converting the infrared rays into an electrical signal. The inside of the radiation exclusion tube 8 is painted with black paint that is infrared-absorbing. Since the infrared rays that enter the radiation exclusion tube 8 are absorbed by the black paint, the influence of scattered infrared light between the upper heater unit 2a and the lower heater unit 2b is suppressed, enabling more accurate measurement of the surface temperature of the workpiece W using the radiation thermometer 4. It is desirable that the radiation exclusion tube 8 be formed in a shape that does not prevent radiant light (infrared rays) from entering the lens 4b. If the diameter of the radiation exclusion tube 8 is too large, more scattered light will enter the lens 4b, which may reduce measurement accuracy. On the other hand, if the diameter of the radiation exclusion tube 8 is too small, less radiant light will enter the lens 4b, which may reduce measurement accuracy. 1(b), the radiation elimination tube 8 has a length that allows its tip to be positioned between the infrared heater 2 (upper heater unit 2a) and the workpiece W. This prevents scattered light emitted from the upper heater unit 2a from entering the radiation elimination tube 8. In other words, by using a radiation elimination tube 8 with an appropriate diameter and length, the surface temperature of the workpiece W can be measured more accurately using the radiation thermometer 4.

[0013] Next, a method for heating the workpiece W using the heating device 1 will be described. FIG. 3 is a graph showing the output of the infrared heater and the transition image of the surface and cross-sectional center temperatures of the workpiece during the heating process. First, the workpiece W is placed on the stage 3, and then the stage 3 is moved. As the stage 3 moves, the workpiece W moves into the heating device 1. After the workpiece W has been moved into the heating device 1, as shown in FIG. 3, the control unit 5 causes the infrared heater 2 to rapidly heat the workpiece W at a first output (here, 100% output) so that the surface temperature of the workpiece W reaches a predetermined target temperature (heating turn H). In heating turn H, high-power near-infrared rays are emitted from the infrared heater 2. Because the workpiece W is heated from the surface at high output, the internal temperature of the workpiece W is lower than the target temperature. Because the wavelength range of near-infrared rays overlaps with the measurement range of the radiation thermometer 4, in heating turn H, the radiation thermometer 4 detects scattered light from the infrared heater 2, preventing accurate measurement of the surface temperature of the workpiece W. Therefore, in heating turn H, it is necessary to rapidly heat the workpiece W to near the target temperature in a short period of time using a predetermined temperature pattern confirmed in advance. In this application, near-infrared rays refer to infrared rays in the wavelength range of 0.7 μm to 1.5 μm. Furthermore, mid-infrared rays refer to infrared rays in the wavelength region of 1.5 μm to 4.0 μm, and far-infrared rays refer to infrared rays in the wavelength region of 4.0 μm to 1000 μm.

[0014] After the surface temperature of the workpiece W reaches near the target temperature, the control unit 5 changes the output of the infrared heater 2 to a second output (10% output in this case). Then, while maintaining the surface temperature of the workpiece W near the target temperature, the internal temperature of the workpiece W is raised to near the target temperature (heat retention turn K). In heat retention turn K, low-power infrared rays, i.e., mid-infrared to far-infrared rays, are emitted from the infrared heater 2. The wavelength range of mid-infrared to far-infrared rays does not overlap with the measurement range of the radiation thermometer 4. Therefore, it is possible to measure the surface temperature of the workpiece W with a predetermined accuracy or higher using the radiation thermometer 4. Furthermore, although it is conceivable that a certain amount of measurement error may occur due to scattered light, the radiation exclusion tube 8 provided in the radiation thermometer 4 absorbs the scattered light, thereby almost completely eliminating measurement errors due to scattered light and narrowing the measurement target to infrared rays from the surface of the workpiece W, enabling accurate temperature measurement of the workpiece W (measurement at a normal emissivity setting of 0.9 to 0.95). Since the radiation thermometer 4 makes it possible to accurately measure the surface temperature of the workpiece W, in the heat retention turn K, the control unit 5 automatically controls the output of the infrared heater 2 according to the measured temperature. As a result, the heating device 1 maintains the surface temperature of the workpiece W while performing appropriate heating processing until the internal temperature of the workpiece W reaches the target temperature. In this way, by performing the heating turn H and the heat retention turn K by changing the output of the infrared heater 2, the heating device 1 can be designed to be smaller than large conventional heating devices that require a long furnace length. Furthermore, in the heat retention turn K, the output of the infrared heater 2 is reduced, the infrared rays emitted are changed from mid-infrared to far-infrared, and a radiation exclusion tube 8 is provided on the radiation thermometer 4, which enables accurate measurement of the surface temperature of the workpiece W by the radiation thermometer 4, and therefore enables automatic control of the output of the infrared heater 2, i.e., the heating temperature, by the control unit 5 based on the measured temperature. This makes it possible to properly heat the workpiece W until its internal temperature reaches the target temperature, while preventing the surface temperature of the workpiece W from deviating from the target temperature.

[0015] Next, the results of a heating test using the heating device 1 of the present invention will be shown. FIG. 4 is a graph showing the results of the heating test. In the heating test, a workpiece W made of CFRP with a thickness of 4 mm and a size of 100 mm square was heated for 30 seconds using heating device 1, and temperatures were measured at the surface and interior at the center of the workpiece, the surface and interior at a point 30 mm from the center of the workpiece, and the surface and interior at a point 45 mm from the center of the workpiece. Temperature measurements at each measurement point on the surface and interior of the workpiece W were performed using thermocouples. The internal temperature was the temperature at a point 2 mm deep from the surface.

[0016] The results of the heating test are shown in Figure 4. The graph in Figure 4 shows the temperature measured at each of the measurement points mentioned above, as well as the power (output of the infrared heater 2) and the changes in the surface temperature of the workpiece W detected by the radiation thermometer 4. The radiation thermometer 4 measured the surface temperature at the center of the workpiece. First, in the heating turn H, the power was set to 90 kW (the output of the infrared heater 2 was 100%, which was the first output), and the workpiece W was heated until its surface temperature reached the target temperature of 200°C. As time passed, the surface temperature of the workpiece W rose rapidly and almost uniformly from the start of heating at the center, 30 mm from the center, and 45 mm from the center, reaching the target temperature in approximately 10 seconds. On the other hand, the internal temperature of each part of the workpiece W was still around 120°C even after 10 seconds had passed, which is clearly a large difference from the surface temperature of the workpiece W. At this time, it is also clear that the radiation thermometer 4 is unable to measure the temperature accurately due to scattered light from the infrared heater 2.

[0017] After the surface temperature of the workpiece W reached the target temperature, the heat retention turn K was switched on, the power was reduced to approximately 10 kW (the output of the infrared heater 2 was approximately 10%, which became the second output), and the workpiece W was heated until its internal temperature reached the target temperature of 200°C. In the heat retention turn K, the power is finely adjusted by the control unit 5. As the surface temperature of the workpiece W, which had been overshooting, transitions toward the target temperature, the internal temperature of the workpiece W gradually rises, and approximately 30 seconds after the start of heating, both the surface temperature and the internal temperature of the workpiece W reached the target temperature at all measurement points. In this way, by performing the heating turn H and the heat retention turn K, it is possible to uniformly heat a 4 mm thick object even in a short time of 30 seconds. It can also be seen that at this time, the radiation thermometer 4 is able to accurately measure the surface temperature of the workpiece W as the output of the infrared heater 2 approaches approximately 10%. This is because, by reducing the output of the infrared heater 2, the infrared heater 2 begins to emit mid-infrared to far-infrared rays that do not overlap with the measurement area of ​​the radiation thermometer 4, and by excluding scattered light from the radiation thermometer 4 using the radiation exclusion tube 8, it is now possible for the radiation thermometer 4 to accurately measure the surface temperature of the workpiece W.

[0018] FIG. 5 is a graph showing the relationship between the difference between the workpiece surface temperature measured using a thermocouple and the workpiece surface temperature measured using a radiation thermometer, and the output of an infrared heater. FIG. 5 is a graph showing the relationship between the difference between the surface temperature of the workpiece W measured using a thermocouple and the surface temperature of the workpiece W measured using the radiation thermometer 4 and the output of the infrared heater 2. When the output of the infrared heater 2 is 100%, i.e., the first output, the difference between the surface temperature of the workpiece W measured using the thermocouple and the surface temperature of the workpiece W measured using the radiation thermometer 4 is approximately Δ60°C. Therefore, it can be seen that, when the output is the first output, the radiation thermometer 4 is not able to accurately measure the surface temperature of the workpiece W. When the output of the infrared heater 2 was set to 50%, the difference between the surface temperature of the workpiece W measured using the thermocouple and the surface temperature of the workpiece W measured using the radiation thermometer 4 was approximately Δ20°C. Furthermore, when the output of the infrared heater 2 is reduced to 10%, i.e., set to the second output, the difference between the surface temperature of the workpiece W measured using the thermocouple and the surface temperature of the workpiece W measured using the radiation thermometer 4 is approximately Δ0°C. Therefore, when set to the second output, the radiation thermometer 4 can accurately measure the surface temperature of the workpiece W.

[0019] The heating device 1 configured as described above comprises an infrared heater 2 for heating the workpiece W, a control unit 5 for controlling the output of the infrared heater 2, and a radiation thermometer 4 for measuring the surface temperature of the workpiece W, and the infrared heater 2 is capable of arbitrarily changing its output between a first output that rapidly heats the workpiece W until the surface temperature of the workpiece W reaches a predetermined target temperature, and a second output that radiates mid-infrared to far-infrared rays at a lower output than the first output and maintains the surface temperature of the workpiece W until the internal temperature of the workpiece W reaches the target temperature, and the second output is controlled by the control unit 5 in accordance with the surface temperature of the workpiece W measured by the radiation thermometer 4. Therefore, by making the output of the infrared heater 2 variable, the heating device 1 can be designed to be smaller than conventional large heating devices that require a long furnace length. Furthermore, by reducing the output of the infrared heater 2 and changing the infrared radiation from mid-infrared to far-infrared, it becomes possible to measure the surface temperature of the workpiece W using the radiation thermometer 4, and based on the measured temperature, the output of the infrared heater 2, i.e., the heating temperature, can be automatically controlled by the control unit 5. This makes it possible to properly heat the workpiece W until its internal temperature reaches the target temperature, while preventing the surface temperature of the workpiece W from deviating from the target temperature.

[0020] The radiation thermometer also includes a radiation excluding tube the inside of which is coated with an infrared absorbing material. Therefore, the infrared rays that enter the radiation exclusion tube 8 are absorbed by the black paint as they travel, thereby reducing the influence of scattered light from the infrared rays emitted from the surface of the workpiece W, enabling more accurate measurement of the surface temperature of the workpiece W using the radiation thermometer 4.

[0021] The present invention has been described above based on the illustrated examples, and the technical scope of the present invention is not limited thereto. For example, the first output and the second output can be set arbitrarily as long as the object to be heated can be heated to the target temperature in the desired time. Furthermore, the shape and number of infrared heaters to be installed are not limited as long as they can heat the object to be heated. Furthermore, the infrared heaters may be installed only above or only below the object to be heated. Furthermore, multiple radiation thermometers may be provided, and the installation locations are not limited. Furthermore, the radiation exclusion cylinder can be designed to have any length, shape, etc., as long as the surface temperature of the object to be heated can be measured accurately. Furthermore, the control unit may be configured to automatically control the output of the infrared heater, or to manually change the output of the infrared heater via the control unit, as long as it can change the output of the infrared heater. Furthermore, the stage is not limited to one that moves on rails by a known drive mechanism, and the stage itself may be formed of a belt conveyor, for example. The heating device may also be provided with a heating area in which an infrared heater with a first output heats the surface of the object to be heated to a target temperature, and a heat retention area in which a control unit adjusts the second output to heat the object evenly to the inside at the target temperature, and the object to be heated is heated by moving a stage on which the object to be heated is placed from the heating area to the heat retention area. In addition, the heating of the object to be heated may be carried out using a heating device comprising an infrared heater that emits mid-infrared to far-infrared rays to heat the object to be heated, a control unit that controls the output of the infrared heater, and a radiation thermometer that has a radiation exclusion tube the inside of which is painted with an infrared-absorbing material and measures the surface temperature of the object to be heated, with the output of the infrared heater being controlled by the control unit in accordance with the surface temperature of the object to be heated measured by the radiation thermometer until the surface temperature and internal temperature of the object to be heated reach a predetermined target temperature. [Explanation of symbols]

[0022] 1·· Heating device, 2·· Infrared heater, 4·· Radiation thermometer, 5·· Control unit, 8·· Radiation exclusion tube, W·· Work (object to be heated).

Claims

1. The heating device includes an infrared heater for heating an object to be heated, a control unit for controlling the output of the infrared heater, and a radiation thermometer for measuring the surface temperature of the object to be heated, the infrared heater is capable of arbitrarily changing its output between a first output that radiates near-infrared rays and heats the object until the surface temperature of the object reaches a predetermined target temperature, and a second output that radiates mid-infrared rays to far-infrared rays at an output lower than the first output and maintains the surface temperature of the object until the internal temperature of the object reaches the target temperature; The heating device is characterized in that the second output is controlled by the control unit in accordance with the surface temperature of the object to be heated measured by the radiation thermometer.

2. 2. The heating device according to claim 1, wherein the radiation thermometer comprises a radiation excluding tube the inside of which is coated with an infrared absorbing material.

3. 3. The heating device according to claim 1, wherein the first output is a maximum output of the infrared heater.

4. Using the heating device according to any one of claims 1 to 3, a heating cycle in which the temperature of the object to be heated is increased by the infrared heater with the first output until the surface temperature of the object to be heated reaches a predetermined target temperature; a heat retention cycle in which the surface temperature of the object to be heated is maintained by the infrared heater of the second output until the internal temperature of the object to be heated reaches the target temperature; A heating method characterized in that, in the heat retention turn, the second output is controlled by the control unit in accordance with the surface temperature of the heated object measured by the radiation thermometer.

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