Space environment condition metal melting temperature control device and method

Abstract

The invention discloses a metal melting temperature control device and method under the space environment condition. The device comprises an X-axis and Y-axis moving platform, a Z-axis moving platform, a motion controller, an electron beam welding gun, a wire feeder, an infrared thermal imaging detector, a flexible heat conduction device and an electron beam power source. In the process of space cutting, welding or additive manufacturing, an infrared thermal imager is used for obtaining temperature data of a molten pool and a rear position with the distance being d in real time, and when the temperature value exceeds a set threshold value, according to a measurement calculation result, a method for changing the heat transfer rate of a flexible heat conduction device, regulating and controlling the moving speed of a sample and adjusting the power of a power source is adopted; and the value of heat input into the component and lost by the component in unit time is changed, the metal melting temperature is controlled, and the forming quality of the metal component in the space environment is guaranteed.

Description

Technical Field

[0001] The invention relates to a device and method for controlling the temperature of metal melting under space environment conditions, belonging to the technical field of metal material manufacturing under space environment conditions. Background Art

[0002] The processing and manufacturing of metal structures is an essential technology in the process of exploring and developing extraterrestrial space resources, and is crucial to the implementation of various extraterrestrial space projects.

[0003] Electron beam technology has the advantages of high energy utilization, fast manufacturing speed and good adaptability to vacuum environment. It can weld, cut and perform additive manufacturing operations on metal materials in space environment. However, under space environment conditions, the heat released during the metal solidification process can only be carried away by structural contact heat conduction, and the heat dissipation efficiency is limited. The large amount of heat generated during the continuous heating process of the electron beam will continue to accumulate, causing the temperature of the metal components to rise, making it difficult for the liquid metal to solidify.

[0004] At present, the space station uses a heat pipe solution to cool high-temperature objects. The principle is to use a pump group to drive the cooling medium to flow in the cold plate to achieve heat transfer, which consumes a lot of power. At the same time, during the cutting, welding and additive manufacturing process, the position of the metal sample will constantly change. Due to the rigid mechanical structure, the heat pipe and cold plate components cannot move freely, making it difficult to meet the heat dissipation requirements during the sample movement process. Summary of the invention

[0005] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose a metal melting temperature control device and method under space environment conditions to solve the problem of difficulty in controlling the melting temperature of metal materials caused by factors such as low heat transfer efficiency in the space environment and continuous changes in the sample position during processing.

[0006] The technical solution of the present invention is: a metal melting temperature control device under space environment conditions, comprising: an XY axis moving platform, a Z axis moving platform, a motion controller, an electron beam welding gun, a wire feeder, an infrared thermal imaging detector, a flexible heat conducting device and an electron beam power supply;

[0007] The XY axis moving platform and the Z axis moving platform are connected to the motion controller through the 1553B industrial bus, and the electron beam welding gun is connected to the Z axis moving platform through a fixture; during the processing, the XY axis moving platform receives the instruction of the motion controller to adjust the position of the sample, and adjusts the heat input to the sample per unit time by changing the sample moving speed, so as to adjust the sample temperature; the Z axis moving platform receives the instruction of the motion controller to adjust the position of the electron beam welding gun; the wire feeder is connected to the electron beam welding gun through a fixture, and the wire is fed to the bottom of the welding gun during the manufacturing process, and the wire feeding speed value is determined according to the power output power of the power supply; the infrared thermal imaging detector is fixed to the side of the electron beam welding gun through a fixture, and the temperature of the sample is measured in real time during the processing; the flexible heat conduction device can change the heat dissipation rate of the sample and adjust the sample temperature by changing the contact area between the split heat conduction plate and the XY axis moving platform; the electron beam power supply is connected to the electron beam welding gun through a cable, and adjusts the heat input to the sample per unit time by changing the power output power during the processing, so as to adjust the sample temperature.

[0008] The movement travel of the XY axis moving platform in the X and Y directions is more than 300mm, and the movement travel of the Z axis moving platform is more than 50mm; the positioning accuracy in the three directions of X, Y and Z is 0.1mm.

[0009] The wire feeder is connected to the electron beam welding gun, and the wire feeding speed adjustment range is 0-2m / min, and the adjustment accuracy is 0.1m / min.

[0010] The infrared thermoforming detector has a temperature measurement range of 0-1000°C, a measurement accuracy of ±1°C, and a maximum measurement frequency of 20Hz.

[0011] The maximum output power of the electron beam power supply is 1000W, and the initial power of the electron beam power supply is greater than 500W.

[0012] The flexible heat-conducting device is composed of an end heat-conducting metal, a flexible heat-conducting belt, a split heat-conducting plate, a slide rail, a ball screw, and an external cold plate. The end heat-conducting metal and the flexible heat-conducting belt are connected by tin-based solder, and the end heat-conducting metal and the split heat-conducting plate are connected by tin-based solder. The flexible heat-conducting belt can move in a planar trajectory along with the XY-axis moving platform during the processing process, ensuring that the flexible heat-conducting device can regulate the heat dissipation rate of the sample during the movement of the sample.

[0013] The equivalent thermal conductivity of the flexible thermal conductive belt is not less than 800W / m 2 ·K.

[0014] The split heat conducting plate adopts a modular design and can independently control the sliding of each split part. During the processing, the contact area between the split heat conducting plate and the XY axis moving platform is changed by sliding different parts of the split heat conducting plate, so as to regulate the heat dissipation rate of the sample.

[0015] A method for controlling metal melting temperature, comprising:

[0016] Cutting, welding and additive manufacturing of metal materials using electron beam as a heat source;

[0017] During the processing, an infrared thermal imaging detector is used to measure the temperature of the molten pool and the position at a distance d behind it. According to the temperature value and change trend, the sample temperature is always controlled within the range of L1-H1. The specific control process is as follows:

[0018] (1) When the temperature at a distance d behind the molten pool exceeds H1:

[0019] When the temperature is in the range of L1-H1, 50% of the area of ​​the split heat conduction plate is in contact with the XY axis moving platform. When the temperature is greater than H1, the contact area between the split heat conduction plate and the XY axis moving platform is increased by sliding the split heat conduction plate to improve the heat dissipation rate of the sample. When the temperature stops increasing or starts to decrease, the contact area between the split heat conduction plate and the XY axis moving platform is no longer increased. When the temperature continues to increase to H2, the entire area of ​​the split heat conduction plate is in contact with the XY axis moving platform.

[0020] When the split heat conduction plate is in full contact with the XY axis moving platform, the heat dissipation rate of the sample reaches the maximum value, but the temperature continues to rise to above H2, the XY axis moving platform is controlled to increase the movement speed of the sample and reduce the heat input to the sample per unit time; when the temperature is no longer increasing or the temperature begins to decrease, the movement speed of the sample is no longer increased; when the temperature continues to increase to H3, the movement speed of the sample is increased to 1.2 times before regulation;

[0021] When the sample movement speed increases to 1.2 times of that before regulation, but the sample temperature continues to rise to above H3, the output power of the power supply is gradually reduced to reduce the heat input to the sample per unit time, but the power supply power is reduced to 90% of the original output power at most;

[0022] When the power output is reduced to 90% of the original output power, but the sample temperature continues to rise, stop the processing;

[0023] (2) When the temperature at a distance d behind the molten pool is lower than L1:

[0024] When the temperature is in the L1-H1 range, 50% of the area of ​​the split heat conducting plate is in contact with the XY axis moving platform. When the temperature is lower than the threshold value L1, the split heat conducting plate is slid to reduce the contact area between the heat conducting belt and the substrate, thereby reducing the heat dissipation rate of the sample. When the temperature stops decreasing or starts to increase, the contact area between the split heat conducting plate and the XY axis moving platform is no longer reduced. When the temperature drops to L2, the contact area between the split heat conducting plate and the XY axis moving platform is 0.

[0025] When the contact area between the split heat conducting plate and the substrate is 0, the heat dissipation rate reaches the minimum value, but the sample temperature continues to drop below L2, the XY axis moving platform is controlled to reduce the movement speed of the sample and increase the heat input to the sample per unit time; when the temperature no longer decreases or starts to increase, the movement speed of the sample is no longer reduced; when the temperature reaches L3, the movement speed of the sample is reduced to 80% of the speed before regulation;

[0026] When the sample movement speed is reduced to 80% of the pre-regulation speed, but the sample temperature continues to drop below L3, gradually increase the output power of the power supply to increase the heat input to the sample per unit time, but the power supply power is increased to 110% of the original output power at most;

[0027] When the power output increases to 110% of the original output power but the sample temperature continues to decrease, the processing process is stopped.

[0028] The material type of the end heat-conducting metal is aluminum alloy with a thickness of 2 mm; the distance between the temperature measurement point behind the molten pool and the center of the molten pool is d=6 mm; the initial power of the electron beam power supply is 500 W; the initial movement speed of the sample is 200 mm / min; H3=500°C, H2=450°C, H1=400°C, L1=350°C, L2=300°C, L3=250°C.

[0029] The advantages of the present invention compared with the prior art are:

[0030] 1. The device uses an XY-axis mobile platform to control the planar trajectory movement of the workpiece, and uses a Z-axis mobile platform to adjust the height of the electron beam welding gun, thereby realizing the motion decoupling of the workpiece and the welding gun, simplifying the mechanical structure of the mobile device, and reducing the difficulty of path planning.

[0031] 2. Compared with the traditional cold plate solution, the flexible heat conductive belt can move with the sample on the XY plane, solving the mechanical, mechanical structure decoupling and thermal control design problems between the XY axis moving platform and the thermal control device.

[0032] 3. The temperature control device controls the heat transfer rate of the sample by changing the contact area between the split heat conduction plate and the XY axis moving platform. Compared with the traditional heat pipe solution that uses a motor to drive the cooling medium, it can greatly reduce the power of the thermal control device and reduce the occupation of limited space resources.

[0033] 4. The flexible heat-conducting tape used in the heat-conducting device has the advantages of light weight, high heat conduction efficiency and long life, and is particularly suitable for use in space environments.

[0034] 5. Use infrared thermal imaging detector to obtain temperature data of the molten pool and the rear position as the basis for controlling the metal melting process. It has the advantages of non-contact, high measurement accuracy and wide measurement range.

[0035] 6. By adjusting the heat transfer rate of the flexible heat conducting device, the sample moving speed, and the power supply, the metal melting temperature can be controlled to ensure the high-quality forming of metal components in the space environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structure of the metal melting temperature control device.

[0037] Figure 2 This is the front view of the flexible heat conducting device.

[0038] Figure 3 Top view of the flexible thermal conductive device

[0039] Figure 4 Schematic diagram of the temperature of the molten pool and the rear position.

[0040] Figure 5 Schematic diagram of the threshold temperature of metal material components and the control method. DETAILED DESCRIPTION

[0041] The present invention provides a device for controlling the temperature of metal melting under space environment conditions. The device mainly comprises an XY axis moving platform, an electron beam welding gun, a Z axis moving platform, a wire feeder, an infrared thermal imaging detector, a flexible heat conducting device and an electron beam power supply. The appearance and structure of the device are as follows: Figure 1 shown.

[0042] The movement stroke of the XY axis mobile platform in the X and Y directions is 300mm, the movement stroke of the Z axis mobile platform is 50mm, and the positioning accuracy of the three directions of X, Y and Z is 0.1mm. The wire feeder is connected to the electron beam welding gun, and the wire feeding speed adjustment range is 0-2m / min, and the adjustment accuracy is 0.1m / min. The temperature measurement range of the infrared thermoforming detector is 0-1000℃, the measurement accuracy is ±1℃, and the maximum measurement frequency is 20Hz. The maximum output power of the electron beam power supply is 1000W.

[0043] The XY-axis mobile platform is used to adjust the position of the sample, and the Z-axis mobile platform is used to adjust the position of the welding gun, which realizes the motion decoupling of the sample and the welding gun, simplifies the mechanical structure, and reduces the difficulty of path planning. The error compensation and vibration suppression algorithms are independently developed to ensure the smooth movement of the sample and the welding gun and the accuracy of the spatial position. During the sample processing, the input heat value per unit length of the component is adjusted by adjusting the movement speed to meet the process requirements of component cutting, welding and additive manufacturing.

[0044] The structure of the flexible heat conducting device is as follows: Figure 2 and Figure 3 As shown, the device is mainly composed of end heat-conducting metal, flexible heat-conducting belt, split heat-conducting plate, external cold plate, slide rail, and ball screw. Tin-based solder is used to connect the end heat-conducting metal and the flexible heat-conducting belt, and tin-based solder is used to connect the end heat-conducting metal and the split heat-conducting plate, so that the heat-conducting belt can transfer the heat generated during the sample processing to the external cold plate. The flexible heat-conducting belt can move in a plane trajectory with the XY axis moving platform, and the heat transfer efficiency of the component per unit time can be regulated during the movement of the component. The equivalent thermal conductivity of the heat-conducting belt is not less than 800W / m2·K. The split heat-conducting plate adopts a modular design, and each split part can be independently controlled to slide. During the processing, the contact area between the split heat-conducting plate and the XY axis moving platform is changed by sliding different parts of the split heat-conducting plate, so as to realize the regulation of the heat transfer rate of the sample per unit time.

[0045] The present invention also provides a method for controlling the metal melting temperature, which uses an infrared thermal imaging detector to obtain the thermal radiation distribution data of the molten pool and the position behind it during the component processing process. The infrared feature information is enhanced by enhancing image details, improving contrast, and suppressing noise. A dual-band infrared radiation temperature measurement method is used to establish a radiation attenuation correction model, and the temperature measurement value is temperature compensated to calculate the temperature distribution gradient data on the object surface. The temperature value of the molten pool and the position at a distance d behind it is calculated and used as the basis for controlling the metal melting temperature. The value of d is determined based on parameters such as the type of metal material, plate thickness, and process parameter values. The temperature distribution of the molten pool and nearby positions is as follows: Figure 4 The threshold temperature of metal material components and the control method are shown in Figure 5 As shown, based on the temperature measurement results at the position with a distance d from the molten pool, the heat transfer rate of the flexible heat conduction device, the sample moving speed, the power supply power and the wire feeding speed parameters are changed to change the heat value of the input component and the heat dissipated by the component per unit time, so as to realize the regulation of the melting temperature of the metal material. The specific control method is as follows:

[0046] (1) When the temperature at a distance d behind the molten pool exceeds H1:

[0047] 1) When the temperature is in the range of L1-H1, 50% of the area of ​​the split heat conductive plate is in contact with the XY axis moving platform. When the temperature is greater than the threshold value H1, the contact area between the split heat conductive plate and the XY axis moving platform is increased by sliding the split heat conductive plate to improve the heat dissipation rate of the sample. When the temperature no longer increases or the temperature begins to decrease, the contact area between the split heat conductive plate and the XY axis moving platform is no longer increased. When the temperature continues to increase to H2, the entire area of ​​the split heat conductive plate is in contact with the XY axis moving platform.

[0048] 2) When the split heat conduction plate is in full contact with the XY axis moving platform, the heat dissipation rate of the sample reaches the maximum value, but the temperature continues to rise to above H2, the XY axis moving platform is controlled to increase the movement speed of the sample and reduce the heat input to the sample per unit time. When the temperature is no longer increasing or the temperature begins to decrease, the movement speed of the sample is no longer increased. When the temperature continues to increase to H3, the movement speed of the sample increases to 1.2 times before regulation.

[0049] 3) When the sample movement speed increases to 1.2 times that before regulation, but the sample temperature continues to rise to above H3, gradually reduce the output power of the power supply to reduce the heat input to the sample per unit time, but the power supply power can be reduced to a maximum of 90% of the original output power.

[0050] 4) When the power output is reduced to 90% of the original output power, but the sample temperature continues to rise, stop the processing.

[0051] (2) When the temperature at a distance d behind the molten pool is lower than L1:

[0052] 1) When the temperature is in the range of L1-H1, 50% of the area of ​​the split heat conducting plate is in contact with the XY axis moving platform. When the temperature is lower than the threshold value L1, the split heat conducting plate is slid to reduce the contact area between the heat conducting belt and the substrate, thereby reducing the heat dissipation rate of the sample. When the temperature stops decreasing or starts to increase, the contact area between the split heat conducting plate and the XY axis moving platform is no longer reduced. When the temperature drops to L2, the contact area between the split heat conducting plate and the XY axis moving platform is 0.

[0053] 2) When the contact area between the split heat conducting plate and the substrate is 0, the heat dissipation rate reaches the minimum value, but the sample temperature continues to drop below L2, the XY axis moving platform is controlled to reduce the movement speed of the sample and increase the heat input to the sample per unit time. When the temperature no longer decreases or the temperature begins to increase, the movement speed of the sample is no longer reduced. When the temperature reaches L3, the movement speed of the sample is reduced to 80% before regulation.

[0054] 3) When the sample movement speed is reduced to 80% of the pre-regulation speed, but the sample temperature continues to drop below L3, gradually increase the output power of the power supply to increase the heat input to the sample per unit time, but the power supply power is increased to a maximum of 110% of the original output power.

[0055] 4) When the power output increases to 110% of the original output power, but the sample temperature continues to decrease, stop the processing.

[0056] The material type of the end heat-conducting metal is aluminum alloy with a thickness of 2 mm; the distance between the temperature measurement point behind the molten pool and the center of the molten pool is d=6 mm; the initial power of the electron beam power supply is 500 W; the initial movement speed of the sample is 200 mm / min; H3=500°C, H2=450°C, H1=400°C, L1=350°C, L2=300°C, L3=250°C.

[0057] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A device for controlling the temperature of metal melting under space environment conditions, characterized in that: include: XY axis mobile platform, Z axis mobile platform, motion controller, electron beam welding gun, wire feeder, infrared thermal imaging detector, flexible thermal conductive device and electron beam power supply; The XY axis mobile platform and the Z axis mobile platform are connected to the motion controller via the 1553B industrial bus, and the electron beam welding gun is connected to the Z axis mobile platform via a fixture; during the processing, the XY axis mobile platform receives instructions from the motion controller to adjust the position of the sample, and controls the heat input to the sample per unit time by changing the sample movement speed, thereby controlling the sample temperature; The Z-axis moving platform receives the instruction of the motion controller to adjust the position of the electron beam welding gun; the wire feeder is connected to the electron beam welding gun through a clamp, and the wire is fed to the bottom of the welding gun during the manufacturing process, and the wire feeding speed value is determined according to the output power of the power supply; the infrared thermal imaging detector is fixed to the side of the electron beam welding gun through a clamp, and the temperature of the sample is measured in real time during the processing; the flexible heat conduction device can change the heat dissipation rate of the sample and regulate the temperature of the sample by changing the contact area between the split heat conduction plate and the XY-axis moving platform; The electron beam power supply is connected to the electron beam welding gun through a cable. During the processing, the heat input to the sample per unit time is regulated by changing the output power of the power supply to regulate the temperature of the sample.

2. The device for controlling the temperature of metal melting under space environment conditions according to claim 1, characterized in that: The movement travel of the XY axis moving platform in the X and Y directions is more than 300mm, and the movement travel of the Z axis moving platform is more than 50mm; the positioning accuracy in the three directions of X, Y and Z is 0.1mm.

3. The device for controlling the temperature of metal melting under space environment conditions according to claim 1, characterized in that: The wire feeder is connected to the electron beam welding gun, and the wire feeding speed adjustment range is 0-2m / min, and the adjustment accuracy is 0.1m / min.

4. The device for controlling the temperature of metal melting in space environment conditions according to claim 1, characterized in that: The infrared thermoforming detector has a temperature measurement range of 0-1000°C, a measurement accuracy of ±1°C, and a maximum measurement frequency of 20Hz.

5. The device for controlling the temperature of metal melting in space environment conditions according to claim 1, characterized in that: The maximum output power of the electron beam power supply is 1000W, and the initial power of the electron beam power supply is greater than 500W.

6. The device for controlling the temperature of metal melting in space environment conditions according to claim 1, characterized in that: The flexible heat-conducting device is composed of an end heat-conducting metal, a flexible heat-conducting belt, a split heat-conducting plate, a slide rail, a ball screw, and an external cold plate. The end heat-conducting metal and the flexible heat-conducting belt are connected by tin-based solder, and the end heat-conducting metal and the split heat-conducting plate are connected by tin-based solder. The flexible heat-conducting belt can move in a planar trajectory along with the XY-axis moving platform during the processing process, ensuring that the flexible heat-conducting device can regulate the heat dissipation rate of the sample during the movement of the sample.

7. The device for controlling the temperature of metal melting in space environment conditions according to claim 6, characterized in that: The equivalent thermal conductivity of the flexible thermal conductive belt is not less than 800W / m 2 ·K.

8. The device for controlling the temperature of metal melting in space environment conditions according to claim 6, characterized in that: The split heat conducting plate adopts a modular design and can independently control the sliding of each split part. During the processing, the contact area between the split heat conducting plate and the XY axis moving platform is changed by sliding different parts of the split heat conducting plate, so as to regulate the heat dissipation rate of the sample.

9. A method for controlling the temperature of metal melting by using the device according to claim 1, characterized in that: include: Cutting, welding and additive manufacturing of metal materials using electron beam as a heat source; During the processing, an infrared thermal imaging detector is used to measure the temperature of the molten pool and the position at a distance d behind it. According to the temperature value and change trend, the sample temperature is always controlled within the range of L1-H1. The specific control process is as follows: When the temperature at a distance d behind the molten pool exceeds H1: When the temperature is in the range of L1-H1, 50% of the area of ​​the split heat conduction plate is in contact with the XY axis moving platform. When the temperature is greater than H1, the contact area between the split heat conduction plate and the XY axis moving platform is increased by sliding the split heat conduction plate to improve the heat dissipation rate of the sample. When the temperature stops increasing or starts to decrease, the contact area between the split heat conduction plate and the XY axis moving platform is no longer increased. When the temperature continues to increase to H2, the entire area of ​​the split heat conduction plate is in contact with the XY axis moving platform. When the split heat conduction plate is in full contact with the XY axis moving platform, the heat dissipation rate of the sample reaches the maximum value, but the temperature continues to rise to above H2, the XY axis moving platform is controlled to increase the movement speed of the sample and reduce the heat input to the sample per unit time; when the temperature is no longer increasing or the temperature begins to decrease, the movement speed of the sample is no longer increased; when the temperature continues to increase to H3, the movement speed of the sample is increased to 1.2 times before regulation; When the sample movement speed increases to 1.2 times of that before regulation, but the sample temperature continues to rise to above H3, the output power of the power supply is gradually reduced to reduce the heat input to the sample per unit time, but the power supply power is reduced to 90% of the original output power at most; When the power output is reduced to 90% of the original output power, but the sample temperature continues to rise, stop the processing; When the temperature at a distance d behind the molten pool is lower than L1: When the temperature is in the L1-H1 range, 50% of the area of ​​the split heat conducting plate is in contact with the XY axis moving platform. When the temperature is lower than the threshold value L1, the split heat conducting plate is slid to reduce the contact area between the heat conducting belt and the substrate, thereby reducing the heat dissipation rate of the sample. When the temperature stops decreasing or starts to increase, the contact area between the split heat conducting plate and the XY axis moving platform is no longer reduced. When the temperature drops to L2, the contact area between the split heat conducting plate and the XY axis moving platform is 0. When the contact area between the split heat conducting plate and the substrate is 0, the heat dissipation rate reaches the minimum value, but the sample temperature continues to drop below L2, the XY axis moving platform is controlled to reduce the movement speed of the sample and increase the heat input to the sample per unit time; when the temperature no longer decreases or starts to increase, the movement speed of the sample is no longer reduced; when the temperature reaches L3, the movement speed of the sample is reduced to 80% of the speed before regulation; When the sample movement speed is reduced to 80% of the pre-regulation speed, but the sample temperature continues to drop below L3, gradually increase the output power of the power supply to increase the heat input to the sample per unit time, but the power supply power is increased to 110% of the original output power at most; When the power output increases to 110% of the original output power but the sample temperature continues to decrease, the processing process is stopped.

10. The method according to claim 9, characterized in that The material type of the end heat-conducting metal is aluminum alloy with a thickness of 2 mm; the distance between the temperature measurement point behind the molten pool and the center of the molten pool is d=6 mm; the initial power of the electron beam power supply is 500 W; the initial movement speed of the sample is 200 mm / min; H3=500°C, H2=450°C, H1=400°C, L1=350°C, L2=300°C, L3=250°C.

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