Device and process for preparing high-purity oxygen-free copper by multi-channel deoxidation and impurity removal in continuous casting and rolling

Abstract

The application discloses a kind of high-purity oxygen-free copper multi-channel deoxidization and impurity removal preparation devices and preparation processes for continuous casting and rolling, including sequentially connected smelting unit, continuous casting unit, continuous rolling unit, and reduction gas injection interface and exhaust purification mechanism are arranged on the top of smelting furnace of smelting unit;It is also provided with a composite reduction unit composed of multiple-stage reduction channels, including: porous charcoal reduction mechanism, rare earth additive injection mechanism, and oxygen sensor is used to monitor the oxygen activity of melt in real time, and the reduction gas flow, the replacement frequency of porous charcoal reduction mechanism and the rare earth addition rate are dynamically adjusted.The composite reduction system of multi-channel reduction in the application efficiently removes oxygen and impurities, improves the quality of oxygen-free copper products, realizes integrated control of the whole process of continuous casting and rolling, realizes accurate adjustment of process parameters based on real-time feedback of oxygen sensor, significantly improves product consistency, realizes integrated continuous processing of continuous casting and rolling, avoids repeated smelting, reduces energy consumption, and reduces the amount of rare earth addition, so the cost is controllable.

Description

Technical Field

[0001] This invention relates to the field of oxygen-free copper preparation technology, and in particular to the preparation apparatus and process for high-purity oxygen-free copper by continuous casting and rolling. Background Technology

[0002] High-purity oxygen-free copper (oxygen content ≤10 ppm) has become a core material for key components in electronics, aerospace, and high-speed communications due to its extremely low oxygen content and excellent electrical and thermal conductivity, as well as its machinability. The low oxygen content makes it less prone to oxidation during high-temperature processing, maintaining its excellent metallic properties; it also reduces the scattering of electrons by oxides, bringing its resistivity and thermal conductivity close to theoretical values; furthermore, it enhances its plasticity and machinability, alleviates stress concentration and crack initiation, and adapts to the deformation requirements of various processing techniques.

[0003] Continuous casting and rolling is the mainstream process for large-scale production of oxygen-free copper rods. Its core challenge lies in the efficient removal of oxygen and impurity elements from the melt, which directly determines the purity and performance of the product. Existing technologies, such as oxidation-reduction refining and reducing gas protection, have significant limitations: traditional reverberatory furnace oxidation-reduction methods have low precision in oxygen concentration control, easily leading to over-reduction and hydrogen embrittlement risks, or insufficient oxidation resulting in impurity residues; easily soluble impurity elements such as nickel and arsenic are difficult to remove directionally, requiring repeated oxidation-reduction processes or dilution with pure copper, resulting in long process flows, high energy consumption, and increased costs. Impurity elements can introduce strong scattering centers, weakening electrical and thermal conductivity, forming solid solutions that cause lattice distortion and grain boundary segregation, reducing plasticity, and affecting corrosion resistance, inducing intergranular corrosion and localized corrosion. At the equipment level, the existing continuous casting system structure is not fully optimized, the contact between the melt and the reducing medium is insufficient, and the impurity diffusion efficiency is low; the reducing gas degassing system is not coordinated with the chemical reduction process, the deoxidation effect is limited, and it is prone to secondary oxygen absorption due to insufficient sealing, making it impossible to achieve dynamic and precise control of oxygen content.

[0004] Compared with international advanced levels, China's high-purity oxygen-free copper production technology lags significantly behind. Internationally leading processes, such as Lafarge's FRHC technology in Spain, employ composite additives to control impurity morphology and are equipped with online monitoring systems, consistently maintaining oxygen content below 5 ppm. However, this approach incurs high equipment investment and maintenance costs. While major domestic companies have introduced technologies like dip coating and upward continuous casting, their products generally have oxygen content exceeding 10 ppm, exhibiting low impurity control and defects such as coarse grains and shrinkage porosity in the cast billets, failing to meet the stringent requirements of high-end applications for material consistency and reliability. The core issue lies in the lack of multi-channel synergistic coupling in the deoxidation and impurity removal process. Physical degassing, chemical reduction, and trace element purification operate in isolation, resulting in low deoxidation efficiency and high impurity residue. Furthermore, the independent operation of each unit in continuous casting equipment, lacking integrated design and intelligent control mechanisms, hinders precise dynamic control of oxygen content and impurities. Currently, key performance indicators such as conductivity and elongation of oxygen-free copper rods do not meet the application thresholds for high-end fields, restricting the competitiveness and added value of domestically produced high-purity copper materials. Summary of the Invention

[0005] Purpose of the invention: One purpose of this invention is to provide a deoxidation and impurity removal preparation device for high-purity oxygen-free copper produced by continuous casting and rolling. Another purpose of this invention is to provide a corresponding preparation process, which, through the synergistic and optimized control of a multi-channel reduction mechanism, significantly reduces the oxygen content and impurity element content of continuously cast and rolled copper materials.

[0006] Technical solution: A multi-channel deoxidation and impurity removal preparation device for high-purity oxygen-free copper through continuous casting and rolling, comprising a smelting unit, a continuous casting unit, and a continuous rolling unit connected in sequence. The top of the smelting furnace in the smelting unit is equipped with a reducing gas injection interface and an exhaust purification mechanism. A composite reduction unit is also provided, consisting of multiple reduction channels, including: The porous charcoal reduction mechanism is located in the flow channel between the smelting furnace of the smelting unit and the holding furnace of the continuous casting unit. The molten material flows through the porous charcoal reduction mechanism. The rare earth additive injection mechanism is located at the inlet of the holding furnace in the continuous casting unit and injects a quantitative amount of composite rare earth wire containing lanthanum and yttrium into the holding furnace. The oxygen activity of the melt is monitored in real time by an oxygen sensor, and the flow rate of reducing gas, the replacement frequency of the porous charcoal reduction mechanism, and the rare earth addition rate are dynamically adjusted.

[0007] Furthermore, the porous charcoal reduction mechanism is made of birch charcoal that has been calcined at high temperature. The porous charcoal reduction mechanism has several channels, which are wavy. The channels are arranged in the same direction and in an array. The pore size of the channels is 5-10 mm, and the porosity formed by the channels is 60-70%.

[0008] Furthermore, the longitudinal section of the flow channel is circular or rectangular.

[0009] Furthermore, the oxygen sensor is a zirconium oxide oxygen sensor.

[0010] A manufacturing process for the above-mentioned multi-channel deoxidation and impurity removal apparatus for continuous casting and rolling of high-purity oxygen-free copper includes the following steps: S10, Raw material pretreatment: After removing surface oxides from the raw cathode copper by mechanical cutting, it is treated by an integrated pickling spray line, then rinsed with deionized water to remove residual acid and dried. S20: Smelting and preliminary deoxidation: The pretreated cathode copper is put into the smelting furnace, and reducing gas with a flow rate of 1 to 3 L / min is continuously introduced into the smelting furnace through the reducing gas injection port. The cathode copper is heated to 1150 to 1200℃ under the reducing atmosphere to melt and undergo preliminary degassing. S30, Multi-channel reduction: The melt flowing out of the smelting furnace passes through the porous charcoal reduction mechanism in the flow channel, with a contact time of ≥30s, and then flows into the holding furnace. Composite rare earth wires are quantitatively injected into the holding furnace from the rare earth additive injection mechanism, with an addition amount of 0.01~0.05% of the melt mass; S40, continuous casting: The holding furnace temperature is 1100~1150℃, so that the temperature of the melt is uniform and stable in the holding furnace. Then the melt enters the crystallizer for cooling through the zirconia sizing nozzle with a diameter of φ8~12mm. The billet pulling speed is 1.5~2.5m / min, and the copper liquid solidifies to form a billet. S50, continuous rolling and subsequent processing: the billet undergoes multiple hot rolling, cold rolling and intermittent annealing.

[0011] Furthermore, in step S10, the nitric acid mass concentration of the integrated pickling spray line is 5-10%, the temperature is 40-60℃, and the treatment time is 30-60s.

[0012] Furthermore, in step S30, the porous charcoal reduction mechanism is automatically replaced every 8 to 10 hours; the amount of composite rare earth wire added is 0.01 to 0.05% of the melt mass; and the mass ratio of lanthanum to yttrium in the composite rare earth wire is 1:1.

[0013] Furthermore, in step S40, the crystallizer is cooled by cooling water at a flow rate of 20-30 m³ / h. 3 / h.

[0014] Furthermore, in step S40, the initial rolling temperature of hot rolling is 850-900℃, the final rolling temperature is 500-550℃, and the annealing temperature is 400-450℃ for 1-2 hours.

[0015] Beneficial effects: This invention utilizes a multi-channel reduction composite reduction system to efficiently deoxidize and remove impurities, improving the quality of oxygen-free copper products. The oxygen content is ≤5 ppm, conductivity ≥101% IACS, and elongation ≥25%, significantly higher than existing products with oxygen content >10 ppm, conductivity <100.3% IACS, and elongation <20%, making it more suitable for high-end fields such as 5G communication and integrated circuits. The integrated intelligent dynamic control preparation method achieves integrated control of the entire continuous casting and rolling process. Based on real-time feedback from oxygen sensors, precise adjustment of process parameters is achieved, avoiding errors from manual intervention and significantly improving product consistency. The integrated continuous casting and rolling process avoids repeated smelting, reducing energy consumption by more than 20%, and requires less rare earth addition, making costs controllable. Attached Figure Description

[0016] Figure 1 Metallographic image of the cross-section of the oxygen-free copper product prepared in Example 1, in its as-cast state. Figure 2 Metallographic image of the as-cast microstructure of the oxygen-free copper product obtained in Example 1; Figure 3 This is a longitudinal cross-sectional view of a porous charcoal reduction mechanism; Figure 4 A side view of a porous charcoal reduction mechanism; Figure 5 This is a top view of a porous charcoal reduction mechanism. Detailed Implementation

[0017] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0018] A multi-channel deoxidation and impurity removal preparation device for high-purity oxygen-free copper by continuous casting and rolling includes a smelting unit, a continuous casting unit, and a continuous rolling unit connected in sequence according to the melt flow direction.

[0019] The main equipment of the smelting unit is the smelting furnace, which is a closed induction smelting furnace. The top of the furnace is equipped with a reducing gas injection port and an exhaust purification mechanism. The inner wall of the furnace is coated with high-purity magnesium oxide refractory material to prevent molten material contamination.

[0020] The main equipment in the continuous casting unit is the holding furnace.

[0021] A composite reduction unit is also provided between the smelting unit and the continuous casting unit. The composite reduction unit consists of multiple reduction channels, including: The porous charcoal reduction mechanism is arranged in the flow channel between the smelting furnace and the holding furnace, combined with the attached... Figure 3-5As shown, the porous charcoal reduction mechanism is made of birch charcoal that has been roasted at a high temperature of 700-800℃. It has several flow channels 1 through which the melt flows. The flow channels 1 are wavy along the flow direction, and the longitudinal section of the flow channels 1 is circular or rectangular. The pore size is 5-10mm. Several flow channels 1 are arranged in the same direction and are arranged in an array in the horizontal and vertical directions, as shown in the attached figure. Figure 3 The porosity of the porous charcoal reduction mechanism shown in the longitudinal section is 60-70% formed by several flow channels. The total contact time between the melt and the porous charcoal reduction mechanism can be calculated by combining the melt viscosity and the flow channel length. The porous charcoal reduction mechanism can be constructed by stacking several corrugated plates vertically. The melt flows through the porous charcoal reduction mechanism, which forms a continuous reduction interface, increases the contact area and contact time between the melt and the reducing medium, and improves the reduction efficiency. A rare earth additive injection mechanism is installed at the entrance of the holding furnace. Through this mechanism, composite rare earth wires containing lanthanum and yttrium are quantitatively injected into the holding furnace. The system uses an intelligent control system based on oxygen sensors to monitor the oxygen activity of the melt in real time, and dynamically adjusts the flow rate of reducing gas, the replacement frequency of the porous charcoal reduction mechanism, and the rare earth addition rate through a PID algorithm.

[0022] The oxygen sensor uses a zirconia oxygen sensor.

[0023] The process for preparing high-purity oxygen-free copper by continuous casting and rolling using the above-mentioned preparation apparatus specifically includes steps S10 to S50.

[0024] S10, Raw material pretreatment: The raw material cathode copper (Cu≥99.97%, mass content) is mechanically cut to remove surface oxides, and then treated by an integrated pickling spray line. The integrated pickling spray line has a nitric acid mass concentration of 5-10%, a temperature of 40-60℃, and a treatment time of 30-60s. After that, it is rinsed with deionized water to remove residual acid and then dried.

[0025] S20: Smelting and preliminary deoxidation: The pretreated cathode copper is put into the smelting furnace, and a reducing gas with a flow rate of 1 to 3 L / min is continuously introduced into the smelting furnace through the reducing gas injection port. The cathode copper is heated to 1150 to 1200℃ under the reducing atmosphere to melt. The reducing gas performs preliminary degassing to remove some impurity gases in the melt, laying the foundation for subsequent composite reduction.

[0026] S30, Multi-channel Reduction: The melt flowing out of the smelting furnace passes through the porous charcoal reduction mechanism in the flow channel. The porous charcoal reduction mechanism extends the melt flow path and dynamic contact area, ensuring that the total contact time between the melt and the porous charcoal reduction mechanism is stable at ≥30s. To ensure the stability of the reduction effect, the intelligent control system monitors the oxygen activity of the melt in real time. When the oxygen content of the melt at the outlet of the porous charcoal reduction mechanism continuously exceeds the set threshold, or when the operating time of the porous charcoal reduction mechanism reaches 8-10 hours, the system automatically issues an alert and initiates the replacement procedure. The robotic arm removes the saturated porous charcoal reduction mechanism and replaces it with a new one. The melt after reduction flows into the holding furnace, and composite rare earth wire is quantitatively injected into the holding furnace through the rare earth additive injection mechanism. The amount of composite rare earth wire added is 0.01-0.05% of the melt mass. The mass ratio of lanthanum to yttrium in the composite rare earth wire is 1:1, and the diameter of the composite rare earth wire is φ1-2mm.

[0027] Utilizing the extremely strong chemical reactivity of rare earth elements and their affinity for impurities such as oxygen, sulfur, phosphorus, and hydrogen, they can preferentially form rare earth oxides and sulfides as desolvation precipitates in molten copper. Simultaneously, rare earth elements can also form intermetallic compounds with readily soluble impurities such as nickel and arsenic, reducing their solubility in molten copper and thus achieving targeted removal.

[0028] S40, continuous casting: The holding furnace temperature is controlled at 1100-1150℃ to ensure a uniform and stable temperature of the molten metal flowing into the furnace. The molten metal then enters the crystallizer through a zirconia sizing nozzle with a diameter of φ8-12mm. The crystallizer is cooled by cooling water at a flow rate of 20-30m³. 3 The casting speed is 1.5 to 2.5 m / min, which allows the molten copper to cool and solidify rapidly in the crystallizer to form a casting billet.

[0029] S50, continuous rolling and subsequent treatment: The billet undergoes multiple hot rolling, cold rolling and intermittent annealing. The initial rolling temperature of hot rolling is 850-900℃, the final rolling temperature is 500-550℃, and the annealing temperature is 400-450℃ for 1-2 hours.

[0030] The principle of this invention is as follows: Physical degassing with reducing gas protects and initially reduces the surface of the melt. The reducing gas is injected counter-currently from top to bottom in the smelting furnace, enhancing the mass transfer between bubbles and the melt. As the generated bubbles rise, they carry away hydrogen and inclusions. Chemical reduction with porous charcoal increases the contact area between the melt and the reducing agent, continuously deoxidizing the melt and maintaining the atmosphere. Rare earth additives provide trace element purification, achieving deep grain boundary purification and microstructure optimization of the melt. The three work synergistically to form a complete and coordinated deoxidation and impurity removal system, which progresses from the surface to the interior of the melt, from deoxidation to impurity removal, and is organically combined and optimized. This results in an overall deoxidation efficiency improvement of over 40%, achieving oxygen content ≤5ppm, nickel ≤0.005%, and arsenic ≤0.0005% in oxygen-free copper products, thus realizing ultra-low impurity control and improved deoxidation efficiency in oxygen-free copper.

[0031] Advantages of this invention: 1. Through a multi-channel reduction composite reduction system, oxygen and impurities are efficiently removed, improving the quality of oxygen-free copper products. The oxygen content is ≤5 ppm, conductivity is ≥101% IACS, and elongation is ≥25%, which is significantly higher than the performance of existing products with oxygen content >10 ppm, conductivity <100.3% IACS, and elongation <20%. It is more suitable for high-end fields such as 5G communication and integrated circuits. 2. The integrated intelligent dynamic control preparation method realizes integrated control of the entire continuous casting and rolling process. Based on real-time feedback from oxygen sensors, it enables precise adjustment of process parameters, avoids errors caused by human intervention, and significantly improves product consistency. 3. The integrated continuous casting and rolling process avoids repeated smelting, reduces energy consumption by more than 20%, and requires less rare earth addition, making costs controllable.

[0032] The materials used in the examples and comparative examples are as follows: the raw material is cathode copper Cu-CATH-1 grade (GB / T 467-2010); the porous charcoal reduction mechanism is made of birch charcoal that has been calcined at 700℃, with a pore size of 1 mm and a porosity of 75%; the reducing gas is a mixture of natural gas and nitrogen, with a volume ratio of approximately 1:10 and a flow rate of 1.5 L / min; the composite rare earth wire is a lanthanum and yttrium composite wire, with a lanthanum to yttrium mass ratio of 1:1, and the addition amount is 0.03% of the melt mass.

[0033] Example 1

[0034] According to the preparation process of the present invention, the melting temperature in step S20 is 1180℃, the contact time between the melt and the porous charcoal reduction mechanism in step S30 is 30s, and the holding furnace temperature in step S40 is 1120℃ and the billet pulling speed is 2m / min, so as to obtain oxygen-free copper.

[0035] Product testing revealed the following properties: oxygen content 3.2 ppm, nickel content 0.004%, arsenic not detected; conductivity 101.2% IACS, elongation 26.5%. (See attached image) Figure 1 , 2 The figures shown are cross-sectional (transverse) and side (longitudinal) metallographic images of the oxygen-free copper product obtained in this embodiment, in its as-cast state. Figure 1 This indicates that the grain size is uniform and there are no shrinkage cavities, porosity, or cracks. Figure 2 This indicates that directional solidification is good.

[0036] Comparative Example 1 The difference compared to Example 1 is that no composite rare earth wire was added in step S30.

[0037] Product testing revealed the following properties: oxygen content 9.3 ppm, nickel content 0.007%, arsenic content 0.008%; conductivity 100.9% IACS, elongation 22.6%.

[0038] Comparative Example 2 The difference compared to Example 1 is that a porous charcoal reduction mechanism is not provided in step S30.

[0039] Product testing revealed the following properties: oxygen content 8.2 ppm, nickel content 0.01%, arsenic content 0.008%; conductivity 100.3% IACS, elongation 21.6%.

[0040] Comparative Example 3 The difference from Example 1 is that no reducing gas was introduced in step S20.

[0041] Product testing revealed the following properties: oxygen content 7.8 ppm, nickel content 0.009%, arsenic content 0.01%; conductivity 100.6% IACS, elongation 22.3%.

[0042] Comparative Example 4 Compared with Example 1, the difference is that: no porous charcoal reduction mechanism was set in step S30 and no composite rare earth wire was added.

[0043] Product testing revealed the following properties: oxygen content 12.8 ppm, nickel content 0.011%, arsenic content 0.01%; conductivity 100.1% IACS, elongation 19.6%.

[0044] Comparative Example 5 Compared with Example 1, the difference is that: no reducing gas was introduced in step S20 and no porous charcoal reduction mechanism was set in step S30.

[0045] Product testing revealed the following properties: oxygen content 13.1 ppm, nickel content 0.012%, arsenic content 0.011%; conductivity 99.8% IACS, elongation 20.3%.

[0046] Comparative Example 6 Compared with Example 1, the difference is that: no reducing gas was introduced in step S20 and no composite rare earth wire was added in step S30.

[0047] Product testing revealed the following properties: oxygen content 12.6 ppm, nickel content 0.012%, arsenic content 0.012%; conductivity 100.3% IACS, elongation 21.5%.

[0048] Comparative Example 7 The traditional reverberatory furnace oxidation-reduction process is adopted.

[0049] The product's performance was tested as follows: oxygen content 18 ppm, nickel content 0.015%, arsenic content 0.002%; conductivity 99.5% IACS, elongation 18%.

[0050] As can be seen from the comparison between Example 1 and Comparative Examples 1-7, the oxygen-free copper prepared by the preparation apparatus and process of the present invention has significantly improved performance.

Claims

1. A multi-channel deoxidation and impurity removal apparatus for preparing high-purity oxygen-free copper by continuous casting and rolling, comprising a smelting unit, a continuous casting unit, and a continuous rolling unit connected in sequence, characterized in that: The top of the smelting furnace in the smelting unit is equipped with a reducing gas injection port and an exhaust purification mechanism; A composite reduction unit is also provided, which consists of multiple reduction channels, including: The porous charcoal reduction mechanism is located in the flow channel between the smelting furnace of the smelting unit and the holding furnace of the continuous casting unit. The molten material flows through the porous charcoal reduction mechanism. The rare earth additive injection mechanism is located at the inlet of the holding furnace in the continuous casting unit and injects a quantitative amount of composite rare earth wire containing lanthanum and yttrium into the holding furnace. The oxygen activity of the melt is monitored in real time by an oxygen sensor, and the flow rate of reducing gas, the replacement frequency of the porous charcoal reduction mechanism, and the rare earth addition rate are dynamically adjusted.

2. The multi-channel deoxidation and impurity removal preparation device for high-purity oxygen-free copper by continuous casting and rolling according to claim 1, characterized in that: The porous charcoal reduction mechanism is made of birch charcoal that has been roasted at high temperature. The porous charcoal reduction mechanism has several channels, which are wavy. The channels are arranged in the same direction and in an array. The pore size of the channels is 5-10 mm, and the porosity formed by the channels is 60-70%.

3. The multi-channel deoxidation and impurity removal preparation device for high-purity oxygen-free copper by continuous casting and rolling according to claim 2, characterized in that: The longitudinal section of the flow channel is circular or rectangular.

4. The multi-channel deoxidation and impurity removal apparatus for preparing high-purity oxygen-free copper by continuous casting and rolling according to claim 1, characterized in that: The oxygen sensor is a zirconia oxygen sensor.

5. A preparation process for the multi-channel deoxidation and impurity removal apparatus for continuous casting and rolling of high-purity oxygen-free copper according to any one of claims 1 to 4, characterized in that... Includes the following steps: S10, Raw material pretreatment: After removing surface oxides from the raw cathode copper by mechanical cutting, it is treated by an integrated pickling spray line, then rinsed with deionized water to remove residual acid and dried. S20: Smelting and preliminary deoxidation: The pretreated cathode copper is put into the smelting furnace, and reducing gas with a flow rate of 1 to 3 L / min is continuously introduced into the smelting furnace through the reducing gas injection port. The cathode copper is heated to 1150 to 1200℃ under the reducing atmosphere to melt and undergo preliminary degassing. S30, Multi-channel reduction: The melt flowing out of the smelting furnace passes through the porous charcoal reduction mechanism in the flow channel, with a contact time of ≥30s, and then flows into the holding furnace. Composite rare earth wires are quantitatively injected into the holding furnace from the rare earth additive injection mechanism, with an addition amount of 0.01~0.05% of the melt mass; S40, continuous casting: The holding furnace temperature is 1100~1150℃, so that the temperature of the melt is uniform and stable in the holding furnace. Then the melt enters the crystallizer for cooling through the zirconia sizing nozzle with a diameter of φ8~12mm. The billet pulling speed is 1.5~2.5m / min, and the copper liquid solidifies to form a billet. S50, continuous rolling and subsequent processing: the billet undergoes multiple hot rolling, cold rolling and intermittent annealing.

6. The preparation process according to claim 5, characterized in that: In step S10, the nitric acid mass concentration of the integrated pickling spray line is 5-10%, the temperature is 40-60℃, and the treatment time is 30-60s.

7. The preparation process according to claim 5, characterized in that: In step S30, the porous charcoal reduction mechanism is automatically replaced every 8 to 10 hours; the amount of composite rare earth wire added is 0.01 to 0.05% of the melt mass; the mass ratio of lanthanum to yttrium in the composite rare earth wire is 1:

1.

8. The preparation process according to claim 5, characterized in that: In step S40, the crystallizer is cooled with cooling water at a flow rate of 20-30 m³ / h. 3 / h.

9. The preparation process according to claim 5, characterized in that: In step S40, the initial rolling temperature of hot rolling is 850-900℃, the final rolling temperature is 500-550℃, and the annealing temperature is 400-450℃ for 1-2 hours.

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