10-kw class deep penetration laser welding method and auxiliary material, and auxiliary material preparation method

Abstract

A 10-kW class deep penetration laser welding method and auxiliary material, and an auxiliary material preparation method. The 10-kW class deep penetration laser welding method comprises: during 10-kW class laser welding, simultaneously feeding a flux into a molten pool as an auxiliary material, to achieve full coverage of the surface of the molten pool.

Description

A method for kilowatt-level laser deep penetration welding, auxiliary material and preparation method of auxiliary material TECHNICAL FIELD

[0001] The present application relates to the technical field of welding manufacturing, in particular to a method for kilowatt-level laser deep penetration welding, an auxiliary material and a preparation method of the auxiliary material. BACKGROUND

[0002] Laser processing technology is an advanced processing technology with wide application prospect at present. Laser processing technology is known as "the green processing technology of the future" and is an important new processing method in manufacturing industry. In recent years, with the industrial laser in China entering the kilowatt era, the cost of fiber laser is greatly reduced, the output power is stable, and the beam quality is stable, which has penetrated into the fields of national defense and military industry, ocean engineering, rail transportation and the like.

[0003] However, how to use high-quality high-power laser to carry out efficient and high-quality welding has become a technical problem in the field of welding. Compared with kilowatt-level laser welding, kilowatt-level laser welding increases the input of laser energy in the limited welding area by nearly ten times, the evaporation of the material inside the welding hole is more intense, and the interaction between the metal vapor and plasma above the welding hole and the laser beam is more intense. Therefore, in the process of thick plate welding, problems such as shallow weld penetration, surface spatter, internal porosity, upper surface depression, poor weld protection and difficulty in realizing the performance regulation of the molten pool are prone to occur, thereby leading to the difficulty of kilowatt-level laser welding in practical production.

[0004] At present, the method for improving the quality of high-power laser welding known by the inventor mainly includes: adjusting welding protective gas, external energy field and welding in vacuum environment. The welding protective gas is usually protected by helium and nitrogen. When welding is carried out by using helium protection, although the area of plasma is reduced and the weld penetration is increased, the plasma and spoon hole have unstable characteristics, and a large number of pores are easily formed inside the weld. In order to reduce the internal pores, a proper amount of nitrogen is added to the helium for protection. The addition of nitrogen causes the periodic disappearance and appearance of plasma and spoon hole, which is beneficial to the exclusion of internal pores of spoon hole and the reduction of internal pores of weld. However, this method changes with the change of welding materials, and can only be effectively used in suitable materials to reduce pores, and does not have universal applicability. At the same time, the molten pool of ten-kilowatt laser welding is large, and too small welding protective gas has poor protective effect on the molten pool, and too large protective gas causes disorder of the molten pool, so it is difficult to realize the all-round protection of the molten pool by using the protective gas method. The external energy field usually changes the flow mode of the molten pool by adding external magnetic field, and the external magnetic field can also realize the stirring of the molten pool to reduce the internal pores of the weld. However, the addition of high-frequency magnetic field device will cause electromagnetic interference to other parts of the device, and the high-frequency magnetic field will also harm the human body, so it is difficult to be widely used in engineering. Welding in vacuum environment can significantly increase the weld penetration, increase the stability of welding process, reduce welding spatter, reduce internal pores of weld, solve the problems of weld surface depression and poor weld protection, etc. However, the welding process needs to be vacuumized, which needs a vacuum chamber and a vacuum pump set, significantly increasing the welding cost. SUMMARY

[0005] The present application provides a ten-kilowatt laser deep penetration welding method. When ten-kilowatt laser welding is used, flux is synchronously delivered into the molten pool as auxiliary material to realize full coverage of the molten pool surface. BRIEF DESCRIPTION OF DRAWINGS

[0006] Fig. 1 is a schematic diagram of the ten-kilowatt laser deep penetration welding method in the embodiment of the present application;

[0007] Figs. 2a-2c are schematic diagrams of the influence of different auxiliary material (i.e. flux) flow rates on the stability of the welding process in the embodiment of the present application;

[0008] Figs. 3a-3b are comparative diagrams of the weld surface topography of the ten-kilowatt laser deep penetration welding method and the traditional gas shielded welding in the embodiment of the present application;

[0009] Figs. 4a-4b are comparative diagrams of the weld cross-sectional topography of the ten-kilowatt laser deep penetration welding method and the traditional gas shielded welding in the embodiment of the present application;

[0010] Wherein: 1, laser; 2, optical fiber; 3, powder feeding pipe; 4, double-cylinder powder feeder; 5, laser coaxial flux feeding head; 6, test plate to be welded. DETAILED DESCRIPTION

[0011] The advantages and features of the present application can be more easily understood by those skilled in the art from the following detailed description of the present application taken in conjunction with the accompanying drawings and preferred embodiments, and the scope of the present application will be made more clearly defined.

[0012] The purpose of the present application is to provide a kilowatt-level laser deep penetration welding method, auxiliary material and auxiliary material preparation method, which uses flux as auxiliary material to replace the protective gas in traditional laser welding, and can solve the problems of shallow weld penetration, surface spatter, internal porosity, surface depression, poor weld protection and difficulty in realizing molten pool organization performance control during kilowatt-level laser welding of thick plates (single-pass weld penetration depth greater than 10mm).

[0013] The present application has the following technical effects:

[0014] When performing kilowatt-level laser deep penetration welding, the present application uses flux as auxiliary material to replace the protective gas, which solves the problems of shallow weld penetration, surface spatter, internal porosity, surface depression, poor weld protection and difficulty in realizing molten pool organization performance control during kilowatt-level laser welding of thick plates.

[0015] Example 1:

[0016] In view of the outstanding technical problems of shallow weld penetration, surface spatter, internal porosity, surface depression, poor weld protection and difficulty in realizing organization performance control during kilowatt-level laser gas shielded welding (single-pass weld penetration depth greater than 10mm), a kilowatt-level laser deep penetration welding method is proposed.

[0017] When using kilowatt-level laser deep penetration welding, the traditional method of conveying protective gas is abandoned, and flux is synchronously conveyed into the molten pool as auxiliary material to achieve full coverage of the molten pool. By introducing flux as auxiliary material during kilowatt-level laser deep penetration welding, the molten pool is fully protected by the flux, and the molten pool is covered by the flux, which can reduce the convection heat dissipation of the molten pool and air, increase the solidification time of the molten pool, and thus reduce the porosity of the weld.

[0018] In the kilowatt-level laser deep penetration welding, the flux as auxiliary material is composed of molten salt, metal oxide and micro-alloying element. The molten metal in the flux can compensate for the problem of weld surface depression caused by spatter during welding, and the micro-alloying element in the flux can transition to the molten pool to realize the problem of weld organization performance control,

[0019] In an embodiment, active agents can be added to the flux. The addition of active agents in the flux can increase the weld penetration depth without increasing the power.

[0020] In an embodiment, during welding, in order to match the laser power, the flux flow should be:

[0021] Wherein: L0 is the set reference flux flow, in this example, 20 L / min; P0 is the set reference power of the laser, in this example, 10 kW; P1 is the actual output power of the laser during welding, kW; L is the actual required flux flow during welding, L / min.

[0022] The reference power of the laser and the reference flux flow are matched in advance, and the required flux flow is calculated according to the actual output power of the laser during welding.

[0023] In an embodiment, a swing type laser is used.

[0024] When using a ten-kilowatt laser for deep penetration welding:

[0025] Firstly, design the groove form of the workpiece to be welded, and pretreat the surface of the workpiece to be welded to remove oil stains and oxides on the surface of the workpiece to be welded. As an example, an I-shaped groove form is used, and the groove gap is 0 mm; the workpiece groove is cleaned by mechanical grinding, and the cleaned groove is wiped with acetone or alcohol to make it leak the original color of the metal. The workpiece to be welded is any one of carbon steel, high-strength steel, stainless steel and other metal materials.

[0026] Then, set the welding parameters, including: laser type and fiber core diameter, laser power, welding speed, defocusing amount, laser beam swing mode, laser beam swing amplitude and frequency, and flux flow during welding.

[0027] In an embodiment, the laser is selected from a fiber laser or a YAG solid-state laser, the fiber core diameter is 200 μm to 400 μm, the laser power is 10 kW to 20 kW, the welding speed is 0.6 m / min to 2 m / min, the defocusing amount is -30 mm to 10 mm, the laser beam swing mode is a triangle or an ellipse, when the triangle swing mode is used, an equilateral triangle is used, when the ellipse swing mode is used, the aspect ratio of the ellipse is 1.5 to 4, each scanning path has two different beam movement directions of clockwise and counterclockwise, the laser beam swing amplitude is 1 mm to 2 mm, and the laser beam swing frequency is 200 Hz to 600 Hz.

[0028] In an embodiment, the axis of the laser is inclined forward by an angle of 0° to 10° relative to the normal of the workpiece to be welded.

[0029] Finally, after checking the running state of each part of the welding device, the welding device is started to perform welding, and after the welding is completed, the slag shell on the surface of the weld is removed to complete the welding.

[0030] An embodiment of the method of deep penetration welding with kilowatt-level laser coaxial flux feeding is given below:

[0031] The workpiece to be welded is Q345B steel with a thickness of 40 mm, and an I-shaped groove is used with a gap of 0 mm. The groove of the workpiece to be welded is cleaned by mechanical polishing, and the polished groove is wiped with alcohol to make it leak the original color of the metal. The laser used is a fiber laser with a fiber core diameter of 400 μm. The normal angle between the laser and the workpiece to be welded is 5°, the laser power is 10 kW, the welding speed is 0.6 m / min, the defocusing amount is -10 mm, the laser beam oscillation mode is triangular, the laser beam oscillation amplitude is 1 mm, and the laser beam oscillation frequency is 200 Hz. According to the above formula (1), the flux flow is calculated to be 20 L / min. Before welding, the running state of the welding device is checked, and then the welding device is started for welding. During the laser welding process, the flux is synchronously fed into the molten pool as an auxiliary material to achieve full coverage of the molten pool. After welding, the slag shell on the surface of the weld is removed to complete the welding.

[0032] Figures 2a-2c are the effects of different flux flows on the stability of the welding process. The effects of different flux flows on the welding process can be observed by high-speed photography. When the flux flow is 18 L / min (Figure 2a), it can be seen that the molten pool after welding is not tightly wrapped by the flux and is in contact with the atmosphere. At this time, the weld is not well protected, so the flux flow of 18 L / min cannot meet the use conditions. When the flux flow is 20 L / min (Figure 2b), it can be seen that the molten pool after welding is tightly wrapped by the flux. At this time, the flux has a good protective effect on the molten pool, and the welding process is stable. When the flux flow is 22 L / min (Figure 2c), the laser welding spoon is buried in thick and heavy flux, and the welding process is unstable and bright and dark. Therefore, the flux flow must be strictly calculated according to formula (1).

[0033] Figures 3a-3b are comparative diagrams of the surface morphology of the weld joint of kilowatt-level laser coaxial flux feeding welding (Figure 3a) and the surface morphology of the weld joint of kilowatt-level gas shielded welding (Figure 3b). It can be seen from the comparison that the surface protection effect of kilowatt-level laser coaxial flux feeding welding is better than that of kilowatt-level gas shielded welding, and the weld spatter is significantly reduced, and the upper surface is not recessed.

[0034] Figures 4a-4b are comparative diagrams of the cross-sectional morphology of the weld joint of kilowatt-level laser coaxial flux feeding welding (Figure 4a) and the cross-sectional morphology of the weld joint of kilowatt-level gas shielded welding (Figure 4b). It can be seen from the comparison that the weld penetration of kilowatt-level laser coaxial flux feeding welding is increased by 12.75% compared with that of kilowatt-level gas shielded welding.

[0035] Table 1 is a comparison of the mechanical properties of the welds of the 10-kilowatt laser coaxial flux feeding welding and the 10-kilowatt gas shielded welding. The comparison shows that the yield strength of the 10-kilowatt laser coaxial flux feeding welding is increased by 8.14%, the tensile strength is increased by 6.93%, the elongation is increased by 12.9%, the impact toughness is increased by 14.29%, and the porosity of the weld is reduced by 35% compared with the 10-kilowatt gas shielded welding.

[0036] Table 1 Mechanical properties and porosity of welded joints

[0037] Example 2

[0038] On the basis of the above-mentioned example 1, this example gives a 10-kilowatt laser deep penetration welding device.

[0039] As shown in FIG. 1, the welding device includes a laser 1, an optical fiber 2, a double-cylinder powder feeder 4, and a laser coaxial flux feeding head 5, the double-cylinder powder feeder 4 and the laser coaxial flux feeding head 5 are connected through a powder feeding pipe 3; the laser 1 is a 10-kilowatt swing type optical fiber laser, the laser coaxial flux feeding head 5 is a ring sleeve structure, which is coaxially sleeved outside the laser beam, and a plurality of flux feeding channels are uniformly and spacedly distributed in the inside of the laser coaxial flux feeding head 5 in the circumferential direction, each flux feeding channel is connected with a double-cylinder powder feeder 4. Thus, in the welding process, the double-cylinder powder feeder 4 feeds the flux into the molten pool of the to-be-welded test plate 6 through the flux feeding channel, and the circumferential arrangement of the flux feeding channel ensures that the 10-kilowatt laser welding molten pool is completely covered by the flux.

[0040] Example 3

[0041] On the basis of the above-mentioned example 1, this example gives a formula of the flux as an auxiliary material of the 10-kilowatt laser deep penetration welding method.

[0042] The auxiliary material of the 10-kilowatt laser deep penetration welding method is a flux composed of molten salt, metal oxide, and micro-alloying elements; the mass percentage (Wt / %) of each component is as follows: SiO2: 8% to 10%, CaO: 12% to 14%, Mn: 15% to 18%, TiO2: 5% to 8%, Ce: 0.5% to 1%, Nb: 0.5% to 1%, CaF2: the balance.

[0043] SiO2 in the flux can improve the metal fluidity and promote the removal of molten slag from the molten pool; however, when the added amount is too high, it will increase the burning loss of alloying elements of the deposited metal and increase the crack tendency, so the content of SiO2 is limited to 8% to 10%.

[0044] CaO in the flux can reduce the content of S and P in the weld, reduce the tendency of hot cracking, and also reduce the activity of SiO2 in the slag, inhibit the transition of Si element from the slag to the weld. At the same time, CaO is a good activator, and appropriate addition can ensure that the welding penetration is increased without increasing the laser power, which can effectively improve the anti-high laser power capability of the flux and improve the formation of the ten-kilowatt laser welding. However, when the addition amount is too high, it will further increase the welding penetration and increase the risk of weld bottom crack and pore defects, so the content of CaO is limited to 12% to 14%.

[0045] Mn powder in the flux can reduce the content of O element in the weld, improve the mechanical properties of the joint, and require Mn / Si>1.5 to ensure that the joint has high impact toughness, but too high Mn element will form MnS impurities with S element in the steel, so the content of Mn powder is limited to 15% to 18%. The purity of Mn powder is ≥99%.

[0046] TiO2 in the flux can reduce the melting temperature of the flux, improve the fluidity of the slag, promote the reduction products of the weld metal to gather and be excluded to the slag, and the increase of TiO2 content will make the slag shell easy to fall off, and the weld metal smooth. At high temperature, it can react with CaF2 to form TiF4, which has the effects of anti-pore and inhibiting the concentration of plume.

[0047] The micro-alloying elements in the flux include rare earth elements Ce and Nb, and the addition of rare earth elements Ce and Nb can ensure that the weld metal grain is small and uniform under the condition of high-speed welding of ten-kilowatt laser welding, and improve the tensile properties and impact toughness of the weld. The purity of Ce powder and Nb powder is ≥99.5%.

[0048] CaF2 in the flux can reduce the viscosity of alloy elements in the flux, increase the spreadability of the slag, and be more conducive to the protection of the molten pool during the flux process. Higher CaF2 content can ensure the protection effect of the weld pool during ten-kilowatt laser welding at high welding speed.

[0049] Example 4:

[0050] Based on the above example 3, the present embodiment provides a preparation method of a flux as an auxiliary material for ten-kilowatt laser deep penetration welding method.

[0051] Step 1: Dry mixing: the components of the flux, molten salt, metal oxide and micro-alloying elements, are composed of SiO2: 8% to 10%, CaO: 12% to 14%, Mn: 15% to 18%, TiO2: 5% to 8%, Ce: 0.5% to 1%, Nb: 0.5% to 1%, CaF2: the balance, according to the mass percentage (Wt / %) ratio. Pour the weighed dry powder into the container and mix and stir until the dry powder is uniform in color and free of lumps.

[0052] Step 2: Add binder: Potassium-sodium mixed water glass is used as the binder, and the amount of potassium-sodium mixed water glass added is generally 14% to 16% of the weight of the dry powder. The density of the potassium-sodium mixed water glass is in the range of 1.35 g / cm 3 ~ 1.42 g / cm 3 When adding potassium-sodium mixed water glass, slowly pour the potassium-sodium mixed water glass into the container of the mixed dry powder. If the addition speed is too fast, it will cause great difficulty in subsequent wet mixing and granulation.

[0053] Step 3: Wet mixing: After pouring the potassium-sodium water glass into the container of the mixed dry powder, do not immediately wet mix, but wait for the potassium-sodium water glass to completely "disappear" (2 min to 3 min), and then wet stir until uniform and semi-solid, as wet material.

[0054] Step 4: Granulation: Wet mixing is a key part of the flux production process; the uniformly stirred wet material is repeatedly rubbed back and forth in the container basin, and sieved through a sieve to ensure that the flux has a mesh size of 5 mesh to 10 mesh.

[0055] Step 5: Drying: The flux particles just completed granulation contain a lot of water, and the shape and size of the flux particles are unstable and are prone to caking. Therefore, the flux should be spread out and dried before drying. In this flux production process, the drying process is: the granulated flux is placed in a well-ventilated room for 5 to 6 hours to dry.

[0056] Step 6: Drying: The dried flux is placed in a drying oven, and the main purpose of drying is to further remove the attached water in the sintered flux. In order to prevent the sintered flux from caking during drying, the drying temperature should be slowly increased, and the drying process used is: 200°C x 0.2h + 250°C x 0.5h.

[0057] Step 7: Sintering: The purpose of sintering is to completely remove the water in the flux and increase the strength of the particles. The dried flux particles are placed in a sintering furnace and heated to 750°C to 800°C, and the sintering time is 2.5h to 3h.

[0058] Step 8: The sintered flux is dried in a drying oven to remove the water in the flux, and the dried flux is stored in a powder feeder for use when welding. As an example, the temperature of the drying oven is 100°C to 150°C, and the drying time is 60 min to 90 min.

[0059] An example of preparing the above auxiliary material is given as follows:

[0060] The composition of the flux, molten salt, metal oxide and micro-alloying element is as follows in terms of mass percentage (Wt / %): SiO2: 8%, CaO: 14%, Mn: 16%, TiO2: 7%, Ce: 0.8%, Nb: 0.6%, CaF2: balance. Among them, Mn / Si=2, the purity of Mn powder is 99.5%, the purity of Ce powder is 99.95%, and the purity of Nb powder is 99.95%.

[0061] The weighed dry powder is poured into a container for mixing and stirring according to the determined ratio of the composition of the flux, molten salt, metal oxide and micro-alloying element, until the color of the powder is uniform and there is no caking. Potassium-sodium mixed water glass with a weight of 15% of the dry powder is added, and the density of the potassium-sodium mixed water glass is 1.40 g / cm 3 When the potassium-sodium mixed water glass is added, the potassium-sodium mixed water glass is slowly poured into the container with mixed dry powder, then the water glass is completely "disappeared" (3 min), and then wet stirring is carried out until it is uniformly semi-solid. The wet material stirred uniformly is repeatedly rubbed in the container basin and sieved through a 10-mesh sieve to ensure that the mesh number of the flux is 5-10. The flux particles just completed granulation contain a lot of moisture, and the shape and size of the flux particles are unstable and are prone to caking. Therefore, the flux should be spread and dried before drying. The granulated flux is placed at room temperature and ventilated conditions for about 6 h for drying. The dried flux is placed in a drying oven. In order to prevent the caking of the sintered flux during drying, the drying temperature is slowly increased, and the drying process adopted is: 200 DEG C x 0.2 h + 250 DEG C x 0.5 h. The dried flux particles are heated to 800 DEG C in a sintering furnace, and the sintering time is 2.5 h. The sintered flux is dried in a drying oven to remove the water in the welding, and the dried welding is placed in a powder feeder for use when welding. The temperature of the drying oven is 100 DEG C, and the drying time is 60 min.

[0062] The technical solution of the present application can also achieve the following technical effects:

[0063] (1) In the present application, in the process of welding, the flux flow is set to ensure that the molten pool formed after welding is tightly wrapped by the flux to form a slag crust, which can realize the all-round protection of the molten pool on the surface of the weld, improve the problem of surface depression of the weld, and at the same time, the molten pool is covered by the flux to reduce the heat dissipation of the molten pool and air convection, increase the solidification time of the molten pool, and thus reduce the porosity of the weld, and strengthen the protection effect on the weld.

[0064] (2) The auxiliary material (i.e. flux) for the ten-kilowatt laser welding given in the application, alloy elements in the auxiliary material melt and transition to the weld, which makes up the problem of the upper surface depression caused by welding spatter; the beneficial alloy elements Ce and Nb in the auxiliary material can transition to the molten pool to realize the weld structure performance regulation, and improve the strength and plasticity and toughness of the welded joint.

[0065] (3) The auxiliary material (i.e. flux) for the ten-kilowatt laser welding given in the application, CaO is added to realize the increase of the weld penetration depth under the condition of not increasing the power.

[0066] (4) The auxiliary material (i.e. flux) for the ten-kilowatt laser welding given in the application, TiO2 is added to inhibit the concentration of the welding halo in the welding process, and increase the stability of the welding process.

[0067] To sum up, the above is only a preferred embodiment of the application, and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method of kilowatt class laser deep penetration welding, characterized by: When a ten-kilowatt laser is used, flux is synchronously delivered into the molten pool as an auxiliary material to achieve full coverage of the molten pool surface.

2. The 10-kilowatt class laser deep penetration welding method as claimed in claim 1, characterized in that: The flux flow rate is: In the formula, L0: set flux reference flow, L / min; P1: power output of the laser used during welding, kW; P0: set reference power of the laser, kW; L: flux flow required during welding, L / min.

3. The 10-kilowatt class laser deep penetration welding method as claimed in claim 1, characterized in that: The components in the auxiliary material are as follows in terms of mass percentage: SiO2: 8-10%, CaO: 12-14%, Mn: 15-18%, TiO2: 5-8%, Ce: 0.5-1%, Nb: 0.5-1%, CaF2: balance.

4. The multi-kilowatt laser deep penetration welding method according to claim 1 or 2 or 3, characterized in that: A swing-type laser is used.

5. The multi-kilowatt laser deep penetration welding method according to claim 4, characterized in that: The power of the laser is 10-20 kW, and the defocusing amount is -30-10 mm; the swing mode of the laser beam is triangular or elliptical; when the triangular swing mode is used, an equilateral triangle is used; when the elliptical swing mode is used, the length-diameter ratio of the ellipse is 1.5-4; the swing amplitude of the laser beam is 1-2 mm; and the swing frequency of the laser beam is 200-600 Hz.

6. The multi-kilowatt laser deep penetration welding method according to claim 1 or 2 or 3, characterized in that: The angle of inclination of the axis of the laser relative to the normal of the workpiece to be welded is 0-10°.

7. A kilowatt class laser deep penetration welding auxiliary material, characterized by: The components in the auxiliary material are as follows in terms of mass percentage: SiO2: 8-10%, CaO: 12-14%, Mn: 15-18%, TiO2: 5-8%, Ce: 0.5-1%, Nb: 0.5-1%, CaF2: balance.

8. The ten-kilowatt class laser deep penetration welding auxiliary material according to claim 7, characterized by: In the auxiliary material, the purity of the Mn powder is ≥99%, and the purity of the Ce and Nb powders is ≥99.5%.

9. A method for preparing auxiliary materials for megawatt laser deep penetration welding, characterized in that: The auxiliary material is prepared by the method of claim 9; Step 1: dry mixing: the dry powders of the components are weighed according to the set ratio, poured into a container, and mixed and stirred to form a dry powder mixture; Step 2: a binder is added to the dry powder mixture formed in step 1, and wet stirring is performed until the mixture is uniformly semi-solid, serving as a wet material; Step 3: granulation to form flux particles with a set mesh size; Step 4: drying; Step 5: drying: the dried flux particles are placed in a drying oven for drying; Step 6: sintering: the dried flux particles are placed in a sintering furnace and heated to 750-800°C, and the sintering time is 2.5-3 h; Step 7: the sintered flux is dried in a drying oven; the temperature of the drying oven is 100-150°C, and the drying time is 60-90 min.

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