A pipe inner wall coating process

Abstract

The present application provides a tube inner wall coating process, which belongs to the field of coating technology. The tube inner wall coating process includes providing a tube whose inner wall is covered with a slurry; and sequentially performing a first and a second drying on the slurry. Along the axial direction of the tube, the tube has a first tube opening and a second tube opening that are relatively arranged. The first drying includes rotating the tube around its axial direction at a first rotational speed, so that a first airflow enters the interior of the tube from the first tube opening and flows out from the second tube opening. The second drying includes rotating the tube around its axial direction at a second rotational speed, so that a second airflow enters the interior of the tube from the first tube opening and flows out from the second tube opening. During the first drying and the second drying, the first tube opening is located above the second tube opening. The first rotational speed is greater than the second rotational speed, the temperature of the first airflow is greater than the temperature of the second airflow, and the flow rate of the first airflow is less than the flow rate of the second airflow. The tube inner wall coating process provided by the present application can not only improve the uniformity of the film thickness of the tube inner wall, but also can obtain a film layer of preset thickness without relying on the control of slurry and tube material.

Description

Technical Field

[0001] The present application relates to the field of coating technology, and in particular to a pipe inner wall coating process. Background Art

[0002] Coating the inner wall of the tube is a common production process. For example, coating the inner wall of the tube with a gold reflective layer to change the radiation direction of the heating element, or coating the inner wall of the tube with a rare earth layer to improve the light efficiency.

[0003] In the prior art, coating the inner wall of a pipe is commonly done by pouring or spraying. The pipe is then placed vertically to allow the slurry on the inner wall to "flow evenly" under the action of gravity. However, this method not only results in poor thickness uniformity of the film layer formed on the inner wall of the pipe, which is prone to the phenomenon of "the film layer at the top of the pipe is thin and the film layer at the bottom of the pipe is thick", but also leads to a long and inefficient coating cycle. At the same time, the film layer on the inner wall of the pipe is also highly dependent on the properties of the slurry itself and the surface tension of the inner wall material, making it impossible to accurately control the film thickness to form a predetermined thickness. Summary of the Invention

[0004] The present application provides a pipe inner wall coating process, which aims to improve the uniformity of the thickness of the pipe inner wall film layer while reducing the dependence of the pipe inner wall film layer thickness on the slurry and the pipe inner wall material, so as to accurately control the thickness of the pipe inner wall film layer.

[0005] The present application provides a process for coating the inner wall of a tube, comprising: providing a tube whose inner wall is covered with a slurry; and then sequentially performing a first drying and a second drying on the slurry. Particularly, along the axial direction of the tube, the tube has a first tube opening and a second tube opening that are relatively arranged. The first drying step comprises: while the tube rotates at a first rotational speed around its axial direction, a first airflow enters the interior of the tube from the first tube opening and flows out from the second tube opening. The second drying step comprises: while the tube rotates at a second rotational speed around its axial direction, a second airflow enters the interior of the tube from the first tube opening and flows out from the second tube opening. During the first drying and the second drying, the first tube opening is located above the second tube opening. The first rotational speed is greater than the second rotational speed, the temperature of the first airflow is greater than the temperature of the second airflow, and the flow rate of the first airflow is less than the flow rate of the second airflow.

[0006] In the tube inner wall coating process provided in the present application, compared with the second drying treatment, the first drying treatment adopts the method of "relatively higher rotation speed and air flow temperature, relatively lower air flow rate", which can make the solvent in the slurry in the first tube mouth area (i.e., the upper end area of the tube inner wall) evaporate quickly during the first drying process, the viscosity of the slurry in the first tube mouth area increases rapidly (i.e., the fluidity of the slurry in the first tube mouth area decreases rapidly) and the internal flow resistance of the slurry increases, and the friction between the slurry and the tube inner wall increases, which is conducive to avoiding the situation where "the slurry in the first tube mouth area flows quickly to the second tube mouth" due to the large fluidity of the slurry in the first tube mouth area and the excessively fast flow rate of the first airflow under the action of gravity, and thus helps to avoid the situation where the thickness of the film layer covering the upper end area of the tube inner wall and the lower end area of the tube inner wall is greatly different during the first drying process, and helps to improve the uniformity of the film thickness covering the tube inner wall.

[0007] Compared with the first drying process, the second drying process adopts the method of "relatively lower rotation speed and air flow temperature, relatively higher air flow rate", so that during the second drying process, the slurry on the inner wall of the tube will not solidify quickly and still have a certain fluidity, and the "internal flow resistance of the slurry and the friction between the slurry and the inner wall of the tube" are weaker than those in the first drying process. Under a relatively high air flow rate, the excess slurry outside the preset film thickness on the inner wall of the tube can continuously flow to the second tube mouth and flow out from the second tube mouth, reducing the dependence of the thickness of the film layer on the inner wall of the tube on the slurry and the material of the inner wall of the tube, so as to accurately control the thickness of the film layer on the inner wall of the tube; and the relatively high air flow rate can also smooth the interface between the film layer in the upper end area of the inner wall of the tube and the film layer in the lower end area of the inner wall of the tube, which is also conducive to further improving the uniformity of the film thickness covering the inner wall of the tube.

[0008] In an optional embodiment of the present application, the first drying time is shorter than the second drying time.

[0009] The above technical solution, by adjusting the first drying time and the second drying time, is conducive to avoiding the situation where "the overall fluidity of the slurry on the inner wall of the tube is relatively small due to the first drying time being too long", and is further conducive to avoiding the situation where "less slurry can flow down to the second tube mouth during the second drying process", resulting in a thick film at the top end of the tube.

[0010] In an optional embodiment of the present application, during the first drying and the second drying, the tube is placed in a vertical direction.

[0011] The above technical solution is conducive to achieving "high uniformity of film thickness on the inner wall of the tube" so that excess slurry beyond the preset film thickness can flow out from the second pipe mouth, which is conducive to accurately controlling the thickness of the film layer formed on the inner wall of the tube.

[0012] In an optional embodiment of the present application, the surface of the inner wall of the tube has a first region, and in a direction from the first tube opening to the second tube opening, the first region has a first side and a second side that are opposite each other, the first side and the second side being parallel to the radial direction of the tube, and the second side being located on a side of the first side away from the first tube opening; the distance from the first side to the first tube opening is defined as a first distance, and the distance from the second side to the first tube opening is defined as a second distance, with the first distance and the second distance accounting for 7% and 25% of the length of the tube, respectively. During the first drying process, the second drying is performed when the average solids content of the slurry covering the first region increases by 10-50%.

[0013] The above technical solution is conducive to avoiding the situation where the thickness of the film layer covering the upper end area and the lower end area of the inner wall of the tube is greatly different during the first drying process, so as to improve the uniformity of the film thickness covering the inner wall of the tube.

[0014] In an optional embodiment of the present application, the temperature T1 of the first airflow satisfies: T1≥0.6T0, where T0 is the boiling point of the solvent in the slurry; during the first drying, the centrifugal force M1 exerted on the slurry satisfies: M1≥0.009N.

[0015] In the above technical solution, the temperature T1 of the first air flow satisfies: T1 ≥ 0.6T0, T0 is the boiling point of the solvent in the slurry, which can make the solvent in the slurry in the first nozzle area (i.e., the upper end area of the inner wall of the tube) evaporate quickly during the first drying process, and the viscosity of the slurry in the first nozzle area increases rapidly (i.e., the fluidity of the slurry in the first nozzle area decreases rapidly), so that the internal resistance of the slurry in the first nozzle area increases; during the first drying, the centrifugal force M1 on the slurry satisfies: M1 ≥ 0.009N, which can increase the friction between the slurry and the inner wall of the tube; it is conducive to avoiding the situation where "the slurry in the first nozzle area flows quickly to the second nozzle due to the greater fluidity of the slurry in the first nozzle area under the action of gravity", and thus it is conducive to avoiding the situation where the thickness of the film layer covering the upper end area of the inner wall of the tube and the lower end area of the inner wall of the tube is relatively different during the first drying process, and it is conducive to improving the uniformity of the film thickness covering the inner wall of the tube.

[0016] Optionally, T1 satisfies: T0≥T1≥0.6T0.

[0017] Optionally, M1 satisfies: 0.02N≥M1≥0.009N.

[0018] In an optional embodiment of the present application, the surface of the inner wall of the tube has a second area, and in the direction from the first tube opening to the second tube opening, the second area has a third side and a fourth side relative to each other, the third side and the fourth side are parallel to the radial direction of the tube, and the third side is arranged on the side of the fourth side away from the second tube opening; the distance from the third side to the second tube opening is defined as the third distance, and the distance from the fourth side to the second tube opening is defined as the fourth distance, and the third distance and the fourth distance account for 50% and 75% of the length of the tube respectively; during the second drying process, when the average solid content of the slurry covering the second area increases by 10-50%, the second drying is ended.

[0019] The above technical solution can effectively control the second drying time on the basis of "allowing excess slurry beyond the preset film thickness to flow out from the second pipe mouth, so as to facilitate the formation of a film layer of preset thickness", which is conducive to avoiding a long second drying time and improving the efficiency of the entire pipe inner wall coating process.

[0020] In an optional embodiment of the present application, the temperature T2 of the second airflow satisfies: 0.6T0>T2≥0.4T0, where T0 is the boiling point of the solvent in the slurry; during the second drying, the centrifugal force M2 exerted on the slurry satisfies: M2≤0.009N.

[0021] In the above technical solution, the temperature T2 of the second air flow satisfies: 0.6T0>T2≥0.4T0, T0 is the boiling point of the solvent, so that during the second drying process, the slurry on the inner wall of the tube will not solidify quickly and still have a certain fluidity; during the second drying, the centrifugal force M2 on the slurry satisfies: M2≤0.009N, which can make the friction between the slurry and the inner wall of the tube relatively weaker than that during the first drying process, and thus during the second drying process, the excess slurry outside the preset film thickness on the inner wall of the tube can continuously flow to the second tube mouth and flow out from the second tube mouth, thereby controlling the thickness of the liquid film on the inner wall of the tube, and thus controlling the thickness of the dry film layer finally formed on the inner wall of the tube; and the relatively high air flow velocity can also smooth the interface between the film layer in the upper end area of the inner wall of the tube and the film layer in the lower end area of the inner wall of the tube, which is also conducive to further improving the uniformity of the film thickness of the inner wall of the tube.

[0022] Optionally, M2 satisfies: 0.002N≤M2≤0.009N.

[0023] In an optional embodiment of the present application, the tube inner wall coating process also includes: after the second drying, performing intermediate treatment on the tube; the intermediate treatment step includes: allowing a third airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; wherein the flow rate of the third airflow is greater than the flow rate of the second airflow.

[0024] The above technical solution uses a third airflow with a flow rate greater than the second airflow, which can further quickly flow out the excess slurry outside the preset film thickness on the inner wall of the tube from the second pipe mouth, which is conducive to accurately controlling the thickness of the film layer formed on the inner wall of the tube.

[0025] Optionally, the time of the intermediate treatment is shorter than the time of the first drying and the time of the second drying.

[0026] Optionally, the intermediate treatment is performed while the tube is rotated about its axial direction at a third rotational speed; wherein the third rotational speed is greater than the second rotational speed.

[0027] Optionally, the mass of the slurry flowing out of the second pipe port is defined as the discharge amount. During the intermediate treatment, when the discharge amount is ≤0.5 mL / min, the intermediate treatment is terminated.

[0028] Optionally, during the intermediate treatment, the centrifugal force M3 applied to the slurry satisfies: M3 ≥ 0.009N.

[0029] Optionally, during the intermediate treatment, the centrifugal force M3 applied to the slurry satisfies: 0.1N≥M3≥0.009N.

[0030] In an optional embodiment of the present application, when the solid content of the slurry is 10-35wt% and the viscosity of the slurry is 300-5000cp, the wind pressure P1 of the first airflow at the first pipe mouth satisfies: P1<120Pa, the wind pressure P2 of the second airflow at the first pipe mouth satisfies: 120Pa≤P2≤400Pa, and the wind pressure P3 of the third airflow at the first pipe mouth satisfies: P3>400Pa.

[0031] The above technical solution, for slurry with a solid content of 10-35wt% and a viscosity of 300-5000cp, the above parameter ranges can make the film thickness covering the inner wall of the tube more uniform and the thickness of the film layer controllable.

[0032] Optionally, P1 is 30-50Pa, P2 is 150-300Pa, and P3 is 800-1000Pa.

[0033] Optionally, the first drying time is 0.5-2 minutes, the second drying time is 2-4 minutes, and the intermediate processing time is less than 10 seconds.

[0034] Optionally, the first rotational speed is 500-1000 rpm, and the second rotational speed is 100-500 rpm.

[0035] In an optional embodiment of the present application, the inner wall coating process of the tube further includes: after the second drying, the slurry is subjected to a third drying and a fourth drying in sequence; the third drying step includes: allowing a fourth airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; the fourth drying step includes: placing the tube at a second preset temperature for drying; wherein, during the third drying, the first pipe opening is located above the second pipe opening; the flow rate of the fourth airflow is less than the flow rate of the second airflow, and the temperature of the fourth airflow is less than the second preset temperature.

[0036] In the above technical solution, compared with the fourth drying, the third drying adopts the method of "a fourth airflow at a relatively lower temperature", which is beneficial to avoiding the situation where "a solidified layer is quickly formed on the surface of the film layer on the inner wall of the tube due to the high temperature of the third drying, and the residual solvent inside the film layer has no time to evaporate evenly and slowly and quickly vaporizes and destroys the solidified layer", thereby helping to improve the quality of the film layer formed on the inner wall of the tube; and the fourth drying treatment can fully solidify the film layer covering the surface of the inner wall of the tube.

[0037] Optionally, the third drying time is shorter than the fourth drying time.

[0038] Optionally, the temperature T4 of the fourth air flow satisfies: 0.6T0>T4≥0.4T0, where T0 is the boiling point of the solvent in the slurry.

[0039] Optionally, the second preset temperature T5 satisfies: T5 ≥ 0.6T0, where T0 is the boiling point of the solvent in the slurry.

[0040] In an optional embodiment of the present application, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, the wind pressure P4 of the fourth airflow at the first pipe opening satisfies: P4<120Pa.

[0041] The above technical solution, for slurry with a solid content of 10-35wt% and a viscosity of 300-5000cp, when the fourth airflow meets the above limitations, is conducive to avoiding the situation where "a solidified layer is quickly formed on the surface of the film layer on the inner wall of the tube due to the high temperature of the third drying, and the residual solvent in the film layer has no time to evaporate evenly and slowly and quickly vaporizes and destroys the solidified layer", which is conducive to improving the quality of the film layer formed on the inner wall of the tube.

[0042] Optionally, P4 is 80-100Pa.

[0043] Optionally, the third drying time is 2-10 minutes, and the fourth drying time is greater than 4 minutes.

[0044] In an optional embodiment of the present application, the step of providing a tube having an inner wall covered with slurry includes: spraying the slurry from a first nozzle onto the inner wall of the tube while the tube rotates about its axis at a fourth speed; wherein, during the spraying, the first nozzle is located above the second nozzle; and the spraying time t m Satisfaction: t m ≥2t n , t n It is the time when the slurry reaches the second nozzle during spraying.

[0045] The above technical solution is conducive to ensuring that the inner wall surface of the tube is evenly and fully covered with slurry, which is conducive to ensuring that the thickness of the film layer formed in the subsequent process is more uniform.

[0046] Optionally, when the solid content of the slurry is 10-35 wt % and the viscosity of the slurry is 300-5000 cp, the fourth rotation speed is 300-500 rpm. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 Flow chart of the pipe inner wall coating process provided for this application. DETAILED DESCRIPTION

[0049] The present application provides a pipe inner wall coating process, which comprises: providing a pipe whose inner wall is covered with slurry; and then sequentially performing a first drying and a second drying on the slurry.

[0050] The tube has a first nozzle and a second nozzle disposed opposite each other along its axial direction. The first drying step includes rotating the tube at a first rotational speed about its axial direction, causing a first airflow to enter the interior of the tube from the first nozzle and flow out from the second nozzle. The second drying step includes rotating the tube at a second rotational speed about its axial direction, causing a second airflow to enter the interior of the tube from the first nozzle and flow out from the second nozzle. During both the first and second drying steps, the first nozzle is located above the second nozzle. The first rotational speed is greater than the second rotational speed, the temperature of the first airflow is greater than the temperature of the second airflow, and the flow rate of the first airflow is less than the flow rate of the second airflow.

[0051] The tube inner wall coating process provided herein comprises a first drying step and a second drying step, performed sequentially. The tube rotation speed, the temperature of the first airflow, and the flow rate of the second airflow are adjusted during the first and second drying steps to dry and film the slurry coating the tube inner wall surface. During the first and second drying steps, the airflow velocity and temperature gradually decrease from the first tube opening to the second tube opening, and the airflow becomes increasingly turbulent.

[0052] Compared with the second drying process, the first drying process adopts a method of "relatively higher rotation speed and air flow temperature, and relatively lower air flow velocity".

[0053] In the first drying process, the relatively high air flow temperature, and the air flow temperature at the first nozzle region (i.e., the upper end region of the tube inner wall) is greater than the air flow temperature at the second nozzle region (i.e., the lower end region of the tube inner wall), can cause the solvent in the slurry in the first nozzle region to evaporate quickly, the viscosity of the slurry in the first nozzle region to increase rapidly, and the internal flow resistance to increase (i.e., the fluidity of the slurry in the first nozzle region to decrease rapidly), while the slurry in other regions of the tube inner wall (i.e., other regions of the tube inner wall excluding the first nozzle region) still has a relatively high fluidity. The above situation is conducive to avoiding the situation where "the slurry in the first nozzle region flows rapidly to the second nozzle region due to the influence of gravity on the slurry in the first nozzle region", and further helps to avoid the situation where the thickness of the film covering the upper end region and the lower end region of the tube inner wall in the first drying process is greatly different, and helps to improve the uniformity of the film thickness covering the tube inner wall in the direction from the first nozzle to the second nozzle; it is also conducive to allowing excess slurry beyond the preset film thickness to flow to the second nozzle region and out of the tube in the subsequent second drying process.

[0054] During the first drying process, a relatively high tube rotation speed can increase the friction between the slurry and the inner wall of the tube, preventing it from flowing downward. This helps avoid the situation where the slurry in the first tube opening area is affected by gravity, resulting in "the slurry in the first tube opening area flowing rapidly to the second tube opening." This, in turn, helps avoid a large difference in the thickness of the film covering the upper end area and the lower end area of the tube inner wall during the first drying process, and helps improve the uniformity of the film thickness covering the tube inner wall along the direction from the first tube opening to the second tube opening. In addition, a relatively high tube rotation speed can also ensure a high uniformity of the film thickness of the tube inner wall along the tube diameter.

[0055] During the first drying process, the relatively low air flow rate is conducive to avoiding the situation where "the slurry in the first pipe mouth area has no time to solidify due to the fast air flow rate, and flows rapidly to the second pipe mouth under the dual effects of gravity and high air flow rate". This is conducive to avoiding the situation where the thickness of the film layer covering the upper end area and the lower end area of the inner wall of the tube is greatly different during the first drying process, and is conducive to improving the uniformity of the film thickness covering the inner wall of the tube in the direction from the first pipe mouth to the second pipe mouth.

[0056] Compared with the first drying process, the second drying process adopts a “relatively lower rotation speed and air flow temperature, and relatively higher air flow velocity” approach.

[0057] Among them, during the second drying process, the relatively low air flow temperature can prevent the slurry on the inner wall of the tube from solidifying quickly during the second drying process, and still have a certain fluidity, so that the excess slurry beyond the preset film thickness on the inner wall of the tube can continuously flow to the second pipe mouth and flow out from the second pipe mouth, reducing the dependence of the film layer thickness of the inner wall of the tube on the slurry and the material of the inner wall of the tube, so as to accurately control the thickness of the film layer on the inner wall of the tube.

[0058] During the second drying process, the relatively high airflow velocity exerts a certain thrust on the fluid slurry. This allows excess fluid slurry on the inner wall of the tube, beyond the predetermined film thickness, to flow continuously toward the second tube opening under the combined effects of airflow thrust and gravity, and then out of the second tube opening, thereby forming a film layer of the predetermined thickness on the inner wall of the tube. Furthermore, the relatively high airflow velocity can smooth the interface between the film layer in the upper and lower regions of the inner wall of the tube, further improving the uniformity of the film thickness along the direction from the first tube opening to the second tube opening.

[0059] During the second drying process, the relatively low tube rotation speed can make the friction between the slurry and the inner wall of the tube relatively weaker than that during the first drying process, so that the friction between the slurry and the inner wall of the tube is weaker and easier to flow down, which is beneficial for the excess slurry beyond the preset film thickness on the inner wall of the tube to continuously flow to the second tube port and flow out from the second tube port, thereby facilitating the formation of a film layer of preset film thickness on the inner wall of the tube.

[0060] Furthermore, since the tube rotates about its axis during both the first and second drying processes, centrifugal force is used to increase the friction between the slurry and the tube's inner wall, thereby improving the bonding strength between the film layer formed on the tube's inner wall and the tube's inner wall, as well as the uniformity of the film's thickness along the tube's diameter. Furthermore, since airflow occurs during both the first and second drying processes, wind turbulence is more likely to occur at the second tube opening. Rotating the tube about its axis helps prevent the surface morphology of the film layer on the tube's inner wall from being affected by wind turbulence inside the tube, thereby ensuring film quality.

[0061] Therefore, the tube inner wall coating process provided in the present application can not only improve the uniformity of the thickness of the tube inner wall film layer, but also reduce the dependence of the tube inner wall film layer thickness on the slurry and the tube inner wall material, so as to accurately control the thickness of the tube inner wall film layer, and can also improve the bonding force between the film layer formed on the surface of the tube inner wall and the tube inner wall.

[0062] Figure 1 For the process flow chart of the inner wall coating of the pipe provided for this application, please refer to Figure 1 The inner wall coating process of the tube includes the following steps performed in sequence:

[0063] S10, providing a pipe whose inner wall is covered with slurry.

[0064] In the present application, the tube has a first tube opening and a second tube opening that are arranged opposite to each other along the axial direction of the tube, and the tube is a straight tube; this content will not be described in detail below.

[0065] In some optional embodiments of the present application, the step of providing a tube with an inner wall covered with slurry includes: spraying the slurry onto the inner wall of the tube from the first tube opening while the tube rotates around its axis at a fourth rotational speed.

[0066] In the above manner, the tube rotates around its axis, so that the slurry on the inner wall of the tube is subjected to centrifugal force, which is beneficial to increasing the friction between the slurry and the inner wall of the tube, and is beneficial to increasing the bonding force between the film layer formed on the surface of the inner wall of the tube and the inner wall of the tube.

[0067] In some optional embodiments of the present application, when the slurry is sprayed from the first nozzle onto the inner wall of the tube while the tube rotates about its axis at a fourth rotational speed, the first nozzle is located above the second nozzle. This allows the slurry to flow toward the second nozzle under the action of gravity during spraying, thereby facilitating uniform coverage of the inner wall of the tube with the slurry and, in turn, ensuring greater uniformity in the thickness of the film layer formed on the inner wall of the tube in subsequent steps.

[0068] Furthermore, when the pipe rotates at a fourth speed around its axis, the slurry is sprayed from the first nozzle to the inner wall of the pipe, and the first nozzle is located above the second nozzle, and the spraying time t m Satisfaction: t m ≥2tn , t n The time when the slurry reaches the second nozzle during spraying is beneficial for evenly and fully covering the inner wall of the tube with the slurry, thereby promoting a higher uniformity in the thickness of the film layer formed on the inner wall of the tube in subsequent processes.

[0069] It should be noted that, in the present application, "the first pipe opening is located above the second pipe opening" does not only mean that the first pipe opening is located directly above the second pipe opening and the tube is placed in the vertical direction; it can also mean that the axial direction of the tube is inclined relative to the vertical direction, as long as the height of the first pipe opening is higher than the height of the second pipe opening when the tube is placed; this content will not be elaborated below.

[0070] Furthermore, when the pipe rotates at a fourth speed about its axis and sprays the slurry from the first pipe opening onto the inner wall of the pipe, the first pipe opening is located above the second pipe opening, and the pipe is placed in a vertical direction, which is conducive to evenly covering the inner wall surface of the pipe with the slurry.

[0071] In some optional embodiments of the present application, the step of providing a tube having an inner wall covered with slurry includes: spraying the slurry from the first nozzle onto the inner wall of the tube while the tube rotates about its axis at a fourth rotational speed; when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-500 cp, the fourth rotational speed is 300-500 rpm. This allows the slurry having a solid content of 10-35 wt% and a viscosity of 300-5000 cp to be evenly and fully coated on the inner wall of the tube.

[0072] As an example, the solid content of the slurry can be any value among 10wt%, 20wt%, 25wt%, 27wt%, 30wt%, 32wt%, 34wt% and 35wt%, or a range value between any two of them; the viscosity of the slurry can be any value among 300cp, 1000cp, 1500cp, 2000cp, 2200cp, 2500cp, 2700cp, 3000cp, 3500cp, 4000cp and 5000cp, or a range value between any two of them; the fourth speed can be any value among 300rpm, 320rpm, 350rpm, 370rpm, 400rpm, 450rpm and 500rpm, or a range value between any two of them.

[0073] It should be noted that in other feasible implementations, the conventional method of "covering the inner wall surface of the tube with slurry" in the prior art may also be adopted, as long as the inner wall surface of the tube is covered with slurry.

[0074] S20, performing a first drying on the slurry covering the inner wall of the tube.

[0075] In the present application, the first drying step includes: rotating the tube at a first speed around its axis so that a first airflow enters the interior of the tube from a first tube opening and flows out from a second tube opening; wherein the first tube opening is located above the second tube opening.

[0076] It should be noted that the present application does not limit the composition of the first airflow. For example, it can be air or nitrogen, as long as it does not react with the slurry.

[0077] It should be noted that the present application does not limit the method of achieving "the first airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening"; for example, the first airflow can be blown into the tube at the first pipe opening, so that the first airflow flows through the tube and then flows out from the second pipe opening; or negative pressure ventilation can be performed on the tube at the second pipe opening, so that during the first drying process, the gas in the environment enters the tube from the first pipe opening under the action of negative pressure and then flows out through the second pipe opening.

[0078] As an example, in an embodiment of the present application, the first airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening, adopting the method of "negative pressure ventilation in the tube at the second pipe opening".

[0079] In some optional embodiments of the present application, the tube is placed vertically during the first drying process. This facilitates achieving a high uniformity of film thickness on the inner wall of the tube, allowing excess slurry beyond the preset film thickness to flow out from the second tube opening, thereby facilitating accurate control of the thickness of the film layer formed on the inner wall of the tube.

[0080] In the present application, the surface of the inner wall of the tube has a first area, and in the direction from the first tube opening to the second tube opening, the first area has a first edge and a second edge relative to each other, the first edge and the second edge are parallel to the radial direction of the tube, and the second edge is arranged on the side of the first edge away from the first tube opening; the distance from the first edge to the first tube opening is defined as the first distance, and the distance from the second edge to the first tube opening is defined as the second distance, and the first distance and the second distance account for 7% and 25% of the length of the tube, respectively.

[0081] In other words, the first side of the first area is located above the second side, the distance from the first side to the first pipe opening accounts for 7% of the length of the entire tube, and along the direction from the first pipe opening to the second pipe opening, the length of the first area accounts for 18% of the length of the entire tube.

[0082] In some optional embodiments of the present application, during the first drying process, when the average solid content of the slurry covering the first area increases by 10-50%, the first drying is terminated and the second drying is performed.

[0083] The above method is conducive to avoiding the situation where the thickness of the film layer covering the upper end area and the lower end area of the inner wall of the tube is greatly different during the first drying process, so as to improve the uniformity of the film thickness covering the inner wall of the tube.

[0084] It should be noted that, in the present application, “the average solid content of the slurry covering the first area increases by 10-50%” means that the average solid content of the slurry covering the first area increases by 10-50% relative to the solid content of the slurry before the first drying.

[0085] As an example, during the first drying process, when the average solid content of the slurry covering the first area increases by any value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% or any range value between two of them, the first drying is ended and the second drying is carried out.

[0086] In some optional embodiments of the present application, during the first drying process, the temperature T1 of the first airflow satisfies: T1 ≥ 0.6T0, where T0 is the boiling point of the solvent in the slurry; during the first drying, the centrifugal force M1 exerted on the slurry satisfies: M1 ≥ 0.009N.

[0087] During the first drying process, the temperature T1 of the first air flow satisfies: T1 ≥ 0.6T0 (T0 is the boiling point of the solvent in the slurry), which can make the solvent in the slurry in the first nozzle area evaporate quickly during the first drying process, and the viscosity of the slurry in the first nozzle area increases rapidly (that is, the fluidity of the slurry in the first nozzle area decreases rapidly), so that the internal resistance of the slurry in the first nozzle area increases; during the first drying, the centrifugal force M1 on the slurry satisfies: M1 ≥ 0.009N, which can increase the friction between the slurry and the inner wall of the tube; it is conducive to avoiding the situation where "the slurry in the first nozzle area flows quickly to the second nozzle due to the greater fluidity of the slurry in the first nozzle area under the action of gravity", and thus it is conducive to avoiding the situation where the thickness of the film layer covering the upper end area of the inner wall of the tube and the lower end area of the inner wall of the tube is relatively different during the first drying process, which is conducive to improving the uniformity of the film thickness covering the inner wall of the tube.

[0088] Furthermore, during the first drying process, the temperature T1 of the first airflow satisfies the following conditions: T0 ≥ T1 ≥ 0.6 T0. This helps to further avoid a situation in which a large difference in thickness of the film layer covering the upper end region and the lower end region of the tube inner wall is formed during the first drying process, thereby further improving the uniformity of the film thickness covering the tube inner wall.

[0089] As an example, during the first drying process, the temperature T1 of the first airflow can be any value among 0.6T0, 0.65T0, 0.7T0, 0.75T0, 0.8T0, 0.85T0, 0.9T0 and T0, or a range value between any two of them.

[0090] Furthermore, during the first drying process, the centrifugal force M1 applied to the slurry satisfies the following conditions: 0.02 N ≥ M1 ≥ 0.009 N. If the centrifugal force M1 applied to the slurry during the first drying process is too large, the friction between the slurry and the inner wall of the tube may be too strong, which may hinder the excess slurry beyond the preset film thickness from flowing toward and out of the second tube orifice, thereby hindering the formation of a film layer of the preset film thickness.

[0091] As an example, during the first drying process, the centrifugal force M1 applied to the slurry may be any value among 0.009N, 0.01N, 0.012N, 0.015N, 0.017N, 0.019N and 0.02N, or a range of values between any two of them.

[0092] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, the wind pressure P1 of the first airflow at the first pipe opening satisfies: P1 < 120 Pa. This approach can ensure that the film thickness formed on the inner wall of the pipe by the slurry having a solid content of 10-35 wt% and a viscosity of 300-5000 cp is highly uniform.

[0093] As an example, the solid content of the slurry can be any value among 10wt%, 20wt%, 25wt%, 27wt%, 30wt%, 32wt%, 34wt% and 35wt%, or a range value between any two of them; the viscosity of the slurry can be any value among 300cp, 1000cp, 1500cp, 2000cp, 2200cp, 2500cp, 2700cp, 3000cp, 3500cp, 4000cp and 5000cp, or a range value between any two of them; the wind pressure P2 of the second airflow at the first pipe mouth can be any value among 20Pa, 30Pa, 40Pa, 50Pa, 60Pa, 70Pa, 80Pa, 90Pa, 100Pa, 110Pa and 119Pa, or a range value between any two of them.

[0094] Furthermore, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, P1 is 30-50 Pa. If the wind pressure P1 of the first airflow at the first pipe opening is too low, the first drying process may take a relatively long time, which is not conducive to improving the production efficiency of the pipe inner wall coating.

[0095] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt %, the viscosity of the slurry is 300-5000 cp, and the pressure P1 of the first airflow at the first pipe opening satisfies: P1 < 120 Pa, the first drying time is 0.5-2 minutes. This is beneficial for ensuring a high uniformity of the film thickness formed on the inner wall of the pipe.

[0096] As an example, the first drying time may be any value among 0.5 min, 1 min, 1.2 min, 1.4 min, 1.5 min, 1.7 min and 2 min, or a range between any two of them.

[0097] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, and the wind pressure P1 of the first airflow at the first pipe opening satisfies: P1 < 120 Pa, the first rotation speed is 500-1000 rpm. This is conducive to further improving the uniformity of the film thickness of the film layer formed on the inner wall of the pipe in the pipe diameter direction.

[0098] As an example, the first rotational speed may be any value among 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm and 1000 rpm, or a range of values between any two of them.

[0099] S30, performing a second drying on the slurry covering the inner wall of the tube.

[0100] In the present application, the second drying step includes: rotating the tube at a second rotational speed about its axis, causing a second airflow to enter the interior of the tube from a first tube opening and flow out of the second tube opening; wherein the first tube opening is located above the second tube opening; the first rotational speed is greater than the second rotational speed, the temperature of the first airflow is greater than the temperature of the second airflow, and the flow rate of the first airflow is less than the flow rate of the second airflow.

[0101] It should be noted that the present application does not limit the composition of the second airflow. For example, it can be air or nitrogen, as long as it does not react with the slurry.

[0102] It should be noted that the present application does not limit the method of achieving "the second airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening"; for example, the second airflow can be blown into the tube at the first pipe opening, so that the second airflow flows through the tube and then flows out from the second pipe opening; or negative pressure ventilation can be performed on the tube at the second pipe opening, so that during the second drying process, the gas in the environment enters the tube from the first pipe opening under the action of negative pressure and then flows out through the second pipe opening.

[0103] As an example, in an embodiment of the present application, the second airflow enters the interior of the tube from the first tube opening and flows out from the second tube opening, adopting the method of "negative pressure ventilation in the tube at the second tube opening".

[0104] In some optional embodiments of the present application, the tube is placed vertically during the second drying process. This facilitates achieving a high uniformity of film thickness on the inner wall of the tube, allowing excess slurry beyond the preset film thickness to flow out from the second tube opening, thereby facilitating accurate control of the thickness of the film layer formed on the inner wall of the tube.

[0105] In some optional embodiments of the present application, the first drying time is shorter than the second drying time. The above technical solution, by adjusting the first drying time and the second drying time, helps avoid the situation where "the overall fluidity of the slurry on the inner wall of the tube is relatively low due to "the first drying time being too long" and thus helps avoid the situation where "less slurry can flow down to the second tube opening during the second drying process", resulting in a thick film at the top of the tube.

[0106] In the present application, the surface of the inner wall of the tube has a second area, and in the direction from the first tube opening to the second tube opening, the second area has a third side and a fourth side relative to each other, the third side and the fourth side are parallel to the radial direction of the tube, and the third side is arranged on the side of the fourth side away from the second tube opening; the distance from the third side to the second tube opening is defined as the third distance, and the distance from the fourth side to the second tube opening is defined as the fourth distance, and the third distance and the fourth distance respectively account for 50% and 75% of the length of the tube.

[0107] In other words, the third side of the second area is located above the fourth side, the distance from the third side to the first pipe opening accounts for 50% of the length of the entire tube, and along the direction from the first pipe opening to the second pipe opening, the length of the second area accounts for 25% of the length of the entire tube.

[0108] In some optional embodiments of the present application, during the second drying process, when the average solid content of the slurry covering the second area increases by 10-50%, the second drying is terminated.

[0109] The above technical solution can effectively control the second drying time on the basis of "allowing excess slurry beyond the preset film thickness to flow out from the second pipe mouth, so as to facilitate the formation of a film layer of preset thickness", which is conducive to avoiding a long second drying time and improving the efficiency of the entire pipe inner wall coating process.

[0110] It should be noted that, in the present application, “the average solid content of the slurry covering the second area increases by 10-50%” means that the average solid content of the slurry covering the second area increases by 10-50% relative to the solid content of the slurry before the first drying.

[0111] As an example, during the second drying process, the second drying is ended when the average solid content of the slurry covering the second area increases by any value among 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50% or any range value therebetween.

[0112] In some optional embodiments of the present application, the temperature T2 of the second airflow satisfies: 0.6T0>T2≥0.4T0, where T0 is the boiling point of the solvent in the slurry; during the second drying, the centrifugal force M2 exerted on the slurry satisfies: M2≤0.009N.

[0113] The temperature T2 of the second air flow satisfies: 0.6T0>T2≥0.4T0, where T0 is the boiling point of the solvent. This ensures that during the second drying process, the slurry on the inner wall of the tube will not solidify rapidly and will still have a certain fluidity. During the second drying process, the centrifugal force M2 applied to the slurry satisfies: M2≤0.009N, which makes the friction between the slurry and the inner wall of the tube relatively weaker than that during the first drying process. This allows the slurry outside the preset film thickness on the inner wall of the tube to continuously flow toward the second tube port and out from the second tube port during the second drying process, thereby controlling the thickness of the liquid film on the inner wall of the tube and thereby controlling the thickness of the dry film layer finally formed on the inner wall of the tube. The relatively high air flow rate can also smooth the interface between the film layer in the upper end area of the inner wall of the tube and the film layer in the lower end area of the inner wall of the tube, which is also beneficial to further improve the uniformity of the film thickness of the film layer on the inner wall of the tube.

[0114] Furthermore, during the second drying, the centrifugal force M2 applied to the slurry satisfies: 0.002 N ≤ M2 ≤ 0.009 N. If the centrifugal force M2 applied to the slurry during the second drying is too small, the thickness uniformity of the tube inner wall film layer in the tube radial direction may be reduced.

[0115] As an example, during the second drying process, the temperature T2 of the second air flow can be any value among 0.4T0, 0.42T0, 0.45T0, 0.47T0, 0.5T0, 0.52T0, 0.55T0, 0.57T0 and 0.59T0, or a range value between any two of them; during the second drying process, the centrifugal force M2 applied to the slurry can be any value among 0.002N, 0.003N, 0.004N, 0.005N, 0.006N, 0.007N, 0.008N and 0.009N, or a range value between any two of them.

[0116] In some optional embodiments of the present application, when the solid content of the slurry is 10-35wt% and the viscosity of the slurry is 300-5000cp, the wind pressure P2 of the second airflow at the first nozzle meets the following conditions: 120Pa≤P2≤400Pa. If the wind pressure P2 of the second airflow at the first nozzle is too low during the second drying process, the slurry flowing out of the second nozzle will be reduced, thereby increasing the thickness of the film layer on the inner wall of the tube. If the wind pressure P2 of the second airflow at the first nozzle is too high, it may cause more obvious "wind turbulence" in the second nozzle area, which will affect the morphology of the film surface and is not conducive to ensuring the surface quality of the film.

[0117] As an example, the solid content of the slurry can be any value among 10wt%, 20wt%, 25wt%, 27wt%, 30wt%, 32wt%, 34wt% and 35wt%, or a range value between any two of them; the viscosity of the slurry can be any value among 300cp, 1000cp, 1500cp, 2000cp, 2200cp, 2500cp, 2700cp, 3000cp, 3500cp, 4000cp and 5000cp, or a range value between any two of them; the wind pressure P2 of the second airflow at the first pipe mouth can be any value among 120Pa, 150Pa, 200Pa, 220Pa, 250Pa, 300Pa, 350Pa and 400Pa, or a range value between any two of them.

[0118] Furthermore, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, P2 is 150-300 Pa. This can ensure that the film thickness covering the inner wall of the tube is highly uniform, the film thickness is controllable, and the surface quality of the film is high.

[0119] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt%, the viscosity of the slurry is 300-5000 cp, and the wind pressure P2 of the second airflow at the first pipe opening satisfies the following conditions: 120 Pa ≤ P2 ≤ 400 Pa, the second drying time is 2-4 minutes. This helps to ensure that a film layer of controllable thickness can be formed on the inner wall of the pipe.

[0120] As an example, the second drying time can be any value among 2 min, 2.2 min, 2.5 min, 3 min, 3.2 min, 3.5 min, 3.7 min and 4 min, or a range between any two of them.

[0121] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt%, the viscosity of the slurry is 300-5000 cp, and the wind pressure P2 of the second airflow at the first pipe opening satisfies the following conditions: 120 Pa ≤ P2 ≤ 400 Pa, the second rotation speed is 100-500 rpm. This can ensure that the film thickness covering the inner wall of the pipe is highly uniform, the thickness of the film layer is controllable, and the surface quality of the film layer is high.

[0122] As an example, the second rotation speed may be any value among 100 rpm, 200 rpm, 300 rpm, 400 rpm and 500 rpm, or a range of values between any two of them.

[0123] S40, performing intermediate processing on the tube.

[0124] In some optional embodiments of the present application, the intermediate processing step includes: allowing a third airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; wherein the first pipe opening is located above the second pipe opening, and the flow rate of the third airflow is greater than the flow rate of the second airflow.

[0125] The third airflow with a flow rate greater than the second airflow is used to perform a third drying on the slurry on the inner wall of the tube, which can further quickly flow out the excess slurry on the inner wall of the tube from the second pipe mouth, so as to further reduce the thickness of the film layer formed on the inner wall of the tube, so that a film layer with controllable thickness is formed on the inner wall of the tube.

[0126] It should be noted that the present application does not limit the composition of the third airflow. For example, it can be air or nitrogen, as long as it does not react with the slurry.

[0127] It should be noted that the present application does not limit the method of achieving "the third airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening"; for example, the third airflow can be blown into the tube at the first pipe opening, so that the third airflow flows through the tube and then flows out from the second pipe opening; or negative pressure ventilation can be performed on the tube at the second pipe opening, so that the gas in the environment during intermediate processing enters the tube from the first pipe opening under the action of negative pressure and then flows out through the second pipe opening.

[0128] As an example, in an embodiment of the present application, the third airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening, adopting the method of "negative pressure ventilation in the tube at the second pipe opening".

[0129] In some optional embodiments of the present application, the tube is placed in a vertical direction during the intermediate treatment, which is conducive to allowing excess slurry beyond the preset film thickness to flow out from the second tube opening, thereby facilitating accurate control of the thickness of the film layer formed on the inner wall of the tube.

[0130] In some optional embodiments of the present application, the intermediate treatment time is shorter than the first drying time and the second drying time. This not only helps shorten the entire tube inner wall coating process time, but also helps avoid the situation where "the higher flow rate of the third airflow significantly disturbs the tube inner wall film surface due to "excessive intermediate treatment time", which is not conducive to ensuring the surface morphology quality of the film layer formed on the tube inner wall surface."

[0131] In some optional embodiments of the present application, the mass of the slurry flowing out of the second nozzle is defined as the discharge rate. During the intermediate treatment process, when the discharge rate is ≤ 0.5 mL / min, the intermediate treatment is terminated. The above method is conducive to effectively controlling the time consumed by the intermediate treatment, not only facilitating the accurate control of the thickness of the film layer formed on the inner wall of the tube, but also facilitating the surface morphology quality of the film layer formed on the inner wall of the tube.

[0132] In some optional embodiments of the present application, intermediate treatment is performed while the tube rotates about its axis at a third rotational speed; the third rotational speed is greater than the second rotational speed to increase centrifugal force. Furthermore, during intermediate treatment, the centrifugal force M3 applied to the slurry satisfies the requirement: M3 ≥ 0.009 N. The higher rotational speed generates higher centrifugal force, reducing the impact of the airflow within the tube on the bottom membrane layer.

[0133] Furthermore, during the intermediate processing, the centrifugal force M3 on the slurry satisfies the following requirements: 0.1 N ≥ M3 ≥ 0.009 N. While ensuring the airflow's effect on the film layer, avoid excessively high rotation speed affecting the fixture.

[0134] As an example, during the intermediate treatment, the centrifugal force M3 applied to the slurry can be any value among 0.009N, 0.01N, 0.02N, 0.05N, 0.07N, 0.09N and 0.1N, or a range of values between any two of them.

[0135] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, the wind pressure P3 of the third airflow at the first pipe opening satisfies: P3 > 400 Pa. This allows as much slurry as possible to flow out of the second pipe opening, thereby further reducing the thickness of the film layer formed on the inner wall of the pipe, thereby forming a film layer with controllable thickness on the inner wall of the pipe.

[0136] As an example, the solid content of the slurry can be any value among 10wt%, 22wt%, 25wt%, 27wt%, 30wt%, 32wt%, 34wt% and 35wt%, or a range value between any two of them; the viscosity of the slurry can be any value among 300cp, 1000cp, 1500cp, 2000cp, 2200cp, 2500cp, 2700cp, 3000cp, 3500cp, 4000cp and 5000cp, or a range value between any two of them; the wind pressure P3 of the third airflow at the first pipe mouth can be any value among 401Pa, 450Pa, 500Pa, 600Pa, 700Pa, 800Pa, 900Pa and 1000Pa, or a range value between any two of them.

[0137] Furthermore, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, P3 is 800-1000 Pa. If the wind pressure P3 of the third airflow at the first nozzle is too high, the airflow velocity will be too high, resulting in a decrease in the surface morphology quality of the film layer; if the wind pressure P3 of the third airflow at the first nozzle is too low, the slurry flowing out of the second nozzle will be reduced, which is not conducive to accurately controlling the thickness of the film layer formed on the inner wall of the tube.

[0138] In some optional embodiments of the present application, when the solids content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, and the pressure P3 of the third airflow at the first pipe opening satisfies: P3 > 400 Pa, the intermediate treatment time is less than 10 seconds. This helps avoid the situation where "the higher flow rate of the third airflow significantly disturbs the film surface on the inner wall of the tube due to "excessive intermediate treatment time", which is not conducive to ensuring the surface quality of the film layer formed on the inner wall of the tube."

[0139] It should be noted that, in some feasible implementations of the present application, after performing step S30, step S40 may not be performed, but the steps after step S40 may be performed directly.

[0140] S50, performing a third drying on the slurry covering the inner wall of the tube.

[0141] In some optional embodiments of the present application, the third drying step includes: allowing a fourth airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; wherein the first pipe opening is located above the second pipe opening; and the flow rate of the fourth airflow is less than the flow rate of the second airflow.

[0142] The third drying adopts the method of "a fourth air flow at a relatively lower temperature", which is beneficial to avoid the situation where "a solidified layer is quickly formed on the surface of the film layer on the inner wall of the tube due to the high temperature of the third drying, and the residual solvent inside the film layer has no time to evaporate evenly and slowly, and is quickly vaporized and destroyed." The film layer covering the inner wall surface of the tube is gradually solidified into a dense solidified layer, which is beneficial to improving the quality of the film layer formed on the inner wall of the tube.

[0143] It should be noted that the present application does not limit the composition of the fourth airflow. For example, it can be air or nitrogen, as long as it does not react with the slurry.

[0144] It should be noted that the present application does not limit the method of achieving "the fourth airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening"; for example, the fourth airflow can be blown into the tube at the first pipe opening, so that the fourth airflow flows through the tube and then flows out from the second pipe opening; or negative pressure ventilation can be performed on the tube at the second pipe opening, so that during the third drying treatment, the gas in the environment enters the tube from the first pipe opening under the action of negative pressure and then flows out through the second pipe opening.

[0145] As an example, in an embodiment of the present application, the fourth airflow enters the interior of the tube from the first pipe opening and flows out from the second pipe opening, adopting the method of "negative pressure ventilation in the tube at the second pipe opening".

[0146] In some optional embodiments of the present application, the temperature T4 of the fourth airflow satisfies the following condition: 0.6T0 > T4 ≥ 0.4T0, where T0 is the boiling point of the solvent in the slurry. This helps avoid the situation where, due to the high temperature of the third drying process, a solidified layer quickly forms on the inner wall of the tube, causing the residual solvent inside the film layer to rapidly vaporize and destroy the solidified layer without sufficient time to evaporate evenly and slowly, thereby improving the quality of the film layer formed on the inner wall of the tube.

[0147] As an example, the temperature T4 of the fourth airflow may be any value among 0.4T0, 0.42T0, 0.45T0, 0.47T0, 0.5T0, 0.55T0 and 0.59T0, or a range of values between any two of them.

[0148] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, the wind pressure P4 of the fourth airflow at the first pipe opening satisfies: P4 < 120 Pa. This helps avoid the situation where "the fourth airflow is too fast" and "a solidified layer quickly forms on the surface of the film layer on the inner wall of the tube, and the residual solvent in the film layer does not have time to evaporate evenly and slowly, resulting in rapid vaporization and destruction of the solidified layer." This helps improve the quality of the film layer formed on the inner wall of the tube.

[0149] As an example, the solid content of the slurry can be any value among 10wt%, 22wt%, 25wt%, 27wt%, 30wt%, 32wt%, 34wt% and 35wt%, or a range value between any two of them; the viscosity of the slurry can be any value among 300cp, 1000cp, 1500cp, 2000cp, 2200cp, 2500cp, 2700cp, 3000cp, 3500cp, 4000cp and 5000cp, or a range value between any two of them; the wind pressure P4 of the fourth airflow at the first pipe mouth can be any value among 75Pa, 80Pa, 90Pa, 100Pa, 110Pa and 119Pa, or a range value between any two of them.

[0150] Furthermore, when the solid content of the slurry is 10-35 wt% and the viscosity of the slurry is 300-5000 cp, P4 is 80-100 Pa. If the wind pressure P4 of the fourth airflow at the first pipe opening is too low, the third drying time will be increased, which is not conducive to improving the production efficiency of the pipe inner wall coating process.

[0151] In some optional embodiments of the present application, when the solid content of the slurry is 10-35 wt%, the viscosity of the slurry is 300-5000 cp, and the pressure P4 of the fourth airflow at the first pipe opening satisfies: P4 < 120 Pa, the third drying time is 2-10 minutes. This facilitates the complete volatilization of the residual solvent in the film layer, thereby improving the quality of the film layer formed on the inner wall of the tube.

[0152] As an example, when the solid content of the slurry is 10-35wt% and the viscosity of the slurry is 300-5000cp, and the wind pressure P4 of the fourth airflow at the first pipe mouth satisfies: P4<120Pa, the third drying time can be any point value among 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min and 10min or a range value between any two of them.

[0153] It should be noted that, in other feasible implementations of the present application, step S50 may not be performed and step S60 may be performed directly.

[0154] S60, performing a fourth drying on the slurry covering the inner wall of the tube.

[0155] In some optional embodiments of the present application, the fourth drying step includes drying the tube at a second preset temperature, wherein the second preset temperature is greater than the temperature of the fourth air flow. The fourth drying step can fully solidify the film layer covering the inner wall surface of the tube.

[0156] In some optional embodiments of the present application, the fourth drying time is longer than the third drying time; this is beneficial for ensuring that the film layer covering the inner wall surface of the tube is fully solidified.

[0157] In some optional embodiments of the present application, the second preset temperature T5 satisfies: T5 ≥ 0.6T0, where T0 is the boiling point of the solvent in the slurry; this is beneficial for ensuring that the film layer covering the inner wall surface of the tube is fully solidified.

[0158] In some optional embodiments of the present application, when the solid content of the slurry is 10-35wt% and the viscosity of the slurry is 300-5000cp, the fourth drying time is greater than 4 minutes; this is beneficial to ensure that the film layer covering the inner wall surface of the tube is fully solidified.

[0159] It should be noted that for the solution that does not perform step S50, after step S60 is completed, the area located at the second pipe mouth needs to be cut out from the entire pipe body to ensure that the film thickness of the film layer in all areas of the entire inner wall of the pipe is highly uniform and the film thickness is controllable.

[0160] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0161] Example 1

[0162] This embodiment provides a pipe inner wall coating process, including the following steps performed in sequence:

[0163] (1) A straight tube with an inner diameter of 6 mm and a length of 347 mm was taken and fixed on a rotating mechanism in the vertical direction so that the first tube opening of the straight tube was located at the top and the second tube opening of the straight tube was located at the bottom; and the straight tube was set to rotate around its tube axis. During the rotation of the straight tube, a spraying device was used to spray the slurry from the first tube opening of the straight tube to the inner wall of the straight tube. The spraying time was 20 s.

[0164] Among them, the solid content of the slurry is 20wt%, the viscosity is 2000cp, and the boiling point of the solvent in the slurry is 204°C; the rotation speed of the straight tube is 500rpm; the feed pressure of the spray device is 0.1MPa, and the spray gun air pressure of the spray device is 0.15MPa.

[0165] (2) The straight tube with the inner wall covered with slurry and the rotating mechanism are quickly transferred to a temperature zone of 150°C for the first drying. During the first drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air at the second tube opening of the straight tube.

[0166] The rotation speed of the straight pipe is 700 rpm, the wind pressure at the first pipe opening is 40 Pa, and the first drying time is 1 min.

[0167] (3) The straight tube with the inner wall covered with slurry and the rotating mechanism are quickly transferred to a temperature zone of 90°C for secondary drying. During the secondary drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air at the second tube opening of the straight tube.

[0168] The rotation speed of the straight pipe is 400 rpm, the wind pressure at the first pipe opening is 280 Pa, and the second drying time is 3 minutes.

[0169] (4) After the second drying, the intermediate treatment is carried out quickly. During the intermediate treatment, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; and the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air from the second tube opening of the straight tube.

[0170] Among them, the rotation speed of the straight pipe is 1100rpm, the wind pressure at the first pipe outlet is 900Pa, and the intermediate processing time is 2s.

[0171] (5) The straight tube with the inner wall covered with slurry is quickly transferred to a temperature zone of 100°C for the third drying. During the third drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; a negative pressure exhaust device is used to exhaust air from the second tube opening of the straight tube.

[0172] Among them, the wind pressure at the first pipe opening is 90Pa, and the third drying time is 3 minutes.

[0173] (6) After the third drying, transfer the straight tube to a temperature zone of 130°C and let it stand for 5 minutes.

[0174] Example 2

[0175] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the first drying time is 2 minutes and the second drying time is 2 minutes.

[0176] Example 3

[0177] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the first drying time is 20 seconds.

[0178] Example 4

[0179] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the first drying time is 2.5 minutes.

[0180] Example 5

[0181] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the temperature of the temperature zone in step (2) is 122°C.

[0182] Example 6

[0183] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the temperature of the temperature zone in step (2) is 204°C.

[0184] Example 7

[0185] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the temperature of the temperature zone in step (2) is 115°C.

[0186] Example 8

[0187] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the rotation speed of step (2) is 500 rpm.

[0188] Example 9

[0189] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the rotation speed of step (2) is 400 rpm.

[0190] Example 10

[0191] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the second drying time is 1.5 minutes.

[0192] Example 11

[0193] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the second drying time is 4.5 minutes.

[0194] Example 12

[0195] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the temperature of the temperature zone in step (3) is 82°C.

[0196] Example 13

[0197] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the temperature of the temperature zone in step (3) is 122°C.

[0198] Example 14

[0199] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and embodiment 1 is that the temperature of the temperature zone in step (3) is 75°C.

[0200] Example 15

[0201] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the rotation speed of step (3) is 500 rpm.

[0202] Example 16

[0203] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the rotation speed of step (3) is 100 rpm.

[0204] Example 17

[0205] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the rotation speed of step (3) is 600 rpm.

[0206] Example 18

[0207] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the solid content of the slurry is 35wt% and the viscosity is 5000cp.

[0208] Example 19

[0209] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the solid content of the slurry is 10 wt% and the viscosity is 3000 cp.

[0210] Example 20

[0211] This embodiment provides a pipe inner wall coating process. The difference between this embodiment and Example 1 is that the solid content of the slurry is 15 wt% and the viscosity is 300 cp.

[0212] Example 21

[0213] (1) A straight tube with an inner diameter of 6 mm and a length of 347 mm was taken and fixed on a rotating mechanism in the vertical direction so that the first tube opening of the straight tube was located at the top and the second tube opening of the straight tube was located at the bottom; and the straight tube was set to rotate around its tube axis. During the rotation of the straight tube, a spraying device was used to spray the slurry from the first tube opening of the straight tube to the inner wall of the straight tube. The spraying time was 20 s.

[0214] Among them, the solid content of the slurry is 40wt%, the viscosity is 6000cp, and the boiling point of the solvent in the slurry is 204°C; the rotation speed of the straight tube is 500rpm; the feed pressure of the spray device is 0.04MPa, and the spray gun air pressure of the spray device is 0.3MPa.

[0215] (2) The straight tube with the inner wall covered with slurry and the rotating mechanism are quickly transferred to a temperature zone of 150°C for the first drying. During the first drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air at the second tube opening of the straight tube.

[0216] The rotation speed of the straight pipe is 700 rpm, the wind pressure at the first pipe opening is 40 Pa, and the first drying time is 1 min.

[0217] (3) The straight tube with the inner wall covered with slurry and the rotating mechanism are quickly transferred to a temperature zone of 90°C for secondary drying. During the secondary drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air at the second tube opening of the straight tube.

[0218] The rotation speed of the straight pipe is 400 rpm, the wind pressure at the first pipe opening is 280 Pa, and the second drying time is 2.5 min.

[0219] (4) After the second drying, the intermediate treatment is carried out quickly. During the intermediate treatment, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; and the straight tube is rotated around its tube axis, and a negative pressure exhaust device is used to exhaust air from the second tube opening of the straight tube.

[0220] Among them, the rotation speed of the straight pipe is 1000rpm, the wind pressure at the first pipe outlet is 1000Pa, and the intermediate processing time is 8s.

[0221] (5) The straight tube with the inner wall covered with slurry is quickly transferred to a temperature zone of 100°C for the third drying. During the third drying process, the straight tube is placed in a vertical direction, with the first tube opening of the straight tube at the top and the second tube opening at the bottom; a negative pressure exhaust device is used to exhaust air from the second tube opening of the straight tube.

[0222] Among them, the wind pressure at the first pipe opening is 90Pa, and the third drying time is 3 minutes.

[0223] (6) After the third drying, transfer the straight tube to a temperature zone of 130°C and let it stand for 5 minutes.

[0224] Comparative Example 1

[0225] This comparative example provides a pipe inner wall coating process. The difference between this comparative example and Example 1 is that step (2) is different. Step (2) of this comparative example is as follows:

[0226] The straight tube, its inner wall covered with slurry, and the rotating mechanism are quickly transferred to a 90°C temperature zone for the first drying process. During the first drying process, the straight tube is placed vertically, with the first tube opening positioned at the top and the second tube opening at the bottom. The straight tube rotates around its axis, and a negative pressure exhaust device is used to extract air from the second tube opening.

[0227] The rotation speed of the straight pipe is 400 rpm, the wind pressure at the first pipe opening is 280 Pa, and the first drying time is 1 min.

[0228] Comparative Example 2

[0229] This comparative example provides a pipe inner wall coating process. The difference between this comparative example and Example 1 is that step (3) is different. Step (3) of this comparative example is as follows:

[0230] The straight tube, its inner wall covered with slurry, and the rotating mechanism are quickly transferred to a 150°C temperature zone for secondary drying. During the secondary drying process, the straight tube is placed vertically, with the first tube opening positioned at the top and the second tube opening at the bottom. The straight tube rotates around its axis, and a negative pressure exhaust device is used to extract air from the second tube opening.

[0231] The rotation speed of the tube is 700 rpm, the wind pressure at the first tube opening is 40 Pa, and the second drying time is 3 min.

[0232] Experimental Example 1

[0233] The thickness and accuracy of the film layer on the inner wall formed by the tube inner wall coating process of Examples 1-19 and Comparative Examples 1-2 were tested.

[0234] The comparison of the relevant parameters of the pipe inner wall coating process of Examples 1-19 and Comparative Examples 1-2 is shown in Table 1, and the test results of the film thickness and accuracy are shown in Table 2.

[0235] Among them, the testing method for the thickness of the film layer is: the testing equipment is a thickness gauge, one end of the straight tube is marked, and the marked end and the 0° line on the side of the thickness gauge tooling are aligned as the starting radial test line. The second radial test line is rotated 120° clockwise, and the third radial test line is rotated 240° clockwise. After determining the test line, the marked end and 3 cm to the left of the probe vertex are used as the 0 point, and points are taken for testing at intervals of 7 cm. More than 5 points are taken on 1 radial line, and a total of 3 radial test lines are taken. The average of all the test points used is used as the film thickness value.

[0236] The test method for the accuracy of the film layer is: the film thickness data of 15 points on 3 radial test lines are processed as standard deviation, and the obtained standard deviation is the accuracy.

[0237] Table 1

[0238]

[0239] Note: In Table 1, “ / ” indicates that the corresponding parameter was not tested.

[0240] "First area" refers to: an area on the inner wall surface of the tube, in the direction from the first tube opening to the second tube opening, the first area has a first side and a second side relative to each other, the first side and the second side are parallel to the radial direction of the tube, and the second side is arranged on the side of the first side away from the first tube opening; the distance from the first side to the first tube opening is defined as the first distance, and the distance from the second side to the first tube opening is defined as the second distance, and the first distance and the second distance account for 7% and 25% of the length of the tube, respectively.

[0241] "The increase in solid content of the slurry in the first area after the first drying is S m " refers to the increase in the slurry solid content S1 in the first area after the first drying relative to the slurry solid content S0 during spraying. The calculation formula is: S m (%)=[(S1-S0) / S0]×100%.

[0242] "Second area" refers to: an area on the inner wall surface of the tube, in the direction from the first tube opening to the second tube opening, the second area has a third side and a fourth side relative to each other, the third side and the fourth side are parallel to the radial direction of the tube, and the third side is arranged on the side of the fourth side away from the second tube opening; the distance from the third side to the second tube opening is defined as the third distance, and the distance from the fourth side to the second tube opening is defined as the fourth distance, and the third distance and the fourth distance respectively account for 50% and 75% of the length of the tube.

[0243] "The increase in the solid content of the slurry in the second area after the second drying is completed S n " refers to the increase in the slurry solid content S2 in the second area after the second drying relative to the slurry solid content S0 during spraying. The calculation formula is: S n (%)=[(S2-S0) / S0]×100%.

[0244] Table 2

[0245]

[0246]

[0247] The preset film thickness corresponding to Examples 1-17 and Comparative Examples 1-2 is 35 μm.

[0248] It can be seen from Table 1 and Table 2 that compared with Comparative Examples 1-2 (the temperature, tube rotation speed and air flow rate are all equal during the first drying and second drying processes), the tube inner wall coating process provided by Examples 1-21 of the present application can make the film layer precision value smaller; it shows that: the first drying treatment adopts the method of "relatively higher rotation speed and air flow temperature, relatively lower air flow rate", and the second drying treatment adopts the method of "relatively lower rotation speed and air flow temperature, relatively higher air flow rate", which can effectively improve the thickness uniformity of the tube inner wall film layer.

[0249] It can be seen from Examples 1-17 that by adjusting the "temperature, air flow pressure, drying time and tube rotation speed" during the first drying and second drying processes, the thickness of the film layer formed on the inner wall of the tube can be close to the preset film thickness.

[0250] From the comparison between Example 1 and Example 2, it can be seen that compared with the "first drying time and second drying time are equal" in Example 2, the "first drying time is less than the second drying time" in Example 1 is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0251] From the comparison between Examples 1-2 and 3-4, it can be seen that compared with "the increase in the solid content of the slurry in the first area after the first drying is 8%" in Example 3 and "the increase in the solid content of the slurry in the first area after the first drying is 55%" in Example 4, "the increase in the solid content of the slurry in the first area after the first drying is 30%" in Example 1 and "the increase in the solid content of the slurry in the first area after the first drying is 50%" in Example 2, which are more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0252] From the comparison between Example 1 and Examples 5-7, it can be seen that the temperature in the first drying temperature zone will affect the thickness uniformity of the film layer on the inner wall of the tube and whether the film layer is close to the preset film thickness. When the relationship between the temperature T1 in the first drying temperature zone and the boiling point T0 of the solvent in the slurry satisfies "T0 ≥ T1 ≥ 0.6T0", it is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0253] From the comparison between Example 1 and Examples 8-9, it can be seen that the rotation speed of the tube during the first drying will affect the thickness uniformity of the film layer on the inner wall of the tube and whether the film layer is close to the preset film thickness. When the centrifugal force exerted on the slurry during the first drying is "≥0.009N and ≤0.02N", it is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0254] From the comparison between Example 1 and Examples 10-11, it can be seen that compared with Example 10 "the increase in the solid content of the slurry in the second area after the second drying is 8%" and Example 11 "the increase in the solid content of the slurry in the second area after the second drying is 55%", Example 1 "the increase in the solid content of the slurry in the second area after the second drying is 35%", is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0255] From the comparison between Example 1 and Examples 12-14, it can be seen that the temperature in the second drying temperature zone will affect the thickness uniformity of the film layer on the inner wall of the tube. When the relationship between the temperature T2 in the second drying temperature zone and the boiling point T0 of the solvent in the slurry satisfies "0.6T0>T2≥0.4T0", it is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0256] From the comparison between Example 1 and Examples 15-17, it can be seen that the rotation speed of the tube during the second drying will affect the thickness uniformity of the film layer on the inner wall of the tube and whether the film layer is close to the preset film thickness. When the centrifugal force exerted on the slurry during the second drying is "≥0.002N and ≤0.009N", it is more conducive to improving the thickness uniformity of the film layer on the inner wall of the tube and making the film layer closer to the preset film thickness.

[0257] In summary, the tube inner wall coating process provided in the present application can not only improve the uniformity of the film thickness of the tube inner wall, but also make the thickness of the film layer formed on the tube inner wall meet the expected thickness.

[0258] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A pipe inner wall coating process, characterized in that: include: providing a tube having an inner wall covered with a slurry; The step of providing a tube with an inner wall covered with slurry comprises: while the tube rotates about its axis at a fourth speed, spraying the slurry from the first nozzle onto the inner wall of the tube; wherein, during the spraying, the first nozzle is located above the second nozzle; and the spraying time t m Satisfaction: t m ≥2t n , t n The time when the slurry reaches the second nozzle during spraying; the slurry is then subjected to a first drying and a second drying in sequence; Wherein, along the axial direction of the tube, the tube has a first tube opening and a second tube opening which are arranged opposite to each other; The first drying step includes: rotating the tube at a first speed about its axis, causing a first airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening, wherein a temperature T1 of the first airflow satisfies: T0 ≥ T1 ≥ 0.6T0, where T0 is the boiling point of the solvent in the slurry; during the first drying, a centrifugal force M1 applied to the slurry satisfies: 0.02 N ≥ M1 ≥ 0.009 N; The second drying step includes: rotating the tube at a second speed about its axis, causing a second airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening, wherein a temperature T2 of the second airflow satisfies: 0.6T0>T2≥0.4T0, where T0 is the boiling point of the solvent in the slurry; and during the second drying, a centrifugal force M2 applied to the slurry satisfies: 0.002N≤M2≤0.009N; During the first drying and the second drying, the tube is placed in a vertical direction, and the first tube opening is located above the second tube opening; The first rotation speed is greater than the second rotation speed, the temperature of the first airflow is greater than the temperature of the second airflow, and the flow rate of the first airflow is less than the flow rate of the second airflow.

2. The pipe inner wall coating process according to claim 1, characterized in that: The first drying time is shorter than the second drying time.

3. The pipe inner wall coating process according to claim 1, characterized in that: The surface of the inner wall of the tube has a first area, and in a direction from the first tube opening to the second tube opening, the first area has a first side and a second side opposite to each other, the first side and the second side are parallel to the radial direction of the tube, and the second side is arranged on a side of the first side away from the first tube opening; A distance from the first side to the first pipe opening is defined as a first distance, and a distance from the second side to the first pipe opening is defined as a second distance, wherein the first distance and the second distance account for 7% and 25% of the length of the pipe, respectively; During the first drying process, when the average solid content of the slurry covering the first area increases by 10-50%, the second drying is performed.

4. The pipe inner wall coating process according to claim 1, characterized in that: The pipe inner wall coating process further comprises: performing an intermediate treatment on the pipe after the second drying; The intermediate processing step includes: allowing the third airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; Wherein, the flow rate of the third airflow is greater than the flow rate of the second airflow.

5. The pipe inner wall coating process according to claim 4, characterized in that: The time of the intermediate treatment is shorter than the time of the first drying and the time of the second drying.

6. The pipe inner wall coating process according to claim 4, characterized in that: The intermediate treatment is performed while the tube is rotated about its axial direction at a third rotational speed; wherein the third rotational speed is greater than the second rotational speed.

7. The pipe inner wall coating process according to claim 4, characterized in that: The mass of the slurry flowing out of the second pipe port is defined as the discharge rate. During the intermediate treatment process, when the discharge rate is ≤0.5 mL / min, the intermediate treatment is terminated.

8. The pipe inner wall coating process according to claim 4, characterized in that: During the intermediate treatment, the centrifugal force M3 applied to the slurry satisfies the following requirement: M3 ≥ 0.009N.

9. The pipe inner wall coating process according to claim 8, characterized in that: During the intermediate treatment, the centrifugal force M3 applied to the slurry satisfies the following conditions: 0.1N≥M3≥0.009N.

10. The pipe inner wall coating process according to claim 4, characterized in that: When the solid content of the slurry is 10-35wt% and the viscosity of the slurry is 300-5000cp, the wind pressure P1 of the first airflow at the first pipe mouth satisfies: P1<120Pa, the wind pressure P2 of the second airflow at the first pipe mouth satisfies: 120Pa≤P2≤400Pa, and the wind pressure P3 of the third airflow at the first pipe mouth satisfies: P3>400Pa.

11. The pipe inner wall coating process according to claim 10, characterized in that: The P1 is 30-50Pa, the P2 is 150-300Pa, and the P3 is 800-1000Pa.

12. The pipe inner wall coating process according to claim 10, characterized in that: The first drying time is 0.5-2 minutes, the second drying time is 2-4 minutes, and the intermediate treatment time is less than 10 seconds.

13. The pipe inner wall coating process according to claim 10, characterized in that: The first rotation speed is 500-1000 rpm, and the second rotation speed is 100-500 rpm.

14. The pipe inner wall coating process according to any one of claims 1 to 13, characterized in that: The pipe inner wall coating process further includes: after the second drying, sequentially performing a third drying and a fourth drying on the slurry; The third drying step includes: allowing a fourth airflow to enter the interior of the tube from the first pipe opening and flow out from the second pipe opening; The fourth drying step comprises: drying the tube at a second preset temperature; During the third drying, the first pipe opening is located above the second pipe opening; the flow rate of the fourth airflow is lower than the flow rate of the second airflow; and the temperature of the fourth airflow is lower than the second preset temperature.

15. The pipe inner wall coating process according to claim 14, characterized in that: The third drying time is shorter than the fourth drying time.

16. The pipe inner wall coating process according to claim 14, characterized in that: The temperature T4 of the fourth air flow satisfies: 0.6T0>T4≥0.4T0, where T0 is the boiling point of the solvent in the slurry.

17. The pipe inner wall coating process according to claim 14, characterized in that: The second preset temperature T5 satisfies: T5≥0.6T0, where T0 is the boiling point of the solvent in the slurry.

18. The pipe inner wall coating process according to claim 14, characterized in that: When the solid content of the slurry is 10-35 wt % and the viscosity of the slurry is 300-5000 cp, the wind pressure P4 of the fourth airflow at the first pipe opening satisfies: P4<120 Pa.

19. The pipe inner wall coating process according to claim 18, characterized in that: P4 is 80-100Pa.

20. The pipe inner wall coating process according to claim 18, characterized in that: The third drying time is 2-10 minutes, and the fourth drying time is greater than 4 minutes.

21. The pipe inner wall coating process according to any one of claims 1 to 13, characterized in that: When the solid content of the slurry is 10-35 wt % and the viscosity of the slurry is 300-5000 cp, the fourth rotation speed is 300-500 rpm.

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