A processing technology for negative pressure resistant fluorine lined pipe

Abstract

The present invention discloses a processing technology for a negative pressure resistant fluorine-lined pipe, and the specific steps are as follows: prepare a polytetrafluoroethylene tube; push and pull the polytetrafluoroethylene tube into a stainless steel pipe by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is slightly larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube is tightly fitted to the inner wall of the stainless steel tube; a first relaxation treatment is performed to eliminate the harmful stress generated during the push-pull process; a cold drawing process is adopted to reduce the outer diameter of the stainless steel pipe by a shrinking die, so that the inner wall of the stainless steel pipe is tightly fitted to the outer wall of the polytetrafluoroethylene tube; a second relaxation treatment is performed to eliminate the harmful stress generated during the cold drawing process. The present invention uses a cold drawing process to reduce the outer diameter of the stainless steel pipe by a shrinking die, so that the inner wall of the stainless steel pipe is tightly fitted to the outer wall of the polytetrafluoroethylene tube, and the two relaxation treatments are combined to eliminate the harmful stress, which works together to improve the negative pressure resistance of the fluorine-lined pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline processing, and in particular relates to a processing technology for a negative pressure resistant fluorine lined pipeline. Background Art

[0002] Fluorine-lined pipes refer to steel-lined polytetrafluoroethylene pipes, which have excellent temperature resistance and corrosion resistance. They are ideal transportation equipment for corrosive solvents such as nitric acid, sulfuric acid, hydrofluoric acid, and mixed acid. They are widely used in power plants, chemical industry, pharmaceutical preparation and other fields.

[0003] At present, polytetrafluoroethylene resin (or processed profiles) is usually placed on the inner wall of the steel pipe by molding or inlaying, thereby forming a fluoroplastic lining on the inner wall of the steel pipe. However, the thermal expansion and contraction of the fluoroplastic lining is 10 times greater than that of the steel pipe shell, and the lining is prone to creep, resulting in easy damage to the lining. Existing fluorine-lined pipes are prone to falling off, bulging, shrinking, and expansion and deformation. In particular, they are not resistant to negative pressure and are prone to shrinkage under high negative pressure conditions.

[0004] Patent CN102615861B discloses a manufacturing process for fluorine-lined pipes, which uses a prefabricated metal pipe as an outer hard mold, and uses a molding process to line the inner wall of the cavity with a polytetrafluoroethylene lining, and the polytetrafluoroethylene lining is turned outward at both ends of the metal pipe, and the metal pipe with the polytetrafluoroethylene lining is tightly lined; a substance that can be vaporized at the sintering temperature is added to the polytetrafluoroethylene lining, and the amount of the substance added is controlled so that the expansion pressure generated by the vaporization in the lining during the sintering process reaches 0.06 Mpa, and the assembled pipe is placed in an oven for sintering; the temperature is between 375 and 385 ° C, and the temperature is kept for 4 hours; and finally, after the air pressure of 0.06 Mpa tends to stabilize, the temperature is kept for 2.5 hours, and finally the heating is stopped, and the air pressure is maintained at 0.06 Mpa until it is cooled to room temperature, and the pipe is taken out at room temperature. The fluorine-lined pipe obtained by this patented technology has poor negative pressure resistance when the diameter is large.

[0005] Patent application CN109822930A discloses a production process of fluorine plastic pump lined fluorine pipe, including the following steps: S1, mold processing: according to the shape and size of the pump pipe, a tire and a mold suitable for the shape and size of the product are made; S2, pipe processing: the polytetrafluoroethylene powder raw material is fed into the extruder and extruded into a tube through the mold; S3, spraying: the outer surface of the tubular polytetrafluoroethylene is sprayed with composite glue through a spraying device, so that the glue on the outer surface of the tubular polytetrafluoroethylene is evenly attached; S4, compounding: the pipe interface part on the pump is placed on a heating device for local heating, the heating temperature is between 150℃ and 170℃, and then the tubular polytetrafluoroethylene is inserted into the pipe interface, melted and compounded together, and the temperature is further raised to between 200℃ and 230℃. This patent application enhances the bonding force between polytetrafluoroethylene and steel pipe by spraying composite glue, but the improvement of negative pressure resistance performance is very limited. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a processing technology for negative pressure resistant fluorine lined pipes.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0009] S1. Preparation of polytetrafluoroethylene tube;

[0010] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is slightly larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0011] S3. The first relaxation treatment eliminates harmful stress generated during the push-pull process;

[0012] S4. Use cold drawing process to reduce the outer diameter of the stainless steel tube through the shrinking die, so that the inner wall of the stainless steel tube fits closely to the outer wall of the polytetrafluoroethylene tube;

[0013] S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing.

[0014] Preferably, the specific method of step S1 is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and molded under the static pressure of high-pressure air to obtain a tube blank, and sintered to obtain a polytetrafluoroethylene tube.

[0015] Further preferably, the molding process conditions are: first use 10 to 15 minutes to uniformly increase the pressure to 20 to 25 MPa, maintain the pressure for 20 to 30 minutes, then use 3 to 5 minutes to uniformly increase the pressure to 35 to 40 MPa, maintain the pressure for 8 to 10 minutes, and finally use 15 to 20 minutes to uniformly reduce the pressure to 0.

[0016] More preferably, the sintering process conditions are: firstly heating to 250-270°C at 10-15°C / min, keeping warm for 20-30 minutes, then heating to 360-380°C at 3-5°C / min, keeping warm for 2-3 hours.

[0017] Preferably, the inner diameter of the polytetrafluoroethylene tube obtained in step S1 is 2 to 300 mm, and the wall thickness is 1 to 5 mm.

[0018] Preferably, before entering step S2, the polytetrafluoroethylene tube is pretreated, and the specific method is: firstly the polytetrafluoroethylene tube is plasma treated to obtain a plasma-treated polytetrafluoroethylene tube; then polyborosiloxane, cage silsesquioxane, vermiculite powder, polytetrafluoroethylene powder, and titanate coupling agent are mixed to form a mixed powder, and then the mixed powder is evenly electrostatically sprayed on the outer wall of the plasma-treated polytetrafluoroethylene tube.

[0019] Further preferably, the process conditions for plasma treatment are: the working gases are argon and nitrogen, the working gas pressure is 50-60 Pa, the power is 10-12 kW, the temperature is 25-28°C, and the treatment time is 4-5 minutes; wherein the argon flow rate is 200 sccm and the nitrogen flow rate is 150 sccm.

[0020] Further preferably, in parts by weight, the mixed powder is prepared by the following method: first, 8 to 10 parts of polyborosiloxane are heated to 140 to 150° C., then 8 to 10 parts of cage-type silsesquioxane are added, mixed evenly, and then 3 to 5 parts of vermiculite powder, 3 to 5 parts of polytetrafluoroethylene powder, and 0.8 to 1 part of titanate coupling agent are added, stirred and mixed, naturally cooled to room temperature, and crushed to a particle size of less than 10 μm.

[0021] Further preferably, the process conditions for electrostatic spraying are: temperature 30-35°C, humidity 30-40%RH, gun inlet pressure 0.4-0.5MPa, and gun opening pressure 0.3-0.35MPa.

[0022] More preferably, the spraying amount of the mixed powder during electrostatic spraying is 0.9-1.2 mg / cm 2 .

[0023] More preferably, after the electrostatic spraying is completed, a heat treatment is performed at 350 to 380° C. for 30 to 40 minutes.

[0024] Preferably, in step S2, the outer diameter of the polytetrafluoroethylene tube is 10-15% larger than the inner diameter of the stainless steel tube.

[0025] Preferably, in step S3, the process conditions for the first relaxation treatment are: first heating to 180-200°C at 10-15°C / min, keeping warm for 10-15 minutes, then heating to 220-230°C at 2-3°C / min, keeping warm for 15-20 minutes.

[0026] Preferably, in step S4, the drawing speed during cold drawing is controlled to be 3-4 m / min.

[0027] Preferably, in step S5, the process conditions for the second relaxation treatment are: first heating to 150-170°C at 8-10°C / min, keeping warm for 30-40 minutes, then heating to 200-210°C at 5-6°C / min, keeping warm for 40-50 minutes.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The invention provides a processing technology for a negative pressure resistant fluorine-lined pipe, and the specific steps are as follows: preparing a polytetrafluoroethylene tube; pushing and pulling the polytetrafluoroethylene tube into a stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is slightly larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube is tightly fitted to the inner wall of the stainless steel tube; performing a first relaxation treatment to eliminate harmful stress generated during the pushing and pulling process; adopting a cold drawing process to reduce the outer diameter of the stainless steel tube by a shrinking die, so that the inner wall of the stainless steel tube is tightly fitted to the outer wall of the polytetrafluoroethylene tube; performing a second relaxation treatment to eliminate harmful stress generated during the cold drawing process.

[0030] The processing technology of the present invention improves the negative pressure resistance of the lining through a secondary cold drawing process based on the original push-pull lining process. The external stainless steel tube protects and supports the polytetrafluoroethylene tube to prevent the polytetrafluoroethylene tube from being damaged by impact.

[0031] The outer diameter of the polytetrafluoroethylene tube is slightly larger than the inner diameter of the stainless steel tube. The polytetrafluoroethylene tube is pushed and pulled into the stainless steel tube by a push-pull method, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly to the inner wall of the stainless steel tube.

[0032] The present invention uses a cold drawing process to reduce the outer diameter of the stainless steel pipe by a shrinking die, so that the inner wall of the stainless steel pipe is closely attached to the outer wall of the polytetrafluoroethylene pipe, and combines two relaxation treatments to eliminate harmful stress, which work together to improve the negative pressure resistance of the fluorine-lined pipeline.

[0033] The polytetrafluoroethylene tube of the present invention is prepared by the following method: first, polytetrafluoroethylene powder is loaded into a mold, sealed, and then the mold is transferred to a container, molded under the static pressure of high-pressure air, and a tube blank is obtained, and sintered. Before the casing, the polytetrafluoroethylene tube is pretreated, and the specific method is: first, the polytetrafluoroethylene tube is plasma treated to obtain a plasma-treated polytetrafluoroethylene tube; then, polyborosiloxane, cage-type silsesquioxane, vermiculite powder, polytetrafluoroethylene powder, and titanate coupling agent are mixed to form a mixed powder, and then the mixed powder is evenly electrostatically sprayed on the outer wall of the plasma-treated polytetrafluoroethylene tube. The polytetrafluoroethylene tube of the present invention has excellent performance itself, and through pretreatment, the negative pressure resistance after combining with the stainless steel tube is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the relaxation process;

[0035] Figure 2 Schematic diagram of the cold drawing process. DETAILED DESCRIPTION

[0036] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The polytetrafluoroethylene powder involved in the present invention was purchased from Dongguan Jincheng New Material Technology Co., Ltd. (DuPont MP1200, USA).

[0038] Unless otherwise specified, all commodities in this invention are purchased through market channels.

[0039] Example 1

[0040] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0041] S1. Preparation of polytetrafluoroethylene tube;

[0042] The specific method is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and formed under the static pressure of high-pressure air to obtain a tube blank, which is sintered to obtain a polytetrafluoroethylene tube.

[0043] The molding process conditions are as follows: first, uniformly increase the pressure to 20 MPa in 10 minutes, maintain the pressure for 20 minutes, then uniformly increase the pressure to 35 MPa in 3 minutes, maintain the pressure for 8 minutes, and finally uniformly reduce the pressure to 0 in 15 minutes.

[0044] The sintering process conditions are: first increase the temperature to 250°C at 10°C / min, keep it at that temperature for 20 minutes, then increase the temperature to 360°C at 3°C / min, and keep it at that temperature for 2 hours.

[0045] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is 10% larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0046] S3. Figure 1 As shown, the first relaxation treatment eliminates the harmful stress generated during the pushing and pulling process;

[0047] The process conditions for the first relaxation treatment are: first increase the temperature to 180°C at 10°C / min, keep it at that temperature for 10 minutes, then increase the temperature to 220°C at 2°C / min, and keep it at that temperature for 15 minutes.

[0048] S4. Figure 2 As shown, the cold drawing process is adopted to reduce the outer diameter of the stainless steel tube through a shrinking die, so that the inner wall of the stainless steel tube is closely attached to the outer wall of the polytetrafluoroethylene tube;

[0049] During cold drawing, the drawing speed is controlled to be 3m / min.

[0050] S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing;

[0051] The process conditions for the second relaxation treatment are: firstly heating to 150°C at 8°C / min, keeping warm for 30 minutes, then heating to 200°C at 5°C / min, keeping warm for 40 minutes.

[0052] Example 2

[0053] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0054] S1. Preparation of polytetrafluoroethylene tube;

[0055] The specific method is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and formed under the static pressure of high-pressure air to obtain a tube blank, which is sintered to obtain a polytetrafluoroethylene tube.

[0056] The molding process conditions are as follows: first, uniformly increase the pressure to 25 MPa for 15 minutes, maintain the pressure for 30 minutes, then uniformly increase the pressure to 40 MPa for 5 minutes, maintain the pressure for 10 minutes, and finally uniformly reduce the pressure to 0 for 20 minutes.

[0057] The sintering process conditions are as follows: firstly, heating to 270°C at 15°C / min, keeping the temperature for 30 minutes, then heating to 380°C at 5°C / min, keeping the temperature for 3 hours.

[0058] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is 15% larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0059] S3. Figure 1 As shown, the first relaxation treatment eliminates the harmful stress generated during the pushing and pulling process;

[0060] The process conditions for the first relaxation treatment are: firstly, heating to 200°C at 15°C / min, keeping warm for 15 minutes, then heating to 230°C at 3°C / min, keeping warm for 20 minutes.

[0061] S4. Figure 2 As shown, the cold drawing process is adopted to reduce the outer diameter of the stainless steel tube through a shrinking die, so that the inner wall of the stainless steel tube is closely attached to the outer wall of the polytetrafluoroethylene tube;

[0062] During cold drawing, the drawing speed is controlled to be 4m / min.

[0063] S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing;

[0064] The process conditions for the second relaxation treatment are: firstly heating to 170°C at 10°C / min, keeping warm for 40 minutes, then heating to 210°C at 6°C / min, keeping warm for 50 minutes.

[0065] Example 3

[0066] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0067] S1. Preparation of polytetrafluoroethylene tube;

[0068] The specific method is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and formed under the static pressure of high-pressure air to obtain a tube blank, which is sintered to obtain a polytetrafluoroethylene tube.

[0069] The molding process conditions are as follows: first, uniformly increase the pressure to 25 MPa for 10 minutes, maintain the pressure for 20 minutes, then uniformly increase the pressure to 35 MPa for 5 minutes, maintain the pressure for 10 minutes, and finally uniformly reduce the pressure to 0 for 15 minutes.

[0070] The sintering process conditions are: firstly heating to 250°C at 15°C / min, keeping the temperature for 30 minutes, then heating to 380°C at 3°C / min, keeping the temperature for 2 hours.

[0071] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is 15% larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0072] S3. Figure 1 As shown, the first relaxation treatment eliminates the harmful stress generated during the pushing and pulling process;

[0073] The process conditions for the first relaxation treatment are: firstly, heating to 200°C at 10°C / min, keeping warm for 10 minutes, then heating to 220°C at 3°C / min, keeping warm for 20 minutes.

[0074] S4. Figure 2 As shown, the cold drawing process is adopted to reduce the outer diameter of the stainless steel tube through a shrinking die, so that the inner wall of the stainless steel tube is closely attached to the outer wall of the polytetrafluoroethylene tube;

[0075] During cold drawing, the drawing speed is controlled to be 3m / min.

[0076] S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing;

[0077] The process conditions for the second relaxation treatment are: firstly heating to 150°C at 10°C / min, keeping the temperature for 40 minutes, then heating to 210°C at 5°C / min, keeping the temperature for 40 minutes.

[0078] Before entering step S2, the polytetrafluoroethylene tube is pretreated, and the specific method is: firstly the polytetrafluoroethylene tube is plasma treated to obtain a plasma-treated polytetrafluoroethylene tube; then polyborosiloxane, cage silsesquioxane, vermiculite powder, polytetrafluoroethylene powder, and titanate coupling agent are mixed to prepare a mixed powder, and then the mixed powder is evenly electrostatically sprayed on the outer wall of the plasma-treated polytetrafluoroethylene tube.

[0079] The process conditions of plasma treatment are: working gas is argon and nitrogen, working gas pressure is 60Pa, power is 10kW, temperature is 28°C, and treatment time is 4 minutes; wherein the argon flow rate is 200sccm and the nitrogen flow rate is 150sccm.

[0080] The mixed powder is prepared by the following method: firstly, 10kg of polyborosiloxane is heated to 140°C, then 10kg of cage-type silsesquioxane is added, mixed evenly, 3kg of vermiculite powder, 5kg of polytetrafluoroethylene powder, and 0.8kg of titanate coupling agent are added, stirred and mixed evenly, cooled naturally to room temperature, and crushed to a particle size of less than 10μm.

[0081] The process conditions of electrostatic spraying are: temperature 35℃, humidity 30%RH, gun inlet pressure 0.5MPa, gun opening pressure 0.3MPa.

[0082] The spraying amount of mixed powder during electrostatic spraying is 1.2mg / cm 2 .

[0083] After the electrostatic spraying is completed, heat treatment is performed at 350°C for 40 minutes.

[0084] Example 4

[0085] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0086] S1. Preparation of polytetrafluoroethylene tube;

[0087] The specific method is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and formed under the static pressure of high-pressure air to obtain a tube blank, which is sintered to obtain a polytetrafluoroethylene tube.

[0088] The molding process conditions are as follows: first, uniformly increase the pressure to 22 MPa for 12 minutes, maintain the pressure for 25 minutes, then uniformly increase the pressure to 38 MPa for 4 minutes, maintain the pressure for 9 minutes, and finally uniformly reduce the pressure to 0 for 18 minutes.

[0089] The sintering process conditions are: first increase the temperature to 260°C at 12°C / min, keep it at that temperature for 25 minutes, then increase the temperature to 370°C at 4°C / min, and keep it at that temperature for 2.5 hours.

[0090] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is 12% larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0091] S3. Figure 1 As shown, the first relaxation treatment eliminates the harmful stress generated during the pushing and pulling process;

[0092] The process conditions for the first relaxation treatment are: first increase the temperature to 190°C at 12°C / min, keep it warm for 12 minutes, then increase the temperature to 225°C at 2.5°C / min, and keep it warm for 18 minutes.

[0093] S4. Figure 2 As shown, the cold drawing process is adopted to reduce the outer diameter of the stainless steel tube through a shrinking die, so that the inner wall of the stainless steel tube is closely attached to the outer wall of the polytetrafluoroethylene tube;

[0094] During cold drawing, the drawing speed is controlled to be 4m / min.

[0095] S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing;

[0096] The process conditions for the second relaxation treatment are: firstly heating to 160°C at 9°C / min, keeping warm for 35 minutes, then heating to 205°C at 5°C / min, keeping warm for 45 minutes.

[0097] Before entering step S2, the polytetrafluoroethylene tube is pretreated, and the specific method is: firstly the polytetrafluoroethylene tube is plasma treated to obtain a plasma-treated polytetrafluoroethylene tube; then polyborosiloxane, cage silsesquioxane, vermiculite powder, polytetrafluoroethylene powder, and titanate coupling agent are mixed to prepare a mixed powder, and then the mixed powder is evenly electrostatically sprayed on the outer wall of the plasma-treated polytetrafluoroethylene tube.

[0098] The process conditions of plasma treatment are: working gas is argon and nitrogen, working gas pressure is 50Pa, power is 12kW, temperature is 25°C, and treatment time is 5 minutes; wherein the argon flow rate is 200sccm and the nitrogen flow rate is 150sccm.

[0099] The mixed powder is prepared by the following method: firstly, 8kg of polyborosiloxane is heated to 150°C, then 8kg of cage-type silsesquioxane is added, mixed evenly, 5kg of vermiculite powder, 3kg of polytetrafluoroethylene powder, and 1kg of titanate coupling agent are added, stirred and mixed evenly, cooled naturally to room temperature, and crushed to a particle size of less than 10μm.

[0100] The process conditions of electrostatic spraying are: temperature 30℃, humidity 40%RH, gun inlet pressure 0.4MPa, gun opening pressure 0.35MPa.

[0101] The spraying amount of mixed powder during electrostatic spraying is 0.9mg / cm 2 .

[0102] After the electrostatic spraying is completed, heat treatment is performed at 380°C for 30 minutes.

[0103] Comparative Example

[0104] A processing technology for a negative pressure resistant fluorine lined pipe, the specific steps are as follows:

[0105] S1. Preparation of polytetrafluoroethylene tube;

[0106] The specific method is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and formed under the static pressure of high-pressure air to obtain a tube blank, which is sintered to obtain a polytetrafluoroethylene tube.

[0107] The molding process conditions are as follows: first, uniformly increase the pressure to 20 MPa in 10 minutes, maintain the pressure for 20 minutes, then uniformly increase the pressure to 35 MPa in 3 minutes, maintain the pressure for 8 minutes, and finally uniformly reduce the pressure to 0 in 15 minutes.

[0108] The sintering process conditions are: first increase the temperature to 250°C at 10°C / min, keep it at that temperature for 20 minutes, then increase the temperature to 360°C at 3°C / min, and keep it at that temperature for 2 hours.

[0109] S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is 10% larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube;

[0110] S3. Figure 1 As shown, relaxation treatment eliminates harmful stress generated during pushing and pulling;

[0111] The process conditions of the relaxation treatment are: firstly heating to 180°C at 10°C / min, keeping the temperature for 10 minutes, then heating to 220°C at 2°C / min, keeping the temperature for 15 minutes.

[0112] S4. Figure 2 As shown, the cold drawing process is adopted to reduce the outer diameter of the stainless steel tube through a shrinking die, so that the inner wall of the stainless steel tube is closely attached to the outer wall of the polytetrafluoroethylene tube;

[0113] During cold drawing, the drawing speed is controlled to be 3m / min.

[0114] For the convenience of comparison, the processing techniques of Examples 1 to 4 and the comparative example were used to prepare fluorine-lined pipes with an inner diameter of 300 mm and a wall thickness of 3 mm, and the high temperature resistance and negative pressure resistance of the fluorine-lined pipes were investigated. The specific methods are as follows:

[0115] 1. High temperature resistance: Place the fluorine-lined pipe in a 260℃ oven, take it out after 2 hours, and observe whether the surface of the lining changes.

[0116] 2. Negative pressure resistance: The fluorine-lined pipes are subjected to negative pressure treatment and the conditions of the fluorine-lined pipes under negative pressures of -0.1MPa and -1MPa are observed.

[0117] The results are shown in Table 1.

[0118] Table 1. Performance investigation of fluorine-lined pipes

[0119] High temperature resistance Negative pressure resistance (-0.1MPa) Negative pressure resistant type (-1MPa) Example 1 Smooth surface, no bubbles, no ripples No change There are bulges on the surface Example 2 Smooth surface, no bubbles, no ripples No change There are bulges on the surface Example 3 Smooth surface, no bubbles, no ripples No change No change Example 4 Smooth surface, no bubbles, no ripples No change No change Comparative Example Rough surface with bubbles and ripples There are bulges on the surface and it is deflated Severely deflated

[0120] It can be seen from Table 1 that the fluorine-lined pipes obtained in Examples 1 to 4 have excellent high temperature resistance and negative pressure resistance, and can still withstand -0.1 MPa negative pressure conditions under a large diameter of 300 mm. In Examples 3 and 4, the polytetrafluoroethylene pipes are pretreated before entering step S2, and the negative pressure resistance is further improved, and can withstand -1 MPa negative pressure conditions.

[0121] In the comparative example, the second relaxation treatment is omitted, and the high temperature resistance and negative pressure resistance of the fluorine-lined pipe are significantly deteriorated, indicating that the cold drawing treatment and the two relaxation treatments of the present invention work synergistically to improve the performance of the fluorine-lined pipe.

[0122] The present invention illustrates the technical concept of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of individual raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A processing technology for negative pressure resistant fluorine lined pipe, characterized in that: The specific steps are as follows: S1. Prepare polytetrafluoroethylene tube; S2. Push and pull the polytetrafluoroethylene tube into the stainless steel tube by a push-pull method, wherein the outer diameter of the polytetrafluoroethylene tube is slightly larger than the inner diameter of the stainless steel tube, so that the polytetrafluoroethylene tube and the stainless steel tube have an interference fit, and the polytetrafluoroethylene tube fits tightly against the inner wall of the stainless steel tube; S3. The first relaxation treatment eliminates harmful stress generated during the push-pull process; S4. Use cold drawing process to reduce the outer diameter of the stainless steel tube through the shrinking die, so that the inner wall of the stainless steel tube fits closely to the outer wall of the polytetrafluoroethylene tube; S5. Second relaxation treatment to eliminate harmful stress generated during cold drawing; Before entering step S2, the polytetrafluoroethylene tube is pretreated, and the specific method is: firstly, the polytetrafluoroethylene tube is plasma treated to obtain a plasma-treated polytetrafluoroethylene tube; then, polyborosiloxane, cage-type silsesquioxane, vermiculite powder, polytetrafluoroethylene powder, and titanate coupling agent are mixed to form a mixed powder, and then the mixed powder is evenly electrostatically sprayed on the outer wall of the plasma-treated polytetrafluoroethylene tube; Wherein, in step S3, the process conditions of the first relaxation treatment are: firstly heating to 180-200°C at 10-15°C / min, keeping warm for 10-15 minutes, then heating to 220-230°C at 2-3°C / min, keeping warm for 15-20 minutes; Wherein, in step S5, the process conditions of the second relaxation treatment are: firstly heating to 150-170°C at 8-10°C / min, keeping warm for 30-40 minutes, then heating to 200-210°C at 5-6°C / min, keeping warm for 40-50 minutes; Wherein, in step S2, the outer diameter of the polytetrafluoroethylene tube is 10 to 15% larger than the inner diameter of the stainless steel tube; The process conditions of plasma treatment are: working gas is argon and nitrogen, working pressure is 50-60 Pa, power is 10-12 kW, temperature is 25-28° C., and treatment time is 4-5 minutes; wherein the argon flow rate is 200 sccm and the nitrogen flow rate is 150 sccm; In parts by weight, the mixed powder is prepared by the following method: first, 8 to 10 parts of polyborosiloxane are heated to 140 to 150° C., then 8 to 10 parts of cage-type silsesquioxane are added, mixed evenly, 3 to 5 parts of vermiculite powder, 3 to 5 parts of polytetrafluoroethylene powder, and 0.8 to 1 part of titanate coupling agent are added, stirred and mixed evenly, cooled naturally to room temperature, and crushed to a particle size of less than 10 μm; The process conditions of electrostatic spraying are: temperature 30-35℃, humidity 30-40%RH, gun inlet pressure 0.4-0.5MPa, gun opening pressure 0.3-0.35MPa; the spraying amount of mixed powder during electrostatic spraying is 0.9-1.2mg / cm 2 After electrostatic spraying, heat treatment is performed at 350-380°C for 30-40 minutes.

2. The processing technology of the negative pressure resistant fluorine lined pipe according to claim 1 is characterized in that: The specific method of step S1 is as follows: first, polytetrafluoroethylene powder is loaded into a mold and sealed, then the mold is transferred to a container, and molded under the static pressure of high-pressure air to obtain a tube blank, and sintered to obtain a polytetrafluoroethylene tube.

3. The processing technology of the negative pressure resistant fluorine lined pipe according to claim 2 is characterized in that: The molding process conditions are: first use 10 to 15 minutes to evenly increase the pressure to 20 to 25 MPa, hold the pressure for 20 to 30 minutes, then use 3 to 5 minutes to evenly increase the pressure to 35 to 40 MPa, hold the pressure for 8 to 10 minutes, and finally use 15 to 20 minutes to evenly reduce the pressure to 0.

4. The processing technology of the negative pressure resistant fluorine lined pipe according to claim 2 is characterized in that: The sintering process conditions are: first increase the temperature to 250-270°C at 10-15°C / min, keep warm for 20-30 minutes, then increase the temperature to 360-380°C at 3-5°C / min, and keep warm for 2-3 hours.

5. The processing technology of the negative pressure resistant fluorine lined pipe according to claim 1 is characterized in that: The inner diameter of the polytetrafluoroethylene tube obtained in step S1 is 2 to 300 mm, and the wall thickness is 1 to 5 mm.

6. The processing technology of the negative pressure resistant fluorine lined pipe according to claim 1 is characterized in that: In step S4, the drawing speed is controlled to be 3-4 m / min during cold drawing.

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