Hot pressing process of fluoroplastic-metal valve core

Abstract

The application belongs to the technical field of plastic forming process and mechanical manufacturing, and particularly discloses a fluoroplastic-metal valve core hot-pressing process, which comprises the following steps: (1) determination of cold-pressing pressure; (2) determination of hot-pressing temperature; (3) cold pressing of formal parts; and (4) hot pressing of formal parts. Through the fluoroplastic-metal valve core hot-pressing process, the cold-state pressure test is first performed to find the suitable cold-pressing pressure, and then the temperature of the fluoroplastic granular material at different positions during the state transition is monitored to quickly and accurately obtain the parameters, such as the hot-pressing temperature, pressure and time, which are closely related to the shape structure, so that the hot-pressing process is suitable for small fluoroplastic-metal valve cores. The small valve core in the application has a diameter less than 10 mm, can be suitable for hot-pressing parts of various shapes and structures, can be suitable for hot-pressing parts of various shapes and structures, is suitable for the multi-batch and small-batch production characteristics of cold-pressed parts, saves cost and improves efficiency.

Description

Technical Field

[0001] This invention relates to the fields of plastic molding technology and mechanical manufacturing technology, specifically to a hot pressing process for fluoroplastic-metal valve cores. Background Technology

[0002] Fluoroplastics are high-performance thermoplastic materials with excellent electrical insulation and superior chemical stability. They can withstand corrosion from various strong acids, strong alkalis, and strong oxidants, and even aqua regia. Therefore, they are very suitable for making valve materials with strong corrosion resistance and are commonly used as valve seals.

[0003] Fluoroplastics, as valve sealing materials, are mainly manufactured through cold pressing and hot pressing processes.

[0004] The main process of cold pressing is as follows: a ring or groove is machined into a metal base, and then a fluoroplastic ring or disc is pressed in. In order to prevent the fluoroplastic from returning to its original shape after cold deformation and to ensure the sealing of the press joint, sometimes a pressure ring is used to press the fluoroplastic to the base from the other end and fix it with laser spot welding.

[0005] The main process of hot pressing is as follows: fluoroplastic granules are filled into a metal tank and mold, and the fluoroplastic is melted at high temperature to bond with the metal base and form in the mold. Then, the sealing surface is obtained through demolding and machining.

[0006] Currently, hot pressing processes suffer from high costs and low efficiency, making them unsuitable for multi-variety, small-batch production. Summary of the Invention

[0007] The purpose of this invention is to provide a low-cost, high-efficiency fluoroplastic-metal valve core hot pressing process that can adapt to the characteristics of multi-variety, small-batch production.

[0008] To achieve the above objectives, the present invention provides a fluoroplastic-metal valve core hot pressing process, which includes:

[0009] (1) Determination of cold pressing pressure: Divide the fluoroplastic granules into 3-5 parts by weight. Fill one part of the fluoroplastic granules into the material groove of the metal matrix. Test press it on a hydraulic press using a hot pressing mold and record the pressure value. Press the remaining parts of the fluoroplastic granules in the same way and record the pressure value. Record the total thickness H of the fluoroplastic granules after cold pressing and calculate the average number P of the pressure values.

[0010] (2) Determination of hot pressing temperature: Take three portions of fluoroplastic granules of the same weight and place them in the material tank of the metal matrix, the bottom and the top of the hot pressing mold, respectively. First heating: record the temperature T1 at which the last portion of the fluoroplastic granules changes from the glassy state to the high elastic state at the three locations, and then hold the temperature for the first time. Second heating: record the temperature T2 at which the last portion of the fluoroplastic granules changes from the high elastic state to the viscous flow state at the three locations, and then hold the temperature for the second time. First cooling: record the temperature T3 at which the last portion of the fluoroplastic granules changes from the viscous flow state back to the high elastic state at the three locations, and then hold the temperature for the third time.

[0011] (3) Cold pressing of formal parts: Take the fluoroplastic granules of the same amount as in step (1) and divide them into 3-5 parts by weight, and cold press them in sequence. The cold pressing pressure is P, and the total thickness of the fluoroplastic granules after cold pressing is ≤ H.

[0012] (4) Hot pressing of formal parts: The fluoroplastic granules after cold pressing in step (3) are placed together with the hot pressing mold on a hydraulic press. Under the initial pressure, the temperature is raised to T1 for the third time, kept warm for the fourth time, raised to T2 for the fourth time, kept warm for the fifth time, cooled down to T3 for the second time, and kept warm for the sixth time. The hot pressing mold is pressed by the pressure of the hydraulic press, and the pressure is kept warm and the temperature is reduced.

[0013] Preferably, in step (2), the first heat preservation includes: a time of 5-15 minutes and a temperature of T1.

[0014] Preferably, in step (2), the second heat preservation includes: a time of 5-15 minutes and a temperature of T2.

[0015] Preferably, in step (2), the third heat preservation includes: a time of 20-40 minutes and a temperature of T3.

[0016] Preferably, in step (4), the initial pressure is 0.3-0.5 MPa.

[0017] Preferably, the third heating includes a heating rate of 15-25℃ / min.

[0018] Preferably, the fourth heat preservation includes: a time of 5-15 minutes and a temperature of T1.

[0019] Preferably, in step (4), the fourth heating includes a heating rate of 5-15℃ / min.

[0020] Preferably, the fifth heat preservation includes: a time of 5-15 minutes and a temperature of T2.

[0021] Preferably, in step (4), the second cooling includes a cooling rate of 5-15℃ / min.

[0022] Preferably, the sixth heat preservation includes: a time of 5-15 minutes and a temperature of T3.

[0023] Preferably, in step (4), the pressure of the hydraulic press is not greater than (P-0.3) MPa and not less than (P-1) MPa.

[0024] Preferably, in step (4), the pressure holding and heat preservation includes: a time of 10-20 minutes and a temperature of T3.

[0025] Preferably, the pressure reduction and cooling includes: pressure ≤ 1 MPa and temperature ≤ 100℃.

[0026] According to the above technical solution, the fluoroplastic-metal valve core hot pressing process of this invention includes: determining the cold pressing pressure, determining the hot pressing temperature, cold pressing of the final product, and hot pressing of the final product. Through the fluoroplastic-metal valve core hot pressing process of this invention, a suitable cold pressing pressure is first determined through cold-state testing. Then, by monitoring the temperature during the state transition of the fluoroplastic granules at different locations, parameters closely related to the shape and structure, such as temperature, pressure, and time, are quickly and accurately obtained. This process is suitable for the hot pressing of small fluoroplastic-metal valve cores. "Small" in this invention specifically refers to valve cores with a diameter less than 10mm. It can adapt to hot-pressed parts of various shapes and structures, and is suitable for the multi-batch, small-volume production characteristics of cold-pressed parts, saving costs and improving efficiency.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0028] The following is a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0029] This invention provides a hot pressing process for fluoroplastic-metal valve cores, which includes:

[0030] (1) Determination of cold pressing pressure: Divide the fluoroplastic granules into 3-5 parts by weight. Fill one part of the fluoroplastic granules into the material groove of the metal matrix. Test press it on a hydraulic press using a hot pressing mold and record the pressure value. Press the remaining parts of the fluoroplastic granules in the same way and record the pressure value. Record the total thickness H of the fluoroplastic granules after cold pressing and calculate the average number P of the pressure values.

[0031] (2) Determination of hot pressing temperature: Take three portions of fluoroplastic granules of the same weight and place them in the material tank of the metal matrix, the bottom and the top of the hot pressing mold, respectively. First heating: record the temperature T1 at which the last portion of the fluoroplastic granules changes from the glassy state to the high elastic state at the three locations, and then hold the temperature for the first time. Second heating: record the temperature T2 at which the last portion of the fluoroplastic granules changes from the high elastic state to the viscous flow state at the three locations, and then hold the temperature for the second time. First cooling: record the temperature T3 at which the last portion of the fluoroplastic granules changes from the viscous flow state back to the high elastic state at the three locations, and then hold the temperature for the third time.

[0032] (3) Cold pressing of formal parts: Take the fluoroplastic granules of the same amount as in step (1) and divide them into 3-5 parts by weight, and cold press them in sequence. The cold pressing pressure is P, and the total thickness of the fluoroplastic granules after cold pressing is ≤ H.

[0033] (4) Hot pressing of formal parts: The fluoroplastic granules after cold pressing in step (3) are placed together with the hot pressing mold on a hydraulic press. Under the initial pressure, the temperature is raised to T1 for the third time, kept warm for the fourth time, raised to T2 for the fourth time, kept warm for the fifth time, cooled down to T3 for the second time, and kept warm for the sixth time. The hot pressing mold is pressed by the pressure of the hydraulic press, and the pressure is kept warm and the temperature is reduced.

[0034] By implementing the above technical solution, the fluoroplastic-metal valve core hot pressing process of the present invention first performs cold pressure testing to find a suitable cold pressing pressure, and then monitors the temperature of the fluoroplastic granules at different locations during the state transition to quickly and accurately obtain parameters closely related to the shape and structure, such as temperature, pressure, and time of hot pressing. This process can adapt to hot pressing parts with various shapes and structures, and is suitable for the multi-batch, small-volume production characteristics of cold pressing parts, saving costs and improving efficiency.

[0035] In this invention, the amount of fluoroplastic granules used is determined by the size of the hot press mold and its density; the metal matrix refers to the valve core base, which generally has a circular or annular material groove, into which the fluoroplastic granules to be hot-pressed are filled; the hot press mold refers to the positioning, guiding, and forming workpiece, which positions and fixes the metal matrix and fluoroplastic filler and can press the filler into shape on a hydraulic press through the mold.

[0036] The metal substrate and hot pressing mold described in this invention should generally be made of the same batch and type of metal material.

[0037] In a preferred embodiment of the present invention, the metal substrate and hot pressing mold need to be treated before the cold pressing pressure is determined. The treatment includes: first cleaning, first drying, sandblasting, second cleaning, and second drying of the metal substrate and hot pressing mold.

[0038] The first cleaning, first drying, sandblasting, second cleaning, and second drying are conventional methods in the field and can be selected from a wide range of options.

[0039] For example, the first cleaning includes: ultrasonic cleaning in pure water for 20-40 minutes; the first drying includes: first drying with compressed air for 10-20 seconds, and then drying at a temperature of 55-65°C for 0.5-2 hours; the second cleaning includes: first blowing with compressed air for 10-20 seconds, and then ultrasonic cleaning in alcohol for 20-40 minutes; the second drying includes: first drying with compressed air for 10-20 seconds, and then drying under vacuum at a temperature of 55-65°C for 0.5-2 hours; the sandblasting includes: sandblasting pressure of 0.5 MPa, and sandblasting material is rhombic quartz sand with an abrasive particle size ≤30 mesh.

[0040] The pressure value in step (1) is required to compress the fluoroplastic granules into a uniform flat shape without causing significant deformation in any part of the hot press mold or the metal matrix.

[0041] In a preferred embodiment of the present invention, in step (2), the first heat preservation includes: a time of 5-15 min and a temperature of T1.

[0042] In a preferred embodiment of the present invention, in step (2), the second heat preservation includes: a time of 5-15 min and a temperature of T2.

[0043] In a preferred embodiment of the present invention, in step (2), the third heat preservation includes: a time of 20-40 min and a temperature of T3.

[0044] In a preferred embodiment of the present invention, in step (4), the initial pressure is 0.3-0.5 MPa.

[0045] In a preferred embodiment of the present invention, the third heating includes a heating rate of 15-25°C / min.

[0046] In a preferred embodiment of the present invention, the fourth heat preservation includes: a time of 5-15 minutes and a temperature of T1.

[0047] In a preferred embodiment of the present invention, in step (4), the fourth heating includes a heating rate of 5-15℃ / min.

[0048] In a preferred embodiment of the present invention, the fifth heat preservation includes: a time of 5-15 minutes and a temperature of T2.

[0049] In a preferred embodiment of the present invention, in step (4), the second cooling includes a cooling rate of 5-15℃ / min.

[0050] In a preferred embodiment of the present invention, the sixth heat preservation includes: a time of 5-15 minutes and a temperature of T3.

[0051] In a preferred embodiment of the present invention, in step (4), the pressure of the hydraulic press is not greater than (P-0.3) MPa and not less than (P-1) MPa, that is, (P-1) MPa ≤ pressure of the hydraulic press ≤ (P-0.3) MPa.

[0052] In a preferred embodiment of the present invention, in step (4), the pressure holding and heat preservation includes: a time of 10-20 min and a temperature of T3.

[0053] In a preferred embodiment of the present invention, the pressure reduction and cooling includes: pressure ≤ 1 MPa and temperature ≤ 100°C.

[0054] In a preferred embodiment of the present invention, after the fluoroplastic-metal valve core is hot-pressed, further machining is required. The machining includes turning the surface of the fluoroplastic-metal valve core using a jewel turning tool.

[0055] In a more preferred embodiment of the present invention, the hot pressing process steps and specific parameters of the fluoroplastic-metal valve core are as follows:

[0056] (1) Metal valve core and hot pressing mold processing: Ultrasonic cleaning in pure water for 30 min, compressed air drying for 15 s, drying at 60±5℃ for 1 h, sandblasting, compressed air blowing for 15 s, ultrasonic cleaning in alcohol for 30 min, compressed air drying for 15 s, drying in a vacuum chamber with a vacuum degree better than 100 Pa at 60±5℃ for 1 h.

[0057] The preferred abrasive material for sandblasting is rhombic quartz sand with an abrasive particle size of less than 30 mesh, and the preferred sandblasting pressure is 0.5 MPa.

[0058] (2) Determination of cold pressing pressure: Select two valve cores from each batch that need to be hot-pressed for determining the cold pressing pressure. Alternatively, process parts made of the same batch of materials can be used for cold pressing test.

[0059] The specific steps are as follows: Weigh an appropriate amount of fluoroplastic granules according to the volume of the hot press mold. Divide the weighed fluoroplastic granules into 3-5 equal parts by weight. Fill the first part of fluoroplastic granules into the material groove of the metal matrix. Use the hot press mold to press the fluoroplastic granules on a hydraulic press. The fluoroplastic granules should be pressed into a uniform flat shape without any obvious deformation of the mold or any part of the metal matrix. Record the pressure value (MPa) of the hydraulic press at this time. Press the remaining parts of fluoroplastic granules in the same way and record the pressure value (MPa). After all the fluoroplastic granules have been cold-pressed, record the total thickness H (mm) of the fluoroplastic granules and calculate the average pressure value P (MPa).

[0060] (3) Determination of hot pressing temperature: Select two valve cores from each batch that need to be hot pressed for determining the hot pressing temperature. Alternatively, process parts made from the same batch of materials can be used to determine the hot pressing temperature.

[0061] The specific steps are as follows: Take 15 fluoroplastic granules and divide them into 3 equal parts, with 5 granules in each part. Place the first part in the material trough of the metal substrate, place the second part at the bottom of the hot press mold, and place the third part at the top of the hot press mold. Heat the above specimens in a heater, and observe and record the following while heating:

[0062] Turn on the heater and observe the temperature at which the three granules transition from a glassy state to a highly elastic state, recording the heater's displayed temperature at this point (recorded as T11, T12, and T13, respectively). Continue this process until the last granule transitions to a highly elastic state, then maintain the heater at this temperature for 10 minutes.

[0063] After the heat preservation is completed, turn on the heater to continue heating, observe the temperature at which the three granules change from a highly elastic state to a viscous flow state, and record the displayed temperature of the heater at this time (recorded as T21, T22, and T23 respectively). Continue heating until the last granule changes to a viscous flow state, then adjust the heater to maintain the temperature for 10 minutes.

[0064] After the heat preservation is completed, turn off the heater and observe the temperature at which the three granular materials change from a viscous flow state back to a highly elastic state, and record the displayed temperature of the heater at this time (recorded as T31, T32, and T33 respectively). Continue this process until the last sample changes to a highly elastic state, then adjust the heater and maintain the temperature for 30 minutes.

[0065] Take the maximum value of T11, T12, and T13, and record it as T1;

[0066] Take the maximum value of T21, T22, and T23, and record it as T2;

[0067] Take the minimum value of T31, T32, and T33 and record it as T3.

[0068] (4) Cold pressing of formal parts: Take the same amount of fluoroplastic granules as in step (2) and divide them into 3-5 parts by weight. Fill them into the material groove of the metal matrix in sequence. Use a hot pressing mold to cold press the fluoroplastic granules on a hydraulic press. The cold pressing pressure is P (MPa). After cold pressing, ensure that the total thickness of the granules is ≤ H (mm).

[0069] (5) Hot pressing of formal parts: The hot pressing steps for formal parts that have passed the cold pressing are as follows:

[0070] The cold-pressed part, together with the hot-press mold, is placed on a hydraulic press. An initial pressure of (0.3-0.5) MPa is applied to the mold. The heater is turned on, and the temperature is gradually increased to T1 at a rate of 20℃ / min. The temperature is then maintained for 10 minutes.

[0071] Turn the heater back on and heat to T2 at a rate of 10℃ / min, then hold for 10 minutes. (Note: During this stage, due to the volume shrinkage of the fluoroplastic granules, a gap is formed between the hydraulic press and the mold. Therefore, the pressure exerted on the mold by the hydraulic press is 0, and it is only affected by the weight of the mold itself.)

[0072] Adjust the heater to cool down to T3 at a rate of 10℃ / min, hold for 10min, then press the hot press mold with a hydraulic pressure of not more than (P-0.3)MPa and not less than (P-1)MPa, and maintain both pressure and temperature for 15min.

[0073] Turn off the heater and gradually reduce the pressure to below 1 MPa and the temperature to below 100°C to complete the hot pressing process.

[0074] (6) Post-processing: The metal-fluoroplastic valve core after hot pressing needs to be machined. A jewel turning tool is used to turn the surface of the fluoroplastic-metal valve core.

[0075] Because no release agent is used in this invention to ensure the purity of the fluoroplastic, the mold cannot be demolded from the metal base. Therefore, it is necessary to use machining to cut off the mold and process a qualified fluoroplastic surface.

[0076] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0077] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0078] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A hot-pressing process for a fluoroplastic-metal valve core, characterized in that, The fluoroplastic-metal valve core hot pressing process includes: (1) Determination of cold pressing pressure: Divide the fluoroplastic granules into 3-5 parts by weight. Fill one part of the fluoroplastic granules into the material groove of the metal matrix. Use a hot pressing mold to test press it on a hydraulic press. The test pressure is based on the standard that the fluoroplastic granules are pressed into a uniform flat shape and no obvious deformation occurs in any part of the hot pressing mold and the metal matrix. Record the pressure value. Press the remaining part of the fluoroplastic granules in sequence according to the above steps and determine the test pressure according to the same standard. Record the pressure value. Record the total thickness H of the fluoroplastic granules after cold pressing and calculate the average number P of the pressure values. (2) Determination of hot pressing temperature: Take three portions of fluoroplastic granules of the same weight and place them in the material tank of the metal matrix, the bottom and the top of the hot pressing mold, respectively. First heating: record the temperature T1 when the last portion of the fluoroplastic granules changes from the glassy state to the high elastic state at the three locations, and then hold the temperature for the first time. Second heating: record the temperature T2 when the last portion of the fluoroplastic granules changes from the high elastic state to the viscous flow state at the three locations, and then hold the temperature for the second time. First cooling: record the temperature T3 when the last portion of the fluoroplastic granules changes from the viscous flow state back to the high elastic state at the three locations, and then hold the temperature for the third time. (3) Cold pressing of formal parts: Take the fluoroplastic granules of the same amount as in step (1) and divide them into 3-5 parts by weight, and cold press them in sequence. The cold pressing pressure is P, and the total thickness of the fluoroplastic granules after cold pressing is ≤ H. (4) Hot pressing of formal parts: The fluoroplastic granules after cold pressing in step (3) are placed together with the hot pressing mold on a hydraulic press. Under the initial pressure, the third heating is carried out to T1, the fourth heat preservation, the fourth heating to T2, the fifth heat preservation, the second cooling to T3, and the sixth heat preservation. The hot pressing mold is pressed by the pressure of the hydraulic press, and the pressure and heat preservation are maintained, and the pressure and temperature are reduced. In step (2), the temperature of the first insulation is T1; The temperature of the second insulation is T2; The temperature of the third insulation is T3; In step (4), the temperature of the fourth insulation is T1; The temperature of the fifth insulation is T2; The temperature of the sixth insulation is T3; The pressure of the hydraulic press is not greater than (P-0.3) MPa and not less than (P-1) MPa; The pressure and heat preservation temperature is T3.

2. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (2), the first heat preservation time is 5-15 minutes.

3. The fluoroplastic-metal valve core hot pressing process according to claim 1 or 2, characterized in that, In step (2), the second heat preservation time is 5-15 minutes.

4. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (2), the third heat preservation time is 20-40 minutes.

5. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (4), the initial pressure is 0.3-0.5 MPa; The third heating includes a heating rate of 15-25℃ / min; The fourth heat preservation time is 5-15 minutes.

6. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (4), the fourth heating includes a heating rate of 5-15℃ / min; The fifth heat preservation time is 5-15 minutes.

7. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (4), the second cooling includes a cooling rate of 5-15℃ / min; The sixth heat preservation time is 5-15 minutes.

8. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (4), the pressure and heat preservation time is 10-20 minutes.

9. The fluoroplastic-metal valve core hot pressing process according to claim 1, characterized in that, In step (4), the pressure reduction and cooling includes: pressure ≤ 1 MPa and temperature ≤ 100℃.