Pfa rod extrusion molding device and molding method

Abstract

The application discloses a PFA rod extrusion forming device and a forming method, and the forming device comprises an extruder, a die, a melt shaping sleeve, a cooling sleeve and a damping machine, the die at the port of the extruder is connected with the melt shaping sleeve and the cooling sleeve, and the damping rod of the damping machine is inserted into the melt flow channel of the melt shaping sleeve and the cooling sleeve. Through parameter control on the die cavity and the compression section, the density of the melt is as high as possible under the condition of guaranteeing the melting flow of the PFA rod. Meanwhile, the melt shaping sleeve with the length of 2-5 times of the diameter of the formed rod is additionally arranged at the die cavity outlet, so that the melt in the melt shaping sleeve is uniformly pressed when the rod is extruded, and then the melt is accelerated and cooled and shaped through the cooling sleeve. Through density control and cooling speed control on the molten PFA, the pressure transmission effect is improved, the temperature difference between the center and the surface of the rod is reduced, and the problems of uneven density of the rod product and difficult control caused by the large melt viscosity and poor flowability of the PFA rod during the extrusion forming of the PFA rod are solved.

Description

Technical Field

[0001] This invention relates to the technical field of extrusion molding of PFA rods, which are melt-processable fluoroplastics, and more specifically, to an apparatus and method for extruding PFA rods. Background Technology

[0002] Among the series of melt-processable fluoroplastic materials, PFA (tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer) has good mechanical strength, strong corrosion resistance, good wear resistance and excellent high and low temperature resistance. It can be widely used to make equipment linings, sealing components and gaskets in various strong acid and strong alkali media environments, and can also be used as special seals in high-tech fields.

[0003] Research and development of melt-processable fluoroplastic raw materials in my country started relatively late, with PFA only achieving commercialization in the 1990s. With the continuous expansion of the application market, research teams specializing in PFA processing and molding technologies have also grown rapidly in the fluoroplastic products processing industry, achieving technological breakthroughs in various aspects of PFA processing, including compression molding, blow molding, and tube extrusion molding. Currently, PFA rods are produced through compression molding, but during extrusion molding, it is difficult to maintain density uniformity and rod product stability.

[0004] CN202210581101.7 discloses a method for preparing polychlorotrifluoroethylene (PTFE) rods by extrusion molding. A cooling and shaping sleeve with a cooling and shaping device is added to the output end of the extruder. When the plasticized melt enters the cooling zone from the mold cavity, the melt that is not rapidly cooled is in a highly elastic state. Under the resistance of the damping machine, it generates internal pressure. Because the highly elastic state is in a semi-molten state and has good compressibility, it is simultaneously pressurized into the cooling zone of the shaping sleeve along with the melt in the center of the cooling zone. After cooling, the rod can achieve a consistent density at the center and edge, overcoming the problem of rod bending and deformation caused by inconsistent density, thus improving product quality. Tetrafluoroethylene and perfluoroalkyl vinyl ether copolymers (PFA) are also a type of fluorinated material with high processing temperatures and strong corrosiveness. Compared to PTFE, PFA has a melting point of 302-310℃ and a melt viscosity of 10 at 380℃. 4 -10 5 Poisson's polymer (PFA) has a melt flow index of 2-20 and a wide molecular weight distribution. Furthermore, as the degree of polymerization increases, the molecular weight of PFA increases, and the melt viscosity also increases. Therefore, during rod extrusion molding, because the material itself still has the characteristics of high polymerization degree and low melt index, the melt viscosity after plasticization is relatively high, and the fluidity is low, making it difficult to control the density of the product. Conversely, using resins with low molecular weight, low melt viscosity, and high fluidity during rod extrusion can easily cause blistering and rupture of the rods under pressure from the damper. Therefore, PFA is difficult to mold in rod extrusion. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of PFA rod extrusion molding, such as high melt viscosity, poor fluidity leading to uneven density of rod products and difficulty in control, and to provide a PFA rod extrusion molding apparatus and molding method.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A PFA bar extrusion molding apparatus includes an extruder, a die, a melt shaping sleeve, a cooling sleeve, and a damper. The extrusion port of the extruder is connected to the die, the outlet of the die is connected to one end of the melt shaping sleeve, the other end of the melt shaping sleeve is connected to the cooling sleeve, and the damping rod of the damper is inserted into the melt flow channel of the melt shaping sleeve and the cooling sleeve.

[0008] The mold includes a mold cavity and a compression section. The compression ratio of the cavity is 2-2.5, which can ensure the density of the melt and avoid friction and heating caused by the mutual compression of molecules during the melt transportation process, which could lead to melt fracture and polymer decomposition.

[0009] The compression section is 2.5-2.7 times the diameter of the bar stock, which can increase the density of the plasticized melt in the mold cavity. If it is too long, it will lead to high extrusion resistance of the bar stock.

[0010] The melt shaping sleeve includes an inner shaping sleeve and an outer shaping sleeve. The inner shaping sleeve and the outer shaping sleeve form a sealed circulating liquid channel. The length of the melt shaping sleeve is 2-5 times the diameter of the forming rod.

[0011] The cooling jacket includes an inner cooling jacket and an outer cooling jacket, which together form a sealed coolant flow channel. The length of the cooling jacket is 5-8 times the diameter of the formed rod.

[0012] This invention improves the pressure transmission effect of the forming rod by controlling the cooling of the forming rod through the melt shaping sleeve and cooling sleeve, so that the damping pressure can be effectively transmitted, and solves the problems of excessively rapid cooling of the surface of the extruded rod, uneven pressure transmission, and insufficient pressure in the center of the rod.

[0013] Furthermore, flow control valves are provided on the pipes of the melt shaping sleeve and the cooling sleeve.

[0014] Furthermore, the flow control valve controls the temperature of the melt shaping sleeve at 180-200℃ by circulating the liquid; the flow control valve controls the temperature of the cooling sleeve at 40-60℃ by controlling the flow of the coolant.

[0015] Furthermore, the extruder has a length-to-diameter ratio of 20:1 and a compression ratio of 2.5:1.

[0016] Furthermore, the mold cavity has a trumpet-shaped structure and a smooth surface without sharp corners or dead angles, preventing the plasticized melt from accumulating during the conveying process or from being decomposed due to prolonged accumulation, which could cause black spots and other decomposition products on the bar.

[0017] Furthermore, the damping machine employs a clamping plate structure to clamp the damping rod.

[0018] Furthermore, the clamping pressure value of the damping rod is 0.3-0.8 MPa.

[0019] A method for extruding PFA rods, comprising the following steps:

[0020] S1. Select a resin raw material of tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer with a melt index of 3-5 and dry it;

[0021] S2. Set the extruder temperature to 250-385℃ and the die temperature to 380℃, heat up, then turn on the main unit, control the screw speed to 3-4 rpm / min, and feed the material;

[0022] S3. After the material is extruded from the die, adjust the screw speed to 4-8 rpm / min, the clamping pressure of the damper on the damping rod to 0.3-0.8 MPa, control the rod extrusion speed to 3-12 cm / min, and start the circulation of the circulating liquid in the melt shaping sleeve and the cooling liquid in the cooling sleeve. The rod density should reach 2.12-2.17 g / cm³. 3 This means obtaining qualified PFA bars.

[0023] Furthermore, the temperature of the extruder barrel is set to four stages: the first stage temperature is 250-280℃, the second stage temperature is 330-370℃, the third stage temperature is 375-380℃, and the fourth stage temperature is 380-385℃.

[0024] Furthermore, the temperature of the mold is 375-385℃.

[0025] Compared with existing technologies, the beneficial effects are:

[0026] This invention controls the parameters of the conveying and compression sections of the mold cavity to maximize the melt density while ensuring the molten flow of PFA bars. Simultaneously, a melt-stabilizing sleeve, 2-5 times the diameter of the formed bar, is added at the mold cavity outlet. By maintaining the circulating fluid within the melt-stabilizing sleeve at 180-200℃, the hardening rate of the melt surface in the stabilizing section is controlled. This ensures that the melt within the stabilizing sleeve is uniformly compressed during bar extrusion, followed by accelerated cooling and stabilization via a cooling sleeve. By employing different cooling methods and rates, this invention reduces the temperature difference between the melt center and surface in the stabilizing section, improves pressure transmission, and achieves consistent density in the extruded PFA bars. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, and back), these directional indications are only used to explain the relative positional relationships and movement of the components in a specific posture. If the specific posture changes, the directional indications will also change accordingly. If the embodiments of the present invention involve descriptions such as "first" and "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" and "second" may explicitly or implicitly include at least one of those features.

[0029] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0031] Example 1

[0032] This embodiment provides a PFA bar extrusion molding apparatus, including an extruder, a die, a melt shaping sleeve, a cooling sleeve, and a damping machine. The extrusion port of the extruder is connected to the die, the outlet of the die is connected to one end of the melt shaping sleeve, the other end of the melt shaping sleeve is connected to the cooling sleeve, and the damping rod of the damping machine is inserted into the melt flow channel of the melt shaping sleeve and the cooling sleeve.

[0033] The extruder is a single-screw extruder with a screw length-to-diameter ratio of 20:1 and a compression ratio of 2.5:1.

[0034] The mold includes a cavity and a compression section. The cavity has a funnel-shaped structure with a smooth surface and no sharp corners or dead angles, preventing the plasticized melt from accumulating during transportation or decomposing due to prolonged accumulation, which could cause black spots on the bar. The compression ratio is 2-2.5. The length of the compression section is 2.5-2.7 times the diameter of the bar.

[0035] The melt shaping sleeve includes an inner shaping sleeve and an outer shaping sleeve. The inner shaping sleeve and the outer shaping sleeve form a sealed circulating liquid channel. The flow of the circulating liquid is controlled by a flow control valve to keep the temperature of the melt shaping sleeve at 180-200℃. The length of the melt shaping sleeve is 2-5 times the diameter of the forming rod.

[0036] The cooling jacket includes an inner cooling jacket and an outer cooling jacket. The inner cooling jacket and the outer cooling jacket form a sealed coolant flow channel. The flow of coolant is controlled by a flow control valve to keep the temperature of the cooling jacket at 40-60℃. The length of the cooling jacket is 5-8 times the diameter of the formed rod.

[0037] The damping machine includes upper and lower clamping plates and a damping rod. One end of the damping rod is clamped in the clamping plate, and the other end extends into the cooling jacket and the melt shaping jacket. The diameter of the damping rod is slightly smaller than the rod material specification by 1 mm.

[0038] Example 2

[0039] According to the PFA rod extrusion molding method provided in Example 1, the molding equipment parameters are as follows:

[0040] The mold includes a cavity and a compression section, wherein the compression ratio of the cavity is 2. The length of the compression section is 2.5 times the diameter of the bar.

[0041] The temperature of the melt shaping sleeve is controlled at 200℃, and the length of the melt shaping sleeve is 3 times the diameter of the forming rod.

[0042] The temperature of the cooling jacket is controlled at 50°C, and the length of the cooling jacket is 5-8 times the diameter of the forming rod.

[0043] The steps include:

[0044] S1. Select PFA resin with a melt flow index of 3 to make rods with a diameter of 15mm.

[0045] S2. Set the extruder barrel temperature as follows: first stage temperature 260℃, second stage temperature 370℃, third stage temperature 380℃, fourth stage temperature 380℃, mold temperature 380℃, heat up, then turn on the main unit, control the screw speed to 3-4 rpm / min, and feed the material.

[0046] S3. After the melt flows out normally, clean the extrusion port, install the melt shaping sleeve and cooling sleeve, turn on the coolant circulation and insert a damping rod with a diameter of 14.9mm into the melt shaping sleeve, and adjust the pressure of the damping machine clamping the damping rod to 0.6MPa;

[0047] S4. By controlling the screw speed to 5 rpm / min and the bar extrusion speed to 8 cm / min, qualified PFA bars can be obtained.

[0048] Example 3

[0049] This embodiment provides a PFA rod extrusion molding apparatus and its molding method, the steps of which include:

[0050] S1. Select dried PFA resin with a melt index of 5 to make rods with a diameter of 30mm.

[0051] S2. Set the extruder barrel temperature as follows: first stage temperature 270℃, second stage temperature 375℃, third stage temperature 380℃, fourth stage temperature 380℃, mold temperature 380℃, heat up, then turn on the main unit, control the screw speed to 3-4 rpm / min, and feed the material.

[0052] S3. After the melt flows out normally, clean the extrusion port, install the melt shaping sleeve and cooling sleeve, turn on the coolant circulation and insert a damping rod with a diameter of 29.9mm into the melt shaping sleeve, and adjust the pressure of the damping machine clamping the damping rod to 0.6MPa;

[0053] S4. By controlling the screw speed to 7 rpm / min and the bar extrusion speed to 5 cm / min, qualified PFA bars can be obtained.

[0054] Comparative Example 1

[0055] The process of this comparative example is the same as that of Example 2, except that the melt index of the PFA resin used in this comparative example is 1.

[0056] Comparative Example 2

[0057] The process of this comparative example is the same as that of Example 2, except that the melt index of the PFA resin used in this comparative example is 7.

[0058] Comparative Example 3

[0059] The process of this comparative example is the same as that of Example 2, except that the mold used in this comparative example does not use a funnel-shaped cavity with a compression ratio of 2:1, but a straight cylindrical cavity.

[0060] Comparative Example 4

[0061] The process of this comparative example is the same as that of Example 2, except that the compression section of the mold cavity used in this comparative example has a length of 1 times the diameter of the bar.

[0062] Comparative Example 5

[0063] The process of this comparative example is the same as that of Example 2, except that the compression section of the mold cavity used in this comparative example has a length of 3.5 times the diameter of the bar.

[0064] Comparative Example 6

[0065] The process of this comparative example is the same as that of Example 2, except that the circulating liquid temperature of both the melt shaping jacket and the cooling jacket in this comparative example is controlled at 50°C.

[0066] Comparative Example 7

[0067] The process of this comparative example is the same as that of Example 2, except that the temperature of the circulating liquid in the melt shaping sleeve of this comparative example is controlled at 150°C.

[0068] Comparative Example 8

[0069] The process of this comparative example is the same as that of Example 2, except that the length of the melt shaping sleeve used in this comparative example is 8 times the diameter of the forming rod.

[0070] Comparative Example 9

[0071] The process of this comparative example is the same as that of Example 2, except that the damping rod is clamped by a damping machine at a pressure of 0.1 MPa in this comparative example.

[0072] Comparative Example 10

[0073] The process of this comparative example is the same as that of Example 2, except that the damping rod in this comparative example is clamped by a damping machine at a pressure of 1 MPa.

[0074] The comparison results of the bars produced according to Example 2 and the comparative example are shown in Table 1 below:

[0075] Table 1

[0076] <![CDATA[Density (g / cm 3 )]]> bar quality Example 2 2.12-2.17 The bar has a smooth and straight surface. Example 3 2.12-2.17 The bar has a smooth and straight surface. Comparative Example 1 \ Rods cannot be formed Comparative Example 2 \ Bubbling in the bar stock Comparative Example 3 \ Bar stock conveying has holes, making it impossible to form. Comparative Example 4 \ Difficulty in forming bars Comparative Example 5 \ Increased extruder load leads to greater resistance in bar forming. Comparative Example 6 \ The bar stock exhibits bending, uneven density, and shrinkage cavity in the center. Comparative Example 7 1.5-1.7 The bar has severe shrinkage cavities in the center. Comparative Example 8 2.12-2.17 Extruder load increased Comparative Example 9 1.6-1.8 The bar stock is bent and deformed, with bubbles and shrinkage cavities. Comparative Example 10 \ Increased extruder load and operational difficulties

[0077] As shown in the table above, PFA resin with a melt index in the range of 3-5 ensures that the PFA resin can achieve sufficient plasticization within the extrusion molding temperature range while maintaining a certain degree of fluidity, preventing bubbling and cracking during the extrusion process under damping pressure. High molecular weight, high melt viscosity, and poor fluidity of PFA resin make it difficult to mold. Conversely, the produced rods will exhibit quality problems such as bubbling and cracking, uneven density, and central shrinkage cavities. During the extrusion process, proper parameter settings can reduce the torque on the extruder, ensuring extrusion safety.

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for extruding PFA rods, characterized in that, The method is based on an extrusion molding device, which includes an extruder, a die, a melt shaping sleeve, a cooling sleeve, and a damper. The extrusion port of the extruder is connected to the die, the outlet of the die is connected to one end of the melt shaping sleeve, the other end of the melt shaping sleeve is connected to the cooling sleeve, and the damping rod of the damper is inserted into the melt flow channel of the melt shaping sleeve and the cooling sleeve. The mold includes a funnel-shaped mold cavity and a compression section. The compression ratio of the mold cavity is 2-2.5, and the length of the compression section is 2.5-2.7 times the diameter of the bar. The melt shaping sleeve includes an inner shaping sleeve and an outer shaping sleeve. The inner shaping sleeve and the outer shaping sleeve form a sealed circulating liquid channel. The length of the melt shaping sleeve is 2-5 times the diameter of the forming rod. The temperature of the melt shaping sleeve is controlled at 180-200℃. The cooling jacket includes an inner cooling jacket and an outer cooling jacket. The inner cooling jacket and the outer cooling jacket form a sealed coolant flow channel. The length of the cooling jacket is 5-8 times the diameter of the formed rod. The temperature of the cooling jacket is controlled at 40-60℃. The steps include: S1. Select a resin raw material of tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer with a melt index of 3-5 and dry it; S2. Set the extruder temperature to 250-385℃ and the die temperature to 380℃, heat up, then turn on the main unit, control the screw speed to 3-4 rpm / min, and feed the material; S3. After the material is extruded from the die, adjust the screw speed to 4-8 rpm / min, the clamping pressure of the damper on the damping rod to 0.3-0.8 MPa, control the rod extrusion speed to 3-12 cm / min, and start the circulation of the circulating liquid in the melt shaping sleeve and the cooling liquid in the cooling sleeve. The rod density should reach 2.12-2.17 g / cm³. 3 This means obtaining qualified PFA bars.

2. The PFA rod extrusion molding method according to claim 1, characterized in that, Flow control valves are installed on the pipes of the melt shaping sleeve and the cooling sleeve.

3. The PFA rod extrusion molding method according to claim 1, characterized in that, The extruder has a length-to-diameter ratio of 20:1 and a compression ratio of 2.5:

1.

4. The PFA rod extrusion molding method according to claim 1, characterized in that, The cavity surface of the mold is smooth and has no sharp corners or dead angles.

5. The PFA rod extrusion molding method according to claim 1, characterized in that, The damping machine uses a clamping plate structure to clamp the damping rod.

6. The PFA rod extrusion molding method according to claim 1, characterized in that, The extruder barrel temperature is set to four stages: the first stage temperature is 250-280℃, the second stage temperature is 330-370℃, the third stage temperature is 375-380℃, and the fourth stage temperature is 380-385℃.

7. The PFA rod extrusion molding method according to claim 1, characterized in that, The temperature of the mold is 375-385℃.