A method for preparing a large-size TPI cylinder

Abstract

The present invention relates to a molding method for TPI (thermoplastic polyimide) products, specifically a method for preparing large-sized TPI cylinders. This method addresses the shortcomings of existing large-sized TPI product production, including the tendency for defects to form during the molding process, significantly affecting the product yield, and the excessively high compression ratio that prevents production using conventional molding equipment. The large-sized TPI cylinder molding die comprises a mold frame, a pressing plate, a base plate, and a mold core. The die has the advantages of a simple structure and easy operation. A positioning ring is provided on the retaining ring to effectively prevent flashing during thermoplastic molding. The present invention has low molding equipment requirements and is highly versatile.

Description

Technical Field

[0001] The present invention relates to a molding method for TPI (thermoplastic polyimide) products, in particular to a preparation method for a large-sized TPI cylinder. Background Art

[0002] TPI (thermoplastic polyimide) is an engineering plastic with the advantages of high temperature resistance, ultra-low temperature resistance, corrosion resistance, wear resistance, and high strength. It has been widely used in aerospace, semiconductors, industrial equipment, petrochemicals and other fields.

[0003] The preparation process of existing TPI products has the following problems: (1) Due to the high melt viscosity of TPI, defects such as shrinkage holes, glue deficiency, and uneven melting are easily formed on the inner wall of the product during the product molding process. In particular, large-sized TPI products with a height of more than 200 mm are more prone to defects, which greatly affects the product qualification rate; (2) The commonly used raw materials for TPI are powdered and cannot be produced by injection molding. Therefore, a molding process is used for production. However, the molding compression ratio between the powdered raw material and the finished product is usually 5.5:1. For large-sized TPI products with a height of more than 200 mm, the theoretical calculation shows that the mold height will exceed 1 m, and general molding equipment cannot reach this stroke. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the existing preparation of large-sized TPI products, such as the easy formation of defects in the products during the molding process, which greatly affects the product qualification rate, and the excessively large molding compression ratio making it impossible to use general molding equipment for preparation, and to provide a method for preparing large-sized TPI cylinders.

[0005] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides the following technical solutions:

[0006] A die for molding large-sized TPI cylinders, characterized in that it comprises a mold frame, a pressure plate disposed at the top of the mold frame, and a base plate disposed at the bottom of the mold frame; the base plate comprises a retaining ring and an outer ring plate disposed sequentially from the inside out; the retaining ring is provided with an axial protrusion extending toward the top of the mold frame, the axial protrusion serving as a mold core extending into the mold frame and being coaxially disposed with the mold frame; the mold core is provided with a temperature control hole axially connected to the bottom; the top surface of the outer ring plate is fixedly connected to the bottom of the mold frame; the outer ring plate and the mold frame each comprise two symmetrical parts along the plane containing the axis;

[0007] A demoulding hole is provided in the center of the pressing plate, and a pressing ring is provided on the bottom surface of the pressing plate. The pressing ring is located between the mold core and the mold frame, and fits with the outer wall of the mold core and the inner wall of the mold frame. The pressing plate and the pressing ring are connected by threads;

[0008] A molding cavity is formed among the mold frame, the pressure ring, the mold core, and the fixing ring.

[0009] Furthermore, the top surface of the fixing ring is provided with a positioning ring located between the mold frame and the mold core, the outer wall of the positioning ring is provided with a radial concave ring, and the inner wall of the mold frame is provided with a convex ring adapted to the radial concave ring for positioning the mold core and preventing overflow.

[0010] Furthermore, the outer wall of the mold core and the inner wall of the mold frame are both tapered surfaces that are smaller at the top and larger at the bottom, and the angle between the tapered surface line and the axis of the mold frame is 1 to 3 degrees, which is conducive to demoulding.

[0011] Furthermore, a connecting hole is provided on the top of the mold core for connecting with a lifting ring to facilitate lifting of the mold core.

[0012] At the same time, the present invention provides a method for preparing a large-sized TPI cylinder, which uses the above-mentioned large-sized TPI cylinder molding die, and the method is special in that it includes the following steps:

[0013] Step 1: Using TPI powder as raw material, dry it; press the dried raw material into a cake shape at room temperature using a cold pressing mold at a pressure of 4-6 MPa, and then crush the cake into centimeter-level pieces to reduce the compression ratio between the powdered raw material and the finished product, thereby reducing the molding stroke;

[0014] The cold pressing die comprises a shell and a pressing head, wherein the shell is provided with a groove adapted to the pressing head;

[0015] Step 2: Add material to the mold;

[0016] Add the raw material obtained in step 1 to the molding cavity of the molding die. After the molding cavity is filled with raw materials, use a pressure ring to compact the raw materials, and repeat several times until the preset weight of raw materials is added;

[0017] Step 3: pre-pressing;

[0018] Heat the mold to 290-310°C and pressurize it to 40-45 MPa using a pressure ring. Maintain the temperature and pressure for 25-35 minutes in an airtight condition.

[0019] Step 4: compression molding;

[0020] Heat the mold to 370-390°C, and after the temperature stabilizes, pressurize it to 60-65 MPa using a pressure ring. Then keep the temperature and pressure for 1-1.5 hours, and perform exhaust operations by reducing pressure several times during this period to discharge the residual gas on the inner wall of the product.

[0021] Step 5: demoulding;

[0022] The molding die is cooled down. When the temperature drops below 200°C, spacers are placed at the bottom of the fixed ring and the outer ring plate. The mold core is pressed down through the demoulding hole. The pressing plate is then removed from the pressing ring. The spacer at the bottom of the fixed ring is then removed. The outer ring plate and the mold frame are separated into two symmetrical parts along their symmetry planes. The product is then separated from the mold core by pressing down the pressing ring. This completes demoulding.

[0023] Step 6, post-processing;

[0024] The product obtained in step 5 is kept at 210-230° C. for 10-12 hours, and then cooled to room temperature to complete the preparation.

[0025] Furthermore, in step 1, the drying is specifically: drying the raw material at 210-230° C. for 3.5-4.5 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention provides a large-size TPI cylinder molding die, which includes a mold frame, a pressure plate, a base plate, a mold core, and a pressure ring. The base plate includes an outer ring plate. The outer ring plate and the mold frame can be extended to form two symmetrical parts along their symmetry plane. The pressure plate and the pressure ring are connected by threads. The molding die has the advantages of simple structure and convenient operation. A positioning ring is provided on the fixed ring, which can effectively avoid the problem of overflow during thermoplastic molding. The present invention has low requirements for molding equipment and strong versatility.

[0028] (2) The present invention provides a method for preparing a large-sized TPI cylinder using the above-mentioned molding die. The large-sized TPI cylinder produced by the method has stable quality, is free of defects such as shrinkage cavities, cracks, glue deficiency, and uneven sol, and has high mechanical strength that can approach the structural limit.

[0029] (3) The present invention provides a method for preparing a large-sized TPI cylinder, which first cold-presses the powdered raw material into a centimeter-level size and then hot-presses it to reduce the molding compression ratio between the powdered raw material and the finished product, thereby reducing the molding stroke, thereby solving the problem that the molding compression ratio is too large and cannot be prepared using general molding equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a structural schematic diagram of an embodiment of a molding die for a large-sized TPI cylinder of the present invention;

[0031] Figure 2 Schematic diagram of the structure of the cold pressing mold used in step 1 of Example 1, Example 2, and Example 3 of the method for preparing a large-sized TPI cylinder of the present invention;

[0032] Figure 3 for Figure 2 AA section view.

[0033] The reference numerals are as follows: 1-mold frame; 2-pressing plate, 21-demolding hole; 3-bottom plate, 31-fixing ring, 32-outer ring plate; 4-mold core, 41-temperature control hole, 42-connecting hole; 5-positioning ring; 6-pressing ring; 7-shell; 8-pressing head. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to the accompanying drawings and exemplary embodiments.

[0035] Reference Figure 1 A molding die for a large-size TPI cylinder includes a mold frame 1, a pressing plate 2 arranged on the top of the mold frame 1, and a base plate 3 arranged at the bottom of the mold frame 1.

[0036] The base plate 3 includes a fixing ring 31 and an outer ring plate 32 which are arranged in sequence from the inside to the outside; an axial protrusion extending toward the top of the mold frame 1 is provided in the fixing ring 31, and the axial protrusion extends into the mold frame 1 as the mold core 4 and is coaxially arranged with the mold frame 1, and the mold core 4 is axially provided with a temperature control hole 41 connected to the bottom for controlling the temperature of the molding die, and a connecting hole 42 for connecting to the hanging ring is provided on the top of the mold core 4; a positioning ring 5 located between the mold frame 1 and the mold core 4 is provided on the top surface of the fixing ring 31, and a radial concave ring is provided on the outer wall of the positioning ring 5, and a convex ring adapted to the radial concave ring is provided on the inner wall of the mold frame 1 for positioning the mold core 4 and preventing overflow; the top surface of the outer ring plate 32 is fixed to the bottom of the mold frame 1 by bolts, and the outer ring plate 32 and the mold frame 1 both include two parts symmetrical along the plane where the axis is located.

[0037] A demoulding hole 21 is provided at the center of the pressing plate 2, through which the mold core 4 can be ejected from the mold frame 1 from top to bottom. A pressing ring 6 is provided on the bottom surface of the pressing plate 2. The pressing ring 6 is located between the mold core 4 and the mold frame 1, and fits with the outer wall of the mold core 4 and the inner wall of the mold frame 1. The pressing plate 2 and the pressing ring 6 are connected by threads. During the production process, pressure is applied to the raw material by the pressing ring 6 for molding.

[0038] A molding cavity is formed between the mold frame 1 , the pressure ring 6 , the mold core 4 , and the fixing ring 31 .

[0039] Due to the large height of the product, in order to ensure demoulding, the outer wall of the mold core 4 and the inner wall of the mold frame 1 are both tapered surfaces with a smaller top and a larger bottom, and the angle between the cone line and the axis of the mold frame 1, that is, the mold draft angle, is 1 to 3°.

[0040] Example 1

[0041] A method for preparing a large-sized TPI cylinder, using the aforementioned large-sized TPI cylinder molding die, comprises the following steps:

[0042] Step 1: Dry TPI powder at 220°C for 4 hours to ensure that the moisture in the raw material is completely removed to prevent the moisture from forming pores in the product.

[0043] The dried raw materials are pressed into cakes at room temperature using a cold pressing die at a pressure of 4-6 MPa, and then the cakes are crushed into centimeter-level pieces.

[0044] The cold pressing die comprises a shell 7 and a cylindrical pressing head 8, wherein the shell 7 is provided with a groove adapted to the pressing head 8;

[0045] Step 2: Add material to the mold;

[0046] Add the raw material obtained in step 1 to the molding cavity of the molding die. After the molding cavity is filled with the raw material, use the pressing ring 6 to compact the raw material. Then continue to add the powdered raw material and use the pressing ring 6 to compact the raw material again. Repeat this process several times until the preset weight of raw material is added.

[0047] Step 3: pre-pressing;

[0048] The temperature of the molding die is raised to 300°C and the pressure is increased to 40-45 MPa through the temperature control hole 41 to make the raw materials more densely filled and conducive to good heat transfer. The temperature and pressure are then maintained for 30 minutes under air-tight conditions to ensure that the temperature of all raw materials in the molding cavity is balanced.

[0049] Step 4: compression molding;

[0050] The molding die is heated to 380°C through the temperature control hole 41, and after the temperature stabilizes, the pressure is increased to 60-65 MPa, and then kept at this temperature and pressure for 1 hour. During this period, the pressure is reduced several times for exhaust operation to discharge the residual gas on the inner wall of the product;

[0051] Step 5: demoulding;

[0052] Since the wall thickness and height of the product are relatively large, direct demoulding at a high temperature stage will cause the product to directly contact with the air at room temperature, which is extremely likely to cause defects such as cracks and shrinkage holes on the inner wall of the product. Therefore, the molding die needs to be cooled first. When the temperature drops below 200°C, pads are set at the bottom of the fixed ring 31 and the outer ring plate 32. The mold core 4 is pressed down through the demoulding hole 21, and then the pressing plate 2 is removed from the pressure ring 6. The pad at the bottom of the fixed ring 31 is removed, and the outer ring plate 32 and the mold frame 1 are separated into two symmetrical parts along their symmetry planes. Then, the pressure ring 6 is pressed down to separate the product from the mold core 4, and the demoulding is completed.

[0053] Step 6, post-processing;

[0054] The product obtained in step 5 is kept at 220°C for 12 hours, and then cooled to room temperature to complete the preparation;

[0055] Step 7: Testing the product prepared in this embodiment;

[0056] Step 7.1: Observe and determine whether the product's external structure is intact, without defects such as gaps, broken edges, or shrinkage marks. If any of the above defects exist, the product will be deemed scrapped and the process will end. Otherwise, proceed to step 7.2.

[0057] Step 7.2: Use NB / T 47013.3-2015 pressure-bearing equipment to perform ultrasonic non-destructive testing on the internal structure of the product to determine whether there are any shrinkage holes or cracks inside the product. If any of these defects are present, the product will be deemed scrapped and the process will end. Otherwise, proceed to step 7.3.

[0058] Step 7.3: Take samples from the inside of the product and test their tensile strength. The results are shown in Table 1. The average tensile strength of the samples is 90.74 MPa. It can be seen that the tensile properties of the product are close to those of the raw material. Considering the influence of the wall thickness of the product, it can be seen that the above-mentioned molding die and preparation method have reached the optimal state.

[0059] Table 1

[0060] Sample number Cross-sectional dimensions (mm) Tensile strength (MPa) Is it broken? Example 1 2.96*5.12 87.813 Unbroken Example 2 2.94*5.20 92.957 Unbroken Example 3 2.90*5.10 91.603 Unbroken

[0061] The product prepared in this embodiment has a height of 220 mm and a wall thickness of 30 mm.

[0062] Example 2

[0063] A method for preparing a large-sized TPI cylinder, using the aforementioned large-sized TPI cylinder molding die, comprises the following steps:

[0064] Step 1: Dry TPI powder at 210°C for 3.5 hours to ensure that the moisture in the raw material is completely removed to prevent the moisture from forming pores in the product.

[0065] The dried raw material is pressed into a cake shape at room temperature using the cold pressing mold in step 1 of Example 1 at a pressure of 4 to 6 MPa, and then the cake shape is crushed into centimeter-level pieces;

[0066] Step 2: Add material to the mold;

[0067] Add the raw material obtained in step 1 to the molding cavity of the molding die. After the molding cavity is filled with the raw material, use the pressing ring 6 to compact the raw material. Then continue to add the powdered raw material and use the pressing ring 6 to compact the raw material again. Repeat this process several times until the preset weight of raw material is added.

[0068] Step 3: pre-pressing;

[0069] The temperature of the molding die is raised to 290°C through the temperature control hole 41, and the pressure is increased to 40-45 MPa to make the raw materials more densely filled and conducive to good heat transfer. The temperature and pressure are then maintained for 25 minutes under air-tight conditions to ensure that the temperature of all raw materials in the molding cavity is balanced.

[0070] Step 4: compression molding;

[0071] The molding die is heated to 370°C through the temperature control hole 41, and after the temperature stabilizes, the pressure is increased to 60-65 MPa, and then kept at this temperature and pressure for 1 hour. During this period, the pressure is reduced several times for exhaust operation to discharge the residual gas on the inner wall of the product;

[0072] Step 5: demoulding;

[0073] Since the wall thickness and height of the product are relatively large, direct demoulding at a high temperature stage will cause the product to directly contact with the air at room temperature, which is extremely likely to cause defects such as cracks and shrinkage holes on the inner wall of the product. Therefore, the molding die needs to be cooled first. When the temperature drops below 200°C, pads are set at the bottom of the fixed ring 31 and the outer ring plate 32. The mold core 4 is pressed down through the demoulding hole 21, and then the pressing plate 2 is removed from the pressure ring 6. The pad at the bottom of the fixed ring 31 is removed, and the outer ring plate 32 and the mold frame 1 are separated into two symmetrical parts along their symmetry planes. Then, the pressure ring 6 is pressed down to separate the product from the mold core 4, and the demoulding is completed.

[0074] Step 6, post-processing;

[0075] The product obtained in step 5 is kept at 210°C for 10 hours, and then cooled to room temperature to complete the preparation;

[0076] Step 7: Testing the product prepared in this embodiment;

[0077] Step 7 of this embodiment is the same as that of the first embodiment.

[0078] The product prepared in this embodiment has a height of 220 mm and a wall thickness of 30 mm.

[0079] Example 3

[0080] A method for preparing a large-sized TPI cylinder, using the aforementioned large-sized TPI cylinder molding die, comprises the following steps:

[0081] Step 1: Use TPI powder as raw material and dry it at 230℃ for 4.5 hours to ensure that the moisture in the raw material is completely removed to prevent the moisture from forming pores in the product;

[0082] The dried raw material is pressed into a cake shape at room temperature using the cold pressing mold in step 1 of Example 1 at a pressure of 4 to 6 MPa, and then the cake shape is crushed into centimeter-level pieces;

[0083] Step 2: Add material to the mold;

[0084] Add the raw material obtained in step 1 to the molding cavity of the molding die. After the molding cavity is filled with the raw material, use the pressing ring 6 to compact the raw material. Then continue to add the powdered raw material and use the pressing ring 6 to compact the raw material again. Repeat this process several times until the preset weight of raw material is added.

[0085] Step 3: pre-pressing;

[0086] The temperature of the molding die is raised to 310°C through the temperature control hole 41, and the pressure is increased to 40-45 MPa to make the raw materials more densely filled and conducive to good heat transfer. The temperature and pressure are then maintained for 35 minutes under air-tight conditions to ensure that the temperature of all raw materials in the molding cavity is balanced.

[0087] Step 4: compression molding;

[0088] The molding die is heated to 390°C through the temperature control hole 41, and after the temperature stabilizes, the pressure is increased to 60-65 MPa, and then kept at this temperature and pressure for 1.5 hours. During this period, the pressure is reduced several times for exhaust operation to discharge the residual gas on the inner wall of the product;

[0089] Step 5: demoulding;

[0090] Since the wall thickness and height of the product are relatively large, direct demoulding at a high temperature stage will cause the product to directly contact with the air at room temperature, which is extremely likely to cause defects such as cracks and shrinkage holes on the inner wall of the product. Therefore, the molding die needs to be cooled first. When the temperature drops below 200°C, pads are set at the bottom of the fixed ring 31 and the outer ring plate 32. The mold core 4 is pressed down through the demoulding hole 21, and then the pressing plate 2 is removed from the pressure ring 6. The pad at the bottom of the fixed ring 31 is removed, and the outer ring plate 32 and the mold frame 1 are separated into two symmetrical parts along their symmetry planes. Then, the pressure ring 6 is pressed down to separate the product from the mold core 4, and the demoulding is completed.

[0091] Step 6, post-processing;

[0092] The product obtained in step 5 is kept at 230°C for 12 hours, and then cooled to room temperature to complete the preparation;

[0093] Step 7: Testing the product prepared in this embodiment;

[0094] Step 7 of this embodiment is the same as that of the first embodiment.

[0095] The product prepared in this embodiment has a height of 220 mm and a wall thickness of 30 mm.

[0096] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. For ordinary professional and technical personnel in this field, the specific technical solutions recorded in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.

Claims

1. A method for preparing a large-sized TPI cylinder, characterized in that: A large-size TPI cylinder molding die is used, the large-size TPI cylinder molding die comprises a mold frame (1), a pressure plate (2) arranged at the top of the mold frame (1), and a bottom plate (3) arranged at the bottom of the mold frame (1); the bottom plate (3) comprises a fixing ring (31) and an outer ring plate (32) arranged in sequence from the inside to the outside, the fixing ring (31) is provided with an axial protrusion extending toward the top of the mold frame (1), the axial protrusion serves as a mold core (4) extending into the mold frame (1) and being coaxially arranged with the mold frame (1), the mold core (4) is axially provided with a temperature control hole (41) connected to the bottom, the top surface of the outer ring plate (32) is fixedly connected to the bottom of the mold frame (1), and the outer ring plate (32) and the mold frame (1) both comprise two parts symmetrical along the plane where the axis is located; The center of the pressing plate (2) is provided with a demoulding hole (21), and the bottom surface of the pressing plate (2) is provided with a pressing ring (6). The pressing ring (6) is located between the mold core (4) and the mold frame (1), and is in contact with the outer wall of the mold core (4) and the inner wall of the mold frame (1). The pressing plate (2) and the pressing ring (6) are connected by threads. A molding cavity is formed between the mold frame (1), the pressure ring (6), the mold core (4), and the fixing ring (31); The preparation method of a large-size TPI cylinder includes the following steps: Step 1: Using TPI powder as raw material, dry it; press the dried raw material into a cake shape at room temperature using a cold pressing mold at a pressure of 4-6 MPa, and then crush the cake into centimeter-level pieces to reduce the compression ratio between the powdered raw material and the finished product, thereby reducing the molding stroke; The cold pressing die comprises a shell (7) and a pressing head (8), and the shell (7) is provided with a groove adapted to the pressing head (8); Step 2: Add material to the mold; Add the raw material obtained in step 1 to the molding cavity of the molding die. After the molding cavity is filled with the raw material, use the pressing ring (6) to compact the raw material, and repeat this process several times until the preset weight of raw material is added; Step 3: pre-pressing; The molding die is heated to 290-310° C. and pressurized to 40-45 MPa using a pressure ring (6), and the temperature and pressure are maintained for 25-35 minutes under air-tight conditions; Step 4: compression molding; The molding die is heated to 370-390°C, and after the temperature stabilizes, the die is pressurized to 60-65 MPa using a pressure ring (6), and then kept at this temperature for 1-1.5 hours, during which the die is repeatedly decompressed and vented to discharge the residual gas on the inner wall of the product; Step 5: demoulding; The molding die is cooled. When the temperature drops below 200° C., pads are provided at the bottom of the fixed ring (31) and the outer ring plate (32). The mold core (4) is pressed down through the demoulding hole (21). The pressing plate (2) is then removed from the pressing ring (6). The pads at the bottom of the fixed ring (31) are removed. The outer ring plate (32) and the mold frame (1) are separated into two symmetrical parts along their symmetrical planes. The product is then separated from the mold core (4) by pressing down the pressing ring (6). Demolding is completed. Step 6, post-processing; The product obtained in step 5 is kept at 210-230° C. for 10-12 hours, and then cooled to room temperature to complete the preparation.

2. The method for preparing a large-size TPI cylinder according to claim 1, characterized in that: The top surface of the fixing ring (31) is provided with a positioning ring (5) located between the mold frame (1) and the mold core (4); the outer wall of the positioning ring (5) is provided with a radial concave ring; the inner wall of the mold frame (1) is provided with a convex ring adapted to the radial concave ring.

3. The method for preparing a large-sized TPI cylinder according to claim 2, characterized in that: The outer wall of the mold core (4) and the inner wall of the mold frame (1) are both conical surfaces that are smaller at the top and larger at the bottom, and the angle between the conical surface line and the axis of the mold frame (1) is 1 to 3 degrees.

4. The method for preparing a large-sized TPI cylinder according to claim 3, characterized in that: The top of the mold core (4) is provided with a connection hole (42) for connecting with a lifting ring to lift the mold core (4) out of the molding equipment.

5. The method for preparing a large-sized TPI cylinder according to any one of claims 1 to 4, characterized in that: In step 1, the drying is specifically: drying the raw material at 210-230° C. for 3.5-4.5 hours.

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