Sealing rubber cap manufacturing method, polysulfide sealing rubber cap and mold system

Abstract

The invention relates to the technical field of aerospace high-precision sealing component manufacturing, in particular to a manufacturing method of a sealing rubber cap, a polysulfide sealing rubber cap and a mold system.The manufacturing method of the sealing rubber cap comprises the steps that the mold system is prepared, specifically, the mold system comprises a male mold and a female mold, and the male mold and the female mold are assembled to form a mold cavity of the sealing rubber cap; burdening: preparing a polysulfide sealant; filling: filling the prepared polysulfide sealant into a cavity of the female die; mold pressing: closing the female mold and the male mold; vulcanizing: heating and pressurizing the mold system; demolding: opening the mold and demolding the molded sealing rubber cap; wherein in the burdening and / or mold pressing process, the polysulfide sealant is subjected to vacuumizing treatment. On the premise of strictly prohibiting the use of a release agent, nondestructive demolding of the sealing rubber cap is realized, internal bubbles and appearance defects are eliminated, and the forming quality and the qualification rate of the sealing rubber cap are ensured.

Description

Technical Field

[0001] This invention relates to the field of high-precision sealing component manufacturing technology for aerospace, and more specifically, to a method for manufacturing a sealing cap, a polysulfide sealing cap, and a mold system. Background Technology

[0002] Sealing caps are core sealing components in critical parts of the space shuttle's fuel and hydraulic systems. Their internal quality, dimensional accuracy, and surface integrity have a decisive impact on sealing reliability and spacecraft operational safety. Polysulfide sealants are considered ideal materials for manufacturing these sealing caps due to their excellent oil resistance, low gas permeability, and good adhesion to various substrates. However, the inherent high viscosity and strong polarity of polysulfide sealants present two major technical bottlenecks when using precision molding processes: 1. Dilemma in mold material selection: It is difficult to balance demolding performance with mold precision and lifespan. Because the use of release agents is strictly prohibited during the molding process of polysulfide sealants (to avoid affecting the performance of the sealing caps), their severe adhesion tendency places extremely high demands on the mold's release performance. Existing technologies mainly rely on low surface energy non-metallic mold materials, but these have significant shortcomings: 1) Nylon molds: Although they have certain demolding properties, they have low hardness and poor wear resistance. After multiple molding cycles, they are prone to cavity scratches and permanent deformation, resulting in poor dimensional consistency of the sealing caps. This makes it difficult to meet the strict requirements of the aerospace field for the interchangeability and assembly precision of seals.

[0003] 2) Pure polytetrafluoroethylene molds: They have excellent non-stick properties, but the material is too soft and has low mechanical strength. They cannot withstand the mold closing pressure and vulcanization temperature required for the molding process, which can easily cause defects such as flash and material shortage in the sealing caps. In addition, the mold life is short and it is difficult to apply to large-scale, high-precision industrial production.

[0004] 3) In contrast, metal molds possess high mechanical strength, hardness, and excellent thermal conductivity, which can meet precision requirements. While there is a demand for precision molding, the strong chemical adhesion and mechanical interlocking between polysulfide sealant and metal surfaces cause the molded caps to adhere firmly to the mold, making non-destructive demolding impossible. Forced demolding will result in tearing or permanent deformation of the caps. Therefore, metal molds have long been considered a technical no-go zone in the manufacture of polysulfide sealing caps.

[0005] (II) Challenges in controlling bubble defects: a gap exists between process capability and quality requirements The high viscosity of polysulfide sealants makes them highly susceptible to air entrainment during mixing and feeding, forming internal bubbles. These bubbles can become leakage initiation points and stress concentration sources under subsequent high-pressure and variable-temperature conditions, seriously threatening sealing performance. Existing process systems based on non-metallic molds are limited by insufficient mold structural strength and rigidity, making it difficult to stably match with efficient vacuum degassing systems, resulting in poor degassing effects and an inability to completely eliminate bubble defects.

[0006] In summary, there is an urgent need in this field to develop a mold solution that enables non-destructive demolding, in order to fundamentally overcome the technical obstacles in the precision molding of polysulfide sealing caps. Meanwhile, the problem of air bubble defects has long remained unresolved due to the inherent limitations of mold systems. Summary of the Invention

[0007] To address the technical problems of difficult demolding and air bubbles in existing polysulfide sealing cap manufacturing processes, this invention provides a sealing cap manufacturing method, a polysulfide sealing cap, and a mold system.

[0008] This invention fundamentally solves the demolding problem by adopting a new mold system; at the same time, it reduces air bubbles through vacuuming. The polysulfide sealing cap manufacturing method provided by this invention produces polysulfide sealing caps with high reliability and yield.

[0009] The technical solution of this invention: A method for manufacturing a sealing cap includes the following steps: Preparation of the mold system: The mold system includes a male mold and a female mold, which are joined together to form a mold. The mold cavity for sealing the rubber cap; both the male mold and the female mold are metal substrates, and the parting surfaces of the male mold and the female mold are coated with polytetrafluoroethylene.

[0010] Ingredients: Formulate polysulfide sealant; Filler: The prepared polysulfide sealant is filled into the cavity of the female mold; Compression molding: merging the female mold and the male mold together; Vulcanization: Heating and pressurizing the mold system; Demolding: Open the mold and remove the formed sealing cap; In particular, the polysulfide sealant is subjected to vacuum treatment during the batching and / or molding process.

[0011] Furthermore, the vacuuming process includes: a first vacuuming process, which is carried out after the polysulfide sealant is prepared and before the filler is applied, with a vacuum degree ≤ -0.09MPa and a duration of 1~3 minutes.

[0012] Furthermore, the vacuuming process also includes a second vacuuming process, which is performed after the mold is closed; The second vacuuming process is a multi-stage gradient vacuuming process with a vacuum degree ≤ -0.09MPa and a duration of 1 to 3 minutes; the multi-stage gradient vacuuming includes vacuuming at least two different vacuum degrees.

[0013] Furthermore, the multi-level gradient vacuum includes three vacuum levels, which are -0.06MPa, -0.08MPa and -0.09MPa respectively, and each vacuum level is maintained for 1 minute.

[0014] Furthermore, the mold preparation system also includes mold system preheating, with a preheating temperature of 50℃~70℃. Furthermore, in the filling step, the amount of polysulfide sealant filler is at least 1 / 2 of the cavity volume.

[0015] Furthermore, in the vulcanization step, the heating temperature is 50℃~70℃, and the holding time is 6 hours ± 2 hours.

[0016] Furthermore, the vulcanization step further includes room temperature vulcanization for a holding time of 10-24 hours. Hour.

[0017] A polysulfide sealing cap manufactured by the above method, wherein the polysulfide sealant is prepared by mixing base paste and vulcanizing paste in a weight ratio of 10:1.0~1.4.

[0018] A mold system applied to the above method, wherein the polytetrafluoroethylene coating has a thickness of 50~100μm and a surface roughness Ra of 0.4~0.6μm.

[0019] The beneficial effects of this invention are as follows: 1. Solved the demolding problem: By using a metal mold coated with polytetrafluoroethylene (PTFE), non-destructive demolding of polysulfide sealing caps was achieved under the premise that the use of mold release agents was strictly prohibited. This avoided contamination of the polysulfide sealant cap surface caused by mold release agent residue, thereby avoiding the risk of adhesion failure and reduced sealing performance caused by this, and ensuring the consistency and stability of the polysulfide sealant cap performance.

[0020] 2. Elimination of internal air bubbles and appearance defects: By employing metal molds coated with polytetrafluoroethylene (PTFE), these molds can be used in the manufacture of high-viscosity polysulfide sealant caps, providing high-precision and high-strength molds for polysulfide sealant production. Thanks to these high-precision and high-strength molds, vacuum processes can be performed during polysulfide sealant formulation and filling, efficiently eliminating gas from the interior of the polysulfide sealant and the mold cavity. This fundamentally solves appearance defects such as air bubbles and pitting, greatly improving the density and quality of the polysulfide sealant caps and meeting the reliability requirements of the aerospace industry. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the molding die structure; Figure 2 This is a schematic diagram of the injection mold structure; Figure 3 This is a schematic diagram of the pressing mold structure; Figure 4 This is a flowchart of the method in Example 2; Figure 5 The polysulfide sealing cap produced in Example 2; Figure 6 The polysulfide sealing cap produced in Example 3; Figure 7 The polysulfide sealing cap produced in Example 4; Figure 8 The polysulfide sealing cap produced in Example 5; Figure 9 Comparison chart showing the impact of the vacuuming process on the appearance quality of polysulfide sealing caps; Figure 10 Comparison of polysulfide sealing caps manufactured using traditional pure polytetrafluoroethylene molds and the molds of this invention; Figure 11 A mold system for manufacturing polysulfide sealing caps of different shapes; Figure 12 This invention is a flat vulcanizing machine for use with molding. In the picture: 1. Molding mold; 10. Molding mold base; 11. Cavity; 12. Overflow channel; 13. Reserved groove; 14. First positioning hole; 15. Second positioning hole; 2. Injection mold: 20. Injection mold base; 21. Recessed part; 22. Metering core; 23. Injection hole; 24. First locating pin; 25. Third locating hole; 3. Pressing mold: 30. Pressing mold base; 31. Boss; 32. Pressing part; 33. Second positioning pin. Detailed implementation method Example 1 This embodiment 1 provides a mold system, including a molding mold 1, an injection mold 2, and a pressing mold 3; when the mold is closed, the pressing mold 3, the injection mold 2, and the molding mold 1 are pressed together from top to bottom to form the mold cavity of the polysulfide sealing cap, and the pressing mold 3, the injection mold 2, and the molding mold 1 are connected by pins.

[0022] Specifically: See Figure 1 The molding die 1 includes a molding die base 10. The molding die base 10 is a rectangular mold steel base, and the outer surface of the mold steel base is coated with polytetrafluoroethylene.

[0023] The upper end face of the molding mold base 10 is provided with a cavity 11. Multiple cavities 11 are provided, preferably nine cavities with the same shape and size, and the nine cavities 11 are distributed in a matrix.

[0024] To further optimize the process and facilitate the outflow of excess polysulfide sealant from the mold cavity during pressing, an overflow channel 12 is provided, through which the mold cavities 11 are connected. Specifically, the overflow channel 12 includes four branch channels, which are arranged along the edge of the mold cavity 11 in a grid pattern and are interconnected.

[0025] The edge of the molding die base 10 is provided with a reserved groove 13 for easy demolding; the side is provided with a handle for easy picking; a first positioning hole 14 is provided at one diagonal position on the upper surface of the molding die base 10, and a second positioning hole 15 is provided at the other diagonal position.

[0026] See Figure 2 The injection mold 2 includes an injection mold base 20, which is a rectangular mold steel base of the same size as the forming mold 1.

[0027] A recess 21 is provided on the injection mold base 20. A metering core 22 is provided on the recess 21. Multiple metering cores 22 are provided and distributed in a matrix. The position of the metering core 22 corresponds to the position of the cavity 11.

[0028] The metering core 22 is provided with a metering cavity for containing polysulfide sealant. The metering cavity includes a side wall and a bottom surface. An injection hole 23 is opened at the center of the bottom surface. The metering cavity is connected to the cavity 11 through the injection hole 23.

[0029] The injection mold base 20 is provided with a handle on the side for easy handling.

[0030] A first positioning pin 24 is provided at a diagonal position on the upper end face of the injection mold base 20, and the position of the first positioning pin 24 corresponds to that of the second positioning hole 15.

[0031] A third positioning hole 25 is provided at another diagonal position on the upper end face of the injection mold base 20, and the position of the third positioning hole 25 corresponds to that of the first positioning hole 14.

[0032] When the mold is closed, the metering core 22 extends into the cavity 11, so that the first positioning pin 24 is inserted into the second positioning hole 15, thereby making the injection hole 23 aligned with the center of the bottom surface of the cavity 11, and the metering core 22 and the cavity 11 form the inner and outer surfaces of the polysulfide sealing cap.

[0033] See Figure 3 The pressing mold 3 includes a pressing mold base 30, which is a rectangular mold steel base of the same size as the forming mold 1. The pressing mold base 30 is provided with a handle on the side for easy handling.

[0034] A boss 31 is provided on the upper end face of the pressing mold base 30, and a pressing part 32 is provided on the boss 31. The shape of the pressing part 32 is adapted to the metering cavity. There are 9 pressing parts 32, and the 9 pressing parts 32 are distributed in a matrix.

[0035] A second positioning pin 33 is provided at a diagonal position on the upper end face of the pressing mold base 30, and the position of the second positioning pin 33 corresponds to the position of the third positioning hole 25 and the first positioning hole 14.

[0036] When the mold is closed, the pressing mold 3 needs to be flipped over. The boss 31 of the pressing mold 3 matches the recess 21 of the injection mold 2. The second positioning pin 33 is inserted into the third positioning hole 25 and the first positioning hole 14, so that the pressing part 32 extends into the metering cavity. The pressing part 32 is aligned with the injection hole 23. The pressing part 32 presses the polysulfide sealant in the metering cavity into the cavity 11 through the injection hole 23.

[0037] The thickness of the above-mentioned polytetrafluoroethylene coating is 50~100μm. Depending on the polysulfide sealant to be processed, the thickness of the polytetrafluoroethylene coating is further preferably 50μm, 80μm or 100μm.

[0038] The surface of the aforementioned polytetrafluoroethylene coating is micro-textured, with a surface roughness Ra of 0.4~0.6 μm. For polysulfide sealants requiring further processing, the surface roughness Ra is preferably 0.4 μm or 0.6 μm.

[0039] Example 2 See process Figure 4 This embodiment 2 provides a method for manufacturing a sealing cap: (1) Mold Preparation: Prepare the mold system described in Example 1 above. The pressing mold 3, injection mold 2, and molding mold 1 are all metal substrates, and the parting surface of the metal substrate is coated with polytetrafluoroethylene. Based on the shape and size of the polysulfide sealing cap, manufacture the pressing mold 3, injection mold 2, and molding mold 1, so that the cavity 11 of the molding mold 1, the metering core 22 of the injection mold 2, and the pressing part of the pressing mold 3, after being closed, form a mold cavity that matches the polysulfide sealing cap. For actual use, please refer to... Figure 11 It is a mold system for manufacturing polysulfide sealing caps of different shapes, and one of them is selected as the mold system of this embodiment 2.

[0040] (2) Ingredients: Weigh 100 parts by weight of polysulfide sealant base paste and 12 parts by weight of vulcanizing paste, and place them in a planetary system. In a mixer, mix at 250 rpm for 4 minutes. After mixing, perform a first vacuum treatment on the sealant paste at a vacuum level of -0.09 MPa for 2 minutes.

[0041] (3) Preheating and filling: Preheat the entire mold system to 60°C. Then, fill the metering cavity of the metering core 22 with the sealant paste after the first vacuum treatment, and control the amount of filling to be about 60% of the final total volume of the mold cavity. The combination of mold preheating and controlling the amount of filling (≥1 / 2 cavity volume) effectively improves the fluidity and filling of the high viscosity polysulfide sealant and completely prevents the occurrence of material shortage.

[0042] (4) Mold Closure and Degassing: The pressing mold 3, injection mold 2, and molding mold 1 are pressed together and pinned from top to bottom, followed immediately by a second vacuuming process: the second vacuuming process adopts a three-stage gradient vacuuming, first maintaining at -0.06MPa for 1 minute, then at -0.08MPa for 1 minute, and finally at -0.09MPa for 1 minute. Thanks to the mold system with both high precision and high strength, vacuuming can be performed during the molding process of polysulfide sealant. In particular, the multi-stage gradient vacuuming process efficiently removes gas from the inside of the polysulfide sealant and the cavity, fundamentally solving the appearance defects such as bubbles and pits, greatly improving the density and internal quality of the polysulfide sealant cap, and meeting the reliability requirements of the aerospace field for sealants.

[0043] (5) Heating and vulcanization: Transfer the mold system after mold closing to a flat vulcanizing machine preheated to 60°C, apply a pressure of 0.8 MPa, and maintain the temperature and pressure under these conditions for primary vulcanization for 6 hours. In this embodiment, the flat vulcanizing machine used in conjunction with the molding process is as follows: Figure 12 As shown.

[0044] Room temperature vulcanization: After the main vulcanization is completed, the workpiece is left to stand at room temperature for 10-24 hours for vulcanization.

[0045] Low-temperature long-time primary vulcanization (50-70℃, 6±2h) combined with subsequent room-temperature vulcanization ensures that the polysulfide sealant cap has a smooth and defect-free appearance and sufficient internal curing, thereby significantly improving the production qualification rate.

[0046] (6) Demolding and trimming.

[0047] The polysulfide sealing caps prepared in Example 2 above are as follows: Figure 5 As shown, the polysulfide sealing cap prepared by the method in Example 2 has a wall thickness that is 15% to 20% thinner than that of polysulfide sealing caps prepared by traditional processes. It has a smooth and flat appearance, without defects such as bubbles, dents, missing materials, and discolored stripes. It also has high dimensional accuracy and fully meets the requirements for use on the space shuttle.

[0048] The sealing cap manufacturing method provided in Example 2 achieves non-destructive demolding of polysulfide sealing caps by using a metal mold coated with polytetrafluoroethylene (PTFE) without the need for release agents. This avoids contamination of the polysulfide sealant cap surface by release agent residue, thereby preventing the risk of adhesion failure and reduced sealing performance, and ensuring the dimensional consistency and stability of the polysulfide sealant caps.

[0049] Meanwhile, thanks to the high-precision and high-strength manufacturing molds, a vacuum process can be carried out during the preparation and filling of polysulfide sealant, which efficiently removes gas from the inside of the polysulfide sealant and the cavity, fundamentally solving the appearance defects such as bubbles and pits, greatly improving the density and quality of the polysulfide sealant caps, and meeting the reliability requirements of the aerospace field for seals.

[0050] Example 3 The difference between this embodiment and Embodiment 2 lies in the composition of the polysulfide sealant used; the ratio of base paste to vulcanizing paste is 10:1.0. The mold preheating temperature and main vulcanization temperature are both set to the upper limit of 70°C, and the vulcanization pressure is 0.5 MPa. The PTFE coating thickness of the pressing mold 3 is 50 μm. The second vacuuming is performed only once, with a vacuum level of -0.09 MPa, lasting for 3 minutes.

[0051] The polysulfide sealing cap produced in Example 3 is as follows: Figure 6 As shown, the polysulfide sealing caps prepared by the method in Example 3 have a smooth and flat appearance, free from defects such as bubbles, dents, material shortages, and discolored stripes. They also have high dimensional accuracy and fully meet the requirements for use on the space shuttle.

[0052] Example 4 The difference between this embodiment and Embodiment 2 lies in the composition of the polysulfide sealant used; the ratio of base paste to vulcanizing paste is 10:1.4. The mold preheating temperature and main vulcanization temperature are both set to the lower limit of 50°C, and the vulcanization pressure is 1.0 MPa. The PTFE coating thickness of the pressing mold 3 is 100 μm, and its substrate surface roughness Ra... The thickness is 0.8 μm. A second vacuum is not performed after mold closing; degassing is achieved solely through vacuuming during the preparation stage.

[0053] The polysulfide sealing cap produced in Example 4 is as follows: Figure 7 As shown, the polysulfide sealing caps prepared by the method of this Example 4 have a surface that is not as smooth and flat as the polysulfide sealing caps produced in Example 2, but they are basically free of obvious defects such as bubbles, dents, material shortages and discolored stripes.

[0054] Example 5 The difference between this embodiment and Embodiment 2 is that the PTFE coating surface of the pressing mold 3 is micro-textured, resulting in a surface roughness Ra of 0.4 μm. The amount of polysulfide sealant filler is controlled to occupy 1 / 2 (50%) of the cavity volume. The second vacuum treatment uses a two-stage gradient: first, maintaining at -0.07 MPa for 1 minute, and then maintaining at -0.09 MPa for 2 minutes.

[0055] The polysulfide sealing cap produced in Example 5 is as follows: Figure 8 As shown, the polysulfide sealing caps prepared by the method in Example 5 have a smooth and flat appearance, without obvious defects such as bubbles, dents, material shortages, and discolored streaks.

[0056] Comparative Example 1 See details Figure 9 Figure a shows a polysulfide sealing cap manufactured without vacuuming, exhibiting numerous bubbles and material shortages. Figure b shows a polysulfide sealing cap manufactured using the mold system and method in Example 2, with a smooth and even surface, free from bubbles, dents, material shortages, and discolored streaks. Through comparative experiments, it is evident that the vacuuming process significantly impacts the surface quality of the polysulfide sealing cap; therefore, a vacuuming step must be added during formulation and mold pressing.

[0057] Comparative Example 2 See details Figure 10 Figure a shows a polysulfide sealing cap made using a traditional pure polytetrafluoroethylene mold, which has obvious defects such as numerous air bubbles and material shortages. Figure b shows a polysulfide sealing cap made using the mold system and method in Example 4, which has a smooth and flat surface without obvious defects such as air bubbles, dents, material shortages, and discolored streaks. Through experimental comparison, the mold system provided by this invention has a significant impact on the surface quality of the polysulfide sealing cap.

[0058] In summary, the mold system and complete process method provided by this invention, while ensuring that the polysulfide sealant caps meet aerospace-grade performance indicators, effectively reduce unit production costs and material waste due to the long lifespan of the mold system, the absence of release agents, and the high production qualification rate, thus possessing excellent prospects for industrialization and economic benefits.

Claims

1. A method for manufacturing a sealing cap, characterized in that, Includes the following steps: Prepare the mold system: The mold system includes a male mold and a female mold, which are closed to form a mold cavity with a sealing cap; the male mold is a metal substrate, and the parting surface of the male mold is coated with polytetrafluoroethylene (PTFE); the female mold is a metal substrate, and the parting surface of the female mold is coated with PTFE. Ingredients: Formulate polysulfide sealant; Filler: The prepared polysulfide sealant is filled into the cavity of the female mold; Compression molding: merging the female mold and the male mold together; Vulcanization: Heating and pressurizing the mold system; Demolding: Open the mold and remove the formed sealing cap; In particular, the polysulfide sealant is subjected to vacuum treatment during the batching and / or molding process.

2. The method for manufacturing a sealing cap according to claim 1, characterized in that, The vacuuming process includes: a first vacuuming process, which is carried out after the polysulfide sealant is prepared, with a vacuum degree ≤ -0.09MPa and a duration of 1 to 3 minutes.

3. The method for manufacturing a sealing cap according to claim 2, characterized in that, The vacuuming process also includes a second vacuuming process, which is performed after the mold is closed. The second vacuuming process is a multi-stage gradient vacuuming process with a vacuum degree ≤ -0.09MPa and a duration of 1 to 3 minutes; the multi-stage gradient vacuuming includes at least two stages of vacuuming at different vacuum degrees.

4. The method for manufacturing a sealing cap according to claim 3, characterized in that, The multi-level gradient vacuuming includes vacuuming at three vacuum levels: -0.06 MPa, -0.08 MPa, and -0.09 MPa, respectively, with each vacuum level maintained for 1 minute.

5. The method for manufacturing a sealing cap according to claim 1, characterized in that, The mold preparation system also includes mold system preheating, with a preheating temperature of 50℃~70℃.

6. The method for manufacturing a sealing cap according to claim 1, characterized in that, In the filling step, the amount of polysulfide sealant filler shall be at least 1 / 2 of the cavity volume.

7. The method for manufacturing a sealing cap according to claim 1, characterized in that, In the vulcanization step, the heating temperature is 50℃~70℃, and the holding time is 6 hours ± 2 hours.

8. The method for manufacturing a sealing cap according to claim 1, characterized in that, The vulcanization step further includes room temperature vulcanization for 10-24 hours.

9. A polysulfide sealing cap manufactured by the method according to any one of claims 1 to 8, characterized in that, The polysulfide sealant is prepared by mixing base paste and vulcanizing paste in a weight ratio of 10:1.0 to 1.

4.

10. A mold system applied to the method of any one of claims 1 to 8, characterized in that, The polytetrafluoroethylene coating has a thickness of 50–100 μm and a surface roughness Ra of 0.4–0.6 μm.

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