Rapid forming mold for expanded polytetrafluoroethylene sealing element and preparation method of rapid forming mold

Abstract

The invention discloses a rapid forming mold for an expanded polytetrafluoroethylene sealing element and a preparation method of the rapid forming mold. The mold is composed of a composite resin matrix, a composite abrasive, a nano reinforced phase, a lubrication modifier and a structure modifier according to specific mass percent, the composite resin matrix is a combination of polyether-ether-ketone and polyimide, the composite abrasive is a mixture of diamond and cubic boron nitride, and all the components are pretreated and then prepared through an in-situ polymerization-mold pressing integrated process. During forming, microwave segmented heating is adopted to initiate a polymerization reaction, then precise mold pressing curing is performed, and a titanium nitride coating and an independent temperature control unit are arranged on the inner wall of the mold. Stress release and plasma polishing treatment are carried out after molding, and dry cutting and cold air cooling are adopted during use. The surface roughness of the die is smaller than or equal to 0.01 mu m, the Rockwell hardness is 65-70 HRC, the forming period is 30-45 minutes, the abrasion loss is 7.8-9.5 mg / 1000 turns, and the die has high precision, high hardness and high abrasion resistance and can be used for rapidly forming the expanded polytetrafluoroethylene sealing element.

Description

Technical Field

[0001] This invention relates to the field of composite material mold technology, specifically to a rapid prototyping mold for expanded polytetrafluoroethylene (ePTFE) seals and its preparation method. Background Technology

[0002] In the field of industrial processing, molds, as core processing tools, directly affect the processing accuracy, production efficiency, and processing costs of workpieces. Currently, traditional molds mostly use a combination of a single resin base and ordinary abrasives, prepared through physical mixing or simple molding processes, which has many technical limitations: insufficient interfacial bonding between the resin base and the abrasive results in low mold hardness and poor wear resistance, and abrasive shedding is prone to occur during high-load processing, affecting processing stability; the molding process lacks precise temperature control and reaction regulation mechanisms, which not only results in long molding cycles but also easily causes uneven internal structure of the mold, leading to stress concentration and reduced impact resistance; at the same time, the surface roughness of traditional molds is difficult to meet the requirements of high-precision processing, limiting their applicability. As the requirements of high-end manufacturing industries for processing accuracy, efficiency, and cost control continue to increase, existing molds can no longer meet the processing needs of high-hardness, high-precision workpieces. There is an urgent need to develop a mold that combines high hardness, high wear resistance, high precision, and rapid prototyping characteristics, and to solve the performance shortcomings of traditional molds through material system optimization and molding process innovation, so as to meet the actual application needs of industrial production. Summary of the Invention

[0003] This invention provides a rapid prototyping mold for expanded polytetrafluoroethylene (ePTFE) seals and its preparation method, solving the problems of insufficient surface precision of traditional molds, easy scratching of the ePTFE seal surface during processing, damage to the flatness of the sealing surface, and impact on sealing performance; poor hardness and wear resistance of the mold, making it difficult to adapt to the low friction and corrosion resistance characteristics of ePTFE, resulting in abrasive shedding and excessive mold wear during processing, which reduces the dimensional accuracy of the seal and increases processing costs; lack of precise control of the molding process, leading to uneven internal structure and stress concentration in the mold, weak impact resistance, easy cracking under high load processing, and long molding cycle, which cannot meet the efficiency requirements of mass production of seals; poor processing compatibility between the mold and ePTFE material, with abrasive particles generated during processing easily contaminating the seal surface or embedding in the material pores, affecting the stability and reliability of the seal.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A material-based rapid prototyping mold is synergistically composed of a composite resin matrix, a composite abrasive, a nano-reinforcing phase, a lubricant modifier, and a structure modifier in a specific mass percentage. The composite resin matrix consists of 18%-25% polyetheretherketone (PEEK) and 12%-18% polyimide; the composite abrasive consists of 15%-20% diamond and 10%-15% cubic boron nitride; the nano-reinforcing phase is 3%-8% nano-alumina; the lubricant modifier is 2%-5% polytetrafluoroethylene (PTFE) micropowder; and the structure modifier consists of 1%-3% hydroxyapatite and 2%-4% silicon nitride. The components are pretreated and then prepared using an in-situ polymerization-molding integrated rapid prototyping process. During molding, the mixed raw materials are first placed in a microwave heating device... The temperature is raised to 300-340℃ at a set rate, initiating an in-situ polymerization reaction that lasts for 20-30 minutes to form a polymer precursor. The precursor is then transferred into a molding die with an independent temperature control unit, and a molding pressure of 1.2-1.8MPa is applied and held for 30-45 minutes to complete the curing process. The composite resin matrix and composite abrasive form a chemically bonded and dense interface through polymerization. The nano-reinforcing phase is uniformly dispersed in the resin matrix to enhance the overall structural strength. The lubricating modifier forms a stable friction-reducing film on the surface of the mold, and the structure regulator precisely controls the size and distribution of micropores inside the mold to avoid stress concentration. This process achieves short-cycle molding of the mold while also providing high hardness, high wear resistance, and precise machining performance across all working conditions from rough grinding to polishing.

[0005] Furthermore, the composite resin matrix contains 22% polyetheretherketone by mass and 15% polyimide by mass. Before in-situ polymerization, both resins are subjected to plasma treatment with a power of 80-120W for 5-8 minutes. Plasma etching enhances the surface activity of the two resins, strengthens interfacial compatibility and bonding force, and makes the overall mechanical properties of the resin matrix more stable.

[0006] Furthermore, the diamond in the composite abrasive has a particle size of 20-50μm, and the cubic boron nitride has a particle size of 15-35μm. After the two are mixed in a 1:1 mass ratio, a silane coupling agent is used for surface modification treatment. The modification temperature is controlled at 80-100℃ and the modification time is 1-2 hours. Through the molecular bridging effect of the coupling agent, the bonding strength between the abrasive and the composite resin matrix is ​​strengthened, and the abrasive is prevented from falling off during processing.

[0007] Furthermore, the nano-reinforcing phase is γ-type nano-alumina with a particle size of 50-100nm, which is dispersed in the composite resin matrix by ultrasonic dispersion. The ultrasonic power is set to 300-500W and the ultrasonic time is 30-60 minutes. During the dispersion process, 0.5%-1% of dispersant by mass is added. Through the synergistic effect of ultrasonic vibration and dispersant, the long-term dispersion stability of nano-alumina is maintained and agglomeration is avoided.

[0008] Furthermore, the lubricant modifier is polytetrafluoroethylene micro powder with a particle size of 1-5 μm. Its surface is treated with plasma grafting, and the grafting monomer is methyl methacrylate. The grafting rate is controlled at 3%-5%. Grafting modification improves the compatibility between the micro powder and the composite resin matrix, ensuring that it is evenly distributed on the surface of the mold and forming a continuously effective friction-reducing surface.

[0009] Furthermore, the mass ratio of hydroxyapatite to silicon nitride in the structure modifier is 1:2. Hydroxyapatite controls the micropore size inside the mold to 0.1-0.5μm, while silicon nitride fills the gaps between the micropores to form a three-dimensional support skeleton. The two work together to improve the structural stability, impact resistance, and thermal conductivity of the mold, and avoid performance degradation due to local overheating during processing.

[0010] Furthermore, 0.3%-0.8% by mass of benzoyl peroxide is added as an initiator during the in-situ polymerization process. Microwave heating adopts a segmented heating mode, first heating to 280°C at a rate of 5°C / min and holding for 10 minutes, and then heating to 320°C at a rate of 3°C / min to continue the polymerization reaction. Segmented heating avoids violent local reactions and ensures uniform and sufficient polymerization reaction.

[0011] Furthermore, the inner wall of the molding cavity of the molding die is coated with a titanium nitride coating with a thickness of 5-10μm. The coating is prepared by physical vapor deposition. During the molding process, the temperature of the molding cavity is maintained at 280-300℃, and the cooling rate is controlled at 2-3℃ / min. The coating improves the demolding performance and wear resistance of the mold, and the precise temperature control avoids internal stress and deformation after the mold is formed.

[0012] The preparation method involves placing the molded mold in a 200℃ oven for 2 hours to release stress, followed by plasma polishing treatment with a power of 150-200W and a treatment time of 10-15 minutes. Plasma bombardment removes residual impurities and microburrs from the mold surface and optimizes the surface roughness. The final surface roughness of the mold is controlled below 0.01μm, thereby improving the surface quality of the processed workpiece.

[0013] Furthermore, during the processing, the grinding tool speed is set to 3000-5000 r / min, and a dry cutting method is adopted. The contact pressure between the workpiece and the grinding tool is controlled at 0.8-1.2 MPa. The processing area is cooled by cold air at a temperature of 5-10℃ and a wind speed of 10-15 m / s. Through the synergy of high speed, precise pressure control and cold air cooling, efficient cutting is achieved while avoiding thermal deformation of the workpiece and overheating of the mold, making it suitable for the entire process of processing high-hardness and high-precision workpieces.

[0014] The beneficial effects of this invention are: At the mold level, through composite system design and integrated process, the surface roughness is stabilized at 0.007-0.009μm, the Rockwell hardness reaches 65-70HRC, the impact strength is 16.2-19.3kJ / m², the wear is 7.8-9.5mg / 1000 revolutions, and the molding cycle is only 30-45 minutes, achieving a balance between high precision, high strength, long life and fast prototyping.

[0015] For expanded polytetrafluoroethylene (ePTFE) seals, the ultra-low surface roughness of the mold prevents scratches on the seal surface during processing, ensuring the flatness of the sealing surface and improving the sealing fit and leakage prevention capability. The high hardness characteristic matches the low friction and corrosion resistance of the material, enabling precise cutting and forming, ensuring that the dimensional accuracy of the seal meets the standards. The high wear resistance of the mold reduces the generation of abrasive particles during processing, preventing contamination of the seal surface or embedding in material pores, ensuring its stability in use. The rapid prototyping process is suitable for the mass production needs of seals, improving processing efficiency while reducing performance loss during material processing, helping the seal maintain excellent structural integrity and reliability in use. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0017] Material composition (by mass percentage): polyetheretherketone 22%, polyimide 15%, diamond 17.5%, cubic boron nitride 12.5%, γ-type nano alumina 5%, polytetrafluoroethylene micro powder 3.5%, hydroxyapatite 1.5%, silicon nitride 3%.

[0018] Preparation process: The composite resin base is plasma treated (100W, 6 minutes); the composite abrasive is mixed at a 1:1 mass ratio and modified with a silane coupling agent (90℃, 1.5 hours); nano-alumina is ultrasonically dispersed (400W, 45 minutes) with the addition of 0.7% dispersant; polytetrafluoroethylene micropowder is plasma grafted and modified (grafting rate 4%); in-situ polymerization is performed with the addition of 0.5% benzoyl peroxide, and microwave segmented heating is carried out (heating to 280℃ at 5℃ / min and holding for 10 minutes, then heating to 320℃ at 3℃ / min); the inner wall of the molding die is coated with an 8μm titanium nitride coating, the molding temperature is 290℃, the cooling rate is 2.5℃ / min, the molding pressure is 1.5MPa, and the holding time is 38 minutes.

[0019] Post-processing: 200℃ oven for 2 hours, plasma polishing (180W, 12 minutes). Example

[0020] Material composition (by mass percentage): polyetheretherketone 18%, polyimide 12%, diamond 15%, cubic boron nitride 10%, γ-type nano alumina 3%, polytetrafluoroethylene micro powder 2%, hydroxyapatite 1%, silicon nitride 2%.

[0021] Preparation process: The composite resin base is plasma treated (80W, 5 minutes); the composite abrasive is mixed at a 1:1 mass ratio and modified with a silane coupling agent (80℃, 1 hour); nano-alumina is ultrasonically dispersed (300W, 30 minutes) with the addition of 0.5% dispersant; polytetrafluoroethylene micropowder is plasma grafted and modified (grafting rate 3%); in-situ polymerization is performed with the addition of 0.3% benzoyl peroxide, and microwave segmented heating is carried out (heating to 280℃ at 5℃ / min and holding for 10 minutes, then heating to 320℃ at 3℃ / min); the inner wall of the molding die is coated with a 5μm titanium nitride coating, the molding temperature is 280℃, the cooling rate is 2℃ / min, the molding pressure is 1.2MPa, and the pressure is held for 30 minutes.

[0022] Post-processing: 200℃ oven for 2 hours, plasma polishing (150W, 10 minutes). Example

[0023] Material composition (by mass percentage): Polyetheretherketone 25%, Polyimide 18%, Diamond 20%, Cubic Boron Nitride 15%, γ-type Nano Alumina 8%, Polytetrafluoroethylene Micropowder 5%, Hydroxyapatite 3%, Silicon Nitride 4%.

[0024] Preparation process: The composite resin base is plasma treated (120W, 8 minutes); the composite abrasive is mixed at a 1:1 mass ratio and modified with a silane coupling agent (100℃, 2 hours); nano-alumina is ultrasonically dispersed (500W, 60 minutes) with the addition of 1% dispersant; polytetrafluoroethylene micropowder is plasma grafted and modified (grafting rate 5%); in-situ polymerization is performed with the addition of 0.8% benzoyl peroxide, and microwave segmented heating is carried out (heating to 280℃ at 5℃ / min and holding for 10 minutes, then heating to 320℃ at 3℃ / min); the inner wall of the molding die is coated with a 10μm titanium nitride coating, the molding temperature is 300℃, the cooling rate is 3℃ / min, the molding pressure is 1.8MPa, and the holding time is 45 minutes.

[0025] Post-processing: 200℃ oven for 2 hours, plasma polishing (200W, 15 minutes).

[0026] II. Comparative Example Comparative Example 1 Material composition (by weight): vinyl acetate resin 17.4%, polybutylene terephthalate 21.3%, polydimethylsiloxane 15%, glass fiber 3.3%, silicon carbide 31%, brightener 1%, paraffin wax 11%.

[0027] Preparation process: First, resin base, glass fiber and abrasive are made into micro-particle prepreg, heated to 90℃ and stirred evenly, and infiltrated under 0.45MPa pressure to form composite material particles; heated to 225℃ to melt and inject, injection pressure 0.7MPa, initial pressure holding 40 minutes (0.6MPa), secondary pressure holding 120 minutes (0.45MPa), and demolded.

[0028] Post-processing: No special post-processing is required; natural cooling is sufficient.

[0029] Comparative Example 2 Material composition (by weight): vinyl acetate resin 13.6%, polybutylene terephthalate 17.3%, polydimethylsiloxane 14.4%, glass fiber 1.4%, silicon carbide 26%, brightener 0%, paraffin wax 7%.

[0030] Preparation process: Same as Comparative Example 1.

[0031] Post-processing: No special post-processing is required; natural cooling is sufficient.

[0032] Comparative Example 3 Material composition (by weight): Polybutylene terephthalate 33%, polydimethylsiloxane 22%, glass fiber 4%, silicon carbide 34%, brightener 1%, paraffin wax 7%.

[0033] Preparation process: Same as Comparative Example 1.

[0034] Post-processing: No special post-processing is required; natural cooling is sufficient.

[0035] III. Testing Methods and Standards Surface roughness: Tested according to GB / T3505-2009 "Geometric Specifications for Products (GPS) - Surface Structure Profile Method: Terminology, Definitions and Parameters".

[0036] Rockwell hardness: Tested according to GB / T230.1-2018 "Metallic materials Rockwell hardness test - Part 1: Test method" (tested after mold surface treatment).

[0037] Abrasion resistance: According to GB / T9265-2009 "Determination of abrasion resistance of architectural coatings" (adapted to mold testing scenario), the wear amount of the mold is tested under set working conditions. The smaller the wear amount, the better the abrasion resistance.

[0038] Molding cycle: Record the total time from raw material mixing to finished product demolding.

[0039] Impact strength: Tested according to GB / T1843-2008 "Determination of impact strength of plastic cantilever beam".

[0040] IV. Test Results project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Surface roughness (μm) 0.008 0.009 0.007 0.020 0.035 0.080 Rockwell hardness (HRC) 68 65 70 42 40 43 Abrasion resistance (abrasion amount mg / 1000 rpm) 8.2 9.5 7.8 25.6 28.3 24.1 Molding cycle (minutes) 38 30 45 165 170 168 Impact resistance (kJ / m²) 18.5 16.2 19.3 10.8 9.5 11.2 illustrate The test indicators of Examples 1-3 are all better than those of Comparative Examples 1-3, which demonstrates the advantages of the technical solution of the present invention in terms of processing accuracy, hardness, wear resistance, molding efficiency and structural stability.

[0041] The surface roughness of all embodiments is ≤0.01μm, meeting the requirements of high-precision machining; the Rockwell hardness is ≥65HRC, which is far higher than the hardness level of existing molds, ensuring cutting performance; in terms of wear resistance, the wear amount of the embodiments is only about 1 / 3 of that of the comparative examples, and the service life is significantly extended; the molding cycle is shortened by more than 50% compared with the method mentioned in publication number CN 102717341 A, greatly improving production efficiency; the impact strength is increased by more than 50%, and the structural stability is better.

[0042] The test results of Comparative Examples 1-3 further verified the significant differences and inventiveness between the technical solution of this invention and the prior art.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A material-based rapid prototyping mold, characterized in that, The product is composed of a composite resin base, composite abrasive, nano-reinforcing phase, lubricant modifier, and structure regulator by mass percentage. The composite resin base consists of 18%-25% polyetheretherketone and 12%-18% polyimide. The composite abrasive consists of 15%-20% diamond and 10%-15% cubic boron nitride. The nano-reinforcing phase consists of 3%-8% nano-alumina. The lubricant modifier consists of 2%-5% polytetrafluoroethylene micropowder. The structure regulator consists of 1%-3% hydroxyapatite and 2%-4% silicon nitride. After pretreatment, each component is prepared by an integrated in-situ polymerization-molding rapid prototyping process. During molding, the mixed raw materials are first placed in a microwave heating device and heated to 300-340℃ to initiate an in-situ polymerization reaction, which is carried out for 20-30 minutes to form a polymer precursor. Then, the precursor is transferred into a molding die with an independent temperature control unit, and a molding pressure of 1.2-1.8MPa is applied and held for 30-45 minutes to complete the curing and molding.

2. The material-based rapid prototyping mold according to claim 1, characterized in that, The composite resin matrix contains 22% polyetheretherketone by mass and 15% polyimide by mass. Before in-situ polymerization, both are subjected to plasma treatment with a power of 80-120W for 5-8 minutes.

3. The material-based rapid prototyping mold according to claim 1, characterized in that, The composite abrasive has a diamond particle size of 20-50 μm and a cubic boron nitride particle size of 15-35 μm. The two are mixed in a 1:1 mass ratio and then surface modified with a silane coupling agent at a temperature of 80-100℃ for 1-2 hours.

4. The material-based rapid prototyping mold according to claim 1, characterized in that, The nano-reinforcing phase is γ-type nano-alumina with a particle size of 50-100nm, which is dispersed in the composite resin matrix by ultrasonic dispersion. The ultrasonic power is 300-500W and the ultrasonic time is 30-60 minutes. During the dispersion process, 0.5%-1% of dispersant by mass is added.

5. The material-based rapid prototyping mold according to claim 1, characterized in that, The lubricating modifier is polytetrafluoroethylene micro powder with a particle size of 1-5 μm, and its surface is treated with plasma grafting. The grafting monomer is methyl methacrylate, and the grafting rate is 3%-5%.

6. The material-based rapid prototyping mold according to claim 1, characterized in that, The mass ratio of hydroxyapatite to silicon nitride in the structure modifier is 1:2, and the hydroxyapatite controls the micropore size inside the mold to be 0.1-0.5 μm.

7. The material-based rapid prototyping mold according to claim 1, characterized in that, In the in-situ polymerization process, 0.3%-0.8% by mass of benzoyl peroxide is added as an initiator. The microwave heating adopts a segmented heating mode, first heating to 280°C at a rate of 5°C / min and holding for 10 minutes, and then heating to 320°C at a rate of 3°C / min to continue the polymerization reaction.

8. The material-based rapid prototyping mold according to claim 1, characterized in that, The molding cavity of the molding die is coated with a titanium nitride coating with a thickness of 5-10 μm. During the molding process, the temperature of the molding cavity is maintained at 280-300℃, and the cooling rate is controlled at 2-3℃ / min.

9. A method for preparing a mold, used to prepare a molding mold as described in any one of claims 1 to 8, characterized in that, After molding, the mold is first placed in a 200℃ oven for 2 hours to release stress. Then, it is treated with plasma polishing with a power of 150-200W and a treatment time of 10-15 minutes. The plasma bombardment removes residual impurities and microburrs from the mold surface and optimizes the surface roughness. Finally, the surface roughness of the mold is controlled below 0.01μm, which improves the surface quality of the processed workpiece.

10. The method according to claim 9, characterized in that, During the processing, the grinding tool speed is set to 3000-5000 r / min, and a dry cutting method is adopted. The contact pressure between the workpiece and the grinding tool is controlled at 0.8-1.2 MPa. The processing area is cooled by cold air with a temperature of 5-10℃ and a wind speed of 10-15 m / s.