PFA Molding Process Guide
Dina Zhou (fluoropolymer)
Fluoropolymer Specialist ▏FEP PTFE PVDF PFA ETFE Resin ▏Fluoroplastic Semi-finished Products in Sheet, Tube, Rod, Film
Introduction of PFA
PFA (perfluoroalkoxy polymer) is a high-performance fluoroplastic with excellent chemical stability, high temperature resistance, low friction coefficient and good electrical insulation performance. PFA products play an indispensable role in many high-end manufacturing fields, such as semiconductors, chemicals, aerospace, etc. The PFA molding process is the key technology for processing PFA materials into various complex shaped products. A deep understanding of the operating procedures and key points of the PFA molding process is extremely important for ensuring product quality, improving production efficiency and ensuring production safety.
Operation Procedures of PFA Molding Process
1. Raw Material Selection
PFA resin powder or granules should be selected to meet specific application requirements and quality standards. The purity, particle size distribution, melt flow rate and other parameters of the raw materials should be strictly tested to ensure that they are within the allowable tolerance range. For example, for the molding production of high-precision electronic parts, the particle size of the PFA raw material may be required to be more uniform to ensure the dimensional stability of the product.
2. Drying Process
PFA has a certain degree of water absorption, and even a small amount of water may cause defects such as bubbles during the molding process. The raw materials are usually pre-treated by vacuum drying or hot air drying. The drying temperature is generally controlled at 120-150°C, and the drying time depends on the initial moisture content of the raw materials and the efficiency of the drying equipment, usually 2-4 hours. During the drying process, it is necessary to ensure that the raw materials are heated evenly, which can be achieved by appropriate stirring or turning.
1. Mold Design
The design of the mold should fully consider the characteristics of PFA. The demoulding slope is generally designed between 1-3° to facilitate the smooth demoulding of the product. The runner system should be as short and thick as possible to reduce pressure loss and material retention time to prevent excessive degradation of PFA. At the same time, the parting surface of the mold should fit tightly to prevent material leakage. For example, when designing a PFA seal mold with a complex shape, a multi-cavity structure and a special cooling water channel layout are required to ensure consistent molding quality in all parts.
2. Mold Cleaning and Preheating
Before molding, the mold must be thoroughly cleaned to remove oil, impurities and residual materials from the previous molding process. Special mold cleaning agents and ultrasonic cleaning equipment can be used for cleaning. After cleaning, the mold needs to be preheated. The preheating temperature is usually 180-220°C and the preheating time is about 30-60 minutes. The purpose of preheating is to make the mold reach a temperature close to that of the PFA material, reduce the temperature difference when the material is injected into the mold, and thus reduce the internal stress and molding cycle of the product.
1. Feeding
According to the weight and volume requirements of the product, accurately weigh the appropriate amount of PFA raw material. The feeding method can be manual feeding or automatic feeding device. For manual feeding, pay attention to the uniformity and speed of feeding to avoid material accumulation or spillage. For automatic feeding, the feeding amount and feeding speed must be calibrated in advance to ensure the accuracy of each feeding.
2. Mold Closing and Pressurization
Slowly close the mold to the initial contact position, and then pressurize with appropriate pressure. The initial pressure is generally 3-5 MPa, and then gradually increase the pressure according to the shape and size of the product. The maximum pressure can reach 20-30 MPa. During the pressurization process, pay attention to the steady rise of pressure to avoid excessive pressure fluctuations that may cause uneven product density or stratification.
3. Heating and Temperature Holding Time
While applying pressure, the mold starts to heat up. The heating rate should be controlled at 10 - 20°C/min to prevent PFA from decomposing due to too fast heating. When the mold temperature reaches the melting temperature range of PFA (usually 320 - 340°C), keep the temperature constant for a period of time. The constant temperature period depends on the thickness of the product, usually 2 - 3 minutes per millimeter of thickness. During this process, the PFA material gradually melts and fills the mold cavity.
4. Pressure Holding and Cooling
After the holding period is over, the pressure is kept constant and the holding period begins. The holding period is about 5-10 minutes. The purpose of holding is to keep the product stable in shape during the cooling process to prevent defects caused by shrinkage. After the holding period is over, the mold begins to cool. The cooling method can be water cooling or air cooling, and the cooling rate is generally controlled at 15-25°C/min. When the mold temperature drops below 100°C, the cooling can be stopped and demolding can be prepared.
1. Demolding
During demoulding, the mold should be opened slowly to avoid damage to the product due to excessive demoulding force. For some products with complex shapes or difficult demoulding, demoulding agents or auxiliary demoulding devices can be used. The demoulding agent should be compatible with PFA and not affect the performance of the product, and the amount of the demoulding agent and the uniformity of the application should be strictly controlled.
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2. Post-processing
After demolding, the product may have defects such as flash and burrs, which need to be trimmed. Manual trimming, mechanical grinding or frozen trimming can be used. For some products with high requirements for dimensional accuracy and surface quality, secondary processing such as polishing and machining may also be required. In addition, in order to eliminate the internal stress generated by the product during the molding process, the product can be annealed. The annealing temperature is generally 150-200°C and the annealing time is 1-3 hours.
Key Points in PFA Molding Process
1. Pressure Control
Pressure is a key factor affecting the density and dimensional accuracy of PFA products. Too high pressure may cause overflow, excessive internal stress, or even cracking of the product; too low pressure will cause insufficient density and reduced strength of the product. During the molding process, the pressure parameters should be accurately set and strictly controlled according to the shape, size and characteristics of the product and the PFA raw materials, and the pressure changes should be closely monitored and adjusted in time.
2. Temperature Control
Temperature plays a decisive role in the melting, flow and solidification of PFA. High temperature will cause PFA degradation and reduce the performance of the product. Too low temperature will lead to poor material fluidity, failure to fill the mold cavity or cause defects in the product. Therefore, it is necessary to precisely control the temperature rise, insulation and cooling temperature of the mold, as well as the time of each stage, to ensure that the PFA is completed under the right temperature conditions.
3. Time control
The time of each stage in the molding process needs to be set reasonably. If the feeding time is too long, the material will stay in the barrel for a longer time and easily decompose due to heat; if the mold closing, pressurization, heating, temperature holding, pressure holding and cooling time are insufficient or too long, they will have an adverse effect on the quality of the product. The best time parameters should be determined through experiments and experience accumulation, and the operation should be strictly in accordance with the set time.
1. Raw Material Quality Control
Strictly inspect the various indicators of PFA raw materials to ensure that they meet the requirements of the molding process. Raw materials from different batches may differ and should be fully mixed and homogenized before use. At the same time, pay attention to the storage conditions of the raw materials to avoid affecting their performance due to moisture, heat or contamination.
2. Material of Mold and Precision
Mold materials should have good high temperature and high pressure resistance and dimensional stability. Commonly used mold materials include stainless steel, alloy steel, etc. The manufacturing accuracy of the mold directly affects the dimensional accuracy of the product. High-precision processing equipment and processes should be used to ensure that the mold cavity size, surface roughness meet the design requirements.
1. Safety Protection Measures
The PFA molding process involves high temperature and high pressure operation, which has certain safety risks. Operators should be equipped with necessary personal protective equipment, such as high temperature protective clothing, protective gloves, goggles, etc. At the same time, the molding equipment should be installed with perfect safety protection devices, such as safety valves, temperature sensors, pressure sensors, etc., to ensure that the equipment can be stopped in time in abnormal circumstances to ensure the safety of personnel.
2. Compliance with Environmental Protection Requirements
During the PFA molding production process, a small amount of waste gas, waste water and solid waste may be generated. Effective environmental protection measures should be taken to purify the waste gas and discharge it after it meets the standards; treat and recycle the waste water; and classify and collect and properly treat the solid waste to reduce pollution to the environment.
The PFA molding process is a complex and delicate processing process. It is necessary to strictly follow the operating procedures and pay close attention to key precautions in order to produce high-quality, compliant PFA products while ensuring the safety and environmental protection of the production process.