Precautions for Injection Molding of PTFE Plastic

PTFE (Polytetrafluoroethylene), as a special engineering plastic with excellent temperature resistance, corrosion resistance, wear resistance and self-lubricating properties, is widely used in high-end fields such as chemical industry, electronics, automotive and medical care. However, due to its own characteristics such as extremely high viscosity, poor flowability and special thermal stability, the injection molding process is much more difficult than ordinary plastics. If the operation is improper, it is easy to have problems such as insufficient filling, warpage deformation, surface defects, etc., which not only affects the product quality, but also may damage the equipment and increase the production cost. Therefore, mastering the core precautions of PTFE plastic injection molding and standardizing every production link are the keys to ensuring smooth processing and qualified products. Combined with practical operation experience, the following details the precautions for the whole process of PTFE injection molding.

I. Key Points of Raw Material Pretreatment

PTFE raw material has extremely high viscosity and poor flowability. Before injection molding, the drying and cleanliness must be strictly controlled to avoid moisture absorption or mixing of impurities. Usually, it needs to be dried at 120~150℃ for 2~4 hours to ensure no moisture inside, so as to prevent bubbles, delamination or surface pitting during molding. At the same time, mixing with other plastics is prohibited to avoid affecting the core performance of the product such as temperature resistance and corrosion resistance. In addition, the raw material particles should be uniform to avoid uneven plasticization caused by different sizes. If the raw material is stored for too long, it needs to be dried again before use.

II. Requirements for Injection Equipment and Mold Adaptation

The equipment should choose a model with high injection pressure and high clamping force to cope with the extremely poor flowability of PTFE and ensure that the melt can fill the cavity smoothly. The mold runner should be designed to be short, thick and smooth, with as few bends as possible. The gate should be a large-size direct or fan gate to avoid insufficient filling caused by thin gate. The mold temperature should be stably controlled at 100~150℃, which not only improves the melt flowability, but also ensures uniform cooling of the product, reducing internal stress and warpage deformation. At the same time, the mold cavity needs to be polished smooth to avoid difficult demolding or surface defects caused by rough surface.

III. Key Points of Process Parameter Control

In terms of temperature, the barrel temperature needs to be set in sections at 320~380℃ to ensure full melting without thermal decomposition. The injection pressure needs to be adjusted to a higher range, combined with a slower injection speed, to prevent melt injection, trapped air and short shots. The packing pressure should not be too high to avoid cracking caused by excessive internal stress of the product. The cooling time needs to be appropriately extended to ensure that the product is fully shaped before demolding.

IV. Prevention and Treatment of Molding Defects

PTFE injection molding is prone to problems such as insufficient filling, weld lines, warpage deformation and rough surface. In production, insufficient filling can be improved by increasing mold temperature, enlarging gate size and optimizing venting; deformation can be reduced by balanced cooling and reasonable packing; surface finish can be improved by stabilizing temperature and injection speed. At the same time, it should be noted that PTFE has a large shrinkage rate (usually 2%~5%), so sufficient shrinkage margin should be reserved in mold design to ensure accurate finished product size.

V. Post-processing and Safety Protection

The formed products can be annealed according to requirements to eliminate internal stress and improve dimensional stability. The temperature is generally set at about 200℃, and then slowly cooled after heat preservation. The processing site should be well ventilated to avoid harmful gases generated by high-temperature decomposition; before the equipment is shut down, the barrel must be completely emptied to prevent carbonization of residual raw materials, which will affect the next production and damage the equipment. Operators need to wear high-temperature resistant gloves, protective glasses and other protective equipment to avoid scalding by high-temperature melt.

VI. Storage and Use Specifications

PTFE raw materials should be stored in a dry, cool and ventilated environment to avoid moisture absorption due to long-term exposure to the air, and away from high temperature and fire sources to prevent deterioration of raw materials. It is strictly prohibited to add ordinary recycled materials during production, otherwise the density and weather resistance of the product will be greatly reduced. For precision parts and wear-resistant parts, it is necessary to strictly control the process stability throughout the process, and keep the parameters consistent for the same batch of products to ensure the unity of performance and size.

VII. Summary

In summary, the core of PTFE plastic injection molding is "precise control and standardized operation". Every link from raw material pretreatment, equipment and mold adaptation, to process parameter adjustment, defect prevention, and then to post-processing and safety protection cannot be ignored. Only by strictly following the above precautions, fully combining the material characteristics of PTFE and optimizing the production process, can we effectively reduce defective products, reduce production costs, ensure that the processed PTFE products meet the quality requirements, give full play to the excellent performance of its special materials, and meet the high-end application needs of various industries.