Material Selection for PTFE Molds
Material selection for PTFE molds must be based on the special characteristics of PTFE: high temperature resistance, strong corrosion resistance, low friction, high thermal expansion and low mechanical strength. Different molding processes such as compression molding, extrusion and injection molding require different material combinations to meet requirements of structural support, molding surface performance, demolding and dimensional stability.
Core Principles of Material Selection
First, temperature adaptability is essential. PTFE sintering temperature can reach 350–400°C, so mold materials must maintain stability at high temperatures without softening or deformation. Second, corrosion resistance is required to avoid chemical reactions or contamination when contacting strong acids, alkalis or solvents.Third, high rigidity is necessary to resist pressure and thermal expansion. Fourth, the molding surface must have good wear resistance and low friction to ensure smooth demolding and long service life.
Material Selection for Compression Molding Molds
Compression molding is the most common process for PTFE products. The mold bears high pressure and high temperature during sintering. The mold base and load-bearing structure can use 45 steel, S50C or pre-hardened steels such as P20 and 718H, which provide sufficient strength and stability.Cavity and core materials are selected according to application requirements: 304 or 316L stainless steel for general applications; S136 or 2316 for high-precision and mirror-finish requirements; nickel-based alloys for extreme corrosion and high-temperature environments. A PTFE or nickel-PTFE coating can further improve demolding performance.
Material Selection for Extrusion Molds
Extrusion molds for PTFE wires, tubes and films require low resistance and uniform flow. The outer mold sleeve is usually made of H13 or 420 stainless steel for high rigidity and wear resistance. The inner core and molding surface are commonly made of pure PTFE or modified PTFE lining, which provides natural non-stick performance and low friction.The composite structure of metal sleeve plus PTFE inner liner is widely used to balance strength, heat resistance and demolding performance.
Material Selection for Injection Molds
PTFE injection requires high temperature and high pressure. The mold must have excellent heat stability and corrosion resistance. 17-4PH stainless steel is commonly used for its high strength, corrosion resistance and good machinability. Ejector pins and guide components use heat-resistant mold steels such as SKD61 or SUJ2 bearing steel for durability and precision.
Key Avoidance Points in Material Selection
Pure PTFE should not be used for load-bearing structures due to low strength and large deformation. Ordinary carbon steel is not suitable for molding surfaces because of poor corrosion resistance. Coatings must be compatible with base materials to avoid peeling at high temperatures. Shrinkage and thermal expansion of PTFE must be considered in mold design.
| Application Scenario | Mold Base/Bearing Material | Cavity/Core Material | Surface Treatment | Applicable Batch |
|---|---|---|---|---|
| Small-medium batch compression molded PTFE products | 45# steel (quenched and tempered) | 304/316L stainless steel | None/PTFE coating | 10,000-100,000 shots |
| High-precision mirror finish compression molded PTFE products | P20/718H (pre-hardened) | S136/2316 (corrosion-resistant steel) | Polished to Ra≤0.02μm | 100,000-1,000,000 shots |
| Extruded PTFE cables/tubes | H13 hot work steel | Pure PTFE/modified PTFE liner | None/Ni-PTFE composite coating | Continuous mass production |
| High-temperature & high-pressure injection molded PTFE products | 17-4PH (precipitation hardening) | 17-4PH (matching) | Surface nitriding | Medium batch |
| Extreme strong corrosion/high-temperature conditions | Nickel-based alloy (Hastelloy) | Nickel-based alloy/PTFE composite | PTFE coating | Customized special applications |
Practical Material Selection Summary
For small-batch general PTFE products, 45 steel with 304/316L cavity is cost-effective. For high-precision mirror molds, P20/718H with S136 is preferred. For extrusion products, H13 with PTFE liner is the standard solution. For extreme environments, nickel-based alloys are used. Proper material combination ensures stable quality, long service life and high cost efficiency.
