I. Differences in core thermophysical properties
Different thermal decomposition temperatures: General-purpose materials like PP and PE have thermal decomposition temperatures far exceeding conventional processing temperatures, allowing them to withstand rapid heating. Materials like PVC and POM have extremely low degradation trigger temperatures; rapid heating easily exceeds the decomposition threshold, thus requiring a limited heating rate.
Different thermal conductivity coefficients: Glass fiber reinforced materials have much higher thermal conductivity than pure resin, allowing for faster heat diffusion within the runner, thus allowing for a more appropriate heating rate. Transparent materials like pure PC and PMMA have slow thermal conductivity; rapid heating easily creates localized temperature differences, necessitating a reduced heating rate.
Different thermal inertia: High-filler materials have high melt specific heat capacity; rapid heating can easily lead to a false normal phenomenon of surface overheating and internal temperature lag, requiring a reduced heating rate to ensure overall temperature uniformity.
II. Differences in Processing Safety Boundaries
Different Degradation Risk Levels: PVC decomposes and releases corrosive hydrogen chloride; POM is prone to chain depolymerization and spraying when overheated. These high-risk materials must have strictly limited heating rates to avoid safety accidents. General-purpose materials do not have such extreme risks and can be heated rapidly.
Different High-Temperature Tolerance Durations: Materials such as PET and PA66 will rapidly hydrolyze and break chains when exposed to residual moisture at high temperatures. Rapid heating can easily lead to localized moisture vaporization and heat absorption, creating temperature blind spots. The heating rate must be slowed down to ensure thorough dehumidification.
III. Differences in Final Product Quality Requirements
Ordinary Structural Parts: Temperature uniformity requirements are low, allowing for high heating rates to shorten production cycles.
Optical-Grade Transparent Parts: Temperature difference across the entire flow channel must be ≤±2℃. Rapid heating can easily cause uneven localized thermal stress, resulting in poor light transmission and stress marks. The heating rate must be significantly reduced.
High-precision multi-cavity medical components: all cavities must have completely consistent melt temperatures. The heating rate must be slowed down to ensure uniform temperature across the entire runner plate and avoid molding quality deviations between cavities.
