1. Fundamental Properties of Raw Materials
Quality of PPR-Specific Compounds: Raw materials form the foundation. High-quality PPR-specific compounds (random copolymers of propylene and ethylene) exhibit more stable molecular chain structures and superior temperature resistance. Research indicates that ethylene monomer content and distribution influence crystallization behavior, thereby determining the material's long-term creep resistance at elevated temperatures.
Additive System: To resist thermal-oxidative aging at elevated temperatures, stabilizers and antioxidants must be incorporated into the raw material. The types and concentrations of these additives directly influence the service life and performance retention of pipes during prolonged high-temperature operation.
2. Production Process and Temperature Control
Extrusion Temperature Settings: Precise temperature control across all sections from the extruder to the die head is critical on the production line.
Too Low Temperature: Inadequate material plasticization occurs, with insufficient fusion of molecular chains. This results in poor pipe density and reduced temperature resistance.
Too High Temperature: May cause material decomposition (producing char particles and black streaks). This not only damages the material structure but also accelerates aging, making the material more temperature-sensitive during subsequent use.
Screw Speed and Shear: Screw speed determines the shear force applied to the material and its residence time within the barrel. An appropriate speed ensures thorough plasticization; excessive speed may generate excessive friction heat, causing material overheating and degradation, which similarly compromises the pipe's long-term temperature resistance.
3. Die and Cooling Technology
Die Design: Die structures (such as spiral or basket dies) must ensure uniform melt flow to minimize weld lines. Weld lines represent weak points in pipes, prone to failure under high temperature and pressure.
Cooling and Setting: Control of cooling rate and cooling water temperature directly impacts PPR crystallinity.
Proper cooling (typically maintaining water temperature at 15-25°C) promotes the formation of a uniform, fine crystalline structure, which enhances temperature resistance.
Inadequate or improper cooling induces internal stress, leading to deformation or cracking during high-temperature use.
4. Equipment Configuration and Process Parameters
Extruder Capability: The screw's length-to-diameter ratio (L/D) and whether its design is optimized for PPR material properties determine plasticization quality and efficiency.
Tensioning and Cutting: Tensioning speed must precisely match extrusion speed. Excessive tensioning causes pipe wall thinning and internal stress, compromising dimensional stability and pressure resistance at elevated temperatures.
5. Testing and Standards
Performance Validation: The temperature resistance of the final pipe material must be validated through a series of tests, including Vicat softening temperature (VST), hydrostatic strength (particularly at 95°C), and thermal oxidation induction time (OIT). These test results serve as the most direct evidence for evaluating whether the production line process meets standards and whether the raw materials are qualified.
To produce PPR pipes with excellent temperature resistance, it requires the combined efforts of high-quality specialized raw materials, precise process temperature control, optimal screw and mold design, and a stable cooling and traction system.