1. PVC has extremely poor thermal stability
PVC decomposes easily when heated, releasing hydrogen chloride gas. Once the temperature exceeds its safe upper limit (typically 190–200°C), decomposition accelerates rapidly, causing the material to char, blacken, and emit smoke, and may even corrode equipment and molds.
2. The melting temperature window is very narrow
The processing temperature range for PVC is only approximately 140–190°C, with the ideal range for stable production typically spanning just 10–20°C. Below the lower limit (<140°C), plasticization is incomplete; above the upper limit (>200°C), decomposition occurs immediately. There is no margin for error.
3. The quality of the plasticization process directly determines the performance of the pipe.
If the temperature is too low: The material does not melt sufficiently, leaving unmelted powder and particles inside the pipe. This results in a significant decrease in impact strength, ring stiffness, and pressure resistance, causing the pipe to become brittle and crack.
If the temperature is too high: The material overheats and decomposes, causing black spots, yellow streaks, and bubbles to appear on the pipe's surface, as well as pores inside the pipe. This leads to a drastic deterioration in mechanical properties, potentially causing the pipe to shatter upon the slightest impact.
4. Impact on Dimensional Accuracy and Appearance
Temperature fluctuations cause changes in melt viscosity, leading to fluctuations in extrusion pressure. This results in uneven wall thickness, excessive diameter deviations, a rough surface, and a lack of luster, making the product unable to meet national standards and customer requirements.
5. Production Safety and Environmental Risks
The hydrogen chloride gas produced by thermal decomposition is toxic and corrosive. It not only endangers the health of operators but also corrodes equipment (such as screws, barrels, and molds), shortening the machine's service life. Additionally, the company may face environmental penalties due to excessive emissions.
6. High Economic Costs
Uncontrolled temperatures directly result in defective products, wasting raw materials and electricity. Frequent shutdowns for cleaning decomposition byproducts, replacing filters, and repairing equipment significantly reduce production efficiency. Industry data indicates that approximately 30% of quality issues in PVC pipe production are related to improper temperature control.