Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with over 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.
In the PVC pipe extrusion process, many processing anomalies are often mistakenly attributed to insufficient lubrication. When torque rises, melt flow becomes unstable, or the pipe surface turns rough, the immediate reaction in many factories is to add more lubricant. In the short term, torque drops, material flow improves, and the production line runs more smoothly, leading to the easy conclusion that the problem has been resolved.
Excessive lubrication is usually not intentional but rather develops gradually through repeated process adjustments. When the production line encounters pressure fluctuations, rough surfaces, occasional material jamming, poor fusion, or increased extrusion load, operators tend to incrementally add lubricant. Initial production indeed becomes smoother. However, when the lubricating effect becomes too strong, resin particles tend to slip excessively within the barrel before being fully melted. This leads to a decreased melting rate, reduced melt cohesion, unstable plasticization, and a consequently narrower processing window. Since the equipment still appears to run smoothly, such issues are often difficult to detect promptly on the shop floor.
Another common misconception is that "lower torque means better lubrication." In reality, PVC extrusion relies on controlled melting and shearing processes. Excessive lubrication weakens the effective shearing action of the screw, resulting in insufficient energy transfer for melting. Although the material flows more easily, this can readily cause incomplete fusion, dull or whitish surfaces, unstable vacuum sizing, reduced impact strength, wall thickness fluctuations, insufficient weld line strength, dimensional instability, and die buildup—particularly pronounced during high-speed extrusion.
For highly filled CaCO₃ formulations, this issue becomes even more prominent. The large quantity of filler weakens the effective bonding between resin particles, while excessive lubricant further reduces melting efficiency. This results in slower plasticization, melt pressure fluctuations, decreased melt strength, brittle mechanical properties, and reduced processing consistency across different shifts. Some factories, in an effort to improve flowability, continue to add more lubricant, inadvertently pushing the formulation further away from the optimal processing balance. This is a significant reason why many highly filled PVC pipe formulations, though easy to start up, struggle to maintain long-term stable production.
Therefore, lubrication cannot be evaluated in isolation from the entire processing system. Its effectiveness is jointly influenced by multiple factors, including filler content, ACR, CPE, stabilizer system, screw geometry, extrusion speed, temperature profile, and die design. The same lubrication scheme that performs well in a low-filler system may trigger inadequate fusion in a highly filled system.
Experienced processors are not concerned with "which lubricant is the strongest," but rather whether the "lubrication system maintains the optimal fusion balance." An excellent PVC formulation does not pursue the lowest possible torque; instead, it aims for the best balance among fusion quality, melt flow, processing stability, and mechanical properties. In actual production, low torque is merely a process indicator, not a quality indicator. The true objective is always stable fusion, stable dimensions, stable surface quality, and long-term consistent production. After all, a formulation that appears to offer better flowability today may very well become the source of quality complaints tomorrow.
If you need more information, Ningbo Fangli Technology Co., Ltd. welcomes you to contact for a detailed inquiry, we will provide you with professional technical guidance or equipment procurement suggestions.