Proper lubrication is a fundamental aspect of achieving reliable and high-quality PVC pipe extrusion. Lubricants, such as stearates and waxes, are key components of the PVC dry blend formulation.
Role in Preventing Burning and Friction
Sufficient lubrication is critical to create adequate wall slip between the PVC melt (rubber-like solid during extrusion) and the metal surfaces of the extruder screws and die. This slip prevents excessive local friction and heat build-up, which can lead to burning of the polymer. Burning causes defects like burned particles that negatively impact pipe performance in tests such as burst pressure and impact.
Influence of Melt Point (Waxes)
Lubricants include waxes with different melting points. For reliable production at higher outputs and to prevent issues like beard grow (die drool), practice shows it is beneficial to shift the balance of lubricants towards higher melting waxes. Double compression dies, for instance, allow the use of formulations with external lubricants at higher melting points, further reducing the risk of burning.
Impact on Pipe Quality and Output
Beyond preventing degradation, adequate lubrication contributes to a smoother inner bore surface of the pipe and helps maintain consistent wall distribution, especially when combined with advanced die designs like double compression tooling. A well-lubricated formulation processes more consistently, contributing to lower reject rates and the ability to achieve higher output levels. Insufficient wall slip, regardless of heat stabilizer level, can lead to burning.
Technical Specifications (Lubricant-Related Data from Source)
Why is lubrication so important for PVC pipe extrusion, even with heat stabilizers?
While heat stabilizers prevent thermal degradation of the polymer itself, lubricants provide essential wall slip between the PVC melt and machine surfaces. This slip prevents excessive friction and local heat build-up, directly preventing burning, which heat stabilizers alone cannot fully address. Burning creates defects that reduce pipe performance.
How does adjusting the melt point of waxes in a PVC formulation help improve processing?
The source indicates that shifting the balance towards higher melting waxes helps improve processing reliability, particularly at higher extrusion speeds. This adjustment contributes to better wall slip, preventing issues like beard grow and reducing the risk of burning, thereby maintaining or improving pipe quality.
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Patrick van Bezouw
