When PVC foam board becomes as brittle as a cookie, we often immediately suspect a “formulation problem.” However, the culprit for over 90% of board breakage isn’t the formula itself, but rather “improper plasticization” during equipment operation.

This guide will provide a complete solution, from core concepts to practical steps, to thoroughly address the root cause.

1. Core Concept: Forget the Formulation, Focus on Plasticization

What is Plasticization?

Simply put, plasticization involves melting the PVC dry powder in an extruder through heat and the intense shear (stirring and kneading) of the screw. This allows the molecular chains to completely untwist and entangle. This process is like kneading dough: Only by thoroughly kneading it can the dough become chewy, resilient, and unbreakable.

Consequences of Improper Plasticization:

If plasticization is insufficient, the PVC molecular chains are not fully fused. The board’s interior resembles countless loose grains of sand, barely glued together. The loose structure and poor toughness make it naturally brittle and break easily.

Core Conclusion:

The key to solving the problem of broken sheets lies not in adjusting the stabilizers and lubricants in the formulation, but in managing and optimizing the “plasticization” process in the extruder.

2. Accurate Diagnosis – Understanding the “Heartbeat” of the Extruder

How to determine whether plasticization is good? Don’t rely on intuition or simply observe the appearance of the sheet. Instead, learn to understand the “heartbeat” of the extruder – the main motor current.

As the name suggests, main motor current is the current consumed by the main motor driving the extruder screw. It directly reflects the resistance encountered by the screw during rotation.

• Too low current: This is the most typical sign of poor plasticization. Low current indicates that the screw rotates easily, the material is too “slippery,” and it is pushed out of the screw before forming a viscous melt, without being fully “kneaded.”
• Too high current: Excessive resistance may be caused by low temperature or formulation problems, leading to equipment overload and risk of damage.
• Stable current within a reasonable range: This indicates that the material has formed a uniform, viscous melt in the barrel, generating constant and stable resistance to the screw. This is a sign of good plasticization.

3. Practical Steps – How to “Tame” the Extruder

Once you understand the core concepts and diagnostic methods of plasticization, problem solving becomes simple and scientific. The correct solution is to precisely control the extruder’s process temperature to control the extruder current, thereby achieving optimal plasticization.

Step 1: Establish a Benchmark

First, find the extruder current value that produces acceptable sheet material with your current formulation and equipment. This value is your “target current.”

Step 2: Zoned Temperature Control for Accurate “Drag”

If the extruder current is too low, it indicates insufficient plasticization and the material is too slippery. Here’s what you need to do:

• Increase the temperatures in zones 3 and 4: These zones are critical for plasticization and compression. Moderately increase their set temperatures (for example, by 2-3°C). This will increase the material’s melt viscosity, thereby increasing the screw’s rotational resistance and increasing the extruder current.
• Adjust the subsequent temperatures accordingly: After the temperature in the plasticizing zone rises, slightly increase the temperatures in the five subsequent zones, the confluence core, and the die to ensure smooth passage of the material.

Step 3: Take small steps and observe patiently

Temperature adjustment isn’t a one-time process. After each adjustment, allow the equipment 15-20 minutes to stabilize and continuously observe changes in the main unit current. Don’t rush for quick results; continue to fine-tune until the main unit current stabilizes near your target current.

Step 4: Verify the results and experience the changes

Once the main unit current stabilizes, the toughness of the produced sheet will be significantly improved. You can perform a simple bend test on a sample to observe the change in toughness. If the toughness meets the requirements, congratulations! You’ve mastered the core technology to solve the problem.

4. Three key strategies to eliminate sheet breakage

1. Forget the formula, focus on plasticization: Poor plasticization is the main culprit for sheet breakage.
2. Replace your feelings with data: Main unit current is the most reliable indicator of the degree of plasticization.
3. Master temperature control and dominate production: Learning to precisely adjust process temperature to control the current flowing through the main machine is the ultimate problem-solving tool.

This scientific management approach not only eliminates board breakage but also improves the overall mechanical properties of your product, elevating your product quality to a higher level.