Why need PVC WPC SPC Crushing & Milling (Pulverizer) & Mixing System for PVC Extrusion?
In PVC extrusion—whether you are producing PVC pipes/profiles, WPC (Wood-Plastic Composite) decking, or SPC (Stone-Plastic Composite) flooring—the trio of Crushing, Milling (Pulverization), and Mixing forms the absolute backbone of the production line.
Without this integrated system, it is practically impossible to achieve a high-quality finished product, control raw material costs, or run a stable extrusion process.
Here is exactly why this system is completely indispensable:
1. The High Cost of Waste: The Role of Crushing & Milling (Pulverizing)
Extrusion lines naturally generate scrap. This includes start-up waste, off-spec products, trimming edges (especially in SPC and WPC flooring), and defective runs. PVC is a highly recyclable material, but an extruder cannot swallow large, rigid chunks of scrap.
The Crusher (The First Step): Heavy-duty shredders or crushers break down large, bulky scrap pieces (like rejected SPC tiles or long PVC pipes) into manageable, small flakes (typically 4–8 mm).
The Pulverizer/Miller (The Crucial Refinement): Extruders require a uniform feed. You cannot feed coarse flakes directly into a PVC twin-screw extruder because it causes uneven melting, surging, and screw wear. The pulverizer grinds those crushed flakes into a fine, consistent powder (usually 20–40 mesh).
The Bottom Line: By turning scrap back into high-quality powder, you create a closed-loop recycling system. This allows you to reintroduce 10% to 50% (depending on the product specs) of recycled material back into the production line, drastically slashing raw material costs.
2. Material Complexity: Why a Mixing System is Mandatory
Unlike basic polymers like PE or PP, which can often be fed raw into an extruder, PVC is inherently unstable and highly sensitive to heat. Raw PVC resin cannot be extruded on its own; it must be compounded into a "dry blend" first.
A high-speed heating and cooling mixing system is required to blend the PVC resin with a complex cocktail of additives:
Additive Distribution in the Mixer:
Stabilizers (Lead, Ca-Zn): Prevent the PVC from degrading and burning under the high heat and shear of the extruder.
Lubricants (Internal & External): Reduce friction between PVC molecules and between the PVC melt and the metal barrel/die.
Processing Aids & Impact Modifiers: Improve melt strength and the impact resistance of the final product.
Fillers (CaCO3): Used heavily in SPC (up to 70–80% calcium carbonate) and PVC to add rigidity and reduce costs.
Wood Powder (for WPC): The mixer encapsulates the wood fibers with PVC resin to ensure the wood doesn't burn in the extruder and absorbs no moisture.
The high-speed mixer uses intense friction to heat the material to roughly 115°C–125°C, ensuring the lubricants melt and uniformly coat every single PVC particle. It is then quickly dropped into the cooling mixer to drop the temperature to around 40°C–45°C, preventing agglomeration and keeping the dry blend free-flowing.
| Material Type | Unique Processing Requirement | Why the System is Essential |
| Traditional PVC (Pipes/Profiles) | Heat sensitivity and high-gloss surface requirements. | Mixing ensures zero stabilizer hot-spots (which cause burning). Milling ensures recycled scrap doesn't introduce large un-melted particles that ruin the smooth finish. |
| WPC (Wood-Plastic Composite) | Severe moisture risk and blending of incompatible materials (wood + plastic). | Mixing drives out moisture from the wood flour and bonds it with the PVC. Crushing/Milling allows defective profile boards to be instantly re-ground and saved. |
| SPC (Stone-Plastic Composite) | Extreme filler ratios ($\text{CaCO}_3$ can be 3 to 4 times the weight of PVC resin) and heavy edge-trim scrap. | Mixing ensures the massive amount of stone powder is perfectly dispersed so the floor isn't brittle. Crushing/Milling is vital because SPC edges are continuously trimmed during production, creating massive volume of scrap that must be recycled immediately. |
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