Applicable Raw Materials And Outputs For Underwater Granulators
The underwater pelletizing technology of twin-screw extruder is one of the core processes in modern polymer material processing, especially suitable for large-scale and continuous production. I will provide you with a detailed analysis from four aspects: principle, function, applicable raw materials, and final product:
1,Underwater Particle Cutting Principle (Core: High Temperature Melt → Instantaneous Cooling and Shaping Under Water)
1. Melt extrusion
After the raw materials (such as plastic particles/powders) are melted, mixed, and homogenized by twin-screw, they are high-pressure pushed to the porous template (die head) to extrude the molten strip.
2. Rotary cutting
The high-speed rotating cutter closely attached to the template cuts the extruded molten strip into particles, and the entire process occurs in a sealed water chamber.
3. Water cooling solidification
At the moment when the particles are cut, they are wrapped in circulating cooling water at a temperature of 20-60 ℃, and the heat is rapidly carried away, causing the surface of the particles to shrink, harden, and solidify.
4. Water particle separation
The water particle mixture is transported through pipelines to a centrifugal dryer/vibrating screen for dehydration and screening, ultimately obtaining dried finished particles.
2, Core role and advantages
| Function | Detailed Explanation |
|---|---|
| Efficient cooling and shaping | Water directly contacts particles, with a much higher heat transfer efficiency than air cooling (such as air-cooled cutting), preventing adhesion |
| Improve surface quality | Water pressure suppresses melt drawing, with regular particle shapes (spherical/cylindrical) and smooth surface without burrs |
| High output continuous production | Suitable for 24-hour continuous operation, single line production capacity can reach several tons/hour (such as PP/PE cutting line) |
| Reduce oxidative degradation | Isolate oxygen underwater and protect thermosensitive materials (such as PVC and biodegradable plastics) |
| Low dust pollution | Water medium suppresses dust generation, improves working environment, and reduces raw material loss |
3, Applicable raw material types
1. Universal plastics
PP (polypropylene), PE (polyethylene), PS (polystyrene), ABS : accounting for more than 80% of underwater cutting applications, such as daily necessities and packaging materials.
Case: HDPE bottle recycling material is melted and filtered by twin-screw, and then cut into particles underwater. The surface smoothness of the regenerated particles is comparable to that of new materials.
2. Engineering plastics
PA (nylon), PC (polycarbonate), PBT, PET: It is necessary to strictly control the water temperature to prevent rapid crystallization (such as PA66 requiring water temperature>70 ℃).
Attention: After PET granulation, crystallization drying is required, and underwater granulation is only an intermediate step.
3. Special materials
-Heat sensitive plastics: PVC (stabilizer added), PVA (polyvinyl alcohol)
-Elastic body: TPE (thermoplastic elastomer), TPU (polyurethane elastomer)
-Biodegradable plastics: PLA (polylactic acid), PBAT (requires low-temperature water to prevent adhesion)
4.Filling/Modified Materials
-Fiberglass reinforced plastic (such as GF-PA6, with wear-resistant coating required for cutting blades)
-Flame retardant engineering plastics (such as flame retardant ABS, smoke suppression in underwater environments)
-High filling masterbatch (calcium carbonate filling up to 70%, underwater cutting to prevent dust flying)
Not applicable:
Water soluble materials (such as unsealed PU)
Ultra low viscosity melt (such as some hot melt adhesives, easy to draw and difficult to cut)
4,Typical product form and application
1. Standard plastic pellets
-Shape: cylindrical/spherical particles with a diameter of 2-4mm
-Application: Injection molding (toy, home appliance shells), extruded pipes/sheets, blow molded containers
2. Specialized modified particles
-Conductive particles: Carbon black filled PE (anti-static packaging)
-Masterbatch: High concentration pigment carrier (such as textile fiber coloring)
-Foam masterbatch: Supercritical CO ₂ injection into PLA (food cushioning packaging)
3. Recycling and regenerating particles
-Waste film → cleaning → melt filtration → underwater granulation → regenerated LDPE particles (garbage bag raw material)
4. Special functional particles
-Slow release fertilizer coating: Polymer coating for controlled release of nitrogen and phosphorus (underwater cutting ensures particle size uniformity)
-Pharmaceutical Carrier Microspheres: Biodegradable PLGA Microspheres (Particle Size Accuracy ± 0.1mm)
If you have any needs or questions in this regard, please feel free to contact Nanjing Kelongwell Chemical Machinery Co., Ltd. at any time. We will provide professional Underwater Pelletizer and services.
