Commissioning a New Two-Stage Pelletizing Line: The Essential Pre-Start Checklist

The successful installation and initial startup of a two-stage pelletizing system (twin-screw compounding coupled with single-screw extrusion) are critical for the machine's long-term performance.

To help operators safely navigate the initial break-in period, we have compiled this comprehensive Standard Operating Procedure (SOP) for pre-startup checks. Even novice operators can quickly master these essential steps.

01. Comprehensive Pre-Start Inspection: Eliminating Safety Hazards

Before turning on the main power, a thorough visual and mechanical inspection must be conducted.

1. Feeder System Validation

Observe the feeding screw to ensure the correct rotation direction (clockwise). Thoroughly clean the hopper to remove any impurities, dust, or agglomerated materials that could block the feeding channels.

2. Sealing & Vacuum System Integrity

Visually inspect the sealing rings of the twin-screw exhaust chamber. They must be perfectly installed with no signs of wear or deformation. Damaged seals will cause poor venting and material leakage, severely impacting pellet quality.

• Test: Activate the vacuum pump and verify that the vacuum degree reaches the required standard (recommended ≥ -0.08 MPa). Ensure there are no air leaks or insufficient suction.

3. Screw & Transmission System (Manual Barring)

• Power Check: Ensure the main power supply is completely switched off (Lockout state) to eliminate safety risks.

• Manual Turning: Manually rotate the couplings of both the single-screw (main stage) and twin-screw (compounding stage) extruders. The rotation must be smooth without any jamming, and the bearings should produce no abnormal noises.

• Lubrication: Check the gearbox oil level against the indicator mark. If the level is low, replenish it with the specified industrial gear oil and tighten the sealing cap securely.

4. Electrical & Auxiliary Systems

Inspect all electrical wiring for secure connections and ensure motor insulation is intact.

• Water System: Turn on the pelletizing water circulation system in advance to verify smooth water flow. This prevents the initial polymer melt from sticking to the cutting blades.

• Cutter: Confirm that the pelletizer blades are sharp, free of chips, and securely mounted.

02. Precise Parameter Setting: Preparing for Extrusion

Operating parameters must be strictly tailored to the specific characteristics of the raw materials (e.g., PP, ABS) to prevent polymer degradation or uneven plasticization.

1. Temperature Configuration (Segmented Control)

Set the heating zones according to the specific processing recipe, adhering to the principle of segmented temperature control.

• Twin-Screw Section: The feeding, plasticizing, and homogenizing zones are typically set between 100°C and 160°C. This prevents the material from softening and sticking too early while ensuring thorough plasticization later in the barrel.

• Single-Screw Section: As a general rule, the temperature of the single-screw extruder should be set approximately 15% higher than the twin-screw section, though this must be fine-tuned based on the specific resin's melt index.

2. Speed Synchronization

• Feeder: Set the initial feeding speed to a low rate (10% - 15% of the rated value) to prevent rapid overloading and blockages.

• Extruders: The rotation speed of the single-screw extruder should be set slightly lower than that of the twin-screw extruder to ensure a smooth, unpressurized transfer of the melt.

• Pelletizer: Match the cutter speed to the extruder output. Start at a low-to-medium speed and make micro-adjustments later based on the desired pellet size.

03. Preheating & Thermal Soaking: The Indispensable Step

Once parameters are set, the machine must enter the preheating and thermal soaking phase. This directly determines the quality of the initial melt and protects the mechanical components. Never skip or shorten this step.

1.Uniform Heating: Turn on the main power and start the heating system. Closely monitor the difference between the actual and set temperatures across all zones. Ensure the heating is stable, keeping the temperature variance within ±5°C.

2.Thermal Soaking (Crucial): Once all zones on the twin-screw reach their target temperatures, you must maintain this heat for 30 to 45 minutes (extend to 60 minutes for larger machines or high-melting-point resins). This ensures the internal screw core and barrel metal are uniformly heated, preventing un-melted "cold spots" that can cause the screw to jam or snap.

3.No-Load Test Run: After thermal soaking is complete, perform a final system check. Start the equipment without material for 1 to 2 minutes. If there are no abnormal vibrations or noises, begin feeding material in very small quantities to transition into normal production.

• Emergency Protocol: If you encounter loud grinding noises, smoke, or a sudden spike in motor current, press the Emergency Stop immediately and inspect the machine.

Conclusion

By strictly adhering to these pre-startup procedures, operators can safely navigate the initial break-in period (typically the first 7-10 days) of a new machine. At Nanjing Haisi Extrusion, we engineer our two-stage pelletizers for maximum durability, and proper commissioning is the first step toward years of stable, high-yield production.

NANJING HAISI is professional manufacturer of Plastic Extruder Machine, we supply Twin Screw Extruder, Single Screw Extruder, Plastic Recycling Extruder, Two Stage Extruder, Lab Scale Extruder, Mixing and Feeding Machine, Cooling and Pelletizing Machine, Crushing Machine and so on.