Fiber spinning pellets, mainly polyester and nylon pellets used as raw material for chemical fiber spinning, come from both virgin and recycled sources. The full production process has five main stages: raw material pretreatment, melt extrusion, pelletizing, post-treatment, and packaging and storage. Each stage needs tight process control to keep pellets uniform and suitable for downstream spinning.
Raw material pretreatment
Pretreatment depends on the raw material type.
Virgin fiber spinning material, such as fiber-grade polyester chips, only needs drying and dehumidifying. Keep temperature at 120 to 150°C for 4 to 8 hours. Reduce moisture content below 0.005%. This prevents polymer degradation during melting.
Recycled fiber spinning material, such as waste PET bottle flakes and old textile fibers, needs a sequence of steps. Sorting separates different materials, for example removing HDPE caps from PET bottle flakes. Crushing reduces large pieces to 5 to 10 mm. Washing uses alkaline washing and water washing to remove oil, labels, and residue. Drying uses the same parameters as virgin material. The goal is to remove impurities and moisture completely.
Melt extrusion
Feed the pretreated material into the hopper of a dedicated extruder. The screw uses zone-controlled temperatures for conveying, compression, and plasticizing.
Screw zone temperatures: feed zone 180 to 220°C, compression zone 220 to 250°C, homogenization zone 250 to 280°C. Adjust these parameters slightly based on the material.
The melt passes through an 80 to 200 mesh filter screen to remove impurities. It then goes through a static mixer to keep melt composition uniform and prevent later pellet performance fluctuation. Hansheng Automation can machine custom filter screens, static mixer components, and pelletizer cutter parts from customer drawings, in single pieces or small batches.
Pelletizing
Three pelletizing methods are common, and each fits a different production scale.
Underwater pelletizing: First choice for large-scale production. Melt is extruded from the die head and cut directly by high-speed water, then cooled and solidified into pellets. Pellet uniformity is high, with stable particle size at 2 to 4 mm.
Water ring pelletizing: Melt is extruded and cut by a cutter in a water ring, then cooled. It suits medium production.
Strand pelletizing: Melt is drawn into strands, cooled in a water bath, and cut into pellets by a pelletizer. It suits small and medium custom production.
Cutter speed must match melt extrusion speed. This avoids undersized or oversized off-spec pellets.
Post-treatment
Drying: Pellets from underwater or water ring pelletizing need a second drying step. Keep moisture content below 0.003%.
Screening: A vibrating screen separates large pellets and fine powder. Keep qualified pellets. Return off-spec material to pelletizing.
Optional modification: Based on downstream spinning needs, add antioxidants, color masterbatch, flame retardants, and other additives to adjust pellet performance and appearance.
Packaging and storage
Packaging: Use industrial moisture-proof bags or ton bags. Label material type, batch number, production date, and other information.
Storage: Keep pellets in a ventilated, dry warehouse. Control ambient temperature at 25°C or below and relative humidity at 60% or below. This prevents moisture absorption and caking. Virgin fiber spinning pellets should be stored no more than 12 months. Recycled pellets have a shorter storage period.
Beyond spinning pellet equipment, our precision component customization covers more than one industry. We machine yacht precision components, RC car precision components, tobacco packaging machinery parts, filling machinery parts, medical device components, printing machinery parts, and food machinery parts. Hansheng Automation works from customer drawings and delivers one-off or batch parts to the required material, tolerance, and surface finish. Our scope is precision components, not complete machines.
