Chinese Plastic Molds: Specification for PC/ABS Alloy Injection Molding Process Parameter Settings
PC/ABS alloy blends combine high‑impact toughness from polycarbonate and excellent flowability of ABS, widely applied in electronic housings, home‑appliance components and automotive interior parts manufactured by Chinese plastic mold enterprises. This blended material is highly hygroscopic with a relatively narrow processing window. Improper parameter settings frequently trigger surface silver streaks, weld lines, residual‑stress cracking, sink marks and warpage. Standardized process parameter settings help balance surface appearance, dimensional accuracy and mechanical performance for stable mass production matched with Chinese plastic mold production conditions.
1. Raw Material Pre‑Drying Specification
Moisture inside PC/ABS pellets causes polymer hydrolysis under high barrel temperature, resulting in silver marks, material blooms and degraded mechanical strength, so pre‑drying represents the primary procedure before molding. Desiccant dryers are preferred over ordinary hot‑air dryers to achieve qualified low moisture content. For general‑grade PC/ABS, drying temperature ranges from 85℃ to 100℃ with drying duration of 2‑4 hours. Flame‑retardant grades shall be dried at 85‑90℃ for 3‑5 hours. The moisture content should be controlled below 0.04%, and high‑demand cosmetic parts require moisture under 0.02%. Dried pellets need thermal insulation inside hopper dryers to avoid re‑absorbing ambient moisture. The mixing proportion of regrind material should not exceed 30%. Regrind shall be blended with virgin resin and re‑dried before processing. Drying time needs extension under high‑humidity workshop conditions. Seal material hoppers for production stops longer than half an hour, and empty residual pellets for long‑time shutdown to prevent moisture re‑absorption.
2. Barrel and Nozzle Temperature Parameters
Barrel temperature shall adopt moderate values that guarantee complete plasticization while avoiding thermal degradation. Feeding zone temperature is set between 220℃‑240℃, plasticizing zone 240℃‑260℃, front zone close to nozzle 245℃‑265℃. Nozzle temperature maintains 240℃‑260℃, slightly lower than front‑barrel temperature to prevent stringing and drooling. High‑flow grades can reduce overall temperature by 5‑10℃. Thin‑wall long‑flow‑path products can adopt upper‑limit temperature values. For flame‑retardant PC/ABS, maximum barrel temperature shall not exceed 265℃ to restrain decomposition of flame‑retardant additives. Keep barrel insulated at 200℃ for short‑term stops within 20 minutes. Empty molten material and lower barrel temperature down to 180℃ for shutdown over one hour to avoid long‑term melt residence and degradation. Complete barrel purging is required before material change‑over to eliminate residual contaminants such as POM or PVC.
3. Mold Temperature Setting Requirements
Mold temperature directly determines surface gloss, weld‑line quality and residual‑stress level. Mold water circuits should achieve even circulating cooling with temperature deviation controlled within ±4℃. For ordinary matte structural parts, mold temperature is set from 50℃‑65℃ for shorter cooling cycles and improved productivity. For electroplating‑grade and high‑gloss cosmetic components, mold temperature shall reach 70℃‑82℃ to optimize weld‑line appearance and surface gloss. For snap‑fit and load‑bearing assembly parts, mold temperature of 75℃‑88℃ helps reduce internal stress and prevent assembly cracking. Vent slots with depth of 0.02‑0.05mm shall be opened at filling terminals and rib intersection positions for gas discharge, preventing burning and gas‑mark defects. Mold temperature should not drop below 45℃, otherwise rapid surface cooling creates heavy stress concentration on molded products.
4. Injection, Holding Pressure and Injection Speed Parameters
General injection pressure ranges from 80‑110MPa. Thin‑wall complex shell parts may increase injection pressure up to 110‑120MPa, while flame‑retardant formulations reduce pressure to 70‑90MPa. Insufficient injection pressure produces short shots and sink marks, yet excessive pressure raises residual stress and flash risks. Multi‑stage injection speed is recommended. Apply low velocity near gate position to reduce shear heat, adopt medium‑high speed for thin‑wall filling and medium‑low speed for thick‑wall sections, and slow down speed before filling completion to avoid air entrapment and flash. Holding pressure takes 50%‑70% of injection pressure with two‑stage holding mode. First‑stage high pressure compensates melt shrinkage rapidly, and second‑stage low pressure stabilizes part shaping. Holding time varies according to wall thickness: 8‑15 seconds for thin‑wall articles, 15‑30 seconds for thick‑wall components, adjusted to eliminate sink marks. Excessively high holding pressure brings heavy internal stress. Keep 3‑6mm cushion stroke to ensure stable pressure transmission.
5. Screw Plasticizing, Cooling and Ejection Parameters
Screw rotation speed is controlled at 40‑70 rpm under medium‑low settings to minimize shear‑induced frictional heat. Screw speed can be slightly raised for color mixing to achieve uniform pigment dispersion. Back pressure ranges from 0.3‑0.7MPa. Low back pressure causes uneven plasticization, while excessive back pressure generates extra shear heat and triggers material degradation. Cooling time matches product wall thickness. Basic cooling duration is 12‑20 seconds. Every additional 0.5mm wall thickness adds 3 seconds cooling time for full solidification and prevention of ejection deformation. Medium‑low ejection speed is adopted to avoid whitening and scratching on part surfaces.
Summary
For PC/ABS alloy injection molding under Chinese plastic mold production environment, raw‑material drying acts as the fundamental guarantee for qualified parts. Temperature, pressure and velocity parameters need coordinated adjustment rather than single‑parameter modification. Production workshops must strictly control pellet moisture, keep barrel temperature away from thermal‑degradation zones, select proper mold temperature according to cosmetic and mechanical requirements, implement multi‑stage injection velocity and segmented holding pressure to reduce weld lines and residual stress. Optimize screw plasticizing conditions with low‑shear principles, and enforce shutdown management and barrel purging specifications. Adopt conservative processing windows on the premise of complete cavity filling, so as to raise finished‑product rate and realize stable mass‑production of PC/ABS molded components.
