AS (SAN) plastic has high transparency, good rigidity and stable size performance, widely used in electronic shells, instrument panels and daily transparent products. However, it is sensitive to moisture and high temperature, brittle and easy to produce internal stress. Unreasonable injection molding parameters and operation will cause silver lines, bubbles, welding lines and cracking. Standardized pretreatment, process control and mold optimization are required to ensure stable production.
I. Raw Material Pretreatment ManagementAS plastic absorbs trace moisture in the air. Moisture gasification during high-temperature molding will cause silver lines and bubbles. Raw materials must be dried at standard temperature and time before production. Materials after drying should be used immediately, and re-drying is required after long-term shutdown. The proportion of recycled materials is strictly controlled to avoid impurities and yellowing affecting transparency. Different AS grades are prohibited from mixing to prevent unstable fluidity.
II. Injection Temperature ControlAS has a narrow processing temperature range and high thermal sensitivity. Low temperature causes poor fluidity, insufficient filling and obvious welding lines. Excessively high temperature leads to material degradation, yellowing and increased brittleness. The barrel adopts gradient temperature setting to ensure stable plasticization. Nozzle temperature is reasonably controlled to prevent salivation and cold material blockage. Mold temperature is adjusted according to wall thickness to optimize surface gloss and avoid shrinkage and cold lines.
III. Pressure and Speed Matching ControlAppropriate injection pressure ensures complete cavity filling. Excessive pressure causes internal stress and product warpage. Holding pressure and time are set reasonably to compensate cooling shrinkage and prevent sink marks. Thin-walled products adopt medium-high speed to reduce welding lines; thick-walled products use low speed to avoid gas trapping and scorching. Screw speed and back pressure are adjusted to ensure uniform plasticization and reduce bubbles.
IV. Mold Structure OptimizationAS products are easy to trap gas and generate welding lines. The mold adopts reasonable side gates or fan gates to shorten flow paths. Sufficient venting grooves are set at melt terminals and welding positions to exhaust gas in time. Reasonable demolding inclination and uniform ejection structure prevent whitening and cracking during demolding. Smooth polished runners reduce material retention and degradation.
V. Production Operation and Quality Control
The screw and barrel are thoroughly cleaned before production to avoid material mixing pollution. Low-speed and low-pressure trial molding is adopted for startup. Workshop humidity is strictly controlled to prevent secondary moisture absorption. Release agent is used in a small amount evenly to avoid fogging. Regular cleaning of venting carbon deposits ensures stable venting performance.
VI. Post-Processing and SummaryAS products have large internal stress and need annealing treatment to eliminate stress and prevent cracking. First article inspection and regular sampling are carried out to control appearance and size quality. In conclusion, the key points of AS injection molding are moisture drying, precise temperature control, reasonable parameter matching and mold venting optimization. Standardized whole-process control can effectively avoid defects and realize stable mass production.
