company news about Why is the Injection Mold Equipped with an Exhaust System?

  An efficient exhaust system is a critical, often overlooked, aspect of injection mold design, especially critical in high-speed molding where trapped air cannot escape quickly enough. (1) Sources of Gas in the Mold Cavity: 1) Air present in the runner system and cavity. 2) Water Vapor generated from residual moisture in inadequately dried hygroscopic resins (e.g., PA, PC, PET). 3) Decomposition Gases produced from overheating the polymer beyond its thermal stability limit. 4) Gases Released from volatilization or chemical reactions of certain additives (e.g., lubricants, flame retardants). (2) Hazards of Poor Venting (Trapped Gas): 1) Short Shots/Incomplete Fill: Trapped air acts as a compressible barrier, preventing the melt from completely filling the cavity. 2) Burns/Dieseling: Compressed air heats up rapidly (adiabatic compression), potentially burning the resin, resulting in black or brown charred streaks, typically at the end-of-fill areas or weld lines. 3) Surface Defects: Gas entrapment can cause visible flaws like silver streaks (splay), voids, poor surface gloss, or bubbling. 4) Weak Weld Lines: Air trapped at flow fronts prevents proper molecular bonding/melding, creating weak and visually apparent weld lines. 5) Varied Filling Speeds: Uneven venting can cause different cavities in a multi-cavity mold to fill at different rates, leading to part inconsistency. 6) Reduced Efficiency: The mold may require lower injection speeds to allow air escape, increasing cycle times and reducing productivity. Proper venting, typically via shallow channels at the end of flow paths or at parting lines, is essential for producing high-quality, cosmetically sound, and structurally robust parts efficiently.