会社のニュース Optimizing the Injection Molding Process for PBT Engineering Plastics

  Successful injection molding of PBT requires careful attention to its specific process parameters. The melting temperature is critical, with a narrow range of 250-260°C; processing below 240°C can cause condensation, while temperatures above 270°C lead to thermal degradation. A barrel constant temperature of 210°C is recommended. The mold temperature should be maintained between 60-80°C. Injection pressure is typically set at 100-140 MPa, with a holding pressure at 50-60% of the injection pressure. A back pressure of 5-10 MPa is advised to avoid excessive frictional heat. Due to PBT's high solidification and crystallization rates, high injection speed is required to prevent the melt from cooling prematurely; it is also crucial to ensure good mold venting to prevent trapped air from causing burn marks (coking). The maximum screw speed should not exceed a linear speed of 0.5m/s. The metering stroke should be (0.5-3.5)D, as PBT melt is sensitive to overheating, and the total residence time in the barrel should not exceed 5 minutes. Pre-drying is essential: 4 hours at 120°C. For recycled material, if the PBT contains a flame retardant, no more than 10% recycled content should be used, provided it is properly dried and not degraded. For non-flame retardant grades, up to 20% can be added. Shrinkage is highly dependent on mold temperature; higher temperatures yield greater shrinkage, typically 1.4%-2.0%. Adding 30% glass fiber reduces this to 0.4%-0.6%. For the gate system, avoid sharp edges with glass-filled PBT; use direct or pinpoint gates. Hot runner systems must have closed-loop temperature control. Standard screws, non-return rings, and straight nozzles are suitable. For machine downtime, turn off the heat and operate like an extruder to purge; upon restart, purge until no bubbles are present.