company news about 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.