PBT (Polybutylene Terephthalate) plastic, renowned for its exceptional mechanical properties, electrical insulation, and chemical resistance, plays a pivotal role in industries such as automotive, electronics, and electrical appliances. Drawing from extensive practical experience, we delve into the key aspects of PBT plastic injection molding to provide manufacturers with insights into achieving superior product quality.
Pre-Injection Drying
PBT plastic is hygroscopic, meaning it readily absorbs moisture. Therefore, thorough drying and preheating before injection molding are crucial to eliminate surface bubbles and silver streaks caused by water vapor, while also promoting plasticization and reducing surface stains. It is essential to maintain the moisture content of PBT raw materials below 0.02% to ensure optimal molding results.
Temperature Control in PBT Injection Molding Machines
The relationship between injection temperature and PBT melt viscosity differs from that of other amorphous plastics. As the melting temperature rises, the viscosity of PBT decreases minimally until it reaches the plastication temperature. Beyond this point, further temperature increases can lead to thermal degradation of PBT, increasing melt viscosity and making molding more difficult, while also compromising the mechanical properties of the molded parts.
Different types and compositions of PBT require varying furnace temperatures. It has been observed that greater temperature fluctuations can result in more defects such as weld lines, poor gloss, flash, sticking, and discoloration.
Pressure Control in PBT Molding Machines
During the PBT injection molding process, the pressure within the mold cavity when the gate closes significantly influences the surface quality of the molded part. Insufficient pressure can lead to significant shrinkage, increased likelihood of the part detaching from the cavity surface, and a foggy appearance on the part surface. Conversely, excessive pressure increases friction between the plastic and the cavity surface, potentially causing sticking.
Injection Speed for PBT Plastic
PBT material performs best under moderate injection speeds. Excessively fast injection speeds can cause the plastic to burn or decompose, generating steam and leading to defects such as weld lines and poor gloss. However, when producing thin-walled, complex parts, ensuring a sufficiently high injection speed is essential to achieve proper filling.
Mold Temperature for PBT Injection Molding
PBT requires relatively high molding and mold temperatures. Typically, the mold temperature for PBT injection molding ranges from 80°C to 120°C. When molding large, complex, or thin-walled parts, special heating of the mold may be necessary. To shorten production cycles and maintain a relatively stable mold temperature, alternative mechanical cooling methods can be employed after part ejection to compensate for cooling time.
Feed Quantity Control
To enhance part quality, dimensional stability, uniform surface gloss, and color tone, it is recommended to set the injection quantity at approximately 50% of the nominal injection capacity.
The aforementioned points represent some of our recommendations for PBT plastic mold manufacturing. Other issues encountered during production should be addressed through specific analysis and tailored solutions.
