Molding Process
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PBT Shrinkage Rate 1.5-2.8%
Fenómeno del problema
Large dimensional deviation of the product, obvious shrinkage differences in different directions, assembly dimension chain out of tolerance
Análisis de la causa
Pure PBT has a shrinkage rate of 1.5-2.8% and the shrinkage difference in different directions is more obvious than other plastics; after 30% glass fiber reinforcement it drops to 0.3-1.6% but the longitudinal-transverse inconsistency intensifies
Solución
①Leave allowance in the mold according to the grade's shrinkage rate; ②Calculate directional shrinkage separately; ③Correct precision parts after mold trial; after adjustment, take samples continuously to verify the effect, and resume mass production only after confirming stability
Conclusión clave
PBT has large shrinkage and strong directionality; allowance must be calculated by direction, and mold-trial correction is the necessary path for precision parts; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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