Polybutylene Terephthalate (PBT)

(1) Barrel Temperature

  Feed Zone    50–70°C (70°C recommended)
  Zone 1        230–250°C (240°C recommended)
  Zone 2        240–260°C (250°C recommended)
  Zone 3        250–260°C (260°C recommended)
  Zone 4        250–260°C (260°C recommended)
  Zone 5        250–260°C (260°C recommended)
  Nozzle       250–260°C (260°C recommended)

The values in parentheses are recommended as basic settings, with a stroke utilization of 35% and 65%, and a flow-length-to-wall-thickness ratio of 50:1 to 100:1.

(2) Melt Temperature  250–260°C; the processing window is narrow. The material tends to solidify below 240°C and may degrade thermally above 270°C.

(3) Barrel Constant Temperature  210°C.

(4) Mold Temperature  60–80°C.

(5) Injection Pressure  100–140 MPa (1000–1400 bar).

(6) Holding Pressure  50–60% of the injection pressure.

(7) Back Pressure  5–10 MPa (50–100 bar); avoid generating frictional heat.

(8) Injection Speed  High speed is required due to the high solidification and crystallization rates. Avoid cooling and solidification of the melt during injection. Good venting in the mold is essential; otherwise, trapped air can cause burning at the end of flow paths.

(9) Screw Speed  Maximum screw speed corresponds to a linear velocity of 0.5 m/s.

(10) Metering Stroke  (0.5–3.5)D. The melt is sensitive to overheating and prolonged residence time in the barrel; residence time should not exceed 5 minutes.

(11) Cushion  2–5 mm, depending on the metering stroke and screw diameter.

(12) Pre-drying  Dry at 120°C for 4 hours.

(13) Regrind Ratio  For flame-retardant grades, up to 10% regrind may be used provided it is pre-dried and shows no thermal degradation. For non-flame-retardant grades, up to 20% regrind can be added.

(14) Shrinkage  Shrinkage depends largely on mold temperature; higher mold temperature leads to greater shrinkage. Typical shrinkage is 1.4–2.0%. Adding 30% glass fiber can reduce shrinkage to 0.4–0.6%.

(15) Gating System  For glass-fiber-reinforced grades, avoid center-direct sprue and pin-point gates. The gate location should ensure uniform filling of the cavity. Hot-runner systems must be equipped with closed-loop temperature control.

(16) Machine Shutdown Period  Turn off the heating system and run the machine like an extruder until no more plastic is expelled. When restarting after a production interruption, purge until the melt is free of bubbles.

(17) Barrel Equipment  Standard screw, non-return valve, and open nozzle.