Meaning
Outward expansion of a cylindrical component occurs as its temperature increases during the moulding process. This radial growth affects the fit between the nozzle and the gate or the core and the cavity. Designers account for the change in diameter to prevent components from seizing.
Dimensional Change
Calculating the increase in diameter requires the coefficient of thermal expansion and the temperature delta. As a nozzle heats up, the radial growth reduces the clearance between it and the surrounding mould steel.
Sealing Mechanism
Managing the fit at the gate involves using the expansion to create a tight interface. Some designs rely on radial growth to press the nozzle tip against the gate insert for a leak-proof seal. This requires extremely tight machining tolerances to ensure the seal works at the target temperature.
Component Stress
Excessive expansion against a rigid outer wall leads to mechanical failure of the parts. When radial growth is constrained by the surrounding steel, it generates internal stresses that can crack the nozzle. Providing enough room for the metal to move safely is a necessary part of the engineering process.
Precise calculation of the clearance prevents the metal from reaching its yield point during the heating cycle. Every component in the assembly must have space to expand without interfering with the operation of the valve pins.
