Determining Cavitation Count and Cycle Time in Multi Cavity Injection Molds
Determining cavitation count and cycle time requires balancing thermal cooling physics against clamping limits, runner shear, and capital amortisation curves.
Machine Plasticating Rate
Meaning
Throughput capacities of an injection unit specify the maximum weight of material the screw can melt and prepare in a given time. The machine plasticating rate determines if the equipment can keep up with the cycle time of a fast running mould. This value depends on the material type, screw design, heater power and back pressure.
Recovery Period
Screw rotation must finish before the cooling time ends to avoid delaying the cycle. If the machine plasticating rate is too low, the press sits idle while the material melts, which increases the cost per part. High speed production requires an injection unit with a high plasticating capacity.
Heat Input
Most of the energy used to melt the polymer comes from the mechanical shear of the screw rather than the heater bands. A machine plasticating rate that is too high for the shot size can lead to uneven melt temperatures. This variation affects the viscosity and the final dimensions of the part.
Yield Boundary
Limits on the machine plasticating rate often define the maximum number of cavities a tool can have. Moulders must balance the total shot weight against the ability of the screw to recover. Staying within seventy percent of the rated capacity ensures a more uniform melt.