Meaning
Injection pressure duration denotes the interval during which a moulding machine sustains hydraulic force against a melt before the gate freezes. Operators use bar seconds as a quantitative measure of the total work delivered to a cavity by multiplying the pressure in bars by the time in seconds. This metric accounts for the combined influence of packing force and cooling duration on the final part density.
Excessively low values result in sinks or voids, while high totals cause flash or parts that stick within the mould.
Injection Process
Machine controllers hold this value as a primary indicator of process stability across consecutive production cycles. When thermal conditions vary, the controller adjusts the timer to maintain a stable total of bar seconds. Shifts in viscosity or material temperature alter the flow rate, yet this target remains the constant for dimensional consistency.
Small deviations in the hold phase often lead to weight discrepancies in parts manufactured from amorphous resins.
Cooling Dynamics
Heat transfer limits dictate the operational ceiling for the hold phase. Thermal energy must exit through the tool steel for the part to become rigid enough for ejection. If the hold duration extends too long, the part becomes brittle or traps stresses that eventually lead to warp.
Short durations trap molten core material, which creates internal shrinkage defects as the part attempts to reach equilibrium at room temperature.
Economic Calculation
Resin costs determine the trade off between cycle speed and quality specifications. High pressure levels allow for shorter hold times, but higher machine demand increases the wear on tool steel and electrical usage. Manufacturers balance these factors to ensure the part meets tolerance limits without excessive energy consumption.
Stable control of this parameter reduces the volume of regrind produced by correcting quality issues before they become permanent scrap.
