I. Method for Balancing Root Causes in Runner Systems
The risk of uneven filling after speed increases is eliminated by employing a symmetrical runner layout, which guarantees that the length, diameter, and bending angle of each cavity's runner are completely consistent, with a flow resistance deviation of ≤5%.
The interior walls of the runners are meticulously polished to Ra 0.8 or lower, and all corners are rounded to minimise melt flow friction resistance, thereby enhancing flow efficiency without increasing shear heat.
In order to pre-balance the feed speed of each cavity for asymmetrical mould layouts, the runner resistance is manually levelled using flow-blocking stages. This ensures that a sufficient process window is available for subsequent speed increases.
II. Coordinated Speed Increase Method for Hot Runner Temperature Control
The temperature of each hot runner nozzle is independently controlled by PID, ensuring a temperature accuracy of ±0.5℃ and a temperature deviation of ≤3℃ between zones. This ensures a uniform and stable melt viscosity and prevents sudden changes in local cavity flow rates after speed increases.
The dissolve viscosity is reduced by increasing the overall hot runner temperature by 5-10°C within the material's allowable temperature limit. This temperature-based speed increase mitigates the shear-thermal unevenness that results from a mere increase in injection speed.
The needle valve hot runner employs timing control to open the gate at the far end of the cavity 0.1-0.2 seconds in advance, thereby compensating for flow latency and guaranteeing synchronised injection into all cavities following a speed increase.
III. Curve Control Method for Segmented Injection Speed
Throughout the filling process, a three-segment injection speed curve is employed: the main runner section delivers the melt at a low and stable speed to prevent uneven heating due to high-speed shear; the main cavity section fills at a uniform high injection speed to shorten the overall filling time; and the final cavity section significantly reduces speed to prevent local cavities from being quickly filled and overflowing.
The filling speed is gradually increased from low to high. Before increasing the speed further, a short-shot test is conducted to ensure that the filling length deviation of all cavities is ≤2% after each speed increase. This prevents excessive speed increases that could result in filling imbalance.
The upper limit of filling speed is established by preventing air entrapment, scorching, and flash defects, thereby ensuring a stable melt flow following a speed increase.
IV. Pressure and Transfer Point Dynamic Matching Method
In order to prevent delayed filling in distant cavities due to insufficient pressure, a 70% to 80% reserve of injection pressure is maintained to ensure that the dissolve has the necessary power to simultaneously fill all cavities after the speed increase.
Control the holding pressure transition point with precision. The hold pressure is uniformly switched after all cavities have completed 95% filling simultaneously, thereby preventing premature overfilling of certain cavities and underfilling of others.
In order to prevent instantaneous high-pressure impacts that could disrupt filling uniformity and ensure synchronous shrinkage compensation in each cavity, a stepped diminishing holding pressure is employed.
V. Closed-Loop Guarantee Method for Digital Monitoring
In order to guarantee that the curve overlap is ≥95% and the filling time difference is ≤0.1s following a speed increase, an in-mold pressure sensor is installed at the gate of each cavity to capture the pressure-time curves of each cavity in real time.
Develop a mechanism for verifying the relationship between uniformity and filling speed. Simultaneously verify the coefficient of variation (CV) of weight for 20 moulded products each time the pace is adjusted, ensuring that the CV is less than 1.3%. After verifying that uniformity meets the standard, the parameters should be finalised.
Your current precision hot runner multi-cavity mould injection moulding production line is fully compatible with this methodology. It can achieve a dual enhancement in efficiency and yield by reducing the overall filling time by 20% to 30% while maintaining filling uniformity once it is implemented.
