I. Fundamental Balancing of the Runner System
A symmetrical balanced runner layout is implemented to guarantee that the length, diameter, and bending angle of each cavity runner are entirely consistent, with a flow resistance deviation of ≤5%. This eliminates the possibility of inconsistent filling as the speed increases.
All corners of the runner are rounded to reduce melt flow friction resistance and enhance flow efficiency without increasing shear heat, and the inner wall is exquisitely polished to Ra 0.8 or lower.
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 additional speed increases.
II. Coordinated and Accurate Temperature Control of Hot Runners
With a temperature control accuracy of ±0.5℃ and a temperature deviation of each zone ≤3℃, each hot runner nozzle is equipped with an independent PID temperature control system. This system guarantees a uniform and stable melt viscosity and prevents abrupt changes in the local cavity flow rate as the 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 approach sacrifices speed in order to prevent the shear-thermal unevenness that is induced by merely increasing the injection speed.
The needle valve hot runner utilises timing control to open the gate at the far cavity 0.1-0.2 seconds in advance, thereby compensating for flow lag and guaranteeing synchronised injection into all cavities following a speed increase.
III. Segmented Curve Precision Control of Injection Speed
In order to prevent uneven heating caused by high-speed shear, a three-segment injection speed curve is employed throughout the filling process. The main runner section delivers the melt at a low and stable speed, while the main cavity section fills at a uniform high injection speed, compressing the overall filling time. The final cavity section significantly reduces speed to prevent localised cavities from being quickly filled and overflowing.
The filling speed is gradually increased from low to high. A short-shot test is conducted following each speed increase to ensure that the filling length deviation of all cavities is ≤2% before further speed increases are made. 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
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.
A precise control of the holding pressure switching point is implemented. The holding pressure is uniformly transferred 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, a stepped decreasing holding pressure is implemented to ensure synchronous shrinkage compensation in each cavity.
V. Closed-Loop Guarantee for Digital Monitoring
The pressure-time curves of each cavity are collected in real time by an in-mold pressure sensor that is mounted at the gate of each cavity. This ensures that the curve overlap is ≥95% after the speed increase and the filling time difference is ≤0.1S.
Develop a mechanism for verifying the relationship between uniformity and filling speed. The weight of 20 moulded products is simultaneously verified to ensure that the coefficient of variation (CV) is less than 1.3% with each adjustment of the speed. The parameters are only finalised after the standard is met and uniformity is verified.
This collaborative solution is fully compatible with your current precision hot runner multi-cavity mould injection moulding production line. It can achieve a dual improvement in efficiency and yield by reducing the overall filling time by 20% to 30% and assuring filling uniformity after implementation.
