I. Geometric Balance Design of the Runner
To guarantee that the path length, cross-sectional dimensions, and bending angle from each cavity to the main runner are entirely consistent, with a melt flow resistance deviation of no more than 5%, implement an H-type or X-type symmetrical runner layout.
In order to mitigate variations in melt flow friction resistance and eliminate dead zones, the inner wall of the runner is meticulously polished to Ra 0.8 or lower.
Runner size compensation and levelling are implemented for moulds with an asymmetrical layout. The runner is widened to reduce resistance in cavities with slow feed, while a flow-blocking step is added to the front end of cavities with excessively rapid feed.
II. Accurate Temperature Control Balance for Hot Runners
Each hot runner nozzle is endowed with a PID temperature control module that is independent, ensuring that the temperature control accuracy is within ±0.5℃ and the temperature deviation between zones is ≤3℃. This prevents filling differences that may be caused by variations in melt viscosity.
In order to account for flow lag and achieve synchronous glue injection into each cavity, a needle valve-type hot runner timing control is employed, with the gate of the far cavity opening 0.1 to 0.2 seconds in advance.
To guarantee long-term production temperature stability and eliminate temperature drift, it is essential to calibrate the hot runner temperature sensor on a regular basis.
III. Unified Balancing of Venting and Gating Systems
In order to guarantee uniform instantaneous melt flow, all cavity gates must be identical in size, location, depth, and breadth, with a cross-sectional area difference of ≤1%.
In order to prevent confined air in individual cavities from obstructing melt flow and causing filling delays, ventilation slots are symmetrically positioned in each cavity, with a uniform venting depth and location.
IV. Dynamic Balancing of Injection Moulding Process Parameters
To guarantee consistent melt density and viscosity for each injection, it is necessary to maintain a uniform barrel temperature, employ a moderate back pressure of 3-8 bar, and maintain a consistent screw speed during the plasticising stage.
Injection utilises a multi-stage, layered injection speed control system, which includes a low-speed, stable melt delivery in the initial stage, a uniform, overall filling in the middle stage, and a final, slowed injection speed for unified sealing.
A unified pressure switch is instituted to prevent premature overflow in certain cavities and underfilling in others after all cavities have been filled to a 95% level simultaneously.
V. Support for Digital Operation and Maintenance and Cooling
In order to guarantee complete synchronisation of cooling rates and prevent mould temperature discrepancies from causing filling discrepancies, a parallel conformal cooling water system is implemented, with a cooling water temperature difference of ≤1℃ between cavities.
In order to capture pressure-time curves in real time, pressure sensors are installed at the gate of each cavity. During the filling stage, a curve overlap of ≥95% and a pressure peak difference of ≤3% are required.
In order to prevent mould ageing from disrupting the filling balance, cavity wear is monitored and carbonised residues in the hot runner nozzles are cleansed every 5000 mould cycles.
This end-to-end balancing solution is seamlessly integrated with your current precision hot runner multi-cavity mould injection moulding production line. It is capable of achieving a stable mass production yield of over 98% and a high level of uniformity in the weight, dimension, and physical properties of mass-produced products following its implementation.
