Design of the Main Runner and Runner System in Injection Molds
The main runner and runner system in injection molds serves as the channels through which molten plastic is conveyed from the injection unit into the mold cavity. Their design significantly influences product quality and production efficiency.
I. Main Runner Design
The main runner connects the nozzle of the injection machine to the runner system.
Function: Transports molten plastic from the injection machine to the runner system.
Location: Typically perpendicular to the parting line, or located on the parting line in straight-angle injection machines.
Shape: Commonly conical (for easy demolding) or cylindrical (for straight-angle injection machines).
Material: Generally made of high-temperature, wear-resistant tool steel.
Design considerations:
Taper angle: The taper angle of a conical main runner is usually 2° to 6°.
Surface finish: The inner surface of the main runner should be smooth to minimize melt flow resistance.
Length: The main runner should be as short as possible to reduce the cooling and pressure loss of the melt.
Removable design: The main runner section is often designed as a removable main runner bushing for easy maintenance and replacement.
II. Runner System Design
The runner system connects the main runner to the gate and distributes molten plastic to individual cavities.
Function: Distributes molten plastic and ensures that all cavities are filled simultaneously.
Location: Typically located on the parting line.
Shape: Commonly circular, trapezoidal, or U-shaped.
Design considerations:
Cross-sectional shape: Circular cross-section runners have the least flow resistance but are more difficult to machine. Trapezoidal cross-section runners are easier to machine and have relatively low flow resistance.
Length: The runner should be as short as possible to reduce the cooling and pressure loss of the melt.
Cold slug well: A cold slug well should be designed at the end of the runner to accommodate cold material and prevent air from entering.
III. Design Principles for Main Runner and Runner Systems
Minimize cooling and pressure loss of the melt: The main runner and runner system should be as short as possible with smooth surfaces to minimize flow resistance.
Ensure complete filling of the mold: The runner system should ensure that the melt can fill all cavities quickly and uniformly.
Facilitate machining and maintenance: The design of the main runner and runner system should facilitate machining and maintenance.
Consider material flow properties: Different materials have different flow properties, and the runner system should be designed according to the material characteristics.
