Parting Line Steel Preload Calculation for Multi Cavity Injection Moulds
Calculate multi cavity parting line preload by balancing machine clamp force against internal hydraulic separation force to maintain positive shut-off land sealing stress.
Residual Sealing Stress
Meaning
Latent internal forces remain inside a moulded part after it has been removed from the tool and cooled to room temperature. Developing residual sealing stress occurs during the transition from the packing phase to the cooling phase at the gate. These stresses can cause the part to warp or crack weeks after it was manufactured.
Controlling the gate freeze time is the primary way to manage these forces.
Part Distortion
Uneven cooling across the part geometry leads to sections that pull against each other. High levels of residual sealing stress result in a part that does not meet its flatess requirements. This problem is especially common in semi crystalline resins like polypropylene or nylon.
Structural Tension
Internal loads can weaken the part and make it prone to failure under external impact. When residual sealing stress is concentrated around the gate, it creates a brittle area that can snap during assembly. Reducing the packing pressure often lowers this tension but might cause sink marks.
Gate Cooling
Balancing the temperature at the injection point ensures a gradual transition for the polymer molecules. Optimizing the gate size and hold time minimizes the negative impact of residual sealing stress on the finished part. This stability is required for components that must maintain their shape in high heat environments.