Are there any other hot runner vibration cases?

Case 1: Appearance flaws are caused by hot runner vibration in 3C thin-walled items.

Background: Mobile phone charger casings with thin walls (only 0.8 mm thick) are made at a 3C electronics plant. When a single-nozzle hot runner is used for direct injection, the product surface often shows alternating bright and dark vibration marks during mass production. This can lead to a failure rate of up to 22%, totally failing to meet appearance criteria.

Cause of Vibration: Extremely high injection speeds are necessary for thin-walled injection. Fluid pulsation is produced by the high-speed melt traveling through the hot nozzle. This pulsation causes high-frequency vibration since the hot nozzle is not individually damped and fixed (the measured frequency reached 42Hz, beyond the safe range). Periodic vibration marks are left on the product's surface as a result of this vibration being immediately transferred to the mold cavity.

Solution: To reduce the nozzle vibration amplitude, a high-temperature resistant stainless steel dampening sleeve was installed on the hot nozzle. Concurrently, the injection speed was lowered from 120 mm/s to 85 mm/s. Following the correction, the defect rate fell to less than 0.3%, the vibration frequency dropped to 18Hz, and the vibration markings vanished entirely.

Case 2: Resonance Failure Caused by Active Vibration-Assisted Hot Runner Parameter Errors

Background: To increase the flowability of high-filler melts, a new material modification injection molding facility bought a hot runner system with active vibration. 50 Hz was chosen as the default vibration frequency. The hot runner manifold's connecting screws all broke, the heating coil separated, and the system became unworkable after just three days of trial production.

Vibration Cause: System resonance resulted from the active vibration frequency of 50 Hz coinciding with the hot runner manifold's inherent frequency. Stress was increased by high-frequency resonance, which quickly caused metal fatigue fracture.

In order to avoid the resonance range, the manifold was rebuilt and its natural frequency was changed to 70 Hz. The active vibration frequency was reduced to 25 Hz at the same time. No vibration-induced structural damage happened during the following three years of production, and the active vibration's ability to improve flowability persisted.