Plastic Part Cosmetic Defect – Jetting | Definition, Causes & Inspection Criteria | Justway

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Plastic Part Cosmetic Defect – Jetting | Definition, Causes & Inspection Criteria

Last updated on Jul 22, 2026

Definition & Mechanism

(1) What is Jetting? (Visual Appearance)

Normally, molten resin flows in a laminar fashion. However, when resin flows from a narrow channel into a wide cavity at excessive velocity, the melt may arc forward and travel without contacting the mold surface. This phenomenon is defined as Jetting. Jetting may appear as band-like or hazy patterns on part surfaces, but the root cause remains identical for both forms.

*Figure 1: Jetting on appearance evaluation specimen (Specimen approx. 20cm / Material: Duracon M90)

Formation Mechanism (Schematic)

Melt ejected from narrow runner

Free jet flow without contact with mold surface

Creates visible patterns once the melt finally contacts the mold

Inspection Criteria

Observe band-shaped or hazy texture

Focus on regions near the gate

Distinguish between flow marks and jetting

Retain defective samples and photos

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