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The impact of venting on mold design – Vent groove design. In a sense, an injection mold is also a type of displacement device; the plastic melt enters the mold cavity, thereby displacing the air that is already present there. In fact, the air inside the mold is not confined to the cavity; especially in three-plate injection molds, the air present in the flow channels cannot be ignored. Furthermore, plastic melts produce trace amounts of decomposition gases. These gases must be vented in a timely manner. If the mold has poor venting performance, defects such as bubbles, silver streaks, misting, incomplete filling, surface scorching, and intermittent injection are likely to occur. Therefore, the mold must be equipped with a well-structured venting system to avoid defects in the products resulting from poor ventilation. The common types of venting methods are as follows: 1. Venting function via vent grooves. For molds used to manufacture large and medium-sized plastic parts, a large amount of gas needs to be removed; therefore, exhaust grooves are usually provided, typically on the side of the cavity on the parting surface. The location of the vent groove should be at the end of the melt flow, and its size should be such that gas can be discharged smoothly without causing overflow. The width of the vent groove is generally around 3–5 mm, the depth is less than 0.05 mm, and the length is usually 0.7–1.0 mm; the standard depth values for vent grooves can be found in relevant references. 2. Parting surface venting function. For small molds, venting can be achieved using the parting line gap, but the parting line must be located at the end of the melt flow. 3. Venting of gaps in the mosaic assembly. For modular cavities or molds, exhaust can be utilized through the gaps between their components. 4. Exhaust air from the push rod clearance. Vent air by utilizing the clearance between the push rod and the template or core, or intentionally increase the clearance between the push rod and the template. 5. Venting of the powder sintered alloy ingot. Powder sintered alloys are materials made by sintering spherical particle alloys; they have relatively low strength but a porous structure that allows gases to pass through. Placing a piece of such alloy in the area where exhaust is required will meet the exhaust needs, but the diameter of the ventilation holes at its bottom should not be too large to prevent it from being deformed by the pressure in the mold cavity. 6. Exhaust from the vent well. Outside the junction of the plastic melts, a cavity is provided for gases to be discharged into, which also yields good exhaust results. 7. Mandatory exhaust. An exhaust rod is installed at the area where the gas is trapped; this method provides effective gas extraction, but it leaves marks of the rod on the plastic part, so the exhaust rod should be placed in a concealed location on the part.