Function Moulds Venting

When the cavity space injected by plastic material, automatically empty space on the cavity will be filled with plastic material, the air in the cavity will be shifted to another place, what would happen if the air can not move, the air  will experience a high pressure , so the temperature rises even higher, resulting in plastic that fills the cavity will be burning, the defect is called a burn, because of the importance of venting a lot of products that fail due to not properly inject the gas vent, especially for products that have a rib that thin and tall, as compared to thick products. 

The function of the venting is Compressed  air release when compressed air is not expelled from the cavity, the plastic flow is inhibited, the result will be formed on a short shot of the product. Compressed  air will produce a gas with high temperature and burn the plastic around it, resulting in a defect burn marks, the product looks like a burn, this will greatly affect the look of the product. When  the gas mixed with plastic, the plastic will generate an uneven structure, which will reduce the strength of the product / mold parts produced, stress concentration also common in this region, which occurs due to the plastic notch.
part of venting, can divide on 2 section, land and groove, land is always contact with plastic melt, it's deep about 0.01 mm until 0.02 mm, depend on viscosity of material, relief of vent or gas land is about 1 mm until 2mm, but you must remember for rubber all the number above can't applied, gas vent on rubber material is very special, because rubber has low viscosity.
when designing the gas vent / venting on injection mould, make sure that all of the groove must have exhaust groove that connect to atsmosfer.
In modern plumbing, a drain-waste-vent  is part of a system that removes sewage and grey water from a building and regulates air pressure in the waste-system pipes, facilitating flow.  Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped section of pipe that always contains water.  All fixtures must contain traps to prevent sewer gases from leaking into the house.  Through traps, all fixtures are connected to waste lines, which in turn take the waste to a soil stack, or soil vent pipe.  At the building drain system's lowest point, the drain-waste vent is attached, and rises (usually inside a wall) to and out of the roof. Waste is removed from the building through the building drain and taken to a sewage line, which leads to a septic system or a public sewer. Cesspits are generally prohibited in developed areas.

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