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Mold design
7. Mold design
7.5 Gas vents
If gas vents are poorly designed, filling may be impeded or gas burn may occur; therefore, sufficient attention should be paid to gas vents. Basically, it is effective to vent the gas from all over the circumference of molded products to the flow end.
Also, if the cold slug well of the sprue and runner is gas-vented, air in the sprue and runner will be discharged from there, so that the resin flow to cavity becomes efficient.
Sprues, runners and flow end of molded products should be vented 2/100 m and 1/100 to 2/100 mm, respectively, approximately 3 mm in width, and then grooved approximately 1 mm in depth for guiding out of mold. It should be approximately 1/100 mm for places in the middle of the flow of molded products and for molded products that should not be severely burred.
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