注塑模具venting-wenkub
2022-08-29 16:51:33 本頁面
【正文】 work by pressing air to about 22 bar ? cavity pressures in phone moulding can go up to 3000 bar ? fast fill speed gives best surface finish (resinrich surface) ? fast fill speed gives stronger weld lines ? fast fill speed gives more equal pressure transfer through cavity ? can’t sell parts with burn marks or poor surface finish ? moulder doesn’t want to ruin the tool by burning away steel Efficient Venting Page 4 What blocks vents? ? carbonised polymer from diesel effect ? flash ? additives/pigments/volatiles in the material ? degraded material (molecular weight reduced during moulding) ? incorrect machine startup procedures ? incorrect hot runner start up procedures ? low viscosity material, especially wet nylon Efficient Venting Page 5 What venting methods are there? ? apply a vacuum to the cavity before injection fill ? make the tool (or parts of it) from porous metal ? recognise that venting is a priority at the tool design stage ? then put the maximum venting into the tool Efficient Venting Page 6 Vacuum venting: ? most efficient method, no air left to press and burn ? needs very careful tool design, plus an exhaust mechanism ? will increase overall cycle time by a few seconds ? needs a gasket surrounding the plete split line ? difficult to do this with some split lines and side actions ? may need seals around ejector pins, moving cores etc ? works best with tools that have hot runner valve gates ? will not stop degraded material giving mould deposit Efficient Venting Page 7 Porous materials of mould construction? ? porous = sintered ? sintered inserts are used for venting, particularly where surface aspect is not critical ? various particle sizes are available to suit different polymers ? material used for insert must have strength, pressures involved
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