Taking a second look at nonreturn valves

摘要

One of the most important details of the hundreds of details involved in injection molding is the non-return valve,or check ring.There are various versions of this: the three-piece,four-piece,full-flow,ball-check,et cetera.Leakage upon injection continues to be a problem,especially on small shot sizes.Most processors recognize the issue,but few do anything about it.So,what's needed for a”good” nonreturn valve? The basic functions of a non-return valve are: 1.To allow plastic for flow through it-not over it-during screw rotation to develop the required shot size for your part.There should be no dead spots for the plastic to accumulate or hang up.The flow path for the polymer should have minimum pressure drop and no shear stress due to sharp corners.