screw tip assembly

There are two competing aspects: backflow vs. material stagnation when it come to discussing non-return screw tips in general. Screw tips with high backflow are not very well suited for high precision molding or materials with very low viscosity. Adversely, screw tips which cause material stagnation have dead-spots where material can become caught and remain indefinitely. Material stagnation is avoided when processing heat sensitive materials or products which require frequent material or color changes.
Check Ring – Moderate Backflow & Moderate Stagnation – These tips are the most widely used non-return valve because the versatility of applications which can process using check rings.
Smear Tips – High Backflow & Low Stagnation – These screws are ideal for high viscosity, heat sensitive materials such as PVC.
Ball/Poppet Valves – Low Backflow & High Stagnation – These tips are ideal for low viscosity materials which are not heat sensitive such as polyolefins.
One thing you just keep in mind, the conclusions we made above focuses on the general uses of these screw tips. There are a wide array of screw tip designs for each of the general categories above. We have seen some check ring designs which have very little backflow, and some ball valves which have very little stagnation.