If perhaps available, a valve method need to be utilised while running polymers. This has several advantages while in comparison with a few other hot melt transmitting methods. With valve gates, the melt channel is externally heated ,as well as the mechanical shutoff feature allows better entrance vestige manipulation.
The gate sizing is generally larger , compared to other obtainable techniques. The valve pin is retracted throughout the filling process, which result in a less obstructed run. The end result is less shear heating and push drop.
It is important to maintain suggested plastic mould temperatures at the interface with the part. An independent cooling circuit is generally suggested. One more viable solution for temperature regulation is usually a water-jacketed insert. These are sometimes custom fabricated but are also accessible as typical items from many manufacturers. These usually result in an observation around the entrance which may desire to be taken into attention. Exceptional care should also be taken to make sure the valve pin seats well to make certain superior contact. Even with acceptable cool and excellent contact, you will discover limitations with gates dimension.Entrance sizes 3.10 mm (0.125 in.) and below generally result in the finest appearance. Gates greater than this are often hard to cool and result in poor gates looking because of sticking. One more aspect affecting gate space aesthetics is crystallization. The stage of crystallization will vary ,using the different polymer, propensity to crystallize, and a technological service representative ought to be consulted to establish if or not this shall be an issue with your particular polymer supplier.
Watchful concern to the number of insulation applied at the drop through the mould tool is even so wanted with valve gates. Vespel insulators have also been suggested for these gates.
Processing environments utilising hot runner methods
Generally, manifold and drop temperatures ought to be set near the actual on-cycle melt temp value. The manifold and
drops needs to be balanced for uniform run. A lot of molders utilize hot drops to entrance directly into a little, cold subrunner. This permits the benefits of cold runner gates while reducing regrind or scrap.
Some polyester materials just like PET tend to crystallize and whiten at the gates. Thus, it can be typically beneficial to gate directly into noncritical areas or to entrance into a post or tab that can be hidden
or taken out. Consult your Eastman Technological Representative and hot runner vendor for more comprehensive knowledge on gates placement, gate size, and alternative hot runner system data.