The following types of gate are commonly used for Desmopan® and Texin™:
- Edge Gate
- Film gate
- Diaphragm gate
- Pinpoint gate
- Ring gate
- Sprue gate
- Tunnel gate
- Hot runner gate
The gates, runners and sprues should be 25 - 50 % larger than for hard thermoplastics (Fig. 1).
Significant pressure drops in the gating system should be avoided.
Fig. 1: Design of a sprue bushing
As far as the runners are concerned, the flow channel must be designed in such a way that the full diameter of the runner is used and that it is positioned in one or both halves of the mold (Fig. 2).
Fig. 2 Runner cross-sections
In multi-cavity molds, e.g. two-plate or three-plate types, the runners should be arranged in such a way that the flow paths are all roughly the same length (Fig. 3).
Fig. 3 : Runners for multi-cavity molds
Pin-point gates must have a weakened point on the gate cross section to ensure a clean tear-off. Large pin-point gates must not involve any jetting, otherwise squeeze marks can occur on the component. With axially symmetric parts, it may be useful to work with ring-type or diaphragm gates to prevent the formation of flow lines. Mold filling and venting must be kept under tight control (Fig. 4).
Fig. 4: Gate forms
A film gate is an advantage with large fl at, long parts, as the mold is optimally filled (Fig. 5).
Fig. 5: "Coathanger" type film gate
A tunnel gate is the best solution if the gating point is not visible (Fig.6).
Fig. 6 : Tunnel gate with lenticular feed