TABLE OF CONTENTS The feed system of an injection mould tool comprises four main components (see Figure 17.1):
The sprue (for a cold runner tool)
Cold slug well (for a cold runner tool)
The runner
The gate
This should be tapered 3-5 inclusive angle in order for it to be pulled out of the tool more easily. It should also be highly polished in the line of draw to assist withdrawal and in the direction of flow of the melt for more efficient flow. The diameter at the narrow end should be larger than the machine cylinder nozzle opening.
This is designed to trap the cooler advancing front of the melt, thus permitting hotter melt to reach the cavities and gates. It usually has a snatch or pull pin or sucker pin underneath it to positively pull the sprue out of the sprue bush. Three basic designs are used for ejection pin systems and a slightly different system with an undercut pin for stripper plate ejection, as shown in Figure 17.2. The diameters of each design are based on the diameter of the sprue where it meets the runner. It is important to avoid any obstruction to the melt flow; therefore, the pins should always be designed to avoid its protruding into the runner area.
Figure 17.2(a) shows a basic back-tapered hole design. Figure 17.2(b) shows a...
