Feed system and runner of crate mould

It is necessary to provide a flow-way in the crate injection mould to connect the nozzle (of the injection machine) to each impression. This flow-way is termed the feed system. Normally the feed system comprises a sprue,runner and gate. These terms apply equally to the flow-way itself, and to the moulded material which is removed from the flow-way in the process of extracting the crate.

It is seen that the material passes through the sprue， main runner, branch runners and gate before entering the impression. It is desirable to keep the distance that the material has to travel down to a minimum to reduce pressure and heat losses. It is for this reason that careful consideration must be given to the impression layout.

The purpose of the cold slug well, shown opposite the sprue，is theoretically to receive the material that has chilled at the front of the nozzle during the cooling and ejection phase. Perhaps of greater importance is the fact that it provides positive means whereby the sprue can be pulled from the sprue bush for ejection purposes

RUNNER

The runner is a channel machined into the crate mould plate to connect the sprue with the entrance (gate) to the impression. In the basic two-plate crate mould the runner is positioned on the parting surface while on more complex designs the runner may be positioned below the parting surface.

The wall of the runner channel must be smooth to prevent any restriction to flow. Also, as the runner has to be removed with the moulding， there must be no.machine marks left which would tend to retain the runner in the mould plate. To ensure that these points are met，it is desirable for the mould designer to specify that the runner (channel) is polished ‘in line of draw’.

There are some other considerations for the designer to bear in mind:

• (i) the shape of the cross section of the runner，
  
• (ii) the size of the runner and 
  
• (iii) the runner layout.