The feed system in an extrusion
equipment is utilized for holding the solid material and delivering it to
the extruder. It comprises of two main components they are the hopper and
feed throat. A material handling system transports the raw material to the
hopper.
Hopper
A hopper's function is to hold the solids before they enters the
barrel. A dryer can sometimes be integrated with the hopper. The hopper
must be maintained at a near-full level as in case of single screw
extruders they are mostly flood fed. Flood feeding takes place when the
throat area is kept full, thus allowing the screw channels to fill
completely with each of the screw rotation. Some times, single screw
extruders may be starve fed. This becomes necessary in case of materials
like powder which are difficult to feed.
- Feed throat
The feed throat is a sort of pre-barrel component whose location is
just under the hopper. It is typically cored with cooling channels. The
throat is cooled for keeping the solids moving through the feed throat
so that there is more flow of the solids and there is no occurrence of
premature sticking of the solids. In some instances the feed throat
comprises shallow grooves that is machined into internal surfaces. The
aim of these grooves is to boost a higher feed rate down the barrel.

Design of the Feed System
A perfectly designed feed system should consider the following points.
- The design of the hopper should be done in a manner to prevent
hang-up of material during its flow down into the feed throat.
- The design should also take into account the form of the feed
material. For example in case of pellets may be fed perfectly in a
hopper that has a relatively large cone angle. But in case of powder
there may be a requirement of a much smaller cone angle.
- By and large, the hopper shape should be circular and designed to
minimize friction with the feed material.