the interface is an apparatus that is attached to the outlet of a hopper to assist and control the discharge of particulate material onto the loading surface of a feeder , such as a moving belt . the interface results in a saving of 50 to 75 percent in the power required to drive the feeder . three structural innovations contribute to this saving in power . first , a plate that extends vertically and in the direction of movement of the feeder is introduced into the stream of material within the interface to reduce downward pressure on the loading surface of the feeder . second , the lower edge of the strike - off plate is arched upwardly , which reduces the power required for maintaining the shearing action . third , the interface is provided with vertical skirts that prevent lateral spreading of the material so that a narrower feeder can be used .