The material hopper is an integral part of the feeding system. Typically, it is capable of holding approximately 5–10 kg of material.
Low level sensors are mounted in the hopper to signal an alarm, shut off the machine or activate a feeding mechanism to deliver more material when the product falls below this level.
The material hopper should be symmetrical with steep discharge angles to promote mass flow and prevent funnel flow (rat holing) in the granulation. The discharge outlet of the hopper should be as large as possible reaching into the feeder to prevent material bridging.
On many machines the base of the hopper is equipped with a valve to shut off material flow to the feeder if necessary. Depending on the nature of the granulation, the hopper valve can contribute to material bridging.
For materials with very poor flow characteristics, a slide valve may be preferable to a butterfly valve.
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