Series discharging and refilling
Part 1: the hopper discharge unit

In our new series, we examine typical problems of discharging and refilling and explain the corresponding technical solutions. We start with the hopper discharge unit.

How does the hopper discharge unit work?

  • The hopper discharge unit is installed underneath a hopper or silo.
  • With its’ vibrating discharge bottom, it ensures even and continuous product discharge from the silo or hopper. 
  • The crucial element for this is the annular gap – the gap between the relief plate and the ring-shaped outer wall. Acting as a “double bottom”, the relief plate absorbs the material pressure of the product mass in the hopper to prevent the material pressure from weighing on the outlet of the discharge bottom and prevents product backup.
  • If the annular gap is too large, the improvement effect for the flow characteristics provided by the relief plate is canceled out. The capacity is therefore always calculated based on the size of the annular gap. The ratio between ring gap and outlet diameter is the decisive factor here.
  • If required, the annular gap can be precisely adapted to the individual requirements of the application with different variation options.

Additional option: venting nozzles

There is an option to equip the side wall of the discharge bottom with compressed air nozzles. The blasts of compressed air ejected from the flat nozzles form a lateral air cushion between the adhering product and the hopper wall, reducing friction and activating (without fluidizing) the compacted product in the discharge area. With downstream feeding, the screw feeder can no longer ensure precise control of the product which now has a greatly changed flow behavior. Sufficient ventilation should also be ensured at all times to avoid affecting the feeding process.

Good vibrations

Depending on the size of the hopper discharge unit, the vibrations are generated with one or two vibration motors.

  • The smaller units up to model 1504 often have a higher speed and frequency, which causes the bottom to vibrate.
  • The large units are equipped with two motors, to prevent the product being discharged unevenly. The two motors are installed in opposite positions and are self-synchronizing.
  • The vibration motor transfers the vibrations generated by unbalance weights to the discharge bottom, to which it is permanently connected. The unbalance weights consist of two half discs, whose relative position to one another determines the level of the unbalance. The unbalance is adapted to the application and discharge conditions in each case.
  • If the unbalance on the vibration motor is set too high, there is a risk of the product backing up or compacting in the discharge bottom, or the device can be damaged.
  • If the unbalance is set differently on each of the two motors, undefined spinning motions can destroy the device. 
  • The two vibration motors consequently always have to be run with the same unbalance setting.

Less is more

Brabender Technologie can deliver everything from a single source und manufacture the hopper discharge units individually tailored to the conditions of the specific application if necessary. Customers who are unsure about the flow characteristics of their product should consult Brabender Technologie first. We can analyze a sample beforehand to ensure that the hopper discharge unit will later be precisely matched to the application.

Less is more – this applies to the hopper discharge unit. If customers ensure economical energy input and clever use of the annular gap, ‘the Brabender’ will reward them with a long service life.