Bulk Bag Weigh Batch System Cuts Labour, Dust & Disposal Costs

Nutec Ltd., a contract manufacturer and packager of animal feed and medicinal products, converted from manual dumping of 20 kg bags of raw material to automated, dust-free discharging of 1 tonne bulk bags using a bulk bag weigh batch discharger.

Previously, pallets of bags containing the raw material were forklifted onto a 3-m high mezzanine, adjacent to a receiving hopper into which the bags were emptied. A 150 mm diameter Flexicon flexible screw conveyor transported the material 4.5 m to a 2 tonne capacity blender. Because bags varied by up to 0.1 kg, the amount of additive fed to the blender was adjusted by a controller receiving weight gain signals from load cells that supported the blender. The blended compound was then conveyed for packaging into 10-25 kg bags.

Components of Product Transfer System

The new system, capable of transferring 12 tonnes per day of material supplied in bulk bags, is comprised of the following components:

  1. Bulk bag discharger frame
  2. 0.2 cu m capacity hopper
  3. 2m long, 10.2-cm diameter flexible screw conveyor housed in a UHMW polyethylene tube
  4. 0.8 cu m capacity transfer bin, free standing on a platform scale
  5. Dust collection system
  6. Control panel for gain-in-weight weigh batching of raw material

Dust-Tight Connection at Bag/Hopper Interface

The straps of a 1 tonne bulk bag are hooked to a lifting frame that is raised by forklift and set into receiver cups comprising the top of each discharger post. The bulk bag/hopper interface consists of a manual Spout-Lock(TM) clamp ring positioned above a pneumatically actuated Tele-Tube(TM) telescoping tube, which facilitates dust-tight connections between the bag spout and hopper, and automatically elongates the bag as it empties to promote flow and evacuation.

The telescoping tube pneumatically raises the clamp ring assembly allowing connection to the bulk bag spout, sealing the clean side of the bag spout to the clean side of the telescoping tube. It then lowers until the bag spout is pulled taut. Once the spout is untied, the telescoping assembly exerts continual downward tension on the spout, elongating the bag as it empties. The dust-tight seal between bag spout and clamp ring allows full-open discharge from the bag with no dusting.

Air and dust in the hopper displaced by bulk material discharging from the bag are fully contained by a remote dust collection unit. From the receiving hopper, material gravity feeds into the intake adapter of the 10 cm diameter, 2m long flexible screw conveyor and is conveyed at a 45 degree incline for discharge into the 0.8 cu m capacity transfer bin.

Gain-in-Weight Control Achieves Batch Accuracy

The transfer bin is mounted on a platform scale that transmits gain-in-weight data to a controller. When the operator initiates a cycle, the first set point runs the conveyor at high feed rate for rapid fill. Immediately prior to reaching the target batch weight, the second set point reduces the feed rate to dribble speed, stopping the conveyor when the precise batch weight of 400kg has been achieved within +/- 200 gm.

A forklift truck lifts the bin to the 3m mezzanine, lowering it onto the hopper. A manually opened butterfly valve allows raw material to drop through the hopper into a flexible screw conveyor that feeds batches of precise weights into a blender where it is compounded with an additive.

To clean the flexible screw conveyors, an operator removes the outer tube screw cap and reverses the drive, evacuating any residual material prior to thorough flushing of the units crevice-free interior surfaces using a cleaning solution. Fitting into a small, available space, the system enabled a major changeover in production techniques with minimal disruption. In addition to reducing labor, it eliminated the need for bag disposal and dramatically reduced operator exposure to airborne dust.

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