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Bulk Bag Unloader Weigh Batching

Posted on 7th June 2016 by

Bulk Bag Unloader Weigh Batching

A weigh batching bulk bag unloader system can improve batching efficiency and reduce ingredient and handling costs.

A loss-in-weight bulk bag batching system includes a bulk bag unloader whose outlet is directly coupled to a feed control device such as a flexible screw conveyor. The feed device is typically supported by the bulk bag unloader support structure. A microprocessor based batch weigh controller is also included in any system.

The following information is required to design a bulk bag unloader batching system:

  • Batch size (min. and max.)
  • Time to dispense batch (min. and max.)
  • Tamped and untamped ingredient bulk density

There are 3 ways to batch directly from a bulk bag:  two loss-in-weight methods and an add weigh method.

Bulk Bag Unloader Weigh Batching Loss-in-weight 1

The first loss-in-weight method, which is the most efficient, is where the entire bulk bag unloading station is weighed and the batch controlled by measuring the weight loss as the material is fed into a conveying system or directly into a receptacle (mixer, blender, tank, etc.).

Bulk Bag Unloader Weigh Batching Loss-in-weight 2

The second, more costly loss-in-weight method requires a separate loss-in-weight feeder complete with refill hopper and refill valve, which is suspended below the unloader outlet.

Bulk Bag Unloader Weigh Batching Add-Weigh Method

The add weigh method involves feeding product from the bulk bag into a weighed vessel.

Choosing the correct system application for your process requires examination of three main criteria: accuracy, cost, and space availability.

A loss-in-weight bulk bag unloader weigh batching system where the entire station is weighed is suitable for dispensing batches over 100 lbs. in weight with an accuracy of ± 1-2 lbs. and is the least costly of the three configurations.

For batch sizes less than 100 lbs. , or for accuracies greater than 1-2 lbs. a loss-in-weight feeder, or add weigh system should be considered. The loss-in-weight screw feeder system will provide the highest possible accuracies approaching ± 1 lb, but is the most costly and will require the most headroom of the three configurations.

bulk bag unloader weigh batching add weigh system can achieve very high accuracies based on the volume of the weighed receptacle and the resolution of its load cells. However, this configuration typically consumes the most floor space as the weighed receptacle must be supported outside of the unloader frame unless the mixer, blender, tank itself is the weighed receptacle and the unloader feed device dispenses directly into it.

Note that each of these system types is constrained by a minimum batch dispensing time of 30 seconds. Care must be taken to ensure proper system design to allow switching bags in mid-batch. For batch sizes of over 100 lbs, Spiroflow offers a screw feeder, or flex conveyor integrated with one of a range of unloader models. The system comes pre-wired and tested with load cells and batching control panel. It achieves an accuracy of ±1-2 lbs per batch.

Another batching station suitable for food or pharmaceutical applications is provided by the Iso Flo unloader, the perfect bulk bag unloading machine for situations where the operator, or the operating environment, must have no contact with the ingredient being discharged. Within a negative pressure isolation chamber, the bag liner or outlet spout is clamped to ensure that no dust escapes from the system. If a liner is used, a heavy duty liner tensioner tightens the liner to completely empty the liner of ingredient. The Iso Flo with an integrated feeder provides very efficient batching, reducing ingredient and handling costs, and delivers an accuracy of ±1-2 lbs per batch.

Batching directly from a bulk bag unloader using either of the two loss-in-weight methods is extremely efficient with respect to time, capital cost and compactness.

Direct batching from a bulk bag eliminates the need for duplication of feed devices (vs. one feeder to empty the bag and a second to measure the batch at the process) thereby reducing equipment cost and maintenance requirements, and improving reliability.

Dispensing the batch at the unloader station can reduce process cycle times and system operating complexity.

As well, the bulk bag direct batching station is a compact, self-contained system which can be positioned either close to, or distant from the process thereby providing greater layout and operational flexibility.

Not sure which weigh batching method is right for your process? Spiroflow has worked with customers for years to determine the best weigh batching solution.  Call us today at 704-246-0900 or email us directly at for more information or you can request a quote here. We look forward to helping you!

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Carolynn Sarver

Director of Marketing
Carolynn has been with Spiroflow Systems, Inc. for nearly six years. Previously she led marketing initiatives at Fortune 500 companies & international tech firms in the US, Canada & Australia.