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July 24, 2018

How to Batch Material from Bulk Bags

There are several ways that material can be batched or weighed from Super Sacks®. These include volumetric (rate/time) designs and gravimetric (scale-based) systems. They can be metered from the bulk bag frame or into the downstream equipment. If you’re wondering how to batch material from bulk bags, scroll down to view a few of the most common ways these systems can be designed.

How to Batch Material from Bulk Bags

Volumetric Batching

With a down-stream metering device that can deliver predictable, repeatable feed rates, and material bulk density that doesn’t vary much, a volumetric batching system can save considerable expense and complexity.

These systems work by first catching and weighing a sample over a known time (a 5-gallon bucket filled for 30 seconds, then weighed). Once that time/weight rate is known, a simple formula can be derived to create a batch simply by running the metering device for the required time to complete the batch. For instance, let’s assume a screw feeder delivers 1 pound per second, and the batch requirement is 100 pounds. We then know we need to run the system for 100 seconds to hit our desired batch.

These systems often use simple timers or programmable logic controllers (PLCs) with pounds-to-time ratios pre-programmed. The upsides to these systems are low cost and simplicity. The downside is there is no positive record that these batches were completed. In fact, if the bag is emptied during the batch and not replaced, then the batch total will be light. Low level alarms can help counter these situations but add to the complexity and cost of the system, which may make scale-based systems more appealing.

FormPak volumetric screw feeder

Scale-Based Batching: LIW (Loss-in-Weight)

Loss-in-weight batching is by far the most common way of dispensing a known amount of material from bulk bags. These systems may incorporate nearly any type of conveying/feeding device. The key, however, is to keep the entire system “on-scale.”

The two most common scenarios are valve (slide gate, rotary valve) and feeder (screw, vibratory, inclined, etc.) metered systems. When an operator enters in the desired batch to the scale controller, the scale tares itself to zero, then actuates the metering device in bulk mode (fast in the case of feeders or conveyors, fully open in the case of a valve), then in slow or dribble mode (in the case of a valve), then stopping or closing at target weight. These systems are accurate, easy to use, and stand-alone.

FormPak fork loaded frame with LIW flexible screw and hoist & trolley frame with LIW rotary valve

Scale-Based Batching: GIW (Gain-in-Weight)

While not as popular as loss-in-weight systems, gain-in-weight systems can be more accurate and verifiable, and some are even certified by the NTEP (National Type Evaluation Program) – an independent testing and certifying organization for scale accuracy and calibration.

These systems also use a metering device (valve, feeder, etc.), but the scale is part of the downstream system. This can be a simple platform scale that a bin or hopper is placed on directly under the unloader, or the scale may be built into a blender, mixer, or scale hopper and material is conveyed up and into it. The process works nearly the same as above: A batch total is entered into the scale controller, the scale downstream is tared to zero, and the metering device is actuated in bulk and dribble modes until the total weight is achieved, and then the metering device is de-activated.

FormPak gain-in-weight platform scale & flexible screw AND gain-in-weight platform scale & slide gate valve

Multi-Ingredient Batching

If you’re wondering how to batch material from bulk bags using multiple bag unloaders, check out multi-ingredient batching. These are systems that use multiple bag unloaders to create a recipe of several ingredients. They can be set up with volumetric or gravimetric metering, can be automatic or manual, and can even include traversing bin or bag filling systems to create a batch in a container for use later in down-stream equipment (blending, packaging, etc.).

For example, a series of unloaders can be lined up with valves and a conveyor running under them to a blender. All of the unloaders can dispense the amount of that ingredient required into the conveyor all at once. Or, a hopper may be sitting on a scale but fed by multiple unloaders with screw feeders or conveyors and will gain the weight required from each unit in series. The second example is slower but only requires one scale, and it can potentially be more accurate if a smaller scale is used that requires on the bag unloader GIW arrangement. A couple of examples of these are shown below, but there is a myriad of ways to design these systems depending on recipe, accuracy, and rate.

FormPak bag unloaders feeding a gain-in-weight scale hopper via flexible screws

FormPak super sack unloaders with continuous loss-in-weight batching

FormPak form loaded bulk bag unloaders with loss-in-weight vibratory feeders to a bucket elevator

FormPak hoist & trolley super sack dispensers with flexible screws building a gain-in-weight batch to a blender on scale

As you can see, batching from bulk bags can be a simple or complex arrangement, may or may not use scales, and can utilize a number of different metering devices, but ultimately it provides accurate, predictable, and even verifiable weighments and recipes.

For more information regarding how to batch material from bulk bags, please contact your FormPak sales rep or one of our sales team members. We are able to construct ingredient batching systems for use with bulk bags, drums, and small bags. With over 50 years of combined experience in the dry materials field, we can assist your company with bulk bag filling, unloading, lifting, as well as fully integrated batching systems, bag break stations, and flexible screws. To discuss the requirements of your bulk bag or dry material handling project or to learn more about how to batch material from bulk bags, please give us a call or contact us online today.