Supply chain groups or logistics departments spend 10 – 20% of their days studying, developing, and controlling unloading operations with the main objective of improving the efficiency of the process.

A good portion of this time is dedicated to the unloading processes of bulk solids carried into ISO marine containers.

After loading and transporting hard-to-flow bulk solids in ISO containers and using container liner bags, some products become even harder to flow. Some other products that were not considered hard-to-flow start to be defined due to compaction generated by time and vibration or bouncing.

loading hard-to-flow

There are similiar difficulties with unloading and loading hard-to-flow products. Somehow, it is expected that the solutions would be similar for both operations, too.

There are products that are not hard-to-flow while loading, but some issues turn them hard-to-flow during the trip.

The main hard-to-flow characteristic is that the friction results when the plastic deformations from the contact between particles is somehow higher than in regular bulk solids, as it may also exist between particles and walls.

point of start-to-flow

As a result, there is a delay on the “point of start-to-flow,” or a slope angle is needed to start the flow. For the hard-to-flow products, it is normally high and, sometimes, because of these very high angles and delay, there are some avalanches that create some trouble to the unloading hard-to-flow process.

Some bulk solid products become harder to flow while they are transferred from the supplier to the buyer via shipping. There may be several different logistics operations that leave the containers waiting for transfers for many days, or the container is transported by sea for several days, then waits for customs clearance, and so on.
This is one of the biggest challenges that the logistics managers or supervisors face. It implies a dramatic behavior changes for the material.

shipping containers

For instance, a container carried from China to Brazil and vice-versa will bounce or cycle, moving from one side to the other in a ship, approximately one million times, while it takes up to thirty five to forty five days “in route,” on some other routes.

It also sits for ten to fifteen days in customs for clearance. Plus, sometimes, it takes seven more days of internal travel until it reaches the final destination.

The container will cycle another five hundred thousand times, with a higher frequency that makes the compacting even higher, while being transferred by truck for an average 300 km. This will create blockages (bridging) on the way out from a silo, tanker, or a bulk container liner.

container transport

There is always the question: Can it be done more efficiently?

With the exception of the last method that we will present, Bulk-Flow created these to optimize the use of bulk container liners to carry bulk solids. All other methods require some tilting for the unloading hard-to-flow operation.

These are the common methods for tilting the container for the unloading operation.

Sometimes, there are companies for which it is the whole truck, boogie and container that are tilted at the same time.

The most common ways to unload the containers, no matter the type of bulk solid products carried are:

Pneumatic Unloading

pneumatic unloading

A vacuum hose with a slide gate is connected to the liner. The container is tilted gradually in timed intervals as the product flows.

Gravity Unloading

gravity unloading

The unloading port – sleeve is connected to an air seal (rotary valve) that sends the bulk solids to a pneumatic conveying line.
The container is tilted in gradually timed intervals as the product flows.

Gravity funnel unloading


The same as the previous method, but the unloading sleeve discharges into a funnel – hopper. The container is tilted in gradually timed intervals as the product flows.

At some companies, or at some sites, the unloading hard-to-flow is done directly over a silo or a reservoir where it will be transferred to the final storage silo, but the methods are like the ones shown above.

The problem with hard-to-flow products will always be the need for a high tilted angle.

Ways to reduce those angles:

Use Fluidizing Liner


It is a good start.
Bulk-Flow developed state-of-the-art fluidizing liners that significantly reduce the slope angle to increase the process efficiency and safety.


This is the most recently developed unloading system at Bulk-Flow that allows the container to remain horizontal during the entire process. Unloading hard-to-flow can happen even in places that do not have special equipment to receive the bulk solids.


Both systems were created to help with the inventory once it speeds up part of the process.
As with most liners, the packaging cost is reduced when compared to other methods.
The fluidizing liners and the tilt-less liners reduce labor, operating costs, and most aspects related to the operational logistics’ efficiency.

Our goal is to helps you choose the most efficient unloading hard-to-flow method – time and labor wise, or in terms of equipment usage – maximizing the use of available resources, which are important to all logistics’ business.

Request a free assessment, we are ready to help you!

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Posted by Team Bulk-Flow

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