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The art of bagging dry bulk

Whether doing so by weight or volume, a wide range of equipment is available for bagging different materials.

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The operator in the foreground initiates a bulk bag filling cycle
The operator in the foreground initiates a bulk bag filling cycle
Bagging up dry bulk materials is common in logistics chains. End-users often require smaller quantities of a given material to reduce inventory and meet the demands of just-in-time production.

Bulk materials are usually loaded into sacks, flexible intermediate bulk containers (FIBCs or ‘bulk bags’), or drums.

However, transferring materials into smaller containers like these is not as easy as one might think at first sight. Take the filling of bulk bags. There are a variety of methods and machines that can be used, and operators can choose to fill either by weight or by volume, depending on the application.

Spiroflow, one company that offers a range of bag filling machinery, says the right filler can quickly and safely fill a bag without dust escaping. The biggest factor in determining which filler will best handle a particular application at the best price falls to the question of weight or volume.

Generally, if a product is sold by weight, then, naturally, a filler that fills by weight will be needed. Alternatively, products sold by volume require a bulk bag filler that fills by volume. These fillers are also useful in plants that fill bulk bags with raw or intermediate materials that are stored or moved to another plant. In this scenario, the bags are emptied into an external device such as a bulk bag discharger or a hopper with load cells that measures the material as it is discharged.

In the frame

Volumetric bulk bag fillers consist of a bulk bag support frame with a filling head at its top. The frame can either support the bag on a pallet, or suspend the bag from its lifting loops over lifting arms on the filler. A supply vessel, process vessel, or conveyor located above the filler discharges material into the filling head for loading into the bulk bag.

An inflatable neck seal, adjustable clamping strap, or large rubber band holds the bag’s inlet spout tightly around the filling head to prevent dust from escaping from the bag during filling. The filling head consists of an inner annulus, through which the material flows into the bag, and an outer annulus, which releases the air displaced by the incoming material. For dusty materials, the outer annulus ducts the displaced air to a dust collection system, so it can be cleaned and safely exhausted to the atmosphere.

An optional operated blower on the bulk bag filler frame provides airflow for inflating the empty bulk bag before it is filled. Inflating the bag ensures that it is correctly formed to accept the material, so the bag can be filled evenly and to its maximum capacity. Bag inflation also eliminates fabric creases that could hinder the bag’s complete filling. The filler frame can be designed to handle the plant’s headroom limitations and, depending on the model, can be adjusted manually or automatically to adjust to bulk bag height variations.

The filler can be operated manually or automatically once the bulk bag is loaded onto the filler and inflated. In manual operation, an operator typically opens the supply or process vessel’s outlet valve (or starts the conveyor) and closes the valve (or stops the conveyor) when the mate rial reaches a certain level in the bag, or completely fills it.

Level sensors

The level sensor is located in the supply or process vessel at the point where the material level equals the correct bulk bag volume. When the material loaded into the vessel reaches this volume, the level sensor signals the vessel’s outlet valve to open, discharging the vessel’s entire contents through the filling head into the bag. You can also use a level sensor to stop the material loading into the supply or process vessel and discharge the vessel’s contents to the bag.

The sensor is suspended from the filling head and positioned to detect the point in the bulk bag where the material will reach the required volume. It then signals the supply or process vessel’s outlet valve to close or the conveyor to stop.

Depending on the material’s characteristics, the filler can be equipped with an electrically or pneumatically operated vibration device to de-aerate and compact the material as it fills the bulk bag and after filling is complete. This ensures that the bulk bag has a stable shape for safe handling, storage, and transport. Materials that easily fluidise, like flour and carbon black, require vibration for compaction, while this is not required for non-fluidisable materials, such as coarse sand and plastic granules.

Gravity

Gravimetric fillers fill by weight. These consist of a bulk bag support frame, a filling head, and an electronic scale with load cells and a control panel. The filling head is the same as that for a volumetric filler, and can be held tightly on the bag inlet spout by the same devices. As with the volumetric filler, a supply vessel or conveyor supplies material to the gravimetric filler, and a blower on the filler frame provides bag inflation. This type of filler can also be equipped with a vibration device to de-aerate and compact the material as it fills the bulk bag, and the frame can be designed to handle the bulk bag height and headroom limitations.

The filler frame and scale can be configured in different ways. The filler can have a platform-weighing design in which the load cells are under a platform that supports the bag on its pallet. Alternatively, a filler can have a hang-weighing design, in which the load cells suspend the lifting arms holding the bulk bag. In a filler with a platform-weighing design, the weighing platform is usually load-cell-mounted and an integral part of the filler. In some cases, the filler manufacturer incorporates a proprietary platform scale into the filler. The scale in any platformweighing or hang-weighing filler requires appropriate weighing equipment to meet national standards.

Weighing it up

 

After the operator loads the bulk bag on the gravimetric filler, inflates the bag, and uses the scale’s control panel to start the filling process, the scale senses the weight of material in the bulk bag as it fills, and automatically sends output signals to the supply or process vessel’s outlet valve to close, or to the conveyor controls to stop the conveyor.

 

When selecting a platform-weighing or hang-weighing gravimetric filler, it is worth noting that the hang-weighing filler offers two advantages. The major advantage is in relation to how much weight the suspended scale must measure. Both platform-weighing and hangweighing scales must be tared (i.e. zeroed out) between weighments to ensure that only the bag’s contents are weighed. But when the bag and its contents, the pallet and the platform support structure under the pallet rest on load cells, as in the platform-weighing filler, the scale must weigh all of these items. With support lifting loops, as in the hangweighing system, the scale weighs only the lifting arms, the bag, and its contents. This requires weighing and taring less metal in relation to the bag’s contents, so the suspended scale can provide greater accuracy.

 

The second advantage is that the suspended scale’s load cells are mounted high up in the filler frame, protecting them from potential forklift damae. When the platform in a platform-weighing filler is hit hard by a forklift, the resulting lateral forces can damage the load cells. While the load cells can be protected by installing a strong buffer that can stop the forklift before it hits the platform, a hang-weighing filler’s load cells are intrinsically protected from forklift damage.

 

Dusted down

 

Ensuring a healthy workplace environment is an important consideration when choosing bag filling equipment.

 

Chemical products company Kaneka North America needed an efficient, dust-free method of repackaging PVC modifiers to replace manual methods in place since 2003. The plant packages grades of modifier products into bulk bags (907 kg, 771 kg, 454 kg) and 23 kg sacks based on projected customer orders for product grades in specific bag sizes. When the actual orders don’t match the projections, the plant needs to transfer products from one bulk bag size to another.

 

Previously, forklifts suspended a bulk bag above the hopper of a portable screw conveyor that transferred the material into the desired size bulk bag. Similarly, material was discharged from a bulk bag into the hopper of a valve bag filling machine for 23 kg sacks. Both operations presented safety risks from the suspended bulk bags, and generated high levels of dust. Product loss also occurred, and operations frequently had to stop for cleaning and removing dust that would pose a safety hazard.

 

“Re-bagging was inefficient, and the fine powders generated dust,” said Brian Wilson, staff reliability engineer. In the new system, supplied by Flexicon, a flexible screw conveyor transfers powder from the first of two BulkOut bulk bag dischargers to a Twin-Centerpost bulk bag filler. The second bulk bag discharger empties into the hopper of the valve bag filler for 23 kg sacks located under the discharger.

 

In Kaneka’s ‘bulk-to-bulk’ transfer system, the loops of bulk bags are connected to a bag lifting frame that is forklifted onto a cradle at the top of the Bulk-Out discharger, model BFF-C-X.

 

A Spout-Lock clamp ring, which is raised pneumatically by a Tele-Tube telescoping tube, makes a secure, sealed connection to the bag spout, preventing contamination of the plant environment with dust during material discharge. The telescoping tube maintains constant downward tension on the bag as it empties and elongates, promoting material flow into a 226-litre hopper.

 

As the bag lightens, PopTop extension arms at the top of the four discharger posts increasingly stretch the bag upward into a cone shape, as Flow-Flexer bag activators raise opposite bottom sides of the bag into a ‘V’ shape on timed cycles, promoting total discharge from the bag.

 

The receiving hopper of the discharger is equipped with a hinged lid and bag tray support, allowing material to be dumped manually from sacks, boxes and other containers.

 

A 3.6m-long flexible screw conveyor, inclined at 45 degrees, transfers the PVC modifiers from the hopper to Twin-Centerpost bulk bag filler with height-adjustable fill head to accommodate a wide range of bag sizes.

The operator attaches the bag loops to retractable hooks that support the bag during filling. Under PLC control, plant air inflates the bag while an inflatable collar seals the bag spout, which, together with a filtered air displacement vent, prevents the escape of dust.

 

Load cells supporting the filler transmit weight gain information to the PLC, which stops the flexible screw conveyor once the target weight is achieved.

 

In Kaneka’s ‘bulk-to-sack’ transfer system, the Bulk-Out model BFC-C-X bulk bag discharger empties contents of the bulk bag into the hopper of the valve bag filling machine for 23 kg sacks.

 

The BFC Series discharger differs from the BFF Series discharger, in that bags are lifted from the plant floor by means of a cantilevered Ibeam with hoist and trolley, eliminating the need for a forklift. This hoist assembly was installed to fit limited headroom where the bulk bag discharger is located. As with the ‘bulk-to-bulk’ transfer system, the discharger employs a Spout-Lock clamp ring and Tele-Tube telescopingtube.

Volumetric bag fillers are useful for filling bulk bags with raw or intermediate material
Volumetric bag fillers are useful for filling bulk bags with raw or intermediate material

Dust-tight system

 

From start to finish, both operations are completely enclosed, greatly reducing dust emissions. Dust control for both transfer systems has been further improved by connecting to a recently installed dust collection system with explosionprotection. Vent hoods and mass balance dust collectionspouts were installed, as required, to make the system as clean and safe as possible.

 

“Dust generated from the re-bagging operation has been significantly reduced. The new system improves our productivity by an order of magnitude,” Wilson concluded.

 

A twist on conventional bagging systems was recently installed by Dutch company Van Beek for Finnish logistics firm RL Trans.

 

Effectively, Van Beek developed a process for bagging to work in reverse. RL Trans was looking for a solution to meet customer demands for the storage and transhipment of bulk goods. The logistics firm had completed a bulk terminal for this purpose so that, as soon as a client received an order for materials, RL Trans could load the client’s packed bulk goods directly into trucks, and drive them to their destination.

 

“We are increasingly being asked whether we can deliver bulk goods packed, for example, in big bags. This led us to look for a way of quickly loading big bags into our bulk trucks,” said Andreas Lindedahl, marketing manager at RL Trans.

 

The maximum weight for trucks in Finland (76t) is higher than in other EU countries. “We can therefore get 53t into a silo truck,” says Lindedahl. “But transhipment soon becomes a timeconsuming and expensive job. We were therefore looking for a machine with a high capacity and a fast loading time.”

 

RL Trans chose Van Beek’s Dino DS400 with loading bellows and a capacity of 90 m3 /hr. The Dino can be used to fill 53t into the extra-large bulk trucks within two hours. Because Dino is easy to clean, such that it can quickly change between different bulk goods, this became a decisive factor in the logistics firm’s choice.

 

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