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Bulk Bag Filler Used at First Industrial-Scale Nanotube Facility

June 17, 2009

Spiroflow Ltd, a sister company of Spiroflow Systems Inc. (Monroe, NC), has installed and started up its highest accuracy Spirofil bulk bag filler. The machine is capable of filling 45- and 110-lb bulk bags at the world’s first industrial-scale nanotube manufacturing facility in Sambreville, Belgium.

The customer, Nanocyl S.A., considered other suppliers, but project engineer, Michel Wattiaux, and process inventor, Christoph Bossout, were convinced by Spiroflow’s guarantees of accuracy. Wattiaux had an earlier positive relationship with Spiroflow and its local Belgium agent while working for a major Belgian chemical company. The order for the bulk bag filler was secured by Spiroflow with the assistance of PHC International, the company’s agent in Belgium.

What Is a Carbon Nanotube?

The Spiroflow Spirofil ‘Fill-by-Weight’ bulk bag filler at Nanocyl is shown in place with the safety cage open for rigging.

A carbon nanotube is a tube-shaped material made of carbon that has a diameter measuring on the nanometer scale. A nanometer is 1 one-billionth of a meter, or about 1 ten-thousandth the thickness of a human hair. The graphite layer appears somewhat like rolled-up chicken wire with a continuous unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons. Carbon nanotubes have many structures, differing in length, thickness, type of helicity, and number of layers. Although they are formed from essentially the same graphite sheet, their electrical characteristics differ depending on these variations, acting either as a metal or semiconductor. Carbon nanotubes typically have a diameter ranging from below 1 up to 50 nm. Their length is typically several microns, but recent advancements have made them much longer, in the centimeter range.

Nanocyl: The Carbon Nanotube Specialists

Nanocyl produces the full field of carbon nanotubes, ranging from single-walled nanotubes to double-walled and multiwalled versions. The preferred manufacturing technology is catalytic carbon vapor deposition (CCVD), which is currently best adapted to large-scale production. Nanocyl commercializes its products in the form of powders, pellets, liquid dispersions, and films.

Typical applications using the mechanical reinforcement properties of carbon nanotubes include sporting goods such as tennis rackets and bicycle frames, industrial parts such as windmill blades and printing cylinders, and applications in industries such as automotive, marine, and aerospace. Quantities used range from several pounds to several tons, depending on the application.

The Spiroflow Spirofil ‘Fill-by-Weight’ bulk bag filler at Nanocyl is shown in place with the safety cage closed.

For most industrial applications, Spiroflow traditionally offers bulk bag fillers with weighing platforms using weigh scales or load cells, which typically achieve accuracies of ±2.2 lb. To meet Nanocyl’s requirement of a weighing resolution accuracy of ±0.7 oz, Spiroflow engineers decided to successfully adopt the ‘hang-weighing’ principle. This meant that the highly sensitive load cells could be mounted high up in the structure of the filler, thereby out of harm’s way. Not only does the filler weigh the contents of bulk bags, it’s so accurate that it’s also used to fill 4.4-lb bags. Accuracy is particularly critical when handling high-value products such as nanotubes, which typically have a very low bulk density of 3.1 lb/cu ft.

Bulk Bag Filler at Nanocyl

At Nanocyl, bulk bag filling takes place under a nitrogen blanket.

A folded, flat bag is rigged onto the filler and then the bag is inflated with nitrogen. Given that the ambient air around the filler is 78% nitrogen (by volume) anyway, the nitrogen that is displaced as the bag is filled is vented through a special filter unit into the atmosphere.

During filling, the base of the filler intermittently rises to vibrate the bag. The bag then lowers to allow weighing to continue. The bag is given a final vibration once the target weight has been achieved and recorded. This vibration is critical to ensure that the contents of each bag are consolidated to render the bags in a stable and safe condition for handling and storage.

The controls were designed and manufactured by Spiroflow, which has a dedicated team of electrical engineers and technicians. The heart of the control box is a high-accuracy-weighing instrument that receives signals from the high-sensitivity, high-accuracy load cells. These support the bag-hanging frame, complete with its quick-release bag loop hooks. The weighing instrument is connected to a printer so that batch records can be made and kept.

The Spirofil bulk bag filler has been in operation for more than a year, and, according to Nanocyl’s production representative, “It is an excellent machine, tailor-made for us to our exact specification. It has performed to our complete satisfaction and we are very pleased with it.”

Spiroflow Systems Inc. is a worldwide supplier of a wide range of both standard and custom powder-handling equipment. For more information, visit www.spiroflowsystems.com. To learn more about Nanocyl, its products and its applications, visit www.nanocyl.com.