In the bag

An investment in bulk bag dischargers and flexible screw conveyors by compounder Styron Netherlands has increased productivity, worker safety and plant cleanliness.

The company, which runs eight compounding lines in a 5,000 m2 plant and employs 80 staff, recently installed two Bulk-Out BFC-X Bulk Bag Discharging systems with integral flexible screw conveyors from Flexicon.

One system unloads and conveys talc used to improve the mechanical properties of polypropylene compounds, and the other unloads and transports an impact modifier in polycarbonate/ABS formulations.

A lower density means more talc volume, reducing the amount that gets added to a formulation

Styron Netherlands’ Ron Drabbe

The bulk bag dischargers were installed to replace manual unloading, says Ron Drabbe, senior improvement specialist at Styron Netherlands (formerly Dow Benelux).

The equipment also promotes complete evacuation of bulk bags and conveying of material to blending hoppers on compounding extruders.

Bag handling was labour intensive

With each bulk bag weighing 600 kg, unloading a bag previously required three workers, says Drabbe.

Two would mechanically hoist a bag above a hopper while a third, working from a platform atop the hopper, connected the bag to a discharge unit and dislodged trapped residue by hand. Non-free-flowing talc was especially prone to lodging in corners of the bags.

Apart from the risk of injury in handling bulk bags and climbing up and down platforms, “unloading generated dust, which settled on the plant floor,” says Drabbe.

Each bulk bag discharger frame includes a cantilevered I-beam with an electric hoist and trolley, allowing a single worker to raise and position a bulk bag above the unit’s receiving hopper.

Because the discharger is automatic and dust-free, Drabbe says Styron Netherlands can now discharge as many bulk bags as are needed, both rapidly and safely.

Bulk bag dischargers ease operation

A cross-shaped bag-lifting frame attaches to the straps on each corner of the bag, and the electric hoist lifts the bag into place on the discharger frame.

The operator pulls the bag’s outlet spout through a Power Cincher flow-control valve, whose elliptically-contoured bars close concentrically around the spout, preventing product leakage.

The clean side of the bag spout attaches to the clean side of the discharger by means of a Spout-Lock clamp ring, which is mounted atop a Tele-Tube telescoping tube that maintains constant downward tension on the bag as it empties and elongates, promoting material flow through the bag spout.

Pneumatically-actuated Flow-Flexer flow-promotion devices raise and lower opposite bottom sides of the bag, forming a ‘V’ shape to promote total discharge into the hopper.

The hopper is vented to a Bag-Vac dust collector that vacuums displaced air and dust from the sealed system as talc or impact modifer discharge from the bag, which Drabbe says improves plant cleanliness.

Conveyor maintains talc quality

As material enters the hopper, a flexible screw conveyor transports talc or GRC at a 45º incline to an inlet hopper for blending with other additives and resins prior to compounding.

The conveyor’s stainless steel screw has specialised geometry to handle non-freeflowing materials.

One benefit of this screw design is its ability to convey talc consistently regardless of its moisture content, and Drabbe says the density of talc often decreases when it is conveyed because ambient air reduces moisture content.

“A lower density means more talc volume, reducing the amount that gets added to a formulation and affecting production throughput in a negative way,” he says.

Styron Netherlands evaluated a number of pneumatic, vacuum and mechanical materialshandling systems. Drabbe says the Bulk-Out BFC-X Bulk Bag Discharging equipment outperformed all of these.

Only one other materials-handling system that he evaluated was unaffected by talc density, but Drabbe says it was unable to handle bulk bags.

A programmable logic controller governs operation of the two dischargers and conveyors.

Limit switches stop the conveyors from running when the hoppers under the dischargers become empty, and proximity sensors stop the conveyors when material has been transported to the compounding hoppers.

The throughput, dust-free operation and minimal operator involvement of the discharger stations have met expectations. Styron Netherlands says it plans to add a third bulk bag discharging station for talc, says Drabbe.

There is no timetable for this as yet, but it is “on the list of things to do.”