APCO Packaging, a leading contract packager with expertise in difficult-to-handle materials, recently signed a contract with a customer to blend and package expanded perlite, an amorphous powder used to clean up environmentally hazardous spills.

“Our customer had a tight deadline for introduction of the product and we have a policy of guaranteed on-time delivery of difficult-to-handle materials with fast turnaround times,” says Greg Hinton, President of APCO. “It seemed like an ideal fit.”

Challenges quickly arose, however, when APCO learned that the material, which would be delivered to its facility in 245kg, 1.8m high bulk bags, would be more problematic to handle than they had anticipated. “Using an overhead crane to empty the bulk bags directly into the packaging equipment would have required a ceiling height of 8.5m, but our ceilings are only 7.9m high,” says Hinton.  “Installation of such a system would have required going through not only the ceiling, but also the roof, we needed a better solution.”

The contract packager turned to bulk bag handling specialist Flexicon to custom engineer a flexible screw conveyor that met the height restrictions and could deliver it in only two weeks—in time to begin supplying product by the contracted date.’

The decision to call in Flexicon was not difficult since for a number of years APCO has successfully used Flexicon bulk bag dischargers, hoppers and flexible screw conveyors for powder handling in its repackaging of industrial, household and personal care products. For example, three bulk bag dischargers and flexible screw conveyors transfer heavy powders such as powdered metals and special formulations based on soda ash (sodium carbonate) for repackaging, this including four different powdered metals with bulk densities ranging from 1,280 to 1,922 kg/m3. APCO also dedicates other flexible screw conveyors for packaging single products that it continually runs for other customers.

Perlite poses special handling problems

Perlite is an amorphous volcanic glass with a relatively high water content produced when lava from a volcano cools rapidly without forming crystals.  It occurs naturally and has the unusual property of greatly expanding when heated to temperatures of 850-900°C. Water trapped in the structure of the material vaporizes and escapes, causing expansion to 7–16 times its original volume.  The expanded material is a brilliant white, due to the reflectivity of the trapped bubbles, with a bulk density of only 160kg/m3. Owing to its excellent absorption properties, it is often used to clean up liquid spills but its light weight and flaky structure can cause it to cling to solid surfaces by static electricity, making it difficult to handle.

“We supplied samples of the blended material and Flexicon custom designed a special screw to accommodate its special characteristics,” says Hinton.  “Since the material is so light and fluffy particles can easily become airborne so we need to keep the material contained, especially as a pneumatic turbine vibrator in the hopper agitates the particles to prevent them from adhering to its interior walls because of static electricity.”

Flexible screw conveyor surmounts height restriction

The new perlite transfer system consists of a 0.23m3 capacity stainless steel hopper measuring 91.4cm square by 96.5cm high, and a 9m long flexible screw conveyor that transports the perlite mixture to the intake hopper of the packaging machine at a height of 6.7m. The advantage of the Flexicon flexible screw conveyor is that it can move material at any angle, a useful factor at APCO where it is inclined to fit within the company’s ceiling height of 7.9m. The specially designed, flexible helix rotates within a flexible 11.4cm diameter polymer tube and is powered by an electric motor at the discharge end.

Perlite moves from bulk bags to re-sealable bags

A forklift operator unloads a bulk bag of perlite into an enclosed ribbon blender located on a platform 2.7m above the plant floor. The material gravity feeds into the blender as the operator unties the bag spout after clamping it to the blender’s inlet tube. A small amount of a proprietary performance-enhancing additive, which changes the bulk density of the perlite, is then added. After blending, the inlet of the original bulk bag is fastened below the ribbon blender for the material to gravity feed into it.

The forklift operator then positions the bag above the hopper of the flexible screw conveyor, clamps the spout to an inlet tube in the hopper lid and unties the spout, allowing material to gravity discharge. The flexible screw conveyor transports the material to the ceiling-high hopper above the packaging machine, which is equipped with high and low level sensors that turn the conveyor on and off to maintain an adequate volume of material in the hopper while 454g re-sealable bags are being filled.

APCO packages many materials using flexible screw conveyors and hoppers therefore to prevent cross contamination between product runs, an operator removes the clean-out cap covering the intake end of the plastic tube, allowing rapid emptying and pressure cleaning of the tube, as well as enabling disassembly and cleaning of components and stainless steel screw.