Six years after a Flexicon bulk bag discharger and screw conveyor operation first went live at The Plastics Group’s production facility in Woonsocket, Rhodes Island the company has re-invested in a second, duplicate Flexicon system that feeds additives to a new twin-screw compounding line in the manufacture of thermoplastics.
Flexicon’s bulk handling systems have enabled the company to keep all its processing lines on a single floor level, "avoiding the multi-level platforms of most twin-screw lines, which hold feeders and other auxiliary systems", says Duane T. Delaney, Technical Manager of the Plastics Group. "These can rise to 9m, making it difficult and dangerous to clean and maintain equipment as well as adding upwards of $200,000 to the cost of a compounding line for platforms, railings and steps".
One of the constraints affecting installation was plant headroom, 5m maximum, however with careful planning the original single screw compounder was replaced by a twin, 70mm diameter screw compounder, the use of a Flexicon bulk bag discharger and conveyor enabling the company to fit everything on one level of its 5,600 m2 building. This configuration worked so well that when the Plastics Group set about to increase productivity with the introduction of a new high-speed twin screw line it ordered another bulk bag discharger and flexible screw conveyor from Flexicon Europe.
Protecting additive properties
The company supplies filled and reinforced polypropylene, along with recycled-content polyolefin, high-impact polystyrene and ABS, for automotive, recreation, packaging, construction, appliances, toys, household durables and other applications.
During the process additives fillers and reinforcements, from talc, mica, calcium carbonate and barium sulphate to glass fibres and beads, are fed to four resin hoppers on the twin-screw extruder by pneumatic lines from silos. Transporting these powdered additives and fillers to a feeder by a pneumatic or mechanical system would mean a relatively high cost for the conveyor and installation, as well as increased maintenance. Also conveying glass fibres longer distances could result in potential damage to the material and thus affect compound properties.
It was decided that a bulk bag discharging system paired with a lower cost, lower maintenance flexible screw conveyor installed near the compounding line would prove the ideal solution, providing rapid transfer of additives. The discharger would empty bulk bags into a hopper at its base and the flexible screw conveyor would convey additives through an inclined tube to a feeder on the compounding line. This plant configuration would prove to be more efficient—and safer—than having workers manually open and empty 25kg bags of additives into the feeder hopper from a platform, a process that could introduce bag scraps and other contaminants into the compounding operation, take up floor space for bag storage and create a costly waste-disposal problem with the empty bags.
Additives arrive at the plant in bags weighing in the main between 450 to 1130kg but some are shipped at 1360kg therefore Flexicon ensure that the BFC Bulk Bag Discharger frames had a safety load rating of 1800kg. Each bag is attached to a four-cornered low-profile lifting cradle with Z-Clip™ bag-strap holders and raised into position by an electric trolley hoist mounted on a cantilevered I-beam. A pneumatic Power-Cincher® flow-control valve regulates flow through the bag spout, this prevents material leakage and permits the spout to be closed and retied if a bag is partially unloaded.
The design also includes a Spout-Lock® clamp ring that attaches the bulk bag spout to a Tele-Tube telescoping tube, this maintains downward tension on the clamp ring, keeping the spout taut and preventing material from bulging out or falling in during discharge and creating flow restrictions.
Due to the diversity of additives used and their inherent properties, the dischargers were also equipped with pneumatic Flow-Flexer® agitation plates, these raise and lower the bottom of a bag to maintain positive flow and achieve full discharge.
Discharger has multiple features
The original 150mm diameter flexible screw conveyor is installed at a 35-degree angle and transports material 5.2m to the feeder hopper. As the flexible screw turns, it self-centres within the polymer outer tube, providing efficient delivery of material to the feeders without damage to the glass fibres and other reinforcements. The second flexible screw conveyor is 115mm diameter and runs 8.4m at a shallow angle to empty material into the twin-screw extruder’s additive feeder.
Each screw conveyor can handle between 20 to 900kg per hour, dependant on the material being compounded with a loss-in-weight system controlling flow as the feeder hopper reaches its preset weight levels.
The Plastics Group has bought into the proven reliability and operational performance of Flexicon systems. With a material change one or two times a day on average and a typical run lasting 18hrs, each line capable of compounding 32,000kg per hour, a less reliable discharger and flexible screw conveyor system could create major production problems since there is no backup.
Mr. Alan Walton
General Sales Manager
Flexicon (Europe) Ltd
89 Lower Herne Road,
Kent CT6 7PH
Tel: +44 (0) 1227 374710
Fax: +44 (0) 1227 365821