A Difficult Application for Webster Griffin at Rohm & Haas, Scotland
11 October 2006
Rohm & Haas, Scotland - Grangemouth, integrated automated FIBC filling and handling system
Webster Griffin were selected to manufacture a turn-key FIBC filling and packaging system for acrylic resin powder - an impact modifier used in the manufacture of high-quality extruded plastic profiles at Rohm & Haas in Scotland. This project presented Webster Griffin with several problems - in particular because the product, although being non-corrosive, was combustible and deemed to be capable of a dust explosion. This fine white powder is free-flowing and becomes aerated when handled or poured into bags. Therefore, powder densification and special bag-handling techniques were required. The throughput of the plant is fast - twenty four 500kg bags or 12 1t bags per hour - and must be achieved with one operator plus a part-time forklift truck driver.The bag is a heavy-duty woven polypropylene bag with a 6:1 safety ratio, four top lifting loops, a bottom discharge spout and a top filling spout. It is manufactured from flat woven polypropylene extrusion-coated bags and has a static conductivity strip.
Webster Griffin's supply includes an integrated product settling hopper and two stage product dosing valves above the filling machine. An automatic empty pallet in the feed system, with a pallet magazine, an automatic slip-sheet applicator, a bag filling and product consolidation station, a check weighing station, accumulating conveyors for filled bags and an operators platform are also incorporated.
To minimise the risk of combustion, the powder is nitrogen-purged in the silo and surge hopper above the filling equipment. To prevent dust escaping during filling, the filling spout on the machine has an inflatable collar to provide a dust-tight seal between the bag neck and the spout. The spout has an inner and outer tube, while the acrylic resin powder flows into the bag through the central tube, displaced dust laden air escapes via the outer tube or plenum and is ducted directly to the client's dust-extraction system
In order to avoid floppy unmanageable filled bags they are suspended during filling and intermittently vibrated to de-aerate and consolidate the powder in the bag. Care is taken to ensure that vibration is not transmitted to the precision load cells that account for the fine weight accuracy achieved on this system.
The Webster Griffin control panel and wiring are intrinsically safe and owing to the low melting temperature of the powder, overheating of any component or motor is monitored automatically. Thus the motors are also explosion-proof.
For ease of changeover, the machine is self-adjusting for different sizes of bags and has a stainless-steel telescopic filling spout. The weigh system is digitally programmed for alternative bag weights and stores 100 coded weighing programmes in its memory.
