Kason and Allied Cooperate to improve machine performance
At Allied Chemical Corporation's Baton Rouge, LA, facility, engineers are always looking for ways to assure that the high density polyethylene (HDPE) they manufacture remains at highest purity. Several years ago, they increased production capacity to meet customer demands and simultaneously achieve greater efficiency from one of their extruders. Allied had been using a Kason VIBROSCREEN. circular vibratory separator to screen out overs and fines, and provide uniform quality HDPE in the 3 to 8 mesh size. But when throughput was increased from 18,000 pounds per hour to about 21,000 pounds per hour, screen failures seriously affected efficiencies.
To increase capacity, the standard stainless steel 72 in. diameter VIBROSCREEN which had operated reliably for many years was replaced with a new VIBROSCREEN having an auxiliary discharge frame. This unit, with its 3 and 8 mesh market grade stainless steel screens and custom designed product distributor, enabled production capacity to rise to about 22,000 pounds per hour. At the same time, however, it was noticed that a significant quantity of on-spec pellets were leaking from the fines and oversized pellet discharge chute. It was initially thought that the 8 mesh (on spec.) screen deck had failed.
The maintenance engineering department began an investigation into the source of the pellet leak. An examination of the screens showed that they were not the cause of the pellet loss. After further disassembly and inspection, it was determined that the neoprene gasket between the exterior of the fines discharge chute and a collar that extends up from the "on-spec" product ramp of the circular screening unit was missing. They concluded that the constant vibration had caused the neoprene gasket to disintegrate. This resulted in the leaking of on-spec pellets and presented the possibility of on spec product contamination.
A call to Kason resulted in the suggestion to install a new white neoprene gasket, using an alternate procedure, to prevent the pellets from leaking into the fines. Allied maintenance engineers decided that the risk of further disintegration and potential for contamination could not be tolerated. So a brainstorming session was held that included Maintenance Engineer Gary Baudouin, Maintenance Foreman Emerson Dougherty, and Mechanics Steve Peairs and Don Holmes Sr .
After several alternatives were discussed, the group decided to eliminate the gasket. It was proposed that the gasket and flange be removed and a diverter be installed. During a 12-hour downtime period, the angle iron that held the gasket was removed, 16 gauge sheet metal was rolled into a circle and tack welded onto the product deck.
The overlap was added to prevent pellets from bouncing into the gap between the vertical extension and the downcomer on the feed tray.
The simpler design does not depend on proper gasket installation, making setup easier and quicker. Reports from the Allied Chemical quality control group shows that there has been no problem with contamination and no pellet loss from the classifier for the eight months the modified unit has been in service.
Screen Tips - Volume 4, Number 1 Winter 1989