Removing Lumps from Metal Powders in Restricted Area
When a metal processor that produces auto parts wanted to make sure that pre-screened and blended metal powders are completely free of lumps and contaminants, it decided to re-screen the powders before filling "cans" when hot isostatic pressing is used or "bags" when cold isostatic pressing is used. Unlike most applications where there is adequate height for various screeners, this company only had 30 in. (762 mm) of headroom between an upstream blender and downstream mobile hoppers. Furthermore, the blender outlet and hopper inlet are on the same centerline. This eliminates the use of conventional circular screen separators because their gyrator motors, which are located under the screen, prevent discharge along the centerline but instead lead to discharge from the side of the separator. This takes the product away from the centerline.
Quality standards call for producing lump-free and contaminant-free blends in a short period. This puts a heavy burden on the separator since batch quantities are typically. about 5000 Ibs (2268 kg) and screening must occur as quickly as possible to maintain high productivity of metal automotive parts.
After considering alternatives, the metal processor/auto parts producer selected a Kason 'Flo-Thru' Circular Screen Separator. The 60 in. (1530 mm) unit equipped with a 64 tensile bolting cloth screen can screen 1000 Ibs (454 kg) of metal powder per minute. These powders, which look like fine sands, have a density of about 200 Ibs per cubic foot (3204 kg per cubic meter). The high density of these metal powder blends makes it imperative to use a reverse tie-down for the screen. This device pulls the center of the screen up slightly by means of a collar that's raised along a centerpost. It ensures that powders move across the screen rather than simply fatiguing the screen's central area.
Screen blinding does not occur since the 'Flo-Thru' unit includes a ball tray under the screen. Bouncing balls dislodge metal powder grains that might otherwise blind the screen.
A flexible, two-ply neoprene and nylon dust cover over the screen minimizes loss of powders. Expansion joints that inflate to form a seal at the 'Flo-Thru' inlet and outlet also prevent powder losses and frequent housekeeping chores.
The plant personnel will also appreciate the 'Flo-Thru ' unit when maintenance is needed or if it becomes necessary to make adjustments to eccentric weights because the type of powder being screened changes significantly. With its two gyrator motors at the sides, it is easy to access the weights. The gyrator motor covers are easily lifted off after removing some nuts from the bolts. There's no need to open access doors or work near floor level.
This 'Flo-Thru' Separator has successfully solved several problems for this auto part manufacturer. Knowing that the powders it uses are free of lumps and contaminants helps keep managers confident that quality is high and defects near zero.
Screen Tips - Volume 9, Number 2 Summer 1994