Centrifugal Sifter Meets High Flow, Low Headroom Challenge

Engineering a new system to load gypsum stucco for ceiling tile manufactured at a sister plant, the United States Gypsum Company plant in Sperry, IA, faced the challenge of screening gypsum materials at 30 tons/hour in a low-headroom area. The raw material, which contained on-size and oversize gypsum particles, paper fuzz, blasting cord pieces and tramp metals from upstream mining and milling operations, was delivered by an overhead screw conveyor whose outlet was positioned only 4 feet above the inlet of an existing 4-ton-capacity surge bin which receives the screened material.

A drag chain conveyor transports milled gypsum from a 170-ton bin to the inlet of a screw conveyor (above) which carries it to the separation system.

With such limited vertical space available to accommodate high capacity screening equipment, plant management could not employ the "inclined shaker" type of screening equipment used elsewhere in the facility; a shaker screen having 30 ton/hour capacity would be 10 feet long at a 35m incline and consume twice the amount of vertical space available. As a result, the plant turned to a low profile Centri-Sifter^® centrifugal sifter from Kason Corporation, which handled the required capacity and was offered in a low profile configuration measuring only 2 feet in height.

Intricate Separation and Conveying System

Jay Holt, U.S. Gypsum engineer, faced the challenge of laying out a separation system in this low headroom space in addition to a conveying system to move the screened gypsum to a bulk tanker truck.

Low profile, high capacity Centri-Sifter centrifugal sifter fits restricted vertical space between magnetic separator chute and existing surge bin.

A drag chain conveyor transports the milled gypsum from a 170-ton bin to the inlet of a screw conveyor, which carries it to the separation system. The stucco falls through a slide gate valve and a split-flow magnet separator positioned above the screener to remove any tramp metals introduced during upstream mining and milling operations. Below the magnet separator, the Kason Corporation Centri-Sifter centrifugal sifter screens the stucco to below 14 mesh. The sized material falls through the center of the sifter directly into a surge bin while oversized particles are discharged from the sifter's tangential spout through an 8" diameter hose into a dumpster. A 200-cfm dust collector adjacent to the surge bin collects dust in the separation area.

The pneumatic conveying system moves the on-size material from the surge bin through a 50 cu. ft. pressure pot and 6" tube to fill a bulk tanker trailer. The pressure pot vacuum-loads and pressure-discharges 18-24 times to fill a tanker, with a 100-hp, 950 cfm capacity blower moving the bulk gypsum at 30 ton/hour. A second dust collector, rated at 950 cfm, captures and recycles dust that the incoming material kicks up in the truck tank.

Sized material falls through the sifter into a surge bin while oversized particles are discharged from a tangential spout into a dumpster.

A pneumatic conveyor moves the on-size material from the surge bin through a 50 cu. ft. pressure pot and 6" tube to fill a bulk tanker trailer.

Sifter Provides High Capacity in Low Profile

Despite its compact size (25-1/2" high by 21-1/2" wide), the 7-1/2 hp Centri-Sifter model YOB separates the required 30 ton of gypsum per hour. Helical paddles rotating immediately above a 14 mesh stainless steel cylindrical screen, impart centrifugal force to the gypsum particles, propelling them continuously against and through the screen, breaking down soft agglomerates and increasing screening rates. To accommodate the high loading of abrasive material, a heavy-duty profile wire basket was substituted for the standard basket of nylon screen.

To prevent "blinding," air nozzles integral with the rotating paddles dislodge oversize particles from screen openings.

After learning that U.S. Gypsum's Southard, OK plant employed Centri-Sifter separators successfully, Holt sent his plant's most-difficult-to-screen product to Kason's laboratory -- ground up reclaimed wallboard, which contains highly abrasive paper and gypsum particles. "It's the worst stuff that will ever come across the screen," he says. Kason recommended the YOB model after successfully screening the test material.

Five to six truckloads per week deliver the screened stucco from Sperry to USG Interior's Walworth, WI plant, which manufactures acoustical ceiling tile, ceiling suspension grid, and relocatable wall systems. (Both USG Interiors, Inc. and United States Gypsum Company are subsidiaries of Chicago-based USG Corporation.) Since the new system went operational in June 1998, it is bringing new business to the Sperry plant. Another company is considering taking three or four truckloads per week of the screened product.

"The system meant a lot of work, and was a challenge to put together, but it is working out well," says Holt. "It succeeds especially since Kason solved my height dilemma."