TECHNICAL LIBRARY

 

Circular Screen Separation Helps Brass Foundry Cut Tramp Metal 75%

Reprinted from FOUNDRY Management & Technology

STUDIES AT STANLEY G. FLAGG & CO., Stowe, PA, showed that an unacceptably high percentage of castings produced did not meet the company's standard for surface quality. To solve the problem, a specialized task force was created to find ways to improve sand quality and increase the number of acceptable castings by 50%. Flagg, a division of Amcast Industrial Corp., makes brass sil-braze fittings for marine piping systems, threaded brass fittings, solder fittings, and brass gas stops for plumbing systems.

The task force found that continuous and automatic removal of oversized material, including flash, metal shot, and core butts from sand could be a cost-effective means of reducing the problem. Such a procedure would cut the need for sieving by molders, and it would reduce the amount of grinding and machining required to achieve the required surface finish.

Although there was a built-in muller rotating screen with openings of 3/16 X 3/4 in., oversized material was still getting through to the molders and cutting productivity. In addition, breakdown of the recycled sand over time created fines. Those fines filled the voids between sand grains and prevented gases from escaping properly, resulting in fissures or cracks in the castings.

During one of the initial task force meetings, the use of a vibrating screen separator was suggested. It was felt that a single, double-deck Kason VIBROSCREEN unit would be able to remove oversized flash, tramp metal, and core butts, and possibly fines also, before the sand was recycled to the muller. Plans called for the unit to be installed between the 70-ton sand tank and a mechanical conveyor.

At the end of 1989, a unit with a 60 in. diameter, two-deck vibrating screen was installed 'to remove both oversize particles and fines.

The fines were removed rapidly and relatively easy by the lower of the two screens, but the excessive weight of this 250-mesh screen caused breakdowns that increased in frequency as the percentage of fines diminished.

It was decided to concentrate on removing large inclusions from the sand and to put fines removal into future efforts. Consequently, the lower frame and screen were removed, which made the separator a single deck machine with a 20-mesh screen. To keep the screen from plugging, hollow plastic rings are moved underneath the screen by the multiplane inertial vibration action of the unit.

The top cover of the circular separator was removed to expose the sand to the atmosphere and reduce the area where moisture could collect. Condensing vapor from the moisture in hot sand had tended to block the sand in the feed pipe from the storage tank.

An electrically operated hydraulic metering valve was added to control feed. This improved screen life by reducing the impact of rapidly falling sand and reducing overloading. Sand flows intermittently at an average rate of 4-6 TPH.

Since the installation of the unit, surface appearance has improved dramatically and molders are no longer required to sieve sand.

(See article CH-157 for more information)