Circular Screen Separator Helps Brass Foundry Cut Tramp Metal by 75%
Stanley G. Flagg & Company, a division of Amcast Industrial Corp., located in Stowe, PA, has a number of standing committees dedicated to improving quality as cost effectively as possible. As specific problems emerge, however, specialized task forces are created. One such group was formed to determine the best way to improve the quality of the molding sand. The reason for the special committee was obvious. Studies at the company showed that an unacceptably high percentage of the castings produced did not meet Flagg's high standard for surface quality. The subcommittee's target was to improve that level by 50% according to Pete Nazare, brass foundry superintendent.
From the cost viewpoint, it was obvious that if over-sized material, including flash, metal shot and core butts could be continuously and automatically removed from the recycled sand, there would be appreciably less need for sieving by molders and grinding and machining the cast surfaces to achieve the appearance level desired. And appearance is extremely important to Stanley G. Flagg & Company, which has built a reputation for the production of quality castings since it first opened its doors for business in 1854. Less machining, of course, would enable the company to substantially reduce machining costs and reduce the amount of material on the blanks.
During one of the initial committee meetings, a member suggested the use of a Kason vibrating circular screen separator. It was felt that one double-deck VIBROSCREEN® unit would be able to remove the oversized flash/tramp metal/ core butts and possibly the very fine sand material before being recycled to the muller. Plans called for locating it between the 70-ton sand tank and the mechanical conveyor.
In spite of the existing built-in muller rotating screen with openings of approximately 3/16 by 3/4 inch, oversized material in the molding sand was getting through to the molders and cutting productivity. It didn't take much in the way of tramp brass to seriously affect the mold surface, creating voids that rendered the castings useless, or lumps requiring costly cleaning and machining.
In addition, over a period of time the breakdown of the recycled sand creates a superfine powder. This powder fills the voids in-between the large sand grains and prevents gases from properly escaping, resulting in fissures or cracks in the casting. The initial installation during the last quarter of 1989 involved a 60 inch diameter, two deck VIBROSCREEN unit designed to selectively remove both the oversize and undersize material. While it accomplished this task there were also problems. Removing the fines was performed rapidly and with relative ease by the lower of the two screens. But the excessive weight on this 250 mesh screen resulted in breakage problems which increased with time. The committee next decided to remove the frame and screen, converting the unit to a single deck machine, and to utilize dust collection in future removal efforts. The committee focused its efforts on keeping the oversize material from impairing casting surfaces. It now relies solely on the single 20 mesh screen to accomplish that task. To keep the screen from plugging, hollow plastic Kleen Screen Rings move in a controlled manner underneath the screen. The movement is induced by the multiplane inertial vibration action of the VIBROSCREEN unit. Another problem noted was the condensing vapor from the moisture in the hot sand coming from the storage tank directly into the feed inlet of the VIBROSCREEN. This tended to block sand in the feed pipe. The decision was made to remove the top cover of the circular separator, exposing the sand to atmosphere and reducing the area where moisture could collect and cause problems. In addition, an electrically operated hydraulic metering valve was added to control the feed. This improved screen life since it reduced the impact of rapidly falling sand and reduced overloading. The sand now flows intermittently. at an average rate of 4 to 6 tons per hour. Because of the vibrating screen unit, (as well as regular monitoring of moisture, permeability, green compression strength and compactability) the surface appearance has improved dramatically. In addition, molders are no longer required to sieve their sand.
Currently Stanley Flagg's Brass Foundry is producing numerous designs of threaded brass fittings, solder fittings, and brass gas stops for plumbing systems. Brass sil-braze fittings, primarily used for naval vessels' piping systems, are also being produced at the foundry.
Quality assurance personnel are involved in every manufacturing step to ensure premium quality products. Process control and process improvement are ongoing tasks. Incoming raw materials are thoroughly analyzed, from sand to ingot, before use in production. Spectrographic and wet analysis are continuously used to check initial chemistry. Highly trained metallurgists closely scrutinize physical characteristics and microstructures. The never-ending routine devotion to the manufacture of high quality castings has helped the company grow from a cottage industry to a large industry leader that serves customers throughout the world.
The VIBROSCREEN unit's multiplane motion is imparted by a gyrator with a double extension shaft fitted at each end with variable eccentric weights. The motor is rigidly mounted to the main screen assembly which is supported on a circular base by rugged springs that allow the screen assembly to vibrate freely while completely preventing vibration transmission to the floor supporting the machine. All parts above the spring level, including the motor, are integrated as a rigid structure. The spring isolation from the support base results in a self-balancing system that requires only minimal power and avoids excessive mechanical stress.
Top and bottom eccentric weights of VIBROSCREEN separators are independently variable for mass and angular relationship, giving a great degree of control over the complex pattern of vibration. This results in the ability to obtain optimum conditions for screening nearly any material. Adjustments can be made in a few minutes. At Stanley G. Flagg the weights were adjusted several times until the operators felt that they had achieved optimum separation.
The 60 inch diameter VIBROSCREEN is powered by a 1 hp gyrator motor that rotates at 1200 rpm. This provides optimum motion at minimal cost for energy. The key element of the gyrator is a heavy duty bearing designed for vibratory service that gives years of trouble-free service when lubricated regularly with the specified grease.
Screen Tips - Volume 5, Number 2 Fall 1990
Kason VIBROSCREEN Circular Screen Separator removes tramp brass from molding sand used for molds at Stanley G. Flagg & Company, Stowe, PA. Castings now require less cleaning and machining, and the vibratory unit has helped cut sand tramp material from almost 8% to less than 2%.