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Go lean with fluidized beds in aluminum heat treating.

While heat treatment often is necessary for aluminum castings, the process itself can violate lean manufacturing principles. The low heat transfer rate in convection furnaces leads to a lengthy holding time to ensure the adequate quality of heat treated parts. The transition of liquid metal to the solid phase takes minutes, but heat treatment takes hours, making it difficult to create a one-piece process flow within a manufacturing facility.


Arizotah Enterprises, Plymouth, Minn., offers a heat treating solution using fluidized bed technology for aluminum castings that can reduce that time dramatically. A fluidized bed consists of a fine, hard media, such as sand, that is partially suspended by a gas. As the gas passes through the media, the particles become able to slide easily past one another, acting like a fluid, and thus allow continuous contact between solid particles and the parts being heat treated. This leads to a high rate of energy transfer and temperature control, allowing the solution heat treated castings to function at temperatures close to the solidus temperature and reducing the net solution heat treating time.

Fig. 1 shows the microstructure evolution of as-cast material undergoing heat treatment through a convection furnace and heat treatment through the fluidized bed. The silicon particles of the microstructure evolved quicker in the fluidized bed, increasing the ductility of the alloy and shortening the time needed for solution heat treating.

A typical fluidized bed system consists of a solution bed, water quench tank and aging bed. A walking beam conveys the parts through the bed, and a sentry robot inserts and removes castings from the beds. The fluidized bed approach allows the metalcaster to adhere more closely to a work-in-progress flow, de-clog congestion in the heat treating department, reduce material handling and avoid moving castings from production to temporary storage and back into the production line.


By using the one-layer racking method, rather than several layers in a batch as typical with convection furnaces, all parts experience parallel heating and cooling rates. Because every individual casting is exposed to heat at the same rate, the shadowing effects commonly encountered with convection furnaces are not seen. This leads to high quality parts with little or no reworking or scrapping.

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Title Annotation:New Product
Publication:Modern Casting
Date:Feb 1, 2008
Previous Article:CMI course schedule.
Next Article:Multi-stage vacuum diecasting broadens process's applications.

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