A briquetting technique which overcomes one of the major problems of pellet preparation, that is, seizure and galling of the die assembly, has been developed for the preparation of powder samples. A new product—"Spec-Cap" is utilized in the briquetting technique. The Spec-Cap,
shown in Fig. 1, is a 30-mm diameter shell with a 5/16-in. skirt of 0.0125-in. aluminum and an exterior coating of lacquer. In preparing the pellet, the cap is filled with powder and then centered in a 1 1/4-in. diameter briquetting mold assembly. As the diameter of the Spec-Cap (30 mm) is
less than the diameter of the mold (31.8 mm), the metal, upon pressing, forms a slight roll-over or lip on the pressed face. The powder is, therefore, totally contained within the cap and not allowed to extrude between the walls of the die. The height of the cap is reduced in size depending
upon the compactability of the powder. The coating of lacquer on the exterior acts as an antifriction surface and prevents die seizure. Unpainted caps require application of lubricant to either the cap or die. The thin-gage aluminum allows maximum energy for compacting the sample rather than
compressing the metal. The pellets have uniform diameter. Spec-Caps of 0.009- and 0.0125-in. aluminum were tested, and the latter was selected for use. Although the roll-over or lip is not as large with the thicker aluminum, the pellets exhibit greater rigidity. Figure 2 shows a sample of
bauxite prepared with the Spec-Cap. Sample weight for this material averages 4.9 g.
Alcoa Research Laboratories, New Kensington, Pennsylvania
Publication date: July 1, 1966
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