| 摘要 |
PROBLEM TO BE SOLVED: To obtain a sphere which can substitute for a high-sepcific-gravity sphere made of lead, a hard metal, or the like by mixing a tungsten powder mainly comprising primary particles with a thermoplastic resin or elastomer in a specified ratio and injection molding the resultant mixture so that the specific gravity of the resultant molded item is a specified value. SOLUTION: A mixture mainly comprising 45-75 vol.% tungsten powder which is obtained by cracking agglomerates occurring in the production process and mainly comprises primary particles and 25-55 vol.% thermoplastic resin or elastomer is molded so that a molded item with a specific gravity of 9-15 is obtained. The use of a biodegradable resin as the thermoplastic resin is environmentally preferable since it gives a sphere which decomposes even when left behind as a bullet or a fishing sinker in a mountain or in the sea. The surface of the sphere may be coated with e.g. a fluororesin, graphite, or molybdenum disulfide to improve the heat resistance or slipperiness. Thus, the spheres can be mass-produced at a high precision.
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