| 摘要 |
PROBLEM TO BE SOLVED: To improve the flatness of a seat surface without cutting and polishing and prevent deterioration of flatness in a manufacturing process by forming a piston by a sintered body, and connecting the peripheral edge of a valve seat surface to the reference surface of a piston side surface by a gentle slope. SOLUTION: A die is filled with powder 64, and an upper die 71 is lowered to perform compression molding, thereby forming a surface 74 as a valve seat surface, a surface 75 as a reference surface and a surface 76 as a gentle slope. The surfaces 74, 75 are compacted by compressive force in the arrows A, B of the upper die 71, the compressive force in the arrow C vertical to the gentle slope 76 works, and drifting of powder 64 near the surface 76 due to the friction between the upper die 71 and the poweder 64 is decreased, whereby the powder density near the corner part where the surfaces 74, 76 intersect can be kept to a designated value or more. The compressed powder after compression is hardened to form a sintered body 77. The valve seat surface 81 provided in the periphery of the gentle slope 78 is improved in flatness by equalizing the powder density. Thus, the disc valve 82 can be made adhere to the seat surface 81, and polishing for the seat surface 81 is not needed to shorten the machining time and improve productivity.
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