| 摘要 |
PURPOSE:To reduce the manufacturing cost by filling a hole formed at the center of a heat resistant steel billet with a core material such as graphite, forming a valve stem and a valve head by hot extrusion and press upsetting respectively, and closing the hole by welding. CONSTITUTION:A hole 3 is formed at the center of a heat resistant steel billet 4 by warm or hot backward extrusion and the hole 3 is filled with a core material 7 such as graphite. The blank 4 is hot extruded using a die and punch to form a valve stem 10 at the opposite side of the hole 3. In that time, the graphite as the core material enters the center of the stem 10 uniformly. A valve head 14 is formed by hot press upsetting using a die and punch, a part of the core material 7 is removed through the opening of the hole 3, and the hole 3 is closed with a heat resistant steel plug 15 by welding. In this method, the complicated boring process is eliminated, so that the manufacturing cost is reduced remarkably.
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