| 摘要 |
PURPOSE:To attain firm engagement of the main body of a metal piston and a piston head made of a ceramics material and to prevent concentration of stress of the same, by threading the piston head into the main body of the piston by means ofa round thread which is designed such that the ratio of the height to the pitch of the thread stands within a particular range. CONSTITUTION:A female screw 3 of round thread is formed in the internal surface of a recess 2 that is formed at the top of the main body 1 of a metal piston, and a piston head 4 is fitted to the top of the main body 1 by driving a male screw 6 of round thread formed on the outer surface of a piston head 4 made of a ceramics material into said recess 2. Here, relative rotation between the piston head 4 and the main body 1 is prevented by a baffle pin 6 which is welded at its top. In such an arrangement, the round thread formed on the piston head 4 and the main body 1 is so designed that the ratio of the height ot the pitch of the thread ridges lies within the range of 1/5-1/1, or preferably 1/4-1/2. By employing such an arrangement, it is enabled to attain firm engage ment between the main body 1 and the piston head 4 of a piston and to prevent concentration of stress of the same.
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