| 摘要 |
PURPOSE:To shorten the length of a plunger guiding part of a guide and to improve reliability by forming the joint part of the guide and spring housing by butt welding. CONSTITUTION:The upper part of a drive tube is supported by fitting the front end thereof into the notched part of an upper grid plate to position the tube. The plunger 1 at the top end is, therefore, constructed to be elongated and contracted vertically by using a spring 2 in order to fit the drive type into the upper grid plate. Since the plunger 1 moves to elongate and retreat, an auxiliary plunger part 7 is provided to the guide 3. This auxiliary part 7 is formed to the length shorter than a spacing so as not to comply with the spacing condition possessed by the potential to be generated by the stress corrosion cracking (crevice SCC) generated in the spacing part. The inside diameter of the guide 3 and the inside diameter at the top end of the spring housing 4 are set larger than the diameter in the middle stage of the plunger 1 to take the spacing so as not to comply with the spacing conditions of the crevice SCC. On the other hand, the joint part of the guide 3 and the housing 4 is formed by butt welding to eliminate the spacing structure. The reliability is thus enhanced.
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