| 摘要 |
PURPOSE:To enable to substantially reduce the necessary attracting force of a permanent magnet by a method wherein the means to be attracted is engagingly contacted to an attracting means when the engagement of a cover and the main body is released. CONSTITUTION:The titled engaging means consists of an attracting means A and the means to be attracted B. The ferromagnetic protrusion 4 projectingly formed on the ferromagnetic plate 31, provided on the poleface 1a of the permanent magnet 1 whereon the attracting means A is formed, and the ferromagnetic protrusion 12 protrudingly provided on the ferromagnetic plate 11, whereon the means B to be attracted is formed, are constituted in such a manner that they are detachably attracted in the hole 1e provided in the center of the magnet 1. When a cover 21 is closed, the contacted surface of the flange 12a of the means B to be attracted is attracted to the center part of the contacted surface of the protrusion 4, and the cover 21 and the main body 22 are engaged by the high degree of magnetic attracting force F which works between the flange 12a and the protrusion 4. Besides, under the above- mentioned condition, the ferromagnetic plate 11 is brought to come in contact with the case 2, and the weak attracting force (f) working between the flange 12a and the pole-face 1b is brought in the state of balance.
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