PURPOSE: To obtain a dead thin type waterproof timepiece by brazing a core consisting of a usual stainless steel material to the inside surface of a back cover consisting of a hard metallic material whose modulus of longitudinal elasticity is above a prescribed value, and generating a recessed warp of the inside on the back cover.
CONSTITUTION: A back cover 12 consists of a hard alloy whose modulus of longitudinal elasticity is ≥25,000kg/mm2 such as a Co alloy, etc., and a reinforcement ring 13 consisting of a usual stainless steel material for forming a part of an O-ring box 14 is stuck to its inside surface by a brazing method, etc. When sticking it, because of a difference of a coefficient of linear expansion of both material qualities, the back cover 12 becomes a recessed warp b' against the reinforcement ring 13. Therefore, the maximum deflection amount of the center part of the back cover 12, which is generated by external force can be absorbed by the recessed warp b' of the back cover 12 without making large a gap (b) between a module 7 and the back cover 12. In this way, a dead thin type waterproof timepiece is obtained.
ENOMOTO TADAO
ITOU NOBUO
