| 摘要 |
PROBLEM TO BE SOLVED: To prevent deformations due to contraction of a bottom wall and surrounding walls in a casing at contraction, after forming the casing by preparing a recessed part surrounding a drive shaft inserting hole separated from a sidewall between the driving shaft inserting hole in the bottom wall and the sidewall. SOLUTION: Ring-like recessed parts 23 concentric with drive shaft inserting holes 22 are provided in a lower casing 2, and inner and outer edge parts of the recessed parts 23 are combined with surrounding thick-wall parts via inclined surfaces 27, in order to smooth the flow of resin at the time of forming. The recessed part 23 are formed into walls thiner than the other part, the recessed parts 23 are completely solidified when corner parts where a bottom wall 24 and sidewalls 25 meet are solidified, and tensile force due to forming and contraction is not transmitted to the side of the drive shaft inserting holes 22. Therefore, camber with not be generated in the lower casing 2, and thereby the casing having superior flatness is obtained. When fluidity of resin at the time of forming taken into consideration, since sharp variations of plate thickness is not preferable, a boundary with the recessed part 23 be preferably formed in the inclined surface 27 or the bottom part of the recessed part be preferably formed into a round shape.
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