Patent ID: 7762752
Filing Date: 2010-07-27
Classification: B21H,F16B

Abstract:
1. A thread rolling die used for the manufacture of a bolt for screwing into a nut in a screwing-in revolution direction, said bolt including a shank portion extending along an axis and having a free end, said shank portion being formed with a thread having a bottom, said thread having an entrance which is adjacent said free end and being made discontinuous by notching crosswisely said thread as deep as the bottom, said thread rolling die having a thread forming part to form said thread wherein said thread forming part has forming sections of a plural number of substantially triangular notched faces, each of said substantially triangular notched faces being a leading edge surface of a portion of the discontinuous thread and having a base extending at a constant radial distance from said axis, and said forming sections include a forming section to form a substantially triangular entrance notched face at the entrance of the thread having a base that, as viewed in projection in a plane containing said axis, extends toward said free end at an angle α to said axis ranging between +15° and +80°, and at least one forming section to form at least one substantially triangular inner notched face, each said substantially triangular inner notched face having a base that, as viewed in projection in a plane containing said axis, extends toward said free end at an angle θ to said axis ranging between −15° and −80°, wherein + and − respectively designate directions toward and away from the screwing-in revolution direction with respect to said axis, and wherein, when said bolt is screwed into a nut, said entrance notched face corrects oblique screwing.