Bolt

Abstract: The present invention relates to a bolt (101) having a threaded shank portion (103) wherein a notch (103B) slanting toward the end of said threaded shank portion at an angle in the range between 15° to 80° for the axis of said threaded shank portion is formed at the beginning of the complete thread part to expand the width (W) of the entrance (103E) of the thread part of said thread shank portion is provided in the invention. The problems of seizure, and thread damage are effectively solved.

Description: The present invention relates to a bolt wherein oblique screwing of said bolt into a nut is prevented. More particularly, the present invention relates to a bolt having a threaded shank portion wherein a notch slanting toward the end of said threaded shank portion at an angle in the range between 60° to 80° for the axis of said threaded shank portion is formed at the beginning of the complete thread part of said thread shank portion. It has been known that encroaching, seizure, or racing between a bolt and a nut is caused by the oblique screwing of the bolt into the nut. Hitherto a bolt having a guide boss (204) has been provided as shown in Fig 5. Said bolt (201) consists of a head portion (202), a shank portion (203) on which a thread part (203A) is formed (a threaded shank portion) and the guide boss (204) extending from the end of said shank portion (203). The outer diameter Db of said guide boss (204) is set to be a little smaller than the inner diameter Dn of a nut (105) into which said bolt (201) is screwed. By employing said bolt (201) having the guide boss (204), the oblique screwing of said bolt (201) into said nut (105) is possibly prevented because when said bolt (201) is screwed into said nut (105), said guide boss (204) whose outer diameter Db is a little smaller than the inner diameter Dn of said nut (105) is first inserted into a threaded hole (105A) of said nut (105). Nevertheless in said traditional bolt (201), a little play exists between said guide boss (204) of said bolt (201) and the inside (105C) of said nut (105) such that oblique screwing can not be prevented completely. Therefore, the problems of encroaching, seizure, and racing are still not solved. EP-B-0 625 644 describes a positive thread start fastener. The bolt start end is chamfered at an ocute back angle of about 45°. Accordingly, an object of the present invention is to solve effectively the problems of encroaching, seizure, and racing. This object is achieved with the features of the claims. Said object can be attained by employing a bolt having a threaded shank portion wherein a notch slanting toward the end of said threaded shank portion at an angle in the range between 60° and 80° for the axis of said threaded shank portion is formed at the beginning of the complete thread part of said thread shank portion. Preferably said thread rises from the beginning of the thread part attaining to the height of the complete thread within the range from the beginning of the thread part to a position revolving at 50° from the beginning of the thread part. Further, preferably said expanded width of the entrance of the thread part is set to be larger than the pitch of the thread part and smaller than 1.5 times of the pitch of the thread part. More preferably, a guide boss extends from the end of said shank portion. More preferably, a spiral guide groove is formed on said guide boss, said spiral guide groove continuing to the root of the thread part of said threaded shank portion and being deeper than the root of the thread part except the boss end parts of said spiral guide groove. Since said notch (103B) slanting to the end of said threaded shank portion is formed at the beginning of the complete thread part of the thread part (103A) to expand the width W of the entrance (103E) of the thread part, the entrance (103E) of the thread having an expanded width W is smoothly guided by the thread (105B) of said nut (105), and oblique screwing of said bolt (101) is corrected by said notch (103B) when said bolt (101) is obliquely screwed into the threaded hole (105A) of said nut (105). In case a guide boss (104) extends from the end of said shank' portion (103) of said bolt (101), when said bolt (101) is obliquely screwed into the threaded hole (105A) of said nut (105), said oblique screwing is previously corrected by said guide boss (104) such that the correction of said oblique screwing by said entrance having an expanded width W of the thread part (103A) of said bolt (101), and said notch (103B) is more smoothly performed. Further, in case where a spiral guide groove (104A) is formed on said guide boss (104), said spiral guide groove (104A) is screwed into the thread (105B) of said nut (105) and guided such that the previous correction of oblique screwing of said bolt (101) is more smoothly performed. Fig. 1 is a side view of a bolt of the present invention. Fig. 2 is an enlarged side view of the end part of a bolt. Fig. 3 is a sectional view taken along line A-A of Fig. 2. Fig. 4 is an end view when a bolt of the present invention is screwed into a nut. Fig. 5 is a side view of a traditional bolt having a guide boss. In the drawings, (101) bolt (103) shank portion (threaded shank portion) (103A) thread part (103B) notch (103C) root of the thread (103D) thread (103E) entrance (103F) incomplete thread part (104) guide boss (104A) spiral guide groove AX axis P pitch W expanded width  angle α range Referring now to Fig 1, a bolt (101) consists of a head portion (102), a shank portion (103) on which a thread part (103A) is formed (a threaded shank portion), and a guide boss (104) extending from the end of said threaded shank portion (103). The thread part (103A) consists of a thread (103D) and a root of the thread (103C). As shown in Fig 2, a notch (103B) is formed at the beginning of the complete thread part of the thread part (103A) by notching, plastic working or the like. Said notch (103B) slants toward the end of said threaded shank portion (103) at an angle () in the range between 15° to 80° (15°≤≤80°) for the axis AX of said threaded shank portion (103) to expand the width W of the entrance (103E) to 1.5 times of the pitch P of the thread part (103A) of said shank portion (103) (W = 1.5P). Said width W of the entrance (103E) may be set to be larger than P or smaller than 1.5P (P<W≤1.5P). As above described, an incomplete thread part (103F) the height of which gradually increases from 0 to the height of the complete thread (103D) is formed at the beginning of the thread part (103A) by notching the beginning of the thread part (103A). As shown Fig 3, said incomplete thread part (103F) rises from the beginning of the thread part (103A) to attain to the height of the complete thread (103D) within a range (α) from the beginning of the thread part (103A) to a position revolving at 50° from the beginning of the thread part (103A) (α≤50°), and α may preferably be 15°. Further the external diameter Db of said guide boss (104) is set to be a little smaller than the internal diameter Dn of a nut (105) into which said bolt (101) is screwed. Further, the external diameter Db of said guide boss (104) is preferably set to be a little larger than the root diameter Dv of said thread part (103A). In this embodiment, the circumferential edge at the end of said guide boss (104) is chamfered. A spiral guide groove (104A) is formed on said guide boss (104) of said bolt (101). Said spiral guide groove (104A) continues to the root (103C) of the thread part (103A) and the pitch P of said spiral guide groove (104A) is set to be equal to the pitch of the thread part (103A). Furthermore said guide groove (104A) is set to be deeper than the root of the thread part (103A) except the boss end parts of said guide groove (104A), and the depth of said guide groove (104A) is preferably 10% to 70% of the height of the thread (105B) of said nut (105) into which said bolt (101) is screwed. Supposing that the root diameter of the thread part (103A) is Dv, the root diameter of said guide groove (104A) of said guide boss (104) is Dg, and the height of the thread (105B) of said nut (105) be Dx, 0.1Dx < (Dv―Dg)/2 < 0.7Dx. In a case where said bolt (101) is screwed into the threaded hole (105A) of said nut (105), first said guide boss (104) is inserted into the threaded hole (105A) of said nut (105). Since the external diameter Db of said guide boss (104) is set to be a little smaller than the internal diameter Dn of said nut (105), a big slant of said bolt (101) for the threaded hole (105A) of said nut (105) is previously corrected by guiding said guide boss (104) into the threaded hole (105A) of said nut (105). As a play exists between said guide boss (104) and the threaded hole (105A) of said nut (105), said bolt (101) is occasionally a little obliquely inserted into the threaded hole (105A) of said nut (105). Nevertheless since the guide groove (104A) is formed on said guide boss (104) of said bolt (101), the guide groove (104A) of said guide boss (104) is screwed into the thread (105B) of said nut (105) and said bolt (101) is moved into the threaded hole (105A) of said nut (105) being guided by said screwing between the guide groove (104A) of said guide boss (104) of said bolt (101) and the thread (105B) of said nut (105), and as a result said nut (105) moves toward the head portion (102) of said bolt (101). When the end E of said guide groove (104A) of said guide boss (104) reaches the beginning of the thread (105B) of said nut (105) the thread part (103A) of said bolt (101) begins to be screwed into the thread (105B) of said nut (105). In this case, the thread (105B) of said nut (105) is smoothly introduced into the root (103C) of the thread part (103A) and final correction of the slant of said bolt (101) is performed by said notch (103B) of said incomplete thread part (103F). As above described, the slant of said bolt (101) is corrected and the thread (103D) of said bolt (101) and the thread (105B) of said nut (105) engage normally with each other to prevent encroaching, seizure, or racing caused by oblique screwing of said bolt. Further in a case where the range (α) of said incomplete thread part (103F), from the beginning of thread part (103A) to the position attaining the height of the complete thread (103D), is within 50° (α≤50°), and is preferably 15°, said correction of the slant of said bolt (101) is more smoothly performed and the encroaching caused by the oblique screwing of said bolt (101) is more effectively prevented. Further in a case where said notch (103B) slants toward the end of said shank portion preferably at 60° (=60°), the thread (105B) of said nut (105) is smoothly introduced into the thread (103D) of said bolt (101). It is to be understood that the invention is not limited to the embodiment specifically set herein above, but may be carried out in other ways. For instance, said guide boss (104) is not necessary for the invention and the guide groove (104A) of said guide boss (104) is also not necessary for the invention. Further the chamfering of the circumferential edge at the end of said guide boss (104) is also not necessary for the invention and the shape of the head portion (102) of said bolt (101) is not limited to a hexagon. Further a head portion may have a flange and further said bolt may be a stud bolt. In the present invention, encroaching, seizure, and racing between the bolt and the nut are effectively prevented.

Claims: A bolt having a threaded shank portion (103), characterized in that a notch (103B) slanting toward the end of said threaded shank portion (103) at an angle in the range between 60° to 80° for the axis of said threaded shank portion (103) is formed at the beginning of the complete thread part (103A) of said thread shank portion (103). A bolt in accordance with claim 1, wherein said thread rises from the beginning of the thread part (103A) attaining to the height of the complete thread within the range from the beginning of the thread part to a position revolving at 50° from the beginning of the thread part (103A). A bolt in accordance with claim 1 or 2, wherein said expanded width of the entrance of the thread part (103A) is set to be larger than the pitch of the thread part and smaller than 1.5 times of the pitch of the thread part. A bolt in accordance with claims 1-3 wherein a guide boss (104) is extends from the end of said shank portion. A bolt in accordance with claim 4, wherein a spiral guide groove (104A) is formed on said guide boss, said spiral guide groove (104A) continuing to the root of the thread part of said threaded shank portion and being deeper than the root of the thread part excepting the boss end parts of said spiral guide groove.

Inventors: KATO TAKASHI, KATO, TAKASHI
Applicants: MEIDOH CO LTD, MEIDOH CO., LTD.
Application year: 2001
Main classification: F16B33
IPC codes: F16B35, F16B33