JP2000291620A - Bolt and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve engagement between a bolt and a nut at the initial engagement time. SOLUTION: Either a first taper-like chamfered part (7) having a chamfering angle equal to the flank angle of an internal thread part is formed at the end part of an opening on the bolt-inserting side of a nut or a second taper-like chamfered part having an angle larger than the flank angle is formed outside the first chamfered part (7). Moreover, a bolt-side chamfered part 22 having an angle equal to the angle of the first chamfered part 7 on the nut side is formed at the tip part of the bolt. By seating the bolt-side chamfered part 22 on the first chamfered part 7 of the nut, the attitude of the bolt-and-nut can be adjusted so that the axes of the bolt and the nut further coincide with each other. Since the chamfering angles of both first chamfered part 7 of the nut and the chamfered part 22 of the bolt are nearly equal to the flank angle of the internal thread, the length of an incomplete thread part can be shortened, and consequently defective engagement of the bolt-and-nut becomes hard to occur.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nut and a method for manufacturing the nut. Here, the nut is used as a general term for a product (female screw member) in which a female screw is formed mainly at the shaft center.

[0002]

2. Description of the Related Art Conventionally, in a nut provided with a tapered bolt guide on the bolt insertion side (on the side where the nut starts screwing), the tapered portion is formed uniformly at the same angle up to the female screw root diameter. Further, the angle of the tapered portion is not considered in correlation with the angle of the thread, and is larger than the angle of the thread (flank angle).

[0003]

In the conventional nut, even if there is a bolt guide in the tapered portion, when the bolt and the nut are assembled, the axis of the nut and the axis of the bolt are displaced.
It is not always easy to engage due to inclination, and if you try to forcibly screw in that state, the incomplete thread of the nut and that of the bolt may be engaged, and the bolt and nut It is necessary to carefully and concentrically engage with.

[0004]

The nut according to the present invention has a tapered inner peripheral surface having an angle substantially equal to the flank angle of the female screw portion of the nut on the inner peripheral side of the opening at the screwing start side of the nut. Is formed as a chamfer, and the chamfer is left as the base point (starting end or end) while leaving the chamfering
A female screw portion is formed.

[0005] A female screw portion is formed in a helical shape with a tapered inner peripheral surface (chamfered portion) having an angle substantially equal to the flank angle of the female screw portion. At least a part of the tapered inner peripheral surface is formed by a nut. It remains on the screwing start end side, and the end of the bolt (general term for the male screw member) sits here,
Bolts are likely to be positioned concentrically with nuts. In particular,
If the end of the bolt has a tapered outer peripheral surface formed at an angle substantially equal to the tapered inner peripheral surface, the
Although it is easy to increase the concentricity of the nut, even for general bolts, the flank face of the male screw part at the tip of the bolt is easy to engage with the chamfered part on the nut side at an angle almost corresponding to it, so concentric A simple positioning function is exhibited. Further, since the internal thread portion is formed with the tapered inner peripheral surface (chamfered portion) having an angle substantially equal to the flank angle of the internal thread portion as a base point (start end or end), the length of the incomplete thread portion is reduced as compared with the conventional case. For example, it can be shortened to about 1/2 to 1/3. Accordingly, even if the nut and the bolt are inclined, biting is less likely to occur, which is effective in reducing poor meshing.

In a further preferred nut of the present invention, a tapered inner peripheral surface having an angle substantially equal to the flank angle of the female screw portion of the nut is formed as a first chamfered portion on the inner peripheral side of the opening at the screwing start side of the nut. Then, a female screw portion is formed with the first chamfered portion as a base point (a start end or an end) while leaving the first chamfered portion, and the female screw portion is formed outside the first chamfered portion so as to be connected to the outer peripheral edge thereof. A tapered inner peripheral surface larger than the flank angle of the female screw portion is formed as a second chamfered portion, and the female screw portion is not formed in the second chamfered portion.

[0007] In this nut, the tip of the bolt is guided toward the nut axis relative to the nut by the outer tapered inner peripheral surface (the second chamfered portion having an angle larger than the flank angle of the female screw portion). Furthermore, the inner tapered inner peripheral surface (the first chamfered portion having an angle substantially equal to the flank angle of the female screw portion) corrects the nuts and the bolts so that the inclined state is concentrically close. Therefore, the initial screwing of the bolt and the nut can be smoothly performed by the synergistic (double) guide or positioning effect of the second and first chamfers.

The outer diameter of the chamfered portion or the first chamfered portion is desirably substantially equal to the root diameter of the female screw portion. By doing so, the outer diameter of the bolt substantially corresponds to the outer diameter of the bolt, and the tip of the bolt is easily seated on the chamfered portion or the first chamfered portion.

The above-mentioned nut can be manufactured, for example, as follows. That is, a tapered inner peripheral surface having an angle substantially equal to the flank angle of the female screw portion of the nut is formed as a chamfer on the inner peripheral side of the opening of the pilot hole for forming the female screw portion on the screwing start side in advance. And a female screw portion including the chamfered portion is formed.

[0010] Further, a more desirable manufacturing method is such that a prepared hole for forming a female screw portion is provided with a tapered inner circumferential surface having an angle substantially equal to the flank angle of the female screw portion of the nut in advance on the inner circumferential side of the opening at the screwing start side. The surface is defined as a first chamfered portion, and the tapered inner peripheral surface having an angle larger than the flank angle of the female screw portion is defined as a second chamfered portion outside the first chamfered portion so as to connect to the outer peripheral edge thereof. Each of them is formed, and the female thread is not formed in the second chamfer, and the first chamfer is formed.
The female screw portion is formed so that the chamfered portion becomes a base point of the female screw.

According to such a manufacturing method, it is possible to easily obtain a nut having a bolt guide or a positioning function capable of reducing or eliminating the misalignment or the inclined state when the nut and the bolt are screwed as described above.

In the above description, chamfers having angles corresponding to each other are provided at the opening on the bolt insertion side of the nut and the tip of the bolt, and these are engaged with each other. Even if the first chamfered portion as described above is formed and the bolt inserted therein is the same as the conventional one, a certain posture adjustment function is achieved and the bolt is hard to bite. Conversely, a bolt chamfer is formed at the tip of the bolt equal to the flank angle of the thread,
Even if this is screwed into a nut similar to the conventional one, a certain posture adjusting function and a certain bite suppressing function are achieved.

[0013]

Embodiments of the present invention will be described below with reference to embodiments shown in the drawings. The nut 1 shown in FIG. 1 is in the form of a cap nut, for example. Of course, a simple nut other than the cap nut may be used. The nut 1 is provided with a shaft-shaped main body 2, a female screw portion 3 is formed concentrically so as to penetrate therethrough, and a cover 4 is integrated with the main body 2 by welding or the like so as to cover (close) an opening on the outlet side thereof. Have been. Body 2
A flange 5 is formed at an intermediate portion of the body 2, and a washer 6 is mounted on the outer periphery of the main body 2 so as to be adjacent to the flange 5. The washer 6 is adjacent to the flange 5 on the inlet side of the female screw portion 3, and is prevented from coming off the main body 2 by serrations (not shown) formed on the outer periphery of the main body 2.

For example, a bolt 20 is screwed into the nut 1. The nut 1 is screwed into an end A of the nut 1 on the bolt insertion side, in other words, an opening A on the screwing start side of the female screw portion (screw hole) 3 of the nut 1. As shown in FIG. 2B, a first chamfered portion 7 formed of a tapered inner peripheral surface and a second chamfered portion 8 formed of a tapered inner peripheral surface having a different angle from the first chamfered portion 7 are formed. ing. Here, φD indicates a female screw root diameter (a screw outer diameter based on a bolt to be screwed), and φd indicates a female screw thread diameter (a screw inner diameter). The angle θ1 formed between (the surface of) the first chamfered portion 7 in the cross section including the axis of the nut 1 and a straight line or a plane perpendicular to the axis of the nut 1 is
The flank angle of the internal thread (i.e., the angle (θf) between each flank measured in a cross section including the axis of the screw and a straight line perpendicular to the axis of the screw) is substantially equalized.

For example, in a nut having a female thread having a flank angle of 30 °, the angle θ 1 of the first chamfered portion 7 is about 30 °.
° degree. Generally speaking, assuming that the flank angle of the female thread portion 3 of the nut 1 is θf, the angle θ1 of the first chamfered portion 7 is approximately ± 20%, more preferably ± 10% of θf.
%, In other words, θ1 can be set to about 0.8 to 1.2 θf, more preferably about 0.9 to 1.1 θf.

The first chamfered portion 7 has a taper angle of an inner peripheral surface of the cone (an angle between two generatrix lines of the cone in an axial cross section of the screw) α1 in addition to a plane perpendicular to the screw axis as a reference. Can also be represented by In this case, the taper angle α1 of the first chamfered portion 7 is, for example, about 120 ° for a nut having a flank angle of 30 °. If the length (depth) of the first chamfered portion 7 in the screw axis direction of the nut 1 is L, L is, for example, １ ／ of the female screw portion 3.
It can be about the pitch. In addition to the above L,
For example, for 1/5 to 2 pitches of the female screw portion 3, preferably 1
It can be set appropriately within the range of / 3 to 1 pitch.

The inner peripheral edge of the first chamfered portion 7 is
The second chamfered portion 8 is located on the outer peripheral side of the first chamfered portion 7 following the outer peripheral edge of the first chamfered portion 7. The angle θ2 between the second chamfered portion 8 and a plane or a straight line perpendicular to the screw axis is larger than the angle θ1 of the first chamfered portion 7, and for example, the angle θ1 of the first chamfered portion 7 is 30.
If it is about °, the angle θ2 of the second chamfered portion 8 can be set to about 45 °. In this case, when the second chamfered portion 8 is viewed at the taper angle α2, it is about 90 °. The outer peripheral edge of the second chamfered portion 8 continues to an annular end surface 9 on the bolt insertion side of the nut 1, and a tapered outer peripheral surface is formed on the outer peripheral side of the end surface 9 as an outer peripheral chamfered portion 10 at the nut end. Have been. For example, when the nut 1 is used as a hub nut for fixing a wheel of an automobile to a hub, the outer chamfer 10 facilitates the insertion of the nut 1 into a nut insertion hole formed in a wheel (not shown).

The relationship between the angles θ 1 and θ 2 of the first and second chamfers 7 and 8 (may be replaced by the relationship with the taper angles α 1 and α 2) is θ 2 / θ 1 (or α 1 / α 2). For example, about 1.1 to 2.5, preferably 1.2 to 2.2.
About 0 is good. The angle θ2 of the second chamfered portion 8 is set to 90 ° or less. Considering that the second chamfered portion 8 functions as a bolt guide for guiding the bolt tip to the screw axis side, the angle θ2 is 90 °. Less than °.

If the first chamfered portion 7 and the second chamfered portion 8 are projected onto a plane perpendicular to the screw axis of the nut, the widths of the chamfered portions 7 and 8 are defined as w1 and w2, respectively. The width dimension w1 of the first chamfered portion 7 is
Is approximately equal to the thread height. In other words,
The outer diameter of the first chamfer 7 is substantially equal to the root diameter (φD) of the internal thread of the nut 1, and the width w 2 of the second chamfer 8 is larger than the width w 1 of the first chamfer 7. can do. Alternatively, w1 and w2 can be the same. When the angle θ2 of the second chamfered portion 8 is considerably large, w1 may be larger than w2, but in a preferred embodiment, w1 / w2 is 0.1 to 0.9,
Especially, it can be set to about 0.2 to 0.5.

Conventionally, as shown in FIG. 2 (a), a nut 1 'is provided with a single chamfered portion 8' at the opening on the bolt insertion side of the female screw portion 3 '. The angle θ ′ of the portion 8 ′ is larger than the flank angle of the nut 1 ′, for example, if the flank angle of the nut 1 ′ is 30 °, for example, θ ′ = 45 °. In addition, if the chamfered portion 8 'is represented by a taper angle, it is 90 °. On the other hand, in a preferred embodiment of the present invention, the first chamfered portion 7 in which θ1 is approximately equal to the flank angle is approximately 30 °, and the second chamfered portion 8 in which θ2 is approximately 45 ° larger than the flank angle. It has a double (two-stage) chamfer (in terms of taper angle, about 120 ° and 90 °).

FIG. 3A shows an example of a conventional nut 1 'in which a single threaded portion 3' is formed on a single chamfered portion 8 'having an angle larger than the flank angle. Is the base point of the internal thread 3 '(starting point of incomplete thread) R1
From the end to the end R2 of the incomplete thread is about 270 °,
The length of the incomplete thread is long. In contrast, FIG.
In the preferred embodiment of the present invention shown in (b), an imperfect thread portion is formed with one location of the first chamfered portion 7 substantially equal to the flank angle of the female thread portion 3 as the starting end S1, and the terminal end S2 thereof.
, The length of the incomplete thread is less than half the length of the conventional nut 1 ', and can be suppressed to about 1/3 of the entire circumference of the screw hole.

Further, as shown in FIG.
The first chamfer 7 having an angle substantially equal to the flank angle of
As represented by a multipoint, regardless of the formation of the internal thread, most of the thread remains at the opening end of the nut 1 on the screwing start side (opening end on the bolt insertion side). In other words, from the start end S1 to the end S2 of the imperfect thread portion, the shape is such that it is partially helically cut off, but in the other range, the first chamfered portion 7 exists as a tapered inner peripheral surface. Then, if a part which is partially missing is added, it appears in the entire circumference of the nut 1 or in a range close to the entire circumference.

FIG. 4 shows part A of FIG. 2 in a three-dimensional section, and the incompletely threaded portion of the female screw portion 3 is conceptually represented by an imaginary line. Then, A 'of the conventional nut 1' of FIG.
In the structure of the part, as shown in FIG.
When the screw is rolled from the chamfered portion 8 ′, a protruding portion 13 (which can be said to be an incomplete screw portion) protruded toward the opening side is remarkably generated, and the protruding portion 13 becomes an obstacle in the screw axis direction when a bolt is inserted. Cheap. That is, when the nut and the bolt are concentrically approached in the axial direction, the outer peripheral edge of the tip of the bolt easily interferes with the raised portion 13. On the other hand, in the present invention, as shown in FIG.
The thread rolling starts from the first chamfered portion 7 substantially equal to the flank angle of the screw, and as a result, the flank angle of the rolling die 12 and the angle of the first chamfered portion 7 are substantially equal. Such a large bulge 13 is unlikely to occur. Therefore, the relative insertion of the bolt into the nut can be performed smoothly.

If the first and second chamfers 7 and 8 of the nut 1 as described above are first and second chamfers, the tip of the male thread 21 of the bolt 20 in FIG. In addition, a tapered outer peripheral surface can be formed as a bolt side chamfered portion (hereinafter, also simply referred to as a chamfered portion) 22. The bolt 20 has a head 23, but may be a bolt without a head (for example, a stud bolt). As schematically shown in FIG. 6, the chamfered portion 22 formed as a tapered outer peripheral surface at the tip end of the bolt 20 has an angle θB between a straight line or a plane perpendicular to the axis of the bolt and the screw 20 of the bolt 20. When the flank angle of the mountain is θfB, the flank angle is approximately equal to θfB. For example, if the flank angle θfB is 30 °, the angle θB of the bolt chamfer 22 is approximately 30 °.
Is set to

More generally, the bolt chamfer 2
2 is the flank angle θfB of the male screw part 21.
(This can also be regarded as the flank angle θf of the female screw portion 3 of the nut 1 on the other side to which the bolt is screwed.)
0%, more preferably about ± 10%, in other words, θB
Is from 0.8 to 1.2 θfB (or θf), more preferably, from 0.8 to 1.2θfB (or θf).
It can be set to about 9 to 1.1 θfB (or θf). Further, the outer peripheral edge of the bolt chamfer 22 is connected to the threaded cylinder of the bolt external thread 21, and the bolt chamfer 2 is formed.
The inner peripheral edge of 2 can be made to coincide with the thread root cylinder of the external thread portion 21 or can be deliberately shifted. That is,
The outer diameter of the screw of the male screw part 21 is φDB, and the inner diameter of the screw is φ.
Assuming dB, the outer diameter of the chamfered portion 22 is equal to the screw outer diameter φDB, and the inner diameter of the chamfered portion 22 may be equal to the screw inner diameter φdB, or may be smaller or larger than the screw inner diameter φdB.

As an example, as shown in FIG. 6, the inner diameter φd1 of the chamfered portion 22 is made smaller by a certain amount than the inner diameter φdB of the screw. In other words, the chamfered portion 22 is made to exceed the inner diameter of the screw, and when the chamfered portion 22 is projected on a plane perpendicular to the axis of the bolt 20, the width dimension WB in the direction perpendicular to the axis becomes the thread height (trough depth) of the male threaded portion 21. Larger) (for example, 1 to
About 20%, more preferably about 2 to 10%). By doing so, even when the bolt 22 and the nut 1 are slightly displaced or inclined at the time of assembling for screwing, the chamfered portion 22 of the bolt 22 can be fixed to the first chamfered portion 7 on the nut side. It is more preferable to perform a corrective action for the misalignment or the inclination of the center.

The length Q of the bolt chamfer 22 in the screw axis direction is preferably one of the threads of the male screw 21.
It is preferable that the inner diameter φd1 of the chamfered portion 22 is larger than the inner diameter φdB of the screw (it is placed between the outer diameter φDB of the screw and the inner diameter φdB of the screw). obtain. Generally, the length dimension Q of the bolt chamfer 22 in the screw axis direction is 1/5 to 1.5, more preferably 1/3 of the thread pitch of the male screw 21.
It can be set to about 1.0. If the bolt chamfered portion 22 is defined by the taper angle, when the flank angle of the male screw portion 21 is 30 °, the taper angle of the bolt chamfered portion 22 is about 120 °.

The external thread 21 of the bolt 20 is formed by rolling or cutting with one of the chamfers 22 as a base point. The angle of the chamfer 22 is substantially equal to the flank angle of the external thread 21. Therefore, the length of the incomplete screw portion can be shorter than that of the conventional one. In other words, if FIG. 3 used for the description of the nut is used with reference to the bolt, the imperfect thread portion of the conventional bolt (FIG. 3A) is about 3% of the entire circumference of the screw.
On the other hand, in the bolt 20 having the bolt chamfer 22 substantially equal to the flank angle, the bolt 20 has about １ ／ (at most １ ／ or less) of the entire circumference of the screw.

Conventionally, as shown in FIGS. 8A and 9A, a bolt 20 'is screwed (inserted) into a nut 1'.
At this time, although there is a chamfered portion 29 at the tip of the bolt 20 ', the angle does not correspond to the chamfered portion 8' of the nut 1 ', and is set irrespective of the flank angle of the male screw portion 21'. If the axes of the bolts and nuts are displaced or the axes of the bolts are inclined at the time of assembly, the action to correct them is not sufficient, and it can be said that the axes of the bolts and nuts can be easily made concentric. hard. Also, bolt 2
Since the incompletely threaded portions of both 0 'and nut 1' are long, biting is likely to occur in the above-mentioned inclined state or the like.

On the other hand, according to the present invention, FIGS.
(B), as shown in FIG. 9 (b), nut 1 and bolt 2
In the process of screwing the nuts 0 (relatively inserting the bolts 20 into the nuts 1), the bolts 2 are attached to the second chamfered portions 8 of the nuts 1.
0, the bolt 20 is guided toward the center of the nut 1, and the bolt chamfer 22 and the nut chamfer 7 which are equal in flank angle are engaged with each other. The situation is such that the axes easily match.
In other words, when the chamfered portion 22 of the bolt 20 is seated on the chamfered portion 7 on the center side of the nut 1, the two chamfered portions 7 and 22 have almost the same angle, so to say, the tapered outer peripheral surface and the tapered outer surface of the angles corresponding to each other. It looks like the peripheral surfaces are fitted together, and in this state, the axes of the bolt 20 and the nut 1 tend to be unambiguously concentric (coaxial).

As a result, the posture of the nut 1 is adjusted so that the axis of the nut 1 and the axis of the bolt 20 are more coincident with each other, and the position adjustment (posture adjustment) of the two is automatically performed. Easy to insert. In addition, since both the bolt 20 and the nut 1 have short incomplete thread portions, even if both of them are inclined, biting is less likely to occur than in the conventional case. From these, bolt 20 and nut 1
At the time of initial screwing, the occurrence of poor meshing is effectively avoided, and a state in which the axes of both threads are more consistent with each other is obtained, and the meshing at the time of initial screwing is performed better than before. Become.

FIG. 10 and FIG.
1 shows a bolt / nut fastening device 24 (combined as a set (unit)) using a nut 1. However, such a bolt and nut fastening device 24
At the angle θB of the bolt chamfer 22 (FIG. 6)
And the angle θ1 of the nut side (first) chamfer 7 (FIG. 2)
It is desirable to make θ1 and θB substantially equal to each other in such a manner that the flank angles of the screws are almost equal to each other. Irrespective of the angle, the angles .theta.1 and .theta.B of the bolt chamfer 22 and the nut chamfer 7 can be made substantially equal (for example, within a range of. +-. 20%, preferably within. +-. 10%). In this case, the angles θ1 and θB may be larger or smaller than the flank angle of the screw, and do not always coincide with the flank angles. Also in this mode, the posture can be controlled so that the axes of the bolt and the nut are aligned.

As shown in FIGS. 12A and 12B, the first chamfered portion 7 on the nut side is not an accurate conical surface (tapered surface), but has, for example, an outwardly convex (bulging) cross section. Or a curved surface 7 ″ having an inwardly convex (bulging) cross section (the nut 1).
6, 17). In this case, the original chamfered portion 7 may be tangent (tangent surface) to those curved surfaces 7 'or 7''. Further, as shown in FIG.
And the second chamfered portion 8 is formed by a smooth curved surface 7 ″ ′ slightly inwardly recessed, and at positions substantially corresponding to the chamfered portions 7 and 8 having different inclinations (chamfered portions). In the part 7, the flank angle is almost equal to that in the chamfered part 8
In this case, it is also possible to form each tapered inner peripheral surface (having a larger inclination than the flank angle) (nut 18). When the nut material is actually formed by forging or the like, the first and second nuts are used.
The boundary between the chamfers 7 and 8 does not always appear sharp, and the boundary may be rounded in a round shape.

The bolt side chamfer 22 is also
Although not shown, the situation is the same. Even if the chamfered portion 22 does not have a strictly conical surface, the chamfered portion 22 is formed by a curved surface slightly bulging outward or slightly concave inside, and is formed into a substantially tapered outer peripheral surface. It may be.

Further, as in the case of the nut 19 shown in FIG. 13, the direction of insertion of the bolt is not uniquely determined, and the bolt can be inserted from either side opening of the nut. First and second chamfered portions 7 and 8 can be provided in the openings on both sides of the portion 3 respectively.

The first chamfer 7 and the second chamfer 7
In addition to the form in which both the chamfered portions 8 are provided to form a step in the middle, as shown in FIG. 14, the second chamfered portion 8 is omitted, and a single nut-sided chamfered portion without a step is provided. 7, the outer peripheral edge of the chamfered portion 7 is
Can be extended to In this case, the nut chamfered portion 7 is made substantially equal to the flank angle of the female screw portion 3 as described above, or almost coincides with the bolt chamfered portion 22 (FIG. 7 and the like) regardless of the flank angle. It will be.

Next, a method for manufacturing the above nut and bolt will be described. FIG. 15A shows that a nut material N1 previously formed by cold forging or the like is accommodated in a cavity 32 of a first mold 31 (lower mold), and this is a second mold 30 (upper mold). To form a nut material N2 as shown in FIG. Here, a portion to be one opening of the prepared hole of the nut material N2 is provided with a recess 33 'by a punch 33, and the other portion to be an opening is the above-mentioned portion A (FIGS. 1, 2 and the like). ). A punch 34 formed integrally with or separately from the second mold 30 is inserted into the portion A, and the first nut chamfer 7 and the second nut chamfer 8 described above are formed. , In advance by cold forging or the like. As shown in the enlarged view of the portion A, a shallow recess 34 'is formed substantially in parallel to the axial direction from the inner peripheral edge of the first chamfered portion 7, and this recess 34' is used as a reference for punching a pilot hole in a subsequent process. Become. Indent 3 on the other side as described above
The 3 'and the recess 34' are formed in the same size and concentrically.

Thereafter, as shown in FIG.
2 and a punching hole 37 at the center part
0 'is punched. N3 'is a punched hazel,
The punching punch 37 is movably disposed in the cylindrical portion 36 of the first die (lower die) 35, and the second die 38 presses the nut blank N2 and receives a punching reaction force. As a result, the first nut chamfered portion 7 (substantially equal to the flank angle of a female screw formed later) is formed in one opening of the prepared hole 40 'of the nut material N3 and the second nut having a larger inclination than the flank angle. The nut material N3 having the chamfered portion 8 is obtained.

Further, as shown in FIGS. 16 (a) and 16 (b), this nut material N3 is fixed to a mold 39, and for example, while the rolling die 40 is being rotated, a screw pilot hole 40 'of the nut material N3 is formed. (FIG. 17C)
(See (d)), the female screw portion 3 is rolled on the inner peripheral surface of the screw lower hole 40 '. At this time, as shown in FIG. 16 (b), when the leading end of the rolling die 40 reaches the opening where the first and second chamfered portions 7 and 8 of the nut material N3 are formed, the rolling die 40 is rotated. Since the flank angle and the angle of the first chamfered portion 7 are substantially equal to each other, the initial rolling is performed in such a manner that the above-mentioned raised portion hardly occurs and the incompletely threaded portion is also short. When the rolling is completed through FIGS. 17 (c) and (d), the female screw portion 3 is formed in the prepared screw hole 40 '. In this state, the second chamfered portion 8 is formed on the portion A as a matter of course. A considerable portion of the first chamfered portion 7 remains in the opening.

In the case where the female thread portion 3 is formed by cutting instead of rolling, there is basically no significant difference in the process except that the rolling die 40 is basically replaced by a thread cutting die. However, in the case of the rolling die 40, since the internal thread portion is formed by the movement of the wall of the screw pilot hole 40 ', the outer diameter of the rolling die 40 is the thread diameter and the thread root diameter of the planned internal thread portion. In the case of the thread cutting die, the outer diameter thereof substantially coincides with the thread root diameter.

FIG. 18 shows an example of steps of a method of manufacturing a bolt. In this example, a bolt material B is provided in a forged cavity forming portion 43 of a first mold 42 (for example, a lower mold).
In the part (part B) that should become the tip of the bolt, see Fig. 6
A cavity 44 having a mold surface corresponding to the chamfered portion 22 is formed so that the bolt side chamfered portion 22 shown in FIGS. In the cavity 44, the bolt material B1 is hit in the axial direction by the punch 50 on the second mold (for example, upper mold) 45 side, so that the bolt material B1 should become the bolt chamfer 22 at the tip end of the bolt material B1. A part is formed. The chamfered portion 22 is made substantially equal to the flank angle of the male screw portion formed later as described above.
The upper die 45 has a cavity forming portion 46 provided with a cavity 47 for further forming a head with respect to the bolt material B1. Then, as shown in FIG. 18B, the second mold 45 moves relatively to the first mold 42, and becomes a bolt material B2 having a head forged by the punch 50 in the cavity 47. .

Further, as shown in FIGS. 19 (a) to 19 (c), external thread portions are formed on the legs (body portions) of the bolt material B2 by using rolling dies 52 and 53. Rolling dies 5
Reference numerals 2 and 53 move relative to each other as shown by the arrow with the body of the bolt material B2 sandwiched therebetween, and the bolt material B2 is rolled to form an external thread portion on the outer periphery thereof to form a bolt material B3. . At the tip of the bolt material B3, the bolt chamfer 22 described with reference to FIGS. 6, 7 and the like remains at an angle substantially equal to the flank angle of the thread. Note that, in addition to such rolling of the bolt, a male screw portion may be formed by cutting.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a nut according to an embodiment of the present invention.

FIG. 2 is a diagram showing a main part of the nut in comparison with a conventional example.

FIG. 3 is a diagram showing a length of an incomplete thread portion formed in the nut in comparison with a conventional example.

FIG. 4 is a perspective sectional view showing a main part of the nut.

FIG. 5 is a diagram showing inconvenience of the conventional example in comparison with the embodiment of the nut of the present invention.

FIG. 6 is a diagram schematically showing a main part of an example of an embodiment of a bolt.

FIG. 7 is a view showing an embodiment using a combination of bolts and nuts.

FIG. 8 is a diagram showing the operation of this embodiment in comparison with a conventional example.

FIG. 9 is a view showing a similar operation of the present embodiment in comparison with a conventional example.

FIG. 10 is a front view showing an embodiment of a bolt and nut fastening device.

FIG. 11 is a sectional view of a main part thereof.

FIG. 12 is a schematic view showing a modified example of a nut.

FIG. 13 is a half sectional view showing another embodiment of the nut.

FIG. 14 is a partial cross-sectional view showing a main part of still another nut embodiment.

FIG. 15 is a process chart showing an example of a method for manufacturing a nut.

FIG. 16 is a process drawing following FIG. 15;

FIG. 17 is a process drawing following FIG. 16;

FIG. 18 is a process chart showing an example of a method for manufacturing a bolt.

FIG. 19 is a process drawing following FIG. 18;

[Explanation of symbols]

 1, 15, 16, 17, 18, 19 Nut 7 First chamfered portion 8 Second chamfered portion 20 Bolt 22 Bolt side chamfered portion 24 Bolt / nut fastening device

Claims (6)

[Claims] 1. A tapered inner peripheral surface having an angle substantially equal to the flank angle of a female screw portion of the nut is formed as a chamfered portion on the inner peripheral side of the opening at the screwing start side of the nut. A nut having a female screw portion formed starting from a chamfered portion. 2. A tapered inner peripheral surface having an angle substantially equal to the flank angle of a female screw portion of the nut is formed as a first chamfered portion on the inner peripheral side of the opening at the screwing start side of the nut. A female screw portion is formed starting from the first chamfered portion while leaving the chamfered portion, and the first threaded portion is formed.
A tapered inner peripheral surface having an angle smaller than the flank angle of the female screw portion is formed as a second chamfered portion on the outside so as to be connected to the outer peripheral edge of the chamfered portion, and the female screwed portion is formed on the second chamfered portion. A nut characterized by not being formed. 3. The chamfer of claim 1 or the first of claim 2
The nut whose outer diameter of the chamfer is almost equal to the root diameter of the female thread. 4. A tapered inner peripheral surface having an angle substantially equal to the flank angle of the female screw portion of the nut is formed in advance on the inner circumferential side of the opening of the pilot hole for forming the female screw portion on the screwing start side. A method for manufacturing a nut, comprising forming a female thread portion including a chamfered portion. 5. A tapered inner peripheral surface having an angle substantially equal to the flank angle of the female screw portion of the nut is formed on the inner peripheral side of the opening of the pilot hole for forming the female screw portion on the screwing start side in advance.
A tapered inner peripheral surface having an angle larger than the flank angle of the female screw portion is formed as a second chamfered portion on the outer side so as to be connected to the outer peripheral edge of the first chamfered portion. A method of manufacturing a nut, comprising: forming a female thread on the second chamfer without forming a female thread on the second chamfer, so that the first chamfer is a base point of the female thread. 6. The chamfered part according to claim 4, or the first part according to claim 5.
A method of manufacturing a nut, wherein the outer diameter of the chamfered portion is substantially equal to the root diameter of the female screw portion.