Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having structure to restrict rotation of threaded – mating... – Structure is coaxial – distinct member that restricts nut piece
Reexamination Certificate
2002-11-15
2004-09-07
Wilson, Neill (Department: 3679)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having structure to restrict rotation of threaded, mating...
Structure is coaxial, distinct member that restricts nut piece
C411S433000, C411S935000
Reexamination Certificate
active
06786690
ABSTRACT:
TECHNICAL FIELD
The invention relates to a locking fastener which comprises a bolt, a washer, and a nut and certainly prevents looseness of the fastener by a simple structure.
BACKGROUND ART
Generally, as a fastener, a fastener comprising a bolt and a nut or a fastener comprising a bolt, a nut, and a washer is used. Naturally, it is desirable that the fastener has the washer to protect a member to be fastened. The most important portion which is coupled by the fastener is a coupling portion of an airplane, a train, or the like or a coupling portion of a building, a steel tower, a bridge of a freeway, or the like. A locking fastener is used, particularly, for such a portion which is subject to an influence of looseness due to vibration caused by running of vehicles or vibration caused by the wind or the like.
Many fasteners having a locking effect have been proposed. For example, in JP-A-9-79247, there has been disclosed a fastener constructed in a manner such that a seat surface of a washer is formed as a convex portion or a concave portion having an inclined surface, a back surface of a nut or a back surface of a head portion of a bolt is formed as a concave portion or a convex portion having an inclined surface corresponding to the convex portion or the concave portion of the washer, and a frictional force caused by compression is allowed to act on the inclined surfaces of the washer and the nut which are fitted to each other, thereby providing the locking effect.
According to the above fastener, in the case of forming the convex portion, a serious disadvantage such that a part of a screw portion of the nut is lost for providing the inclined surface is compensated by a frictional portion formed in such a part of the screw portion. However, it is difficult that the frictional force caused only in such a limited span resists a strong loosing force. In the case of forming the concave portion, a thickness for engaging the nut has to be added, so that a strange thick washer is obtained, a resistance force depends on the frictional force caused only in such a limited span in a manner similar to the case where the convex portion is formed, and it is difficult.
In addition to it, according to the above proposed fastener, it is difficult to expect that reliability of the washer endures, and a construction such that a pin for stopping rotation is provided for the washer so as to be projected therefrom for the purpose of preventing the washer from being rotated against the spiral engagement of the bolt and the nut has also been described. However, to form the rotation stopping pin onto the washer, a fitting portion for fitting the pin needs to be provided for the side of a plate to be fastened or the nut in correspondence to the rotation stopping pin formed on the washer. Thus, there is also a problem such that a structure becomes complicated and productivity and generality deteriorate. There is, eventually, unreasonableness such that the resistance force depends on a shearing force of the pin.
Further, since the locking results from the integrated structure of the nut and the bolt, even if the washer and the nut are completely integrated, looseness which is exerted to the bolt as a separate member cannot be blocked and the proposed fastener has a large defect.
In JP-A-11-6516, there has been proposed a double nut having a locking effect and comprising: a first nut in which a tapered outer peripheral surface whose diameter decreases toward an upward position in an axial hole direction is formed around a screw hole and a convex portion whose outer peripheral surface is slightly decentered from the screw hole is formed; and a second nut into which the convex portion of the first nut is fitted, for which a concave portion having an inner peripheral surface that is concentric with the screw hole is provided, and which is attached later.
According to the double nut, a resin or a soft metal is coated onto the side of the eccentric direction of the first nut, the convex portion of the first nut is fitted into the concave portion of the second nut, and when the first nut is fastened by the second nut, the decentered convex portion of the first nut is fitted into the concave portion of the second nut that is concentric with the screw hole, thereby providing wedge-like action and accomplishing the locking effect.
That is, when the concave portion of the second nut which is attached later is fitted to the convex portion of the first nut which is attached ahead and a female screw of the second nut and a screw portion of the bolt are screwed, since the convex portion of the first nut is decentered, while the first nut presses the bolt from the eccentric side, a fastening force acts, and the position of the first nut is slightly deviated to the other side in the eccentric direction, and while the second nut presses the bolt from the other side in the eccentric direction, a fastening force acts.
In upper and lower opposite positions of a fitted laminate of the first and second nuts, strong pressing forces act from the directions which cross perpendicularly to a bolt axis, and the locking is performed by a frictional force of the tapered surfaces of the first and second nuts.
According to the proposed fastener, since the strong pressing forces of the disadvantageous shearing forces are applied to the bolt axis in the upper and lower positions from the opposite orthogonal directions, a burden on the bolt is heavy.
According to the double nut, since the two nuts are overlappingly used, there is a damage to thread ridges, it cannot endure repetitive use, and it becomes expensive.
Further, since a space enough for the convex portion of the first nut is necessary, there is also restriction of use such that the double nut cannot be used in a narrow space where the first nut and the convex portion cannot be allowed.
In JP-A-10-306819, as shown in
FIG. 22
, there has been proposed a locking structure comprising: a ring-shaped locking member
20
in which an outer surface is formed in a tapered shape whose diameter decreases upward in a bolt axial direction, a female screw
23
which is continuous with a female screw portion
11
of a nut is formed on an inner peripheral surface, and a notched portion
22
in that a part of a circumference is cut away in a bolt axial direction; and a nut
2
with a tapered concave portion
30
a
having a tapered inner peripheral surface into which the ring member
20
is fitted.
When a bolt
3
and the nut
2
are fastened, a diameter of the ring-shaped locking member
20
decreases and the locking member
20
becomes a filling coupling member between the bolt
3
and the nut
2
and enters the tapered concave portion
30
a
of the nut
2
.
Stresses in the axis orthogonal directions which repulse the compression of the locking member
20
and are directed toward both of the bolt
3
and the nut
2
act and a fastening force increases, thereby preventing the looseness of the screw.
According to the proposed fastener, although a part of the screw of the nut is sacrificed in a manner similar to the foregoing JP-A-9-79247, it differs therefrom with respect to a point that a filling coupling member (locking member
20
) whose diameter can be freely decreased exists in the sacrificial portion.
The locking effect relies eventually on the frictional force caused by the contact of the tapered outer peripheral surface of the locking member
20
with the tapered concave portion
30
a
of the nut
2
, and the locking member
20
is integrated with the bolt
3
at the back surface (the integration effect cannot be expected with respect to the spiral moving direction because of the engagement of the screw). However, since there is a limitation at the contact surface which is provided only in such a limited span, it is necessary that the tapered concave portion
30
a
is formed in a wide diameter portion
30
obtained by increasing a diameter of an upper portion of the nut
2
. Since the nut
2
has a special shape, a problem of an increase in manufacturing costs is caused. In a manner sim
Oliff & Berridg,e PLC
Wilson Neill
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