JPH04248012A - Plastic fastening bolt - Google Patents

Abstract

PURPOSE:To improve the axial force of a bolt and increase the available frequency of reuse by setting the diameter of the axial portion of the bolt with no thread ridge to be smaller than the diameter giving the effective cross section of the thread portion and larger than the minor diameter of the thread portion. CONSTITUTION:The diameter (d) of the axial portion 2 of a bolt is set larger than the minor diameter (d1) of the thread portion 1 and smaller than the diameter (d2) giving the effective area of the thread portion 1. The diameter (d') of the axial portion 2' is set equal to the outer diameter (d3) of the thread portion 1. The outside is connected with a circular arc and a taper to ease stress concentration. In this way, fastening causes the axial portion 2 to be only plastically deformed because the cross section of the axial portion 2 is smaller than the effective cross section giving the real tensile strength of the thread portion 1, so that the axial force generated in the bolt is almost constant. Also, the thread portion 1 is not plastically deformed and so the available frequency of reuse is increased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bolts used for plastic tightening.

0002

[Prior Art] Bolts are generally used in the elastic range,
At this time, the members are tightened by the axial force generated in the bolt. The axial force generated in the elastic region of the bolt is
It is proportional to the amount of tensile strain of the bolt. When joining parts,
Multiple bolts are often used, and it is desirable that the same axial force be generated in these bolts, but even if the same torque is applied to these bolts, there will be considerable variation in the coefficient of friction of the threads of each bolt. Because of this, the amount of tensile strain generated in each bolt is not constant, and therefore the axial force generated in each bolt is not constant.

[0003] Therefore, in order to make the axial force generated in each bolt constant, the bolt plastic tightening method described in JP-A-1-182612 is effective. As a result, the bolts are used in the plastic region, and the axial force generated in each bolt is less affected by the difference in the amount of tensile strain of each bolt than in the elastic region, and is almost constant.

0004

[Problems to be Solved by the Invention] There are usually two types of bolts used in the above-mentioned plastic tightening method: threaded bolts and shaft threaded bolts. The diameter is larger than the effective diameter of the screw. Therefore, in a threaded bolt, the part that undergoes plastic deformation is the threaded portion, which poses a problem in that the number of times the bolt is reused is reduced. Further, in a normal bolt with an extended shaft, since the shaft portion is thinner than the thread root diameter, there is a problem in that the axial force is small. An object of the present invention is to simultaneously improve the axial force of a plastic tightening bolt and ensure the number of reuses.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides that at least a portion of the unthreaded shaft portion of a bolt is smaller than a diameter giving an effective cross-sectional area of the threaded portion, and To provide a plastic tightening bolt characterized by having a diameter larger than a root diameter of a portion.

[0006]

[Operation] When using the above-mentioned plastic tightening bolt, the shaft without threads is weaker than the threaded part, so the shaft is plastically deformed without the threaded part being plastically deformed. The axial force generated in the bolt is constant and larger than that of conventional axial extension bolts, and this bolt can be reused more frequently.

[0007]

Embodiment FIG. 1 shows an embodiment of the present invention. (A) is a side view, and (B) is a front view. In the figure, 1 is a threaded portion, 2 and 2' are non-threaded shaft portions, and 3 is a head that immobilizes the bolt in order to tighten a nut (not shown) to the bolt. FIG. 2 is an enlarged view showing the dimensional relationship between the threaded portion 1 and the shaft portions 2, 2'. In the figure, the diameter d of the shaft portion 2 is
It is set larger than the root diameter d1 of the threaded portion 1 and smaller than the diameter d2 which provides the effective cross-sectional area of the threaded portion 1. The diameter d' of the shaft portion 2' is equal to the outer diameter d3 of the threaded portion 1. The exterior is connected by arcs and tapers to relieve stress concentration.

When this bolt is plastically tightened with a nut at a constant torque, the cross-sectional area of the shaft portion 2 becomes
Since it is smaller than the effective cross-sectional area that provides substantial tensile strength of the threaded portion 1, only the shaft portion 2 is plastically deformed. The amount of tensile strain at this time varies depending on the bolt due to variations in the coefficient of friction of the threaded portion 1, but since it is plastic deformation, the axial force generated in each bolt is approximately constant.

Furthermore, no plastic deformation occurs in the threaded portion 1, which increases the number of times this bolt can be reused compared to a threaded bolt. Furthermore, the diameter d of the shaft portion 2 is
By making the root diameter d1 larger and making the cross-sectional area of the shaft portion 2 as large as possible, a larger axial force can be obtained with the same amount of plastic deformation as a conventional shaft extension bolt, and the yield strength of this part is increased. This increases the number of times it can be reused compared to conventional shaft extension bolts.

0010

[Effects of the Invention] As described above, by using the plastic tightening bolt of the present invention, the number of times of reuse can be increased because the threaded portion does not undergo plastic deformation, and the shaft portion can be Since the area is set to , a large axial force can be obtained,
This also increases the number of times it can be reused.

[Brief explanation of the drawing]

FIG. 1 is a plastic tightening bolt according to the present invention, (A)
is a side view, and (B) is a front view.

FIG. 2 is an enlarged view of section Q in FIG. 1;

[Explanation of symbols]

1...Threaded part 2, 2'...Shaft part

Claims (1)

[Claims] 1. A plastic tightening bolt characterized in that at least a part of the non-threaded shank of the bolt has a diameter smaller than a diameter giving an effective cross-sectional area of the threaded part and larger than a root diameter of the threaded part. .