JP3327615B2 - Bolts and their usage limit management method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bolt and a method of managing a service limit thereof.

[0002]

2. Description of the Related Art FIG. 3 shows the structure of a conventional bolt of this kind. In FIG. 3, reference numeral 21 denotes a bolt, and a head 22
And a shaft portion 23 and a screw portion 24. Such bolts 21 are used, for example, for fastening various mechanical parts, such as mounting an automobile engine, and are tightened to a plastic region in a nut or a screw hole (plastic region tightening). By tightening the bolt 21 in the plastic region, the entire bolt 21 is pulled in the axial direction to the plastic region, so that the bolt 21 undergoes plastic deformation (that is, plastic elongation). That is, the threaded portion 24 of the bolt 21 (exactly, the portion that does not screw with the female screw of the threaded portion 24) undergoes plastic elongation, and the outer diameter of the threaded portion 24 is reduced by an amount corresponding to the plastic elongation. Therefore, when the bolt 21 is repeatedly tightened in the plastic region many times, the thinning due to the plastic elongation of the bolt 21 is accumulated, and the bolt 21 eventually breaks. That is,
Each time the bolt 21 is attached to or detached from a machine part and the bolt 21 is retightened, the plastic elongation of the bolt 21 progresses, and the bolt 21 is damaged while repeating this several times.

Therefore, the allowable value of the plastic elongation of the bolt 21 is set in advance, and the elongation of the bolt 21 is controlled, and the use limit is controlled. Conventionally, bolt 2
1 by measuring the length under the neck or utilizing the fact that the screw portion 24 becomes thinner due to the plastic elongation of the bolt 21.
The elongation of the bolt 21 is managed by measuring the outside diameter of the bolt 21 each time the bolt 21 is loosened and examining the amount of change in each. FIG. 4 shows a specific example of the elongation management of the bolt 21. Each time the bolt 21 is tightened in the plastic region, a plastic elongation of about 0.2 mm is generated. As a whole, the bolt 21 reaches a maximum tensile load Fmax of 2 m.
m is set as the service limit of the bolt.

[0004]

However, in the conventional bolt, the length under the neck varies due to the dimensional tolerance, and by measuring the length under the neck, the elongation of the bolt is accurately controlled. It is difficult. In the case of the bolt 21 shown in FIG. 3, since there is a dimensional tolerance of ± 0.5 mm in the length under the neck due to manufacturing, it is necessary to perform machining to accurately manage the plastic elongation of the use limit of 2 mm. Cost increases.

Further, in the conventional bolts, the dimensions of the outer diameter of the threaded portion itself cannot be made with high precision, so that it is difficult to accurately predict the elongation of the bolt by managing the outer diameter of the threaded portion. . For example, in the case of the bolt 21 shown in FIG. 3, as shown in FIG. 5, a proportional relationship of about 1:10 is provided between the change in the outer diameter of the screw portion 24 (that is, the difference in the outer diameter) and the plastic elongation of the bolt 21. The outer diameter of the screw portion 24 is smaller by 0.001 mm than the plastic elongation of the bolt 21 is 0.1 mm (millimeter). However, since the outer diameter of the screw portion 24 has a tolerance of 0.1 mm, the working limit is 2 mm.
There was a problem that the plastic elongation of the steel sheet could not be accurately controlled.

Accordingly, an object of the present invention is to provide a bolt capable of accurately and easily managing the elongation of the bolt and a method of managing the service limit thereof.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of plastic elongation by crushing a screw near the center of a non-threaded portion of a screw with a female screw. A smooth screw portion for measuring the change in the outer diameter of the screw portion is provided, and the use limit of the bolt is controlled by measuring the outer diameter of the smooth screw portion. It is desirable that the crushing of the thread is performed to such an extent that the effective sectional area of the thread does not change.

[0008]

According to the present invention, the following functions are provided by the above-described structure. In the vicinity of the center of the non-threaded portion of the screw portion of the bolt with the female screw, a smooth screw portion for crushing the screw portion and measuring the amount of change in the outer diameter of the screw portion due to plastic elongation is provided. The smooth screw portion can be machined with high precision in dimension setting, and a predetermined outer diameter can be set to the smooth screw portion with high accuracy with a small tolerance. Therefore, by measuring the outer diameter of the smooth thread portion, it is possible to measure the exact change in the outer diameter of the thread portion that does not screw with the female screw, and accurately predict the elongation of the bolt based on the obtained value. Use limit can be managed.

Further, since the outer diameter dimension measurement position of the screw portion is specified by the smooth screw portion, the measurement position does not differ depending on the operator, the elongation of the bolt is accurately predicted, and the use limit is easily managed. can do.

[0010]

FIG. 1 shows the structure of a bolt according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a bolt,
The head 14 includes a head portion 12, a shaft portion 13, and a screw portion 14. The screw portion 14 is a smooth screw formed near a central portion in the axial direction, that is, a non-threaded portion with a female screw 16 provided on a machine component or the like. It has a part 15. This bolt 11 first forms a screw portion 14 by cutting a groove along a helical winding on the peripheral surface, and then crushes the vicinity of the central portion of the portion of the screw portion 14 which does not engage with the female screw by rolling. Thus, the smooth screw portion 15 is formed there. FIG. 2 is a partially enlarged view showing an example of the structure of the smooth screw portion 15 of the bolt 11 in this embodiment. As is clear from this figure, in the smooth screw portion 15, the ridge portion of the screw groove is crushed as compared with the other screw portions 14, and has a flat shape. The crush of the screw part 14
It is desirable to perform the process so that the effective sectional area of the screw portion 14 does not change. By this processing, the smooth screw portion 15
The outer diameter can be formed with high accuracy within a small tolerance of about 0.02 mm, and a constant value can be set for the outer diameter. In FIG. 2, reference numeral 14 a denotes a thread before forming the smooth screw portion 15, and 15 a denotes a thread of the smooth screw portion 15.

Next, a method of managing the elongation of the bolt 11 will be described with reference to FIG. First, in the initial state before the use of the bolt 11, the outer diameter of the smooth screw portion 15 is converted into data. Then, each time the bolt 11 is used to fasten a mechanical part, the outer diameter of the smooth screw portion 15 is measured every time the bolt 11 is removed from the mechanical part, and the amount of change in the outer diameter caused by the tightening of the bolt 11, ie, decrease Convert values to data. The state of elongation generated in the bolt 11 is managed from the numerical values obtained thereby.

As described above, according to the above-described embodiment, the vicinity of the center of the portion of the screw portion 14 of the bolt 11 which does not engage with the female screw 16 is crushed by rolling to provide a high-precision with a small tolerance. Since the smooth screw portion 15 is formed, and the elongation of the bolt 11 is controlled based on the numerical value obtained by measuring the outer diameter of the smooth screw portion 15, the use limit of the bolt 11 is accurately controlled. be able to. The smooth screw portion 15 may be formed over the entire circumference of a portion of the screw portion 14 that does not engage with the female screw, or may be formed as a pair of parallel surfaces.

Further, since the smooth screw portion 15 is provided in the vicinity of the center of the portion of the screw portion 14 which does not engage with the female screw 16, the outer diameter measurement position of the screw portion 14 can be specified.
The measurement position does not differ depending on the operator, and the change amount of the outer diameter of the bolt screw portion 14 can be accurately and easily measured.

[0014]

As described above, the present invention provides a smooth screw for measuring the amount of change in the outer diameter of a screw portion due to plastic elongation by crushing a non-threaded portion of a screw portion of a bolt with a female screw. Since the portion is provided and the elongation of the bolt is controlled by measuring the outer diameter of the smooth screw portion, it is possible to accurately and easily manage the use limit of the bolt.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a bolt according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view showing a structural example of a smooth screw portion of the bolt in the embodiment.

FIG. 3 is a schematic front view of a conventional bolt.

FIG. 4 is a graph for explaining management of bolt elongation;

FIG. 5 is a graph showing a relationship between a plastic elongation generated in a bolt and a difference in outer diameter.

[Explanation of symbols]

 11, 21 Bolt 12, 22 Head 13, 23 Shaft 14, 24 Thread 15 Smooth thread

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01M 13/00 F16B 31/02

Claims (2)

(57) [Claims] 1. A smooth screw portion is provided on an outer periphery of a non-threaded portion of a screw portion with a female screw by crushing the screw portion, and the smooth screw portion is formed by plastic deformation when tightening a bolt. A bolt that measures the change in outer diameter. 2. A smooth screw portion is provided on an outer periphery of a non-threaded portion of a screw portion of a bolt with a female screw by crushing the screw portion to such an extent that an effective sectional area does not change. A limit management method for a bolt, wherein the elongation of the bolt is controlled based on a value obtained by measuring an outer diameter of the bolt.