JPS5830630A - Managing method for bolt axial force utilizing ultrasonic wave - Google Patents

Abstract

PURPOSE:To enable to perform an easy measurement of an axial force applied to a bolt and a management of an appropriate bolt axial force, by a method wherein ultrasonic probes are located across the bolt, and a time, for which an ultrasonic pulse propagates along the surface of the tightening part of the bolt, is measured. CONSTITUTION:A wrench socket 8 mating a wrench engages a head part of a bolt 2 to substances 10 and 11 to be tightened. A socket 9, in which ultrasonic probes 14 and 16 are situated in a symmetrical positional relation, is installed at the outside of the wrench socket 8. In the wrench so constituted, an ultrasonic pulse transmitted from the probe 14 advances along the surface of the substance 10 to be tightened and reaches the probe 16 at a receiving side, but the arrival time is shortened in inverse propportion to a compression stress caused to the substance 10 to be tightened by the axial force of the bolt 8. Thus, when the bolt 8 is tightened by the wrench, a time, which has elapsed until the ultrasonic pulse reaches the probe 16, is measured, and this permits finding of the axial force applied to the bolt.

Description

[Detailed Description of the Invention] The present invention relates to a bolt axial force management method using ultrasonic waves,
In particular, the present invention relates to a bolt axial force management method that can reduce the cost required for bolt axial force management.

Bolts and nuts are widely used for fastening objects such as two steel plates together. It is extremely important for safety to control the tightening force of the bolt when tightening the bolt, in other words, the axial force of the bolt. Conventionally, methods for managing the axial force of bolts during tightening include the torque method and the nut rotation angle method. Among these, the torque method is based on the relationship between torque T and bolt axial force F: T=kdF (
This method utilizes the relationship between k and d, where k is a torque coefficient and d is the nominal diameter of the bolt, and the axial force F is managed by treating k and d as constants and controlling the torque T. However, in this torque method, the torque coefficient k is not actually constant due to the influence of uneven roughness of the bolt seating surface and threaded part, and therefore the range of the bolt axial force relative to the torque T is There is a problem that the axial force is difficult to manage sufficiently as the axial force becomes large and large.

Furthermore, the conventional NAND rotation angle method focuses on the relationship between the rotation angle of the nut and the axial force of the bolt, and attempts to manage the axial force by setting the NAND rotation angle to a predetermined value. . This nut rotation angle method rotates the nut and tightens the bolt in the plastic range, so
Even if there is some variation in the rotation angle of the nut, the variation in the axial force F is small, and therefore the axial force can be managed more stably than in the above torque method. However, in this nut rotation angle method, since the bolt is tightened to the plastic range, there is a risk of the bolt breaking, which makes it difficult to use bolts made of materials with low ductility. . When considering axial force management in the elastic region, in the nut rotation angle method, the rotation angle of the NAND is read visually, so a large axial force F corresponding to the reading error of the rotation angle is calculated. cause an error. Therefore, it has been impossible to manage the axial force using the conventional nut rotation angle method in the elastic range.

In addition to such an axial force management method, an axial force management method as described in F has been proposed.

Figures 1 to 3 are explanatory diagrams showing a conventional bolt axial force management method using ultrasonic waves. A graph showing the relationship between the rate of change in the propagation time of a sound wave and the axial stress of the bolt. Figure 3 shows a comparison of the ultrasonic nopulse waveform before bolt tightening and the ultrasonic pulse waveform during bolt tightening. FIG.

In Fig. 1, 1 is an ultrasonic probe, and 2 is a bolt constituting a fastening part.In this conventional method, the ultrasonic probe 1 is placed on the head of the bolt 2 as shown in the figure. Then, an ultrasonic wave is projected from the head of the bolt 20 as shown by the broken line, and the propagation time of this ultrasonic wave is measured. The propagation time of this ultrasonic wave changes depending on the axial force generated on the bolt 2, as will be described later.The relationship between the axial force of the bolt 2 and the rate of change in the propagation time of the ultrasonic wave is shown in Fig. 2. There is.

In addition, in Fig. 3, 6 is the previous pulse waveform of the bolt tightening of the ultrasonic wave, 4 is the subsequent pulse waveform of the bolt tightening, 5 is the N-reflection echo in pulse waveform B, and 6 is the N pulse waveform in pulse waveform 4. This is a reflex echo. As shown in FIG. 6, when no axial force is generated on the bolt 2, the ultrasonic wave forms a pulse waveform 3. However, when the bolt 2 is tightened and an axial force is generated on the bolt 2, the bolt 2 stretches slightly as shown in Figure 1, and this elongation of the bolt 2 and the decrease in the sound speed due to the stress generated inside the bolt 2 go hand in hand. Throughout, the propagation time increases as shown in pulse waveform 4 in FIG. The amount of change Δt in the propagation time can be approximately determined as shown in the following equation.

Δt=α・Δl+β・Δc (1) Here, Δ is the elongation of bolt 2, ΔC is the amount of decrease in the speed of sound, and α
, β is a proportionality constant. However, this relational expression only holds within the elastic limit of the bolt material. Also, (1) above
Expressing Δt in the equation as a rate of change Δ1/1 to find the axial stress σ of the bolt, we get 1 Δt, , (2). Furthermore, in order to convert the axial stress σ into an axial force Ff, it is sufficient to multiply the effective cross-sectional area of the bolt 2. As mentioned above, the initial value 1° when no axial force is generated on the bolt 2 is measured, and the proportionality constant k is determined in advance.
If you know this, you can find the axial force of the bolt in question.

However, in the conventional bolt axial force management method performed in this manner, there are the following limitations in axial force management. In other words, ■Both end surfaces of the second bolt head and screw bottom are flat (W or more).
To be.

■ Both end faces of Pol 120 must be parallel (within ±2°).

■ The markings (embossed letters) on the head of bolt 20 must be removed.

■ The diameter of the bolt 2 must be 1 [] mm or more, and the length of the bolt 2 must be 1 m or less.

In this conventional axial force management method, as long as the limitations shown in (1) to (4) above are observed, accurate and reliable axial force management can be performed. However, on the contrary, the above ■~
If the limit shown in (2) is to be observed, the number of man-hours required to manufacture the bolt 2 will increase, and the cost required for axial force management will increase.

The present invention was made in view of the problems in the prior art, and its purpose is to accurately manage the axial force of the bolt during tightening without increasing the man-hours for manufacturing the bolt that constitutes the fastening part. The purpose of the present invention is to provide a bolt axial force management method that can be used to control bolt axial force.

In order to achieve this objective, the present invention is equipped with a socket having an ultrasonic probe forming the transmitting side and an ultrasonic probe forming the receiving side.The bolts forming the fastening part are tightened using a wrench. As the filter bolt is tightened, ultrasonic waves are projected from the ultrasonic probe forming the transmitting side to the ultrasonic probe forming the receiving side and along the surface of the fastening part. Bolt tightening is designed to measure the change in energy compared to the previous energy.

Hereinafter, the bolt axial force management method of the present invention will be explained based on the drawings. 4 to 9 are explanatory diagrams showing one embodiment of the management method of the present invention, and FIG. figure(
b) is a sectional view of the AA' part in Fig. 4(a), Fig. 5 is an explanatory diagram showing an enlarged view of the socket part of the wrench shown in Fig. 4, and Fig. 6(a) is shown in Fig. 4. An explanatory diagram showing the placement position of the ultrasonic probe in the socket provided in the wrench, Figure 6 (
1)) is a sectional view taken along line B-B' in Figure 6(a');
Figure (a) is a plan view showing the progress mode of ultrasonic waves, Figure 7 (b)
) is a side view showing the progress of the ultrasonic wave, FIG. 8 is an explanatory diagram showing the pulse waveform before bolt tightening, and FIG. 9 is an explanatory diagram showing the pulse waveform at the time of bolt tightening.

First, a wrench equipped with a socket having an ultrasonic probe used in the present invention will be explained with reference to FIGS. 4 to 6. In FIG. 4, 7 is a wrench, 8 is a wrench socket, and 9 is a socket arranged so as to surround the wrench socket 8. Note that 10.11 is an object to be tightened. The above-mentioned wrench socket 8 and socket 9 are slidable relative to each other via a bearing 12, as shown in FIG. Further, in FIG. 5, 13 is a magnet added to the F end of the socket 9, and 14 is an ultrasonic probe embedded inside the socket 9. Note that this ultrasonic probe 14 is used for ultrasonic waves.
The beams are projected from the surface portion 15 of the screen. The ultrasonic probe 14 described above forms the transmitting side. As shown in FIG. 6, an ultrasonic probe 16 forming a receiving side is provided at a position symmetrical to this contactor 14.

The method of the present invention will be sequentially described below. if first,
As shown in FIG. 4, the bolt 2 is used to fasten the object 1011 to the extent that no axial force is generated in the bolt 2. Next, the wrench socket 8 fitted with the wrench 7 is fitted into the head of the bolt 2. At this time, the socket 9 is fixed by a magnet 13 provided at its lower end being fixed to the surface of the object 10 to be tightened. In this state, ultrasonic waves are projected into the inside of the object to be tightened 10 from the ultrasonic probe 14 forming the transmitting side. This ultrasonic wave clearly advances to the edge of the hole of the bolt 2, that is, to the surface of the object 10 to be fastened, as shown by the solid line 17 in FIG. This ultrasonic wave is then extracted as a pulse waveform shown in FIG.

In FIG. 8, 18 indicates the first pulse, and 19 indicates the second pulse. If the arrival time of the ultrasonic wave from the transmitting side to the receiving side is t, then the second S-Rus 19 arrives with a delay of t from the first Hulles 18.

When the wrench 7 is turned to tighten the bolt 2 in the state shown in FIG. A bearing surface pressure corresponding to the axial force is generated in the under-neck dust of No. 2, and furthermore, as shown by arrow 22, the object 10 to be tightened on the under-neck seating surface is
, and compressive stress occurs in its vicinity. Generally, when stress occurs inside a steel member, the sound speed of the ultrasonic wave flowing inside changes. When tensile stress is added and the steel member stretches, the sound speed decreases, and conversely, when compressive stress is added, the sound speed decreases. It has the property of increasing. Therefore, when the bolt 2 is tightened to generate an axial force and the object 10 to be tightened is subjected to compressive stress, the ultrasonic wave reaches the object faster than before. Therefore, when compressive stress is generated in the object to be fastened 10 as in this case, the ultrasonic waves form a pulse waveform shown by the solid line in FIG. In the figure, 23 indicates the first pulse, 24 the second pulse, and 25 the Nth pulse. As is clear from the figure, the arrival time of the first pulse 23 is Δt compared to the previous supercross pulse when tightening the bolt shown in FIG.
In the Nth pulse 25, N
・The length becomes shorter by Δt. As mentioned above, the propagation time of this ultrasonic wave is approximately proportional to the stress generated in that area.
Further, the axial force generated in the bolt 2 and the compressive stress generated in the lower bearing surface of the bolt neck are also proportional. Therefore, as mentioned above, by using ultrasonic waves to reduce the compressive stress generated in the vicinity of the bolt neck seat, the axial force of the bolt at the time of tightening can be detected, and the axial force is determined to be suitable for the bolt. It is possible to manage whether it is axial force or not. Although the above embodiment has been explained by taking up the propagation time of ultrasonic energy, the axial force may be managed by determining the change in the magnitude of energy separately from this.

As described above, the bolt axial force management method using ultrasonic waves of the present invention projects ultrasonic waves along the surface of the fastening part and measures the change in the energy of the ultrasonic waves, so it is different from the conventional method. There is no need to machine the bolt head and both end faces of the screw bottom, there is no restriction on the bolt length, there is no need to increase the man-hours for manufacturing the bolt, and the axial force of the bolt can be reduced. Management costs can be kept low. In addition, since the ultrasonic probe can be placed in a fixed state under constant pressure against the object to be tightened, there is little variation in measurement values, and the axial force can be detected while tightening the bolt. Enables highly accurate bolt axial force management.

[Brief explanation of the drawing]

Figures 1 to 6 are explanatory diagrams showing the bolt axial force management method using conventional ultrasound waves. Figure 1 is an explanatory diagram showing the arrangement of the ultrasound probe, and Figure 2 is A graph showing the relationship between the rate of change in propagation time and bolt axial stress. Figure 3 is an explanation showing a comparison between the ultrasonic nopulse waveform before bolt tightening and the ultrasonic pulse waveform during bolt tightening. 4 to 9 are explanatory diagrams showing an embodiment of the bolt axial force management method using ultrasonic waves of the present invention, and FIG. 4(a) shows a wrench used in this management method. An explanatory diagram showing a state in which
FIG. 4(b) is a cross-sectional view of the AA' part in FIG. 4(a),
Fig. 5 is an explanatory diagram showing an enlarged view of the socket portion of the wrench shown in Fig. 4, and Fig. 6(a) shows the placement position of the ultrasonic probe in the socket provided in the wrench shown in Fig. 4. Explanatory diagram, FIG. 6(b) is a sectional view of the B-B' portion of FIG. 6(a), FIG. 7(a) is a plan view showing the progress mode of ultrasonic waves, and FIG. 7(b) is a Similarly, Fig. 8 is a side view showing the progress mode of ultrasonic waves, and Fig. 8 is an explanatory drawing showing the pulse waveform before bolt tightening.
The figure is an explanatory diagram showing a pulse waveform when tightening a bolt. 2... Bolt 7... Wrench 8... Wrench socket 9... Socket 10.11... Tightened object 12... Bearing 13... Magnet 14.16... Ultrasonic probe Child 15...Surface Partial Representative Patent Attorney Junnosuke Nakamura 11 Fig. 2. Ukeba hoste 4 Ki 1 h Matsu 1 ken (Y 1 group f9 figure

Claims (1)

[Claims] (1) In a bolt axial force management method for managing the axial force of bolts constituting a fastening part of a structure, a socket having an ultrasonic probe forming a transmitting side and an ultrasonic probe forming a receiving side is used. The bolt is tightened using a wrench provided with the bolt, and as the bolt is tightened, the bolt is moved from the ultrasonic probe forming the transmitting side to the ultrasonic probe forming the receiving side, and at the fastening portion. An ultrasonic wave is projected onto the surface of KG, and the bolt tightening of the ultrasonic wave is determined by measuring the change in energy when tightening the bolt relative to the previous energy, and from the correlation between this energy change and the bolt axial force. 17. A bolt axial force management method using ultrasonic waves, characterized in that the axial force generated in the bolt is detected and managed to determine whether the bolt axial force is appropriate.