JPS60186B2 - Bolt tightening load detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bolt tightening load detection device in an assembled structure using bolts.

In general, in assembled structures using bolts, the material, dimensions, etc. of the bolts are considered and adopted from the viewpoint of structural strength at the design stage of the structure.

Particularly in applications where bolted structures exhibit dynamic behavior, an appropriate bolt tightening load is required; failure to do so may result in major accidents due to fatigue breakage of the bolts, or even damage to the bolts. Sometimes. Therefore, currently, as a means of detecting this rare load on bolts, a leg torque wrench is used, a side dial gauge is used to detect the vertical load from changes in the dimensions of the bolt, and stress measurement using a resistance wire strain gauge is used. .

However, these methods are inferior in accuracy and reliability in the case of simple methods such as ■ and 'B}, and in the case of highly accurate methods such as }, the inspection efficiency is poor and the simplicity is poor. It wasn't practical. In addition to this, magnetic application is being considered as another stress detection means.

This is the first relationship between the mechanical properties of structural materials and magnetic properties.
Since there is a correlation as shown in the figure, a magnetic sensor 2 consisting of a U-shaped iron core 2a and a coil 2b wound around a U-shaped iron core 2a is placed at a location where residual stress is a problem in the structure 1 as shown in Figure 2. , the stress at that location is converted into a magnetic output, that is, a secondary output voltage or impedance of the magnetic sensor 2, which is indirectly measured by the indicator 3. However, this means has problems with the shape of the magnetic sensor, measurement accuracy, etc., and therefore is not used as a bolt tightening load detection device. The present invention has been made in view of the above points, and an object of the present invention is to provide a bolt tightening load detection device that can simply and accurately detect an appropriate bolt tightening load in an assembled structure using bolts. purpose.

For this reason, in the present invention, as a result of research, we have found that there is a close relationship between the stress of a material and its magnetic properties, particularly its coercive force or iron neck properties, as shown in Figures 3 and 4. A guide hole is provided in the center of the bolt, and a magnetic sensor that can be inserted into the guide hole is manufactured so that the tightening load of the bolt can be indirectly detected from its holding force or iron loss characteristics.

An embodiment of the present invention will be described below with reference to the drawings. In general, the measurement circuit for holding force measurement is more complicated than that for iron loss measurement, so here we will mainly explain a bolt-attached load detection device that applies simple iron loss characteristics. FIG. 5 shows a sectional view of the attachment of a tightening bolt to, for example, a water turbine runner.

That is, in FIG. 5, 11 is a part of the water turbine runner, 12 is a tightening bolt for this water turbine runner 1, and this tightening bolt 12 is provided with a bolt heating guide hole 13 in its center. Reference numeral 14 denotes a magnetic sensor according to the present invention, which is inserted into the guide hole 13 of the tightening bolt 12 in order to detect the bolt tightening load.

On the other hand, FIG. 6 is a block diagram of the structure of the magnetic sensor 4 shown in FIG. 5 and the bolt-attached load detection section.

That is, as shown in FIG.
An excitation coil 14b and an output secondary voltage coil 14c are wound around 4a, and a magnetic sensor guide rod 15 is attached to this. In such a magnetic sensor 4, the excitation coil 14b is connected to the power supply 16 and the current terminal of the wattmeter 17, and the output secondary voltage coil 14c is connected to the voltage terminal of the wattmeter 17 and the voltmeter 181. Further, the output terminal of the wattmeter 17 is connected to a load indicator 19 equipped with an arithmetic circuit that calculates the change in iron loss as a rate of change in iron loss and converts it into a vertical load. Next, the operation of the bolt continuous load detection device constructed as described above will be described.

If the magnetic sensor 14 is now inserted into the guide hole 13 of the tightening bolt 12 via the magnetic sensor guide rod 15, the magnetic relationship between the magnetic sensor 4 and the tightening bolt 12 will be as shown in FIG. That is, the excitation coil 14b is activated by the power source 16.
When energized, the magnetic flux a from the magnetic sensor core 14a flows in the bolt 12 parallel to the tension direction of the bolt, forming a closed magnetic path that returns to the magnetic core 14a again. Therefore, if the tightening load of the rare bolt 12 changes, the magnetic characteristics of the bolt will naturally change, and this is detected as a change in magnetic characteristics by the output secondary voltage coil 14c of the magnetic sensor 14, and the wattmeter 17 and It is applied to the voltmeter 18 and also to the load indicator 19. In the load indicator 19, an arithmetic circuit calculates the iron loss change as an iron loss change rate and converts it into a tightening load. FIG. 8 is an example of measuring the tightening load of the tightening bolt 12 using the magnetic sensor according to the present invention.

An example is given in which the magnetic sensor has a magnetic frequency of 200 Hz and a ratio of 1000. The iron loss change rate is 2 within the bolt vertical load usage range.
It is about 2% for 0 dish Z and about 10% for 1000Hz, which is a sufficient value compared to conventional detectors.
It is also excellent in terms of simplicity. Note that the magnetic sensor excitation frequency is preferably 100 centigrade or less in order to improve measurement accuracy, since a skin effect occurs in the process of magnetic flux flowing through the bolt 12.

In the above embodiment, in order to increase the sensitivity of the magnetic sensor, the magnetic sensor is constructed using a magnetic core 20a shaped as shown in FIG. What is necessary is to reduce the magnetic resistance. FIG. 10 shows a magnetic sensor 21 according to another embodiment of the present invention, which shows that, as shown in FIGS. 3 and 4, the magnetic properties of the material are better under compressive stress than under tensile stress. Since the two are closely related to each other, it has been devised so that the stress applied to the bolt when it is tightened can be detected as compressive stress.

That is, when the bolt is tightened, the stress in the axial direction of the bolt becomes a tension force, but in the orthogonal direction, a compressive force acts according to the Poisson's ratio of the material, so it is devised to utilize this compressive force. FIG. 11 is a cross-sectional view of the magnetic sensor 21,
FIG. 12 shows the magnetic relationship between the tightening bolt 12 and the magnetic sensor 21 at this time. The magnetic flux b from the magnetic core 21a flows in the circumferential direction within the vertical bolt 12, and returns to the magnetic core 2.
It now returns to 1a. Therefore, since the stress of the magnetic flux path within the bolt acts as a compressive force as described above, the stress detected in the bolt 12 by the magnetic sensor 21 becomes a compressive force proportional to the bolt tightening load. FIG. 13 shows the magnetic sensor 21 for the tightening bolt 12 used in FIG.
This is an example of vertical load measurement inside.

The rate of change in iron loss acts positively in the case of compressive stress, and the rate of change is larger than that in tensile stress and is approximately proportional to the load. In each of the above embodiments, a magnetic sensor having a magnetic core 14a shown in FIG. 7, a magnetic triple core 20a shown in FIG. 9, a magnetic core 21a shown in FIG. We have explained the vertical bolt load detection device that applies loss change rate or holding force change rate, but
It goes without saying that in the present invention, similar effects can be obtained with a magnetic sensor that does not use a magnetic core.

As described above, according to the present invention, a magnetic sensor is inserted into a bolt having a center hole to determine the amount of change in magnetic properties of the bolt material due to tightening force, so that the tightening load of the bolt can be accurately and Since it is easy to detect, and changes in bolt tightening force over time can be easily detected, a practical bolt tightening load detection device can be provided.

[Brief explanation of drawings]

Figure 1 is a characteristic curve diagram showing the relationship between stress and magnetic properties of structural materials, Figure 2 is an explanatory diagram of stress detection means for general structural materials, and Figure 3 is a diagram showing the relationship between holding force and stress. Fig. 4 is a characteristic curve diagram showing the relationship between iron loss and stress, Fig. 5 is a sectional view of the attachment of a bolt to a water turbine runner, and Fig. 6 is a magnetic diagram showing an embodiment of the present invention. A block diagram of the sensor and bolt-attached load detection device, Fig. 7 is an explanatory diagram showing the flow of magnetic flux between the magnetic sensor and the tightening bolt, Fig. 8 is a diagram showing the measurement example in Fig. 7, Fig. 9 10 is a side view of a magnetic sensor for compressive stress detection according to another embodiment of the present invention, and FIG.
Figure 1 is a cross-sectional view taken along the X-X line in Figure 10; Figure 12 is an explanatory diagram showing the flow of magnetic flux between the magnetic sensor in Figure 10 and the bolt attached; Figure 13 is the magnetic sensor in Figure 10. It is a figure which shows the example of measurement by the iron loss change rate of the bolt tightening force by. 11... Part of the water wheel runner, 12...
- Bolt having center hole 13, 14... Magnetic sensor, 15... Magnetic sensor guide rod, 16...
... Power supply, 17... Wattmeter, 18... Voltmeter, 19... Load indicating instrument. Figure 1'Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8Figure 9Figure 10Figure 11, Figure 2Figure 13

Claims (1)

[Claims] 1. A magnetic sensor that is movably inserted into a center hole provided in a bolt that tightens a structure, a device that uses the output of this magnetic sensor to determine the amount of change in magnetic properties of the bolt material due to tightening force, and and a device for measuring the tightening force of the bolt based on the amount of change in magnetic properties.