JPS5945929B2 - 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.

In particular, when a bolted structure is used for dynamic behavior, an appropriate bolt tightening load is required, and if this occurs, a major accident may occur due to bolt fatigue fracture or brittle fracture. There is. Therefore, currently, as means for detecting the tightening load of bolts, an A torque wrench is used, a B dial gauge or the like detects the tightening load from dimensional changes in the bolt, and a C resistance wire strain gauge is used to measure stress.

However, these methods are inferior in accuracy and reliability in the case of simple methods such as A and B, and poor inspection efficiency in the case of highly accurate methods such as C. It wasn't. 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 wrapped around a U-shaped iron core 2a is installed at a location where residual stress is a problem in the structure 1 as shown in Figure 2. The stress at that point is converted into a magnetic output, that is, a secondary output voltage or impedance of the magnetic sensor 2, and the resultant 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 material stress and magnetic properties, especially iron loss properties, as shown in Figure 3. This makes it possible to indirectly detect the tightening load of a bolt from its iron loss characteristics.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows a cross-sectional view of an installation in which a magnetic sensor is arranged on a bolt.

In FIG. 4, 11a and Ilb are parts of the structure, 1
2 is a tightening bolt to this structure 11a3llb, and the head of this tightening bolt 12 is equipped with a magnetic sensor 13 according to the present invention.
is located. Also, this magnetic sensor 13 & A iron core 1
4 is equipped with an excitation coil 15a and an output secondary voltage coil 15b. On the other hand, FIG. 5 is a block diagram of a bolt tightening load detecting device according to the present invention.

That is, in FIG. 5, 14 is a magnetic sensor, and in this magnetic sensor 14, an excitation coil 15a is connected to a power source 16 and a current terminal of a wattmeter 17, and an output [ヮ沒dpressure coil 1
5b is connected to the voltage terminal of the wattmeter 17 and the voltmeter 18.
Furthermore, the output terminal of the wattmeter 17 is connected to a load indicator 19VC which is 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 tightening load. Next, the operation of the bolt tightening load detection device of the present invention will be explained.

If the excitation coil 15a of the magnetic sensor 14 is excited with alternating current,
A magnetic circuit is formed by the magnetic sensor 14 and the head of the bolt 12. Here, at the head of the bolt 12, due to the skin effect, the magnetic flux flows to the surface layer without penetrating inside and returns to the magnetic sensor 14 again. Here, Figure 6 shows the stress distribution in the radial direction near the bolt head surface when bolts M and O are tightened, and Figure 7 shows the stress distribution in the circumferential direction under the same conditions as in Figure 6. It shows. A
, B, and C are each 0.51t1 from the bolt head surface.
11,1.511r! The stress distribution at the points 11 and 2.51n indicates that the stress is compressive stress and the magnitude is in the range of 10 to 20 kg/n when the bolt axis direction is 40 kg/n. This relationship is proportional within the elastic range. For this purpose, the magnetic sensor according to the invention is placed on the bolt head, the flow of magnetic flux at the bolt head corresponds to the compression direction, and the bolt axial force can be easily determined from the iron loss characteristics obtained from the magnetic sensor in this state. can be detected. Moreover, FIG. 8 shows a modification of the magnetic sensor of the present invention.

A magnetic sensor 21 using coaxial ferrite as the iron core 20
is shown in which the magnetic flux flows radially from the center of the bolt head to the outer circumference.

By using such a magnetic sensor, it becomes possible to perform highly reliable measurements that can cope with eccentric loads applied to bolts. As described above, according to the present invention, since the iron loss is determined by the magnetic sensor placed on the bolt head, the tightening load of the bolt can be detected easily and accurately, and the tightening force of the bolt can be detected easily. Since changes 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 the relationship between iron loss and stress. Figure 4 is a cross-sectional view of the installation in which the magnetic sensor is placed on the bolt.
Fig. 5 is a program diagram showing one embodiment of the present invention, Figs. FIG. 8 is a sectional view showing a modification of the magnetic sensor of the present invention. 11a, 11b...Structure, 12...Bolt, 13
, 21... Magnetic sensor, 14, 20... Iron core, 15
a, 15b...Coil, 16...Power supply, 17...
Power meter, 18... Voltmeter, 19... Load indicating instrument.

Claims (1)

[Claims] 1. A magnetic sensor placed on the head of the bolt that measures the tightening force, a device that uses the output of this magnetic sensor to determine the alternating current magnetic loss of the bolt material due to the tightening force, and an iron loss determined by this device. and a device for measuring the tightening force of the bolt based on the bolt tightening force.