JP2015131364A - Bolt axial force test apparatus and bolt axial force test method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bolt axial force test apparatus and a bolt axial force test method.SOLUTION: A bolt axial force test apparatus 1 for acquiring the relation between a fastening torque T and an axial force of a bolt 2, comprises: fastening torque detection means 3 detecting the fastening torque T of the bolt 2; load detection means 5 arranged between base materials 4a and 4b that are fastened by the bolt 2 and detecting a compressive load, the load detection means 5 including a hollow cylinder 51 into which the bolt 2 is fitted with a play and a strain gauge 7 disposed circumferentially on an outer circumferential surface of the hollow cylinder 51; and correlation calculation means 6 outputting a relation between the fastening torque T detected by the fastening torque detection means 3 and the load (axial force F) detected by the load detection means 5.

Description

  The present invention relates to a bolt axial force test apparatus and a bolt axial force test method, and in particular, increases the accuracy of axial force management by measuring a compressive load using a load detection means between base materials in a fastening means, and a product. The present invention relates to a bolt axial force test apparatus and a bolt axial force test method that contribute to reliability.

Fastening means, that is, fastening structures using bolts, are employed in all mechanical structures. Bolts are used when two or more members are to be connected, and a certain external force is often applied to the base material.
As a design standard of the bolt, a threshold value of the axial force is often set with respect to the external force for the purpose of preventing the coupling surface from slipping or preventing the coupling surface from separating.
When tightening a bolt in the process of manufacturing a product, the axial force of a bolt is usually not measured at the time of tightening the bolt, but indirectly by specifying a tightening torque that correlates with the axial force. Managing power.
Although there is a theoretical formula for the relationship between torque and axial force, the coefficient of friction of the base metal, bolt size, thread shape type, machining accuracy, etc. have a great influence on the relationship between torque and axial force, and there are large variations. Therefore, it is difficult to obtain a predetermined axial force with high accuracy by using the torque calculated by the theoretical formula.
Therefore, it can be understood that the management of axial force is an important requirement for improving product reliability.

  At present, in order to measure the axial force of a bolt, a bolt axial force gauge is applied to all the bolts to be tested, and calibration is performed to obtain the relationship between the gauge output (strain) and load. A test is being conducted. The relationship between the bolt torque and the axial force is as shown in the figure. Torque records the setting of the torque wrench, and axial force samples bolt axial force gauge data with a measuring instrument.

Patent Document 1 discloses an elastic / plastic zone tightening screw performance testing device.
In this patent document 1, it was proposed in order to clarify the plastic phenomenon of the tightening screw from the plastic region tightening to the external force load, and has both a material tensile tester and a screw tightening tester. . That is, in Patent Document 1, the tightening torque, the seating surface torque, the thread surface torque, the bolt axial force, the external force, the bolt extension and torsion angle, the compression force of the object to be fastened, and the rotation angle of the nut can be measured. A load cell provided with first, second, and third strain detecting means, a nut tightening means, an external force generating means, and a displacement meter are provided.
This makes it possible to easily and in detail test the behavior of bolts and nuts when an external force in the axial direction is applied after screw tightening over the plastic range.

Japanese Patent Laid-Open No. 62-42032

However, in the bolt torque and axial force calibration tests, the number of tests is increased as much as possible for the purpose of evaluating variation, so that all the specimens are subjected to gage installation and calibration tests. There are inconveniences that the cost is high due to the large number of processes and the delivery time tends to be delayed.
In addition, when using a bolt axial force gauge, a through hole for inserting the bolt is provided in the base material, and when a female screw for screwing the bolt into the through hole is formed or when a nut is used, the axial force Measurement is possible, but if the hole in which the female thread is formed is not a through hole, the measurement line of the bolt bearing gauge cannot be taken out, so the axial force cannot be measured.
The present invention has been proposed in order to solve such problems. Instead of the bolt axial force gauge, the load detecting means is arranged between the base materials and the compressive load is measured. It is an object of the present invention to provide a bolt axial force test apparatus and a bolt axial force test method that can contribute to improvement of product reliability by improving the accuracy.

  In order to solve the above-described problems, the present invention provides a bolt axial force test apparatus for acquiring a relationship between bolt tightening torque and axial force, a tightening torque detecting means for detecting the bolt tightening torque, and a bolt And a load detecting means for detecting the axial load of the bolt, and the load detecting means is provided on the outer periphery of the hollow cylinder and the hollow cylinder for loosely fitting the bolt. And a correlation calculating means for outputting a relationship between the tightening torque detected by the tightening torque detecting means and the load detected by the load detecting means. It is characterized by.

Thereby, only one load detection means is manufactured, and the load detection means can be used for load detection of other bolts. Therefore, it is not necessary to install an axial force gauge for each bolt and perform a calibration test, and a significant improvement effect can be expected in terms of cost and delivery time.
Further, even if the hole in which the female screw is formed is not a through hole in the base material, the axial force can be measured if the load detecting means is arranged between the base materials.

  In one embodiment of the present invention, the outer diameter of the hollow cylinder is larger than at least the outer diameter of the bolt head, and the strain gauge is disposed in a small diameter portion formed on the outer peripheral surface of the hollow cylinder. It is characterized by being.

  As a result, the load from the entire bolt head is applied to the hollow cylinder having an outer diameter larger than the outer diameter of the bolt head, and the load detecting means is less likely to buckle.

  In one embodiment of the present invention, the mounting surface of the strain gauge on the outer peripheral surface of the hollow cylinder is closer to the bolt axis than the outer edge of the bolt head.

  As a result, the load from the entire bolt head is accurately detected as a stress that is uniformly applied to the hollow cylinder having an outer diameter smaller than the outer diameter of the entire bolt head on the strain gauge mounting surface on the outer peripheral surface of the hollow cylinder. be able to.

  In one embodiment of the present invention, the tightening torque detecting means is composed of a torque detector that continuously acquires a torque value as digital data.

  Thereby, since the torque value can be continuously acquired, the relationship between the bolt tightening torque and the axial force can be acquired efficiently.

  In one embodiment of the present invention, the torque detector includes a strain gauge provided on the arm of the detector.

  Thereby, by tightening the torque detector, the strain value obtained by the strain gauge can be converted into a torque value.

  Furthermore, in one embodiment of the present invention, a tightening torque detecting means for detecting the tightening torque of the bolt, and a load detecting means for detecting a load in the axial direction of the bolt disposed between the base materials fastened by the bolt. A bolt axial force test method for acquiring a relationship between bolt tightening torque and axial force, an axial force calculating step for calculating the axial force of the bolt by the load detecting means, and a tightening torque detecting means. , The tightening torque for rotating the bolt around the shaft in a single tightening operation, the tightening torque calculation step to obtain continuously, the tightening by the axial force calculation step and the tightening torque calculation step A correlation calculation step of acquiring a relationship with torque.

In the axial force calculation step, the axial force of the bolt is calculated by the load detection means, and then in the tightening torque calculation step, the tightening torque for rotating the bolt around the axis is tightened once by the tightening torque detection means. In operation, the tightening torque can be calculated continuously.
Furthermore, in the correlation calculation step, the correlation between the axial force in the axial force calculation step and the tightening torque in the tightening torque calculation step can be calculated.

  In this way, data on the relationship between torque and axial force can be acquired with a single measuring instrument. With conventional torque wrenches, the torque has to be tightened in steps from a small value, so there were many test procedures. However, since the relationship between torque and axial force can be obtained in real time by measuring the torque, one tightening is performed. Necessary data can be acquired.

According to the present invention, only one load detecting means is manufactured, and the load detecting means can be used for load detection of other bolts. Therefore, it is not necessary to install an axial force gauge for each bolt and carry out a calibration test, which leads to simplification of the work procedure, and can be expected to have a remarkable improvement effect in terms of cost and delivery time.
Further, even if the hole in which the female screw is threaded is not a through hole in the base material, the axial force can be measured if the load detecting means is arranged between the base materials.
Furthermore, data on the correlation between torque and axial force can be acquired with a single measuring instrument. That is, in the conventional torque wrench, the torque has to be tightened in steps from a small value, so there were many test procedures, but by measuring the torque, the correlation between torque and axial force can be acquired in real time, Necessary data can be acquired with one tightening.

It is a top view showing an example of a bolt tightening model concerning a 1st embodiment of the present invention. FIG. 2 is a block diagram according to a first embodiment of a bolt axial force test apparatus using the bolt tightening model shown in FIG. 1. It is a graph which shows an example of the relationship between the torque of a volt | bolt, and axial force. It is a block diagram of the bolt axial force test apparatus concerning 2nd Embodiment of this invention. It is a graph which shows an example of the relationship between the torque of a volt | bolt, and axial force. It is a top view showing an example of a bolt tightening model concerning a 3rd embodiment of the present invention. FIG. 7 is a block diagram according to a third embodiment of a bolt axial force test apparatus using the bolt tightening model shown in FIG. 6. It is a flowchart for performing a bolt axial force test method. It is a graph which shows an example of the relationship between the torque of the volt | bolt in 3rd Embodiment, and axial force.

  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

(First embodiment)
1 and 2 show a first embodiment for carrying out a bolt axial force test apparatus according to the present invention.
A bolt axial force test apparatus 1 according to the present embodiment is an apparatus for acquiring a relationship between bolt tightening torque and axial force using a bolt tightening model as shown in FIGS. A tightening torque detecting means 3 for detecting a tightening torque T of the bolt 2; a load detecting means 5 for detecting an axial load of the bolt 2 disposed between the base materials 4a and 4b fastened by the bolt 2; It comprises.
Further, the bolt axial force test apparatus 1 includes a correlation calculation unit 6 that outputs a relationship between the tightening torque T detected by the tightening torque detection unit 3 and the load detected by the load detection unit 5.

  The bolt 2 in the tightening model includes a shaft portion 2a threaded on the tip side and a hexagonal bolt head portion 2b.

  The tightening torque detecting means 3 is a known so-called torque wrench and has a function of inserting a torque head into the bolt head 2b of the bolt 2 to be tested and acquiring a torque value as digital data by a tightening operation.

  As for the base materials 4a and 4b fastened with the bolt 2, those of the same material and dimensional standard are used assuming a fastening position of an actual machine that is fastened using the bolt 2. That is, the base materials 4a and 4b are formed with through holes 4ah and 4bh that pass through the shaft portion 2a of the bolt 2 along the central axis. A female screw is engraved in the through hole 4ah of the base material 4a. On the other hand, the through hole 4bh on the base material 4b side is formed to have a slightly larger outer diameter than the outer diameter of the shaft portion 2a of the bolt 2.

The load detecting means 5 includes a hollow cylinder 51 in which the bolt 2 is loosely fitted, and a strain gauge 7 disposed on the outer peripheral surface of the hollow cylinder 51 in the circumferential direction.
The hollow cylinder 51 here corresponds to the dimension of the shaft portion 2a of the target bolt 2 and is provided with a design guideline of a shape to be described later.

The strain gauge 7 has a lead wire as a lead wire attached to, for example, a grid-like metal foil produced by photoetching on a thin resin electrical insulator. In this case, four strain gauges 7 are attached to the outer peripheral surface of the hollow cylinder 51 every 90 degrees in the circumferential direction, and are manufactured according to the dimensions of the bolt 2 and the maximum value of the axial force F to be acquired. Thus, the axial force F can be measured with high accuracy. In addition, as for the sticking position of the strain gauge 7, the center of a height direction is desirable.
In this case, the load detection means 5 performs a calibration test in advance to obtain the relationship between the average strain of the four strain gauges 7 and the compression load, and the average of the load detection means 5 is measured when measuring the axial force of the bolt 2. The axial force F is calculated backward from the strain.

The hollow cylinder 51 corresponds to the dimension of the shaft portion 2a of the target bolt 2 as described above, and a design guide for the shape is given for the following reason.
That is, when the shape of the hollow cylinder 51 is too high (cross-sectional area is too large), the strain value to be detected is too small and the detection resolution becomes coarse. On the other hand, if the strength is too small (the cross-sectional area is too small), the hollow cylinder 51 is plastically deformed, the relationship between the load and strain loses linearity, and the load cannot be detected.

The design guidelines for the hollow cylinder 51 are:
Di≈1.1D,
σ = 0.6σy = Fmax / (π / 4 × (Do ² -Di ² ))
[However, the outer diameter D of the bolt, the inner diameter Di, the maximum axial force to be obtained Fmax, the compressive stress generated in the hollow cylinder σ, and the yield stress of the hollow cylinder σy],
It has become. This design guide means that the maximum axial force Fmax is set in the elastic region of the bolt 2.

The correlation calculating means 6 inserts the tightening torque detecting means 3 into the bolt head 2b of the bolt 2 to be tested, acquires and records the torque value as digital data by the tightening operation, The correlation calculation means 6 takes in the output of the load detection means 5, calculates the average strain of the four strain gauges 7, and calculates the axial force F from this average strain.
Thus, the relationship between the obtained tightening torque T and the corresponding axial force F can be shown as shown in FIG. Therefore, based on the correlation between the tightening torque T and the axial force F obtained with this bolt tightening model, the axial force F can be managed from the tightening torque T at the actual fastening position.

As described above, in this embodiment, the hollow cylinder 51 is disposed between the base materials 4 a and 4 b fastened by the bolt 2, and the compressive load is applied by the strain gauge 7 disposed in the circumferential direction of the hollow cylinder 51. It can be measured and acquired as the axial force F of the bolt 2 from the compression load.
Thus, if one load detection means 5 is manufactured, the load of various bolts can be detected by using this load detection means 5 in addition to the target bolt 2. It is not necessary to install an axial force gauge every time and perform a calibration test, and a significant improvement effect can be expected in terms of cost and delivery time.
Further, in the base material 4a, the axial force F of the bolt 2 can be measured by inserting the load detecting means 5 between the base materials 4a and 4b even if the hole 3ah into which the female screw is threaded is not a through hole. Will be able to.

The hollow cylinder 51 has an outer diameter D, an inner diameter Di, a maximum axial force Fmax, a compressive stress generated in the hollow cylinder σ, and a yield stress of the hollow cylinder σy based on σy.
Di≈1.1D,
σ = 0.6σy = Fmax / (π / 4 × (Do ² -Di ² ))
The dimensions are set according to the design guidelines given in
(1) When the intensity is too high (the cross-sectional area is too large), the detected strain value is too small and the detection resolution becomes coarse.
(2) If the strength is too small (the cross-sectional area is too small), the hollow cylinder 51 will be plastically deformed, and the relationship between the load and strain will lose linearity, which will prevent the load from being detected. Such inconvenience can be avoided.

(Second Embodiment)
The bolt axial force test apparatus according to the present invention can also be implemented as follows.
Note that, in the apparatus according to the second embodiment, components that are substantially the same as those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
In the second embodiment, since the shaft portion 2a of the bolt 2 to be tested is long, if the dimension of the load detection means 5, that is, the height dimension is relatively large, there is a concern about buckling. This is because, when buckling occurs, the linearity of the relationship between load and strain is lost, and measurement becomes impossible.
In the second embodiment, the shape of the hollow cylinder 51 is set to the shape shown in FIG. 4 because buckling is more likely to occur as the height dimension of the cylinder is larger and the wall thickness is thinner. .

  That is, in the second embodiment, the outer diameter of the hollow cylinder 51 is larger than at least the outer diameter of the bolt head 2 b, and the strain gauge 7 is a portion embedded in the outer peripheral surface of the hollow cylinder 51, that is, a hollow A small-diameter portion 52 in which the outer peripheral surface of the cylinder 51 is formed in steps is arranged as an attachment surface. In this case, the diameter of the small diameter portion 52 is smaller than the outer diameter of the bolt head portion 2b, and the mounting surface of the small diameter portion 52 is closer to the bolt axis than the outer edge of the bolt head portion 2b.

As a result, the load from the entire bolt head 2b is applied to the hollow cylinder 51 having an outer diameter larger than the outer diameter of the bolt head 2b, and the load per unit area applied to the hollow cylinder 51 is reduced. Therefore, the load detecting means 5 which is difficult to buckle can be obtained.
Further, the load from the entire bolt head 2 b can be accurately detected as a stress that is uniformly applied to the small-diameter portion 52 that is the mounting surface of the strain gauge 7 on the outer peripheral surface of the hollow cylinder 51. Therefore, it leads to highly accurate measurement.

Also in the second embodiment as described above, the tightening torque detecting means 3 is inserted into the bolt head 2b of the bolt 2 to be tested, and the torque value is acquired and recorded as digital data by the tightening operation. On the other hand, the correlation calculation means 6 takes in the output of the load detection means 5, calculates the average strain of the four strain gauges 7, and can obtain the axial force F from the average strain by back calculation.
In this way, the relationship between the obtained tightening torque T and the corresponding axial force F can be shown as shown in FIG. Therefore, based on the correlation between the tightening torque T and the axial force F obtained with this bolt tightening model, the axial force F can be managed from the tightening torque T at the actual fastening position.

(Third embodiment)
The bolt axial force test apparatus according to the present invention can also be implemented as follows.
In the third embodiment, the torque detector 8 used for the bolt tightening model in the first embodiment omits a detailed description, but the torque value is continuously acquired as digital data. It comprises a detector 8 (see FIGS. 6 and 7).

The torque detector 8 has an arm 81 having a square cross section, and a strain gauge 82 is provided at a position close to the head portion 8H (the rotation center of the bolt) inserted into the bolt head 2b to be tested. Further, the torque detector 8 sets the base end side of the arm 81 as a load point 8P to which the load F is applied during the tightening operation.
That is, the torque detector 8 is designed to satisfy the following expression.
σ = 0.6σ _y = F · X / (1 / 6xbh ² )
[However, the height is h, the width is b, the distance from the load point 8P to the center of rotation is L, the distance from the center of rotation to the position of the strain gauge 82 is X, the expected tightening torque is T, and the resulting bending stress is σ, yield stress σ _y , and load at load point 8P F].
The shape design of course means that it is set on the premise that it is executed in the elastic region of the bolt 2.
The tightening torque T is calculated based on the load F in the tightening operation calculated from the strain gauge 82 from the relationship T = F · L.

That is, in the third embodiment, the bolt axial force test method for acquiring the relationship between the bolt tightening torque and the axial force is executed in the following procedure (see FIG. 8).
In this bolt axial force test method, the axial force calculation step (S1) for calculating the axial force of the bolt 2 by the output of the strain gauge 7 of the load detection means 5, and the tightening operation of the torque detector 8 (single tightening) The tightening torque calculating step (S2) for continuously acquiring the tightening torque T for rotating the bolt 2 around the axis from the strain gauge 82 output by the tightening operation) and the axial force calculating step (S1). A correlation calculating step (S3) for obtaining a correlation from the axial force and the tightening torque T in the tightening torque calculating step (S2).

In the third embodiment as described above, the axial force of the bolt 2 is calculated in the axial force calculating step (S1) based on the output of the strain gauge 7 of the load detecting means 5.
On the other hand, in the tightening torque calculation step (S2), the tightening torque T for rotating the bolt 2 around the axis from the strain gauge 82 output by the tightening operation (one tightening operation) of the torque detector 8. Can be calculated continuously.
In the correlation calculation step (S3), the correlation between the axial force in the axial force calculation step (S1) and the tightening torque T in the tightening torque calculation step (S2) can be calculated.

  In this way, data on the relationship between torque and axial force can be acquired with a single measuring instrument. With conventional torque wrenches, the torque has to be tightened in steps from a small value, so there were many test procedures. However, since the relationship between torque and axial force can be obtained in real time by measuring the torque, one tightening is performed. Necessary data can be continuously acquired (see FIG. 9).

  The bolt axial force test device and the bolt axial force test method of the present invention can be applied to the axial force management of the bolt fastening portion of any device.

DESCRIPTION OF SYMBOLS 1 Bolt axial force test apparatus 2 Bolt 2a Shaft part 2b Bolt head 3 Tightening torque detection means 4a, 4b Base material 4ah, 4bh Through-hole 5 Load detection means 51 Hollow cylinder 52 Small diameter part 6 Correlation calculation means 7 Strain gauge 8 Torque detector 81 Arm 82 Gauge conversion means

Claims (6)

A bolt axial force test device that acquires the relationship between bolt tightening torque and axial force,
Tightening torque detecting means for detecting the tightening torque of the bolt;
A load detecting means disposed between the base materials fastened by the bolts and detecting a load in the axial direction of the bolt;
The load detecting means includes a hollow cylinder in which the bolt is loosely fitted, and a strain gauge disposed in the circumferential direction on the outer peripheral surface of the hollow cylinder,
Correlation calculating means for outputting a relationship between the tightening torque detected by the tightening torque detecting means and the load detected by the load detecting means;
A bolt axial force test apparatus comprising:   The outer diameter of the hollow cylinder is larger than at least the outer diameter of the bolt head, and the strain gauge is disposed in a small diameter portion formed on the outer peripheral surface of the hollow cylinder. The bolt axial force test apparatus according to claim 1, wherein the bolt axial force test apparatus is characterized.   3. The bolt axial force test apparatus according to claim 1, wherein an attachment surface of the strain gauge on an outer peripheral surface of the hollow cylinder is closer to a bolt shaft center than an outer edge of the bolt head.   2. The bolt axial force test apparatus according to claim 1, wherein the tightening torque detecting means comprises a torque detector that continuously acquires a torque value as digital data.   The bolt axial force test device according to claim 4, wherein the torque detector includes a strain gauge provided on an arm of the detector. A tightening torque detecting means for detecting a tightening torque of the bolt, and a load detecting means for detecting a load in the axial direction of the bolt, which is disposed between the base materials fastened by the bolt; A bolt axial force test method for obtaining a relationship with an axial force,
An axial force calculating step of calculating an axial force of the bolt by the load detecting means;
A tightening torque calculating step of continuously acquiring a tightening torque for rotating the bolt around an axis by the tightening torque detecting means in one tightening operation;
A bolt axial force test method, comprising: a correlation calculation step of acquiring a relationship between an axial force in the axial force calculation step and a tightening torque in the tightening torque calculation step.

Images