Method for determining the reusability of steel parts, and system for determining the reusability of steel parts

Abstract

This invention provides a method and system for determining whether steel parts are reusable, which can appropriately determine whether or not steel parts are reusable. [Solution] A method for determining whether a steel part 21 subjected to repeated stress can be reused includes acquisition steps S2 to S3, which acquire multiple data for different usage times: the usage time of the steel part 2 subjected to repeated stress and the full width at half maximum (FWHM) of the steel part 2 measured by X-ray diffraction; setting steps S4 to S7, which set a range of usage time and FWHM where the FWHM decreases as the usage time increases from the start of use of the steel part 2 as the reuse range R of the steel part 21; and determination steps S11 to S14, which acquire the usage time and FWHM for determination of the steel part 21 to be reused, and determine that the steel part 21 is reusable if the usage time and FWHM for determination are within the reuse range R.

Description

Technical Field

[0001] The present invention relates to a method for determining the reusability of steel parts and a system for determining the reusability of steel parts.

Background Art

[0002] As a technique of this kind, for example, Patent Document 1 describes a method for estimating the remaining life of a gear. In this method, the half-value widths of the highest and lowest parts of the Hertz pressure acting on the tooth surface of the gear to be evaluated are measured by X-ray diffraction analysis, and the relative half-value width is obtained by dividing the half-value width of the highest part by the half-value width of the lowest part. On the other hand, based on an experiment using a gear of the same product as the gear to be evaluated, a characteristic curve showing the relationship between the relative half-value width of the gear to be the experimental object and the life ratio with the total number of rotations at the time of tooth surface damage set to 1 is obtained. The current relative half-value width of the gear to be evaluated is compared with this characteristic curve to read the value of the current life ratio, and the remaining life is estimated based on this value of the life ratio.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even if the life ratio of a steel part subjected to repeated stress is obtained using the above technique, this life ratio is not an index assumed for determining the reusability of the steel part. Therefore, it is difficult to make an optimal determination that the steel part can be reused using this life ratio as an index.

[0005] The present invention has been made in view of such points, and an object thereof is to provide a method for determining the reusability of steel parts and a system for determining the reusability that can appropriately determine whether or not a steel part can be reused. [Means for solving the problem]

[0006] In view of the above-mentioned problems, the present invention provides a method for determining whether a steel part subjected to repeated stress can be reused, comprising: an acquisition step of acquiring multiple usage times of the steel part subjected to repeated stress and the full width at half maximum measured by X-ray diffraction for different usage times; a setting step of setting a range of usage times and a range of full width at half maximum in which the full width at half maximum decreases as the usage time increases from the start of use of the steel part, as the reuse range of the steel part; and a determination step of acquiring a usage time and a full width at half maximum for determination of the steel part subject to reuse determination, and determining that the steel part is reusable if the usage time and the full width at half maximum for determination are within the reuse range.

[0007] Furthermore, in view of the above issues, the steel part reuse determination system according to the present invention is a reuse determination system that determines whether or not a steel part subjected to repeated stress can be reused, the reuse determination system comprises a storage device that stores data for reuse determination, and a calculation device that performs a calculation for reuse determination based on the reuse determination data, the storage device stores a plurality of reuse determination data obtained for different usage times, the usage time of the steel part subjected to repeated stress, and the full width at half maximum measured of the steel part by X-ray diffraction, the calculation device sets a range of usage time and a range of full width at half maximum where the full width at half maximum decreases as the usage time increases from the start of use of the steel part, based on the reuse determination data, and determines that the steel part is reusable when the usage time and full width at half maximum of the steel part subject to reuse determination are within the reuse range. [Effects of the Invention]

[0008] According to the present invention, it is possible to appropriately determine whether or not a steel part is reusable. [Brief explanation of the drawing]

[0009] [Figure 1] This is a functional block diagram of the reuse determination system for steel parts subjected to repeated stress according to this embodiment. [Figure 2] This is a schematic explanatory diagram showing how the coil spring, as a steel component according to this embodiment, is used. [Figure 3] This is an explanatory diagram of the half-width according to this embodiment. [Figure 4] This graph shows the relationship between the life ratio and the full width at half maximum of an unused coil spring according to this embodiment. [Figure 5] This graph shows the relationship between the operating time ratio and the half-width ratio of the coil spring used in this embodiment. [Figure 6] This is a flowchart of the method for determining the reusability of steel parts subjected to repeated stress according to this embodiment. [Modes for carrying out the invention]

[0010] [Embodiment] The embodiments of the present invention will be described in detail below with reference to Figures 1 to 6. Note that the embodiments described below are only one aspect of the present invention and do not limit the technical scope of the present invention.

[0011] <Structure> Figure 1 is a functional block diagram of the reusability determination system 1 for steel parts subjected to repeated stress according to this embodiment. The reusability determination system 1 includes an input device 11, a storage device 12 for storing data for reusability determination, a calculation device 13 for performing calculations for reusability determination based on the data for reusability determination, and an output device 14 for outputting the calculation results. The reusability determination system 1 according to this embodiment is used to determine whether steel parts of the same type as those steel parts are reusable, based on data obtained from a plurality of steel parts of the same type that have been subjected to repeated stress. In this embodiment, a coil spring 2 is used as an example of a steel part for acquiring data, and a coil spring 21 is used as an example of a steel part to be determined as to be reusable. The reusability determination system 1 according to this embodiment can be applied to steel parts that are subjected to repeated stress within the range of elastic deformation, such as coil springs 2 and 21.

[0012] The coil spring 2 (or coil spring 21) according to this embodiment is a component mounted on a large work machine 4 such as a power shovel, as shown in Figure 2. The coil spring 2 is used as a shock absorber for the idler wheels of a pair of crawlers 41 provided on the running body of the work machine 4, specifically, it is mounted on the inside of each of the left and right frames (not shown) and absorbs vibrations of the main body 42 of the work machine 4 when it is running. Since the coil spring 2 is an indispensable component for the running of the work machine 4, determining whether the above-mentioned coil spring 21 can be reused is meaningful in evaluating the safety associated with the running of the work machine 4. In addition, dampers (not shown) are also mounted on the inside of each of the left and right frames of the pair of crawlers 41, which can dampen the vibrations absorbed by the coil spring 2. As a result, vibrations of the coil spring 2 are suppressed, and the work machine 4 can be run stably.

[0013] The surfaces of coil springs 2 and 21 are generally subjected to a surface treatment that mechanically hardens them to extend their lifespan. Examples of surface treatments include tempering and shot peening, which harden the surface layers of coil springs 2 and 21. In addition, the surface layers of coil springs 2 and 21 contain at least martensite, and repeated stress acting on these surface layers causes dislocations in the martensite to move, softening the surface layers of coil springs 2 and 21. This reduces the full width at half maximum (FHA) of the surface layer of coil springs 2 and 21 (explained in detail using Figure 3 below). As described above, by hardening the surface layers of coil springs 2 and 21 in advance, the amount of change in hardness when coil springs 2 and 21 soften can be increased. Since this amount of change is reflected in the change in FHA, it is thought that it becomes easier to more clearly identify the reuse range R shown in Figure 5 below.

[0014] In this embodiment, an X-ray diffractometer 3 is used to measure the full width at half maximum (FWHM) of multiple coil springs 2 with respect to their usage time, for each coil spring 2 mounted on multiple work machines 4 with different usage times, using an X-ray diffraction method in which X-rays are irradiated onto multiple identical coil springs 2. The input device 11 is, for example, a keyboard, and stores the measured FWHM of the coil springs 2 with respect to their usage time in the storage device 12 as data for determining reuse. As a result, the storage device 12 stores multiple data for determining reuse, obtained for different usage times, consisting of the usage time of the coil springs 2 subjected to repeated stress and the FWHM of the coil springs 2 measured by the X-ray diffraction method. Based on the reuse determination data stored in the storage device 12, the setting unit 131 of the arithmetic unit 13 sets the range of usage time and range of FWHM, where the FWHM decreases as the usage time increases from the start of use of the coil spring 2, as the reuse range R of the coil springs 21 to be determined for reuse. Alternatively, the X-ray diffractometer 3 may be connected to the input device 11 or the storage device 12 to directly input and store the measured FWHM.

[0015] Similarly, for the coil spring 21, the determination half-width for determination is measured using the X-ray diffraction method with the X-ray diffractometer 3. The determination unit 132 of the calculation unit 13 determines that the coil spring 21 is reusable if the determination usage time and determination half-width of the coil spring 21 are within the above-mentioned reuse range R set in the setting unit 131. With the above configuration of the reuse determination system 1, it is possible to appropriately determine whether or not the coil spring 21 is reusable. The determination result from the determination unit 132 is output to an output device 14, such as a monitor, in a way that is easily visible.

[0016] <Graph> Here, the full width at half maximum (FWHM) according to this embodiment will be explained using Figure 3. As a method for measuring the FWHM, first, a fatigue test is performed on an unused coil spring (not shown) of the same type as coil spring 2, which is used for the experiment. The coil spring is stretched and contracted with a constant force within the range of elastic deformation until a crack occurs. Next, a mark is made on the surface of coil spring 2 at the same location where the crack occurred. Finally, X-rays of a constant wavelength are irradiated at the marked location from an X-ray diffractometer 3 while changing the angle. As a result, the X-rays are scattered by the structure of the surface of coil spring 2, and a diffraction phenomenon occurs where the scattered X-rays interfere and reinforce each other under specific conditions. The X-ray intensity with respect to the diffraction angle is measured by a detector (not shown). The width of the diffraction angle with respect to the X-ray intensity at half the peak value of the X-ray intensity obtained as a result is the FWHM.

[0017] The half-width measured in this way decreases as the repeated stress acts on the surface part of the coil spring 2. However, even for coil springs 2 that have been subjected to the same number of repeated stresses, variations in the half-width may occur due to differences in dimensions during processing or surface treatment of the coil springs 2. Therefore, it is difficult to simply assume that the half-width is common to all products of the same type. In order to use it as an index common to all coil springs 2 of the same type, it is preferable to use the relative ratio to a certain standard instead of the half-width. For this reason, in the present embodiment, the time corresponding to the number of repetitions is set as the above-mentioned usage time, and the value obtained by dividing the half-width measured for each of a plurality of different usage times by the half-width of the unused coil spring 2 is obtained as the half-width ratio, and it is preferable to obtain the change in the half-width ratio of the coil spring 2 for a plurality of different usage times. Thereby, it is possible to suppress variations in the half-width among a plurality of coil springs 2 of the same type. However, when there are almost no variations in the half-width among a plurality of coil springs 2 of the same type, the change in the half-width of the coil spring 2 for a plurality of different usage times may be obtained.

[0018] Figure 4 is a graph showing the relationship between the life ratio and the half-width ratio of an unused coil spring (which is of the same type as the coil springs 2 and 21 described above but different) according to the present embodiment. This graph is a graph in which the vertical axis is the axis of the above-mentioned half-width ratio, the horizontal axis is the axis of the life ratio, and the life ratio and the half-width ratio are plotted, and the change in the half-width ratio of the coil spring is obtained as experimental data. Here, when performing a fatigue test in which a coil spring is repeatedly expanded and contracted a plurality of times with a constant force within the range where the coil spring elastically deform, with one expansion and contraction as one cycle, the above-mentioned life ratio refers to the ratio of each cycle number to the cycle number when cracks occur in the coil spring due to the dislocation behavior of a structure such as martensite. By setting the horizontal axis as the axis of the life ratio, it is possible to suppress variations in the life ratio among a plurality of coil springs of the same type, similar to the case of the half-width ratio.

[0019] For the graph plotting the life ratio and the half-value width ratio, the setting unit 131 sets a first approximate straight line L1 with a negative slope and a second approximate straight line L2 with a slope of zero by two-line approximation, and calculates the intersection point of the first approximate straight line L1 and the second approximate straight line L2 as the inflection point P. As described above, due to the repeated stress acting on the surface layer part of the coil spring, the coil spring softens, and thereby the half-value width of the surface layer of the coil spring decreases, so its half-value width ratio also decreases. However, it is clear that in the range of the life ratio larger than the life ratio at the inflection point P, until cracks occur in the coil spring, the half-value width ratio hardly changes even if the life ratio increases.

[0020] Here, in the section (period) where the half-value width hardly changes in response to the increase in the life ratio, it is difficult to predict the timing of crack occurrence in the coil spring (it is difficult to estimate the remaining life of the coil spring) due to subsequent use, and it cannot necessarily be said that the coil spring is reusable. On the other hand, when the half-value width of the surface layer of the coil spring extremely decreases according to the usage time, there may be a possibility that stress exceeding the assumption has acted on the coil spring. Also in this case, it is difficult to estimate the remaining life of the coil spring, and it cannot necessarily be said that the coil spring is reusable.

[0021] Therefore, for the coil spring 2 that was actually mounted on and used in the work machine 4, a graph is set up as shown in Figure 5, with the vertical axis being the axis of the half-width ratio, similar to Figure 4, and the horizontal axis being the axis of the operating time ratio, plotting the operating time ratio and the half-width ratio set by the setting unit 131. Here, the operating time ratio is the value obtained by dividing the operating time of the work machine 4 equipped with the coil spring 2 by the warranty period of the work machine 4. Note that the warranty period of the work machine 4 does not differ depending on the type of coil spring 2 mounted on the work machine 4, so the horizontal axis may be the operating time of the work machine 4. Operating time is the time during which repeated stress is actually applied within the range of elastic deformation when the work machine 4 is in operation, and the usage time of the coil spring 2 can be estimated from the operating time ratio (operating time) of the work machine 4. In addition, the position where repeated stress is applied to the coil spring 2 is the same as the position where cracks occurred in the coil spring as a result of the fatigue test described above. Furthermore, in the graph of Figure 5, the vertical axis represents the half-width ratio. Therefore, it is necessary to measure the half-width of coil spring 2 in its initial state, i.e., when the number of cycles is 0, beforehand. In this case, the vertical axis may also be the half-width axis.

[0022] The reason for measuring the full width at half maximum (HWHM) ratio based on the elapsed operating time ratio (operating time) of the coil spring 2 actually mounted and used in the work machine 4 is that it is difficult to measure the number of cycles of the coil spring 2 mounted in the work machine 4. However, the operating time is a value proportional to the number of times a predetermined repeated stress is applied within the elastic deformation range of the coil spring 2, and the inventors' investigation has shown that the relationship between the life ratio and the HWHM ratio, which can be shown by a two-line approximation shown in Figure 4, can also be applied to the relationship between the operating time ratio and the HWHM ratio, shown in Figure 5. For this reason, the graph showing the relationship between the operating time ratio and the HWHM ratio can be set based on the graph obtained as experimental data showing the relationship between the life ratio and the HWHM ratio in Figure 4. That is, for the graph showing the relationship between the operating time ratio and the HWHM ratio in Figure 5, the setting unit 131 can set the first approximation line L1 and the second approximation line L2 using a two-line approximation, and calculate the intersection point of the first approximation line L1 and the second approximation line L2 as the inflection point P.

[0023] After calculating the inflection point P, the setting unit 131 sets the range of usage time and range of half-width (the range enclosed by the dashed line in Figure 5) where the half-width decreases as the usage time increases from the start of use of the coil spring 2 as the reuse range R of the coil spring 21. The setting unit 131 can easily set the reuse range R of the coil spring 21 using a graph showing the relationship between the operating time ratio and the half-width ratio. When determining whether the coil spring 21 subject to reuse determination can be reused, if the operating time ratio and half-width ratio for determination of the coil spring 21 are within the reuse range R, the determination unit 132 determines that the coil spring 21 can be reused. The output device 14 outputs the determination result that it can be reused.

[0024] On the other hand, if the operating time ratio and the width at half maximum ratio for determination of the coil spring 21 are outside the reusable range R, the determination unit 132 determines that the coil spring 21 is unusable. Let the operating time ratio and width at half maximum ratio at the inflection point P be A and B, respectively. For example, if the operating time ratio and the width at half maximum ratio for determination of the coil spring 21 are in the range of less than A and less than B, respectively, that is, if the operating time ratio is small and the work machine 4 equipped with the coil spring 21 travels on extremely rough roads, the determination unit 132 determines that the load acting on the coil spring 21 is excessive and the amplitude of the coil spring 21 is also excessive, and therefore determines that the coil spring 21 is unusable. Furthermore, if the operating time ratio and the width at half maximum ratio for the coil spring 21 are both within the ranges of A or greater and B or greater, respectively, that is, if the operating time ratio is large but the work machine 4 equipped with the coil spring 21 is hardly moving, the determination unit 132 determines that the coil spring 21 is unusable, based on the assumption that although the engine is running during the operating time, the machine is not moving and therefore hardly any load is acting on the coil spring 21. The output device 14 similarly outputs a determination result indicating that the coil spring is unusable.

[0025] Thus, by using the reuse determination system 1, it is possible to appropriately determine whether or not the coil springs 21 are reusable. This allows for the selection of only reusable coil springs 21, ensuring safety in the reuse of coil springs 21, and reducing the disposal of reusable coil springs 21.

[0026] <Flowchart> The flowchart below illustrates the method for determining whether a coil spring 21 subjected to repeated stress can be reused according to this embodiment, using Figure 6. In this flowchart, steps S1 to S7 show the process up to the point in which the setting unit 131 sets the reuse range R of the coil spring 21 based on a plurality of coil springs 2, and steps S8 to S14 show the process up to the point in which the determination unit 132 determines whether or not the coil spring 21 can be reused based on the reuse range R.

[0027] The flow of the method for determining the reuse of the coil spring 21 according to this embodiment is as follows: First, in step S1, multiple work machines 4 with different usage times are selected. Next, in step S2, the coil springs 2 that have been subjected to repeated stress and mounted on each work machine 4 are analyzed by X-ray diffraction using an X-ray diffractometer 3. Next, in step S3, the full width at half maximum (FWHM) of each coil spring 2 is calculated. Next, in step S4, the setting unit 131 obtains multiple data for the usage time of the coil springs 2 subjected to repeated stress and the FWHM measured by X-ray diffraction for different usage times, and plots them on a graph with the vertical axis representing the FWHM axis and the horizontal axis representing the usage time axis. Note that since there may be variations in the FWHM among multiple identical coil springs 2, instead of the FWHM, the FWHM ratio, which is the value obtained by dividing the FWHM measured for multiple different usage times by the FWHM of an unused coil spring 2, may be used. Alternatively, instead of usage time, the operating time of the work machine 4 equipped with the coil spring 2, or the operating time ratio, which is the value obtained by dividing the operating time by the warranty period of the work machine 4, may be used. Here, steps S2 and S3 correspond to the acquisition process in the present invention.

[0028] Next, in step S5, the setting unit 131 sets a first approximate line L1 with a negative slope and a second approximate line L2 with a zero slope using two-line approximation for the plotted graph. In step S6, the setting unit 131 calculates the intersection point of the first approximate line L1 and the second approximate line L2 as the inflection point P. Next, in step S7, the setting unit 131 sets the range in which the usage time at the inflection point P is less than or equal to the half-width at the inflection point P and is greater than or equal to the half-width at the inflection point P as the reuse range R for the coil spring 21. This completes the preparation for appropriately determining whether or not the coil spring 21 is reusable. Here, steps S4 to S7 correspond to the setting process in the present invention. The above steps S1 to S7 are performed each time the setting unit 131 sets the reuse range R.

[0029] Next, in step S8, the operating time of the work machine 4 to be judged is obtained. Next, in step S9, the usage time of the coil spring 21 to be judged, that is, the coil spring 21 mounted on the work machine 4 to be judged, is estimated. Next, in step S10, the coil spring 21 is analyzed by X-ray diffraction using the X-ray diffractometer 3, as in step S2. Next, in step S11, the full width at half maximum of the coil spring 21 is calculated, as in step S3. Next, in step S12, the usage time and full width at half maximum of the coil spring 21 for judgment are obtained, and the judgment unit 132 determines whether the usage time and full width at half maximum for judgment are within the reuse range R set in step S7.

[0030] If the usage time and half-width of the coil spring 21 used for determination are within the reuse range R (step S12: Yes), the determination unit 132 determines that the coil spring 21 is reusable (step S13). If they are outside the reuse range R (step S12: No), the determination unit 132 determines that the coil spring 21 is not reusable (step S14). This makes it possible to appropriately and easily determine whether or not the coil spring 21 is reusable. Here, steps S11 to S14 correspond to the determination process in the present invention. Steps S8 to S14 above are performed by the determination unit 132 each time it determines whether or not the coil spring 21 is reusable.

[0031] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of symbols]

[0032] 1: Reusability determination system, 12: Memory device, 13: Processing unit, 2: Coil spring, 21: Coil spring to be determined for reuse, R: Reusability range, S2-S3: Acquisition process, S4-S7: Setting process, S11-S14: Determination process

Claims

1. A method for determining whether a steel part subjected to repeated stress can be reused, An acquisition step is to acquire multiple values ​​for different usage times of the steel component subjected to repeated stress, and the full width at half maximum (FWHM) of the steel component measured by X-ray diffraction. A setting step of setting the range of usage time and the range of half-width, within which the half-width decreases as the usage time increases from the start of use of the steel part, as the reuse range of the steel part; A method for determining the reusability of a steel part, characterized by including a determination step of obtaining the determination usage time and determination half-width of the steel part subject to reuse determination, and determining that the steel part is reusable if the determination usage time and determination half-width are within the reuse range.

2. The aforementioned steel component is a component mounted on a work machine. The method for determining the reuse of steel parts according to claim 1, characterized in that, in the acquisition step, the usage time and the half-width of the steel parts mounted on each of the plurality of work machines are acquired.

3. The method for determining the reuse of a steel part according to claim 1, characterized in that the steel part is a coil spring attached to a part of the work machine that moves, and absorbs vibrations of the main body of the work machine when it is moving.

4. In the setting step, the vertical axis is the axis of the half-width and the horizontal axis is the axis of the usage time, and the usage time and the half-width obtained in the acquisition step are plotted. For the plotted graph, a first approximation line with a negative slope and a second approximation line with a zero slope are set using a two-line approximation method. The intersection point of the first approximate line and the second approximate line is calculated, A method for determining the reuse of a steel part according to claim 1, characterized in that the range in which the usage time of the intersection is less than or equal to the half-width of the intersection is greater than or equal to the reuse range of the steel part.

5. The method for determining the reusability of a steel part according to claim 3, characterized in that the surface of the coil spring is subjected to a surface treatment that hardens it mechanically.

6. A reuse determination system for determining whether a steel part subjected to repeated stress can be reused, The reuse determination system comprises a storage device for storing data for reuse determination, and a computing device that performs calculations for reuse determination based on the reuse determination data. The storage device stores multiple data sets for determining reuse, which are obtained for different usage times, consisting of the usage time of the steel part subjected to repeated stress and the full width at half maximum (FWHM) of the steel part measured by X-ray diffraction. Based on the data for determining reuse, the calculation device sets the range of usage time and the range of half-width, in which the half-width decreases as the usage time increases from the start of use of the steel part, as the reuse range of the steel part. A steel part reuse determination system characterized in that, if the usage time and half-width used for determination of the steel part subject to reuse determination fall within the reuse range, the steel part is determined to be reusable.

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