JP2737120B2 - Indentation hardness tester - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indentation hardness tester for applying a test load to an indenter and obtaining the hardness of the sample from the indentation depth of the indenter into the sample surface at that time. . [Prior art] An indenter with a sharp tip such as a quadrangular pyramid is pressed into the surface of a test piece, and the indentation hardness test, which determines the surface hardness from the indentation depth and load at that time, is used as one of the hardness measurement methods. Have been. In this indentation hardness tester, a sample is placed on a sample table, the pressure is lowered with respect to the sample at a fixed position, the point at which the indenter contacts the sample surface is detected, and the load at this point is measured. In addition to the point O of the load, the displacement of the indenter thereafter is detected as the indentation depth. [Problems to be Solved by the Invention] In the conventional indentation hardness tester, when the indenter contacts the sample surface, the speed of the indenter decreases due to the resistance of the sample, so that the speed of the indenter is reduced to a certain speed or less. Since the time point was detected as the contact point, an error occurred between the time point and the actual contact time point. As a means for loading the indenter, an electronic balance or the like is used, and a spring constant of the load transmitting unit is added. Therefore, there is a difference between the load output of the balance and the load actually applied to the indenter. Had occurred. For example, in the characteristic diagram showing the relationship between the load and the displacement shown in FIG. 2, the case where the curve A is based on the conventional method is shown. In the figure, the displacement and load at the time when the indenter actually contacts the sample are D ₀ and P ₀ , but the points to be measured are D _{1 to} which the detection error of the indenter contact is added, and the displacement of the balance is required. P _{1 with} load (indicated by the dashed line in the figure)
The displacement and load measurement points at the end of pushing are D ₂ , P ₄
Becomes The measured hardness value H ₁ based on these measured values is H ₁ = (K /
(D ₂ −D ₁ ) ² ) · (P ₄ −P ₁ ), and the theoretical value H ₀ is calculated by considering the load P ₂ required for displacement of the balance with respect to the displacement point D ₂ , H ₀ =
(K / (D ₂ −D ₀ ) ² ) · (P ₄ −P ₂ ). Therefore, in the measurement by the conventional device, there is a problem that the load measurement includes an error in the detection of the contact point and needs to be corrected, so that an accurate hardness measurement cannot be performed. Further, although the hardness can be measured at a constant load increasing speed, there is a problem that a constant displacement load cannot be performed. [Means for Solving the Problems] In order to solve the above problems, the present invention employs the following configuration. That is, the indentation hardness test apparatus according to the present invention comprises a load means for applying a load to the indenter so as to hold the indenter at a predetermined position against a force applied when the sample is engaged, and A load detecting means for detecting a load applied to the indenter, a movable table for linearly moving the placed sample toward the indenter held at the predetermined position, and contacting the indenter; and a movable table. Driving means for driving the movable table, displacement detecting means for detecting the displacement of the movable table, and detecting contact between the indenter and the sample from a reaction force received by the indenter when the sample contacts the indenter by movement of the movable table. Means. [Operation] When the sample placed on the movable table which moves linearly by the driving means comes into contact with the indenter held at a predetermined position, the load detecting means by the reaction force received by the indenter detects the load. The time of load detection can be used as the contact point. When the movable table is further moved to the indenter side after the contact between the indenter and the sample, the indenter is pushed into the surface of the sample, but the displacement of the movable table at this time is detected by the displacement detecting means, and the depth of pushing of the sample is determined. You can ask. Further, the load applied to the sample can be detected by the load detector. Embodiment FIG. 1 is a schematic diagram showing one embodiment of the present invention.
The indentation hardness tester 1 has a roberval mechanism 9 composed of a lever 3 supported by a fulcrum A and a load lever 4 supported by a base point B and transmitting the load of a load generating unit 6 to the indenter 2. The distal ends of the levers 3 and 4 are provided with a vertical indenter holding rod 5 for holding the indenter 2 directly above the sample 8.
Is pivoted to. The load lever 4, the load generator 6, and the like constitute an electronic balance type load mechanism 10. The indenter holding rod 5 is provided with a differential transformer type displacement detector 7 for detecting the displacement of the indenter 2. The sample 8 is placed on the table 12,
Is mounted on a moving device 13 for moving the placed sample 8 up and down with respect to the indenter 2. The moving device 13 includes a frame 15
An electromagnetic coil section 16 is provided at a central portion of the inside, and the table 12 is configured to be moved by an electromagnetic force generated in the electromagnetic coil section 16. In other words, the core portion 18 inserted into the electromagnetic coil portion 16 utilizes a force pushed up to the table side by the electromagnetic force generated in the electromagnetic coil portion 16. This transmission unit will be described. The protruding portion 18a formed at the upper end of the core 18 is inserted into the center hole of the disc spring 19 attached to the upper end of the frame 15 with a bolt 22, and is partially inserted into the recess 24a of the upper holding plate 24. Mated. The core 18, the disc spring 19, and the holding plate 24 are integrally fixed by a fastening screw 21 inserted therein. Core part 18
Move upward by electromagnetic force while resisting the reaction force of the leaf spring 19. On the holding plate 24, a table mounting table 26 is provided via spacers 25,..., And the table 12 is mounted on the table mounting table 26. A differential transformer type displacement detector 28 for detecting the displacement of the table is provided on the back surface of the table mounting table 26. A description will be given of the hardness measurement in the embodiment apparatus configured as described above. First, the electronic balance 10 is set to a fixed position based on the output signal of the displacement detector 7. Next, when the electromagnetic coil section 16 is energized, the core section 18 rises while resisting the elastic force of the disc spring 19, and the sample 8 placed on the table 12 approaches the indenter 2. At this time, the electromagnetic force generated in the electromagnetic coil section 16 and the reaction force of the disc spring 19 are equal. Further, when the sample 8 rises and comes into contact with the indenter 2, the displacement detector 7 detects the contact. The coil of the load generator 6 is energized, and a load is applied to the indenter 2 by the load mechanism 10. The amount of this load is controlled by the amount of current supplied to the load generator 6. After the sample 8 comes into contact with the indenter 2, the sample 8 is further pressed against the indenter 2. At this time, the electromagnetic force of the electromagnetic coil 16 that pushes up the sample 8 depends on the reaction force of the indenter 2 (load (The load by the mechanism 10). At this time, the relationship between the reaction force W of the disc spring 19 and the displacement δ of the disc spring 19 is δ = α · (Wa ² / Et) (E: longitudinal elastic coefficient of the disc spring, t:
Thickness of disc spring, a: outside radius of disc spring, b: inside radius of disc spring, α: constant by supporting method (when b / a = 0.4, α
= 0.044). Therefore, if the load applied to the indenter with respect to the reaction force W of the disc spring 19 is made very small, the electromagnetic force and the displacement of the disc spring become almost proportional. Therefore,
The disc spring 19 is controlled by controlling the current of the electromagnetic coil 16.
, That is, the displacement speed of the sample 8 pushed by the indenter 2 can be controlled. In addition, since the load generator 6 can be energized in response to a detection signal from the displacement detector 7, loop-type load control is facilitated. The load when the sample 8 is pressed against the indenter 2 and the indenter 2 is pressed into the surface of the sample 8 is applied to the load generating unit 6 of the load mechanism 10.
Of the indenter 2
The depth to which the sample is pushed into the sample is measured from the difference between the displacement of the table 12 detected by the displacement detector 28 and the displacement of the indenter 2 detected by the displacement detector 7. The load-displacement characteristic is shown by a characteristic curve B in FIG. That is, the sample load from the point D ₁ in contact with the indenter is applied to the indenter, moreover, the load applied to the indenter, as the output of the loading mechanism 10, when moving the indenter into the specimen surface by conventional electronic balances as Since the load required for the initial displacement of the balance itself is not applied, it is not necessary to correct the spring constant of the balance in the load measurement, and the load is accurately measured. In addition, since the load is detected on the balance side and the point in time is set as the contact point, it does not include the indentation depth error (D ₁ -D _{0 in} FIG. 2) before the contact detection as in the related art. Therefore, if the measured displacement and load are D ₃ and P ₃ ,
The hardness H measured by this device is H = (K / (D ₃ −P ₁ )) · P ₃
And accurate hardness measurement can be performed. Since the indenter loading mechanism and the table moving mechanism are configured independently of each other, the indenter is used as in the conventional device in which the table on which the sample is placed and the mechanism for pushing the indenter into the sample are assembled in a U-shaped machine frame. When the sample is pushed into the sample surface, a reaction force acts on the machine frame of the sample machine, and the measurement error of the displacement caused by the machine frame being distorted can be eliminated, and the measurement accuracy can be improved. In the above embodiment, the means for pushing up the table is constituted by using electromagnetic force. However, the means for pushing up the table may be constituted by using a hydraulic pressure, a screw or the like. [Effects of the Invention] As is clear from the above description, according to the indentation hardness tester according to the present invention, the point of contact between the indenter and the sample can be accurately detected, and the indenter can be applied to the indenter by a load means such as an electronic balance. The applied load can be detected with high accuracy. Therefore, since the load can be detected accurately without performing correction in consideration of the spring constant of the balance, the hardness measurement of the sample can be performed accurately. In addition, since the sample side is moved in a straight line, not in an arc, and is brought into contact with the indenter, it is possible to perform the detection with high accuracy while keeping the displacement speed almost constant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing one embodiment of an indentation hardness test apparatus according to the present invention, and FIG. 2 is a load-displacement characteristic measured by a conventional apparatus and an embodiment apparatus. FIG. 1 ... indentation hardness tester, 2 ... indenter 8 ... sample, 10 ... load mechanism 12 ... table, 13 ... table moving mechanism 16 ... electromagnetic coil, 19 ... disk spring 28 ... displacement Detector

Claims (1)

(57) [Claims] Load means for applying a load to the indenter so as to hold the indenter at a predetermined position against the force applied by the sample being engaged, load detecting means for detecting the load applied to the indenter by the load means, A movable table that linearly moves the placed sample toward the indenter held at the predetermined position and makes contact with the indenter; a driving unit that drives the movable table; and a displacement of the movable table is detected. And a means for detecting contact between the indenter and the sample from a reaction force received by the indenter when the sample comes into contact with the indenter by movement of the movable table.