JPH05264487A - Heat treatment oil cooling tester - Google Patents

Abstract

PURPOSE:To measure characteristic temperature of a heat treatment oil without any personal difference in a cooling test of the heat treatment oil used for hardening of a metal. CONSTITUTION:A cooling speed curve (first derivative) is obtained by performing first-order differentiation of a cooling curve (change of test piece temperature with time). Then, a test piece temperature E at a cooling time D when a maximum value C appears in the cooling speed curve B is detected. Furthermore, an average change rate (inclination F) of the test piece temperature from measurement initiation to the cooling time D is obtained. Then, a point where an inclination F' which is obtained by translating the inclination F is tangential to the cooling curve A is set to a characteristic temperature G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling tester for heat-treated oil used for quenching metals, and more specifically,
The present invention relates to a cooling tester capable of accurately measuring a characteristic temperature of heat treated oil by performing a cooling test of heat treated oil specified by JIS and performing data processing by a computer.

[0002]

2. Description of the Related Art A cooling test of heat-treated oil used for quenching steel and other metals is
It is specified in JIS-K2242. In this test, as shown in FIG. 5, a test piece c having a structure in which an alumel wire b is embedded in the surface of a silver test piece a is used (d is a silver pipe, e is a silver wire, and f is a support rod). .. Then, as shown in FIG. 6, after heating the test piece c to 800 ° C. in the heating furnace g and putting it in the heat-treated oil h, the change with time of the temperature of the test piece c was measured, and the cooling performance was obtained from the obtained cooling curve. Is to evaluate. In FIG. 6, i is a test piece automatic lifting device, j is a dropping switch, and k is a recorder for outputting a cooling curve.

FIG. 7 shows an example of a cooling curve. From this cooling curve, the following three cooling processes can be seen. Steam film stage: A test piece heated to 800 ° C is covered with a steam film generated by thermal decomposition of heat-treated oil at a high temperature, and this steam film interferes with cooling. Boiling stage However, when the temperature of the test piece falls to some extent, the vapor film breaks and the heat-treated oil comes into direct contact with the test piece, so that cooling is accelerated. Convection stage After that, the specimen is sufficiently cooled, followed by gentle cooling due to convection and conduction.

Characteristic temperature is one of the measurement items of the cooling test described above. This characteristic temperature is the temperature at which the vapor film collapses in the quenching and cooling process as shown in FIG. 7, and is the test piece temperature at the time of transition from the vapor film stage to the boiling stage. Conventionally, the characteristic temperature is detected by outputting a cooling curve to a recorder and visually reading a point at which the temperature rapidly changes from the cooling curve. However, such a method of visually reading the characteristic temperature has a large reading error due to individual differences, and thus the conventional method has a problem of low measurement accuracy. Moreover, it was difficult to quantitatively evaluate the repeatability of 5 ° C. defined by JIS.

The present invention has been made in view of the above circumstances, and provides a heat treatment oil cooling tester capable of eliminating the error caused by visually reading the characteristic temperature and measuring the characteristic temperature of the heat treated oil without individual differences. The purpose is to do.

[0006]

In order to achieve the above object, the present invention provides, as a first invention, a measuring unit for measuring a change with time of a test piece temperature when a heated test piece is cooled with heat-treated oil. Then, the first derivative of the time-dependent change of the test piece temperature is performed to calculate the first derivative, and the average change rate of the test piece temperature from the start of measurement to the time when the extreme value of the first derivative appears is calculated, A heat treatment oil cooling tester comprising: a calculation / comparison section for comparing the average rate of change with the first derivative and outputting the test piece temperature when the two become substantially equal as the characteristic temperature of the heat treatment oil. provide.

As a second aspect of the present invention, a measuring unit for detecting a time-dependent change in the temperature of the test piece when the heated test piece is cooled with heat-treated oil, and a first-order differential and a higher-order differential of the temperature change of the test piece are performed. The first derivative and the higher derivative are calculated, and the average change rate of the test piece temperature from the start of measurement to the time when the first extreme value of the higher derivative appears is calculated. Provided is a heat treatment oil cooling tester, comprising: a calculation / comparison unit that compares a derivative and outputs a test piece temperature when the two become substantially equal as a characteristic temperature of heat treatment oil.

The concept of the present invention is illustrated in FIG. That is, A in FIG. 1 indicates a cooling curve. In the first invention, first, a cooling curve (change in test piece temperature with time) A
To obtain a cooling rate curve (first derivative) B. Next, the test piece temperature E at the cooling time D when the maximum value C appears on the cooling rate curve B is detected. Furthermore, the average change rate of the test piece temperature from the start of measurement to the cooling time D,
That is, the gradient F (E-800) / D (° C / sec) determined by the temperature (800 ° C) of the test piece at the start of measurement and the temperature E of the test piece
Ask for. Then, a gradient F ′ obtained by translating this gradient F
Is the characteristic temperature G at the point of contact with the cooling curve A. This last operation compares the average rate of change (gradient F) of the temperature of the test piece from the start of measurement to time D with the first derivative (cooling rate curve B), and the test piece when both are equal This is an operation for obtaining the temperature as the characteristic temperature G of the heat-treated oil.

When the actual measurement is performed, the cooling curve A from the start of measurement to the characteristic temperature G becomes uneven, and the slope F'contacts the cooling curve A even at a temperature higher than the characteristic temperature G. (See FIGS. 3 and 4). Therefore, in actual measurement, the average rate of change and the first derivative are sequentially compared in the direction going back to the measurement start time, and the temperature of the test piece when both are equal is defined as the characteristic temperature G.

Further, in FIG. 1, the characteristic temperature G exists at the rising point H of the peak in the cooling rate curve B. The second aspect of the invention is to perform a higher-order differentiation of the cooling curve A to obtain a slope determined by the temperature of the test piece at the start of measurement and the temperature of the test piece until the first extreme value of the higher derivative appears. By making the point of parallel movement and contact with the cooling curve A the characteristic temperature G, the temperature E of FIG. 1 is made closer to the characteristic temperature G (location H). In this case, the higher the higher order differential is, the closer the temperature E becomes to the characteristic temperature G, and finally the temperature E converges to the characteristic temperature G.

When the actual measurement is carried out, the cooling curve A from the start of measurement to the characteristic temperature G becomes uneven, and even if the temperature is higher than the characteristic temperature G, a small extreme value is present in the higher derivative. Yes (see FIGS. 3 and 4). Therefore, in the actual measurement, the first extreme value in the portion corresponding to the peak of the cooling rate curve B is the first extreme value of the higher derivative.

According to the present invention, an extreme value always appears when the cooling curve of heat treated oil is differentiated, and a gradient determined from the test piece temperature at the time when this extreme value first appears and the test piece temperature at the start of measurement. It is necessary to detect the characteristic temperature of the heat-treated oil without individual differences by defining the temperature of the test piece at this contact point as the characteristic temperature when it moves in parallel with the cooling curve at the substantially same point as the characteristic temperature. This was made as a result of the findings of the inventor.

[0013]

EXAMPLES Next, the present invention will be illustrated concretely by examples, but the present invention is not limited to the following examples. FIG. 2 shows a heat treatment oil cooling tester according to an embodiment of the present invention, and this apparatus comprises a measuring unit 1 and a comparing / calculating unit 2. Here, the tester unit 1 is the test piece of FIG.
FIG. 6 having a heating furnace, a test piece automatic lifting device, heat treatment oil, etc.
A tester unit 3 similar to that shown in (but no recorder is provided) and a start signal to the tester unit 3 are amplified, and the electromotive force of the thermocouple is amplified and sent to the comparison / calculation unit 2. It is composed of an amplifier unit 4. The comparison / arithmetic unit 2 is composed of a personal computer unit 5 having a hard disk, a keyboard, a display, a printer and the like.

The heat treatment oil cooling tester of this example automatically conducts a cooling test of heat treatment oil specified in JIS in the tester unit 3, and sends the result to the personal computer unit 5 via the amplifier unit 4, Data processing is performed by the personal computer unit 5.

Next, a measurement example will be shown. Measurement Example 1 A cooling test of a dioctyl phthalate-containing standard solution specified in JIS-K2242 was conducted using the tester of the above-mentioned example. The results (printer output) are shown in FIG. 3 and Table 1. Here, FIG. 3 is a graph showing test piece temperature (cooling curve), cooling rate and cooling acceleration, and Table 1 is cooling time (Time, 0.05 second interval), test piece temperature (Temp.), Cooling rate (Vel.). And a part of numerical output of cooling acceleration (Accel.).

[0016]

[Table 1]

In this example, the characteristic temperature is displayed as 507.1 ° C. above the graph of FIG. 3 (not shown). this is,
This is based on the following calculation and comparison results (see Table 1). That is, the extreme value C of the cooling rate is −306.0 ° C. /
Since the cooling time D at this time is 3.95 seconds and the test piece temperature E is 474.1 ° C., the average rate of change of the test piece temperature from the start of measurement to the cooling time D is (474.1-800 ) /3.95=−82.4° C./sec. This average rate of change and the cooling rate at every moment are sequentially compared in the direction going back to the measurement start time, and the temperature of the test piece at the point where the difference between the cooling rate and the average rate of change (-82.4 ° C / sec) is the minimum is determined. The characteristic temperature G (507.1 ° C.) of the heat-treated oil is used.

When the characteristic temperature is detected by using the cooling acceleration (second derivative) obtained by performing the second derivative,
Average rate of change of test piece temperature [(489.4-800) /3.90=-79] from the start of measurement to the time D'when the first extreme value I (see FIG. 3 and Table 1) of the cooling acceleration appears. 0.6 ° C
/ Sec] is calculated, and this average rate of change and the instantaneous cooling rate are sequentially compared in the direction going back to the measurement start time, and the temperature of the test piece at the point where the difference between the cooling rate and the average rate of change is minimized Characteristic temperature G ′ (507.1 ° C.).

Measurement Example 2 A cooling test of a commercially available heat-treated oil was conducted using the tester of the example. The results (printer output) are shown in FIG. 4 and Table 2. FIG. 4 and Table 2 show the same as FIG. 3 and Table 1, respectively.

[0020]

[Table 2]

In the present example, the characteristic temperature is displayed as 609.3 ° C. above the graph of FIG. 4 (not shown). this is,
This is based on the following calculation and comparison results (see Table 2). That is, the extreme value C of the cooling rate is −533.5 ° C. /
Since the cooling time D at this time is 2.75 seconds and the test piece temperature E is 520.0 ° C., the average change rate of the test piece temperature from the start of measurement to the cooling time D is (520.0 −800) /2.75=−101.8° C. /
Seconds. This average rate of change and the momentary cooling rate are sequentially compared in the direction going back to the measurement start time, and the temperature of the test piece at the point where the difference between the cooling rate and the average rate of change (-101.8 ° C / sec) is the minimum is determined. The characteristic temperature G (609.3 ° C.) of the heat-treated oil is used.

When the characteristic temperature is detected by using the cooling acceleration (second derivative) obtained by performing the second derivative,
Average change rate of test piece temperature [(571.7-800) /2.65=-86] from the start of measurement to the time D'when the first extreme value I (see FIG. 4 and Table 2) of the cooling acceleration appears. 2 ° C
/ Sec] is calculated, and this average rate of change and the instantaneous cooling rate are sequentially compared in the direction going back to the measurement start time, and the temperature of the test piece at the point where the difference between the cooling rate and the average rate of change is minimized Characteristic temperature G ′ (614.2 ° C.).

Measurement Example 3 Using the tester of the example, the same heat-treated oil was used as a sample.
One cooling test was performed. The results (printer output) are shown in Tables 3 and 4. Tables 3 and 4 show the same as Table 1.

[0024]

[Table 3]

[0025]

[Table 4]

In this example, as a result of obtaining the characteristic temperature by using the cooling rate to determine the cooling time D, the first characteristic temperature G is 607.8 ° C. and the second characteristic temperature G is 608.
The temperature was 8 ° C and the repeatability was 1.0 ° C.

In the above measurement examples 1 to 3, the test piece temperature at which the difference between the average rate of change of the test piece temperature and the cooling rate until the cooling time D or D'is the minimum is defined as the characteristic temperature G or G '. There is. The reason is that the accuracy specified in JIS can be sufficiently secured by this method, but if necessary, the test piece when the average rate of change and the cooling rate of the test piece completely match by a method such as proportional distribution. The temperature may be the characteristic temperature.

[0028]

As described above, according to the present invention, it is possible to accurately measure the characteristic temperature of heat-treated oil by eliminating visual errors.

[Brief description of drawings]

FIG. 1 is a graph illustrating the concept of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a heat treatment oil cooling tester of the present invention.

FIG. 3 is a graph obtained in Measurement Example 1.

FIG. 4 is a graph obtained in measurement example 2.

FIG. 5 is a schematic view of a test piece used for a cooling test of heat-treated oil.

FIG. 6 is a schematic view of an apparatus used for a heat treatment oil cooling test.

FIG. 7 is a graph showing a cooling curve obtained in a heat treatment oil cooling test.

[Explanation of symbols]

1 Measurement part 2 Calculation / comparison part A Cooling curve B Cooling rate curve C Maximum value of cooling rate D Cooling time at which maximum value of cooling rate appears E Test piece temperature at cooling time D From measurement start to cooling time D Average rate of change in specimen temperature G Characteristic temperature of heat treated oil G'Characteristic temperature of heat treated oil

Claims (2)

[Claims] 1. A first-order derivative is calculated by performing a first-order differentiation of the time-dependent change of the temperature of the test piece when measuring the time-dependent change of the temperature of the test piece when the heated test piece is cooled with heat-treated oil. The average change rate of the temperature of the test piece from the start of the measurement to the time when the extreme value of the first derivative appears is calculated, and the average change rate is compared with the first derivative to make both substantially equal. A heat treatment oil cooling tester, comprising: a calculation / comparison unit that outputs the test piece temperature as a characteristic temperature of heat treatment oil. 2. A measuring unit for detecting a time-dependent change in the temperature of a test piece when a heated test piece is cooled with a heat-treated oil, and a first derivative and a higher derivative of the temperature change of the test piece to perform a first derivative and Calculate the high-order derivative, calculate the average rate of change of the specimen temperature from the start of measurement to the time when the first extreme value of the high-order derivative appears, and compare this average rate of change with the first derivative. Then, the heat treatment oil cooling tester is provided with a calculation / comparison section that outputs the test piece temperature when the two become substantially equal as the characteristic temperature of the heat treatment oil.