Method and apparatus for cooling material test pieces

Abstract

To provide a cooling method and cooling device for material test pieces, the cooling device being configured to offer a minimized amount of liquid nitrogen ejected, reduced temperature adjustment time, a simplified design, and portability that allows the device to be placed next to a Charpy testing device.SOLUTION: A method and device for cooling a material test piece 5 to a low test temperature using liquid nitrogen 3 in a container 2 is provided, the method involving floating a test piece mounting table 4 made of a heat insulation material on a surface of liquid nitrogen and placing the material test piece 5 on the test piece mounting table to cool the material test piece. Preferably, the method involves attaching a weight on the test piece mounting table to adjust test temperature by changing the distance between the material test piece and the surface of the liquid nitrogen.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for cooling a material test piece used in material testing, and more particularly to a method and apparatus for cooling a material test piece for a Charpy impact test in which an impact value is measured to evaluate the toughness of a steel material such as a thick steel plate. [Background technology]

[0002] The Charpy impact test described in JIS Z 2242 is a commonly known material test for evaluating the impact properties of metallic materials. The impact value of many metallic materials varies depending on the test temperature, so the test must be performed at a specified temperature. If the temperature is not room temperature, the material test piece (hereinafter simply referred to as "test piece") must be heated or cooled to the specified temperature under controlled conditions. For low carbon steel in particular, tests are generally performed at 0°C or below due to the environment in which it will be used.

[0003] The test specimen can be cooled either by immersing it in a liquid to cool it to the liquid temperature or by cooling it with cold gas. When cooling by immersing the test specimen in a liquid, the temperature that can be adjusted is between the boiling point and the freezing point of the liquid. For example, as described in Non-Patent Document 1, when ethyl alcohol is used as the liquid, the temperature can be adjusted from room temperature to -75°C, which is close to the freezing point, by adding dry ice. Also, when liquid nitrogen, which is often used industrially, is used, the temperature can be adjusted to -196°C.

[0004] However, when it comes to cooling using liquids that are generally available industrially, there are currently no liquids that can adjust the temperature in the range from -75°C or below to -196°C. If rare liquid argon or liquid xenon is used, it is possible to adjust the temperature only to the liquefaction temperatures of -186°C or -109°C, but when testing by lowering the temperature in 10°C increments, for example, the inability to adjust the temperature beyond the liquefaction temperature is an issue.

[0005] As a method for solving the above problem, there is a method of cooling by using cold gas. When using cold gas, the temperature can be adjusted by supplying the gas within the insulating layer, and the temperature can be set to a temperature higher than the vaporization temperature of the gas by adjusting the supply amount. For example, Patent Document 1 discloses an apparatus for cooling metal test pieces to a predetermined cryogenic temperature, in which dry ice is placed on an air-permeable storage shelf in a tank to which liquid nitrogen is supplied, and the test pieces are placed on top of the dry ice. However, in such an apparatus, in order to keep the level of liquid nitrogen constant, liquid nitrogen is supplied while the overflow is discharged, which causes a problem of wasting liquid nitrogen.

[0006] Furthermore, cooling devices that adjust the amount of liquid nitrogen sprayed when liquid nitrogen is supplied by spraying are commercially available. These cooling devices are widely used because they can adjust the temperature to any value between room temperature and the temperature of liquid nitrogen (-196°C). However, because these cooling devices adjust the temperature by repeatedly spraying liquid nitrogen, the problem is that it takes time to reach the target temperature and to maintain that temperature. Another problem is that cooling devices that spray liquid nitrogen are large-scale facilities and difficult to install alongside Charpy testing machines. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Utility Model Application Publication No. 60-146841 [Non-patent literature]

[0008] [Non-Patent Document 1] Harumichi Okamoto and 1 other, "Methods of Material Testing of Metals at Liquid Nitrogen Temperature and the Results," Cryogenics, Vol. 3, No. 1 (1968) pp. 9-15 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a cooling method and device for material test pieces that solves the problems of the conventional technology, reduces the amount of liquid nitrogen sprayed, which is a problem with liquid nitrogen spray devices, shortens the temperature adjustment time, simplifies the device, and is portable so that it can be installed next to a Charpy testing machine. [Means for solving the problem]

[0010] The present inventors have conducted extensive research in order to achieve the above-mentioned object. The reason why the temperature adjustment time for liquid nitrogen jet cooling becomes longer was examined by measuring the temperature of the test piece during cooling. As a result, it was found that the temperature inside the insulation layer and the test piece fluctuated greatly depending on the timing of jetting liquid nitrogen to adjust the temperature inside the insulation layer, and that the temperature became constant when the jetting was stopped.

[0011] As a method for eliminating this temperature fluctuation, the inventors further investigated a method for adjusting the temperature of the test piece to a predetermined temperature without spraying liquid nitrogen, and discovered that the temperature of the test piece can be kept constant by putting liquid nitrogen in a heat-retaining container, placing the test piece on a heat-insulating stand, and floating it on the surface of the liquid nitrogen.

[0012] Furthermore, they discovered that by submerging part of an insulating platform floating on the surface of the liquid nitrogen and changing the distance between the liquid nitrogen surface and the test specimen, it is possible to adjust the temperature of the test specimen to any temperature below -90°C (above -196°C). The research experiments that led to the above findings and their results will be described later.

[0013] The present invention was completed based on these findings and through further investigation, and the gist of the present invention is as follows. [1] A method for cooling a material test piece to a low test temperature by a liquid refrigerant in a container, A test piece mounting table made of a heat insulating material is floated on the liquid surface of the liquid refrigerant, the material test piece is placed on the test piece mounting table, and the material test piece is cooled. A method for cooling a material test piece, comprising: [2] A method for cooling a material test piece according to [1], characterized in that a weight is attached to the test piece mounting table and the test temperature is adjusted by changing the distance between the material test piece and the liquid surface of the liquid refrigerant. [3] A method for cooling a material test piece according to [1] or [2], characterized in that the test temperature is -90°C or lower. [4] A method for cooling a material test piece according to any one of [1] to [3], characterized in that the material test piece is a Charpy test piece. [5] A method for cooling a material test piece according to any one of [1] to [4], characterized in that the liquid refrigerant is liquid nitrogen or liquid helium. [6] A cooling device for cooling a material test piece to a low test temperature by a liquid refrigerant in a container, comprising: The container; The liquid refrigerant; a test piece mounting table made of a heat insulating material that floats on the liquid surface of the liquid refrigerant; A cooling device for a material test piece, comprising: [7] The cooling device for material test pieces according to [6], characterized in that the test piece mounting table has a means for attaching and detaching a weight. [8] A cooling device for material test pieces according to [6] or [7], characterized in that the test temperature is -90°C or lower. [9] A cooling device for a material test piece according to any one of [6] to [8], characterized in that the material test piece is a Charpy test piece.

[10] A cooling device for material test pieces according to any one of [6] to [9], characterized in that the liquid refrigerant is liquid nitrogen or liquid helium. Effect of the Invention

[0014] According to the present invention, the temperature of a material test piece can be made to reach a target temperature in a short time and can be maintained at that temperature without ejecting the liquid refrigerant even at or above the vaporization temperature of the liquid refrigerant, which provides an industrially outstanding effect of being able to efficiently determine the Charpy impact value for evaluating the safety of a steel structure. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic perspective view showing one embodiment of a cooling device for a material test piece according to the present invention. [Diagram 2] 1 is a schematic vertical cross-sectional view showing one embodiment of a cooling device for a material test piece according to the present invention. [Diagram 3] FIG. 2 is a schematic perspective view showing an embodiment of a test piece mounting table in a cooling device according to the present invention. [Figure 4] FIG. 2 is a schematic diagram illustrating temperature changes during cooling of a material test piece in the present invention and the prior art. [Diagram 5] FIG. 2 is a schematic diagram illustrating a temperature change during cooling of a material test piece in the present invention. [Figure 6] FIG. 2 is a schematic diagram showing the relationship between the distance from the liquid nitrogen surface and the temperature of a test piece in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Representative embodiments of the cooling method and cooling device for material test pieces according to the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these. Also, since the drawings are intended to conceptually explain the present invention, the dimensions of each member shown and their ratios may differ from the actual ones.

[0017] [Cooling method] The method for cooling a material test piece according to the present invention is a method for cooling a material test piece to a low test temperature by a liquid refrigerant in a container, characterized in that a test piece mounting table made of an insulating material is levitated on the surface of the liquid refrigerant, the material test piece is placed on the test piece mounting table, and the material test piece is cooled.

[0018] The present invention also provides a method for cooling a material test piece, which can adjust the test temperature of the material test piece by attaching a weight to the test piece mounting table and changing the distance between the material test piece and the liquid surface of the liquid refrigerant.

[0019] That is, by floating a test piece mounting table made of a heat insulating material on the surface of the liquid refrigerant, the temperature of the material test piece can be kept constant by the cold air vaporized from the liquid refrigerant. The temperature of the cold air vaporized from the liquid refrigerant becomes constant according to the distance d from the liquid refrigerant surface, so the material test piece can be cooled to a target temperature by adjusting the distance d from the liquid refrigerant surface to the material test piece placed on the test piece mounting table.

[0020] The distance d from the liquid surface can be adjusted by changing the height of the test piece mounting table above the liquid surface.

[0021] One specific example of such a method is to attach multiple detachable weights to a test specimen mounting table floated on the liquid surface, and to sink a part of the test specimen mounting table to change the distance d between the liquid surface of the liquid refrigerant and the material test specimen. In this method of attaching weights, the degree to which the mounting table sinks can be changed by changing the weight of the weights or the number of multiple weights to be detached, so the weight of the weights can be selected so as to achieve the target test specimen temperature.

[0022] Furthermore, the test temperature is preferably -90°C or lower. More preferably, it is -90°C or lower and -196°C or higher, and furthermore, it is -256°C or higher. This is because the target material test is a low-temperature Charpy impact test, and therefore the material test piece is preferably a Charpy test piece. Note that the present invention can also be applied to material test pieces used in material tests such as low-temperature impact tests other than the Charpy impact test.

[0023] Next, liquid nitrogen is preferable as the liquid refrigerant. Liquid nitrogen is a liquid with a boiling point of -196°C (77.35K) and is used for various purposes as a coolant or refrigerant. Liquid helium can also be used as a refrigerant with a lower boiling point. The boiling point of liquid helium is -269°C (approximately 4.2K) and is used when conducting material testing at the extremely low temperature of -256°C.

[0024] [Cooling device] Next, one embodiment of the cooling device for material test pieces according to the present invention will be described with reference to Figures 1 and 2. Figure 1 is a perspective view of the device, and Figure 2 is a vertical cross-sectional view.

[0025] The material test piece cooling device 1 of the present invention is a cooling device that cools a material test piece 5 to a low test temperature using liquid nitrogen 3, which is a liquid refrigerant, in an insulated container 2, and is equipped with the insulated container 2, liquid nitrogen 3, which is a liquid refrigerant, and a test piece mounting table 4 made of an insulating material that floats on the surface of the liquid nitrogen 3.

[0026] It is also preferable that the test piece mounting table 4 has a means (not shown) for attaching and detaching a plurality of weights. By changing the total weight of these weights, a part of the test piece mounting table 4 sinks below the surface of the liquid nitrogen 3, and the distance d between the surface of the liquid nitrogen 3 and the bottom surface of the material test piece can be changed. By adjusting this distance d, the material test piece can be cooled to a target temperature.

[0027] The test piece mounting stage 4 made of the levitated insulating material is preferably made of polystyrene foam insulating material (so-called expanded polystyrene), but other insulating materials such as expanded polypropylene can also be used.

[0028] Furthermore, in order to stabilize the levitation of the test piece mounting table 4, it is preferable to use a four-legged table as shown in Fig. 3(a). The number of legs 4a is at least the three-legged table as shown in Fig. 3(b), and it is preferable to use a table with more legs than that. The legs 4a are stable even if they do not reach the bottom surface of the thermal insulation container 2, but from the viewpoint of the restoring force due to buoyancy, it is more stable and preferable for them to be longer from the liquid nitrogen surface.

[0029] Here, the shape and structure of the thermal insulation container 2 are not particularly limited, but it is preferable that the thermal insulation container 2 is an open-type rectangular prism container that is portable and easy to pour liquid nitrogen into. An open-type container is a container that does not have a tightly sealed lid. In addition, it is preferable that the walls and bottom of the container have a double structure with a vacuum insulation layer.

[0030] Furthermore, a plurality of material test pieces 5 can be placed on the test piece mounting table 4 . The temperature of these material test pieces 5 can be measured by attaching a thermocouple to a dummy sample of the same material and shape as the test piece, and placing the dummy sample adjacent to the material test piece 5.

[0031] Although liquid nitrogen was used as the liquid refrigerant in the thermal container, it is possible to use liquid helium instead, as mentioned above. In that case, it will be possible to adjust the temperature to -256°C or higher.

[0032] [Experimental study on cooling of test specimens and its results] Here, an experiment on the temperature change during cooling of a material test piece and the results thereof will be described.

[0033] FIG. 4 shows the results of temperature changes during cooling of a material test piece in the cooling method of the present invention and the liquid nitrogen spray cooling method of the prior art. In the experiment of FIG. 4, the target test piece temperature was set to -150°C in the present invention example and -170°C in the prior art example, and the time lapse until the test piece temperature became stable enough to be tested was investigated. The solid line in FIG. 4 shows the temperature change in the present invention example, and the dotted line shows the temperature change in the prior art example. In the prior art example, when liquid nitrogen was poured (spouted), the test piece temperature dropped sharply, but it immediately rose again, so liquid nitrogen was poured in each time, and 232 minutes passed before the testable temperature was kept constant for 30 minutes. In contrast, in the present invention example, if liquid nitrogen was poured in once and left in the container, the test piece temperature stabilized without refilling liquid nitrogen, and only 111 minutes passed before the test was possible. In other words, the time was significantly reduced by 121 minutes compared to the prior art example.

[0034] Next, Fig. 5 shows the results of investigating the state of temperature change for each target cooling temperature when cooling a test piece in the cooling method of the present invention. From Fig. 5, it was found that the higher the cooling temperature, the longer it takes for the temperature to stabilize (become constant).

[0035] Furthermore, Figure 6 shows the results of investigating the relationship between the distance d from the liquid surface and the cooling temperature. The target cooling temperature is adjusted by changing the type of weight attached to the test specimen mounting table, thereby varying the distance d between the bottom of the test specimen on the mounting table and the liquid nitrogen surface. It was found that the shorter the distance d, i.e., the closer the test specimen is to the liquid surface, the closer the temperature is to the liquid nitrogen temperature of -196°C, and the longer the distance d, i.e., the farther the test specimen is from the liquid surface, the higher the temperature is. EXAMPLES

[0036] The results of the Charpy impact test according to JIS Z 2242 are explained below. First, the test pieces were taken from the thick steel plate. The test pieces were 10 mm square x 55 mm long, and three pieces were prepared for each temperature. A heat-retaining container with a diameter of 300 mm and a height of 350 mm was used as the cooling device according to the present invention (invention example) described above. A commercially available liquid nitrogen jetting device (Shimadzu Corporation cooling device) was used as a conventional device for comparison. Liquid nitrogen was poured into each and the cooling time was measured. This cooling time was the total time from starting cooling from room temperature to maintaining the target temperature at ±1°C for 30 minutes (testable time) according to JIS Z 2242. The temperature of the test pieces was measured using the above-mentioned thermocouple. In the present invention example, the target temperature was adjusted by changing the weight of the weight attached to the test piece mounting base made of polystyrene foam insulation material and changing the distance between the test piece and the liquid nitrogen liquid surface. In the comparative example, the temperature was adjusted by adjusting the amount of liquid nitrogen jetted.

[0037] Table 1 summarizes the comparison of target temperatures and cooling times.

[0038] [Table 1]

[0039] Comparing No. 1 and No. 5 with a target temperature of -100°C, the present invention example (cooling time of No. 1: 113 minutes) completed cooling in 113 / 240=47% of the time required for the comparative example (cooling time of No. 5: 240 minutes). Comparing No. 2 and No. 6 with a target temperature of -140°C, the present invention example (cooling time of No. 2: 96 minutes) completed cooling in 96 / 210=46% of the time required for the comparative example (cooling time of No. 6: 210 minutes). Comparing No. 3 and No. 7 with a target temperature of -165°C, the present invention example completed cooling in 35% of the time required for the comparative example. Comparing No. 4 and No. 8 with a target temperature of -180°C, the present invention example completed cooling in 27% of the time required for the comparative example.

[0040] As described above, by applying the cooling method of the present invention, it is possible to cool in less than 50% of the time required by the conventional method of spraying liquid nitrogen because liquid nitrogen is not sprayed. This enables a significant reduction in cooling time and contributes greatly to improving testing efficiency.

[0041] Furthermore, since the cooling device of the present invention is a simple device that simply requires placing liquid nitrogen in a portable insulated container, it can be easily transported and does not require a large-scale cooling device that sprays liquid nitrogen, so it can be installed near a Charpy testing machine. [Explanation of symbols]

[0042] 1 Cooling device 2 Thermal container 3 Liquid nitrogen (liquid refrigerant) 4 Test piece placement table 4a Test specimen placement table legs 5 Material test pieces d Distance between the liquid nitrogen surface and the bottom of the test piece

Claims

1. A method for cooling a material test specimen to a low test temperature by a liquid refrigerant in a container, comprising: A test piece mounting table made of a heat insulating material is floated on the liquid surface of the liquid refrigerant, the material test piece is placed on the test piece mounting table, and the material test piece is cooled. A method for cooling a material test piece, comprising:

2. 2. A method for cooling a material test piece according to claim 1, wherein the test temperature is adjusted by attaching a weight to the test piece mounting table and changing the distance between the material test piece and the liquid surface of the liquid refrigerant.

3. 3. The method for cooling a material test piece according to claim 1, wherein the test temperature is −90° C. or lower.

4. 3. The method for cooling a material test piece according to claim 1, wherein the material test piece is a Charpy test piece.

5. 3. The method for cooling a material test piece according to claim 1, wherein the liquid refrigerant is liquid nitrogen or liquid helium.

6. A cooling device for cooling a material test piece to a low test temperature by a liquid refrigerant in a container, comprising: The container; The liquid refrigerant; a test piece mounting table made of a heat insulating material that floats on the liquid surface of the liquid refrigerant; A cooling device for a material test piece, comprising:

7. 7. The cooling device for a material test piece according to claim 6, further comprising a means for attaching and detaching a weight to said test piece mounting table.

8. 8. The cooling device for a material test piece according to claim 6, wherein the test temperature is -90° C. or lower.

9. 8. The cooling device for a material test piece according to claim 6 or 7, wherein the material test piece is a Charpy test piece.

10. 8. The cooling device for a material test piece according to claim 6, wherein the liquid coolant is liquid nitrogen or liquid helium.

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