Evaluation method of sealing property of joint material

Abstract

To provide a method for further precisely evaluating the sealing property of a joint material.SOLUTION: After a sealed space inside a test piece, formed by sandwiching a joint material between at least two members, is depressurized using a vacuum pump, the depressurization by the vacuum pump is stopped, and the change in the degree of vacuum inside the sealed space thereafter is continuously measured. Of time-series data of the degree of vacuum obtained by this measurement, the time-series data of the degree of vacuum from the initial degree of vacuum inside the sealed space immediately after the depressurization by the vacuum pump is stopped to the pressure recovery of 30 to 70% is fitted with the approximation formula p=p0×exp(-t / τ) (where p is the degree of vacuum inside the sealed space (Pa), p0 is the initial degree of vacuum (Pa), t is elapsed time (s), and τ is the pressure recovery coefficient (s)), and the sealing property is evaluated based on the magnitude of the obtained pressure recovery coefficient τ.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the sealing property of a joint material used in the joints of refractories used in continuous steel casting equipment and the like. [Background technology]

[0002] In continuous steel casting equipment, many refractories are joined together, and air entrapment at these joints can cause problems such as oxidation and nitrogen pickup, which can lead to deterioration in the purity and quality of the steel and abnormal melting of the joints. Therefore, the role of the joint materials used at these joints is extremely important.

[0003] Since one of the main evaluation indices for joint sealants is their ability to maintain their sealing ability under hot conditions, it is necessary to evaluate their sealing ability while applying surface pressure to the joint sealant installed in a high-temperature environment. Conventionally, evaluation has generally been based on the time it takes for pressure to return to atmospheric pressure after being reduced in pressure under hot conditions, known as pressure recovery time (see, for example, paragraph 0019 of Patent Document 1). However, because conventional evaluation methods focus only on time, while it is possible to compare products with clearly different sealing abilities, there are cases where it is difficult to determine the superiority or inferiority of products with the same pressure recovery time but different pressure recovery behavior, making evaluation impossible.

[0004] Meanwhile, the present inventors have disclosed in Non-Patent Document 1 that the difference in the quality of sealing performance can be precisely evaluated by digitally recording the pressure recovery behavior. However, Non-Patent Document 1 only provides a conceptual disclosure and does not disclose a specific evaluation method for precisely evaluating sealing performance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-175872 [Non-patent literature]

[0006] [Non-Patent Document 1] Ryohei Yoneya, Tetsuo Igata, Kiyoshi Goto, Katsumi Morikawa: Refractories 75[3] 132(2023) Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a method for more precisely evaluating the sealing property of a joint material. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided the following method for evaluating the sealing property of a joint material. After depressurizing an enclosed space inside a test body formed by sandwiching a joint material between at least two members with a vacuum pump, the depressurization by the vacuum pump is stopped, and the change in the degree of vacuum in the enclosed space thereafter is continuously measured; Among the time series data of the degree of vacuum obtained by this measurement, the time series data of the degree of vacuum from the initial degree of vacuum in the sealed space immediately after the decompression by the vacuum pump is stopped to the pressure recovery of 30 to 70% is fitted with an approximation formula of p=p0×exp(-t / τ) (where p is the degree of vacuum in the sealed space / Pa, p0 is the initial degree of vacuum / Pa, t is the elapsed time / s, and τ is a pressure recovery coefficient / s), A method for evaluating the sealing property of a joint material, in which the sealing property is evaluated based on the magnitude of the obtained pressure recovery coefficient τ. [Effects of the Invention]

[0009] According to the present invention, the sealing property of a joint material can be evaluated more precisely. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a test device used in the present invention. [Figure 2] 10 is a graph showing the relationship between the coefficient of determination R2 and the pressure recovery coefficient τ when the fitting range is changed. [Figure 3]10 is a graph showing an example of a fitting result when the fitting range is set to 33%. DETAILED DESCRIPTION OF THE INVENTION

[0011] In an embodiment of the present invention, the sealing property of a joint material is evaluated using a testing device shown in Fig. 1. The procedure is as follows. (1) After heating the base metal 1 in the test device to a predetermined temperature (for example, 600°C), a test specimen 4 having an internal sealed space 4a is formed by sandwiching a joint material 3 of a predetermined shape between the base metal 1 and an upper metal 2. At this time, a predetermined surface pressure (for example, 2 kN) is applied to the joint material 3 by pressing the upper metal 2 with a pressing mechanism 5 including a coil spring. (2) With a predetermined surface pressure applied, the sealed space 4a is depressurized by the vacuum pump 6. (3) After a predetermined time has elapsed since the start of decompression, the stop valve 7 is closed to stop the decompression by the vacuum pump 6. (4) The subsequent change in the degree of vacuum within the sealed space 4a is continuously measured by the vacuum gauge 8. (5) The time series data of the vacuum degree obtained by this measurement is used to evaluate the sealing performance of the joint material 3. In FIG. 1, reference numeral 9 denotes a thermocouple and reference numeral 10 denotes a heater.

[0012] Next, the above (5) will be explained in detail. In the above (5), the time series data of the degree of vacuum obtained by the measurement in the above (4), from the initial degree of vacuum in the sealed space 4a immediately after the decompression by the vacuum pump 6 is stopped to the time series data of the degree of vacuum restored to 30 to 70%, is fitted with the approximation formula p=p0×exp(-t / τ) (where p is the degree of vacuum in the sealed space / Pa, p0 is the initial degree of vacuum / Pa, t is the elapsed time / s, and τ is the pressure recovery coefficient / s), and the sealing performance is evaluated based on the magnitude of the obtained pressure recovery coefficient τ. Note that the fitting can be performed by a known method such as the least squares method.

[0013] First, the technical meaning of the above approximation formula will be explained. Volume V(cm 3 ) from a vacuum chamber with an exhaust speed of S (cm 3 ·s -1 ) The amount of gas at pressure p (Pa) exhausted for Δt (s) is equal to the amount of gas exhausted from the vacuum chamber -VΔp, so the following equation is obtained: VΔp=-SpΔt Solving this with the initial condition p=p0 gives the following equation: p=p0×exp(-S / V t) If V / S is defined as the pressure recovery coefficient τ, the above approximate formula is obtained. That is, when the time series data of the degree of vacuum is fitted to the above-mentioned approximate formula, the sealability can be evaluated based on the magnitude of the obtained pressure recovery coefficient τ. Specifically, the larger the value of the pressure recovery coefficient τ, the better the sealability can be evaluated.

[0014] Next, the range of time-series data of the degree of vacuum used for fitting in the present invention, that is, the fitting range, will be described. Depending on the type of joint material, the pressure may not return to atmospheric pressure, making it difficult to determine the end point. Differences in the endpoint determination can result in discrepancies between the measured and calculated values, i.e., reduced fitting accuracy. Therefore, in this invention, based on various test results, the fitting range is determined using time-series data on the vacuum level from the initial vacuum level to a pressure recovery of 30 to 70%. In other words, according to this invention, by setting the fitting range within this range, fitting accuracy is improved, and as a result, the sealing performance of the joint material can be evaluated more precisely. [Example]

[0015] Among various tests conducted to determine the appropriate range of fitting in the present invention, the results of typical tests will be described below. The sealing performance of two types of joint sealants, Material 1 and Material 2, was evaluated using the test equipment shown in Figure 1. Specifically, the joint sealants were placed in the test equipment heated to 600°C and a surface pressure of 2 kN was applied. Two minutes after the application of the surface pressure, the vacuum pump was started to reduce the pressure. Two minutes after the start of the pressure reduction, the vacuum pump was stopped and the vacuum level was measured. The vacuum level at this time was -0.072 MPa for Material 1 and -0.075 MPa for Material 2, which became the initial vacuum level p0 for each material. The vacuum level was measured every 5 seconds after the vacuum pump was stopped, and measurements were continued until the change in vacuum level leveled off. Table 1 shows the time series data for the measured vacuum level by material. Table 1 also shows that the pressure recovery time, a conventional evaluation index, was 35 seconds for both Material 1 and Material 2.

[0016] [Table 1]

[0017] As described above, in the present invention, the pressure recovery coefficient τ is basically determined by fitting the time-series data of the vacuum degree obtained by measurement with the above approximation formula, but since the early and late stages of the pressure recovery process may be affected by generated gases depending on the test conditions and the material of the joint material, it is necessary to select an appropriate fitting range. Therefore, in order to determine an appropriate fitting range, the inventors changed the fitting range and performed fitting within each range.

[0018] As an example, Figure 2 shows the coefficient of determination R for material 1 when the fitting range is changed. 2 and the pressure recovery coefficient τ. The horizontal axis of Figure 2, "fitting range," indicates the percentage (%) of pressure recovery from the initial vacuum. In other words, a fitting range of 100% is the range up to which the change in vacuum leveled off (effectively reaching atmospheric pressure).

[0019] From Figure 2, when the fitting range is below 30% or above 70%, the coefficient of determination R 2It can be seen that this is inappropriate because it reduces the pressure recovery coefficient τ and increases the fluctuation in the value of the pressure recovery coefficient τ. Taking other test results into consideration, the inventors have determined that a fitting range of 30 to 70% is appropriate. In other words, in the present invention, fitting is performed using time-series data on the degree of vacuum from the initial degree of vacuum to the pressure recovery of 30 to 70%.

[0020] As an example, the fitting results when the fitting range was set to 33% are shown in Figure 3. The pressure recovery coefficients τ obtained by this fitting were 9.7 for Material 1 and 11.7 for Material 2. On the other hand, as a comparative example, the pressure recovery coefficient τ obtained by fitting when the fitting range was set to 100% was 11.5 for both material 1 and material 2.

[0021] Table 2 summarizes the results of these evaluations.

[0022] [Table 2]

[0023] In the conventional example, which used pressure recovery time as an index, and the comparative example, which had a fitting range of 100%, there was no difference in sealing ability between material 1 and material 2, but in the example, which had a fitting range of 33%, the evaluation result showed that material 2 had better sealing ability than material 1. This evaluation result is consistent with the difference in pressure recovery behavior between material 1 and material 2 shown in Table 1 and Figure 3. In this way, it was demonstrated that the evaluation method of the present invention allows for more precise evaluation of the sealing ability of joint materials. [Explanation of symbols]

[0024] 1 Base hardware 2 Upper hardware 3 Joint material 4 Test specimen 4a Confined spaces 5 Pressing mechanism 6. Vacuum pump 7 Stop valve 8 Vacuum gauge 9 Thermocouples 10. Heater

Claims

[Claim 1] After depressurizing an enclosed space inside a test body formed by sandwiching a joint material between at least two members with a vacuum pump, the depressurization by the vacuum pump is stopped, and the change in the degree of vacuum in the enclosed space thereafter is continuously measured; Among the time series data of the degree of vacuum obtained by this measurement, the time series data of the degree of vacuum from the initial degree of vacuum in the sealed space immediately after the decompression by the vacuum pump is stopped to the pressure recovery of 30 to 70% is defined as p = p ０ × exp(-t / τ) (where p is the degree of vacuum in the sealed space / Pa, p ０ is the initial vacuum degree / Pa, t is the elapsed time / s, and τ is the pressure recovery coefficient / s.) A method for evaluating the sealing property of a joint material, in which the sealing property is evaluated based on the magnitude of the obtained pressure recovery coefficient τ.

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