JP2002303560A - Method for testing airtightness performance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for testing airtightness performance capable of performing an accurate airtightness performance test even when leaking quantity increases under a minute pressure condition and a test pressure greatly drops, and in addition capable of rapidly and surely obtaining a test result even when conditions such as internal volume, detecting time, and a test pressure change. SOLUTION: Coefficient C relating to a leaking clearance inherent to an object sample 13 is obtained from time transition data of a generated differential pressure considering a change in the test pressure, and the test of airtightness performance is conducted by using the coefficient C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airtightness test for measuring the airtightness of a work (test sample) such as a vent valve, which has a large amount of leakage under a small pressure and a test pressure is lowered. About the method.

[0002]

2. Description of the Related Art Conventionally, when performing an airtightness test for measuring the airtightness of a sample of this type, a general principle of the airtightness test by an air leak test is based on Boyle-Charle's law and a standard product. The amount of leak is determined from the differential pressure from the sample. At this time, Hagen-Poiseuille's law that the leak amount is proportional to the time is applied, and the leak amount is calculated with the leak amount per time being substantially constant.

[0003] Representative examples of the leak detection method include an internal pressure detection method for detecting a differential pressure of an internal pressure with respect to a sealed test pressure, and an external pressure detection method for detecting a differential pressure of an leaked external pressure while supplying pressure. There is a detection method. The former method of detecting the internal pressure is a method of detecting the pressure drop by pressurizing and sealing the inside of the sample, and is effective when the leak amount is small and can be approximated to linear characteristics. Further, this detection method is effective as a pressure detection method when the test pressure to be applied requires a long time to equilibrate when the test pressure is high, and when the test pressure is low.

[0004] On the other hand, the latter method of detecting external pressure is a method in which a test sample is mounted in a closed container, and a constant pressure is applied to the test sample to detect a pressure rise in the closed container. In this case, even when the leak amount is large, it can be treated as a linear characteristic, and since the time until the pressure is equilibrated is short, it is effective when the test pressure is higher than the internal pressure detection method.

[0005]

In the internal pressure detecting method, the leak per hour is limited only when the amount of leak from the test sample is small so as not to be affected by a large drop in the test pressure to be applied. The amount can be calculated as substantially constant.For example, when the test pressure is a small pressure, the leak amount becomes larger than this pressure, or the internal volume of the valve is small, When the ratio of the leak amount becomes large in comparison, there is a problem that the influence of the leak amount on the test pressure cannot be ignored.

On the other hand, the external pressure detection system can be used as a detection result only when the initial pressure in the closed vessel, that is, the pressure rise from the atmospheric pressure is small. On the other hand, when the test pressure is a small pressure and the pressure rise is large, Means that the change in the pressure inside the closed vessel is uniform to the test pressure, and it is impossible to accurately measure the leak amount under the actual condition of releasing the pressure under the atmospheric pressure. As in the case of the system, it has been difficult to consider that the amount of leak per time is almost constant. In addition, this detection method has a problem that it needs to be a test device for a container or the like having a stable degree of sealing, or that the number of steps for mounting a work increases.

When an airtightness test of a vent valve or the like is performed, the test pressure to be supplied is desirably a slight pressure because the actual pressure change is a slight pressure. The method is suitable. However, in the internal pressure detection method, as described above, it is difficult to obtain a linear characteristic when the leak amount is large, while the external pressure detection method has the above-described problem.

The present invention has been developed as a result of intensive research to solve the conventional problems. Even when the test pressure drops greatly due to a large amount of leakage under a small pressure condition, the airtight performance can be accurately determined. It is intended to provide a method for measuring airtight performance that can perform tests and that can quickly and reliably obtain test results even when conditions such as internal volume, detection time, and test pressure change. And

[0009]

In order to achieve the above object, the invention according to claim 1 relates to a leak gap specific to a target specimen from time variation data of a generated differential pressure in consideration of a change in test pressure. This is an airtightness test method in which a coefficient is obtained and a test of airtightness is performed using the coefficient.

According to the second aspect of the present invention, a coefficient relating to a leak gap peculiar to a target test sample is determined from the differential pressure data generated during the detection time in consideration of a change in test pressure, and a test for airtight performance is performed using this coefficient. This is an airtight performance test method to be performed.

According to the third aspect of the present invention, a constant leak amount per time at the time of supplying a constant pressure is obtained by the above coefficient, and the leak amount is measured under a micro pressure condition by comparing with a judgment reference.

The invention according to claim 4 is an airtightness test method in which the time variation data of the generated differential pressure or the generated differential pressure data at the detection time is the differential pressure data of the internal pressure drop in the internal pressure detection method.

The invention according to claim 5 is an airtight performance test method in which the time difference data of the generated differential pressure or the generated differential pressure data at the detection time is the differential pressure data of the rising pressure in the container in the external pressure detection method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment in which the airtightness test method according to the present invention is performed under a small pressure condition will be described in detail based on a flow chart and experimental data, taking an airtightness test of a vent valve as an example. . The vent valve (test sample) 13 in this example has the structure shown in FIG. 11, and enables accurate measurement even when the amount of leakage increases under a small pressure condition and the test pressure drops significantly. In this figure, a vent valve 13 is attached to the end of a vent pipe, and when the pressure in the pipe is normal atmospheric pressure, a disc 22 provided in the main body 20 closes a valve seat 24 via a seal member 23, and when draining, The disc 22 is opened by a negative pressure generated in the pipe, and when a positive pressure is generated, the disc 22 is pressed down so that the odor is not discharged. Thus, the vent valve needs to have a predetermined airtight performance.

FIG. 1 is a schematic diagram showing the configuration of an airtightness test apparatus according to the present invention, and FIG. 2 is an explanatory view of the system configuration of the same. In this embodiment, a vent valve based on an internal pressure detection system is used. 1 shows an embodiment of an airtightness test of the present invention. According to the present invention, a coefficient relating to a leak gap peculiar to a target specimen is obtained from time change data of a generated differential pressure in consideration of a test pressure change, and the coefficient is used to determine a constant leak amount per time at a constant pressure supply. It is a test method to ask for. First, various setting values are input to the setting value input means 1 as initial settings of the air leak tester 15. The set values at this time include a volume value in the work 13 as a test sample, a supply pressure value supplied from a pressure supply source such as a compressor (not shown), a pressurization time, a differential pressure measurement time, and whether the product can be used. The leak amount determination values obtained by calculating independently are input, and these values are stored in the storage means 2.

A master 12 serving as a reference product and a work 13 serving as a test sample are installed.
Make the settings for At the time of measurement, a signal is sent from the control means 3, and based on this signal, the pressure supply means 4 operates to start pressure supply. In addition, as the pressure supply means 4,
An opening / closing valve 4a is provided in the flow path on the master 12 side, and a valve 4b is provided in the flow path on the work 13 side.

The compressed air is supplied from a pressure supply source,
When the valves 4a and 4b are opened, the master 1
2, and a pressure is supplied to each ventilation valve of the work 13, and compressed air is supplied from this pressure supply source by an appropriate pressure set in advance by the regulator 14.

The pressure supply is continuously performed for a predetermined time, and the pressure value at this time is measured by the pressure measuring means 6 which is a pressure sensor, and is displayed on a display means 18 such as a display.
Will be displayed. The time for pressurization is measured by the time measuring means 5, and when the pressurizing time reaches a predetermined time, the pressure value at this time is measured by the pressure measuring means.

Next, the pressure determination means 7 indicates the measured pressure value and the supply pressure required for measuring the differential pressure.
The supply pressure set value (set pressure value) stored in the storage means 2 is compared. If the comparison result at this time is “measured pressure value <set pressure value”, it means that the pressure required for measurement has not been supplied to the master 12 and the work 13, and the measurement of the differential pressure is stopped. . In this case, a display indicating that the measurement is stopped is displayed on the display means 18 based on the signal from the control means 3, so that the valve 4a
The entire pressure of the air leak tester 15 is released to the atmosphere by operating the valve 4c provided in the flow path before the branch between the valve and the valve 4b. Thereafter, the work 13 is once removed, the work 13 is mounted again, and the measurement is started again.

The result of the comparison of the supply pressure is “measured pressure value =
If it is “set pressure value”, the master 12 and the work 13
Proceed to the differential pressure measurement process to measure the differential pressure generated between
The leak gap coefficient C is calculated from the determined differential pressure.
I have. First, the master 4 is closed by closing the valves 4a and 4b.
2. Keep the pressure between the workpieces 13
You. In this state, the differential pressure measuring means 8 which is a differential pressure sensor is used.
The predetermined differential pressure measurement time between the master 12 and the work 13
Differential pressure value ΔP after t seconds _(T)And the differential pressure value
ΔP_(T)Is displayed on the display means 18.

Next, using the determined differential pressure value ΔP _(t) , the calculating means 9 calculates a leak gap coefficient C and a leak amount Qa. The operation formula at this time will be described below. Assuming that the test pressure (absolute pressure) is P (Pa), the internal volume of the work 13 is V (ml), and the amount of air leak generated under the test pressure is ΔV, from the Boyle's law, PV = (P−Δ
P) (V + ΔV), and ΔV ≒ (ΔP · V) / P. When the above equation is converted into the leak amount ΔV of the pressure _Patm under the atmospheric pressure, ΔV ≒ (ΔP ・ V) / _Patm , and thus ΔP ≒ (≒ V ・_Patm ) / V --- (1) Become.

Here, the shape of the leak gap of the work 13
Is assumed to be a capillary having a uniform circular cross section, and
Assuming that the body is laminar (viscous flow), the typical leakage
According to Hagen-Poiseuille's law, which is the theoretical formula,
Holds. Leakage per hour in air (compressed fluid)
Qa (m³/ S) is the radius of the capillary hole R (m), the hole
Is L (m) and the viscosity of air is μa ｛18.2 × 10
^{− 6}(Pa · s)｝, Qa = πR⁴(P²−P_atm ²) / (16μa ・ L ・ P_atm) (2), but as shown in the present embodiment, a small test pressure P
The amount of leak is large and the change in test pressure P cannot be ignored
Case, that is, the test pressure P in the above equation changes
Means that the amount of leak per hour Qa
It will change every moment. Therefore, this test pressure P change
It is necessary to calculate the amount of leakage in consideration of the formation of a leak. So,
Work gap coefficient C = πR⁴/ L, equation (2) is given by Qa = C (P²−P_atm ²) / (2.91 × 10^-4・ P_atm−−− (3), and when the time required for pressure detection is t, the initial test
Pressure P_t0Then, the integrated leak amount ΔV_(T)Is the following
It is thought to be. ΔV_(T)= C∫ ｛[(P_t0−ΔP_(T-dt))²−P_atm ²] / (2.91 × 10^-4 ・ P_atm)｝ Dt −−− (4) Therefore, the generated differential pressure ΔP_(T)About the pressure detection time
Equation (1) ΔP considering t_(T)= (ΔV_(T)・ P
_atm) / V and equation (4) yields the following equation:
One. ΔP_(T)= (P_atm/ V) · C∫ ｛[(P_t0−ΔP_(T-dt))²−P _atm ² ] / (2.91 × 10^-4・ P_atm)｝ Dt --- (5) ΔP in equation (5)_(T)At time t (s)
Substitute the value of leak gap coefficient C by substituting the measured value of differential pressure
You. In other words, the time variation of the generated differential pressure considering the test pressure change
From the position data, the leak gap specific to the target
A coefficient C is obtained.

Here, using Equation (5), an arbitrary leak
When the change in the generated differential pressure at the clearance coefficient C is calculated, FIG.
Can be represented as shown in FIG. At this time,
When t = 0, ΔV_{t = 0}= 0, and the work internal volume V =
767 (ml), test pressure P _t0= 400 (Pa)
ing. In this graph, in the same work 13
When the leak gap count C is changed, the leak gap coefficient C becomes
When it is small, the generated differential pressure is close to the linear characteristic
However, when the leak gap coefficient C increases, the generated differential pressure becomes parabolic.
It changes linearly. In the present invention, the generated differential pressure is
Effective airtightness for parabolic specimens
It is a test.

FIG. 6 is obtained by verifying the above-mentioned formula, and the initial test pressure is P _{t 0} = 400 (Pa).
In the case of (1), the leak amount (developed differential pressure) was measured for the works 13 having different internal volumes, and the measured value and the theoretical value of the change of the leak amount with respect to the time t (s) for each work were shown on a graph so as to be comparable. In this example, the internal volume V of the work 13 is 524 and 76, respectively, as shown in FIG.
7 shows a comparison between an actually measured value of the generated differential pressure Pa in the case of 7, 1575 (ml) and a theoretical value calculated from the leak gap coefficient C. As a result of examining the relational expression between the leak amount and the pressure change in the measured actual value, it was proved that the actual measured value almost coincided with the theoretical value diagram, and therefore, the leak amount could be calculated using the above-described formula. Was.

Next, the leak amount Qa is calculated by substituting the calculated leak gap coefficient C and test pressure P into equation (3). As described above, using the determined differential pressure value ΔP _(t) , the leak amount Qa calculated by the calculating means 9 is determined by the leak amount determining means 10 as the leak amount determination reference value stored in the storage means 2. Is compared with the value, and when “the actual calculated leak amount ≦ the leak amount determination value”, the work 1
3 is determined to have the predetermined airtightness, and the display means 8 displays a display content indicating that the airtightness has passed.

If "actual calculated leak amount> leak amount determination value", it is determined that the work 13 does not have the predetermined airtightness, and the display means 8 is rejected. Is displayed.

Further, when performing an airtightness test on the next work 13, the valves 4 a and 4 b are opened, and the valve 4 c is operated so as to be in an open state. After venting the pressure to atmosphere,
The work 13 is removed, a work 13 to be newly measured is attached, and the differential pressure value is measured in the same manner.

FIG. 7 is a graph of equation (5).
The initial test pressure to P_t0= 400 (Pa) and differential pressure
Differential pressure and leak when measuring time is t = 10 (s)
This shows the relationship with the gap coefficient C. Leak gap clerk
Since the number C is a value specific to the sample, the specific leak amount
The pass / fail judgment of the test sample can be performed without calculating
You. For example, a leak amount determination reference value, that is, a leak gap
The coefficient reference value is 1.82 × 10^-8If you set
The actual differential pressure of a 50A test sample is about 70 (Pa).
Then, the value of the gap coefficient C is about 1.0 × 10^-8Is
Is judged as pass. On the other hand, the obtained differential pressure is about 220 (P
In the case of a), the value of the gap coefficient C is about 4 × 10 ^-8And
Judge as unacceptable.

FIG. 8 shows the relationship between the generated differential pressure and the leak amount based on FIG. This graph is obtained when 400 (Pa) is constantly applied during pressure supply. In advance, set the leak amount determination reference value to 0.05 (ml /
s), if the measured differential pressure value is about 100 (Pa) in a sample of size 50A, the leak amount is about 0.
Since it is 04 (ml / s), it is determined to be acceptable. on the other hand,
If the obtained differential pressure is about 210 (Pa), the leak amount is about 0.1 (ml / s), and it is determined to be unacceptable.

When the sample is a vent valve, the internal volume differs depending on the size.
The leak amount Qa and the leak gap coefficient C have a linear relationship as shown in FIG.
a can be easily calculated. Also, the generated differential pressure,
The ratio C / V of the aforementioned leak gap coefficient C to the volume value in the work
The graph shows a constant relationship as shown in FIG. 10 even if the internal volume value is different, which confirms that the leak gap coefficient C can be calculated back from the differential pressure. 9 and 10
Is an initial test pressure P _t0 = 400 (Pa), and the differential pressure value in FIG. 10 is a value after a lapse of 10 seconds.

As described above, in the present invention, the leak gap coefficient C relating to the inherent gap of the target work 13 can be obtained from the generated differential pressure data. It is possible to obtain a constant leak amount per time and compare it with a criterion. In the present invention, since the value of the leak gap coefficient C can be specified from the generated differential pressure detected in advance, a substantially accurate leak amount Qa can be obtained using the leak gap coefficient C.

Further, another invention obtains a coefficient relating to a leak gap specific to a target test sample from the generated differential pressure data at the detection time while taking into account the change in test pressure, and from this coefficient, a constant pressure supply when a constant pressure is supplied. The airtightness test is performed under a slight pressure condition by obtaining a constant amount of leak per time and comparing it with a criterion. This will be described with reference to FIG. 5. For example, if the value of the generated differential pressure ΔP _{(t = 20)} at the time t = 20 (s) is obtained by actual measurement, the leak gap coefficient is calculated based on Expression (5). This means that C is unambiguously determined, and a comparison with a criterion is performed using this coefficient C.

In addition to the present embodiment, by providing the air leak tester 15 with an arithmetic function, even if the setting conditions such as the test pressure, the internal volume data, and the detection time are changed, it is possible to immediately respond. . Also, FIG.
The graph in FIG. 8 may be input as a numerical value to the calculating means 9 in advance.

[0034]

As is clear from the above, according to the present invention, it is possible to perform an accurate airtightness test even when the amount of leakage increases under a small pressure condition and the test pressure drops significantly. Yes, it is particularly suitable for the airtightness test of the ventilation valve, and the leak amount can be calculated by obtaining the leak gap coefficient from the generated differential pressure.
This is a method for measuring airtight performance that can quickly obtain test results even when setting conditions such as the internal volume, detection time, and test pressure change.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an airtight performance test apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a system configuration of an airtightness test of the present invention.

FIG. 3 is a flowchart showing the working steps of the airtightness test of the present invention.

FIG. 4 is a flowchart showing the working steps of an airtightness test according to the present invention.

FIG. 5 is a graph showing a change in generated differential pressure of an arbitrary leak gap coefficient C in a theoretical formula.

FIG. 6 is a graph showing measured values of change in generated differential pressure of works having different internal volumes and theoretical diagrams.

FIG. 7 is a graph showing these relationships when a leak gap coefficient is converted from a generated differential pressure.

FIG. 8 is a graph showing these relationships when the leak amount is converted from the generated differential pressure.

FIG. 9 is a graph showing a relationship between a leak amount and a leak gap coefficient when a constant pressure is supplied.

FIG. 10 is a graph showing a relationship between a generated differential pressure and a leak gap coefficient / internal volume.

FIG. 11 is a vent valve for testing in the present invention (sample).
FIG. 3 is a half sectional view showing one example.

[Explanation of symbols]

13 Sample (workpiece) 15 Air leak tester C Leak gap coefficient Qa Leakage ΔP _t Differential pressure value P _t0 Initial test pressure

Claims (5)

[Claims] 1. A coefficient relating to a leak gap specific to a target specimen is obtained from time change data of a generated differential pressure in consideration of a change in test pressure, and a test of airtightness is performed using the coefficient. Characteristic airtightness test method. 2. From the generated differential pressure data at the detection time,
An airtightness test method characterized in that a coefficient relating to a leak gap inherent to a target sample in consideration of a change in test pressure is obtained, and a test of airtightness is performed using the coefficient. 3. The airtightness test method according to claim 1, wherein a constant leakage amount per unit time at the time of supplying a constant pressure is obtained from the coefficient and compared with a criterion. . 4. The airtightness test method according to claim 1, wherein the time difference data of the generated differential pressure or the generated differential pressure data at the detection time is differential pressure data of an internal pressure drop in an internal pressure detection method. 5. The airtightness test method according to claim 1, wherein the time difference data of the generated differential pressure or the generated differential pressure data at the detection time is differential pressure data of an in-vessel rising pressure in an external pressure detection method.