JPH0377041A - Leakage inspection instrument for airtight product - Google Patents

Abstract

PURPOSE:To inspect many kinds of airtight products efficiently with one refer ence tank by using the reference tank which is larger in internal capacity than the airtight products. CONSTITUTION:When the leakage inspection of an airtight product 4 is started, the airtight product 4 to be inspected is connected to one pipe 2. Then while an inspection pressure release valve V3 and a pressure holding valve V7 are closed, inspection pressure application valves V1 and V2 and stop valves V5 and V6 are opened. Consequently, specific inspection pressure having the same value is applied to the product 4, reference tank 5, and a thermal mass flowme ter 7. When a pressure switch 10 is operated with the inspection pressure, the valves V1 and V2 are closed and the product 4, tank 5, and flowmeter 7 are held under the inspection pressure. In such a state, the flowmeter 7 measures the flow rate of the air in a bridge pipe 6. When the measurement result is less than a set value at this time, it is judged that the product 4 is normal, but when the result is larger than the set value, it is judged that the product has a leak and is a defective.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a leak testing device for airtight products such as hoses or containers that require airtightness. This invention relates to a leak testing device for airtight products, which tests for leaks in airtight products by measuring the flow rate of airtight products.

[Prior art] As a conventional leak test device of this type, Figs.
The techniques shown in the figure can be mentioned.

Figure 4 is an air circuit diagram showing a conventional leak inspection device for airtight products, Figure 5 is a time chart showing the opening and closing timing of valves in the air circuit in Figure 4, and Figure 6 is a thermal type diagram in the air circuit. FIG. 7 is a schematic diagram showing the configuration of the mass flowmeter, and a characteristic diagram illustrating the measurement principle of the thermal mass flowmeter.

As shown in FIG. 4, a pipe 2 and a pipe 3 extend in parallel from the air supply source 1, and one pipe 2 has an airtight product 4 (a hose in the illustrated example) to be inspected, and the other pipe 3 A reference tank 5 whose complete airtightness has been confirmed is connected to. A plurality of reference tanks 5 are prepared, and one with almost the same internal volume as the airtight product 4 is selected and connected to the piping 3.

On the air supply source 1 side, the piping 2 is provided with an inspection pressure applying valve v1, and the piping 3 is provided with an inspection pressure release valve V2. During each inspection, the output of valves V1 and V2 is
] side, a bridge pipe 6 is connected between the pipe or the pipe 3, and a thermal mass flow meter 7 is disposed on the bridge pipe 6. An inspection pressure release valve V3 is connected to the piping 2 between the thermal mass flowmeter 7 and the heavy equipment 4 through an exhaust pipe 8. Further, an inspection pressure release valve (4) is connected to the pipe 3 between the thermal mass flowmeter 7 and the reference tank 5 via an exhaust pipe 9.

As shown in FIG. 6, the thermal mass flowmeter 7 includes a bypass pipe 11 connected to the bridging pipe 6 and a capillary tube 12, and the capillary tube 12 is equipped with a pair of self-heating resistors. R
1 and R2 are wound.

Furthermore, the upstream side of the capillary tube 12 is a self-heating resistor R1.
Therefore, the downstream side can be heated by the same thermoelectric power by the three self-heating resistors R2. [3] The temperature difference between the self-heating resistor R1ε and the white self-heating resistor 1 and 2 is detected by the bridge circuit 15, and is transmitted via the amplifier circuit 16 and the correction circuit 17 to the control circuit 181. : Manpower is exhausted.

Here, when the flow rate is "0", the temperature distribution of the capillary tube 12 is symmetrical with respect to its center position, as shown by the solid line in FIG. 7. On the other hand, when air flows, the self-heating resistor R1 on the −L flow side is deprived of heat and its temperature drops, while the self-heating resistor R2 on the downstream side is given heat and its temperature decreases. As a result, the temperature distribution in the capillary tube 12 becomes an asymmetrical shape that is biased toward the downstream side, as shown by the broken line in FIG. At this time, the self-heating resistor R1 and the self-heating resistor R
A certain relationship is established between the temperature difference dt of 2 and the mass flow rate of air. Therefore, the control circuit 18 calculates and measures the air flow rate based on the temperature difference, dt, and displays the measured value on the display section 19.

Next, in the configuration shown in L, a conventional leak test method for an airtight product will be explained based on the time chart of FIG.

First, the airtight product 4 to be inspected is connected to one pipe 2, and a reference tank 5 having approximately the same internal volume as the airtight product 4 is connected to the other pipe 3. Next, test pressure release valve V3. With V4 closed, test pressure release valve V1. Open V2 for a predetermined time. As a result, the same predetermined horizontal opening pressure is applied to the airtight product 4 and the reference tank 5, respectively. Next, test pressure applying valves Vl, V2
is closed and the gas-tight product 4, reference tank 5 and thermal mass flow meter 7 are held under the test pressure.

Next, in this state, the flow rate of air in the bridging pipe 6 is measured using the thermal mass flow meter 7. If the measurement result is less than the set value, the airtight product 4 is determined to be a good product, and conversely, if the measurement result is greater than or equal to the set value, the airtight product 4 is determined to be a defective product with a leak.

In this way, when the inspection of one airtight product type is completed, the inspection pressure release valve V3 and the inspection pressure release valve V4 are opened, and the inspection pressure of the airtight product 4, the base wall tank 5, and the thermal mass flow meter 7 is released into the atmosphere. Thereafter, the airtight product 4 is replaced, and if its internal volume changes, the reference tank 5 is also replaced and the next inspection is started.

The conventional example described above is configured to measure the flow rate between the airtight product 4 and the reference tank 5 using the thermal mass flowmeter 7. Japanese Patent Publication No. 55-63732 discloses a leakage measurement device configured to measure the pressure difference between an airtight product and a reference tank using a differential detector.

[Problem to be Solved by the Invention] However, in the conventional leak testing device for airtight products, as shown in L, the internal volumes of the airtight product 4 and the reference tank 5 are approximately approximated to perform the inspection. Each time the internal volume of tank 4 changes, the reference tank 5 also has to be replaced with another one, which is a hassle.

Moreover, if the inspection is performed by approximating the internal volume, if there is a leak in the airtight product 4, the airtight product 4 will leak from the reference tank 5.
The flow rate of air flowing through the thermal mass flow meter 7 toward the radiator is approximately half of the leakage amount. That is, since the measured value of the thermal mass flowmeter 7 is about 1/2 of the actual leakage amount, it is necessary to use a highly accurate thermal mass flowmeter 7 that can measure even minute flow rates. This led to high costs. Moreover, in this case, the ratio between the measured value and the actual leakage amount differs depending on the internal volume ratio of the airtight product 4 and the reference tank 5, so in order to accurately measure the flow rate, it is necessary to adjust the internal volume ratio each time. It is necessary to calculate the value and correct the measured value accordingly. Therefore, in the past, in order to omit this correction of measured values,
In reality, inspections were carried out by making the internal volumes of the reference tank 5 and the airtight product 4 equal, even though they were prepared for the hassle of replacement work.

Furthermore, the temperature difference between the pair of self-heating resistors R1 and R2, dt
When using a thermal mass flowmeter 7 configured to measure the flow rate based on It is necessary to make the temperature of R1 and R2 equal before measurement.

Otherwise, the measured value of the thermal mass flowmeter 7 will not be stable.
Substantial leakage of the hermetic product 4 cannot be accurately measured. However, the conventional leak testing device for airtight products releases the test pressure in the reference tank 5 every time the test for one airtight product 4 is completed, and then applies the test pressure to the reference tank 5 again when testing the next airtight product 4. Since it is configured to apply the voltage, there is a waste of time in having to wait each time to judge whether the airtight product 4 is good or bad until the measured value becomes stable.

Therefore, the problem of the present invention is to be able to efficiently inspect many types of airtight products using one reference tank, and to make the measured value approximate the actual leakage amount without using a high-precision thermal mass flowmeter. Another object of the present invention is to provide a leak testing device for airtight products that can accurately and easily measure the amount of leakage, quickly stabilize the measured value, and shorten the testing time.

[Means for Solving the Problems] In order to solve the above problems, the leak testing device for airtight products of the present invention includes a reference tank having a larger internal volume than the airtight product to be tested, and a reference tank for the airtight products and the reference tank. An inspection pressure applying means that applies the same inspection pressure by a fluid, and a thermal mass that measures the flow rate of the fluid based on the temperature difference accompanying the fluid flow between the airtight product and the reference tank under the inspection pressure. A flowmeter, an inspection pressure applying means for releasing the inspection pressure of the airtight product after measurement by the thermal mass flowmeter, and a pressure holding means for maintaining the reference tank at approximately the inspection pressure after measurement by the thermal mass flowmeter. It is configured.

[Function] In the leak testing device for airtight products of the present invention, a reference tank with a larger internal volume than the airtight product is used.
Even if the internal volume of an airtight product changes, it can be handled with one reference tank, eliminating the need for replacement work and making inspections simple and efficient. Additionally, by using a reference tank with a larger internal volume than the airtight product, if there is a leak in the airtight product, air will flow through the thermal mass flow meter at a flow rate that approximates the actual leakage amount, allowing the thermal mass flow rate to be A total of 7 measured values are approximately equal to the actual leakage amount.

Therefore, it is possible to accurately measure the leakage amount of an airtight product without using a highly accurate thermal mass flowmeter, and the trouble of re-correcting the measured value is eliminated.

In addition, when the inspection of one airtight product is completed, the reference tank is maintained at almost the inspection pressure by the pressure holding means, so when the next airtight product is inspected, it takes time to fill the large volume reference tank with air. You can save money. Moreover, if the reference tank is already pressurized when air is supplied by the inspection pressure imparting means, almost no supplied air will flow into the reference tank, and cooling due to adiabatic expansion here will be suppressed, resulting in heat generation. The temperatures on the inlet and outlet sides of the mass flowmeter become equal at an early stage. As a result, the measured value of the thermal mass flowmeter quickly stabilizes, and inspection time is significantly reduced.

[Example] Hereinafter, an example embodying the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is an air circuit diagram showing an embodiment of the leak inspection device for airtight products according to the present invention, and FIG.
Figure 3 is a time chart showing the opening/closing timing of the valve.
It is a time characteristic diagram.

As shown in FIG. 1, in the leak testing device for airtight products of this embodiment, 1. An airtight product 4 (a hose in the illustrated example) can be connected to one piping 2 extending from the air supply source 1, and a reference tank 5 having a larger volume than the airtight product 4 is connected to the other piping 3. There is. Reference tank 5
It is desirable to make the internal volume as large as possible without being affected by the outside air temperature at the installation location. For example, if the internal volume of the airtight product 4 is about 25 cc, it is desirable that the target volume of the reference tank 5 is about 500 cc.

Further, as for the reference tank 5, of course, one that has been confirmed to be completely airtight is used.

On the air supply source 1 side, an inspection pressure I-j valve v1 and an inspection pressure m9 valve V2 are provided on the pipe 2 and on the pipe 3F to apply a predetermined test pressure to the airtight product 4 and the reference tank 5. It is being Then, pipe 2 and pipe 3ε
The bridging pipe connecting the earth, as explained earlier according to Figs.
■Temperature difference due to air flow between and reference tank 5, Jt
A thermal mass flowmeter 7 is installed to measure the air current based on the current. Historically, piping 2 has the thermal type "j!1f"
An inspection pressure release valve V3 for releasing the inspection force on the airtight product d after measurement by the fl flowmeter 7 is connected via an exhaust pipe Σ3.

On the opposite side of the inspection pressure release valve V3, an E switch 10 is connected to the airtight product 4, which detects clogged hose holes.A thermal mass flowmeter 7 and an inspection pressure release valve 4 are connected to the airtight product 4. A stop valve V5 is provided in the pipe 2k between the valve V3 and a stop valve V6 is provided in the pipe 3F between the thermal mass flowmeter 7 and the reference tank 5.

A pressure holding valve V7 is connected to the pipe 3 between the stop valve v6 and the reference tank 5 via a pipe 9. This pressure holding valve V7 is opened only when the air in the reference tank 5 is drained, such as when starting an inspection, and is always closed during the inspection.
The reference tank 5 is maintained at the test pressure after measurement by the test pressure.

In this embodiment, the inspection pressure m9 valve V1°V2,
Inspection pressure release valve V3, stop valve V5. The air bypass valve is used up as V6 and pressure holding valve V7. Unlike the electromagnetic valve L, the air pilot valve does not generate heat 7 itself, so there is little risk of adversely affecting the measured value of the thermal mass flowmeter 7. Furthermore, in order to reduce the effects of changes in outside temperature caused by air conditioners, etc., it is preferable to house the air circuit in a hermetically insulated room. As for the pipes 2, 3.9, the bridge pipe 6, and the exhaust pipe B, it is better to use metal pipes than plastic pipes such as nylon, which easily expands when pressurized. Stable under weight. Furthermore, the piping 2.3 behind the inspection pressure applying valves Vl and V2 is a thermal type, so that the same value of inspection pressure is quickly applied to the airtight product 4 and the base tank 5. It is desirable to have one of the pipes as short as possible, at the same distance from the mass flow meter 7, and in parallel to each other.

In the above configuration, next, a method for inspecting leakage of an airtight product according to this embodiment will be explained based on the time chart of FIG. 2.

When no test is being performed, the test pressure lj-valve v'1. v2, stop valve v5. V6, inspection pressure release valve 3, and pressure holding valve V7 are each closed. In this state, a leak test of the airtight product 4 is started, and first, the airtight product 4 to be tested is connected to one of the pipes 2. Next, test pressure release valve v
3 and I″f: With force holding valve V7 closed, test pressure applying valves Vl, V2 and stop valve V5.V
6 is released. As a result, the same predetermined test pressure is applied to the airtight product 4, the reference tank 5, and the thermal mass flowmeter 7, respectively. When the pressure switch 10 is activated by the test pressure, the test pressure applying valve V
1, V2 are closed to keep the gas-tight product 4, reference tank 5, and thermal mass flow meter 7 under test pressure.

Subsequently, in this state, the bridge pipe 6 is measured by the thermal mass flow meter 7.
The air flow rate at is measured. If the measurement result is less than the set value, the airtight product 4 is determined to be a good product, and conversely, if the measurement result is greater than or equal to the set value, the airtight product 4 is determined to be a defective product with a leak.

In this way, when the inspection of one airtight product 4 is completed, the stop valve V5. After V6 is closed, test pressure release valve V3 is opened. As a result, the thermal mass flowmeter 7
is held at the test pressure, while the hermetic product 4 is depressurized to atmospheric pressure. At this time, the reference tank 5 is held at the test pressure because the stop valve v6 and the pressure holding valve V7 are both closed. Then, in this state, the airtight product 4 for the test liquid is removed, and the next airtight product 4 is attached.

The next test is started with the thermal mass flowmeter 7 and reference tank 5 held at the test pressure. Then, inspection pressure applying valves Vl, V2 and stop valve V5. When V6 is opened, the supplied air fills the airtight product 4 within a short time without flowing into the reference tank 5 having a large internal volume. In this way, by repeating each of the steps described above, a large number of airtight products 4 are sequentially inspected.

In this way, the leak testing device for airtight products of this example is as follows:
A reference tank 5 having a larger internal volume than the airtight product 4, and an inspection pressure applying valve Vl as an inspection pressure applying means that applies the same inspection pressure by air to the airtight product 4 and the reference tank 5.
, V2, a thermal mass flowmeter 7 that measures the air flow rate based on the temperature difference Jt accompanying the air flow between the airtight product 4 and the reference tank 5 under the test pressure, and the thermal mass flowmeter 7. an inspection pressure release valve v3 as an inspection pressure applying means for releasing the inspection pressure of the airtight product 4 after measurement by Total 7;
A pressure holding valve V7 is provided as a pressure holding means for holding the reference tank 5 at approximately the test pressure after measurement by the thermal mass flowmeter 7.

Therefore, according to the leak test device for airtight products of the above embodiment, the reference tank 5 has a larger internal volume than the airtight product 4.
is used, so even if the internal volume of the airtight product 4 changes, it can be handled with one reference tank 5, eliminating the need for replacement work and making inspections simple and efficient.

Furthermore, if a reference tank 5 with a larger internal volume than the airtight product 4 is used, if there is a leak in the airtight product 4, a flow rate of air that approximates the actual leakage amount will be supplied to the thermal mass flowmeter 7.
The measured value of the thermal mass flowmeter 7 becomes almost equal to the actual leakage amount. As a result, unlike conventional methods, it is possible to accurately measure the leakage amount of the airtight product 4 without using a highly accurate thermal mass flowmeter 7, and the measured value cannot be used during normal inspection. There is no need to worry about re-correcting. However, if higher measurement accuracy is required, it is necessary to correct the measured value based on the internal volume ratio of the airtight product 4 and the reference tank 5.

Further, according to this embodiment, when the inspection of one airtight product 4 is completed, the pressure holding valve V7 causes the reference tank 5 to
Since the pressure is maintained at approximately the inspection pressure J, it is possible to save time for filling the reference tank 5 with a large internal volume with air when the next airtight product 4 is inspected. Moreover, according to this embodiment, if the reference tank 5 is already pressurized when air is supplied by the inspection pressure imparting valves Vl and V2, almost no supplied air will flow into the reference tank 5. Cooling due to adiabatic expansion is suppressed, and the temperatures of the pair of self-heating resistors R1 and R2 of the thermal mass flowmeter 7 become equal. As a result, the measured value of the thermal mass flowmeter 7 becomes stable quickly, and the inspection time is significantly shortened.

Confirming this point based on the experimental results shown in Fig. 3, if the reference tank 5 is depressurized after each test, as shown by the dashed line in the same figure, the air content when the next test pressure is applied is large. As a result, the measured value of the thermal mass flowmeter 7 is not stable for a long time in the negative region, and as a result, the test becomes impossible. On the other hand, if the reference tank 5 is held at the test pressure after the test is completed, if the airtight product 4 is m-type, the measured value of the thermal gastric scattering current = 17, as shown by the solid line in the same figure. stabilizes in the positive region within a short time. Furthermore, if there is a leak in the airtight product 4, the measured value will stabilize at a higher level than in the case of a non-defective product, as shown by the broken line in the same figure, so this can be determined as a defective product.

Although air is used as the riverbed medium in Example L, the present invention is not limited to this, and it is also possible to use a liquid such as water or oil as the pressurizing medium. be.

[Effects of the Invention] As described above, the leak testing device for airtight products of the present invention has the following effects:
A reference tank with a larger internal volume than the airtight product, an inspection pressure applying means for applying the same test pressure with fluid to the airtight product and the reference tank, and a test pressure applying means for applying the same test pressure to the airtight product and the reference tank, and A thermal mass flowmeter that measures the flow rate of fluid based on the temperature difference accompanying the fluid flow between the thermal mass flowmeter; It consists of one pressure holding stage ε that holds the reference tank at approximately the test pressure after measurement using a type mass flowmeter, so it is possible to efficiently test many types of airtight products with one reference tank, and also to check the actual measurement value. By approximating the leak amount of There is an effect called ε.

[Brief explanation of drawings]

Fig. 1 is an air circuit diagram showing an embodiment of the leak testing device for airtight products of the present invention, Fig. 2 is a time chart showing the opening/closing timing of valves in the air circuit of Fig. Figure 1 is a current-time characteristic diagram showing the experimental results of the leak testing device, Figure 4 is an air circuit diagram showing the leak testing equipment for conventional airtight products, and Figure 5 is the diagram of the valve in the air circuit in Figure 4. A time chart showing the opening/closing timing, FIG. 6 is a schematic diagram showing the configuration of the thermal mass flowmeter in the air circuit of FIGS. 1 and 4, and FIG. 7 explains the measurement principle of the thermal mass flowmeter. between the characteristics of In the figure, 4: Airtight product 5: Reference tank 7: Thermal mass flowmeter Vl, V2: Inspection pressure imparting valve V3: Inspection ff release valve v7: Pressure holding valve. In the drawings, the same reference numerals and the same reference characters indicate the same or corresponding parts. Figure 3

Claims (1)

[Scope of Claims] A reference tank having a larger internal volume than the airtight product to be inspected; inspection pressure applying means for applying the same inspection pressure with a fluid to the airtight product and the reference tank; A thermal mass flowmeter that measures the fluid flow rate based on the temperature difference associated with the flow of fluid between the airtight product and a reference tank; and an inspection that releases the inspection pressure of the airtight product after measurement by the thermal mass flowmeter. A leak testing device for an airtight product, comprising a pressure release means and a pressure holding means for holding the reference tank at approximately the test pressure after measurement by the thermal mass flowmeter.