Measuring and testing – With fluid pressure – Leakage
Patent
1987-02-06
1990-01-30
Chapman, John
Measuring and testing
With fluid pressure
Leakage
G01M 332
Patent
active
048965308
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for leak testing containers wherein the container is pressurized or evacuated and a pressure value is measured as an indication of the degree of leakage, in other words a change in the container pressure, in the difference between the pressure in the container and an ambient pressure, in the ambient pressure or values dependent thereon, and wherein a limiting pressure value or a corresponding limiting value is preselected to determine whether a container is considered to be tight or leaky.
It should be emphasized that a value referred to hereinbelow as a "pressure value" can be a pressure differential, an absolute pressure, or a value derived therefrom such as mechanical deformation, etc.
The invention also refers to a leak testing device, for example to work this method, as well as a temperature measuring arrangement for such a leak testing device, and also to a method of measuring a temperature value on a body, which is significant for the thermal energy content of the body, by means of a quasi point temperature measurement.
Containers are manufactured today at a high manufacturing speed. This is especially true for soldered cans. The increase in production rate on the one hand and the use of increasingly thinner-walled material on the other require a high degree of precision in the manufacturing process to ensure a high degree of tightness for the containers. Likewise, on a filling line, in other words from the standpoint of the can user, a high degree of tightness is required so that foods do not spoil and environmentally hazardous or very valuable materials do not escape from the containers. Both the manufacturer and the user of such containers require a smoothly functioning, reliable quality control process. Even the smallest leaks must be detectable. This severe requirement on leak testing can already be met.
Tightness can be tested in various ways. The container can be pressurized or evacuated using air or a gas. If a leak is present, air or gas then flows in or out of the environment, changing the internal pressure in the container.
In some methods, the internal pressure of the container is observed, i.e. the internal pressure difference of the container is measured over a pre-determined time interval and compared with a limit pressure change value occurring for a container with the largest leak still tolerable. If the measured internal pressure change is greater than the preset limit pressure difference, the container is labeled a reject. In this case, therefore, a change in the internal pressure of the container is observed as a pressure value. In other methods, the container to be tested is enclosed in an autoclave. The air escaping from the container under test flows into the autoclave and increases the pressure in it, which is recorded in turn. In this instance, the pressure value registered is a change in the ambient pressure surrounding the container.
In view of the fact that the internal pressure of the container drops as a result of leakage (or increases when evacuated), and the ambient pressure surrounding the container increases (decreases when evacuated), it is also quite possible to use the behavior of the internal pressure of the container relative to the outside pressure surrounding the container in combination.
In view of these different methods, we will refer in the following in our discussion of leak testing to the recording of a pressure value. It makes no difference how the latter is measured, directly or indirectly, within the scope of the present invention.
The containers are leak-tested either after manufacture or after being filled. In both cases they are at undefined temperatures depending on the manufacturing steps that have gone before. This temperature not only varies from system to system, but also at a given point within a given system. Among the reasons for this temperature spread are the processing of different containers or a variable production rate, a variable ambient temperature at various points, or differences in conta
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Chapman John
Roskos Joseph W.
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