Leak Testing Components with High Temperature

Powertrain-related components (engine, transmission etc.) reaches high temperatures during their manufacturing process; leak testing such components can cause many issues. Temperature offset function has been developed to eliminate issues when leak testing high-temperature components. This page discusses the principles of the temperature offset function.

Issues with Temperature Offsetting/Previous Measurement Method

Issues in the Manufacturing Process
In general, it is known that leak measurement is severely compromised if the tested component has a temperature that is higher than a certain level. Methods as shown in Figure 1 have been used to avoid this issue. However, there are many 'wastes' associated with these methods such as the requirement of additional cooling process and/or cooling line and additional footprint, as well as reduction of defect-free rate due to incorrect test results.
Figure 1: Wastes caused to handle test components with high temperature
1. Waste in the cooling process 2. Waste in the cooling line
3. Wasted space for cooling 4. Waste of defect-free rate decrease due to incorrect test results
Issues with Previous Offset Method
When the component subject for leak testing has a high temperature, the temperature of the said component as well as jigs and room temperature were measured to work out the correlation with leak measurements and obtain the correlation coefficient, which were applied to the leak test (see Figure 2). However, there are following issues associated with this method.
Figure 2: Common offset method when testing components with a high temperature

▼ Graph 1 shows the heat dissipation characteristics of sections ▼
A-D of the tested component as shown in Figure 2.

Issues1:It is difficult to determine which section will have a correlation with the leak measurement, as heat dissipation characteristics differ between different sections of the tested components.
Issues2:Practical application range of thermometers is limited - it can only be used in sections where the temperature of the tested component is exceptionally close to room temperature (±5°C), meaning that they are easily influenced by the surrounding temperature

Graph 1: Differences in heat dissipation characteristics between sections of the tested component

Temperature drops gradually in sections with large heat capacity

Temperature of seal base is relatively similar to room temperature

Temperature drops gradually in section with small heat capacity

In sections where the contact area with the test component is large, the temperature of the tested component is transferred, increasing the temperature gradually.

Fukuda's temperature offset system was developed in order to help overcome these issues.

Fukuda's Temperature Offset Method

Principle of Leak Tester with Temperature Offset
Fukuda's leak tester with temperature offset considers the temperature effect as the changes in air temperature within the tested component. This means that the overall changes in temperature that incorporates not only the temperature of the tested component, but also the surrounding temperature. In addition, the data gained from differential pressure gauge is used to determine the temperature, instead of the use of thermometers. As shown in Figure 3, an enclosed structure (temperature sensing elements) is set up to collect only the temperature changes within the tested component, and the leak testing of this section is carried out with a TMD unit, with the changes in air temperature being worked out by measuring the changes in differential pressure. Leak measurement of tested components is carried out as per normal using FL-612. From these leak test values, data as shown in graphs 2 and 3 are obtained. Plotting this relationship in a scatter diagram (Graph 4) reveals a certain level of correlation, which can then be expressed as a correlation coefficient. Temperature offset can be applied by subtracting the changes in temperature from the measured value based on the above correlation.
Figure 3: Principle/Measurement of Temperature Offset
Graph 2: Differential pressure during FL-612 detection time
Graph 3: Differential pressure during TMD unit detection time
Graph 4: Correlation between FL-612 and TMD unit

▼ A practical temperature offset can be applied by doing calculations based on ▼
the correlation coefficient gained from the method described above (Figure 4).

Figure 4: Measurements before/after the offset being applied

▼ The circuitry diagram of the temperature offset measurement circuit system is as follows. ▼

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