Leak localisation
Technical data
Specification
A typical specification (Volkswagen/Audi) for leak testing of Alloy Wheels is:
A decay of pressure of 0,2 bar within 6 month at a volume of 25 l at 3 bar absolute test pressure versus 1 bar absolute pressure outside (atmosphere) at constant temperature and constant volume is accepted. Leak testing to be done with unpainted wheels!
| Machine capacity | |
| USLT-AW-A-1Sx6A |
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| Capacity |
200 pcs./h |
| Effective cycle time | 18 s |
| Product range | |
| Max. weight | 30 kg |
| Diameter | 15" - 22" |
| Width | 5" - 12" |
| batch size | Min. 1 |
Resulting leak rate
| Test method | USLT | Helium Vacuum | ||
| Test Pressure | 4 bar (absolute) | 2 bar (absolute) | ||
| Pressure outside | 1 bar (Atmosphere) | 0 bar (Vacuum) | ||
| ∆p | 3 bar | 2 bar | ||
| Test gas | Air | 100 % Helium | ||
| Leak rate | 6,00·10-4 mbar·l/s | 1,47·10-4 mbar·l/s | ||
| 35 bubbles with a diameter By using Helium-Air mixture, e.g. of 1 mm within 30 s) | By using Helium-Air mixture, e.g. 20 % Helium anliumd due to the calibration factor the mass spectrometer has to detect leak rates down to 10-7 mbar·l/s
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Background
As operator testing is not objective and reliable, Helium leak testing was established in the last decades too. While water bath testing is done with the unpainted Alloy Wheels, Helium testing is sometimes done with painted Alloy Wheels. Today there are some problems with leaking Alloy Wheels in the field.
One assumption is that these problems are due to testing of the painted Alloy Wheels instead of testing unpainted ones. Now, if looking to the Helium testers, it seems that it is more difficult to test unpainted Alloy Wheels according to the specification compared to painted wheels. In some cases you can find a fast rising Helium-background while testing unpainted wheels leading to 100% NOK results. The reason may be a rougher surface of the unpainted wheels.
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