How to choose the method for wheel hub airtightness test

How to choose the method for wheel hub airtightness test
The commonly used methods for wheel hub airtightness are immersion method and differential pressure method, with the former being intuitive and the latter being quantifiable. Production lines often use differential pressure method in conjunction with sampling and immersion review.
Immersion method: intuitive but dependent on human eyes
Inflate the wheel hub and immerse it in a water tank to observe the location of bubbles. The test pressure is usually set at 0.6-0.8MPa and held for 30-60 seconds.
The advantage is that it can directly locate the leakage point, which is convenient for subsequent analysis. The disadvantage is that it relies on the human eye, and small leaks can easily be missed.
It is recommended to control the water temperature in the sink at 20-30 ℃. When the water temperature is too high, bubbles form quickly but are prone to rupture, making it difficult to interpret.
Differential pressure method: quantifiable and suitable for mass production
The pressure difference method determines the leakage rate by measuring the pressure attenuation per unit time, with an accuracy of up to 0.1%.
The test pressure is also taken as 0.6-0.8MPa, and the holding time is adjusted according to the wheel volume, usually 30-120 seconds.
The differential pressure method requires a sealed fixture, and the sealing performance of the fixture itself can affect the results. The tooling needs to be regularly checked for standard leaks.
Helium detection: high precision but high cost
The sensitivity of helium mass spectrometry leak detection is the highest, which can detect extremely small leaks and is commonly used in high-end car models or safety components.
Equipment investment often amounts to hundreds of thousands of yuan, and helium consumption is also a continuous cost. Production lines are rarely fully adopted.
Mostly used for retesting during failure analysis or certification stages, not as a routine full inspection method.
How to determine the experimental parameters
The test pressure shall be executed according to product standards or customer drawings. Wheel hubs commonly have a pressure range of 0.6-0.8MPa, below which slight leaks may not be detected.
The holding time should be sufficient to stabilize the pressure. The pressure holding time needs to be extended for wheels with large volume.
The leakage rate is often judged as "less than 1%" as qualified, and the specific value is based on the drawing. The judgment criteria for different customers may vary.
Tooling and Sealing
Sealing fixtures often use rubber or polyurethane sealing rings. The aging of the sealing ring can lead to misjudgment, and it is recommended to replace it every 3 months.
The pressure gauge of the tooling needs to be calibrated regularly, and the recommended accuracy is above 0.4 level. If the expression is inaccurate, the judgment loses its meaning.
When delivering the wheel hub mold, Xinfeng Mold will prompt customers to configure specialized airtight fixtures according to the wheel type, avoiding using generic fixtures.
Common misjudgments
The first type is to classify tooling leakage as casting leakage. Block the tooling interface for retesting first, it can be ruled out.
The second type is to treat pressure fluctuations caused by temperature changes as leaks. Before the experiment, the workpiece needs to be equilibrated with the ambient temperature.
The third type is insufficient holding time. The pressure reading is not yet stable, and the result is either high or low.
Record and Trace
Record the test pressure, holding time, leakage rate, and judgment results for each item, and the data retention period shall be in accordance with customer requirements.
When tracing in batches, being able to retrieve raw data by batch is more valuable than leaving only "qualified" conclusions.
The first piece of airtight tooling shall be checked with standard leak holes once per shift to confirm that the equipment itself has no leaks.
Frequently Asked Questions
Q: What is the pressure for the airtight test?
Answer: Wheel hubs are commonly 0.6-0.8MPa.
Q: How to choose between immersion method and pressure difference method?
Answer: The pressure difference method is used for mass production, and the immersion method is used for failure analysis.
Q: Is helium testing necessary?
Answer: For high-precision scenarios, it is not necessary for regular mass production.
Q: What is the standard for leakage rate?
Answer: It is often considered qualified if it is less than 1%, and it should be executed according to the drawings.
Q: Will the tooling be misjudged?
Answer: Yes, aging of the sealing ring is a common cause.
Question: How long should the data be saved?
Answer: According to customer requirements, it is usually consistent with the batch traceability period.
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