Against the backdrop of the rapid development of new energy vehicles and intelligent connected technology, the wire harness test bench serves as the core equipment for quality inspection ofvehicle electrical systems. The sealing reliability of its cylinder components directly impacts test accuracy and equipment stability. This article systematically elucidates the pivotal role of sealing testing technology, incorporating the ISO 8573-1 pneumatic system contamination control standard and the automotive industry's VDA 6.3 process audit requirements.
1. Preparation before testing
Sample pretreatment
Clean the oil and dust on the cylinder surface, and ensure that the connecting parts (such as the inlet and outlet air connections, and the gap between the piston rod and the end cap) are free from impurity blockage.
Check the cylinder status: ensure that the piston rod extends and retracts normally without any clamping stagnation; the seals (such as the piston rod seal ring and the piston seal ring) are intact, undamaged, or not aged (if the seals are known to be damaged, they need to be replaced before testing).
Tools and equipment
Sealing tooling: used to block the cylinder's inlet and outlet connections (such as plugs with sealing rings, pneumatic quick connectors), ensuring no leakage at the connection points (to avoid interfering with test results).
Water tank or sink: The volume should be sufficient to fully immerse the cylinder (or the sealing part to be tested), with the depth adjusted according to the size of the cylinder.
Air pressure source: Provides compressed air (0.1-0.6 MPa, adjustable) and connects to the cylinder inlet.
Pressure gauge: monitors the internal pressure of the cylinder, with an accuracy of ≥0.01MPa.
Timer: Record the holding time.
Observation tools: Strong light flashlight (for observing bubbles underwater) and marker pen (for marking leakage points).
II. Core Detection Methods (Adapted for Different Scenarios)
Static immersion method (applicable to non-high pressure water environment)
Applicable scenario: Testing overall sealing performance.
Testing steps:
1. Blocking the interfaces: Use sealing tooling to block the inlet and outlet interfaces of the cylinder, leaving only one interface connected to the air pressure source and pressure gauge.
Inflation and pressure maintenance: Inject compressed air into the cylinder, with the pressure set at
1.0-1.1 times its rated working pressure (if the rated pressure is 0.6MPa, inflate to 0.6-0.66MPa). Maintain the pressure for 1 minute, and confirm that the internal pressure of the cylinder is stable (no pressure drop, and eliminate interference from internal leakage).
2. Water immersion observation: Immerse the cylinder completely in the water tank (with the water level being at least 5cm above the highest point of the cylinder), maintain the internal pressure constant, and observe for 3-5 minutes.
3. Key observation areas: sealing clearance between the piston rod and the front cover, joint surface between the cylinder head and the cylinder barrel, sealing blockage of the interface, and welding seam of the cylinder body (if any).
Qualification criteria: No bubbles are generated underwater; if there are bubbles, the diameter of a single bubble should be ≤0.5mm, and the cumulative number of bubbles within 5 minutes should be ≤2 (microbubbles may be air adhering to the surface, and it is necessary to distinguish between "continuous bubbling" and "one-time bubbles").
III. Analysis and judgment of leakage causes
If a leak is detected, the root cause of the problem needs to be determined based on the location of the leak point:
Bubbles emerging from the piston rod seal: The seal failure may be caused by wear or misalignment of the piston rod seal ring, or excessive clearance in the guide sleeve; if the leakage is more obvious during dynamic operation, it may be due to wear on the lip of the seal ring or insufficient lubrication. Leakage at the cylinder head joint surface: Loose cylinder head mounting bolts, or aging or damaged sealing gaskets at the joint surface; Deformation of the mating surface between the cylinder barrel and the end cap (such as thread slippage leading to poor sealing).
Leakage at the interface sealing: Poor sealing of the sealing tooling (not a problem with the cylinder itself), or insufficient machining accuracy of the cylinder interface threads (such as burrs, missing threads).
Leakage at cylinder block weld seams: Welding quality defects (such as cold solder joint, sand hole) are commonly found in welded structural cylinders.
IV. Precautions
Pressure matching: During testing, the internal pressure of the cylinder needs to be close to the actual working pressure. Too low a pressure may mask leaks (as seals deform more significantly under high pressure, making leaks easier to expose).
Temperature influence: If the cylinder is used in high-temperature or low-temperature water environments, it needs to be tested at the corresponding temperature (for example, testing high temperature resistant seals in hot water to avoid changes in seal hardness caused by temperature variations, which could affect the results).
Repeat testing: Ifa leak is detected during the initial testing, repeat testing is required after repair to ensure stable sealing performance (especially after replacing the sealing components, it is necessary to verify whether the installation is correct).
V. Special operating condition testing (as needed)
For cylinders used in harsh environments (such as high temperature, dust, and corrosive gases), special inspections need to be added:
High temperature resistance: Underrated operating temperature (such as 150℃), maintain operation in a ventilated state for 1 hour, and test the sealing performance and operational stability (aging of seals can lead to a significant increase in leakage).
Corrosion resistance: Conduct a salt spray test on the metal parts of the cylinder block (according to GB/T 10125 standard), and after 48 hours, inspect the surface for rust and check if the function is normal.
Anti-Dust: When operating in a dusty environment (or in a simulated dust test chamber), disassemble and inspect the cylinder after operation to see if any dust has entered (if the dust seal of the piston rod fails, dust can enter and wear the sealing components)
Through the aforementioned methods, the sealing performance of the cylinder can be precisely evaluated, ensuring its reliable operation and prolonging its service life.
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