Automotive Design
Fig. 3. The results: Values below the black horizontal line indicate that applying the chemicals has impaired the membrane. The test membrane has only limited suitability for wetting with corrosion protection (removal) agents, but lies within the prescribed standards for all other chemicals tested.
designed process to create a membrane with very fine pores and in which the nodes are interconnected by fibrils. This material, called expanded polytetrafluoroethylene or ePTFE, is extremely hydrophobic (water resistant) thanks to its low surface tension, which means that any water droplets on the surface are unable to penetrate the membrane structure. The membrane is also oleophobic (oil resistant) and repels liquids with low surface tensions, such as oils. ePTFE’s oil-repelling properties are particularly important as the likelihood is very high that vehicle components will come into contact with motor oil, cleaning agents or other auto fluids.
To test how well venting solutions are able to withstand up to 20 different chemicals (in accordance with the ISO 16750-5 standard), the vents are exposed to each test liquid and then left for 24 hours at room temperature (21 to 23 °C) or heated for 96 hours in an oven. Airflow and water entry pressure are measured before and after the test. Both results must lie within prescribed specifications.
Another advantage of PTFE is its extremely high resistance to extreme temperatures. The trend toward reducing
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engine size usually pushes temperatures above the 125°C threshold that electronic housings have been designed to cope with until now. It is no longer uncommon for temperatures to reach 150°C and above.
There are several proven methods of testing vents to determine their ability to withstand extreme temperatures (ISO 16750-4).
In the temperature resistance test, the vent is exposed to a maximum temperature of up to 150°C for 2,000 hours, or a minimum of -40°C for 1,000 hours. In the ice dunk test, the vent is placed in a sealed housing and heated at between 80 and 120°C in an oven for 40 to 60 minutes. The housing is then rapidly cooled to between 0 and 4°C by placing it in iced water containing 5% sodium chloride, a solution designed to simulate the salt water that electronic housings are likely to come into contact with in the winter. This procedure is repeated 10 to 20 times.
Choosing the right membrane to suit each particular application and its requirements is vital. To cover all application areas, membrane manufacturers offer adhesive and weldable vents as well as moulded parts. Adhesive vents are coated with a
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