Sealing engines on the fly. (WIP).
"We replaced a 44-cent oil seal that had to be placed by hand with an approximately 11-cent seal that's injected in place," says Tom Jacobs, chemist, Automotive & Transportation, Wacker Silicones. The main modification to the part is the addition of a small filling port through which the material is injected, and attaching the pump to the engine prior to the addition of the gasket. "Because the material expands a controlled amount," says Jacobs, "we are able to retain the Fastener pre-load without overstressing the bolts. And since the material is pushing outward against the mating surfaces, it not only helps reduce vibration levels, it is much less susceptible to seal Failure." Seal shrinkage, Jacob says, is less than 0.2%.
LIS starts a two-part polymer that is injected through a static mixer into the gasket fill port. There it displaces the air in the gap. Wacker claims the material can deal with debris and fluid film, a wide variety of surface finishes, and seal mating surfaces with gaps that are as much as 0.040-in. larger than specification. Volume and fill rates are monitored throughout the process; anomalous readings are often the first sign of cracked or porous castings. "There have been three Failures out of 400,000 oil pump seals made so Far," he says, "and all were traced back to the castings." This information is being used to identify defective parts before they can cause a quality concern.
Curing time for the silicone can range from 30 seconds to an hour. "The flash provides the initial seal," says Jacobs, "and prevents fluids From infiltrating into the seal area by creating a 'wall' that blocks their entry." At room temperature, the gasket can provide 300 psi of initial sealing force before it is completely cured. This is enough to consider a radical rethink of how gaskets are applied and powertrains built.
"Imagine," Jacobs says, "injecting the gasket material after the engine and transmission are built and bolted together, introducing the fluids and installing the power-train in the car." This wouldn't pose a problem because the Flash can hold against the initial pressure, and cure time accelerates by 200% for each 10[degrees]C rise in temperature. "In the worst case," says Jacobs, "by the time the engine is up to operating temperature, the seals are completely cured." In his example Jacobs includes valve covers and, pans, and any other surface with a bolt tension setting in need of a seal.
Other advantages claimed for the technology include: reduced seal installation costs, rapid adaptability to design or process changes, increased process robustness, and a reduction in in-plant material handling and inventory. "We have 13 years of research behind the material and process," says Jacobs, which includes a system for replacing seals in the field.
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|Author:||Sawyer, Christopher A.|
|Publication:||Automotive Design & Production|
|Date:||Apr 1, 2003|
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