Development of the New FKM O-Ring for a Cooling Device
Date Published: 2005-04-11
Paper Number:2005-01-1753
DOI: 10.4271/2005-01-1753
Citation:
Yamaguchi, Y., Shojima, D., Ogata, C., Oya, K. et al., "Development of the New FKM O-Ring for a Cooling Device," SAE Technical Paper 2005-01-1753, 2005, doi:10.4271/2005-01-1753.
With high performance, weight savings and space savings being provided by motor vehicles, high performance, compact sizes and weight savings are required of cooling devices for use in automobiles in recent years. Typical examples of the members for which O-rings are used are radiators that are sealed against cooling water, oil coolers and cylinder liners that are sealed against two types of liquids: cooling water and engine oil.
In addition, requirements for heat resistance are strictly specified to O-rings for use in cooling devices. For example, oil resistance and cooling-water resistance at a temperature near 150°C are required of oil coolers and cylinder liners. For use in a cooling device, silicone rubber (VMQ) O-rings have been widely used, but the polymer structure of a VMQ O-ring tends to be subjected to acids and alkalis in engine oil with additives, or to hydrolysis in hot water, water vapor or engine oil.
Figure 1
and
2
show the actual examples of the hydrolysis that occurred in a new VMQ product, especially the outside appearance before and after deterioration.
As a countermeasure, an increase in bridging density is considered for VMQ O-rings, but this may be a cause for concern about the hydrolysis resistance of a polymer structure. For heat resistance, countermeasures can be considered with use of fluorine rubber (FKM) O-rings. However, a general-purpose FKM O-ring is excellent in oil resistance, but there is a case where cracks may develop in hot water or water vapor. A special-purpose FKM O-ring is superior in oil resistance, hot-water resistance and water-vapor resistance, but it tends to be inferior in durability (in compression set) and low-temperature properties (near TR
10
= -5°C).
A special-purpose FKM O-ring has oil resistance, hot-water resistance and water-vapor resistance, while a general-purpose FKM O-ring has durability (in compression set) and low-temperature properties. For this reason, a new FKM O-ring having these excellent properties of a general- purpose and special-purpose FKM O-rings was developed and verified for its performance.
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