Elastomer Sealing Systems

Greater performance at less weight, reduced fuel consumption, and lower emission levels—these central demands of the power plant engineer mean greater demands on sealing systems. Thus, engine components and attached assemblies are more frequently manufactured from plastic for weight and functional reasons.

Reduced component stiffness (lower Young’s modulus) in comparison to the aluminum and magnesium previously used are the consequences. When parts are clamped, greater deformation is encountered, and the sealing system has to compensate for this.

The elastomer-based sealing systems are superb in satisfying these exacting requirements. On the one hand, the sealing pressure required by elastomers is very low, and, on the other hand, their superior elastic properties enable tolerance compensation over a broad range. Because of elastomer materials’ ability to resist extreme temperatures, these are used exclusively for containing liquids and gases. A metallic structure is used in elastomer gaskets to seal off the combustion chamber.

Suitable elastomers are selected to suit the medium to be sealed, the prevailing temperatures, and the requirements profile.

Figure 7-312 gives an overview of the elastomer compounds available and typical applications.

Fig. 7-312. Elastomer materials

Elastomer Seals. Elastomer seals, Fig. 7-313, have no substrate. To prevent overloading the elastomer profile, these seals are, for instance, installed in a groove in the component. These components are always designed so as to eliminate any external deformation. The height-to-width ratio is characteristic for the design of this seal.

Fig. 7-313. Intake manifold gasket

The cross section is considerably thicker (higher) along the direction of the compression forces than it is wide. At compression of 20% to 30%, this gives a very broad working range for the seal, and also enables sealing plastic components, which are subject to severe deformation. This type of gasket is used, in particular, in combination with valve covers, intake manifolds, or water flanges made of plastic.

When sealing camshaft bearings and other threedimensional passages in components, the elastomer gasket is the only option for sure management of the sealing point.

With special cross sections calculated using the finite element method (FEM), the gasket’s profile is matched to the specific properties of the component being sealed. As a result of these calculations, a rectangular cross section is only seldom employed.

The T section is the preferred sealing profile for acoustic purposes. In combination with specially designed decoupling elements for the bolts, this design is used for valve cover seals that integrate acoustic decoupling. Since the components being sealed are pressed together by elastomer elements (see Fig. 7-314), this system can no longer be calculated with the engineering methods used in the past.

To make these systems more functionally reliable, an analysis of the complete mounting system—comprising the seal, the decoupling element, bolt, and bushing— by FE calculations is unavoidable (see Figs. 7-320 and 7-322 below in Section 7.21.4.1).

Requirements made of acoustically decoupled systems include
- Decoupling structural sound
- Positive bolting of components
- Sealing
- Preassembly of individual parts

The interplay of finite-element calculations, laboratory simulation, and material development work is the basis for tailor-made, acoustically decoupled sealing systems.