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Current trends in environmental and emissions regulations are driving changes in new engine systems, and increasing the need for more effectively sealed joints in exhaust systems. At the high temperatures in these exhaust systems it is difficult for traditional gaskets to provide an effective seal, as they degrade at high operating temperatures. This paper introduces a coating that has both excellent temperature stability and good compliance, thus forming an excellent sealing enhancement for metallic layers in exhaust system gaskets. Temperature stability data is presented along with sealing data, which illustrate the superior performance of this material compared to current systems.

This paper discusses gasket technology to address the increasing demands of providing effective sealing solutions for exhaust systems. Increasingly, effectively sealed joints are required in exhaust systems to meet environmental and emissions regulations. These applications are especially demanding for sealing. With low load joints, significant flange movement, and temperatures in excess of 850°C (1550°F), it is difficult for traditional gaskets to provide an effective seal, typically degrading or creeping at operating temperatures. Utilizing multi-layer steel gasket technology, this paper details a solution to these problems. Temperature stability and sealing data is presented demonstrating the superior performance of this material. Also presented is information from recent field experience.

This paper discusses a new gasket technology to address the increasing demands of providing effective sealing solutions for exhaust systems. Increasingly, effectively sealed joints are required in exhaust systems to meet environmental and emissions regulations and provide accurate engine management data. These hot gas applications are especially difficult to seal. With low load joints, significant flange movement and distortion plus temperatures in excess of 850°C (1550°F), traditional gaskets often do not provide an effective seal, typically degrading or creeping at operating temperatures. This paper details a solution to these problems by utilizing a new multi-layer metal gasket technology. The solution consists of a portfolio of new high temperature alloys (HTAs). Each HTA has a unique operating range, all of which are beyond the functional temperature of the commonly used 300 series stainless steel. In addition, the HTAs are all coated with a unique high temperature coating.

Life estimation for complex systems ultimately involves a suite of models for the various potential product failure modes. The advances in gasket test and analysis techniques presented in this paper lay the foundation for development of this future predictive capability. Static sealing performance factors of creep-relaxation, fatigue resistance, and leak rate are three principal determinants of application sealing success. This paper explores progress in each of these areas and presents concepts needed to integrate them into a coherent, probabilistic methodology.

The paper shows how processing parameters of an injection transfer-moulding machine can be controlled to create and identify moulding faults of valve-stem seals. By controlling the processing parameters to produce typical valve-stem seal moulding faults at the system design stage, causes for waste can be identified. Detailed knowledge of the manufacturing process is fed into a knowledge based SPC quality system to monitor and control the manufacturing process. This information is used in the manufacture of valve-stem seals to improve quality and reduce waste.

The reliability of a valve stem seal (VSS) is directly related to its ability to deliver the correct rate of lubrication. Too little lubrication may result in valve stem wear; too much may result in ‘burnt’ valves and seats. The correct operational envelope will therefore depend upon an engineer's ability to predict how parameters such as seal geometry and material properties change over the life of the seal. This paper discusses the use of accumulative leakage measurements to study the life performance of a VSS as changes are made to ‘key’ design sealing features. A standard design VSS is used for ‘normal’ leakage bench marking. The results are to be used in the development of predictive leakage models that use both close scrutiny leakage testing and continued lubrication theory development.

The study of material properties is fundamental to the design, analysis, and service life estimation of rubber products. To investigate the usefulness of material test data the paper compares material test properties with those of a moulded product. The material properties include the stress-strain relationship, ageing properties in air and oil and abrasion properties. The study revealed the crucial material properties that directly affect the performance of a valve stem seal (VSS). In addition, a modified least square method is introduced to the Mooney-Rivlin fitting procedure.

The development of any sealing product invariably involves some form of physical leakage testing, and although this evaluates the performance of the product, it gives no insight to the fundamental sealing mechanism of the design. Elastohydrodynamic lubrication theory was used to study this problem. The study of hydrodynamic lubrication, where there is fluid flow, is, from a mathematical standpoint, the application of a reduced form of the Navier-Stokes equation with the continuity equation. This equation is well known as the Reynolds equation. However, normally, the Reynolds equation is derived from Cartesian co-ordinates where the curvatures of surfaces are ignored. However, a valve stem seal (VSS) works in an axisymmetric environment. This paper discusses the development of the elastohydrodynamic lubrication theory in a cylindrical co-ordinate system and its usefulness in the prediction of metered leakage across a valve stem seal.

Gasket sealability test techniques are used to characterize gasket material properties as they relate to sealing performance. Increasing use of coated metal gasket materials with formed sealing features extends this test method to also characterize the influence of gasket design features known as embosses or beads. The essence of gasket sealability test methods involves compressing the gasket specimen between flat and presumably parallel surfaces of the test platens. This paper explores the effects of platen parallelism on sealability test results. Initial investigations have revealed platen parallelism has a significant effect on observed test results with certain gasket materials. The primary focus of this work involves rigidly mounted platens as opposed to spherically mounted, or wobble platens. Techniques for evaluating the rotational bending stiffness of platen and loading fixture configurations are also presented.