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Mechanical Engineer´s Handbook P31

CHAPTER 22 SEAL TECHNOLOGY Bruce M. Steinetz NASA Lewis Research Center Cleveland, Ohio 22.1 22.2 INTRODUCTION STATICSEALS 22.2.1 Gaskets 22.2.2 O-Rings 22.2.3 Packings and Braided Rope Seals 629 629 629 634 637 22.3 DYNAMICSEALS 22.3.1 Initial Seal Selection 22.3.2 Mechanical Face Seals 22.3.3 Emission Concerns 22.3.4 Noncontacting Seals for High-Speed/Aerospace Applications 22.3.5 Labyrinth Seals 22.3.6 Honeycomb Seals 22.3.7 Brush Seals 638 638 642 644 646 650 653 654 22.1 INTRODUCTION Seals are required to fulfill critical needs in meeting the ever-increasing system-performance requirements of modern machinery. Approaching a seal design, one has a wide range of available seal choices. This chapter aids the practicing engineer in making an initial seal selection. | CHAPTER 22 SEAL TECHNOLOGY Bruce M. Steinetz NASA Lewis Research Center Cleveland Ohio 22.1 INTRODUCTION 629 22.3 DYNAMIC SEALS 638 638 22.3.1 Initial Seal Selection 22.2 STATIC SEALS 629 22.3.2 Mechanical Face Seals 642 22.2.1 Gaskets 629 22.3.3 Emission Concerns 644 22.2.2 O-Rings 634 22.3.4 Noncontacting Seals for 22.2.3 Packings and Braided High-Speed 1 Aerospace Rope Seals 637 Applications 646 22.3.5 Labyrinth Seals 650 22.3.6 Honeycomb Seals 653 22.3.7 Brush Seals 654 22.1 INTRODUCTION Seals are required to fulfill critical needs in meeting the ever-increasing system-performance requirements of modem machinery. Approaching a seal design one has a wide range of available seal choices. This chapter aids the practicing engineer in making an initial seal selection and provides current reference material to aid in the final design and application. This chapter provides design insight and application for both static and dynamic seals. Static seals reviewed include gaskets O-rings and selected packings. Dynamic seals reviewed include mechanical face labyrinth honeycomb and brush seals. For each of these seals typical configurations materials and applications are covered. Where applicable seal flow models are presented. 22.2 STATIC SEALS 22.2.1 Gaskets Gaskets are used to effect a seal between two mating surfaces subjected to differential pressures. Gasket types and materials are limited only by one s imagination. Table 22.1 lists some common gasket materials and Table 22.21 lists common elastomer properties. The following gasket characteristics are considered important for good sealing performance.2 Selecting the gasket material that has the best balance of the following properties will result in the best practical gasket design. Chemical compatibility Heat resistance Compressibility Microconformability asperity sealing Recovery Creep relaxation Erosion resistance Compressive strength crush resistance Tensile strength blowout resistance Shear strength flange .