Seal Materials

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

Gasket A semirigid or flexible sealing material fitted in the connection between two surfaces. 

Duct mastic has replaced duct tape as the most effective sealing material. Mastic is a fibrous, elastomeric compound that permanently seals duct connections and seams. In addition, the boot connections between ducts and floors and between walls and ceilings should be fully caulked and/or foamed airtight. Lastly, air handlers that house the... 

In a fully synthetic FR fluid, the fire resistance is due to the chemical nature of the fluid in the others, it is afforded by the presence of water. The other main distinction between the two groups is that the fully synthetic fluids are generally better lubricants and are available for use at operating temperatures up to 150°C (272°F), but are less likely to be compatible with the conventional sealing materials and paints than are water-based products. 

Both physical and process-material considerations influence the choice and use of shaft seals in the industry. It is essential that the seal material is compatible with any process material and the operating variables. 

Nitrile rubbers, including fiber-reinforced varieties, are used both as radial shaft-seal materials and as molded packing for reciprocating shafts. They have excellent resistance to a considerable range of chemicals, with the exception of strong acids and alkalis, and are at the same time compatible with petroleum-based lubricants. Their working temperature range is from —1°C to 107°C (30°F to 225°F) continuously and up to 150°C (302°F) intermittently. When used on hard shafts with a surface finish of, at most, 0.00038 mm root mean square (RMS), they have an excellent resistance to abrasion. 

Face-seal materials can be chosen from filled, molded or reinforced resins with which water, hydraulic fluids, mineral oils or synthetic oils are all compatible. Their maximum temperature in service depends on the brittle point of the resin but, generally, the range is from —50°C to 100°C (122°F to 212°F). Abrasion resistance is generally good but, as far as possible, resins are not used in the presence of foreign solids. 

For the cathode seal material, there is a criterion that the thermal expansion coefficient of the metal component must be lower than that of the a-alumina header. A nickel-cobalt-iron alloy (NiloK) with a... 

The anode seal which closes the sodium compartment is a nickel—chromium alloy (Inconel 600). The application of Inconel 600 minimizes the growth of thick inter-metallics and it was shown that seals of this material have been operated for over three years. Contrarily to Inconel, the application of mild steel as the anode seal material gave a life of only 6000 h due to gross intermetallic growth which caused sodium attack of this intermetallic layer in the mild steel. 

Development of Self-Lubricating. Piston-Seal Materials for High-Pressure, Oil-Free Air Compressors , Rept No PAS-75-21, Naval Ship R D Center, Annapolis (1975) 3) T. Toshiaki ... 

Thus, from the second point, even if the physical properties of a seal material remained totally constant during the service life, the stiffness characteristics of the seal would alter because the shape factor changes—see Figure 23.1. 

Norwegian standard NORSOK M-710 Rev. 2, Qualification of non-metallic sealing materials and manufacturers, October 2001. 

Hoetzeldt, K., Bochmann, G., and Passler, W., Cold sprayable, low flammability and watertight molding or sealing material used for the preparation of elastic work layers for road, play or sports surfaces, German Patent, DE 4416570 A1 19,951,116, 1995. 

The considerations above apply to zeolite membranes as applied on the macrolevel (e.g., PBMR). Zeohte membranes apphed on the particle level or smaller might lead to a more optimistic outlook since this type of application neither involves expensive modules and supports nor expensive sealing material. 

Shaped seal material Optically clean glass Wire electrode material Plantinum... 

Strip packages represent an alternative form of packaging for unit-dose medication. Strips can be produced from single- or multiple-ply laminated materials provided the two inner plies can be sealed by heat or pressure (e.g., cold self-adhesive seals). Materials can range from relatively permeable plies to those that incorporate a foil ply of sufficient thickness and effectiveness of seal so that an individual hermetic seal is produced for each dosage. Strip packages are produced at lower speeds and occupy greater volume than blisters. 

This material finds use as a sealing material in automotive applications and marine motor lead wire insulation. It has also been used as the base polymer for low flammability, halogen free, cable jacketing compounds. 

Coating or sealing materials must not react with agent. 

Sealants. Gaskets, and Beads. All gaskets or beads are required to be at least 3/8 inch wide with a Shore "A" durometer hardness of 50 and conform to ASTM Specification C509-84 (Cellular Elastomeric Preformed Gasket and Sealing Material). 

Blast resistant doors and conveyor gates to seal material handling penetrations during hazardous operations. 

---