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About Gaskets
Gaskets are used to create a tight seal between two
parts. The seal prevents gas or fluid from leaking. A proper seal will
prevent leakage during temperature or pressure changes. Some gaskets
are made to withstand electromagnetic and radio frequency interference
(EMI and RFI). Gaskets should be more pliable than the two adjoining
surfaces. In order for gaskets to work properly, they must mold to the
groves of both components. Additionally, gaskets must be chemically compatible
with the two joining surfaces. This ensures a tight seal with no fluid
or gas leaks. Gasket manufacturers produce gaskets to be used in the
aerospace, automotive, aviation, electronics, military and transportation
industries. Some applications include air frames, appliances, business
machines, compressors, elevators, escalators, medical equipment, meters,
turbines and valves.
While there are many types of gaskets, jacketed gaskets optimize temperature
and chemical performance. These gaskets combine the temperature resistance
of a metal jacket with the sealing performance of a soft filler. Pressure
needs, gasket geometry and sealing issues are factors in selecting types
of jacketed gaskets. Single jacket gaskets are the most basic type. Double
jackets gaskets are available with double shell and corrugation options.
French style jacket gaskets with two- or three-piece construction have
irregular shapes.
Determining whether or not gaskets and their accessories are necessary
and, if so, what type of material should be used can be confusing. If
the application is calling for something to be sealed in or out between
environments (e.g. to prevent leakage of a fluid from one area to another),
then it is necessary to use a seal, o-ring or gaskets. If there is a
gap between two assemblies or surfaces, then a shim is required. Shims
act as leveling devices or as seals to prevent leakage. Whether or not
to use metallic or non-metallic gaskets depends on the substance being
contained and the ambient environment. Other factors include internal
forces such as blowout pressure and hydrostatic end force, the flange
load, the temperature and the liquid or gas medium against which the
gaskets are to seal.
Gasket manufacturers use many, many materials to make gaskets. Types
of rubber include Neoprene, PVC, Hypalon, pure gum, Viton and food grade
(FDA). Plastics commonly used include Teflon, nylon, polyethylene (PE),
polyurethane and Mylar. Sponge rubber, such as silicone and open- and
closed-cell rubber, is also used. Gaskets may be made out of non-asbestos
sheets, such as carbon filament, fiberglass, ceramic and Kevlar. There
many types of available soft materials, including the following: compressed
sheet, composition cork, felt, vegetable fiber, vulcanized hard fiber,
chipboard and fishpaper. Polyether, polyester and filter foam are three
types of foam rubber. Of course, gasket manufacturers use metal to make
gaskets, some of which are carbon steel, stainless steel, nickel, aluminum,
brass and copper.
Featured
Articles
http://www.boltscience.com/pages/gasket.htm
http://www.ce-mag.com/archive/01/11/Hug.html
Types of Gaskets
- are custom-fit to individual applications
and are typically applied with a gasket dressing or adhesive in assembly
and sealing. Composite gaskets are made from any combination of the
following materials: cork, rubber, paper and felt.
- are metal gaskets that may be surface-treated
with ceramic, non-asbestos or flexible graphite. Corrugated gaskets,
which
may be used with Teflon envelopes, provide a seal at low seating stress.
- are made of materials that can be cut before assembly.
- are corrugated gaskets that are suitable for
high temperature, high pressure applications and consist of a metallic
core
over which a seamless flexible graphite is applied. ElastaGraph gaskets
have a high density inner ring to increase sealability and provide
low minimum seating stress.
- consist of a gasket of one material and a continuous
layer of another material, typically Teflon, which completely encloses
the gasket.
- consist of a gasket of one material and an envelope
of another material, typically Teflon, which covers the gasket.
- are diecut, water-jet cut or formed gaskets or rings
that provide a seal between two surfaces.
- have protruding rims or lips that aid in the attaching
process.
- are cut from sheet metal in an almost infinite variety of
sizes and shapes. Mating
surfaces must be perfectly aligned for flat solid metal gaskets to
provide good seals.
- are made out of strips of plastic, foam or rubber.
- are inserted between the cylinder head and the engine
block. Head gaskets prevent coolant from entering the cylinders.
- have a tubular cross section that is typically
made out of rubber or plastic.
- combine the durability of a metal jacket with the
sealing capability of a soft gasket.
- consist of two or more layered materials and are
often enclosed in an envelope.
- (http://www.o-rings.org),
also referred to as “donut-shaped” gaskets,
are circular rings, having a variety of cross-sectional configurations
that are specified by their dimensions, material and hardness.
O-rings are installed in a gland to close off a passageway, preventing
the
escape or loss of fluids or gases.
- are solid metal gaskets with surface
grooves, which facilitate a good seal with low seating stress.
To protect flange surfaces, profile and serrated gaskets can be
jacketed.
- are rubber components that create a seal between two parts.
- (formed-in-place) are made from an uncured blend
of a silicone compound that is applied to the mating parts
and allowed to cure after assembly.
- are gaskets made out of solid metal, yet they
must be softer than the materials of the two adjoining surfaces.
Solid metal
gaskets are used for extreme pressures or temperatures.
- are made of a thin metallic strip and a soft
nonmetallic filler that are wound together. Spiral wound
gaskets can withstand
high pressure and extreme temperature.
- are gaskets designed to resist sticking to the adjoining
materials.
- are
made of a synthetic tube that is resistant to heat, oil, and various
acids.
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