Gaskets

View A Video on Gaskets - A Quick Introduction

Innovations in gasket design and manufacturing have contributed significantly to improved safety and efficiency of all kinds of industrial products: vehicles, pumping equipment and pipelines are just a few examples. Of particular importance to the gasket manufacturing industry have been advancements in the field of synthetic rubber development. Gaskets materials must always be carefully chosen with regard to the conditions in which the gaskets will be applied. Viton gaskets, EPDM gaskets, neoprene gaskets, silicone gaskets and other synthetic rubber gaskets each offer different qualities of tensile strength, heat resistance, non-reactivity, corrosion resistance, extreme temperature performance and chemical compatibility. In addition to the increasing availability of new gasketing materials, innovative gasket configurations have given professionals control over the most demanding and irregular connections. Spiral wound gaskets, high temperature gaskets, jacketed gaskets, Teflon gaskets and other special configurations allow for the creation of reliable seals even in the presence of extreme weather conditions or hazardous chemicals. Gaskets can also be specialized according to their application. For example, exhaust gaskets are only used for exhaust management purposes, and head gaskets are almost exclusively used to seal engine blocks and cylinder heads in combustion engines.

Across industry, gaskets of all shapes, sizes and compositions are used for sealing applications. The aerospace, automotive, aviation, electronics, military, transportation and countless other industrial operations make extensive use of gaskets. Airframes, appliances, business machines, compressors, elevators, escalators, medical equipment, meters, turbines, pumps, valves, engines, plumbing systems and a host of other varieties of equipment require the use of gaskets in order to function safely and effectively. Seals between joints are critical in many hydraulic, pneumatic and aerospace applications responsible for maintaining air or fluid pressure; in commercial aircraft, for example, gaskets throughout the aircraft keep the cabin from depressurizing. Gaskets have historically played a very important role in the safe operation of equipment. Gasket failure can have catastrophic consequences, as was the case in the explosion of the Challenger space shuttle in 1986. The failure of an O-ring gasket used in the shuttle's fuel system was attributed to low-temperature exposure, which made it become brittle. Engineers give very careful consideration to all of the factors that contribute to gasket operation; when gaskets fail, their failure can devastating.

Most rubber gaskets are die cut from flat rubber or metal sheets. Die cutting allows gasket manufacturers significant design flexibility, and gaskets are cut in shapes as simple as basic rings or as complex as automotive engine blocks. For applications that require simple gaskets with thick, strong construction, rubber molding is used as an alternative to die cutting. Gasket manufacturers use a wide number of both natural and synthetic rubbers to manufacture gaskets with application-specific tolerances. Common elastomeric materials include silicone, neoprene, nitrile, EPDM and Viton. Plastics commonly used for either gasket material or for jacketing include Teflon, nylon, polyethylene (PE), polyurethane and mylar. Sponge rubber like open or closed cell silicone is also used for applications requiring a more flexible seal. Gaskets may be made out of non-asbestos sheets such as carbon filament, fiberglass, ceramics and Kevlar. Metal gaskets and shims, which are flat metal gaskets similar to washers, are used alone or in combination with rubber gaskets to fill additional gaps that may occur within flanges, which is similar to the way metal jacketed gaskets are used to create extra seal strength and corrosion resistance.

Gaskets range in their design from very simple to very complex. The simplest gasket variety is the O-ring, which, as its name suggests, is merely a thin, O-shaped ring. They are almost always made of natural or synthetic rubber, though some metal and plastic ring gaskets could be described as O-rings. More complex gaskets can be textured to fit more effectively in a connection point; such shaped gaskets can be tapered, grooved, ridged or otherwise shaped to create a seal between two objects. In situations in which the point of a connection may be subject to stress, tension or movement, spiral wound gaskets can maintain a tight seal and provide the flexibility necessary to allow movement without breaking. These seals feature interwoven or combined metal and filler materials to provide a combination of strength, flexibility and effective sealing. Head gaskets are among the most complicated gasket varieties. They are used to create a seal between engine blocks and cylinder heads in combustion engines. They must combine features of strength, heat resistance and chemical resistance as they are exposed to the chemicals and heat involved in fossil-fuel combustion engines. Whatever the gasket configuration, every design is engineered to accommodate the conditions of a specific application, and the importance of anticipating all of those conditions cannot be overstated.

Images Provided by Reliant Rubber Company

Gaskets Types

• Composite 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.
  
• Corrugated gaskets 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.
  
• Die cut gaskets are made of materials that can be cut before assembly.
  
• ElastaGraph gaskets 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.
  
• Encapsulated gaskets consist of a gasket of one material and a continuous layer of another material, typically Teflon, which completely encloses the gasket.
  
• Envelope gaskets consist of a gasket of one material and an envelope of another material, typically Teflon, which covers the gasket.
• EPDM gaskets are made of a synthetic rubber that serves as a seal between two mating surfaces in machine parts.
• Exhaust gaskets provide a seal on exhaust parts in vehicles to guarantee that when gases leave the engine, they stay in the exhaust system until they are expelled into the atmosphere.
• Fibre seal rings are diecut, water-jet cut or formed gaskets or rings that provide a seal between two surfaces.
  
• Flange gaskets have protruding rims or lips that aid in the attaching process.
  
• Foam gaskets are made out of strips of plastic, foam or rubber.
• Gasket materials are various materials with sealant qualities that are used in gasketing applications.
• Head gaskets are inserted between the cylinder head and the engine block. Head gaskets prevent coolant from entering the cylinders.
• High temperature gaskets help prevent leakage of fluids and gas by providing an airtight seal between gaps in machine parts whose temperatures may exceed 500° F.
• Hollow tube gaskets have a tubular cross section that is typically made out of rubber or plastic.
  
• Jacketed gaskets combine the durability of a metal jacket with the sealing capability of a soft gasket.
  
• Laminated gaskets consist of two or more layered materials and are often enclosed in an envelope.
• Neoprene gaskets are made of synthetic rubber and create a long-lasting seal for gaps on machine parts in several industries.
• O-rings 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.
  
• Profiled and serrated gaskets 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.
  
• Rubber gaskets are rubber components that create a seal between two parts.
• Silicone gaskets (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.
  
• Solid metal gaskets 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.
  
• Spiral wound gaskets 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.
  
• Teflon gaskets are gaskets designed to resist sticking to the adjoining materials.
• Viton gaskets are made of a synthetic tube that is resistant to heat, oil, and various acids.

Gaskets Terms

Anti-Extrusion Rings - Also referred to as "back-up rings," they are rings designed to fit behind rubber o-ring seals in order to prevent extrusion into the gap between the metal pieces.
 
Beryllium Copper - A lightweight metal that resists corrosion and is used in aerospace materials, springs and gaskets.
 
Blowout Pressure - The internal forces that exert pressure against a gasket, which may cause the unsealing of the gasketed joint.
 
Bonded Seals - Flat steel washers in the center of which a rubber sealing ring is molded to fit over a bolt, providing a seal.
 
Die Cutting - Cutting shapes out of material using a die. The die is a pre-formed stencil.
 
Electromagnetic Interference - An interruption produced by an electric current, which can be filtered out by some gaskets.
 
Flange Load - The total force that creates a seal through compression of the gasket.
 
Hydrostatic End Force - The internal forces working against the flanges holding the gasket in place.
 
Mismatch - The unevenness of a seal due to differences in the two adjoining surfaces.
 
Nebar - A specialized gasket material that is used in electrical transformers.
 
Neoprene - A rubber used in weather resistant products, adhesives, paints, rocket fuel and gaskets.
 
Parback - A back-up ring that is used as an anti-extrusion ring for an o-ring. Parbacks are concave-shaped on one side.
 
Rings - Circular sealing devices. Seal Strips - Strips comprised of multiple layers of metal that are welded together to allow gaskets to be used in extreme heat or pressure.

Slip O-ring - A type of ring that relieves friction by fitting over an o-ring.

Shims - Used as spacers between a gasket and the adjoining material.

Static Seal - A seal, created by a gasket, between two unmoving parts.

Washers - Flat, circular rings placed under the head of a bolt to serve as spacers, gaskets or slip devices.