Gaskets: Types and Considerations

Chapter 1: What is a Gasket?

Gaskets are mechanical seals designed to prevent leakage by filling the spaces between stationary mating surfaces. Both polished and unpolished surfaces, especially metal ones, feature inherent roughness or microscopic asperities that can create gaps through which fluids might escape. When a compressive force is applied, the gasket deforms to match the surface profile, effectively sealing the gaps between the surface's peaks and valleys.

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Gaskets are widely used across various industries involving both pressurized and non-pressurized liquids and gases. They are commonly found in equipment that contains fluids, including pipes, tanks, heat exchangers, and combustion engines. Gaskets come in different forms and ratings to match the specific requirements of each application.

What is the Difference between a Gasket and an O-Ring?

Gaskets and O-rings are both used as sealing components in mechanical and engineering applications to prevent fluid or gas leaks. Despite their similar function, they differ in design, shape, and application. Below are some key distinctions between gaskets and O-rings:

Shape and Design

• Gaskets: Gaskets are typically flat or irregularly shaped seals made from a wide range of materials, including rubber, paper, metal, or composite materials. They are often cut or molded into custom shapes to fit the specific sealing requirements of a particular application.
• O-rings: O-rings are round or toroidal seals with a circular cross-section. They are usually made from elastomeric materials like rubber or silicone and have a uniform, donut-like shape.

Cross-Section

• Gaskets: Gaskets can have various cross-sectional shapes, such as flat, oval, square, or irregular, depending on the application and the geometry of the sealing surface.
• O-rings: O-rings have a consistent circular cross-section, which allows them to provide a uniform seal when compressed within a groove or between two mating surfaces.

Application

• Gaskets: Gaskets are commonly used for static sealing applications where two stationary surfaces need to be sealed against each other, such as in flanges, pipe connections, or cylinder heads.
• O-rings: O-rings are primarily used for dynamic sealing applications where there is relative motion between the sealing surfaces, such as in hydraulic and pneumatic systems, rotating shafts, and valves.

Sealing Mechanism

• Gaskets: Gaskets rely on the compression of the material to fill the gaps and irregularities between the mating surfaces, creating a barrier that prevents the escape of fluids or gases.
• O-rings: O-rings create a seal by being compressed between two mating surfaces, and the circular shape of the O-ring ensures even distribution of pressure around the circumference, providing an effective seal.

Materials

• Gaskets: Gaskets can be made from a wide range of materials, including rubber, cork, paper, metal, and various composite materials, chosen based on the specific requirements of the application.
• O-rings: O-rings are typically made from elastomeric materials like nitrile, silicone, Viton, or EPDM, which offer flexibility and resilience for sealing under various conditions.

Installation

• Gaskets: Installing gaskets often involves positioning them between two mating surfaces and securing them with bolts or fasteners. Proper torque and compression are crucial to achieving a reliable seal.
• O-rings: O-rings are typically placed within a groove or gland on one of the mating parts. When the two parts are assembled, the O-ring is compressed to create a seal.

Versatility

• Gaskets: Gaskets are more versatile in terms of shape and application, making them suitable for a broader range of sealing requirements.
• O-rings: O-rings are highly specialized for specific dynamic sealing applications, particularly those involving rotating or reciprocating motion.

Are Gaskets and Seals the Same Thing?

Gaskets and seals both play a vital role in preventing leaks in mechanical systems such as engines, pipes, and containers, but they are not identical.

A gasket is a specific mechanical component typically made from materials such as rubber, metal, or composites. It is designed to fill gaps between two mating surfaces, creating a tight seal when compressed. Gaskets are generally used in static situations where the sealed parts do not move significantly.

A seal, on the other hand, is a broader term that includes various sealing devices, such as gaskets, O-rings, and lip seals. Seals can be dynamic, meaning they are used in applications where there is relative movement between the mating parts, such as in hydraulic cylinders or rotating shafts.

Although both gaskets and seals are crucial for leak prevention, they differ in design, functionality, and the types of applications they are best suited for.

How Gaskets, O-Rings, and Seals are Related

Seals, O-rings, and gaskets are all mechanical sealing components used to prevent the leakage of fluids or gases in various applications. Although they share the basic function of sealing, they differ significantly in design, shape, and specific applications. Below are the similarities and differences among them:

Similarities

Purpose

• Seals, O-rings, and gaskets are all designed to create a barrier to prevent the escape or entry of fluids (liquids or gases) between two mating surfaces.

Materials

• They can all be made from a variety of materials, including rubber, silicone, elastomers, plastics, metals, and composite materials, depending on the specific application requirements.

Compression

• All three rely on compression to create a tight seal. When they are compressed between two surfaces, they deform to fill gaps and irregularities, preventing leakage.

Differences

Shape and Design

• Seals: "Seal" is a broad term that encompasses various types of sealing devices. Seals can have different shapes, such as flat, square, rectangular, or custom shapes, depending on the specific application. They are often used in rotating equipment like pumps, valves, and shafts.
• O-rings: O-rings are round, doughnut-shaped seals with a circular cross-section. They are typically used in static or dynamic applications where they fit into grooves or recesses to form a sealing barrier. O-rings are commonly used in hydraulic and pneumatic systems.
• Gaskets: Gaskets are typically flat or irregularly shaped seals used to create a seal between two flat surfaces, such as between flanges in pipes, engines, or machinery. They come in various shapes and can be cut or formed from sheets of material. Gaskets are often used in static applications.

Applications

• Seals: Seals are used in a wide range of applications, including hydraulic and pneumatic systems, automotive engines, and industrial machinery, where they are used to prevent leakage and control fluid flow.
• O-rings: O-rings are frequently used in applications involving rotating or reciprocating motion, such as in pumps, cylinders, and valves. They are particularly well-suited for sealing dynamic components.
• Gaskets: Gaskets are commonly used to seal flanged joints in pipelines, engines, and other equipment. They are designed for static sealing applications and are often used in environments with minimal movement.

Sealing Mechanism

• Seals and O-rings primarily rely on compression of the circular cross-section to create a sealing barrier.
• Gaskets rely on their flat or irregular shape to create a seal when compressed between two mating surfaces. They often require the use of bolts or clamps to provide the necessary compression.

Chapter 2: How Gaskets are Made?

Gasket manufacturing involves a range of techniques and processes, including cutting, die pressing, and punching. The method selected depends on the material being used and the desired strength and application of the final product. Regardless of the technique, the process always starts with selecting the appropriate material, which is essential for the gasket's performance.

Rotary Die Cutting

Rotary die cutting utilizes a cylindrical die mounted on a rotary press to cut and shape non-metallic materials. In this process, the material is fed into the cutting station where it interacts with both an anvil cylinder and the rotary die. The anvil and cylinder die move in opposite directions along their horizontal axis. As the cylinder die presses against the anvil, it cuts out the gaskets. This method is efficient for producing large volumes of gaskets with uniform shapes.

Kiss Cutting

Kiss cutting employs a rotary cylinder to cut gaskets from non-metallic materials, similar to rotary die cutting. However, in kiss cutting, the die only partially cuts through the material, leaving a backing layer intact. This backing, which can be made of adhesive material, helps ensure more secure installation of the gasket.

Press Die Cutting

Press die cutting is a widely used method for producing gaskets, particularly for metal and other rigid non-metallic materials. This technique involves a traditional press where the die is mounted on the ram, which then lowers onto the material to cut out the gasket. The force needed varies based on the material being processed. Presses used in this method can be hydraulic, pneumatic, or electrical, with manual operations providing more precise cuts.

Flatbed Die Cutting

Flatbed die cutting is a more straightforward method compared to press die cutting. It features a stationary flat base with a movable head that traverses across the material. The cutting die consists of steel rule strips, which are shaped to form the gasket. These dies are supported by a foam surface that compresses during cutting but shields the sharp steel strips when not in use. This process is particularly well-suited for short production runs due to its simplicity.

Knifeless Die Cutting

Knifeless cutting employs a blade to shape the gasket and is driven by a computer numeric control (CNC) system. This process uses computer-aided design (CAD) to program the dimensions of the gasket, which are then fed into the CNC machine to execute the cut.

Waterjet Cutting

Waterjet cutting, although slower than die cutting, does not require traditional tools like dies. This technique uses pressurized water to cut through the material, generating minimal waste and no fumes. The only byproduct is a light mist of water, making waterjet cutting a popular choice for its environmental benefits.

Laser Cutting

Laser cutting achieves extremely precise gasket tolerances of ±0.. Various lasers, including CO2 and ultraviolet types, are used in this process. With ongoing advancements and the introduction of new designs, laser cutting has become the preferred method for producing custom gaskets. Like knifeless and waterjet cutting, it relies on CAD designs that are programmed into CNC machines.

Compression Molding

Compression molding involves the use of a heated mold where the gasket material is placed in the heated mold and compressed. The compressed material is allowed to cure prior to being released from the mold. It is the perfect process for short low production runs and less intricate gaskets. The process of compression molding is ideal for manufacturers with limited space since the compression mold equipment has a small footprint. The compression molding process is ideal for the fabrication of flexible rubber materials.

Rubber to Metal Bonding

Several factors must be considered in the rubber-to-metal bonding process before manufacturing the gasket. One key factor is the type of metal used, which is typically steel but can also be aluminum. This bonding procedure is a sophisticated chemical process that involves the interaction between the metal and the rubber.

The process begins with treating the metal gasket either mechanically or chemically to prepare its surface for the application of the rubber compound.

Its surface is then prepared for the rubber compound application. The bonding mixture comprises a precisely measured blend of bonding agent and solvent, which can be applied to the metal surface by dipping or spraying.

To achieve a secure bond, the metal-rubber gasket is compressed. This step is crucial to prevent any potential detachment or peeling of the rubber from the metal.

Leading Manufacturers and Suppliers

Chapter 3: What are the different types of gaskets?

Material and form are critical specifications for gaskets, as they determine the gasket's resistance to corrosive environments, extreme temperatures and pressures, mechanical stresses from mating surfaces, and dynamic operational conditions. Based on the material and design, gaskets are categorized into non-metallic, semi-metallic, and metallic types.

Non-metallic Gaskets

Non-metallic gaskets are generally employed for applications with low to moderate fluid pressures. They can handle a wide range of temperatures, depending on the material used. These gaskets are easily produced and supplied as sheets, which can be shaped through die-cutting, kiss cutting, or die pressing. This flexibility means suppliers don&#;t need to stock various forms, as gaskets can be customized to fit specific requirements.

Key advantages of non-metallic gaskets include their ease of compression and effective sealing with minimal torque. Their adaptability allows them to conform to the specific shape of the application they are intended to seal.

Non-metallic gaskets are made from uniform materials such as flexible graphite sheets, virgin PTFE, or composite fibers and granules embedded in an elastomeric resin. Advances in technology are leading to the development of new, proprietary materials by manufacturers. Examples of common non-metallic gaskets include:

Polytetrafluoroethylene (PTFE) Gaskets

Among the various non-metallic gasket materials, PTFE is the most commonly utilized due to its advantageous properties: it boasts a high melting point, is hydrophobic, chemically inert, features a low friction coefficient, and exhibits remarkable flexural strength. PTFE is particularly valued in chemical processing for its high bonding energy, which provides excellent resistance to chemical reactions and corrosion. However, PTFE can be degraded by fluorinating agents, magnesium, and molten alkali metals.

While PTFE is inherently strong, its mechanical properties are often enhanced by incorporating various fillers. These fillers, which can include glass fibers, carbon, bronze, graphite, and molybdenum sulfide, improve PTFE&#;s wear resistance, deformation strength, electrical characteristics, thermal conductivity, and friction coefficient.

In addition to its superior chemical resistance, PTFE also offers excellent insulating properties, toughness, and impact resistance. The primary forms of PTFE include virgin PTFE, filled PTFE, biaxially oriented PTFE, and expanded PTFE.

• Virgin PTFE &#; Virgin PTFE is a pure material that is made without the use of recycled PTFE and has exceptional chemical resistance. It has excellent physical properties, retains flexibility at low temperatures, and is Food and Drug Administration (FDA) approved for use in food and pharmaceutical manufacturing.
• Filled PTFE &#; Filled PTFE has added fillers such as glass fibers, carbon, or bronze and comes in various grades such as PTFE-GF glass-filled, PTFE-CGF graphite filled, PTFE-MoS2 molybdenum filled, and PTFE-BR bronze filled. Each of the different grades contains a percentage of filler varying from 5% to 15%.
• Biaxially Oriented PTFE &#; Biaxially oriented PTFE has its particles biaxially oriented to create exceptional longitudinal and transverse directional strength. The nature of this unique matrix, with added fillers, resists creep and cold flow when subjected to a load. As with filled PTFE, biaxially oriented PTFE comes in various grades according to the type and percentage of filler.
• Expanded PTFE &#; Expanded PTFE is manufactured using virgin PTFE. It has all the properties of regular PTFE, but it is more resistant to creep and cold flow. A major differentiation of expanded PTFE over other forms of PTFE is its exceptional compressibility due to its multidirectional fibrous texture that allows it to perform well under varying pressures. It readily adapts to the necessary sealing requirements of an application and can be adjusted for different hardnesses, surface energies, and other physical properties.

Plastic Gaskets

Plastics are cost-effective, versatile materials created from a diverse array of plastic compounds. They are characterized by their lightweight nature, low friction, and effective sealing and insulation properties. Plastics offer high durability and can endure a wide range of temperatures, making them a viable alternative to metal gaskets.

In addition to PTFE, gaskets can be made from various plastics such as ABS, Acetal, Nylon, different types of polyethylene, and polypropylene. The extensive range of plastics available allows for selecting the most suitable material based on sealability, pressure ratings, and temperature requirements for specific applications.

Plastics are generally categorized into two main types: thermoplastics and thermosetting polymers. These categories are distinguished by their production processes and the properties they exhibit, which are influenced by the methods and materials used in their manufacture.

• Thermoplastics - Thermoplastics are a solid resin material at room temperature that becomes soft and pliable when heated. They are processed using injection molding, extrusion, or blow molding, where the thermoplastic takes the shape of the mold. Thermoplastics are reversible and can be reheated and melted multiple times to shape new products. The common types of thermoplastics include polyethylene, polycarbonate, and polyvinyl chloride. Their reversibility is one of the negative aspects of thermoplastics since they will deform and melt when subjected to intense heat and high temperatures.
• Thermosets - Thermosetting polymers are a liquid material at room temperature that hardens into an irreversible plastic when heated. Placed in a mold and heated, thermosetting polymers solidify into the shape of the mold and form bonds called cross-links that hold the molecules in place. Unlike thermoplastics, thermosets deform when exposed to overheating but do not return to their fluid state. Processes used to shape thermosetting polymer gaskets include compression molding and resin transfer molding. Common thermosets are epoxy, polyimide, and phenolic.

Flexible Graphite Gaskets

Flexible graphite gaskets are produced by expanding graphite flakes through a combination of intercalation, heating, and compression processes. First, high-quality graphite flakes are treated with acids like nitric, phosphoric, and sulfuric. This treatment generates graphite intercalation compounds, which expand significantly upon heating. During exfoliation, the graphite expands extensively as the intercalated compounds vaporize, creating gas pockets. The result is worm-like or vermiform structures with highly active, rough surfaces. These structures interlock mechanically when compressed, forming a flexible graphite sheet. Although flexible graphite gaskets generally have lower tensile strength compared to other non-metallic options, their strength can be enhanced by incorporating reinforcements, laminates, and inserts.

Typically, flexible graphite gaskets include fillers such as foils or tangs, often made of stainless steel, although other materials may also be used.

• Stainless Steel Tang - Graphite gaskets with stainless steel tang are reinforced with stainless steel grade 316, composed of chromium, nickel, molybdenum, and carbon, and highly resistant to corrosion. Stainless steel tang graphite gaskets are used for industrial fluid sealing applications.
• Stainless Steel Foil - Stainless steel foil graphite gaskets are also made of stainless steel grade 316 with the addition of 0.002 inches (0.05 mm) of grade 316 foil.
• Wire Mesh - Wire mesh reinforced graphite gaskets are expandable and flexible. They have a metal mesh made of stainless steel grades 304 or 316 or a carbon steel mesh with a graphite content of more than 98%. They have permanent elasticity over the entire temperature range with long-term uniform compressibility.
• Tinplated Carbon Steel Tang - Tinplated carbon steel tang has a thick, 0.007 inches (0.178 mm) tinplated carbon tang insert that is mechanically bonded to the graphite material and resistant to high temperatures, chemicals, and blowout. It is a non-aging material with no creep relaxation. Tinplated carbon steel tang graphite gaskets are widely used in the automotive industry for head gaskets and exhaust gaskets.

Phyllosilicate (Mica and Vermiculite Minerals) Gaskets

Phyllosilicates are a group of minerals from the mica family used to make non-oxidizing, high-temperature gasket materials. As non-oxidizing properties, they solve the problem with graphite gaskets, which is their tendency to oxidize, or &#;coke,&#; at high temperatures in environments containing oxygen or other oxidizing agents.

The primary phyllosilicates used in gasket production are mica and vermiculite, both of which offer similar temperature and chemical resistance properties. Mica gaskets are created from sheets made by combining mica mineral with a polymer and subjecting them to high heat. Vermiculite, a form of expandable mica, is produced by the flash conversion of water molecules between the layers of its crystal structure.

Mica exhibits excellent resistance to temperatures exceeding 900°F (482°C), where flexible graphite is not suitable. As a gasket material, mica is effective in high-temperature applications and remains stable in the presence of oxygen. It is available in various forms, including laminated, flexible, or rigid, and can be tanged with stainless steel to handle higher pressures. Additionally, mica can be combined with polymers through heat treatment to enhance its flexibility, addressing its otherwise poor sealability.

Vermiculite gaskets offer exceptional heat and chemical resistance, capable of withstanding temperatures up to °F (°C). When tanged with stainless steel, vermiculite gaskets can endure pressures of up to 740 psi while maintaining excellent sealability. The superior strength of vermiculite allows it to survive oxidation conditions that would compromise graphite and other gasket materials. Due to its thermal insulation properties, vermiculite gaskets are used in exhaust gas recirculation (EGR) systems where blocking heat flow is essential.

Elastomer (Rubber) Gaskets

Elastomers are polymers characterized by their highly elastic properties, formed by cross-linking long polymer chains into amorphous structures. The weak intermolecular forces between these polymer chains allow them to be reconfigured when stress is applied. This elasticity enables elastomer gaskets to easily conform to the surface profiles, ensuring a tight seal.

Contact us to discuss your requirements of Rubber Bellows. Our experienced sales team can help you identify the options that best suit your needs.

There is a broad selection of elastomers available to meet various requirements, although their chemical and temperature resistance tends to be less than that of PTFE. Depending on the type of curing reaction or vulcanization, elastomers may degrade when exposed to water, ultraviolet light, oils, and certain solvents. High temperatures can cause elastomers to expand and melt, while low temperatures can render them brittle. Common elastomers used in gasket manufacturing include nitrile (NBR), ethylene propylene diene monomer (EPDM), neoprene, silicone, and fluoroelastomer (FKM).

Extruded Rubber Gaskets

Extruded rubber gaskets are flexible, lightweight, long-lasting, and exceptionally durable. They are made to endure hostile, harsh, and extreme environments, such as applications that involve exposure to chemicals or extremely high temperatures. Extruded rubber gaskets are manufactured using the extrusion process, where the softened rubber is forced through a die and comes in hollow sections, cord shapes, and squares. The properties of hollow cross-sections have exceptional sealing compression.

Extruded gaskets are used in a wide range of applications, such as sunroofs, garage doors, windows, windshields, and boat hatches. Their tensile and sealing strength helps to block noise and protect against moisture and extreme weather conditions. The extrusion process, known for its cost-effectiveness and ability to produce high-quality products, is commonly employed in the manufacture of gaskets.

Compressed Fiber Gaskets

This type of gasket is made from naturally occurring mineral or synthetic polymer fibers. Asbestos gaskets, one of the earliest forms of compressed fiber gaskets, were used in industrial applications. Asbestos, a naturally occurring silicate mineral with long, thin fibrous crystals, is now being phased out due to health risks such as asbestosis and cancer. Alternatives to asbestos include carbon, graphite, glass, aramid, and other fibers.

Compressed fiber gaskets are made using a process known as beater addition, which is often proprietary. During this process, minerals are beaten to fibrillate the main fibers into tiny fibrils. This spreading of the fibers allows elastomer resins to be added, which bind the fibers together. Common elastomers used in this process include styrene-butadiene rubber (SBR), NBR, neoprene, and EPDM.

Cork Gaskets

Cork is suitable for low-temperature and low-pressure applications. Gaskets are made by compressing granulated cork bark and binding it with an elastomer resin. Cork gaskets are lightweight, flexible, and resistant to water, oil, and other petrochemicals.

Special Types of Non-Metallic Gaskets:

• Compressed Non-Asbestos: Compressed non-asbestos gaskets combine non-asbestos fibers with rubber to improve the temperature and pressure properties of a gasket. Combining organic and inorganic fibers makes it possible to achieve a wide variety of mechanical properties such as excellent sealability, torque retention, and heat resistance. Compressed non-asbestos gaskets can be used in applications involving air, water, steam, oil, acids, and most chemicals
• Santoprene Gaskets: Santoprene gaskets are made of rubber from thermoplastic vulcanizates (TPV) or thermoplastic polymers (TPE). It is a patented material composed of a dynamically vulcanized ethylene propylene diene monomer (EPDM) dispersed in a polypropylene matrix. As a thermoplastic, Santoprene can be melted, recycled, and reused as raw material for new gaskets. Santoprene is resistant to degrading factors such as ultraviolet light and ozone.

• Poron Gaskets: Poron is a patented gasket material made from multicellular polyurethane. Its porous structure makes it well suited for thermal insulation, vibration dampening, acoustic dampening, and shock absorption. Polyurethane's inherent resilience and rebound properties make it suitable for sealing because of its reduced creep relaxation.

  
  
• RN- Gaskets: This is another patented gasket made from a composite of low-density cellulose fiber material with high rubber filler content dispersed in a nitrile rubber matrix. It is well suited for sealing oil and water even at low bolt loads. They are commonly used in engine heads, transmission pans, water pumps, and environmental seals.

Semi-metallic Gaskets

These gaskets are composites of metallic and non-metallic materials. The metallic component provides structural strength and increased toughness, while the non-metallic part enhances sealing. The various combinations of metal and non-metal components, along with different available styles, make semi-metallic gaskets suitable for almost every condition. However, semi-metallic gaskets are supplied in specific sizes and shapes and cannot be cut and shaped like non-metallic gaskets. They must be dimensionally compatible with the mating surfaces, usually flange faces for piping. The different types of semi-metallic gaskets are as follows.

Spiral-wound Gaskets

This type of semi-metallic gasket consists of V-shaped metal strips wound alternately with a filler material. The gasket is supported by an inner and outer ring. The inner ring, which is in contact with the process liquid, has higher material requirements compared to the outer ring, which is typically made of carbon steel. Generally, the inner ring and metal windings are made from stainless steel, while the filler material can be PTFE, non-asbestos fibers, or graphite.

Jacketed Gaskets

This type features a filler material that is partially or entirely enclosed within a metal jacket. Various forms and configurations are available, including single, double, and corrugated jackets. Sealing is achieved through the deformation of the metal overlap, which is thicker than the rest of the envelope. This thicker section handles most of the compressive load, ensuring a reliable seal.

Corrugated Metal Gaskets (CMG)

Corrugated metal gaskets consist of a thin metal ring with a wave or corrugated pattern and are coated with a soft layer of non-metallic material, such as graphite, PTFE, or ceramic. These gaskets work by allowing the soft layer to conform to surface irregularities. They are particularly suited for uneven flanges or flanges with surface imperfections.

CMG gaskets are designed for specialty flanges and are not intended for use with piping. Their applications are somewhat limited, so careful consideration is needed when choosing them for a particular use. The optimal applications for CMG gaskets are in heat exchangers and expansion joints within petrochemical industries, where they offer resistance to radical shearing and provide slight compressibility and recovery.

Camprofile Gaskets

This type of semi-metallic gasket features a grooved metal ring covered with a non-metallic facing material. Similar to corrugated gaskets, sealing occurs as the gasket is compressed, causing the soft material to conform to the flange surface. The grooves in the metal create concentric rings that apply additional pressure to the soft material, enhancing sealing performance and providing structural support. However, the facings on Camprofile gaskets are very thin, approximately 0.020 inches (0.50 mm), which limits their ability to conform to uneven flange surfaces. Consequently, these gaskets require flanges to be flat and free of surface irregularities for effective sealing.

Metallic Gaskets

Non-metallic gaskets and filler sealing materials fail under extremely high temperatures and pressures. In such cases, solid metallic gaskets are necessary. These gaskets are commonly used for sealing boilers and heat exchangers. Like semi-metallic gaskets, metallic gaskets come in standard shapes and sizes and must be dimensionally compatible with the mating surfaces. The primary types of metallic gaskets include ring-joint, flat metal, and grooved metal gaskets.

Ring-type Joint (RTJ) Gaskets

These gaskets feature thick cross-sections designed for high-temperature and high-pressure applications. They function by being tightly compressed between mating surfaces, which forces the metal into any surface imperfections and leak paths. The materials used for these gaskets are softer than the flange material. Examples of RTJ gasket materials include soft iron, low carbon steel, stainless steel, and special alloys such as Inconel and Hastelloy.

Flat Metal Gaskets

Unlike RTJ gaskets, this type of metal gasket features a thinner cross-section. These gaskets are cut from sheet metal, allowing them to be made to fit any surface shape and size. They function similarly to non-metallic gaskets but are more suitable for higher temperature applications. Additionally, they are intended for use only in applications with high bolt loads.

Grooved Metal Gaskets

Grooved metal gaskets are similar to flat metal gaskets but feature serrations or grooves on their surface. The peaks of these concentric rings experience higher stresses when the gasket is loaded. Sealing is achieved by creating a labyrinth seal effect along the grooved surface. Grooved metal gaskets are often made from materials such as stainless steel or other alloys.

Welded Gaskets

This type of gasket does not primarily rely on compression along the mating surfaces for sealing. Instead, it achieves sealing through a permanent welded connection between the surfaces. Welded gaskets are commonly made from materials such as stainless steel, carbon steel, or other metals that offer good resistance to corrosion and high-temperature conditions.

Chapter 4: What should you consider when choosing a gasket?

When selecting a gasket for an application, it is crucial to explore all the application parameters in detail to ensure the proper choice. To simplify this process and guide customer decisions, manufacturers have developed an acronym that represents the essential factors to consider: S.T.A.M.P., which stands for "Size, Temperature, Application, Media, and Pressure."

S: Size and Dimensions

Choosing the right gasket for any application requires a thorough examination of various factors. To help streamline this process and assist customers in making informed decisions, manufacturers use the acronym S.T.A.M.P., which stands for "Size, Temperature, Application, Media, and Pressure." This acronym encapsulates the key considerations for selecting an appropriate gasket.

T: Temperature and External Environment

Temperature has a significant impact on both the mechanical and chemical properties of gaskets. Mechanically, two key effects are influenced by temperature: creep and relaxation. Creep refers to the gradual thinning of the gasket when exposed to a constant load, while relaxation denotes the reduction in compressive stress under continuous deformation. As temperatures rise, these issues become more pronounced, diminishing the gasket's sealing effectiveness. Chemically, high temperatures can adversely affect materials such as graphite and elastomer resins. Graphite gaskets may suffer from oxidation at elevated temperatures, which depletes the material and compromises sealing ability. Similarly, elastomer resins in full elastomer gaskets or as binders can undergo additional curing or vulcanization due to heat, leading to increased brittleness and reduced tensile strength. It is essential to review the pressure-temperature curves or maximum operating limits of gaskets before purchase to ensure they meet the requirements of the specific application.

A: Application and Installation

Choosing the appropriate gasket size involves considering the specific application and the equipment it will be fitted into. The application type and the gasket's installation environment guide the selection process and influence the choice of materials for manufacturing the gasket.

M: Chemical Media Compatibility

The characteristics of the process fluid, such as pressure and temperature, play a crucial role, while environmental effects are less significant. The nature of the process fluid also affects gasket compatibility. Exposure to oxidizing agents, acids, alkalis, oils, water, and abrasive substances can deteriorate the material in contact with the fluid. Composites are often favored in such scenarios because they feature a highly chemical-resistant inner layer that withstands fluid attacks while preserving the sealing and structural integrity of the remaining components.

P: Pressure, Resistance, and Load Capacity

During normal operation, gaskets are subjected to three primary forces: the bolt or flange load, hydrostatic end force, and blowout force from internal pressure. The internal pressure within a vessel or pipe affects both hydrostatic and blowout forces. If these forces surpass the gasket's tensile strength, it may lead to rupture or leakage. It is essential that the gasket can withstand the maximum internal pressure, typically tested at 1.5 times the working pressure. Gaskets are often rated with pressure classifications or standards set by engineering organizations like ASME and DIN.

Required Thickness

The thickness of gaskets typically doesn&#;t impact metal and semi-metallic types significantly, as these are manufactured to specific thicknesses based on their pressure ratings. However, for non-metallic gaskets, thickness plays a more critical role. Thicker non-metallic gaskets usually come with reduced pressure and temperature tolerances. To achieve effective sealing, these thicker gaskets require more compressive force. On the other hand, thinner non-metallic gaskets generally provide superior blowout resistance, reduced creep and relaxation, and enhanced compressive strength. Ideally, choosing the thinnest non-metallic gasket that can adequately conform to the flange surface is recommended for optimal performance.

Chapter 5: What are the benefits of using gaskets?

Gaskets function as mechanical seals designed to bridge the gap between two surfaces to prevent leaks of fluids, gases, or other materials. They provide numerous advantages in a range of industrial and mechanical settings:

• Leak Prevention: Gaskets are primarily used to create a leak-tight seal between two mating surfaces. They prevent the escape of fluids, gases, or contaminants, which is crucial in applications where containment is necessary.
• Sealing Reliability: Gaskets provide a reliable and consistent sealing solution, even under varying temperatures, pressures, and environmental conditions. They can withstand a wide range of operating conditions.
• Versatility: Gaskets come in various materials, such as rubber, cork, paper, metal, and composite materials. This versatility allows them to be used in a wide range of applications, from automotive engines to industrial pipelines.
• Pressure Resistance: Gaskets are designed to withstand high levels of pressure, making them suitable for applications in which maintaining a seal under significant pressure is essential.
• Temperature Resistance: Some gasket materials are engineered to withstand extreme temperatures, making them suitable for applications that involve high or low-temperature environments.
• Chemical Resistance: Depending on the material used, gaskets can resist exposure to a variety of chemicals and corrosive substances, ensuring the integrity of the seal in chemical processing industries.
• Vibration Damping: Gaskets can help dampen vibrations and reduce noise levels in machinery and equipment, improving the overall performance and longevity of mechanical systems.
• Easy Replacement: Gaskets are relatively easy to replace when compared to other sealing methods like welding or brazing. This reduces downtime during maintenance and repairs.
• Cost-Effective: Gaskets are often a cost-effective sealing solution, especially for applications where frequent maintenance or replacement is necessary.
• Customization: Gaskets can be custom-designed to meet specific application requirements, ensuring a precise fit and optimal sealing performance.
• Environmental Sealing: Gaskets are used to seal enclosures and junctions in electronic and electrical equipment to protect them from environmental factors such as dust, moisture, and contaminants.
• Hygienic Sealing: In food, pharmaceutical, and biotechnology industries, gaskets made from FDA-compliant materials are used to maintain sanitary conditions and prevent contamination.

Chapter 6: What are the applications and uses of gaskets?

Gaskets find extensive use across various industries. Below are some typical applications and functions of gaskets:

• Automotive Industry: Gaskets are used in engines, transmissions, and exhaust systems to seal various components, such as cylinder heads, oil pans, and exhaust manifolds.
• Aerospace Industry: Aircraft engines, hydraulic systems, and fuel systems utilize gaskets to maintain the integrity of seals in critical components.
• Oil and Gas Industry: Gaskets are essential for sealing joints and connections in pipelines, valves, and pressure vessels to prevent leaks in oil and gas processing facilities.
• Chemical Industry: Gaskets are used in pumps, reactors, and pipelines to prevent chemical leaks and ensure the safety of the processes.
• Pharmaceutical Industry: Gaskets are employed in pharmaceutical equipment to maintain a sterile environment and prevent contamination in manufacturing processes.
• Food and Beverage Industry: Gaskets are used in processing equipment, such as pumps, mixers, and heat exchangers, to ensure hygienic and leak-free operations.
• Manufacturing Industry: Various manufacturing processes rely on gaskets to seal machinery, including stamping presses, injection molding machines, and extruders.
• HVAC and Refrigeration: Gaskets are used in air conditioning systems, refrigerators, and heat exchangers to maintain proper insulation and prevent refrigerant leaks.
• Power Generation: Power plants, including nuclear, thermal, and hydroelectric facilities, use gaskets in steam turbines, valves, and generators to maintain seals and prevent energy loss.
• Marine Industry: Gaskets are used in ship engines, propulsion systems, and other marine equipment to prevent water intrusion and maintain operational efficiency.
• Mining Industry: Gaskets are employed in mining equipment, such as crushers, pumps, and conveyor systems, to protect against abrasive materials and maintain sealing integrity.
• Electronics Industry: Gaskets are used in electronic enclosures and cabinets to provide electromagnetic interference (EMI) shielding and protect sensitive electronic components.
• Construction Industry: Gaskets are used in various construction equipment and machinery to prevent leaks and maintain the structural integrity of buildings and infrastructure.
• Water and Wastewater Treatment: Gaskets are used in pipes, valves, and filtration equipment to prevent leaks and ensure efficient water and wastewater treatment processes.
• Petrochemical Industry: Gaskets are critical in refineries and petrochemical plants for sealing joints and connections in equipment used for processing and transporting petrochemical products.

Chapter 7: What are the common causes of gasket failures?

In a system, safety mechanisms are intentionally designed to fail in the event of process abnormalities to protect other components. Gaskets, being one of the weakest points in the system, often fail first during overpressure situations in pipes or pressure vessels. Even with proper specifications, gaskets can still fail due to various reasons. The following are some of the most frequent causes of gasket failures:

• Uneven Compression: Uneven compression of gaskets creates areas of low and high compressions. High compression areas have a higher resistance to blowout. Low compression areas have lower gasket conformity against the mating surface, making them prone to leaks and blow-out. Gaskets perform well when the surfaces are parallel with each other. In flanges, parallel surfaces can be achieved by tightening opposite bolts with equal turns until gasket compression, or using torque wrenches to ensure that all bolts exert equal forces. For gaskets clamped by asymmetric bolting, take note of the bolt arrangement. Areas with closer bolts can create higher compression.

• Over Compression: Over compression can lead to permanent gasket failure. Signs of over-compression are bulging or extrusion of the gasket material, or inward buckling for spiral wound gaskets. Non-metallic gaskets are typically limited to 15,000 psi. Metallic gaskets are designed to be crushed at higher pressures up to 30,000 psi.

  
  
• Under Compression: As mentioned, the three forces that act on a gasket are the bolt compression force, hydrostatic end force, and the blowout or force from internal pressure. Hydrostatic end force is caused by the vessel's internal pressure, which breaks the flange or sealing surfaces apart. The bolt compression force counters this. Not enough bolt compression can lead to less gasket conformity, making it easier for a blowout.
• Overheating: Temperature has significant effects on the performance of gaskets. In process or operation upsets, higher than normal temperatures can occur. This can hasten creep and relaxation effects which leads to torque loss. As tension gradually decreases, leakage will eventually occur.It is important never to reuse gaskets. This may be a general rule for most industrial plants. Equipment switch-overs and quick inspections may tempt operations or maintenance personnel to reuse gaskets, especially if the vessel or pipe undergoes frequent opening. Gaskets, when used plastically, deform according to the irregularities of the mating surface. They do not fully rebound to their original thickness. Thus, after use, most of its sealing characteristics are already gone.
• Chemical Attack: Gaskets are made from various polymers and minerals that can oxidize or react to certain process fluids. Composites composed of fillers, binders, inserts, and laminations must be noted regarding their chemical resistances. Some signs of chemical attack on gaskets are brittle cracking, softening, tearing, erosion, and discoloration. If these signs are found after service, it is best first to eliminate the possible effect of fluctuating temperature. If overheating is not the case, the next action is to change the type of gasket material.
• Improper Materials: The gasket material and its density, compressibility, recovery, relaxation, and seating stress are essential factors in determining the correct gasket for an application. Premature and disastrous failure can occur due to incorrect gasket material, which can lead to a less than effective seal and leakage because the material cannot withstand the load.

Conclusion

• Gaskets are mechanical seals that inhibit leakage by filling the gaps between static mating surfaces. As a compressive force deforms the gasket, it conforms to the profile of the surface and fills the gaps between its peaks and troughs.
• The different methods of cutting gaskets include rotary die cutting, kiss cutting, press die cutting, flatbed die cutting, knifeless die cutting, waterjet cutting, and laser cutting.
• Depending on the material and construction, gaskets can be divided into three main categories: non-metallic, semi-metallic, and metallic gaskets.
• Non-metallic gaskets are either made of homogeneous materials such as flexible graphite sheets and virgin PTFE or a composite of fibers and granules embedded in an elastomer resin. These types of gaskets are suited for low to medium pressure applications.
• Semi-metallic gaskets are composites of metallic and non-metallic materials. The metallic component provides structural strength and increased toughness, while the non-metallic part offers enhanced sealing.
• Metallic gaskets are used for extremely high pressure and temperature applications.
• In selecting a gasket, it is important to evaluate the process fluid&#;s pressure, temperature, and chemistry. For non-metallic gaskets, take note of the thickness. Thinner gaskets with the same ratings have better sealing performance.
• Improper compression, overheating, gasket reuse, chemical attack, and improper materials are the most common reasons gaskets fail.

Canada Rubber Group (CRG) fabricates gaskets from a wide variety of quality sheet rubbers. Understanding the properties and characteristics of the various rubbers we use is a key component of our business. In many cases, we are able to solve many sealing issues and challenges by recommending the preferred rubber gasket materials to our customers.

CRG stocks a wide selection of rubber gasket materials from our recognized raw material supply partners, such as Teadit and Interface Performance Materials. Types of materials that we offer include the following:

Ethylene-Propylene (EPDM) Rubber. EPDM rubber has good resistance to ozone, steam, strong acids and alkali. This type of rubber is not recommended for producing gaskets which will be used in applications involving solvents and aromatic hydrocarbons.

Fluoroelastomer (FKM). Sometimes known by the trade name Viton®, this rubber offers excellent resistance to strong acids, oils, gasoline, chlorate solvents and aliphatic and aromatic hydrocarbons. It is not recommended for producing gaskets which will be used in applications involving amino acids, esters, ketones and steam.

Nitrile (NBR) Rubber. Known also as Buna-N, nitrile rubber offers good resistance to oils, and alipahatic hydrocarbons and gasoline. Because it offers little resistance to strong oxidant agents, chlorate hydrocarbons, ketones and esters, it is not a good choice for gaskets which need to service these media.

Red Rubber (SBR). Commonly referred to as "synthetic rubber", this rubber was developed as an alternative to natural rubber. It is recommended for gaskets which service cold and hot water, air, steam and some weak acids. Gaskets made from SBR should not be used with strong acids, oils, grease and chlorates. SBR gaskets also offer little resistance to ozone and the majority of hydrocarbons.

Silicone Rubber (SI). Silicone rubber gaskets offer excellent resistance to aging as the rubber is unaffected by sunlight or ozone. Silicone gaskets can also service a wide temperature range, and because the material is relatively inert, they are a preferred choice for sanitary applications. Silicone rubber gaskets do not resist aliphatic and aromatic hydrocarbons or steam.

Natural Rubber. Also referred to as &#;gum rubber&#;, gaskets made from this material have excellent resilience, good compression set, and high resistance to tearing and abrasion. Natural rubber gaskets are flexible and conform well to surface irregularities. While gaskets made from natural rubber are resistant to acids, alcohol, organic salts, and alkalis, these gaskets will deteriorate when exposed to oils, fuels, solvents, and hydraulic fluids.

CRG maintains an extensive inventory of the above rubber gasket materials in various thicknesses and durometers (hardness). Using our advanced production capabilities, including waterjet, rotary die and flex/flash cutting, we are able to precision cut gaskets from these materials in any quantity. All aspects of production are controlled under our ISO : quality management system. Our production lead times are the lowest in the industry and emergency service is also available upon request.