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This article takes an in-depth look at rubber gaskets.
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Rubber gaskets are elastic components used for mechanically sealing the microscopic gap between two mating surfaces or joints. Examples of these surfaces are flange faces of piping and fittings, mating surfaces of an automotive cylinder head and engine block, tank rims and covers, door edges, frames, and so on. Rubber gaskets seal surfaces by flowing in and filling the surface irregularities of rigid parts. The sealing effect is created by the parts exerting compressive forces, which plastically deform the gasket.
The sealing capability of rubbers is attributed to their elastomeric nature. Rubbers, natural or synthetic, belong to a family of materials called elastomers. Elastomers are classes of polymers that have a highly elastic nature created by cross-linking long polymer chains into amorphous structures. The intermolecular forces between the polymer chains are relatively weak; this allows them to be reconfigured upon application of stress. Because of this property, elastomeric gaskets can easily conform to many surface profiles, creating a tight seal.
Rubber gaskets, compared to their metallic and other non-metallic counterparts, offer several benefits due to their unique set of properties. Elasticity, or the ability to be deformed, is the key attribute of rubber that allows it to form tight seals. Rubber gaskets are also easier to process and can be formulated from different raw materials. Below are some of the advantages of rubber gaskets.
Rubber gaskets are manufactured by combining raw rubber and additive materials and forming them into the desired profile. Like any other polymers, rubbers have excellent formability. In its liquid or uncured state, whether it be the thermosetting or thermoplastic type, rubber flows easily into molds and dies. Once hardened or cured, the material can be easily cut or machined to near-perfect dimensions. In contrast with metallic and other non-metallic gasket types, the production of rubber gaskets requires low heat and pressure. Thus, cheaper tooling is used, and lower operating costs are involved.
Due to their unique microstructure, rubbers can be stretched or compressed without incurring damage or degradation of their properties. This allows rubber gaskets to form effective seals since they can easily deform according to the surface of the part they are sealing. They form a more effective seal than some metallic gaskets, which rely on grooved, serrated, or corrugated surfaces creating a labyrinth effect. Metallic gaskets also exhibit some degree of deformation, but the sealing is still metal-to-metal.
Unlike other gasket types, there is a degree of flexibility and freedom in choosing the right material for a particular application. This is due to the nature of producing elastomeric materials. Raw elastomers such as raw synthetic rubbers can be produced from different hydrocarbon compounds. After producing this raw material, its properties are further modified by different additives such as stabilizers, fillers, antioxidants, and reinforcements. This design flexibility allows the production of countless engineered rubber gasket materials, most of which are patented by large manufacturers.
For comparison, metallic gaskets are typically limited to stainless steel, mineral gaskets are narrowed to mica and vermiculite, and graphite gaskets are restrained to highly pure, exfoliated graphite. The only gasket type with comparable range to rubber gaskets are compressed fiber gaskets; these also use elastomeric materials.
Rubber gaskets, when used within their specifications, are a very stable material. They can resist all kinds of chemical and environmental attacks such as acids, alkalis, oxygen, ozone, water, heat, and UV light. Of course, this all depends on the type of rubber and compounded additives. Gaskets made from fluorocarbon-based elastomers have excellent corrosion resistant properties. Examples of these are FKM and PTFE. Other materials with good chemical and aging resistances are SBR, Butyl, and EPDM.
This is another advantage of rubber gaskets attributed to the different raw materials used in compounding. Some of their physical properties are hardness, compression set, compressive modulus, tensile strength, and elongation. These are varied depending on the amount of force applied to the gasket to create an effective seal and the pressure exerted by the fluid. For example, being too soft or pliable makes a rubber gasket fail prematurely when subjected to higher pressures. Being too hard, on the other hand, requires higher compressive loads exerted by the flange bolts. Rubber gaskets can be compounded to meet the right balance between these properties to better suit the application.
Rubber gaskets, unlike metallic types, can be initially manufactured as gasket sheets of gasket paper. These sheets are supplied to fabricators and end-users for making custom gaskets for sealing odd-shaped mechanical joints and surfaces. Fabricators can create custom gaskets by widely available machining processes such as hand cutting, die-cutting, water-jet cutting, and laser cutting. Laser cutting is a popular fabrication method for precision gaskets.
Fabrication processes other than cutting processes are available for forming rubber gaskets. Elastomer forming techniques are also used such as extrusion and injection molding. These processes involve creating a tool or mold for shaping the gasket. The tool is not constrained to one profile but is customizable to match the geometry of the mating surfaces. It is typically machined by computer-aided manufacturing (CAM) techniques, which ensure the precision of the profile.
Rubbers can be specially formulated to meet the requirements set by the FDA for food, beverage, and drug manufacturing. Some of the rubbers formulated for such applications are nitrile, neoprene, silicone, EPDM, and FKM. To become a food-grade gasket, the rubber material must be made from FDA-approved compounds. The FDA ensures that the substances added in the rubber compounding process do not pose any health risks to consumers should the substance come into contact with the product. Moreover, the rubber compounds must have additional properties such as resistance to bacterial growth, chemical stability, thermal stability, and unnoticeable taste and odor.
Rubber gaskets are used in every industry. They are most suitable in general purpose applications that involve low to medium pressures and temperatures. Where they truly shine are applications involving chemicals, water, and hydrocarbons. Certain formulations of rubber make them resistant to a specific group of chemicals.
Below are some of the applications of rubber gaskets.
Rubber gaskets are often used in industrial plants for utility and chemical processing lines. These gaskets are limited to low to medium pressures. Most rubber gaskets are limited to around 150 psi (10 bars), while some engineering-grade types, such as PTFE, can reach up to 800 psi (55 bars).
Rubber gaskets are the most popular sealing material for plumbing. This is due to their low cost and resistance to corrosion and degradation from water, chlorides, and other biological factors. Gasket materials can be seen in household utility fixtures such as faucets and drains.
There are two types of rubber gaskets used in an automotive vehicle. The first types are those used in sealing low pressure and passive components such as doors and windows. These are made entirely from rubber; they are designed to absorb any shocks and seal the interior from ingress of water and air. Moreover, oil and solvent-resistant rubber gaskets are used in fuel supply and hydraulic lines.
The second types are those used in engine and transmission parts such as the oil pan gasket, exhaust gasket, and head gasket. These are typically composite gaskets. Thus, they do not belong to the rubber gasket classification. Most of these gaskets use mineral fibers or steel reinforcements impregnated in a rubber matrix.
Aerospace applications of rubber gaskets include sealing fuel supply, hydraulic, propellant, and oxidizer systems. Their mechanical, chemical, and thermal properties are designed to allow them to operate in harsher environments since they must be exposed to higher stresses and operating temperatures. In case of exposure to combustion or high heat, they are imparted with flame retardance to prevent fire from spreading. Other special properties such as electrical conductivity and antistatic are added to protect the aircraft‘s instruments and sensitive signals from the interference of stray currents or external electromagnetic fields. These gaskets that offer electromagnetic shielding properties are called EMI gaskets.
Rubber gaskets are used in marine equipment and ships for sealing hatches, doors, and windows. Rubbers are desired in this application due to their resilience. Having excellent resilience allows the material to absorb shocks and impacts. It also permits high amounts of deflection and compression upon exposure to high loads. Rubbers are also resistant to corrosion from environments with high amounts of chlorides.
Rubber is one of the most suitable materials for sealing covers, nozzles, holes, and ports of liquid or bulk solid containers. This is because of rubber‘s cheap cost, tight sealing, and resistance to degradation and reaction from fluids. Different types of rubbers exhibit different chemical resistances. Examples are nitrile and neoprene, which are resistant to fuels, oils, and other petroleum-based solvents. Acids and alkali resistances are best offered by fluorocarbon-based rubber gaskets. Silicone gaskets are commonly used for wet services because of their water and moisture resistance.
As mentioned in the previous chapter, rubber is the material of choice when it comes to food and drug manufacture. Rubbers can be made from non-toxic, consumer-safe substances that are approved by the FDA. Rubber gaskets are typically seen in food, beverage, and drug processing plants for sealing valves, pipe joints, and equipment ports and fixtures.
Rubbers are generally classified according to the type of monomers used in making their polymer chain. These monomers can be different hydrocarbons such as ethylene, methylene, propylene, isoprene, fluorocarbons, and so on. The type of polymer chain dictates the base properties of the rubber compounds. The other components, such as curatives and additives, impart additional characteristics that create subclassifications under the main types.
Below are some of the most common rubber gasket materials available on the market.
Ethylene propylene diene monomer (EPDM) is an elastomer made from the copolymerization of ethylene and propylene. Its desirable characteristics are good weathering resistance, good insulating and dielectric properties, and excellent mechanical properties both at high and low temperatures. Regarding its chemical properties, it has good resistance to acids, alkalis, alcohol, and ketone-based solvents. It also has sufficient resistance to water and steam.
Nitrile, also known as acrylonitrile butadiene or NBR, is a rubber made from the copolymerization of acrylonitrile and butadiene. They are widely used for their resistance to fuels, oils, and petroleum-based solvents. They are suitable for sealing automotive engine parts. However, they have below-average mechanical properties and poor low-temperature performance when compared to other rubber gasket materials. Reinforcing fillers are added to solve these problems.
Neoprene is a rubber material produced from the emulsion polymerization of chloroprene (CR). It is widely known for its flame-retardant grades. Regarding its weathering properties, the presence of chlorine in the polymer chain improves resistance to oxidation, ozone, and oil. However, its range of oil resistance is not as wide as that of nitrile types. Moreover, they are more expensive than natural rubber and have poor low-temperature performance.
Natural rubber comes from latex harvested from barks of the Hevea tree. It contains the polymer chain polyisoprene. Natural rubber is known for its resilience and fatigue resistance, however, its overall performance can easily be surpassed by synthetic types. Also, natural rubber gaskets have poor ozone and oil resistance.
Silicone rubbers have a silicon-oxygen chain instead of a carbon-based backbone. They have good oxygen, ozone, heat, light, and moisture resistance. However, they are more expensive and have fair mechanical properties than organic (carbon-based) rubbers. They also have poor resistance to petroleum-based chemicals.
Butyl rubber (IIR) is a copolymer of isobutylene and isoprene. The amount of isoprene is controlled to give a desired level of unsaturation. The low unsaturation of butyl rubber enables it to repel most chemicals (gas and liquids), and it is highly resistant to aging when vulcanized properly. Because of its excellent impermeability, it is widely used in sealing equipment handling compressed air and process gas.
Styrene-butadiene rubber (SBR) is a product from the emulsion polymerization of styrene and butadiene. It is typically referred to as red rubber, which is a popular commercial blend. SBR is a general-purpose rubber that competes with natural rubber because of their comparable tear, abrasion, and thermal resistance properties. SBR gaskets are usually preferred because of their lower cost.
This is proprietary gasket material that belongs to the family of thermoplastic vulcanizates (TPV) or thermoplastic polymers (TPE). It is composed of a dynamically vulcanized EPDM dispersed in a polypropylene matrix. Because of its thermoplastic property, it can be melted and recycled. Regarding sealing characteristics, it has good resistance against degrading factors such as ultraviolet light and ozone. Santoprene is a trademark currently owned by ExxonMobil.
Polyurethane, or urethane, is prepared by the reaction of a polyether or polyester glycol with diisocyanates and curatives. This is a popular material due to its wide range of physical properties through different blend formulations. They have excellent resilience, abrasion resistance, and weathering resistance properties.
Poron is a patented gasket material made from multicellular polyurethane or polyurethane foam. Because of its porous structure, it is well suited for thermal insulation, vibration dampening, acoustic dampening, and shock absorption. The inherent resilience and rebound properties of polyurethane make it suitable for sealing because of the reduced effect of creep relaxation.
FKM, or fluorocarbon rubbers, is a family of rubber composed of vinylidene fluoride (VDF) copolymerized with chemicals such as hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and so on. It is known commercially by its trade name, Viton. Viton gaskets are expensive, high-performance products. They are typically used in extreme applications, for example, as seals for automotive and aircraft engines. They can operate well under high temperatures and resists oils, fuels, acids, and alkalis.
Though technically a plastic, PTFE is a common gasket material in chemical processing industries due to its high bonding energy. This characteristic makes PTFE resistant to chemical reactions, particularly corrosion. PTFE also has a low coefficient of friction, excellent insulating properties, high toughness, and good impact strength.
There are different types of rubber gasket manufacturing processes. They differ in the quality and precision of the finished product and the nature of the cutting process. Each process offers several advantages and limitations. Enumerated below are some of these processes.
Die-cutting is a mass fabrication process that involves cutting shapes from a flat stock material using a tool called a die. A die is a specialized tool that contains the two-dimensional profile of the product. It has a sharp edge on one side, which is referred to as the steel rule. Cutting is performed by pressing the die into the material placed on the bed of the machine. A single downward stroke shears the material to the required shape.
Die-cutting is one of the most popular rubber gasket manufacturing processes because of its simplicity, cheap tooling cost, low material wastage, and high production rates. Die-cut gaskets are usually used in general purpose applications such as plumbing and container sealing.
Water jet cutting is a non-conventional fabrication process that uses a concentrated stream of water traveling at high speeds for cutting different types of materials, including rubber. This is achieved by pumping water at high pressures and forcing it through a small nozzle that converts fluid pressure into velocity. Because of its high velocity, the water jet cuts the material by impingement and erosion.
Water jet cutting is suitable for fabricating gaskets that are sensitive to pressure and temperature. This process places less stress on the material than die-cutting. It also does not burn the edges of the finished product. The only limitation is that the type of stock material must be resistant to water.
Laser cutting is another non-conventional type of cutting technology that uses a highly concentrated beam of light called a laser. In this process, a cut is made by passing the laser beam through the cutting lines on the material. The material exposed quickly vaporizes or sublimates, leaving a cut.
Laser cutting is desired due to its precision and clean cutting process. It does not involve wetting the product; this is desirable as wetting may lead to swelling and degradation. The equipment used is also low maintenance compared to equipment used in water jet cutting.
Flush cutting is a mechanical cutting process that uses a small oscillating knife to cut through soft and semi-rigid materials such as rubber. The knife is mounted to a robotic system controlled by a CNC program.
Flush cutting is also a precision cutting technology similar to water jet and laser cutting. The advantage of this process is that it does not expose the material to pressure, high temperature, or water. However, it is less effective in cutting harder materials.
Injection molding is typically a plastic forming process that can also be applied for molding rubbers. This process involves melting the rubber to a manageable level of viscosity so that it can be processed. Other types of rubbers do not need melting since they are liquid in their uncured state. After this initial process, the rubber is injected into a mold. The mold contains a negative image of the final product. Inside the mold, the rubber solidifies, cures, and cools. After this hardening phase, the molded rubber gasket is released.
The main use of injection molding in rubber gasket manufacture is fabricating rounded products such as O-rings or products that have a distinct three-dimensional shape. Unlike the previous cutting methods, injection molding is not limited to producing gaskets with flat profiles.
Rubber gasket extrusion is a process that involves forcing or pushing a rubber compound, under extreme pressure, through a die with the cross section of the desired product. Any form of rubber can be shaped using the extrusion process, including EPDM, silicone, neoprene, Viton, and natural rubber.
The extrusion process begins by feeding, pouring, or dumping the rubber compound into a hopper placed at the top of a barrel containing a helical screw. The most common type of hopper is wide at the top and narrows at its connection to the barrel. Many modern extruders have automated hoppers for feeding the raw rubber.
Pressure is the key to rubber extrusion, which builds as the screw moves the raw rubber along the barrel. To make the rubber more pliable and malleable, it is heated by various forms of heating devices placed along the barrel. During the progression of the raw material, pressure and temperature continue to increase as the raw material approaches the die to the point that it is forced, under pressure, through the die opening. As the newly formed rubber gaskets exit the die, they swell to various degrees depending on the hardness of the gasket and the type of rubber compound.
After the extruded rubber exits the die, it is subjected to the vulcanization process, where it is heated and cured to reach the desired tensile strength. The various processes used to vulcanize extruded rubber include steam curing, continuous curing, and cutting to length. Vulcanization is a biochemical process for curing rubber that usually involves the use of sulfur. During vulcanization, a rubber component will swell or shrink in its cross section and length, depending on the contents of its rubber compound.
Vulcanization is a chemical process used to improve the physical properties of rubber components. It increases the tensile strength of rubber and enhances its resistance to swelling and abrasion. The basic process of vulcanization is heating rubber parts in the presence of sulfur.
The process of vulcanization was discovered by Charles Goodyear in the middle of the first industrial revolution. He discovered that an accelerator could be used to increase the speed of the vulcanization process at lower temperatures. Sulfur, as a fundamental part of the process, chemically combines with rubber to form cross links in rubber’s long molecule chains.
Steam curing is used for small batches of extruded rubber and is a safe method of vulcanization. Rubber that is steam cured has excellent wear performance, especially when gaskets are used for bonding installations.
Continuous curing is for larger batches or larger gaskets. It uses microwaves or a salt bath to gradually vulcanize rubber gaskets. The process of continuous curing requires very little energy. Rubber gaskets vulcanized by this process have more consistent profiles.
Hot splicing uses heat, pressure, and a splicing polyethylene film to connect the ends of rubber profiles into tightly bonded gaskets. The heat used for hot splicing can be either conventional or infrared heating to bond the polyethylene film. The process of hot splicing creates stronger bonds at the molecular level than vulcanization. It can only be performed on gaskets that have been water jet cut so the cuts are clean and straight.
There are many machines available to produce rubber gaskets, and they are important in today's society because they enable efficient and precise manufacturing of sealing components used in various industries, such as automotive, aerospace, and marine, ensuring reliable seals and preventing leaks. Below, we discuss many notable brands known for providing machines used for producing rubber gaskets:
Atom FlashCut offers the FlashCut Gasket Cutting System, which is known for its precision cutting capabilities, versatile software, and the ability to handle various rubber materials used in gasket production. Its efficiency, accuracy, and flexibility contribute to its popularity.
Dieffenbacher specializes in the Fiberforge machine, which combines extrusion and lamination processes to produce rubber gaskets with continuous lengths, customized profiles, and excellent sealing properties. This innovative approach and the resulting high-quality output make it a popular choice.
Zemat Technology Group provides the Zemat RCE Gasket Cutting Machine, known for its efficiency, high cutting speed, and accuracy in producing rubber gaskets. Its performance and reliability have contributed to its popularity.
Sutherland Presses specializes in gasket-specific compression molding presses, including models suitable for rubber gaskets. These machines offer precise control over temperature, pressure, and molding time, ensuring consistent quality and sealing properties. Their reliability and quality output make them popular in the industry.
Rolmacon Global Ltd specializes in the Rolmacon Gasket Die Cutting Machine, which provides accurate and efficient die cutting capabilities for rubber gaskets. This machine's speed, accuracy, and ability to handle various gasket designs have contributed to its popularity.
Please note that the availability of specific models, features, or components may have evolved since this last update. For the most up-to-date information, I recommend consulting the respective manufacturers or industry resources regarding their current offerings of machines used for producing rubber gaskets in the United States and Canada.