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Nitrile rubber, also known as nitrile butadiene rubber, NBR, Buna-N, and acrylonitrile butadiene rubber, is a synthetic rubber derived from acrylonitrile (ACN) and butadiene.[1] Trade names include Perbunan, Nipol, Krynac and Europrene. This rubber is unusual in being resistant to oil, fuel, and other chemicals.
NBR is used in the automotive and aeronautical industry to make fuel and oil handling hoses, seals, grommets, and self-sealing fuel tanks. It is also used in the food service, medical, and nuclear industries to make protective gloves. NBR's stability at temperatures from &#;40 to 108 °C (&#;40 to 226 °F) makes it an ideal material for aeronautical applications. Nitrile butadiene is also used to produce moulded goods, footwear, adhesives, sealants, sponges, expanded foams, and floor mats.
Its resilience makes NBR a useful material for disposable lab, cleaning, and examination gloves. Nitrile rubber is more resistant than natural rubber to oils and acids, and has superior strength, but has inferior flexibility.
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Nitrile rubber was developed in at BASF and Bayer, then part of chemical conglomerate IG Farben. The first commercial production began in Germany in .[2][3]
IG Farben plant under construction approximately 10 kilometres (6.2 mi) from Auschwitz,The Buna-Werke was a slave labor factory located near Auschwitz and financed by IG Farben. The raw materials came from the Polish coalfields.[4] Buna rubber was named by BASF A.G., and through Buna was a remaining trade name of nitrile rubber held by BASF.
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Krynac F nitrile rubber balesEmulsifier (soap), acrylonitrile, butadiene, radical generating activators, and a catalyst are added to polymerization vessels in the production of hot NBR. Water serves as the reaction medium within the vessel. The tanks are heated to 30&#;40 °C to facilitate the polymerization reaction and to promote branch formation in the polymer. Because several monomers capable of propagating the reaction are involved in the production of nitrile rubber the composition of each polymer can vary (depending on the concentrations of each monomer added to the polymerization tank and the conditions within the tank). There may not be a single repeating unit throughout the entire polymer. For this reason there is also no IUPAC name for the general polymer.
Monomers are usually permitted to react for 5 to 12 hours. Polymerization is allowed to proceed to ~70% conversion before a &#;shortstop&#; agent (such as dimethyldithiocarbamate and diethylhydroxylamine) is added to react with (destroy) the remaining free radicals and initiators. Once the resultant latex has &#;shortstopped&#;, the unreacted monomers are removed through a steam in a slurry stripper. Recovery of unreacted monomers is close to 100%. After monomer recovery, latex is sent through a series of filters to remove unwanted solids and then sent to the blending tanks where it is stabilized with an antioxidant. The yielded polymer latex is coagulated using calcium nitrate, aluminium sulfate, and other coagulating agents in an aluminium tank. The coagulated substance is then washed and dried into crumb rubber.[3]
The process for the production of cold NBR is very similar to that of hot NBR. Polymerization tanks are cooled to 5&#;15 °C instead of heating up to 30&#;40 °C close to ambient temperature (ATC). Under lower temperature conditions, less branching will form on polymers (the amount of branching distinguishes cold NBR from hot NBR).
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The raw material is typically yellow, although it can also be orange or red tinted, depending on the manufacturer. Its elongation at break is &#; 300% and possesses a tensile strength of &#; 10 N/mm2 (10 MPa). NBR has good resistance to mineral oils, vegetable oils, benzene/petrol, ordinary diluted acids and alkalines.
An important factor in the properties of NBR is the ratio of acrylonitrile groups to butadiene groups, referred to as the ACN content. The lower the ACN content, the lower the glass transition temperature; however, the higher the ACN content, the better resistance the polymer will have to nonpolar solvents as mentioned above.[5] Most applications requiring both solvent resistance and low temperature flexibility require an ACN content of 33%.
Property Value Appearance Hardness, Shore A 30&#;90 Tensile failure stress, ultimate 500- PSI Elongation after fracture in % 600% maximum Density Can be compounded around 1.00 g/cm3[
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A disposable nitrile rubber gloveThe uses of nitrile rubber include disposable non-latex gloves, automotive transmission belts, hoses, O-rings, gaskets, oil seals, V belts, synthetic leather, printer's form rollers, and as cable jacketing; NBR latex can also be used in the preparation of adhesives and as a pigment binder.[citation needed]
Unlike polymers meant for ingestion, where small inconsistencies in chemical composition/structure can have a pronounced effect on the body, the general properties of NBR are insensitive to composition. The production process itself is not overly complex; the polymerization, monomer recovery, and coagulation processes require some additives and equipment, but they are typical of the production of most rubbers. The necessary apparatus is simple and easy to obtain.
In January , the European Commission imposed fines totaling &#;34,230,000 on the Bayer and Zeon groups for fixing prices for nitrile butadiene rubber, in violation of the EU ban on cartels and restrictive business practices (Article 81 of the EC Treaty and Article 53 of the EEA Agreement).[6]
Hydrogenated nitrile butadiene rubber (HNBR)[
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Hydrogenated nitrile butadiene rubber (HNBR) is produced by hydrogenation of NBR. Doing so removes the olefinic groups, which are vulnerable to degradation by various chemicals as well as ozone. Typically, Wilkinson's catalyst is used to promote the hydrogenation. The nitrile groups are unaffected. The degree of hydrogenation determines the kind of vulcanization that can be applied to the polymer.[7]
Also known as highly saturated nitrile (HSN), HNBR is widely known for its physical strength and retention of properties after long-term exposure to heat, oil, and chemicals. Trade names include Zhanber (Lianda Corporation), Therban (Arlanxeo [8]), and Zetpol (Zeon Chemical). It is commonly used to manufacture O-rings for automotive air-conditioning systems.[9] Other applications include timing belts, dampers, servo hoses, membranes, and seals.[10]
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Depending on filler selection and loading, HNBR compounds typically have tensile strengths of 20&#;31 MPa at 23 °C. Compounding techniques allow for HNBR to be used over a broad temperature range, &#;40 °C to 165 °C, with minimal degradation over long periods of time. For low-temperature performance, low ACN grades should be used; high-temperature performance can be obtained by using highly saturated HNBR grades with white fillers. As a group, HNBR elastomers have excellent resistance to common automotive fluids (e.g., engine oil, coolant, fuel, etc.).
The unique properties and higher temperature rating attributed to HNBR when compared to NBR has resulted in wide adoption of HNBR in automotive, industrial, and assorted, performance-demanding applications. On a volume basis, the automotive market is the largest consumer, using HNBR for a host of dynamic and static seals, hoses, and belts. HNBR has also been widely employed in industrial sealing for oil field exploration and processing, as well as rolls for steel and paper mills.
Carboxylated nitrile butadiene rubber (XNBR)[
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An alternative version of NBR is carboxylated nitrile butadiene rubber (XNBR). XNBR is a terpolymer of butadiene, acrylonitrile, and acrylic acid.[11] The presence of the acrylic acid introduces carboxylic acid groups (RCO2H). These groups allow crosslinking through the addition of zinc (Zn2+) additives. The carboxyl groups are present at levels of 10% or less. In addition to these ionic crosslinks, traditional sulfur vulcanization is applied.
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O-Rings are unassuming yet indispensable components that play a critical role in sealing applications across a myriad of industries. Their versatile nature and efficient functionality make them an essential choice for sealing solutions. However, with the plethora of O-Ring types available, selecting the right one for your specific needs can often feel like navigating a labyrinth. In this guide, we&#;ll equip you with the knowledge to make informed decisions regarding which O-Ring is right for your application.
O-Rings are circular, loop-shaped elastomeric rings primarily employed for sealing gaps between two or more parts. They&#;re deceptively simple yet incredibly effective. When compressed between mating surfaces, O-Rings form a reliable barrier that prevents the escape of fluids or the entrance of contaminants. This makes them useful in countless industries and applications as diverse as manufacturing, automotive, aerospace, pharmaceuticals, and many more. Whether used to contain hydraulic fluids or maintain the integrity of delicate medical equipment, O-Rings are a tried-and-true sealing tool.
Flare-O O-Rings, often composed of Buna-N or Viton, are specifically designed for use in hydraulic fittings. These O-Rings provide a highly effective seal, eliminating hydraulic leaks when correctly implemented. They are particularly well-suited for SAE 37° flared tube fittings, serving as leak-proof replacements and contributing to the overall integrity of hydraulic systems.
Bonded Seal O-Rings, often referred to as Dowty Seals or Dowty Washers, are a staple in hydraulic equipment, frequently employed as bolt seals. These seals consist of a metal outer ring and a rubber elastomer inner ring, effectively forming a gasket that provides sealing action. Their versatility extends beyond hydraulic systems, offering a reliable solution for a range of applications where rubber-to-metal or plastic bonding is necessary.
O-Ring boss (ORB) seals play a vital role in connecting two fluid-carrying components, such as pipes, hoses, or tubing. In an ORB system, a male-threaded part is inserted into a female-threaded part, creating a mechanical seal. To ensure a fluid-tight seal, an additional nut is tightened over an O-Ring, which is positioned in a chamfered area. These seals are particularly effective in applications involving hydraulics, compressed air systems, and vacuum pumps. They offer a reliable means of joining components while preventing leakage.
Flange seals are designed to provide front-face static sealing in flange connections. These seals are suitable for both internal and external pressure applications and are available in a diverse range of materials. Flange connections are commonly used in tubing applications with larger outer diameters or those subjected to high pressures. In typical scenarios, an O-Ring is utilized to seal the joint, effectively containing pressurized fluid within split-flange fittings. These fittings consist of permanent flanged heads connected to tubes, along with O-Rings and mating clamp halves. The elastomeric O-Ring is seated within a groove on the flange and mates with a flat surface on the port. Mounting bolts are used to secure the O-Ring flange onto the flange clamps, ensuring a secure and leak-free connection.
Buna-N, also known as Nitrile, is a frequently employed material in quick couplings. This versatile material boasts resistance to solvents, oils, and water, making it suitable for various applications. It can withstand temperatures ranging from -40°F to 250°F (-40°C to 121°C), making it a resilient choice for a wide range of environments. Buna-N is commonly utilized in engines, gearboxes, and other applications, including those found in aircraft and everyday household items. Its adaptability allows for both rotary and linear movement, making it an excellent choice for face-to-face gasket-style seals or shaft seals.
In the realm of sealing solutions, Peroxide Cured EPDM, also known as Ethylene-propylene-diene rubber, emerges as a definitive choice, setting new benchmarks for O-Rings employed in various applications. This exceptional material not only upholds its stature in medical-grade polypropylene couplings but extends its influence across diverse industries such as automotive manufacturing and wastewater systems. Its unparalleled resistance to an array of chemicals bestows it with a unique status, rendering it invaluable in challenging environments where O-Ring durability and reliability are paramount. Remarkably, this versatile elastomer even finds its place within the confines of common household appliances due to its outstanding chemical resistance properties.
Viton O-rings are prized for their exceptional resistance to extreme temperatures and various chemicals. They offer protection against ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics, and a range of solvents and chemicals. With qualities such as excellent permeability, compression set resistance, and low gas permeability, Viton O-Rings find their niche as gaskets in fuel line system sealing applications. Additionally, other fluorocarbon compounds provide enhanced resistance to acids, fuels, water, and steam.
Kalrez® O-Rings, crafted from perfluoroelastomer (FFKM), are also renowned for their resilience against chemicals and high temperatures. These robust O-Rings find extensive use in various industries, boasting an extended service life and impressive resistance to a multitude of elements. Kalrez® stands as a standout material capable of withstanding extreme temperatures and pressures while maintaining superior chemical resistance.
Silicone O-Ring material excels in applications characterized by dry heat. With a safe operating temperature range from -70°F to 400°F (-57°C to 204°C), these O-Rings are widely used in medical devices, food storage products, electronics, automotive manufacturing, and home repair and hardware items.
Two primary types of O-Ring seals are employed in flared fittings, specifically those utilizing O-Ring face seals (ORFS):
These fittings incorporate a replaceable elastomeric O-Ring seated in a groove on the fitting's face. Designed to address leakage concerns in high-pressure hydraulic systems, this configuration utilizes a Buna-N, 90 Durometer O-Ring. When the connection is tightened, the O-Ring compresses against a flat face sleeve that is brazed onto the end of a tube, forming a secure metal-to-metal seal. This design minimizes twisting of the tube and offers support during assembly.
Also known as Flare-O O-Rings, these seals cater to 37° flare fittings compliant with SAE J514 and ISO -2 standards. Predominantly made from Buna-N or Viton, the 37° flare AN seal finds its role in tubing end connections. In this arrangement, a nut is affixed to the end of the tube, which is flared using a specialized tool. The threaded nut is then inserted into a flare fitting, creating a seal that encompasses the flared tube. Flare-O seals for 37° flare fittings are particularly prevalent in aerospace, marine, and select older applications that have not transitioned to flareless tube fittings.
Conical seals, available in aluminum, copper, nickel, and stainless steel, serve as reliable seals on the end of 37-degree flared fittings of similar dash numbers. These seals are designed to mitigate the impact of minor nicks or defects in the fitting that may compromise proper sealing. Soft annealed 37° conical seals function as crush washers on a male AN flare, enhancing the reliability of seals while safeguarding tubing and AN fittings from damage.
O-Rings, those unsung heroes of the sealing world, come in an array of types, each tailored to meet the unique demands of various industries. From withstanding scorching temperatures to battling corrosive chemicals, these unassuming rings play a pivotal role in ensuring that machines operate seamlessly, and fluids remain where they should. Armed with the insights from this comprehensive guide, you are now equipped to navigate the labyrinth of O-Ring types and make informed decisions that will set the stage for efficient and reliable sealing solutions across diverse applications.
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