Nitrile sealing material

Nitrile rubbers, including fiber-reinforced varieties, are used both as radial shaft-seal materials and as molded packing for reciprocating shafts. They have excellent resistance to a considerable range of chemicals, with the exception of strong acids and alkalis, and are at the same time compatible with petroleum-based lubricants. Their working temperature range is from —1°C to 107°C (30°F to 225°F) continuously and up to 150°C (302°F) intermittently. When used on hard shafts with a surface finish of, at most, 0.00038 mm root mean square (RMS), they have an excellent resistance to abrasion. 

The workhorse of the industry, NBR is considered very adequate as a seal material up to and around 100°C. It falls down badly at temperatures in excess of this, and in particular in sour oil environments. In spite of this, permanent packer elements of nitrile work very well. In fact the hardening that occurs in service at higher temperatures actually seems to benefit the well system. For retrievable packers, where flexibiUty must be maintained, other elastomers are now being increasingly used. Nitrile rubber is also used regularly in BOP seal systems, both ram and annular types. 

The rubbers may be vulcanised by conventional accelerated sulphur systems and also by peroxides. The vulcanisates are widely used in petrol hose and seal applications. Two limiting factors of the materials as rubbers are the tendency to harden in the presence of sulphur-bearing oils, particularly at elevated temperatures (presumably due to a form of vulcanisation), and the rather limited heat resistance. The latter may be improved somewhat by Judicious compounding to give vulcanisates that may be used up to 150°C. When for the above reasons nitrile rubbers are unsatisfactory it may be necessary to consider acrylic rubbers (Chapter 15), epichlorohydrin rubbers (Chapter 19) and in more extreme conditions fluororubbers (Chapter 13). 

The molded liners for the inlet head, cylinder section, and conical sections have Integral molded gaskets for sealing at the flanged joints. Molded liners and vulcanized linings are offered in gum rubber, polyurethane, nitrile rubber, butyl. Neoprene , Viton , Hypalon , and other liner materials can be supplied. 

The metering valve in an MDI is the critical component in the design of an effective delivery system. The main function of the metering valve is to reproducibly deliver a portion of the liquid phase of the formulation in which the medication is either dissolved or dispersed. The valve also forms the seal atop the canister to prevent loss of the pressurized contents. The valves generally comprise at least seven components that are constructed from a variety of inert materials. Typical materials of construction are acetal or polyester for the valve body, stainless steel or acetal for the valve stem, generally anodized aluminum for the ferrule, and butyl, nitrile, or neoprene for the elastomers used in the seals and gaskets [43],... 

Frequently applied gasket materials such as nitrile, neoprene, and Viton limit the operating temperature to 200 °C [88]. Above 200 °C, metallic gaskets are the choice. A disadvantage of the concept of sealing by gaskets is the need to insert screws and thus to have a bulky housing. Especially for smaller devices, the thermal mass is increased considerably, which, for example, increases the start-up time. 

Ruororubbers and silicones are the best materials to make seals resistant to extreme temperature conditions. Viton, a fluororubber marketed by M/S Du Pont USA, can operate at 200°C in contact with oils and lubricants. Polysulfide rubbers have low compression set, but exhibit excellent fuel resistance. For improved compression set, it is admixed with relatively cheap conventional nitrile rubbers. The fluorine-containing rubbers, such as fluororubber, possess outstanding resistance to heat, fuels and hydraulic fluids coupled with extremely good aging characteristics. The reversible physical effects with respect to the ultimate tensile strength of this rubber vulcanizate is a noteworthy phenomenon since this is not associated with the deterioration of the rubber itself. Fluororubber is resistant to most fluids used in the aircraft industiy, such as synthetic, ester type lubricants, aromatic and aliphatic hydrocarbons, and water. 

Py-LVEIMS and PyHRMS were used in the determination of structure and composition of clinically important polyurethanes, PEUUs (Biomer, Lycra Spandex, Tecoflex and Pellethane) [746]. The antioxidants found in Biomer and Lycra Spandex were identified as well as an AO in Pellethane and an antistatic agent or residual catalyst in Biomer and Lycra Spandex. These tools are valuable for QC of implant material. PyMS is widely used in quality control of industrial products, such as foils and packaging materials [747], silicone and nitrile rubbers [748], can coatings and rubber sealing and tobacco [749]. In particular, it appears that Py-FIMS finds application not only for research in structure determination of non-volatile polymers, but also in product control. Schulten et al. [692] have described the application of Py-FIMS to paints (commercial can coatings), epoxy and polyester resins. Polyamides, acrylic and methacrylic resins, have been analysed in the same way [750-753], Py-FIMS is well suited for these investigations and allows identification of different polymer sub-units, such as monomers, dimers, backbone fragments, etc. Moreover, the technique enables differentiation of the examined compounds, which is of interest to industrial quality control. 

Synthetic Rubber. Many different types of synthetic rubber are suitable raw materials for adhesives and sealing compounds. Particularly significant are polychlo-roprene rubber, styrene-butadiene rubber (SBR), nitrile rubber, and polyisobutylene. Unless these rubbers are available as directly soluble types, they have to be degraded by mastication on rolls or in kneaders and solubilized before dissolution. 

The effects of stresses and associated strains on O-rings used in sealing pressurised fluids are discussed. Results are presented of studies of ageing and property changes of stressed and unstressed elastomers exposed to a hot aqueous solution of ethylene diamine, transient effects of temperature on sealing force, and the influence of memory effects on gas induced fracture by explosive decompression. Materials examined included fluoroelastomers, nitrile mbber and hydrogenated nitrile rubber. 7 refs. 

Hydrogenated nitrile mbbers were evaluated for use in seals and hoses for automotive air conditioning systems. Studies were made of the resistance of these materials to hydrofluorocarbon refrigerants and polyalkylene glycol and mineral oil based lubricants, and permeation resistance, explosive decompression and low temperature performance characteristics were investigated. Designed experiments were undertaken to study the effect of compounding techniques on permeation and explosive decompression. 4 refs. 

All of the O-rings were of WS1.957 type according to TGL 106-70101. They were initially manufactured from nitrile butadiene caoutchouc (rubber). Although results are given in [221] which provide evidence that this material can be used in the required range of temperatures and pressures, these elastomer O-rings have been replaced with Viton MK 634 seals (from Merkel/GNB) based on experience with transporting CASTOR containers. 

Sealant Applications. The repair of engine bodies has been reported using a nitrile rubber/ phenolic composition as a sealant. The wing fuel tanks of Cl30 aircraft have also used nitrile rubber/phenolic materials to seal the tanks.Finally, electrolyte leakage in a sheet battery has been prevented using nitrile rubber/ phenolic adhesives. 

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