Remerciez-le!

Remerciez @Admin pour avoir partagé cet document gratuitement, de la manière la plus simple, en partageant sur les réseaux sociaux.

DuPont™ Viton® Selection Guide Technical Information—Rev. 7, July 2010 Introduc

DuPont™ Viton® Selection Guide Technical Information—Rev. 7, July 2010 Introduction DuPont™ Viton® fluoroelastomer was introduced in 1957 to meet the needs of the aerospace industry for a high-performance seal elastomer. Since then, the use of Viton® fluoroelastomer has expanded to many other industries, especially in the automotive, fluid power, appliance, and chemical fields. With over 40 years of proven performance, Viton® fluoroelastomer has developed a reputation for outstanding performance in high temperature and extremely corrosive environments. Valuable Properties of Viton® Fluoroelastomer Vulcanizates based on Viton® provide an exceptional balance of physical property characteristics, including the following features: • Resistance to temperature extremes: Heat—Compared to most other elastomers, Viton® is better able to withstands high temperature, while simultaneously retaining its good mechanical properties. Oil and chemical resistance are also essentially unaffected by elevated temperatures. Compounds of Viton® remain substantially elastic substantially indefinitely when exposed to laboratory air oven aging up to 204 °C or to intermittent exposures up to 316 °C. High temperature service limits are generally considered to be: 3,000 hr at 232 °C 1,000 hr at 260 °C 240 hr at 288 °C 48 hr at 316 °C Cold—Viton® is generally serviceable in dynamic applications to temperatures of –18 to –23 °C. Special formulations permit its use in static applications down to –54 °C. Also, Viton® has proven to be satisfactory for static seals used under conditions approaching absolute zero. Viton® is characterized by its: • Resistance to degradation by a greater variety of fluids and chemicals than any nonfluorinated elastomer. Excellent resistance to oils, fuels, lubricants, and most mineral acids. • Extremely low permeability to a broad range of substances, including particularly good performance in oxygenated automotive fuels. • Resistance to aliphatic, aromatic hydrocarbons that dissolve other rubbers. • Exceptionally good resistance to compression set, even at high temperatures. • Exceptionally good resistance to atmospheric oxidation, sun, and weather. Excellent resistance to fungus and mold. • Good electrical properties in low voltage, low frequency applications. • Low burning characteristics; inherently more resistant to burning than other, non-fluorinated hydrocarbon rubbers. 2 Safety and Handling As with many polymers, minute quantities of potentially irritating or harmful gases may diffuse from uncured DuPont™ Viton® even at room temperature. Therefore, all containers should be opened and used only in well-ventilated areas. In case of eye contact, immediately flush the eyes for at least 15 min with water. Always wash contacted skin with soap and water after handling Viton®. Potential hazards, including the evolution of toxic vapors, may arise during compounding, processing, and curing of the raw polymers into finished products or under high-temperature service conditions. Therefore, before handling or processing Viton®, make sure that you read and follow the recommendations in the DuPont bulletin “Handling Precautions for Viton® and Related Chemicals.” Compounding ingredients and solvents that are used with Viton® to prepare finished products may present hazards in handling and use. Before proceeding with any compounding or processing work, consult and follow label directions and handling precautions from suppliers of all ingredients. The Various Families and Types of Viton® Fluoroelastomer Standard types of Viton® fluoroelastomer products are designated as A, B, or F according to their relative resistance to attack by fluids and chemicals. The differences in fluid resistance are the result of different levels of fluorine in the polymer, which is determined by the types and relative amounts of copolymerized monomers that comprise the polymer. In general, Viton® exhibits outstanding resistance to attack from a wide variety of fluids, including mineral acids and aliphatic and aromatic hydrocarbons. The higher the fluorine content of the polymer, the less will be the effect, as measured by volume increase, for example. The most significant differences between A, B and F types of Viton®, in terms of resistance to volume change or retention of physical properties, are exhibited in low molecular weight, oxygenated solvents (such as methanol and methyl t-butyl ether). As mentioned above, the fluid resistance of Viton® A, B, and F types improves with increasing fluorine levels. This is shown in Table 1 (note the volume increase after aging in methanol at 23 °C). As the fluorine content increases, however, the low temperature flexibility of the polymer decreases, and a compromise must be made between fluid resistance and low temperature flexibility of the final vulcanizate. For those applications that require the best performance in both fluid resistance and low temperature flexibility a number of specialty types of Viton® were developed that contain a copolymerized fluorinated vinyl ether monomer. Polymers that contain this monomer exhibit significantly improved low temperature flexibility, compared to standard types of fluoroelastomer. Viton® GLT, introduced in 1976, was the first commercial fluoroelastomer to incorporate this fluorinated vinyl ether monomer. This polymer provides the same excellent resistance to heat and fluids that is typical of the A types of Viton® fluoroelastomer. Viton® GFLT, like Viton® GLT, exhibits significantly improved low temperature flex characteristics compared to standard types of fluoroelastomer. In addition, Viton® GFLT provides the same superior resistance to fluids that is typical of the F types of Viton® fluoroelastomer. Types of DuPont™ Viton® Extreme™ Fluoroelastomers that contain copolymerized vinylidene fluoride(VF2) are subject to attack by high pH materials, including caustics and amines. In addition, standard fluoroelastomers are not resistant to low molecular weight carbonyl compounds, such as methyl ethyl ketone, acetone, or methyl tertiarybutyl ether. Viton® Extreme™ ETP-600S is a copolymer of ethylene, tetrafluoroethylene (TFE), and perfluoromethylvinyl ether (PMVE). This unique combination of monomers provides outstanding resistance to fluids and is an example of an ETP polymer. The ETP types of Viton® exhibit the same excellent resistance to acids and hydrocarbons typical of A, B and F types of Viton®. Unlike conventional fluoroelastomers, however, ETP types of Viton® also provide excellent resistance to low molecular weight esters, ketones, and aldehydes. In addition, these unique polymers are inherently resistant to attack by base, and thus provide excellent resistance to volume swell and property loss in highly caustic solutions and amines. Additional information regarding performance differences between the various families and types of DuPont™ Viton® fluoroelastomer is presented in Tables 3–6 to assist in selecting the particular grade of Viton® that is best suited for both a given end-use application and for a specific manufacturing process. 3 Table 1 Polymer Fluorine Content versus Fluid Resistance and Low Temperature Flexibility Standard Types Specialty Types A B F GLT-S GFLT-S ETP-S Nominal Polymer Fluorine Content, wt% 66 68 70 64 67 67 Percent Volume Change in Fuel C, 168 hr at 23 °C* 4 3 2 5 2 4 Percent Volume Change in Methanol, 168 hr at 23 °C* 90 40 5 90 5 5 Percent Volume Change in Methyl ethyl Ketone, 168 hr at 23 °C* >200 >200 >200 >200 >200 19 Percent Volume Change in 30% Potassium Hydroxide, 168 hr at 70 °C* (Samples too swollen and degraded to test) 14 Low Temperature Flexibility, TR-10, °C* –17 –13 –6 –30 –24 –12 *Nominal values, based on results typical of those obtained from testing a standard, 30 phr MT (N990) carbon black-filled, 75 durometer vulcanizate. These are not intended to serve as specifications. Curing Systems for Viton® Fluoroelastomer In addition to inherent differences between the various types and families of Viton® fluoroelastomer, a number of compounding variables have major effects on the physical property characteristics of the final vulcanizates. One very important variable is the crosslinking or curing system that is used to vulcanize the elastomer. Diamine curatives were introduced in 1957 for crosslinking Viton® A. While these diamine curatives are relatively slow curing, and do not provide the best possible resistance to compression set, they do offer unique advantages. For example, compounds cured with diamines exhibit excellent adhesion to metal inserts and high hot tensile strength. Most fluoroelastomers are crosslinked with Bisphenol AF, a curative introduced in 1970, in the first commercial curative-containing precompound, Viton® E-60C. Compounds of Viton® that use this curative exhibit fast rates of cure and excellent scorch safety and resistance to compression set. In 1987, an improved bisphenol curative was introduced, which was made available in several different precompounds. The modified system provides faster cure rates, improved mold release, and slightly better resistance to compression set, compared to the original bisphenol cure system used in Viton® E-60C and E-430. Additional precompounds of Viton®, incorporating this modified curative, were introduced in 1993, including Viton® A-331C, A-361C, B-601C, and B-651C. A brief description of all these products can be found in Table 6. In 1976, efficient peroxide curing of fluoroelastomers was made possible for the first time with the introduction of Viton® GLT. The peroxide cure system provides fast cure rates and excellent physical properties in polymers such as GLT and GFLT which cannot be readily cured with either diamine or bisphenol crosslinking systems. In the case of polymers such as Viton® GF, GBL-200, and GBL-900, the peroxide cure provides enhanced resistance to aggressive automotive lubricating oils and steam and acids. Generally, vulcanizates of Viton® fluoroelastomers cured with peroxide do not show any significant difference in resistance to other fluids uploads/Geographie/ viton-selection-guide.pdf