THE ROLE OF THE

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Seal and Gasket Design 119 table 8.5 Properties of ePdm dienes termonomer cure and Property Features long chain branching ENB Fastest and highest state of cure good tensile; good compression set resistance DCPD Slow sulfur cure; good compression set resistance table 8.6 Features of ethylene–Propylene elastomers monomer content [4]. Using a table like this, the material engineer or chemist who needs good compression set resistance may want to choose a high diene content in the EPDM. Ethylene–propylene elastomers are one of the main choices of automotive chem- ists and material engineers for sealing applications, as well as isolation systems, weather stripping, electrical components, etc. Heat aging resistance up to 130°C can be expected with certain sulfur cures and up to 160°C with peroxide-cured com- pounds [3]. They also respond well to high filler and plasticizer loads. Typical properties are shown in Table 8.7 [4]. Low to moderate High characteristics High low Ethylene Content Good green strength Fast mixing Flow at high extrusion temps Low-temp. flexibility High tensile strength, modulus Low hardness and modulus High loading (reduced cost) Calendering and milling Diene content Cure degree and fast rate Scorch resistance Acceleration versatility High-heat stability Good compression set High modulus, low set Low hardness and modulus Molecular weight Good tensile, tear modulus, set Fast mixing High loading and oil extension High extrusion rates Good green strength Good calendering Collapse resistance Low viscosity, low scorch MWD Overall good processing Low die swell Extrusion feed and smoothness Fast extrusion rate Collapse resistance High cure Good calendering and milling Good physicals
120 The Role of the Chemist in Automotive Design 8.7 natural rubbers table 8.7 Properties of ethylene–Propylene elastomers Polymer Properties Mooney viscosity, ML 1–4 at 125°C 5–200+ Ethylene content (wt. %) 45–80 Diene content (wt. %) 0–15 Specific gravity (g/mL) 0.855–0.88 vulcanizate Properties Hardness (Shore durometer) 30A–95A Tensile strength (MPa) 7–21 Elongation (%) 100–600 Compression set B (%) 20–60 Useful temperature range (°C) −50 to +160 Tear resistance Fair to good Abrasion resistance Good to excellent Resilience Fair to good Electrical properties Excellent Natural rubber is utilized mainly as an isolation material in CRFMs in HVAC components. Natural rubber is tapped from the Hevea brasilienis tree in the form of latex or a colloidal suspension. These trees produce more rubber when they are wounded, thereby providing a renewable source of rubber. Figure 8.10 shows the two base components present in natural and synthetic rubbers. The repeating units consist of isoprene and some diene monomer such as butadiene shown in the figure and natural impurities. Synthetic rubber is typically made with isoprene and butadiene. Due to the structure of natural rubber, with its conjugated system of double bonds and the ability to reduce the unwanted dynamic motions associated with a mounting system, isolation is its most important use. However, natural rubber use in seals and gaskets is a natural fit. The automotive chemist chooses natural rubber for several reasons. The elastic behavior of rubber can be attributed to electrostatic strain H H CH 3 2-Methyl-buta-1,3-diene (Isoprene) CH 2 H 2 C FIgure 8.10 Structure of isoprene and 1,3-butadiene. 1,3,-Butadiene CH 2
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THE ROLE OF THE CHEMIST IN AUTOMOTI
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CRC Press Taylor & Francis Group 60
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Contents Preface...................
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Contents ix 6.6 Thermal Properties
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Contents xi 11.4 Glass Microspheres
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The Author Herman Phlegm was born i
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2 The Role of the Chemist in Automo
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10 The Role of the Chemist in Autom
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3 3.1 IntroductIon Component Materi
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Component Materials in Automobiles
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Page 130 and 131: Seal and Gasket Design 113 table 8.
Page 132 and 133: Seal and Gasket Design 115 The main
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Page 140 and 141: Seal and Gasket Design 123 F F F F
Page 142 and 143: Seal and Gasket Design 125 R R O ma
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190 Index Carbon dioxide emissions,
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192 Index heat exchanger designatio
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194 Index Power train, 95 Power tra
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