EPDM rubber discs

The problem of curing various sorts of rubber compounds simultaneously sometimes arises, for instance, when bilayers with different properties on each side are desired. In one particular example shown in the literature, two thin EPDM rubber discs are cured together, the one containing 2% sulfur as a vulcanizing agent whereas the other has 10 or 20% sulfur [28,29]. 

Azaar K., I.D. Rosea, and J.M. Vergnaud. 2002. Anisotropic swelling of thin EPDM rubber discs by absorption of toluene. Polymer. 43 4261-67. 

The kinetics of absorption of toluene by the EPDM rubber discs are drawn (Figure 7.6) as they are obtained from experiments (dots) and by calculation (full fine) when the percentage of peroxide is 2,10, and 20. The dimensionless number is used, expressing the weight of toluene absorbed as a fraction of the initial weight of the discs free from liquid. 

FIGURE 7.6 Kinetics of toluene absorption by three EPDM rubber discs with 2, 10, and 20 parts peroxide. Amount (w/w) of toluene absorbed as a fraction of the initial weight of rubber free from liquid. (With permission of Elsevier, Figure 2 in Polymer, 2002, 43, p. 4261 K. Azaar, I. D. Rosea, and J. M. Vergnaud.)... 

An example is shown, drawn from a recent paper [16] where EPDM rubbers cured separately with 2% and 10% peroxide are submitted to the stages of absorption of toluene up to equilibrium, followed by the stage of drying. These two rubber discs, 0.235 cm thick, cured at 187°C so as to have a state of cure of 90% and 96%, are immersed into toluene over more than 300 minutes, this time being necessary to attain equilibrium with a flat profile of liquid concentration through the thickness of the discs. These discs presaturated of toluene are thus exposed to air at room tan-perature (25°C) with a slight agitation. 

Flow measurement is by magnetic meters with ethylene-propylene-diene elastomer (EPDM) lining and Hastelloy C electrodes. The control valve can be a rubber-lined butterfly valve with a rubber-coated or Monel disc. 

Special check valves are available for sewage and slurry flows. The Red Valve Company Series 39 valves (Figures 2-19 and 2-20) feature a special reinforced elastomer check sleeve. The valve check sleeve seals under reverse flow or back-pressure and opens under pressure from the pump. It does not incorporate any discs that may wear on contact with slurry. This type of valve is therefore different in design than the type shown in books on water flows. The consultant engineer should therefore request from the manufacturer of the slurry check valves the estimated K factor for pressure losses. The Red Valve Company Series 39 slurry check valves are available in sizes up to 48" (1220 mm), with a choice of elastomers such as pure gum rubber, neoprene, Hypalon, chlorobutyl, Buna-N, EPDM, and Viton. 

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