Ebonites characteristics

While considering swelling characteristics of ebonite two facts are noteworthy 1) high sulphur and adequate cure reduce both the... 

Many moulded components are affixed on the rubber-lined surface such as anode sleeves in mercury cells used in caustic soda industry. These moulded components are either made from natural soft or ebonite rubbers or Neoprene rubber compounds. While moulding, the flow characteristics of the rubber compound and shrinkage need to be taken into consideration. Some aspects of mould designs are described next. 

Poisson s ratio is a measure of the reduction in the cross section accompanying stretching and is the ratio of the transverse strain (a contraction for tensile stress) to longitudinal strain (elongation). Poisson s ratio for many of the more brittle plastics such as polystyrene, the acrylics, and the thermoset materials is about 0.3 for the more flexible plasticized materials, such as cellulose acetate, the value is somewhat higher, about 0.45. Poisson s ratio for rubber is 0.5 (characteristic of a liquid) it decrease to 0.4 for vulcanized rubber and to about 0.3 for ebonite. Poisson s ratio varies not only with the nature of the material but also with the magnitude of the strain for a given material. All values cited here are for zero strain. 

Tribological characteristics confirm the influence of sulfur modification of metal counter face on lowering fiiction for the metal-polymer couples studied. In the case of ebonite, the coefficient of friction reduced significantly for the whole experimental mn, whereas application of SBR vulcanizate or polysulfide rubber was effective only during the first period of experimental cycles. Any improvement of tribiological characteristics was not assigned for polysulphone. The polymer was observed to worn the surface of iron counterface, what resulted in increase of the coefficient of friction in this case. 

Tribological characteristics of pol rmer materials sliding against Arm-co iron are demonstrated in Fig. 14.6. Friction force and energy curves vary from material to material due to their different chemical stmcture and related mechanical properties. From tribological point of view, the most efficient modification has to be subscribed to ebonite - iron fiic-tion couple. In this case median of the friction force and discrete levels... 

FIGURE 14.6 Tribological characteristics of Armco iron - polymer material friction couple. A - ebonite/20 N - 1 st cycle B - ebonite/20 N - 2nd cycle C - SBR vulcanizate - 1st cycle D - SBR vulcanizate - 2nd cycle E - poly sulfide rubber - 1st cycle F -poly sulfide rubber - 2nd cycle G - polysulphone - 1st cycle F - polysulphone - 2nd cycle. 

Ebonite shows very low water absorption and has good resistance to most aqueous reagents, except nitric acid. It is swollen by aromatic and chlorinated hydrocarbons. Ebonite has good electrical insulation characteristics and the major application is for car battery cases. 

---