This is the second paper of a series that describes the curing process of styrene-butadiene-rubber packed in a cylindrical mold with inner diameter of 74.6 mm. Present paper mainly describes the curing process under the mold cooling stage. Sulfur was used as the curing agent and the sulfur concentration ranged from 1.0 to 5.0 weight percent. The mold temperature was controlled in two stages. The mold was heated at 414 K for 45 min. then switched off, and the mold was cooled by natural convection to the surroundings up to 75 min. Time-dependent radial distributions of the temperature profile and the crosslink density were measured in the cooling stage. It was confirmed that the curing reaction was related strongly to the temperature field. In the cooling stage, rubber temperature decreased in the outer zone whereas overshooted in the inner zone. The degree of cure at the rubber center reached to around 0.8 at time 45–60 min. elapsed after taking the heater off for sulfur concentration of 1 and 3 weight percent.

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Change and restoration in carbon black filler network in SBR through reversing double-step large shear deformations were studied by the use of differential dynamic modulus. Unfilled rubber showed drop and complete recovery in G′ after elimination of step shear strain γ=0.5, showing drop in G′ is not due to chain scission but due to filler network rupture. Filled rubber also shows similar change and recovery in G′, but rises over the initial value at long time region. This long time behavior may be due to physical aging. Elimination of the effect of physical aging allowed us to estimate relaxation time in restoration process. It was concluded that (a) differential dynamic modulus measured in recovery process is useful for the characterization of filler network, (b) carbon black filler network ruptured by strain recovers to the original structure by particle diffusion process, and (c) recovery rate of carbon black filler network is independent of amount of filler loading and deformation history.

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Synchronous belts are rubber-composite materials with rubber, helical cords and facing fabrics. The helical cord is the tension member of the belt and is made of glass fibers, aramid fibers, or steel wires. The recent trend is high stiffness for the rubber belts, because of the stability under high loading conditions. The use of carbon fibers is considered to be an effective way to achieve the high stiffness for the helical cords. The purpose of this paper is to improve the bending fatigue strength of the hybrid cords, where the core strand is made of carbon fibers, and the outer strands are made of glass fibers. The optimum cord composition for high bending fatigue durability was discussed following some bending fatigue tests of the cord and mechanical analysis using a simplified mechanical model. The simplified mechanical model explained reasonably the fatigue failure initiation site in the hybrid cords. Then, it is expected to obtain a better cord construction for the bending fatigue strength using the proposed mechanical model.

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