Viscosity , Relaxation and Stability of Natural Rubber
Mooney viscosity and Mooney relaxation of unaged and oven aged SMR L natural rubber samples were studied. The viscosity was characterized by ML (1+4) 100°C and the rate of stress relaxation by the exponent a in a power law M = k (t) a . With the increasing time of oven aging at 140°C the decrease of both viscosity and stress relaxation rate exponent were observed. Aging of raw natural rubber can therefore be studied by Mooney viscosity and Mooney relaxation tests and obtained results are sensitive enough to be used for characterization of raw natural rubber stability.
Effects of Natural Rubber Origin on Mechanical Properties of Rubber Compound in the Presence of Natural and Commercial Antioxidants
Different origin of rubber gives different effect towards the properties of end products. In this paper, effect of natural rubber (NR) origin on tensile properties and tear strength before and after aging for 4 and 7days were investigated in the presence of natural antioxidant (NA). Effectiveness of NA in different NR origin was compared with commercial antioxidants (TMQ). The NR from Malaysia (SMR CV60), Thailand (STR 5L), Vietnam (SVR 3L) and Cambodia (SCR L) were used in this study and cured using Semi-EV. For tensile and tear strength before aging process, STR 5L / NA shows the highest result followed by SVR 3L, SCR L and SMR CV60. This is due to higher molecular weight of STR 5L compound. But after aging for 4 and 7 days, SMRCV 60 has shown the highest percentage of retention for tensile and tear strength which indicated the lowest breakage of crosslink. From the results of tensile and tear properties, it is verified that different NR origin compound with NA vulcanizate gives reasonable result which are comparable to NR with TMQ vulcanizates.
Joint strength of aluminum ultrasonic soldered under liquidus temperature of Sn–Zn hypereutectic solder
Abstract In order to obtain high-strength aluminum joints, ultrasonic soldering of 1070 aluminum was conducted under liquidus temperature of Sn–Zn hypereutectic solder. A device for ultrasonic soldering was assembled, which propagated ultrasonic vibrations in a direction perpendicular to joining surfaces. This device joined 1070-Al using quasi-melting Sn–Zn hypereutectic solder without using any artificial spacers. The strength of the solder joints was evaluated by tensile tests. The optimum joining conditions were determined, and the effects of solder compositions and soldering temperature on the joint strength and the solder layer thickness were examined. In this ultrasonic soldering process, the highest tensile strength was obtained for the solder joints fabricated at 220 °C for the Sn–23Zn and Sn–40Zn solder compositions. The joint strength was equivalent to that of 1070-Al heat treated at 220 °C. The sound joints were obtained at 300 °C using Sn–82Zn solder, the liquid phase volume fraction of which was theoretically only 0.24. The present work also revealed that the thickness of retained solder layer in the joint after ultrasonic soldering could be estimated. Accordingly, ultrasonic soldering under the liquidus temperature of Sn–Zn hypereutectic solder could be a spacer-free soldering method to obtain high-strength aluminum joints.