Abstract
We reported formerly on a comparison of Hevea, Neoprene GN-A, Hycar-OR-25 and Silicone-T.S. under the same title. In that study, we found merits and demerits of these rubbers and those which have some special merits always possess some great demerits. In designing rubber vibration isolators, it is eagerly desired to make such rubber which would have the merits soley made up from those other kinds of rubbers. In workshops some blended rubbers and coated ones are produced for the purpose of making some improvements on properties. So we prepared some specimens which were blended with two or three of Hevea, Neoprene and Hycar, and some others were coated by Neoprene or Hycar with the thickness of 1mm on the free surface of Hevea stocks. Then we compared such specimens with single rubbers which were reported in the 1st. report by the resonant method. And we observed their dynamical charcteristics, amplitude dependency, oil resistancy along with some other data.
(1) Dynamical characteristics of blended rubber....spring constant k and damping coefficient c were calculated, their variations in relation to temperature have same tendencies with single rubbers. And their values of spring constant decreased and damping coefficient generally increased. So loss factors L became large, which is considered as a bad tendency.
(2) Amplitude dependency of the blended rubber....This tendency of blended rubber is more remarkable than in single one. The position of the peak of the curve in relation to stress amplitude and characteristic function φ(s) moves to the larger side of stress amplitude.
(3) Oil resistancy....After immersing rubbers in machine oil for more than 60 days, we measured the considerable decrement of spring constant and internal friction and found that the oil resistancy of blended rubber was less than that of each component of single rubber. But when Hevea was coated by Neoprene or Hycar, though its oil resistancy was some-what less than that of single Neoprene or Hycar, they fulfiled their requirements very well as the oil-proof material for the Hevea.
These three characteristics chiefly are caused by the structure of blended rubber molecules.
