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Up to the time of the beginning of the recent World War, comparatively little was known about the low-temperature characteristics of rubber, in spite of the fact that a number of investigators (1–16) had studied the subject. This can be at least partly explained by the fact that natural rubber, the only important elastomer known at that time, retained its flexibility over a rather wide range of temperatures extending down to -70 F. or even lower. Applications requiring flexibility or elasticity at temperatures lower than -70 or -75 F. were relatively rare, and, as a result, much of the work on this subject was largely academic in nature. Two important factors quickly changed the emphasis from academic to highly practical considerations. First of all, aircraft ceilings were being continually raised, making it necessary for tires, airplane de-icers, engine mountings, and tubing to withstand lower and lower temperatures. Secondly, it was soon discovered that the synthetic rubbers which had to be substituted for natural rubber, without exception, became inflexible or even brittle at temperatures considerably higher than natural rubber. Other factors also contributed to the demand for knowledge of the behavior of elastomers at low temperatures. Tanks and trucks had to operate efficiently in the arctic as well as in the tropic regions. Airplanes, tanks, and ships carried more and more sensitive equipment for communication and direction of gunfire, all of which had to be mounted on vibration-absorbing supports in order to retain their accuracy during actual operations. Then too, in order to decrease transmission of vibration and shock as much as possible, rubber-like materials were used more and more as prime mounts for vehicles, that is, in the form of tank treads, tires, and bogie rollers on tanks. The majority of tests developed in recent years (17–26) to measure low-temperature serviceability, fall roughly into two classes: one, a method for determining the so-called brittle-point temperature; and, two means for measuring the rate of stiffening or hardening with decrease in temperature. Some atempts have also been made to measure physical properties under dynamic conditions at low temperatures (24), but so far these methods have not been developed very completely nor have they received any general acceptance. For these reasons, they will not be discussed in any detail in this paper, though their importance, when more fully developed, should not be minimized.
Liska, John W.
The Firestone Tire and Rubber Co., Akron, Ohio