Rubber Vibration Insulators. Some Characteristic Properties and Tests

Insulating of vibrating parts of engineering devices and structures is one of the vital problems of this age. The original purpose of carriage and automobile tires was, as indeed the major purpose of their use today still is, the suppression and elimination of shocks and vibrations during travel. This is true in spite of the importance of the “increased mileage” obtained by the use of rubber tires—a factor of no mean importance. This purpose is not so self-evident in the case of belting, hose, rubber-covered rolls, etc., where flexibility and/or elasticity are apparently prime requisites, but nevertheless the interception and safe-transmission of impulses or stresses with a minimum of vibration and noise are certainly of inestimable value. The use of rubber parts elsewhere in the automobile and general engineering field is unquestionably solely for the suppression or elimination of vibration. Recognition of the importance of rubber parts for such service came with the organization early in 1927, at the request of the Society of Automotive Engineers, of a committee to make a study of the most important characteristics of rubber necessary in such service and finally to set up standards of tests for these properties. This committee was formed by the American Society for Testing Materials and is composed of a number of the leading automotive engineers of the country and rubber technologists from the leading rubber companies. The S. A. E. also has an official representative. The scope of the work of this committee includes hardness testing, deflection under compression and compression-set (cold flow), resistance to cold, and dynamic fatigue, but to date its active efforts have been confined largely to the first two. The trend toward the use of rubber vibration insulators in railway work, both between ties and rails and in the cars themselves, is opening up a virgin field of enormous importance, and certainly shows the importance of these properties and the necessity for standardized tests. Of course, good aging qualities, resistance to abrasion, oil and heat, and relatively high tensile, shear, cutting and tearing strengths are important in the life of the part (but to varying degrees depending on the service intended). In addition, a standardized test for the adhesion of rubber to metal is now imperative. At present most specifications for motor supports in which rubber is bonded to metal require a direct pull, perpendicular to the metal-rubber interface, of 250 lbs. per sq. in. minimum, with actual values ranging up to over 1000 lbs. per sq. in.