Effect of Tire Cord Uniformity on the Strength of Tire Fabrics

Abstract

The strength of tire fabrics, which largely determines tire carcass strength, is dependent not only upon the average strength of the tire cords of which the fabric is made but also upon their uniformity. The degree of uniformity can be measured by the coefficient of variation of strength and of elongation, but such data do not, by themselves, show directly the influence of tire cord uniformity on fabric strength. Various methods of estimating the effective strength of tire cord are discussed. A formula is presented which permits a simple calculation of the effective cord strength from the coefficient of variation of cord strength. The various methods show a satisfactory degree of correlation. The effective cord strength of several rayon and cotton tire cords has been calculated. THE cord fabric used in the carcass of automobile tires differs from most ordinary fabrics chiefly in one respect: it possesses strength either entirely or almost exclusively in only one. direction-namely, parallel with the lay of the tire cords composing it. In the crosswise direction the cords may be held together by weak filling yarns, spaced widely apart, which are just strong enough to hold the cords in place during the calendering operation; or the cords may be calendered directly from a creel. These filling yarns, if they are present, are expected to break either before or soon after the tire is put into service. The strength of the tire fabric, which largely determines carcass strength, is therefore dependent exclusively upon the tensile strength and stretch characteristics of the cords making up the fabric.One commonly used method of estimating the strength of the carcass is to multiply the average single-cord strength by the number of cords per inch in each ply and to add these figures together to obtain an index of the total carcass strength. Such an estimate is based upon the assumption that the cords possess the same strength in the tire fabric that they show when broken individually. It is generally recognized, however, that the effective strength of * Present address, the cord in the fabric depends not only upon the average strength of the cord but also upon its uniformity. As a measure of uniformity the spread of the traces on the load-elongation charts and the range Qf strength and elongation values have been employed in routine measurements. For more exact comparisons the coefficient of variation of the strength readings has been used. However, it has not been possible to evaluate the effect of a given degree of non-uniformity on the strength of the tire-cord fabric, or to express the difference in uniformity of two different cords in terms of carcass strength.With the advent of new industrial fibers such as rayon and nylon, in the tire-cord field attention is focused on this factor of uniformity because some of the new synthetic tire cords may have a different degree of uniformity from that of the cotton cords heretofore used in tires. Accordingly, it becomes more important than ever to be able to evaluate the influence...

Mechanics of Elastic Performance of Textile Materials

“…The relationship between fiber properties and yarn performance is expressed mathematically by a method involving a generalized extension of the work of Hamburger [2] and Philipp [7]. The mathematical formulas representing the mechanical behavior of cordage yarns are shown to be useful by a comparison between theoretically calculated and experimentally obtained data.…”