Experimentally-Determined vs. Theoretical Values of Roving Strength

The aim of this investigation was to assess the agreement of roving strength values, as calculated from Zurck's and Braschler's theoretical formulae, with experimental results. The strength of a roving depends on the elementary ad hesion force of a fiber, the roving geometry parameter, and fiber characteristics. Tests were made on rov ings of cotton, viscose staple, and modified viscose staple. Physical quantities like fiber parameters, density in a rov ing, and an elemen tary adhesion force of the fiber, each of them needed to calculate roving strength on the basis of theoretical formulae, have been determined by experiments. As far as an elementary adhesion force of the fiber is concerned, it has been defined for the untwisted strands which reveal the density adequate to that of the roving.

Tenacity values obtained from the theoretical formulae were made the subject of comparisons with experiment results. The effect of the mentioned procedures was that the elementary adhesion force of the fiber depends on the de nsity of fibers in a strand; likewise, the elementary force is not to be taken into consideration as a constant quantity.

The strength calculated from Zurek's formula appears to be compatible w ith experimental results in the interv al of tw ists used in rovings that is, up to α _m ~ 35. If higher twists of rovings are concerned, the theorotical values of strength become lower than the experimental ones and not consistent, in practice, with theoretical values.

When the elementary adhesion force is taken into account as a varying value in the function of density of a roving, values in Braschler's formula seem to be much higher and incompatible with the experimental results, in the w hole interv al of tw ists.