DRAG COEFFICIENTS OF FILAMENTS IN AIR FLOW DURING THE SPINNING

Abstract

Drag coefficients of polypropylene filaments in the flow during spinning were investigated in order analyse the melt spinning process.Experimental apparatus is shown in Fig. 1. Drag coefficients are calculated from tension difference between the top and bottom of the spinning chimney b in Fig. 1, using equation (1) (2) and (3). Measurements of filament tension were performed in stagnant air in the chimney during the spinning as well as in air flow of co-or counter-current.Experimental conditions and results are presented in Table 1 and 2 respectively.In Fig. 2, tension of filaments at the top of the chimney increases linearly with spinning velocity. At the bottom of the chimney, tension is affected by air flow in the chimney; it decreases in the co-current air flow and increases in the counter current. The ratio of the drag force to tension at the bottom of the chimney increases with spinning velocity. When spinning velocity is over 800 (m/min), the ratio exceeds more than 50 (%).The following equation is obtatined experimentaly between drag coefficient Cf and Reynolds number, (Fig. 3):Cf=0.68 Re-0.8Number of filaments and_??_/R, the ratio of mean distance from nozzle and radius of filaments, has no effects on this relation.In Fig. 5, Experimental equation was compared with values of the literatures such as the boundary layer theory of moving continuous cylinder3) and flat plate7) and the analogy equation estimated from heat transfer coefficients5)6).