LATERAL SPREADING OF FIBER TOWS

In the manufacture of fibre-reinforced polymer composite materials, th e standard technology involves an intermediate product, 'prepreg'. To make this, the fibres are unwound from a reel in the form of a continu ous bundle, or tow, impregnated with the resin matrix and spread out i nto a thin flat tape. The fibre tow is pulled through a bath of molten resin, passing over a series of bars in zig-zag fashion. The bars ser ve to locate the tow, control the tension, spread it laterally (and si multaneously reduce its thickness) and squeeze the resin in. The paper presents a simple theory of this spreading and thinning process, givi ng the spread width w in terms of the cross-section area A of the tow and the lateral offset of the spreader bar H by the simple explicit fo rmula w = (12AH)(1/3). Simple experiments to check the theory are repo rted. The theory also gives an estimate of the thickness, which is mor e important in the impregnation process, but not readily accessible to direct measurement.