Boundary Layer Hydrodynamics and Mass Transfer Rates in Flax Roving Swelling
Hydynamic boundary layer reduction in wet-spinning troughs accelerates core hydration, stabilizing swelling and lowering yarn count CV percent.
Roving Twist Levels
Structural Cohesion
Twist inserted into the assembled flax fibres provides the necessary mechanical strength to withstand tension during the spinning process. These roving twist levels determine the balance between the cohesion of the fiber bundle and its draftability on the spinning frame. Wet spinning lines require a precise amount of twist to prevent the wet roving from falling apart before drafting.
Drafting Performance
Drafting rollers must overcome the frictional resistance between the fibres to draw them out into a fine yarn. If the roving twist levels are too high, the fibers are held together too tightly, which prevents them from sliding past each other and causes drafting breaks or thick spots. On the other hand, a twist level that is too low results in premature drafting where the roving stretches and breaks under the tension of the feed rollers.
Finding the optimum twist involves analyzing the average fiber length and moisture content of the flax batch. Spinners adjust the flyer speed relative to the delivery speed to maintain this optimum level across different batches of flax.
Liquid Absorption
Mechanical twist also affects how quickly water can penetrate the core of the flax roving during the wetting stage. High twist levels compact the fibres, which reduces the internal capillary size and slows down the absorption of the softening solution. This slow absorption leads to dry cores and uneven drafting.
Spun yarn made from under-wetted roving suffers from high mass variation and reduced tensile strength.