Wet spinning(2)

The spinning solution is sent to the spinning machine by the circulating pipe, measured by the metering pump, and then enters the spinneret (CAP) through the candle filter and connecting pipe. The spinneret is generally made of gold and platinum alloy or tantalum alloy. Several holes are regularly distributed on the spinneret, with an aperture of 0.05-0.08mm. The fine flow of the original liquid from the spinneret hole enters the coagulation bath, the solvent in the fine flow of the original liquid diffuses to the coagulation bath, and the coagulant penetrates into the fine flow, so that the fine flow of the original liquid reaches the critical concentration, and the fiber is formed by precipitation in the coagulation bath. Diffusion and solidification in wet spinning are physicochemical processes, but some chemical fibers change at the same time. For example, viscose fiber and cellulose xanthate are decomposed into cellulose regenerated fiber.

The speed of wet spinning is much lower than that of melt spinning because of the limitation of double diffusion speed of solvent and coagulant and fluid resistance of coagulation bath. The ratio of the linear speed of the first guide disk to the extrusion speed of the spinning solution is called the spinneret stretch ratio. The drawing ratio of wet spinning is generally negative, zero or very small positive value, in order to improve the stability of forming process.

Spinning solution is a kind of elastic viscoelastic body with both viscosity and elasticity. When the original liquid is pressed out from the spinneret, there is the effect of orifice swell (Burroughs effect), which makes the diameter of extrusion fine flow larger than the spinneret hole diameter. In the process of wet spinning, the swell ratio is generally 1-2.

Under the tensile force of the first guide disk, the extrusion fine flow gradually thinned after passing the maximum diameter, and the refining process continued until the original liquid fine flow completely solidified. The change of the diameter of fine flow in wet spinning is not only the result of tensile deformation, but also related to the mass transfer process. The spinning process from spinneret to curing point is fiber forming area, which is the key area of fiber structure formation.

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