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The direct spinning process avoids the stage of solid polymer pellets. The polymer melt is produced from the raw materials, and then from the polymer finisher directly pumped to the spinning mill. Direct spinning is mainly applied during production of polyester fibers and filaments and is dedicated to high production capacity (>100 ton/day).
In order to produce the polyester melt with a high efficiency, high-output processing steps like staple fiber (50–300 tonnes/day per spinning line) or POY /FDY (up to 600 tonnes/day split into about 10 spinning machines) are meanwhile more and more vertically integrated direct processes.
Melt spinning is a metal forming technique that is typically used to form thin ribbons of metal or alloys with a particular atomic structure. [ 1 ] Some important commercial applications of melt-spun metals include high-efficiency transformers ( Amorphous metal transformer ), sensory devices, telecommunications equipment, and power electronics.
Before drawing, polymer melt is pushed through a die with a large number of small holes, known as a spinneret. Typically, the fibers are air cooled without any need for curing. If curing is needed, two methods are available: dry and wet spinning. In wet spinning, the polymer is dissolved and extruded through a spinneret into a chemical bath.
A spinneret is a device used to extrude a polymer solution or polymer melt to form fibers. [1] Streams of viscous polymer exit via the spinneret into air or liquid leading to a phase inversion which allows the polymer to solidify. The individual polymer chains tend to align in the fiber because of viscous flow. [2]
HFM production, commonly referred to as "spinning", can be divided into four general types: Melt Spinning, in which a thermoplastic polymer is melted and extruded through a spinneret into air and subsequently cooled. [3] Dry Spinning, in which a polymer is dissolved in an appropriate solvent and extruded through a spinneret into air. [4]
In order to protect the spinnerets, an efficient filtration of the melt is, in any case is necessary. For the time-being, the amount of POY made of 100% recycling polyester is rather low because this process requires high purity of spinning melt. Most of the time, a blend of virgin and recycled pellets is used. [citation needed]
In dry spinning (acetate and triacetate), the polymer is contained in a solvent that evaporates in the heated exit chamber. In melt spinning (nylons and polyesters) the extruded polymer is cooled in gas or air and then sets. [4] Some examples of synthetic fibers are polyester, rayon, acrylic fibers and microfibers.