The principle of high-speed spinning is the same as conventional spinning, but due to the increase in spinning speed, the tension on the spinning process increases, resulting in higher requirements for the melt. So the process flow of POY is different from UDY. It is a primary silk produced by melting, extrusion, spinning, and high-speed winding of dried slices. The production process of POY includes dry slicing, melt extrusion, pre filtration, mixing, metering, filtration, spinning, cooling and forming, oiling, winding, and POY tube.

1. Melt extrusion

The pre crystallized and dried polyester chips enter the screw extruder. The screw extruder has functions such as chip supply, melt extrusion, mixing, and metering extrusion. Polyester chips are fed into the screw groove of the screw extruder from the feeding port. Due to the rotation of the screw, the chips are carried forward and continuously absorb the heat supplied by the heating device; On the other hand, due to the friction between slices, slices, screws, and sleeves, as well as the shear effect between liquid layers, a portion of mechanical energy is converted into thermal energy. As the slices move forward, the temperature increases and they gradually melt into a molten material. During the melting process, polyester polymers undergo changes in temperature, pressure, and morphology, transitioning from a solid (glassy state) to a high elastic state. With further increase in temperature, plastic flow occurs, becoming a viscous fluid (viscous flow state). The viscous flow state of polyester macromolecules is uniformly mixed by the push of the screw and the resistance at the screw outlet, and the pressure increases, extruding the melt. This process is called the melt extrusion process.

There are two types of screw extruders: horizontal and vertical. Screws installed horizontally in space are horizontal, while those installed vertically are vertical. The horizontal screw extruder is easy to install, disassemble, and maintain, but the screw extends outward and the measuring section is prone to wear and tear. The screws of a vertical screw extruder are not easily bent and have less head wear, but the height of the factory increases, making assembly, disassembly, and maintenance more difficult. At present, screw extruders are generally used horizontally.

Screw extruders can be divided into single thread, double thread, single screw, and double screw extruders based on the number of thread heads and screw pieces. According to the speed of the screw, it can be divided into ordinary type (with a speed less than 100r/min) and high-speed extruder. In recent years, the development speed of screw extruders has been rapid, moving towards large-scale, large aspect ratio, and high-speed development.

2. Pre filtration

Because the melt contains certain mechanical impurities and unmelted gel particles, direct spinning will not only affect its spinnability, but also affect the quality of the product. Therefore, in order to ensure the purity of the melt and stabilize the fiber quality, in addition to setting filter components in the spinning component, it is generally necessary to set filters in the melt conveying pipeline or the melt distribution pipeline of the spinning machine, commonly referred to as pre filters. Before spinning, the melt is filtered to remove mechanical impurities and incomplete gel particles, so as to improve spinning performance and extend the service life of spinning components. The pre filter is generally a dual chamber filter, with one chamber used first. When the pressure drop exceeds 5-10MPa, the filter is switched. Usually, the switching period is 10-20 days and the switching time is 2-3 minutes. The commonly used filtering media include woven metal mesh and sintered metal fiber felt, with shapes such as rectangular, folded or flat mesh. In order to improve filtration performance, two or more filtering media are often selected to form a filtering element.

The pre filtration of the melt increases the residence time and the viscosity decrease of the melt. Therefore, if the slicing quality is good and there are no mechanical impurities brought in by the feeding system, a pre filter can be omitted.

3. Melt distribution pipeline

The melt distribution pipeline transports and distributes polyester melt to various spinning boxes. Require the pipeline to be as short as possible, with a uniform delivery time to each box, minimal heat dissipation of the melt in the pipeline, and no dead corners of the melt.

4. Static mixing

Static mixing is achieved through a mixer installed in the melt conveying pipeline. High viscosity polymer melt flows in a laminar state in pipelines, resulting in gradient differences in temperature, residence time, and viscosity along the radial direction. By installing a static mixer in the pipeline, the adverse effects of this difference on spinning can be reduced. When slicing and spinning, it is sometimes necessary to add various additives such as high polymers of different compositions or certain stabilizers and anti-static agents. In order to mix evenly, a dedicated static mixer can be installed at the head of the screw extruder. When mixing ordinary polyester chips with dyeing masterbatch to produce colored polyester, a screw extruder with a static mixer can be used. The static mixer has two basic functions: first, it has a mixing effect on the material, which refers to dividing the material into fine streams and then mixing it; The second is the mixing effect on materials, which refers to continuously changing the flow state of the material liquid, thereby producing a certain shear plasticization effect on the material liquid.

Therefore, installing a static mixer in the melt pipeline can reduce the stratified flow caused by high viscosity in the melt, and make the physical properties of the melt uniform. If the melt has been fully mixed in the screw extruder and there are few dead corners in the melt distribution pipe, the static mixer can be omitted.

5. Measuring pump

The metering pump is a high-precision standard component used in melt spinning and is one of the key components in the spinning process. The melt is accurately measured and sent to the spinneret assembly through a metering pump, and then extruded from the spinneret hole to form fibers, ensuring uniform filament thickness. At the same time, the metering pump can pressurize the melt to meet the needs of spinning.

6. Spinning components

The spinning component consists of a spinneret, a distribution plate, and a melt filtration material. It finally filters the melt sent by the metering pump, and the filter material further filters the mechanical impurities and gel particles in the melt to prevent blocking the spinneret hole; Fully mix the melt to prevent viscosity differences between the melts; Distribute the melt evenly into each small hole of the spinneret to form a uniform fine flow. The requirements for the module are: the melt should be evenly distributed to the small holes of the spinneret, the channel resistance is the same, and there should be no dead corners in the module, so as to avoid cracking or forming gel due to the long residence time of the melt; Good sealing and filtering effect, long service life, convenient disassembly and assembly of components, and reliable sealing; Parts that come into direct contact with the melt must be resistant to high temperature and corrosion. Due to the high extrusion volume and flow resistance of high-speed spinning, it is required that the particle size of the filter material be slightly larger than that of conventional spinning; Meanwhile, due to the high spinning speed and high shear stress during spinning, the aspect ratio of the spinneret hole is higher than that of conventional spinning.

7. Cooling forming

The fine flow of molten material sprayed from the spinneret solidifies into filaments under the action of side blowing, and is stretched 100-250 times by the effect of winding traction, which is about 2-4 times larger than conventional spinning. During the solidification of the melt and the cooling of the filament, a large amount of heat is released into the surrounding air. These heat are mainly carried away through convective heat transfer with flowing air (side blowing). The cooling speed of the filament should be uniform, the solidification point position should be fixed, and it should not be affected by the surrounding air flow and produce violent shaking. Due to the high output and heat released by high-speed spinning, the cooling and blowing air has higher wind speed and humidity, and lower wind temperature.

8. Bundle oiling

After the fibers are cooled and formed, they are bundled and oiled before entering the spinning channel to reduce the winding tension. There are two ways to apply oil: using an oil pan to apply oil and using an oil nozzle to apply oil. Due to the high running speed and high oil content of high-speed spinning filaments, a metering pump is generally used to supply oil to the nozzle.

9. POY winding

The key to high-speed spinning is high-speed winding: under high-speed conditions, issues such as the smoothness of equipment operation, the quality of filament tube forming, and the convenience of operation are more prominent than conventional spinning. Require that the winding tension, winding speed, as well as the reciprocating speed and linear speed of the guide disc, friction roller, transverse guide, etc., remain stable during operation to ensure uniform structure and linear density of the primary fibers.

The winding tube of POY should have tail threads left, so that knots can be tied at the head and tail during the processing of DTY, reducing the number of hair growth. There are two ways to leave the tail wire. One is to first make a head at one end of the tube, and then guide the wire into the wire guide for normal winding; Another method is to first wrap the bottom layer of wire on the tube, then push the wire strip to one end of the tube, wrap the tail wire a few times, and then introduce the wire guide for normal winding. To reduce the waste silk when changing the drum after it is full, automatic or semi-automatic drum changing and winding machines are mostly used.

The winding machine is divided into two types: non guide wire disc and guide wire disc. Due to the high winding tension of high-speed spinning, a winding machine without a guide wire is generally used.