Melt Spinning in textile is a process of manufacturing synthetic fibers. The high-molecular polymer is heated and melted into a spinning melt with a certain viscosity. Then the melt is continuously and uniformly squeezed to the spinneret by a spinning pump. The fiber stream is discharged through the pores of the spinneret. After being cooled and solidified in air or water, the fiber is stretched into synthetic yarn.
According to the different properties of fiber-forming polymers, the spinning methods of chemical fibers mainly include melt spinning and solution spinning. In addition, there are special or unconventional spinning methods. According to different solidification methods, solution spinning is divided into wet spinning and dry spinning. In the production of chemical fibers, most of them are produced by melt spinning, followed by wet spinning, and only a few are made by dry or other unconventional spinning methods.
Melt spinning is divided into the direct spinning method and the chip spinning method.
Direct spinning is to send the melt after polymerization directly to spinning.
Chip spinning requires the melt to go through the pre-spinning preparation procedures such as casting belt and pelletizing and then send it to spinning. Hubei Decon is the manufacturer of various chips for polyester yarn spinning.
- Melt extrusion
The chip melting process is usually carried out in a screw extruder. Controlling the temperature of the extruder can change the temperature of the melt to make it have appropriate viscosity and good spinnability. The melt from the screw extruder is sent to the spinneret assembly through a metering pump. The assembly is composed of a filter screen, a distribution plate, and a spinneret. Its function is to remove impurities in the melt and send the melt to the spinneret evenly.
Melt viscosity and temperature are the main parameters of melt spinning. At a certain temperature, the melt viscosity mainly depends on the molecular weight of the fiber-forming polymer. If the melt viscosity is too high, the flow will not be uniform, making the nascent fiber easy to produce hair and break ends when stretching.
The melt temperature can be controlled by that of each section in the screw extruder. If the melt temperature is too high, it will cause the polymer to degrade and form bubbles; if the temperature is too low, the melt viscosity will be too high. Both conditions make the spinning process work improperly.
- Cooling and Solidification
After the thin stream of melt is sprayed out, it is cooled and solidified by cold air. The temperature of the melt gradually decreases during the cooling process, and the viscosity continues to increase. When the viscosity increases to a certain critical value and the winding tension is not enough to make the fiber continue to thin, it reaches the solidification point.
The solidification length refers to the length of the melt stream from the spinneret orifice to the solidification point, which is the key area for the formation of the fiber structure.
The wind speed and temperature of the cold air blowing out of the cooling chamber must be uniform and constant to ensure that the temperature distribution, velocity distribution, and solidification point position of the melt stream in the spinning process are constant. Only when the axial tension of the fiber is constant can the fiber with uniform thickness and structure be obtained.
The cold wind blows to the fiber from all around, which is suitable for the porous spinning of short fiber and can effectively improve the fiber quality.
- Adding Oil
The melt-spun fiber is almost dry when it is just formed. And it is easy to accumulate static, the cohesive force between the fibers is poor, and the friction with the equipment is large, so it must be treated with oil and moisture before winding.
The oil is mainly composed of surfactants, which can form a directional adsorption layer on the surface of chemical fibers, that is, an oil film. The hydrophilic base of the oil film absorbs moisture in the air, forming a continuous water film on the surface of the fiber, allowing charged ions to migrate on the water film, reducing the accumulation of static charges due to friction, thereby reducing the surface resistance of the fiber and increasing conductivity.
The oil film isolates the fiber and has a certain affinity for the fiber so that it produces a certain degree of clustering without being scattered.
It also gives the fiber a certain degree of smoothness, so that the fiber is not damaged during the friction process, and has a good hand feeling. It can smoothly go through the winding, stretching, drying, and other processes during spinning.
It can also eliminate the effect of static in textile processing, reduce abnormalities such as wool and broken ends, and ensure the quality of fiber products.