What factors should be considered when choosing a melt spinning machine?
Spinning method introduction
There are about three current spinning methods. The first is wet spinning. During the spinning process, a spinning dope needs to be prepared and a coagulation bath is prepared, followed by steps such as heating, drawing, and yarn collection. The characteristics of wet spinning are that the number of spinneret holes is large, but the spinning speed is slow, which is suitable for spinning short fibers, while dry spinning is suitable for spinning filaments. Generally, the same kind of chemical fiber obtained by dry spinning has a uniform structure and better quality than wet spinning.
Wet spinning requires not only a wide variety of and bulky dope preparation and spinning preparation equipment, but also coagulation baths, circulation and recovery equipment. Because of the complex process flow, large investment in plant construction and equipment, and low spinning speed, the cost higher.
The second method is melt spinning, which is a molding method in which a polymer melt is used as a raw material and is spun by a melt spinning machine. Any polymer that can be melted or transformed into a viscous fluid state by heating without significant degradation can be spun by melt spinning. During melt spinning, the bulk polymer is melted in the screw extruder and sent to the spinning position, quantitatively fed into the spinning assembly by the spinning pump, filtered, and extruded from the capillary holes of the spinneret.
The liquid strands gradually solidify when passing through the cooling medium, and then are drawn into filaments at a high speed by the lower winding device. The filaments are primary fibers, which are post-processed into fibers. In order not to make the filaments cooling too fast to make the filaments difficult, isothermal melt spinning is sometimes used, that is, an isothermal greenhouse (called a spinning tunnel) is added to the spinneret. The stretching speed of the winding device is very high, up to 1500~3000 m/min, depending on the type of material and rheological properties.
The draw ratio of melt spinning is large, the yield is high, and it can be adjusted in a wide range. Polyester (polyester fibers), nylon and polypropylene fibers are melt spun. Compared with wet spinning, melt spinning has less pollution, does not need to recycle the coagulation bath and thus has a lower cost, is more environmentally friendly, and has a faster spinning speed.
The third is electrospinning, which is a special fiber manufacturing process in which a polymer solution or melt is jet-spun in a strong electric field. Under the action of the electric field, the droplet at the needle changes from a spherical shape to a conical shape (that is, a "Taylor cone") and extends from the tip of the cone to obtain fiber filaments. In this way, polymer filaments with nanometer diameters can be produced. Electrospinning also belongs to solution spinning. At this stage, it is mainly dealt with in the research stage, and has not yet been popularized in production. I won't introduce too much here.
How to choose a spinning machine?
According to the different properties of polymer, the spinning methods of chemical fiber mainly include melt spinning method and solution spinning method. In addition, there are special or unconventional spinning methods. Among them, according to the different solidification methods, solution spinning is divided into wet spinning and dry spinning two kinds. In the production of chemical fibers, most of them are produced by melt spinning, followed by wet spinning, only a small amount of them are produced by dry spinning or other unconventional spinning methods. In practice, you can choose your own spinning machine according to your own needs.
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