Methods of Stretching
Time：
2025-06-05 10:08
Stretching occurs because the velocity of the filament extruded from the spinneret is lower than the moving speed of the winding device, i.e., the stretching speed is higher than the spinning speed, causing the diameter of the as-spun fiber to be smaller than that of the spinneret orifice. In chemical fiber production, stretching can be carried out continuously following the spinning process, or separately from the spinning process using wound yarn or as-spun fibers pre-wound on bobbins or in silk cans.
The stretching of as-spun fibers can be completed in one step, or it may require (stage-wise stretching). The total draw ratio of the fiber is the product of the draw ratios of each stage. Generally, the total draw ratio for melt-spun fibers is approximately 3.0–7.0; for wet-spun fibers, the draw ratio can reach 8–12 times; for certain high-strength and high-modulus fibers produced by gel spinning, the draw ratio can reach tens to hundreds of times.
Due to differences in fiber types and spinning methods, the structure and properties of as-spun fibers vary, leading to different stretching conditions and methods. Classified by the medium in which the fiber is stretched, the main stretching methods are dry stretching, steam bath stretching, and wet stretching.
(1) Dry Stretching
During dry stretching, the as-spun fiber is surrounded by air, with heat transfer occurring between the fiber, the air medium, and the heater. Dry stretching can be further divided into room-temperature stretching and hot stretching. Room-temperature stretching is generally suitable for as-spun fibers with a glass transition temperature (Tg) near room temperature; hot stretching uses heated disks, plates, or ovens and is suitable for fibers with higher Tg, greater stretching stress, or thicker diameters. Heating raises the fiber temperature above Tg, promoting the movement of molecular chain segments, reducing stretching stress, and facilitating smooth stretching.
(2) Steam Bath Stretching
In steam bath stretching, the fiber is surrounded by saturated steam or superheated steam. Due to the heating effect and the plasticizing action of water molecules, the stretching stress of the fiber is significantly reduced.
(3) Wet Stretching
During wet stretching, the fiber is surrounded by a liquid medium, involving heat transfer and possibly mass transfer or even chemical reactions during the stretching process. As the fiber is completely immersed in the solution, heat and mass transfer between the fiber and the medium occur rapidly and uniformly. Additionally, the spray method, where hot water or hot oil is sprayed onto the fiber for simultaneous heating and stretching, is also a type of wet stretching.
In recent years, melt high-speed spinning (see 8.5.3) has been adopted, in which partially oriented yarns (POY) obtained are close to fully oriented yarns (FOY), eliminating the need for post-stretching and allowing direct use in textured yarn processing. There is also fully drawn yarn (FDY) produced by combining high-speed spinning with stretching, achieving spinning and stretching in one step.
Sumino Heavy Machinery Industry (Nanjing) Co., LTD.
CONTACT US
Adress：No. 116, Suyuan Avenue, Jiangning District, Nanjing
Messages