The polyester filament production process has rapidly advanced with the progress of mechanical manufacturing and chemical processing techniques, resulting in various types of processes. It can be categorized into conventional spinning, medium-speed, and high-speed spinning processes based on spinning speed. According to Polyester raw materials, it can be divided into melt spinning and chip spinning. Melt spinning involves directly feeding molten polymer from the polymerization reactor into the spinning machine for spinning. Chip spinning, on the other hand, involves melting chips produced through polymerization, solidifying, and pre-spinning drying using a screw extruder before spinning. The processes include three-step, two-step, and one-step methods.

Conventional Spinning Process

Conventional spinning, also known as low-speed spinning, was one of the earliest industrialized production processes. It follows a three-step process of spinning, drawing, and false twisting (UDY-DY-TY). The spinning speed ranges from 1000 to 1500m/min, drawing and twisting speeds from 600 to 1100m/min, and false twisting speed from 120 to 160m/min, with a post-processing drawing ratio of 3.5 to 4.2 times (before false twisting). It can produce filaments ranging from 33 to 167dtex.

Conventional spinning can produce both stretched and deformed yarn, which is characterized by a mature process, stable operation of equipment, good product quality, and good dyeing uniformity.

Medium-Speed Spinning Process

Medium-speed spinning, a two-step process, produces medium-oriented yarn (MOY) with a spinning speed of 1800 to 2500m/min. There are two routes for medium-speed spinning:

MOY-DY Process: Involves medium-speed spinning and low-speed drawing. Spinning speed ranges from 1800 to 2500m/min, and drawing and twisting speeds range from 800 to 1200m/min, producing drawn yarns with a range of 33 to 167dtex. The common ones are 75dtex and 50dtex. The production efficiency is lower than that of high-speed spinning, and the product quality is worse than that of conventional spinning.

MOY-DTY Process: Involves medium-speed spinning and high-speed drawing-twisting. MOY’s residual drawing ratio is 2.1 to 2.4 times, with a drawing-twisting speed of 400 to 500m/min, producing textured yarns of 55 to 88dtex. This process is less efficient and produces lower-quality yarn compared to POY-DTY.

High-Speed Spinning Process

High-speed spinning, with speeds ranging from 3000 to 3600m/min, produces partially oriented yarn (POY) through three routes.

POY-DTY Process: Utilizes high-speed spinning and high-speed drawing-twisting, representing a typical two-step process for producing textured yarns. Post-processing speed for POY is typically 400 to 800m/min, producing 50 to 167dtex drawn yarns (DTY) with high efficiency and quality. It is characterized by short process flow, high production efficiency, and low investment in infrastructure. POY can be stored for a long time and transported long distances. DTY quality is excellent.

POY-TY Process: Involves high-speed spinning and low-speed false twisting (rotor false twisting), producing drawn yarns of 111 to 167dtex. This process is economically unreasonable.

POY-DY Process: Involves high-speed spinning and low-speed drawing-twisting, producing drawn yarns of 55 to 110dtex. Using general drawing-twisting machines, this process results in DY with lower performance compared to UDY.

Spinning-Drawing One-Step Process

This process combines spinning and drawing into a single step using a spinning-drawing integrated machine, resulting in Fully Drawn Yarn (FDY). There are two variations: one with a spinning speed of 900 to 1500m/min, a drawing speed of 3200 to 4000m/min, and a drawing ratio of 3.5, producing drawn yarns of 55 to 165dtex; the other with a spinning speed of 2600 to 3500m/min, drawing speed of 5100 to 5500m/min.

Other Spinning Processes

Apart from the mentioned processes, there are additional polyester filament production methods such as High Oriented Yarn (HOY) and High Crystalline Yarn (HCY). HOY, also known as Fully Oriented Yarn, involves a one-step ultra-high-speed spinning process with a spinning winding speed of 5500 to 6000m/min. Due to a large increase in the nozzle stretch, the orientation of the fiber is greatly improved. But the crystalline particles are large, the orientation of the amorphous region is low, and the dyeing performance of the fiber is good, but the elongation length is too large (about 40%), even if the winding speed is increased to 7000 ~ 8000m/min, the elongation length still can not meet the general consumption requirements, and it is still in the experimental production stage.

A step drawing process of high-speed spinning heat pipe prepared high crystalline filament (HCY). In the ordinary high-speed spinning process, a heat pipe is added before the fiber solidifies and bunched with oil, and hot air heats the filament above the glass transition temperature (below the softening point), so that the solidified filament can be further stretched under the action of winding traction.