Polyester Yarn Manufacturing Process – From Chips to Yarn

Polyester yarn is currently an important yarn type among synthetic fiber yarns, because of the fastest development speed and the highest output.

The production of polyester yarn can be roughly divided into two steps: melt spinning and post-processing.

The manufacturing process of polyester yarn is shewn as below.

Melt Spinning Process

Melt spinning is a method in which the fiber-forming polymer melt flows out of a thin stream of melt through a spinning spinneret, and is cooled and solidified in ambient air (or water). Polyester filament yarn and polyester staple fiber are produced by melt spinning method. This method has short process, high spinning speed, spinning speed is generally 900 to 1200 meter/min, high-speed spinning can reach more than 3600 meter/min, low cost, but the number of spinneret holes is small, making polyester filament yarn The number of holes is 1 to 150, generally 300 to 800 holes when making polyester staple fibers, and the highest can reach 1000 to 2600 holes, or even more. If the conventional circular spinneret holes are used, the cross-section of the spun fibers is mostly circular; if the special-shaped spinneret holes are used, the spun fiber cross-sections are special-shaped. This method is suitable for polyester fibers and other polymers that can melt, flow easily, and are not easily decomposed.

According to the spinning speed, the melt spinning process of polyester yarn can be divided into conventional spinning process, medium-speed spinning process, high-speed spinning process and ultra-high-speed spinning process.

Generally speaking, the product after the conventional spinning process is polyester undrawn yarn (UDY), the product after the medium-speed spinning process is polyester medium-oriented yarn (MOY), the product after the high-speed spinning process is polyester pre-oriented yarn (POY), and the product after the ultra-high-speed spinning process is polyester high-oriented yarn (HOY) or polyester fully drawn yarn (FDY).

The table below is for your better understanding.

We will use high-speed spinning, the most commonly used process route for the production of textured yarns, to illustrate the melt spinning process of polyester yarn. 

The spinning speed of high-speed spinning is 3000 to 3600 meter/min, and the product after this process is pre-oriented yarn (POY). 

The principle of the process is to feed polyester chips into the chips hopper, then melt them, and ensure that the melt flows stably in the screw extruder. 

In the screw extruder, the melt is filtered and pressed into the spinneret to spray out a thin stream of melt, and then quickly condensed by cold air to form a solidified tow fiber. 

During this process, pre-stretching of the polyester yarn is generated due to the function of the yarn guide, and it also makes the fiber thinner. 

The nascent fiber is wound into a roll with a certain shape by the winding system. 

Post-processing

The post-processing of polyester yarn refers to the processing that can make the spun nascent  polyester fiber suitable for textile production. After a series of post-processing, the structure and properties of the polyester yarn are improved. 

Post-processing can be roughly divided into the following five steps: POY to DTY, twisting, hanking, dyeing, and winding. 

POY to DTY

Combining the drawing and twisting process on the same machine, the produced yarn is called drawn textured yarn – DTY.

Drawn textured yarn (DTY), generally using POY as raw material, is a low-elasticity yarn obtained by one-step stretching and deformation; it has a certain elasticity, and the hand feel is not as soft as conventional textured yarn, but the quality is stable, and the strength and elongation have met the requirements of taking.

The processing technology of polyester DTY is slightly complicated, which is not discussed here, but roughly includes the following steps:

A. Polyester POY raw material feeding;

B. Stretching; stretch the polyester POY raw material to obtain a product; the stretching ratio is generally 1-1.1 times;

C. Heat deformation of product a to obtain product b; the temperature of heating deformation is 160-180 °C;

D. Cooling the product b to obtain the product c;

E. Perform false twisting treatment on product c to obtain product d;

The products F and d are processed by the network nozzle to obtain the product e; the network pressure of the network nozzle is 1.4-1.6 kg;

G. Heat and shape product e to obtain product f;

H. Perform oiling and winding treatment on the f product in turn to obtain the finished polyester DTY.

The polyester DTY obtained through the above steps has basically met the requirements of textile yarns, but in order to obtain better properties such as elasticity and wear resistance, and to dye different colors, subsequent processes are required.

Twisting Process

Twisting process of polyester yarn refers to combining two or several single yarns together and twisting them through a machine to produce strong, elastic strands, with the properties of uniform thickness, smooth surface, and wear-resistance,  to meet the requirements of the subsequent process.

In fact, in the previous step “POY to DTY”, some twist was also imparted to the polyester yarn. But for some textiles that require high-twist yarns as raw materials, these twists are not enough.

Hanking Process

The purpose of hanking is to loosen the twisted polyester yarn so that the dye can penetrate into the yarn completely during the dyeing process.

During the process of hanking, workers will add some water appropriately to tighten the yarn a little bit.

After hanking, the product becomes “bread yarn”. Then it will be packed, bagged, and then transported to our dyeing factory for dyeing.

Dyeing Process

In the existing dyeing process, the dyeing of high-elastic polyester yarn usually adopts the hank dyeing process of bread yarn. The hank dyeing of polyester yarn is to stack the fiber yarn in the dyeing machine in a hank shape, and use a pump or mechanical device to circulate or agitate the dye liquor, so that the polyester yarn can be dyed uniformly.

Before the mass dyeing, professional color staff will prepare the color formula according to the customer’s sample and dye it with a dyeing machine. Then, they compare the dyed sample with the customer’s sample under the specified lighting environment. After confirming that there is no color difference, mass dyeing will be carried out.

Dyeing is a link that tests experience and technology the most, because this process requires not only precise dye ratios, but also temperature control. At the same time, workers must add additives at appropriate times based on experience for the corresponding functions, such as waterproof, heat preservation, antibacterial, etc. 

Winding Process

Winding is the last process of yarn post-processing.  Its task is to process the hanked and dyed polyester yarn into the tube yarn, which is the polyester yarn product that our customer can directly use to produce the textile products, such as socks and medical bandages. 

Before winding, workers will place the dyed bread polyester yarn in a cool place and dry it with the wind.  This process generally lasts 2 to 3 days. 

Then the workers put the dried bread yarn on a shelf, spread it out evenly, and cut off the surface yarn that has been exposed to air for a long time. 

When it’s all done, workers will place it on the machine to wind it to the final polyester yarn product. 

After winding, the tube polyester yarn will be placed on a shelf, and after passing the inspection by the workers, it will be packed, stored and sent out to our customers.