Yarn Dyeing:
The process of coloring yarn before knitting or weaving is called yarn dyeing. Yarn dyeing is a promising sector in Bangladesh. Today, we will learn in detail about yarn dyeing.
A yarn dyeing factory typically has the following sections:
1. Soft Winding
2. Dyeing Section
3. Finishing Section
4. Hard Winding Section
Yarn Dyeing Process:
1. Soft Winding
2. Batching
3. Dyeing
4. Hydro
5. Dryer
6. Hard Winding
7. Packing
8. Delivery
1. Soft Winding: Usually, the yarn produced in the spinning section comes to the yarn dyeing section in the form of paper cones. Soft winding is a process where the yarn is transferred from paper cones to plastic or steel cones.
Typically, polyester yarn is transferred to steel cones for dyeing because dyeing polyester yarn requires a temperature of 120 to 130 degrees Celsius.
Objectives of Soft Winding:
1. To make the yarn suitable for dyeing by softening it.
2. To transfer the yarn from paper cones to perforated plastic or steel cones.
3. To reduce the density of the yarn package.
4. To remove any impurities present in the yarn package.
There are three types of machines used for soft winding:
1. SSM PS 6 Plus W
2. SSM TW 2 WL
3. Fedis Machine
2. Batching: In this process, yarn packages are arranged in batches for dyeing. The soft yarn packages obtained from soft winding are loaded onto the carrier spindles. The yarn is manually pressed and secured to the spindles, preparing it completely for dyeing.
Yarn Dyeing: The yarn dyeing machine has three parts:
1. Preparation Tank
2. Dosing Tank
3. Main Tank
3. Yarn Dyeing Process:
1. Pretreatment
2. Dyeing
3. After Treatment
a) Pretreatment: After loading the yarn onto the carrier, demineralization is done first at a temperature of 50 degrees Celsius with a pH of 4.5. After this process, scouring and bleaching are done at 100 degrees Celsius for 40 minutes. Scouring removes any dust present in the yarn package, and bleaching removes the natural color of the yarn package, making it whiter. Acetic acid is used to neutralize the yarn package, and this process is done at 50 degrees Celsius for 20 minutes. After neutralization, a hot wash is done with the help of peroxide chemicals at 60 degrees Celsius for 20 minutes. Finally, the yarn package is drained and made completely ready for dyeing.
b) Dyeing Process: At the beginning of dyeing, the dye bath is prepared with a labeling agent and salt, and the machine is run at 60 degrees Celsius for 20 minutes with a pH of 6. Then, color dosing is done at 60 degrees Celsius for 20 minutes, and the machine is run for 10 minutes. Typically, the steaming temperature for yarn color is 80 degrees Celsius, and the machine is run at this temperature for 20 minutes. Then, cooling is done at 60 degrees Celsius, and soda dosing is done for 30 minutes at this temperature. The dyeing run time is 60 minutes for dark shades, 40 minutes for medium shades, and 30 minutes for light shades. Finally, if the sample is okay, the dye bath is drained.
c) After Treatment: After-treatment is crucial for fixing the color on the yarn. For after-treatment, the yarn package is first rinsed with cold water. After dyeing, the yarn is neutralized at 50 degrees Celsius for 20 minutes. After neutralization, the yarn is drained. Then, a hot wash is done with a softening agent. To soften the yarn package, finishing chemicals are used, and the machine is run at 60 degrees Celsius for 20 minutes. Finally, the yarn package is drained and unloaded.
4. Hydro and 5. Dryer: The hydro machine is used to completely remove excess water from the yarn package, and the dryer is used to completely dry the yarn package.
6. Hard Winding: Hard winding is the final process in yarn dyeing, where the dyed yarn is transferred from plastic or steel cones to paper cones.
7. Packing and 8. Delivery: Finally, the yarn package is packed and sent to the knitting section, where dyed fabric is produced through knitting.