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Hank yarn dyeing process:
Colouration( dyeing) of textile materials ie fibres, yarns, fabrics, and garments is carried out by using different dyeing methods according to the form of the textile materials. If the textile material is dyed in the yarn form, the used dyeing process is known as the yarn dyeing process. There are two methods used to dye the yarn:
1- Hank dyeing method.
2- Package dyeing method.
Hank dyeing method:
If the yarn is dyed in the hank form, this yarn dyeing process is called the hank dyeing method of yarn dyeing. The hank dyeing process is carried out in an open vessel. The hank dyeing method has temperature limitations. The hank dyeing gets suitable for the dyeing of those yarn in which the colour gets fixed at 100-degree centigrade maximum. The different processes involved in the hank dyeing method are given below:
Normally, the yarn is sold in package form( cone or cheese) now these days. There may be two possibilities ie dyer already has the required yarn in either hank form or in the package form. If the yarn is already available with dyer in the hank form, the hank preparation does not require in this condition. If the yarn is available with the dyer in the package form then the hank preparation process is required. The hanks are prepared with the help of a yarn reeling machine. If you work at a very small scale, the single-end yarn reeling machine gets useful. In the case of large-scale work, multi-ends yarn reeling is used to prepare the hanks of yarn.
Scouring, bleaching and dyeing:
These processes are carried out in the hank dyeing manually or mechanical hank dyeing machine. The yarn hanks are loaded into the machine. The hanks are hung up on the rotating cylinders. The required water level is maintained in the colour and chemical trough. Now, the required chemicals liquor is prepared in the side tank step by step and the dosing of each liquor is done one by one according to the process.
Structure and working of hank dyeing machine:
The basic structure of the semi-automatic hank dyeing machine is given below:
Colour and chemicals trough:
The colour and chemicals trough is made of stainless steel. The corrosion-resistant stainless steel is used for this trough. The water is filled in this trough during processing. The colour or chemical dosing is also carried out in this trough through the side tank. The yarn is impregnated with the colour or chemical liquor during the process. If the machine has a spray unit, the liquor is collected into this trough after spraying. The water supply pipe is connected at the top of the trough and the drainage pipe is connected at the bottom of the trough. A steam pipe is connected with the trough to maintain the required liquor temperature. This is the fixed part of the machine.
Side tank and colour dosing system:
A side tank is used for the preparation of colour or chemical liquor and its dosing into the trough. A small stainless steel tank is used, and the required amount of the chemical or colour is dissolved in the side tank. A motorised stirrer is fitted inside the side tank. The stirrer helps to blend and mix the colour or chemicals in the water properly. The side tank is connected to the trough with the help of a pipe. The controlled dosing of liquor is done manually by regulating the liquor dosing valve.
Hank rotating cylinders and spray unit:
The hanks are hung upon hank rotating cylinders. These cylinders rotate in clockwise and anticlockwise directions intermittently. The perforated liquor spray pipes are also fitted with rotating cylinders and rotate together with these cylinders. The liquor sprays upon hanks by these perforated pipes.
Liquor circulation pump:
The inlet of the liquor circulation pump is connected to the colour and chemical trough. The pump takes the liquor and feeds it into the perforated spray popes. The liquor coming out of spray pipis drops onto the colour and chemicals trough.
Motor and reduction gearbox arrangement:
A suitable reduction gearing arrangement is used to control the rotating speed of the hank rotating cylinders. The electric motor provides a rotating motion that is transferred to the hank rotating cylinders through the gearbox.
In some types of yarns, the dyeing temperature is increased and reduced gradually. The cooling coil helps to bring the below dye bath temperature gradually.
The steam injection into the trough is carried out by a steam pipe connected between the steam supply and the liquor trough. An automatic steam supply valve is connected with this steam pipe to switch on/off the steam supply. If electrical heaters are used, this steam supply pipe is not required.
Water supply connection:
The liquor trough is connected with a freshwater supply pipe. A valve is used to start/stop the water supply in the liquor trough as per requirement.
Drainage pipe and valve:
The drainage pipe and valve are fitted at the bottom of the liquor trough. The water is drained into the wastewater line by this valve.
The sensing part of the temperature sensor is fitted inside the trough and it gets in contact with liquor. The temperature sensor is connected to the digital controller through a cable. It sends a signal to the digital controller.
Digital process controller:
Basically, it controls the whole dyeing process. The required temperature is preset in the controller. The steam supply or electric supply of the heater is controlled by this digital controller. The processing time of each process is preset in this digital controller.
If we dye cotton yarn or any other cellulosic yarns, the scouring of the yarn gets compulsory. The natural impurities present in the yarn are removed in this process. First of all, the yarn is treated with caustic soda, a wetting agent, and a sequesting agent.
If the re-generated and manmade yarns ie viscose rayon, bamboo rayon, modal, and Tencel are dyed, the yarn is washed with hot water and treated with a wetting agent only.
The bleaching process is used for natural cellulosic fibre only before dyeing. The hydrogen peroxide and peroxide stabilizing agents are added to the bath in the next step. The temperature is raised up to 90 degrees centigrade. The bath is drained finally. The yarn is now washed with fresh water and treated with peroxide killer to remove the residue of hydrogen peroxide. The yarn is treated with mild acetic to neutralise the material. The yarn gets ready for the colouration process. This process gets bypassed in the case of re-generated and manmade yarns ie viscose rayon, bamboo rayon, modal, and Tencel or synthetic yarns.
The required water level is maintained in the colour and chemical trough. Now, the dye and other chemicals are dissolved in the side tank. The dosing of the liquor is done gradually in the dye bath. The fixing agent and exhausting agent are dosed in the dye bath according to the standard dyeing process. The temperature is raised up to a certain point. As the required shade is achieved, the dye bath is drained. Next, soaping is done to remove the unfixed colour from the yarn and the yarn is washed with fresh water and neutralised with mild acetic acid. Finally, yarn is treated with a fixing agent and the bath is drained. the material is taken out from the machine.
The material coming out of the machine contains a lot of moisture in it. The yarn hanks are placed into the hydro extractor. The material is placed in the machine in such a way that it could not affect the centre of gravity of the machine after loading the material. In the other words, the weight of the material should be equally distributed in the machine during material placement. When the machine rotates, the maximum amount of water eliminates from the yarn due to centrifugal force getting developed during machine rotation. The yarn is taken out of the machine now.
The yarn still contains an excess amount of water in it after the hydro extraction process. Now, this moisture is evaporated by drying the yarn either by sun-drying or in a hot air oven. In the sun drying process, the hanks are hung upon the wooden structure. The yarn is exposed to the sunlight, the moisture is evaporated, and the yarn is dried after a certain exposure yarn to sunlight.
If the yarn is dried in a hot air oven, the yarn is placed in the hot air chamber specially designed for hank yarn. A blower fan blows the hot air upon the yarn. Electrical heaters or steam-heated pipes are used to heat the air. The heating temperature is kept around 105-110 degrees centigrade. The thermostat is used to control the inside temperature of the drying chamber.
Hank to cone winding:
The hank yarn can not be used directly in the weaving knitting or stitching process. The hank yarn is required to convert it into the cone form. Now, the dried yarn passes through the hank to the cone winding machine. The hanks are converted into the cone form after this process.
Please click on the below video link to watch the full article in Hindi:
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CHEMICAL COMPOSITION OF COTTON FIBRE, CHEMICAL FORMULA OF COTTON FIBRE, CROSS SECTIONAL VIEW OF THE COTTON FIBRE
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GENERAL TERMS TO BE USED IN TEXTILE
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