Benefits of using some mechanical improvements in knit textile dyeing

Dr.S.M Mominul Alam(Dalim), A.K.M Nayab-Ul-Hossain,      Email:, 
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The advancements in mechanical development in different stages of knit textile dyeing have a significant impact on the aesthetic and functionality of material. Advances in the textile dyeing machinery & dispensing system facilitate production of diverse desirable properties, and are therefore of great interest in the production of textile products with enhanced performance characteristics. Some of such latest developments are helping in better process control and improving dyeing and dyehouse efficiency.

  1. Introduction:

In the coloration process and other wet process operations so many parameters need to be checked & controlled. The development of modern science provide new ideology to monitor & adjust these check points. This article will discuss briefly some of such mechanical development involved in textile dyeing especially in knit fabric dyeing.

2. Improvement in pH checking:

Figure 1: Typical pH meter used inside dyeing machine for real time checking of pH.
Figure 1: Typical pH meter used inside dyeing machine for real time checking of pH.

PH is one of the basic parameters of dyeing. It should be checked at so many stages. In the beginning of dyeing, the water should be carefully adjusted to a neutral to slightly acidic PH, as otherwise premature hydrolysis of dyestuff will take place and cause (a) uneven dyeing and (b) lighter depths than the previous batches (c) batch to batch variation will occur. If the fabric or yarn has not been neutralized properly the core alkali/acid will adversely affect the subsequent operations, forming patchy uneven dyeing. Finally after completing the dyeing, before unloading, if we do not keep the PH    neutral, alkaline PH will slowly hydrolyze the dyestuff in the fiber and acid P will tender the cotton fiber itself.   In dyeing floor operators take out water from machine and check PH manually. It takes at least 8-10 minutes .With the advancement of modern technology, now the machine water PH is checked and controlled automatically. This is basically a PH meter which is installed at the outlet water valve of machine. When machine comes to the program of controlling PH, the meter is automatically switched on and adjusts the PH and shows the value on monitor.  We can say that for a single time of PH check, it saves at least 8-10 minutes by using this meter. In full dyeing process, PH needs to be adjusted at least 5 times. So this saves approximately 1 hour in full process of dyeing.

Similar control equipment could be used in real-time measuring of other important parameters to better control the dyeing operation. Proper control can lead a process to blind dyeing. That in terns improve dyehouse performance in a great deal.

2.1 Specification of a pH meter installed in dyeing machine:

Enclosure Polycarbonate
Dimension Overall 1558x155x131mm
PH Seonsor Model 3500 – HT or 399-VP
4 mA 0 pH,20 mA 14 pH
Cell constant 3.000 /cm
temperature units  °C
Ambient Temperature 0 to 55 degree celsius


2.2 Advantage of using PH meter:

  • Help to reduce operation time
  • Fully automatic
  • Reading shows on monitor & also on plan board monitor.
  • Easy installment
  • Easy calibration process

3. Fully controllable continuous rinsing system:

Figure 2: Mechanical arrangements for ‘Aquachron’ system in a Sclavos dyeing machine being used in a Bangladeshi knit dyeing factory.
Figure 2: Mechanical arrangements for ‘Aquachron’ system in a Sclavos dyeing machine being used in a Bangladeshi knit dyeing factory.

Rinsing is very important for proper dyeing with maintaining good quality. This is very vital the fabric to be washed properly after pretreatment so that the bleached fabric is well prepared for dyeing. After the completion of dyeing, this is necessary to remove unfixed dyes from the surface of fabric. Washing plays a vital role here to remove unfixed dyes which ultimately resulting in good fastness quality. The two basic methods for washing off a fabric are the classical “drain-fill” method and “the continuous rinsing method”. Wash temperature, liter/min/chamber in machine can’t be controlled by these 2 methods & the possibility of thermal shock is more. “Aquachron”, a rinsing system developed by Sclavos which is a fully controllable continuous rinsing system.

By this system the controlling parameters are as wash temperature, Gradient / min, Lt. / min / chamber, Liters/kg. Aquachron enables to preheat the incoming water to the desired process temperature, regardless of flow rate and incoming water temperature, before the water arrives at the fabric. In this way, quality problems, which may arise due to thermal shock, are avoided and the ideal fabric environment is always obtained. By Aquachron system dyer can do rinsing without cooling, draining, filling and re-heating the liquor, thereby considerably reducing process time. Besides, being able to rinse whilst maintaining the temperature, Aquachron enables the rinsing with cooling gradient.

In this process the machine automatically drain (without stopping the fabric revolution) and will maintain the aforementioned machine levels throughout the process, resulting in significant savings in time and water consumption.

Similar facilities are available in other modern dyeing machines with slight variations. However reduced use of water in rinsing operation is very important as typically rinsing itself consumes more than 60-70 percent of water a complete process requires. Use of modern improvements in controlling rinsing is very vital.

4. Dry salt dosing System:

Figure 3: Picture and schematic diagram of dry salt dosing system.
Figure 3: Picture and schematic diagram of dry salt dosing system.

The textile substrate and dye molecule, not necessarily should have of homogeneous characteristics to combine with each other. In such cases, we require some catalyst to facilitated dyeing action of fabric.  Salt plays this crucial role of catalyst. Conventional methods of handling salt transfer use machine’s additional tank for diluting salt in fresh water and then transfer the dilution into the machine or stock tank. However this is a painful and time consuming job. Additionally in many cases fresh water usage increases liquor ratio. Modern Machine is equipped with separate hopper, which reserves full quantity of dry salt for specific batch. This salt quantity can be transferred or dosed automatically at any linear rate up to 50 kgs/min. Here, No need for fresh water use. No operator involvement.

5. Auto dispensing systems:

During the production of fabric dyeing, we waste time, chemicals, dyes. Sometimes fault occurs without having any fault. This is very important to control the quantity of chemical and dyestuff in order to obtain better achievement of RFT & exact batch to batch shade continuity. Conventional method is to weigh the dyes and chemicals manually & transfer into machine with the help of additional tank. Here is the possibility of faulty measure, wrong element selection and the process is time consuming. Automation, i.e- Auto dispensing is suitable to use sending for liquid chemicals and dyestuff preventing any acidic, corrosion, basic environment conditions. Powder form dye stuff can weigh, and dissolving in tanks and sending through the system.

Figure 4: Dyehouse automation using auto dispensing systems.
Figure 4: Dyehouse automation using auto dispensing systems.

5.1 Advantage of using auto dispensing:

  • Saving approx. 10-15 % chemical consumption.
  • Saving approx. 6 % salt and Soda-ash consumption.
  • Saving > 10 % time advantage from wasting time with manual steps.
  • Easily to find process mistakes through report that we can collect from software.
  • Saving time for labor cost and production time period.
  • All dyeing process were standardized and at the end all textile has same result like earlier.

6. Low liquor dyeing machine:

Figure 5: Low liquor dyeing machine
Figure 5: Low liquor dyeing machine

Water is the key element for dyeing. If the quantity of water used for dyeing is more, the quantity of chemicals will also be more which ultimately affects production cost. In conventional dyeing machine, the use of material to liquor ratio is high. If we tried to operate a winch machine at very low liquor ratio it would almost certainly get an unlevel dyeing & fabric ropes sometimes tangle. The pump require a minimum level of water to rotate water and fabric. So, water could not be conserved mush due to the mechanical limitations.

Machines with internal winches have been developed to make the passage of fabric smoother to reduce tension which reduces the process time and total energy consumption like water, electricity, quantity of chemicals etc. Modern machines provide the opportunity for rapid dyeing using high air & liquor flow, combined with fast heating and cooling rates.

7. Conclusion:

This study illustrates how to utilize the dyeing parameters efficiently and effectively by using mechanical benefits. More additional improvement can be made to make the dyeing process more efficient. Innovation has already started and this will be going forward day by day.

8. Reference:

  • Sclavos Dyeing Machine Factory(Greece)
  • Small Biz Textile machine spares-support.
  • Square Knit Fabrics Limited

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