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Dyeing, Printing and Finishing Continuous washing parameters and their effects on pre- treatment results Table 1: Water consumption by Muhammad Moosa Abdul Rehman1 and Muhammad Awais Imran2. in wet processing Process Water consumed washing efficiency in a Cold-Pad-Batch Abstract: This paper presents...

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Dyeing, Printing and Finishing

Continuous washing parameters and their effects on pre-treatment results Table 1: Water consumption by Muhammad Moosa Abdul Rehman1 and Muhammad Awais Imran2. Abstract: This paper presents some practical hints for efficient pretreatment of the some fabrics including (PC, PC denier & CVC denier) in a continuous process. The work was performed in a well-known textile mill in Karachi. The study was done to determine effect of some important parameters to save on water and energy (steam and electricity) consumption. This paper may help the industry to determine the maximum efficiency in a continuous open-width washing process. The authors would like to acknowledge the Assistant Manager Bleaching, Mr. Faraz Farooqui, Gul Ahmed Textile Mills Ltd. for useful suggestions. Key Words: Tegewa (The Association of Textile Auxiliaries’ Suppliers), Water Flow rate, Absorbency, Cold Pad Batch, Turbulence.

1. Introduction Washing of the pretreated cotton fabric is an essential part of the preparation or pretreatment processes, where all the impurities and non-cellulosic components of the material are removed by a continuous rinsing process. The excessive quantities of water used in the textile wet processing stage add to the running cost of preparatory processes. Consumption of water in the wet processing of the cotton fabrics is shown in Table 1[1]. It is important to note that excessive proportion of water is being used at the pretreatment stage. This article highlights the effect of various washing parameters such as speed, water flow rate and temperature at a constant pressure of a padder on the

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washing efficiency in a Cold-Pad-Batch (CPB) bleaching process for some fabrics including polyester/cotton blend, CVC and CVC denier. The washing efficiency was determined by parameters of absorbency, Tegewa rating and whiteness and effort has been made to determine the optimum conditions. It may however, be pointed out that the results of the findings are not confined to washing in the CPB process, but are also applicable in general to all the washing off processes including desizing, scouring, bleaching, mercerizing, dyeing, printing and even some finishing processes. Complete removal of impurities after scouring and bleaching of the cotton fabrics is very important because their inadvertent presence is detrimental for subsequent processing. Even for the white fabrics, it affects absorbency, colour and handle of the fabric. Along with these considerations one has to keep in mind the quantity of water used to obtain the optimum results, because firstly it is not free of cost and more importantly the effluent has to be treated to achieve certain standards of purity at considerable cost. 1.1. Background theory In order to remove the impurities and residual chemicals, a fabric has undergone different treatments during pretreatment, desizing, scouring and bleaching, The washing process after pretreatment discussed here is the one which is carried out in the open width washing machine. In general the washing process can be divided into three phases.[3] (a) loosening of extraneous matter, (b) transfer of extraneous matter and (c) removal of extraneous matter. In the first phase, the extraneous matter must swell and loosen as quickly as possible. In the second phase the matter is transported by

in wet processing Process

Water consumed

Bleaching

38%

Dyeing

16%

Printing

8%

Boiler

14%

Other uses

24%

diffusion to the layer of liquor flowing next to the surface of the textiles. In the third phase the extraneous matter is carried away by flow of the washing liquor and movement of goods. In actual practice all the three phases overlap and therefore, the optimum washing is characterized by maximum efficiency combined with significant savings in water, electricity, heat and chemicals. The efficiency of the washing action is promoted by mechanical movement, flow rate and counter-flow to the run goods. 1.2. Washing efficiency The washing process is characterized by its washing efficiency, which is the amount of the impurities removed divided by the total amount that could have been removed. The washing efficiency depends on the following factors.  Machine Design.  Dipping roll.  Roll configuration.  Numbers of roll.  Roll diameter.  Simulator height.  Water flow rate, fresh water addition techniques and water temperature.  Impurities and chemical concentration.  Counter-current flow, water flow pattern and water bath design.  Fabric speed, fabric GSM/GLM and fabric contamination.  Fabric tension.  Fibre content and yarn twist.  Last process efficiency.

Dyeing, Printing and Finishing The picture shows that the cleanest product is washed with the cleanest water and and the most contaminated product is washed with dirtiest water.





Although all these parameters are significant, yet some can be controlled, while some parameters would be out of control, if not considered before choosing the washing equipment, for example machine design, roll configuration, water bath design, etc. 1.3 Counter-current flow The countercurrent washing method is now common in textile washing process due to its efficient and economical processing techniques. Basically, the least contaminated water from the final wash is reused for the next-to-last wash and so on until the water reaches the first wash stage,[2] after which it is discharged. This technique is useful for washing after continuous bleaching, dyeing and printing process. The counter-current systems are vertical and horizontal but the “horizontal” or inclined washing are more efficient because of the inherent countercurrent nature of water flow within the process. The mechanical construction of an inclined or horizontal countercurrent washer is much better than a traditional vertical washer. However, sloppy roll settings, weak or undersized rolls, unevenness, bends, bows, biases and bearing play or other misalignments within the machine are much more important in a horizontal or inclined washer because the weight of water pressing down on the fabric can cause it to sag, balloon or stretch. If properly constructed and maintained, the horizontal or the inclined washers can produce high quality fabrics, while saving money and water. The purpose of washing is to reduce the amount of impurities in the substrate, therefore, as much water as possible must be removed between sequential washing steps in multistage washing operations. The water containing contaminants that is not removed is “carried over” into the next step, contributing to washing inefficiency. Therefore, proper draining in the batch drop/fill washing and proper

into the last wash of the washing series. The wastewater is then circulated from the last step to the next preceding step and so on up the line. The cleanest product is washed with the cleanest water and and the most contaminated product is washed with dirtiest water. The system leads to huge savings in water use.

2. Experiment extraction between steps in the continuous washing process are important. Often, almost 350% water on weight of goods is carried over in a typical drop/fill procedure. The operations of countercurrent flow are given as under:  Counter-current washing is often practiced by introducing raw water

2.1 Materials: As shown in table 2. 2.2 Apparatus: Continuous washing range with 4 washing boxes, each containing 3500 liters of water. 2.3 Method: Continuous washing, counter-flow, up-and-down threading, without soaping. Drain at first box and water inlet flow from 4th box. The machine speed range 30-80 meters/min. (Table 3 and 4)

Table 2: Materials Fabrics

Construction

GSM / GLM

Width

PC

76 x 52/30 x 30

110/237

85’’

PC Denier

76 x 44/30 x 150D

94/180

75”

CVC Denier

114 x 62/75D x 30

92/219

94’’

Table 3: Method and machines Continuous washing, counter-flow, up-and-down threading, without soaping Chamber

Temperature

Padder Pressure

1st

95oC

2 Bar

2nd

85oC

3 Bar

3rd

75oC

3 Bar

4th

65oC

4 Bar

Table 4: Requirements of pretreatment results for pigment printing Fabrics

pH

Tegewa

Absorbency

Whiteness

Cotton

6-7

>3

5mm-20mm

67-72

PC

6-7

>3

5mm-20mm

67-72

PC Denier

6-7

>3

5mm-20mm

67-72

CVC

6-7

>3

5mm-20mm

67-72

CVC Denier

6-7

-

5mm-20mm

67-72

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Dyeing, Printing and Finishing 3. Results and discussion

Table 5

Material ONE CVC Denier Fabric/Const.

Padder Pressure

GSM

GLM

Width

Speed

Total Meters

CVC 114 x 62/75D x 30

Std

92

219

94’’

70

5000

Normal Operation Temp. 1,2,3,4

Whiteness

Flow Rate

Tegewa

Absorbency

pH

95,85,80,70

70-80

6-7

7-8

5 mm

6.5

Pretreated via cold pad batch unwashed fabric was taken X length, each length and weight of fabric is mentioned and run at a speed accordingly in meters/min, the counter flow was set and water flow rate, speed and temperature were analyzed on the basis of results. The padder pressure in each washing box was set according to standard (depend on the construction of fabric) which is given above in table. For GLM calculation: GLM = GSM X Fabric width/39.37

Recommended Operation Temp. 1,2,3,4

Whiteness

Flow Rate

Tegewa

Absorbency

pH

80,75,70,60

70-80

3-4

7-8

5 mm

6.5

To calculate the fabric weight (FW) passing through the machine per minute: FW = GLM X Machine Speed / 1000 Taking 100% pick-up, the total amount of water (TW) required was calculated as:

Material TWO PC Denier Fabric

TW = FW X Pick-up / 100

Fabric/Const.

Padder Pressure

GSM

GLM

Width

Speed

Total Meters

The Water flow rate is expressed in l/kg (liters per kg):

76 x 44/30 x 150D

Std

94

180

75”

65

5650

Water Flow Rate = Liters/min x 1000 / GLM x Speed.

Normal Operation

Please refer to table 5 and following observations.

Temp. 1, 2, 3, 4

Whiteness

Flow Rate

Tegewa

Absorbency

pH

95, 85, 80, 70

65-72

8.5

2

15mm

6.5

Material ONE 

Recommended Operation Temp. 1,2,3,4

Whiteness

Flow Rate

Tegewa

Absorbency

pH

95, 90, 85, 70

65-72

6-7

3*

15 mm

6.5

Material THREE PC Fabric 

Fabric/Const.

Padder Pressure

GSM

GLM

Width

Speed

Total Meters

76 x 56/30 x 30

Std

106

230

85”

65

6000 

Normal Operation Temp. 1, 2, 3, 4

Whiteness

Flow Rate

Tegewa

Absorbency

pH

95, 85, 80, 70

65-72

6-7

3-4

10 mm

6.5

Recommended Operation

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Temp. 1, 2, 3, 4

Whiteness

Whiteness

Tegewa

Absorbency

pH

90, 80, 70, 60

65-72

6

3-4

10 mm

6.5



We can save water and steam consumption by reducing water flow rate and by lowering the temperature, because there is no concept of size material (Tegewa) in said material due to denier polyester is interlaced in warp direction. Secondly, this material is processed in low recipe during cold pad bleaching so less amount of chemicals present within the fabric structure. Secondly, this material is processed in low recipe during cold pad bleaching so less amount of chemicals are present within the fabric structure. As far absorbency, no requirement here because of very fine structure of the fabric which does not create any problem in pigment printing. The major advantage is that we can super impose the CVC filament fabric in washing machine, because fabric thickness is comparatively low but this is a little complicated and needs an extra winder for batching.

Dyeing, Printing and Finishing Material TWO

4. Conclusions

In the “Normal operation’ the flow rate was high, but you can see Tegewa rating is not improved. We have observed that the same Tegewa result on flow rate at 6.5; it shows that improvement is required in Tegewa rating.

The core focus of this report was on water flow rate, as the key factor of washing efficiency is turbulence. The flow rate is set on the basis of results, such as contamination in water and conductivity parameters [4]. It is observed that water flow rate have shown very efficient results in between 56 liters/kg and authors recommend the following optimized water flow rate, which is found efficient and effective water flow rate for cold bleached CVC, PC, PC denier Fabrics as shown in table 6.



Alteration in Cold Pad Batch Recipe: To improve desizing results, use of sodium persulfate is recommended. Increase quantity of Sodium hydroxide in Cold Pad Batch bleaching. To run at optimized Speed (50-55 m/min) by keeping flow rate 6 or 6.5 (Increase in Interaction with Hot water). Increase the temperature as given in the recommended operation.

 



Material THREE We can take results as good as the existing process by changing following parameters, 

Flow rate could be set 5 litre/kg or even at 4 litre/kg, but we have analyzed that the contamination, TDS remains in bath and hence in fabric which is adverse effect of low water flow rate so 6 litre/kg is effective. By increasing the speed (more turbulence of water, the turbulence in the liquor produces a high liquor exchange).The diffusion into the core of the fibers begins immediately and makes additional penetration time superfluous. Lower the temperature of tanks as given in recommended operation. Besides saving energy, lower temperature also increases life of the padder.





S. No 1

2 3 4

[Recommended water flow rate is only for cold pad bleached PC, CVC denier fabric not for the desized and 100% cotton fabric. For 100% cotton materials, water flow rate may be increased to 8-9 liters per kg]. This recommended water flow rate is set by considering the water properties as well such as turbidity, conductivity, pH, TDS, TSS and colour.

In this report, it has been analysed that washing process can be effective and efficient by considering and controlling the simple parameters Table 6 such as water Recommended water flow rate flow rate, its temperature Water Flow Efficiency Tegewa Absorbency pH and speed of Rate (l/kg) the fabric. It is important to 3-4 Relatively low 2 5-10 mm 6.5 consider the fabric type, 5-6 Optimum >3 10-15 mm 6.5 construction and level of 6-7 Normal >3 15-20 mm 6.5 impurities in the fabric. >7.5 Normal >3 15-20 mm 6.5 Again, the

parameters which are given earlier in washing efficiency heading, we can used all parameters for available washing system or choosing new washing equipment, so we can save energy and water consumption by simply altering the said parameters.

References [1] Water conservation in textile industry, PTJ November 2009. [2] http://infohouse.p2ric.org/ref/01 /0069203.pdf. [3] Chemical Technology of Textile Pretreatment, by Karmakar, Elsevier Science. [4] Comments Asst. Manager bleaching, Mr. Faraz Farooqui, BE Textile, ME Textile (Russia).

Study References   

Wet Processing of Cellulosic Textiles, by Dr. Ahmed Niaz. Cellulosic Dyeing, by John Shore, SDC. Chemical Technology of Textile fibre, by E.R Trotman.

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