Bath ratio is an important technological condition in water dyeing of rope fabric. The air-flow dyeing bath ratio is low, and the accuracy and stability of the bath ratio have great influence on the control of dyeing quality. In the air-flow dyeing process, how to control the bath ratio accurately, avoid the fluctuation of the bath ratio in the dyeing process, and reduce the influence of the factors of the bath ratio on the dyeing quality are discussed in this paper.
One
Composition of dyeing bath in airflow dyeing
A characteristic of airflow dyeing machine is that the main driving force of fabric circulation is high-speed airflow. In dyeing, besides the dye solution on the fabric surface, the circulating fabric is separated from the free dye solution. Therefore, strictly speaking, the dye bath in airflow dyeing consists of the following parts:
.bmp)
.bmp)
The first part
It is the dye solution in the filter and the circulating pipeline. The dye volume of this part should satisfy two conditions at the same time. One is the need to dissolve dyes adequately, the other is the need of the dye circulation in the main pump and pipeline circulating system. The dye volume of this part is constant, which is determined by the cylinder type of the airflow dyeing machine. The cylinder type has the same magnitude. Of course, the magnitude may vary among different equipment manufacturers.
The second part
It is the dyeing solution which is free flowing on the surface of the fabric without penetrating into the inner pore of the fiber after moisture absorption and swelling. It is called non-binding free dyeing solution.
Third parts
The dyeing solution that permeates into the inner pore of the fibers after moisture absorption and swelling is called binding dyeing solution.
The sum of the last two parts of dyeing liquids is actually the amount of liquids in the dyeing process of fabrics, which is related to the variety of fabrics and the weight of dyed fabrics. The same kind of fabrics has different weight of dyed fabrics, and the required liquids are different for different kinds of fabrics, even if the weight of dyed fabrics is different, the liquids required are also different. Old and regular varieties have experience values. For new varieties, they can be obtained through experiments. Therefore, in the dyeing process, the amount of liquid required for moisture absorption and swelling of any kind of fabric is known.
2. Water inflow mode and liquid level control of airflow dyeing
2.1-nbsp; water intake and liquid level control before fabric entering cylinder-nbsp;
In airflow dyeing, before entering the cylinder, the fabric first opens the water intake valve through the control system. The water intake is controlled automatically by the pre-set liquid level and the electrical control system. When the water intake reaches the set liquid level, the water intake valve closes automatically and stops the water intake. In fact, this amount of liquid is to meet the main pump and pipeline circulation and dissolution of dyes and chemicals required for the liquid volume, that is, the first part of the dye.
Because the air flow dyeing machine uses differential pressure transmitter analog precise liquid level control, the analog value is displayed on the control computer, not the actual liquid value. In the actual application process, when the equipment is initially installed and debugged, the actual liquid volume corresponding to each liquid level is obtained by calculating and adjusting the water level. Air flow dyeing machines and equipment manufacturers generally provide tables corresponding to the actual value of simulated liquid level and liquid volume. Therefore, the actual value of water inflow can be known by computer display of simulated liquid level. For the same cylinder type, the water inflow is the same, that is, the liquid level set by the control system is constant. In fact, it is the protective liquid level to meet the normal operation of the dye circulation system of the airflow dyeing machine. Once set, the general situation does not need to change at will.
It should be noted that the setting of the liquid level should not be higher than that of the PTFE pipe at the lowest position of the storage tank in the cylinder block. This part of the liquid volume of the air flow dyeing machine is generally stored in the filter at the bottom, and the liquid level is lower than that of the PTFE pipe at the lowest position of the storage tank. The reason is that the liquid level is lower than that of the PTFE pipe at the lowest position of the storage tank.
Firstly, if the water level is above the PTFE pipe, the fabric in the storage tank will be immersed in the dyeing solution, which will increase the resistance of the fabric. The fabric will not run smoothly in the storage tank, which will easily cause the cloth wrapping and pressing. At the same time, the water carrying capacity of the cloth will be increased and the resistance of the cloth lifting will be increased, which will increase the resistance of the cloth lifting. Fabric tension. Therefore, the air flow dyeing machine should not add the water required for the dyeing bath ratio to the cylinder at one time before the fabric is put into the cylinder, but take the way of automatic water replenishment for the second time when the fabric is put into the cylinder, because the water level of the air flow dyeing bath ratio exceeds the PTFE pipe at the lowest point of the storage tank.
Secondly, the exchange of air-flow dyed fabrics with dye solution is accomplished in the nozzle system. If in the storage tank, some of the fabrics piled up below are immersed in dye solution, while some of the fabrics piled up above are not immersed in dye solution, the probability of contact between each section of fabrics and dye solution will be inconsistent.Because of the difference in temperature and concentration of dyes and chemicals between this part of dye solution and the dye solution exchanged with the fabric in the nozzle system, it is easy to cause dyeing quality problems such as poor dyeing quality and poor dyeing segment.
This water level is too high, in fact, it increases the dyeing bath ratio and the dyeing production cost. On the premise that the bath ratio can meet the dyeing conditions, it is completely unnecessary to artificially increase the bath ratio.
2.2-nbsp; water intake and level control of fabric in cylinder
After the first water level is set, the rope fabric can enter the cylinder. At the same time, through dye circulation, the fabric will gradually absorb moisture and swell in the nozzle system, which will consume part of the dye solution. Therefore, the original liquid level in the cylinder will be reduced. At this time, the water intake valve will be opened through the control system for automatic water replenishment. The filling process of the fabric into the cylinder is a dynamic process, which is completely controlled by the automatic control system. When the dyeing liquid is lower than the set level, it will automatically replenish water. When the dyeing liquid reaches the set level, it will automatically stop replenishing water. When the fabric is completely in the cylinder, the liquid level is stable at the set level, the fabric will enter the cylinder. The process of replenishing water is completed.
The amount of water supply when the fabric is put into the cylinder is essentially the amount of liquid needed for the moisture absorption and swelling of the fabric in the cylinder, which is the sum of the dye liquids of the second and third parts mentioned above. This part of the liquid volume can be obtained by the following two methods:
The first method is to calculate the weight of the dyed fabric in the dyeing vat, because the water carrying capacity of the dyed fabric per unit weight is known. The water carrying capacity of the dyed fabric multiplied by the weight of the dyed fabric per unit weight is the liquid value of this part.
The second method is that for an airflow dyeing machine equipped with an intake flowmeter, this liquid value can also be obtained directly by measuring the intake flowmeter. It is worth noting that when calculating the bath ratio, if the moisture content of the fabric before entering the cylinder is higher and this moisture content has certain influence on the bath ratio, if the measurement value of this flowmeter is used to calculate the bath ratio as the liquid content required for the moisture absorption and swelling of the fabric, the moisture content of the fabric before entering the cylinder should also be included in the water content of the moisture content before entering the cylinder. Quantity. The reason is that under the same environmental conditions, the amount of liquid required for the moisture absorption and swelling of the fabric per unit weight of the same variety is constant, and it will not vary with the moisture content of the fabric before it enters the cylinder. In the process of airflow dyeing, the total amount of liquid required for the moisture absorption and swelling of the fabric in the cylinder is actually the moisture content of the fabric itself before it enters the cylinder, together with the amount of water supply when the fabric enters the cylinder.
3. Bath Ratio and Bath Ratio Control
3.1-nbsp; calculation of bath ratio
The bath ratio of airflow dyeing is smaller, cotton fabric is less than 1:4, polyester fabric is less than 1:3. When calculating the bath ratio, the water volume is generally the sum of the water intake before the fabric is put into the cylinder and the water carrying capacity after the fabric is absorbed and swollen. Taking a two-tube dyeing machine for 450 kg fabric as an example, the water intake of two-tube dyeing machine fabric before entering cylinder is 350 Kg, which is the water required for dye circulation system and dissolving agent, and is generally set to a constant value. If the total amount of water required for moisture absorption and swelling of 1kg pure cotton fabric is 3Kg, then the total amount of water required for 450kg pure cotton fabric is 1350Kg, then the dyeing bath ratio is 450Kg/(350Kg+1350Kg), that is, the bath ratio is about 1:3.77; & nbsp; if the total amount of water required for moisture absorption and swelling of 1kg pure polyester fabric is 1.5Kg, then 450Kg pure polyester. The total water requirement for the fabric is 675 Kg. The dyeing bath ratio is 450 Kg/(350 Kg+675 Kg), i.e. the bath ratio is about 1:2.27.
3.2-nbsp; fluctuation of bath ratio and control of bath ratio
In airflow dyeing, because of the low bath ratio and a little change in liquid volume, the bath ratio may fluctuate greatly, and the fluctuation of bath ratio is very disadvantageous to ensure the quality of dyeing and the reproducibility of dyeing results. Therefore, in order to control the bath ratio accurately, airflow dyeing must prevent the fluctuation of the bath ratio.
3.2.1-nbsp; factors affecting the fluctuation of bath ratio
In airflow dyeing, the main factors causing the fluctuation of bath ratio are as follows:
(1) Because of the need of dyeing process, in the process of dyeing, when various additives are needed to dissolve the material, if the material is recycled in the cylinder, the bath ratio will not change. If the external hydrate is used, the bath ratio will change. For example, in the case of 450Kg polyester dyed by the two-pipe machine mentioned above, if 200 kg of external clean water is fed into the feeding barrel to make the chemical, the actual water consumption is 350 Kg+675 Kg+200 Kg=1225 Kg, & nbsp, and the bath ratio is 450 Kg/1225 Kg=1:2.72 instead of 1:2.27, and the fluctuation of bath ratio is 20%.
(2) If the weight of the fabric dyed in different batches of the same variety and the same type of cylinder is not the same, the bath ratio will also be different. The bath ratio of 450 kg polyester fabric per VAT is 1:2.27. If 400 kg polyester fabric is dyed per vat, the water consumption for dyeing is 350 Kg+400× 1.5 Kg=950 Kg; the bath ratio is 400 Kg/950 Kg=1:2.38, & nbsp; the bath ratio increases and fluctuates about 5%.
(3) Even if the weight of each dyed tube is the same, the average water intake of each tube is the same before the fabric is put into the cylinder, and the dyeing bath ratio of the same variety and batch of fabrics may be inconsistent. For example, 900K polyester dyed in four-tube VAT (that is, the weight of the dyed fabric is twice that of the two-tube vat), if the water intake of the fabric before entering the VAT is 700 Kg (that is, twice as much as 350 Kg of the two-tube vat), the water consumption during dyeing is 700 Kg+900× 1.5 Kg=2050 Kg, and the bath ratio is 900 Kg/2050 Kg=1:2.15 instead of 1:2.27, and the bath ratio decreases by about 5%.
3.2.2-nbsp; prevent the fluctuation of bath ratioAccurate control of bath ratio
The air flow dyeing machine has a high degree of automation control system. It can accurately control the bath ratio by using the precise control of analog liquid level. However, in the practical application of some enterprises, there have been some problems of color difference or unequal dyeing quality caused by improper control of bath ratio. The main reasons are as follows: first, the working principle and mode of airflow dyeing machine are not well understood, the factors causing the fluctuation of bath ratio are not well understood, and there is a big deviation between the calculation of bath ratio and the actual bath ratio of dyeing production process; second, the dyeing idea of overflow machine is used to, the overflow dyeing bath is larger, and the bath is larger. The sensitivity of air flow dyeing machine to the change of liquid volume is lower, and the influence on dyeing quality is not obvious. The sensitivity of air flow dyeing machine to the change of liquid volume is higher, especially when some sensitive colors are dyed.
Therefore, in order to prevent the fluctuation of bath ratio, reduce the influence of bath ratio on dyeing quality and improve the one-time success rate of dyeing, the following measures should be taken:
(1) Deeply understand the composition of dyeing bath in airflow dyeing and accurately calculate the bath ratio. If the fabric has a high moisture content before dyeing, this part of the liquid content should be taken into account when calculating bath ratio.
(2) Dyeing process should take full account of the change of liquid volume during dyeing process, especially the addition of dyes and chemicals. Is the soluble material recycled or boiled water? If the process needs to be boiled water chemical, attention should be paid to the influence of water volume on bath ratio.
(3) When processing the same batch of fabrics in the same cylinder type, first, we should pay attention to the basic consistency of the distribution of the same cylinder per tube; second, we should pay attention to the basic consistency of the distribution of different cylinders in the same round; third, we should pay attention to the basic consistency of the distribution of each cylinder in the last and next round of processing. The same amount of cloth per cylinder is mainly to reduce the difference in the number of fabric cycles and avoid the difference in dyeing pipes. The same amount of cloth per cylinder is to ensure the same bath ratio.
(4) When processing fabrics of the same variety and batch with different cylinder shapes, attention should be paid to the consistency of bath ratio and other technological conditions.
As in the example above, the bath ratios of 900 kg polyester dyed in four cylinders and 450 kg polyester dyed in two cylinders are 1:2.15 and 1:2.27, respectively. In order to adjust the consistency of the bath ratios of the two machines, there are generally two methods as follows:
One method is to adjust the distribution of fabric between cylinders to achieve uniform bath ratio by fixing the water level set before the fabric enters the cylinder. If we adjust the distribution of two tubular cylinders to 538Kg, the bath ratio is 538Kg/(350Kg+538× 1.5Kg) = 1:2.15, which is the same as the bath ratio of 900Kg fabric dyed by four tubular cylinders, but at this time, the dyeing capacity of each tubular cylinder is 225Kg, while the dyeing capacity of each tubular cylinder is 269Kg, the difference between the two tubular cylinders is 44Kg, and the length of each tubular fabric of the same variety is equal. Under the same cloth speed, the fabric cycle frequency and the number of dye exchange with the dye solution in the nozzle system will be different.Thus, the difference of dyeing tube or cylinder is brought. Therefore, in this case, attention should be paid to the consistency of process conditions such as distribution speed.
Another method is to adjust the water intake level of the fabric before entering the cylinder with the same amount of cloth in each cylinder, such as adjusting the water intake level of the two cylinders from 350 kg to 292.5 kg, the bath ratio is 450 Kg/(292.5 Kg+450× 1.5 Kg) = 1:2.15, & nbsp; that is, the bath ratio is the same as that of the four cylinders dyeing 900 Kg fabric. Generally speaking, this method is simpler and more reasonable, because there is no need to adjust other process conditions. However, it should be noted that if the adjusted liquid level is less than the original set liquid level, we should pay attention to the liquid level. While meeting the needs of the main pump and pipeline dye circulation in the dyeing process, if the dyeing material is dissolved with the recycled liquid, we should also meet the needs of the recycled liquid level; if the adjusted liquid level is used, we should also meet the needs of the recycled liquid level. If the liquid level is larger than the original one, it should be noted whether the liquid level has exceeded the PTFE pipe at the lowest point of the storage tank. However, in general, these factors are taken into account in the water level value of the fabric before entering the cylinder and the design volume of the filter below the storage tank of the airflow dyeing machine. Both positive and negative values have a larger affluence value, which can fully meet the needs of liquid level adjustment.
(5) In the process of air-flow dyeing, the process procedures and process requirements should be strictly complied with and can not be changed at will. For example, the feeding mode of feeding chemicals, the set water level in the cylinder, the dyeing quantity of each tube in each cylinder, etc., should be strictly complied with the process requirements, because the process design has been taken into account. The factors causing the change of bath ratio determine the amount of dyes and chemicals according to the calculated bath ratio. If the operation process is not strictly carried out according to the process, it will probably cause the actual bath ratio and the calculated bath ratio of the process to be inconsistent, which is very harmful to the reproduction of dyeing quality and results.
4, summary
Nbsp; & nbsp; & nbsp; & nbsp; & nbsp; Understanding the composition of air-flow dyeing bath and the way of infusion during dyeing is conducive to correctly calculating the dyeing bath ratio and preventing the fluctuation of bath ratio in dyeing process, thus accurately controlling the bath ratio and avoiding the dyeing quality problems caused by the factors of bath ratio.
