Fabrics speed is an important process parameter in air-flow dyeing, which has a great impact on the dye uptake rate and levelness, as well as fabric performance.
Air flow dyeing fabric speed Generation
1. The formation of airflow in the airflow circulation system
In the airflow dyeing machine, the circulating high-speed airflow is the traction and The main driving force for the operation of rope-like fabrics. The air circulation system is mainly composed of high-pressure centrifugal fans, air ducts, air filter ducts and air nozzle systems.
The airflow duct
is usually divided into three parts: the first part It is a section of pipeline channel from the fan outlet to the outlet of the air flow nozzle in the nozzle system; the second part is a section of pipeline channel from the cloth guide ring of the suction port to the outlet of the air flow nozzle, and there is a cloth lifting roller in the channel; the third part is the air flow nozzle A section of pipeline channel from the outlet to the left and right ports. The high-speed airflow generated by the fan flows through the first part of the pipeline channel to the gas-liquid two-phase mixing chamber of the nozzle system. In the mixing chamber, it is mixed with the dye liquor sprayed from the dye liquor nozzle for two-phase gas-liquid mixing, and then through the outlet of the air flow nozzle After the spray passes through the third part of the pipeline channel, it flows from the left and right openings into the cylinder. This part of the air flow is called the active air flow, which has the function of further atomizing the dye liquor and exchanging the spray with the fabric.
The airflow nozzle
is composed of two parts, one part is poly-Si There is an annular narrow gap formed by the outer cone surface of the fluoroethylene nozzle and the throat. The active airflow is ejected from this place and then flows to the third part of the pipeline channel; the other part is the inner hole of the PTFE nozzle. Due to the ejection of the active airflow, the gas molecules staying at the outlet of the airflow nozzle hole will suddenly accelerate with the high-speed flow of the active airflow and flow to the third part of the pipeline channel. Due to the acceleration of this part of the gas molecules, the orifice generates negative pressure, causing part of the gas in the dye vat to pass through the cloth suction port guide ring, flow into the second part of the pipeline channel, and then eject from the inner hole of the air flow nozzle to merge with the active air flow.
The airflow formed in the second part of the pipeline channel due to the negative pressure is called passive airflow, which has the function of absorbing and threading cloth. The airflow after the active airflow and the passive airflow merge is called the merged airflow. The combined airflow flows into the master cylinder after passing through the third part of the pipeline channel. In the airflow dyeing process, the converging airflow is the main driving force for the operation of the rope-like fabric.
Fan and air filter duct
The suction port of the fan and The air flow filter duct located in the main cylinder is connected, so the air flow entering the fan from the cylinder has been filtered. When airflow dyeing, due to the high-speed rotation of the centrifugal fan impeller, the gas in the cylinder is sucked in from the fan suction port, and the high-speed airflow generated enters the first part of the airflow duct from the fan outlet, forming the above-mentioned active airflow, passive airflow and Combine the airflow to complete the airflow circulation during airflow dyeing.
2. The operation of rope fabric and the generation of fabric speed
When the rope-like fabric enters the cylinder, the cloth head enters through the cloth suction port and guide ring. The passive airflow brings the rope-like fabric into the second part of the channel to run. After bypassing the fabric lifting roller, it passes through the inner hole of the air flow nozzle. Entering the nozzle system, and then under the traction of the converging airflow, the fabric passes through the third part of the channel, and falls into the fabric storage trough through the left and right openings.
After the fabric is completely put into the cylinder, it is connected end to end. Under the traction of the air flow circulation, the cyclic operation of the fabric is completed. The fabric is only driven by the passive airflow when it first enters the cylinder; after entering the airflow nozzle, it is driven by the converging airflow. The faster the airflow speed, the faster the traction fabric will run.
The air flow speed is determined by the air volume sent by the fan. Since the cross-sectional area of the air duct vent is constant, the greater the air volume, the greater the gas flow per unit time in the same cross-section, that is, the faster the air flow speed; conversely, the slower the air flow speed. Therefore, the air volume of the fan determines the air flow speed, and the air flow speed brings the cloth speed. Therefore, the fabric speed of airflow dyeing is mainly determined by the air volume of the fan.
During airflow dyeing, the fabric must pass through the fabric lifting roller before entering the airflow nozzle. The fabric lifting roller has two main functions:
The first is to guide the fabric in an ideal running trajectory and avoid cloth blocking, wrapping and knotting; the second is to assist in the movement of the fabric. If the fabric lifting roller is a passive roller, then when the air flow pulls the fabric through the fabric lifting roller, it must overcome the friction resistance between the fabric and the fabric lifting roller, and the cloth speed will slow down. If the resistance of the cloth lifting roller is not considered, the cloth speed is v1. When considering overcoming this resistance, the cloth speed slows down to v2. Then, the speed consumed by the resistance of the cloth lifting roller is Δv=v1-v2. However, the fabric lifting roller of the airflow dyeing machine is an active roller driven by an AC variable frequency motor. It can not only compensate for the fabric speed Δv consumed by the resistance of the fabric lifting roller itself, but also overcome the gravity of the fabric and accelerate the fabric operation. When the relative sliding between the fabric lifting roller and the fabric is not considered, this speed is the linear speed at the maximum diameter of the fabric lifting roller.
So, during airflow dyeing, the running speed of the fabric is actually determined by the air volume of the fan and the speed of the fabric lifting roller. Under normal circumstances, the air volume of the fan is mainly determined, and the auxiliary operation of the cloth lifting roller is supplemented.
The cloth speed affects the airflow.Since the speed of the fabric is not exactly equal to the linear speed at the maximum diameter of the fabric lifting roller, it is difficult for the control system to obtain the real-time fabric speed of the fabric. For the above reasons, the control system of some airflow dyeing machines does not display the actual cloth speed value during dyeing. When controlling the cloth speed, the control system only displays the frequency of the circulating fan motor and the frequency of the cloth lifting roller motor (some equipment manufacturers convert is the control value of the motor power).
2. Cloth speed control of different fabrics
1) Fabric speed control for fabrics with larger grammage
When fabrics with larger grammage are air-dyed, the fabric speed will be increased and the damage to the fabric will generally not be obvious. , therefore, the frequency of the fan motor and the frequency of the cloth lifting roller motor can be set as high as possible.
On the one hand, this can speed up the running speed of the fabric and increase the number of exchanges with the dye liquor, so that the dye can be dyed quickly and evenly; on the other hand, the air volume and pressure can be increased, making it easier to When the fabric is blown open, the dye solution can easily penetrate into the fabric fibers to achieve rapid dyeing and leveling. However, the frequency of the cloth-lifting roller motor cannot be set too high. Otherwise, if the speed given by the cloth-lifting roller to the fabric is greater than the speed given by the airflow to the fabric, it may cause overfeeding of the fabric. When it enters the airflow nozzle, it is easy to tangle, block, and tear the fabric. Knot. When parking, you must first stop the cloth roller motor, and then stop the fan motor, for the same reason.
2) Cloth speed control of light and thin fabrics
For easy When air-dyeing “delicate” fabrics that damage and cause defects, the fabric speed should not be too fast.
The principles for controlling fabric speed are:
First, ensure that the air volume of the fan can blow open and drive the fabric;
Second, on the premise of ensuring the dyeing quality of the fabric, reduce the fabric speed as much as possible to avoid damaging the fabric;
Third, Try to make the speed of the air flow to the fabric close to the speed of the fabric lifting roller to avoid the speed difference between the two being too large, resulting in greater fabric tension and damage. During specific operations, the motor frequency of the fan can be appropriately reduced and the motor frequency of the cloth lifting roller can be increased. Reduce the frequency of the fan motor to reduce the air volume. The purpose is to avoid excessive speed and violent vibration of the fabric, which will intensify the friction between it and the pipe wall. The purpose of increasing the motor frequency of the fabric lifting roller is: first, to meet the speed required for fabric operation and compensate for the reduced cloth speed due to reduced air volume; second, to reduce the speed difference between the air flow and the fabric lifting roller to the fabric to avoid causing larger fabric tension. But it should also be noted that excessive speed of the fabric lifting roller should be avoided to cause fabric overfeeding.
Therefore, for air-flow dyeing of light and thin “delicate” fabrics, in order to ensure the dyeing quality of the fabric and avoid defects in the fabric, the air volume of the fan and the speed control of the fabric lifting roller must be adjusted Cloth speed is the key, that is, the frequency of the fan motor and the frequency of the cloth lifting roller motor must have the best matching value. Fabrics of different weights and varieties have different matching values, which need to be explored in long-term production practice.
In air-flow dyeing, the cloth speed has a certain impact on the dye uptake rate, level dyeing and the fabric itself. If not properly controlled, some light and “delicate” fabrics prone to damage. Therefore, in practical applications, for light and thin fabrics with small weight, the air volume of the fan and the speed of the fabric lifting roller should be strictly controlled. For different fabrics, the best matching values of the fan motor frequency and the fabric lifting roller motor frequency must be determined accordingly.
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