Textile products are taken to the drying process after wet finishing processes or washings. We can define drying as the removal of water on the product after wet finishing processes and washings.
This process is done for two purposes;
>> Minimizing the amount of liquor taken
>> Completing the process by fixing the liquor taken by heat treatment in the product
Removing the water retained by the textile product with the help of heat is an expensive process. Therefore, as much of the water as possible should be removed mechanically. Thus, drying, which is an expensive step, can be done more economically. Knowing in which situations the water on the textile material is present is very important in terms of applying the most efficient drying method. Water is present on the textile product in the following forms:
>> dripping water: It is water that does not bond with the fibers and flows downwards with its own weight. All are easily removed by mechanical means.
>> Surface water: It is water that binds to the surface of the threads by adhesion forces. It can be removed by mechanical means.
>> Capillary water: It is water that binds to the surface of the fibers forming the threads by adhesion forces. However, some of them can be removed by mechanical means.
>> Inflatable water: It is water that binds to fiber molecules by dipole forces. It causes Swelling of the fiber section. However, it can be removed with the help of drying methods applied using heat energy.
>> Hygroscopic moisture, crystal water: It is the water that should be present in a dry textile product under normal conditions. After a well-done drying, this water should remain in the fibers. Otherwise, the behavior of the product will deteriorate. Once removed, it is impossible to get the same amount again.
The process of removing the water in the product, which can be removed by mechanical means, with less energy consumption. pre-drying is called. In order to save on the drying process;
>> Working by taking less liquor from the product,
>> It is necessary to apply a more effective pre-drying method.
Pre-drying is done in three ways:
It is made by passing the wet textile product between rollers rotating at a certain speed around its axis under a certain pressure. It is the most applied pre-drying method today. The most important issue in squeezing rollers crimping efficiencyd.
Factors that determine the amount of water remaining on the fabric as a result of spinning:
>> Pressure applied to the fabric:
It is expressed by dividing the total load applied to the ends of the rollers by the roller length (kg/cm). The increase in pressure reduces the water remaining on the product.
>> Hardness of roller surface:
Hard roller is generally preferred for woven fabrics. Thus, the fabric undergoes less deformation as a result of pressure. Higher pressure can be applied. Therefore, less water remains on the product.
>> The temperature of the water in the product:
The amount of water taken on the product decreases with the increase in temperature.
>> Fabric pass speed:
The speed of passing between the rollers plays little role on the water removal values.
>> Roller diameter:
This factor also has little effect on water removal. Smaller diameter rollers have less contact area, creating higher pressure.
The most known of the squeezing rollers are the padding rollers. Generally, there are squeezing rollers between the chambers in open width pretreatment and washing machines. The aim is to prevent the liquor from carrying it to the other boat.
Squeezing machines, called water calenders, consist of two or more squeezing rollers. Since the fabric is transversely open and stretched, there is no danger of wrinkles and a smooth squeezing effect is achieved.
In normal water calenders, one of the rollers is made of stainless steel, while the other; It is made of iron covered with cotton, jute or a synthetic material. That is, the second roller has a certain flexibility. The diameter of the elastic roller is twice that of the steel roller. For woollens, both rollers should be covered with rubber.
Rope squeezing rollers are used to tighten the wrinkle-free products. The squeezing effect is not equal in all parts of the product. Squeezing pressure is lower than water calenders.
Balloon squeezing machines are developed for the pre-drying of circular knitting products. It is used to minimize the water on the tubular fabrics.
Reasons why open-width crimping machines cannot be used;
>> Knitted products are sensitive to stretching.
>> There is edge lettuce in transverse open drying.
>> In open-width crimping, there is a risk of fracture scarring as a result of edge crushing.
The purpose of squeezing balloons,
>> It is to remove excess water on the fabric.
>> It is to open the fabric that is treated as a rope in the form of a tube.
>> It is to inflate the fabric by giving air and to eliminate the fold traces.
It is the removal of surface water and capillary water in the wet textile product with the help of centrifugal forces. A more effective drying is provided than the wringing method. The speed of centrifuges used in textile enterprises is generally between 500-1500 rpm. The water removal capacity varies in proportion to the number of revolutions. It can reduce the amount of water on the product by 30% - 60%. The advantage of centrifugation; It can be applied to all kinds of textile products such as fiber, yarn, fabric, ready-made clothing. The disadvantage is that the intermittent work creates the danger of wrinkles as the fabric is stacked in a rope.
It is based on the principle of placing the wet textile product in a perforated basket and turning it at a certain speed to remove the excess water on it with the help of centrifugal forces.
Perforated baskets are made of stainless steel. Placing the product properly in the machine is provided by the filling mechanism. This arrangement ensures that the rope fabric is placed in the basket, which is rotated at a constant and low speed at a constant speed. Proper placement is important to avoid causing dangerous vibrations in the rapidly rotating machine.
In knitted fabrics At the end of the centrifuge, wet peeling should be done. This process is not done only for the purpose of opening and correcting the product and creating a marker. At the same time, it aims to eliminate the loop deformation by working with transverse opening and lengthwise advance.
In coil centrifuge machines, the coils are placed on the back and forth moving bars on the table. When the table is full, it is placed in the centrifuge machine. Adhering to the machine walls due to centrifugal force The coils do not remain round as a result of pre-drying, but come out in an oval shape.
removal by suction,
It is a drying method that is carried out by removing the water on the product by vacuuming. It is used in products that have a high risk of wrinkling and are sensitive to squeezing with pressure.
It is based on the principle of suction of air by vacuum through the textile product passing through the machine in the transverse open state, and that the sucked air carries the excess water on the product with it. Although suction removal is the most effective pre-drying method, it is the machine with the highest energy consumption due to vacuum pumps.
The removal of water on the product with the help of heat is called drying or main drying. Drying is the most expensive step of the process. Requires high temperature. At this time, heat transfer occurs. Heat transfer can occur physically in four ways. Therefore, drying can be applied according to four principles.
>> Convection drying
>> Contact drying
>> IR (infrared) drying
>> High frequency (microwaves) drying
Convection drying is a drying method applied by the contact of hot drying gas with moist textile products.
>> During this drying, a two-sided heat and mass transfer occurs.
>> Heat transfer takes place from the hot drying gas to the moist textile product.
>> Water vapor transfer takes place from the damp textile product to the drying gas.
In order for heat and water vapor exchanges to take place, the thin air boundary layer on the surface of the fibers must be exceeded. Therefore, this limit, the thinner the layer, the higher this rate of change, hence the drying rate. When hot air is sprayed parallel to the fabric, the boundary layer is the thickest as it will lick and pass through the fabric. When the hot air is sprayed vertically from the top and bottom of the fabric, the boundary layer thickness decreases, and when the hot air is passed through the fabric, it becomes the thinnest. Therefore, the fastest drying among them is provided in dryers where hot air is passed through the fabric.
Stenters (Framed dryers)
Although they are the most expensive dryers, the most preferred dryers are the stenters, as the width and length adjustment of the fabric can be achieved. In stenters, the movement of the fabric in the machine is provided with the help of endless chains consisting of large links on both sides of the stenter. There are pins or latches on the links of the chain. The fabric moves with the chain by attaching to these pins from both sides or being held by the pegs. It is possible to open the width of the fabric by increasing the spacing between the chains in the section from the entrance of the machine to the first drying chamber.
By decreasing this gap gradually, the fabric is pulled through the width while passing freely. Length adjustment of the fabric can also be made in stenters with needle carriers. If the fabric is conveyed to the machine at a speed higher than the chain movement speed, it gets caught in the chains in a large amount and shortens by pulling in the warp direction while passing through the dryer. Therefore, when using products sewn from such a fabric, they do not shrink much when washed.
If the fabric is fed to the machine at a speed lower than the chain speed, it is attached to the chains in a very taut way, which causes them to stretch in the warp direction. Products sewn from such a fabric will shrink a lot when washed during use.
In stenters, hot drying gas is sprayed on the fabric vertically through holes or slits called nozzles. Therefore, the drying rate is quite high. However, since the stenters take less fabric, a large area is required and still cannot be operated at high speeds. For this reason, multi-layer stenters are also manufactured especially for the drying of heavy wool fabrics.
Since the inlet and outlet of the fabric are generally in the same direction in multi-layer stenters, a worker can easily operate them. However, two workers are normally required to operate single-storey stenters, at the entrance and exit of the stenter. Today, with the help of the transmitter placed at the entrance, the sand output can also be controlled by the worker at the entrance.
Other advantages of stenters are;
>> Drying and condensation processes can be carried out after impregnation of finishing materials such as wrinkle-proofing and water-repellent with the help of the foulard in front of it,
>> Thermofixing of synthetic fabrics,
>> Thermosol method (heat fixation of dyed and printed fabrics) is applicable.
Conveyor belt and air cushion dryers
In conveyor belt dryers, the fabric is conveyed through the dryer on an endless perforated belt. It is a tension-free dryer type since it is not necessary to pull the fabric horizontally and longitudinally to move it.. However, the fabric, which is laid on the conveyor belt, still does not have the opportunity to get rid of its internal tensions. If the upper and lower nozzles are not in a position opposite each other and are in a slipped position, it is better to get rid of internal tensions, since the fabric will not remain on the conveyor belt and will make sinus movements. Especially if a kind of kneading effect can be achieved, such as the fabric getting up from the conveyor belt and hitting somewhere above and then falling back onto the belt, with special nozzle constructions, the shrinkage of the products sewn from this fabric decreases during their use. Currently, such special vibrating conveyor belt dryers, It is the most used dryer type for drying circular knitted fabrics.
Another dryer that the textile product can pass through without tension is the air cushion dryer. Air is sprayed vertically on the fabric through holes or slits called nozzles. In air cushion dryers, an air cushion is formed under the textile product, thus allowing the product to pass through the dryer without touching anything. Despite the difficulties in adjusting the upper and lower airflows according to the type of product, the product has the advantage of passing through the dryer without touching anything.
The transition of the fabric through the hot-flues is similar to that of the roller boats. There is a row of delivery rollers at the bottom and top of the dryer, and the fabric passes through the dryer by moving from top to bottom and from bottom to top over these delivery rollers. Due to this transition pattern, hot-flues have a high fabric pick-up capacity. On the other hand, since hot air is sprayed parallel to the fabric in hot-flues, the drying speed is very slow. The most important drawbacks of hot-flues are that they cannot be adjusted in width and length, and even stretching the fabric in order to move them is in question.
The basis of contact drying is to pass the wet textile product to the heated rollers and at the same time to remove the water by evaporation. The most commonly used dryer type for contract drying is roller dryers. They usually consist of hollow steel cylinders with a diameter of 570 mm. Cylinders can be placed on top of each other, side by side or in an inclined position. The common rollers are stacked on top of each other and are "vertical roller dryers".
Drying with IR (Infrared) Rays
The basis of drying by irradiation is the transfer of heat from the hotter material to the colder material in the form of electromagnetic waves. Rays longer than the wavelength visible to the eye IR Yani infrared rays is called. Heat transfer takes place during the absorption of IR rays by the product. Because of this feature, IR rays are used in drying. In IR drying, efficiency increases depending on the absorption degree of the product. For this reason, dyeing textile products in light or dark colors, the type of fiber and the form of the product affect drying.
It is the type of pre-drying generally used when shock drying is required. For this reason, it is used to prevent migration in pad-steam and thermosol methods. Especially since the product passes without touching anywhere, it is suitable for shock drying of dyed products.
High Frequency Drying
It is a drying method based on the formation of dipoles by water molecules on the textile product passing between two capacitor plates connected to high frequency alternating current. The biggest advantage of this drying; even in materials such as bobbins and tops, it is possible to provide a drying process that has penetrated into it.
Batch Forming on Drying
Generally, batches are formed from the products to be dried in stenters according to the desired width and length settings. Knitted products are dried in separate batches, pile products in separate batches, and woven fabrics in separate batches. Because while width and length are important in woven fabrics, weight is important in terry fabrics. Therefore, the stenter settings differ.
In centrifugal drying, the products to be dried with the same desired properties are made into batches according to the machine capacity.
Working Suitable for Drying Types
In pre-drying, it is important to remove the maximum amount of water that can be removed from the product. However, care should be taken not to deform the fabric in the squeezing rollers. This becomes more prominent especially in rope tightening. In centrifugation, it has gained importance in the pre-drying of terry fabrics. Then, in order to both fluff the piles and give it a voluminous attitude, and to relieve it from internal tensions by pulling it from the width and length. turban passed through the dryer. Due to the beaters in the machine, the pile of the fabric swells while the fabric is beaten. While squeezing is preferred as pre-drying for woven fabrics, centrifuge and balloon squeezing are used for knitted fabrics.. Convection drying is the most preferred for main drying. Since contact drying is economical, it finds use in drying after pre-treatment and drying after printing.
The Importance of Leveling
The fabric is exposed to stretching and shrinkage during weaving and in the finishing processes, and weft and may slips may occur as a result of irregular transitions. This occurs in two ways:
>> Slipping from one edge to the other (skew) while running through the machine
>> Weft shift that occurs in the form of curvature in the middle of the product
Sometimes it can be caused by the misalignment in the stenters, and sometimes as a result of running the dryer too fast. To fix these errors leveling process, that is, smoothing is done. For this reason, leveling has generally gained importance as the last step. Especially since the unevenness in striped and checked fabrics is more striking, it is even more important in this type of fabrics. While leveling, it is necessary to pay attention to the width, height adjustment and desired square meter weight of the product. This process is easier for woven fabrics than for knitted fabrics. Because the shrinkage rate is less and more easily detected (due to the form of the product).
Attaching the Fabric to the Machine for Leveling
At the end of the finishing processes, the machines in which the control of the width and length adjustment is made;
>> Stenter for woven fabrics,
>> They are steam residue, leveling stenter and stenter for knitted fabrics.
The leveling process is easily applied during the drying processes in the stenter due to the structure of the stenter. However, the products that we do not do the drying process in stenters are passed through stenters for leveling purposes. Leveled ramoses consist of fewer chambers. Because the aim is not drying, but leveling. The most equalization is achieved by bringing the transport chains in the shamous closer together and away from each other. Length leveling is provided by advance feeding (giving non-shrinkage property) or by feeding (stretching) the fabric more slowly than the chain.
If the desired width or length cannot be achieved at the end of the finishing processes, the desired values are gained by passing through the leveling stenter.
Even though the fabric is dried, if there is weft or warp slippage, the product in this form cannot be put on the market, so it is passed through a dry stenter. Weft arrangement is made at the entrance of the stenter. The fabric is shipped to the holders to eliminate this error while entering the truss. Once the required settings are met, the created batch is migrated. The fact that the lines are parallel in the striped fabric and that the squares are in the desired dimensions in the plaid fabrics show that the settings are correct.
In knitted fabrics (especially towels), weight is more important. For this, ramos are used.
Equalizing by Passing through the Foulard
In order to make the leveling easier, if necessary, it can be worked by taking water into the padding trough in front of the stenter. Thus, while passing through the scarf, the fabric, which is moistened by taking a certain amount of liquor, passes through the weft adjusters and comes to the pallets. The work is completed by giving the calculated advance amount while being shipped to the machine with the grippers adjusted to the desired width.
Equalizing in the stenter
They are the most used machines for leveling purposes. The application area is wide for both woven fabrics and knitted fabrics. Leveling stenters or stenters are used in the process of easily adjusting the width and length, fixing the desired weight in knitted fabrics, and removing the unevenness in knitted fabrics.
Leveling With the Help of Automation
If the weft curvature is not excessive in the fabric, weft adjustments are made at the stenter entrance and the machine is connected to the automatic. The fabric, which passes through the seesaw application, which ensures the proper centering of the fabric at the machine entrance, comes to automatic sensors that detect weft slippage. Errors are automatically detected here. The fabric coming to the weft correctors gets rid of its dishedness with the help of curved rollers. With the help of steel rollers, it gets rid of its distortions. Thus, the entire batch comes out the same width and smoothed. After the weft slips are corrected and the width of the fabric coming to the needles is adjusted, it is subjected to steaming before entering the chambers. Thus, the damp fabric is more easily leveled. The same is true for height stability. Especially in plaid products, correction is made by means of rollers.
Automatic operation can be performed by adjusting the input supply, heating of the chambers (according to the desired humidity rate) and accordingly the speed of the machine. The moisture content is automatically controlled when the fabric passing through the cooling section at the exit passes through the humidity sensors. Accordingly, depending on the degree of drying, the temperature of the chambers can be increased or decreased if desired. Then, the leveling process of the fabric, which is usually stacked and stacked, is completed.
It is an application made by the workers in order to correct the curvature in the fabric. If the drift in the lot is large, the control panel is adjusted manually. Weft slippage is tried to be eliminated by keeping it under constant control by the workers. The camber or diagonal is adjusted by hand in a controlled manner.