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After finishing, the moisture content of the non-woven fabric exceeds the permissible range of quality requirements. In addition to affecting product quality, shelf life, measurement accuracy, and packaging quality, excess moisture can cause the product to breed bacteria and become moldy. Therefore, drying is an important link in the production process of non-woven fabric finishing. Its function is to remove excess water from the product and ensure product quality. For some specialty products, the drying process is still a process of activating the function of the treatment agent. In the production of non-woven fabrics, heating drying is mostly used, and there are four commonly used heating drying methods as follows.
1. Far infrared drying
The far-infrared dryer is a drying equipment designed using the principle of infrared radiation. The infrared generating devices of the far-infrared dryer include infrared lamps, infrared electric heating tubes, electric heating plates, far infrared electric heating tubes, electric heating plates, etc. To improve the efficiency of infrared drying, dryers are often equipped. A forced convection ventilation system removes hot air attached to the surface, reduces product surface moisture and accelerates water evaporation. Because far-infrared drying does not require an intermediate medium, the energy directly enters the product to heat the product, so its efficiency is higher than that of hot air drying.
The infrared dryer has the advantages of a compact structure, easy installation, high output power, high drying efficiency and good sanitary conditions. However, because the surface temperature of the heating element is much higher than the melting point of the non-woven fabric, if the product is in a stationary state or direct contact with the heating device, the product can easily melt and cause a fire accident. Therefore, the corresponding safety measures should be set in the equipment.
2. Hot air drying
Hot air drying is a process in which water in the product is heated, vaporized, and removed by air flow using the energy of the hot air flow. Products dried by hot air are limited by the airflow temperature of the hot air. Generally, the method of increasing the contact time between the hot air and the product is used to improve the heat energy utilization rate and the drying efficiency of the hot air. Therefore, the product needs to be wound in a reciprocal and circuitous form in the drying equipment, and the size of the drying box is large.
Hot air drying mainly depends on hot air convection heat exchange. Although the drying efficiency is not high, the drying process is light, the temperature is uniform and the dried product still maintains a good hand. Therefore, in the post-finishing and drying process of non-woven fabrics, hot air drying is also a commonly used process.
3. Cylinder drying
Cylinder drying is placing the high-moisture non-woven fabric near the surface of the high-temperature drying cylinder and heating the non-woven fabric by heat conduction so that the moisture in it evaporates. Achieving the objective of drying. Drum drying is a drying process widely used in the paper industry and a drying method used in nonwoven finishing production lines.
In the drying cylinder dryer, the cylinder is made of red copper with good thermal conductivity. When the finishing agent is corrosive or the product has high hygienic requirements, it needs to be made of stainless steel. The dryer is usually equipped with multiple drying cylinders, and the drying cylinders can be arranged horizontally or vertically. Non-woven fabric and drying cylinders are often wound on a route with a large wrap angle (such as Ω type) and a large contact area so that the front and back sides of the product can be dried.
The drying efficiency of a drying cylinder dryer is related to the drying cylinder's surface temperature and ambient humidity. The drying cylinder can be heated by steam or heat transfer oil. The higher the temperature, the higher the drying efficiency, but the higher the energy consumption of the processed products. During the drying process of the product, there will be a large temperature difference between the surface of the drying cylinder and the temperature of the side in direct contact with the other surface. Turmeric affects product quality.
To meet the high-speed operation requirements of the production line, the drying cylinder dryer is equipped with a large number of drying cylinders, which occupy more space and space on the site, and its drying efficiency is not as good. Hot air penetration dryer. Therefore, spunbond products, it is less used in the drying process of spun bond melt composite products.
4. Hot air through drying
Hot air infiltration drying uses the principle of air circulation to allow hot air to directly penetrate the non-woven fabric and at the same time transfer heat to the non-woven fabric to evaporate moisture and take away moisture, realizing the process. Heat and mass transfer and the product dries quickly.
The main component of the hot air infiltration dryer is the drying drum, and the surface of the drum is a porous structure with high air permeability. The negative pressure pulls the hot air outside the drum through the non-woven fabric into the drum, the hot air heats the fabric, the moisture in the fabric evaporates, and then it is taken away by the airflow of the drum and the product. A small part of the hot and humid air stream lifted from the drying drum is discharged to the atmosphere through the dehumidification valve, and most of it enters the main circulation pipeline and then re-enters the air heater to continuously heat and dry the product. Air heaters can use steam, gas, or heat transfer oil as the energy source, adjust the temperature of hot air by changing the flow rate of steam, gas, or heat transfer oil, and control the drying effect.
The hot air infiltration dryer not only has the advantages of accurate temperature control, uniform temperature distribution, drying process, energy saving, etc. but also has a good hand feeling of the dried product, controllable sanitary condition and small excess tension. The hot air through the dryer occupies a small area and can not only be used for the off-line finishing of products but can be configured as the main process equipment for on-line drying in the production line.
Source: Online/NAN
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