Ultrasonic Washing Technology in Denim Fabrics

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Golam Rabbani

Ultrasonic cleaning is a system that works through high frequency sound waves. These waves are transmitted by liquid to clean the surface of immersed parts. Usually, the waves of 40kHz agitate the solvent and it causes the cavitation of solution molecules. Cavitation forms when sonic waves create a void that gets trapped in a liquid solution of water as a bubble. This microscopic bubble implodes with such a force that contaminants clinging to surfaces are dislocated. The implosions of tiny bubbles clean the surface. Ultrasonic technology is suitable for cleaning a wide range of materials. Such as metals, glass, rubber, ceramics, some hard plastics and so on. This method of cleaning is a lot more useful for removing tightly adhered contaminants from intricate items with blind holes, and cracks. The contaminants removed through ultrasonic technology can be dust, dirt, oil, grease, pigments, flux agents, fingerprints, polishing compounds, etc. The fluid used in the industrial process of cleaning can be either water based or, solvent based. In an ultrasonic system, both types of cleaning solutions contain wetting agents to reduce surface tension and increase cavitation. Aqueous cleaning solutions are generally more limited in cleaning effectiveness but better for the environment. The discovery of ultrasonic waves compelled us to think about new possibilities. Ultrasonic systems have been used in many areas of life. One of these areas has been cleaning which started to develop with human history. New methods of cleaning have been developed with time. With these developing methods, ultrasonic washing technology was developed simultaneously.

Ultrasonic washing technology has been used in the fields such as industry, health, and the jewelry sector. Recently, it has been tested for denim fabrics as a textile product.

The classical washing method and the ultrasonic washing method were compared experimentally. From the experimental data obtained, it was determined that the ultrasonic washing method yielded more effective results than the classical washing method and it was found to be economical and environmentalist. The field of ultrasonic is still making progress towards perfection.

With the existence of human beings, the need for cleaning has become an indispensable element. New methods have been continuously developed to meet the need of growing human demands. The cleaning method with ultrasonic sound waves is one of the finest technologies. Ultrasonic is the science of sound waves above the limits of human audibility. In the history of ultrasonic sound waves, Francis Galton’s “Galton Whistle” is the first step in the production of these high frequency waves. In 1880, Pierre Curie and his brother Jacques Curie have shown that certain crystals have piezoelectric properties. When an alternating voltage is applied to the crystal in the converter, vibration occurs in the crystal. In this way, an ultrasonic sound wave occurs when the vibration frequency and the frequency of the electrical signal are equal. The human ear can hear sounds in the frequency range of 20Hz-20kHz. Ultrasonic sound wave starts from 20kHz. The frequency of ultrasonic cleaning used in the industry range is between 20kHz-250kHz. The frequency of the ultrasonic sound wave to cleaning objects is selected as 40kHz. There had been used ultrasonic cleaning systems; ultrasonic cleaning vessels, ultrasonic transducers, ultrasonic generators (signal generator) and cleaning solutions for the experimental washing of denim. Textile materials that had to be cleaned in the ultrasonic cleaning process were placed in the cleaning vessel. Afterward, ultrasonic transducers analyze the incoming electrical signal. They produce a mechanical sound signal with a high frequency depending on its amplitude and frequency. By transmitting the signals to the liquid in the vessel, the pressure in the liquid in the tank was increased. As the liquid is compressed in the high-pressure phase, pressure is suddenly released. As the pressure in the liquid decreases, in the microscopic core, the spaces enlarge. These spaces or, cavitation are narrowed by the high pressure and grow at low pressure. As this process continues, the gap between fabrics grows and the bubble reaches such a critical size that it cannot maintain its size any longer and becomes too strong during the pressure-increased phase. Then it explodes. During this powerful explosion, shock waves occur which are radiating in all directions. Shock Plasmas formed by the effect of waves collide with objects in the liquid. So the unwanted particles are cleaned. This process was used in the washing of Denim Fabrics that improved chemical substances and temperature parameters in the cleaning process. Ultrasonic Signal Generators send the electrical signal by converting it into a frequency signal that is received from the network of the ultrasonic transducer. The transducers consist of a ceramic crystal sandwiched between a pair of tin strips. Crystallization occurs through the tension between strips. This phenomenon is called the piezoelectric effect. On this cleaning 40W power converters at 40kHz frequency were used. In the classical washing method, sodium salt of polyacrylic acid is used as soap and acetic acid is used to adjust the pH balance of the fabric. In this ultrasonic washing method, soft washing liquid and water were used.

This was an experimental comparison of the classical washing method and ultrasonic washing technology. The results were quite impressive which shows that by using only ultrasonic sound signals at lower temperatures without even chemicals and acids, more effective results can be obtained.

All the textile products are subjected to a variety of finishing processes including industrial washing, and they are also subjected to domestic washing. The cleaning process of laundry is synergistic action between mechanical energy, chemical energy, thermal energy, and time. Conventional apparel washing techniques require a large amount of water and chemical consumption. Studies carried out on the ultrasonic washing method have shown that the ultrasonic washing method has many advantages including; superior cleaning properties, reduction in process time, energy, and chemical and also ultrasonic agitation produces fewer fiber migrations when compared to the conventional washing method. Ultrasonic energy generates millions of bubbles or cavities into the liquid with a very high frequency which constantly strike at the target material surface and as a result, remove dirt off the fibers. The laundering of apparel has always been an important matter for mankind even in the early stages of world history. The main aim of the developments for laundering is better cleaning with lower damage to the textile fabrics. In this case, ultrasonic energy can offer a good cleaning with a lower effect on the fabric’s properties. The fabrics which are ultrasonically washed have better flexural rigidity values. Conversely, the fabrics which are washed conventionally can lose their yarn and fabric formations. Most of the fabrics which are washed ultrasonically have higher thermal conductivities in comparison with conventionally washed fabric. Water consumption and energy consumption are less in Ultrasonic Washing. Cold washing is also fine in this system. This process can be done in 1-3 phases instead of the 4-8 phases of classical washing. Less chemical is used in this process so it’s environmentally helpful too. Now it is quite clear and correct that ultrasonic washing technology is a way more excellent cleaning system than conventional washing.

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