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Radiation Hazards
Published in Dag K. Brune, Christer Edling, Occupational Hazards in the Health Professions, 2020
Ultrasound is used in a wide range of power levels in applications from mechanical industry to medical examinations. High-power applications use power densities above 100 W/cm2 and some examples are given below. Ultrasound cleaning uses levels of 100 to 1000 W/cm2 with frequencies around 20 to 80 kHz. The objects to be cleaned are submerged in a bath of cleaning liquid in contact with a ultrasound generator. The cleaning process takes place by cavitation and mechanical scrubbing of the objects. The scattering of ultrasound into the air is insignificant in this process, but in direct physical contact with the ultrasound cleaner, efficient transfer of ultrasound energy to the hands is obtained. Therefore thick protective gloves are recommended. Ultrasound plastic welding uses levels of about 10 to 100 W/cm2 at 20 kHz. Other uses of ultrasound are production of emulsions and aerosols, process control, burgler alarms, material testing, remote controls for televisions, and other domestic electronics.
Industrial Applications
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Anil Kumar Chohadia, Yasmin, Neelam Kunwar
Ultrasonic plastic welding (UPW) requires much higher power densities (about hundreds of watts per square inch), as compared to ultrasound cleaning. Plastic welding horns operate at amplitudes at about 10 times higher than cleaning for such power densities. Very sharp mechanical resonances are exhibited due to high energy storage. They must accommodate a wide variety of loads depending on the application, and mechanical loading may vary during the welding. In this case, a new class of equipment had to be developed to satisfy these requirements taking ultrasonic power technology to a new level.
A novel dryer design with carbonic heating film technology and drying of high moisture lignite coal
Published in International Journal of Coal Preparation and Utilization, 2022
Hasan Hacifazlioglu, Buse Bolat
There is no need for a material environment for the transfer of heat by radiation. As long as there is a temperature difference between the exposed surfaces, heat transfer by radiation is possible. Radiation heating can be carried out by means of ultraviolet, radio waves, microwave, and infrared radiation. The infrared radiation heats only the light-impermeable objects without heating the air around them. Infrared heating has also become popular in industry in areas such as paint drying, plastic production, annealing, plastic welding, and fruit drying. The choice of infrared frequency according to the characteristics of the material significantly affects the energy efficiency. There are basically three types of infrared rays. These are short, long, and medium wave infrared rays. The main difference between them is the processing depth of radiation. While the long waves heat only the surface of the material, the short waves work up to the inside of the material. Medium-wave infrared rays can operate at a depth equal to the average depth of long and short waves. The penetration power of infrared rays depends on the chemical composition, physicochemical state (liquid-solid-powder, frozen-unfrozen, dispersion-emulsion-solution, etc.) of the material and its physical properties (density, porosity, and amount of water). As the temperature of the infrared source increases, the amount of radiation energy transferred to the material increases and the wavelength of the infrared ray decreases. Infrared radiation passes through water molecules at short wavelengths, and is absorbed by the material surface at long wavelengths. Therefore, it is more efficient to dry thin-film materials by long-wave and thicker materials by infrared radiation at short-wavelength. The penetration power of short-wave infrared radiation is 10 times higher than that of long-wave infrared radiation (Krishnamurthy et al. 2008; Mujumdar 2006; Sakai and Hanzawa 1994; Tuncel and Tuncel 2016). When a material absorbs infrared rays, vibrations, and rotational movements are observed in its molecules and the distances between atoms change and the absorbed infrared rays turn into heat. Water molecules in material exposed to infrared radiation vibrate in the frequency range of 60000 to 150000 MHz. This causes the water vapor pressure in the material to rise and the material to heat up. The infrared rays are divided into three according to their wavelength and emission temperature. These, (1)- Short wave or near IR region (NIR): 0.72–2 µm (3870–1180°C), (2)- Medium wave or middle IR region (MIR): 2–4 µm (1180–450°C), (3)- Long wave or far infrared region (FIR): 4–1000 µm (<450°C).
Investigation of ultrasonic welding of carbon fiber reinforced thermoplastic to an aluminum alloy using a interfacial coating
Published in Materials and Manufacturing Processes, 2021
For the development of lightweight engineering structures, aluminum alloy and fiber-reinforced polymer composite plays a vital role. In many applications, joining of such multi-materials is needed. Different techniques are available for joining polymers to metals.[1,12] The most predominant techniques are mechanical fastening, adhesive bonding, and welding. Joining by fasteners creates an additional weight, and the application of chemical adhesive degrades the polymer performance. Multi-material joints by welding were found to be efficient across the automobile and aerospace industries. It includes friction welding,[3–6] laser welding,[7–9] induction welding,[10,11] and ultrasonic metal welding.[12–14] Direct welding of thermoplastic composites into metals was achieved by the application of heat at material interface to melt polymers and applying pressure to hold substrates for curing. The effectiveness of these joints is achieved by mechanical interlocking rather than chemical bonding, as thermoplastics are chemically inert. Out of various welding techniques, ultrasonic plastic welding is considered for this research study because it is a quick method for joining thermoplastics with low energy requirement and possibility of process automation that meets Industry 4.0 requirements. The heat required to melt materials is much lower than that in other welding techniques. Frictional heat generated through high-frequency ultrasonic vibrations melts materials at joint interface and fuses together with an applied pressure.[15–17] The process requires a special geometrical feature at joint interface known as energy director. Its shape and dimensions are crucial for the joint performance. It helps in focusing ultrasonic energy to joining location and subsequently initiating melting of polymers by viscoelastic heating. Traditional energy directors are triangular shaped with a sharp tip directly molded onto plastic parts. For long and continuous fiber-reinforced thermoplastics, a separate thermoplastic film is needed between joining substrates to improve the speed of welding. Neat and flat-shaped energy directors are predominantly used by researchers in joining thermoplastics.[18–20] Conte and coworkers[21] studied ultrasonic joining of a carbon fiber-reinforced thermoplastic to an aluminum alloy using a separate layer of thermoplastic energy director between substrates. The joint strength was mainly influenced by mechanical interlocking and adsorption of polymer over aluminum surface. Bolt[22] investigated the usage of a thin layer of thermoplastic coated on a metallic adherend prior to ultrasonic plastic welding with carbon fiber-reinforced thermoplastics. The method of coating created a bulge rather than a flat surface that significantly alters the welding process in achieving a consistent joint quality.