Ultrasonic working principle

Update: 21-04-2020

When an object vibrates, it makes a sound. Scientists c […]

When an object vibrates, it makes a sound. Scientists call the number of vibrations per second the frequency of sound, and its unit is hertz. The frequency of sound waves that our human ears can hear is 16 to 20,000 Hz. Therefore, when the vibration of an object exceeds a certain frequency, that is, above the upper limit of the human hearing threshold, people cannot hear it. Such sound waves are called "ultrasonic waves". The frequency of ultrasound usually used for medical diagnosis is 1 to 5 MHz.
Although humans can't hear ultrasound, many animals have this ability. They can use ultrasound to "navigate", hunt down food, or avoid dangerous objects. You may have seen many bats flying back and forth in the courtyard on a summer night. Why are they flying without light and not disoriented? The reason is that bats can emit ultrasonic waves of 20,000 to 100,000 Hz, which is like an active "radar station". Bats use this "radar" to determine whether an insect or obstacle is in front of the flight.
We humans didn't learn to use ultrasonic waves until the First World War. This is to use the principle of "sonar" to detect underwater targets and their status, such as the position of the submarine. At this time, people send a series of ultrasonic waves of different frequencies to the water, and then record and process the reflected echoes. From the characteristics of the echoes, we can estimate the distance, shape and dynamic changes of the detected object. The earliest use of ultrasound in medicine was in 1942, the Austrian doctor Dusick first used ultrasound technology to scan the brain structure; later in the 1960s doctors began to apply ultrasound to the detection of abdominal organs. Nowadays, ultrasound scanning technology has become an indispensable tool for modern medical diagnosis.
The working principle of medical ultrasound examination is similar to that of sonar, that is, the ultrasound is emitted into the human body. When it encounters an interface in the body, it will reflect and refract, and may be absorbed and attenuated in human tissue. Because the morphology and structure of various tissues of the human body are different, the degree of reflection and refraction and absorption of ultrasonic waves are also different. Doctors are distinguishing by the characteristics of the wave mode, curve, or image reflected by the instrument they. In addition, combined with anatomical knowledge, normal and pathological changes, it can be diagnosed whether the organ under examination is diseased.
Sound waves with a frequency higher than 20000 Hz (Hertz). The acoustic branch that studies the generation, propagation, and reception of ultrasound, as well as various ultrasound effects and applications, is called ultrasound. The ultrasonic generating devices include mechanical ultrasonic generators (such as air whistle, whistle and liquid whistle, etc.), electric ultrasonic generators made using the principle of electromagnetic induction and electromagnetic action, and the electrostrictive effect and ferromagnetic using piezoelectric crystals Electroacoustic transducers made of the magnetostrictive effect of substances.

Principle of ultrasonic welding
Transmit ultrasonic energy to the welding zone through the upper weldment. Due to the large acoustic resistance of the welding zone, that is, the interface between the two welds, local high temperature will be generated. Due to the poor thermal conductivity of the plastic, it cannot be distributed in time, and it gathers in the welding area, which causes the contact surface of the two plastics to melt quickly. After a certain pressure is added, it is merged into one. When the ultrasonic wave stops functioning, let the pressure continue for a little holding time to make it solidify and form, so as to form a strong molecular chain to achieve the purpose of welding, the welding strength can be close to the strength of the raw material.
Sonic welding principle
The electronic energy is converted into mechanical energy by ultrasonic vibration, and then the energy is transmitted to the contact surface of the plastic bow and arrow by the welding head (HORN), which causes the intense friction between the molecules and the heat generation principle, which prompts the product to melt and combine into one. The processing speed is fast, clean, beautiful and economic.
Welding scope: toy industry, stationery industry, home appliance industry, electronics industry, food industry, communication industry, transportation industry, etc.
Ultrasonic welding example:
Commodity industry: powder box, cosmetic mirror, hair comb, lock ring, thermos cup, sealed container, seasoning bottle, water pipe joint, handle,
Bottle caps, food containers ... etc.
Toy industry: all kinds of ball toys, stationery, water guns, plastic gifts, music toys, and all kinds of plastic toys ... etc.
Electrical industry: electronic clock, steam iron, vacuum cleaner, telephone, computer keyboard, electric fan, battery, etc.
Automotive industry: direction lights, rear mirrors, various types of plastic products ... etc.
Rotary welding principle
It is designed for circular plastic products. The heat generated by the friction of plastic workpieces melts the contact surface of the plastic workpieces. The external pressure drives the solidification of the upper and lower workpieces and becomes a permanent combination. .
Examples of spin melting: RO filter, freezing cup, thermos cup, vase, carburetor, shower head, thermos gas tank, and street and so on.
Hot plate welding principle
Use the template to heat it to the required temperature, and then place it in the middle of the joint surface of the plastic workpiece and the workpiece, so that the thermal force is concentrated on the two joint surfaces. When the heat generates melting, exit the hot template and then use the external pressure. This makes the workpieces unite into one and becomes a solid and durable function. It can process welded products. It has high hardness, complex shape and large volume. All products can be solved.
Examples of hot melt: car lights, outdoor refrigerators, door panels, pumps, water storage tanks, vacuum cleaners, hole balls, CD boxes, washing machine balance rings, rhythm dance pedals, etc.
Edit this paragraph fusion welding method
Welding method
Under moderate pressure, the welding head vibrating with ultra-sonic wave produces frictional heat at the joint surface of the two pieces of plastic and instantaneously melts the joint. The welding strength is comparable to that of the body. The suitable work piece and reasonable interface design can achieve watertightness. And airtight, and avoid the inconvenience caused by the use of auxiliary products, to achieve efficient and clean welding.
Ultrasonic welding head with ultra-high frequency vibration is pressed against the protruding tip of the plastic product, so that it instantly heats and melts into a rivet shape, so that different materials are mechanically riveted together.
Through the preaching of the welding head and appropriate pressure, the metal parts (such as nuts, screws, etc.) are squeezed into the reserved plastic holes and fixed at a certain depth. After completion, regardless of the pulling force and torque, they can be comparable to the traditional mold. The strength can avoid the defects of damage to the injection mold and slow injection.
This method is similar to the riveting and welding method. The concave welding head is pressed against the outer ring of the plastic product. After the welding head produces ultrasonic ultra-high frequency vibration, the plastic is melted and formed to cover the metal object to fix it, and the appearance is smooth and beautiful. This method is mostly used in the fixing of electronics and speakers, and the fixing of cosmetics lenses.
spot welding
A. Welding two pieces of plastic in a separate point without the need to design a welding wire in advance, to achieve the purpose of welding.
B. For relatively large workpieces, it is not easy to design the welding line to carry out spot welding, and to achieve the welding effect, you can spot weld multiple points at the same time.
Cutting seal
Using the principle of ultrasonic vibration at the moment, cutting chemical fiber fabrics, its advantages are smooth and clean without cracking or drawing. High-frequency and ultrasonic are two different concepts. High-frequency refers to electromagnetic waves with a frequency greater than 100Khz, and ultrasonic refers to sound waves with a frequency of more than 20 kHz. High-frequency welding principle and welding principle are also different from ultrasonic wave. High-frequency wave uses high-frequency electromagnetic field to make the molecules inside the material collide with each other to generate high temperature to achieve the purpose of welding and welding. Ultrasonic wave uses the principle of friction heat to generate a lot of heat To achieve the purpose of welding and welding.
Application range of ultrasonic welding machine
Ultrasonic welding machine is mainly used for the secondary connection of thermoplastics. Compared with other traditional processes (such as gluing, ironing or screw fastening, etc.), it has the obvious advantages of high production efficiency, good welding quality, environmental protection and energy saving. Ultrasonic plastic welding equipment is widely used in medical machinery, packaging, auto parts, fishing gear and other industries, such as disposable infusion filters and plasma separation cups, ziplock bags, plastic wine bottle caps, dishwasher water wheels, plastic toys, car lights, Welding of plastic fake bait, charger shell and mobile phone sling, welding of lighter shell, etc., manufacturing body plastic parts, car door, car instrument, headlight mirror, sun visor, interior parts, filter, reflective Materials, reflective road studs, bumpers, cables, motorcycle plastic filters, radiators, brake fluid tanks, oil cups, water tanks, fuel tanks, air ducts, exhaust gas purifiers, tray filter plates; plastic electronics: prepaid Water meters, electricity meters, communication equipment, cordless phones, mobile phone accessories, mobile phone cases, battery cases, chargers, valve-controlled sealed maintenance lead-acid batteries, 3-inch floppy disks, U disks, SD cards, CF cards, USB connectors, Bluetooth; Toys and stationery: folders, photo albums, folding boxes, PP hollow plates, pen sets, ink cartridges, toner cartridges; medical daily use: watches, kitchen utensils, oral liquid bottle caps, drip bottle caps, mobile phone accessories, gold soft brushes, Daily necessities, hygiene products, children's products, air mattresses, hangers, knife handles, garden supplies, kitchen sanitary ware, showers, gold soft brushes, shower heads, anti-counterfeit bottle caps, cosmetic bottle caps, coffee pots, washing machines, air dehumidifiers , Electric iron, electric kettle, vacuum cleaner, speaker metal cover and civil grille, etc.
Ultrasonic effect
When the ultrasonic wave propagates in the medium, due to the interaction of the ultrasonic wave and the medium, the medium undergoes physical and chemical changes, resulting in a series of mechanical, thermal, electromagnetic and chemical ultrasonic effects, including the following four effects:
Mechanical effect
The mechanical action of ultrasound can promote the emulsification of liquid, the liquefaction of gel and the dispersion of solid. When a standing wave is formed in the ultrasonic fluid medium, the tiny particles suspended in the fluid are condensed at the node due to the mechanical force and form periodic accumulation in the space. When ultrasonic waves propagate in piezoelectric materials and magnetostrictive materials, induced polarization and induced magnetization due to the mechanical action of ultrasonic waves (see Dielectric Physics and Magnetostriction).
Ultrasonic waves can produce a large number of small bubbles when acting on liquids. One reason is that the local tensile stress in the liquid forms a negative pressure. The decrease in pressure makes the gas originally dissolved in the liquid supersaturated and escapes from the liquid to become small bubbles. Another reason is that the strong tensile stress "tearing" the liquid into a cavity, called cavitation. Inside the cavity is liquid vapor or another gas that dissolves in the liquid, maybe even a vacuum. The small bubbles formed by cavitation will continue to move, grow or burst with the vibration of the surrounding medium. When it bursts, the surrounding liquid suddenly bursts into the bubbles to generate high temperature and high pressure, as well as shock waves. The internal friction associated with cavitation can form an electric charge and cause luminescence in the bubbles due to discharge. The technology of ultrasonic treatment in liquid is mostly related to cavitation.
Thermal effect
Due to the high ultrasonic frequency and high energy, it can produce a significant thermal effect when absorbed by the medium.
Chemical effect
The action of ultrasonic waves can promote or accelerate certain chemical reactions. For example, pure distilled water produces hydrogen peroxide after ultrasonic treatment; nitrogen-dissolved water undergoes ultrasonic treatment to produce nitrous acid; and the dye aqueous solution will change color or fade after ultrasonic treatment. These phenomena are always accompanied by cavitation. Ultrasound can also accelerate the hydrolysis, decomposition and polymerization processes of many chemical substances. Ultrasound also has a significant effect on photochemical and electrochemical processes. After the ultrasonic treatment of various aqueous solutions of various amino acids and other organic substances, the characteristic absorption spectrum band disappeared and showed uniform general absorption, which indicated that cavitation had changed the molecular structure.