release time:2016/10/17 8:54:45
Ultrasonic cleaning is the ultrasonic vibration energy spread to the cleaning solution, the use of the combined effect of the two to clean the dirt on the cleaning parts. Ultrasonic cleaning in the industrial application of a wide range, mainly for zero, parts cleaning requirements of more stringent occasions, such as parts in the finishing process of cleaning, pre-assembly cleaning, geometric shape complex (porous, deep hole, Blind holes, microporous) of the hole parts of the cleaning, as well as dirt adhesion of small and medium parts cleaning. Ultrasonic cleaning In addition to cleaning zero, the surface of the oil components, the surface of the residual parts of the grinding paste, polishing paste and other paste dirt also has a good cleaning effect. In addition, it can also be used to remove mild rust or oxide on the surface of the part. Ultrasonic cleaning for the removal of carbon deposition effect is very good (need to use specially prepared cleaning fluid), and has a more mature experience. In the diesel locomotive manufacturing and repair department, ultrasonic cleaning has been applied to some small parts and precision parts cleaning, such as cylinder head, rolling bearings, gears, valve parts, pump parts, a variety of filter components, , High-pressure pump plunger, fuel injector needle, high-pressure oil pump out of the valve, such as cleaning. In foreign countries, has adopted high-power ultrasonic cleaning equipment, to clean the diesel engine body and locomotive on the large zero, parts. Some of our diesel repair factories have also begun to use high-power ultrasonic cleaning machine to clean the diesel engine to be repaired (bore 150 ~ 230 mm), and achieved the desired cleaning effect. The use of ultrasonic cleaning, simple process, easy operation, low labor intensity, good cleaning quality, high cleaning efficiency, and easy to achieve zero, parts cleaning automation, which is a very promising cleaning method. The following are the same as the "
First, the principle of ultrasonic cleaning
Ultrasonic waves are essentially the same as acoustic waves, and are the propagation of mechanical vibrations in elastic media. The difference between ultrasonic and acoustic waves is only in the frequency range. Sound waves refers to the human ear can hear the sound, generally believed that the frequency of sound waves in the range of 20 ~ 20000 Hz, and vibration frequency of more than 20 kHz or more sound waves are called ultrasound. Ultrasonic vibration frequency of 100 kHz or less called low-frequency ultrasound; vibration frequency of 100 kHz to tens of MHz called high-frequency ultrasound. Ultrasonic used for cleaning the frequency used by 20 to 400 kHz, belonging to the low frequency and high frequency ultrasonic range. Ultrasonic cleaning, the role of ultrasound, the mechanical vibration spread to the cleaning tank cleaning fluid, so that the cleaning fluid alternately appear in the dense phase of the vibration, the liquid is constantly being stretched and compressed. Sparse place is stretched to form microbubbles (holes); dense places are compressed. Since the inside of the cleaning solution is frequently stretched and compressed by the vibration of the ultrasonic wave, the microbubbles are continuously generated and continuously broken. Microbubble rupture, the surrounding cleaning fluid at a great speed from all directions toward the center of the bubble, resulting in water hammer. This phenomenon can be observed directly by the naked eye, that is, in the cleaning fluid can be seen in the activities of the bubble, and cleaning fluid up and down convection. At this point if the finger immersed in the cleaning solution, there is a strong feeling of acupuncture. This phenomenon is called ultrasonic cavitation. In the ultrasonic cavitation for a certain time, the dirt on the cleaning parts gradually fall off (of course, there is the role of cleaning fluid itself), which is the basic principle of ultrasonic cleaning. A longer period of ultrasonic cavitation, will make the surface of the substrate to be a certain degree of peeling off, which is called cavitation erosion. Ultrasonic shock wave can produce micro-flow in the liquid, with stirring effect. In the immiscible two-phase liquid, micro-flow can promote the two liquid phase to accelerate each other dispersed, with emulsification. The cavitation of the cavitation is carried out by the cavitation nucleus, and the surface of the surface of the cleanser is just the center of the cavitation core. In short, ultrasonic cleaning is ultrasonic cavitation, erosion, agitation, emulsification and cavitation effect of the comprehensive performance. Which cavitation in the ultrasonic cleaning is the main role, it can damage the dirt particles in the cleaning surface of the adhesive surface. Coupled with the role of micro-flow, so that the cleaning fluid to produce vibration and stirring, the dirt from the surface to be cleaned clean. And the emulsification effect is to wash the oil quickly dispersed, emulsified in the cleaning solution. It should be noted that the ultrasonic cleaning process, in addition to the role of ultrasound, the use of cleaning fluid infiltration, soaking, emulsification, dispersion and dissolution and other effects, the result will greatly speed up the cleaning process to improve the cleaning effect. The following are the same as the "
Second, ultrasonic cleaning equipment
Ultrasonic cleaning equipment mainly by the ultrasonic generator and cleaning tank composed of two major parts. In the case of a large batch of washing parts, a cleaning liquid circulation device is also attached; sometimes, in order to realize the cleaning process, the cleaning member conveyance device is attached. In general, the ultrasonic generator and the cleaning tank are two structurally independent devices, which are connected by only one cable to transmit electrical power. But some of the ultrasonic cleaning equipment is the combination of the generator and cleaning tank. The ultrasonic generator is the power source that generates the ultrasonic frequency signal. Commonly used ultrasonic generator from the structure is divided into: tube, transistor, SCR and high frequency motor four. One SCR tube ultrasonic generator small size, high efficiency, easy to operate. CFS-3 type ultrasonic generator belongs to this type. The external structure of the ultrasonic generator is a box with a variety of electrical components. In order to ensure the normal operation of these electrical components, in the power of the ultrasonic generator is also equipped with a cooling fan. The generator is equipped with a console, a power switch, a high voltage switch, a power adjustment knob, a frequency adjustment knob, and a current and voltage table that show the cathode current and the screen voltage. Thyristor tube type ultrasonic generator without frequency adjustment knob. Ultrasonic cleaning tank by the stainless steel tank, transducer and bracket and other components. The transducer is the main part of the ultrasonic cleaning equipment. The function of the transducer is to convert the electric power delivered by the ultrasonic generator into the mechanical vibration of the ultrasonic wave, and then through the radiation of the stainless steel tank, the cleaning liquid also causes the ultrasonic liquid vibration. Commonly used transducers are magnetostrictive and piezoelectric. The magnetostrictive transducer is made of ferromagnetic material such as iron, nickel or diamond or its alloy, and the magnetostrictive effect is used to generate ultrasonic vibration of the ultrasonic wave in the magnetic field formed by the high frequency current. Piezoelectric transducer is made of piezoelectric crystal materials (such as zirconium lead acid, barium titanate, etc.), the use of its piezoelectric effect, the electrical energy into ultrasonic mechanical vibration. Magnetostrictive transducer excitation of the ultrasonic mechanical vibration is a low frequency (frequency 20 ~ 60 kHz), suitable for larger zero, parts of the ultrasonic cleaning. Piezoelectric transducer excited ultrasonic mechanical vibration is a high frequency (frequency of 100 kHz to 1 MHz), suitable for small parts and complex parts of the cleaning. In order to achieve high conversion efficiency, the transducer should be operated as much as possible at its natural frequency. Because only when the frequency of the applied voltage and the natural frequency of the transducer is equal or similar, it will resonate, then the output of the ultrasonic wave has the largest amplitude value, can get the maximum output power. Piezoelectric transducer transducer conversion efficiency than the magnetostrictive transducer is high, and the structure is simple, uniform ultrasonic distribution, it is widely used. Structurally, piezoelectric transducers are two lead zirconate titanate piezoelectric crystals placed between two different densities of material - iron and aluminum - and then clamped by bolts to make. In general, a number of transducers are often uniformly distributed in a cleaning tank, depending on the magnitude of the output power of the ultrasonic generator. The impedance of the same set of transducers should be equal or similar so that the load on each transducer is equalized. (Frequency difference should be within ± 0.1% of the range), so that each transducer can have a higher conversion efficiency. To this end, the same device of the transducer must be impedance and operating frequency of matching, matching a good transducer with E-1 glue in the bottom of the tank tank cleaning tank. The combination of the transducer and the cleaning tank and the formulation of the E-1 glue are attached to the end of this section. In order to meet the needs of ultrasonic cleaning large parts, there is a soaking in the cleaning fluid can work in the so-called submerged transducer. In the case of a submerged transducer, there is a sealed housing which, when used, allows the transducer to be freely placed in the cleaning tank according to the shape of the large workpiece to achieve the use of a smaller power transducer to clean larger parts purpose. Cleaning tank made of stainless steel plate welding, with corrosion resistance, fatigue resistance, good acoustic performance, high strength, light weight and so on. The tank is made of stainless steel because the cleaning tank may use a variety of acid and alkali cleaning solution, and the ultrasonic energy in the ultrasonic cavitation area is very concentrated, the strength of the tank material requirements are higher. Medium and small cleaning tank groove wall thickness is generally 1 to 2 mm, large cleaning tank groove wall thickness of 3 to 4 mm. The bottom of the cleaning tank requires smoothing and smoothing. The connection between the bottom and the bottom of the tank should be tightened so as to avoid vibration and noise during leakage and cleaning. In general, an ultrasonic generator is equipped with a cleaning tank, but a high-power ultrasonic generator can also be equipped with several smaller power cleaning tanks, as long as they can match the power can be equal. In the cleaning of large parts or the use of large cleaning tank, in addition to the use of high-power ultrasonic generator, but also often several small and medium-sized ultrasonic generator combination. Such as the use of three power each 2 kilowatts of ultrasonic generator combination of cleaning the spline of the spline shaft is an example. In order to optimize the working condition of the ultrasonic cleaning equipment, the output impedance of the generator should be consistent with the total dynamic impedance of the transducer, and the operating frequency of the generator and the transducer should be consistent. In this way, in the rated operating conditions, the ultrasonic generator through the transducer to convert out the maximum sound power.
Third, the ultrasonic cleaning process analysis
Ultrasonic cleaning effect depends on the correct selection of ultrasonic cleaning process. To this end, for some process parameters (such as ultrasonic frequency, ultrasonic power density, ultrasonic cleaning time), the placement of the cleaning parts, the requirements of cleaning fluid and its formula for a brief analysis. The following are the same as the "
(A) the ultrasonic frequency
In the ultrasonic cleaning, we must first choose the correct frequency of ultrasound. Ultrasonic frequency is a decisive role in the process parameters, because it has a direct impact on the cavitation. The lower the ultrasonic frequency, the stronger the cavitation effect, the cleaning effect is also ideal, but the noise is greater. So the general use of the ultrasonic frequency of about 20 kHz, this time the cavitation effect is strong, cleaning effect is also better. For parts with high surface finish and hole parts with smaller diameters, it is advisable to use high-frequency ultrasonic cleaning with a shorter wavelength and more concentrated energy. But the high-frequency ultrasonic vibration in the cleaning fluid in the larger attenuation, the role of a shorter distance, cavitation strength is weak, so the cleaning efficiency is low. In addition, due to the direction of high-frequency ultrasound generated by the "shadow", will cause some parts of the cleaning parts can not wash the phenomenon. In the use of non-frequency tracking ultrasonic cleaning machine, the need to constantly adjust the ultrasonic generator "frequency adjustment" knob, so that the frequency of its output signal and the transducer's natural frequency is always consistent, so as to achieve the strongest cavitation, Cleaning effect the best purpose. The following are the same as the "
(B) ultrasonic power density
Ultrasonic cleaning, the cleaning effect is increased with the increase in ultrasonic power density. However, excessive power density can cause erosion of the surface of the object to be cleaned (the so-called cavitation corrosion) due to excessive cavitation, resulting in damage to the surface of the object to be cleaned. This phenomenon, especially on the workpiece on a variety of coatings and aluminum alloy is more prominent. For this reason, for the serious degree of oil pollution, the shape of complex, deep hole and blind hole of the cleaning parts, and in the cleaning tank deeper, cleaning fluid viscosity, you can choose a larger power density. High-frequency ultrasonic cleaning, the power density can also be selected to offset some of its attenuation, the role of short distance weakness. If rinsing is performed in a smaller viscosity cleaner, the ultrasonic power density can be chosen to be smaller. The following are the same as the "
(C) cleaning time
The effect and quality of ultrasonic cleaning is related to the time of ultrasonic cleaning. Cleaning time is too short will not meet the quality requirements of cleaning; but the cleaning time is too long, not only reduce the efficiency, but also because of ultrasonic cleaning of the surface of the cavitation corrosion of the parts affected the surface quality. The degree of oil pollution, the shape of complex parts cleaning time should be slightly longer; with a variety of coating parts, aluminum and aluminum alloy cleaning time should be shorter; surface finish higher parts, under normal circumstances the oil will be relatively less, At this time cleaning time should not be too long. The specific cleaning time for different pieces should be determined by testing. The following are the same as the "
(4) Placement and cleaning of the parts to be cleaned
Commonly used ultrasonic cleaning method is to be washed parts in the cleaning tank cleaning solution for cleaning, which is mainly applied to the general, small parts. For large parts with large external dimensions, local cleaning methods can be used. Will be part of the cleaning parts will be immersed in the cleaning solution for cleaning, to be cleaned and then have not yet cleaned the site immersed in the cleaning solution to continue cleaning, followed by completely washed all over. For large parts (such as crankshaft) that can be lowered in the cleaning tank, an immersion transducer can be used for ultrasonic cleaning. For the serious degree of oil parts, can be heated to dip or rinse, and then use ultrasonic cleaning. This can improve cleaning efficiency and reduce cleaning costs. For the more complex geometric shapes (such as holes of different sizes, concave angle, etc.), you can use a variety of frequencies of ultrasonic cleaning, that is, at several different ultrasonic frequencies for cleaning. For demanding workpieces, several different formulations of cleaning fluid can be used, sub-tank followed by ultrasonic cleaning. If the use of water-based cleaning fluid (such as alkaline cleaning solution and metal cleaning agent cleaning solution) for cleaning, the final application of hot water on the workpiece rinse. In the same cleaning tank, the cavitation intensity of the ultrasonic wave is not uniform. In the vertical direction of the cleaning tank, it is divided into cavitation strong and non-intense areas. Cavitation strong area and not strong area and phase, ultrasonic cleaning, the parts should be placed in the cavitation strong area, in order to obtain a better cleaning effect. If the workpiece is large, the workpiece can be slowly moved during cleaning. Cavitation strong area, the more close to the ultrasonic source, the higher the cavitation strength. To this end, ultrasonic cleaning, should be washed as close as possible to the ultrasonic source. If the cleaning element is too far away from the ultrasonic source, part of the energy of the ultrasonic wave will be absorbed by the cleaning solution. For those parts with high accuracy, during the ultrasonic cleaning process, in order to prevent them from colliding with each other