Cleaning the equipment can effectively extend the service life of the equipment; cleaning the equipment is conducive to energy saving and reducing the amount of cooling water; cleaning the equipment is an effective way to reduce the occurrence of safety accidents. To sum up, there are energy saving, consumption reduction, water saving, safety, stable production, improving product quality, speeding up production, extending equipment service life, reducing environmental pollution, appearance and human health. In this sense, in many industrial production processes, the effective cleaning of the dirt generated in the equipment itself is in the category of green chemistry.
1.3 chemical cleaning and physical cleaning comparison In chemical cleaning, mainly use various acids, alkalis, organic solvents, surfactants, corrosion inhibitors, chelate (complex) and other raw materials to prepare cleaning agents to remove dirt. At the same time as the dirt is removed, a large amount of waste liquid and exhaust gas are generated, which causes great damage to the environment. In order to speed up the cleaning, many industrial cleanings are chemically reacted with the scale at a relatively high temperature to achieve the purpose of removing dirt at a relatively high temperature, which requires consumption of certain energy and raw materials. Physical cleaning uses various physical, thermal, acoustic, optical, electrical and other physical effects to remove dirt. Its technical level is mainly reflected in the equipment and its optimized configuration and comprehensive application. Physical cleaning does not require the consumption of various raw materials, only requires a certain amount of energy, and does not produce various waste liquids to pollute the environment. According to the current development status of cleaning technology, chemical cleaning can clean almost all equipment and dirt, and physical cleaning can only clean the internal structure of storage tanks, pipelines, heat exchangers, etc. because of the limitations of cleaning equipment. equipment. Therefore, chemical cleaning also dominates the industrial cleaning.
2. Ultrasonic cleaning equipment In the field of industrial cleaning, ultrasonic cleaning machines have shown great advantages compared to other cleaning methods. Especially in specialized and group-oriented production enterprises, ultrasonic cleaning machines have gradually replaced traditional dipping, brushing, pressure washing, vibration cleaning and steam cleaning. Ultrasonic cleaners are highly efficient and clean, thanks to the penetrating and cavitation shock waves that their sound waves travel through the medium. Therefore, it is easy to clean the parts with complicated shape, inner cavity and fine space. For the general degreasing, rust prevention, phosphating and other processes, it takes only two or three minutes to complete under the action of ultrasonic waves. It can be several times to several tens of times higher than the traditional method, and the cleanliness can also reach a high standard. This is more prominent in many occasions where the surface quality and productivity of the product are high, which is difficult to achieve or irreplaceable by other treatment methods. result. Advantages of ultrasonic cleaning:
a. The cleaning effect is good, the cleanliness is high and the cleanliness of all the workpieces is consistent.
b. The cleaning speed is fast, the production efficiency is improved, and the cleaning liquid is not required to be touched by human hands, which is safe and reliable.
c. The deep holes, slits and hidden parts of the workpiece can also be cleaned.
d. No damage to the surface of the workpiece, saving solvent, heat, work site and labor.
Ultrasonic cleaning methods are more common than conventional cleaning methods, especially the surface of the workpiece is complex, such as some surface irregularities, mechanical parts with blind holes, some products that are particularly small and have high requirements for cleanliness such as watches and clocks. Precision mechanical parts, electronic components, circuit board components, etc., can achieve very good results by ultrasonic cleaning. The principle of ultrasonic cleaning is the high-frequency oscillating signal emitted by the ultrasonic generator, which is converted into high-frequency mechanical oscillation by the transducer and propagated to the medium-cleaning solvent. The ultrasonic waves are densely dispersed in the cleaning liquid to make the liquid forward. It flows and produces tens of thousands of tiny bubbles.
These bubbles form and grow in the negative pressure region in which the ultrasonic waves propagate longitudinally, and rapidly close in the positive pressure region. In this process known as the "cavitation" effect, the bubble closure can form an instantaneous high pressure of more than 1000 atmospheres, and the continuous generation of instantaneous high pressure is like a series of small "explosions" constantly impacting the surface of the object, so that the surface of the object and The dirt in the gap is quickly peeled off, thereby achieving the purpose of purifying the surface of the object.
The mechanism of ultrasonic cleaning mainly has the following aspects
: A strong shock wave is generated when the cavitation bubble is broken, and a part of the dirt layer is peeled off, dispersed, emulsified, and peeled off under the action of the shock wave. Because of the bubbles generated by the cavitation phenomenon, the gap between the dirt layer formed by the impact and the surface layer and the gap penetrates, because the small bubble and the sound pressure expand and contract simultaneously, the physical force such as peeling repeatedly acts on the dirt layer, the dirt The layers are peeled off and the bubbles continue to penetrate inward until the dirt layer is completely stripped. This is the secondary effect of cavitation. The impact of ultrasonic vibration of cleaning fluid on dirt in ultrasonic cleaning. Ultrasonic accelerated chemical cleaning agent dissolves the dirt, chemical and physical forces combine to accelerate the cleaning process.
Main parameters of ultrasonic cleaning: frequency: ≥20KHz
Cleaning media:
Ultrasonic cleaning, generally two types of cleaning agents: chemical solvents, water-based cleaning agents. The chemical action of the cleaning medium can accelerate the ultrasonic cleaning effect, the ultrasonic cleaning is a physical action, and the two functions are combined to fully and thoroughly clean the object.
Power density:
Power density = transmission power (W) / emission area (cm2) is usually ≥ 0.3W / cm2, the higher the power density of the ultrasonic wave, the stronger the cavitation effect, the faster the speed, the better the cleaning effect. However, for precision, high-surface finish objects, long-term high-power density cleaning can cause "cavitation" corrosion on the surface of the object.
Ultrasonic frequency:
The lower the ultrasonic frequency, the easier the cavitation generated in the liquid, the greater the force generated, and the stronger the effect, which is suitable for the initial washing of the workpiece (rough, dirty). The high frequency makes the ultrasonic direction strong, which is suitable for fine object cleaning.
Cleaning temperature:
In general, the cavitation effect of ultrasonic waves at 40 ° C to 50 ° C is the best. The higher the temperature of the cleaning agent, the more significant the effect. Generally, when the ultrasonic wave is actually applied, an operating temperature of 50 ° C to 70 ° C is employed.
2. Cleaning solution
Because of the limitations of current physical cleaning, chemical cleaning technology is still widely used in China. At present, industrial cleaning in the world has been developed from the traditional solvent cleaning, water washing and surfactant cleaning methods to the stage of fine cleaning and green cleaning. With the advancement of fine organic synthesis technology, biotechnology, detection technology and other related technologies, chemical cleaning technology has also been developed, and is developing towards green environmental protection: a green environmentally friendly chemical cleaning agent with biodegradability and enzyme catalysis will be synthesized; A weakly acidic or neutral organic compound will replace a strong acid strong base; a linear organic compound and a plant extract will replace an aromatic compound; a phosphorus-free, fluorine-free cleaning agent will replace a phosphorus-containing fluorine-containing cleaning agent; a water-based cleaning agent will Replace solvent-based and emulsion-type cleaners; biodegradable green cleaners will replace difficult-to-decompose contaminating cleaners. Green chemistry requires that the negative impact on the environment be as small as possible. It is an idea and a goal that people should try their best. Therefore, in the application of industrial chemical cleaning technology and research and cleaning new technology, engineering and technical personnel should choose non-toxic and harmless raw materials according to the principle of green chemistry, improve the utilization rate of atoms, and strive to achieve "zero emission." At the same time, the toxic and harmful substances contained in the cleaning waste liquid generated during the cleaning process must be treated to meet the relevant national emission standards before being discharged.
2.1. Hydrocarbon cleaning agent
2.1.1 Hydrocarbon cleaning agent has good environmental protection characteristics and cleaning ability, and gradually becomes one of the important industrial cleaning agents. Hydrocarbon cleaning agents are divided into: ordinary hydrocarbon cleaning agents and narrow-cut hydrocarbon cleaning agents.
Ordinary hydrocarbon cleaning agents have a wide distillation range, complex composition, irregular molecular structure, and high toxicity of aromatic hydrocarbons. Among them, the light weight fraction reduces the flash point of the cleaning agent, and the heavy mass deteriorates the cleaning power and the drying property. The narrow distillation hydrocarbon cleaning agent has a distillation range of 150 to 190 ° C. It is combined with four major factors (air, metal, water, impurities) that cause solvent acidification in industrial cleaning. It is a special stabilizer for metal cleaning agents, which can prevent solvent decomposition. It neutralizes the acid at the initial stage of decomposition and has superior acid resistance to ensure that the cleaning material is not corroded.
Features of hydrocarbon cleaning agent:
Appearance: transparent colorless liquid
Smell: slight
Structural formula: CnH2n+2
Density: 0.77 (25 ° C)
Solubility to water: poorly soluble
Vapor pressure (20 ° C, KPA): 0.6
Viscosity (20 ° C, mm 2 / s): 1.0
Surface tension (20 ° C, dyne / cm): 24
Total aromatics content %weight::<0.01
2.1.2 Advantages of hydrocarbon cleaning agent:
a, cleaning performance is good. Hydrocarbon cleaning agents are non-polar in petroleum fractions with most lubricating oils, rust preventive oils, and machined oils. Hydrocarbon cleaners are better at cleaning hydrocarbon oils than halogenated hydrocarbons and waters according to similar compatibility principles. Base cleaning agent.
b, evaporation loss is small. The boiling point of the hydrocarbon cleaning solvent is above 150 ° C. The volatilization loss during storage is small, and the sealing requirements for packaging materials and equipment are very low.
c, the toxicity is extremely low. According to the toxicological test, the hydrogen absorption and detoxification, oral toxicity and skin contact toxicity of the hydrocarbon cleaning agent are ultra-low toxicity, and are not carcinogenic substances, and the cleaning operator is safer to use.
d, material compatibility is good. The hydrocarbon cleaning agent does not contain moisture and corrosive substances such as chlorine and sulfur, and does not cause corrosion or oxidation to various metal materials. Hydrocarbon cleaning agents are also non-polar solvents that do not dissolve, swell and embrittle most plastics and rubber.
e. The cleaning process is simple. Simply cleaning - cleaning - rinsing - rinsing - drying (or drying), there is no corrosion of the workpiece.
f, can be completely evaporated without residue. Hydrocarbon cleaning agent is a very pure refined solvent that can be completely volatilized at room temperature and under heating without any residue.
g, does not damage the environment. The hydrocarbon cleaning agent can be degraded automatically. The cleaning waste liquid can be put into a coal-fired or oil-fired boiler for incineration. The incineration product is mainly CO2 and water, and has no pollution to the air. Chlorine cleaning agent does not initiate chlorine, and the coefficient of damage to ozone is zero.
2.1.3 Application range of hydrocarbon cleaning agent
Hardware, jewelry, watches, electronics, electrical, liquid crystal, semiconductor and other industries, can effectively remove all kinds of oil, grease and soldering resin, polishing wax
2.1.3 Selection of raw materials for hydrocarbon cleaning agents
120#, 160# solvent oil, D40, D80 deodorizing solvent kerosene, alkanes, alcohol solvents, etc.
2.2 Aqueous cleaning agent
2.2.1 Principles of raw material selection for cleaning solutions
The following principles should be considered when selecting the raw materials for cleaning: use less harmful substances as much as possible; use less materials that are difficult to treat as much as possible; minimize the discharge of cleaning waste liquid; try to recycle the cleaning liquid as much as possible. Take the cleaning of a device as an example, compare the traditional pickling method with the weak acid organic compound cleaning method currently being researched and developed: traditional pickling method: formula (mass fraction): hydrochloric acid, fluoride, corrosion inhibitor, Water weak acid organic compound cleaning method: formula (mass fraction): organic acid, surfactant, corrosion inhibitor, water
3. Introduction to water-based cleaning agent process
3.1 Desulfurization ultrasonic cleaning process comparison
3.1.1 Typical Process for Trichloroethylene Cleaning Ultrasonic rough oil removal→ ultrasonic fine oil removal→ solvent steam degreasing
3.1.2 General Process of Hydrocarbon Cleaning Agent Ultrasonic rough oil removal→ ultrasonic fine oil removal→ ultrasonic fine oil removal→drying 3.1.3 General process of water-based cleaning agent
3.1.3.1 Stainless steel workpiece cleaning process (general ordinary parts) ultrasonic rough degreasing → ultrasonic fine degreasing → municipal water rinsing → municipal water rinsing → municipal water rinsing → compressed air drying (or centrifugal drying) → drying the above process Also suitable for the cleaning of some aluminum alloy workpieces. 3.1.3.2 Stainless steel workpiece cleaning process (precision parts) ultrasonic rough oil removal → ultrasonic fine oil removal → municipal water rinse → municipal water rinse → pure water rinse → pure water rinse → compressed air blow dry (or centrifugal drying) → drying
3.1.3.3 Carbon steel parts, copper parts, workpiece cleaning process, ultrasonic rough degreasing → ultrasonic fine oil removal → municipal water rinsing → municipal water rinsing → deoxidation (rust removal) cleaning → municipal water rinsing → municipal water rinsing → pure water rinsing → Anti-oxidation protection→Pure water rinsing→Pure water rinsing→Compressed air drying (or centrifugal drying)→Drying
3.1.3.4 Aluminum battery shell workpiece cleaning process ultrasonic rough oil removal → ultrasonic fine oil removal → ultrasonic fine oil removal → municipal water rinse → municipal water rinse → municipal water rinse → compressed air blow dry (or centrifugal drying) → drying
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