Classification of Industrial Cleaning
After understanding the classification of industrial cleaning, we can choose suitable cleaning process according to object to be cleaned to achieve the purpose of cleaning. Industrial cleaning can be classified from different perspectives. For example, according to cleaning principles, it can be divided into chemical cleaning, physical cleaning and microbial cleaning. For physical cleaning, it can be divided into thermal molecular power cleaning, jet cleaning, scrubbing, ultrasonic cleaning, light cleaning (etc.) according to the generation of cleaning. According to the cleanliness, it can be divided into conventional and precision industrial cleaning. According to cleaning method, it can be divided into wet cleaning and dry cleaning (etc.).
Classification According to Cleaning Principle
1. Chemical Cleaning
The cleaning that uses chemicals to react with dirt to dissociate the dirt from the surface of the cleaning object and dissolve it into the water is called chemical cleaning. The chemicals used in the chemical cleaning process are called chemical cleaning agents. Common chemical cleaning agents include various inorganic or organic acids, alkalis, oxidants, metal ion chelating agents and so on. For example, mineral acid is used to remove rust and scale on metal surfaces, bleaching oxidants are used to remove stains on the surface of objects, fungicides and disinfectants are used to kill microorganisms and remove dirt or mildew attached to the surface of objects. Chemical cleaning generally needs to use other composite cleaning methods such as high-pressure water jet, rinsing, electrolysis (etc.) to achieve the cleaning purpose.
2. Physical Cleaning
Physical cleaning refers to crush dirt, decompose and peel off the surface of the object through various mechanical external forces and energy to achieve cleaning. That is, all methods that use the principles of heat, mechanics, acoustics, optics, and electricity to remove surface dirt should be classified as physical cleaning. Common physical cleaning methods include ultrasonic cleaning, spraying, rinsing, high-pressure water jet cleaning, dry ice cleaning, plasma cleaning, laser cleaning and blast cleaning. Physical cleaning also requires the participation of certain chemicals to improve the efficiency of cleaning.
This book mainly focuses on ultrasonic cleaning.
3.Microbial Cleaning
Microbial cleaning mainly refers to enzymatic cleaning. Enzymes refer to protein with catalytic ability produced by plants, animals and microorganisms.
The high-efficiency special biocatalysis of enzymes is used to decompose the oil or protein pollution on the surface of industrial parts and equipment to be cleaned, and convert them into non-toxic and harmless water-soluble substances and remove them. Using this kind of enzymatic cleaning to completely decompose pollutants is truly environmentally friendly cleaning technology.
Classification According to Cleanliness of Cleaning
According to the cleanliness of cleaning, cleaning can be roughly divided into three categories: conventional, precision and ultra-precision industrial cleaning.
1. Conventional Industrial Cleaning
Conventional industrial cleaning is also called traditional industrial cleaning. This cleaning method started after entering industrial production, purely for assembly and cleaning. During the production of machine parts, cutting oil, coolant, cutting debris, powder (etc.) are attached to the surface. The traditional parts cleaning is mainly to clean the dirt and metal chips on the surface of the parts before the machine assembly, but after cleaning, there will be more residual fiber and hair.
Generally, diameter of the particulate that can be observed with the naked eye and touched by hand is about 10μm, which belongs to the range of conventional industrial cleaning product. Conventional industrial cleaning is only suitable for products with low cost, large assembly dimensional tolerances, low precision requirements and not very sensitive to pollutants.
2. Precision Industrial Cleaning
The meaning of precision industrial cleaning has two aspects: one is that the cleaned product is more precise with high performance, high reliability and miniaturization, the other is that the cleaned product has fewer and smaller residual pollutants and has relatively high cleanliness.
Compared with conventional industrial cleaning, precision industrial cleaning has stronger cleaning methods, cleaning capabilities, higher cleaning efficiency, more advanced cleaning techniques, cleaning technical equipment and testing methods. After precision industrial cleaning, no water marks can be seen on the surface of the object (handprints, hair, dander, etc.). The remaining dirt particles are less than 1μm of diameter, which can usually be observed with optical microscope. The diameter of the particles that can be observed by optical microscope is 10¯ 7～10¯5m.
3. Ultra-precision Industrial Cleaning
The continuous innovation and development of high technology has opened up a huge market, but it is also very sensitive to pollutants in production, and has stricter requirements on the cleanliness of parts and assembly. For the strong demand, ultra-precision industrial cleaning came into being. For example, the diameter of the dirt particles required to be removed in the semiconductor electronics industry such as silicon wafers can even be as small as 10 ¯ 10㎡. Such small particles cannot be observed even with an electron microscope, because ordinary electron microscopes can observe particles ranging from 10¯9 to 10¯7m. Usually, the washing that requires such small dirt particles to be removed is called ultra-precision industrial cleaning.
List 1-1 will give readers a specific concept of industrial cleaning grade and dirt particle size.
Sheet 1-1 Industrial cleaning grade and the range of dirt particle diameter
Classification According to Cleaning Method
1. Dry Cleaning
Removal of dirt is carried out in the air or in an inert gas medium such as nitrogen and argon. The cleaning method using gas as the medium is called dry cleaning. Using soot blowers to purge boiler burners in power plants is one of the easiest dry cleaning practices.
For example, sandblast cleaning of castings in large equipment manufacturing plants, dry ice cleaning of parts, laser cleaning of micro silicon wafers and plasma cleaning are all belonged to dry cleaning.
2. Wet Cleaning
Immersing the workpiece to be cleaned in the solution, the liquid medium is used to wet the surface of the workpiece, and then the chemical molecular force or physical impact is applied to cut, crush, wrap, and roll off the dirt attached to the surface of the workpiece for cleaning, then assisted with diffusion, dilution, volatilization and other methods to recover the dry state of the workpiece. This cleaning method of immersing objects in solution medium is called wet cleaning. Ultrasonic cleaning belongs to wet cleaning method.
Classification by Cleaning Medium
Ultrasonic cleaning must be carried out in liquid which should be conducive to the transmission of ultrasonic energy, and removing the dirt from the surface of the workpiece, also dispersed in the cleaning liquid. This cleaning fluid is called cleaning medium. Ultrasonic cleaning is divided into three categories according to different cleaning medium: water-based cleaning, organic solvent cleaning, and semi-aqueous cleaning.
1. Water-based Cleaning
Water is strong polar solvent, which has strong cleaning ability for polar and ionic pollutants. Due to the easy access to water and low price, most industrial ultrasonic cleaning uses water-based cleaning.
In addition to using different grades of pure water and ionized water (functional water) for ultrasonic cleaning and rinsing during fine wash, water-based cleaning can also use city water (tap water) to add certain proportion of acid, alkali, salt, surface active agent and chelating agent(etc.) to the water and formulate into solution, which can be used for rough & semi-fine washing for different workpiece pollutants, which can greatly improve the cleaning efficiency.
However, water is not inexhaustible. Per capital hold of water resources are 2700㎡in our country, which is only 1/4 of the world average. Water-based cleaning requires a lot of water resources. In recent years, with the progress of society and the rapid development of productivity, water consumption for production and living has been increasing. In fact, water resources are insufficient. Therefore, protecting the water environment, saving water resources, and controlling water pollution are strategic measures to implement sustainable development in our country. The recycling of water and the scientific treatment and reuse of waste water after cleaning are indispensable.
2. Organic Solvent Cleaning
Organic solvent cleaning agents mainly refer to organic solvents that do not contain water in their ingredients. Most of them use hydrocarbons (petroleum), chlorinated hydrocarbons, fluorinated hydrocarbons, brominated hydrocarbons, alcohols (etc.) as the main cleaning agent. Organic solvents are mainly used to dissolve some water-insoluble substances (such as grease, wax, resin, rubber, dyes, etc.) and varieties of organic dirt. It is characterized by being liquid at room temperature and pressure, with good fluidity, small viscosity, greater volatility, less residue on the surface of the substance after cleaning, and the properties of the solute and solvent are unchanged during the dissolution process. Since organic solvents are easily volatile and enter the environment, not only pollute the air, but also fat-soluble, and are toxic to the human body, the development of organic solvent cleaning agents with lower toxicity and less volatility has become the development direction in recent years, there are HCFC (hydrochlorofluorocarbon) cleaning agents, PFC cleaning agents, HFE solvents, various non-ODS cleaning agents.
At present, the cleaning industry is very optimistic about petroleum hydrocarbon solvents (H, C). Practice has proved that hydrocarbon solvents with low flash point and high boiling point meet the quality applicability standards. Its characteristics are strong cleaning power, low use cost, recyclable, safe for people and environment.
3. Semi-aqueous Cleaning
The solution in which water or surface active agent is added to the organic solvent is called semi-aqueous cleaning agent. In some literatures, it is also called emulsion cleaning agent or microemulsion cleaning agent. The semi-aqueous cleaning agent not only maintains the advantages of the original solvent-based cleaning agent for oil dirt cleaning and good wet penetration of the matrix, but also improves the removal ability of water-based dirt. Compared with organic solvent cleaning agents, it has expanded the ability to clean dirt. Due to the addition of water, the flash point of the cleaning agent is increased, the volatility is reduced, the safety of the original solvent is improved, and the application range becomes wider.
According to the difficulty of dissolving in water, organic solvents can be generally divided into water-soluble solvents and insoluble solvents. Water-soluble solvents are mainly alcohols, ethers and ketones. They have good removal effects on oil dirt and water-based dirt. The disadvantage is that they are flammable. Adding little amount of water to form semi-aqueous cleaning agent can reduce their flammability, and safe while using. Insoluble solvents are mainly petroleum hydrocarbon solvents. The shortcomings of these organic solvents, terpene hydrocarbon solvents and halogenated hydrocarbons are low flash point, flammable and explosive, and when such organic solvents are made into semi-aqueous cleaning agents, due to there are big difference between non-aqueous organic solvents and water, only add water will cause incompatibility and stratification. Surface active agent must be added to reduce the interfacial tension between them and improve their compatibility to achieve mixing effect.