Cleaning refers to the removal of liquid and solid contaminants on the surface of fasteners to achieve a certain degree of cleanliness. Cleaning is an intermediate process that cannot be ignored in the production of fasteners. Contaminants on the surface of the fastener directly enter the heat treatment furnace or flow, volatilize or burn in the workshop, which is likely to cause environmental pollution. Cleaning is a category of cleaner production. The cleaning process is the interaction between cleaning media, contaminants and fastener surfaces. It is a complex physical and chemical process.
1, cleaning methods and methods
1.1 Cleaning type
There are two main cleaning steps in the fastener industry: one is cleaning before heat treatment, mainly cleaning the residual oil, coolant and anti-rust liquid in the previous process; the second is cleaning after heat treatment, mainly cleaning and quenching After the residual quenching oil. According to the cleaning method and principle, it can be divided into: physical cleaning, chemical cleaning, and the like.
1 Physical cleaning Physical cleaning refers to the use of various mechanical external forces and energy to smash, decompose and peel off the surface of the object to achieve the cleaning effect. Commonly used methods are spray, high pressure water jet, agitation, ultrasonic cleaning, and the like.
2 Chemical cleaning Chemical cleaning refers to the use of one or several chemical agents or other aqueous solutions to chemically convert, dissolve, and remove contaminants on the surface of the object with a cleaning agent to achieve a cleaning effect. Common cleaning methods include alkaline water cleaning, solvent cleaning, and the like.
1.2 Common cleaning methods
1 immersion cleaning. A cleaning method is performed by adding a cleaning liquid to the cleaning tank and impregnating the fastener to be cleaned. Since it is cleaned only by the chemical action of the cleaning liquid, the washing ability is weak and it takes a long time.
2 jet cleaning. A jet nozzle is installed in the cleaning tank, and the cleaning liquid is sprayed onto the surface of the fastener to be cleaned with a gas, and the pressure is greater than 2 MPa.
3 jet cleaning. The cleaning liquid is ejected from the side of the tank in the liquid phase, and the washing is promoted by the stirring force (physical action) of the washing liquid. The washing ability is stronger than the dipping cleaning.
4 spray cleaning. A spraying device is installed in the cleaning tank to spray the cleaning liquid onto the surface of the fastener to be cleaned, and the cleaning pressure is less than 0.2 MPa.
5 decompression cleaning. A negative pressure is generated in the cleaning tank, and the detergent can penetrate well between the slits of the fastener to be cleaned due to the pressure reduction. If combined with ultrasonic waves, the cleaning effect is greatly enhanced.
6 spray cleaning. A spray tube is installed in the cleaning tank to spray the detergent onto the surface of the fastener to be cleaned in the gas phase. The pressure is generally 0.2 to 2 MPa.
1.3 Residual oil cleaning method
The cleaning of the residual oil is mainly for the cleaning oil attached to the surface of the fastener during cold heading or cutting, and the cleaning of the residual oil on the surface of the fastener after quenching in the heat treatment oil.
1 alkaline water cleaning method
The simplest alkaline water cleaning is a direct heating or indirect heating cleaning tank, which is 3% to 10% N2CO3 or NaOH aqueous solution.
For self-tapping screws for carburizing or carbonitriding, the intermediate cleaning before tempering is usually carried out with a sodium Carbonate solution heated to 50-70 ° C in 5% to 10%. This is the case with a connected mesh belt furnace. Fastener cleaning generally uses a dual method of spraying and immersing. If the effect is better with hot water, the high pressure airflow is used for drying.
The main disadvantage of the alkaline water cleaning method is that the cleaning effect is not very good, especially the blind holes and the groove portion of the fastener are prone to stains and residues. The wastewater generated by alkaline water cleaning must be neutralized and the waste oil recovered to meet relevant environmental requirements before being discharged.
2 metal cleaning agent cleaning method
In order to overcome the shortcomings of the alkaline water cleaning method and improve the cleaning effect, a special metal cleaning agent can be used at present, the cleaning agent is diluted into a 1% to 3% solution in 40-70 ° C water, and the fastener is soaked in the solution 15 ~ 20 min, then rinsed with hot water, and finally dehydrated with a dehydrator. Can be used in the washing machine.
The disadvantage of the metal cleaning agent cleaning method is that it is expensive and has an unpleasant odor. It has a certain corrosive effect on the fasteners, and the wastewater pollutes the environment. Therefore, the wastewater must be treated and the waste oil recovered.
3 organic solvent cleaning method
It is cleaned with an organic solvent such as trichloroethane or trichloroethylene, and the cleaning effect is good. When the quenching fastener is cleaned by immersion or spraying under normal pressure, the volatilization and splashing of the organic solvent pollute the environment. To this end, a complete set of closed vacuum decompression solvent vacuum cleaning method is used, the vacuum pump is used to discharge the air, and the fastener is in contact with high-density solvent vapor in the absence of air to further improve the cleaning effect, and the solvent and oil are recovered by vacuum evaporation. . The solvent content of the recovered oil is reduced from 20% to less than 4%, which is lower than 50 ppm of the environmental sanitation regulations of trichloroethylene.
4 combustion degreasing method
Cold-pressed or machined fasteners need to be cleaned of the surface oil before entering the heat treatment process. To this end, the fastener can be heated in a degreasing furnace to 350 ° C ~ 400 ° C to vaporize or burn the oil to achieve the purpose of fastener degreasing or surface phosphorus removal.
The combustion degreasing method is only suitable for cleaning before heat treatment, and can also clean light, low viscosity and low boiling oils such as cooling oil and antirust liquid. After the high-viscosity, high-boiling heavy quenching oil is burned, a large amount of residue and carbon black adhere to the surface of the fastener, failing to clean the object.
2, cleaning technology brief
For fasteners requiring high surface cleaning, such as aviation bolts, automobile engine connecting rod bolts, etc., advanced cleaning techniques such as vacuum or ultrasonic are currently used to replace the commonly used chlorinated hydrocarbons that have a destructive effect on the atmospheric ozone layer. The method can achieve efficient and environmentally friendly cleaning.
2.1 Vacuum solvent cleaning technology
Vacuum solvent cleaning uses a hydrocarbon solvent as a cleaning agent and has a strong dissolving ability for quenching oil, cooling oil and anti-rust liquid. Vacuum solvent cleaning machine is used to pre-wash the fastener under vacuum. Cleaning process such as shower, steam spray, circulating spray and vacuum drying, with efficient and stable cleaning ability, excellent cleaning effect, energy saving and environmental protection.
2.1.1 Vacuum water-based cleaning technology
The water-based vacuum cleaning is performed by using a volatile liquid such as quenching oil or cooling oil to reduce the boiling point and heating it together with oil, water, water vapor, etc., and the boiling point thereof is also lowered. Because it is (vacuum) decompression cleaning, it has good cleaning effect on cup-shaped or blind-hole shaped fasteners, and can be vacuum-dried (degreasing), and the cleaning temperature is high. It needs low temperature and medium temperature after carburizing and quenching. The fire screws can be cleaned and tempered. The tempering process is omitted, energy is saved, and energy saving and environmental protection requirements are met. Process and effect:
1 cleaning process loading fasteners (about 1min) → vacuum (about 3min) → pre-washing (about 1min) → fast steam cleaning (about 8min) → circulating spray (about 5min) → vacuum drying (about 7min)→Remove the fasteners (about 2min) for about 35min. 2 Cleaning effect The fastener is effectively cleaned by using a hydrocarbon solvent and a solvent vapor under vacuum, and then the fastener is dried under vacuum. At the same time, the regeneration device distills the solvent under vacuum negative pressure and condenses and recovers the pure solvent. The separated waste liquid is collected and discharged separately, which not only can obtain high-quality cleaning effect, but also is environmentally friendly.
2.1.2 Vacuum water-based cleaning process
1 The front cleaning fastener is sent to the front chamber of the vacuum cleaner, and the micro-jet and air bubble cleaning techniques are employed. First, spray coarse cleaning with warm water without cleaning solution. Then, soak the fastener into the groove. At this time, the air bubbles ejected from the bottom are combined with the jets coming out from the side, and even if no cleaning agent is added, most of the oil is cleaned, and a satisfactory effect can be obtained as compared with the single soaking method.
2 Vacuum cleaning After the front chamber is cleaned, the fasteners are sent to a vacuum chamber, and the remaining oil and water are evaporated by vacuum decompression. Using the principle of vacuum steam distillation and vacuum azeotropic distillation to solve the shortcomings of poor water washing and cleaning ability /
3 After vacuum drying and vacuum cleaning, there is only residual water on the fasteners, and there is no residual oil. To prevent the water from rusting the fasteners, it should be dried quickly. Vacuum drying is the most effective means of rapid drying.
2.2 Ultrasonic cleaning technology
Ultrasonic cleaning technology utilizes the cavitation effect, acceleration effect and sound flow effect of ultrasonic waves to enhance various physical and chemical reactions on the surface of liquids and fasteners, and reduce the relative amount of chemical medium in solution, or to reduce pollution. Weak medium replaces the heavily polluted medium, so ultrasonic technology is an effective and environmentally friendly surface cleaning technology with application value.
2.2.1 Ultrasonic cleaning technology
Ultrasonic cleaning is an ultrasonic alternating signal of up to several tens (20 to 33) KHz per minute. It is converted into a vibration wave that moves up and down through a transducer (an ultrasonic generator that converts electrical energy into mechanical energy) and passes through the bottom of the cleaning tank. Or the side, even the upper part acts on the cleaning solution. Thousands of small micro-electron bubbles are generated in the cleaning liquid, and these bubbles are continuously generated and continuously closed under the action of ultrasonic waves. When closed, they collide with each other to create a shock wave of thousands of atmospheric pressures (this is the ultrasonic "cavitation" effect), thereby destroying the insoluble dirt and dispersing them in the cleaning solution. When the group particles are wrapped by oil and adhere to the cleaning fastener. The slop oil is emulsified and the solid particles are detached, thereby achieving the purpose of surface purification.
2.2.2 Ultrasonic cleaning process parameters
1 cleaning medium: ultrasonic cleaning medium generally uses chemical solvent and water-based cleaning agent, liquid cleaning agent is generally composed of surfactant, chelating agent and other additives. The chemical action of the cleaning medium can accelerate the ultrasonic cleaning effect, and the ultrasonic cleaning is a physical action. The combination of the two functions can achieve sufficient and thorough cleaning. 2 Power density: The higher the power density of the ultrasonic wave, the stronger the cavitation effect, and the faster the speed, the better the cleaning effect. 3 Ultrasonic frequency: The lower the ultrasonic frequency, the easier the cavitation in the liquid is, which is suitable for precision fastener cleaning. 4 cleaning temperature: In general, the ultrasonic effect of the ultrasonic wave at 30 ~ 40 ° C is the best, the higher the temperature, the more significant the effect of the cleaning agent. Generally, when ultrasonic cleaning is used, an operating temperature of 40 to 60 ° C is employed. 5 ultrasonic cleaning process: ultrasonic cleaning → ultrasonic rinsing → spray rinsing → drying and other processes.
2.2.3 Application of ultrasonic cleaning technology
Ultrasonic cleaning technology is an efficient and environmentally friendly surface cleaning technology. At present, the application has been quite mature and extensive, and more than 80% of foreign companies have adopted this technology. Compared with other cleaning methods, ultrasonic cleaning shows great advantages. Ultrasonic cleaning gradually replaces the traditional cleaning process, and it is easy to clean complex shape fasteners. For the general degreasing, anti-rust and other processes, it takes only two to three minutes to complete under ultrasonic action, and the speed is several times or even several times higher than the traditional method. Ultrasonic cleaning and cleanliness of aviation fasteners, automobile engine connecting rod bolts and motorcycle engine bolts are all up to standard, which can achieve good results and save solvent, heat, work space and labor.
3. Types of cleaning agents
The appropriate cleaning agent can be selected according to the type of fastener dirt and the cleaning process used (such as spraying, dipping, ultrasonic, etc.). Commonly used cleaning agents include water-soluble cleaning agents, organic solvent cleaning agents, and hydrocarbon cleaning agents.
3.1 Water-soluble cleaning agent
1 alkaline cleaner This is the most extensive cleaning agent. It is composed of a mixture of a builder and an alkaline earth metal salt of a surfactant. It is capable of removing soluble fats, cutting coolants and corrosive soils at relatively low cost.
2 Synthetic cleaning agent Synthetic cleaning agent is an organic alkaline cleaning agent containing an amine-based substance. A quenching oil and polymer solution that can be used to remove fastener surfaces.
3.2 Highly efficient environmentally friendly cleaning agent
1 Water-based cleaning agent uses water-based cleaning agent, which has strong degreasing ability and good washing performance. It can replace organic solvents such as gasoline, acetone and tetrachloroethylene. This series of cleaning agents is non-toxic and has a certain anti-rust ability. Such as normal temperature degreasing water-based cleaning agent.
2 Vacuum oil-based cleaning agent is washed with light solvent oil to dissolve the heavy oil such as quenching oil and cutting cooling oil. Drying was carried out using a negative pressure (6.6 x 102 Pa) and a low temperature of 150 ° C or lower. The method can completely achieve the cleaning effect of an organic solvent such as trichloroethane. After the cleaning medium is recovered, it is repeatedly used, and no waste liquid is discharged. Since all processes of cleaning and drying are carried out under negative pressure and there is no air contact, the operation is safe and reliable.
3 hydrocarbon solvent hydrocarbon solvent cleaning agent has good cleaning ability and environmental protection performance, and overcomes the shortcomings of conventional cleaning. The solvent type of the hydrocarbon solvent is the fourth type of petroleum hydrocarbon of the fourth type. It has strong permeability to oil, good washing effect, no toxicity, no odor, and can be recycled. It has no impact on the environment and is an efficient and environmentally friendly cleaning agent.
Such as strong hydrocarbon cleaning agent, suitable for cleaning before and after heat treatment, has a strong cleaning power for cooling oil, quenching oil and tempering oil to ensure the cleaning quality. The powerful hydrocarbon cleaning agent has high safety performance, good recovery performance, can be used repeatedly, can achieve zero discharge, has no pollution to the environment, and has no worries about wastewater treatment. Mainly used for carburizing and quenching multi-purpose furnace, mesh belt furnace or vacuum ultrasonic cleaning machine.
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