1. Foreword
As in recent years, continuously improve the performance of motor vehicles using new technologies to reduce pollution of the environment, automobile manufacturing process quality control becomes extremely important, and quality management related to the importance of cleaning processes has become increasingly prominent.
In particular, ozone-depleting substances (ODS) of the cleaning agent Freon (CFC-113) and 1,1,1 - trichloroethane (TCA) risk being left behind. Under the Montreal Protocol, must be a total ban on the use of the area is not limited to automotive precision parts, precision parts manufacturing process of electronic cleaning process also need to re-enact.
CFC-113 and TCA as a substitute for chlorinated solvents is headed to start using water-based cleaning agent, semi-water-based solvents, freon substitutes as well as the hydrocarbon solvent. However, no matter what kind of cleaning agent has its strengths and weaknesses, therefore, a thorough alternative to CFC-113 and TCA solvent is still relatively distant. Table 1 is a summary table of these cleaning agents.
Table 1 Alternative Cleaners
Chlorinated solvents trichloroethane (TCE), dichloromethane (MC)
Bromine-containing solvent 2 - bromopropane (2PB), 1 - bromopropane (nPB)
Fluorine-containing solvent HCFC, HFC, PFC, HFE
Hydrocarbon solvents standard alkanes, iso-alkanes, cycloalkanes
Alcohol-containing solvent IPA, ethanol, alcohol polymer
Semi-aqueous solvent polymeric alcohol (hydrocarbons) + surfactant + water
Water-based cleaning agent alkali saponification, surfactants, water, functional water
From Table 1 select the alternative cleaning agent, the key to consider "clean sex" and "environmental protection" and "economy."
"Cleansing" of means of decontamination force, to prevent the re-adhesion of dirt and dry. "Environmental protection" means the operating environment and the Earth's environment. "Economic" means the cost of purchase of cleaning equipment and cleaning agents and equipment running costs.
So, in the comparison of alternative cleaning agent, be sure to fully analyze these factors. Now, to replace the cleaning agent in the hydrocarbon solvent, for example, for the above factors and technology to us.
2. Comparative analysis of alternative cleaning agent
(1) to replace the cleaning of cleaning agent
Precision parts cleaning vehicles, it is necessary for various shapes of parts cleaning and drying. Therefore, an alternative cleaning agent of the surface tension, boiling point and latent heat of evaporation characteristics are important factors. Table 2 indicates the main alternative to the typical characteristics of cleaning agents.
Table 2 the main alternative to the typical characteristics of cleaning agents
Surface tension boiling point ℃ latent heat of vaporization cal / g
HCFC225 16.2 54 34.6
HFE 13.6 61 30
Water 72.7 100 539.8
Hydrocarbon solvent 21.1 ~ 170 ~ 66
IPA 20.8 82.3 161.8
Dichloromethane 28.5 39.8 78.7
NPB 25.9 71 58.8
Various shapes and precision parts of motor vehicles, there are pore, slit, or even overlap with parts and components of the surface tension of a small cleaning agent cleaning effect is good. In addition, the boiling point and the evaporation latent heat of small, dry parts of the energy consumption is also less. If you dry of energy must, boiling point and the evaporation latent heat of small, dry time is short.
Decontamination using cleaning agents, resulting in the cleaning agent mixed with dirt, the dirt, then adhere to the cleaned parts on. In order to prevent pollution of spare parts again dirt, mixed with dirt cleaning agents need to keep a certain degree of cleanliness. Maintain the cleanliness of the following methods: the use of cleaning agents and processing oil, dirt boiling point is different from the proportion of the different elements of different sizes, as well as other characteristics, to be separated.
As the large latent heat of evaporation of water, using oil-water separator cleaning. The oil-water separation device is the use of oil and water, the proportion of different characteristics. Use of membrane purification, to prevent re-adhere to the components on the dirt. Membrane purification is the use of the principle elements of different sizes.
Water, other than an alternative cleaning agent, due to latent heat of evaporation is small, use of renewable distillation purification equipment to prevent contaminated dirt again. Boiling point distillation regeneration device is the use of a different principle. If the hydrocarbon solvent or solvent boiling point alcohol polymer high-vacuum distillation to adopt clean renewable devices.
(2) an alternative cleaning agent for environmental protection
Ozone-depleting substances (ODS) Detergent --- Freon (CFC-113), and 1,1,1 - trichloroethane (TCA), for the protection of the environment are being banned, so the Earth's environment and operating environment environmental protection become the most important topic. Table 3 indicates the main alternative to the environmental impact of cleaning agents.
Table 3 the main alternative to the environmental impact of cleaning agents
Environmental impact on the Earth's environmental impact on the operations
HCFC225 damage the ozone layer --
HFE - --
Water - --
Hydrocarbon solvents - flammable
IPA - Flammability
Methylene chloride - toxicity
NPB damage the ozone layer? Toxicity?
? : Under investigation
Table 3 clearly point out that the bromine-containing chlorinated solvents and toxic solvents on the human body, some fluorine-containing solvents destroy the ozone layer, warming the earth. Part of the Semi-aqueous solvent and water-based cleaning agent, there are waste water treatment, as well as hormone problems affecting the environment, hydrocarbon solvents and flammable solvents containing alcohol problems.
(3) the economics of alternative cleaning agents
And CFC-113, TCA trough the same three low-boiling point solvent vapor tank cheapest, water-based or high boiling point solvents, the price of hot-air trough over the middle, water-based or high boiling point solvents, vacuum drying plant the most expensive. Equipment, operating costs, depending on the price of cleaning agents and cleaning agents use. Table 4 is the main alternative to the economics of cleaning agent matrix.
Table 4, the main alternative to the economics of cleaning agent
The cost of purchase of cleaning equipment the cost of cleaning agent cleaning agent usage
HCFC225 inexpensive moderate expensive
Inexpensive moderate expensive HFE
Cheap cheap medium of water
Hydrocarbon solvent medium, a small amount of your expensive
IPA middle, your middle-lower
Dichloromethane cheap cheap medium
NPB cheap cheap medium
(4) the choice of an alternative cleaning agent
A variety of alternative cleaning agent has its strengths and weaknesses. In the "cleansing" of areas, water-based cleaning agent is somewhat more difficult. In the "environmental protection", the chlorinated solvents and bromine-containing solvent relatively large impact on the environment, there are also flammable hydrocarbon solvent problems. In the "economic", the fluorine-containing solvents, the most expensive.
3. Hydrocarbon solvent cleaning technology
How to effectively use an alternative cleaning agent with the advantages and disadvantages, the key is to use cleaning effect and CFC-113 and TCA over the same cleaning system. In addition to flammability, shall not affect the use of environmentally friendly cleaning systems using hydrocarbon solvents.
(1) cleaning of
Hydrocarbon solvent purification technology, and CFC-113, TCA, like the use of processing oil, dirt, high boiling point hydrocarbon solvents with boiling point of the different characteristics of regeneration can be separated by distillation. And compared with CFC-113 and TCA, due to the high boiling point hydrocarbon solvents, flammable, you need to vacuum distillation under state regeneration. Distillation pot in the decompression state, often at the boiling point, the hydrocarbon solvent was evaporated in the condenser in the condensate liquid and recycling. Evaporation of high boiling point there is no dirt remain in the distillation pot, with separate cleaning agent. Using this distillation regeneration system, cleaning agent can be kept clean state.
Hydrocarbon solvent system has a hot-air drying system drying and vacuum drying system. High boiling point, flammable hydrocarbon solvents, using vacuum drying method drying time is short. To more effectively carry out vacuum drying, there is need to be cleaned material with sufficient heat.
In the atmospheric pressure (760mmHg) of the boiling point of 170 ℃ or so, decompression state (100mm Hg) of the boiling point of 110 ℃ or so. CFC-113 and TCA, as steam cleaning, in the 100mm Hg vapor under the decompression state cleaning, the cleaning surface of the hydrocarbon solvent on the condensation of liquid temperature about 90 ℃. There are steam cleaning the role of the final rinse, therefore, in terms of precision parts cleaning is indispensable.
Vacuum drying, the isolated solvent vapor, will vacuum up to 10 mm Hg or so. According to Figure 1 of the vapor pressure curve of the degree of vacuum of 10 mm Hg, the hydrocarbon solvent boiling point at about about 60 ℃. At this point, at about 90 ℃ when the adhesion of the solvent, due to over boiling point, boiling into a state of collapse, even the small blind hole can be quickly dried. Therefore, the use of high boiling point combustible solvent, for decompression steam cleaning and vacuum drying, it can be achieved with the CFC-113 or TCA flame resistance with low boiling point solvents such as cleaning the same effect.
Flame resistance and low boiling point solvents, like the vacuum system is a high-boiling point combustible solvent technology, the concrete embodiment.
(2) environmental protection
Hydrocarbon solvents on the environmental impact of operations, mainly flammability issues. In order to hydrocarbon solvents and CFC-113 use the same need to eliminate flammable and dangerous. The three elements of combustion air, combustible material and ignition sources.
In the flammable liquid surface, there is the temperature by evaporation of the liquid itself, the generated gases. The gas is known as the combustible gas. With the rising temperature of the liquid, the resulting combustible gas volume gradually increased. If the ignition source to move somewhere where it will ignite. Measured at this time the ratio of air and combustible gases, the concentration at this time known as the burning of the lower limit, known as the flash point temperature of the liquid.
In the air usually contain 21% of oxygen. High concentration of oxygen in the air, burning speed, on the contrary, the oxygen concentration is low, slow burn, 15% of the oxygen concentration of the lowest concentration of combustion. This means that more than 15% oxygen concentration in a certain range of memory in the flammable gases (flash point flammable gas over), the once a sufficient amount of energy generated by combustion, can cause combustion (explosion).
"Ignition source" There are all kinds of conditions, mainly mechanical sparks, electrical sparks and static electricity spark. Mechanical sparks generated when in contact with hard metal. Commutator motors electric spark means, opening and closing switches, fuses, wiring and equipment, short-circuit generated when the spark. Static spark is a poor conductor or no grounding a good conductor of electric charge accumulated in the mobile when the discharge generated. Heterogeneous objects, when the accumulation of contact and separation of charge, when the electric field exceeds a critical value, the charge movement. Specifically, in the piping in the flow of the liquid jet, spray washing and air supply when the static electricity.
Burning three terms refer to air, combustible materials and ignition sources. These three conditions, if they can completely control a condition, it will never burn.
The explosion-proof handling combustible One is to control the flash point below. General control flash point temperature is -15 ℃. Explosion-proof treatment is to prevent leaks and flow out. Containers and piping, etc. due to such factors as vibration and corrosion split, crack, relaxation, there is the danger of flammable logistics to the outside, once the flow out of dangerous places will lead to the rapid expansion of the problem, therefore, to take adequate measures. In response, the entire liquid double tank, or set Draining tray.
The explosion-proof air treatment is refers to the control of oxygen concentration and combustible gas concentrations. Typically, the combustible gas concentration at lower concentration of combustion of 1 / 4 of the following. The use of flammable liquids to cover up the cleaning tank, and set the air outlet and the exhaust port. Mixed with flammable gases, gases will be forced to be routed to outdoor ventilation to prevent flammable gas concentrations increase. Forced ventilation confirmation of the use of micro-pressure sensor, the amount of the use of exhaust fans and wind exhaust valve control. The minimum oxygen concentration of combustion of more than 15%. Therefore, the effective method is sufficient nitrogen to reduce the oxygen concentration. In the decompression state, the use of hydrocarbons, if the pressure less than 100mmHg, burning rapidly near the upper and lower limits, the flame does not spread, does not burn. To ensure the use of hydrocarbons, 100% safe, need to adopt any of the table 5 a system.
Table 5 fully explosion-proof
Vacuum sealed combustion below the critical pressure (vacuum) 1.33 × 10000Pa (100torr) the following
Replacement sealed below the critical oxygen concentration (nitrogen filled) 10vol% the following
In the "ignition source" one, first of all, to avoid electrical sparks can not be avoided, should try to avoid contact with combustible gas. Electric motors for use in hazardous areas, explosion-proof structure should be adopted to enhance security type or enhanced pressure explosion-proof structure type. The control panel and ultrasonic vibrator, etc., commonly used nitrogen purge, air purge type structure to enhance the internal pressure explosion-proof type. Second, the electric heater is a fire the heat source. Electric heater placed in the liquid, the heater surface temperature increases lead to inflation dirty, flammable gas intrusion into the hot air heater heat exchange took place machine, there is likely to cause a fire. Thus, the general do not have electric heaters heat, instead of using steam or hot hydraulic oil and the indirect heating method.
Table 6 safety standards
Heating body indirect heating (steam, hot hydraulic oil)
Agencies to strengthen safety explosion-proof electrical specifications
Chain body temperature, flow, liquid level, gas concentration, vacuum, etc.
Ultrasonic vibrator internal pressure explosion-proof specifications
Internal pressure explosion-proof control panel specifications
Automatic carbon dioxide fire extinguishing systems, foam extinguishing agent
Fire extinguishing gas pressure linked baffle
There is also a significant ignition source is static. Different types of objects in contact and separation will certainly generate static electricity, can not be completely static. Spray cleaning, if the liquid-like fluid from the nozzle when the large diameter of liquid particles, with the amount of charge less, therefore, need to minimize the pressure spray washing.
"Explosion-proof cleaning device" should be shown in Table 6, the general safety requirements. Avoid heating sector, the electric sector, ultrasound, control panel, etc. as ignition source. Vacuum lifting, chain organizations, ventilation institutions, do not set the burning range. Using this proof system, safe to use flammable hydrocarbon solvents, but also with the CFC-113 can achieve the same cleaning and drying effect.
(3) economic
In the economic costs, the use of hydrocarbon solvent cleaning devices and the use of CFC-113 or chlorinated solvents, flame resistance of the low boiling point solvent cleaning equipment part of the fundamental difference lies in drying facility. Typically, solvent cleaning device is a three-slot from the cleaning tank, rinse tank and drying tank composition. The cost difference is mainly refers to dried trough, solvents boiling hot air occurred institutions or bodies and institutional vacuum. Difference between the cost of explosion-proof sector accounted for 10% of the entire device.
For the running costs in terms of hydrocarbon solvents, cleaning agents to use accounted for the vast majority. As the high boiling point hydrocarbon solvents, steam consumption of less, for CFC-113 for 50% ~ 20%.
4. Automotive Precision Parts Cleaning
Many different types of auto parts, materials are also a wide range. Table 7 is typical of fine cleaning auto parts.
Table 7 Auto Parts
Cylinder Head Cylinder
Boehm? Sintered rotor pump crank shaft
Camshaft Pulley
Precision Valve Parts Computer Case
Brake Blocks trunk
Valve bag with tube
Brake Parts Pump Box
Sintered planetary gear box crank
Back to the dynamic transmission parts clutch drum
Valve Plate Parts Cam Rotor
Sintered with wheel clutch parts
These auto parts after machining, stamping, etc., processing and polishing create. In the process, the adhesion of all kinds of dirt, the assembly before they must be dirt in clean water.
From dirt particles, dust, cutting powder, burr and other solids to the oil processing oil, water-soluble machining oil, anti-rust oil, liquid, a wide variety.
Similar to the oil-like liquid dirt, the general use of common cleaning agent dissolving power of removal. Solid-like dirt, using high-pressure spray washing, ultrasonic, vibration and other physical force removal. Typically, auto parts processed on both the dirt, the general dissolution of the use of cleaning agents cleaning power and physical force.
Author Kitamura, Hiroo