According to a large number of market surveys conducted, it was found that welding fumes are generated during the welding process by oxidizing and condensing high-temperature vapors. Welding fumes are mainly derived from the liquid metal and slag at the end of the electrode or welding wire. The amount of dust generated by welding materials accounts for 80 to 90% of the total amount of welding fumes, and only some of them come from the base metal. Scientific research and health surveys show that there are a large number of inhalable substances (such as manganese oxide, hexavalent chromium, and oxides of potassium and sodium) in the welding fumes. Once these substances enter the human body, they will cause great harm to the human body. Long-term welding operators operating in welding fumes have a significantly higher proportion of respiratory diseases such as chronic bronchitis than others, and inhalable substances are also deposited in the body's bones and blood, leading to decreased sexual ability and even cancer In particular, in recent years, the use of welding materials containing a large amount of Cr, Mn, Ni, and other chemical components has made the influence of welding fumes on occupational health and environmental load increasingly serious.
International research on welding hygiene began in the 1920s and focused on the effects of harmful nitrogen oxides. From the 20th century to the 60th century, the harmfulness of welding fumes was mainly studied. In the 1970s, there were mainly the determination of total soot of welding rods, the recommendations of welding hygienic standards and the establishment of welding hygienic markers; the mechanism and influencing factors of welding soot were studied. First, the influence factors of welding fumes Many factors affect the welding fumes, the main factors include welding materials and processes in two aspects: material refers to the composition of the electrode coating, welding wire, chemical composition of powder, and protective gas composition; The process refers to the selection of welding methods and the setting of process parameters. NJHUDSON et al. pointed out that the welding fumes mainly composed of mixed metal oxides and spinel in the low-alloy MIG welding process are mainly composed of electrode materials, welded alloy materials, process control, protective gas components, and voltage and The current value is determined.
1. Welding materials Welding materials on the role of welding fumes are mainly reflected in the following two aspects:
(1) Welding material is the source of welding fumes. The composition of welding material directly affects the amount of dust generated by welding fumes and the chemical composition of welding fumes.
(2) The welding material influences the welding arc physics. By changing the droplet transfer method, the content of metal vapor generated in the welding process is controlled to enter the atmosphere. Shi Yuxiang et al. found that the welding fumes of single-component and minority-component welding rods are found to be high in dust and fumes produced by marble, fluorspar, and other materials, and the fumes of the welding rods are also high. The dust produced by rutile and other materials is relatively low, and its composition The fumes of the welding rod are also low; methane and other substances produced by the bitter earth itself have higher dust, but they are not necessarily high when forming the welding rod. The coating materials not only affect the welding fumes, but also have a complex relationship with each other. Changing the proportion of the coating composition may achieve the purpose of reducing dust.
Wang Huizhi and others of Beijing University of Technology studied the effect of the amount of iron powder on the dust emission rate of the welding wire and found that the oxide of iron in the smoke accounted for about 50%. When the iron content in the flux-cored wire is 19.5% to 28.7% (mass fraction), the amount of dust generated in the welding wire is 5.5226 to 8.2326 g; the proportion of iron and manganese oxides in soot is large. Under the experimental conditions, the smaller the proportion of Fe powder in the core, the smaller the amount of dust generated per unit mass of wire; the iron powder produced by different manufacturers and different processes has no obvious effect on the amount of dust generated. In addition, they also assessed the environmental impact of the electrode core and some of the accessories. Data collection, environmental impact factor determination, and results analysis revealed that the environmental load of the welding wire and ribbon was large, while the environmental load of the mineral powder production process was relatively high. small.
According to tests conducted by Kobayashi, the amount of dust generated by the CO2 shielded flux-cored wire is proportional to the carbon content of the steel strip used for the welding wire, such as reducing the carbon content of the steel strip from the normal 0.08% to 0.045% or less (preferably 0.02 %) can reduce the amount of dust generated by about 30%, which is basically the same as that of solid wire. For flux cored wire, if the carbon content in the strip and lubricant is reduced, the dust generation rate can be greatly reduced. JHDennis et al. found that the addition of 1% Zn to the welding material used in the FCAW welding process significantly reduced the formation of Cr6+ and ozone.
When Zimmer and Biswas researched aerosols generated during the gas metal argon-arc welding process, they found that the alloy components to be welded had a significant influence on the size distribution of soot particles, as well as the morphology and chemical structure of welding fumes. In addition, the distribution of welding fume particle size is polymorphic and aerodynamic changes occur over time.
2. Process factors Welding parameters affect the dust emission rate of welding fumes. The choice of different welding methods, the change of polarity, the change of current and voltage, and the speed of wire feeding will all affect the amount of dust generated and the chemical composition of welding fumes.
When studying the welding fumes produced during the protection of Al-Mg alloy DC and AC pulsed inert gas shielded welding, it was found that the use of AC pulsed inert gas shielded welding can essentially suppress the generation of soot. When studying the influence of arc voltage and wire feed speed on the amount of dust generated by the welding fumes of solid wire and metal core welding consumables in GMAW, the heat input exceeds the critical value for a solid wire with f1.4mm in the case of DC positive connection. At a value of 9.5 kW, the smoke generation rate attains a minimum value; in the case of a direct-current connection, the solid wire and the metal core wire have the same welding fume generation rate, but the metal core wire obtains the lowest soot incidence and the most suitable arc stability adjustment. Larger range. In the DC reverse connection, for a metal cored wire, a higher welding speed can be used to obtain a satisfactory amount of dust generated by welding fumes.
Ventilation systems include suction ventilation systems, local ventilation systems, global ventilation systems, and personal protective masks. The principle of ventilation system selection is lightness, mobility and practicality. In foreign countries, welders use a large number of movable local ventilation devices. Foreign countries strongly advocate the principles of selection of ventilation systems supplemented by comprehensive ventilation and local ventilation. Various welding fume collecting and purifying devices are developed towards completeness, assembly, mobility, miniaturization, and resource saving, and have achieved good results, especially for various welding fume purification devices that are widely used in various countries. use.
3. Aspirated Ventilators Hewitt et al. have found through a series of tests that during the FCAW welding process, the highest dust emission occurs when the DC reverse connection is used and the voltage is 40V; the DC connection is used when the voltage is 29V and 8% of the assistance is used. Flux, smoke dust emission dropped to 1/3 of the original.
The dust emission rate of CO2 gas shielded welding of stainless steel flux-cored wire, as well as the total amount of Cr and the concentration of Cr6+, were studied and found that the total amount of smoke is significantly related to the input energy. The corresponding dust emission under low, optimum and high heat input conditions were 189-344 mg/min, 389-698 mg/min and 682-1157 mg/min, respectively, and the Cr generation rates were 3.83-8.27 mg/min and 12.75 respectively. ~37.25 mg/min, 38.79 to 76.46 mg/min; Cr6+ production rates were 0.46 to 2.89 mg/min, 0.76 to 6.28 mg/min, and 1.70 to 11.21 mg/min, respectively. The incidence of soot increased exponentially with the increase of heat input by 1.19, with the change of current by 1.75; with the increase of heat input, the concentration of Cr in smoke increased from 1.57% to 2.65% to 5.45% to 8.13. %, the concentration of Cr6+ increases from 0.15% to 1.08%, and the dissolved portion of Cr6+ produced by FCAW corresponds to 80% to 90% of all Cr6+.
Second, welding fume purification and ventilation.
The test found that the suction ventilation device was adopted in the welding of the sheds to effectively control the welding fumes emitted during the operation. After the treatment, the average dust concentration of the operation belt near the sheds complied with the national hygienic standard (below 6mg/m3). ), And because of the necessary small amount of wind, it can reduce power consumption, saving equipment initial investment and operating costs. Therefore, compared with the suction hood, it is not only more reasonable, effective and practical, but also has a certain degree of advancement. At the same time, it provides two methods that can be used for reference to control large-scale welding fume pollution.
1. Pressure-injection local ventilation device The suction-suction ventilation device is a ventilation device that can effectively control the diffusion of pollution sources. The simple use of a suction hood on the shed welding to eliminate large-scale welding fumes has the problems of unsatisfactory results and unreasonable methods, and thus proposes the use of a blowing-suction ventilation device for the control of soot welding dust.
This technology has developed a mathematical model of "short-circuit flow field" theoretically through the development of various prototypes, multiple smoke and dust tests, and a large number of tests. The actual soot and dust test verified its good dust collection effect. Both measured and theoretical calculations show that the use of a short flow field to control the diffusion of smoke and dust is effective, and the effective suction stroke at the suction port is 2 to 3 times more efficient than the traditional method, and the dust collection rate is above 95%.
2. The wind screen sets the soot fan The wind screen set soot fan uses its unique structure, resulting in a reasonable flow field, that is, short-circuit flow field, effective control, capture of welding fumes, increased the effective suction process of smoking dust, remove the traditional use Solid suction hood.
Welding fumes make the occupational health hazards and the deterioration of the ecological environment worsen. The following suggestions are proposed for solving the welding fumes problem:
(1) Strengthen the research on the mechanism and influencing factors of various flux-cored welding soot welding, and make up for the insufficiency of existing research.
(2) Continue to research and develop low-dust and low-toxic welding materials to control the sources of welding fumes and minimize the harm.
(3) Specification of welding practices to eliminate human factors that affect welding fumes.
(4) Improve the mechanized automation of welding, accelerate the research of new welding methods, and promote the use of welding robots.
3. Conclusion Welding in a closed container, welding fumes continue to gather, the concentration continues to rise, sometimes up to 800mg/m3, a serious threat to the health of the welder's health The local ventilation of the sealed container welding operations is necessary measures to improve the working environment. Closed containers typically have only 1 to 2 orifices and the orifice area is small. Some sealed containers have a complex internal structure and a small space. At the same time, in order to control the welding fumes, ventilation facilities are required to be installed near the welding points and they can be moved at any time. This requires that the local ventilation facilities not only have a good ventilation effect, but also be lightweight and simple.
The pressure-injection type local ventilation device is mainly composed of an ejector, a tape duct, and a magnetic fixed bearing. As an effective device for purifying soot in sealed containers, compared to soot dust collectors, the advantages of pressure-injection type local ventilation devices are reflected in the following aspects:
(1) Safe and reliable.
(2) Small size, light weight, and easy to carry.
(3) The effective range of welding fume diffusion control is large, and it is not necessary to frequently move the vents.
(4) Dust-laden air is discharged outside the closed container and further processed by the ventilation facilities of the workshop. But there are also some deficiencies that can generate noise and require a source of compressed air.
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