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Measures and schemes for purifying smoke and dust in arc welding
Measures and schemes for purifying smoke and dust in arc welding
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Measures and schemes for purifying smoke and dust in arc welding
Electric arc welding is a common way of generating smoke and dust in our daily lives. Today, we will introduce its process and smoke and dust purification methods.
Electric arc welding is a common way of generating smoke and dust in our daily lives. Today, we will introduce its process and smoke and dust purification methods.
1.1 Manual arc welding:
This is a common welding process called "flash welding". Mostly used for welding between steel materials. The welding material is welding rod. For welding a large number of structures using low carbon steel and low alloy steel, the most commonly used J422 welding rod (titanium calcium type, acidic welding rod) has a molten steel core composition of C<0.12% and Mn=0.3-0.6%; In the composition of the coating, TiO accounts for 24-48%, CaCO3<20%. The melting temperature of the coating is more than 200 degrees lower than that of the steel core. And J502 welding rod (low hydrogen, alkaline welding rod), CaO accounts for 8-26%, CaF2 accounts for 10-23%.
During manual arc welding, the coating melts first under the high temperature of the arc. The arc stabilizers (Ca and low ionization potential substances such as K and Na), reducing agents (Mn, Ti, Al, Si, etc., which can reduce oxides entering the molten pool and remove S and P), slag making agents and gas making agents, alloying agents, adhesives, slag thinning agents, plasticizers, etc. that make up the coating are largely transformed into welding fumes with particle sizes ranging from 0.10 to 1.25 μ m. The most toxic substances in welding fumes are MnO2 (accounting for about 7.5% of welding fumes), Fe2O3 (accounting for nearly 50% of welding fumes), SiO2 (accounting for nearly 20% of welding fumes), etc., which can cause manganese poisoning and silicosis in welders. Harmful gases include CO, NOx, etc., and F reacts with H to generate harmful gas HF. In response to this, GB16194 "Hygienic Standard for Welding Fume in Workshop Air" stipulates that "the maximum allowable concentration of welding fume in workshop air is 6mg/m3" and "other harmful substances generated during welding shall still be subject to the current sanitary standards for these toxins".
The dust emission during welding with J422 welding rod is 200-280mg/min, and the dust emission of welding materials is 6-8g/kg; The dust emission during welding with J502 welding rod is 350-450mg/min, and the dust emission of welding materials is 11-16g/kg. Similarly, for manual arc welding, the composition of welding fumes and dust emissions varies greatly depending on the welding rod and coating composition. The dust emission of J502 welding rod is about twice that of J422 welding rod, and it contains HF, which should be of greater concern.
The control measures for welding fumes in manual arc welding can use a mobile welding fume purifier when the range of welding station changes is not large. When the welding station has a large range of changes, the mobile welding smoke purifier is inconvenient to use and can be ventilated and diffused for emission; When the amount of welding smoke is large, the measure of "layered air supply" should be taken.
1.2 Submerged arc welding:
The arc generated by the solid welding wire with a diameter of 5 is buried under the small particles of flux, and no arc flash can be seen during welding. For example, the commonly used "fluorine alkali type" flux is composed of CaO+MgO+MnO+CaF2>50%, SiO2<50%, CaF2>15%, with a particle size of 2-0.28mm.
The welding fumes generated during welding contain MnO2, Fe2O3, SiO2, and HF. The amount of dust generated during welding is 10-40mg/min, and the amount of dust generated in the welding material is 0.1-0.3g/kg. The submerged arc welding machine should be equipped with a fixed welding fume purifier randomly.
1.3 CO2 gas shielded welding:
CO2 gas shielded welding belongs to flash welding. It should be noted that there are two types of welding wires used: solid core and flux core.
The main components of CO2 gas shielded welding dust are MnO2, Fe2O3, and harmful gases CO, NOx, and O3. For solid core welding wire (φ 1.6), the dust emission during welding is 450-650mg/min, and the dust emission of the welding material is 5-8g/kg. For flux cored wire (φ 1.6), the dust emission during welding is 700-900mg/min, and the dust emission of the welding material is 7-10g/kg (in addition to the above content, SiO2, HF, etc. are also present in the welding dust).
CO2 gas shielded automatic welding machines should be equipped with fixed welding fume purifiers at random. When the welding station is fixed, a fixed welding fume purifier should be equipped. When the range of changes in the welding station is not large, a mobile welding fume purifier can be used. When the welding station has a large range of changes, the mobile welding smoke purifier is inconvenient to use and can be ventilated and diffused for emission; When the amount of welding smoke is large, the measure of "layered air supply" should be taken.
1.4 Argon arc welding:
Argon arc welding belongs to flash welding, and strong ultraviolet rays are generated during welding. Weldable stainless steel, alloy steel, copper, aluminum, etc. It is divided into non melting electrode argon arc welding (tungsten electrode argon arc welding) and melting electrode argon arc welding (using solid wire and a mixture of argon and CO2 shielding gas).
The atmospheric pollutants generated during welding are mainly NOx, O3, MnO2, and Fe2O3.
For commonly used melting electrode argon arc welding, the diameter of the solid wire is φ 1.6, the dust emission during welding is 100-200m g/min, and the dust emission of the welding material is 2-5g/kg.
Mobile welding fume purifiers can be used for argon arc welding, and it is necessary to ensure good ventilation in the welding station to ensure the health of the welder.
1.5 Pulse Welding:
Pulse welding belongs to flash arc welding, which is a welding method that applies controllable pulse technology to supply power to the welding arc from two parallel operating power sources (arc maintenance power source and pulse power source). Pulse welding can produce a stable pinhole effect, ensuring penetration and increasing deposition rate, and is used for argon arc welding. The analysis of welding fumes is the same as that of argon arc welding.
1.6 Plasma Welding:
Plasma welding belongs to flash arc welding, which is a welding method that melts the base material through a highly concentrated plasma beam (jet velocity of 300-2000m/s, energy density of 105-106W/cm2) arc. Plasma welding has a high welding speed, no need for groove opening, excellent weld performance, small heat affected zone, low welding deformation and residual stress, and can weld various metals, especially for materials with a thickness of 3-8mm. It is an efficient, high-quality, and low-cost arc welding technology.
The ion gas used is high-purity argon, with argon and helium as the main protective gases, and some supplemented with a small amount of hydrogen. Welding smoke analysis is similar to argon arc welding.
There are many types of pollution in the welding workshop, and comprehensive treatment should be carried out from three aspects: pollution sources, treatment methods, and personal protection. The treatment of pollution should be tailored to the specific situation of the workstation, and should not be divorced from reality, which may affect normal production operations. The design of governance plans should fully consider various pollution control methods while ensuring treatment effectiveness, and adopt integrated equipment and facilities to achieve the goal of reducing site occupation and saving investment.
Take effective ventilation and smoke exhaust measures
Ventilation and smoke exhaust are important measures for controlling welding fumes. At present, the ventilation and smoke exhaust measures adopted both domestically and internationally mainly include: point exhaust, local exhaust, whole room ventilation, whole room air purification, and other methods
1) Point smoke exhaust
Point smoke exhaust refers to the direct removal of welding fumes from the vicinity of the welding arc zone. Point smoke exhaust forms include high air volume low-pressure systems, low air volume high-pressure systems, mobile welding fume purifiers, etc. The exhaust air volume and speed of the point exhaust unit must be appropriate. If the air volume is too small, it cannot be extracted, and if the air volume is too large, it will damage the protective atmosphere and affect the welding quality. When using point exhaust, the amount of protective gas used should be correspondingly increased
2) Local exhaust
Local exhaust refers to the direct suction of smoke from the welding point, including ventilation hoods, blowing and suction systems, and pit exhaust systems. This method is mainly used for situations where the welding workpiece is small, the welding station is fixed, or when moving within a small range and there is no crane above the workshop station. Refer to Figures 4 and 5.
Local blowing suction is mainly used for welding inside sealed containers with bidirectional openings, using a smoke exhaust method of blowing air on one side and sucking air on the other side. In the manufacturing process of large containers, smoke exhaust and ventilation are widely used for welding workers inside the container.
The underground smoke exhaust system is mainly used for gas cutting machines and other under table ventilation and smoke exhaust devices. Recently, water cutting workbenches have been used to collect plasma cutting smoke and dust to purify the air.
3) Whole room ventilation
The welding workshop must adopt full room ventilation if it meets the following conditions:
The A welding station cannot be fixed, and point exhaust and local exhaust methods cannot be used;
Only some welding stations are equipped with point exhaust and local exhaust methods, which cannot guarantee that the smoke concentration in the workshop remains within the allowable range.
The main purpose of full room ventilation is to introduce fresh outdoor air to dilute the concentration of welding fumes in the indoor air, so that the average concentration of welding fumes in the work area is controlled below the allowable standard. From the perspective of air balance, the amount of fresh air that needs to be introduced must also exhaust the same amount of indoor air containing welding fumes. This way, as fresh air continues to be introduced, polluted indoor air is continuously discharged, thereby taking away the welding fumes that are constantly generated indoors.
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