Property and harm of welding fume
Welding fume in flue gas is a very complicated matter, the main chemical components of welding fume was Fe2O3, SiO3, MnO, polymer such as alkanes, aldehydes, ketones and CaO composed of fumes, heterocyclic compounds, with large dispersion, deposition slow and easy to float in the air medium, the welding process will produce some harmful gases, such as ozone, nitrogen oxides, carbon monoxide, fluoride and chloride and so on, not only harm the physical and mental health of workers, will enter the inside of the device caused equipment damage, affecting the normal production. The European authoritative environmental protection department of the German social insurance occupation safety and health research results of the soot particles generated by welding the diameter between 0.1 ~ 1 m, can enter the alveoli by human upper respiratory tract and deposition in the lungs (deposition rate of more than 50%), caused by respiratory tract disease and lung cancer. Among them, 0.1 ~ 0.4 m diameter particles accounted for 98.9% of the total smoke. If workers do not have proper protective measures, they will lead to various occupational diseases, such as pneumoconiosis, osteomalacia, anemia, etc.. Harmful gases can also cause pulmonary edema, bronchitis, acute asthma, neurasthenia and chronic respiratory tract inflammation, etc.. Therefore, the state has a strict limit on the concentration standard of pollutants in the operating environment. In the standard GBZ2 - 2002, the workshop can integrate the dust concentration of stem 6mg/m3.
Present situation of welding fume treatment
At present, the three methods of labor protection, local treatment and traditional mixed air supply are widely used in welding fume treatment. The main difficulties lie in the following aspects:
2.1 the labor protection scheme is to protect the health of workers through the form of vacuum cleaners. The method is limited to welding workers, and the whole workshop environment can not be improved.
The particle size of 2.2 welding fume is small, and its particle size is 0.01-5um, so it is difficult to filter;
The variability of 2.3 welding station makes it difficult to capture welding dust;
2.4 welding fume hot gas retention characteristics ordinary ventilation technology dust removal difficulty;
2.5 welding smoke dust removal equipment has large investment, high operation cost and difficult investment;
2.6 welding smoke treatment line and workshop work equipment crossed, space limited;
A mixture of 2.7 traditional air way to exclude the weld fume, air volume, and high speed, for CO2 gas shielded welding, when the wind speed around the protective gas is more than 1m/s, will blow away the protective gas, thus affecting the quality of welding.
Welding fume treatment in technical workshop
Layered air supply principle
With the traditional mixing ventilation control of welding fume, the scheme using stratified air technology to control the welding fume, in the heat of the workshop, the temperature gradient is stable in height, if the low wind speed (V <0.2 ~ 0.5m/s), large air volume, air temperature will be smaller (At=2 to 4 DEG C) fresh air directly into the indoor area, low temperature of the air under the action of gravity to sink, then slowly spread, forming a thin layer of air layer on the ground, and the indoor heat sources of hot air flow, due to buoyancy and rise, and constantly entrainment of ambient air. So, as the hot air flow increased when entrainment, promote air suction effect and subsequent pumping air, the top floor of the fresh air slowly moving upward, forming a uniform flow similar to the work area, so the dirty air is the air replaced. When stable, the indoor air temperature and concentration on the formation of two regions: the upper mixing zone and the lower one-way flow clean area.
Stratified air purifier is composed of welding fume stratified air welding smoke purifier is mainly composed of 4 parts, namely air handling units (including high efficiency centralized welding smoke purifier system), air supply pipe system, air duct, terminal device and control system.
Operation process of stratified air supply system
The polluted air in the workshop is sucked into the air treatment unit through the return air blower, and the filter smoke is filtered out and sent into the workshop through the canister type HEPA filter. In order to ensure the air quality in the workshop, a certain amount of fresh air should be added into the workshop, and the fresh air regulating valve is installed on the air handling unit, which is used to regulate the fresh air volume. In the winter of 20% fresh air volume control, fresh air and return air from the workshop 80% (20% of the return air through the exhaust valve exhaust to the outside the workshop) mixed by fresh air heaters and sent to the workshop, so, to avoid the direct discharge of pollutants causing heat loss in the workshop. In the spring and autumn transition season, fresh air volume of 100%, the use of new wind to take the workshop thermal load, pollution air 100% row to the workshop outside, not only to ensure the comfortable temperature, but also to ensure good air quality.
(1) air duct
The air duct is the key component to realize the layered air supply. It has large air supply, low air supply speed and long distance of air supply. The lower air supply speed ensures that the protective gas can not be blown away, thus ensuring the welding quality. Supply duct is arranged in the valve, according to the distribution of temperature and humidity and pollutant requirements of inside and outside workshop workshop to adjust the temperature, wind direction, to meet at any air temperature could promote welding fume to mobile workshop.
(2) filter cartridge
The high efficiency filter cylinder is used as the filter element, and the filter material used in the filter barrel is different from the traditional filter material, and the surface of the filter cylinder is covered with a polytetrafluoroethylene film. The tiny mesh can block most of sub micron particles, sub micron dust particles in the filter surface aggregation and the formation of dust cake permeable, most of the dust particles in the filter is blocked and can not enter the outer surface of the internal pressure in the material.