In addition to the same electric shock, burns, and fires as manual arc welding, argon arc welding also has high-frequency electromagnetic fields, electrode radiation, arc light damage, welding smoke, and toxic gases that are much stronger than manual arc welding. The most important ones are high frequency electricity and ozone.
1. Preventing damage from high-frequency electromagnetic fields
1. Generation and harm of high-frequency electromagnetic fields
In tungsten arc welding and plasma arc welding, high-frequency oscillators are commonly used to stimulate the arc. Some AC argon arc welding machines also use high-frequency oscillators to stabilize the arc. The frequency of the high-frequency oscillator commonly used in welding is 200-500 thousand cycles, the voltage is 2500-3500 volts, the high-frequency current intensity is 3-7 mA, and the electric field intensity is about 140-190 volts/meter. Long-term exposure of welders to high-frequency electromagnetic fields can cause autonomic nerve dysfunction and neurasthenia. Symptoms include general malaise, dizziness, dreaminess, headache, memory loss, fatigue, loss of appetite, insomnia and low blood pressure.
Reference health standards for high-frequency electromagnetic fields stipulate that the permissible radiation intensity for 8 hours of exposure is 20 V/m. According to measurements, the intensity of the high-frequency electromagnetic field received by all parts of the welder during manual tungsten arc welding exceeds the standard. Among them, the intensity of the hand is the highest, exceeding the health standard by more than 5 times. If a high-frequency oscillator is used only for arc ignition, the impact will be small due to the short time, but long-term exposure is also harmful, and effective protective measures must be taken.
2. Protective measures against high-frequency electromagnetic fields
⑴ For arc ignition and arc stabilization measures in argon arc welding, try to use transistor pulse devices instead of high-frequency oscillation devices, or only for arc ignition. After the arc ignites, immediately cut off the high-frequency power supply.
⑵ Reduce the oscillation frequency, change the capacitor and inductor parameters, and reduce the oscillation frequency to 30,000 cycles to reduce the impact on the human body. to
⑶ For shielded cables and wires, use fine copper braided soft wires, put them around the outside of the cable hose (including the wires in the welding torch and to the welding machine), and ground them. to
⑷Because the voltage of the high-frequency oscillation circuit is relatively high, it must have good and reliable insulation.
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2. Prevention of Radiation Injury
1. Sources and hazards of radiation
The thoriated tungsten electrode used in argon arc welding and plasma arc welding contains 1-1.2% thorium oxide. Thorium is a radioactive substance that is affected by radiation during the welding process and during contact with the thoriated tungsten rod.
Radiation acts on the human body in two forms: one is external irradiation, and the other is internal irradiation when it enters the body through the respiratory and digestive systems. A large number of investigations and measurements on argon arc welding and plasma arc welding have proven that their radioactive hazards are relatively small, because only 100-200 mg of thoriated tungsten rods are consumed every day, and the radiation dose is extremely small and has little impact on the human body. . However, there are two situations that must be paid attention to: first, when welding in the container, the ventilation is not smooth, and the radioactive particles in the smoke may exceed the health standards; second, when grinding thorium tungsten rods and where there are thorium tungsten rods, radioactive aerosols And the concentration of radioactive dust can reach or even exceed health standards. The intrusion of radioactive materials into the body can cause chronic radiation sickness, which is mainly manifested in the weakening of general functional status, obvious weakness and weakness, significantly reduced resistance to infectious diseases, weight loss and other symptoms. to
2. Measures to prevent radiation damage
⑴Thoriated tungsten rods should have special storage equipment. When stored in large quantities, they should be hidden in iron boxes and equipped with exhaust pipes.
⑵ When using a closed cover for welding, the cover should not be opened during operation. During manual operation, an air supply protective helmet must be worn or other effective measures must be taken. to
⑶ A special grinding wheel should be prepared for grinding thoriated tungsten rods. The grinder should be equipped with dust removal equipment. The grinding debris on the ground of the grinder should be cleaned frequently by wet cleaning and concentrated and deeply buried. to
⑷Wear a dust mask when grinding thoriated tungsten rods. After coming into contact with thoriated tungsten rods, you should wash your hands with running water and soap, and wash your work clothes and gloves frequently. to
⑸Choose reasonable specifications when welding and cutting to avoid excessive burning of the thoriated tungsten rod. to
⑹ Try not to use thoriated tungsten rods but use cerium tungsten rods or yttrium tungsten rods, because the latter two are non-radioactive.
3. Prevent arc light damage
1. Hazards of arc radiation
Welding arc radiation mainly includes visible light, infrared ray and ultraviolet ray. They act on the human body and are absorbed by human tissues, causing thermal, photochemical or ionization effects on the tissues, causing damage to human tissues.
⑴ Ultraviolet rays The wavelength of ultraviolet rays is between 0.4-0.0076 microns. The shorter the wavelength, the greater the biological damage. Human skin and eyes are sensitive to excessive exposure to ultraviolet rays. Under the action of strong ultraviolet rays, the skin can cause dermatitis, with erythema appearing on the skin, as if it has been exposed to the sun, and even small blisters, exudate and edema, with burning, itching, tenderness, and later darkening. Peeling. The eyes are most sensitive to ultraviolet rays. Short-term exposure can cause acute keratoconjunctivitis, which is called electrophoto ophthalmia. The symptoms are pain, gritty feeling, excessive tears, photophobia, fear of wind, and blurred vision. Generally, There will be no sequelae. to
The ultraviolet rays of the welding arc have a strong ability to damage fibers, and cotton fabrics are the most severely damaged. White fabric has strong UV radiation resistance due to its strong reflective properties. The ultraviolet rays produced by argon arc welding are 5-10 times that of manual arc welding, and the damage is more serious. Work clothes for argon arc welding should be made of acid-resistant fabrics such as tweed and oak silk.
⑵Infrared ray The wavelength of infrared ray is between 343-0.76 microns. Its main harm to the human body is the thermal effect of tissue. Long-wave infrared rays can be absorbed by the human body, causing people to feel hot; short-wave infrared rays can be absorbed by tissues, causing them to feel hot.
Heats the blood and deep tissues, causing burns. During the welding process, your eyes will be exposed to strong infrared radiation, and you will immediately feel strong burns and burning pain, and flash hallucinations will occur. Long-term exposure may also cause infrared cataracts, vision loss, and in severe cases, blindness. It can also cause retinal burns.
⑶Visible light The light change of the visible light of the welding arc is more than 10,000 times greater than the light change that the naked eye can normally endure. When exposed to radiation, the eyes may feel painful and cannot see clearly for a while. The arc is usually called "dazzling", and the ability to work is lost in a short period of time, but can be restored soon. to
2. Protection against welding arc light
In order to protect the eyes from arc light damage, welders must wear a mask with a special filter when welding. The mask is made of dark steel cardboard, which is well-shaped, lightweight, heat-resistant, non-conductive, and does not leak light. The filter lens mounted on the mask, commonly known as black glass, is commonly used as an absorption filter lens. Its blackness selection should be determined according to the intensity of the welding current. The welder's vision and the brightness of the welding environment should also be considered. Young welders have good eyesight and should use filter lenses with large and dark colors. When welding at night or in a dark environment, darker lenses should also be selected.
There is a kind of reflective protective lens that can reflect strong arc light, weaken the intensity of arc light that damages the eyes, and better protect the eyes. There is also a photoelectric lens that can automatically adjust the light. It has good transparency when the arc is not ignited and can clearly see the scenery outside the mirror. When the arc is ignited, the blackness of the goggles will immediately deepen and it can block light well. This eliminates the need to lift the mask or flip the protective goggles when changing welding rods.
In order to prevent the welder's skin from arc damage, the welder's protective clothing should be made of light-colored or white canvas to increase the reflective ability of the arc light. The pockets of work clothes should be dark. When working, the cuffs should be tied tightly, the gloves should be put on the outside of the cuffs, the collar should be fastened, the trouser legs should not be discounted, and the skin should not be exposed.
In order to prevent auxiliary workers and other workers near the welding site from being injured by arc light, they must cooperate with each other, say hello before starting a fire, and auxiliary workers must wear colored glasses. When welding in a fixed position, a light-shielding screen should be used.
Hazards of Toxic Gases
Under the action of high temperature and strong ultraviolet rays of the welding arc, a variety of harmful gases are formed around the arc zone, among which ozone, nitrogen oxides, carbon monoxide and hydrogen fluoride are the main ones.
1. Ozone Oxygen in the air undergoes photochemical reactions under short-wave ultraviolet irradiation to generate ozone (O3). Ozone is a light blue gas with a pungent odor. When the concentration is high, it has a fishy smell; when the concentration is higher, it has a slightly sour taste in the fishy smell. Its main harm to the human body is that it has a strong stimulating effect on the respiratory tract and lungs. When the ozone concentration exceeds a certain limit, it often causes cough, dry throat, dry tongue, chest tightness, loss of appetite, fatigue, dizziness, nausea, general pain, etc. In severe cases, especially when welding in a closed container with poor ventilation, it can also cause bronchitis.
According to measurements, the ozone concentration in the welding environment is related to factors such as welding methods, welding materials, protective gases, and welding specifications.
According to the results of investigation and research on production sites in my country, the hygienic standard for ozone concentration is 0.3 mg/m3.
2. Nitrogen oxides Nitrogen oxides during the welding process are formed due to the high temperature of the arc, which causes the dissociation and recombination of nitrogen and oxygen molecules in the air. Nitrogen oxides are also irritating toxic gases, but they are less toxic than ozone. Nitrogen oxides mainly have a stimulating effect on the lungs.
The factors that affect the concentration of nitrogen oxides are similar to ozone. During argon arc welding and plasma arc welding, if ventilation measures are not taken, the concentration of nitrogen oxides often exceeds the health standards by more than ten times or even dozens of times. Our country stipulates that the health standard for nitrogen oxides (converted into =nitrogen oxide) is 5 mg/m3.
During the welding process, the possibility of nitrogen oxides existing alone is very small. Usually ozone and nitrogen oxides exist at the same time, so they are more toxic. In general, the presence of two toxic gases at the same time is 15-20 times more harmful than a single toxic gas.
3. Carbon monoxide Carbon monoxide is formed by the decomposition of carbon dioxide gas under the high temperature of the arc. All kinds of open arc welding will produce carbon monoxide gas, among which carbon dioxide shielded welding produces the highest concentration. According to measurements, the carbon monoxide concentration near the welder's mask can reach 300 mg/m3, which is more than ten times higher than the health standard. The concentration of carbon monoxide produced during plasma arc welding is also quite high, so special attention should be paid to working in a poorly ventilated environment.
There is about 1% carbon monoxide in the smoke of manual arc welding, and the concentration in a closed container with poor ventilation can reach 15 mg/m3. my country's health standards stipulate that the carbon monoxide concentration is 30 mg/m3.
Carbon monoxide is an asphyxiating gas. Its toxic effect on the human body is to impede the transportation of oxygen in the body or the function of tissue absorption of oxygen, causing tissue hypoxia and a series of symptoms and symptoms of hypoxia. The symptoms of acute carbon monoxide poisoning are: headache, dizziness, nausea, vomiting, general weakness, weakness in the legs, and even a feeling of fainting. If you leave the scene immediately and breathe in fresh air, the symptoms will disappear quickly. In more severe cases, in addition to the aggravation of the above symptoms, the pulse rate increases, the person cannot move, enters a coma, and may even be complicated by symptoms such as cerebral edema, pulmonary edema, myocardial damage, and cardiac rhythm disorders. Carbon monoxide under welding conditions mainly has chronic effects on the human body. Long-term inhalation can cause neurasthenia such as headache, dizziness, pale complexion, weakness of limbs, weight loss, and general discomfort.
Post time: Feb-22-2024
