Electric welding, also known as arc welding, is a process method that promotes the local heating and melting of the welded metal section to reach a liquid state through the arc thermal effect generated by welding equipment, so that the originally separated metals can be combined into a solid and inseparable joint. According to different welding processes, arc welding can be divided into automatic welding, semi-automatic welding and manual welding. Automatic welding and semi-automatic welding are mainly used in the manufacture of large-scale mechanical equipment, most of which are installed in factories and the workplace is relatively fixed. However, manual welding is widely used in outdoor open-air construction because it is not limited by workplace conditions. Because of the great differences in workplaces, electricity, light, heat and open flames will be produced during work, so there are various hazards in welding operations.
First, it is easy to cause electric shock accidents.
1. In the welding process, because the welder needs to change the covered electrode frequently and adjust the welding current, the welding power supply is usually 220 V/380 V When the electrical safety protection device fails, the labor protection articles are unqualified, and the operators operate illegally, electric shock accidents may be caused. If welding is carried out in metal containers, pipelines or wet places, the risk of electric shock is greater.
2. When the welder is unloaded, the voltage of the secondary winding is generally 60~90V, which is easily ignored by the welder because of its low voltage. But its voltage exceeds the stipulated safe voltage 36V, which is still dangerous. Assume that the welder's no-load voltage is 70V, and the human body resistance R is about1600Ω. If the welder touches the jaw, the current I passing through the human body is: I = V.
3. Because the welding operation is mostly carried out in the open air, the welding machine, the welding handle wire and the power cord are mostly in high temperature, high humidity (construction site) and dust environment, and the cooker is often overloaded, which is easy to make the insulation of the power cord and the electrical circuit aging, the insulation performance is reduced, and the leakage accident is easy to occur.
Second, it is easy to cause fire and explosion accidents.
Because the welding process will produce electric arc or open flame, it is easy to cause fire when working in places with flammable materials. Especially in the area of inflammable and explosive equipment (including pits, ditches, grooves, etc.). ), it is more dangerous to weld containers, towers, tanks and pipelines that have stored flammable and explosive media.
Third, it is easy to cause burns.
Arc and metal slag will be produced during welding. If the welder does not wear special protective work clothes, gloves and leather shoes for welding, especially when welding at high places, welding sparks will splash, and if protective isolation measures are not taken, it is easy to cause skin burns to the welder himself or the construction personnel below the working face.
Fourth, it is easy to cause electro-optic ophthalmia
The visible light of strong flame and a large number of invisible ultraviolet rays produced during welding have strong stimulation and harm to human eyes. Long-term direct exposure can cause eye pain, photophobia, tears and fear of wind. , and easily lead to conjunctival and corneal inflammation (commonly known as electro-optic ophthalmia).
Fifth, it has the function of light radiation.
The arc produced by welding contains infrared rays, ultraviolet rays and visible light, which has radiation effect on human body. Infrared ray has the function of heat radiation, and welding in high temperature environment can easily lead to heatstroke of workers. Ultraviolet rays have photochemical effects and are harmful to human skin. At the same time, long-term exposure to the outside skin will cause skin peeling, and long-term exposure to visible light will cause eye vision decline.
Six, easy to produce harmful gases and smoke.
Because the arc temperature generated in the welding process reaches above 4200℃, covered electrode flux core, flux coating and metal weldments will vaporize, evaporate and condense after melting, resulting in a large number of manganese-chromium oxides and harmful smoke. At the same time, the high temperature and strong radiation of arc light will also produce toxic gases such as ozone and nitrogen oxides in the surrounding air. If you are engaged in welding work under the condition of poor ventilation for a long time, these toxic gases and smoke will be inhaled by human body, which will have a certain impact on human health.
Seven, easy to cause falls.
Due to the need of construction, welders should often climb high to weld. Anti-falling measures are not done well, scaffolding is not standardized, and it is used without acceptance; Take isolation measures when crossing up and down to prevent objects from hitting; Welders have a weak sense of personal safety protection, and they don't wear safety helmet or safety belt when climbing. In case of careless walking and accidental object collision. , may lead to a fall accident.
Eight, easy to cause poisoning and suffocation.
Welders often enter metal containers, equipment, pipelines, towers, storage tanks and other closed or semi-closed places for welding. If toxic and harmful media and inert gases are stored, transported or produced, once the work management is not good and the protective measures are not in place, it is easy to cause workers to be poisoned or suffocated by hypoxia, which mostly occurs in oil refining, chemical industry and other enterprises.
Nine, anti-electric shock measures
The general principle is to take safety measures such as insulation, shielding, isolation, leakage protection and personal protection to prevent the human body from contacting the charged body. The specific method is as follows:
1 to improve the insulation performance of welding equipment and lines. Welding equipment and power cables used must be qualified products, and their electrical insulation performance should be suitable for voltage grade, surrounding environment and operating conditions; Arrange special personnel to carry out routine maintenance on the welder to prevent from sun and rain, so as not to reduce the electrical insulation performance of the welder.
2. When the welding machine breaks down and needs to be overhauled, moved to the work place, replaced with connectors or replaced with safety devices, the power supply must be cut off before operation.
3. When installing power supply for electric welding machine, don't forget to install leakage protector at the same time to ensure that once someone gets an electric shock, the power supply will be automatically cut off. When welding on wet or metal containers, equipment and parts, leakage protectors with rated operating current not greater than 15mA and rated operating time less than 0. 1 s must be selected.
4, butt welding machine shell and the end of the secondary winding lead should take good protective grounding or zero measures. When the power supply is three-phase three-wire system or single-phase system, a protective grounding wire should be installed, and its resistance value should not exceed 4 Ω; When the power supply is a three-phase four-wire neutral grounding system, a protective zero line should be installed.
5. Strengthen the education of workers' electricity safety knowledge and self-protection consciousness, and require welders to wear insulating shoes and special insulating gloves when working. Open-air welding is prohibited in rainy days; When welding in a particularly humid place, people must stand on a dry wooden board or rubber insulating sheet.
6. It is forbidden to use metal structures, pipes, tracks and other metal connectors for wire connection. When welding in metal containers or particularly wet places, safe voltage with a voltage lower than 12V must be used as the power supply for portable lamps.
Ten, fire and explosion prevention measures
1, welding in inflammable and explosive places, before welding, the Hot Work Permit must be handled in advance according to the regulations and approved by the relevant departments.
Construction can only be started after approval, and the "three no hot work" will be strictly implemented.
2. Before formal welding, check whether there are flammable and explosive substances under and around the operation, and whether there are anticorrosive substances such as paint on the operation surface. If so, it should be properly handled in advance. For the welding operations in the production unit area and oil tank area running nearby, a firewall must be established; If there is aerial welding operation, asbestos board or iron plate shall be used for isolation to prevent sparks from splashing.
3. When welding containers, equipment or pipelines that have produced, stored or transported flammable and explosive media, it is necessary to check whether the equipment and pipelines connected with them are closed or blocked with blind plates before welding; Purging, cleaning, replacement, sampling and testing shall be carried out in accordance with regulations, and welding can only be carried out after the analysis is qualified.
XI。 Measures to prevent burns
1. When welding, the welder must wear protective work clothes, insulating gloves and shoes. When welding with high current, the electrode holder should be equipped with a protective cover.
2. The newly welded parts should be covered with asbestos board in time to prevent direct contact between feet and body from causing burns.
3. The covered electrode tips replaced during overhead welding should be piled up in a centralized way, so as not to throw them around, so as to avoid scalding the operators below.
4. Wear protective glasses when cleaning welding slag; When overhead welding or horizontal welding is carried out at high altitude, due to the serious splash of Mars, isolation and protection measures should be taken.
Twelve, measures to prevent electro-optic ophthalmia
According to the welding current, choose the appropriate mask goggles filter in time, and other personnel who cooperate with the welder should wear colored protective glasses when welding.
Thirteen. Radiation prevention measures
When welding, welders and workers around them should wear labor protection articles. Direct observation of arc light is prohibited without welding mask and colored glasses. Minimize skin exposure, and it is forbidden to wear shorts and jackets for welding operations in summer; If possible, apply UV protection cream to exposed skin.
Fourteen, measures to prevent harmful gases and smoke.
1. Reasonably design the welding process, and adopt the single-sided welding and double-sided forming process as far as possible to reduce the welding workload in the metal container.
2. If welding is carried out in a narrow or closed container, forced ventilation measures must be taken to reduce the concentration of harmful gases and smoke in the working space.
3. Try to use automatic welding and semi-automatic welding instead of manual welding, so as to reduce the chance of welding personnel being exposed to harmful gases and smoke.
4. Use covered electrode with low dust and toxicity to reduce the content of harmful smoke and dust in the working space.
5, welding, welders and other personnel around should wear dust masks, reduce smoke inhalation.
Fifteen, fall prevention measures
Welders must have regular physical examinations. Anyone with a history of hypertension, heart disease, epilepsy, etc. It is forbidden to climb to weld. Welders must correctly fasten their seat belts and wear safety helmets when climbing. Before welding, they should check the climbing operation site and surrounding environment to see whether the foothold is stable and safe, and whether the safety protection facilities such as scaffolding meet the safety requirements. If necessary, a safety net should be set under and around the operation. Isolation and protection measures should be taken when crossing up and down.
Sixteen, anti poisoning and suffocation measures
1. Where welding is carried out in a closed or semi-closed place, such as containers, equipment, pipelines, towers and tanks that have stored, transported or generated toxic and harmful media and inert gases, all process equipment connected with them must be cut off before operation, and cleaning, purging and replacement should be carried out at the same time, and the equipment operation permit should be handled according to regulations. Only after sampling and analysis can you enter the operation.
2. In general, the analysis is conducted every 4 hours. If conditions change, samples should be taken and analyzed at any time; At the same time, the site should also be equipped with an appropriate amount of air (oxygen) respirator for emergency use.
3. During the operation, a special person shall be appointed for safety supervision, and welders shall take turns to operate regularly. For operating equipment with strong sealing and easy hypoxia, forced ventilation should be used to supplement oxygen (direct oxygen inhalation is prohibited) to prevent hypoxia and suffocation.