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 the liquid state through the arc thermal effect generated by welding equipment, so as to combine the originally separated metals 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 with relatively fixed workplaces; Manual welding has good flexibility because it is not limited by workplace conditions. At present, it is widely used in open-air construction. Because the workplaces are very different, electricity, light, heat and open flames will be generated 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 often needs to change the covered electrode and adjust the welding current, the welding power supply is usually 220V/380V, which may cause electric shock accidents in the case of electrical safety protection device failure, unqualified labor protection articles, illegal operation by operators, etc. 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 overlooked by the welder because of its low voltage, but its voltage exceeds 36V in safe voltage, which is still dangerous. Assuming that the no-load voltage of the electric welding machine is 70V, people work in a high temperature and humid environment. At this time, the human body resistance R is about1600Ω. If the welder's hand touches the lower jaw, the current I passing through the human body is: I=V/R=70/ 1600=44Ma. Under the action of this current, the welder's hand will spasm, which is easy to cause electric shock accidents.
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, and the insulation performance is reduced, which is easy to lead to leakage accidents.
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 flammable and explosive device areas (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
Because of the strong visible light of fire and a large number of invisible ultraviolet rays produced during welding, it has a strong stimulating and harmful effect on people's 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 also make the skin desquamate, 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. Engaged in welding work under poor ventilation for a long time, these toxic gases and smoke are inhaled by human body, which has 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 cause 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. Specific methods are:
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 the voltage level, surrounding environment and operating conditions used; Arrange special personnel to carry out daily maintenance and maintenance of the welder to prevent sun and rain, so as not to reduce the electrical insulation performance of the welder.
2. When the welding machine breaks down and needs maintenance, moving the work place, replacing the connector or replacing the safety device, the power supply must be cut off before operation.
3. Don't forget to install the leakage protector when installing the power supply for the electric welding machine, so that the guarantor will automatically cut off the power supply in case of electric shock. When welding on wet or metal containers, equipment and parts, a leakage protector with rated working current not greater than 15mA and rated working 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 a metal container or a particularly humid place, the power supply of the traveling lamp must use a safe voltage below 12V.
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 be carried out only after the analysis is qualified.
XI。 Measures to prevent burns
1. When welding, the welder must wear protective work clothes, insulating gloves and welder's shoes correctly. 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 electrode head with cover replaced during high altitude welding should be piled up in a centralized way, so as not to throw it 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 size of welding current, choose the appropriate mask goggles filter in time, and other personnel who cooperate with welders should wear colored protective glasses when welding.
Thirteen. Radiation prevention measures
When welding, welders and surrounding workers should wear labor protection articles. It is forbidden to observe arc directly without wearing welding mask or colored goggles; 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 try to adopt the single-sided welding and double-sided forming process to reduce the welding workload in the metal container.
2, such as welding in a narrow space or closed container, forced ventilation measures must be taken to reduce the concentration of harmful gases and smoke in the workspace.
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 harmful smoke content in the working space.
5. When welding, welders and other people around them should wear dust masks to reduce smoke inhalation.
Fifteen, fall prevention measures
Welders must have regular physical examinations, and anyone with a history of hypertension, heart disease and epilepsy is prohibited from climbing to weld. When working at heights, welders must wear safety belts and safety helmets correctly. Before welding, check the climbing operation point and surrounding environment, whether the foothold is stable and reliable, 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. When welding is carried out in closed or semi-closed places 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 license 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, the operation process should be supervised by special personnel, and the welder should rotate the operation regularly. For operating equipment with strong airtightness and easy hypoxia, forced ventilation should be used to supplement oxygen (direct oxygen inhalation is prohibited) to prevent hypoxia and suffocation.