【 Weak current College 】 welding and cutting jobs fire hazard and safety measures (2)---Power By 【 China power house network 】

(Iv) the fire safety of plasma cutting
(1) plasma cutting is the use of high-temperature plasma (plasma arc) cutting metal. Plasma arc temperature 16000-33000 ℃, any of the existing high melting point of metallic and non metallic materials can be plasma melting. The plasma arc for cutting, shows many other flame cutting of advantages not available. Where oxygen and acetylene and electric arc one can not be cut or difficult cutting of metal materials such as stainless steel, titanium, tungsten, molybdenum and refractory metals and special metal materials, plasma arc cutting, and both can cut narrow, good quality. Plasma cutting has application in China, along with the development of economic construction, plasma cutting technology in the application scope will be more extensive.
(2) cutting large thick workpieces, no-load voltage up to 400 volts, for security reasons, you should try to use automatic cutting.
(3) particular attention in incising process produces large amounts of toxic metal steam and gases on the human body.

3. pressure welding
Pressure welding is one of the three major types of welding technology. Belong to the scope of pressure welding has forged welding, friction welding, welding, pressure welding, cold welding, ultrasonic welding and explosive welding (also known as explosive compound), etc.
Pressure welding works by two metal component connection section heated to plastic State or surface partial melting, and pressure, such as forging and welding, welding, welding and gas welding, friction, similarly you can make two separate metal components to achieve a combination of atoms to form solid metal connection. Pressure welding in explosive welding, is the use of explosive moments generated by the high temperature, high pressure will connect to one of the metal.
Pressure welding and gas welding of fusion welding, arc welding, gas cutting and arc cutting risk factors compared to the much smaller. But pressure welding of explosive welding but of great danger and economic construction, development, and many large metal welding and gas welding, welding cannot be welded metal component will be machined by explosive welding and cold processing of explosive forming, machining range is constantly expanding. So the pressure welding process, special attention should be paid to the explosive welding and explosive forming of fire and explosion safety.
Explosion welding is the use of explosives as an energy source, in the moment of explosion of the high temperature (about 3000 ° c or above), high-pressure [approximately 309 MPA (3.15 tons/cm2)] and high-speed (500-1000 m/sec) of the shock wave, make two separate metals at high temperature, high pressure and high speed of instant reach to link together. This is a new method of welding, the welding process, namely the metal heating and rapid pressure plastic State, metal bonding between atoms, as long as a few microseconds. This new welding methods that do not require sophisticated equipment, the process is simple, low cost, but must pay attention to the following considerations:
(1) must strictly observe the explosives control law. The purchase, Stockpiling and use of explosive substances are subject to local police departments; and the strict implementation of the "dual" system (i.e. the double management, picking, twin double use, double-lock and the bi-oriented account).
(2) explosive venues to choose on the surrounding buildings, people, not places, and with the approval of the local public security department to use.
(3) explosive welding; explosive forming of the operations staff must undergo professional training, examinations, certificates issued to explosives operations to operate independent of personnel are not allowed to enter the explosive job site.
IV. brazing
Brazing is a ancient method of welding. Classification in accordance with the past, brazing is included in fusion welded connection, but the mechanism is through the soldering of the molten solder and solder dissolution of metal surface and the diffusion of the joints, it is characterized by brazing metal is melted, and melting welding principled difference, so in brazing technology evolving circumstances, has gradually formed an independent system, and is listed as one of the three major types of welding technology.
Brazing methods according to their heating: gas flame brazing, soldering iron soldering, brazing, high-frequency electrical contact induction brazing, soaking furnace brazing and soldering of sinking. Brazing is due to the weld (materials) heating temperature is low, thus weld metal and mechanical changes, deformation of small, smooth joints, and welding process simple, high productivity, brazing a wide range of applications.
Brazing process of fire-explosion protection measures are: gas flame brazing mainly uses oxygen-acetylene flame or air a gasoline flame heating, fire safety measures can reference gas welding and flame cutting. With the rapid development of the electronics industry, including soldering iron soldering using range is very extensive, as a result of the use of electric iron accidentally caused fires more prominent. The soldering iron soldering must be aware of the following:
(1) the use of electric iron to strictly adhere to the safe use of electricity.
(2) electric iron must be placed in the non-combustion and thermal insulation of base, combustible, flammable items be stacked next to the electric iron.
(3) after the end of the weld must be immediately cut off the electric iron, soldering and welding workshop, equipment shop etc use soldering iron more processing power, lighting and power for the electric iron must be separated from work, you must close the total power electric iron.
1.3 security measures

First, welding, cutting jobs in accident analysis
Welding, cutting, use of equipment and energy while there is a risk of fire, but fire explosion neither mainly lies in the fact that these devices and energy itself, but mostly because of welding, cutting jobs and paralysis, improper operation, system, security measures are ineffective. The most common cause of the accident are:
(1) in welding, cutting jobs, hot metal Mars splashing is fire and explosion. In particular for gas cutting, molten metal melt from slotting in high pressure oxygen injection, a lot of passionate dross splash, its scope is the scope of welding Mars spatter, temperatures are high, when in contact with flammable, explosive gas or chemical hazardous materials, it will cause a fire and explosion. When metal Mars spatter to cotton, linen, yarn, straw and other combustibleMaterial, can spread, resulting in the fire of smoldering.
(2) for welding, cutting, heat conduction, can also cause fires. These accidents usually happen in chemical equipment repair and ship building and repairing. In welding, cutting, welding, cutting pieces is not removed, heat conduction with metal, easy to make welding, cutting parts on the other end of the fuel on fire.
(3) on the internal structure of the welded parts, nature does not know clearly that blind welding usually occur in the event of an accident. On the recycling of scrap iron and steel cut, due to the variety and scrap iron and steel complex, sometimes hidden in a small amount of waste explosives, weird shapes, while unable to distinguish, in incising will cause accidents. Most of these accidents occurred in the iron and steel plant, recycling or old ship breaking, and other units.
(4) in welding, cutting metal containers, due to the remnants of flammable or explosive gases and liquids are not completely clear, no replacement, flushing, nor after sampling and analysis and blind welding, cutting, the explosion occurred. Especially for automotive fuel tank, the oil drum, acetylene generator, a small metal containers such as welding, cutting, the most prominent.
(5) on the tank, gas tank, and other facilities for welding, cutting, generally are more attention. But on these large facilities of accessories are sometimes more overlooked; there have been numerous domestic large oil storage tank explosion, the reason for this lies in welding, cutting these attachments do not take effective security measures. There are a number of reasons for the explosion occurred on these large facilities after cleaning, without a comprehensive test or measurement of explosive and blasting in the acquisition of parts not comprehensive, such as tank only measuring burst top instead of bottom of the tank, resulting in weld sampling, cutting process to Mars and cause an explosion at the bottom of the tank. Some of the reasons is that despite the explosion of all measuring explosions, welding and cutting is also not an accident, and after a few hours and then go to welding, cutting, but the explosion happened, this is because the tank walls of oil and other impurities after several hours of welding, cutting and evaporation of oil vapour.
(6) on temporary jobs for welding, cutting, no on-the-spot check or are not completely clear of combustible substances and caused a fire and other accidents. Some have been carefully checked, venues around also did not combustible substances, but it ignores the above and the following checks may result in unexpected accident. If there is a three storey Shanghai building chemical plant, at the bottom for gas cutting workshop, the workshop is free of risk factors, but only in gas cutting, second floor, flammable liquid ran occur level, a large number of inflammable materials rapidly from leaking to the second floor, gas cutting field operatives have yet to find that the fire had occurred.
(7) in spray paint, paint shop or just painting, painted parts for welding, cutting jobs from detonations accidents have occurred from time to time. Parking in Shanghai Huangpu River in maintenance of tons of cargo ship "Yixing" fires are caused by the reasons mentioned above. Some fire accident in welding, cutting job with handling of poop flammable liquid and liquefied petroleum gas, oil leaks out of steam or flammable gases, blowing into welding, cutting workplaces, welding, cutting the open fire.
(8) in Cork, straw, cotton, hemp and other combustible materials do insulation layer of warm and cold gas pipeline, constant temperature room, cold storage for welding, cutting, it is easy to cause fires. Because these do insulation layer of combustible material is dry, and hidden in it, when you start smoldering, once the fire is discovered, the fire is difficult, often disastrous.
(9) the installation or maintenance of cooling towers, often use welding and cutting. Due to the cooling tower in large heatsink, is the use of flammable made of polypropylene sheet, pp sheet after the fire, because it is itself a flammable material, plus cooling ventilation are particularly good, so the combustion speed quickly, easily lead to fire.
(10) welding and cutting end left by the fire did not go off and Kindle a fire accident hidden also relatively common. The main one is the Mars spatter in nearby combustibles on timely discovery; the second is welded, cut the piece itself is very hot, piling up in fuel heat due to remaining in the vicinity, causing fuel on fire; the third is the welding worker clothes especially winter wear cotton clothing is welded, cut Mars ignition did not find that in the changing room fire.
(11) electric welding wires, especially back in line for a mess then confusion arising from the accident. In arc welding in all back routes by Head Office also be emitted by EDM, the resulting fire accidents are more prominent.
(12) gas welding, flame cutting use oxygen-acetylene gas, welding, cutting torch gas leakage or ingress of oxygen is not appropriate, leading to the accumulation of acetylene gas in a certain position, welding, cutting open fires caused by the explosion. This explosion of lessons are extremely painful. Common in any of the following three:
① welding, cutting some units to console explosion welding, cutting work tops with sizzling up the container shape. In welding, cutting gap in welding, cutting torch and randomly placed, plus oxygen-acetylene valve does not close down or welding and cutting torch nozzle of air leakage, and itself precisely aligned welding, cutting out the gaps in the oxygen-acetylene gas accumulation in it. When welding, flame cutting, the strong explosion caused by the console.
② welding, cutting operation venue explosion occurred mainly in the workplace, compared the airtight containers, basement; especially the ship of a site for welding, cutting, whenever a ban from work or adjust welding, cutting the workers go to work, welding workers used to his own use of welding, cutting torch it down, but the oxygen-acetylene hose still in these places, a variety of reasons, such as acetylene generator and oxygen cylinder valve is not closed or inherently leak as well as other circumstances, make an acetylene gas mixture of oxygen accumulated in these relatively confined places, when you encounter various fire and explosion accidents.
③ welded, cut workers use Toolbox explosion, welders in the Toolbox at a small hole, welding, cutting torch nozzle as hooks hanging in the Toolbox, for some reason causing oxygen-acetylene gas accumulated in the Toolbox, open fire, explosion caused the Toolbox.
This oxygen-acetylene gas explosion very badly. There's a township enterprises in Shanghai, at the bottom of the Toolbox, hit 10 holes, 5 to 10 of welding, cutting torch — root oxygen and acetylene hose is used through the Toolbox. At the five welding, oxygen cutting torch and 10 root — acetylene hose rings up into the Toolbox and the locks.The next morning, when combined with good calcium carbide, swaps nice oxygen cylinder, open the acetylene generator and oxygen pressure gauge valves, two women sitting in a rest next to the Toolbox, and encountered another group cutting plate of Mars, sudden explosions Toolkit. A female head was the iron off the Toolbox; another woman back exactly against the Toolbox of the other gates, the explosion of this name, facial female workers went aground off the Toolbox about 4 meters of brick wall and put brick tore a huge hole, the women workers from the wall into the wall and died.