Under water, electric works in the construction of underwater parts of different structures, underwater pipelines, power stations, port facilities, bridges, etc., in the salvage, ship repair and salvage operations, and so is often necessary to perform welding work under water. While able to practically apply the water arc welding. Ability to obtain a stable arc discharge in a liquid medium - water, oil, etc. - was determined experimentally at the end of the last century. The arc burns in a gas bubble formed by continuously revolving due to evaporation and decomposition of the surrounding liquid thermal action of the arc discharge.
electric arc under water was first implemented and studied in the Soviet Union in 1932, Konstantin Konstantinovich bad. It was found that the arc of DC when powered by conventional power source burns under water is quite stable, provided that the electrode is covered with thick enough layer of waterproof coating. Particularly surprising that the water arc melts the metal is almost as fast as in air, in spite of the intense cooling of the environment. This fact is explained by self-regulation state arc discharge. Current regulation is established in the discharge source, self-regulation of the arc changes the voltage drop across the individual sectors of the discharge. Increasing the impact energy in the environment automatically increase the voltage and power of the arc to compensate for increased energy efficiency, reduction of energy losses to the environment will cause a voltage drop across the arc discharge.
Cooling the aqueous medium increases the arc voltage and arc teplomoschnost, resulting in an intense melting of the metal. To be successful welding is essential to cover the electrode, it must be sufficiently thick, 30% of the weight of the electrode rod. Coverage of the electrode, washed with water, the electrode rod is melted slowly, so when burning arc coating on the tip of the electrode forms a so-called peak, contributing to the formation and retention of gas bubbles needed for a normal arc.
Gas bubble in the arc burning steadily growing, increasing in volume, then gases erupt, and his rise to the surface, the gas bubble is reduced in volume to a minimum and then begins to rise, which is repeated several times per second. The gas bubble is composed primarily of hydrogen obtained by decomposition of water vapor, in addition, there are products of decomposition of the electrode coating, a pair of iron, water vapor, carbon monoxide, nitrogen, hydrogen, etc., • dissolves in the weld metal to form pores and reduces the plasticity metal. Therefore, a water resistant coating and a lack of moisture in it. Evaporation of water in the coating and electrolysis with abundant evolution of hydrogen on the surface of the electrode rod break down cover, pluck it from the electrode rod, and I quickly lead electrode into disrepair. Especially: to be waterproof coating to work in salt water.
Waterproof electrodes attached to special treatment. After coating, drying and calcining it, I cover is impregnated and coated with a variety of waterproof compounds. For example, boil the electrodes in molten paraffin (this part is very weak, suitable only for fresh water). Best result gives a solution of celluloid in acetone, and bakelite lacquer. The best solution is synthetic resins in dichloroethane. Welding rods electrodes steel wire Sv-08 have a diameter of 4-5 mm.
Pairs of iron and electrode coating materials in contact with water, condenses, forming tiny colloidal particles, particularly iron oxides, and these particles are deposited a long time in water and form in the weld zone of dark brown cloud of haze that interferes with the observation and operation of the welder-diver (Fig. 123). The formation of turbidity depends on the composition of the electrode coating, one of the requirements for him - the minimum turbidity formation.
When satisfactory as electrodes arc almost as stable as you would in air. Usually the work is performed at a constant current of normal polarity. Ability to work on alternating current. At a constant current is quite stable and the carbon arc, but it has no use. Intense melting metal arc allows for the usual forms of welds in all positions.
Satisfactory weld metal strength, contains an increased amount of hydrogen and its ductility indices are lowered. The affected area is narrowed, the structure of the metal is accelerated signs of cooling after welding.
Diver-welder working in a heavy soft diving equipment, telephone communications (Figure). Arc rays passing through a thick layer of water, reduce its intensity, all the same to reduce eye strain in the front window of colored glass inserted into the helmet, changing to an expansion of the head, the welder can be viewed through colored glass, or in addition to it. Electrode holder has a special design, carefully isolated over the entire surface to reduce the leakage current. The welding current is supplied through a flexible cable with reinforced insulation. The diver-welder is in a particularly difficult operating conditions. Visibility weld zone is usually sufficient. Welder hampered in his movements diving equipment, insufficient resistance welder, it constantly blows with a nyatogo-position, with each sudden movement throws the welder to the side. Therefore, for underwater welding is characterized by defects that are not found in ground works, - missing, the failure of welding line, one of the unfused seam edges, etc. Welding is possible both in fresh and salt water, the latter requires careful isolation electrode. Even small areas of bare metal can cause significant leakage current, up to several tens of amperes. In salt water can be ignited arc without touching the electrode, only when it approaches any metal object in the water, even if it is not attached to the wire current source. All metal parts in the welding zone are connected to a power source through the water. Therefore, the result of careless approach of the electrode to the metal parts of diving equipment, such as a helmet or a shirt-front chest, a diver can burn them. Despite the difficulties of the diver-welder and not a very high quality of welded joints, underwater welding was quite a wide application in the salvage, ship repair , rescue and other operations. The successful application of underwater welding contributes to suitability for underwater work without any alterations of normal conventional power sources for welding in air. In conventional studies of underwater welding current is taken in the range 180-240 A, arc voltage 30-35 V, 5-7 against the extra welding on the air going to cover the losses of heat generated by the surrounding aqueous medium. considerable interest is the possibility of welding at great depths . Experience in welding at depths of 100 m showed that the arc was burning steadily, a refiner of its action intensified, which is favorable for welding. There are laboratory studies of the arc at pressures up to 1200 am, which is higher than the pressure at the bottom of the ocean's greatest depths, arcing proceeded normally, and it maintained its usual properties. However, the conditions of underwater work very hard for a man. At a depth of over 20 m begins intensive dissolution of nitrogen in the blood rise when the diver with a decrease in pressure small bubbles of nitrogen are allocated, causing pain (caisson disease). Therefore, the rise of significant life-threatening deep diver, and it is produced slowly, with pauses for a specific schedule. In addition, with increasing pressure at considerable depths of human feeling worse. At depths of 50-70 m, the normal duration of the diver is only 15 minutes, and the duration of his head several times that amount. Therefore, the work becomes almost impossible at depths exceeding 30-40 m only way to increase the performance of underwater welding, and extending it to considerable depths - is the mechanization and automation of the welding process with a maximum reduction of the residence time of a person under water. The main goal of automation in this case, the release of a person to perform work in severe conditions. There are successful results of the semi-automatic and automatic hose in underwater conditions, with a bare wire with a diameter of about 2 mm from the injection of argon shielding gas in the area of the arc or without gas. The use of a simple hose semiautomatic increases productivity diver-welder and cuts during his stay under water by 5-10 times. In the future, with the creation of complex automated devices with TV surveillance and sea control, will be possible underwater welding work at any depth.
See also:
Blacksmith (Forge) Welding
Blacksmith (Forge) Welding Part 2
Induction (high frequency) Welding
Diffusion Welding
Casting or Foundry Welding
Friction Welding
Electrolytic Welding
Welding Under Water
Explosive Welding
Welding Underwater
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