All to protect a gas main role is to cut off oxygen in the air, nitrogen and water vapor, to protect the weld pool and electrode. Protective gas through the torch to enter, ejected from the nozzle, surrounded by the electrode around displaces the air around the electrode in the arc around the pool and form a temporary protective hood. CO2 gas mixture and Ar/CO2 can achieve this goal.
The protective gas for the arc plasma formation, plasma arc welding arc is the current channel. Also affects the protective gas arc type heat conduction and the pool size of the force applied to the arc. On these issues, CO2 and Ar/CO2 mixture performance is not the same.
Characteristics of protective gas
CO2 and Ar arc enthusiastic response in the different. Analysis of these differences can help to understand the characteristics of each gas Welding Electrodes process and how it affects the weld deposition.
Ionization potential. Ionization potential is the size of the gas ionization energy required (for example, the gas charged into the plasma state), the gas can conduct electricity. Ionization potential is lower, the more easily ignite and maintain arc stability. Ionization potential of CO2 is 14.4eV, Ar ionization potential is 15.7eV. Therefore, CO2 shielding gas Ar protection than more easy to ignite the gas arc.
Thermal conductivity. Gas thermal conductivity is the heat capacity of the gas transmission size, it's good or bad will affect the metal transfer method (such as jet transition and large drops of the transition), the arc shape, weld penetration and arc temperature distribution. CO2 gas is heavier than air and Ar/CO2 Ar gas mixture has a higher thermal conductivity.
Reactivity. The reactive gas is gas with the molten weld pool is a chemical reaction. Gas can be roughly divided into two categories: inert gas and reactive gas. Inert gas in the weld pool does not react with other elements. Ar on the part of inert gas. Reactive gases in the weld pool will be combined with other elements or reaction, to form new compounds. At room temperature, CO2 is an inert gas, but in the arc plasma, CO2 will be broken down to form carbon monoxide (CO), oxygen (O2) and some independent oxygen atoms (O). Therefore, CO2 under the arc becomes active gases can occur with other metal oxide. Ar/CO2 mixed gases are reactive gases, but the activity is lower than CO2.
When the other parameters the same welding specifications, different protective gas welding fumes generated by different size. Specifically, compared with CO2 shielding gas, Ar / CO2 shielding gas welding fumes produced less because CO2 has oxidation. In addition, due to the specific welding and Aluminum Electrode sequence of different occasions, the amount of welding fumes are not the same.
Commonly used in DC arc Aluminum Electrode(reverse), can cut carbon steel, stainless steel, cast iron and non-ferrous metals.
Underwater welding and cutting pliers clamp generally universal, open and close the valve is equipped with a clamp, with cuts and interruption of current through the gate. Clamp electrode head for the folder to eat or cut of the chuck.
Cutting oxygen pressure should be higher than the bottom pressure 5 ~ 7Kgf/cm2. Cutting of hollow carbon rods can be used underwater cutting or a dedicated section, the steel tube (diameter 8mm, diameter 3mm), coated with waterproof leather made medicine.
2, underwater plasma arc cutting
Plasma arc cutting is used underwater, the effective power will be reduced, cutting diminished capacity, arc stability deteriorated, arc more difficult. So cutting the power supply should be increased no-load voltage should be increased to 500 ~ 900V. If the cutting depth of 8m thickness of 30 ~ 100mm stainless steel work, the current 300 ~ 1000A, Voltage 180 ~ 450V, D arc current of 75 ~ 100A.
Torch should ensure that all parts sealed. Nozzles mounted an outer nozzle, high-speed rotation of the cooling water from the nozzle end of the pore through the outer nozzle spray out to form a water screen, umbrella, in order to improve the stability of the plasma arc burning.