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Industrial Gases
In addition to the traditional gases oxygen and acetylene for fuel gas welding, cutting, shaping and coating of metals and materials MOX-LINDE also supplies sophisticated shielding mixtures for arc welding, and for laser and plasma cutting and welding. Gases and mixtures for such applications are typically supplied in cylinders and bundles (cylinder manifolded packs), cryogenic cylinders and tanks.
Customer applications include the following :
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Welding
In arc welding, industrial gases - the common ones being Ar, CO2, O2 or mixtures of these, are often used as a general metallurgical shielding of the arc and weld pool. However the shielding gas performs a number of other important functions :
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Arc initiation and formation of the arc plasma
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Stabilises the arc roots on the material surface being welded
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romotes the smooth transfer of molten droplets from the welding wire to the weld point.
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The common gases and gas mixtures adopted in the various arc welding processes of the fabrication sector are :
GMAW : Gas material arc welding or MIG/MAG
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Steels
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Carbon Dioxide (CO2)
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Argon + 2 - 5 % Oxygen
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Argon + 5 - 25% CO2
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Non-ferrous
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Argon (Ar)
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Argon/helium at 70/30 to 25 /75 mixtures
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GTAW : Gas tungsten arc welding or TIG
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Argon (Ar) the most common shielding gas which can be used for welding a wide range of materials including steels, stainless steel, aluminium and titanium.
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Ar + 2-5% H2 the addition of hydrogen to Ar improves the production of cleaner-looking welds without surface oxidation due to the slightly reducing atmosphere.
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Helium (He) and He/Ar mixtures He addition raises the temperature of the arc, promoting higher welding speeds and deeper weld penetration.
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Plasma
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Normal combination of gases is argon for plasma gas, with Ar + 25% hydrogen for the shielding gas.
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Today there has been substantial changes in the range of shielding gases available for arc welding. MOX have introduced to the Malaysian fabrication market, a broad range, covering :
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Pure Gases
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Argon
Helium
CO2
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Argon-Helium
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Alushield Light
Alushield Universal
Alushield Heavy
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Argon-Hydrogen
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Specshield 63
Specshield 64
Specsheild 65
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Argon-CO2
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Specshield 53
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Argon-He-CO2
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Stranshield Heavy
Stranshield Universal
Stranshield Light
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Argon-CO2-O2
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Argoshield Light
Argoshield Universal
Argoshield Heavy
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Argon N2
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Specshield 2 - 5% N2
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For gas-welding, also known commonly as oxy-acetylene welding, the process is still widely practised despite the emergence of the arc welding processes.
In the fabrication market, the process relies on combustion of oxygen and acetylene (the fuel gas). When mixed together in a handheld torch or blowpipe, a hot flame is produced with a flame of about 3200oC; with welding generally carried out using a neutral flame which has equal quantities of oxygen and acetylene. The Acetylene is the fuel gas that when burned with oxygen provides a flame hot enough to weld.
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Cutting
In flame cutting, an oxy-fuel combustion is used with acetylene being the common fuel gas used in Malaysia for a quality cut. It is also the most widely used industrial thermal cutting process, managing cut thicknesses from 0.5 mm to 2,500 mm. The equipment is low cost and be used manually or mechanised.
The benefits of acetylene over other fuel gases (eg. propane, natural gas) is improved cut quality, higher cutting speed, faster cut initiation times and reduced oxygen use. This is essentially due to hotter flame temperature obtained (»3150oC), producing more rapid piercing of the materials being cut. The more intense primary flame and higher cutting speed allowable also contribute to a narrower width of the heat affected zone and the degree of distortion. Plasma arc cutting can be seen as an alternative to the oxy-fuel process, using the heat from the arc to melt the metal. Common variants of this cutting process are :
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Gas plasma
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Dual gas
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Water injection
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Water shrouded
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Air plasma
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Contact cutting
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High tolerance
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Where a gas is used, the cutting or plasma gas is normally argon, argon/H2 or nitrogen, with the secondary gas being air or oxygen, depending on the material being cut.
An emerging, but high quality high speed cutting process is the CO2 laser. Sheet metal cutting is a dominant industrial use of lasers in material processing. The lasing gas is normally a mixture of He + N2/CO2 and the assist gas O2 (for mild steel) and nitrogen (stainless steel, aluminium)
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Coating
An interesting application segment in the fabrication sector is coating or the deposition of coating materials onto components for wear resistance or maintenance build-up. Flame spraying uses the heat from the combustion of a fuel gas (usually acetylene) with oxygen to melt the coating material which then can be fed into the spraying gun as a powder wire or rod.
For powder flame spraying process, powder is fed directly into a flame by a steam of compressed air or inert gas (argon or nitrogen). A more recent addition to flame spraying is the high velocity oxyfuel (HVOF), where the combustion process is internal, and the gas flow rallies and delivery pressure are much higher than those in the atmospheric burning flame spraying process.
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Local Heating
Local heating where preheating of a material is carried normally involves the oxy-acetylene flame process. Preheating aids cutting and in certain metallurgical application helps in the diffusion of hydrogen from a C-Na steel weldment which may cause cracking. Flame brazing uses an oxy-fuel (acetylene) gas flame to melt and flow the filler metal. Normally performed in air, it normally requires the use of a flux with the filler metal fed in the form of wire or rod.
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