Span gas online shop UK: Helium / argon mixtures are sometimes used for their higher heat characteristics. Gas mixtures, usually 25% helium and 75% argon are sometimes used and can help to increase travel speeds when AC – gas tungsten arc welding. Mixtures of more than 25% helium for AC – gas tungsten arc welding are used, but not often, as they can tend to produce instability, under certain circumstances, in the AC arc. Pure helium or high percentages of helium (He-90%, Ar-10%) shielding gas are used primarily for gas tungsten arc machine welding with direct current electrode negative (DCEN). Often designed as seam welders, the combination of GTAW – DCEN and the high heat input from the gas used can provide fast welding speeds and outstanding penetration. This configuration is sometimes used to produce full penetration butt welds, welded from one side only, onto temporary baking with no vee-groove preparation, just a square edged plate.
Low cost, high quality: Argon is widely used because, like CO2, it is low cost. It is odourless, colourless, and known for not reacting to high levels of elements like oxygen or water. So why use it over CO2? As we mentioned, CO2 yields imperfect results, as it leaves openings for oxygen to compromise the weld. Argon, on the other hand, is much more stable and controllable. It keeps the molten weld from getting damaged, becoming brittle and breaking, and can be used with other gases such as helium to enhance the quality. The perfect choice would be a mix of argon and something else. Argon would always be the gas with the largest quantity though.
No shielding gas exists that fits all applications. So the first step is to decide what you want to improve in your welding and match this to the benefits the shielding gas can bring. Just remember the gas may change as the thickness of material increases. For example, with components that have to be painted or coated after MIG welding it is important that the amount of spatter produced is kept to a minimum. Using carbon dioxide can cause large amounts of spatter to be ejected from the weld pool damaging the surface of the component. A change to Argoshield Heavy can halve the amount of spatter produced. Moving to Argoshield Universal can halve it again. Read more details at Span Gas Cylinder.
A perfect welding result, without impairment of corrosion resistance and mechanical properties, can only be obtained when using a backing gas with very low oxygen content. For best results, a maximum of 20 ppm O2 at the root side can be tolerated. This can be achieved with a purging setup and can be controlled with a modern oxygen meter. Pure argon is by far the most common gas for root protection of stainless steels. Formier gas (N2 + 5 – 12% H2) is an excellent alternative for conventional austenitic steels. The gas contains an active component, H2, which brings down the oxygen level in the weld area. Quad gases are mainly used within Marine environments. Quad gases are a four gas mix. Supplied in a range of lightweight cylinders and made from aluminum. Both reactive and non-reactive mixtures are available.
For gas shielded welding processes such as TIG, MIG/MAG, FCAW, shielding gases may be inert gases, such as argon, helium and nitrogen, or argon-based mixtures containing carbon dioxide, oxygen or both. Helium may be added to argon/carbon dioxide mixtures to improve productivity. Carbon dioxide (CO2) may be used, on its own, in MAG and FCAW. With the exception of CO2 , these gases are not defined as hazardous to health under the COSHH Regulations but they are asphyxiants. CO2 has a long-term exposure limit of 5000ppm (8-hour TWA reference period) and 15000ppm short-term exposure limit (15-minute reference period). None of the gases can be seen and none have a smell – so their presence in hazardous concentrations is difficult to detect without prior knowledge or measuring equipment. Source: www.weldingsuppliesdirect.co.uk.