Welding protection gas selection

In the gas shielded welding process, although gas is one of the important parameters in the welding procedure, its importance is often underestimated. The traditional concept generally believes that the cost of welding production depends on the cost of procurement, and the lower the procurement cost of each consumable is, the better. However, with the development of technology, the characteristics of modern welding production are to use the new technology that is constantly emerging to improve the production efficiency of the process and reduce the production cost. As a important parameter in the gas shielded welding process, the protective gas has a significant impact on the welding process and welding results, although the cost is only about 5% of the total welding cost. The protective gas used in welding include: Ar, CO 2, in many cases may be added O 2, H 2, H e N 2 or to improve the welding process. Table 1 lists the physical properties of different gases associated with welding. It is these physical property parameters that determine the different behaviors of different gases during the welding process. The development of shielding gas is the product of the combined application of these physical characteristics.

The important role of welding protective gas
From a technical point of view, the following five important effects on the welding process can be achieved only by changing the composition of the shielding gas:
(1) Increasing the wire deposition rate Compared with the conventional pure carbon dioxide, the argon-rich gas mixture generally brings higher production efficiency. The argon content should exceed 85% to achieve a jet transition. Of course, increasing the welding rate of the wire requires selecting the appropriate welding parameters. The welding effect is usually the result of multiple parameters. The improper selection of welding parameters usually reduces the welding efficiency and increases the post-weld slag work.
(2) Controlling the splash and reducing the low ionization potential of the slag after welding to improve the arc stability and correspondingly reduce the splash. Recent new welding power technology has controlled the splash of CO 2 welding, and under the same conditions, if a mixture is used, the splash and expansion of the welding parameter window can be further reduced.
(3) Control weld formation to reduce excessive welding. CO 2 welds tend to protrude outward, resulting in excessive welding and increased welding costs. Argon mixing is easy to control weld formation and avoids wasted wire.
(4) Increasing the welding speed By using the argon-rich gas mixture, even if the welding current is increased, the splash can be controlled very well. This has the advantage of an increase in the welding speed, especially for automatic welding, which greatly increases the production efficiency.
(5) Control welding fume Under the same welding operation parameters, the argon-rich gas mixture greatly reduces the welding fumes compared with carbon dioxide. The use of an argon-rich gas mixture is an added advantage of reducing source contamination compared to investing in hardware to improve the welding operating environment.
In summary, it can be seen that by selecting a suitable welding protection gas, the welding quality can be improved, the total welding cost can be reduced, and the welding efficiency can be improved. At present, argon gas mixture has been widely used in many industries, but due to her reasons, domestic enterprises mostly use 80% Ar+20% CO 2 . In many applications, this shielding gas does not perform optimally. Therefore, the choice of the best gas is actually the easiest way to improve the product management level on the road of welding-type enterprises. The most important criterion for choosing the best shielding gas is to meet the actual welding needs to the greatest extent. In addition, a suitable gas flow rate is a prerequisite for ensuring the quality of the weld, and a flow rate that is too large or too small is not conducive to welding.
Typical product
(1) Stargold binary argon mixed Stargold argon-rich gas is characterized by stable welding arc, stable welding process, bright surface after welding, no splash, no need to be polished after welding.
In some auto parts industries, due to the presence of oxide scale on the surface of the weld, post-weld painting or electrophoresis cannot adhere to the scale. Reducing gas reactivity can help reduce the production of these surface scales. As shown in Figure 1. With stargold5, the weld surface is clean and bright without splashing.
(2)Robostar This is a ternary mixed gas suitable for automatic welding process. It has strong penetration ability and high welding efficiency. It is suitable for a variety of droplet transfer modes and has high joint fatigue strength. Especially suitable for the automotive industry. Robostar is the best choice for solving problems when there is excessive stress caused by the uneven transition of the weld metal to the surface of the base metal due to the convex surface of the weld, which causes the fatigue strength to drop. As shown in Figure 2, the weld is smoothly transitioned to the base metal without stress concentration.
图1 采用不同保护气体,解决焊缝表面氧化皮太多的问题
Figure 1 Using different shielding gases to solve the problem of too much scale on the surface of the weld

Figure 2 Robostar weld indication
(3) Compared with CO 2 , Stargon can increase the welding speed by 20%~30% and reduce the smoke by 50%~100%. It is a very environmentally friendly protective gas. It is suitable for various droplet transfer forms, the welding process is stable, and the weld is well formed. An example of a typical welding process soot is given in Figure 3.


Figure 3 Typical welding fume photos of different shielding gases

The shielding gas discussed above is primarily for carbon steel. For stainless steel and aluminum alloys as well as other special materials, protective gases have a suitable range of choices. Table 2 lists some of the recommended Prax protection gases based on the thickness of the base metal.
Outlook
With the development of new welding processes and new materials, the welding protective gas has been developing at the same time. Under the premise of satisfying the welding property, the protective gas will mainly improve the welding rate, improve the welding efficiency and reduce the development of welding fumes. More importantly, gas is one of the many welding parameters for welding. Even if the best gas is selected, it is necessary to ensure that the welding process is matched with other suitable welding parameters, otherwise the optimal welding effect cannot be achieved. Based on this, the modern protective gas production and supply enterprises are no longer limited to the knowledge of only gas transmission, but the overall welding technology solution provider around gas applications. The China Welding Technology Center, one of Praxair's five largest laboratories in the world, has been committed to technical research in this area for the past ten years and has consistently applied the results of laboratory research to the customer's production site.
In 2014, for all enterprises engaged in welding production, improving management efficiency, improving product quality and improving process efficiency will be the inevitable development direction. A small change in the welding protection gas can play a key role in the overall welding production. How to use the gas tool is a problem worth considering for every company. At the same time, through cooperation with advanced protective gas production enterprises, a comprehensive understanding of the protective gas mechanism, with the selection of optimized sets of welding parameters, will be the only way for each enterprise to go to efficient production.
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