The traditional solid welding wire is coated with copper on the surface of semi-finished steel wire, which can enhance the electrical conductivity and corrosion resistance of the wire and the welding nozzle, and reduce the friction with the feeding hose or the welding nozzle. The coating thickness of copper-coated wire is generally 0.2 ~ 0.8μm. In the welding process, a part of the copper element melts into the weld, which reduces the mechanical properties of the weld joints, especially the impact toughness and elongation at low temperature. The copper also oxidizes into copper particles and escapes into the air, which is harmful to human health after inhalation. The production of copper-coated welding wire will also produce waste acid and pollution into the environment. Based on these reasons, non-copper wires or copper-free wires have become popular and are favored by welders. Here we will introduce how non-copper coated welding wires are produced.
The Swedish ESAB has been developing non-copper wire since 1997 when it was originally named ECOIG and later renamed Autrod. In 2002, ESAB invented a non-copper wire by using Advanced Surface Treatment Technology (ASC) and named it Aristorod. This treatment makes the surface of the welding wire darken or add another protective layer on the surface while ensuring the surface finish, making it a good electrical conductivity, wire feeding stability, rust resistance and weld performance, has been widely used in diverse fields.
Since 2002, Kobe Steel and Sumitomo Metal Industrial Co., Ltd. have also supplied a series of copper-free solid cored wires for MAG and CO2 welding. South Korea's Kiswell Corporation also applied for a patent for the invention of a copper-free welding wire, which uses surface treatment oil containing alkali metal or alkali earth metal compound, Zn compound and hydrocarbon compound to coat the surface of the welding wire, and strictly controls the amount of coating (0.003~0.006g on 1kg of welding wire).
Some Japanese scholars proposed that coated surface of the welding wire with MoS2, WS2, or C improve its feeding; some proposed the welding wire coated with potassium compounds, sulfur compounds, polyisobutylene to reduce the splash; there are some patents propose to use a mixture of hydrocarbon mineral oil and vegetable oil, as well as a mixture of MoS2, WS2, C, PTFE, fatty acids, metal soap, etc., coated the wire to produce a copper-free wire.
Metal soap extreme pressure agent of stearate type lubricant with an antirust agent, and a certain amount of metal powder such as zinc, copper, aluminum, titanium, etc., mixed into lubrication particles for wire drawing. The particle size of the metal powder is no more than 325#, and the mass fraction is generally about 10% (up to 30%) so that the total mass of the lubricant attached to the surface of the wire is about 0.01% ~ 0.25% of the wire, and the metal powder is 0.001% ~ 0.10%.
Water-soluble liquid lubricants are suitable for low hydrogen welding wires. Firstly, the semi-finished wire is pickled electrolytically with 15% ~ 25% H2SO4 solution.
Secondly, the welding wire after cleaning is pulled out 1 ~ 2 times with a compression rate of 5% ~ 25%. The drawing lubricant is composed of water-soluble sodium soap and water-soluble inorganic rust inhibitor. The typical formula is: the mass fraction of sodium triglyceride hard fatty acid and sodium chromate is 0.75% and 0.75% respectively, the rest is water, and the volume fraction of rust inhibitor is 0.3% ~ 1.5%.
The surface coating of the welding wire should be anti-rust and moisture-proof, and not damage the stability of the arc and the welding metallurgical properties.
Ultra-fine graphite, molybdenum disulfide and fluorine resin without hydrogen as welding wire surface treatment agent or trichloroethylene or carbon tetrachloride as a solvent, and add a small amount of CeO2, K2CO2, CsCO3 as arc stabilizing agent to improve the performance of the welding wire can be according to the need. Some companies use Nashk rust inhibitor coating to manufacture copper-free welding wire. Its rust prevention mechanism is that the single molecular sediment layer is absorbed on the metal surface, which blocks the micro-battery effect on the metal surface in the atmospheric environment and inhibits the occurrence of electrolytic corrosion.
When welding, copper-coated welding wire produced a little yellow smoke, and no copper-coated welding wire sends out blue and white smoke, that is, the smoke does not contain Cu element and reducing the harm to the welders. In the welding process of solid cored wire, soot is mainly produced by the oxidation of metal vapor, and Cu is the main harmful element produced during the welding of copper coated solid cored wire. The Cu content of non-copper wire is much lower than that of traditional copperless wire, so the non-copper wire is more beneficial to protect the health of welders. Statistics show that the amount of smoke without copper-coated wire is about 20% lower than that of copper-coated wire.
non-copper wire in the welding process produced less spatter, which can ensure in consistently high quality welding joints and reduce the post-welding cleaning workload, which mainly depends on welding parameter matching.
Non-Copper welding wire has a good arcing performance. The average short-circuit transition time of the droplet is shorter than that of the copper-coated wire and can withstand the sharp change of the extended length of the wire during welding. Special surface treatment process makes no shedding of copper-coated layer, that can maintain stable wire feeding for a long time, even in the state of high-speed and can get higher welding and deposition efficiency.
Traditionally, it is considered that the copper layer is more rust-resistant because iron is more active than copper. However, the corrosion results of the salt spray test (temperature 30℃, air humidity 80%, stay in 0.01% NaCl solution for 2h) show that the corrosion of copper-coated wire is more serious than that of copper-plated wire.
It is concluded that the serious corrosion of copper-coated wire is due to the rapid corrosion of galvanic cells which is easily formed in the spot where the tiny copper layer cracks or the copper layer peels off. The surface of the non-copper wire does not contact other metals and will not form galvanic cells. The addition of antirust grease makes its antirust ability better than that of the copper-coated wire.
The welding experiments show that the weld forming quality of the non-copper-coated wire is obviously better than that of copper-coated wire.
Non copper coated wire in the welding process shows a series of advantages, such as less welding smoke, less welding spatter, good welding arc stability and weld forming, etc., is a kind of new products that is environmentally friendly and economical, has been widely used in mechanical processing, construction engineering, aerospace, bridge engineering, steel structure processing, etc., can be considered to be the development direction of solid wire.
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