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Service and know-how for welding and cutting

Perfectly joined

Can you remember the last time you saw rust on a car? It is likely to have been a while ago! Steel production and sheet metal working methods have been greatly refined over the past few decades. The trend is towards material mixes that really are fit for particular purposes. The advances in welding have also made a major contribution, thanks in no small part to new gas mixtures.

Messer has always played a part in driving forward improvements in welding and cutting processes through targeted research, development and consultancy. The impetus for this comes from the intensive daily interaction we have with the users. And at Messer, service means active problem-solving and process optimization with a long-term perspective. A large number of specialist suppliers manufacture parts and components for the automotive industry in particular.

Car safety
Staying with the example of the car, in the past an average mid-range car was held together by about 5,000 spot welds and over a hundred welded-on bolts or pins. To improve crash behaviour and corrosion resistance, increasing use is also being made of fusion welding processes such as MAG welding as well as laser welding and soldering. Welding and thermal cutting (dominated by laser and plasma cutting) are highly complex processes in which numerous details need to be considered: How thick is the sheet metal? Are different material combinations involved? Does the material have temporary rust protection or has it been galvanised? What is the direction of welding and from which side is it to take place? What kind of equipment is being used? Are fillers being used or not?

Consideration of influencing factors
“There is a huge number of potential influencing factors, and the sum of possible combinations is not even quantifiable,” says Dr. Bernd Hildebrandt, who is in charge of Technology Management Welding and Cutting Gases at Messer’s Krefeld site. “As a result, there is an almost bewildering variety of possible welding situations, and this is constantly increasing thanks to technical progress. Anyone who wants to keep up with the latest developments needs to have a good grasp of science.” Messer not only has its own laboratories and top-class specialists, it also has a dense network of experts, as Bernd Hildebrandt explains: “Germany is a leader in welding technology thanks to its long tradition in metalworking. Not only is it home to many of the global market leaders in this industry, it also boasts a unique concentration of scientific institutions. We maintain a close working relationship with a considerable number of them and act as an intermediary between research and everyday welding practice.”

Know-how = Problem-solving
Messer can therefore offer customers expert advice at the highest level. Bernd Hildebrandt describes this cooperation using the example of an agricultural machinery manufacturer: when the soil cultivation equipment left the factory, it still looked perfect, but not infrequently the paint at some of the welds would flake off when the appliance was used for the first time. “In a case like this, we would take a close look at the materials used and analyse the process in detail in order to determine the cause of the problem.” The analysis involves looking closely at all the relevant parameters before suggesting solutions. These can refer to parts of the facility, individual process steps or the gases used. In the case of the ploughs, it transpired that silicate islands (slag islands) had formed on the welds. As soon as the appliances were exposed to the forces of tractor and soil, these superficial silicates (slag) became detached and caused damage to parts of the brand new paintwork. The remedy was provided by switching to a welding gas with an oxygen content of four per cent (Ferroline X4), which significantly reduces the formation of slag and weld spatter.

Harmful substances in the hose
When a water molecule (H2O) gets into the arc during welding, it is broken down into its constituent elements – hydrogen (H) and oxygen (O). Both gases can have an extremely disruptive influence. High-alloy chrome-nickel steels react with oxygen, and this can lead to oxidation tint, which remains visible even after paint application. Hydrogen likes to penetrate liquid metal: this leads to unwanted pores with aluminium and can cause cracks in the weld with structural steel. Normal air humidity is often the source of these “harmful gases”. The water molecules do not get into the welding process directly from the air, though, as it is kept away by the shielding gas. However, the shielding gas itself can be contaminated by air humidity. This is generally caused by unsuitable line hoses. In the case of simple compressed-air hoses from DIY superstores, it only takes a few seconds for a significant quantity of H2O to penetrate the rubber jacket in the form of water vapour. While thorough purging with clean shielding gas helps, this is not always feasible with spot welding processes. The most effective precaution is therefore to use high quality hoses. Simple compressed-air hoses are quite unsuitable.

Only hoses specifically intended for welding should be used. These are normally certified in accordance with DIN EN ISO 3821 (formerly DIN EN 559) or DIN EN 1327. Further assistance is provided by the DVS technical bulletin 0971 “Guidance on selecting gas hoses for gas-shielded arc welding”.

Pore formation in the weld not only depends on the moisture content in the gas, but also on the gas mixture itself. For example, when welding aluminium with Argon 4.6, pore formation can be detected from as little as 490 ppm. With Aluline He50, an argon- helium-nitrogen mixture, this figure more than doubles to 1,250 ppm, which means that pore formation only begins when the moisture content is much higher.

Fundamental questions
Time and again, the exchange of information and ideas with users also leads to new, fundamental questions, because there are continual advances in welding. One such example is the question of pore formation with aluminium – pores weaken the weld and therefore the stability of the metal structure as a whole. Particularly with the modern, quick welding processes, very small pores can form in large numbers, which are barely visible when carrying out the normal X-ray check; the result of a recently concluded test at Messer. “But we were also able to show that the risk of pore formation can be significantly reduced by using new ternary mixtures with a high helium content,” explains Michael Wolters, Technology Manager Welding & Cutting.

Partner to medium-sized companies
Be it a research project or user support – the starting point is always the question of process optimisation with and for our customers. In the metalworking industry, we deal with many small and medium-sized companies which are structurally suited to Messer. Messer can have an input into research and development, we offer extensive know-how and are represented in the important industry bodies. The same applies to our international presence, which enables us to provide appropriate support to globally operating customers with, for example, production facilities in China. Michael Wolters: “We are the right size for both.”

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