Steinbeis experts develop non-hazardous and environmentally friendly processing and machine technology for producing welding powders
It is already four years since Intelligent Functional Materials, Welding and Joining Techniques, Implementation – the Steinbeis Innovation Center in Dresden – reached a first milestone in its development partnership with Bavaria Schweißtechnik from Unterschleißheim. In 2016, the project partners developed a production-safe technique for submerged arc-welding heavy-walled aluminum components. The process made it possible to develop laboratory-scale powder formulations for welding aluminum alloys in reproducible quality, also achieving melt-off rates of up to a factor of eight. But there were also drawbacks with the process – certain ingredients in the formulation were potentially hazardous to operators, the process posed greater risk to the environment, and it caused more corrosion damage to apparatus and machinery. Reason enough for both partners to address these disadvantages by working further on the process as part of a ZIM project sponsored by the German federal government.
The aim of the project was to develop and introduce a user-friendly, environmentally friendly processing and machine technology for reliably manufacturing welding powder to be used in the submerged arc welding of aluminum. The innovative part of the project was a “single chamber reactor” – a concept allowing all key subprocesses needed to produce the finished welding powder to be carried out fully automatically inside a closed reaction chamber, without posing a threat to operators or the environment due to emissions. The market demand is there, and the importance of light metals is rising continuously – especially thick-walled aluminum components.
AGGRESSIVE CHEMICALS AND EMISSIONS IN MANUFACTURING
One reason for the problems experienced with powder formulations until now is that they include chemicals that are aggressive and abrasive. This makes it impossible to work with powder formulations in the types of production facilities that were available until now. Emissions and mechanical or chemical harm caused by processing powder mixtures result in so many impurities and damage to iron components used in machinery that it was no longer possible to achieve the required processing standards. The potential hazards meant that the project team had to set up its own production chambers to make the welding powder, taking care to keep incompatible powders well away from other materials. It was also important to develop a production technique that would be 100% safe for workers, machines, and the environment. Equipment would have to be capable of producing materials to a high standard that would not only be ready to use right away, but would also produce virtually zero emissions.
WELL PROTECTED THANKS TO THE SINGLE-CHAMBER REACTOR AND PLASMA POWDER COATING
This was the challenge taken on by the experts at Steinbeis and Bavaria Schweißtechnik. The welding powder used in aluminum submerged arc-welding processes comprises a mixture of materials containing various proportions of minerals, salts, chlorides, and fluorides. This makes it extremely hazardous to operators and harmful to the environment. The chloride and fluoride ingredients are particularly aggressive in chemical terms. As a result, a number of special safety precautions are required when producing powder – such as using the single chamber reactor. The idea with this technology is that all key steps of the production process take place within an enclosed container so that – as far as possible – all potential contact with the outside air or machine operators can be avoided. The manufacturing process involves feeding in raw materials, crushing, mixing, agglomeration (adding binding agents), and heat treatment (drying). Only once all of these steps have been completed can the powder blend be tipped out onto a filtering screen.
The chemically aggressive and abrasive nature of the powder ingredients during crushing and mixing can result in heavy corrosion and wear to components. As a result, the Steinbeis experts added a plasma powder coating to the surfaces of individual components of the single chamber reactor. To do this, they used wear- and corrosion-resistant iron, nickel, and cobalt-based alloys as a matrix material with embedded hardening materials in the form of vanadium carbide. The team examined and tested several material mixtures and powder blends.
PUTTING FUNCTIONAL COMPONENTS THROUGH THEIR PACES
After several rounds of testing, the project team identified a suitable combination of materials to provide a protective layer. The experts then assessed the corrosive and abrasive performance of materials. To provide a corrosion medium, a specially prepared solution of electrolytes was used. This was made from the main ingredients in the powder containing chlorides and fluorides. The functional components of the pilot plant were produced using the same materials, technology, and construction principles as the original concept, so the device included a receptacle and an agitation mixer with small rods mounted on the front of a round plate. Both the receptacle and the mixer come into contact with the welding powder during production. As a result, they were plasma powder-coated to protect their functional surfaces from wear and corrosion. A segment of plasma powder-coated pipe was pressed into shape using a remodeling and compression process to achieve the required rounding and dimensions. The coated sleeve on the pipe was cooled using nitrogen and the base of the receptacle was heated so that the two components could be joined and form-fitted in such a way that no cracks remained inside material layers or the base element.
The second functional part of the pilot plant – a round mixing plate with protruding rods – was produced additively using 3D micro-plasma weld cladding. To do this, 15 millimeters of pre-heated steel were used as a base substrate so that the part could be deposition-welded from above using multi-layering. The base substrate was then removed using a mechanical process before milling the base plate of the mixing tool, complete with rods, out of the layers that had been generated. Not only has this significantly improved the tool life of the functional components produced for the pilot plant, it has also ensured that the production method used for making the welding powder is safe and can be reproduced without having to pour materials from one container into another. The entire process can also be kept separate from operators and the environment.
Systematic experimentation enabled the project team to put the single reactor pilot plant through its paces and conduct testing and assessments of the process. Aside from checking the smooth functioning and reliability of the entire pilot plant, the experts observed operational parameters and processes for any damage to the protective layers. They also monitored the performance of peripheral components in terms of resistance to dust and emissions. The project team can now confirm results: The single-chamber reactor pilot plant has achieved its required function and is capable of producing welding powder for use in aluminum submerged arc-welding processes. It has also performed successfully in practical application.