Compressed air in the metalworking industry
The metalworking industry encompasses both the production and processing of metal. This means that the manufacturing of steel and non-ferrous (NF) metals, foundries and metalworking are all part of the metalworking industry.
The branch is one of the energy-intensive industries. Compressed air is used as a flexible medium in many production processes in metalworking and metal-producing operations. Compressed air is an often underrated parameter for reducing energy intensity and thus increasing energy efficiency.
Alongside the importance of compressed air for energy efficiency, the right compressed air quality is crucial to avoiding problems in production and faults in the final product. By treating compressed air according to their requirements, metal-producing and metalworking industries can reduce costs, improve energy efficiency as well as avoid scrap and production standstill.
Applications in the metal branch
Steel is made in two steps in the blast furnace: in the first step, iron ore is reduced to pig iron, in the second step it is processed into raw steel in the converter. Compressed air is used during the first step. The blast furnace is charged from the top, which means layers of coke and iron ore alternate in the blast furnace. At the bottom, so-called hot blast air is blown in through tuyères. The term hot blast air described heated compressed air enriched with oxygen and hydrocarbon fuel. This is necessary for effective iron melting.
Compressed air is also used for air cooling. Cooling influences the properties of the steel, thus special demands are made on steel cooling and the medium used. One example is accelerated cooling, which takes place in moving air (falling air).
During the production process of metal and metal parts, the surface must be cleared completely of deposits and particles, since this could otherwise have a negative influence on the downstream working processes such as surface treatment. One method used for this is sandblasting, which is also known as abrasive jet machining. This technology is used to free the material from residual paint, soiling and rust, to shape the workpiece and work the surface structure.
Compressed air is used to accelerate the blasting agent passing through the nozzle, since the blasting agent must collide with the surface at high speed for the treatment.
Powder-coating, also known as powder-painting, is a coating method suitable for metallic and non-metallic objects. Two methods are used: electrostatic powder spraying (EPS) and fluidized-bed coating.
Compressed air is used to blow off the workpiece, convey the powder and for fluidizing. In addition, compressed air can be used in the coating booth as dosing air and spraying air. The quality of the compressed air influences the final product, e.g. oil-contaminated compressed air can cause problems such as open spots (craters) in the coating layer or bubbles or craters in the fluid tank.
Another process which involves compressed air is direct current anodising using sulphuric acid, an electrolytic process that is often used for aluminium production. Electrolyte motion is required for electrolytic oxidisation: purified, oil-free compressed air is blown in for this.
In addition, thermal spraying processes are used for surface finishing. Flame spraying and light air spraying are two of those to be mentioned in the compressed air context. With this application, compressed air serves as an atomiser gas which sprays the spray material onto the surface.
Cutting and welding
Laser processes are often used for cutting and welding metal. Compressed air is used for both laser welding and laser cutting. Oil-free, dry and clean compressed air is required for these applications to avoid problems occurring in the process and with the final product.
During laser welding, compressed air at a pressure of up to max. 8 bar is used to divert material particles and material vapours away from the welding optics and prevent damage. This process takes place with the aid of the so-called crossjet unit.
During laser cutting, compressed air is required for flushing the mirror channel and blowing out the melt, depending on the process used. Equally, it can be used as cutting gas for the cutting process. The clean compressed air cools the surface of the material and improves cutting quality. Equally, the compressed air ensures that evaporating material and other materials are removed.
Many tools are operated and controlled by compressed air in the metalworking industry too. An adequate compressed air quality is necessary, since production downtime is often caused by excessive steam in the machines and plants as well as corrosion in the pipes.
One example of a pneumatic tool is a pneumatic hammer (refer also to steelmaking); this is used for core ejection and well as for breaking substances out of furnaces and pans. Pneumatic stampers and pneumatic sanding machines are also used.
3D print made of metal powder
The process of 3D metal printing offers several advantages compared with processes used thus far: additive manufacturing permits complicated parts to be produced, saving material, shortening production times and sources of error. During selective laser melting (SLM) components are built up layer by layer. This process usually takes place in an inert gas atmosphere. Nitrogen is often the inert gas used, and is partly generated from compressed air using a nitrogen generator. The compressed air must be of a certain quality so that there is no negative impact on components and processes due to contamination, leading to costs for outage, cleaning and replacement.