Roll straightening

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The manufacturing process roller leveling counts DIN 8586 to the forming process (main group 2). Roll straightening is part of bending, more precisely to bending with rotating tool movement or roll bending . Straightening machines are called roller straightening machines or simply straightening machines. Further subdivisions depend on the properties of the straightening machines.

Other straightening methods are e.g. B. straightening with presses (straightening presses) or straightening by hand (with hammer and flame), to name the most common alternatives. Roller straightening machines are mainly used for straightening coils, metal sheets or sheet metal parts. The main advantages of straightening with roller straightening machines are:

  • high flatness of the sheet
  • Stress reduction in sheet metal
  • quick straightening process
  • largely automated straightening process

Straightening procedure

Straightening with roller straightening machines is a bending process. The material to be straightened is exposed to ever smaller alternating bends. It goes through several alternating bends, which are created by offset rollers. There must be a curvature at the machine infeed which is greater than the greatest curvature in the unplaned sheet metal. Curvatures and deflections must be reduced so much in the direction of the outlet that the material to be straightened at the outlet of the machine springs back into the flat state. Sections that are under tension in the sheet metal part are stretched beyond the yield point so that a uniform fiber length is created. There are strong alternating bends at the entry or at the first straightening rolls. These become weaker and weaker in the direction of the outlet. The course of the bends can be imagined as a decaying sinusoid. In the end, the material to be straightened is flat and almost free of tension due to the alternating bends and the constant reduction in deformation. Since roll straightening is a continuous process in a throughfeed process, it is very fast and also suitable for endless strips ( coils ).

Types of roll straightening machines

Types of straightening machines have become established in which one row of rollers is fixed and another row of rollers is movable. Quality criteria for precise roll straightening machines (also: precision straightening machines) are:

  • Arrangement of the movable row of rollers in the block
  • Number of straightening rolls
  • good support of the straightening rolls (preventing the straightening rolls from bending)
  • small straightening rolls (in relation to the sheet thickness)
  • small distances between the straightening rolls

The control of modern roll straightening machines is becoming more and more important.

Straightening of parts and sheet metal

Tensions are released when punching, laser, oxy-fuel and plasma cutting of sheet metal. The metal sheets or the separate sheet metal parts can have unevenness. In the case of thermal cutting, the cutting beam also ensures that the material is heated up considerably. This creates a strong temperature gradient in the material, which can also lead to tension in the sheet metal. A subsequent (parts) straightening process makes the sheet metal parts level again.

Straightening of coils and strips

Straightening strips or coils makes sense due to the tension and unevenness in the coil. Coil curvature and transverse arching represent the most common flatness errors of coils. Roller straightening machines with 7 to 13 straightening rollers are sufficient to straighten coil curvatures sufficiently. For further flatness errors, up to 21 straightening rollers or additional adjustment axes are required on the straightening machine.

The straightening of coils is usually done in preparation for subsequent processing (punching, forming, etc.). The main task of the leveler is to ensure a reliable follow-up process (including by reducing the stress in the sheet metal).

application

Straightening with roller straightening machines is usually used when large quantities have to be straightened. Compared to other straightening processes, the process is very precise and reliable. (e.g. straightening with presses). Areas of application can be found in the entire industrial sheet metal processing (e.g. automotive industry, aviation, mechanical engineering, electrical industry, shipbuilding, etc.).

literature

  • Horst Bräutigam, Sascha Becker: Straightening with roller straightening machines . Vogel, 2009 ISBN 978-3-8343-3143-4
  • Eckart Doege, Bernd-Arno Behrens: Handbook Forming Technology: Fundamentals, Technologies, Machines . VDI, 2016, ISBN 978-3-662-43890-9

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