Raw seamless tubes received from the tube mill are generally distorted, misshapen and not fit for purpose. To be corrected, they first have to be bent and then straightened.
Our objective was to reduce machine downtime by speeding up the changeover setting position between each tube process, ultimately increasing productivity. Set-points for all position loops are calculated by entering tube dimensions and parameters on the HMI, the control system then calculates the correct settings. The positions can also be set manually, or minor adjustments can be made to fine tune the settings for a particular product.
Overall control was by a Siemens S7 PLC system, whose main functions were to control the speed and torque set-points of the main drives, calculate theoretical set-points for the position loops and execute the position control loops.
The majority of tube straighteners use DC variable speed drives, although more recent machines use AC variable speed inverter driven motors. The operator’s interface was achieved using a Siemens wincc based HMI, while mimics gave overall status indication of the machine, as well as the ancillary hydraulic and lubrication systems.
Tube data can be entered to give the input data to the calculations executed in the PLC. The output data of these calculations are displayed on the screen as set-points for the position loops. The HMI can be linked to a database where recipes for set-points of all position loops could be stored for future use.
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