PLC upgrade improves safety at Sandvik steel rolling mill 17 April 2014

Sandvik Materials Technology has added zoned safety guarding to a large cold rolling mill at its Sandviken plant in Sweden, using ABB's new safety PLC as the controller.

The upgrade follows earlier developments at Sandvik's cold rolling mill, including adding servomotors and new machine controls, in that case using ABB's standard AC500 PLC and touchscreen operator interface panels.

This latest improvement adds PLC modules from ABB's AC500-S PLC to the machine control system to enhance safety on the 20m-long mill.

The system installed uses a networked architecture based on the PROFIsafe protocol over Profinet digital fieldbus to provide independent control of six safety zones.

Torbjörn Pettersson, an engineering development specialist with Sandvik Materials Technology, explains that the zoned arrangement means that parts of the machine can remain operational while an operator gains safe access to other zones, with safety assured by disabling power.

Making that work are around 50 safety PLC I/O channels, employed to link to gate switch and light curtain guarding, and emergency stop buttons. The I/O also monitors pressure switches to sense that hydraulic power has been disabled so that maintenance can take place, and controls power supplies to the motor drives.

Safe speed control is another aspect of the safety control provided by the new PLC - to ensure that hands or fingers cannot be trapped between the mill's belt and rollers.

"We were very pleased to find such an easy solution for adding state-of-the-art protection, in the form of the ABB's safety PLC, which integrated directly with the machine's existing PLC," comments Pettersson.

"The fact that ABB could supply the spectrum of machine control components required for this project – from the non-safety and safety variants of the PLC, to the operator panels, motor drives, contactors and safety hardware – both simplified and speeded this upgrade," states Jonas Rehnberg of ABB Sweden.

"The modularity of the new safety solution also means that it is now very easy to upgrade or modify safety functionality in the future, to enhance the safety of the mill even further, or to integrate additional aspects of the production process."

Pettersson says Sandvik chose ABB's safety PLC because of its good experience of the standard non-safety AC500 PLC architecture on both this machine and other machinery control projects.

The AC500-S safety PLC also meant Sandvik could use floating point numbers, which simplified the safety programming required for this project, for example around calculating speed.

Brian Tinham

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