Replace or refurbish, that is the question

01 November 2007

Unilever, Port Sunlight, UK was faced with a familiar production issue whereby under performing, obsolete equipment presented a risk to continuity of supply. The question was to replace the filler with a brand new one or to refurbish the existing line and remove problematic areas. The London-headquartered manufacturer investigated by calling in original machine builder, Farasons, and its technology provider, Capley Marker Systems.

HBM intelligent load cell
HBM intelligent load cell

When Unilever discovered its Hyper Chlorite Bleach production line was showing signs of low performance it knew complete replacement would be expensive and time consuming. Furthermore, the company said particular issues, rather than overall wear and deterioration, limited the performance of the bottle filling.

Following discussions with Farasons it was agreed that new technology intelligent load cells and a new automation controller would bring the machine back into efficient production. Particular productivity problems were associated with all three attributes of OEE. These were performance, the bottle handling and filling was slow; availability, the weighing and control system was unreliable and parts were hard to obtain; and quality, the bottles had to be overfilled by weight to be sure that commercial requirements were satisfied.

Forty HBM intelligent load cells, integrated with a Siemens S7 logic controller, constituted the centre of the solution. The logic controller was physically mounted on the machine carousel to simplify load cell connection, external connections being made through a slip ring assembly. HBM intelligent load cells are used for bottle filling valve control; bottle presence detection, through TARE; and leak detection, by measuring rate of weight change whilst filling.

The load cells are connected by multi-drop RS485 to the S7 communications port. All values are available in engineering units directly from the intelligent load cells. Additionally, the load cells communicate by digital IO to the controller for valve control for filling. Filling is done in two stages, coarse and fine, to ensure accurate filling by weight.

The carousel mounted PLC communicates externally through a slip ring assembly that carries RS485 to a calibration and programming port and Profibus to a Siemens touchscreen HMI, for machine operation. The power, of 24 VDC, is also fed to the controller via the slip rings.

To facilitate the ease of mechanical upgrade it was possible to fit new intelligent load cells in the space of the old sensors on the machine as they had a similar physical size and mounting.

Due to Unilever’s continuous OEE monitoring the rebuilt filling machine’s performance could be accurately compared with the original one. The company claims filler speed is up by 30%, weighing accuracy is improved and give-away is negligible. There is less spillage by overfilling and less maintenance. The machine runs 24 hours either four or five days a week, depending on schedule, there is therefore spare capacity to respond to market demand changes.

Mark Stuffin, engineer at Unilever, was pleased with the project.

“The refurbishment has proved to be very effective and it was the right decision, being far more cost effective to wholesale machine replacement,” he said.

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