Brakes and clutches avoid costly downtime

ZF hysteresis brakes and clutches have provided Day International (UK) with over 12 months of problem free operation in a high precision pressing machine.

ZF hysteresis brakes and clutches have provided Day International (UK), the UK's largest rubberised printing sheet manufacturer, with over 12 months of problem free operation in a high precision pressing machine.

Following the successful application, two more machines in the process have been upgraded with ZF tension control systems as part of an internal continuous improvement drive, resulting in reduced downtime, minimised waste and standardised spares.

Whether meeting the high-speed requirements of newspaper presses or providing the accuracy to flawlessly print banknotes, the rubberised sheets made by Day International have a tough life as they transfer ink to paper in printing presses.

The quality of the sheets and their final performance is dependent on the speed at which they are fed through each production process, with strict parameters to be maintained on tension control systems.

The machines operate around the clock to produce 40,000m2 of sheeting each month and it is imperative to Day that costly downtime is kept to an absolute minimum.

Over 12 months ago, Willie Allan, Chief Engineer at Day International calculated that it was time to replace the tension control system on the first of three main processing machines at the company's Dundee production facility.

This first major stage involves attaching the rubber to a fabric backing via a highly accurate rolling process.

This complex web application required keeping a consistent tension on the fabric backing as it is fed into the machine, coated with adhesive and attached to the rubber sheeting.

"The company continually looks to improve and develop the way we manufacture our products to provide even greater consistency to our customers and this is an area were we decided we could improve on our existing DC drive based tension control system", comments Allan.

"We then contacted our local drives system supplier JR Power, who recommended that we fit ZF EKU hysteresis clutches to each of the unwind systems and an EBU brake to the onwind assembly".

"We had considered a manual clutch system, but had rejected the idea due to risks of contamination from dust particles, a problem conveniently avoided by the magnetic - noncontact operation of the hysteresis units".

"They were incredibly easy to fit", continues Allan, "and the setup was quick and simple, as we only had to program the parameters into the PLC and the ZF units provided flawless tension control despite a large difference in tension as the material rolls vary in diameter".

"If there is too much tension the sheets become too thin, reducing wear life of the final product and compromising quality".

"Too little tension and the sheets become thicker, causing costly problems with the printing presses and irregularities in the print".

After 12 months of faultless use and associated increase in output, a similar ZF assembly was fitted to a machine that controls the adhesive curing process of the rubber sheeting.

Again, varying tension would have produced inconsistencies in the properties of the rubber, resulting in weaknesses and inaccuracies in the final print.

This three-way web application includes two inputs of rubber sheet, which are spliced together either side of a paper layer, enabling the materials to be separated once they have been pressed and fed through a curing oven.

Another web made little difference to the time taken to set up the new system as adding an extra EKU unit was simple and straightforward.

Operation was proven to be superior to the old inverter based system in terms of setup, downtime and improved end product.

Grinding the surfaces of the cured rubber sheeting is one of the final operations in the process and yet requires the highest levels of tension control.

The three grinding machines employed at Day international flatten the sheets to tolerances of 10um and each require an extremely slow feed system to achieve the desired result.

"Due to the excellent performance of the two other systems we also recently upgraded the crucial final grinding machines with ZF clutches and brakes", explains Allan.

"The results were very favourable, with increased output, reduced wastage and costly downtime".

"Other benefits became apparent as we could standardise on spares and the ZF ERM control interface allowed us to troubleshoot more quickly and easily than any other system we have used".

The ZF range of brakes includes a high power series that offers (continuous) slip powers from 250 to 2,000 watts and peak capabilities of twice these figures.

With four different versions available offering torque capacities ranging from 0.08 to 520Nm, ZF's range of hysteresis clutches are especially useful for winding-on applications in packaging, labelling as well as paper or food packaging industries.

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