Tension-control solution cuts pharmaceutical waste

Edited by the Engineeringtalk editorial team Sep 24, 2003

ZF has refurbished a hot-foil printing machine used by Pharma-Nord to produce pill sheet backings at its factory in Denmark.

ZF has refurbished a hot-foil printing machine used by Pharma-Nord to produce pill sheet backings at its factory in Denmark.

ZF's unique hysteresis EBU 3L brake and EKU 10 clutch units were specified to replace a mechanical system that was causing unacceptable failures and high levels of wastage.

Following installation of the units and a ZF ERM controller system, output has been increased significantly and downtime effectively reduced to zero.

Engineers from ZF were called in by Pharma-Nord to refurbish a machine producing pill sheet backings for their ranges of preventive medicines and nutritional supplements when it began to cause unacceptable levels of wastage.

The problem was identified as a failure of the friction-based control system to maintain consistent tension levels throughout the complex hot-foil process, resulting in improperly wound rolls and irregularities in the printing.

"Control tension or resistance needs to be finely adjusted to account for the varying diameters of rolls during the process", explains ZF Applications Engineer Michael Johansson.

"The foil is drawn into the machine from the initial roll for printing, transferred to the top drum for heating and drying then wound on ready for the next stage in the packing operation.

We therefore replaced the old friction-based tension off-winding controller with an EBU 3L brake and installed an EKU 10 clutch unit to the wind-on arm".

ZF's intelligent ERM system was then used to control both processes via a digital control panel and a series of Honigmann tension sensors.

The easy-to-use system receives information from the sensors and adjusts the torque applied to the roll spindles to maintain a constant tension on the foil.

The process was PID controlled to accurately predict the torque levels needed to produce an even wind, avoiding the common problems of slow raising and release of torque or flapping caused by sudden changes.

When integrated, the ZF system had to maintain tension levels within tight parameters throughout the process, ensuring that the printing was achieved to a high standard and finished foil was wound tight enough to produce rolls with the correct diameter.

Not only was this achieved resulting in a perfect end product, but also saved the client considerable costs as wastage was effectively reduced to zero and the problem of returns minimised.

Although there were other options available, the level of equipment and time required to set up the hysteresis brakes and clutches is minimal in comparison with servo systems, for example.

The slip and synchronous torques of the brakes and clutches are simply set manually in the range from zero up to the maximum value.

The values depend only on the setting of the electric current in the magnetic coil and the torque set is largely speed-independent, also making it effective during standstill.

Because of these factors there are essential differences between hysteresis components and eddy-current units.

In synchronous operation and at standstill the latter units cannot transmit torques and are also difficult to control in the lower speed range.

Hysteresis brake units in ZF Tiratron range are available with (continuous) slip powers in the range from 250 to 2000W and up to 4000W in short-term operations.

The brake units are supplied with torque capacities up to 520Nm and four different clutches are available for winding-on applications with torques ranging from 0.4 to 12Nm.