Pumps: Rising to the challenge

Louise Smyth

From fine paper coating to high-viscosity paint, materials for surface coating represent extreme challenges to pump technology, explains Roger Willis

The printing and ink industry represents one of the most versatile application sectors for delivery systems. The areas of application include the reliable supply of abrasive paper fillers and corrosive gluing agents just as much as the exact metering of high-viscosity printing inks and varnishes.

Standard pumps cannot cover such a wide range of demands, especially since the usually very sensitive media require careful transport. Instead, this industry often uses progressing cavity pumps and rotary lobe pumps from Netzsch, which are marked by their wide adaptability and pressure-stable delivery characteristics. 

One of the major problems for conventional pumps in delivering inks is the lack of fluidity of the medium. Viscosities of 10,000 mPas and more are quite common. Continuous supply can therefore be achieved only with difficulty; in addition, the pumps become clogged quickly. For example, a renowned publishing house struggled with repeated breakdowns at the diaphragm pumps used to refill offset ink at roughly 10,000 mPas from the transport truck to the storage tanks, which delayed the unloading process greatly. What's more, the pumps often required maintenance work and had to be removed and dismantled quite laboriously. To increase performance and economy at this point, the company finally resorted to using Nemo progressing cavity pumps.

Special adaptations

Their delivery principle is based on a rotor that turns in an oscillating motion within a fixed stator. Due to the design of rotor and stator, hardly any pulsation or shearing forces are acting produced on the fluid. Instead, the medium is transported gently and continuously. Consistency and especially the viscosity are not a factor for the flow with this displacement technology; the transported quantity is determined by the speed alone and – in combination with a frequency inverter – can be regulated conveniently and with precision.

A single-stage L-geometry was used for rotor and stator for this concrete application, which allows for a higher delivery rate at low differential pressure. The deliberately chosen undersize of the rotor prevents excessive clamping thereby improving mechanical efficiency. Furthermore, the slim design of the progressing cavity pump allowed the installation of four such pumps – for the four printing inks – together with frequency inverters on a carrier module. This is integrated in the base plate of the transport truck and can be easily removed with a forklift truck. It allows easy access to the devices, in case maintenance work should become necessary at some point. Nonetheless, the pumps generally work much more reliably than the previously employed diaphragm pumps. To top it off, the unloading time for the ink was reduced by nearly half.

Versatile applications thanks to broad adaptability

Positive displacement pumps from Netzsch are used in various areas of the ink and paper industry, for example to transport pigment sludge or additives, for process fluids and binding agents. However, each scenario requires configuring the pump according to its use. The broad experience of the company’s pump experts in the ink and paper market helps at this point to find the respective suitable combination.

Roger Willis is with Netzsch

For more information, visit www.engineerlive.com/process