How to choose the right ink supply system for your printing application
Application areas and characteristics of various ink pump systems in the printing industry
Systematic color management is an essential prerequisite for consistent print results in flexographic printing. An important part of the color management process is to ensure an optimum ink flow in the ink cycle, so that there is always fresh ink circulating and no deposits are created. Furthermore, effective venting mechanisms need to be put into place so that air can escape from the chambered doctor blade, to make sure that the cells of the anilox roller are evenly filled with ink.
What actually makes a good ink flow?
The decisive factor is that the chambered doctor blade is filled with sufficient ink for the respective application. The ink flow for a small-volume ink take-off by the substrate is substantially lower than for a high ink take-off, e.g. when inking, coating or printing large areas. Regulating ink flow in line with the nature of the print job is therefore of central importance, whereby a coherent ratio of ink supply to the chamber and ink return from the chamber must be aimed for.
As far as the ink return is concerned, this should be done by gravity if possible. This type of return is the simplest way to degas the ink and counteract foaming. However, it is often not possible to implement a gravitational return flow in practice for machine design or installation reasons. It is then necessary to control the ink return flow with the aid of a pump. The following principle applies here: the return pump must follow the feed pump, adapted to the chamber doctor blade system.
The ink pump system must ensure that:
- on the one hand, the return pump generates a higher volume flow than the feed pump, so that there is no overpressure in the chamber
- on the other hand, no vacuum is created in the chamber doctor blade system.
For the ink supply, a pulse-free ink flow is ideal. This cannot be achieved with all pump types, so pumps with pulsation dampeners are used in many cases.
Three types of pumps are usually installed in the printing industry:
Puls-free pumps
Centrifugal pumps
Pumps with pulse, equipped with a pulsation damper
(Pneumatic-) diaphragm pumps
(Electric) peristaltic pumps
The design of pulsation dampers varies from manufacturer to manufacturer. AkeBoose has developed a special form of pulsation damper, the interior of which has a very smooth surface and flowing contours.
This makes the damper easily self-cleaning, no ink deposits can accumulate. When cleaning the ink circuit, the pulsation damper is automatically flushed as well.
Which pump type is suitable for which application?
To evaluate suitability, it is useful to look at the characteristics, advantages and limitations of the pump type in question.
Centrifugal pumps
- guarantee a pulse-free ink supply
- are primarily suitable for applications with few ink changes, as cleaning of the pump must be done manually and is relatively time-consuming
- can only be used in combination with gravity return, as the pump design is not suitable for use as a return pump
- are therefore very suitable for sensitive inks that tend to foam, as air can escape from the ink over the long distance of the gravitational return flow
- can pump all ink systems with viscosities up to 150 centipoise (equivalent to 40 sec in a DIN4 outlet cup)
- are inexpensive to purchase
- are not self-priming, therefore must necessarily be installed in the container
EPZ centrifugal pump series
The centrifugal pump series "EPZ" from AkeBoose has an integrated bypass that allows continuous flow regulation from 1 to 25 l/min. The pump unit also includes an ink container with a capacity from 25 to 55 liters. The slanted bottom in the container ensures optimum paint suction even at low filling levels.
Diaphragm pumps
- are also suitable for applications with frequent ink changes because they can be cleaned quickly and easily
- require a pulsation damper for low-pulsation ink supply
- are suitable for all ink systems and all viscosities
- allow simple flow regulation via a compressed air throttle, which however reacts sensitively to changes in viscosity during the printing process - it is therefore advisable to check the viscosity regularly
- have a medium purchase price level
- are almost maintenance-free and inexpensive to maintain
- have a moderate energy balance due to the use of compressed air
- are self-priming
- can be easily integrated into the machine control system
EPQ diaphragm pump series
With the "EPQ" series, AkeBoose offers a compact pump system with two controlled diaphragm pumps for a uniform ink flow in the supply and return of the chamber doctor blade system. The integrated ink reversal supports a quick and uncomplicated cleaning of the system during ink changes. Pump units for up to four printing units can be integrated in a control cabinet to save space.
Peristaltic pumps (electric)
- are very well suited for applications with frequent ink changes, as they are extremely easy to clean
- enable complete media separation by using different hoses and can also be operated in sterile mode, e.g. when used for printing pharmaceutical products
- are suitable for all ink systems
- require a pulsation damper for low-pulsation ink supply
- offer a very reliable flow regulation via frequency controllers
- have a good energy balance
- have higher initial costs than the other pump types, but these are partly offset by their ease of use and low energy consumption
- require regular replacement of hoses; the typical hose life is between 3 - 12 months (depending on the liquid pumped)
- offer very good integration possibilities into the machine control, e.g. to centrally monitor the ink flow or the temperature of the medium.
Customized pump system solutions
AkeBoose GmbH develops and supplies individual pump solutions for specific projects. The adjacent photo shows a double coating supply with conditioning for UV coatings including temperature control. For this system, peristaltic pumps with continuous ink flow control and flow converters for easy emptying of the chamber doctor blade system were used.
