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FLEXO Magazine : June 2013
current flow can be read on the screen as a function of the pumping frequency. The ink pressure is measured at the chamber where the ink is led into the chamber inlet or at the side of the chamber. The pressure measured here is a general indication of the pres- sure loss, which is limited to between 5 and 15 mbar, depend- ing on chamber length and viscosity. It is recommended to set the pressure at between 10 and 20 mbar to ensure a slight excess of pressure in the chamber. An ink supply system is typically one meter tall with a variable flow range, from 5 to 30 liters / minute. The ink supply system provides an essential means of eliminating on-the-job manual intervention on central impression presses, where due to a vertical configuration access to tooling is restricted. When the flow has been stabilized, air regulation will lock the air pressure to the pump. Since both the pressure inside the chamber and the air pressure to the pump are both sta- ble, only a change in ink resistance can change the pumping frequen- cy. This will happen if the pressure in front of the pump is changed. Ink resistance is measured in viscos- ity, expressed by the ink’s inner resistance against flowing. Since the pump frequency is known, it is possible to determine the viscosity by means of software. Strokes are counted to determine when fresh ink is pumped into the system, to ensure precise amounts are dispensed to the chamber, leav- ing minimal residue at the end of the production run. Excess ink can be returned to the bucket for reuse, without waste. The pump minimizes manual intervention of the ink flow. CLEANING SYSTEM The ink supply system also enables automatic cleaning after each production run. A clean- ing system ensures the chamber is clear of residue, so that ink is removed from the system. Cleaning cycles for solvent inks, for example on an eight-color press, are up to 10 minutes, while for water-based inks, between 10 and 15 minutes are required. Sol- vent consumption during the clean- ing process amounts to 13.9 liters over two cycles. If water is used, consumption of 20 – 30 liters with approximately 1 liter of detergent is needed. n About the Author: Henrik Kristensen is sales director, TRESU Ancillary, a subsidiary of TRESU Group, a highly specialized company offering flexible, customized flexo printing machines, printing stations and ancillary products for flexo, offset and gravure printing and coating. TRESU Group has 30+ years of experi- ence and expertise in the development and production of engineered solutions for the package print converter. It maintains produc- tion facilities in Denmark, Lithuania and the USA. The company ’s network of international agencies provides around-the-clock customer support on five continents. Visit the company website at: www.tresu.com. Reservoir Chamber Doctor Blade System, specifically for narrow-web water- and UV-flexo presses, requires no ink pump. It also ensures uniform ink coverage on the anilox roll, boosting yields even when volume requirements are as low as 0.2 liters. Photos: TRESU Ancillary 90 FLEXO JUnE 2013 www.flexography.org