Due to the automation, changing from one varnish to another is no longer a time-consuming task. Users of KBA sheetfed presses can choose between Harris & Bruno's single-line pumping system or Tresu's dual-line system. KBA has found in the test that the results obtained by the two systems are basically the same, but the level of automation and the investment in manual operations involved have changed, so their advantages and basic principles are also different.
At the end of each shift and switching from one type of varnish to another (eg from UV to water-based, or from water-based varnishes with special effect pigments to pigment-free varnishes ), The glazing device and conveying system must be cleaned. Variations in varnishes are part of daily work on composite and dual-varnish printing presses, but can also occur on other types of varnish printing presses. These operations should be very short and require very little input from the press operator.
Manual cleaning is time-consuming and increases downtime. When using a simple varnish pump and scraper cleaning cycle not installed in the conveyor system, the average varnishing time is between 20 and 25 minutes, and the operator cannot perform other tasks during this period.
In contrast, it takes only a few minutes to completely clean all varnish-related parts on an automatic conveyor system such as manufactured by Harris & Bruno, depending on the varnish used and the size of the printing machine Size and degree of automation. But this is not always the case, because for a long time, the level of automation provided for on-line glazing devices cannot always be compared with the level of automation of offset printing units.
Harris & Bruno system: single varnish line
A Harris & Bruno automatic varnish delivery system can be cleaned within three to eight minutes, depending on the type of varnish used and the size of the printing press. Since the cleaning process is started with a button and runs automatically, the operator can switch to other tasks after a few seconds.
Prerequisites for full automation
The level of automation can vary greatly. Fully automatic means that all components related to the varnish-even the return hose of the varnish drum-can be cleaned with the touch of a button, without the need for manual pumping or valves Conversion and subsequent cleanup. In order to achieve completeness, it should be possible to switch from one type of varnish to another in a single delivery system. The use of a single line avoids manual switching of hoses or valves, thereby eliminating the risk of accidental mixing of varnish.
As a prerequisite, the oil scraping system must be completely embedded in the control device, and the filling valve and discharge valve of the scraper chamber must be automatically controlled. This is the case with our Hydro-Comp oil scraping system, which is a standard part of the H & B conveyor system.
In order to prevent different varnishes from mixing in the same pipeline, a part of the cleaning process must be carried out in the way we know about purification (an H & B patent). This requires the use of new varnish to squeeze out all the residue of the cleaning agent or varnish from the system and transport it to the waste container.
There are two optional devices to optimize the automatic operation. An on-line heating module is particularly useful in heating the UV varnish to obtain its optimal viscosity. The module uses sensors to continuously measure the temperature in the anilox roller. There is also a special varnish circulator SCC, which has the function of cooling and agitation, so that varnish with rheological problems can work well.
Single pipeline and dual pipeline system: positive and negative reasons
Previously, to avoid cross-contamination, two separate sets of varnish lines were absolutely required. Although the changeover time is shorter than the basic manual system, Harris & Bruno believes that this improvement was achieved at the expense of automation because of the need to reconnect hoses or otherwise switch valves. Moreover, this device requires twice the number of pumps and valves, which in turn doubles the investment in cleaning and maintenance, and makes the system more prone to failures and operational errors, thereby increasing costs.
In a single varnish pipeline, if the system can perform the operation of the patented purification method, there is no risk of cross-contamination. If this is the case, it can fully automate the system and minimize operator intervention, so preparation and downtime are shorter than using two lines. If one system is half the size of another system, it requires 50% less maintenance and is less affected by operator error.
Nonetheless, a separate varnish delivery system or more precisely SCC is still desirable or necessary for some special applications. This is the case, for example, when using high-viscosity media or expensive varnishes that require very little loading, or when the varnishes require special treatments such as cooling or agitation and gentle pumping. Some examples are varnishes containing pearlescent or rainbow pigments, certain metal pigments (Metalure), perfumes, certain high-viscosity blistering varnishes, UV flexographic printing inks, and certain opaque white paints.
new progress
Harris & Bruno and KBA have continued cooperation to improve the operability and ease of maintenance, reliability and automation of the device. At present, two major projects are gradually approaching maturity.
The first project is to integrate the control of the varnish delivery in the main console of the printing press. The system can then use a graphical user interface like a printing press. This also makes it easier to program the timer settings and generate a visual display of the operating status of the pumping system.
The second project considers the automatic adjustment of the pumping system based on different viscosities or changes in viscosity during the production process. KBA's glazing seminar has made it clear that this is a topic that many printers rarely care about.
Polishing oil pump used
In all anilox roller glazing and inking systems, more than 80% is powered by a diaphragm pump, and in most cases this pump works on compressed air. This type of pump is still the best result of compromises in flow, reliability and price.
The biggest disadvantage of the diaphragm pump is pulsation, but this has no effect on the advanced and stable oil scraping system. On the contrary, pulsation actually has a good effect during the cleaning process.
The consumption of large amounts of air has also been criticized as a disadvantage. A pump with the correct power level fills the doctor blade cavity in the varnish line at a very slow speed. On the Harris & Bruno system, this speed is about one stroke per second, and the pumping volume is about 9 liters per minute. This is more than the maximum absorption of 3.6 liters per minute required for full-field coating in large format printing presses. When operating at this speed, the air consumption of the pump is equal to about 0.3 kilowatts, which is equivalent to the energy consumption of an electric pump of the same flow rate.
in conclusion
The biggest advantage of the well-designed automatic conveying system used in the on-line coating device in offset presses is to reduce the downtime of the press.
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