Due to automation, changing from one coating 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. Since KBA has found in the tests that the results obtained by the two systems are basically the same, the level of automation and the input involved in manual operations have changed, so their advantages and basic principles are also different.
At the end of each shift and conversion from one type of coating to another (eg from UV to water, or from an aqueous coating containing a special effect pigment to a pigmentless coating) In the case of glazing, the glazing unit and conveyor system must be cleaned. Varnish changes are part of the day-to-day work on both compound and dual coater presses, but can also occur on other types of glazing presses. These operations should be very short and require very little input from the press operator.
Manual cleaning takes time and increases downtime. When using a simple glazing pump and squeegee that is not installed in the conveyor system, the average cleaning time is between 20 and 25 minutes, and the operator cannot perform any other work during this period.
In contrast, all components related to coating oil are thoroughly cleaned on an automatic conveyor system such as that manufactured by Harris & Bruno. It takes only a few minutes, depending on the size of the coating and printing press used. Size and degree of automation. However, this is not always the case because the level of automation provided for on-line glazing has not always been comparable to the level of automation of offset presses.
Harris & Bruno System: Single Polishing Line
A Harris & Bruno Automatic Varnish Delivery System can be cleaned in three to eight minutes, depending on the type of coating used and the size of the press. Since the cleanup process is started with a button and runs automatically, the operator can then perform other tasks after a few seconds.
Fully automated prerequisites
The level of automation can be very different. Fully automated means that all parts related to coating oil—even the oil return hoses of the coating tank—can be cleaned with the touch of a button without the need for manual pumping and valves. The conversion and subsequent cleanup. For completeness, it should be possible to convert from one type of coating to another in a single delivery system. The use of a single line eliminates the need for manually changing hoses or valves, eliminating the risk of accidentally mixing the coating.
As a prerequisite, the oil scraping system must be completely embedded in the control device, and the filling and discharge valves of the scraper chamber must be controlled automatically. This is the case with our Hydro-Comp wiper system, which is a standard part of the H & B conveyor system.
In order to avoid mixing of different coatings in the same pipeline, a part of the cleaning process must be carried out in the manner we know of purification (a H&B patent). This requires the use of a new coating that squeezes all of the cleaning agent or any residue of the coating from the system into the waste container.
There are two optional devices that optimize the automation. An inline heating module is particularly useful for warming UV coatings to obtain their optimum viscosity. The module uses sensors to continuously measure the temperature in the anilox roll. There is also a special lacquer circulator SCC, which has the effect of cooling and agitation, allowing the varnishes with rheological problems to work well.
Single-pipeline and double-pipeline system: Reasons for both positive and negative
In the past, if you want to avoid cross-contamination, you absolutely need two sets of separate varnishing lines. Although the conversion time is shorter than the basic manual system, Harris & Bruno believes that this progress is achieved at the expense of automation because hoses must be reconnected or valves must be changed. Moreover, such devices require twice as many pumps and valves, which in turn double the cleaning and maintenance investment, and make the system more prone to malfunctions and operational errors, thereby increasing costs.
In a single glazing line, there is no risk of cross-contamination if the system can perform a patented cleaning method. If this is the case, then the system can be fully automated and operator intervention minimized, so both preparation and downtime are shorter than using two lines. If a system is only half the size of another system, it will require 50% less maintenance and will be less affected by operator errors.
Nevertheless, discrete glazing oil delivery systems or rather SCCs are desirable or necessary for some special applications. This is the case, for example, when using highly viscous media or expensive coatings that require very little loading, or when the coating requires special handling such as cooling or agitation and gentle pumping. Some examples are varnishes containing pearlescent or iridescent pigments, certain metalures, perfumes, certain high-viscosity foaming coatings, UV flexographic printing inks and certain opaque white coatings.
new progress
Harris & Bruno and KBA cooperate on a continuous basis 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 was to integrate the control of the varnishes into the main console of the press. The system can then use a graphical user interface like a printer. This also makes it easier to program the timer settings and can 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 production. KBA's polishing seminar has clearly shown that this is a topic that many printers rarely care about.
Used varnishes
In all anilox roll coating and inking systems, more than 80% are powered by a diaphragm pump, which in most cases is operated by compressed air. This type of pump is still the best result of compromises in terms of flow, reliability and price.
The biggest drawback of diaphragm pumps is pulsation, but this has no effect on advanced and stable oil scraping systems. In contrast, pulsation in the cleaning process can actually have a good effect.
The consumption of large amounts of air has also been criticized as a disadvantage. The pump with the correct power level fills the doctor chamber in the varnishing line at a very slow speed. In Harris & Bruno's 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 light in large format printers. 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 equivalent flow electric pump.
in conclusion
The greatest advantage of a well-designed automated conveyor system for on-line glazing units in offset presses is reduced press downtime.
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