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FAQ

Grounding

What advantages and benefits does a ground monitoring system have for the user?

Ground monitoring systems make sure that existing ground contactors (e. g. ground clamps) are actually used when filling or discharging potentially explosive materials from tanker wagons and silos. Since filling or discharging can only be started after the proper ground link has been identified, this system provides the ultimate degree of safety.

What happens if the ground link is disrupted during the process?

If the ground link is disrupted, the process is instantly discontinued via the floating contact of the grounding system. The process can be restarted only after the ground link has been recovered.

Do I have to use a cable rewinder?

No, the use of a cable rewinder is not absolutely necessary. But it is often found that the cable and the ground contactor are not rolled back up after use and are run over by trucks, resulting in damage to the cable and the ground contactors.

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Measurement

Can the Eltex Influence-E-Fieldmeters be used for continuous measurements?

The Influence-E-Fieldmeters EM02 and EM03 cannot be used for continuous measurements. The EMF58, on the other hand, can be used for continuous measurements. The integrated recorder connection allows the measurements to be recorded.

Can the Influence-E-Fieldmeters also be used in potentially explosive atmospheres?

No, these meters must be used outside the explosion hazard zones.

How often do I have to calibrate the measuring devices?

If used in laboratory conditions, the measuring devices should be calibrated once every year. In any other case, calibration every two years is sufficient.

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Charging

When do I need charging?

Electrostatic charging is used if products must be electrostatically "glued" together for a certain period of time to improve the production process (i.e. exact fixing of melamine film on chipboard before pressing).

Can I touch a charging bar?

Charging bars must not be touched when in operation because they may at times generate very high voltages.

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Discharging

When do I need discharging?

Discharging is always used if materials are charged with static during certain processes which results in disruptions in finishing and postproduction or in contamination of personnel by uncontrolled discharges.

What does Eltex mean by active length, total length and installation length?

The active length of a bar is always measured between the first and the last emission tip of the bar.
The total length is the active length plus the insulation distances beginning from the first/the last emission tip to the beginning of the bar/the end of the bar. For the charging bar R130 (30 kV), this is 70 mm, for instance.
The installation length is the total length of the bar, the length of the cable connection and the bending radius of the cable.

When do I need an air-supported discharging bar?

Air-supported discharging bars should always be used when the surface is to be cleaned with ionized air.
Air-supported discharging bars can also be used if technical conditions are such that the discharging bar cannot be installed in the best possible way in relation to the object to be discharged.

Do I need a bar or a blowing head?

Discharging bars are always used if wide objects or webs - no matter if they are static or moving - need to be discharged.
Ion blower heads are used to discharge smaller surfaces with ionized air and clean off particles sticking to the surface by static. Another application of the Ion blower heads is to blow ionized air into piles of film or paper to ensure that the sheets are fanned and lifted separately (i.e. sheetfed offset).

When do I need a 5 kV and when a 8 kV power supply?

The 8 kV power supply is always used if you want to discharge products with high static charges and high web speed (> 8 m/sec.) and if the distance between the discharging bars and the product is >40 mm.
For all other applications a 5 kV power supply is sufficient.

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Printing assist ESA

How easy is it to handle the ESA, and how safe?

When operating the unit via the Eltex Static Control (ESC), all functions and parameters are permanently under control. If you observe the recommendations given for the remote control, your printing assist system will always be in top condition. Information on the causes of malfunctions and how to rectify these can be retrieved via the service key.

What is the power requirement of an ESA system?

With the new GNH61 Electrostatic Printing Assist by Eltex, the input power requirement is reduced even further. The new bar configuration and the emission tip distance allows the impression roller bar to be mounted even closer to the impression roller. This generates a homogeneous charge field over the entire width of the web. Air resistance and rated output drop accordingly. This means that the likelihood of paper dust and ink vapor settling on the impression roller bar is very low. The result: less downtime and longer cleaning intervals.

Can the Electrostatic Printing Assist be installed in any gravure printing unit? How long does installation take?

The ESA is designed for installation in any commercial gravure printing press. The work involved includes assembling the charging or discharging bars, installing and networking the generators, installing the remote control and wiring the system. Typically, a packaging gravure printing press with six or eight printing units can be fully ESA-equipped and ready for operation within one weekend. A decorative printing press with three or four printing units can be completely print-optimized in a day and a half. Retrofitting an illustration printing press having 8 printing units typically takes two or three days.

Do I have to train my operating personnel or is ESA more or less self-explaining?

With no Eltex Static Control fitted, the ESA unit must be switched on and off and offers no monitoring and no parameter control. The touch screen menu assistance of the Eltex Static Control (ESC) with its integrated help functions allows the operating personnel to quickly familiarize themselves with the system.

As a packaging printer I have to alternate between paper and foils, such as PVC and polyethylene. Can I use ESA for both?

Yes! The Electrostatic Printing Assist works equally well for paper as well as foil. Simply use the appropriate key on the remote control panel to switch over manually to foil operation.

I work with ink systems containing both solvents and water-based inks. Can I use ESA for both?

Yes! Each of Eltex’s Electrostatic Printing Assists, top-loading and side-loading, can be used for both applications. Explosion-proofed bars are used for inks containing solvents; non-Ex bars are used for water-based inks.

Is the remote control actually required or can I operate the ESA without it?

Remote control allows the operator to keep control of all parameters and functions at a glance. Each ESA can be operated fully without remote control. Though it has no impact on the performance and capability of the system, the user without remote control foregoes valuable monitoring and operability functions. However, the safety of the ESA system is guaranteed, even without a remote control.

What can Electrostatic Printing Assist actually do to improve printing?

The Eltex Electrostatic Printing Assist, ESA for short, is based on the principle of the plate type capacitor. This means that a homogeneous electric field is generated between two plates, in which a dielectric is pulled to one side. The electrostatic printing assist applies this principle in the nip - at precisely the point where the ink is to be transferred onto the web. The electric field generated by the ESA (approx. 300 - 1,000 volts) causes the ink to be pulled completely out of the cells and transferred onto the substrate. This principle of ink transfer with electrostatic support works evenly over the entire width of the web and operates reliably from the slowest to the highest production speed.

How do missing dots actually occur?

At first glance, the surface of paper appears to be smooth. But, if you look at it through a microscope, you will see that it has a rough surface. In the nip, this irregular „fiber jungle“ (in a 70 l/cm screen, for example) is faced with 4,900 cells per square centimeter. All of those cells are expected to transfer their ink content to the paper within a split second. This task, already difficult, is made even harder by the fact that paper has poor surface compressibility and is neither elastic nor pliant. Thus, at normal printing speeds, mechanical contact alone does not always result in complete ink transfer from cells-to-paper. This phenomenon worsens at higher printing speeds. Coated substrates and other pre-impregnated materials also exhibit this problem.

Is the required impression roller coating produced by Eltex?

No! Eltex is the world-wide leader in the field of electrostatic print optimization, which includes a large number of different systems. This is made possible because Eltex are engaged in basic research and therefore have remarkable potential to innovate. Also, Eltex often cooperates closely with universities and users in the launch of new developments.That is why Eltex were the first to cooperate with manufactures of impression roller coatings to jointly develop the coating values required for the ESA. The coatings used for the ESA systems are all manufactured by renowned impression roller manufactures, using our specifications.

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Ribbon Tacking

Why do I need an Eltex Ribbon Tacking system?

Only disruption-free production operates economically. Paper webs and ribbons, electrostatically blocked at the right point, keep together during the entire finishing process.

How does a ribbon tacking system work?

The applied high voltage (positive/negative) produces an electric field which displaces the air between the individual paper ribbons, leading to a temporary intensive material bonding.

What are the advantages of electrostatic ribbon tacking?

- No dog ears
- No disruption of the copy stream
- Better opening of the folded signatures
- Disruption-free running of the compensating stacker

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Remoistening

Why does paper grow?

Paper is basically keen to keep the moisture in equilibrium with the ambient surroundings. If the ambient surroundings are drier than the paper, the paper releases moisture. If the ambient surroundings are more humid than the paper, the paper will absorb moisture. While absorbing moisture, the paper fibers swell in cross direction. The paper always grows cross grain!

Why does heat-set dried paper “break” faster than non-dried paper?

During the drying process, most of the moisture content of the paper evaporates. But the moisture in the paper is of decisive importance for the elasticity and suppleness of the paper. The smaller the moisture content of the paper, the more brittle the paper fibers become. The consequence: fiber breakage and dropping-out of wire-stitched signatures!

How can we measure moisture?

The neatest method of measuring moisture in the paper is by defining the water content, the so-called absolute moisture. Even though we have absolute values, a percentage is used as measuring unit, i.e. weight percentage related to the paper weight. When we talk of a 4% absolute moisture or water content, we say that 100 g of paper contains
4 g of water.
Another option is defining the relative humidity: the relative air humidity between the paper sheets is measured by means of a sword-type hygrometer. The measured air layer is in equilibrium with the surrounding paper sheets. This value depends on the temperature and relates to the maximum volume of water amount the ambient atmosphere can absorb at a certain temperature.

How much moisture does paper need?

Strictly speaking, paper needs as much moisture sufficient to maintain an equilibrium with its ambient atmosphere. Common unprinted heat-set web offset paper has a water content of between 4 and 5 %, after drying between 0.5 and 2.5 %, depending on the dryer temperature.
 As a rule of thumb: after remoistening, the paper should regain approx. 80% of its initial value.

What about energy consumption?

To generate the electrical field for electrostatic remoistening, high voltage is used but only a low current intensity in the milliampere range. The power consumption of an electrostatic unit is therefore very low!

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