| The use of fast running web offset printing
machines has brought about a number of problems which show
up in the printed product such as breaking of the fold and
breaking of glue or staple bound products, wavy and uneven
sheets. The problems are mainly caused by an insufficient
moisture content of the paper during the printing process
and, furthermore, by the increase in the web offset printing
capacity the increased printing speed as well as higher thermal
stress caused by higher temperatures in the drying process.
In addition the growing demand for LWC-papers and uncoated
grades with higher qualities call for remoisturizing after
printing. |
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Advanced Electrostatic Spray System
DOX Electrostat Description
To eliminate these problems we install the DOX electrostatic
spray system. Papers, which were delivered with a rel. moisture
content of 40 - 45 %, will be dried down to a rel. moisture content
of 1 - 2 % into the heatset dryer. The DOX Electrostat is able
to remoisture the papers up to a rel. moisture content of 40 -
45 %, which is required by the printers.
The function of the electrostatic remoisturizing is based on the
effect to spray very small water particles (micro drops) in a
high voltage field up to 160 kV. Due to the high electrostatic
loading the micro drops being charched and accelerate without
loss toward the paper web. The sheet will absorb the spray mist
very fast and the micro drops penetrate through the paper pores
into the fibres.
The DOX Electrostat consists of a high voltage frame, spray beams,
a counter roller and a complete PLC control unit. It uses the
method of indirect charging which means that the nozzle bar itself
is not electrically loaded. The flow rates for each nozzle are
controlled from the control cabinet. The water particles are sprayed
by the grounded nozzle damper into the high voltage frame. Only
in this frame are the water particles charged and accelerated
towards the paper web. The water particles besides being charged
within the high voltage field are broken down in size and at the
same time accelerated with high speed towards the paper web.
The spray density in an electrostatic moisturizing system amounts
to 150 - 200 particles per measured unit whereas in conventional
moisturizing systems a density of only 25 - 50 particles p.u.
can be obtained. Particle size in the electrostatic moisturizing
system is approx. 5 microns.
The DOX Electrostat can be installed in web offset machines, paperback
Printing Presses and special converting machines to solve
the descript problems.
Benefits to the Paper Industry
- elimination of electrostatic
- increase of moisture up to 40 - 55 % rel.
- no paper breaks because of dryness of paper
- no waves in printed products
- increase of printing quality
- improving of runability and printability
Technical Features
- two-stage nozzles
- applies a highly atomized, low pressure spray mist into
the high voltage field. Due to the high loading and high
speed of the particles to the paper web the sheet will
absorb the spray mist very fast
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Technical Specifications
- nozzle damping units to spray very fine mist
- high voltage fields for electrostatic loading the small
water particles which accelerated with high speed towards
the paper web
- high voltage generator for 160 kV
- automatic moisture control system
(PLC functionalities)
- moisture increase up to 45 - 50 % rel. moisture
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Options
- one or double side moistening of the printed sheet
- dosing pump to spray special emulsion for better moisture
absorption
- separate key board with display
- integrated control system with PLC (Allen Bradly or Siemens
S7)
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DOX Family
DOX Electrostat
DOX RotoClean/S
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Advanced Electrostatic Spray System Layout
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DOX RotoClean/S
Printing Presses
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