Rotary printing-press offset of press

A rotary offset is a press offset intended for the impression of the newspapers or documents with long pulling. The press is a particular medium of the Imprimerie. The requirements for quality, the number of specimens, need for reducing the expenses of production, the flexibility of the number of pages, colors per page, as well as the moment of end of drafting (the Looping) brought various designs of rotary printing-presses.

Currently, the rotary printing-presses of press turn to 15 m/s what is equivalent to approximately 80.000 specimens per hour for a format Quotidien.

Total sight

In detail

Compensation/Debtor uncurler/

The role of the uncurler is to ensure the food continues in reels, without stopping the press. The uncurlers with changeover in projection to the stop tend to disappear to be replaced by joinings with the flight. This operation remains delicate and can lead to breakages of the band of Papier.

The role of the compensator is to provide a stable power necessary to the groups of impression. It is necessary for that to correct the variations of tension of the band, likely to harm the Repérage of the reel.

The debtor as for him is used to control the tension of the band within a tower of inking. These debtors can be before the groups of impression (in-feed) and/or at exit of turn of impression (out-feed)

Problems on the reels

The quality of the reels is paramount to have an impression without problem. Indeed, with current speeds (approximately from 12 to 15 m/s), if the reel is not regular, it can have a strong swing, then generating vibrations and strong variations of the tension of the band.

Moreover, the folds must be avoided on the reels because they would lead to a fold in the groups of impression and thus a not encrée surface. To reduce that, one can have recourse to the use of “rollers bananas” of smaller diameter in their center.

Regulation

The regulation is an basic element making it possible to keep stable the band in the press and so allows a good quality of location. An imperfect regulation will generate defects such as:

1) Variation of location

2) Transverse movement of band

3) Doubling out of rotary printing-press offset

Print units

Format: Width/Development

On a rotary press, the circumference of the cylinders (development) determines the format of paper and thus the maximum height of the page. To reach other formats, it is necessary to cut paper longitudinally, then one has recourse to various types of foldings.

The cavities on the cylinders, necessary to the fixing of the plate or the strainer impose nonprinting zones which tend to be reduced innovations progressively. Moreover, these cavities add jolts on the machine, which poses problems of tension of the paper band. On a newspaper, the nonprinting zone is about 25 to 35 Misters.

The width report/ratio of width and circumference of the cylinders should not be too important. In the contrary case, the cylinders are curved under their weight and it results from it, at high speed, the appearance of vibrations, prejudicial with the impression.

The rotary printing-presses called to double development have a double circumference, which enables them to print four pages with the daily format by rotation.

The rotary printing-presses called to double width have a double bandwidth, which makes it possible to also print four pages with the daily format by rotation. One can of course also use machines doubles width, double development (eight pages per rotation), but those are reserved for very great pullings or the newspapers with strong pagination. In this case, the posision of the pages of each half-cylinder is shifted of 90° in order to limit the vibrations.

The first part of the page to being printed is the footer. That is relating to the mechanism of folding on the outlet side of the machine. Indeed, the page being clutched by barbs which leave traces, those are more discrete in footer.

Different configurations: group H, Y, planetary configuration

There exists many way of printing the various colors on a newspaper. The rotary printing-presses of press want to be most flexible possible in order to be able to print many types of newspapers. The distribution of the colors in the newspaper does not depend on the machine but there exist several possible configurations on each machine in order to adapt the number of colors and the pagination to the desired page layout.

As the rotary printing-presses offset use the technique of subtractive Synthèse to carry out an image colors and as it is difficult to obtain a pure black color, four colors are needed at least. It is then a quadrichromic impression. In lower part, be colors then are used to underline text, to make titles, for publicities… but not for the images. Above four colors, the quality of the images is improved (still rare in the press) and make it possible to obtain colors fluos, for example.

For the recent rotary printing-presses of press, the groups of impression are of type strainer /blanchet i.e the two sides of paper are simultaneously printed. The strainer of the printing group on the other face plays then the part of cylinder backpressure. One distinguishes the groups in form from Y which make it possible to print two colors on a face and a color on the other, of the groups H which make it possible to print two colors per face.

Currently, the newspapers tend to being printed four colors recto-back. Indeed, for the same site, a publicity is sold more expensive colors than into monochromic.

There exist also planetary groups of impression. In this case, two, three, four or five groups are laid out around a central cylinder of backpressure (of diameter large than its satellites). The advantage of this system is a better location of the colors of the same face (the band is well held and does not have time to become deformed under the effect of the hydrant: ( Fan-out ). On the other hand, one PERT largely of flexibility. It is impossible to choose the number of bands of paper and the colors not used by face cannot be allocated with other paper bands, they are thus " perdues".

Various configurations inking/damping/strainer

Modulate bars of reversal

Principle

The bars of reversal are used to give to a band paper or part of this one another direction as run or another way. One can then change the order of the reels, to turn over the bands (in the case where, not having machine printing four colors per face, one wants to juxtapose pages colors for example).

To arrive to that, the bars of reversal are laid out with an angle of 45° compared to the direction of paper. These bars, not being mobile, are polished and chrome and have tubes blowing of the air between the bar and paper. Paper slips thus on air cushions, which minimizes frictions.

Examples

the simple bars of reversal are used to change the direction of a paper band. That is necessary when several print units are laid out transversely compared to the installation of impression. One uses them in particular with the print rolls doubles width. The combinations obtained allow a good flexibility of the page layout.
the parallel bars of reversal are used to lead half of the band as paper above or in lower part of other half. The moved semi-band is not turned over, but is not in parallel transported compared to the initial direction of walk (the same east coast above, like before).
the cross bars of reversal are also called Bay-Window or Poney . The band which passes by this device is then turned over. The side which was before above finds in lower part. The paper band is then positioned on another or at its sides. One can also change this band of stage (interesting if one cannot print four colors per face).

Folding machine

Cone or funnel of folding

On the rotary printing-presses offset with double width, the paper bands are generally cut then arranged by bars of reversal . This assembly of bands then receives the first long fold on the level of the cone of folding (one can place a rotary knife also there if one wants a format tabloïd).

For the newspapers with strong pagination, it is sometimes necessary to use two assemblies of half-bands. Indeed, it is not possible to use an unspecified number of bands on a cone of fold, from where the use of a second cone. One calls then that a superstructure with double cone. It with the advantage of being able to provide several books which is a editorial advantage (the supplement sport, TV…). This type of stucture makes it possible to obtain two books in normal production and four in accumulated production (see further Production with accumulation ).

Note: In the case of a rotary printing-press with drier, it is to parfoir necessary of réhumidifier or siliconer paper to soften it and prevent that it does not break.

Production without accumulation/with accumulation

The bands of Papier leave the cone to arrive at the folding machine. It is here that it will be cut out. Cutting is carried out transversely using a cylinder equipped with a knife. Once cut out, the paper band must be seized by barbs to be able to control it (from where the trace of small holes in bottom of a daily newspaper, or on the right on the last pages of a format compressed tablet).

In a process without accumulation, the layer is immediately ejected by making a second fold perpendicular to the pil cone. On the diagram opposite, one should not take account of paper in red which corresponds to a production with accumulation.

Indeed, in a process with accumulation, the sheet is not ejected immediately. It is preserved and with the following turn last another will be. What makes it possible to make two books (for example inside a daily newspaper, there will be a supplement sport). On the diagram: in red the paper which is accumulated is ejected with another sheet.

Thereafter, according to the configuration and the wanted page layout, one can add a third fold to him which will be with the choice perpendicular or parallel with the second.

Production with accumulation

Packing/Forwarding

Internal bonds

Offset
Printing works
Flexographie: used for the impression of the newspapers in Italy

External bonds

It is not Sorcier on the press

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