Coating apparatus – With means to apply electrical and/or radiant energy to work... – Radiant heating
Patent
1996-06-27
1998-11-03
Edwards, Laura
Coating apparatus
With means to apply electrical and/or radiant energy to work...
Radiant heating
118 58, 118 62, 118 67, 118 68, 118227, 118244, 118261, 34114, B05C 100
Patent
active
058302751
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a paper coating apparatus comprising a liquid coating medium applying device and a drying device, and particularly relates to a contact free web deflecting device for guiding the web at the drying device.
Such an apparatus is known from DE 43 02 435 A1. However, web speeds as high as those with the present invention are not possible with this apparatus. In particular, however, the invention relates to a paper coating device in on-line arrangements known from Voith publication p. 2771, comprising a device for applying a liquid coating medium onto a moving paper web followed by a drying device having at least one deflecting device for the web which guides the web by means by an air cushion.
In accordance with this, in a known coating apparatus, a means for applying a liquid coating medium onto a moving paper web is arranged in the drying unit of a paper making machine. As a rule, this means is located between two drying groups, each of which has several drying cylinders with the usual drying screen (or drying felt) covering and a commonly available drive. The known coating apparatus as well as that according to the present invention can have a pair of rolls for the one-sided or two-sided indirect application of a liquid coating medium or a single roll for the direct application of the coating medium. In the state of the art the drying of the coated paper web ensues either alone through contact drying by means of the following drying cylinders or through a combination of contactless (for example infrared) dryers and contact drying cylinders.
The so-called "Speedsizer" illustrated in FIG. 2 of the above-mentioned Voith publication is only suitable for the application of pigment-free (size-like) coating mediums because only contact drying is intended.
In FIGS. 3 to 5 of the above-mentioned Voith publication, the application of pigment-containing coating mediums (simultaneously on both web sides) is possible because additional contactless dryers (for example, infrared dryers) are provided upstream of the contact dryers. However, there is a very long passage of the web with sharp deflections from the application device up to the first contact dryer. On account of the associated risk of web tears, such a web guidance is unsuitable for the very high web speeds demanded today.
Therefore, all known arrangements have in common that the maximum possible operation speed is strictly limited. This is also the case in respect of FIG. 5 of the mentioned Voith publication and the coating device described in DE 43 02 435 A1 as a result of the contactless, stationary "Air turn" web deflection devices which are required in this. The contactless, stationary "Airturn" web deflection devices are known to operate with impact air flow, which subjects the web (wet in the application means) to a high load.
The invention is based on the object of improving the initially described known paper coating apparatus in such a manner that it is suitable for very high operating speeds and, in particular, for the application of pigment-containing coating mediums, preferably with simultaneous two-sided application.
The object of the invention is accomplished by having the web deflecting device of the invention comprise the web deflection roll which rotates in the direction of movement of the web through the coating apparatus. Means form an air cushion for flowing between the web and the deflection roll and for flowing in the direction of movement of the web. At least one contactless drying device is arranged in the area of the deflection roll along the path of movement of the web.
Preferably, the air cushion is formed so that it flows between the web and the deflection roll, and flows at least approximately at the speed of the web. The air cushion may be produced by the boundary layer of air that is drawn along with the web to the deflection roll. The peripheral speed of the deflection roll may be adjusted to a value which is as the same as or greater than the speed of the web there passing. T
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Lee, Lester, Choice of Gas vs Electric IR Drying Hinges on Energy Costs, Mills' Needs, Pulp and Paper, May 1982, pp. 108-111.
Quadracci, H. Richard and Vijay Modi, "Cooling of Paper Using Chill Rollers", Drying Technology, 10(1), (1992) pp. 199-212.
Dolge, K., Anwendungstechnische und wirstschaftliche Kriterien zum Einsatz von Elektro-IR-Anlagen in Papiermaschinen, Wochenblatt Fur Papiermfabrikation23/24, 1992, pp. 958-962.
Plomer, Dipl.-Ing (FH) A., "The Speedsizer and its Application", Voith Publication, p/2771e, p. 3-7 (1988).
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Dunlop, J., "Contactless Web Handling and Drying", Paper presented at 1991 Coating Conference May 19-22 1991 Montreal Canada, pp. 439-452.
Riddiford, Alan W., "Airflow between a Paper Web and a Dryer Surface", TAPPI, May 1969, vol. 52. No. 5 pp. 939-942.
Edwards Laura
Voith Sulzer Papiermaschinen GmbH
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