Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2000-09-28
2002-09-03
Chin, Peter (Department: 3752)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S204000, C162S265000, C118S325000, C427S424000
Reexamination Certificate
active
06444090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for spraying a moving fibrous web, in particular a paper or a cardboard web, by at least one jet, in which a preferably controlled volume flow of the corresponding spray is fed to the jet. It further relates to a device for spraying a moving fibrous web, in particular, a paper or cardboard web with at least one jet, to which a preferably controlled volume flow of the corresponding spray agent can be fed.
2. Discussion of Background Information
Spray arrangements are used in the production, refinement, and processing of fibrous webs in order to purposefully influence certain web characteristics. These characteristics can be, for instance, the moisture content, the surface moisture, the surface coating, and/or the like. Alternately or additionally the inoculation of additional materials is possible.
At present the following two general concepts are used in applications in which a variable volume flow is sprayed (compare, e.g., the lateral moisture profiling by jet moisturizers in paper production):
1. Parallel Connection of Valves (Binary Control of Volume Flow)
In such a parallel connection of valves with a binary control of volume flow several valves of different flow amounts are connected in parallel to form a valve block. Each valve can only be either open or closed. By opening separate valves with different volume flows various volume flow totals can be created by addition.
This control concept has the disadvantage that only a stepped volume flow characteristic can be created by addition. Another disadvantage is the large number of separate valves per jet and the resulting large demand for space, and the large expense of the valve block.
2. Sequential Arrangement of Jets (Binary Control of Volume Flow)
In such a sequential arrangement several jets of various flow amounts during spraying are arranged successively in the web travel direction. Each jet is controlled by a valve which can only be either opened or closed. By combining separate open valves different volume flow totals can be created by addition.
This control concept has the disadvantage that only a stepped volume flow characteristic can be created by addition. Another disadvantage is the large number of separate valves per jet and the resulting large expense of the combined spray unit.
At the present state of the art, proportional valves are rarely used in small volume flows since the control range is too narrow and the danger of clogging is too great. Additionally, these valves are very expensive. A pulsed moisturizing spray system is known from DE 689 24 433 T2 which is used to feed a moisturizing liquid to a roll in a printing press.
SUMMARY OF THE INVENTION
It is an aspect of the invention to create a process and a device of the above mentioned type in which the above mentioned disadvantages are removed.
An aspect relating to the process is attained according to the invention in feeding the volume flow of the spray agent to the jet via at least one pulsing valve in which pulses that occur in the volume flow of the spray agent are preferably damped or reduced. Here, the volume flow fed to the jet is preferably controlled by the pulsing valve.
Pulsing valves are preferably used in paper and cardboard machines, in particular jet moisturizers, coating units, starch spray devices, profiling devices etc. In general, they can be used for controlling volume flow of liquids in jets during spraying of fibrous moving webs, in particular in spray devices of paper and cardboard machines, in particular in jet moisturizers, surface coating devices, starch spray devices, profiling devices etc.
Preferably an armature valve is used and, in particular, a plate armature valve. Pulsing valves per se are described already in the publications DE 41 396 71 C2 and DE 44 194 46 C2.
In a preferred practical embodiment, pulses that occur in the volume flow of the spray agent are damped or reduced by at least one pulse damper prepositioned to the jet and/or by the use of a jet with an appropriately large spray width measured in web travel direction and/or by the use of a flexible inlet line to the jet.
Pulsing dampers or impulse dampers use the compressibility of gases to level pressure variations. The arrangement of the inlet line and the outlet line in a substantially larger closed gas volume, compared with the pipe diameter, enables the influx of the liquid until both cross-sections (inlet and outlet) are submerged in the liquid. The remaining gas volume is enclosed and is therefore compressed in accordance with the applied pressure. The pre-filling pressure of the gas is adjusted to the operating pressure. Rapidly occurring pressure changes (pulses) change the volume of the enclosed gases (mostly air). The energy transforming compression and expansion of the gas buffer smooths the occurring pulses.
In the flexible soft jet inlet line, which is used, in particular, in combination with a pulsing valve, the fact is used that the elasticity of such a flexible jet inlet line has a damping effect. The flexible jet inlet line can be formed by, e.g., a polyethylene hose, a polyurethane hose or a polyamide hose. It can, for example, be longer than about 3 m and preferably longer than about 5 m. An equivalent arrangement is preferably used in paper and cardboard machines, in particular, in jet moisturizers, coating devices, starch spray devices, molding devices etc.
Advantageously, a jet is used whose measured spray width in web travel direction is at least about 30% and preferably at least about 50% of the spray width measured crosswise to the web travel direction. In certain cases, it is advantageous when a fan jet is used as the jet. Here, for example, an elliptical fan jet can be used.
Such fan jets can, in particular, be used in combination with the mentioned pulse dampers and/or flexible jet inlet lines which ensure a sufficient damping of the pulses. Fan jets are characterized in that all streams impact the fibrous web at an almost identical angle in the web travel direction. The effectiveness of the moisturization depends on that angle. This has the advantage that the best angle can be adjusted for the maximal moisture effectiveness.
In a preferred practical embodiment a fan jet is used as the jet which sprays opposite to the web travel direction at an angle towards the fibrous web, with the angle being, in particular, smaller than about 80° and preferably smaller than about 70°. With this the effectiveness of the moisturization is increased accordingly and/or fogging is reduced. A corresponding fan jet can be used preferably at web travel speeds larger than, in particular, about 1200 m/min and preferably larger than about 1500 m/min. An appropriate arrangement is preferably used in paper and cardboard machines, in particular in jet moisturizers, coating devices, starch spray devices, molding devices etc.
In certain cases it can also be advantageous if a solid cone jet is used. The volume flow fed by such a pulsing valve is advantageously controlled by pulse-width modulation. Here, the pulsing valve is preferably activated with a constant frequency.
The process described is advantageously used in paper and cardboard machines and, in particular, in jet moisturizers, coating devices, starch spray devices, molding devices and/or the like.
The device according to the invention is characterized in that the volume flow of the spray agent of the jet is introduced via at least one pulsing valve, in which preferably devices are provided to dampen or reduce pulses occurring in the volume flow of the spray agent.
Therefore, based on the process according to the invention as well as the device according to the invention, in particular, pulsing valves as, for example, armature valves and, in particular, plate armature valves, i.e., valves with a plate armature, can be used in paper and cardboard machines. Here, in particular, the use of jet moisturizers, coating devices, starch spray devices, molding devices and/or the like is possible. The relevant pulsing val
Bendig Lothar
Gaa Reinhard
Landvatter Klaus
Oechsle Markus
Wegehaupt Frank
Chin Peter
Greenblum & Bernstein P.L.C.
Hug Eric
Voith Sulzer Papiertechnik Patent GmbH
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