Method for producing or treating a fibrous web

This invention relates to a method for producing or treating a fibrous web, in particular a paper web or paperboard web, with which at least one property of the fibrous web, in particular a CD (cross direction) profile, such as the moisture CD profile, is established such that a preselected quality range is adhered to or a predefined quality value is undershot by no more than a predefined deviation, wherein the power consumption of the method, in particular the heat energy input, is reduced therewith by establishing at least one property such that the lowest permissible value of the quality range or the maximum permissible deviation is reached at least approximately on a straight line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for producing or treating a fibrous web, in particular a paper web or paperboard web, with which at least one property of the fibrous web, in particular a CD (cross direction) profile, such as the moisture CD profile, is established such that a preselected quality range is adhered to or a predefined quality value is undershot by no more than a predefined deviation.

In addition this invention relates to an apparatus for producing or treating a fibrous web, in particular a paper web or paperboard web, having a way which is constructed such that a property of the fibrous web, in particular a CD profile such as the moisture CD profile, is established therewith such that a preselected quality range is adhered to or a predefined quality value is undershot by no more than a predefined deviation.

2. Description of the Related Art

On paper machines there are CD profile actuating apparatuses, in particular for the moisture content of the paper web, whose power consumption lies in the megawatt range. Considerable savings in power can be made therefore by improving the CD profile actuating apparatuses.

A known way to save power is to minimize the mean load of the actuating elements. A certain actuator profile setting, which is calculated using a control algorithm, is required to improve the moisture CD profile. In most CD profile control apparatuses the mean actuator setting is a preselected value. In some apparatuses the actuator setting is slowly and continuously changed with the aim of minimizing the mean value without impairing the CD profile control in its function. The minimum is usually reached when the CD actuator with the smallest actuating value reaches the zero limit or a preselected absolute minimum value. A further decrease of the mean value of all actuators would change the actuating profile shape and impair the paper quality.

What is needed in the art is to enable a further saving of power.

SUMMARY OF THE INVENTION

The present invention provides a method of the type initially referred to in that the power consumption of the method, in particular the heat energy input, is reduced by establishing at least one property such that the lowest permissible value of the quality range or the maximum permissible deviation is reached at least approximately on a straight line.

With an apparatus of the type initially referred to, a way is constructed such that the power consumption of the method, in particular the heat energy input, is reduced therewith by establishing at least one property such that the lowest permissible value of the quality range or the maximum permissible deviation is reached at least approximately on a straight line.

The method of the present invention is thus controlled such that the power consumption is as low as possible, wherein the controlling is performed such that the lowest limit of the permissible quality is just reached. In other words, the method is not controlled to achieve a mean value of the quality range to be adhered to but is consciously controlled to achieve the minimum value. This results in additional potential for saving power, in particular in those cases in which the usual quality control achieves better quality values, meaning smaller 2-sigma deviations, than is really necessary for production.

The moisture CD profile can be a property of the fibrous web to be controlled. When the moisture CD profile of the fibrous web is too good, then the mean value of the actuators is lowered further to the point just where the setpoint quality deviation is not exceeded. An additional power saving is possible as the result.

Another measure when the moisture CD profile is too good is to soften the zonal influence on at least a part of the CD actuators, meaning the actuators arranged side by side in the CD direction of the fibrous web. The control system thus performs only softer CD profile corrections. Peaks in the actuating profile are reduced. If one of these peaks is responsible for the minimum actuator position, potential for a further lowering of the mean actuator set value can be tapped and the power consumption accordingly reduced further.

It is possible in particular for only the zonal influence on the CD actuators in the vicinity of the actuator with the minimum set value to be softened. An intensive lowering of the power consumption can thus be achieved without changing the zonal influence of the other CD actuators.

Similarly it is possible in particular for two or more properties, in particular CD profiles, of the fibrous web to be taken into account for the power reduction. By taking account of two or more properties it is possible to exploit even more potential for the power reduction.

For example it is possible to take account of not only the moisture CD profile but also the coating weight CD profile, in particular on a coater. When the coating weight CD profile is too good, then a part of the quality can be sacrificed in this case too in favor of the moisture CD profile and hence in favor of power optimization. The coating weight CD profile control establishes a compromise of moisture quality and coating quality such that the coating weight CD profile remains in a defined quality range—the setpoint quality of the coating weight—and the moisture deviation in particular near the minimum actuating elements is optimized.

Alternatively or in addition to this, it is possible to take account of not only the moisture CD profile but also the gsm (grams per square meter) substance (herein, the gsm substance is the grams per square meter of the paper web). It is known that the gsm substance of a paper web has an influence on the moisture distribution. Hence it is similarly possible to sacrifice the gsm substance quality in favor of an optimization of the moisture profile in order thereby to lower further the power input during the moisture profile correction.

The properties of the paper web can be established by way of heating actuators. It is also possible however to influence spray nozzles as actuators in particular when establishing the moisture.

Another aspect of the present invention relates to the controlling of a coating unit, which is intended to apply a certain quantity of coating per square meter. Using a corresponding control system, it is possible in this case too for the power consumption resulting from the necessary drying of the mean coating color application per zone to be reduced in that the permissible minimum quality of the coating application is selectively established by the control.

An apparatus according to the present invention includes a way for performing the previously described process steps.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one embodiment of the invention, and such exemplification is not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is shown an apparatus including a coating applicator1, moisture actuating elements such as infrared radiant heaters2, a quality measuring system3and a controller4. The coating applicator1, the moisture actuating elements2and the quality measurement system3are suitably arranged in the vicinity of the fibrous web5, wherein the quality measuring system3is arranged after the coating applicator1and the moisture actuating elements2in the web running direction I.

The controller4is used to control the actuators of the coating applicator1and the moisture actuating elements2. It is constructed such that the power consumed is minimal in that a minimum permissible quality value for the moisture CD profile and/or the coating application is consciously established.

FIG. 2shows the moisture CD profile6of a fibrous web, for example a paper web. The numerals7and8are used to designate the upper and lower limit of the permissible tolerance range for the moisture CD profile.

FIG. 3shows a related actuator setting9of the moisture actuating profile. The numeral10is used to designate the mean setting of the actuators and11the permissible absolute minimum value for the actuator setting. The actuator with the numeral12is thus already at the lower limit. A further lowering of the mean value10of the actuator setting would influence the shape of the actuating profile and hence the quality profile.

When it is found that the moisture CD profile is too good, the mean value of the actuators is lowered further, namely to the point just where the setpoint quality deviation is not exceeded. Or the zonal influence on the CD actuators is softened such that peaks in the actuating profile are reduced. This is done possibly only in the region of the actuator with the minimum set value. Finally, other properties of the fibrous web such as the coating weight CD profile or the gsm substance or the coating application of a coating unit can also be taken into account. The method can be applied in this case to heating as well as non-heating actuators such as spray nozzles. With these measures it is possible to achieve lower production costs in that the quality produced is established by the inventive control apparatus at a level that is only as good as the minimum required.

LIST OF REFERENCE NUMERALS

1Coating applicator2Moisture actuating element3Quality measuring system4Controller5Fibrous web6Moisture CD profile7Upper limit of the tolerance range for the moisture CD profile8Lower limit of the tolerance range for the moisture CD profile9Moisture actuating profile10Mean value of the actuator setting11Absolute minimum value for the actuator setting12Actuator at the limitI Web running direction