Tobacco – Tobacco users' appliance – Supports
Reexamination Certificate
2000-10-26
2003-03-25
Griffin, Steven P. (Department: 1731)
Tobacco
Tobacco users' appliance
Supports
C131S260000, C131S260000, C131SDIG001
Reexamination Certificate
active
06536443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for regulating the breaking length ratio of a manufactured paper web by altering the microturbulence in the vicinity of the headbox nozzle. The invention further relates to a paper machine with a headbox suitable for performing the process according to the invention.
2. Discussion of Background Information
Together with other quality-related parameters, the breaking length ratio of a paper web represents an important criterion in defining the properties and quality of manufactured paper. The breaking length ratio L/Q is defined as the ratio of the breaking length L in the longitudinal direction to the breaking length Q in the transverse direction of a paper web. The breaking length provides a measure of the tensile strength of the paper. The breaking length specifies how long a strip of paper can be before it tears under the load of its own weight. The breaking length ratio L/Q is obtained as a dimensionless number by measuring the breaking length in both the longitudinal and transverse directions and then taking the ratio of the two.
Different paper requirements place different demands on the breaking length ratio L/Q. This is especially true for papers processed in high-speed printing presses, for example, which require that the breaking length in the longitudinal direction L, be correspondingly higher, in order to ensure trouble-free operation of the printing press. In such a case, a high breaking length ratio, which also corresponds to a high Concora value, is required.
It is noted here, that according to the used finish and the production process on the paper machine, the total breaking length potential is limited. This fact is given more or less by the geometric mean (GM) value of the breaking length GM=(L/Q)
½
. Therefore, increasing L/Q means increasing L as well as reducing Q at the same time. Reducing L/Q means reducing L and increasing Q.
Some papers require a high uniform tensile strength in both the longitudinal and transverse directions. For example, these may include format papers and many packaging papers. In this case, the breaking length ratio L/Q should be as close to 1 as possible, i.e., L and Q should each approximate the same value. This means that the tensile strength of the paper is essentially uniform in all directions.
Other papers have different requirements. A further example is provided by the fact that there is no uniform evaluation of the center layer of corrugated board, referred to as flute or fluting. Some customers evaluate flute with the Concora Medium Test (CMT), for which a relatively high breaking length ratio is needed. At the same time, the Short Compression Test transverse to the web (SCT
TRANS
), for which the lowest possible breaking length ratio L/Q is needed (reducing the CMT value), is also commonly used for evaluation. This means that the manufacturers of flute are forced to alternately produce flute with high and low breaking length ratios when supplying to different customers.
The prior art discloses a process for influencing the breaking length cross profile of a moving fiber web. Such a process is described in European patent application EP 0 774 540 A2. The object of this invention is to bring uniformity to the cross profile of the breaking lengths of a paper web, which profile varies across the web width and has values at the edges in particular that deviate from the average. However, this reference does not specify a process for adjusting and regulating of a paper machine in a manner disclosed by the instant invention. It merely suggests the possibility of exercising influence on the cross direction breaking length profile of the paper web in the edge zones.
Thus, the prior art does not address or solve the problem of how a specific breaking length ratio L/Q, corresponding to customer requirements, can be controlled in the manufacturing of paper, and especially doing so in an ongoing manufacturing operation.
SUMMARY OF THE INVENTION
The invention provides a process and apparatus for adjusting and regulating the breaking length ratio L/Q of a paper web while it is being produced, such that it allows for the breaking length ratio L/Q to be adapted to customer specifications and maintained during the production process.
The invention provides that the process for adjusting and regulating the breaking length ratio L/Q of a manufactured paper web, includes the following process steps; producing a fluid fiber layer with the aid of a headbox having a headbox nozzle, producing a paper web from the fluid fiber layer, measuring the current breaking length ratio L/Q
CURR
of the paper web at the running web, comparing the current breaking length ratio L/Q
CURR
with a preset breaking length ratio L/Q
SET
and determining the deviation from a setpoint, raising the microturbulence in the vicinity of the headbox nozzle if the current breaking length ratio L/Q
CURR
is greater than the preset breaking length ratio L/Q
SET
, and lowering the microturbulence in the vicinity of the headbox nozzle if the current breaking length ratio L/Q
CURR
is less than the preset breaking length ratio L/Q
SET
.
According to the invention, it is possible to predetermine a specific breaking length ratio L/Q for a paper web, measure the current value during the manufacturing process, and alter and adjust the microturbulence in the vicinity of the headbox nozzle such that the paper attains the desired breaking length ratio L/Q and the breaking length ratio remains constant during the production process.
Since microturbulence has a major influence on the orientation of the fibers in the paper web, and this orientation of the fibers plays an important part in determining the breaking length ratio, changing the microturbulence in the correct direction can be used to change the breaking length ratio as well and regulate it during production.
The microturbulence in the vicinity of the headbox nozzle can be changed in a variety of ways; for example, additional turbulence generators can be placed in the vicinity of the headbox nozzle, or jets of air or fluid can be applied, or other similar measures can be used.
However, one preferred way is for the headbox to be equipped with at least one movable separating lamella and for the change in microturbulence to be accomplished by moving the separating lamella in the machine direction. Moving the separating lamella changes the cross-section in the exit region of the headbox and thus changes the wall effects in the flow which, in turn, generates the microturbulence.
In addition, it is advantageous to measure the breaking length ratio L/Q
CURR
with the aid of ultrasonic measurement. This ultrasonic measurement makes it possible to determine the breaking length ratio in real time and on-line during operation. Such a mechanism allows for easily regulating the breaking length ratio. However, other conventional measurement devices may be also be used. For example; spectroscopic measurement as disclosed in DE 195 10 009 A1, which is expressly incorporated by reference, may be used in place of ultrasonic measurement.
The determination of the breaking length ratio L/Q in the paper machine is preferably performed using the ultrasonic method. In this method, an ultrasonic transmitter is placed at anyone of a number of measurement points. Additionally, at least two acoustic receivers are positioned at a specific distance, at least one in the longitudinal and at least one in the transverse directions of the web. Both transmitters and receivers are placed in contact with or in the immediate vicinity of the paper web. At regular intervals, the paper web is set into oscillation by the measurement transmitter using short ultrasonic pulses. The time between the transmission and reception of the pulse by the two receivers in the longitudinal and transverse directions is measured simultaneously, and the sound velocities v
L
and v
Q
of the pulse in the longitudinal and transverse directions of the paper web are measured. It is furthermo
Heissenberger Otto L.
Ruf Wolfgang
Greenblum & Bernstein P.L.C.
Lopez Carlos
Voith Sulzer Papiertechnik Patent GmbH
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