CA2102374A1 - Method of making paper - Google Patents
Method of making paperInfo
- Publication number
- CA2102374A1 CA2102374A1 CA 2102374 CA2102374A CA2102374A1 CA 2102374 A1 CA2102374 A1 CA 2102374A1 CA 2102374 CA2102374 CA 2102374 CA 2102374 A CA2102374 A CA 2102374A CA 2102374 A1 CA2102374 A1 CA 2102374A1
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- Prior art keywords
- web
- profile
- deviation
- density
- layer height
- Prior art date
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Abstract
METHOD OF MAKING PAPER
Abstract of the Disclosure A method of making adjustments at the headbox of a web-forming machine to provide a web of relatively uniform density and layer height utilizes a headbox with a plurality of transverse sections, each of which is provided with a web material at a variable flow rate and a variable consistency. The method includes the steps of measuring the layer height profile of the web, measuring the density profile of the web, and comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles. If there are deviations in the layer height and density profiles, the consistency and flow rate of the web material provided to the headbox are adjusted, based on deviations in the layer height profile and the stock density profile and whether the deviations correspond with each other, in order to achieve a uniform stock density profile and layer height profile. The web is preferably dewatered by providing it to a dewatering apparatus, pressed and dried to provide a finished web, and rolled into a roll. The method may be used in connection with a paper machine to form a paper web.
Abstract of the Disclosure A method of making adjustments at the headbox of a web-forming machine to provide a web of relatively uniform density and layer height utilizes a headbox with a plurality of transverse sections, each of which is provided with a web material at a variable flow rate and a variable consistency. The method includes the steps of measuring the layer height profile of the web, measuring the density profile of the web, and comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles. If there are deviations in the layer height and density profiles, the consistency and flow rate of the web material provided to the headbox are adjusted, based on deviations in the layer height profile and the stock density profile and whether the deviations correspond with each other, in order to achieve a uniform stock density profile and layer height profile. The web is preferably dewatered by providing it to a dewatering apparatus, pressed and dried to provide a finished web, and rolled into a roll. The method may be used in connection with a paper machine to form a paper web.
Description
2~ ~237/~
MET~OD OF MARI~G PAP~R
The invention is directed to a method of making adjustments at the headbox of a web-forming machine, such as a paper machine, to provide a web of relatively uniform density and layer height.
A headbox for a paper machine should adjust the pulp density and fiber orientation profile of the paper pulp suspension, at the latest, before the suspension passes through the di~charge ~lit of the headbox, so that the pulp den~ity and fiber orientation profiles of the paper web correspond to the desired requirements ;~-over the entire width of the web, meaning, as a rule, that they are con~tant.
When operating a paper machine, there are many perturbing factor~ which hinder the achievement of the two above requirements. These perturbing factors include, for example, temperature and pressure fluctuations, manufacturing tolerances, and defects in the design or adju~tment of the paper machine for the production process after the paper pulp i9 discharged from the headbox.
The following state of the art has become known for influencing the transverse profile of a paper web.
German publication DE 35 14 554 proposes to change the pulp density locally; that i~, to adjust the pulp density at certain points, depending on demand.
However, it is not described how this should be accomplished.
2 ~ 7 ~
German publication DE 40 19 593 Al recommends that, upon devia~ion of the pulp den~ity profile of the paper web at a certain point of the web width, the concentration CM Of the respective section flow, and thus that of the flow leaving the respective mixer, should be changed correspondingly. In order to achieve this, the ratio of the amounts of control flows QN/QL, introduced to the mixture are changed. However, in the case of valves of the usual construction, it is difficult to avoid deviation of the section flow QM
leaving the mixer from the required value in an uncontrolled and unwanted manner.
In addition, it i9 known from German publication DE-OS 35 38 466 that a change of the volume flow of a section leads to influencing the fiber orientation angle in the discharge section of the headbox. If a section flow deviates from the required value in an uncontrolled manner, the fiber orientation will also change in an uncontrolled manner.
Furthermore, it is known from German publications DE 29 42 966 and DE-OS 35 35 ~49 that one can change the width of the discharge slit, for example, with threaded ~pindles for horizontally swinging or bending the upper lip. As a result, the throughput of the suspension can be altered locally. However, at the same time, the flow direction is also influenced locally, and thus the fiber orientation i3 affected.
Namely, at the narrow parts of the discharge slit, the fibers will be disposed in a different flow direction than at the other part~ of the discharge slit. This 2~2~
means that, although the consistency can be made uniform over the width of the headbox by thi method of control, called displacement control, the originally good fiber orientation i9 de troyed.
It can be seen from the state of the art de3cribed above that there are essentially two parameters that are adjusted at the headbox, namely the flow rate of the paper stock suspension at a given point of the headbox and the stock consistency, and that those two parameters have a different and conflicting influence on the stock density profile and fiber orientation.
The present invention is directed to a method of making adjuqtments at the headbox of a web-forming lS machine to provide a web of relatively uniform density and layer height. The headbox has a plurality of transver~e sections, each of which i9 provided with a web material at a variable flow rate and a variable consistency. The method includes the steps of measuring the layer height transver~e profile of the web at a point along the web, measuring the density transverse profile of the web at a point along the web, and comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles.
If there is a deviation in the density profile without a corresponding deviation in the layer height profile, then the magnitude of the consistency of the web material provided to the transverse section of the 2~ ~2~ 7 ~
headbox associated with the deviation i~ changed in a direction opposite the sign of the deviation.
If there is a deviation in the layer height profile without a corresponding deviation in the density profile, then the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation i9 changed in a direction opposite the sign of the deviation.
If there is a deviation in the density pr~file with a corresponding deviation with the same sign in the layer height profile, then the magnitude of the flow rate of the web material provided to the transverse section of the headbox a~sociated with the deviations is changed in a direction corresponding to the sign of the deviations.
The web i~ preferably dewatered by providing it to a dewatering apparatus, pressed and dried to provide a finished web, and rolled into a roll. The method may be used in connection with a paper machine to fonm a paper web.
Instead of measuring the layer height profile, the fiber orientation profile of the web may be measured, and adjustments in the consistency and flow rate of the ~ web material may be made based on the presence or absence of corre~ponding deviations in the measured fiber orientation and density profiles.
The invention i9 based on the inventors' xecognition that there are two parameters that fundamentally influence the density profile, namely the consistency and the flow rate of the web material at a given point of the headbox, and that the fiber 2~ ~237L~
orientation of the web material is generally influenced only by the flow rate of the web material at a given transverse point or ~ection of the headbox.
These and other feature~ and advantages of the presen~ invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiment, which is made with reference to the drawings, a brief description of which i9 provided below.
Fig. 1 is a schematic illustration of a preferred embodiment of a paper machine in accordance with the present invention; and Fig. 2 illustrates a density profile and a layer height profile of a paper web generated by the paper machine of Fig. 1.
Fig. 1 is a schematic illustration of a paper machine 10 with a headbox 12 on the left side, which i9 fed with a web material such a~ paper pulp, or stock suspension, across a plurality of transverse sections.
The magnitude of the flow of stock ~uspen~ion provided to each transverse section is regulated with a valve ~2. The consistency of the stock suspension provided to each transverse section is de~ermined by the combination of two ~tock flows at a mixer mi, one having a maximum con3istency b~ and the other having a minimum consistency b~. The actual consistency is ~ i32~7~
determined by a valve Vl, which controls the magnitude of the stock flow with the minimum consistency b~.
In the operation of the paper machine 10, the headbox 12 displaces the stock suspension onto a screen 14 for dewatering the stock suspension. The screen 14 is translated past the headbox 12 from left to right in Fig. 1 via a plurality of roller~ 16. The point at which the velocity of the impinging stock suspension is -~
adjusted to the screen velocity i8 designated with S.
At thi~ point, the stock layer height is hi, where i represents a particular transverse portion of the stock suspension, i.e. a particular portion along the width of the web. It should be understood that the layer height of the stock suspension may be different at different transverse points h; of the suspension.
The end of the dewatering section of the screen 14 is designated by Sl, which i9 then followed by a conventional pressing and drying apparatus 1~. After the stock suspen~ion is pressed and dried, at a point S2, it i8 wound up on a roll 20 as paper.
The consistency of the stock suspension at a transverse point i of the headbox 12 is designated herein as b;, and the amount or flow rate of the stock suspension introduced at a transverse point i of the headbox 12 is designated as q;.
After the stock suspension is ejected onto the moving scree~ 14, the velocity of the stock suspension adjusts to the velocity of-the screen 14 at a point S, at which point tho~e two velocities are substantially the same. At that point S, the flow rate of the stock 2 ~ ~ 2 ~ 7 1 suspension is proportional to the layer height hj of the stock suspension. If the velocity of the screen 14 is known, the flow magnitude of the stock suspension can be determined by measuring the layer height hj and multiplying it by the screen velocity.
The layer height hj can be determined in any conventional manner, such aq by a plurality of sensors (not shown), each of which is provided at a different transverse section of the screen 14. The mean or average layer height value haVe is determined by dividing the sum of all the layer height measurements h; by the number of such measurements.
The density of the stock suspension at a transver~e point i i8 designated herein as fj. That density fj, which may be represented for example, in grams/square meter (GSM), can be measured in a conventional manner by a plurality of sensors (not shown), each o~ which is provided at a different tran~verse section of the screen 14, at a position between the points Sl and S2 along the length of the stock suspension.
After the stock density f; at each such point is mea~ured, the average stock density fDve may be determined by dividing the sum of all the transverse density measurements fj by the number of such measurements.
As described below, the consistency bj of the stock suspension and the stock flow rate qj are controlled via the valves Vl and V2, respectively, based J ~ ~ I
upon the measurements of the layer height hj and the stock density fj.
Referring to Fig. 2, a stock density transverse profile f'j is shown above a layer height transverse profile h'j. Each point h'j on the layer height profile is determined from the measurements described above in accordance with the following equation: h'; = (hj -h~Ve)/h~ve. Similarly, each point f'j on the stock density profile is determined from the measurement~
made above in accordance with the following equation:
f i (fi fgve) /f~vc-The stock density f'j is shown to increase above the average stock density at a transverse point A of the paper machine and to decrease below the average stock density at a transverse point ~. At other points on the density profile, the stock density f'j is shown to be approximately equal to the average stock density.
The layer height hj is shown to increase above the average layer height at the transver~e point A and to ~ ~-decrease below the average layer height at a transverse point C. At other points on the layer height profile, the layer height h'; is shown to be about equal to the averag~ layer height.
It should be noted that, since both the layer height h'i and stock density f'j both increa~ed at the same tran~verse point A of the paper machine, there is a high correlation between the layer height and stock density at that point A. Here, one would expect defective fiber orientation and a high density deviation. In order to correct such condition, the 2~ ~3~il flow rate qj is decreased in the region i = A via the valve V~ associated with the transverse point A of the headbox 12.
It should be noted that, at transverse point B of Fig. 2, there is only a deviation in the density f'j, with no corresponding deviation in the layer height h'j. In this case, the deviation in the density f'j is corrected by adjusting the valve Vl associated with the transverse point B of the headbox 12 so that less of the stock solution having the consistency b~ is provided to the headbox 12.
At transverse point C, there is a deviation in the layer height h'j, but no deviation in the density profile f';. In this case, in order to avoid undesirable fiber orientation, the flow rate qj at the transverse point C is increased by adjusting the valve V2 associated with the transverse point C and, at the same time, reducing the stock consistency at the transverse point C by adjusting the valve V~ so that more ~tock solution having the consistency b~ i9 provided to the mixer mi associated with the transverse point C.
In general terms, by determining the deviations in the layer height profile h'j and the stock density profile f'j and whether the deviations correspond with each other, one can determine which of the parameters qj or bj to adjust in order to achieve a uniform stock -~
density profile and layer height profile.
More specifically, the method of control includes the steps of determining the layer height transverse 2~237~
profile of the web at a point along the web, determining the density transverse profile of the web at a point along the web, and comparing a portion of the layer height transverse profile with a corresponding portion of the density transverse profile to determine whether there are corresponding deviations in the profiles.
If there i9 a deviation in the density transverse profile withou~ a corresponding deviation in the layer height profile, then the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation i9 changed in a direction opposite the sign of the deviation.
Thus, at transverse point B of Fig. 2, where the sign of the deviation is negative, i.e. f'j decreased, the change in consistency i9 made positive, i.e. the consistency is increased in response.
If there i9 a deviation in the layer height profile without a corresponding deviation in the density profile, then magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. Thus, at transverse point C of Fig~ 2, where the sign of the deviation is negative, i.e. h'j decreased, the change in flow rate is made positive, i.e. the flow rate is increased in response.
If ~here is a deviation in the density profile with a corresponding deviation with the same sign in the layer height profile, then the magnitude of the 21~2~
flow rate of the web material provided to the transverse section of the headbox associated with the deviations i9 changed in a direction opposite the sign of the deviations. Thus, at transverse point A of Fig.
2, where the signs of the deviations are the same, i.e.
both f'j and h'j increased, the change in flow rate is changed in the opposite direction, i.e. the flow rate is decreased in response.
In the control method, if there is a deviation in the density transver e profile with a corresponding deviation in the layer height profile of opposite sign, then both deviations may be treated separately as uncorrelated deviations.
Also, counter-control may be carried out with the other parameters of the change that was performed. As used herein, the "counter-control" refers to a type of control in which the mathematical product of the stock flow rate and stock consistency i9 held substantially constant. Thu~, if the stock flow rate is increased, the stock consistency would be decreased by an amount so that the product of the two remained constant. If the stock flow rate is decreased, the stock consistency would be increased by an amount to maintain the product of the two constant.
In another preferred method in accordance with the invention, instead of measuring the layer height profile of the web, the fiber orientation profile is ~;~
measured at a point along the web. The fiber orientation can be measured by any conventional manner, such as by ultrasound or with the aid of a laser.
~ ~2~
The remaining steps are similar to the first method described above. In particular, after the fiber orientation profile and the density profile of the web are measured, a portion of the fiber orientation S profile is compared with a corresponding portion of the denRity profile to determine whether there are corresponding deviations in the two profiles.
If there is a deviation in the den~ity profile without a corresponding deviation in the fiber orientation profile, then the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. If there is a deviation in the fiber 15 orientation profile without a corresponding deviation ~ ~ ;
in the density profile, then the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. If there is a deviation in the density profile with a corresponding deviation with the same sign in the fiber orientation profile, then the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations is changed in a direction opposite the sign of the deviations.
The above methods can be applied to all types of headboxes, for example, one layer headboxe~, multi-layer headboxes, headboxes for slit formers, headboxes for long sieves, etc.
2 ~ ~ 2 ~
The above methods could be carried out via any conventional control scheme. For example, a conventional proportional-integral (PI) or proportional-integral-derivative (PID) controller could be provided for each transverse section of the stock solution. Each controller would be connected to receive both the inputs from the sensor~ which measure the stock density and layer height at its transverse point or section, and each controller would be connectPd to control both the valves V~ and V~
associated with its transverse section.
Alternatively, a single controller could be connected to the transversely located sensors for sensing the density and layer height of the web and to the transversely located valve~ for controlling the stock consistency and flow rate. In the case of a single controller, the control method could be accomplished on a time-shared or round-xobin basi~, with each transverse section of the paper machine being controlled sequentially.
Modification~ and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only, and is for the purpose of teaching tho~e skilled in the art the best mode of carrying out the invention. The details of the structure and method may be varied ~ubstantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.
MET~OD OF MARI~G PAP~R
The invention is directed to a method of making adjustments at the headbox of a web-forming machine, such as a paper machine, to provide a web of relatively uniform density and layer height.
A headbox for a paper machine should adjust the pulp density and fiber orientation profile of the paper pulp suspension, at the latest, before the suspension passes through the di~charge ~lit of the headbox, so that the pulp den~ity and fiber orientation profiles of the paper web correspond to the desired requirements ;~-over the entire width of the web, meaning, as a rule, that they are con~tant.
When operating a paper machine, there are many perturbing factor~ which hinder the achievement of the two above requirements. These perturbing factors include, for example, temperature and pressure fluctuations, manufacturing tolerances, and defects in the design or adju~tment of the paper machine for the production process after the paper pulp i9 discharged from the headbox.
The following state of the art has become known for influencing the transverse profile of a paper web.
German publication DE 35 14 554 proposes to change the pulp density locally; that i~, to adjust the pulp density at certain points, depending on demand.
However, it is not described how this should be accomplished.
2 ~ 7 ~
German publication DE 40 19 593 Al recommends that, upon devia~ion of the pulp den~ity profile of the paper web at a certain point of the web width, the concentration CM Of the respective section flow, and thus that of the flow leaving the respective mixer, should be changed correspondingly. In order to achieve this, the ratio of the amounts of control flows QN/QL, introduced to the mixture are changed. However, in the case of valves of the usual construction, it is difficult to avoid deviation of the section flow QM
leaving the mixer from the required value in an uncontrolled and unwanted manner.
In addition, it i9 known from German publication DE-OS 35 38 466 that a change of the volume flow of a section leads to influencing the fiber orientation angle in the discharge section of the headbox. If a section flow deviates from the required value in an uncontrolled manner, the fiber orientation will also change in an uncontrolled manner.
Furthermore, it is known from German publications DE 29 42 966 and DE-OS 35 35 ~49 that one can change the width of the discharge slit, for example, with threaded ~pindles for horizontally swinging or bending the upper lip. As a result, the throughput of the suspension can be altered locally. However, at the same time, the flow direction is also influenced locally, and thus the fiber orientation i3 affected.
Namely, at the narrow parts of the discharge slit, the fibers will be disposed in a different flow direction than at the other part~ of the discharge slit. This 2~2~
means that, although the consistency can be made uniform over the width of the headbox by thi method of control, called displacement control, the originally good fiber orientation i9 de troyed.
It can be seen from the state of the art de3cribed above that there are essentially two parameters that are adjusted at the headbox, namely the flow rate of the paper stock suspension at a given point of the headbox and the stock consistency, and that those two parameters have a different and conflicting influence on the stock density profile and fiber orientation.
The present invention is directed to a method of making adjuqtments at the headbox of a web-forming lS machine to provide a web of relatively uniform density and layer height. The headbox has a plurality of transver~e sections, each of which i9 provided with a web material at a variable flow rate and a variable consistency. The method includes the steps of measuring the layer height transver~e profile of the web at a point along the web, measuring the density transverse profile of the web at a point along the web, and comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles.
If there is a deviation in the density profile without a corresponding deviation in the layer height profile, then the magnitude of the consistency of the web material provided to the transverse section of the 2~ ~2~ 7 ~
headbox associated with the deviation i~ changed in a direction opposite the sign of the deviation.
If there is a deviation in the layer height profile without a corresponding deviation in the density profile, then the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation i9 changed in a direction opposite the sign of the deviation.
If there is a deviation in the density pr~file with a corresponding deviation with the same sign in the layer height profile, then the magnitude of the flow rate of the web material provided to the transverse section of the headbox a~sociated with the deviations is changed in a direction corresponding to the sign of the deviations.
The web i~ preferably dewatered by providing it to a dewatering apparatus, pressed and dried to provide a finished web, and rolled into a roll. The method may be used in connection with a paper machine to fonm a paper web.
Instead of measuring the layer height profile, the fiber orientation profile of the web may be measured, and adjustments in the consistency and flow rate of the ~ web material may be made based on the presence or absence of corre~ponding deviations in the measured fiber orientation and density profiles.
The invention i9 based on the inventors' xecognition that there are two parameters that fundamentally influence the density profile, namely the consistency and the flow rate of the web material at a given point of the headbox, and that the fiber 2~ ~237L~
orientation of the web material is generally influenced only by the flow rate of the web material at a given transverse point or ~ection of the headbox.
These and other feature~ and advantages of the presen~ invention will be apparent to those of ordinary skill in the art in view of the detailed description of the preferred embodiment, which is made with reference to the drawings, a brief description of which i9 provided below.
Fig. 1 is a schematic illustration of a preferred embodiment of a paper machine in accordance with the present invention; and Fig. 2 illustrates a density profile and a layer height profile of a paper web generated by the paper machine of Fig. 1.
Fig. 1 is a schematic illustration of a paper machine 10 with a headbox 12 on the left side, which i9 fed with a web material such a~ paper pulp, or stock suspension, across a plurality of transverse sections.
The magnitude of the flow of stock ~uspen~ion provided to each transverse section is regulated with a valve ~2. The consistency of the stock suspension provided to each transverse section is de~ermined by the combination of two ~tock flows at a mixer mi, one having a maximum con3istency b~ and the other having a minimum consistency b~. The actual consistency is ~ i32~7~
determined by a valve Vl, which controls the magnitude of the stock flow with the minimum consistency b~.
In the operation of the paper machine 10, the headbox 12 displaces the stock suspension onto a screen 14 for dewatering the stock suspension. The screen 14 is translated past the headbox 12 from left to right in Fig. 1 via a plurality of roller~ 16. The point at which the velocity of the impinging stock suspension is -~
adjusted to the screen velocity i8 designated with S.
At thi~ point, the stock layer height is hi, where i represents a particular transverse portion of the stock suspension, i.e. a particular portion along the width of the web. It should be understood that the layer height of the stock suspension may be different at different transverse points h; of the suspension.
The end of the dewatering section of the screen 14 is designated by Sl, which i9 then followed by a conventional pressing and drying apparatus 1~. After the stock suspen~ion is pressed and dried, at a point S2, it i8 wound up on a roll 20 as paper.
The consistency of the stock suspension at a transverse point i of the headbox 12 is designated herein as b;, and the amount or flow rate of the stock suspension introduced at a transverse point i of the headbox 12 is designated as q;.
After the stock suspension is ejected onto the moving scree~ 14, the velocity of the stock suspension adjusts to the velocity of-the screen 14 at a point S, at which point tho~e two velocities are substantially the same. At that point S, the flow rate of the stock 2 ~ ~ 2 ~ 7 1 suspension is proportional to the layer height hj of the stock suspension. If the velocity of the screen 14 is known, the flow magnitude of the stock suspension can be determined by measuring the layer height hj and multiplying it by the screen velocity.
The layer height hj can be determined in any conventional manner, such aq by a plurality of sensors (not shown), each of which is provided at a different transverse section of the screen 14. The mean or average layer height value haVe is determined by dividing the sum of all the layer height measurements h; by the number of such measurements.
The density of the stock suspension at a transver~e point i i8 designated herein as fj. That density fj, which may be represented for example, in grams/square meter (GSM), can be measured in a conventional manner by a plurality of sensors (not shown), each o~ which is provided at a different tran~verse section of the screen 14, at a position between the points Sl and S2 along the length of the stock suspension.
After the stock density f; at each such point is mea~ured, the average stock density fDve may be determined by dividing the sum of all the transverse density measurements fj by the number of such measurements.
As described below, the consistency bj of the stock suspension and the stock flow rate qj are controlled via the valves Vl and V2, respectively, based J ~ ~ I
upon the measurements of the layer height hj and the stock density fj.
Referring to Fig. 2, a stock density transverse profile f'j is shown above a layer height transverse profile h'j. Each point h'j on the layer height profile is determined from the measurements described above in accordance with the following equation: h'; = (hj -h~Ve)/h~ve. Similarly, each point f'j on the stock density profile is determined from the measurement~
made above in accordance with the following equation:
f i (fi fgve) /f~vc-The stock density f'j is shown to increase above the average stock density at a transverse point A of the paper machine and to decrease below the average stock density at a transverse point ~. At other points on the density profile, the stock density f'j is shown to be approximately equal to the average stock density.
The layer height hj is shown to increase above the average layer height at the transver~e point A and to ~ ~-decrease below the average layer height at a transverse point C. At other points on the layer height profile, the layer height h'; is shown to be about equal to the averag~ layer height.
It should be noted that, since both the layer height h'i and stock density f'j both increa~ed at the same tran~verse point A of the paper machine, there is a high correlation between the layer height and stock density at that point A. Here, one would expect defective fiber orientation and a high density deviation. In order to correct such condition, the 2~ ~3~il flow rate qj is decreased in the region i = A via the valve V~ associated with the transverse point A of the headbox 12.
It should be noted that, at transverse point B of Fig. 2, there is only a deviation in the density f'j, with no corresponding deviation in the layer height h'j. In this case, the deviation in the density f'j is corrected by adjusting the valve Vl associated with the transverse point B of the headbox 12 so that less of the stock solution having the consistency b~ is provided to the headbox 12.
At transverse point C, there is a deviation in the layer height h'j, but no deviation in the density profile f';. In this case, in order to avoid undesirable fiber orientation, the flow rate qj at the transverse point C is increased by adjusting the valve V2 associated with the transverse point C and, at the same time, reducing the stock consistency at the transverse point C by adjusting the valve V~ so that more ~tock solution having the consistency b~ i9 provided to the mixer mi associated with the transverse point C.
In general terms, by determining the deviations in the layer height profile h'j and the stock density profile f'j and whether the deviations correspond with each other, one can determine which of the parameters qj or bj to adjust in order to achieve a uniform stock -~
density profile and layer height profile.
More specifically, the method of control includes the steps of determining the layer height transverse 2~237~
profile of the web at a point along the web, determining the density transverse profile of the web at a point along the web, and comparing a portion of the layer height transverse profile with a corresponding portion of the density transverse profile to determine whether there are corresponding deviations in the profiles.
If there i9 a deviation in the density transverse profile withou~ a corresponding deviation in the layer height profile, then the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation i9 changed in a direction opposite the sign of the deviation.
Thus, at transverse point B of Fig. 2, where the sign of the deviation is negative, i.e. f'j decreased, the change in consistency i9 made positive, i.e. the consistency is increased in response.
If there i9 a deviation in the layer height profile without a corresponding deviation in the density profile, then magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. Thus, at transverse point C of Fig~ 2, where the sign of the deviation is negative, i.e. h'j decreased, the change in flow rate is made positive, i.e. the flow rate is increased in response.
If ~here is a deviation in the density profile with a corresponding deviation with the same sign in the layer height profile, then the magnitude of the 21~2~
flow rate of the web material provided to the transverse section of the headbox associated with the deviations i9 changed in a direction opposite the sign of the deviations. Thus, at transverse point A of Fig.
2, where the signs of the deviations are the same, i.e.
both f'j and h'j increased, the change in flow rate is changed in the opposite direction, i.e. the flow rate is decreased in response.
In the control method, if there is a deviation in the density transver e profile with a corresponding deviation in the layer height profile of opposite sign, then both deviations may be treated separately as uncorrelated deviations.
Also, counter-control may be carried out with the other parameters of the change that was performed. As used herein, the "counter-control" refers to a type of control in which the mathematical product of the stock flow rate and stock consistency i9 held substantially constant. Thu~, if the stock flow rate is increased, the stock consistency would be decreased by an amount so that the product of the two remained constant. If the stock flow rate is decreased, the stock consistency would be increased by an amount to maintain the product of the two constant.
In another preferred method in accordance with the invention, instead of measuring the layer height profile of the web, the fiber orientation profile is ~;~
measured at a point along the web. The fiber orientation can be measured by any conventional manner, such as by ultrasound or with the aid of a laser.
~ ~2~
The remaining steps are similar to the first method described above. In particular, after the fiber orientation profile and the density profile of the web are measured, a portion of the fiber orientation S profile is compared with a corresponding portion of the denRity profile to determine whether there are corresponding deviations in the two profiles.
If there is a deviation in the den~ity profile without a corresponding deviation in the fiber orientation profile, then the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. If there is a deviation in the fiber 15 orientation profile without a corresponding deviation ~ ~ ;
in the density profile, then the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation is changed in a direction opposite the sign of the deviation. If there is a deviation in the density profile with a corresponding deviation with the same sign in the fiber orientation profile, then the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations is changed in a direction opposite the sign of the deviations.
The above methods can be applied to all types of headboxes, for example, one layer headboxe~, multi-layer headboxes, headboxes for slit formers, headboxes for long sieves, etc.
2 ~ ~ 2 ~
The above methods could be carried out via any conventional control scheme. For example, a conventional proportional-integral (PI) or proportional-integral-derivative (PID) controller could be provided for each transverse section of the stock solution. Each controller would be connected to receive both the inputs from the sensor~ which measure the stock density and layer height at its transverse point or section, and each controller would be connectPd to control both the valves V~ and V~
associated with its transverse section.
Alternatively, a single controller could be connected to the transversely located sensors for sensing the density and layer height of the web and to the transversely located valve~ for controlling the stock consistency and flow rate. In the case of a single controller, the control method could be accomplished on a time-shared or round-xobin basi~, with each transverse section of the paper machine being controlled sequentially.
Modification~ and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only, and is for the purpose of teaching tho~e skilled in the art the best mode of carrying out the invention. The details of the structure and method may be varied ~ubstantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.
Claims (12)
1. A method of making adjustments at the headbox of a web-forming machine to provide a web of relatively uniform density and layer height, said headbox having a plurality of transverse sections each of which is provided with a web material having a variable flow rate and a variable consistency, said method comprising the steps of:
(a) measuring the layer height profile of the web at a point along the web;
(b) measuring the density profile of the web at a point along the web;
(c) comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles;
(d) if there is a deviation in the density profile without a corresponding deviation in the layer height profile, then changing the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation;
(e) if there is a deviation in the layer height profile without a corresponding deviation in the density profile, then changing the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation; and (f) if there is a deviation in the density profile with a corresponding deviation with the same sign in the layer height profile, then changing the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations in a direction opposite the sign of the deviations.
(a) measuring the layer height profile of the web at a point along the web;
(b) measuring the density profile of the web at a point along the web;
(c) comparing a portion of the layer height profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles;
(d) if there is a deviation in the density profile without a corresponding deviation in the layer height profile, then changing the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation;
(e) if there is a deviation in the layer height profile without a corresponding deviation in the density profile, then changing the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation; and (f) if there is a deviation in the density profile with a corresponding deviation with the same sign in the layer height profile, then changing the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations in a direction opposite the sign of the deviations.
2. A method as defined in claim 1 additionally comprising the steps of:
(g) dewatering the web by providing it to a dewatering apparatus;
(h) pressing and drying the web to provide a finished web; and (i) rolling said finished web into a roll.
(g) dewatering the web by providing it to a dewatering apparatus;
(h) pressing and drying the web to provide a finished web; and (i) rolling said finished web into a roll.
3. A method as defined in claim 1 wherein during said step (a) the layer height profile of a paper web is determined at a point along the paper web and wherein during said step (b) the density profile of a paper web is determined at a point along the paper web.
4. A method as defined in claim 1 additionally comprising the step of:
(g) if there is a deviation in the density profile with a corresponding deviation in the layer height profile of opposite sign, then treating both deviations separately as uncorrelated deviations.
(g) if there is a deviation in the density profile with a corresponding deviation in the layer height profile of opposite sign, then treating both deviations separately as uncorrelated deviations.
5. A method as defined in claim 1, wherein the layer height profile measured in said step (a) is measured at a point along the web in the area of initial dewatering and wherein the density profile of the web is measured in said step (b) at a point along the web after the web has been substantially dewatered.
6. A method as defined in claim 1, additionally comprising the step of maintaining the mathematical product of the consistency of the web material and the flow rate of the web material substantially constant.
7. A method of making adjustments at the headbox of a web-forming machine to provide a web of relatively uniform density and layer height, said headbox having a plurality of transverse sections each of which is provided with a web material having a variable flow rate and a variable consistency, said method comprising the steps of:
(a) measuring the fiber orientation profile of the web;
(b) measuring the density profile of the web;
(c) comparing a portion of the fiber orientation profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles;
(d) if there is a deviation in the density profile without a corresponding deviation in the fiber orientation profile, then changing the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation;
(e) if there is a deviation in the fiber orientation profile without a corresponding deviation in the density profile, then changing the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation; and (f) if there is a deviation in the density profile with a corresponding deviation with the same sign in the fiber orientation profile, then changing the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations in a direction opposite the sign of the deviations.
(a) measuring the fiber orientation profile of the web;
(b) measuring the density profile of the web;
(c) comparing a portion of the fiber orientation profile with a corresponding portion of the density profile to determine whether there are corresponding deviations in the profiles;
(d) if there is a deviation in the density profile without a corresponding deviation in the fiber orientation profile, then changing the magnitude of the consistency of the web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation;
(e) if there is a deviation in the fiber orientation profile without a corresponding deviation in the density profile, then changing the magnitude of the flow rate of web material provided to the transverse section of the headbox associated with the deviation in a direction opposite the sign of the deviation; and (f) if there is a deviation in the density profile with a corresponding deviation with the same sign in the fiber orientation profile, then changing the magnitude of the flow rate of the web material provided to the transverse section of the headbox associated with the deviations in a direction opposite the sign of the deviations.
8. A method as defined in claim 7 additionally comprising the steps of:
(g) dewatering the web by providing it to a dewatering apparatus;
(h) pressing and drying the web to provide a finished web; and (i) rolling said finished web into a roll.
(g) dewatering the web by providing it to a dewatering apparatus;
(h) pressing and drying the web to provide a finished web; and (i) rolling said finished web into a roll.
9. A method as defined in claim 7 wherein during said step (a) the fiber orientation profile of a paper web is measured and wherein during said step (b) the density profile of a paper web is measured.
10. A method as defined in claim 7 additionally comprising the step of:
(g) if there is a deviation in the density profile with a corresponding deviation in the fiber orientation profile of opposite sign, then treating both deviations as uncorrelated deviations.
(g) if there is a deviation in the density profile with a corresponding deviation in the fiber orientation profile of opposite sign, then treating both deviations as uncorrelated deviations.
11. A method as defined in claim 7, wherein the layer height profile measured in said step (a) is measured at a point along the web in the area of initial dewatering and wherein the density transverse profile of the web is measured in said step (b) at a point along the web after the web has been substantially dewatered.
12. A method as defined in claim 7, additionally comprising the step of maintaining the mathematical product of the consistency of the web material and the flow rate of the web material substantially constant.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4237304.2 | 1992-11-05 | ||
| DE4237304 | 1992-11-05 | ||
| DEP4239845.2 | 1992-11-27 | ||
| DE4239845A DE4239845C2 (en) | 1992-11-05 | 1992-11-27 | Procedure for measuring the effect of adjustments on the headbox and for correcting the basis weight and fiber orientation cross profile |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2102374A1 true CA2102374A1 (en) | 1994-05-06 |
Family
ID=25920137
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2102374 Abandoned CA2102374A1 (en) | 1992-11-05 | 1993-11-03 | Method of making paper |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH0849183A (en) |
| CA (1) | CA2102374A1 (en) |
| FI (1) | FI934787A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6174413B1 (en) | 1997-08-02 | 2001-01-16 | Voith Sulzer Papiermaschinen Gmbh | Device for detecting and correcting a fiber orientation cross direction profile change |
| US6179964B1 (en) | 1996-08-30 | 2001-01-30 | Voith Sulzer Papiermaschinen Gmbh | Method and control device for paper web profile control with plurality of sensors |
-
1993
- 1993-10-28 FI FI934787A patent/FI934787A/en unknown
- 1993-11-03 CA CA 2102374 patent/CA2102374A1/en not_active Abandoned
- 1993-11-05 JP JP30124593A patent/JPH0849183A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6179964B1 (en) | 1996-08-30 | 2001-01-30 | Voith Sulzer Papiermaschinen Gmbh | Method and control device for paper web profile control with plurality of sensors |
| US6174413B1 (en) | 1997-08-02 | 2001-01-16 | Voith Sulzer Papiermaschinen Gmbh | Device for detecting and correcting a fiber orientation cross direction profile change |
| US6524441B2 (en) | 1997-08-02 | 2003-02-25 | Voith Sulzer Papiermaschinen Gmbh | Process for detecting and correcting a fiber orientation cross direction profile change |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0849183A (en) | 1996-02-20 |
| FI934787A0 (en) | 1993-10-28 |
| FI934787A (en) | 1994-05-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19991103 |