U.S. patent application number 10/946780 was filed with the patent office on 2005-02-17 for method to measure tension in a moving web and to control properties of the web.
Invention is credited to Beuther, Paul D., Guarnotta, Robert Paul, Lin, Philip Sim, Moore, Bryan Robert, Mullally, Kevin J., Seewoester, Amy Christina.
Application Number | 20050034831 10/946780 |
Document ID | / |
Family ID | 21836533 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050034831 |
Kind Code |
A1 |
Beuther, Paul D. ; et
al. |
February 17, 2005 |
Method to measure tension in a moving web and to control properties
of the web
Abstract
A process for determining the tension in a moving web is
provided. The process includes the step of providing a web that is
moving at a determined speed. The speed has a determined basis
weight. A wave is created in the moving web. The speed of the
propagation of the wave is determined. Also, the tension on the
moving web is determined through a mathematical relationship
between the wave speed, the basis weight of the web, and the speed
of the web. The instability index of the web is greater than or
equal to 0.5.
Inventors: |
Beuther, Paul D.; (Neenah,
WI) ; Seewoester, Amy Christina; (Columbia, MO)
; Guarnotta, Robert Paul; (Evans, GA) ; Moore,
Bryan Robert; (Augusta, GA) ; Lin, Philip Sim;
(Oshkosh, WI) ; Mullally, Kevin J.; (Neenah,
WI) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Family ID: |
21836533 |
Appl. No.: |
10/946780 |
Filed: |
September 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10946780 |
Sep 22, 2004 |
|
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|
10027243 |
Dec 20, 2001 |
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6813941 |
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Current U.S.
Class: |
162/198 ;
162/199; 700/127 |
Current CPC
Class: |
D21F 11/04 20130101;
G01L 5/08 20130101; D21G 9/0027 20130101; D21F 11/14 20130101; D21F
11/145 20130101; G01L 5/042 20130101 |
Class at
Publication: |
162/198 ;
162/199; 700/127 |
International
Class: |
D21F 011/00 |
Claims
1-8. (Canceled)
9. A process for producing a paper web having substantially uniform
properties, comprising the steps of: providing a moving paper web;
determining the tension on the paper web while the web is moving;
and adjusting a process condition of the web that affects modulus
based on the determined tension to produce a web having more
uniform properties, wherein the instability index of the web is
greater than or equal to 0.5.
10. The process for producing a paper web of claim 9, wherein the
step of determining the tension on the paper web is accomplished in
part by use of an air pulse onto the moving web.
11. The process for producing a paper web of claim 9, wherein the
step of determining the tension on the paper web comprising the
steps of: creating a wave in the moving paper web; determining the
speed of the propagation of the wave; calculating the tension on
the moving web through a mathematical relationship between the wave
speed, the basis weight of the paper, and the speed of the web.
12. The process for producing a paper web of claim 9, wherein the
tension that is determined on the web is between about 10 Nt/m and
about 35 Nt/m, and the speed of the moving web is about 25 m/s, and
the basis weight of the web is about 15 gsm.
13. The process for producing a paper web of claim 9, wherein the
step of determining the tension on the moving web occurs when the
instability index of the web is about 0.8 or higher.
14. The process for producing a paper web of claim 11, wherein the
step of creating the wave is accomplished by subjecting the web to
an air pulse; and the step of determining the speed of propagation
of the wave is accomplished by the use of two laser displacement
transducers which each provide a signal and which also are
configured for measuring the speed of the web.
15. The process for producing a paper web of claim 9, wherein the
process condition is selected from the group consisting of: time to
change doctor blades, draw on a winder to maintain uniform tension
in each section of the web, tension in wound roll of the web, flow
adjustment to control cross directional dryer coating of the web,
control of cross directional moisture profile based on a given
basis weight profile and a single point moisture, control of cross
directional basis weight based on a given moisture profile and an
average basis weight from a softroll weight, control of the web
during turn-ups by optimizing sequence to maintain a desired
tension, control of the web during turn-ups by chemical addition to
maintain a desired tension, control of the web instability by
adjusting stabilizing foils in response to the instability index
calculated from the tension measurement, control of the web
instability by creping chemistry in response to the instability
index calculated from the tension measurement, control of the web
handling by keeping the instability index in a desired range by
adjusting creping chemistry at a certain web speed, and control of
the web handling by adjusting foil positions to maintain runability
at a given web speed based on the instability index.
16-19. (Canceled)
20. A process for producing a paper web having substantially
uniform properties, comprising the steps of: providing a moving
paper web; determining the tension on the paper web while the web
is moving, wherein the instability index of the web is greater than
or equal to 0.5; adjusting cross directional dryer coating of the
web based on the determined tension of the web; and adjusting
creping chemistry based on the instability index.
21. The process for producing a paper web of claim 20, wherein the
step of continuing to determine the tension on the moving web
occurs when the instability index of the web is about 0.8 or
higher.
22. A process for producing a paper web having at least two flows
of different strengths, comprising: providing a moving layered
paper web; providing at least one hardwood flow and at least one
softwood flow to form at least one hardwood layer and at least one
softwood layer of the paper web; determining the tension on the
paper web while the web is moving; controlling the tension of the
paper web by increasing the hardwood flow and decreasing the
softwood flow in regions of high tension while maintaining a
uniform basis weight, and by increasing the softwood flow and
decreasing the hardwood flow in regions of low tension while
maintaining a uniform basis weight, such that the tension is
uniform.
23. The process for producing a paper web of claim 22, wherein the
instability index of the web is greater than or equal to 0.5.
24. The process for producing a paper web of claim 23, wherein the
instability index of the web is between about 0.8 and 1.0.
Description
BACKGROUND
[0001] Products made from base webs such as bath tissues, facial
tissues, paper towels, industrial wipers, food service wipers,
napkins, medical pads, and other similar products are designed to
include several important properties. For example, the products
should have a soft feel and, for most applications, should be
highly absorbent. The products should also have good stretch
characteristics and should resist tearing. Further, the products
should also have good strength characteristics, should be abrasion
resistant, and should not deteriorate in the environment in which
they are used.
[0002] In the past, many attempts have been made to enhance and
increase certain physical properties of such products.
Unfortunately, when steps are taken to increase one property of
these products, other characteristics of the products may be
adversely affected. For instance, the softness of non-woven
products, such as various paper products, can be increased by
several different methods such as by selecting a particular fiber
type or by reducing cellulosic fiber bonding within the product.
Increasing softness according to one of the above methods, however,
may adversely affect the strength of the product. Conversely, steps
normally taken to increase the strength of a fibrous web typically
have an adverse impact upon the softness, the stiffness, or the
absorbency of the web.
[0003] In order to produce products of desired characteristics, and
to ensure the processes that create these products runs smoothly,
properties of the web during production are often monitored. One
such property that allows for the characteristics of the web to be
controlled is the tension of the web. Properties which can be
controlled based on the tension of the moving web include but are
not limited to strength related properties such as machine
direction modulus, basis weight, moisture, and properties that
relate to softness. However, other measurements of different
properties of the web must sometimes be made in order to control
some of the aforementioned properties.
[0004] Measurement of the tension is also helpful in preventing
breaks of the web during production of a paper product. A
papermaking machine can be modified if the recorded tension is high
enough to subject the web to breaking. Such a modification of the
production process to avoid these web breaks can prevent downtime
of the papermaking machine.
[0005] Various ways of measuring the tension of a moving web are
known in the art. For instance, U.S. Pat. No. 4,833,928 discloses a
non-contacting tension measurement method by which a microphone
induces sound waves in the web which are subsequently detected by
microphones installed close to the web. Additionally, the tension
in a moving web may be measured by contacting the web with rolls
that have force transducers or load cells mounted therein to
measure the tension in the moving web. Such a way of measuring the
tension of a moving web is known in the art as a contacting tension
measurement system. A non-contacting method to measure the tension
in a moving web exists by forming a wave on the web by means of a
blast of compressed air. The subsequent wave is then measured and
this measurement is used to calculate the tension of the web.
[0006] Another patent indicative of a process and apparatus that
measures tension in a moving web is U.S. Pat. No. 3,854,329. This
patent is directed towards a non-contacting method that makes use
of a loud speaker and a microphone to create and measure a
vibration in the moving web to determine the tension.
[0007] A method of measuring the tension in a moving web when the
tension is low, and the web speed is high is unique to this
application. Additionally, a process of measuring the tension on a
wide commercial tissue machine at both high speed and low tension
is unique to the present application. Also, a method that is
suitable for commercial production is further unique. Current
machines do not disclose a way of measuring the tension on a moving
web when the instability index of the web is greater than 0.5.
Current machines measure the tension by using either a contacting
method that typically will not work on a tissue web at high speeds,
or by means of a sonic method that is only suitable for stiff webs
where the instability index is low, typically less than 0.5.
SUMMARY
[0008] Objects and advantages of the invention will be set forth in
part in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0009] The present invention provides for a process for determining
the tension in a moving web. The process includes the steps of
providing a web that is moving at a determined speed. The web has a
determined basis weight. A wave is created in the moving web, and
the speed of propagation of the wave is determined. The tension on
the moving web is determined through a mathematical relationship
between the wave speed, the basis weight of the web, and the speed
of the web. The instability index of the web is greater than or
equal to 0.5.
[0010] The process also includes an exemplary embodiment where the
instability index of the web is greater than about 0.8.
[0011] The present invention also encompasses a process for
producing a paper web that has substantially uniform properties.
The process includes the steps of providing a moving paper web, and
the determination of the tension on the paper web while the web is
moving. The process also includes the step of adjusting a process
condition of the web that effects modulus based on the determined
tension to produce a web that has more uniform properties. The
instability index of the web is greater than or equal to 0.5.
[0012] The present invention also includes an exemplary embodiment
as immediately discussed where the step of determining the tension
on the paper web includes the steps of creating a wave in the
moving paper web and the determination of the speed of the
propagation of the wave. Also, the step of determining the tension
includes the step of calculating the tension on the moving web
through a mathematical relationship between the wave speed, the
basis weight of the paper, and the speed of the web.
[0013] The present invention also includes an embodiment as
previously discussed where the step of determining the tension on
the moving web occurs when the instability index of the web is
about 0.8 or higher.
[0014] Another exemplary embodiment of the present invention
includes a process for controlling a moving web. The process
involves the provision of a web that is moving at a determined
speed. The web has a determined basis weight. A wave is generated
in the moving web and the speed of the wave in the web is measured.
The process further includes the determination of the instability
index. The instability index is in a desired range, that being
between about 0.6 and 1.0.
[0015] Alternatively, the immediately identified exemplary
embodiment of the present invention may also be modified in
accordance with the present invention where the desired range of
the instability index is between about 0.6 and about 0.9, between
about 0.8 and 1.0, and between 0.7 and 1.0.
[0016] Also provided in accordance with the present invention is an
apparatus for measuring the instability index in a moving web. The
apparatus includes an air pulse that is used to apply a pulse of
fluid to the web to create a wave in the web. As least two laser
displacement transducers are present for measuring the displacement
of the web as the wave moves through the web. A computer is also
present which obtains signals from the at least two laser
displacement transducers. The computer calculates the instability
index in the web based on the speed of the wave in the web and the
speed of the web.
[0017] Alternatively, the present invention includes an exemplary
embodiment of the apparatus as immediately discussed where the
computer calculates the tension in the web while the instability
index of the web is greater that about 0.8.
[0018] The present invention also includes an exemplary embodiment
of a process for producing a paper web that has substantially
uniform properties. The process includes the steps of providing a
moving paper web, and determination of the tension on the paper web
while the web is moving. The instability index of the web is
greater than or equal to 0.5. Further, the process includes the
step of adjusting the cross directional dryer coating of the web
based on the determined tension of the web. Additionally, the
creping chemistry is adjusted based on the instability index.
[0019] Another exemplary embodiment of the present invention
includes a process for producing a paper web that has at least two
flows of different strengths. The process includes the step of
providing a moving layered paper web, and providing at least one
hardwood flow and at least one softwood flow. These flows form at
least one hardwood layer and at least one softwood layer of the
paper web. The tension on the paper web is determined while the web
is moving. The tension of the paper web is controlled by increasing
the hardwood flow and decreasing the softwood flow in regions of
high tension, maintaining a uniform basis weight. Further, softwood
flow is increased and hardwood decreased in regions of low tension
so that the tension is uniform, maintaining a uniform basis
weight.
[0020] Also, the present invention includes an exemplary embodiment
of the process as immediately discussed where the instability index
of the web is greater than or equal to 0.5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] An embodiment of the present invention is described by way
of example with reference to the accompanying drawings, in
which:
[0022] FIG. 1 is a schematic diagram of a web forming machine that
illustrates one exemplary embodiment for forming a web that has
multiple layers in accordance with an exemplary embodiment of the
present invention.
[0023] FIG. 2 is a schematic diagram of a web forming machine that
crepes one side of the web.
[0024] FIG. 3 is perspective view with cut-away portions of a web
forming machine that includes a through-air dryer for removing
moisture from the web.
[0025] FIG. 4 is a schematic view of an exemplary embodiment of the
present invention. FIG. 4 shows the web before a blast of fluid
contacts the web.
[0026] FIG. 5 is a schematic view of an exemplary embodiment of the
present invention. FIG. 5 shows a wave propagating through the
web.
[0027] FIG. 6 is a schematic view of an exemplary embodiment of the
present invention. FIG. 6 shows a wave passing over a first laser
transducer and being measured by the first laser transducer.
[0028] FIG. 7 is a schematic view of an exemplary embodiment of the
present invention. FIG. 7 shows a wave passing over a second laser
transducer and being measured by the second laser transducer.
[0029] FIG. 8 is a graph of the web speed versus the tension in an
exemplary embodiment of the present invention. The graph shows a
0.5 to 1.0 instability index for a 15 gsm web.
[0030] FIG. 9 is a graph of time versus tension for another
exemplary embodiment of the present invention. FIG. 9 shows the
tension during a turn-up with Hercobond addition.
[0031] FIG. 10 is a graph of time versus tension for another
exemplary embodiment of the present invention. FIG. 10 shows the
tension during a turn-up without Hercobond being added.
[0032] FIG. 11 is a graph of crepe ratio versus tension for another
exemplary embodiment of the present invention. FIG. 11 shows the
changes in tension from different crepe ratios on tissue machine
#1.
[0033] FIG. 12 is a graph of the distance from the edge of a sheet
versus tension for an exemplary embodiment of the present
invention. FIG. 12 shows the cross directional profile under tissue
machine #1.
[0034] FIG. 13 is a graph of time versus tension for an exemplary
embodiment of the present invention. FIG. 13 shows the tension
measurements through a continuous softroll on tissue machine
#1.
[0035] FIG. 14 is a graph of time versus tension for another
exemplary embodiment of the present invention. FIG. 14 shows the
tension measured with a DDWS foil that is raised and retracted on
tissue machine #1.
[0036] FIG. 15 is a flow diagram of a process of an exemplary
embodiment of the present invention. FIG. 15 shows the process of
creating a wave in the web, obtaining signals from the laser
displacement transducers, processing the signals, calculating the
tension, and controlling the process as a result of the calculated
tension.
DETAILED DESCRIPTION
[0037] Reference will now be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, and not meant as a limitation of the invention. For
example, features illustrated or described as part of one
embodiment can be used with another embodiment to yield still a
third embodiment. It is intended that the present invention include
these and other modifications and variations.
[0038] The present invention relates to a process and apparatus for
measuring the tension in a moving web. In particular, exemplary
embodiments of the present invention allow for the tension of a
high speed moving web to be monitored and then used to modify
various properties and conditions of the web and of the process
producing the web. Layer splits of the web may be maintained by
monitoring and adjusting the tension profile of the web.
[0039] Webs that may be used in the process of the present
invention can vary depending upon the particular application. In
general, any suitable web or film may be used in the process in
order to measure the tension of the web. Further, the webs can be
made from any suitable type of fiber. It should be understood that
in the claims, the word "web" is defined to include woven webs,
non-woven webs, and films.
[0040] For example, the manner in which the web of the present
invention is formed may vary depending upon the particular
application. In one exemplary embodiment, the web can contain pulp
fibers and can be formed in a wet-lay process according to
conventional paper making techniques. In a wet-lay process, the
fiber furnish is combined with water to form an aqueous suspension.
The aqueous suspension is spread onto a wire or felt and dried to
form the web. Alternatively, the web of the present invention can
be air formed. In this exemplary embodiment, air is used to
transport the fibers and form a web. Air-forming processes are
typically capable of processing longer fibers than most wet-lay
processes, which may provide an advantage in some applications.
[0041] Referring to FIG. 2, one embodiment of a process for
producing a web that may be used in accordance with the present
invention is illustrated. The process illustrated in the figure
depicts a wet-lay process, although, as described above, other
techniques for forming the web of the present invention may be
used.
[0042] As shown in FIG. 2, the web-forming system includes a
headbox 10 for receiving an aqueous suspension of fibers. Headbox
10 spreads the aqueous suspension of fibers onto a forming fabric
26 that is supported and driven by a plurality of guide rolls 34. A
vacuum box 36 is disposed beneath forming fabric 26 and is adapted
to remove water from the fiber furnish to assist in forming the
web.
[0043] From forming fabric 26, a formed web 38 is transferred to a
second fabric 40, which may be either a wire or a felt. Fabric 40
is supported for movement around a continuous path by a plurality
of guide rolls 42. Also included is a pick up roll 44 designed to
facilitate transfer of web 38 from fabric 26 to fabric 40. The
speed at which fabric 40 can be driven is approximately the same
speed at which fabric 26 is driven so that movement of web 38
through the system is consistent. Alternatively, the two fabrics
can be run at different speeds, such as in a rush transfer process,
in order to increase the bulk of the webs or for some other
purpose.
[0044] From fabric 40, web 38, in this exemplary embodiment, is
pressed onto the surface of a rotatable heated dryer drum 46, such
as a Yankee dryer, by a press roll 43. Web 38 is lightly pressed
into engagement with the surface of dryer drum 46 to which it
adheres, due to its moisture content and its preference for the
smoother of the two surfaces. As web 38 is carried through a
portion of the rotational path of the dryer surface, heat is
imparted to the web causing most of the moisture contained within
the web to be evaporated.
[0045] Web 38 is then removed from dryer drum 46 by a creping blade
47. Creping web 38 as it is formed reduces internal bonding within
the web and increases softness.
[0046] In an alternative exemplary embodiment, instead of wet
pressing the base web 38 onto a dryer drum and creping the web, the
web can be through-air dried. A through-air dryer accomplishes the
removal of moisture from the web by passing air through the web
without applying any mechanical pressure.
[0047] For example, referring to FIG. 3, an alternative exemplary
embodiment for forming a base web for use in the process of the
present invention containing a through-air dryer is illustrated. As
shown, a dilute aqueous suspension of fibers is supplied by a
headbox 10 and deposited via a sluice 11 in uniform dispersion onto
a forming fabric 26 in order to form a base web 38.
[0048] Once deposited onto the forming fabric 26, water is removed
from the web 38 by combinations of gravity, centrifugal force and
vacuum suction depending upon the forming configuration. As shown
in this embodiment, and similar to FIG. 2, a vacuum box 36 can be
disposed beneath the forming fabric 26 for removing water and
facilitating formation of the web 38.
[0049] From the forming fabric 26, the web 38 is then transferred
to a second fabric 40. The second fabric 40 carries the web through
a through-air drying apparatus 50. The through-air dryer 50 dries
the web 38 without applying a compressive force in order to
maximize bulk. For example, as shown in FIG. 3, the through-air
drying apparatus 50 includes an outer rotatable cylinder 52 with
perforations 54 in combination with an outer hood 56. Specifically,
the fabric 40 carries the web 38 over the upper portion of the
through-air drying apparatus outer cylinder 52. Heated air is drawn
through perforations 54 which contacts the web 38 and removes
moisture. In one exemplary embodiment, the temperature of the
heated air forced through the perforations 54 can be from about
170.degree. F. to about 500.degree. F.
[0050] As stated, properties of the web 38 and also of the
apparatus that produces the web 38 can be controlled and monitored
if the tension in web 38 is known. The tension in web 38 can be
correlated with several process conditions in order to determine
the process conditions during a particular build of web 38 and make
adjustments. Some of the process conditions which can be varied
based on the tension in web 38 include the following: the chemical
addition rate, the cross directional profile of the basis weight
and moisture in web 38, draws on web 38, crepe ratio, and the
winding profile of a tissue roll off of a tissue machine. By taking
the correlation between the tension in web 38 and these various
process conditions, one can incorporate the speed of web 38 and the
basis weight of web 38 with the tension to produce an on-line
method that controls the machine direction strength and/or modulus
of the tissue web 38. However, adjustments to the machine and
process can be made based on only the tension alone.
[0051] FIG. 4 shows a schematic view of an exemplary embodiment of
a tension apparatus 74 that can monitor and/or control properties
of the web 38 and the process that produces web 38. The exemplary
embodiment of the tension apparatus 74 includes a computer 72 that
is connected to both an air pulse 66 and a first and second laser
transducer 68 and 70 respectively. However, it is to be understood
that in other exemplary embodiments of the present invention, air
pulse 66 along with the first and second laser transducers 68 and
70 do not need to be directly controlled by computer 72. The
tension apparatus 74 is located adjacent to a run of the web 38
that is between two rollers 60 and 62. The web 38 is moving in the
direction shown by arrow V in FIG. 4, and is moving at a velocity
v. Web 38 is wound onto a wound roll 64.
[0052] Tension apparatus 74 can calculate the tension in the web 38
by a non-contacting process. First, the air pulse 66 can fire a
fluid, for instance air, onto web 38 which causes a disturbance in
web 38. Such a disturbance is shown in FIG. 5 as being a wave 75.
Wave 75 will travel in a direction vd shown in FIG. 5 at a velocity
vd away form the air pulse 66. Wave 75 travels through web 38 much
like a stone that is thrown into a pond which causes ripples to
travel across the surface of the pond. Here however, since web 38
is moving in a direction v, the analogy to a stone in a pond is not
entirely accurate. A closer analogy would be to that of a stone
thrown into a moving river since the web 38 is moving at a velocity
v. FIGS. 6 and 7 show the wave 75 being situated above the first
laser transducer 68 and the second laser transducer 70 as the wave
75 moves across the surface of web 38. As wave 75 moves across each
one of these laser transducers 68 and 70, the tension apparatus 74
can measure the speed of wave 75. The use of laser transducers 68
and 70 allow for high speed measurements, an advantage of the
present invention.
[0053] The first and second laser transducers 68 and 70 therefore
determine the exact time that wave 75 travels above the respective
transducer 68 and 70. From this information, the computer 72 can
use an algorithm to determine the speed of the wave 75. The tension
apparatus 74 is also capable of measuring the speed v of the web
38. However, in other exemplary embodiments of the present
invention, the speed v of web 38 is determined not by the tension
apparatus 74, but by some other method. The tension apparatus 74
may use a similar algorithm to calculate the speed v of web 38. The
tension in web 38 may be determined by the computer 72 by taking
into account the wave speed vd, the web speed v, and the basis
weight of the web 38.
[0054] In one exemplary embodiment of the present invention, the
pulse of air from the air pulse 66 is a short duration pulse. The
pulse may be about 15 milliseconds of air at a pressure of about 80
pounds per square inch. The first and second laser transducers 68
and 70 may be high speed transducers with a response time faster
than one millisecond. Faster transducers, such as those that have
response times as fast as 10 microseconds may also be used. The
first and second laser transducers 68 and 70 are aimed at the web
38 and are positioned upstream from the air pulse 66. In one
exemplary embodiment, the first and second laser transducers 68 and
70 are positioned 50 millimeters from the air pulse 66. However, it
is to be understood that in other exemplary embodiments of the
present invention, the first and second laser transducers 68 and 70
may be positioned downstream from the air pulse 66 or at other
distances upstream from the air pulse 66. In another exemplary
embodiment of the present invention, the first laser transducer 68
is spaced 40 millimeters from the second laser transducer 70.
[0055] A computer program that is administered by computer 72 can
control the air pulse 66 to create a wave 75. The computer program
will then record the displacement output from each laser transducer
68 and 70. This resulting data is bandpass filtered to eliminate
any short and long wave length flutter associated with the web 38.
The signal may then be differentiated to amplify any change in
position that is due to the wave 75 passing in front of the laser
transducers 68 and 70. The two signals may than be passed through a
window filter to force the end points to a zero level. However, in
other exemplary embodiments of the present invention it is not
necessary to pass the two signals through a window filter to force
the end points to a zero level. Next, the signals may be
mathematically cross-correlated to determine the most likely time
delay between the two signals. This time delay, in accordance with
the displacement from the first and second laser transducers 68 and
70, yields the actual wave speed vd.
[0056] The tension is determined by the following equation:
Tension=BW.times.(vd+v).sup.2
[0057] In this equation, BW is the basis weight, vd is the measured
wave speed, and v is the web speed. The addition of the wave speed
vd to the web speed v is necessary because the wave 75 is traveling
upstream and is thus slowed down by the movement of web 38. If the
laser transducers 68 and 70 were positioned downstream of the air
pulse 66, the equation for the tension would be changed
accordingly.
[0058] The web speed v and the basis weight may be measured
independently from the tension apparatus 74 in other exemplary
embodiments of the present invention. However, the web speed v can
be measured using the tension apparatus 74 by recording the light
intensity of the reflected laser light from the first and second
laser transducers 68 and 70 and then filtering the signal over a
specific frequency range.
[0059] The instability index of web 38 is a measure of the relative
instability of the moving tissue web. As the instability index
approaches unity, the web 38 becomes unstable. At an instability
index of 1.0, a wave 75 would not be able to travel across the
surface of web 38. Additionally, when the instability index is
high, greater than 0.5, the tension measurements in current
machines will not work. The instability index is governed by the
following equation:
Instability Index=v/c=v/(v+vd)
[0060] Here, v is equal to the web speed and vd is equal to the
measured wave speed. In the equation, c is the critical speed which
is equal to the web speed v plus the measured wave speed vd.
However, it may be the case that the critical speed c is equal to
measured disturbance speed vd minus the web speed v in other
exemplary embodiments of the present invention. This would be the
case, for instance, when the laser transducers 68 and 70 were
located downstream of the air pulse 66 instead of upstream in
relation to the direction of travel of the web 38. The instability
index as stated in the claims is one of these two formulas
depending on the relative location of the laser transducers 68 and
70 and the air pulse 66.
[0061] Therefore, an exemplary embodiment of the present invention
may utilize modern laser transducers 68 and 70 and high speed
computers 72 to measure the tension in web 38. Computer 72 may then
separate the natural flutter of the moving web 38 from the desired
measurement. This is not required when a stable web is
measured.
[0062] A tension profile of web 38 may be taken by placing an array
of laser transducers on the cross direction of web 38. Other
exemplary embodiments of the present invention may use multiple
laser transducers to obtain a tension profile of the web 38 in
order to adjust other properties of web 38.
[0063] Knowledge of the tension in web 38 allows for the process
that produces the web 38 to be monitored or controlled so that the
properties of web 38 are improved or maintained, and the machine
that produces web 38 is controlled or maintained. FIG. 15 shows a
process algorithm of a tension apparatus 74 in accordance with an
exemplary embodiment of the present invention. A sample listing of
the process conditions that may be monitored or controlled by
knowledge of the tension are as follows (this list is not
inclusive):
[0064] wear on blade 47 in order to determine when to change blade
47;
[0065] the draw on a winder to maintain uniform tension in each
section of the web 38;
[0066] the tension in a wound roll 64 of the web 38;
[0067] flow adjustments to control the cross-directional dryer
coating of the web 38;
[0068] control of the cross-directional moisture profile based on a
given basis weight profile and a single point moisture;
[0069] control of the cross-directional basis weight based on a
given moisture profile and an average basis weight from a softroll
weight;
[0070] control of the web 38 during turn-ups by optimizing the
sequence to maintain a desired tension;
[0071] control of the web 38 during turn-ups by chemical addition
on web 38 to maintain a desired tension;
[0072] control of the web 38 instability by adjusting foils in
response to the instability index calculated when performing the
tension measurement;
[0073] control of the web 38 instability by creping chemistry in
response to the instability index calculated when performing the
tension measurement;
[0074] control of the web 38 handling by keeping the instability
index in a desired range by adjusting the creping chemistry at a
certain web speed v;
[0075] control of the web 38 handling by adjusting foil positions
to maintain the runability at a given web speed v based on the
instability index.
[0076] In addition, other control properties may be controlled
based on the tension measured in web 38.
[0077] FIG. 8 shows a plot of the web speed v in relation to the
tension in accordance with another exemplary embodiment of the
present invention. Here, the basis weight of the web 38 is 15 gsm.
The cross-hatched area of FIG. 8 represents an instability index of
0.5 to 1.0.; Although an exemplary embodiment of the present
invention is capable of measuring an instability index of 0.5 to
1.0, it is to be understood that the present invention also
encompasses exemplary embodiments where the instability index may
be less than 0.5. Therefore, the present invention is not limited
to only a tension apparatus 74 that can measure instability indexes
from 0.5 to 1.0, but a tension apparatus 74 that may measure at
various instability indexes.
[0078] An exemplary embodiment of the present invention also
includes a process for producing a paper web 38 that has at least
two flows of different strengths. The at least two flows may be
placed to form fiber layers such as those shown in FIG. 1. Here,
one of the fiber layers 22 may be formed by a softwood while
another fiber layer 20 may be formed by a hardwood. The process
would involve the provision of a moving web 38 along with at least
one hardwood layer 22 and one softwood layer 20. The tension of the
web 38 is measured and may be controlled by increasing the flow
feeding into the hardwood layer 20 or decreasing the flow into the
softwood layer 22 in regions of high tension. The flow into the
softwood layer 22 is increased or the flow into the hardwood layer
20 is decreased in regions of low tension on web 38. Such
modifications allows for a uniform tension in the web 38.
Additionally, a uniform basis weight may be maintained in the
process by adjusting the flows of the hardwood or softwood layers
20 and 22. Therefore, the flow of layers onto the web 38 can be
controlled based on the tension in the web 38.
[0079] In an alternative exemplary embodiment, a stratified web can
be used that has outer layers having a greater tensile strength
than a middle layer. There are various methods available for
creating stratified webs. For instance, referring to FIG. 1, one
exemplary embodiment of a device for forming a multi-layered
stratified fiber furnish is illustrated. As shown, a three-layered
headbox 10 may include an upper headbox wall 12 and a lower headbox
wall 14. Headbox 10 may further include a first divider 16 and a
second divider 18, which separate three fiber stock layers. Each of
the fiber layers 24, 20, and 22 comprise a dilute aqueous
suspension of fibers.
[0080] An endless traveling forming fabric 26, suitably supported
and driven by rolls 28 and 30, receives the layered stock issuing
from headbox 10. Once retained on fabric 26, the layered fiber
suspension passes water through the fabric as shown by the arrows
32. Water removal is achieved by combinations of gravity,
centrifugal force and vacuum suction depending on the forming
configuration.
[0081] Forming multi-layered webs is also described and disclosed
in U.S. Pat. No. 5,129,988 to Farrington, Jr. and in U.S. Pat. No.
5,494,554 to Edwards, et al., which are both incorporated herein by
reference, in their entirety for all purposes in the present
application.
[0082] In forming stratified base webs, various methods and
techniques are available for creating layers that have different
tensile strengths. For example, debonding agents can be used as
described above in order to alter the strength of a particular
layer.
[0083] Alternatively, different fiber furnishes can be used for
each layer in order to create a layer with desired characteristics.
For example, in one exemplary embodiment, softwood fibers can be
incorporated into a layer for providing tensile strength, while
hardwood fibers can be incorporated into an adjacent layer for
creating a weaker tensile strength layer.
[0084] More particularly, it is known that layers containing
hardwood fibers typically have a lower tensile strength than layers
containing softwood fibers. Hardwood fibers have a relatively short
fiber length. For instance, hardwood fibers can have a length of
less than about 2 millimeters and particularly less than about 1.5
millimeters.
[0085] In one exemplary embodiment, the hardwood fibers
incorporated into a layer of the web 38 include eucalyptus fibers.
Eucalyptus fibers typically have a length of from about 0.8
millimeters to about 1.2 millimeters. When added to the web 38,
eucalyptus fibers increase the softness, enhance the brightness,
increase the opacity, and increase the wicking ability of the
web.
[0086] Besides eucalyptus fibers, other hardwood fibers may also be
incorporated into the web 38 of the present invention. Such fibers
include, for instance, maple fibers, birch fibers and possibly
recycled hardwood fibers.
[0087] In general, the above-described hardwood fibers can be
present in the web 38 in any suitable amount. For example, the
fibers can comprise from about 5% to about 100% by weight of one
layer of the web 38.
[0088] The hardwood fibers can be present within the lower tensile
strength layer of the web 38 either alone or in combination with
other fibers, such as other cellulosic fibers. For instance, the
hardwood fibers can be combined with softwood fibers, with
superabsorbent materials, and with thermomechanical pulp.
[0089] As described above, stronger tensile strength layers can be
formed using softwood fibers, especially when adjacent weaker
tensile strength layers are made from hardwood fibers. The softwood
fibers can be present alone or in combination with other fibers.
For instance, in some exemplary embodiments, staple fibers, such as
synthetic fibers, can be combined with the softwood fibers.
[0090] The weight of each layer of a stratified base web 38 in
relation to the total weight of the web 38 is generally not
critical. In most exemplary embodiments, however, the weight of
each outer layer will be from about 15% to about 40% of the total
weight of the web 38, and particularly from about 25% to about 35%
of the weight of the web 38.
[0091] The basis weight of webs made according to the present
invention can vary depending upon the particular application. In
general, for most applications, the basis weight can be from about
5 pounds per 2,880 square feet (ream) (8.5 gsm) to about 80 pounds
per ream (136 gsm), and particularly from about 6 pounds per ream
(10.2 gsm) to about 30 pounds per ream (51 gsm). In one exemplary
embodiment, the present invention can be used to construct a single
ply bath tissue having a basis weight of from about 20 gsm to about
40 gsm. Some other uses of the webs include use as a wiping
product, as a napkin, as a medical pad, as an absorbent layer in a
laminate product, as a placemat, as a drop cloth, as a cover
material, as a facial tissue, or for any product that requires
liquid absorbency.
Experiments Involving Exemplary Embodiments of the Present
Invention
[0092] Applicants have conducted experiments in regards to the
tension apparatus 74 in measuring the tension in a moving web 38.
The objective of the experiments were to verify that the tension
apparatus 74 could accurately measure the tension on a commercial
low tension, high speed machine. Additionally, the experiment was
carried out in order to determine whether the tension could be
monitored over a long period of time on both a tissue machine and a
winder or rewinder. It was found that the tension in the web 38 was
related to certain properties and problems concerning the web 38
and the machine that processes web 38.
[0093] A tension apparatus 74 was placed on a tripod under a moving
web 38 on a tissue machine. The tension apparatus 74 was between
50-60 inches from the drive side edge of the web 38 which was
approximately 204 inches wide. On the tissue machine, the tension
apparatus 74 was able to pick up changes after the addition of
processed chemicals, crepe ratio, and the cross directional
profile.
[0094] During a selected number of turn-ups, a chemical
strengthening agent, Hercobond, was added. Hercobond increases the
web 38 strength so that there is a more likely probability of a
successful turn-up. When the tension apparatus 74 was placed under
the tissue machine, the tension apparatus 74 was able to accurately
pick up the addition of Hercobond. Before the Hercobond was added,
the tension was approximately 10.3 Newtons per meter squared. After
the addition of Hercobond, the peak of the tension averaged to 12.4
Newtons per meter squared. FIG. 9 shows the tension being increased
as Hercobond was added 2000 yards before the turn-up. The web speed
v was 3906 feet per minute, meaning that the chemical addition
occurred 92 seconds before turn-up. The timing of Hercobond
addition is noted in FIG. 9. The downward spike of tension
immediately before the turn-up is unrelated to the Hercobond
addition as this is the moment when the web 38 is being blown over
a new roll before being attached thereon. After the turn-up, it
took approximately 5 minutes before the tension returned to its
original level while the Hercobond was phasing out of the
process.
[0095] FIG. 10 shows a turn-up without Hercobond for comparison.
FIG. 10 demonstrates that the tension does not increase before the
turn-up as it did when Hercobond was added. Tissue samples were
taken from the ends of both rolls once they were on the reel to
verify the increase in tension. Below is a table listing the data
from each roll and it shows that the roll with Hercobond had higher
strength properties:
1 Without Herccobon Hercobon d d MD Strength 1420 1060 CD Strength
834 630 Wet CD 199 149 MD Stretch 30.9 31.6 GMT 1090 814 MD/CD
Ratio 1.7 1.68 WCD/CD Ratio 23.8 23.8
[0096] The tension apparatus 74 was also able to note a change in
crepe ratio. A machine onto which the present experiment was
conducted, tissue machine #1, normally runs at a 1.28 crepe ratio.
For approximately two minutes the crepe ratio was changed to 1.26
to determine whether the tension apparatus 74 could pick up the
change. FIG. 11 shows the change in crepe ratio that the tension
apparatus 74 detected. The error bars shown are with a 99%
confidence level. At 1.26 crepe ratio, the average tension was 9.4
Newtons per meter squared, and at the 1.28 crepe ratio the average
tension was 8.9 Newtons per meter squared. For a higher crepe
ratio, the tension should be lower, meaning that the tension
apparatus 74 accurately picked up the change.
[0097] Across a tissue web 38, the goal is to keep the moisture
profile and basis weight uniform. Here however, the moisture
profile and basis weight was not uniform. Therefore, the tension
across the tissue web 38 is also not uniform. When the tension
apparatus 74 was placed under the web 38, it was moved in six
different positions within one foot to determine whether there were
any variations in the cross direction. Data was collected at each
position for approximately two minutes and then was repeated in a
random manner to eliminate time variables. FIG. 12 shows the cross
directional profile that the tension apparatus 74 recorded. The
error bars shown are with a 99% confidence level. At 56 inches from
the drive side, the tension averaged to 10.6 Newtons per meter
squared. At 75 inches across, the tension averaged to 9.5 Newtons
per meter squared. Using data from tissue samples correlating with
previous strength properties, this 11.4% increase in tension
relates to an 18.2% increase in cross directional strength and a
19.4% increase in MD strength. There is a statistical difference
between the last four inches on the chart. However, upon examining
the scanning profile of the basis weight and moisture profiles, the
differences were not correlated to any specific variable on the
profiles.
[0098] Tension sensor 74 was used to examine a full softroll to
determine whether there were any noticeable trends throughout the
roll. A typical softroll takes approximately 30 minutes to run.
FIG. 13 shows data obtained through a measurement of the softroll.
In the present experiment, before the softroll was started, the
roll prior to it had broken on the turn-up. When this occurs,
Hercobond was added to help get the web 38 back onto the roll. The
addition of Hercobond explains the downward trend in the tension
for the first six minutes as the Hercobond was phased out of the
system. Throughout the rest of the roll, there were not any
dramatic trends. The roll maintained a fairly constant tension at
around 9.0 Newtons per meter squared. FIG. 13 includes a turn-up at
the end without using Hercobond.
[0099] Another measurement that was conducted involves the
installation of a DDWS foil onto the tissue machine. In theory, the
foil provides a layer of air onto which the web 38 rides along,
therefore stabilizing web 38. Usually, the foil is under the web 38
and is rarely used by the operators since CD and MD stability does
not seemingly benefit. The foil was raised for a few minutes to
determine whether or not it helped with stability. FIG. 14 shows
that the tension was fairly stable at about 8.8 Newtons per meter
squared while the foil was not contacting the sheet. Once the foil
was raised, the tension became unstable and higher at about 9.0
Newtons per meter squared. Presumably, the increase in tension is
caused by the foil pressing against the web 38. The variability
could possibly be a result of the layer of air not consistently
hugging the web 38 onto the foil.
[0100] The tension apparatus 74 was able to pick up changes in many
process variables as shown in the preceding experiments. Knowledge
of changes in the process variables can result in a quicker, more
reliable response to successfully controlling the strength in a web
38. Instead of having to wait for lab tests to verify properties,
this on-line method can allow for changes during the production of
a rolled product. The tension apparatus 74 disclosed in the present
invention is therefore capable of being able to read webs 38 that
travel at high speeds v and also have low tensions associated
therewith without contacting the web 38.
* * * * *