Patent Grant
9388530
Not Applicable.
The invention relates to compositions, methods, and apparatuses for monitoring and controlling a creping cylinder/Yankee dryer coating. The Yankee coating and creping application is arguably the most important, as well as, the most difficult to control unit operation in the tissue making process. For creped tissue products, this step defines the essential properties of absorbency, bulk, strength, and softness of tissue and towel products. Equally important, is that efficiency and runnability of the creping step controls the efficiency and runnability of the tissue machine as a whole.
A common difficulty with the tissue making process is the non-uniformity in characteristics of the coating on the creping cylinder in the cross direction. The coating is composed of adhesives, modifiers, and release agents applied from the spray boom, as well as, fibers pulled from the web or sheet, organic and inorganic material from evaporated process water, and other chemicals added earlier to the wet end of the tissue manufacturing process. Inhomogeneity in the coating characteristics is often related to variations in temperature, moisture, and regional chemical composition across the face of the dryer. The variation is often quite significant and can result in variable sheet adhesion, deposits of different characteristics and/or a lack of material on the cylinder that can result in excess Yankee/creping cylinder and creping blade-wear. Degradation of final sheet properties, such as absorbency, bulk, strength, and softness can also result from this variation and/or degradation. As a result of these drawbacks, monitoring and control methodologies for the coating on the creping cylinder surface are therefore desired.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.
To satisfy the long-felt but unsolved needs identified above, at least one embodiment of the invention is directed towards a method of monitoring and optionally controlling the application of a coating containing a Performance Enhancing Material (PEM) on a surface of a creping cylinder. the method may comprise: (a) applying a coating to the surface of a creping cylinder; (b) measuring the thickness of the coating on the surface of a creping cylinder by a differential method, wherein said differential method utilizes a plurality of apparatuses that do not physically contact the coating; (c) optionally adjusting the application of said coating in one or more defined zones of said creping cylinder in response to the thickness of said coating so as to provide a uniform thick coating on the surface of the creping cylinder; and (d) optionally applying an additional device(s) to monitor and optionally control other aspects of the coating on a creping cylinder aside from the thickness of the coating.
The present invention may also provide for a method of monitoring and optionally controlling the application of a coating containing a Performance Enhancing Material (PEM) on a surface of a creping cylinder comprising: (a) applying a coating to the surface of a creping cylinder; (b) providing an interferometer probe with a source wavelength that gives adequate transmission through a coating on the creping cylinder surface; (c) applying the interferometer probe to measure the reflected light from a coating air surface and a coating cylinder surface of the creping cylinder to determine the thickness of the coating on the creping cylinder; (d) optionally adjusting the application of said coating in one or more defined zones of said creping cylinder in response to the thickness of said coating so as to provide a uniform thick coating on the surface of the creping cylinder; and (e) optionally applying an additional device(s) to monitor and optionally control other aspects of the coating on a creping cylinder aside from the thickness of the coating.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description.
A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:
For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated. The drawings are only an exemplification of the principles of the invention and are not intended to limit the invention to the particular embodiments illustrated.
The methodologies and control strategies of the present disclosure are directed to the coating on the creping cylinder surface. Various types of chemistries make up the coating on the creping cylinder surface. These chemistries impart properties to the coating that function to improve the tissue making process. These chemistries will be collectively referred to as Performance Enhancing Materials (PEM/PEMs). An exemplary description of these chemicals and a method to control their application are discussed in U.S. Pat. No. 7,048,826 and U.S. Patent Publication No. 2007/0208115, which are herein incorporated by reference. In one embodiment, one of said plurality of apparatuses utilized is an eddy current sensor. The differential method can involve an eddy current and an optical displacement sensor. In one embodiment, the differential method comprises the steps of: applying the eddy current sensor to measure the distance from the sensor to a surface of the creping cylinder and applying an optical displacement sensor to measure the distance from the coating surface to the sensor. In a further embodiment, the optical displacement sensor is a laser triangulation sensor or a chromatic type confocal sensor.
The second sensor mounted in the enclosure optically measures the displacement of the sensor (do) with respect to the film surface. The optical displacement sensor can be either a triangulation type such as Micro-Epsilon (Raleigh, N.C.) model 1700-2 or a chromatic type such as Micro-Epsilons optoNCDT 2401 confocal sensor. These sensors work on the principle of reflecting light from the film surface. When variations in the coating optical properties exist due to process operating conditions, sensor monitoring location, or properties of the PEM itself, then a high performance triangulation sensor such as Keyence LKG-15 (Keyence—located Woodcliff Lake, N.J.) may be warranted. The Keyence triangulation sensor provides a higher accuracy measurement with built in algorithms for measuring transparent and translucent films. Variation in the transmission characteristics in both the cross direction (CD) and machine direction (MD) may warrant a sensor adaptable to the different coating optical characteristics and the higher performance triangulation sensor can switch between different measurement modes. In general, the majority of commercial triangulation sensors will produce a measurement error on materials that are transparent or translucent. If the film characteristics are constant, angling the triangulation sensor can reduce this error. However, sensor rotation for measurements on processes that have a high variability in the film characteristics is not an option. Both the optical and EC sensors provide the required resolution to monitor PEM films with expected thickness >50 microns. The film thickness is obtained by taking the difference between the measured distances from the EC and optical displacement sensor.
The sensors are housed in a purged enclosure, as shown in
For industrial monitoring on a creping cylinder (also known as a Yankee Dryer), the sensor module shown in
Laboratory results using the combination of EC and optical displacement (triangulation) sensor are shown in
The results from
Recorded measurements from the EC and triangulation sensor are shown in
Similarly
Monitoring results from the coated region with the defect are shown in
Another example showing the detection of uniformities is shown in
Moisture, which may affect the differential calculation, can also be accounted for; specifically moisture can be calculated from the dielectric constant derived from a capacitance measurement. This data can be utilized to decide whether any change in thickness is a result of moisture or the lack of a coating. Another way of looking at the capacitance is that it is a safeguard for a measurement obtained by the described differential method; it provides a more in-depth analysis of the coating itself, e.g. behaviors of the coating such as glass transition temperature and modulus, which is useful in monitoring and controlling the coating on the creping cylinder surface.
One method of accounting for moisture content in the coating is by looking at capacitance and another way is to utilize a moisture sensor. Other techniques may be utilized by one of ordinary skill in the art.
In one embodiment, the method incorporates a dedicated moisture sensor such as the one described in WO2006118619 based on optical absorption of H2O in the 1300 nm region, wherein said reference is herein incorporated by reference. This will give a direct measurement of the moisture level in the film without interferences that the capacitance monitor could experience due its dependence on the dielectic constant of both the coating and moisture. In another embodiment, the method additionally comprises: applying a capacitance probe to measure the moisture content of the coating; comparing the capacitance measurement with the differential method measurement to determine the effect of moisture on the coating thickness; and optionally adjusting the amount and distribution of the coating on the creping cylinder surface in response to the effect moisture has on thickness as determined by the differential method and/or adjust the amount of the coating.
The method can use a module that houses multiple sensors as shown in
Capacitance sensors utilize the electrical property of capacitance that exists between any two conductors that are in close proximity of each other. If a voltage is applied to two conductors that are separated from each other, an electric field will form between them due to the difference between the electric charges stored on the conductor surfaces. Capacitance of the space between them will affect the field such that a higher capacitance will hold more charge and a lower capacitance will hold less charge. The greater the capacitance, the more current it takes to change the voltage on the conductors.
The metal sensing surface of a capacitance sensor serves as one of the conductors. The target (Yankee drum surface) is the other conductor. The driving electronics induces a continually changing voltage into the probe, for example a 10 kHz square wave, and the resulting current required is measured. This current measurement is related to the distance between the probe and target if the capacitance between them is constant.
The following relationship applies:
where C is the capacitance (F, farad), ∈ is the dielectric property of the material in the gap between the conductors, A is the probe sensing area, and d is the gap distance. The dielectric property is proportional to the material's dielectric constant as ∈=∈r∈0, where ∈r is the dielectric constant and ∈0 is the vacuum permittivity constant. For air, ∈r=1.006 and for water, ∈r=78. Depending on which two parameters are being held constant, the third can be determined from the sensor's output. In the case of position, d is measured where air is usually the medium. For our application in Yankee systems, the variability of ∈r in the total gap volume is the measured parameter. In this case, the gap is composed of three main components air, film or coating that could also contain fibrous material, and moisture. A mixture dielectric constant can be expressed as:
∈r=∈fΦ
where φ is the volume fraction with the subscript and superscript referencing the component material (a=air, w=water, f=film). Using Eq 1 and 2 the change in capacitance due to the presence of moisture is given by:
where Cfw is the capacitance for film containing moisture and Cf is the dry film. Taking the log and rearranging Eq. 3 an expression for the volume fraction on moisture is given by:
For monitoring the Yankee film, the mixture capacitance Cfw is measured directly with the capacitance probe. The temperature dependent dielectric constant for water is obtained from literature values. The volume fraction of moisture is then obtained by knowing the dry film capacitance, which can be determined from the film thickness measurement (dc) using the optical sensor and knowing the dielectric constant of the film.
The average dielectric constant for the gap volume is proportionally composed of that for air and the coating. The more coating in the gap, the larger the average dielectric constant is. By controlling d and A, any sensitivity and range can be obtained.
Because capacitance is sensitive to the moisture content of the coating, it may be difficult to separate out variation in coating thickness from changes in moisture content. By incorporating the set of sensors (EC, optical displacement, and capacitance) in the module shown in
An infrared (IR) temperature probe such as OMEGA (Stamford, Conn.) model O536-3-T-240F can provide useful information on the temperature profile of the creping cylinder. Since PEM's will respond differently depending on temperature, temperature information can be used to adjust the chemical composition and level of PEMs applied to the cylinder.
In one embodiment, the method further comprises: (a) applying an IR temperature probe to measure the temperature profile of the creping cylinder; (b) applying an IR temperature probe to measure the coating temperature needed to correct for the temperature dependent moisture dielectric constant; and (c) applying the corrected moisture dielectric constant to the capacitance measurement to determine the correct coating moisture concentration.
The addition of the IR temperature probe in the sensor module provides information on the temperature profile of the crepe cylinder. This is useful in identifying temperature non-uniformities on the crepe cylinder. In addition, the temperature can be used to correct the dielectric constant of the coating. For example, the dielectric constant for water can vary from 80.1 (20° C.) to 55.3 (100° C.).
An ultrasonic sensor may be incorporated into the monitoring methodology. In one embodiment, the method further comprises applying an ultrasonic sensor to measure the modulus of the coating, and optionally wherein the modulus value is used to measure the hardness of the coating.
The ultrasonic sensor is used to detect the viscoelastic property of the coating. The propagation of sound wave (reflection and attenuation) through the film will depend on the film quality, e.g., hard versus soft. Information on the film properties can be used for feedback to a spray system for controlling the spray level or adjusting the spray chemistry, e.g., dilution level, to optimize the viscoelastic film property.
As stated above, an interferometer may be utilized in measuring thickness. Other analytical techniques, such as the ones described in this disclosure can be utilized in conjunction with an interferometry method. In addition, the differential method can be used in conjunction with a methodology that utilizes an interferometer to measure thickness of the coating.
In one embodiment, the method uses interferometry to monitor the coating thickness. If the coating has sufficient transmission, then the use of multiple sensors can be reduced to a single probe head as illustrated in
As stated above, the methodologies of the present disclosure provide for optionally adjusting the application rate of said coating in one or more defined zones of said creping cylinder to provide a uniformly thick coating in response to the thickness of said coating. Various types of apparatuses can carry out this task.
In one embodiment, the method controls the spray zones based on measurements collected during normal operating conditions. For example, measurements from the sensor or sensor(s) discussed above are used to establish a baseline profile on the crepe cylinder. The baseline data is then used to track process variances. Upper and lower control limits established around the baseline profile data (film thickness, film quality, moisture level, viscoelasticity, temperature, etc.) is used to track when process deviations occur. If any of the process monitoring parameters falls outside the limits, then corrective action is taken with the zone control spray application system.
In another embodiment, the plurality of apparatuses are translated across the Yankee dryer/creping cylinder to provide profiles of thickness and/or moisture content and/or temperature, and/or modulus.
In another embodiment, the plurality of apparatuses are located between a crepe blade and a cleaning blade, after the cleaning blade, or prior to a tissue web being pressed into the coating, or any combination of the above.
In another embodiment, the plurality of apparatuses are purged with a clean gas to prevent fouling, mist interference, dust interference, overheating, or a combination thereof.
As described in U.S. Pat. No. 5,328,565 (which is incorporated by reference in its entirety) it is thought by some that chatter might also be caused at least in part by properties of the tissue web which are unrelated to the coating itself. In at least one embodiment the tissue web is measured (before, while and/or after it is contacted with the coating) by any method (including non-contact method) to determine if the tissue web itself will cause chatter. In at least one embodiment this is accomplished by comparing one or more of the measurements of the coating separate from the tissue web, and/or when the two are combined together. As a single representative example of this general concept, in at least one embodiment a capacitance measurement is taken of the tissue web alone, the coating alone, and the contacted coating-tissue web, to determine if it is the coating, the tissue web, or both that are a cause of chatter. In at least one embodiment both the coating and the tissue web contain peaks but only the coating's peaks would cause chatter. In at least one embodiment when the source of the chatter (or would be chatter) is identified only that source is adjusted to prevent the chatter.
While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. All patents, patent applications, scientific papers, and any other referenced materials mentioned herein are incorporated by reference in their entirety. Furthermore, the invention encompasses any possible combination of some or all of the various embodiments mentioned herein, described herein and/or incorporated herein. In addition the invention encompasses any possible combination that also specifically excludes any one or some of the various embodiments mentioned herein, described herein and/or incorporated herein.
The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.
All ranges and parameters disclosed herein are understood to encompass any and all subranges subsumed therein, and every number between the endpoints. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less, (e.g. 2.3 to 9.4, 3 to 8, 4 to 7), and finally to each number 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 contained within the range. All percentages, ratios and proportions herein are by weight unless otherwise specified.
This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.
This application is a continuation in part of co-pending U.S. patent application Ser. No. 12/246,797 filed on Oct. 7, 2008.
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| 3774237 | Hardway, Jr. | Nov 1973 | A |
| 5328565 | Rasch et al. | Jul 1994 | A |
| 5355083 | George et al. | Oct 1994 | A |
| 20070208115 | Grigoriev et al. | Sep 2007 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20140170302 A1 | Jun 2014 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12246797 | Oct 2008 | US |
| Child | 14183510 | US |
