YANKEE DRIER PROFILER AND CONTROL

Abstract

A coating system, a paper machine, and methods of their use are provided.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/048,593, filed Oct. 8, 2013, which claims the benefit of U.S. Provisional Application Ser. No. 61/711,462, filed Oct. 9, 2013.

BACKGROUND OF THE INVENTION

The present disclosure relates to Tissue and Towel paper making machines and, more specifically, to a process of coating a Yankee dryer and the Creping process.

A Yankee dryer is a pressure vessel used in the production of tissue paper. Yankee dryers are primarily used to remove excess moisture from pulp that is about to be converted into paper. The Yankee cylinder can be equipped with a creping blade (in combination with other forms of doctoring blades) where the cylinder is sprayed with adhesives to make the paper stick. Creping is done by scraping the mostly dried paper off the Yankee cylinder surface with the Creping Doctor Blade and thereby creping the paper. The resulting crinkle is controlled by the strength of the adhesive, the helping action of the release component of the coating, the geometry of the Doctor/Creping Blade, and the speed difference between the Yankee and final section of the paper machine and paper pulp characteristics.

BRIEF SUMMARY

The present disclosure includes a Detailed Description that is segregated into three general parts. Part 1 covers, inter alia, a plurality of instruments combined to directly analyze the applied coating to the Yankee drier surface by optical methods. Accordingly, the present disclosure provides for a scanning array of instruments driven back and forth across the surface of the Yankee drier cylinder. This scanning array of instruments includes the following: (i) topography and thickness detecting instrument consisting of a CCD camera microscope and laser source; (ii) a UV-VIS-NIR 200 nm through 1000 nm spectrometer and light source; (iii) a NIR 1000 nm through 2500 nm spectrometer and light source; and (iv) an IR temperature detecting spectrometer.

Part 2 covers, inter alia, a plurality of sensing blocks mounted to the creping blade holder to directly analyze the creping process. Accordingly, the present disclosure also provides for mounting multiple sensor blocks (every few inches) along the creping blade. Each sensor block measures vibration, pressure, and temperature at multiple points along the creping blade.

Part 3 covers, inter alia, a roll-up moisture detecting camera to directly analyze the final moisture content in the finished product. Accordingly, the present disclosure also provides for mounting a moisture detecting camera over the final roll-up station to determine the final moisture content of the tissue product just made.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

FIG. 1 (“Zero Coating Thickness (Uncoated Plate)”) shows a spectrum from 200 nm to 1000 nm under ultraviolet long wave spectrum wherein uncoated stainless steel @16 Ra is used as a reference.

FIG. 2 shows a spectrum wherein stainless steel @16 Ra is used and coated with 0.5 mils adhesive component.

FIG. 3 shows a spectrum wherein stainless steel @16 Ra is used and coated with 0.8 mils adhesive component.

FIG. 4 shows the overview of the system components.

FIG. 5 illustrates the absorption of water in the NIR spectrum through 2500 nm.

FIG. 6 illustrates the components of the Coating Thickness, Topography, and Rheology instruments, and illustrates the layout of the microscope and CCD imaging camera combined with the laser block component, for action on Yankee cylinder.

FIG. 7 illustrates the layout of the dual laser source block and components.

FIG. 8 illustrates the layout of the microscope and CCD imaging camera.

FIGS. 9a to 9f illustrate the results of the coating measurements from FIG. 6.

FIG. 9a+b illustrates the results of the coating measurements at zero mils thickness (uncoated plate) (FIG. 9b—red and blue lasers).

FIG. 9c+d illustrates the results of the coating measurements at 0.5 mils thickness (FIG. 9d—red and blue lasers).

FIG. 9e+f illustrates the results of the coating measurements at 0.8 mils thickness (FIG. 9f—red and blue lasers).

FIG. 10 illustrates the Yankee dryer coating system (Coating Application Manifold/Spraying System).

FIG. 11 illustrates a control scheme to correct defects in the coating process of the Yankee cylinder and, more particularly, the movement of the coating spray wand rebuild/repair mechanism.

FIG. 12 illustrates the laser topography scheme for beams bouncing off an uncoated Yankee drier.

FIG. 13 illustrates the laser topography scheme for beams bouncing off a coated Yankee drier (n=1.5).

FIG. 14 shows the actual screen capture of the laser spots generated on a moving coated Yankee drier surface.

FIG. 15 (top): Shows the spectrometer at zero absorption and the light sources and the stored spectrum for BaSO4 (optically flat).

FIG. 15 (bottom): Shows the reflectance pattern for stainless steel at 16 Ra (similar to an uncoated Yankee surface).

FIG. 16 illustrates an enclosed scanning instrument array including a Topography, Thickness Sensor, The UV-VIS-NIR 200 nm thru 1000 nm Spectrometer, the NIR 1000 nm thru 2500 nm Spectrometer, and IR Temperature Sensors.

FIG. 17 illustrates an interior view of the scanning instrument array of FIG. 16 and the associated air purge action. Collectively, FIGS. 16 and 17 illustrate a scanning instrument array comprising: (i) a topography and thickness detecting instrument comprising a CCD camera microscope and laser source; (ii) A UV-VIS-NIR 200 nm through 1000 nm spectrometer and light source; (iii) a NIR 1000 nm through 2500 nm spectrometer and light source; and (iv) an IR temperature detecting spectrometer.

FIG. 18 illustrates Blade Pressure by Hall Effect Device with Piezio Device for Vibration Pick-up.

FIG. 19 illustrates Blade Pressure by Capacitive Load Cell Device with Piezio Device for Vibration Pick-up.

FIG. 20 illustrates Blade Pressure by Standard Load Cell Device with Piezio Device for Vibration Pick-up.

FIG. 21 illustrates Blade Pressure by Capacitive Plate Device with Piezio Device for Vibration Pick-up.

FIG. 22 illustrates Blade Pressure by LED Intensity Device with Piezio Device for Vibration Pick-up.

FIG. 23 illustrates NIR Spectrometer (for Moisture content) and Temperature sensor moving back and forth across the Final Roll-up Station.

FIG. 24 illustrates Data Cell management of mapped (profiled) data derived from the plurality of instruments in the scanning array driven back and forth across Yankee drier surface at 0.1 inch per cell.

FIG. 25 illustrates the effect of the spot image change, due thickness changes, of an applied coating to a reflective surface.

FIGS. 26a and 26b illustrate the use of multiple sensor blocks to monitor the creping blade conditions, where each sensor component may comprise a pressure sensor, a vibration sensor, a temperature sensor, or combinations thereof.

DETAILED DESCRIPTION

Part 1: Yankee Drier Adhesive/Release Topography, Thickness, and Rheology Instrument.

The present disclosure provides for Yankee Dryer Adhesive and Release Coating Application. An aspect of the disclosure is to implement a means to measure the thickness of the applied coating on the Yankee surface. This measuring instrument will be driven back and forth across the Yankee surface to accurately profile the applied coating thickness (depth) across the Yankee surface in contiguous 0.1 inch increments. The accuracy of the applied coating thickness can be determined to a level of 0.00005 inches or better. It is further disclosed that a profile of the entire Yankee drier surface topography can be measured with this same instrument to an accuracy of 0.000036 inches. The Rheology of the applied coating can be determined from comparing the coating thickness results of a linear grouping of the data cells (0.1 inch each) after each pass of the instrument array across the Yankee to a level of 0.0001 inches or better. Rheology will be a result of the condition of the coating substance expressed in a change in thickness due to flow, caused by stress, but will be a result of the degree of cross linking between polymer chains and the coating moisture content. These properties will be determined by spectroscopic evaluation discussed later in this disclosure. The instrument employs common laws of physics governing reflection vs refraction of light rays passing into a translucent medium from air, and then reflecting off of the Yankee surface and finally refracting back out again exiting the applied coating. Whereas the light from two lasers, one at 670 nm and one at 440 nm, are combined through mirrors and beam-splitters into one dual wavelength beam (FIG. 7). A 0.01 inch to 0.04 inch aperture is utilized to minimize the beam diameter as focused onto the coated Yankee Surface at a beam entry angle of incidence of >=40 degrees. The aperture diameter is chosen such that the smaller the beam diameter you employ will increase the dynamic range in determining the distance of the instrument to the Yankee surface (for topography of the Yankee drier surface) but at the same time will reduce the amount of volume of reflections and refractions through the coating thereby reducing the amount of data available for determining the coating thickness. An aperture of 0.025 inches seems to give the best results for the purpose of this instrument. At this angle, (≧40 degrees) nearly 80% to 90% of the emitted laser light is refracted into the coating medium. This is based on the refractive index of the applied translucent medium. Some wave patterns will be generated by the use of this aperture but they will be of less intensity than the main beam emitted and can be ignored by either adjusting the exposure time of the camera, or by setting a mathematical threshold for pixel response. It is a requirement that the quantum of laser energy emitted be known. Through the use of wavelength specific dichroic filters (BW=10 nm) and photo diode sensors, with the associated amplification circuits, the exact energies of each laser output is determined. As the laser light passes into the coating medium, it will refract through the translucent medium until is reflects off the Yankee metal surface beneath the coating. As the surface finish of the Yankee will be <25 Ra to 12 Ra, the light beams will reflect off of this surface in a mostly predictable manner generating a pattern of reflection relative to the finish/polish of this metal surface and modified by the thickness of the applied coating. As described in ASME B46.1, Ra is the arithmetic average of the absolute values of the profile height deviations from the mean line, recorded within the evaluation length. Simply put, Ra is the average of a set of individual measurements of a surfaces peaks and valleys. Reveal the Ra formula for more insight:

$\mathrm{Ra}=\left(1/L\right){\int }_0^LZ\left(x\right)x$

Some portion of the reflected rays will reflect at different angles than expected due to imperfections (hills and valleys) in the Yankee surface topography (finish) at its current state of polish (Ra value). Even as the Yankee surface becomes more smooth over time, there will always be microscopic defects in the surface which will cause these random reflection patterns relative to the current Ra value. Another disclosure of this technology is based on Snell's Law. It is based on the fact that as light passes from a less optically dense medium such as air into a translucent medium (more optically dense) such as a polymer coating, is that the speed of the light from the laser source will slow down and shift toward a lower wavelength and will also change in direction slightly. This shift in direction will always be toward normal when light is entering into a more optically dense medium. Since we are using two different wavelengths (440 nm and 670 nm), there will be a slightly different resultant angle for the 440 nm beam vs the 670 nm beam. For instance, for a visible wavelength beam entering water (refractive index of n=1.333) at an angle of 42 degrees, the resultant refraction angle entering the water from air would be 30 degrees (sin̂−1(sin 42×1/1.33=30.2)) shifted toward normal on average. This is based on the average refractive index of 550 nm with n=1.333. Depending on the wavelength it will be slightly different for 440 nm vs 670 nm which is n=1.337 and n=1.331 respectively for water. The difference is easily calculated by Snell's Law where sin L×n=sin L×n. The refractive index of the coating should be between 1.333 and 1.6, however, the differences in refractive index (n) between different wavelengths is mentioned here only for reference implying that the actual refraction patterns will differ slightly blue to red. When the laser light beam reflects off of the Yankee surface through the coating, the exact opposite condition results. The internal angle of 30 degrees, travelling through the applied coating, from the refracted initial beam of 42 degrees, will now hit the surface of the coating where 6% of the light will be reflected at 30 degrees again and 96% of this resultant beam will be refracted, and exit the coating medium at 49 degrees from the angle of incidence. Therefore, not only will the original image of the beams be shifted dimensionally, but it will also be dimmer when received by the pixels of the CCD camera microscope by the internal coating reflections as a percentage loss from the original beam intensities. Also, since the medium is not completely transparent, the original beam intensities will be attenuated proportional to its optical translucence properties. The polymer coating will act as a neutral density filter reducing the intensity proportional to its refracted path length through the coating. The amount of change in intensity as well as the amount of dimensional shift of each resultant laser beam received by the microscope will be proportional to the thickness of the applied coating. Rather than trying to analyze individual reflections, of which there are thousands per image, the image can be compared to a reference of an uncoated metal surface of the same Ra value of surface finish. Since the reflections/refractions most often overlap each other, the overall image can be evaluated based on pixel response over an area. Since the reflectivity of the Yankee surface can vary from point to point, a correlation had to be made to compensate for this. It was found that if you determined the area of the image spot in pixels for each laser (440 nm and 670 nm) that the integration of the total pixel responses in that area would vary, mostly in linear fashion, and inversely proportional to the thickness of the applied coating. This is independently true for all coatings tested. However, we would expect changes in pixel response to be effected by the opacity of different materials. However, this effect could be easily corrected for mathematically for a particular substance by using a reference response curve for that material. The following equation correlates the integration of pixel responses over the number of pixels taken up by the image of each spot.

CalMils=a known calibration thickness ex. 1.0 mils

@ ref thickness=refers to a value @ CalMils

Slope Blue Size Thickness=((ln(CalMils)−0)/((Blue size coated thickness@ref thickness×Blue integrated responses@ref thickness)−(Blue size uncoated@0 mils thickness×Blue integrated responses@0 mils thickness))

Offset Blue Size Thickness=ln(CalMils)−(Slope Blue Size Thickness×Blue size coated @ref thickness×Blue integrated responses@ref thickness))

Slope Red Size Thickness=((ln(CalMils)−0)/((Red size coated@ref thickness×Red integrated responses@Ref thickness)−(Red size uncoated@0 mils thickness×Red integrated responses@0 mils thickness))

Offset Red Size Thickness=ln(CalMils)−(Slope Red Size Thickness×Red size coated @ref thickness×Red integrated responses@ref thickness))

Log 10 (Blue Laser Thickness)=(((Blue size@current thickness×Blue integrated responses@current thickness)×Slope Blue Size Thickness)+Offset Blue Size Thickness)/1000

Log 10 (Red Laser Thickness)=(((Red size@current thickness×Red integrated responses@current thickness)×Slope Red Size Thickness)+Offset Red Size Thickness)/1000

These equations closely correlate to actual thickness in inches. However, if necessary, it can be adjusted simply by:

Coating Thickness=(Coating Thickness*slope or gain)+offset

Or

Coating Thickness=Coating Thickness+some offset (Such as −0.00005 mils, which is the current noise floor of the system)

A plotted curve can be made at known thicknesses in order to have fixed reference points while calculating with the equations above to determine thicknesses between known points.

FIG. 12 depicts an uncoated Yankee cylinder where the dual beam laser source reflects off of the surface of the Yankee drier. Since there is not any coating present, 100% of the emitted light will reflect toward the microscope. The degree of dispersion of the reflected beam will coinside with the value Ra surface finish of the current state of the Yankee drier surface. The greater the Ra value, the greater the dispersion will be.

FIG. 13 depicts a more typical situation where as the Surface of the Yankee drier has had a coating applied. The angle of incidense is set to 45 degrees to keep the mathematical explanation simple.

The laser source emits a beam of 440 nm and 670 nm of stable known energy. The dual beam will first encounter the upper coating surface where about 80% to 90% of the laser energy will be refracted into the coating. According to Snell's Law, @ a refractive index of n=1.5, the angle of refraction will be 28 degrees toward the normal of the entering beam. It will then reflect off of the Yankee drier surface back through the coating. This angle of reflection off of the Yankee drier surface will also be at 28 degrees and heading toward the coating surface where about 80% to 90% of this beam will be refracted out of the coating. The angle of refraction exits the coating at 45.24 degrees and shifted by 2×Tan (28 degrees)×the thickness of the coating (for example 0.001 inches thick). At a coating thickness of 1.0 mils or 0.001 inches thick, this would mean a total shift of about 1.0 mils to the left and coupled with the refraction, there will be a total shift of approximately 0.051 inches in the direction away from the laser source when viewed by the microscope verses no shift at all if the coating was not present. Since the beam is not a single particle of light, but is a two dimensional beam, an overlapping of the forward most point of the spot and the rear most point of the spot, will cause an eleogation of the spot as seen by the microscope. This is because part of the beam is being reflected (10% to 20%), which is not shifted, and approximately 80% to 90% of the contributing image is refracted and shifted. There will always be some loss from reflection inside the coating and some of the intensity will be lost due to decreased optical translucency of the coating, as it will act like a neutral density filter. However, what is evident is that the image will become more elongated as the coating thickness increases because of the overlap caused by refraction bending away from the laser source direction combining with the percentage of reflected rays.

Compensation for changes in laser intensity is required to modify the results as well as changes in exposure time of the CCD camera, and any focus adjustments.

The reason we are using two lasers of different wavelengths is due to the fact that different wavelengths reflect differently from different materials. The reflected spot patterns generated from each laser are different (FIG. 14) however, the equations above hold true for both. In other words even though the spot sizes and characteristics maybe different and the integrated pixel responses may be different as perceived by the CCD imaging array, the relationship of integrated pixel response to pixel area of the spot holds true regardless of the wavelengths used.

Another disclosure of this invention is the ability to determine the distance to the Yankee surface from the instrument imaging microscope device. If you first determine the center of the spot image of each laser as by evaluating pixel responses to a threshold by row and column, it is found that since the angle of incidence is known and constant, the center of the evaluated spot image can be determined. This location of the spot center is directly correlated to the distance from the image obtained on the CCD to the Yankee surface plus the evaluated coating thickness measurement. This can be easily translated from the change in the location of the image center, received on the CCD at some known distance, to any changed distance to and from the referenced center location. A correlation is then made by measuring the changes in distance of the Yankee surface closer and further away from the Instrument using a dial indicator to detect changes in distance. The number of pixels changed on the CCD per known movement in mils will correspond. Changes in distance to the Yankee are then determined accurately. This data is then used to profile the topography of the Yankee surface as the instrument array is driven back and forth cross the Yankee Drier. Not only can the Yankee surface topography be profiled in real time, but this current topography can be compared to earlier topography results so that the Yankee surface wear can be monitored and be made available for customer review. Also, the Rheology of the polymer coating can be determined in the same way. By comparing current scan pass data cells, and those from previous Yankee drier scans at the same location, non-Newtonian moment of the polymer coating is determined. Since the differences between data cells, current scans to previous scans, can be used to determine the flow of the polymer, the degree of stress applied to the coating can also be determined. The resolution of the data cells is, again, 0.1 inch for any position across the entire width of the Yankee drier surface.

UV-VIS-NIR Spectrometer for Coating Absorption and Fluorescence

A further aspect of the present disclosure relates to measuring the coating absorption and fluorescence properties in detecting the Yankee dryer adhesive/release coating thickness and coating quality using an industrialized Ultraviolet Visible Near-Infrared (UV-VIS-NIR) spectrometer. The present disclosure provides an industrialized UV-VIS-NIR spectrometer which can optically analyze the adhesive/release coating thickness as well as the quality of the adhesive/release coating applied. The light source used, for this absorption and florescence spectrometer, is comprised of 20 to 30 different LED's, chosen at various wavelengths to insure that a consistent and constant radiant energy is produced across the entire spectrum of the spectrometer range of 200 nm to 1000 nm. The LED's are liquid cooled to remove the heat produced from this process. Each LED is independently controlled for the radiant energy it produces and is verified and servo controlled by the use of dedicated photo diodes and associated amplifier and control circuits for each. The UV-VIS-NIR spectrometer will be driven back and forth (left to right) across, and at a distance of about 6 to 8 inches from the Yankee dryer surface, yielding the actual coating quality/thickness for each 0.1 inch of linear movement across the surface. A different Infra-Red Detector will yield an accurate temperature profile, 20 scans per second, for the entire surface. As the incoming absorption bands shift with temperature fluctuations, the temperature of the reference spectra, which it will be compared to, will have to be corrected for temperature fluctuations. This is easily done by comparing the incoming absorption plot to a reference plot of the coating created in memory, where there must be a slope and offset created for the adjustment for each pixel (0.25 nm) based on temperature drift. These reference absorption curves are created by running absorption scans of the individual (pure) coating components at two different temperatures. The first temperature is at the lowest expected temperature while the second calibration temperature is at the highest expected temperature. Then for each pixel of the absorption band (0.25 nm), the true corrected pixel response for each pixel can be calculated from the reference scans, and corrected for the current temperature of the Yankee surface, as follows:

For each pixel (approx. 0.025 nm each pixel from 200 nm to 1000 nm)

For example: Component #1=Adhesive

Slope for Adhesive=(Pixel Response at High Temp−Pixel Response at Low Temp)/(Temp High−Temp Low)

Offset for Adhesive=Pixel Response at High Temp−(Slope for Adhesive×Temp High)

Then as the new absorption pixels come in, The pixels for the reference plots in memory are adjusted for the current temperatures for the adhesive and release components, and are recalculated for the proper pixel values at the current Yankee Temperature as follows:

For each reference pixel for the calibration plots Adhesive and release separately (approx. 0.025 nm each pixel from 200 nm to 1000 nm)

New Reference Pixel Response Adhesive=(Slope for Adhesive×Current Yankee Temperature)+Offset for Adhesive

Likewise:

New Reference Pixel Response Release=(Slope for Release×Current Yankee Temperature)+Offset for Release

This series of temperature corrections must be done on each pixel (0.25 nm) for each component of the Coating Mix. It is important to point out here that the applied coating is a mixture of several components. Since the Component Mixture Applied is determined by the control mechanism of this system (pump addition rates for each component), the percentages/concentrations of each component are used to create a master component absorption curve for reference to compare the actual incoming absorption curve of the coating being applied. This is done by calculating each pixel as a percentage contribution of each component in the applied mix, based on the flow rates of each component of the applied coating. But before that can be done, it is necessary to calculate absorption contribution of each component pixel response (0.025 nm/pixel) based on the concentration of each component at different concentrations. According to Beer's Law, this will be linear by concentration, but will also vary linearly by the thickness of the applied coating determined at any point a spectrum is taken along the Yankee cylinder.

Beer's Law=A(λ)=log (100/% T)=2.000−log (% T).

Beer's Law states that the absorbance, A(λ), of a species at a particular wavelength of electromagnetic radiation, λ, is proportional to the concentration, c, of the absorbing species and to the length of the path, l, of the electromagnetic radiation through the sample containing the absorbing species. This can be written in the form:

A(λ)=e(λ)lc

The proportionality constant e(λ) is called the absorptivity of the species at the wavelength, λ. The path length here, for the purposes of this invention (l), is the applied coating thickness as evaluated by the Thickness/Topography Instrument described earlier.

Again, we must correct the reference pixels for the actual concentrations of each component in the applied coating, as well as adjusting the reference absorption curve for the applied thickness at any point along the Yankee surface scanned. It was necessary to obtain the spectra of two known concentrations for each component of the applied mix, at a constant thickness for both, and at a constant temperature for both. According to Beer's Law above, a linear relationship exists such that a slope and offset can be calculated per pixel (1 pixel=0.025 nm) to modify the reference absorption curve, per pixel, based on the actual addition rate for any component in the applied coating. The addition rate of each component is a function of this control.

Absorption value for concentration Slope=((A(λ) at high c)−(A(λ) at low c))/(high c−low c)

Absorption value for concentration Offset=(A(λ) at high c)−((high c)×Slope)

Therefore, the reference absorbance value at any pixel (every 0.025 nm) is as follows and corrected for concentration and temperature:

Reference Absorption A(λ)@the current [c] for each pixel=((concentration Slope×(Calculated [c] from current addition rate of component))+concentration Offset

Then we must correct the referenced absorption value per pixel for path cell length. The spectrometer light source will be passing into the coating, then will be reflected back out of the coating or two passes through the coating thickness. However, the reference spectra were also obtained in this same manner. Therefore, we just have the difference of the current coating thickness vs. the thickness of the coatings used to make the reference absorption curves.

Corrected absorption A(λ) per pixel for coating thickness=(Reference Absorption A(λ)@the current [c] for each pixel)×(Current Coating Thickness/Coating thickness for the reference)

This presents us with a perfect representation of what the absorption curve should look like corrected for temperature, concentration and topography/thickness of the current coating component at that particular point across the Yankee surface. The procedure thus far has created a reference absorption curve for each component only. We must add these individual pixel responses (0.025 nm) for each component curve together to get the cumulative reference curve to be compared to the incoming scan of all of the components in the applied coating mix.

Total Pixel Response per pixel from all components=Contribution from Adhesive component+Contribution from Release component+Contribution from Plasticizer component+Contribution from MAP component+Contribution from˜etc.

This will yield an actual reference absorption curve that will reflect ideal conditions at the current temperature of the process and at the appropriate mix concentrations of each component in that mix. It is the tiny differences between the ideal reference absorption scan, which we just calculated, and the actual incoming absorption scan. For instance, if the absorption indicates that the concentration of the incoming scan is to too low or too high in places, this would indicate a problem with another part of the paper making process. Our system control mechanism could then add or subtract a component in that area. If the incoming absorption band for the adhesive would shift slightly toward lower energy, the degree of cross linkage between polymer chains may have decreased resulting in a coating temper problem. Even though the thickness may be sufficient, the quality of that coating in that area may not be of proper quality. These small differences from the incoming absorption curve, from our calculated reference curve, are what matter. The relevance of this invention is to recognize the need to evaluate the quality of the coating applied by evaluating these small differences and to effect changes in the process to achieve the proper chemical characteristics, of the applied coating mix in order to prevent excessive blade wear and improve the quality of the coating resulting in a better quality paper product while reducing the cost to do so. The resolution of 0.1 inches across the Yankee will provide an overall picture of the paper making process on a microscopic level. It will allow us to make the proper decisions in order to correct and control the coating process on a molecular/microscopic level as well.

As a function of Beer's Law, rearranging the equation:

A(λ)=e(λ)lc

to

I=A(λ)/e(λ)c

The actual coating thickness, obtained from the Topography instrument, can thus be verified directly from the absorption curve obtained from the spectrometers.

NIR Spectroscopy 1000 nm to 2500 nm (14000-4000 cm⁻¹)

A further disclosure of the invention is the use of a NIR spectrometer to detect and measure the amount of moisture (H₂O) embedded in the coating. Water has strong absorption bands at bands centered at 1450, 1940, and 2500 nm, with important secondary absorptions at 980 nm, and 1240 nm (Carter, 1991). For the purpose of clarification we will examine the absorption band of 1920 to 1950 nm. Absorption follows the formula; a*v1+v2+b*v3 where a+b=1. Specifically, v1 is symmetrical stretch of the H—O—H water molecule bonding distance of the hydrogen atoms from the Oxygen atom at its center. The v2 is a measure of a changing bond angle from the normal 104.4 degrees at 20 C. Finally, v3 is the asymmetrical stretch where the Hydrogen atoms are in stretch mode but one Hydrogen atom is stretching toward the Oxygen atom and the other away from it. There are many absorption bands for liquid water and they all absorb in a similar manner. Documentation on this is extensive.

The disclosure here is the use of this in order to determine the water (moisture) content of the adhesive component of the coating in real time. The coating will become too hard if there is not a sufficient moisture content. The continuous introduction of paper fiber and ash will also affect the coatings ability to maintain a proper moisture content. The temper of the coating is important. If it becomes too hard (too little moisture) it will cause excessive wear on the creping blades and the coating will not be tacky enough at the roll-nip for adhesion of the paper. The coating will also lose its durability, become brittle and could exhibit cracking. In the case the opposite condition is true, too much water, the adhesive will become jelly like and not adhere to the paper at the roll-nip. It will lose its ability to protect the Yankee cylinder from the damaging effects caused by the creping blade. The overall creping quality will diminish. Knowing and maintaining a proper moisture content will create a coating with good temper and durability. By adjusting the coating component mixture, Introducing the use of plasticizers into the component mix, and/or the use of a driven auxiliary spray wand to fix defective areas, it will be possible to maintain and repair defective areas and maintain the overall quality of the coating temper.

Construction and Components Used in the Scanning Instrument Array

A coating inspection system of the present disclosure may consist of a temperature and humidity controlled NEMA 12 enclosure which will house the instruments described previously. The Instrument housing will be sealed, air tight and water/moisture proof. The atmosphere inside will be liquid cooled and heated in order to maintain a constant temperature of 70 F+/−0.5 F at all times and the atmosphere inside of the housing will be continuously circulated over a bed of replaceable anhydrous CaCl₂ in order to maintain a nearly zero percent humidity. Humidity sensors as well as temperature sensors will be installed inside the scanning head housing in order to give feedback of the internal environmental conditions of the sealed instrument array. The Instrument array will travel back and forth on a lubricated linear ball and guide assembly. The linear ball and guide bars may be made of stainless steel for the shafting with powder coated support beams. The linear ball screws may be continuously lubricated in order to dissolve any build up of sprayed chemicals. A quadrature encoder is provided to track the position of the Yankee dryer instrument array to within about 0.001 inch while traversing the Yankee drier surface during scanning and measuring. Also, a quadrature encoder to track the position of the Yankee dryer rotation and position to a resolution of 0.15 degrees or 0.212 inches of rotation on its surface movement. The assembly can handle dirty environments and ambient temperatures up to 250° F. The radiant intensity controlled UV through NIR Light Sources (200 nm through 2500 nm) for this spectrometer is accomplished by using a combination of 20 to 30 different LED's of different wavelengths and a replaceable incandescent light source. These sources will employ variable power in order to maintain a constant and flat radiant power over the entire range of these spectrometers. Complete temperature profiling of the Yankee Dryer surface will be accomplished by using two infra-red temperature detectors mounted on the scanning instrument array. A 200 nm through 1000 nm spectrometer is provided, which will cover from ultra violet through the entire visual range and into the near infrared, wherein the resolution of the spectrometer is 0.3 nm. A 1000 nm through 2500 nm spectrometer will be used to determine the moisture content of the applied coating wherein the resolution of the spectrometer is 3 nm. A stepper motor drive and electronics will be used for positioning the inspection station to within about 0.001 inch. Clean filtered and electronically monitored air purging pump will be used to keep the lenses clean and debris out of the scanning instrument array. Plant air is dirty and costly, thus controlling the quality of the scanning instrument array purging air by employing electronics to monitor the system for proper flow and filter condition is critical. The intake for this purging air pump will be drawn from outside of the facility to insure the intake supply is as clean as possible to start with. The instrument array is liquid cooled and liquid heated using a filtered coolant and containment tank which will contain antifreeze. This coolant will be heated and cooled as required to maintain proper temperature for the instrument array. The coolant will be pumped through the scanning instrument array to insure that the proper temperatures are maintained. The flow rate of the cooling liquid will be monitored with a pulse type flow meter. This chilled antifreeze will also keep the electronics cool in the main control cabinet. A master pulsed type flow meter and pressure gauge for the incoming process coating manifold will provide feedback to the control and will reflect the current amount of coating being applied as well as providing feedback on changes to the coating addition rates in order to control the coating component mix ratios. The entire scanning instrument array will be supported over its length by using a truss structure which will support the weight of the scanning array and maintain alignment while the instrument array is traversing the Yankee drier. The instrument array housing and truss structure will be entirely encased in a stainless housing to keep the debris, water, and paper out of the linear guide assembly and scanning instrument array contained within. There will be a small opening where the filtered purging air will flow out toward the Yankee drier and provide a positive air pressure for the open area where the scanning instruments peer out. This will keep the lenses clean and free of the process debris.

The Main Control Cabinet Components

The main control cabinet will house multiple networked PC type computers. These will be a minimum of 8 cores each and operate at clock speeds of 5 GHz or faster. The processors will be liquid cooled. The electronics for controlling the instrument array and other devices will be installed in this cabinet also. The cabinet will also be NEMA 12 and will be cooled with an air conditioning unit. The main control will be equipped with a remote operators station which will allow the operator to control and see the operations of this system remotely. The operator will be able to access all function of the unit from this remote control console.

The Control/Coating Correction Mechanisms

The purpose of this invention is to correct blade wear, create and maintain a quality coating which will yield a higher quality crepe paper product. The secondary goal is to reduce chemical and operating cost by applying the chemical coating mix in a more efficient, meaningful manor based on actual real time analysis of the applied coating quality. Based on the data collected from the plurality of instruments in a scanning array, the overall applied coating component mix will be adjusted in order to maintain the best mix for the product being made under the current operating conditions. Individual control of the release, adhesive, MAP, and plasticizers will be implemented by adjusting addition rates of each addition pump. For example, if the coating adhesive component is found to be too thin, then the addition pump for the adhesive component pump speed will increase slightly which will increase the amount of this component applied to the Yankee drier surface. It will be varied as required to maintain a proper thickness and maintain the proper coating temper. If the coating moisture content is insufficient and the coating is becoming too hard, a plasticizer component addition rate will be automatically increased to correct this problem. Each additive component addition rate will be adjusted independently to correct deficiencies over the Yankee drier surface. These decisions will all be based on the results of the plurality of instruments used in the scanning array as it moves back and forth across the Yankee drier.

Also, Problem areas, areas of the Yankee drier surface that are not typical of the overall condition of the Yankee drier surface will be repaired by implementing a single component addition wand. This will employ a proportional valve to vary the level of an addition component in an area that needs repair. The repair wand will be driven back and forth to these troubled locations where a more concentrated solution of adhesive or release component can be sprayed onto those areas building up and repairing these areas as needed. The repair quality will be evaluated as the scanning of this multiple instrument array passes back over those areas in successive scans. The operator will be shown graphically where these areas are being automatically repaired by this machine. The position of the scanning instrument array, the current position of any repair wands, all component addition rates, and a complete overall graphical depiction of the current state of the coating process at a resolution of 0.1 inches, will be shown graphically on monitors at the remote operators control station.

All process temperatures, component addition flow rates, component tank levels, process conditions for the applied coating across the Yankee drier surface, will also be shown graphically. Audio alarms will sound to indicate any parameter that is out of limits and these alarms will be date and time stamped and then saved to permanent record on the system hard drive. All items requiring maintenance will be presented to the operator so that these issues can be resolved.

Part 2: A Further Description of Implementing Sensors in Order to Monitor the Creping Process

In the diagrams presented below, a holder houses the Creping Blade, which is a type of doctoring blade, and applies pressure, at some critical angle, to the blade edge against the Yankee drier cylinder. The pressure and angle of the blade against the Yankee Drier is critical and is adjustable at determined points across the length of the blade. As these blades wear, their effect on the Polymer Coated Yankee Drier Surface and the Creping Blade's ability to affect the proper folding of the tissue as it hits the edge of this Creping blade diminishes. Therefore, it becomes necessary to monitor this part of the tissue process. It is also important to monitor the effects of the creping process along the entire length of the blade by implementing a plurality of sensor blocks every few inches. Each sensor block will consist of a blade pressure sensor, a temperature sensor, and a vibration sensor as well as a transmitter to transmit the sensor data back to a receiving unit. This sensor block data will be encoded by an addressable serial number, for each block. This serial number will tell the receiving unit which block is transmitting as well as the position of that sensor block along the blade. The individual sensors are described further on in this document. The important aspect here is to describe the importance of having multiple sensor blocks along the entire blade. For instance, if the blade were to bite through the protective coating 5 feet downstream of a temperature sensor, the heat transfer through the blade to a distant heat sensor would never occur, and never be detected. The distance between the defective area, where the blade is rubbing against the metal of the Yankee drier surface, and the temperature sensor is too great, the blade between these two points is being cooled by departing this energy against the normally coated and protected area of the Yankee drier surface. The heat transfer between the two critical points, between the problem area and the temperature sensor, would never occur because the blade section between these two points is being cooled. Therefore, applying sensors every few inches is required as the process conditions vary, inch to inch, along the entire Yankee drier surface. The same scenario holds true for blade pressures as well as vibrational frequencies, hence, the need to have multiple sensor blocks across the creping blade is an important part of this disclosure. The technology for each type of sensor contained within a sensor block will be described later in this document.

A Further Description of the Creping Blade Sensor Block Components

A measurement of the folding process (as the tissue hits the Creping Blade) is normally expressed in folds per inch. As the proper number of folds per inch (FPI) increases beyond a desired target FPI, the Tissue will become weak, losing its strength properties, diminishing inter-fiber bonding to a level that is unacceptable. Conversely, if the FPI decreases, the pliability of the product will diminish causing the product to be not as soft as would be desired. Maintaining the desired equilibrium is important. Being able to measure the FPT every few inches across the creping blade, is a required aspect of this disclosure. Since the Tissue Paper is traveling at a speed of around 1232 inches per second, or at about 70 miles an hour, when it encounters the Creping Blade edge, the energy departed onto the Creping Blade edge is substantial. This is evident at how quickly the edges, of the blade, wear even though the edges are made of hardened metal alloy tips. When conditions are just right for this process, it is said that the tissue will explode at the Creping Blade. Under this principle, the Creping process will carry this vibrational (explosion rate) energy from the tip of the blade to its absorbing point, which is the holder. During this process, the plane (width) of the blade is going to oscillate as the energy waves, via the creping process, move through it. These waves will be at a frequency which equals this explosion frequency or a harmonic there of. In other words, the creping blade will act as a speaker humming a tune equivalent to the folds per inch of the Creping process. The creping blade will also produce a lot of frequencies not directly associated to the FPI. Installing a piezoelectric microphone device, or a Hall Effect sensor, or an accelerometer sensor near, or in close contact, along the oscillating plane of the blade will enable one to measure these frequencies. Implementing a dual twin T notch type of filtering on the raw analog signals (removes unwanted frequencies, which will simplify the equations) and further applying Fast Fourier Transforms on the measures of data received will enable the derivation of the FPI (Folds/Inch) of the Tissue creping process.

As the blades increase in wear, a noticeable temperature change will occur due to the corresponding changes in friction experienced by the blade. Placing temperature detectors along the length of the Blade Planes will indicate the amount of wear as temperature differentials move across the blade plane. These will be reported by the individual sensor blocks. In addition, if the Doctor Blade cuts through the applied coating on the Yankee drier surface, the temperature rise at any sensor location will be quickly dramatic, indicating the need for the immediate attention of the operator in that sensor block location. This will emanate as an audio alarm and an appropriate text message and graphic display for the operator.

The force of the blade assembly across the entire length of the Yankee Drier needs to be monitored with multiple sensor blocks. If the force exerted on the Blades is not correct at a particular location, or if a hot spot develops during production, damage to the coating and or Yankee Drier Surfaces in that area will occur. The force exerted on the blade and the blade assembly (holder) will cause a deflection on the blade plane over its width. Changes on this pressure during the process will occur as the blades wear but also could arise for other reasons as well. For instance, if a wet spot is encountered in the tissue web. This condition will soften the coating slightly thereby decreasing the blade force slightly in those sensor block areas. The location of these defects will be graphically displayed as sensor block locations which are in alarm state or out of running specifications. Many conditions can change this force in production, for instance, the Yankee will have an out of roundness within specifications. The out of roundness will cause a rhythmic oscillation in blade pressure detected as the Yankee drier rotates. However, for the purposes of this invention, it is sufficient to say that changes will occur and that those changes will need to be monitored along the entire length of the blade through the use of multiple sensor blocks.

FIG. 18 describes the implementation of a Hall Effect Sensor. The Hall Effect Method takes advantage of a changing blade deflection. This causes the blade assemble to become closer, or farther away, from the fixed magnets. As this happens, a measurable disturbance should occur in the magnetic flux generated by the magnets as received on the Hall Effect Sensor. The sensor is designed to read changes in magnetic flux.

FIG. 19 describes the implementation of a Capacitive Load Cell Sensor. The Capacitive Load Cell works by passing a proportional amount of the square wave charging the outside plates to the center plate. If the outer plates are charged with a square wave at approximately 500 kHz to 1 MHz, and where these square waves are simply out of phase or phase shifted by 90 degrees from each other, then at zero deflection of the inner plate, the resulting signal output on the middle plate should be 45 degrees phase shifted position between the upper and lower plates. As the middle plate deflects toward the upper plate due to load, the phase shift of the middle plate will shift toward that of the phase of the upper plate. If the deflection is negative, the phase shift on the middle plate will shift in the direction of the lower plate.

FIG. 20 describes the implementation of a Load Cell Sensor. The use of Load Cells is a very accurate way to measure the deflection and forces on the blade directly. It works by measuring force by deflecting a strain gauge printed on a metal form. There use is well documented in the literature and as they are a standard industrial method of measuring force, we will not go into further detail about this method since it is obvious.

FIG. 21 describes the implementation of a Capacitive Plate Sensor. The Capacitive Plate method uses the property where two plates will transfer a charge based on the dielectric constant and the distance between two plates. Since the dielectric constant is equal to 1 for air, the distance between the Creping Blade and the charging plate will be a direct function of the degree of deflection between the charging plate and the Creping blade. Therefore, this method is feasible. The system will vary with changes in temperature so a temperature correction mechanism will be used. Also, since the air in a paper mill is extremely humid, and considering that the dielectric constant of water is 80.1 (at 20 C) compared to that of air which is 1, compensation for the humidity of the water vapor between the blade and the charging plate will be required as well.

FIG. 22 Describes the implementation of an LED Sensor. The LED intensity method is also very feasible. This works by sending out a quantum energy of light, which will bounce off of the Creping Blade surface and then be received by the photo diode receiver. As the force on the Creping blade causes deflection, the distance between the Creping blade and the emitter-receiver pair will change. This will present a measurable change in signal, which is proportional, but not linear, to the deflection.

As is now apparent, there are several ways this can be monitored. A Hall Effect sensor, to measure changes in magnetic field, could be used. Creating a magnetic field above and below the Blades assembly will initiate measurable disturbances in that field as blade deflection occurs. This assumes an Iron component to the metallurgy of the blades.

Load cells could be installed which, as deflection occurs, will cause a proportional force to be applied on the load cell device. Placing load cells every few inches along the Blade planes should give accurate description of the blade pressures at any point.

Capacitive change type of detection can be used which works on the principle of changing the distance of the gap between two or more plates will change the microfarad value. If the Creping Blade acts as one plate while another plate mounted above the blade acts as a charged reference, and as the blade deflects due to a changing pressure, the capacitor value of these plates will change proportionally, but not linear. This change can be measured and amplified.

Finally, a changing light intensity can be employed, which will measure the changing distance between the Creping blade and the emitter-receiver pair. This changing distance is proportional to the force on the blade assembly. This change in signal is also not linear.

Part 3: Roll Up Inspection Station

FIG. 23 Describes the implementation of a moisture detecting spectrometer. This station will consist of an x axis linear ball guide to transverse a moisture detecting spectrometer as descried earlier and an IR temperature sensor across the web to record the final product moisture and the temperature as the product is being rolled up. Both of these devices have been described earlier in the Yankee drier instrument array and are of the same type. They are both used in the same mode as described previously. This station includes an encoder to keep track of the linear feet contained in each roll. As the rolls are ended and a new roll is started quality reports, as well as a moisture profile of that roll, will be stored permanently on the system hard drive with a date and time stamp as well as a identifying number so that these permanent records will be available per each roll at any time thereafter. A printable version can be printed if desired by the customer.

In evaluating the residual Coating for Thickness, Topography, its Rheology, its Moisture content and chemical properties, then correlating this data to linear movement across the Yankee Drier surface, we will be able to develop a complete profile of the Yankee Drier Coated surface in real time. Minute changes in the coating Absorption Response, Topography, Temperature, Rheology, and Moisture content as well as Chemical property changes, will be reflective of the quality of the residual coating and to the quality of the tissue being made. It will enable us to vary the original recipe component concentrations in order to effect quality enhancements in the manufacturing of the tissue product in real time, while dynamically maintaining the desired quality of the coating as well. By passing a plurality of Instruments in a Scanning Array back and forth along the Yankee Drier surface, we will be able to develop an applied coating profile. This Profile will pin point problems in manufacturing process such as correcting deficient areas of Coating by adjusting the recipe, changing flow rates, sending out a repair wand to fix an area and warning the operator of problems elsewhere in the process that could affect quality or downtime. An example of the latter would be a wet spot cause by a vacuum problem on the felt or a dry spot caused by insufficient fiber content in the stock being fed at a location in the head box as well as a multitude of other process problems. In any case, correcting the issues mentioned will lead to better overall quality, decreased down time, an increase in profits, and a propensity toward longer Blade life.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting. As used in the specification and appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless otherwise indicated, the numerical properties set forth in the specification and claims are approximations that may vary depending on the desired properties sought to be obtained in embodiments of the present invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. One of ordinary skill in the art will understand that any numerical values inherently contain certain errors attributable to the measurement techniques used to ascertain the values.

Having described the disclosure in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the disclosure defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these preferred aspects of the disclosure.

Claims

1. A paper machine substantially as shown and described herein or comprising one or more of the novel features shown and described herein.

2. A method of operating a paper machine substantially as shown and described herein or comprising one or more of the novel features shown and described herein.

3. A process of coating a Yankee drier of a paper machine substantially as shown and described herein or comprising one or more of the novel features shown and described herein.