US 3399460 A
Description (OCR text may contain errors)
Z LI% LM W 5 a B1 U N8 Au Nd un 1 mF Sept. 3, 1968 3,399,460
PROCESS AND APPARATUS FOR MOISTURE CONTENT i MAX. E .FIELD CHARGE.
GENERATOR INVENTOR. GEORGE F. RUSSELL ATTORNEY United States Patent 3,399,460 PROCESS AND APPARATUS FOR MOISTURE CUN- TENT DE-PEAKING AND EQUALIZATION George F. Russell, 711 St. Helens Ave., Tacoma, Wash. 98402 Filed Aug. 15, 1966, Ser. No. 572,518 5 Claims. (Cl. 34-1) ABSTRACT OF THE DISCLOSURE Equalizing an unevenly distributed moisture content in a moving web of paper or fibre containing moisture during its primary drying process by applying thereto the selective heating effect of a high frequency alternating current field of force for de-peaking areas of moisture content above the average of the web.
My invention relates to a novel, new and commercially practicable process and apparatus for equalizing nonuniform cross machine moisture profiles in paper webs made on papermaking machines and in equalizing the moisture content in other dielectric materials containing a non-uniform moisture distribution. Since non-uniformity of moisture profiles is far more prevalent than even reasonably level ones, my invention of a process for correcting non-uniformity is novel and new to the present state of the art. My invention has commercial value and practicability and has widespread application potential in the papermaking and other fields. My invention may be termed in one of its aspects a process of de-peaking moisture high points or peaks as they occur in a web of paper across the machine direction during drying. Description of my invention will be disclosed in the specification and illustrations which follow. While the herein described invention may be applied to any papermaking or other similar process, I will describe in this specification as an illustration its application in the production of newsprint. In no Wise should the invention be limited as to process or apparatus for accomplishing the purposes of the invention only as to newsprint paper or other paper or paper products, but also is equally applicable to products such as felts or any natural or synthetic fibrous or granular product matted or woven in the form or general substance of a Web or sheet and containing water either originally or added subsequent to matting and drying.
' Other objects and advantages appear as the specification continues. The novel features of the invention will be set forth in the appended claims.
Drawing For a better understanding of my invention, reference should be made to the accompanying drawing, forming part of this specification, in which:
FIGURE 1 is a typical graph extending across the width of a dielectric sheet or web of paper or other material to be treated with radio frequency heating indicating the percentage of moisture carried by the web in spaced areas across the sheet.
FIGURE 2 is a schematic isometric representation of a two element electrode configuration in half wave cross machine mode and illustrates a dielectric web or sheet moving with respect to the electrode configuration.
While I have shown only the preferred form of my invention, it should be understood that various changes, or modifications, may be made within the scope of the annexed claims without departing from the spirit thereof.
Detailed description FIGURE 1 is representative of a cross machine direction moisture profile for a newsprint machine at a point 3,399,460 Patented Sept. 3, 1968 See ahead of the last dryer, typically of one expressed at approximately at the breaker stack position of a newsprint machine which is approximately three-fourthsof the way through the drying process. Specifically FIG- URE 1 is an interpolation of an actual cross machine moisture at the reel modified so as to represent a position on the web approximating the breaker stack position. The line A traces the profile against moisture content in percent of bone dry weight shown on the right hand edge from 8% to 13% at various positions across the web W, numbered 1 through-40 each representing an equal distance in inches from the tending side B to the drive side C. A solid line D indicating an Il /2% moisture content has been drawn across the diagram within the :boundary of the graph A and extended by a dotted line B from the position 4 on the web to the ending edge B; and extended by another dotted line F, from the position 25 to the drive edge C.
FIGURE 2 is an isometric representation of a two element electrode configuration composed by terminus T and stub leads G and H, instantaneously charged positive element I and negative element K, which form part of the configuration contacting, or if not physically contacting, energizing the paper web W traveling in the direction L and leads M and N to the associated generator RF. Between electrodes J and K a ground reference P is shown. The electric field half wave gradient Q, resident on the electrode configuration is shown extending from zero at R.F. to maximum charge position at R, the approximate end point of the half standing (or reflected) wave electrical length and the approximate mid-point of the web W to T the terminus of the configuration. The dotted lines S and U mark the approximate positions of the tending edge and the drive edge of web W in its relationship to the configuration. The base line T to RF. may be considered as a reference for amplitude from zero of the half standing or reflected wave charge. Terminus T may be varied along stubs G and H for fine adjustment of frequency for the system. The electronic element composed of the stub lead H, the electrode K and the lead N may have an instantaneously positive charge while the element composed of the stub lead G, the electrode J and the lead M, may have an instantaneously negative electric field charge, and vice versa, and this may be called a standing or reflected wave in a half standing wave mode. Each element may be considered as being the residence of or sized to accept a half standing wave of the generators frequency; or as Well the whole configuration may be termed a half standing wave configuration; whether the charge on any element is positive or negative at any instant of time.
My research on wet paper, paperboard, wood veneer and other wet webs has shown that the dielectric loss factor, or a materials ability to absorb dielectric high frequency energy from a source of high frequency alternating current which is termed occasionally radio frequency, varies in proportion to a differential of moisture in the Web. The loss factor is made up from two components, dielectric constant and power factor. A material with a low dielectric constant will generally have a small loss factor; one with a high dielectric constant generally speaking will have a higher one. The dielectric constant of heated water, for example, may be figured at an index of 60 to while the dielectric constant of wood may be only 4 or 5 as a comparison with water. Wood fibre and water in combination has relatively high blended dielectric constant such that its loss factor in a high frequency field is high. If more water, in combination with fibre, exists at one place in the web than at another, the loss factor of such an area will be found to be greater than the loss factor at a point or area of lesser moisture content. The loss factor, therefore, will vary from place to place in the web as moisture content varies. High frequency energy applied to a web of varying moisture content will tend to absorb energy in proportion to its blended index of dielectric constant times its blended power factor, which latter factor may be substantially disregarded and will result in energy being applied to a greater degree in the high loss areas, and to a lesser degree in the less high loss areas.
Further, a quality of the high frequency field of force in this application is the fields deep therapy effect. This permits the web to absorb the energy in the center of the thickness of the sheet where moisture is locked to a greater extent during drying than on the surfaces where the fibre generally Will be found drier than in the middie. This phenomenon is more noticeable in board liner or other thick webs than in newsprint or tissue, but the principle applies as well to all. Drying a web pressed against the faces of dryer rolls, first one side then the other of the web contacting successive rolls, causes a case hardening effect particularly in thick webs which tends to prevent escapement of free moisture from the center thickness of the web. R.F. energy is not conduction heat but penetrates into the whole thickness of the web.
When a wood product is subject to drying, the so-called free moisture is the first to evaporate, lastly the moisture or water held in the fibre structure sometimes referred to as hydroscopically held water. When a natural cellulose material dries to a point below about 18% as measured in percent of bone dry weight, mostly hydroscopically held water remains in the cell Walls and it is this water which has been found to be most difiicult to dislodge by heating means applied to the surface of the material sometimes called conduction heat. in combination with the quality of deep therapy of the field of force from a high frequency alternating current generator, the selectivity of the field to seek out high loss areas preferentially gives substance and technical background for the practicability of my invention.
With these factors applied to a paper web, I have invented a process of and apparatus means for de-peaking high points of moisture content in the across machine direction of the web having a variation in moisture content profile by the application thereto of a radio frequency field of force of adequate power.
A modern papermaking machine forms water and fibre into a mat in the form of a web which is passed over by suction, pressure and/or drying means for taking water out of the mixture after it comes from the wet end of the papermaking machine. Upon leaving the couch the paper Web may contain varying percentages of moisture and fibre, but for sake of illustration let us assume a 50% moisture and 50% fibre balance at that point. This, in the papermaking trade is called 50% dry. But the water in the percent of the bone dry weight of the fibre is 100%. From this point a paper web may be carried over squeeze rolls or presses of one kind or another and into a dryer section. The dryer rollers are steam-filled heated rolls five feet or more in diameter and rotating so as to accept the web adjacent to their moving surfaces, moving successively from one to another roll toward the dry end. The dryer rolls in machines vary in width from 200 to 300 inches; many of the older machines being of lesser width and some of the modern ones going to widths which exceed 300 inches. On a high speed newsprint machine there may be 40, 50 or more such dryer rolls in a newsprint making machine over which the Web passes during the course of its drying. After the paper has been dried to the desired degree, run through a calender stack and ironed smooth, it is rolled up on a large reel, transferred to a rewind machine and cut into usable widths for the ultimate consumer.
Cross machine moisture content regulation is a constant headache of the papermaker. It is desirable to get as much moisture in the sheet as is possible, for moisture improves the running condition for web presses on which newspapers are produced, plus added moisture sold by the manufacturer is found money. One percent added moisture in newsprint from a machine capable of producing 120,000 tons per year at 7% moisture will yield an additional 1,200 annual tons with no additional furnish costs. This extra production sold at $140.00 per ton will produce $168,000 per year.
On a newsprint machine, the cross machine moisture profile may vary widely from area to area because of several factors in the process of producing the web on the Fourdrinier wire or drying it after it has been formed. Stock emanating from the head box through the slice may contain more water at one point than at another along the width of the machine. Water, when drained through the Fourdrinier wire may drain non-uniformly and leave a wet streak lengthwise in any part of the web. If such a streak is wetter than the balance of the paper across the machine direction and the same amount of heating effect is applied by the dryer rolls to the entire web, a Wet streak will be left in the web at the calender stack which may cause blackening which does not disappear by moisture equalization after calendering.
Many artifices have been used to compensate for differences in cross machine moisture content such as air jets, felt conditioning, air distribution, air nozzles, hood enclosures and a myriad of devices and variations but limitations to all of these means have been found over the years and no practicable or fully satisfactory means as yet has been developed for satisfactorily equalizing the moisture content in a cross machine profile. Were a correction at the slice made to reduce the moisture content in a web streak in the center of the paper, less fibre would come out of the slice at that point and the sheet would end up thinner than the balance of the web across the machine direction. This only tends to foul up basis weight. Making changes at the slice, therefore, is no real solution to eliminating wet spots in the cross machine direction. Were the slice to remain at a constant aperture, however, to preserve consistent basis weight and means found for correcting deficiencies of moisture in one place and eliminating excess moisture in another, a uniform cross machine direction moisture profile could be obtained while simultaneously preserving a constant basis weight.
One reason a uniform cross machine profile moisture content is desirable is that the end product will result in uniform winding only if the moisture content and basic weight is approximately the same at all points across the web. If the moisture is higher in one end of a 60 inch roll than in another when re-wound from paper made off of a machine, the moisture in the roll will tend to equalize in time after storage to a point where a relatively uniform moisture content equilibrium will exist in the entire roll. If the roll began with a wetter end on one end than on another, after equalization, the wet end would appear to be loosely wound and the dry end would appear to be tightly wound when it is run on a newspaper press. Running a roll where one end is loose and the other is tight on a newspaper web press of speeds up to 60,000 papers per hour (almost 2,000 feet per minute) will cause one side of the web to flop and flap as the web is being pulled from unit to unit in the printing process. If the web goes over an angle bar the tight end is apt to split and cause a web break. On a newsprint press a running web break causes the entire press to stop and be re-threaded, losing valuable production time and a wasting raw material.
A Web of newsprint being manufactured on a paper machine which has non-uniform cross direction moisture content or excess peak areas of moisture will be marked or blackened in the calendering process at points of excessive moisture content. This calender blackening marks the limit to which moisture can be added. When a web is blackened at the calender at a point of high cross direction moisture content, the papermaker tries to reduce this moisture peak by artificial means such as stack or dryer air arrangements or slice adjustment, but generally resorts to the practice of increasing the dryer temperatures to a point where a particular spot disappears. In doing so the web dries out still further in areas which are already dry and this merely results in a poor product with less than a desirable average moisture content.
FIGURE 1 shows a typical cross machine direction moisture profile of a 240 inch wide trim newsprint machine making 32 point basis weight stock. This moisture profile is one which is taken from an actual production machine and was made by a sensor instrument which crossed the web as it was running and took stepless readings of the moisture at the reel, recording same on a chart for reference. It is, however, adjusted to a hypothetical moisture content at the breaker stack. Across FIGURE 1 are numbers from 1 to 40 inclusive, each number representing 2 /z% of the width of the machine or six inches of the web. One half of the machine on the tending side is represented by the numbers 1 through 20 and the other half on the drive side by numbers 21 through 40 respectively. At positions 9, 13, 17, 21 and 24 moisture content peaks occur which read approximately 12 /2% moisture. At position 28 a valley of moisture content appears to be just over moisture content while at the position 40, the moisture content of the web appears to be just over ti /2%. The variation between il /2% and 12 /z% is sufficient to be deleterious to the quality of the end production when out into rolls less than the machine width. It also may result in calender blackening at position 17 and possi bly other points. Since this machine represents a four-roll wide machine trimming 60 inch rolls,-the first roll to be cut at the rewinder would include positions 1 through 10 respectively. The second roll to be cut would contain positions 11 through 20, the third roll would contain positions 21 through 30 respectively and the fourth roll would contain positions 31 through 40. On the third roll, the moisture content on the left end of the roll (position 21 through 24) would run between 12 and 12 /2 while the moisture content just in from the edge of the roll at position 28 approximates 10%. Both figures will be relative but inlesser value at the reel. This roll of paper, when out from the width of the entire machine production would have a wet part on the roll on the left from to 24 and a dryer part from 25 to 30. This roll would turn out to be a loose roll on the end represented by positions 21 through 25 and a tight roll from positions 26 through 30 respectively after storage and natural ambient equalization. When run on a newspaper web press, the left part of roll #3 therefore would flap and the right part of the roll would run tight resulting in a distinct possibility of .a web press break if tension impression and speed combinations were just right for this unfortunate occurrence on a newspaper press.
Further, a papermaker experiencing a cross machine moisture profile like the one represented in FIGURE 1 attempting to increase the moisture content of the total sheet from positions 27 through in order to balance out the cross machine moisture content total, may experience calender blackening at approximately five points across the web, namely at positions 9, 13, 17, 21 and 24. This would therefore limit his ability to procure moisture content of the balanced type and amount desired in the whole sheet unless means were available by which to reduce the peaks, build up the valleys, or a combination of both.
On FIGURE 1, a line has been drawn across the profile at 1l /2% moisture content. The line F is dotted where the cross machine profile shows to be less than this amount and it is solid D in the area from position 4 through 25 where the moisture content is indicated as exceeding this amount. Another solid line has been drawn across the machine direction within the areas of the profile at 12% moisture content. Computations show that the amount of moisture in the web which exceeds 12% is 2.1 pounds,
while the amount of moisture in the sheet between 11 /2 and 12% is 5.3 pounds per ton.
My new process and apparatus makes possible feasible means of equalizing cross machine moisture content profiles and substantially solves the problem of gradients in cross sheet moisture content. High frequency alternating current, sometimes called R.F. (Radio Frequency) energy is applied to the web of paper as it passes a given point on a paper machine and accomplishes de-peaking of peaked moisture gradient areas. In applying a high frequency alternating current through application electrodes to the web across the machines width, the field of force applied to the web will expend its energy into the web to the greatest extent into those areas having the greater conductivity or loss factor. I have found that the most moist areas have the greatest conductivity to the effect of the high frequency alternating current field of force over the entire width of the machine. The field of force seeks out the wettest areas, shuns the dry. Since the web of paper is in the process of drying and heat is being applied from steam heated rollers for the purpose of drying the web, the web itself is at a temperature of almost 212 or something slightly less than this amount. To apply the heat of vaporization for 7.4 pounds of water requires 7,400 B.t.u.s of energy since it requires approximately 1,000 B.t.u.s to evaporate a pound of water. If 12 tons of product per hour pass a given point in a newsprint machine and has a profile as represented in FIGURE 1, 12 times 5.4 pounds of water will be contained in the peaks or areas having over 11 /2 moisture content. The energy required to supply the heat of vaporization to this amount of water approximates 89,000 B.t.u.s/hour. 1 have found in numerous experiments with wood, veneer, paper and other dielectric substances that the selective heating effects of the high frequency alternating current field of force has the unique quality of seeking out the most moist areas to which first to apply its major energy. The deep therapy effect of the RF. field of force in placing energy in the center of thickness rather than on the surfaces is another unique quality of its heating effect. After the application to the web moving at a rate of 12 tons per hour of approximately 89,000 B.t.u.s per hour of R.F. energy the web will be de-peaked to a relatively even Il /2% moisture content from positions 4 through 25. It will also be found that from positions 4 through 25 inclusive after the introduction of the energy indicated above, the calender marking or blackening will be eliminated due to the de-peaking of the moisture gradient points along the cross machine direction at the points previously discussed. After such a de-peaking operation the papermaker may introduce additional moisture into his sheet by reducing the temperature of a dryer section or combinations of adjustments such as to presses, air circulation, hood ventilation or head box adjustment which permits a greater moisture content be left in the finished sheet at those points which experience prior difficulty with calender blackening.
De-peaking of the points of excess moisture across the web is accomplished by the web moving over electrode components energized by the output of a high frequency alternating current generator operating at any one of the radio frequency energy ranges and frequencies compatible with the size, shape and power necessary to accomplish the purpose. The frequency of the generator can vary between wide limits. To describe one usable electronic generator and its associated electrode section, the oscillating center frequency could be 6.78 or 13.56 megacycles (or other frequency) and its output to the work load would approximate 30 kw. of radio frequency energy (i.e., 100,000 B.t.u.s per hour). The generators associated electrode configuration over which the web of paper would pass would contain alternately placed positive and negative elements between which the high frequency alternating current field of force would exist. The elements would be positioned on insulating means. The
web bearing upon the electrode configuration would be a conductive path between the positive and negative elements and would accept energy as the web passed. Two parallel electrodes, one positive and one negative would cross the web width paralleling each other at a distance apart (i.e., 4 or 5 inches) compatible with the frequency and the loading of the generator and the loss factor of the load bearing upon them. The electrode components may consist of two such bars, one positive and one negative or as many over two as it is required or as space permits. The electrodes could run with or without a center grounding bar between each positive and negative field electrode. The ground reference is a practical and convenient means of shutting off the R.F. upon the occurrence of an are starting at an electrode. This is a description of a workable and practical electrode configuration attached to a double ender electronic generator when such a type of RP. generator as a single standing wave generator is employed. Such a generator is described and claimed in Mann-Russell U.S. Patents Nos. 2,506,158 and 2,777,022, of which I am a co-inventor. The apparatus for this invention should not be limited to the use of the double ender type but also is applicable as well to single ender generators with a single (or multiple element) configuration alternately charged and working against ground. I do not wish to limit the scope of this invention to the use of a particular type of radio frequency generator whether single ender, double ender or other variety nor to a specific design of electrode configuration, nor to a specific frequency or power to be employed but merely to indicate the wide variety of generators, electrode configurations, frequencies and powers which might be used in this particular application. Any point on a newsprint web moving at 2,000 feet per minute will pass an electrode configuration with a dwell time of about second which has an overall width of two feet in the with-machine direction and composes six charged electrode elements supported from the machine frame by insulating means. R.F. energy impinging on the web during this time will alternate between positive and negative half cycles 1.35 x 10' times per second when the oscillating frequency of an R.F. generator is 6.78 megacycles per second. Dividing 17 into 1.35 x10 alternations results in 8x10 alternations in a time of A6 second. It will be seen, therefore, that 800,000 alternations from positive to negative will occur as between positive and negative charges of a high frequency alternating current field of force oscillating at approximately 6.7 megacycles during the time a point on the web enters the field of force established on the electrode described until the same point passes out of the field.
It should here be stated that oscillations at a higher frequency will create more alternations per unit of time and an oscillation of lesser frequency will reduce them. The factor more important to de-peaking wet spots or areas is the energy applied in B.t.u.s per unit time rather than the frequency of alternations. Hence differing frequencies may be used without departing from the basic principles outlined herein. I have found that the very high. frequencies in the 100 megacycle or over range tend to improve penetration of very low loss factor dielectrics but where water, a high loss dielectric, is concerned, the frequencies in the low megacycle ranges are sufiiciently effective, and higher power is easier to obtain at the lower frequencies since very high power vacuum tubes are available for operation in these ranges.
An electrode configuration composing four or six spaced but parallel electrode elements with alternate units carrying instantaneously positive and negative charges from an associated. electronic generator and extending across a web 260 inches in width (i.e., perpendicular to the direction of movement of the web), may be sized to operate in conjunction with an associated generator of a desired frequency (for example 6.78 megacycles) when including generator leads and leads to a stub termination and may be dimensioned so as to contain a half standing wave of radio frequency energy. In such a mode the electr c field distribution will arise from the generator at approximately a zero E field position sinusoidally toward the electrical center and fall likewise to approximate zero at the stub terminus. The half standing wave will be so placed that the web riding across the said electrode will be placed in the peak areas of the E field standing wave charge where distribution while maximum at the approximate web center will grade downward only slightly toward the drive and tending edges of the web while the generator leads and the stub terminus respectively contain the steeper gradients toward the zero point of the E field charge in the half standing wave mode.
With modern instrumentation, it is possible to servomechanize the controls of the radio frequency generator energizing an electrode section so that changes in B.t.u. per hour output of the generator based on the requirements of the web may be made at the will of an operator or at the direction of a computer programmed to act upon information procured from the signals of a cross machine direction moisture detecting sensor and programmed also to vary the generator output from time to time in accordance with changes in the readings.
Another aspect of my invention is the addition of moisture to the deficient areas of the moving web where the moisture content is sensed to be less than a desired average. In FIGURE 1 position 26 which covers 6 inches of the width of the 240 inch machine is deficient by approximately one quarter of one percent of a desired amount of moisture in the sheet. Position #36 on the other hand, is deficient to the extent of 2% having 9 /2% moisture content at that point against a desired Il /2% content. Computations indicate that for each ton of newsprint the area of 6 inches occupied by position #37 is deficient to the extent of one pound of water per ton. If 12. tons is the rate of production of a particular newsprint machine in one hour and position #37 is deficient in the amount indicated, it will require 12 pounds of moisture be applied to that area of the web in order to bring the average moisture content of the web up to Il /2% in that area instead of its measured content of 9 /z%.
Moisture can be added by sprays, rollers, doctors or other means which are practicable at the speeds of paper machines. Many mechanical means may be resorted to to accomplish this end, but this invention encompasses separately or in combination the use of radio frequency energy to de-peak excessive areas of moisture content and in the use of artificial means of applying moisture to areas deficient in moisture content compared with a pre-set or predetermined amount or percent of desired moisture content.
It is possible to have a row of water squirters extend across the web W of paper or other dielectric. Where the web was shown to be too dry at certain portions, the water squirters Z overlying these areas could deliver a sufficient amount of water. In the schematic showing of FIGURE 1, the web areas 28, 32, 36, 38 and 40, are shown to be too dry by referring to the graph A. The water squirters Z1 to Z5 inclusive, associated with these dry areas would deliver the proper amount of water to these areas. The other squirters in the row and associated with the other web areas, are not illustrated.
Were addition of water made by sprays Z or otherwise to the web in all deficient areas of the illustration in FIG- URE 1 (i.e., those below the lines F and D across the machine at Il /2%) a total deficiency of 13 pounds per ton is indicated. The excess of moisture in areas above this line extended across the whole sheet are indicated as 7.4 pounds per ton as stated above.
It would, of course, be desirable not to permit the socalled deficient areas to have become so relatively dry in the first place, if this were possible. Therefore, still another aspect of my invention is preventing excessive drying, which accomplishes a similar purpose (i.e., equalization) and comes within the scope of restoring deficient areas to a desired average moisture content to which R.F. de-peaking reduces the so-called peaks of excessive moisture content.
The areas which dry at a lesser rate result in those areas having excess moisture peaks above an average moisture content desired; those which dry at a greater rate result in those areas having a deficiency of moisture in the web compared to the desired moisture content. The former are illustrated by areas 9, 13, 17, 21 and 24; the latter are illustrated by areas indicated at 28, 32 and 35 through 40 in FIGURE 1. A means of preventing excess drying of the paper web consists of moisturing and/or cooling at the positions Z, shown in FIGURE 1, the clothing of a paper machine for keeping the Web cooler over such areas as are found to dry at a greater rate than other areas in the same web. This means of preventing excess drying thus equalizing the web in many cases will be found superior in practice to adding moisture to the web directly to accomplish equalization.
If equalization of deficient areas is accomplished by means through which excessive drying is prevented, cooling of the dryer felts or canvas by moisturing will require the addition of more than 13 pounds per ton of water to the felts or canvases at the positions Z of FIGURE 1, to prevent the 13 pounds of water from evaporating from the paper web in the deficient areas.
The above description of RF. de-peaking has primarily described removal of a portion of the moisture in a web which would bring the average in the areas treated to 11 /2 while deficiencies yet remain in the areas not depeaked. Removal of all of the moisture over 8 /2% however, is within the purview of R.F. de-peaking, leaving out the necessity of adding moisture to deficient areas. Nothing indicated in this specification should limit the use of radio frequency energy to only partially reduce peaks so that an average exists across the whole sheet only by resort to artificially adding moisture in deficient areas below a desired moisture content or preventing drying in such areas.
If the peaks in cross machine direction only exceeded the 11 /2 shown above the line drawn across the figure, and no deficiency existed below this figure, the RF. depeaking would require only approximately 89,000 B.t.u.s/ hour of RE the energy from an RF. generator Whose AC input equals approximately 67 kw. hour for 67 kw. A.C. input generator will approximate 34 per hour and with vacuum tube amortization approximating double this amount, the per ton operating cost get to 8 cents.
If R.F. energy were utilized to evaporate all the water in the web over 8 /2 and not just the peaked total over 11 /2 then 62.2 pounds of water would have to be evaporated with R.F. energy alone. This amount at 1,000 B.t.u.s per pound requires 62,600 B.t.u.s per ton, which for 12 tons per hour would require the services of an electronic generator the RF. output to the load of which was 786,000 B.t.u.s per hour (i.e., 220 kw. R.F.).
Five hundred kw. of AC input power to the generator would approximate the line draw which at mils costs equals $2.50 per hour. Tube cost of $5.00 plus power cost equals $7.50 per hour or 63 per ton.
The illustration on de-peaking to 11 /2 or complete evaporation are ranges between which practical and economic considerations direct a choice of degree to which R.F. energy is to be employed.
One aspect of my invention is to the RF. de-peaking, another is to adding moisture artificially, a third is to the prevention of excess drying and a fourth is to a combination of two or more of such aspects.
It is not necessary that the RF. electrode component sections cover the entire width of the web nor are means of applying added moisture to web or clothing necessarily required to cover all the width of the web, but sectional units of either can be employed if full coverage is found to be unnecessary. A machine having a chronic center moisture peak may have R.F. units only in the center, and moisture addition only at the outside edges, etc.
The radio frequency energy may be applied at any point but practical considerations dictate a position where the percentage of the fibre exceeds the percentage of the moisture in the total web. Were the RF. to be applied at a point where the moisture exceeds the fibre, the amount of radio frequency energy necessary to do a balance or full equalizing job might be found to be in excess of economical proportion. Practice may differ on each machine or as to each different grade or weight of product.
The moisture may be added as at the positions Z of FIGURE 1, at any point along the dryer section whether to the web or the machine clothing or in the press or in the Fourdrinier section for that matter; as a spray or other means of applying additional moisture, or to accomplish the same end result; the shower of the lump breaker roll on the couch may be turned off in the wetter sections and accelerated in the areas represented by Z1 to Z5, inclusive in FIGURE 1. My process of RF. heating is designed to be used in the usual cylinder drying of a moving web of paper or the like.
Prevention of overdrying can be utilized anywhere in the machine length but indications favor stages early in the process of drying.
1. A process of equalizing non-uniformly distributed moisture during the normal drying process of a moving continuous web of paper dimensioned wider than thick and containing more fibre than water by weight as it proceeds through a series of steam dryer drums in a paper machine wherein the moisture is non-uniformly distributed as between areas in the cross machine direction comprising:
(a) the step of reducing the moisture content of the areas having an excess moisture content compared to the average moisture content of the Whole web to a greater degree than a reduction in the areas having an average or less than average moisture content by exposure of the web to the selective heating effects of a high frequency alternating current field of force applied to the web by a standing half-wave that extends transversely across the web and is generated by means of evenly spaced apart and parallel electrode elements disposed adjacent to one of the wider surfaces of the web and substantially perpendicular to the direction of web travel, the electrode elements being electrically connected to a high frequency alternating current generator.
2. A process of equalizing non-uniformly distributed moisture during the removal of moisture from a moving continuous web of fibrous dielectric material dimensioned wider than thick and containing less than 50% moisture content by weight wherein the moisture is non-uniformly distributed as between areas across the width of the web viewed perpendicularly to its direction of travel, comprising:
(a) the step of reducing the moisture content of the areas of the web having an excess of moisture content compared to the webs average moisture content by exposure of the web at a fixed point or points passed by the web to the selective heating effects of a high frequency alternating current field of force applied to the web by a suitable electrode configuration adjacent to one of the wider surfaces of and disposed at least partially across the width of the web substantially perpendicular to the direction of web travel, the configuration being in electrical connection with a high frequency alternating current generator.
3. A process of equalizing non-uniformly distributed moisture during the normal drying process of a moving continuous web of paper dimensioned wider than thick and containing more fibre than water by weight as it proceeds through a series of steam dryer drums in a paper machine, the moisture being non-uniformly distributed as between areas in the cross machine direction of the web, comprising:
(a) the step of reducing the moisture content of the areas having an excess moisture content, compared to the average moisture content of the whole web, to a greater degree than a reduction in the areas having an average or less than average moisture content by exposing the web to the selective internal heating effects of a high frequency alternating current field of force, the excess moisture content areas of the web presenting a higher dielectric loss factor to the field of force than the areas having a less moisture content and therefore the high loss factor areas receiving a higher degree of internal heat than the other areas for evaporating the moisture and equalizing the moisture content in these areas with the other areas, and
(b) the step of adding moisture to the web areas that have a moisture content below the average moisture content of the web for equalizing the moisture content of the Web across its entire width.
4. In a process of de-peaking the higher than average moisture content areas of a moving Web of paper containing a non-uniform distribution of moisture in a direction perpendicular to the direction of travel of the web during its primary drying:
(a) the step of establishing a high frequency alternating current field of force across the web substantially perpendicular to its direction of travel and made to impinge its selective heating effects on the web from one side of the web, the field being established on (b) the step of heating the web by the action of the R.F. field to a greater degree in the areas of moisture having an excess over the average of the total mois- 5. An apparatus comprising: (a) an electronic generator of high frequency alternating current associated with electrode configurations; and
(b) means for supporting said electrodes adjacent to one side of a moving web of moist paper during the course of its drying process in a papermaking machine, the electrode configuration including parallel elongated elements alternately and oppositely charged by said generator and being spaced parallel to and adjacent to each other, their length exceeding their spacing apart by a ratio at least of four to one, the long dimensions of the elements being placed substantially perpendicular to the direction of travel of the paper and each electrode element being placed adjacent to the paper by substantially the same measurement as the other paired element, the terminii of the extremities of the said electrode elements galvanically or capacitively being connected in terminal stubbing configuration, the electrode elements forming the residence of a single half-standing wave field of force along the distance from the generator outlet position to the stubbing point at its opposite extremity longitudinally, at the oscillating frequency of the said generator, said generator establishing a standing wave field of force on the electrode elements and impinging the heating effect of same on the web.
References Cited UNITED STATES PATENTS 2,226,871 12/1940 Nicholas 341 XR 2,433,067 12/1947 Russell 219-10.41 2,599,850 6/1952 Mann et al 219l0.41 2,642,000 6/ 1953 Wieking 341 XR 3,266,164 8/1966 Bennett 34-1 3,267,584 8/1966 Southwell 341 JOHN J. CAMBY, Acting Primary Examiner.