GB2127871A - Apparatus and method for control of the cross-machine moisture profile of a paper web - Google Patents

Abstract

Method and apparatus are provided for controlling the cross- machine moisture profile in a paper web undergoing processing, such as water-removal via a press nip. A compartmentalised steam/airbox 15 is provided in close proximity to web W undergoing dewatering over suction roll 12. Selected compartments, are provided with steam and/or air so as to control the moisture content of the web areas opposite each compartment selectively. Moisture sensors may be used to sense moisture contents across the web and the signals therefrom may be fed to a computer connected to valves associated with the compartments to operate them accordingly. <IMAGE>

Description

SPECIFICATION Apparatus and method for control of the crossmachine moisture profile of a paper web The invention relates to paper-making machines and more particularly to an improved apparatus and method for effective control of cross-machine moisture profile in a travelling paper web undergoing dewatering, as in a press section.

Methods and apparatus for applying steam to aid in dewatering a paper web are known, for example, see U.S. Patent Specifications Nos.

4,272,316 and 4,163,688.

A presently accepted theory for this technique is that as a paper web or sheet is heated by applied steam, the viscosity of water in such web is reduced, making water removal easier. Recent developments in this area include compartmentalised steam boxes having separate cross-machine compartments allowing steam to be selectively applied in the crossmachine direction to a travelling web. Typically, such steam boxes are positioned about the outer surface of a suction roll so that steam can be drawn into the suction box and through the web supported by such roll. The ability to correct or control the cross-machine moisture profile in a web has met with various degrees of success and problems still remain. One of such problems is that each compartment cannot be readily sealed against the surface of the travelling web.One reason for this is that a minimum clearance of about one inch (2.54cm) between the surface of the steam box and the suction roll must be maintained in order to avoid damages from wads, wrap-ups, etc. With such large clearances, much of the applied steam in one compartment is free to migrate to adjacent compartments, with a resultant indiscriminate application of steam.

The invention provides a method and means which overcome the prior art drawbacks and provide a more effective control of cross-machine moisture profile in a travelling paper web undergoing moisture removal in a paper-making machine.

According to the invention there is provided apparatus for control of the cross-machine moisture profile of a paper web in a paper-making machine, comprising fluid-permeable means supporting a travelling paper web undergoing dewatering; a compartmentalised steam/air box positioned in working relation with said fluid permeable means, said box extending in a crossmachine direction substantially across the width of said paper web and having an open front face in fluid communication with said fluid permeable means and being positioned in relatively close proximity thereto, said box having a plurality of separated compartments each in fluid communication with said front face and each having a controllable steam and air outlet located away from said front face so as to allow a stream of steam or air to flood each respective compartment and permeate a corresponding area of said fluid-permeable means; a source of compressed steam and a source of compressed air in fluid communication with said controllable steam and air outlets each compartment; and a water-removal means positioned in working relation with said steam/air box for removing water from said paper web.

The invention also provides a method of controlling the cross-machine moisture profile of a paper web in a paper-making machine, comprising the step of selectively feeding a stream of steam or relatively dry air to select cross-machine areas of a paper web undergoing dewatering in a paper-making machine; and removing water from such paper web.

In an exemplary embodiment of the invention, a steam box having a plurality of cross-machine compartments is positioned in close-running relation to a fluid-permeable means supporting a travelling web, typically a press nip defined by two press members, such as press rolls, one of which can be a grooved roll or a suction roll. The steam box is provided with a first cross-machine header, connected to a steam supply in the papermaking machine. Exiting from such header is a plurality of supply pipes and control valves, each associated with an individual compartment of the steam box. In addition, the steam box is provided with a second cross-machine header, connected to a compressed air source in a paper-making machine, with supply pipes and control valves associated therewith and with each individual compartment.

In preferred embodiments, a single valve means controls both the steam and air flow to an individual compartment. Each valve means can be interconnected to a computer and moisture sensors can be associated with selected transverse areas of a travelling web and be interconnected to the computer so that the valves are appropiately activated by the computer for steam and/or air flow in accordance with the signal generated by the sensors.

The air supply can be used to "flood" a compartment so as to prevent cross-machine migration of steam into that area. Selectively supplying dry air to a select compartment of a steam box is further advantageous in that it can be utilised to control dry areas of a sheet. As air is drawn into a sheet, evaporation cooling occurs, reducing the sheet temperature. At lower sheet temperatures, pressing is less effective. Hence, steam is supplied to control wet streaks in a sheet and air supply to control dry streaks in a sheet.

The following is a detailed description of embodiments of the invention, reference being made to the accompanying drawings in which: Figure 1 is a schematic elevational partial view illustrating a section of a paper-making machine constructed and operating in accordance with the invention; Figure 2 is another somewhat similar schematic elevational view showing another form of the invention; Figure 3 is a partial somewhat schematic elevational view illustrating a steam/air box in association with a grooved press roll; Figure 4 is a partly broken-away top view illustrating one form of header arrangement utilised to supply air/steam to the air/steam box; Figure 5 is an elevated detailed view of a valve arrangement utilised to control steam/air in the air/steam box; Figure 6 is an elevated detailed view of an alternative valve arrangement utilised in the practice of the invention; and Figure 7 is a schematic diagram illustrating a working relation between a computer, moisture sensors and respective valve means of an air/steam box constructed and operable in accordance with the invention.

As illustrated in Figure 1, a newly formed web W is carried on the upper surface of a travelling first endless felt. F1, for example, from a Fourdrinier machine or from a first press section (not shown), into a press nip N1 defined between a lower grooved roll 11 and an upper suction roll 12. A travelling second endless felt F2 is guided by guide rolls (not shown), so as to sandwich the web W between the felts F1 and F2 as they pass through the press nip N1.At the press nip N1, water is removed downwardly into the groove roll ii and from there to a saveall in a conventional manner.On the off-running side of the nip N1, the web W adheres to the second felt F2 as this felt travels around the suction roll 12 in the manner shown. The first felt F1 is guided away from the press nip N1 by a suitable guide roll and back through its endless loop in a conventional manner. The second felt F2, carrying the web W on its outer surface, travels around the suction roll 12 and past the suction gland 13 as illustrated. A profiling steam/air box 1 5 is positioned in close working relation with the outer surface of the suction roll 12 so as to feed air or steam to select areas of the web via a controlled valve 1 5A connected to a steam source S and to an air source A.The supplied steam and/or air streams penetrate through the felt F2 and into the web W and thence into the suction gland 13 of the suction roll 12 to effect temperature control of the associated areas of the web. A plain-surfaced press roll 14 is positioned above the suction roll 12 so as to define a second nip N2. A third endless travelling felt F3 is guided over the surface of the plain press roll and against the web W so as to sandwich the web between the felts F2 and F3. The so-sandwiched web is then carried away for further processing, for example, to another press section or to a dryer section of a paper-making machine.

Figure 2 shows another press section wherein the profiling air/stream box is advantageously employed in accordance with the invention. In the embodiment here illustrated, a newly formed web W is carried on a top surface of a first endless felt F1 into a first press nip N1 defined by an upper plain roll 23 and a lower grooved roll 22. Just prior to the press nip N1, a compartmentalised profiling air/steam box 21 is positioned in close running relation with the felt F1 so as to selectively feed steam and/or air upwardly through the felt F1 and into the web W via a control valve 21 A.At this location, steam aids water removal while dry air retards water removal so that steam can be supplied to control wet streaks in the newly formed web or sheet and air can be supplied to control the dry areas thereof.

After the press nip No ,the felt F1 carries the web W into a second press nip N2 defined by a lower plain roll 24 and an upper suction roll 25 having a suction gland 25a. On the off-running side of the nip N2, the felt F1 is guided away from the web W back through its endless run via a plurality of guide rolls (not shown). The web W continues to adhere to the outer surface of the suction roll 25 because of the suction gland 25a. A second profiling air/steam box 26 is positioned in close running relation with the outer surface of the suction roll in close conformity with the suction gland 25a and selectively feeds air or steam against the web surface via a control valve 26A.

Heated water is more readily withdrawn from the web via the suction gland whereas cooled water (cooled by supplied air) is somewhat more difficult to withdraw so that control of wet and/or dry streaks in the web W can be readily accomplished. A second endless travelling felt F2 is guided around a further plain press roll 27 positioned to define a further press nip N3 with the suction roll 25. On the off-running side of the nip N3, the felt F2 carries the web W on its undersurface away for further processing as desired.

The profiling steam/air boxes of the invention, such as boxes 21 and 26, correct cross-machine moisture profiles in webs undergoing dewatering.

Each steam box is relatively fluid impermeable except for an open front face and is divided into a number of compartments in the cross-machine direction. Cross-machine headers are provided to supply compressed steam and air, respectively, to each compartment, which also includes an individual control valve. As is known, papermaking machines typically include a source of pressurised steam and may include a source of pressurised air. In any event, relatively dry air can be supplied from an external source by a fan or other suitable means. A select air stream can be used to flood a compartment to prevent crossmachine migration of steam into the flooded compartment. Further, such dry air stream provides a means of controlling dry areas of a sheet since as air is drawn into a sheet, evaporation cooling occurs reducing the sheet temperature, making water removal less efficient. In this manner, dry areas can be controlled and by selectively applying steam to other areas, wet streaks can be controlled.

Referring to Figure 3, a grooved roll 35 having a plurality of grooves 35a is shown positioned in working relation with a profiling and/or steam box 30. The box 30 is provided with a back wall 31, an upper wall 32, a lower wall 33 and a forward open face 34, along with appropriate end walls (not shown), all joined together in a relatively fluid-tight manner so as to be able to direct the steam and/or air flow toward the front face 34 of the box 30. The walls are preferably formed from sheet metal and a plurality of individual compartments, for example, about six inches (15.2 cm) in width, are provided along the crossmachine direction of the box. For this purpose, a plurality of compartment walls 31 a, 31 b, 31 C etc.

are suitably secured between the upper and lower walls 32 and 33 of the box, as shown in Figure 4.

Each compartment is provided with a control valve 40 suitably interconnected with the air supply A and the steam supply S. The air supply is connected with an air feed line 43 and the steam supply is connected with a steam feed line 45.

The valve means 40 include a hollow body 42 and a valve stem 41 which carries a double-truncated conical valve body 44 mating with respective valve seats 44a and 44b. Valve seat 44a is formed at the upper portion of valve body 42 while valve seat 44b is formed within the steam pipe 45. By selectively moving the valve steam 41 either the valve seat 44a can be shut while valve seat 44b can be opened, as shown in Figure 5, or the steam may be moved upwardly to shut the steam supply pipe by blocking valve seat 44b while opening the air supply valve seat 44a. As best seen in Figure 4, the compressed air source and steam sources are respectively connected to headers which interconnect with the respective valve means associated with each compartment.The valves are so positioned away from the front face 34 that a pressurised stream of air/steam cannot directly impinge on a surface adjacent the open face.

Figure 6 shows an alternative embodiment of a control valve useful in the practice of the invention. As shown, a ball valve 40A is provided for connecting the steam feed pipe 45 with the box 30 and with the air feed line 43. Movement of the valve stem 41 a allows either steam or air to flow through the valve housing into the steam box 30.

Referring now to Figure 7, a portion of a web W is shown travelling in the machine direction M and extending in a cross-machine direction CM of a paper-making machine. A plurality of moisture sensors S1, S2, S3, S4, etc. are positioned in working relationship with the web W and the steam/air box 30, with each sensor associated with a selected cross-machine area of the web.

Each sensor senses the moisture level in its given area of the web and generates a signal which is fedto an operational computer. The computer is electrically connected to a plurality ofsolenoidoperated valves 40b, each associated with a given compartment of the profiling box 30. In this manner, in accordance with the signal received from the sensors, the computer opens or closes the valves 40b to admit steam or relatively dry air to the particular compartment.

Claims (11)

Claims

1. Apparatus for control of the cross-machine moisture profile of a paper web in a paper-making machine, comprising: fluid-permeable means supporting a travelling paper web undergoing dewatering; a compartmentalised steam/air box positioned in working relation with said fluidpermeable means, said box extending in a crossmachine direction substantially across the width of said paper web and having an open front face in fluid communication with said fluid-permeable means and being positioned in relatively close proximity thereto, said box having a plurality of separated compartments each in fluid communication with said front face and each having a controllable steam and air outlet located away from said front face so as to allow a stream of steam or air to flood each respective compartment and permeate a corresponding area of said fluid-permeable means; a source of compressed steam and a source of compressed air in fluid communication with said controllable steam and air outlets of each compartment; and a water-removal means positioned in working relation with said steam/air box for removing water from said paper web.

2. Apparatus according to claim 1, wherein said fluid-permeable means consists of a travelling endless felt.

3. Apparatus according to claim 1, wherein said fluid-permeable means consists of an outer surface of a suction roll gland.

4. Apparatus according to claim 1, wherein said fluid-permeable means consists of a press nip formed between a first press member and a second press member defining a pressing zone therebetween through which said paper web is carried subject to a dewatering pressure.

5. Apparatus according to claim 4, wherein said first press member is a plain-surfaced press roll and said second press member is a grooved press roll.

6. Apparatus according to claim 4, wherein said first press member is a suction press roll and said second press member is a plain-surfaced roll.

7. Apparatus according to claim 1, wherein said fluid-permeable means consists of a pair of press nips formed between a lower plain-surfaced press roll, an intermediate suction press roll and an upper plain-surfaced roll, each of said plainsurfaced press rolls defining an individual pressing zone with said suction press roll through which said paper web is successively carried subjected to a dewatering pressure, and said compartmentalised steam/air box is positioned in working relation with the suction gland of said suction roll between the respective press nips formed by the respective plain-surfaced press rolls and said suction press roll.

8. Apparatus according to any of Claims 1 to 7 wherein said compartmentalised steam/air box compartments each are provided with a single valve means controlling flow of steam and air into each such compartment.

9. Apparatus according to claim 8, wherein said valve means include a hollow valve housing having an upper wall, a lower wall and side walls joined in a relatively fluid-tight manner, said air outlet being in fluid communication with said hollow valve body, a movable valve stem threadingly supported along the bottom wall of said valve housing and carrying a doubletruncated conical valve body at an outer end thereof, a first valve seat formed in an upper wall of said valve body and mating with a first end of said valve body, said first valve seat being in fluid communication with the associated compartment, and a second valve seat spaced from said first valve seat and formed in an outer wall of said steam outlet and mating with a second end of said valve body whereby pressurised steam from said steam outlet is directed through said second valve seat against said second end of said valve body and pressurised air is directed through said first valve seat against said first end of said valve body so as to permeate the compartment associated with such valve means with steam or air in accordance with the position of the said valve body.

10. Apparatus according to claim 8, wherein said valve means comprise a ball valve in selective fluid communication with said steam and air sources and with a given compartment of said steam/air box and includes an actuating means for selectively providing communication between said steam or air source and said compartment.

11. Apparatus according to claim 8, wherein said valve means comprise a solenoid valve and a plurality of moisture sensors are provided in working relation with selected cross-machine areas of said paper web corresponding to a compartment of said steam/air box, a computer being connected with said moisture sensors and with each of said solenoid valves so that during operation, said moisture sensors feed a signal to said computer in accordance with the moisture level in a paper web area being monitored by such sensor and said computer opens or closes the flow of steam or air into each compartment in accordance with said signal.

1 2. A method of controlling the cross-machine moisture profile of a paper web in a paper-making machine, comprising the steps of selectively feeding a stream of steam or relatively dry air to select cross-machine areas of a paper web undergoing dewatering in a paper-making machine; and removing water from such paper web.

1 3. Apparatus for control of the cross-machine moisture profile of a paper web in a paper-making machine, substantially as hereinbefore described with reference to the accompanying drawings.