Dryer section pocket ventilation
US 3337968 A
Description (OCR text may contain errors)
g- 29, 1-967 G. KRIKORIAN ETAL 3,337,958
DRYER SECTION POCKET VENTILATION Filed Jan. 27, 1966 United States Patent 3,337,968 DRYER SECTION POCKET VENTILATION Garo Krikorian, Paxton, and Nicolas Martin Reitzel, Boylston, Mass., assignors to Rice Barton Corporation, Worcester, Mass., a corporation of Massachusetts Filed Jan. 27, 1966, Ser. No. 523,355 4 Claims. (Cl. 34111) This invention relates to the dryer section of a paper machine and is particularly concerned with new and improved arrangements for ventilating uniformly the pockets which are defined by a felt roll wrapped by a felt and one or more dryer drums, the runs of felt between rolls and drums and the runs of sheet between drums.
In the conventional dryer section with top and bottom rows of dryer drums, two felts, and the paper web running between drums of the two rows alternately, two series of so-called pockets are formed which are open only at each side of the machine. A pocket of one series is formed between an upper felt roll wrapped by the felt and the adjacent lower dryer drum, the remaining walls of the pocket comprising runs of the travelling upper felt and runs of the web itself which separates from the upper felt at the next succeeding upper dryer drum. The pockets of-the other (lower) series are similarly defined by the wrapped lower felt rolls and opposing upper dryer drums, runs of the lower felt and runs of the paper web.
Because of the presence of the pockets, humidity at the center of the machine is higher than at the edges where evaporated moisture can escape more readily, resulting in a reduced drying rate at the center and concomitant non-uniform moisture content of the dried web. If moisture content is plotted against the width of the sheet the resulting graph will be low at each end and high in the middle, sometimes referred to as the moisture profile of the web.
It has been proposed to ventilate the above mentioned pockets by blowing heated dry air through the felt from the outside into the pockets from plenum chambers'located closely adjacent to runs of the felt between dryer drums and a felt roll. For example, in US. Patent 3,1l0,- 575, there is disclosed such an arrangement including provision for simultaneously withdrawing air from the pocket through another adjacent run of the felt by suction means arranged outside such run of the felt.
An inherent difficulty with the arrangements previously proposed is to provide adequate sealing between the edges of the air delivery duct and the felt to force significant quantities of air through the felt. In fact, it is well nigh impossible to produce an adequate air flow by known means through any but the most permeable felts.
The object of the invention is to provide an improved apparatus for ventilating the pockets formed in a paper machine dryer by supplying air to the pockets from the outside through a run of the felt which will develop suflicient static pressure to pass effective quantities of air through felts including even felts having poor permeability and wherein losses through the seals are minimized.
In accordance with the invention there is provided in a dryer section of a paper machine apparatus for moisture profile control by ventilating pockets defined by the wrapped felt rolls, the dryer drums, runs of felt and the paper Web, comprising a plurality of plenums arranged on the side of the felt which does not contact the Web and opening against the felt, each plenum being positioned adjacent a run of the felt where the latter is separated from the paper web and arranged to force dry air through the felt into the pockets. The edges of the open ing which faces the felt are sealed by flexible inwardly directed seals bearing against the felt at either side and by similar seals at each end one of which directly engages the surface of the felt roll and the other of which 3,337,968 Patented Aug. 29, 1967 ice extends transversely inwardly across the running felt and bears thereagainst.
Further objects, features and advantages of the invention will appear from the following detailed description of a presently preferred embodiment thereof taken in conjunction with the accompanying drawings in which:
FIG. 1 is a partially diagrammatic view on a reduced scale of a portion of the dryer section of a paper machine embodying the invention; a
FIG. 2 is a cross-sectional view on an enlarged scale of one of the air supply units of the invention located outside a pocket adjacent a run of felt;
FIG. 3 is a section on line 3-3 of FIG; 2; and
FIG. 4 is a detail view in side elevation of a portion of the plenum unit shown in FIG. 2 illustrating particularly the operation of the side sealing members during passage of a clipped felt joint under the plenum.
Referring to the drawings, banks of upper dryer drums 10 are arranged in staggered relation to banks of lower dryer drums 12. Beneath each upper drum 10 is mounted a felt roll 14 and above each lower dryer drum 12 is mounted a felt roll 16. The upper felt 18 passes alternately from drum 10 to roll 16 and then to the next drum 10 wrapping the same in part and pressing the paper web 20 against the surfaces of the dryer rolls.
It will be seen that two series of pockets are formed in the dryer section, each being defined by one felt roll and one dryer drum and the runs of felt and paper web. Moisture driven from the web by the dryer drum will find it more difiicult to escape from the middle portions of the pockets than from the side portions thus producing the undesired moisture profile in the sheet.
To ventilate the pockets and make more uniform the moisture profile there is mounted adjacent the run of felt as it leaves each dryer drum and before it wraps the next felt roll an end fed manifold or sub-divided plenum chamber 22 extending the width of the felt and located on the side of the felt which does not contact the paper web. The plenum 22 is subdivided into several passageways, in this instance three designated by the numerals 22a, 22b, and 220. The passages terminate against a perforated plate 24 and, preferably the central passage 22b opens against the central one-half of the plate 24 and the other passages occupy each the remaining one quarter of the area thereof.
On the side of the plate 24 toward the felt 18 an air discharge chamber is formed to force air from the plenum through the web into the adjacent pocket. This chamber is defined by the plate 24, the felt 18 itself, and flexible side seals 26 and flexible end seal 28 and end seal 30. Baffles 35 are-located in line with dividing walls 220 and 22b of plenum 22. Baflies 35 operate in close but noncontacting relation with felt 18 to produce gradual pressure transitions between plenum zones. The end seal 28 is a trailing flexible strip which bears against the felt surface to provide a seal while the seal 30, on the contrary, bears directly against the unwrapped surface of the roll 16 where its action .will be the most effective. The side seals 26 are of the usual flexible contact type and bear against the felt at locations slightly inwardly spaced from the marginal edges of the felt.
The presently preferred construction and arrangement of the sealing strips by means of which adequate sealing is provided between the edges of the air delivery duct and felt Will be described in detail as follows:
A flexible end sealing strip 28 which closes the felt entering end of the plenum discharge chamber is formed of a flexible material of good wear properties capable of withstanding the air temperatures utilized. A glassfiber reinforced polyfluoroethylene material for example, has been found suitable for this purpose. The sealing strip 28 is mounted in a recess in the plenum wall 22 and retained by a clamp or clamps 46 held by screws 48. The sealing strip 28 is wider than the separation of the plenum wall 22 from the felt 18 and is bent or sprung inwardly under the plenum 22 and in the direction of travel of the felt. Bending the sealing strip 28 inwardly produces sufiicient contact pressure against the felt to reduce leakage to a minimum. Due to the flexible nature of the seal 28, the seal adapts itself continuously to the rough surface of the travelling felt and to any substantial discontinuities in the 'felt such as a felt seam. Static air pressure within the plenum presses on the inner surface of the sealing strip 28, further increasing the loading of the strip 28 against the felt 18. As plenum static air pressure is increased, the pressure on the inside of the sealing strip 28 increases proportionally, increasing the sealing load on the felt 18 and providing effective sealing at plenum pressures, which are in excess of pressures found practicable in the prior art. The side sealing strips 26 are similarly formed of a'heat, and wear, resistant resilient material, such as the glass-fiber reinforced polyfiuoroethylene material, above referred to, and are mounted in slots extending along the bottom edges of the plenum side walls so that they slope inwardly'under the plenum 22 into engagement with the travelling felt. The strips 26 are held in sealing engagement with the felt by the resilience of the material, reinforced by the static pressure of the air column in the manner above described for the sealing strip 28.
The action of a substantial discontinuity in the felt 18, when travelling in contact with the sealing strips 26 isshown in FIG. 4. A clipped felt seam consisting of clips 50 and pin 52 joining abutting ends of felt 18, and protected from contact with the paper by a flap 54 will deflect the engaged portion of the strip 26 further inwardly while other portions of the strip continue to be pressed inwardly so that contact with felt 18 is maintained undiminished. Each strip 26 is relieved on leading edge at 56 (see FIG. 4) to prevent seam clips 50 from damaging the strip 26 on initial contact. The sealing strip 30,. which closes the felt leaving edge of the plenum discharge chamber, acts against roll 16, and is made preferably of a rigid material. The sealing strip 30 is mounted in a recess in the plenum wall 22, being retained as shown in FIG. 2 by a suitable clamp 58 and screws 60. Springs 62 load the rigid strip 30 against roll 16 with sufficient pressure to seal against loss of air in plenum 22. Alternatively, the seal 30 may be of flexible construction similar to seals 26 and seal 28. It is noted particularly thatthe seal 30, by virtue of engaging the roll 16, is sloped in the direction of the moving surface, thus minimizing the friction and wear therebetween while at the same time advantage is taken of the air pressure built up within the discharge chamber to maintain the seal.
The plenum 22 is fed by a duct 40 which extends to one or both sides of the machine and may be connected to a suitable source of heated, dry air under pressure. Dampers 42 serve to control the flow of air to the respective passages 22a, 22b, and 22c, so that the volume of air supplied at different locations along the width of each pocket may be controlled to produce the desired moisture level in the paper web being dried.
Of particular importance is the effectiveness of sealing the outgoing edge of the discharge chamber against the surface of a roll 16 rather than against the felt thereby to very substantially increase the static pressure in the 4 discharge chamber such as to pass eifective volumes of air through even relatively impermeable felts.
While there is herein disclosed and described a presently preferred embodiment of the invention it will nevertheless be understood that the same is susceptible of modifications and changesby those skilled in the art and therefore it is intended that the scope of the invention be limited only by the proper scope to be afforded the appended claims.
What is claimed is: v
1. In a dryer section of a paper machine web drying apparatus forprofile control by ventilating pockets, defined by the wrapped felt rolls, the dryer drums of one of a series of such drums, and runs of felt and the paper web, the combination of a plurality of plenums overlying that side of said runs of felt' from drum to felt roll which does not contact the paper web, having a discharge chamber with its opening against the felt for forcing air through said felt into the pockets, and sealing devices between the discharge chamber and felt about the edges of the discharge chamber comprising side sealing strips of resilient material extending longitudinally of the felt secured to the sides of said chamber and'sloped inwardly under the chamber against the felt, a sealing strip of resilient material attached to the felt entering side of said chamber and sloped inwardly under the chamber in the direction of felt travel for trailing engagement against the felt, a sealing strip attached to and extending across the felt-leaving end of said chamber for trailing engagement with the running surface of said felt roll, said plenum being adapted to be placed in communicationwith a source of heated dry air under pressure for forcing air through the felt and into said pockets.
2. The combination of claim 1 in which the sealing strip closing the felt-leaving end of the discharge chamber is made of a stiff material, and a yieldingly acting device engages the sealing strip against the felt roll.
3. The combination of claim 1 in which the plenum is formed with a plurality of air inlets including a central inlet and adjacent inlets toward each edge of the trailing felt, means for separately controlling the flow of air in said inlets, and separating baffles for said inlets, each extending into close but non-contracting relation to the i felt providing for separate plenum inlet zones and for gradual pressure transitions between said plenum inlet zones.
4. The combination of claim 3 in which the plenum extends substantially the width of the felt, and is divided into three inlets including a central inlet extending approximately one-half the total width of the plenum, and an inlet at each side thereof extending approximately the width of the plenum.
References Cited 7 UNITED STATES PATENTS 1,759,804 5/1930 Pieron 34160 2,141,403 12/1938 Offen 34155 X 2,192,432 3/1940 Bruker 34-155 2,565,576 8/1951 Runton 34-155 X 3,110,575 11/1963 Justus 34--1l1 3,283,415 11/1966 Schnyder u 341l1 FREDERICK L. MATTESON, 111., Primary Examiner.
A. D. HERRMANN, Assistant Examiner.