US2174744A - Apparatus for pressing a moving web in paper making machines - Google Patents

Description

H. S. HILL Oct. 3, .1939.

APPARATUS FOR PRESSING A MOVING WEB IN APER MAKING MACHINES Filed Feb. 3, 1937 4 Sheets-Sheet l 1731/5172101" HgmwHZLL Mw a fw m 0ct.3,1939. H. s. HILL 2,174,744

APPARATUS FOR PRESSING A MOVING WEB IN PAPER MAKING MACHINES Filed Feb. 5, 1937 4 Sheets-Sheet 2 H. s. HILL 2,174,744

APPARATUS FOR PRESSING A MOVING'` WEB IN PAPER MAKING MACHINES Oct. 3, 17939.

Filed Feb. 5, 1937 4 Sheets-Sheet 3 H. S. HILL Oct. 3, 193.9.

APPARATUS FOR PRESSING 'A MOVING WEB IN PAPER MAKING MACHINES Filed Feb. 3, 1937 4 Sheets-Sheet 4 Y2-m5277171 y JEEWLD 15711;

Patented Oct., 3, 1939 APPARATUS Fon PREssING A Movnvd 1N PAPER MAKING MACHINES Harold s. Hill, Quebec, Quebec, cama' Appiication'rebruary 3, 1937, serial N0.,12

's claims.y (ci. ca -49) This "invention relates to a( method andapparatus of pressing a continuously moving web in paper machines or the like.

A desired improvement in paper machinery is 5 to reduce the water' content of the web prior to its passage through the drying stages of the machine, and the present invention relates particul tion also in the drying stages ofthe machine where this isfound desirable.

`It has been the common practice in paper making to subject theweb, after it has passed from the forming wire, to the usual wet press,

l of which there are several for each paper machine, consisting of two rotating rolls bearing together usually with added weight in order to press as much water as possible from the wet web.

The web is carriedl through the area of contact 20 between the pressing rolls, commonly known as the nip, on an endless woolen felt suitably stretched and guided which, in addition to serving as a carrying medium, provides a medium through which the water pressed from the web 25 may be filtered and removed from the zone of pressure. It is obvious, however, that there is obtained little 'more than line contact between the pressure rolls and up to the present time this has been a fundamental limitation operat- 30 ing against eicient water removal. Several at'- tempts have been made to increase the water extraction at this point in the machinel and suc-` tion presses have been employed wherein the bottom roll is in the form of' a hollow cylinder whose 35 shell is perforated and suction is applied to the interior of this rollin a suitable zone which is at or near the nip so that the water pressed from the wet sheet is largely pulled through the shell 'of the roll instead of being forced back through 40 the nip to flow as best it may over the outside roll.

The suction press effected some improvements over the old style of press but has not overcome the fundamental limitation inherent in the use 45 of roll nip pressure for the extraction of Water from a moving sheet, wherein the time of actual pressing is necessarily very short. Moreover, the

- increase in speed in modern paper machines has reduced the time of active pressure on the wet 50 sheet as it passes through the nip to an exceedingly minute period, Under these conditions, the

problem of overcoming the inertia and viscosity of the water, in combination with the limited filtering capacity of both the wet sheet and the 55 felt, presents a great obstacle to obtain more Y of press.

. beyond the econo eicient Water;- hf thez type Attempts to increasev atei', extraction by means of increasingA th ll pressvur quickly y.reach a practical limit :because oo high, a",nip.pressuref^5 will reduce theol/.VG llg-ilife of the, woolenfelt l pointgandbecause too high a pressure vvillsirrjure,f and ,mark the wet sheet,l and nally because toohi'gh a pressure will defeat its very ypurposelufor- ,Water`r extraction by' `10 compressing the-sheet and v`the 4felt soheavily that their filtering capacity isjreduced 'beyond 'that necessary for the time that is. available during the press of the -fnip s v The use of nip pressure for increased Water extraction, therefore, ,presents certain serious and fundamental difficulties which become accentuated at higher speeds of operation, due largely to the excessively shortjtime of effective action on the sheet during its passage `through the nip.

According to the present invention, an entirely novel and improved method of extracting water from a moving wet sheet is provided which greatly reduces and eliminates the main objections associated with the present use of nip pressure for this purposeand provides for a substantial increase in the,percentage of water extraction. Moreover, thevinvention is also applicable to the preliminary extraction of Water from the web as it passes over the couch roll, to obtain a greater reduction inthe water content of the web prior to its passage to thepress, and to provide for a stronger web as it is fed to the press. The invention also is applicable in a practical manner to the drying stages of a paper machine, that is in hot pressing the web of paper to produce adesired type of surface, increase in strength, etc., effected through pressure over a greater or lesser time limit, as desired. Of course, the latter application of the invention may be extended to include similar hot pressure treatments to a sheet of paper after' it has left the paper machine, as a secondary finishing operation carried out during rewinding of a roll of paper.

In general, the invention provides a means of applying a uniform pressure on a moving web or sheet which may be varied according to requirements and is' elfective over a very much v longer period of time than in the case of nip pressure, Under such conditions it is possible to obtain not only a greater degree of Water extraction but also a more uniform water extraction with less injury to the wet sheet and its carrying felt and, therefore, with less operating diiculties. It also provides for water extraction with the inclusion of a practical heating operation, in the wet end of a paper machine, thus increasing the possibilities of a substantial water' disposed in the form of an endless wet felt or a felt jacket shrunk on the roll. A flexible, im-

I pervious, endless belt is disposed on the outside of the roll to engage and enclose the outer surface of the web throughout the latters contact with. the filtering medium on the roll, the impervious belt moving with the web as it passed around the roll. yFluid pressure 1s then caused to act on the web as it passed around the surface of the nroll, the 'uid pressure being applied through the medium of the flexible belt, either by means of a positively applied external pressure or a pressure effected through suction from the interior of the ro'll, although both methods are preferably employed simultaneously. Consequently as the roll rotates, the wet web as it moves is continuously pressed against an extended, moving, foraminous surface, or in other words is squeezed between the impervious belt and the filtering medium on the surface of the roll while passing over a substantial part of the circumference of the roll, so that, apart from providing for the application of a variable pressure according to requirements, for pressing or squeezing the water from the web, the method provides for a pressing time many times' greater than is practicablypossible with the usual type of nip press roll,.which time of pressing may be varied to a considerable degree, depending upon the size of roll selected and on the amount of its circumference which is utilized.

Similar factors apply for water removal as the web passes over the couch roll, and lalso in hot pressing. In the rst case the outer surface of the web as it passes over a selected area of the couch roll is covered with an impervious endless belt and pressure is obtained on the belt through the effect of suction operating from within the roll, whereas in the case of hot pressing the impervious belt is disposed to cover the web disposed in contact with a desired area of one of the drying rolls or a specially heated roll and a positive pressure is applied to the outer surface of `pose of extracting water from the web, or in the case of hot pressing, to impart a desired type of surface to the web, increase its strength, reduce its thickness, or impart a predetermined design.

The method also includes a special heating operation which is particularly applicable in the case of water extraction, and may also be applied in hot pressing. This consists in heating the pressure uid which may readily be maintained at a desired temperature to heat the web simultaneously with the pressing operation, to increase the possibilities of substantial water extraction or to provide additional heat during h'ot pressing if required.

In order more clearly to, illustrate the invention, reference is Imade to the accompanying drawings.

In the drawings:

Figure 1 is a transverse section taken throu/gh a water extracting roll according to the present invention, illustrating the manner in which the web is fed to and confined on the surface of the roll by the impervious belt, as well as an example of the structure which may be employed for exerting a substantial, external uniform pressure on the belt.

Figure 2 is a side elevation of the apparatus disclosed in Figure 1 with some of the rolls omitted.

Figure 3 is a fragmentary sectional view of the water extracting roll and its mounting.

Figure 4 is a view similar to Figure 1, showing an alternative type of construction.

Figure 5 is a fragmentary sectional view of a suction couch roll of a paper machine, showing the application of the impervious belt to obtain improved Water extraction, and

Figure 6 is a schematic View showing the applicatiorr of my invention to one of the paper machine drying rolls, for the purpose of ho pressing the web.

Referring more particularly to Figures 1 to 3, Ill indicates an endless felt conveying the web I I to the press section of the paper machine. According to the invention, instead of the usual press rolls, there is provided a drainage roll I2 provided with suitable shafts I3 which may be journalled in any suitable manner on the standards or pedestals I 4. Passing around the roll I2 is an endless felt I5 which also passes over the tension roll I6 and forms the base and ltering medium upon which the web lies as it passes over the drainage roll I2. Conning the web II as it passes over a portion of the surface of the drainage roll I2, is an endless impervious belt IT which is disposed upon the pairs of guide rolls I8 and I9, 20 and 2l, the latter pair being adjustable, if desired, to maintain required belt tension.

Around the outside of the cylinder I2, a suitvable casing 22 is positioned to form a chamber 23 between the exterior of the impervious belt I1 and the casing, for receiving fluid under pressure. The casing may be of any desired form, such as, for instance, part of a reinforced vat structure, as illustrated in Figure2, the chamber 23 being suitably sealed to confine the pressure medium to the area of applied pressure. In Figure 1. an illustration of one type of seal which might be employed is shown wherein the sealing members 24 are disposed to engage the rolls I8 and I9 at the top of the structure, side seals being also provided for the ends of the rolls, as indicated at 24a, see Fig. 2. In Figure 3 sealing members 25 are shown disposed in the sides of the casing to engage with the edge of the impervious belt, the belt projecting beyond the foraminous surface of the roll and the web being disposed so that its edges preferably terminate short of the defining edges of the foraminous surface, leaving part of the latter at the edges exposed so that if any leakage occurred between the seal 25 and manner, such as by pump, reservoir, valves etc.

suitably connected to the chamber.

It will be apparent that, with this construction, a variable degree of pressure may be applied to the exterior of the impervious belt over that area of the latter which is disposed on the roll I2. It is clear, therefore, that as the cylinder rotates, the wet sheet is continuously pressed or squeezed between the impervious belt I1 and the felt I5 .disposed over the cylinder I2, which results in squeezing water out of the web through the felll into the roll'` in a continuous and uniform manner. Moreover, by reason -of the fact that the `pressing action occurs throughout the passage of the sheet over a substantial part of the circumference of the roll or, in other words, during its passage over an extended drainage surface, there results, in comparison ;with usual practice, an extended pressing time.

In the construction shown the chamber 21 is subjected to a high degree of suction which is direoted to that portion of the roll where the web nally leaves the roll; while a substantially similar .degree of suction is applied to a remaining larger portion of the roll around whichthe web passes, this being effected from the chamber 21 through the space 28 between a wall of the chamber 21 and a peripheral wall of the roll.

In chamber 29 a lower degree of suction is applied through the opening 30 connecting it with chamber 21, chamber 29 being illustrated as operating upon the balance 4of the peripheral wall of the roll in that area principally where the roll is free of the web and felt, to extract any moisture that may still be retained in the peripheral wall. The degree of suction and the zones to which it is applied may, of course, be varied to meet with requirements.

By subjecting the interior of the roll to partial vacuum two purposes are served. -The 'rst is facilitating the removal of water which has been pressed from the web through the felt, into the holes or orices of the foraminous surface of the roll, as above referred to, and the second purpose is to increase the external pressure `exerted on the belt and for this purpose suction is applied at a zone embracing a part or all of the roll circumin addition to the radial pressure exerted by the belt due to its tension.

It will be apparent, therefore, that pressure for water extraction may be obtained by means of an external positive fluid pressure on the belt or a pressure of this character supplemented by suction from the interior-of the roll. On the other hand, due to the fact that the invention provides for the extraction of water from the web in one long continuous` pressing stage, improved results in extracting Water from the web can be obtained.v

The desired fluid pressure may be by merely subjecting the foraminous surface to suction applied from the interior of theA roll, which in fact does create atmospheric fluid pressure on the belt. It will be realized, therefore,

that the expression subjecting the web to fluid pressure or reference to fluid pressure occurring inl the appended claims of this application may embrace either or both of these two modes of applying fluid pressure. y g

The amount of water which is extracted from the wet sheet will depend largely on the total pressure exerted on and by the belt, but the usefulness of the present invention is in no wise limited to any particular total pressure, nor to the relative magnitudes of the three above men-` the interior of the cylinder in any suitable manner, such as by means of a combined water and vacuum pump connected with the interior of the roll through one or both shafts. In this way the surface of the roll is subjected to suction which may be applied through the use of a stationary but adjustable suction box divided into compartments, if desired, or a number of suction boxes may be employed at .different points within the roll as found necessary. In Figure 1 there is illustrated one form of construction 26 which might be employed for applying suction to the peripheral wall of the roll.l

To increase the possibilities of substantial Water extraction in the pressing operation, heat may be applied in a practicalmanner, according to the present invention, by heating the pressure fluid in chamber 23, and to this end a fluid inlet 3l and a fluid outlet 32 may be included to permit circulation of the water and consequently the maintenance of a substantially uniform heat throughout the area under pressure. Consequently the belt and underlying web may be subjected directly to a substantial degree of heat which may be maintained within a reasonable range.

In Figures 4 to 6 other formsI of construction are illustrated to which the principle of the invention is readily applicable. In Figure 4 a similar construction to that described is illustrated which employs the cylinder I2, the rolls I8 and I9,y and 20 and 2I and the impervious belt I1. In this structure the cylinder is shown with a felt jacket 33 which is shrunk on the cylinder.4

Furthermore, instead of employing a continuous chamber surrounding the cylinder, two

vchambers 34 and 35 are employed, one disposed on each side of the cylinder to avoid upward thrust on the roll, in the case where lt might be necessary to exert a great radial pressure on the impervious belt and web o f paper, and to provide for a balanced pressure. In this structure two additional rolls 36 and 31 are added, similar to rolls I8 and I9, to provide for the two equal and oppositely disposed sealed fluid chambers, sealing members 38 being provided in connection with the casing surrounding the chambers to engage the rolls I8, I9, 36 and 31. A slightly Y different sealing member of suitable'material is here-illustrated and so arranged and adjusted to touch the surfaces of these rolls, the contact besubstantially full atmospheric pressure.

tween the sealing members and the rolls, to provide a seal, being maintained by virtue of the fluid' pressure itself.

Any suitable suction box construction may be employed withinthe roll l2, one construction 39 being illustrated wherein the chambers lll and di are subjected to a high degree of suction and chamber l2 subjected to a slightly lesser degree of suction. The chambers 40, M and d2, it will benot'ed, are positioned in Zones where the web is subjected to pressure from the chambers 3@ and 35, the chamber tu being so positioned that the web, just prior to the point where it leaves the roll l2, is subjected to a high degree of suc-A tion. The chambers i3 and til are subjected to a low degree of suction which may operate to clear the orifices in the foraminous surface of the roll of any moisture thatthey may carry. In the showing of Figure 4, chamber 53 is disposed so that a low degree of suction will operate on the Web just as it leaves the roll and just as it commences to pass over the roll.

The chambers :it and 35 are provided with inlets it and outlets i5 to provide for circulation of the pressure fluid to maintain a substan` tially even heat in the case where the uid is heated to provide for a heating operation simultaneously with the pressure.

The effect of the structure shown in Figure 4 is substantially the same as that obtained in the case of Figure 1, except that instead of providing for one long continuous'pressing stage, the water extraction is effected in two shorter separate pressing stages. However, the area of the belt under pressure is increased when the interior of the roll is subjected to vacuum in addition to the positively applied external pressure, since in this case that portion of the belt on the roll between the chambers 3d and 35 is then subjected to On the other hand, similarly asin the case of Figure 1, when the interior'of the roll is subjected to vacuum alone and no positive external pressure is applied, the web receives the effect of substantially full atmospheric pressure throughout the area of the roll over which it passes.

In Figure 5 the application of the principle of they present invention is shown'on a couch roll 45 wherein the impervious belt I1 is disposed on two rolls 46 and 41 and caused to press against the web as it passes over a surface of the couch roll. lThe suction box 48 is disposed within the couch roll and positioned so that the effect of the suction is directed to that area of the roll y over which the web and belt pass. Consequently, the web, during its passage over the couch roll, will be subjected to a steady uniform pressure effected through the medium of the belt in one continuous operation and for a period of time whose maximum is controlled by the maximum portion of the circumference of the roll,ove1 which the web may be caused to pass. This .use of the belt renders'. it possible to subject the web to a greater degree of pressure exerted over a longer period of time as `the web passes over the couch roll,4 providing for a greater percentage of Water extraction at this point with consequent strengthening of the Web.

In Figure 6 the application of the principle of the invention is shown in conjunction with the drying rolls of the paper machine, wherein the impervious belt l1 is arranged onrolls 5U, 5I and 52 and caused to pass over a substantial part of the circumference of one of the drying rolls 53 around which the web passes. A casing 54 forming a pressure chamber 55 is disposed below the drying roll 53 so that the impervious belt and the web, as they pass around the roll, are confined between the latter and the chamber while suitable sealing members 56 are associated with the casing 5@ to engage the rolls 5l and 55B and thus seal the chamber 55. In this manner a. substantially uniform pressure can be applied through the impervious belt to the web.

Normally the drying rolls of the -machine are heated from the interior, the web being carried into Contact With the rolls under slightly radial pressure by means of the usual felts. In the showing of Figure 5 the felt is omitted in connection with drying roll 53 and replaced by the impervious belt l1, through which the desired pressure is applied to the web, along with heat, to provide ior a desired type of finish, an increase in its strength, reduction in its thickness, or the imparting of a predetermined design.

The drying roll or rolls to which this pressing arrangement may be applied can be heated to a degree most suited for the particular treatment involved. In this connection, however, it will be realized that the desired limited amount of heat required, or in some cases additional heat, could be applied to the web by heating the pressure uid in chamber 55, as described in connection with the other forms of construction illustrated in the present application.

, It is apparent that, in providing for a heat and pressure treatment of thev paper web, the heated roll might be employed before or after the web has passed the drier section of the machine, Whereas such treatment may be employed as a subsequent finishing operation for treating the web of paper after it has passed from the machine,

for instance as it is being unwound from rolls.

From the foregoing it is clear that one ofV the essential features of the present invention is the use of the endless, exible belt through which pressure is applied to the sheet. having the necessary running qualities must be exible enough to readily and eiciently transmit the hydrostatic or fluid pressure to the wet sheet, and must also be essentially impervious to the fluidwhich is used to exert the pressure, whether it be a liquid such as water or a gas such as air. This necessitates a belt made of an impervious material such as rubber, impregnated canvas, thin, high strength steel or the like, but the present invention is not limited to any particular material provided that the belt fulls the above described requirements.

The filtering felt which passes between the wet This belt besides sheet and the roll in the present invention serves essentially the same purpose as the Wet felt on the usual two roll, nip press and obviously its specification may vary considerably depending on the particular product and operation for which the invention is used. In general, however, a ner and closer weave and texture of Wet felt than is commonly employed for nip presses Will be prefvention without departing from the spirit thereof or the scope of the claims, and therefore the exact forms shown are `to be taken as illustrative only and not in a limiting sense, and it is desired that only such limitations shall be placed thereon as are disclosed in the prior art or are set forth in the accompanying claims.

I claim:

1. In the manufacture of paper, apparatus for pressing the paper web comprising a rotatably mounted roll over which the web passes, a casing enclosing that part of theroll over which the Web passes and forming at least one fluid pressure chamber extending around a portion of the suron each side of the roll.

HAROLD S. Bil/ILL.

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