US2717539A - Papermaking machine - Google Patents

Description

Sept. 13, 1 w. w. METCALF PAPERMAKING MACHINE 4 Sheets-Sheet 1 Filed March 21, 1952 a A K.

Efii h/a/zi' r M/Ve a/f Sept. 13, 1955 w. w. METCALF 2,717,539

PAPERMAKING MACHINE Filed March 21, 1952 4 Sheets-Sheet 2 /27 van t on h/a/'er' M f/efi a/f 774's fit'or'ne ys Sept. 13, 1955 w, w METCALF 2,717,539

PAPERMAKING MACHINE Filed March 21, 1952 4 Sheets-Sheet 5 fr; ver'z to)" His M26602")? eys Sept. 13, 1955 w. w. METCALF PAPERMAKING MACHINE 4 Sheets-Sheet 4 Filed March 21, 1952 /7? Vent o2" 14/5/66?" M M85667:

United States Patent PAPERMAKING MACHINE Walter W. Metcalf, Greenwich, N. Y.

Application March 21, 1952, Serial No. 277,781

12 Claims. (Cl. 92-43) My invention relates to papermaking and particularly to improvements in papermaking machines of the cylinder type.

In my U. S. Letters Patent No. 2,162,097 dated June 13, 1939, I have disclosed a cylinder machine which is capable of making a well formed sheet in which the fibers are disposed in almost perfect random relation whereby the paper is of substantially uniform strength throughout and offers substantially equal resistance to tearing in all directions. The machine disclosed in this patent is provided with means for adjusting the velocity at which the stock is delivered to the mold so that it conforms substantially to the surface velocity of the mold itself with the result that an excellent fiber dispersion on the mold is attained.

However, machines of the above mentioned type cannot make quality papers at a speed much in excess of about 600 feet per minute because the newly formed wet web cannot be removed without injury. One of the reasons is that the felt is required to wrap the couch and return on top, with the result that centrifugal force causes drops to fly off the wet sheet on the couch leaving spots of poor formation in the web. Furthermore, beyond a certain critical speed, the centrifugal force exceeds the adhesion of the web to the felt and the entire web may be thrown off at the couch.

Another factor, is the very high velocity of the air flowing past the wet web on its way to and through the bare portion of the mold between the nip of the couch and the usual shower.

The minimum distance between the nip of the couch and the shower in the present types of machines is about 4" or To maintain of water vacuum on the mold, the exhaust fans remove about 10,000 cubic feet of air per minute from the system. About 90% of this volume is pulled through the bare wire area just below the nip. The minimum distance between the shower pipe and the web on the couch cannot be less than about 1 /2", or, the gap through which nearly 9000 cubic feet of air must pass each minute has an area of about 0.77 square foot. Hence, the average air velocity in the gap is of the order of 11,700 per minute, or more than 130 miles per hour. Machines operate successfully with this air velocity in this zone but the velocity cannot be increased materially without very harmful scrubbing of the web.

Thus, machines of the present type have two serious faults which hamper high speed operations:

(1) Centrifugal force causes throw-offs from the web where the felt runs around the couch roll; and

(2) Air rushing by the web on the couch at high velocity is apt to injure the web.

The effect of centrifugal force on the wet web can be eliminated by running the felt straight through the nip of the couch. This is standard practice in the industry for high speed operations but it makes fault No. 2-much worse because the felt is very much closer to the bare wire on the mold than is the case where it wraps the couch. The cleaning shower has to be advanced farther in the 2,717,539 Patented Sept. 13, 1955 direction of mold rotation to keep the top of the shower a safe distance below the felt. This advance of shower position nearly doubles the amount of bare wire and thus the amount of air handled by the exhaust fans is nearly doubled to maintain the same mold vacuum. In practical terms, the air velocity and its effect are nearly doubled, or the velocity of the inrushing air would be of the order of a 250 mile per hour gale. Aside from probable injury to the web on the felt by such a gale, the capacity and power of the exhaust fans become prohibitively high and there is a serious question as to whether such a design would be economically practical to operate.

There the principal object of my invention is to devise a papermaking machine of the cylinder type in which the felt runs in a straight line after leaving the nip of the couch but in which the velocity of the air flowing beneath the wet web to and through the bare portion of the mold surface is very substantially reduced, whereby the speed at which the machine may be operated is greatly increased and the necessity for unreasonably large and powerful exhaust fans is eliminated.

I accomplish this and other objects which will be apparent as the description proceeds, by means of the novel elements and the combinations and arrangements thereof described below and illustrated in the accompanying drawings in which Fig. 1 is a fragmentary vertical cross section of the web forming part of a high speed cylinder machine; showing the cylinder mold, the trunnions, and nozzle adjusting means in side elevation, also the vats, circulating pump, stock approach flow piping and air exhaust system;

Fig. 2 is an enlarged end view of the mold and trunnions with portions of the mold broken away and partly in section and the bafile in section;

Fig. 3 is a fragmentary perspective view of one type of mold body; I

Fig. 4 is a fragmentary cross section of a modified type of mold body;

Fig. 5 is a fragmentary cross section of another type of mold body;

Fig. 6 is an enlarged section of Fig. 1 in the broken planes 6-6;

Fig. 7 is a perspective view of a bafiie and a damperlike arrangement for regulating the flow of air through the bafiie;

Fig. 8 is a perspective view, showing the means of mounting the baffle to the heads of the cylinder vat, and the means employed to put in, or take out, the bafiie from the machine; and 1 Fig. 9 is a fragmentary section in the plane 9--9 of Fig. 1, showing the means of holding and adjusting the baffle in position, and the means of positioning the damper.

The two most important features of my design which cooperate to allow high speed operation are:

(1) A rigid cylinder mold having high resistance to fiexure when supported at the ends only; and whichis free of internal obstructions; and

(2) A stationary internal suction baffle extending through the mold which is rigidly supported and has its lips or marginal portions in close proximity to but not touching the smoothly machined inner surface of the mold and which extends downwardly from the nip of the couch under the bare portion of the mold surface below the felt which is carrying the wet web of paper.

Referring to the drawings I 1 is the cylinder mold which is rotatably mounted in the vat 2 on trunnions 3 and 4 which are mounted on shafts 5 and 6 having bearings 7 and 8, and 9 and 10, respectively, in the side Walls of the vat 2 (see Fig. 6). The vat 2 is covered, as shown at 11 in Fig. 1, where it runs under the felt 12. The stock level must, of course, be maintained at a somewhat higher elevation than the mold, At a speed of 1500 feet per minute the static head required above the top of the mold is of the order of 12 feet of water. This is an increase of about feet of head over the requirement for operation at 600 feet per minute. Thus, for practical reasons of construction the stock vat 63 is made as a separate part of the machine and mounted on supporting steel members 61, 62 and 63 behind and considerably above the mold. Screened stock enters the system through pipe 65, mixes with white water entering from the bottom of vat 2, and is forced by pump 66 through pipe 67 and regulating valve 68 into the bottom of stock vat 60. Internal baffies, 69, 70 and 71, serve to release entrapped air and establish a smooth non-surging flow out of 60. Stock is conveyed from 60 to the mold through pipes 64 and duct 13. The cross-sectional area of the duct 13 is gradually decreased as it approaches the mold so that the stock flowing therein has a gradual and smooth increase in velocity in its passage to the mold. The duct turns upwardly in the zone 14 and continues into a nozzle section designated generally by the numeral 15. The white water level in the vat 2 is indicated by the dash and dot line 16 and is maintained at about this level by drainage through a suction sealed port, such as shown at 17. The inner side of the nozzle which is adjacent the mold terminates at the point 18.

The outer wall of the nozzle is formed of articulated sections which may be moved relative to the mold in order to vary the cross-sectional area of the nozzle section. The fixed portion of the outer wall of the duct adjacent the nozzle section terminates in a micarta plate 19. A shaft 20 extends across the vat and the plate 21 is hinged thereto.

The upper portion of the nozzle comprises an element 22 having a cylindrical portion at the bottom which is tangent to the plate 19. The element 22 is pivotally secured at the top and bottom thereof to the turnbuckles 23 and 24, respectively, which provide for regulating the distances from the mold of the upper and lower portions of the element 22, and the other ends of these turnbuckles are pivotally secured to arms 25 and 26 which aremounted on transversely extending shafts 27 and 28. Thus, by turning the shafts 27 and 28 a quick adjustment of the element 22 with respect to the mold may be effected.

A nozzle of the general character described above is described in greater detail in my Letters Patent aforesaid.

Riding on top of the mold is the usual couch roll 29, and the felt 12 runs straight through the nip 31 thereof instead of running around the roll, as in my patent aforesaid. 32 is the usual shower and 33 is the usual rubber apron which runs in contact with the mold surface.

The mold 1 comprises a hollow, metal cylinder which may be a centrifugal-cast bronze tube or a plate of stainless steel of the proper thickness rolled into cylindrical form and welded at the joint. The tube is machined to a smooth surface both on the outer and inner sides thereof, and longitudinally extending grooves 34 are machined therein to provide a multiplicity of circumferentially spaced drainage spaces extending all of the way around the exterior surface of the tube. The grooves are separated from each other by radial ribs 35 so that drainage spaces, say about 1" wide and /2 to /1 deep, are formed therebetween. The ribs should not exceed about /8" in width at the top. Holes 36 are drilled through the bottom of each groove which will allow both water and air to pass through the shell of the mold. The aggregate area of all of such holes is preferably about 30% of the area of the inner surface of the mold.

The actual thickness of metal required for the wall of the tube will be dictated by the structural requirements for stiffness. The mold body must be rigid or stiff enough to allow less than 0.010" maximum deflection due to bending stresses while in operation, in order that continued flexing of the wire mesh coverings will not unduly shorten their useful life. The forces which act to cause deflection are the dead weight of the mold, the pressure from the couch roll, the pressure of liquid in the formation zone, and the radially inward air pressure due to a partial internal vacuum. The resultant of all these forces is about 65 pounds per square inch of mold face and acts downwardly through the axis of the mold at about 15 from the vertical and about mid-way between the trunnions. The necessary thickness of metal, as measured from the bottoms of the grooves to the inner surface of the mold, will be probably between /2" and l, depending on the length and diameter of the mold.

Although the mold is preferably formed in the manner described above, it is possible to make it from a number of interlocking or welded sections, as shown in Figs. 4 and 5.

Thus, in Fig. 4, the sections 37 are in the form of longitudinally extending members which are welded together, as shown at 38 and 39.

In Fig. 5, the longitudinally extending members 49 are provided with interfitting tongues and grooves 41.

The method of applying the wire cloth covering 42 to the mold is the same as is now used on the present types of cylinder molds. Thus, a round, bronze wire (0.090") is wound tightly around the outside of the mold body on top of the radial ribs and in the form of a continuous helix of about A" pitch. This is covered with a coarse mesh wire cloth, having 20 to 30 meshes per linear inch, which is tightly applied with a welded seam. Finally, several finer mesh wire cloth covers are applied outside the first coarse mesh cover. The result is a smooth, firm, cylindrical, wire mesh covered surface having the proper drainage rate to pass the desired amount of liquid or air under the differential head causing flow-through.

The end construction is somewhat similar to that now used on cylinder molds except that the collars 43 are heavy rings rather than spoked wheels. These collars are machined about to the section shown in Figs. 6 and 9 and pressed into the ends of the mold body. They may be secured in place by cap screws 44 (see Figs. 6 and 9) having their heads disposed in some of the grooves in the mold under the wire cover. In order to seal the internal vacuum in the mold, the usual straps 45 (see Fig. 6) extend around the upper portion of each end of the mold between the points A and B indicated in Fig. l. The end collars 43 ride on the trunnions, as shown in Figs. 1, 2 and 6.

Referring now more particularly to Figs. 1, 2, 6, 7, 8 and 9, I have shown a battle 46 adjustably secured to the side walls of the vat, by cap screws 47, which pass through slotted holes 43 in the top of vat heads 2, to suspend the weight of bafile 46 in position. Set screws 59 and 81 serve to locate and adjust the radial clearances of the bafiie 45 passing through the mold 1. The bathe is provided with upstanding arcuate flanges 5 at the ends thereof which conform in curvature to the inner surface of the mold and are positioned in close proximity thereto at the ends of the mold. The opposite marginal portions of the baffie are provided with arcuate lips 51 and 52 conforming in curvature to the inner surface of the mold and which are positioned in close proximity to said inner surface. Between the lips 51 and 52 the bafiie is appreciably spaced from the inner surface of the mold and, if desired, this portion may be provided with perforations 53 therein (see Fig. 7) with a perforated, slidable, damper-like element 54 cooperating therewith to close the perforations 53 or open them to the desired extent by means of a tapped block 55, rigidly attached to the damper 54 at one end thereof, and a pull screw 56, and two push set screws, 57 and SS. 82 denotes the rectangular front end flange of bafile 46, and 83 denotes the corresponding rectangular rear end flange of said bafile. Three clearance holes, 8'4, in flange 82', allow the passage of screws, '56, 57

and 58. 85 is a front end seal plate; 86 is a rear end seal plate. Pull screw 56 passes through clearance hole 87 in plate 85, while two tapped holes 88 and 89, receive the push screws, 57 and 58, respectively. 90 is an upper half baflle head and 91 is a lower half bafile head. In use the flanges of 90 and 91 are bolted together through holes 92 and the assembly attached to vat end 2 by cap screws, 93, thus forming a partial cover for the large opening 94 in vat head 2, said cover thus having a rectangular flanged opening that will surround with proper clearances the rectangular end flange 82, or 83, of baffle 46. Tapped holes 94 and 95 in the upper half baffle head 90 receive adjusting screws 80 and 81 respectively. The seal plates, 85 and 86, are attached to the end flanges 82 and 83 of baflle 46 by several cap screws 96, assembled through clearance holes 97 in the seal plates and extending into tapped holes 98 in the end flanges 82 and 83.

With cap screws 96 tightened, the seal plates 85 and 86 are held securely against the machined end surface of the rectangular flanged openings of baffle hoods 90 and 91, thus completing the closure of large opening 94; yet allowing such up and down and sidewise shifting of said seal plates against the flanged rectangular opening as is necessary to adjust the baffle 46 with respect to the inner surface of mold 1. The longitudinal position of the baffle v46 within the mold 1 may be adjusted by changing the relative tightening of screws 96 at the back side of the machine and screws 96 at the front side of the machine. Thus, if the rear side screws 96 be loosened and the front side screws be tightened a corresponding amount, baffle 46 will move toward the front side of the vat 2. All of these adjustments of baffle position may be visually checked through the manholes 97, one in each vat head 2, and large enough to allow actual entry into mold 1.

It is further necessary that the mounting of the baffle 46 to the vat 2 be such that the baffle can be put into or removed from the machine with the mold 1 in position on the trunnions 3 and 4. The steps to follow in removal of the baflle are as follows:

1. Remove screws 56 and 96 and seal plates 85 and 86.

2. Take out bolts through holes 92 in parts 90 and 91, and cap screws 93 which attach lower half baffle head 91 to vat 2. Remove parts 91.

3. Slide part 99, a standard structural steel channel beam which is about twice as long as baflle member 46, through the lower part of large opening 94 of the front vat head 2, and through the mold 1 until the end rests on the lower part of opening 94 of the rear vat head 2. Thus placed, 99 will be about onehalf its length through the machine, resting on the bottoms of openings 94 with the flange on one side of 99 bearing against shoulders 100 of openings 94 which are so positioned as to cause substantial alignment of the channel member and baffle 46 above it. The onehalf of member 99 which projects from the front side of the machine is to be supported at its outer end by temporary shoring (not shown).

4. Suspension cap screws 47, at front and back sides of the machine are loosened evenly, thus lowering the baffle until its lower flanges 101 come to rest on the web of and between the flanges of channel 99. Cap screws 47 are now completely removed.

5. The remaining cap screws 93 are removed and upper half baffle heads 90 are taken off.

6. Slide member 46 along 99 until it is completely outside of vat 2, and then lift said member off the channel.

7. Remove the channel 99 from the machine, thus completing the baflle removal. 7

The replacement of the baffle in the machine is accomplished by the same steps executed in reverse order.

By reference to Fig. 1, it will be noted that the lip 51 of the bafie is positioned substantially at the nip' of the couch roll and that the lower lip 52 is illustrated as extendingsomewhat below the shower 32. In other words, the baflle is disposed under that portion of the mold Where the Wire surface is bare. It completely seals off that portion of the mold where the Wire is bare except for the small running clearances between it and the inner surface of the mold which form passages of restricted cross-sectional area for the flow of air and water therethrough.

The function of the baflle is to reduce the vacuum acting on the wire cloth surface of the mold in that part thereof which extends from the couch nip to the shower and chamber seal point. As illustrated, the baflie extends through about 45 or 50 of the mold surface.

The same amount of air will pass through the bare Wire and mold structure above the baffle chamber into the chamber, as passes from the baflle chamber through the clearance spaces around 50, 51 and 52, and the regulating holes 53 into the higher vacuum zone within the mold 1 and exterior to the baflle 46. In each case, flow is caused by a differential air pressure on the two sides of the opening through which flow occurs. Thus, for example, if the pressure outside the bare wire is atmospheric, the pressure within the baffle is assumed at /2" water, and the pressure within the mold is -18" water, a differential pressure of A2" water causes the flow into the baffle; and a differential pressure of 17 /2" water causes the flow of air out of the bafl le. In each case of flow the equation for flow where:

Q equals amount of air flow, per unit of time.

K equals a constant depending on the units and the conditions of flow, and closely numerically the same for each case above considered.

h equals differential pressure causing flow.

A equals aggregate area through which flow occurs,

Let:

Q1 equal flow into baflle, through area A1, caused by head of /2" water,

Q2 equal flow out of bafiie, through area A2, caused by head of 17 /2" water.

We may now write:

i=kA1\/% and Q2=KA2VW But Q1=Q2, therefore:

I 11/ f n/E Thus, if the aggregate area of openings through the bare wire be of the order of 300 sq. in., the aggregate clearance and damper openings from the baffle should be adjusted to about 4 of 300, or 17.9 sq. in. to cause the baffle chamber suction to be water as assumed, with a mold suction of 18" water. A value of 17.9 sq. in. for A2 is easy to attain with the structure as described as the clearances of 50, 51 and 52, from the inside surface of mold 1, could be something over all around.

It is not desirable to cut off all the suction in the zone behind the baflle because, after the couch nip there is free water in the mold drainage grooves. With no suction to hold this water back, it would be liable to fly outwardly through the wire face and hit and injure the wet paper web on the under side of the felt. However, the suction needed to overcome centrifugal force is lower than that required for web formation. A vacuum of /2" of water is more than suificient at the bare wire, whereas a vacuum of 15 to 20 of water is required in the formation zone for high speed web formation. Thus, the ratio of the desired vacuums in those interior spaces of the mold outside the bafile and the space inside the baffle is of the order of 25-40 to 1.

The running clearance between the inner surface of the mold and the flanges 50 and the lips 51 and 52 of the baflle do not have to be exceedingly small. clearance all around is small enough to maintain the desired ratio of the vacua and yet large enough to insure no contact or rubbing due to operating deflections or slight inaccuracies of machining or adjustment. Thus, the baffle may be readily secured to the vat heads so that a fixed clearance is positively provided betweenthe bafiie and the mold and the vacuum between the baffie and the immediately adjacent portion of the mold surface may be varied and adjusted by means of the damper shown in Fig. 7.

In operation, the vacuum within the baflied space will be adjusted to the minimum that will prevent all throwoff of water from the wire surface into the web of paper carried by the felt. It may be that, under some operating conditions, the damper can be entirely closed and, if so, a material reduction in the amount of air handled by the fan and also its required horsepower will be realized.

It is understood, of course, that air is withdrawn from the sealed portion of the vat, through an opening 102 in the side thereof in the usual manner by means of a duct 103 and fan 104 (see Fig. 1).

What I claim is:

1. In a paperrnaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a nozzle for delivering stock to said mold in a zone substantially confined to the upper ascending quadrant thereof; a couch roll; a felt running through the nip of said couch roll and, thereafter, in a substantially straight line over said vat; whereby the effect of centrifugal force acting on a wet web of paper if carried by said felt around said couch roll is eliminated; a shower beneath the straight running portion of said felt; and a suction baffle within said mold extending downwardly from the nip of said roll throughout a substantial portion of the upper descending quadrant of said mold and spaced from but closely adjacent the inner surface of said mold at least at the marginal portions thereof, whereby, to restrict the volume and velocity of the air flowing to and through said mold past a wet web of paper carried by said felt.

2. The structure set forth in claim 1 together with means operable from a point exterior of said vat for varying the extent to which said air flow is restricted by said baflie.

3. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder tomaintain a partial vacuum therein; the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a nozzle for delivering stock to said mold in a zone substantially confined to the upper ascending quadrant thereof; means for varying the velocity at which the stock is delivered from said nozzle to said mold, whereby to correlate said velocity with the peripheral speed of said mold; a couch roll; a felt running through the nip of said couch roll and, thereafter, in a substantially straight line over said vat; whereby the effect of centrifugal force acting on a wet web of paper if carried by said felt around said couch roll is eliminated; a shower beneath the straight running portion of said felt; and a suction baffie within said mold extending downwardly from the nip of said roll throughout a substantial portion of the upper descending quadrant of said mold and spaced from but closely adjacent the inner surface of said mold at least at the marginal portions thereof, whereby, to restrict the volume and velocity of the air flowing to and through said mold past a wet web of paper carried by said felt.

4. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a couch roll; a felt running through the nip of said roll and thereafter substantially straight over said vat; a baffle within said mold having its marginal portions spaced from but in close proximity to the inner surface of said mold to restrict the flow of air therebetween; said baffle extending through an are substantially coextensive with that portion of said mold in the upper descending quadrant thereof which is exposed to the flow of circumambient air therethrough; the opposite sides of said vat being provided with openings through which said battle may be inserted into said mold and withdrawn therefrom; and detachable means normally forming closures for'said openings.

5. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a couch roll; a felt running through the nip of said roll and thereafter substantially straight over said vat; a baffle within said mold having its marginal portions spaced from but in close proximity to the inner surface of said mold to restrict the flow of air therebetween; said baffle extending through an arc substantially coextensive with that portion of said mold in the upper descending quadrant thereof which is exposed to the flow of circumambient air therethrough; means for suspending said baflle from said vat; and means for adjusting the clearance between said baffle and the interior surface of said mold.

6. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a couch roll; a felt running through the nip of said roll and thereafter substantially straight over said vat; a baflie within said mold having its marginal portions spaced from but in close proximity to the inner surface of said mold to restrict the flow of air therebetween; said baffle extending through an arc substantially coextensive with that portion of said mold in the upper descending quadrant thereof which is exposed to the flow of circumambient air therethrough; means for suspending said baffle from said vat; means for adjusting the clearance between said baffle and the interior surface of said mold; and means for adjusting the position of said baffle relative to said mold in a direction axially of said mold.

7. A papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, comprising a vat, a cylinder mold rotatably mounted in said vat, a couch roll, a felt running approximately straight through the nip of said roll; a baflle positioned within said mold and extending downwardly within the upper descending quadrant thereof a substantial distance from a zone immediately adjacent the nip of said roll and providing air passages of restricted cross-sectional area between the top and bottom thereof and the inner surface of said cylinder mold; whereby to reduce the volume and velocity of the air flowing to and through that portion of the mold immediately adjacent the wet web of paper carried by said felt.

8. The structure set forth in claim 7 in which said baffle is provided with air passages therethrough and means operable from a point exterior of said vat for regulating the flow of air through said passages.

9. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, thecombination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a couch roll; a felt running through the nip of said couch roll and, thereafter, in a substantially straight line over said vat; a shower beneath said straight running portion of said felt; and a baffle within the upper descending quadrant of said mold extending from a zone immediately adjacent the nip of said couch roll downwardly to said shower; said baflle being substantially spaced from the inner surface of said mold except at the top, bottom, and ends thereof where it is closely spaced from said surface to provide air passages of restricted cross-sectional area therebetween; whereby to provide a substantially less vacuum in the space within said baflie than within the balance of said mold and thereby reduce the volume and velocity of the air flowing to and through that portion of said mold immediately adjacent the wet web of paper carried by said felt.

10. The structure set forth in claim 9 in which said baffie is provided with air passages therethrough and means operable from a point exterior of said vat for regulating the flow of air through said passages.

11. In a papermaking machine of the cylinder type in which air is withdrawn from the cylinder to maintain a partial vacuum therein, the combination with a vat; of a cylinder mold; trunnions in said vat on which said mold is rotatably mounted; a couch roll; a felt running through the nip of said couch roll and, thereafter, in a substantially straight line over said vat; a shower beneath said straight running portion of said felt; and a baffle within the upper descending quadrant of said mold extending from a zone immediately adjacent the nip of said couch roll downwardly to said shower; means securing said baffle to theopposite sides of said vat with the marginal portions thereof within said mold in close proximity to the inner surface of said mold; whereby to, maintain a lower vacuum in the space between said bafile and the adjacent inner surface of said mold than in the other portions of said mold by restricting the passage of air therebetween, and thereby to reduce the volume and velocity of the air flowing to and through that portion of said mold immediately adjacent the wet web of paper carried by said felt.

12. The structure set forth in claim 11 in which said baffie is provided with air passages therethrough and, means operable from a point exterior of said vat for regulating the flow of air through said passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,162,097 Metcalf June 13, 1939 FOREIGN PATENTS 48,240 Norway Aug. 4, 1930

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