US2998846A

US2998846A - Dandy roll for high speeds

Info

Publication number: US2998846A
Application number: US679843A
Authority: US
Inventors: Hornbostel Lloyd
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1957-08-23
Filing date: 1957-08-23
Publication date: 1961-09-05
Anticipated expiration: 1978-09-05

Description

Sept. 5, 1961' L. HORNBOSTEL 2,998,846

7 DANDY ROLL FOR HIGH SPEEDS Filed Aug. 25, 1957 United States Patent 2,998,846 DANDY ROLL FOR HIGH SPEEDS Lloyd Hornbostel, Beloit, Wis., assignor to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Filed Aug. 23, 1957, Ser. No. 679,843 4 Claims. (Cl. 162--297) This invention relates to dandy rolls for paper making machines and more particularly to a novel dandy roll structure for use in high speed machines.

The purpose of a dandy roll on a Fourdrinier type paper making machine is to smooth and finish the forming sheet on the Fourdrinier Wire. The dandy roll eliminates bubbles, foam and major inequalities in formation, and it compacts the fibers and marks the web with a water mark pattern. The dandy roll is ordinarily mounted on hearing or rotatable means which carry the weight thereof and preferably the dandy roll is driven by means cooperating with the means for rotatably mounting the same.

At higher speeds of operation in the F ourdrinier paper making machine the conventional dandy roll (even though driven at the speed desired) tends to create an obstruction to the layer of fiber and water, then forming the web moving on the wire, which causes the surface of this web to rise in front of the dandy roll as though there were a dam present. This disrupts the formation which has already taken place in the Web. It is caused by the resistance of the foraminous peripheral surface portion (usually in the form of a wire screen) of the dandy roll through which the water in the web cannot pass as readily as it would in the absence of the dandy roll. Also,on the leaving side or off-running side of the dandy roll water and some fibers tend to be separated from the main web 7 and carried up part way or all the way around the dandy roll, so that they-may ultimately be thrown back onto the moving very loose web (or stream of moving fibers-in water) so as to cause bubbles or holes. the speed of operation of the conventional dandy roll for wire marking has been limited to approximately 800 feet per minute.

Present-day paper machine speeds are preferably greater than 800 feet per minute. The instant invention provides an improved dandy roll structure which permits such greater operating speeds without causing the defects mentioned in the previous paragraph. In the instantinvention, means are provided for applying a slight pressure differential at the off-running side of the contact areabetween the foraminous dandy roll surface and the wet web. This pressure differential involves a slightly superatmospheric pressure within the dandy roll urging water and particles of fiber back off the travelling foraminous surface portion of the dandy roll, so as to avoid the tendency for such water and particles to adhere to the foraminous surface portion and ultimately be thrown back down onto the wet web. In addition, the instant invention provides for a slightly sub-atmospheric pressure region at'the oncoming side of the area of contact between the foraminous dandy roll'surface portion and the travelling wet web. This slight pressure dilferential across the foraminous surface portion overcomes the tendency for the foraminous surface or screen to resist the flow of the water; and the dam like effect caused by highoperating speeds with .the conventional dandy roll is overcome, so that no buildup of liquid occurs at the on-coming side. It will be appreciated that the pressure differentials created at the oncoming and off-running sides of the area of contact are of a low order. For example, it is not desired to draw water up through the screen and into the interior of the dandy roll at the on-coming side, nor is it desired to blow air back through the dandy roll screen at the ofi-running side to such an extent that disturbance of the wet web Because of this, i

c cc

sure differentials are employed so as to obtain substantiallythe flow pattern of the wet web that is obtained .Patented Sept. 5, 1961 using conventional dandy rolls at low paper machine speeds.

Itis, therefore, an importantobjectl of the instant invention to provide an improved dandy roll structure, f

It is another object of the instant inventiojn'to provide an improved dandy roll for paper making machines com'-" prising a hollow cylindrical roll having a foraminous pen'pheral'sur-face portion and havingacontact area of said foraminous surface extending along its axial length adapted to engage a travelling web supported by a forming wire, and a gland within said roll defining a pressure ar a along the axial length of the roll at the off-running side of said contact area for-urging web particles and water tending to remain on the foraminous surface back onto the web, and defining a low pressure area along the axial length of the roll at the on-coming side ofsaid contact area for preventing buildup .of web particles and water on the outside of the foraminous surface.

Other and further objects, features and advantages of the present invention will becomeapparenttothose skilled in the art from the following detailed disclosure thereof.

and the drawings attached hereto and made a part hereof.

On the drawings: I c FIGURE 1 is .an elevational view, with parts broken away and parts shown in section, showing one embodi ment of the instant invention;

FIGURE 2 is an elevational view, withparts broken: away and parts shown in section, showing a second er g bodiment of the instant invention; and

FIGURES is an elevational view, with parts broken away and parts shown in-section, of a third embodiment of the instant invention.

QAs shownon the drawings:

In FIGURE 1, there is shown a dandy roll generally by the reference numeral 10 whichis mounted on suitable means (not shown) for rotationof. the dandy; roll 10 and for driving thedandy roll. 10 so. as to have substantially the peripheral speed .of a .web W trayelling on a forming wire 11 (in the direction indicatedby the arrow) between two suction flat boxes. shown only partial;' ly atlZ and 13 in a Fourdrinier type'paper machine.

The dandy roll 10 is a hollow cylindrical roll having a fonaminous peripheral surface portion 14 in the form of a fine Wire screen (atthe extreme peripheral surface) mounted on heavier wires and radial fins in the conventional manner of construction for dandy rolls. ."Ihe wire screen may have an ornamentalpattern thereon for water marking purposes. The screenl la atthe extremeperiphery of the roll is a relatively fine screen which tends,

to resist to a limited extent the flow of water therethrough,

Of course, a relatively slow flowing strearnlmay'pass through this screen 14a without anyapparent-resistance and thisis the case at low paper machine operating speeds. At higher speeds, however, the netelfectis'that.

gaging the travelling web W supported by the wire '11."

There is also an off-running area C, whereat there is'a' tendency for the water and fibers ofthe wet web W1 to adhere to the screen 14a. jSuch particles of water and-- fibers may then be thrown back onto the web W to cause 7 holes or bubbles therein.

. 'I'he instant invention avoids the buildup ofa waveiof water at the on-coming side A by creating a slightly reduced pressure on the inside of the screen 14a (so as to overcome the resistance in the screen to water flow); and the instant invention overcomes the tendency for particles to adhere to the off-running side C of the screen 149, by creating a slight superatmospheric pressure at the inside of the screen 14a. This is accomplished by the use of a gland indicated generally by the reference numeral .6. The gland is similar insome respects to the structure of the suction, glands used in suction rolls, although the function of the instant gland G is different. The instant gland G comprises three

strips

15, 16 and 17 which are mounted upon a cross piece 18 that extends the full width of dandy roll and is mounted in a stationary manner (held against rotation) through suitable supports (not shown) extending axially into the dandy roll 10. The

strips

15, 16 and 17 extend generally radially from the.

center mounting element 18 to define ends a, 16a and 17a, respectively, which are mounted in close running relation to the inner periphery of the foraminous periphenal surface portion 14. Housing walls 19, 19 (only the rear ,wall 19 being shown) are mounted at opposite ends of the

strips

15, 16 and 17, so as to define a first closed chamber 20 between the

end walls

19, 19 and the longitudinally extending

strips

15 and 16, and a second closed chamber 21 between the

end walls

19, 19 and the longitudinally extending strips 16 and 17. An air outlet 22 is provided in the back wall 19 for the first chamber 20 and is connected (as shown diagrammatically) to a source of reduced pressure V. It will be appreciated that the reduced pressure of the source V is only slightly below ambient atmospheric pressure, because it is not desired to actually draw water up into the chamber 20. Instead, it is desired only to overcome the inherent resistance of the screen 14a to the flow of water therethrough at the high operating speeds desired. This is overcome by creating only a slight negative pressure on the backside of the screen 14a.

The second chamber 21 is provided with an air inlet 23 in the back wall 19 which, as is shown diagrammatically, is connected to a source S of air under pressure. Only a slight amount of air is required in the chamber 21, because it is not desired to create a blast of air through the screen 14a. Instead, it is desired only to create a slight pressure against the inside of the screen 14a so as to avoid the tendency for droplets of waterand fiber partioles to adhere to the screen 14a as the screen 140: rises away from the travelling .web W It will be appreciated that the foraminous peripheral surface .portion 14 cannot be operated in engagement with a sealing strip, for example, but the ends 15a, 16a and 17a of the.

strips

15, 16 and 17, respectively, are mounted in closerunning relation soas to effect a seal which is good enoughfor .the present operating conditions. In other words, this seal is effective for the very slight pressure differentials which are created across the screen 1411 (in view ofthe high speed operating conditions).

Referring now to FIGURE 2, it will be seenthat FIG- Zsliows a dandy roll indicated generally by the referencenumeral 30 having a foraminous peripheral surface portion 34 mounting a fine wire screen 34a, which hass'ubstantially the structure of the foraminous peripheral portion 14 of FIGURE 1. The foraminous peripheral portion 34 defining the outer surface of the roll 30 is, however, mounted on a perforate shell 44. The perforate shell :44yis structurally similar to the perforate shell of the suction roll'in a paper machine press, except that the shell44 is of much lighter weight (since it is not used :as partof a'press). The perforations 44a therein, however, are of sufficient size and frequency to effect the creation of substantially the same pressure at the inner periphery of the shell44 as is created at the inner periphery of the foraminous peripheral surface portion 34.

cross piece 38 mounts a gland G-l which is defined by end walls 39, 39 (only one of which is shown) and longitudinally extending

strips

35, 36 and 37. The

longitudinally extending strips

35, 36 and 37 terminate with sealing strips 350:, 36a and 37a, respectively, which are urged against the inner periphery of the perforate shell 44 so as to form a seal therewith. This results in the formation of a first compartment 40 defined by the

end walls

39, 39 and the strips 35 and 36 at the oncoming side of the region of contact between the foraminous peripheral surface portion 34 and a web W travelling on a wire 31 in the direction indicated by the arrow. The contact region is indicated generally by the reference numeral 45. At the off-running side of the contact region 45 there is a second chamber 41 defined by the

end walls

39, 39 and the longitudinally extending strips 36 and '37, at which chamber 41 a slight superatmospheric pressure is created. In the back wall 39 there is again provided an opening 42 connected to a source of vacuum (not shown) and an opening 43 connected to a source of air under pressure (not shown) in the manner hereinbefore described. The function of the dandy roll 30 is similar to that of the dandy roll 10, although the structure of the dandy roll 30 is somewhat more complicated in order to obtain better control of the air pressures in the

chambers

40 and 41.

Referring now to FIGURE 3, it will be seen that there is shown a dandy roll indicated generally by the reference numeral 50 which has a foraminous peripheral surface portion 54 with outside wire screen 54a that is substantially the same as the

structure

14, 14a of 'FIGURE 1. An axially extending surface portion (indicated generally by the reference numeral of the foraminous periphery 54 engages a web W travelling on a forming wire 51 moving in the direction indicated by the arrow. At the off-running side (indicated generally by the reference numeral 66) of the contact area 65, there is provided means M for creating a slight superatmospheric pressure at the inner periphery of the peripheral foraminous surface 54. Such means M are in the form of a manifold 67 secured to a cross piece 58 extending the width of the roll 50 and depending

strips

68 and 69 which extend toclose running relation with the foraminous peripheral surface portion 54. Also, there are end walls 70, 70 (only the rear wall 70 being shown) and there is an opening 71 in the rear wall 70 connected to a suitable source of air under pressure (not shown), so that a slight pressure differential may be created within the manifold 67 and between the depending strips 68 and .69 for the purpose of creating a slight superatmospheric pressure at the inner periphery of the foraminous screen portion 54a. This creates the desirable condition of the off-running side 66 which has already been described, namely, the elimination of the tendency for water and fibers to adhere to the screen 54a as the screen 54a rises away from the web W.

It will be understood that modifications and variations may be eifected without departing from the spirit and scope of the novel concepts of the present invention.

I claim as my invention:

1. In a highspeed paper machine, a traveling forming wire having a horizontal forming reach carrying a stream of pulp for forming a paper web, suction means for drawing water through the wire, and a dandy roll structure above the wire, and dipping into the pulp on the wire in the region above said suction means, said dandy roll structure comprising a hollow cylindrical roll having a foraminous peripheral surface portion in the form of a fine wire screen mounted on heavier wire and radial fins and having a contact area of said foraminous surface extending along its axial length adapted to engage the upper surface of a traveling web supported by a forming wire horizontally movable beneath the roll, and a gland within said roll defining an area of slightly superatmospheric pressure extending radially outwardly from the interior of the roll and along the axial length of the roll at the off-running side of said contact area for urging web particles and water tending to remain on the foraminous surface back onto the Web, and defining an area of slightly subatmospheric pressure along the axial length of the roll at the on-coming side of said contact area for preventing buildup of web particles and water on the outside of the foraminous surface.

2. In a high speed paper machine, a traveling forming wire having a horizontal forming reach carrying a stream of pulp for forming a paper web, suction means for drawing water through the wire, and a dandy roll structure above the wire, and dipping into the pulp on the wire in the region above said suction means, said dandy roll structure comprising a hollow cylindrical roll having a foraminous peripheral surface portion in the form of a fine wire screen mounted on heavier wire and radial fins and having a contact area of said foraminous surface extending along its axial length adapted to engage the upper surface of a traveling web supported by a forming wire horizontally beneath the roll, a gland within said roll defining a low pressure area extending radially outwardly from the interior of the roll and along the axial length of the roll at the on-coming side of said contact area for preventing buildup of web particles and water on the outside of the foraminous surface, and means connecting said gland to a source of subatmospheric pressure at a level less than sufiicient to remove Water from the traveling web.

3. In a high speed paper machine, a traveling forming wire having a horizontal forming reach carrying a stream of pulp for forming a paper web, suction means for drawing water through the wire, and a dandy roll structure above the wire, and dipping into the pulp on the wire in the region above said suction means, said dandy roll structure comprising a hollow cylindrical roll having a foraminous peripheral surface portion in the form of a fine wire screen mounted on heavier wire and radial fins and having a contact area of said foraminous surface extending along its axial length adapted to engage the upper surface of a traveling web supported by a forming wire horizontally movable beneath the roll, peripherally spaced sealing strips adjacent the inner periphery of the shell along the axial length of the roll at the ofi-running side of said contact area, and a gland connected to a source of gas under slightly superatmospheric pres- 6 sure and extending radially outwardly from the interior of the roll mounting said sealing strips'for urging web particles and water tending to remain in the foraminous surface back onto the web,

4. In a high speed paper machine, a traveling forming Wire having a horizontal forming reach carrying a stream of pulp for forming a paper web, suction means for drawing water through the wire, and a dandy roll structure above the wire, and dipping into the pulp on the wire in the region above said suction means, said dandy roll structure comprising a hollow cylindrical roll having a foraminous peripheral surface portion in the form of a fine wire screen mounted on heavier wire and radial fins and having an arcuate contact area of said foraminous surface extending along its axial length adapted to engage the upper surface of a traveling web supported by a forming Wire horizontally movable beneath the roll, and peripherally spaced sealing strips adjacent the inner periphery of the shell cooperating with a gland within said roll defining an arcuate pressure area of slightly superatmospheric pressure along the axial length of the roll at the off-running side of said contact area for urging web particles and water tending to remain on the foraminous surface back onto the web and defining an arcuate low pressure area of slightly subatmospheric pressure along the axial length of the roll at the oncoming side of said contact area for preventing buildup of web particles and water on the outside of the foraminous surface, the pressure area at the off-running and on-eoming sides of the contact area being of substantially the same arcuate lengths and each being of relatively lesser arcuate length than the contact area.

References Cited in the file of this patent UNITED STATES PATENTS 1,581,656 Monaghan Apr. 20, 1926 1,739,038 Millspaugh ..Dec. 10, 1929 1,953,060 Berry Apr. 3, 1934 2,669,912 Goodwillie et a1. Feb. 23, 1954 2,718,825 Goodwillie Sept. 27, 1955 2,843,025 Holden July 15, 1958