US 3537955 A
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Description (OCR text may contain errors)
Nov. 3, 1970 A. HUERTA ET 3,537,955
I PICKUP ARRANGEMENT FOR PAPERMAKING MACHINE Filed Nov. 6, 1967 3 Sheets-Sheet 1 mvamoa 0 4 HIJK7I4 EUGENE 5 sK/N/vm Nov. 3, 1970 L. A. HUERTA ETAL 3,537,955
PICKUP ARRANGEMENT FOR PAPERMAKING MACHINE Filed Nov. 6. 1967 a 3 Sheets-Sheet 150' HUX 151/6065 5 s/fm/Mm Nov. 3, 19 70 L. A. HUERTA ETAL 3,537,955
PICKUP ARRANGEMENT FOR PAPERMAKING MACHINE Filed Nov. 6, 1967 3 Sheets-Sheet 3 FIG. 3.
Patented Nov. 3, 1970 3,537,955 PICKUP ARRANGEMENT FOR PAPERMAKING MACHINE Leo A. Huerta, Turin, Italy, and Eugene S. Skinner, Eslier, England, assignors to Beloit Corporation, Beloit, Wis., a corporation of Delaware Filed Nov. 6, 1967, Ser. No. 680,903 Int. Cl. DZlf 1/00 US. Cl. 162306 7 Claims ABSTRACT OF THE DISCLOSURE A pickup arrangement for removing a web from a forming surface wherein an endless felt is urged against the forming surface by means of a guide member having a curved surface in contact with said felt and a substantially flat surface diverging away from said felt thereby creating a pressure differential across the felt.
This invention relates to a felt pickup arrangement for removing a paper web from a traveling forming wire. In the making of paper, the sheet of paper formed on the Fuordrinier wire is transferred from the Fourdrinier wire to the press or dryer section of the papermaking machine by a felt urged into engagement with the sheet and wire by means of a roll, commonly termed a pickup roll. The direction of the felt is changed to diverge from the wire with the sheet adhering to the felt. The felt is normally trained about an upper felt roll downwardly to the pickup roll to be pressed into engagement with the sheet and wire by the pickup roll. As the felt is trained about the pickup roll, the pressure of the roll on the felt and the wire, rapidly squeezes water out of the felt into the web or sheet and urges the sheet into the wire by the rapid flow of water from the felt through the sheet as it is squeezed by the wire. This causes the sheet to become entangled into the wire and makes the subsequent washing of the sheet onto the felt more difficult as the felt expands when it leaves the wire. When the pressure on the felt decreases as it turns away from the wire, the expansion of the felt will cause a back flow of water from the underside of the wire which flow must be of sufficient velocity and volume to tear the base fibers of the sheet loose from the wire. This velocity of back flow is limited by the rate of felt expansion, as it leaves the wire.
It has been found that the elfectiveness of the above described prior art pickup devices varies directly with the pressure between the pickup roll and the Fourdrinier wire between which the felt and the web is sandwiched. This pressure is defined by the formula P: T/R in which:
P is the pressure between the wire and the web in pounds per square inch;
T is the tension in the Fourdrinier wire in pounds per linear inch;
R is the radius of the pickup roll in inches.
It therefore follows that in order to increase the pressure it is necessary to either reduce the radius of the roll or to substantially increase the tension in the wire.
The centrifugal force F =S /R wherein S is the speed of the web; R is the radius of the path through which the web travels,
also aids in the transfer of water from the felt to the web. From the above defined relationship it is also apparent that the radius R should be reduced in order to increase the centrifugal force F. Therefore, by reducing the radius R of the web transfer device a dual advantage is obtained in that both the pressure and the centrifugal force are increased with attendant results.
The radius of the conventional pickup roll practical for dynamic balance and deflection limits the possibility of obtaining the desired pressure and the problems resulting from an increase in wire tension are also not considered acceptable to justify the desirability of obtaining a higher pressure.
It has therefore been proposed to remedy the foregoing disadvantages in the transfer of paper from the wire to the press section of a paper making machine by eliminating the conventional felt pickup roll and replace it with a stationary slipper or shoe having a relatively small radius of curvature thereby increasing the unit pressure between the wire and the sheet at the shoe so that an increase in the compression and expansion rate of the felt and the flow of water back into the felt by the expansion thereof is obtained.
Actual trials in the field have indicated that the results obtained with this approach are quite satisfactory, however, it has also been found that, although the transfer of the web from the wire to the felt by means of the small radius transfer device is quite satisfactory, there appears to be a continuing problem with retaining the web on the felt immediately following the transfer zone. It should be borne in mind that due to the increased pressure at the transfer point a considerable amount of water is forced to flow back into the felt immediately following the maximum point of pressure thereby causing the felt to be relatively moist with the attendent problem of retaining the newly transfered web onto the felt.
Furthermore, as the felt diverges from the wire after the pickup point and travels around a surface having a small radius the centrifugal force throws olf part of the water and tends to throw off the web retained by the felt with consequent damage to the web which is effectively transferred.
A principle object of the present invention is to remedy the foregoing problem in the transfer of paper from the wire to the press section of a papermaking machine by the provision of a vacuum generating means on the inside of the felt immediately following the point of transfer.
Another object of the present invention is to provide for a web transfer device which includes means for creating a pressure differential across the felt at a point on the felt immediately following the point of transfer of the web from the wire to the felt.
Yet another object of the present invention is to provide for a web transfer device which includes means for creating a pressure differential across the felt at a point starting immediately following the point of transfer of the Web from the wire to the felt and whereby this pressure differential is sustained for an extended period of time.
A still further object of the present invention is to improve upon the pickup of a newly formed web from the Fourdrinier wire by providing for a means for removing water from the inside of the pickup felt immediately following the pickup device. These and other objects of the invention will appear from time to time as the following specification proceeds and with reference to the accompanying drawings wherein:
FIG. 1 is a diagrammatic view of a felt pickup arrangement constructed in accordance with the principles of the present invention;
FIG. la is a diagrammatic view of a modification of the arrangement shown in FIG. 1.
FIG. 2 is an enlarged view of a pickup device constructed in accordance with the principles of the present invention; and
FIG. 3 is a diagrammatic illustration of a further embodiment of the present invention.
In the embodiment illustrated in FIG. 1 of the drawings, the discharge end or portion of a looped Fourdrinier wire 10 is shown as having a newly formed web W thereon and contacted by an endless pickup felt 12, picking the web from the wire by the backfiow of water onto the felt caused by expansion of the felt as the felt is urged against the wire and then gradually released therefrom. The wire 10, is shown as being trained downwardly about a roll 13 in a downwardly inclined discharge run, to and about a roll 15 spaced a substantial distance in advance and below the roll 13 and about which the wire changes its direction for the return run of the wire.
The pickup felt 12 may be a conventional form of felt commonly used for pickup purposes and trained in an endless loop. The felt 12 has a top run 14 which may be uniformly cleaned and moistened, and turns about an idle roll 16, disposed above and shown in FIG. 1 as directing the felt into an approaching run to the Fourdrinier wire 10. From the idler roll 16 the felt passes downwardly in an inclined direction and is pressed to engage and travel with the sheet W and wire 10 by a pickup shoe 17, contoured and positioned to provide a relatively intense contact pressure between the .felt and the wire and to provide for a small angle of divergence of the felt and web from the wire. The pickup shoe 17 and its mounting and contour will hereinafter be more clearly described as this specification proceeds.
A uniform quantity of moisture may be supplied to the back sideof the felt by a water shower or other siutable device 18 to facilitate the sliding of the felt 12 over the shoe 17.
After the web W has been removed from the wire 10 by the felt 12 is it conveyed to a press section 19 for further removal of water by pressing action between a plurality of rolls. The press section 19 may be of any suitable design depending on the nature of the web W formed on the wire 10.
In FIG. la a scraper 35 is provided immediately following the shoe 17. The scraper 35 removes the water extracted from the felt 12 by means of the diverging portion 21 of the shoe 17. Attached to the scraper 35 is a saveall 36 designed to catch the'water removed by the scraper 35 and to convey the water away from the machine by gravity in a conventional manner.
In FIG. 2 of the drawings we have illustrated the development of the shoe contour which will achieve the flow of water from the felt through the sheet and the wire in the quantity desired at the required location resulting in'a substantially instant termination of pressure so that the felt expansion can take place rapidly and the sheet can be effectively transferred to the felt and retained thereon.
In the design of the shoe the unit pressure exerted on the shoe by a felt or wire pulled around the shoe is a function of the tension in the felt or wire and the contour of the surface of the shoe.
The unit pressure is equal to the tension in the wire or felt divided by the radius or the mean radius of the contoured surface of the shoe.
The wire thus exerts the foregoing unit pressure on the moist felt as the felt and wire wrap the surface of the shoe. This unit pressure causes water to flow from the felt through the sheet and wire to the underside of the wire in the pickup zone.
In FIG. 2 the contour of the entrance face of the shoe is shown as being struck from a relatively small radius R1 which may be a radius varying from inch to approximately 10 inches depending on the particular felt and wire arrangement. The entrance face 20 terminates and merges into a relatively straight surface 21. The surface 21 commences at 22 and is tangent to the entrance surface 20. The surface 21 diverges away from the felt 12 at an angle A which may vary from approximately /2" to 5". The divergence between the felt 12 and the surface 21 creates an area Z of intense vacuum which 4 greatly assists in retaining the web W on the under side of the felt 12.
While in some cases the shoe may be so constructed that the angle A is fixed, it is also possible to adjust the angle by rotating the shoe about the centre of the radius R1. Such an adjustment will permit optimum operating conditions for different quantities of water in the web and felt following the pickup point. It is understood that surface 21 may be slightly curved and that the curvature might be adjusted if the surface 21 were made of a flexible or thin material. If the pickup shoe is made of a rigid material, adjustment of angle A would be permitted by constructing enclosure 24 to incorporate suitable flexibility. While the angle A is preferably within the range of from /z to 5 larger angles may be advantageously used for special applications such as for example where a relatively low felt tension is used.
The surface 21 may have a small curvature, starting at the tangent point 22, in the form of a very large radius or of a variable radius often described as a foil.
Due to the high unit pressure created between the felt 12 and the wire 10 in the contact zone 20 defined in part by the entrance face a substantial amount of water is pressed out of the felt and through the sheet and wire due to the relatively instantaneous compression of the felt in the pressure zone. The Water, thus forced through the wire washes the web W from the wire by releasing the web fibers which are entangled in the interstices of the Fourdrinier wire. When the pressure is reduced the water is forced to flow in the opposite direction, that is, from the wire back into the web W and felt 12 taking the web W with it. The spontaneous expansion of the previously compressed felt causes this return flow of water. The intensity of the flow of the water from the felt into the web and through the wire is relatively abrupt and occurs at high velocity whereas the reverse flow is much more gradual since the pressure is released more gradually. With the gradual return flow of water a substantial portion of the water will remain on the underside of the felt 1 2 which is the side to which the web W has been transferred. Due to this uneven distribution of the water in the felt and the effect of centrifugal force the web W has a tendency to drop off the felt 12. The creation of a vacuum as previously explained, by means of the diverging surface 21 and the virtual elimination of centrifugal force because of the substantially flat surface, will cause the web W to become firmly adhered to the felt 12 and as the felt 12 travels along the vacuum zone a substantial portion of the water in the felt will be transferred to the inside surface of the felt.
The water thus transferred to the inside of the felt 12 may be effectively removed from the felt by means of a scraping device 23 located in scraping contact with respect to the felt and immediately following the vacuum zone Z.
In order to further assist in the creation of a vacuum in the zone Z and to assist in the removal of the water removed from the felt by the scraping device 23 it may be desirable to form a vacuum chamber V by means of an arcuately shaped wall portion 24 one end of which is attached to the pickup shoe at 25 and the other end of which is attached to the scraping device 23 at 26. The vacuum chamber may also be designed so as to assist in the removal of Water scraped off the felt by the scraping device 23.
It is understood that a number of different press arrangements might be employed following the pickup device to remove water from the web W which is adhering to the felt 18. For example, the felt 18 with the web W may be directed to transfer the web W directly to a drying cylinder or other drying means.
FIG. 3 illustrates another embodiment of the present invention in which the point of transfer is directly in contact with the forming wire trained around a cylinder. The cylinder is constructed with an open surface created by drilling grooves or a grid pattern, with other portions of the forming wire surface being used for the formation of the web.
In FIG. 3 a cylinder 30 of suitable construction is Wrapped around its circumference by the forming wire 31. The web W could be formed on any portion of the forming wire sufficiently removed from the pickup device so as to not interfere with the pickup. The felt enters the pickup shoe essentially as in FIG. 1 making contact with the Web W and causes the Web to adhere thereto.
It will thus be seen that I have provided for an improved pickup arrangement for removing a paper Web from a traveling Fourdrinier wire and while we have herein shown and described one form in which the invention may be embodied, it should be understood that various modifications and variations in the invention may be obtained without departing from the spirit and scope of the novel concepts.
We claim as our invention:
1. In a papermaking machine, a looped Fourdrinier Wire for forming a paper web thereon,
an endless pickup felt,
a guide member extending transversely of said felt for urging said felt into contact with the paper web on said wire,
said guide member having a curved peripheral surface in contact with said felt and a substantially fiat surface diverging away from said felt in the direction of travel of said felt at an acute angle of from /2 degree to five degrees for sufiicient length to create a substantial vacuum between said felt and said flat surface.
2. The structure of claim 1, wherein said curved peripheral surface has a radius of from inch to 10 inches.
3. The structure of claim 1, wherein a scraping device is urged into contact with said felt immediately following said guide member.
4. The structure of claim 3, wherein said guide member and said scraping device are connected to each other by means of a vacuum chamber.
5. The structure of claim 1, wherein said flat surface is connected to adjustment means whereby the vacuum created by said surface may be varied.
6. The structure of claim 5, wherein said adjustment means comprises means to vary the curvature of said surface.
7. The structure of claim 5, wherein said adjustment means comprises means to vary the angle of said surface with respect to the felt.
References Cited UNITED STATES PATENTS 3,093,535 6/1963 Blauns et al 162-274 X 3,207,658 9/1965 Lamb 162 306 3,309,263 3/1967 Grobe 162-306 3,432,385 3/1969 Thorp 162-297 REUBEN FRIEDMAN, Primary Examiner T. A. GRANGER, Assistant Examiner US. Cl. X.R. 162-274, 363