US3514372A - Headbox method and means for blending of multiple jets - Google Patents

Description

May 26, 1970 w. B; BOY(C=E ETAL HEADBOX METHOD AND MEANS FOR BLENDING OF MULTIPLE JETS Filed Nov. 29, 1966 2 Sheets-Sheet 1 [NVENTUR5 mum/w 5. 50 v65 Jseorv/e pfieez/wsx/ i ATTORNEYS May 26, 1970 w, B BOYCE EI'AL 3,514,372

HEADBOX METHOD AND MEANS FOR BLENDING 0F MULTIPLE JETS Filed Nov. 29. 1966 2 Sheets-Sheet 2 I N VENTOR5 VV/LL/AM 5. flax c5 Jaea/we P eez/msK/ BY M .'\TT()RNEYS United States Patent 3,514,372 HEADBOX METHOD AND MEANS FOR BLENDIN G 0F MULTIPLE JETS William B. Boyce, Rockton, Ill., and Jerome P. Brezinski,

Neenah, Wis., assignors to Beloit Corporation, Beloit,

Wis., a corporation of Wisconsin Filed Nov. 29, 1966, Ser. No. 597,738 Int. Cl. D21f 1/06 US. Cl. 162-216 8 Claims ABSTRACT OF THE DISCLOSURE Method of and means for delivering stock to the travelling forming wire of a papermaking machine. The stock is delivered under pressure from a distributor to a chamber having a slice opening to the forming Wire. Inside the chamber the stock is divided into a plurality of separate streams in expanding diffuser nozzles in which the velocity of the stock is decreased, then the stock is discharged to flow in separate streams through flow passages in a flow element after which the streams are merged with one another, thereby eliminating eddy currents and cross-currents upstream of the slice.

This invention relates to the handling of fluid slurries, and more particularly, to the maintenance of desired fiber dispersions in stock slurries such as papermaking and the like. Specifically, the present invention is directed to a method and means for controlling the mixing or blending of multiple jets so that undesirable flow patterns such as vortexes do not develop in the fluid.

Prior attempts to establish uniform distribution of fibers in the stock slurry and to maintain fiber distribution, once established, along the fiow path or stream in the head box in the so-called pre-slice area prior to disposition of the stock on the forming surface have involved employment of complicated auxiliary equipment used to mechanically vibrate, shake or stir the stock, all of which actions induce turbulent flow of currents of large amplitude in the stock slurry.

For example, such devices as rectifier and stave rolls, perforated plates, rod banks, baffles, etc., have been used to control cross currents and other undesirable flow patterns which are caused in the slurry passing through the head box. The disadvantages of those devices which align the flow in the machine direction by presenting a resistance to the flow is that they cause a turbulent wake, since the streams which they divide the flow into must coalesce downstream of the device. The effect is diminished by having a higher percent open area, as for example, in a rectifier roll. However, the flow-aligning capacity is somewhat less than desired, and the narrower land area can cause fiber hang-up and lumps. Further, a rectifier roll must rotate to remain clean, making it and its auxiliary equipment expensive.

One such method used to eliminate eddy currents in fiow boxes of high production papermaking machines is disclosed in an application Ser. No. 459,311, filed May 27, 1965, now Pat. No. 3,400,044, which is assigned to the same assignee.

Therefore, one of the primary objects of the present invention is to provide means for blending a plurality of stock jets in such a manner so as to substantially eliminate eddy currents or cross currents within the flow box of high production papermaking' machines.

Another important object of the present invention is to provide an improved method and apparatus for effecting the desired distribution of fibrous material in a liquid vehicle, such as the fibers in a papermaking stock or slurry, by use of a stock flow controlled method and means which include at least one sequence or bank or devices which effeet a high entrance loss, minimum velocity head gradient or variation in the downstream flow, and a high percentage opening area at the exit side so as to obtain stable flow through the slice.

A feature of the present invention is the use of a flow element which is positioned downstream of a plurality of stock diffuser nozzles, and which flow element provides uniform blending of jet streams when they coalesce.

Briefly, fibrous material in liquid suspension is delivered to a flow box or pre-slice chamber, and thereafter through a slice onto a forming wire. A distributor is positioned within the pre-slice chamber to distribute the stock to a plurality of diffuser nozzles or other flow resistance devices. The distributor is so arranged as to provide substantially the same pressure at the entrance of each diffuser nozzle. The stock is forced through the diifuser nozzles and thereafter subjected to a flow element, which has a plurality of individual compartments each positioned in front of a corresponding diffuser nozzle. The flow element has a greater cross-sectional open area than the open area of the diffuser nozzles. This feature allows the stock to diverge within the passage formed by the side walls of the flow element thereby expending much of its kinetic energy part of which is converted into pressure. As the stock moves through the fiow element the velocity thereof is substantially reduced due to the high percentage open area of the flow element. Therefore, as the stock leaves the flow element it will blend or coalesce uniformly and be substantially free of eddy currents, as compared to prior art devices which merely reduce the amplitude of such eddy currents.

The stationary fiow element of the present invention has a high open area of approximately 84%, and as a result there is little turbulent activity downstream caused by blending of the jets from the individual compartments of the flow element. The upstream side of the stationary flow element has an open area of 84% as well, and the thin partition walls are kept free from fiber buildup by turbulent activity and back-flow induced by the tube bank diifuser jets. There also exists an extremely turbulent zone between the diifusers and the stationary flow element which dissipates part of the kinetic energy of the jets. Furthermore, the large amount of solid surface ofifered by the stationary flow element compartments also absorbs kinetic energy of the diffuser jets, and slows the jets down which also aids in the conversion of jet kinetic energy to pressure energy.

Other objects and features and advantages of the present invention will become apparent to those skilled in the art from the following detail description when taken in conjunction with the accompanying drawings wherein like reference numerals throughout the various use of the drawings are intended to designate similar elements or parts and wherein:

FIG. 1 is a somewhat diagrammatic perspective view of a flow box having a portion cut away to clearly illustrate the flow element therein;

FIG. 2 is an elevational perspective view showing one of the flow passages of the flow element in conjunction with a corresponding diifuser nozzle;

FIG. 3 is an elevational front view of the flow element of FIG. 1 showing the diffuser nozzles in alignment therewith;

FIG. 4 is an alternate embodiment with the flow element of FIG. 3; and

FIG. 5 is still another alternate embodiment of the flow element of FIG. 3;

FIG. 6 is still another alternate embodiment of the flow element of FIG. 3.

As seen in FIG. 1, a pre-slice chamber 10 is provided with a slice 11 for delivering fibrous material in liquid suspension to a forming wire 12. The forming wire 12 may be considered a continuously moving wire which is wrapped about a plurality of rollers, such as the roller 13.

Aninlet 14 is provided for receiving stock which is to be delivered to the slice 11. However, the stock is first delivered to adistributor 16 which is in fluid communication with a plurality of diffuser nozzles 18 through a corresponding number of openings or apertures 19 formed in a Wall member or transversestock flow barrier 19a. The stock is delivered to thedistributor 16 with sufi'icient pressure to cause the stock to be forced through the diffuser nozzles 18 extending downstream with a gradually expanding cross-section en route to the slice 11. The downstream end of the diffuser nozzles 18 define a plurality ofopenings 20 through which the stock flows at a relatively high rate. The total cross-sectional open area of theopenings 20 is substantially less than the total crosssectional open area of the downstream portion of the pre slice chamber 10. Therefore, the stock leaving the diffuser nozzles 18 will form a plurality of high velocity jet streams which slowly diverge and come together to form a substantially solid mass of stock enroute to the slice 11. However, as the jet streams of the stock merge together, eddy currents are caused. These eddy currents are an undesirable effect in the manufacture of paper since they form clots and other deformations on the web being formed on the forming wire 12.

To eliminate such eddy currents, a flow element 21 is positioned downstream of and in spaced relation to the diffuser element 17 and has substantially the same crosssectional dimension along the length thereof in the direction of the flow. The flow element 21 comprises a plurality offlow passages 22 which are in alignment with corresponding ones of the diffuser nozzles 18. The crosssectional open area transverse to the stock flow of eachflow passage 22 is greater than the cross-sectional open area of theopenings 20. Therefore, the jet stream of stock will diverge toward the side walls of theflow passages 22, thereby dissipating much of the kinetic energy of the jet streams. The eddy currents caused by the high velocity jet streams are experienced in the upstream portion of theflow passages 22, but as the stock passes through the flow passages, the velocity thereof is substantially reduced and the effects of eddy currents are substantially eliminated. Therefore, as the stock leaves theflow passages 22, the stock will coalesce substantially free of eddy currents. It it is believed that this desirable phenomenon is accomplished by the deceleration effect which the flow element 21, which has a uniform cross-section along the length thereof, offers the stock passing therethrough as well as the cross-sectional configuration of the jet stream leaving the flow element. For example, the cross-section of the jet stream leaving the diffuser nozzles 18 is cylindrical, therefore only the tangential peripheral portions of the jet streams initially engage one another thereby leaving a relatively large open area between each of the jet streams for eddy currents to develop. On the other hand, the cross-section of the open area of the flow element 21, as seen in FIG. 3, is square, thereby effectively providing a larger peripheral surface area between adjacent jet streams and essentially eliminating the open area Where eddy currents might develop. Therefore, as the stock leaves the flow element 21 it is substantially free of eddy currents and the stock will be delivered to the slice 11 in a stable manner free of clots or other defects.

The distributor 1-6 is continuously tapered having the larger end in proximity to theinlet 14 and the smaller end in proximity to anoutlet 23. This feature provides a substantially uniform pressure gradient across the apertures 19, which, in turn, cause substantially uniform flow of the stock through the diffuser nozzles 18. Theoutlet 23 of thedistributor 16 is connected to asecondary inlet passage 26 through aline 27. Therefore, the stock which is delivered to thedistributor 16 but which does not pass through the diffuser nozzle 18 is recirculated to the sec- 4ondary inlet 26 to combine with the stock entering theinlet 14, of thedistributor 16. It will be understood that suitable pump means may be provided in theline 27 to increase the flow pressure of the stock passing therethrough.

Seen in FIG. 2 is the detail construction of one of the diffuser nozzles 18 and a portion of the flow element 21 defining one of theflow passages 22. In the illustrated embodiment of the present invention the following dimensions of the diffuser nozzle 18 and thefiow passage 22 have been found to give excellent results. The reduced diametercylindrical portions 30 has an axial dimension A which is equal to 4 inches and an inside diameter of .8 inch. The conical portion 31 has an axial dimension B which is equal to 10 inches. The reduced diameter end of the conical portion 31 is equal to the diameter of thecylindrical portion 30. The increaseddiameter portion 32 has an axial dimension C which is equal to 10 inches and an inside diameter equal to 1.4 inches. It will be understood that the inside diameter of the large end of the conical portion 31 is substantially equal to the inside diameter of thecylindrical portion 32. Theflow passage 22 is spaced a dimension D which is three inches from the end of the diffuser nozzle 18. The outside dimension of theflow passage 22 is 2.75 inches square while the length E is equal to 12v inches.

When using the specific dimensions illustrated hereinabove, the flow rates of the diffuser nozzle 18 and flowpassage 22 are as follows:

At a given pressure the velocity of the stock passing through thecylindrical portion 30, is 18 feet per second. The velocity of the stock passing through the increaseddiameter portion 32 of the diffuser nozzle 18 is 5.88 feet per second. On the other hand, the velocity of the stock leaving thefiow passage 22 is 1.20 feet per second. Therefore, theflow passage 22 of the flow element 21 substantially reduces the velocity of the stock passing through the pre-sliced chamber 10, thereby allowing the stock to coalesce in a gentle manner and free of eddy currents. This even blending of the jet streams of the stock passing through the pre-slice chamber 10 is attributed partly to the relatively large open area at the exit of the flow element 21. By way of example, the open area of the flow element 21 is 84% that of the cross-sectional area of the pre-sliced chamber downstream thereof. Comparing this to the approximate 17% open area of the diffuser nozzles, it can be seen that the flow element 21 provides a substantial improvement in the manner in which the jet streams blend together. Also, much of the kinetic energy of the jet stream leaving the diffuser nozzle 18 is dissipated within the side walls of theflow passage 22 in the vicinity near the exit of the diffuser nozzle 18. Furthermore, the back flow in the area where the diffuser nozzles discharge into the static flow element 21 keeps the upstream edges of the compartments of the fioW element free of fiber buildup.

Seen in FIG. 4 is an alternate embodiment of the fiow element 21. Aflow passage 22 has a rectangular crosssection. Also, the cross-section of theflow passages 22 may be polygonal as illustrated by thehexagonal passages 22" shown in FIG. 5. In addition, the cross-section of the flow passage may be round as illustrated by thepassages 22 shown in FIG. 6.

Therefore, the present invention has provided a new and improved method and apparatus for substantially eliminating eddy currents in a stock passing through a pre-sliced chamber. Although in the illustrated embodiment of the present invention, the stationary flow element 21 is shown as being positioned downstream of the diffuser nozzle 18, it is not to be construed in a limiting sense. Also, it will be noted that the taper of the diffuser nozzle 18 may vary from 3 degrees to degrees included angle, and that other variations and modifications may be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

1. A method of supplying paper stock to the travelling forming wire of a papermaking machine comprising the steps of:

establishing a flow of paper stock,

dividing the flow into a plurality of parallel diverging diffuser nozzles for reducing the velocity of the streams therethrough,

discharging said streams from cylindrically-shaped outlets of said diffuser nozzles to a corresponding plurality of parallel flow passages aligned with said difi'user nozzles and having larger cross-sectional areas than the outlets of said diffuser nozzles and spaced therefrom to enable said streams to diverge therebetween to create turbulence and to convert kinetic energy to pressure and to reduce the velocity of the streams as they move through the flow passages,

discharging the streams from the flow passages and merging them into a single stream, and

directing the single stream to the travelling wire of a papermaking machine.

2. Apparatus for supplying paper stock to a papermaking machine comprising:

means forming a slice and a pre-slice flow chamber connected to said slice for directing a flow of paper stock to said slice,

said slice being downstream of said chamber,

a portion of said chamber forming means defining a transverse stock flow barrier having a plurality of circular apertures formed therein in generally parallel spaced relation,

a plurality of spaced generally parallel stock diffuser nozzles connected to said barrier each in alignment with a corresponding one of said apertures and in each case having an upstream cross-sectional area that is the same as the aperture cross-sectional area and extending downstream with a gradually expanding cross-section to define a circular discharge opening greater than the aforesaid cross-sectional area,

a flow element positioned in spaced relation to and downstream of said difiuser nozzles having substantially the same cross-sectional dimension along the length thereof in the direction of said flow for reducing the effects of eddy currents of the paper stock passing through the flow chamber,

said flow element comprising means forming a plurality of flow passages of uniform cross-section along the length thereof aligned respectively with said difiuser nozzles,

the cross-section of each said flow passages transverse to the flow being greater than the cross-section of the discharge opening of its corresponding immediately upstream diffuser nozzle, and distributor means upstream of said chamber for delivering paper stock to the diffuser nozzles at a substantially uniform pressure.

3. The apparatus of claim 2 wherein said distributor means comprises means forming a stock inlet and a stock outlet and including circulating means connected to said stock outlet for receiving surplus stock therefrom which does not pass through said diffuser nozzles and delivering such surplus stock back to said stock inlet.

4. The apparatus of claim 2 wherein each of said flow passages has a rectangular cross-sectional configuration transverse to the stock flow.

5. The apparatus of claim 2 wherein each of said flow passages has a square cross-sectional configuration transverse to the stock flow.

6. The apparatus of claim 2 wherein each of said flow passages has a polygonal cross-sectional configuration transverse to the stock flow.

7. The apparatus of claim 2 wherein each of said flow passages has a hexagonal cross-sectional configuration transverse to the stock flow.

8. The apparatus of claim 2 wherein the total crosssectional area of said flow passages is greater than the total area of the discharge opening of said difiuser nozzles.

References Cited UNITED STATES PATENTS 3,400,044- 9/1968 Justus 162343 S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R. 162-343

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