WO1992017644A1

WO1992017644A1 - Method and apparatus for improved twin wire forming

Info

Publication number: WO1992017644A1
Application number: PCT/US1992/001817
Authority: WO
Inventors: Richard J. Krall; Richard W. Schaftlein
Original assignee: Scott Paper Company
Priority date: 1991-04-08
Filing date: 1992-03-03
Publication date: 1992-10-15
Also published as: EP0532741B1; AU656190B2; CA2079227A1; EP0532741A1; AU1752092A; DE69220160D1; JPH05508200A; DE69220160T2; FI925537A0; ATE154082T1; FI925537A; KR930700286A; ES2101845T3; KR100209968B1

Abstract

Disclosed is an improvement to twin wire forming wherein an open support structure in the form of an opened or grilled breast roll or a slotted forming shoe supports at least a portion of the outer wire in the forming throat. In such manner, the gap between the open support structure and the forming cylinder can be narrowed such that the gap is less than or equal to the thickness of the jet of stock injected between the wire to form the web. The jet of stock so injected impinges on both the forming cylinder and the open support structure and immediate drainage is provided through the outer wire without substantially varying the tension or radius of the outer wire thereby generally improving uniformity and, in particular, improving basis weight uniformity of the web produced.

Description

METHOD AND APPARATUS FOR IMPROVED TWIN WIRE FORMING

BACKGROUND OF THE INVENTION 1. Field of the Invention.

The present invention relates generally to paper machines and, more particularly, to twin wire forming for the production of a web.

2. Brief Description of the Prior Art. A variety of what may be characterized as twin wire formers are known in the prior art. One such twin wire former is disclosed in U.S. Patent No. 4,209,360 to Stenberg, et al. Stenberg teaches an apparatus having a head box arranged to inject a jet of stock into a forming throat between inner and outer forming wires. The forming throat may be roughly as the area or gap between a forming roll and a breast roll and extending to include the area between such inner and outer wires supported thereon. This arrangement of a head box which injects stock into the gap between a forming roll and a breast roll is typical of many twin wire formers. Also typical of such twin wire formers is the fact that the breast roll is a solid or smooth roll whereas the forming roll may be an open roll allowing for drainage or a solid roll.

In the operation of such a twin wire former, care must be taken to avoid impinging a jet of stock on the surface of the breast roll. If the jet of stock touches the surface of the breast roll (impinges upon), the jet will be diverted around the breast roll giving rise to jet pumping. Impingement of the jet on a solid breast roll generally results in sheet disturbance and poor formation. This constraint of not impinging on a solid breast roll becomes a limiting factor on the minimum gap setting between the breast roll and the forming roll. The minimum operating gap is constrained by a situation known as jet "pumping" or vacuum pulse. Generally, if the gap is larger, then drainage is delayed to a later location on the outer fabric which adversely effects homogeneous sheet formation, uniformity and stability of basis weight and other web properties. Even more importantly, this delayed drainage can severely affect layer uniformity and purity of a stratified sheet. Further, impingement of the jet directly on the free span of the outer wire commonly results in distortion and corrugation of the outer wire which can significantly contribute to sheet non-uniformities. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved twin wire former which yields a web having improved uniformity.

It is a further object of the present invention to provide an open, substantially rigid support structure to allow for drainage through the outer wire of the twin wire former in the area of the forming throat.

Yet another object of the present invention is to provide an apparatus which allows for the narrowing of the gap between the breast roll and the forming roll in a twin wire former while still avoiding the occurrence of jet pumping. Briefly stated, these and numerous other features, objects and advantages of the present invention will become readily apparent upon a reading of the detailed description, claims and drawings set forth hereinafter. These features, objects and advantages are accomplished by providing the outer wire of the twin wire former with an open, substantially rigid support structure in the area of the forming throat. In such manner, the gap between the open support structure, which may be a grooved breast roll, and the forming roll can be narrowed such that the jet of stock delivered from the head box is impinged upon both the forming roll and the open support structure. This arrangement allows for immediate drainage of the web through the outer wire of the twin wire former while avoiding the undesirable jet pumping. This results in an extended forming throat despite the fact that the gap between the forming roll and the breast roll is narrowed. Thus, an extended drainage area through the outer wire is achieved over that of the typical prior art twin wire former. In this extended area of drainage, the jet of stock is contained between the supported inner and outer wires. Further, because the outer wire is rigidly supported, the position radius and tension of the outer wire are held substantially constant and uniform. This situation results in the reduction of variation in the drainage process yielding greater sheet uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a basic schematic of a typical prior art forming roll/breast roll arrangement for a twin wire former. Figure 2 is a basic schematic of the forming roll/open breast roll arrangement of the present invention.

Figure 3 is a partial section of one open breast roll showing the contoured surface thereof.

Figure 4 is a partial section of another open breast roll showing an alternate pattern for the contouring of the surface thereof.

Figure 5 is a basic schematic of an alternative embodiment of the forming roll/outer wire open support structure of the present invention. Figure 6 is a basic schematic of an alternate embodiment prior art twin wire former having two leading breast rolls.

Figure 6A is a basic schematic of an alternative embodiment of the improved twin wire former of the present invention. Figure 7 is a side view schematic showing the cross- sectional area of the forming throat of a typical, prior art, twin wire former.

Figure 8 is a side-view schematic showing the cross- sectional area of the forming throat achieved with the first above-stated embodiment of present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning first to Figure 1, there is shown a basic schematic of the relative location of the forming cylinder 10 and a solid breast roll 12 of a typical prior art twin wire former. The twin wire former includes head box 14, inner wire 16 and outer wire 18. Head box 14 delivers a jet of stock 20 having a set thickness T into the forming throat 22 between inner wire.16 and outer wire 18. Forming cylinder 10 may be a suction-type open roll or solid. The gap between forming cylinder 10 and solid breast roll 12 must be wide enough to assure that no part of the jet of stock 20 will impinge upon solid breast roll 12. Thus, where the jet of stock 20 strikes the outer wire 18, outer wire 18 is unsupported and jet of stock 20 strikes at a rather shallow angle.

The operation of the twin wire former depicted in Figure 1 is similar to the operation of the twin wire formers described in U.S. Patent Nos. 4,209,360; 4,100,018; 3,876,498; and

3,056,719 which are hereby incorporated by reference herein.

Looking next at Figure 2 there is shown a basic schematic of the forming cylinder/breast roll arrangement of the present invention for use with an otherwise typical twin wire former. As with the prior art arrangement, the forming cylinder 30 may be a suction-type roll or a solid roll. The breast roll 32 is open or grilled such that there are a plurality of annular grooves 34 thereabout. The open breast roll 32 may or may not have a cover sleeve mesh depending upon the design of the outer wire and the particular product application. There is an inner wire 36 travelling about forming roll 30 and an outer wire 38 which travels first around open breast roll 32 and then about forming cylinder 30. Head box 40 delivers a jet of stock 42 having a thickness T into the forming throat 44 between the inner wire 36 and the outer wire 38.

It should be noticed that, even though Figure 1 and 2 are not to scale, the gap between the forming cylinder 30 and the open breast roll 32 is narrower than the gap shown in Figure 1. This is evidenced by the fact that the jet of stock 42 is depicted as impinging on both the forming roll 30 and the open breast roll 32. In such manner, the free span of the outer fabric 38 from the point where it leaves the grilled or open breast roll 32 to the point where it contacts or closely approaches the inner wire 36 on forming cylinder 30 is reduced relative to the free span depicted in Figure 1. Initial and early dewatering through the outer wire 38 is thus accomplished with greater support in the area of the forming throat 44 and with substantially rigid support at beginning area of the forming throat 44. The forming throat 44, from a two-dimensional perspective, is the area defined by the combination of arcs and segments interconnecting point A where the jet of stock 20, 42 impinges upon the inner forming wire 16, 36, the point B where the jet of stock 20 impinges upon the outer forming wire 18, 38, and the point C where the inner and outer forming wires converge. (See Figures 7 and 8). Thus, the shaded area in Figure 7 illustrates representative forming throat 22 of a typical prior art twin wire former while the shaded area in Figure 8 shows the forming throat 44 of the embodiment of the present invention depicted in Figure 2.

It has been shown that the amount of impingement of the jet of stock 42 upon open breast roll 32 can be significantly varied while still attaining improved uniformity. However, test results indicate that impingement upon breast roll 32 should preferably be approximately one-third (1/3) of the thickness T of the jet of stock 42. It is well known to those skilled in the art of twin wire formers that uniformity in the sheet drainage and dewatering processes is of critical importance to the formation of the sheet. It is particularly important to have uniformity in the early, initial drainage because any early non-uniformities influence not only the initial drainage but will continue to be detrimental to later drainage. In the free span area of outer wire 18 in forming throat 44, the forces acting to cause drainage of the jet of stock 42 often can be simply and quantitatively described by the following relationship: Drainage pressure equals the tension in the outer wire divided by the radius of the outer wire. In the cross direction of the machine, the uniformity and time stability of the forces acting to drain the jet depend, to a large degree, on the uniformity on the outer wire tension and the outer wire radius at a given position across the machine width. In order to prevent unstable cross flows during the drainage process it is important to minimize variation of operation parameters, particularly, the outer wire tension and radius. It should also be recognized that uniformity of wire tension and radius may be equally important to both the inner and outer wires since, in some twin wire formers, both wires may be unsupported in the initial drainage stages nearest the head box, as is the case with alternative embodiment twin wire former depicted in Figure 6. The present invention as depicted in Figure 2 hereof describes a method and apparatus to stabilize and reduce the cross direction variation and time variation in the drainage process thereby yielding significant improvements in the uniformity of the sheet. As depicted, the jet of stock 42 is directed so that it contacts or impinges on the outer fabric 38 when the outer fabric 38 is backed by an open, supporting surface 32. In this way, the free span of the outer fabric 44 does not bear the entire force of the jet of stock 42. It becomes imperative to allow for drainage through the outer wire 38 in those locations where the jet of stock 42 strikes the outer wire 38 supported on the stiff surface. This is accomplished by providing an open, stiff surface such as a breast roll 32 having annular grooves 34 thereabout. Grooves 34 may be V-shaped, squared, spiraled, etc. The operation of open breast roll 32 may benefit from a cover mesh (not shown) similar to the typical cover mesh sleeves used on open drainage rolls.

It should be recognized that a number of possible contour designs can be used for the outside surface of breast roll 32 to allow for drainage. Two of such designs are depicted in figures 3 and 4. It has been found that the depth of annular grooves 34 should preferably be in the range of 0.5" to 1.5", although the invention can be practiced with groove depths above and below such range depending upon the type of pulp, the amount of water being drained, the type of product being produced, machine speed, wire design, etc. The width of peaks or tips 35 should generally be as small as possible to avoid sheet disturbances. In other words, the peak 35 structure which supports outer wire 18 should be as fine as is practical yielding a high percentage of open area at the outside surface of the breast roll thereby minimizing drainage marking and resistance. Thus, the width of tips 35 could be as small as 0.25mm. Typically, the width of tips 35 would be in the range of 0.75mm to 1.25mm but could range as high as 2.0mm. The void volume of annular grooves 34 should be great enough to drain a substantial portion of the total jet thickness while leaving an unfilled air space at the bottom of each groove so as to prevent jet pumping. It is believed that further benefit might be achieved if the void volume is large enough to drain the entire jet of stock. It is also believed that if a cover mesh sleeve is used, it will be particularly beneficial to select a mesh with adequate cross- direction stiffness to span from peak 35 to peak 35 without deflecting under the force exerted by jet of stock 42. It should be understood that the contour of the support structure 32 can be opened by means of a grill work, honeycomb, fabric mesh, drilled holes or the like. For purposes of this application, the term "open" shall be defined, when used in conjunction with "breast roll" or "support structure", as a contoured, channel forming surface or other similar or equivalent surface draining structure as mentioned above. "Solid breast roll" is intended to refer to a substantially cylindrical roll having no surface contour, channelling, grill work or openings. A preferred method of construction of open breast roll 32 is to machine annular grooves 34 into a rubber covered roll. It is believed that synthetic rubbers having a P & J hardness in the range of from about 5 to about 15 would be preferable. A P & J hardness of about 10 is believed to be the most preferable. Alternatively, grooves 34 may be machined into a thick walled, metal shell or the void structure may be created by other means well known by those skilled in the art.

There is shown in Figure 5 an alternative embodiment of the present invention which provides for substantially total elimination of any impingement of jet of stock 42 upon a free span of outer wire 38. The open breast roll 32 of Figure 1 has been replaced with an open support structure or forming shoe 50 having a plurality of slots, grooves or channels 52 in the wire contacting surface 53 thereof. Thus, the outer wire 38 goes around a guide or lead roll 54 and then contacts the open support structure 50 in the area of the forming throat 44. Note that the lead end 56 of open support structure 50 is curved to minimize wear of the outer fabric 38. Although Figure 5 depicts forming shoe 50 as being a structure having substantially planar surfaces, it is preferable that forming shoe be convex in the machine direction. Whether the forming shoe 50 is flat, convex or concave, it remains important that the wires 36,38 be caused to converge in the forming throat 44. As depicted, open support structure 50 is pivotally mounted on the stationary base such that the angle formed between the stationary base and forming roll radius R can be varied. In such manner, the volume and shape of the forming throat 44 can be varied. Although no testing has been performed with this alternative embodiment of the present invention, it is believed that the uniformity of the sheet produced thereby will be at least as good as the uniformity of the sheet produced with the first above described embodiment and likely will be better. This is because the structure of the alternative embodiment allows for even greater minimization of the free span of the outer forming wire of 38 in the forming throat 34 such that the free span can be substantially eliminated. Therefore, outer wire tension, radius and drainage pressure in the forming throat 44 along the forming shoe 50 should remain substantially constant.

An important difference between twin wire former operation using the outer wire open support structure 32 or 50 of the present invention as opposed to the standard solid or flat design breast roll is in the minimum gap setting between the forming roll 30 and the open support structure 32 or 50. This gap setting is a determining factor of forming throat geometry including the length of the free span of outerwire 38, the angle of impingement of the jet of stock 42 on inner and outer wire 36, 38 and the amount of impingement upon open support structure 32, 50 and thus significantly affects the rate of drainage of the jet. Generally, if the gap is too large, drainage is delayed which adversely affects the formation of the homogeneous sheet and particularly the stratified sheet in terms of layer coverage and purity. As stated above, the minimum operating gap is constrained by the situation known as jet "pumping" or a vacuum pulse if the jet of stock touches the surface of a solid or flat breast roll. In such situation, the jet of stock 20 is diverted around the solid or flat breast roll. At the point where the jet of stock 20 reaches the free span of the outer wire, it is pushing that free span away from the forming roll 10 and toward the breast roll 12. This action leads to variations in tension of the outer wire 18 as well as variations in the radius of the outer wire 18.

As a general rule, the gap between the forming roll 10 and a solid or flat design breast roll 12 in a typical prior art twin wire former (See Figure 1) is limited to the relative thickness of the jet of stock 20 plus some margin to allow for an air gap clearance between the jet of stock 20 and breast roll 12. The gap may be even wider to accomodate possible jet expansion. The gap can be narrowed when forming roll 10 is an open roll such that some of the jet of stock 20 is drained through inner wire 16. The presence of the grooves 34 or 52 (See Figures 2 and 5) allows the minimum dimension of the gap to be reduced without incidents of jet pumping. In fact, tests show that uniformity of the sheet is greatly improved using a grooved breast roll 32 (Figure 2) when the gap dimension is significantly less than the thickness of the jet of stock 42. The impact of the bottom portion of the jet 42 on outer wire 33 is absorbed by the open or grilled breast roll surface and the reduced free span in the outer wire 18 makes the outer wire 38 more resistant to corrugations from jet impact. As mentioned above, drainage pressure can be expressed as the ratio of the tension of the outer wire divided by the radius of the outer wire. Increases in the uniformity of this ratio across the width of the machine promote a reduced basis weight profile for the web formed. Since fabric corrugation represents areas of non-uniform ratio, it is believed that reduction in corrugations is consistent with improved basis weight profile.

Additional enhancements in the operation of the present invention may be accomplished through a closer coupling of head box 40 such that the head box exit resides in closer proximity to forming throat 44. Such a modification results in drainage beginning earlier relative to the point when the jet of stock 42 exits head box 40.

Figure 6 depicts an alternate embodiment prior art twin wire former. Such former includes inner wire breast roll 70, outer wire breast roll 72, inner forming wire 74, outer forming wire 76, head box 78 and drainage shoe 80. As was the case with the twin wire former depicted in Figure 1, most , if not all of the jet of stock 82 is directed against a free or unsupported span of outer wire 76. Both breast rolls 70, 72 of this prior art former are of solid design.

As shown in Figure 6A, the twin wire former of Figure 6 can be modified to include supported outer wire drainage, a narrowed gap between the inner wire breast roll 90 and the outer wire breast roll 92, and a reduction in the free span length of the outer wire 96. Head box 98 delivers a jet of stock 102 into a forming throat 104. Because at least outer breast roll 92 is of open design as indicated by dotted line 106, jet of stock 102 can be impinged upon outer breast roll 92 without causing jet pumping. Preferably, both breast rolls 90, 92 would be of open design. A summary of the important basis weight profile testing results is contained in Table 1. It should be noted that in addition to the breast roll design condition mentioned in the configuration section of the Table 1, wet end settings which might affect the basis weight profile were held constant. These conditions included forming box vacuum level and location and jet impingement on the forming roll. Also, dry end settings, such as adhesive add-on, yankee pressure and line crepe were held constant. The tests were conducted with two layer forming fabrics (Asten 856A design manufactured by Asten Forming Fabrics Company) and 8" stratifying foils. The test were conducted on a high speed, pilot plant paper machine.

TABLE 1

AVERAGE AVERAGE B . W.

RANGE B . W . B . W.

GAP (GSM) (GSM) Pk-Pk

2.46 27. 7 1 . 35 27 . 4 0.84 28. 5 1. 62 29 . 0 1 . 97 29 . 3 2 . 04 29. 8

0. 62 28. 8

The Average Range data presented in Table 1 represents the web high basis weight minus the web low basis weight for a particular run expressed in grams per square meter. Average B.W. shown in Table 1 is the average basis weight determined for each test run expressed in grams per square meter. B.W. Pk-Pk is the peak-to-peak variation of basis weight for each run expressed as a percentage. Thus, looking at test run A, the average range of 2.46 grams per square meter is approximately 8.8 percent of the average basis weight (27.7 GSM) . Therefore, the basis weight peak-to-peak variation is plus or minus 4.4%. The extreme right column of Table 1 (B.W. CDσ sigma) represents the standard deviation of basis weight in the cross direction of the machine. The testing which resulted in the data presented in Table 1 was performed in accordance with a procedure similar to TAPPI procedure T 545 pm-86 entitled "Cross-machine grammage profile measurement (gramametric method)".

Test run A serves as a control run for the grooved breast roll evaluation. The standard solid breast roll was used with a gap of 49 millimeters between the solid breast roll and the forming roll. This was the nominal minimum gap without giving rise to occurrences of jet pumping. The average range for 12 scans of data collected in accordance with the above identified TAPPI procedure was 2.46 grams per square meter yielding a basis weight peak-to-peak variation of plus or minus 4.4%. Test run B utilized a grooved breast roll with a narrowed gap of 32 millimeters between the grooved breast roll and the forming roll. This configuration resulted in a basis weight average range variation of 1.35 GSM yielding a basis weight peak to peak variation of plus or minus 2.5%. The data clearly demonstrates that the grooved breast roll in combination with a reduced gap between the grooved breast roll and the forming roll results in improved basis weight profile including improved outer wire strata layer coverage and purity. Sheet uniformity has been significantly improved and the properties of the inner and outer strata layers become more balanced.

It has been found that the basis weight of paper made with a grooved breast roll design and a narrowed gap is more uniform, especially in the cross direction. The coefficient of variation (C.O.V.) of paper made with the grooved breast roll is significantly reduced compared to paper made with the typical solid breast roll. In one comparison, the C.O.V. for the grooved breast roll was 1.57% as opposed to a solid roll design which yielded a C.O.V. of 2.52%. These coefficients are based on a positional standard deviation of 0.43 GSM and an average basis weight of 27.35 GSM for the grooved breast roll (test run B) . Corresponding data for the solid breast roll comparison test run (test run A) are 0.70 GSM and 27.74 GSM. In a subsequent comparison, the use of the grooved breast roll yielded a basis weight C.O.V. of 0.49% (based on a positional standard deviation of 0.14 GSM and an average basis weight of 28.47 GSM (test run G) . The solid breast roll test (test run F) yielded a C.O.V. of 2.2% based on a positional standard deviation of 0.66 GSM and an average basis weight of 29.81 GSM.

The decrease in basis weight variation profile is also reflected in post dryer moisture scans recorded on the high speed pilot plant paper machine. The moisture scans corresponding to test runs D, F and G show that the decreased weight profile from run G also resulted in decreased post dryer moisture variation for run G when compared to runs D and F. It has been estimated, through extrapolation of mill data, that for a 29 GSM sheet made at 70% post through dryer dryness, a 1.0% reduction in weight profile will cause a reduction in the peak-to-peak dryness variation of 0.6%.

The grooved breast roll design of the present invention allows the gap between the breast roll and the forming roll to be reduced below that which is possible with a solid breast roll without fear of causing jet pumping. It is believed that the increased level of fabric support and the quicker overall drainage obtained with the grooved breast roll gives rise to the demonstrated improvement in weight profile and in strata coverage efficiency of the outer wire strata. It is further believed that replacing the grooved breast roll 32 depicted in Figure 2 with the open support structure 50 shown in Figure 5 would produce even greater improvement in weight profile uniformity.

The data set forth in Table 1 demonstrates that as the gap was decreased from 49mm to 32mm, sheet uniformity was improved. It is believed that the gap can be narrowed to well less than 32mm so long as the void volume of breast roll 32 is great enough such that it can accommodate the water drained through outer wire 38 without becoming filled thereby eliminating any air gap between the water drained through the outer wire 38 and the bottom of the breast roll void volume. From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are apparent and which are inherent to the apparatus and method. It will be understood that certain features and subcombinations are of utility and may be employed with reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. In a method of producing a web from a jet of stock injected into a forming throat between inner and outer tensioned forming wires run around a peripheral segment of a forming cylinder, the improvement comprising:

(a) providing an open support structure for the outer wire; and

(b) directing the jet of stock to impinge on both the forming cylinder and the open support structure.

2. In a method of producing a web from a jet of stock injected into a forming throat between inner and outer tensioned forming wires run around a peripheral segment of the forming cylinder, the improvement comprising:

(a) providing an open support structure for the outer wire; and

(b) positioning said open support structure such that the gap between said open support structure and the forming cylinder is less than or equal to the thickness of the jet of stock; and (c) directing the jet of stock to impinge on both the forming cylinder and the open support structure.

3. In a method for producing a web from a jet of stock injected into a forming throat between inner and outer tensioned forming wires run around a peripheral segment of a forming cylinder, the improvement comprising:

(a) impinging the jet of stock simultaneously on both the inner and outer forming wires in the forming throat;

(b) providing an open support structure for the outer wire over at least a portion of said forming throat thereby allowing some immediate drainage through said outer wire.

4. In a method of producing a web from a jet of stock injected into a forming throat between inner and outer tensioned forming wires run around a peripheral segment of a forming cylinder, the improvement comprising: (a) providing an open support structure for the outer fabric over at least a portion of the forming throat; (b) setting a gap between said open support structure and said forming cylinder which is less than or equal to the thickness of the jet of stock; and

(c) directing the jet of stock to impinge upon said outer wire where said outer wire is supported by said open support structure, the jet of stock simultaneously impinging upon the forming cylinder.

5. The improved method as recited in claim 1 wherein: said open support structure is a breast roll with a plurality of circumferential grooves therein.

6. The improved method as recited in claim 1 wherein: said open support structure is an open breast roll.

7. The improved method as recited in claim 1 wherein: said open support structure is a cylindrical breast roll with a plurality of orifices in the cylindrical surface thereof.

8. The improved method as recited in claim 1 wherein: said open support structure is a forming shoe having a wire contacting surface, said wire contacting surface having a plurality of channels therein.

9. The improved method as recited in claim 2 wherein: approximately one-third (1/3) of the thickness of said jet of stock impinges on said open support structure.

10. The improved method as recited in claim 1 wherein: said open support structure is pivotally mounted such that the angle between the inner and outer forming wires at the forming throat can be varied.

11. In an apparatus for forming a web comprising a rotatable forming cylinder, inner and outer endless forming wires, means for supporting said inner and outer endless forming wires so that they converge to form a forming throat and thereafter run together over a segment of the surface of the forming cylinder and head box means for injecting a jet of stock into the forming throat between said wires to form a web, the improvement comprising: (a) an open support structure supporting said outer wire over at least a portion of said forming throat;

(b) a narrowed gap between said forming cylinder and said open support structure such that said jet of stock impinges substantially simultaneously on both said forming cylinder and said open support structure.

12. The improved apparatus as recited in claim 11 wherein: said open support structure is an open breast roll.

13. The improved apparatus as recited in claim 11 wherein: said open support structure is a breast roll with a plurality of annular grooves therein.

14. The improved apparatus as recited in claim 11 wherein: said open support structure is a cylindrical breast roll with a plurality of orifices in the cylindrical surface thereof.

15. The improved apparatus as recited in claim 11 wherein: said open support structure is a forming shoe having a wire contacting surface, said wire contacting surface having a p αrality of channels therein.

16. In an apparatus for forming a web comprising a rotatable forming cylinder, inner and outer endless forming wires, means for supporting said wires so that said wires converge to form a forming throat and thereafter run together over a segment of the surface of the forming cylinder and head box means for injecting a jet of stock into the forming throat between said wires to form a web, the improvement comprising:

(a) an open support structure supporting said outer wire over at least a portion of said forming throat; (b) a gap between said forming cylinder and said open support structure which is narrower than the thickness of said jet of stock.

17. The improved apparatus as recited in claim 11 wherein: said open support structure is pivotally mounted such that the angle between the inner and outer forming wires in the forming throat can be varied.

18. The improved apparatus as recited in claim 16 wherein: said open support structure is pivotally mounted such that the angle between the inner and outer forming wires in the forming throat can be varied.

19. The improved method as recited in claim 2 wherein: said open support structure is pivotally mounted such that the angle between the inner and outer forming wires in the forming throat can be varied.

20. The improved method as recited in claim 4 wherein: said open support structure is pivotally mounted such that the angle between the inner and outer forming wires in the forming throat can be varied.