MXPA00012460A - Suction breast roll former - Google Patents

Abstract

A suction breast roll former (10) is disclosed which includes a suction breast roll (14) and a headbox (12). The suction breast roll has a support surface (20) with a plurality of apertures (22) formed therein that are operatively connected to a vacuum source (V). The headbox has a flexible roof (70) extending downstream from a slice opening (46) and disposed adjacent to a support surface of the suction breast roll. The headbox permits the flexible roof to bend over a range of movement relative to the support surface to match the shape of a drainage curve suiting current operating conditions. The method of forming a paper web using the suction breast roll and headbox is also disclosed. The method includes the steps of supplying an aqueous suspension of papermaking fibers to a forming zone (18) created between the suction breast roll and the headbox. The headbox includes a slice body (40) and an apron (42) that define a slice opening therebetween and also has a flexible roof extending from the slice opening and spaced from the support surface to define a forming zone therebetween. A forming fabric (16) is passed through the forming zone to receive the aqueous suspension of papermaking fibers. The flexible roof is permitted to bend over a range of movement relative to the support surface to match the shape of a drainage curve.

Description

SUCTION CHEST ROLLER FORMATOR Field of the Invention The present invention relates generally to a papermaking equipment. More particularly, the invention relates to a suction chest former and to a method of forming the paper using a suction chest former.

Background of the Invention Paper fabrics can be manufactured using a variety of devices such as suction chest roll formers, twin wire formers, roller roll formers or the like. Even though the purpose of the paper forming equipment is generally to produce a uniform sheet in both directions of the machine and transverse to the machine, each type of former has particular advantages and disadvantages.

The current in tissue manufacturing is to produce a sheet with a resistance in the machine direction (MD) to a resistance in the cross machine direction (CD) (MD / CD ratio) which is close to 1.0 for make the most efficient use of the fibers to generate resistance in the leaf. This is particularly necessary in products that are used by consumers in various orientations where the overall strength of the sheet becomes the weakest of the resistance in the machine direction or the resistance in the transverse direction.

A disadvantage associated with the suction chest roll formers is a high degree of variability in the formation depending on the location and operating parameters of the head box. Even when suction chest roll formers are generally good at operating at a set of conditions, less than optimum operating conditions produce less than optimal leaf formation. Typical defects in a tissue sheet produced with a suction chest roll former are the intermittent machine direction stripes randomly oriented on the surface of the sheet. Sheet defects of this type tend to emphasize the MD / CD ratio of the sheet.

There is more demand in the competitive tissue market to have tissue machines that are capable of making a variety of products on the same machine to make the best use of the available equipment. The ability of tissue machines to operate over a wider range of process conditions is becoming more important.

Therefore, what is missing and required in the art is an improved suction chest roll former which maintains consistent tissue formation over a wider range of operating conditions than is currently available. What is missing and required is an improved suction chest roll former that can be easily constructed as a retrofit of the current suction chest roll former.

Synthesis of the Invention It has now been discovered that consistent tissue formation over a wide range of operating conditions can be achieved by using a suction chest roll former in accordance with the present invention. Thus, an embodiment of the invention relates to a suction chest roll former that includes a chest roll and a head box. The chest roller has a support surface defining openings there which are operatively connected to a vacuum source. The head box is positioned in close proximity to the suction chest roll and is adapted to provide an aqueous suspension of paper fibers. The head box includes a slice body and an apron which together define a slice opening of the head box. The head box also includes a flexible ceiling extending from the slice opening and spacing of the breast roller support surface to define therebetween a forming area of the suction chest roll former. The head box is adapted to allow the flexible roof to bend over a range of motion relative to the support surface to match the shape of the drain curve.

The flexible roof is believed to extend to the range of operating conditions over which the suction chest roll former can produce a well-formed sheet. The theory is that the shape of the flexible roof will conform to the changes in pressure in the forming zone that results in changes in the velocity of the aqueous flow in the forming zone. As a result of this, the flexible roof will automatically adjust the shape of the forming zone and the length to compensate for changes in operating conditions.

Because the flexibility of the flexible roof does not allow it to withstand positive fluid pressure, the chest roll is heated with one or more vacuum boxes below the support surface to provide a controlled amount of vacuum in the forming zone . The vacuum is adjusted to a point where the position of the flexible roof is stable and in an optimal location. The chest roll includes openings, such as holes, slots or other open areas to keep water away from the wet tissue until it can be thrown away at a cost saving for a water recycling process. The chest roller is operatively connected to one or more vacuum sources so that the vacuum is supplied in the openings and correspondingly in the forming zone. In particular embodiments, the vacuum box includes section dividers to divide the vacuum box into multiple sections. For example, a first vacuum section provides vacuum to form the sheet and a second vacuum section is used to retain the water within the chest roll. Suction chest rolls suitable for use with the present invention are available from suppliers of papermaking equipment such as Valmet Corporation, Beloit Corporation or Voith Corporation.

In the present suction chest roll former, the flexible roof is used in conjunction with a rigid support surface of the roller; suction chest.

As a result of this, the current suction chest roll formers can be relatively easily and inexpensively retro-fitted with the present invention. In addition, the flexible roof can easily be adapted for use with the current assembly of the slice body. Therefore, one aspect of the invention relates to the method of modifying an existing suction chest roll former. The existing suction chest roll former includes a chest roll and a head box positioned in close proximity to the chest roll.

The chest roll has a support surface defining openings there which are operatively connected to a vacuum source, and the head box is adapted to supply an aqueous suspension to the papermaking fibers. The head box includes a slice body, an apron with the slice body defining between them a slice opening, and a rigid ceiling extending from the slice opening and spaced from the support surface to define a slice. training area between them. The rigid roof is set to fix a gap in relation to the support surface. The method for modifying the existing suction chest roll former comprises the step of replacing the rigid roof with a flexible roof. The flexible roof extends from the slice opening and is spaced from the support surface to define a forming zone therebetween, and is adapted to be bent over a range of motion relative to the support surface to match the shape of the drain curve.

In the illustrated embodiment, the flexible roof has a near edge fixedly attached to a modified version of the slice body and a distant edge in close proximity to the suction chest roll support surface. The far edge of the tail portion of the flexible roof desirably moves over the wet fabric as the fabric leaves the forming zone. Alternatively, the distal edge or the tail portion of the flexible roof may be spaced from the forming fabric, such as from about 0.8 to about X.25 millimeters.

The length of the flexible roof, measured between the proximal and distant edges, can be either fixed or adjustable. For a fixed-length roof, the tail section of the roof after the supply has been drained may leave on the surface of the sheet, depending on the length of the forming zone required for that particular set of forming conditions. The front section of the roof will be more resistant to bending and can be rotated to deflect the flow in the chest roll to control the amount of initial drainage and reduce the amount of hydraulic force on the rest of the roof.

The head box is desirably adapted to allow the flexible roof to bend, for example, in relation to the position of the nearby shore. The roof is desirably flexible in the machine direction, so that the roof can be bent in response to temporary changes in pressure caused by the aqueous suspension of paper fibers, as might occur during starting conditions, and more desirably to conform to the required shape required in the forming zone to provide improved blade formation. Desirably, the flexible roof has infinite flexibility in the direction of the machine, reduced only by the need to have materials of durability and strength suitable for operating in a commercial environment under the present loads. Suitable materials for forming the flexible roof include LEXAN (Polycarbonate, General Electric, Pittsfield, Massachusetts), epoxy resins reinforced with carbon fiber or glass, or other polycarbonate, fiberglass or other composite materials, stainless steel or the like where The married or the orientation of the fiber can achieve the correct flexibility. The fiber reinforced resins can be constructed to preferably bend in the machine direction, while maintaining the rigidity in the cross machine direction.

Flexibility in the cross-machine direction of the flexible roof is generally undesirable, and therefore the flexible roof can include a plurality of degidifying elements in the cross-machine direction. These regidizing elements, which are desirably placed on the flexible roof surface facing away from the forming zone, can be formed of stainless steel, carbon fiber, glass fiber or other compounds, plastic or plastic materials. Similar. In an alternate method it is to produce a compound wherein the stiffness in the cross machine direction is significantly higher than the rigidity in the machine direction.

To improve the formation of tissue by creating turbulence within the suction of the fibers for making paper, the flexible roof may include turbulence generation characteristics placed on a flexible roof surface facing the forming zone. The turbulence-generating features may include, for example, a plurality of outwardly extending projections, giving the flexible ceiling interior surface that is designed to provide micro-turbulence to the fluid flow near the ceiling surface, but without disturbing the sheet.

The wet fabric is formed on a forming fabric that travels through the forming zone between the suction chest roller and the ceiling. The forming fabric is sandwiched between the supporting surface and the distant edge of the flexible roof, with the forming fabric and the aqueous suspension generally moving at the same speed. The term "forming fabric" refers to an endless mesh belt adapted to drain water out of the fibers to make paper and provide support as the fabric is formed. Suitable forming fabrics comprise the synthetic fabrics and are available from fabric suppliers such as Lindsay Wire and Albany International.

It may be desirable to control the amount of bending of the flexible roof during transient conditions, such as the start. In particular, a restriction member may be used to restrict large-scale folding of the flexible member while allowing unrestricted bending over a more limited range. Therefore, another embodiment of the invention relates to a suction chest roll head box that is adapted to supply an aqueous suspension to the papermaking fibers. The head box includes a slice body and an appendage defining between them a slice opening. The head box includes a flexible roof that extends from the slice opening and the head box is adapted to allow the flexible roof to bend over a limited range of motion to hunt the shape of the drain curve. The head box also includes a restraining member separate from the flexible roof but positioned to limit the range of motion of the flexible roof.

Another aspect of the invention relates to a method for forming a paper web. In one embodiment, the method includes the steps of: supplying an aqueous suspension of fibers to make paper to form a forming zone created between a chest roll and a head box, the chest roll has a support surface defining openings therein which are operatively connected to a vacuum source. The head box includes a slice body and an apron defining between them a slice opening, the head box further includes a flexible ceiling extending from the slice opening and spacing from the support surface to define the zone trainer among them; passing a forming fabric through the forming zone to receive the fibers for making paper; and allowing the flexible roof to bend over a range of motion relative to the supporting surface to hunt the shape of the drain curve.

In particular embodiments, the method also includes the step of controlling the speed of the aqueous suspension and the level of vacuum to achieve the removal of water from the forming zone without generating an upward pressure of the flexible roof. The aqueous suspension that is under the flexible roof is desirably under a slight vacuum and therefore a negative pressure with respect to the atmospheric pressure. The apparent negative pressure will drain water from the sheet through the fabric. The fluid will drain more slowly as the sheet accumulates on the fabric and the resistance is increased. The absence of fluid and negative pressure define the shape of the flexible roof and ensure that there is little difference in the speed in the machine direction. In general from an engineering point of view, it is desirable to try to approximate the curve that would be exposed under pressure when it is not under pressure. This will ensure the lowest possible stresses in the ceiling.

There are a number of variables that will increase the length and / or time for training to take place under the flexible roof. These include base weight, speed, supply and consistency. The drainage of free water from the aqueous suspension should be completed before reaching the far end of the flexible lip. To move the dry line upstream of the distant bank and thus achieve a complete drainage of free water, the operator can decrease the flow rate of the aqueous suspension, increase the vacuum, or increase the angle of the tangent jet to the breast roller. .

The operation parameters of the suction chest roller and the head box such as the throat opening, the vacuum levels, and the orientation of the head ca and other operating parameters such as the speed of the Fan pump can be adjusted as will be recognized! by those skilled in the art in order to achieve the desired leaf properties. The type of fiber, the fiber consistency, and other factors will need to be taken into consideration, but by the nature of the invention are less critical of operation with improved formation.

Many types of fiber can be used by the present invention including hardwood or softwoods, straw, flax, bensetose seed fibers, abaca, hemp, soft rush, bagasse, cotton and cane and the like.

All known papermaking fibers can be used, including bleached and unbleached fibers, fibers of natural origin (including wood fibers and other cellulosic fibers, cellulose derivatives and fibers cross-linked or chemically stiffened) or synthetic fibers (synthetic paper fibers including certain forms of fibers made of polypropylene, acrylic, aramides, acetates and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been reduced mechanically pulped (for example ground wood), chemically pulped (including, but not limited to, sulfite and kraft pulping processes), thermomechanically pulped reduction, thermochemically mechanically reduced pulping and the like. Mixtures of any sub-sets of the fiber classes mentioned above or related may be used.

The fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods for preparing the fibers include dispersion for imparting curl and improved drying properties as described in U.S. Patent Nos. 5,348,620 issued December 20, 1994 and 5,501,768 issued March 26. of 1996, both to MA Hermans et al. And in U.S. Patent No. 5,656,132 issued August 12, 1997 to Farrington Jr. and others which are incorporated herein by reference.

Once formed, the tissue paper can be processed using a wide variety of papermaking operations. For example, the tissue paper can be formed into a non-creped continuous dried tissue as described in U.S. Patent No. 5,667,636 issued September 16, 1997 to S.A. Engel and others; and United States of America No. 5,607,551 issued March 4, 1997 to T. E. Farrington Jr., and others which are incorporated herein by reference. The term "paper" is used herein to broadly include writing, printing, wrapping, sanitary and industrial papers, newsprint, cardboard liner, tissue, napkins, wipes, towels or the like.

A single head box or a plurality of head boxes can be used. The headbox or the headboxes can be laminated to allow the production of a multi-layered structure from a single-head jet in the formation of a fabric. In particular the fabric can be produced with a layered or layered headbox to preferably deposit shorter fibers on one side of the fabric for improved smoothness, and with relatively longer fibers on the other side of the fabric or in an inner layer or a fabric that has three or more layers. The multiple embryonic tissues of the multiple head boxes can be layered or mechanically or chemically joined in the wet state to create a single tissue having multiple layers.

Numerous features and advantages of the present invention will be apparent from the following description. In the description, reference is made to the accompanying drawing which illustrates the preferred embodiments of the invention. Such incorporations do not represent the full scope of the invention. Reference should therefore be made to the claims herein to interpret the full scope of the invention.

Brief Description of the Drawing The figure shows a suction chest roll former for making a paper tissue of an aqueous suspension of paper fibers.

Detailed Description of the Preferred Incorporation The invention will now be described in greater detail with reference to the single figure, which shows a simplified cross-sectional schematic view of a suction chest roll former according to the present invention. Conventional papermaking apparatuses and operations (not shown) can be used with respect to the supply preparation, fabric formation, tissue transfers, creping, drying and the like.

The figure shows a suction chest roll former 10 for making a paper tissue of an aqueous suspension of paper fibers. The suction chest roll former 10 includes a paper head box 12 positioned in operable relation to a suction chest roll 14. The head box 12 deposits the aqueous suspension of: the fibers for making paper on the surface of a forming fabric 16 in a forming area 18 of the suction chest roll former 10. The forming fabric 16 forms an endless loop that travels between the head box 12 and the breast roller 14 and around the breast roller 14 in the direction of the arrow 19. The forming process allows partial drainage of a newly formed paper web, for example at a consistency of about 10%.

The suction chest roller 14 includes a support surface 20 defining a plurality of openings 22. The openings 22 are open to one or more vacuum boxes 24 located within the roller 14 at radial locations fixed around the circumference of the roller and operatively connected to a vacuum force V. The vacuum box 24 provides a controlled amount of vacuum in the training area. The illustrated vacuum box 24 includes the section dividers 26 which divide the vacuum box 24 into multiple sections.

The head box 12 receives a suspension of the fibers for making paper through the flow spreader 30 operatively connected to a conventional supply preparation source (not shown). The fibers for making paper move in the direction of the arrow 32. The flow spreader 30 is mounted on a fixed frame structure 34.

The head box also includes a slice body 40 and an apron 42 defining therebetween a throat 44 and a slice opening 46. The apron 42 is mounted on the flow spreader 30 and the head box 12 is positioned on so that the downstream end 50 of the apron is positioned in a close proximity to the support surface 20 of the suction chest roll 14.

The slice body 40 has an upward end 52 and an opposite downstream end 54. The upstream end 52 is pivotally mounted to the flow spreader 30 using a rotating seal 56. The downstream end 54 is subject to a mounting bar 58.

A slice adjustment mechanism 60 is linked by an arm 62 to the mounting bar 58 and therefore indirectly to the downstream end 54 of the slice body 40. The slice adjustment mechanism 60 is adapted to raise and lower the running end. down the slice body 40. For the purposes of the present description, the slice opening 46 is formed between the downstream end 50 of the apron 42 and the downstream end 54 of the slice body. The operation of the slice adjustment mechanism 60 will change the taper of the throat 44 and the size of the slice opening 46.

The head box 12 also includes a flexible roof 70 having a near edge 72 and an opposite distant edge 74. The flexible roof 70 is pivotally mounted along the near edge 72 to the mounting bar 58 using a rotary joint 76. The flexible ceiling 70 is therefore indirectly mounted to the slice body 40 and extends downwardly from both the slice body 40 and the slice opening 46. A fastener or other suitable means 78 can be employed to fix the rotation of the flexible roof 70 in a rotary joint 76.

The flexible roof 70 may be straight or somewhat arched, with the distant edge 74 in a close proximity to the supporting surface 20. In general, the flexible lip 70 will take the required form of the process under the current operating conditions. More particularly, the shape of the flexible roof 70 should be the exact shape of the drainage curve. There will be a large initial drain which can be controlled by the angle made by the jet with the forming fabric 16 and the initial unstressed angle that the flexible roof 70 makes with the arched chest roll surface 20. For the most part, the The flexible ceiling 70 will take the shape that is convex facing the forming fabric 16. The convexity rate of the flexible roof 70 will decrease as the drain takes place. When the drain is completed, there will be a point of inflection in the shape, and the flexible roof 70 will be concave for the far end 74 of the flexible roof 70.

The forming zone 18 is located between the flexible roof 70 and the supporting surface 20. Any the distant edge 74 or the flexible roof 70 or the tail region of the flexible roof 70 near the distant edge 74 can travel on the wet fabric at the be this one In this case, the forming fabric 16 and the sheet will be placed in the form of a sandwich between the supporting surface 20 and the flexible ceiling 70.

The flexible roof 70 is free to bend outward from the support surface 20, for example about an axis through the near edge 72 or the rotary joint 76. Under normal conditions, the free water in the jet will be completely removed. before the distant end 74 of the flexible roof 70 and should be removed several centimeters in front of the far end. Consequently, there will be a zero gap between the roof tip and the forming fabric 16 resulting in improved formation. The expected contact between the flexible roof and the forming sheet operates to seal the vacuum box 24. If a relatively large particle is formed on the sheet, the flexible lip will bene fi cially bend to the airbire locally and allow the particle to pass through. the same to the particle that otherwise would normally have damaged the forming fabric 16.

Optionally, a restriction member 80 may be used to limit the amount of flexing of the flexible roof 70. One end of the illustrated restriction member 80 is attached to the mounting bar 58, and the other end is adjustably mounted using an adjustment mechanism. of separation 82. Significantly, restriction member 80 should not impede the range of bending that would result due to normal variations in the papermaking process. Under the preferred operating conditions, however, wet cloth is formed at a negative pressure and there is essentially an upward force, from flexible roof 70. Correspondingly, during routine operation, restriction member 80 it is not in contact with the flexible roof 70 and does not exert downward pressure on the flexible roof 70.

In the particular embodiments, the flexible roof 70 may include a plurality of stiffener elements 86 extending through the flexible roof 70 in the transverse direction to the machine. In addition, the flexible roof 70 may include turbulence generating features 88 placed on the flexible roof surface facing the forming zone 18. In the illustrated embodiment, for example, the turbulence generating characteristics 88 include the fastener heads attached to the turbulence. the stiffener elements 86. The shape, size, spacing and number of turbulence generating characteristics 88 will depend on the range of operating conditions required for the particular application of this invention.

The above detailed description has been given for the purpose of illustration. Therefore, a number of modifications and changes can be made without departing from the spirit and scope of the present invention. For example, the characteristics and alternatives or options described as part of an incorporation can be used to still perform another incorporation. Additionally, two named components can represent parts of the same structure. In addition, various alternate processes and equipment arrangements can be employed, particularly with respect to the preparation of supply for the forming fabrics. Therefore, the invention should not be limited to the specific embodiments described, but only by the claims and all equivalents thereof.

Claims (20)

R E I V I N D I C A C I O N S

1. A suction chest roll former comprising: a) a suction chest roll having a support surface; Y b) a headbox having a flexible roof that extends downwardly from a slice opening and positioned on one side of said support surface, wherein the headbox allows the flexible roof to flex freely over a range of motion in relation to the support surface.

2. The suction chest roll former, as claimed in clause 1, characterized in that said support surface is rigid.

3. The suction chest roll former, as claimed in clause 1, characterized in that the support surface has a plurality of openings formed therein which are operatively connected to the vacuum sources.

4. The suction chest roll former, as claimed in clause 1, characterized in that said flexible roof contains a plurality of stiffener elements.

5. The suction chest roll former, as claimed in clause 1, characterized in that said stiffener elements are placed in a direction transverse to the machine through the flexible roof.

6. A suction chest roll former comprising: a) a suction chest roll having a support surface with openings there which are operatively connected to a vacuum source; Y b) a head box positioned in close proximity to said suction chest roll and adapted to supply an aqueous suspension of fibers to make the skin to said support surface, said head box includes a slice body and an apron defining a Slit opening therebetween, said headbox further includes a flexible roof extending from said recess aperture and spaced from said support surface to define a forming zone therebetween, said headbox being adapted to allow to the flexible roof bending over a range of motion in relation to said supporting surface to equal the shape of a drainage curve.

7. The suction chest roll former, as claimed in clause 6, characterized in that said flexible roof has a near shore fixedly fixed to said slice body and a distant edge in close proximity to said support surface, said box of head is adapted to transmit to said flexible roof the bending around the nearby shore.

8. The suction chest roll former, as claimed in clause 6, characterized in that the flexible roof contains a plurality of stiffeners placed in the transverse direction to the machine.

9. The suction chest roll former, as claimed in clause 6, characterized in that the stiffener elements are placed on a surface of said flexible ceiling facing away from the forming zone.

10. The suction chest roll former, as claimed in clause 6, characterized in that said flexible roof has a flexibility comparable to polycarbonate materials.

11. The suction chest roll former, as claimed in clause 6, characterized in that it comprises a forming fabric placed in the form of a sandwich between said support surface and a distant edge of the flexible roof.

12. The suction chest roll former, as claimed in clause 6, characterized in that the flexible roof includes turbulence generating characteristics placed on a surface thereof which faces said forming area.

13. A suction chest roll former comprising: a) a suction chest roll that has; a support source with openings formed therein which are operatively connected to a vacuum source; b) a head box positioned in close proximity to said suction chest roll and adapted to supply an aqueous suspension to the fibers for making paper to said support surface, said head box includes a slice body and an apron that define a slit opening therebetween, said headbox further includes a flexible roof extending from said rebate opening and spaced from said support surface to define a forming zone therebetween, said headbox being adapted to allow to the flexible roof bending over a range of motion in relation to said supporting surface in response to the operating conditions; Y c) a restriction member spaced from said flexible roof and positioned to limit the range of movement of said flexible roof.

14. A method for forming a paper web comprising the steps of: a) supplying an aqueous suspension of fibers for making paper to a forming zone created between the suction chest roll and a head box, said suction chest roll having a support surface with openings formed therein which are operatively connected to a vacuum source, said head box includes a slice body and an apron defining a slice opening therebetween, said head box further includes a flexible ceiling extending from said slice opening and being spaced from the surface of the slice. support to define a forming zone between them; b) passing a forming fabric through said forming zone to receive said aqueous suspension of papermaking fibers; Y c) allowing said flexible roof to bend over a range of movement relative to said supporting surface to equalize the shape of a draining curve.

15. The method, as claimed in clause 14, further characterized in that it comprises controlling the speed of said aqueous suspension to achieve the removal of water from the forming zone without generating an upward pressure on said flexible roof.

16. The method, as claimed in clause 14, further characterized in that it comprises controlling the level of vacuum in said vacuum source to achieve the removal of water from the forming zone without generating an upward pressure on the flexible roof.

17. The method, as claimed in clause 14, further characterized in that it comprises controlling the speed of said aqueous suspension and the level of vacuum to achieve the removal of water from the forming zone without generating an upward pressure on said flexible ceiling .

18. A method for modifying an existing suction chest roll former, said existing suction chest roll former comprises a suction chest roll and a head box positioned in close proximity to said suction chest roll, said roller suction chest has a support surface with openings formed there and operatively connected to a vacuum source, said head box is adapted to supply an aqueous suspension of fibers for making paper to said suction chest roll, said box the head includes a slice body and an apron that with the slice body define a slice opening therebetween, and a rigid ceiling extending from said slice opening and spaced from the support surface to define a forming zone therebetween; the same, the rigid ceiling fixed to a fixed separation in relation to said supporting surface, said method comprises the steps of: a) replacing said rigid roof with a flexible roof extending from the slice opening and spacing of the supporting surface to define a forming zone therebetween, said flexible roof being adapted to bend over a range of movement relative to said Support surface to match the shape of a drainage curve.

19. The method, as claimed in clause 18, further characterized in that it comprises controlling the speed of said aqueous suspension to achieve the removal of water from the forming zone without generating an upward pressure on said flexible roof.

20. The method, as claimed in clause 18, further characterized in that it comprises controlling the speed of said aqueous suspension and the level of vacuum to achieve the removal of water from the forming zone without generating an upward pressure on said flexible ceiling . SUMMARY A suction chest roll former is described which includes a suction chest roll and a head box. The suction chest roll has a support surface with a plurality of openings formed therein which are operatively connected to a vacuum source. The head box has a flexible roof that extends downwardly from a slice opening and positioned on one side of a suction chest roller support surface. The head box allows the flexible roof to bend over a range of motion relative to the supporting surface to match the shape of a drainage curve that is suitable for current operating conditions. The method for forming paper tissue uses the suction chest roller and the ca; The head is also described. The method includes the steps of supplying an aqueous suspension of fibers to make pap > the to a forming zone created between the suction chest roller and the head box. The head box includes a slice body and an apron defining a slice opening therebetween and also having a flexible ceiling extending from the slice opening and spaced from the support surface to define a forming zone between the same. The forming fabric is passed through the forming zone to receive the aqueous suspension of papermaking fibers. The flexible roof is allowed to bend over a range of motion relative to the supporting surface to match the shape of a drain curve.