Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/02—Complete machines for making continuous webs of paper of the Fourdrinier type
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F1/00—Wet end of machines for making continuous webs of paper
  • D21F1/48—Suction apparatus
  • D21F1/483—Drainage foils and bars
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type

Definitions

• This invention concerns a vented lead blade for use in a paper making machine.
• an unsupported jet of highly aqueous stock is ejected from the head box slice onto the surface of a moving forming fabric.
• the unsupported jet will typically traverse a distance of from about 6 cm to about 40 cm before impinging the surface of the forming fabric at the point of impingement.
• the angle of impingement, , formed between the stock jet and the plane of the forming fabric at the point of impingement will typically be from about 4° to about 10°. It is well known that improved paper formation can be obtained by minimizing both the angle and the length of the unsupported free jet.
• the impingement pressure I in kPa can be shown to be given by the following relationship:
• Impingement angles greater than about 5° will create peak impingement pressures that may cause sheet marking, low retention of paper making fines and fillers, and plugging of the forming fabric. Therefore, the angle should be made as small as possible so that, ideally, the unsupported stock jet impinges on the fabric substantially tangentially.
• the unsupported stock jet should be made as short as possible to minimize these effects.
• the present invention seeks to provide a lead blade for use in the forming shoe or forming board of a high speed paper making machine which will eliminate or at least substantially reduce all of the aforementioned deficiencies of the prior art by means of a construction and arrangement which at least in part adopts these recommendations.
• This invention seeks to provide a vented lead blade for use downstream of the breast roll, between the breast roll and the fabric supporting elements in the forming section, and located so that the stock jet impinges the forming fabric at, or near to, its trailing edge.
• the vented lead blade does two things. First, it serves to bend the forming fabric before it enters the forming section. Second, it serves to vent at least a substantial proportion of any air which becomes trapped in the wedge shaped space between the surface of the forming fabric and the surface of the stock jet.
• the vented lead blade of this invention thus enables the forming fabric to be positioned so that the angle . can be minimized, and, if desired, by allowing the breast roll to be.
• the vented lead blade of this invention can be used in both an open surface forming section with one forming fabric, or in the forming zone of a two fabric paper making machine.
• this invention seeks to provide a curved vented lead blade for use in a paper making machine upstream of, and immediately adjacent to, the point of impingement of a stock jet ejected from a head box slice onto a moving forming fabric carrying an amount of liquid, which lead blade has a leading edge, a shaped trailing edge portion, including a trailing edge, and a convexly curved surface located between the leading edge and the trailing edge portion, over which the forming fabric moves in sliding contact and wraps through an angle of wrap ⁇ ⁇ the convexly curved surface and the trailing edge portion including a plurality of grooves which begin at the leading edge and end at the trailing edge constructed and arranged to vent at the lead blade trailing edge at least a substantial proportion of any air trapped in the forming fabric from a wedge shaped space between the stock jet and the forming fabric surface, and at least some of the liquid carried by the forming fabric.
• this invention seeks to provide a papermaking machine, having a machine direction and a cross machine direction, which includes: a forming fabric moving in the machine direction; a head box including a head box slice which provides a jet of paper making stock which impinges at an angle of impingement onto the forming fabric at a point of impingement; a roll, having a cylindrical surface whose axis is in the cross machine direction, about which the forming fabric passes, and which is located upstream of the head box slice; a forming section, located downstream of the point of • impingement, including static support elements which define a fabric path through which the forming fabric passes; and a vented lead blade, located upstream of, and immediately adjacent to, the point of impingement of a stock jet ejected from a head box slice onto a moving forming fabric, about which a forming fabric wraps through a wrap angle ⁇ ; wherein the vented lead blade has a leading edge, a shaped trailing edge portion including a trailing
• this invention seeks to provide a paper aking machine, having a machine direction and a cross machine direction, which includes: a first and a second forming fabric each moving in the machine direction; a head box including a head box slice which provides a jet of paper making stock which impinges at an angle of impingement onto at least one of the forming fabrics at a point of impingement; two rolls, each having a cylindrical surface whose axis is in the cross machine direction, about each of which one of the forming fabric passes, and which are located adjacent the head box slice; a forming section, located downstream of the point of impingement, including static support elements which define a fabric path through which the forming fabric passes; and two vented lead blades, each located upstream of, and immediately adjacent to, the point of impingement of the stock jet, about the first of which the first forming fabric wraps through a wrap angle ⁇ lf and about the second of which the second forming fabric wraps through a wrap angle ⁇ 2 ; wherein
• the convexly curved surface is essentially circular, with a constant radius. More preferably, the shaped trailing edge portion conforms to the convexly curved surface. Alternatively, the convexly curved surface is not circular, and the radius of curvature increases towards the trailing edge. Conveniently, the convexly curved surface is not circular, the radius of curvature increases towards the trailing edge, and the shaped trailing edge portion is essentially flat.
• the convexly curved surface has an effective radius of curvature that is from about 50% to about 100% of the radius of the adjacent upstream roll.
• the radius of curvature will not generally be greater than that of the adjacent upstream roll.
• the angle ⁇ , ⁇ ⁇ or ⁇ 2 through which the forming fabric wraps the lead blade is from about 10° to about 40°. More preferably, the angle of wrap is from about 15° to about 30°. Most preferably, the angle of wrap is from about 20° to about 25°.
• the two vented lead blades are the same, and their convexly curved surfaces are the same shape.
• the two vented lead blades are not the same, and their convexly curved surfaces are not the same shape.
• the two vented lead blades are the same, the angles ⁇ -i and ⁇ 2 are the same, and their convexly curved surfaces are the same shape.
• the two vented lead blades are not the same, the angles ⁇ 1 and ⁇ 2 are not the same, and their convexly curved surfaces are not the same shape.
• Figure 1 shows part of an open surface paper making machine including a vented lead blade
• FIGS 2 and 3 show parts of two different twin fabric paper making machines
• Figures 4, 5 and 6 show the effects of wrap angle and vented lead blade effective radius
• FIGS 7, 8 and 9 show three different groove arrangements for the vented lead blade top surface
• Figure 10 shows four different groove shapes.
• Figure 1 shows a paper making machine which includes a vented lead blade according to the teachings of this invention.
• the slice lips 1A and IB of the head box deliver a jet of stock
• the forming fabric 3 passes around the roll 6, wraps the vented lead blade 5, and then passes over the first static support element 4 in the forming section. As the moving forming fabric
• the trailing edge 14 of the vented lead blade 5 is closely adjacent the impingement point I, the trapped air is prevented from interfering in the formation process within the stock in the forming section.
• the grooves 12 are located and dimensioned so that at least a substantial proportion, and preferably all, of the air passing through the forming fabric, together with any liquid carried with the air from the liquid on the forming fabric at this point, is vented as at 13 from the vented lead blade at its trailing edge 14.
• Figures 2 and 3 show a paper making machine which has two forming fabrics, and which incorporates two vented lead blades according to the teachings of this invention.
• the terms "upper” and “lower” refer only to the orientation shown: in practice in a twin fabric machine the forming section is often oriented vertically, or at some angle thereto.
• the slice lips 1A and IB deliver a jet of stock 2 onto the lower forming fabric 31 at the impingement point I.
• the forming fabric 31 wraps the lower vented lead blade 51.
• air 81 in the wedge shaped space between the surface of the stock jet 91, the surface 101 of the head box lip IB, and the surface of the forming fabric 111 becomes trapped and enters the forming fabric 31.
• Figure 3 shows an alternative arrangement to that of Figure 2.
• the arrangement of the lower forming fabric 31 is the same.
• the upper forming fabric 32 converges with the stock jet 2 at the same point as the lower forming fabric 31, more or less at the impingement point I.
• For the upper forming fabric air is now trapped in the space bounded by the upper surface 92 of the stock jet, the lower surface 112 of the upper forming fabric 32, and the upper surface 102 of the head box lip 1A. All of the trapped air, together with some of the liquid in the two forming fabrics, is vented through the' grooves 121, 122 at the trailing edges 141, 142 of the two vented lead blades 51, 52.
• the convexly curved surface 16 of the vented lead blade 5 has a constant radius
• the forming fabric 3 is received tangentially from the adjacent upstream roll 6, and the impingement point I is adjacent the trailing edge 14 of the vented lead blade 5.
• the radius R 4 of the vented lead blade surface 16 is the same as the radius R of the roll 6, which is some distance from the head box slice lips 1A, IB.
• the vented lead blade 5 then has to be relatively wide in order to bend the forming fabric 3 into the forming path 7. If ⁇ and R 4 are both approximately 46 cm, the angle of wrap ⁇ 4 is about 18°. This large radius also implies that the length D 4 of the unsupported stock jet 2 cannot be shortened very much.
• the radius R 5 of the vented lead blade surface 16 is smaller than the radius R x of the roll 6, which is still some distance from the head box slice lips 1A, IB.
• the vented lead blade 5 then still has to be relatively wide in order to bend the forming fabric 3 into the forming path 7. If R x is approximately 46 cm, and R 5 is approximately 23 cm, the angle of wrap ⁇ 5 is about 36°. This smaller radius R 5 allows the length D 5 of the unsupported stock jet 2 to be shortened.
• the radius R 6 of the vented lead blade surface 16 is smaller than the radius R x of the roll 6, which is now closer to the head box slice lips 1A, IB. The vented lead blade 5 is much narrower in order to bend the forming fabric 3 into the forming path 7. If R x is approximately 46 cm, and R 6 is approximately 23 cm, the angle of wrap ⁇ 6 is about 18°. This smaller radius R 5 allows the length D 6 of the unsupported stock jet 2 to be shortened still further.
• vented lead blade of this invention provides considerable flexibility in the geometry of the machine wet end.
• the curved surface of the lead in blade is vented by means of grooves which begin at the extreme upstream edge of the blade and are continuous to its downstream edge.
• Three groove arrangements are shown in Figures 7, 8 and 9.
• the forming fabric moves in the direction of the arrow A.
• the grooves 17 are regularly spaced the same distance apart, and are essentially parallel to the arrow A.
• the disadvantage with. this arrangement is that there is some risk of the forming fabric tracking across the blade.
• Figure 8 where although the grooves 18 are still regular and parallel, they are at an angle ⁇ to the arrow A.
• two sets of angled grooves 18A, 18B can be used as shown in Figure 9. Within each set, the- grooves are parallel to each other and regularly spaced, and each set is at an angle ⁇ to the arrow. A.
• the angle ⁇ in Figures 8 and 9 will be from about 2° to about 30°.
• the purpose of the grooves in the vented lead blade surface is to provide spaces through which at least a substantial proportion of the air is vented which enters the forming fabric from the wedge shaped space essentially between
• Figure 10 shows four possible groove structures for this purpose.
• the blade surface 17 has been shown flat; in practice it will be curved.
• Groove 19 is of constant width for its entire length from the leading edge 17A to the trailing edge 17B.
• the fabric passes over the vented lead blade surface 17, air is continuously entering the forming fabric.
• a groove with an increasing cross section such as the groove 20 which widens, or the groove 21 which deepens, or the groove 22 which both widens and deepens, in each case from the leading edge 17A to the trailing edge 17B.
• the grooves 19, 20, 21 and 22 are from 2 - 8 mm in width, and 1 - 8 mm in depth.
• the forming fabric moves in sliding contact- as it wraps the vented lead blade.
• the fabric may form a small contact angle that is ideally 0.5° or less. It is preferred that the forming fabric is tangential to the vented lead blade surface at this point.
• the leading edge of the blade can be curved to minimize any frictional effects at this point; a suitable edge radius is from about 0.0025 mm to about 0.0065 mm.
• the forming fabric should exit the vented lead blade tangentially to the trailing edge portion of the blade surface, substantially in the path defined by the downstream fabric support elements.
• the downstream path of the forming fabric should be parallel to and in the same plane as the underside of the stock jet, so that the angle of impingement of the stock jet onto the forming fabric is substantially zero.

Landscapes

• Paper (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9898876

Family Applications (1)

Country Status (7)

Cited By (1)

Families Citing this family (4)

Family Cites Families (3)

• 2000
  • 2000-09-05 GB GBGB0021767.9A patent/GB0021767D0/en not_active Ceased
• 2001
  • 2001-08-31 US US09/942,649 patent/US20020046821A1/en not_active Abandoned
  • 2001-09-04 CA CA002356804A patent/CA2356804C/en not_active Expired - Fee Related
  • 2001-09-05 AU AU2001293532A patent/AU2001293532A1/en not_active Abandoned
  • 2001-09-05 WO PCT/CA2001/001260 patent/WO2002020899A1/en active IP Right Grant
  • 2001-09-05 EP EP01973866A patent/EP1315861B1/de not_active Expired - Lifetime
  • 2001-09-05 DE DE60124739T patent/DE60124739T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events