A transfer apparatus for transferring a tail of a web

Abstract: A transfer apparatus (10C) is disclosed for trans­ ferring a tail (TC) of a web (WC) from a press roll(12C) to a dryer (14C) of a dryer section (16C). The apparatus includes a lead-in roll (22C) which is disposed adjacent to and spaced relative to the press roll for leading the tail of the web from the press roll towards the dryer. A dryer felt (20C) extends around the lead-in roll and from the lead-in roll to the dryer such that the tail is supported by the felt from the lead-in roll to the dryer. The felt and the dryer define therebetween a positive air pressure in-going nip. A rotatable suction roll (30) is disposed adjacent to and on the opposite side of the felt relative to the in-going nip such that in use of the apparatus, the suction roll generates a flow of air from the positive air pressure in-going nip through the felt such that when the tail of the web is being transferred from the press roll towards the dryer, the tendency for the positive air pressure in the vicinity of the in-­ going nip to prevent threading of the tail between the felt and the dryer is inhibited.

Description: The present invention relates to a transfer apparatus for transferring a tail of a web from a press roll to a dryer of a dryer section, as defined in the preamble of claim 1. The present invention also relates to a method of transferring a tail of a web from a press roll to a dryer of a dryer section, as defined in the preamble of claim 9. In the manufacture of a paper web, stock is ejected from a headbox onto a forming wire or between a pair of cooperating forming wires where water is removed from the stock in order to form a paper web. The formed web is removed from the forming section by a pick-up roll and is guided through one or more press nips for removing more water from the web. In a typical press section, the pressed web emerges from the last press nip as a sheet approximately 9 m (30 feet) in width and traveling at 26.6 m/s (60 miles per hour). The aforementioned pressed web must then be threaded into and through a dryer section for removing further moisture from the pressed web. Typically, in order to thread the pressed web into the dryer section, a narrow tail, approximately 15.24 cm (6 inches) wide, is cut from the pressed web and the entire width of the web is doctored from the press roll to a broke pit. The narrow tail is then directed by an air wand around a guide roll and into a converging nip defined between a dryer felt and a baby dryer drum of the dryer section. Consequently, considerable skill is required by an operator in effectively handling the tail and directing the tail into the converging nip of the dryer section, which is running at a slightly higher speed than the press section in order to take up any slack in the threaded tail. When the tail of the web has been threaded, the tail is widened to the full width of the web so that the full width of the pressed web is threaded into and through the dryer section. A transfer apparatus of the kind defined in the preamble of claim 1 is disclosed in EP-A-0 254 666. Such an apparatus includes a pair of spaced blow boxes disposed between the lead-in roll and the dryer, and an intermediate support roll disposed in the space between the blow boxes. The intermediate roll supports the felt midway between the lead-in roll and the dryer, thereby reducing the amount of deflection of the felt so as to prevent the felt from contacting the blow boxes. The intermediate roll is a vacuum roll. Since the span between the lead-in roll and the dryer is relatively large the intermediate roll is located too far away from the in-going nip defined between the felt and the dryer for the vacuum generated by the intermediate roll to assist the downstream blow box in reducing the air pressure in the in-going nip. The document EP-A-0 254 666 also discloses a method of the kind defined in the preamble of claim 9. The known method includes the step of guiding the felt first past a first blow box, then past an intermediate support roll and finally past a second blow box before it wraps the dryer, the second box being oriented relative to the felt such that a partial vacuum is generated between the felt and the second box, said partial vacuum causing air to be drawn from the in-going nip through the felt. Since the partial vacuum above the felt often is not sufficient to maintain a tail of the web in close conformity with the felt the assistance of air jets is required which generate a flow of air blowing the tail upwardly in close conformity with the felt. Other transfer apparatus have been proposed, which also include blow boxes or vacuum boxes disposed on the opposite side of the felt relative to the tail of the web, for drawing the tail into close conformity with the felt. Although such arrangements also avoid the problem of the tail detaching from the felt, such arrangements are disadvantageous in that when the necessary vacuum level is applied on the opposite side of the felt, the felt is drawn into frictional contact with the blow box or vacuum box, thereby causing felt wear and premature failure of the dryer felt. A vacuum transfer box of the aforementioned type is disclosed in US-A-3,526,574. A blow box type arrangement is disclosed in US-A-4,551,203. It has unexpectedly been discovered that the real problem of tail detachment resides in the build-up of a positive air pressure at the in-going, or converging, nip defined between the dryer felt and the baby dryer. Moreover, it has been discovered that in the absence of such an over-pressure there exists no need to draw the tail of the web into close conformity with the dryer felt and that the relatively moist tail of the web will readily adhere to the dryer felt between the lead-in roll and the dryer section. However, during the threading operation, as the tail of the web approaches the converging nip of the prior art arrangement, the increased air pressure at the converging nip tends to blow the leading edge of the tail away from the converging nip. Furthermore, an air pocket is generated between the tail of the web and the felt and such air pocket moves from the leading edge of the tail and progresses back towards the lead-in roll, thereby causing detachment of the tail of the web from the felt. An object of the invention is to modify the transfer apparatus and the method so as to apply a relatively high vacuum adjacent to the positive air pressure converging nip but on the opposite side of the felt relative to the nip for drawing air from the converging nip through the dryer felt so that the leading edge of the tail of the web may be readily threaded between the dryer felt and the baby dryer. With regard to the transfer apparatus, the object is achieved by the features of the characterising clause of claim 1, and with regard to the method, the object is achieved by the features of the characterising clause of claim 9. According to the invention, the suction roll generates a flow of air from the positive air pressure in-going nip through the felt. The arrangement is such that when the tail of the web is being transferred from the press roll towards the dryer, the tendency for the positive air pressure in the vicinity of the in-going nip to prevent threading of the tail between the felt and the dryer is inhibited. Preferably the suction roll is disposed at a distance within 2.54 to 5.08 cm (1 to 2 inches) from the dryer so that a positive pressure at the in-going nip is inhibited. Conveniently the suction roll has a rotatable perforate shell and a center shaft which defines a sector-shaped suction zone which is disposed adjacent to the in-going nip and on the opposite side of the felt relative to the in-going nip. Preferably the felt wraps around the perforate shell such that the sector-shaped zone extends towards the dryer a distance within the range 2.54 to 5.08 cm (1 to 2 inches) from a point at which the felt diverges relative to the suction roll for drawing air through the felt from the in-going nip while maintaining a space between the perforate shell and the dryer to accommodate passage of a wad of paper therethrough in the event of the web wrapping the dryer. The sector-shaped zone may extend away from the dryer a distance within the range 2.54 to 5.08 cm (1 to 2 inches) from a point at which the felt converges with the perforate shell. A vacuum of at least 0.99 kPa (4 inches water column) may be provided within the sector-shaped suction zone for drawing away the positive air pressure within the converging nip. The transfer apparatus may include a deflector shield extending between the lead-in roll and the suction roll for inhibiting the build-up of a positive air pressure in the vicinity of a further in-going nip between the felt and the suction roll and for augmenting the flow of air through the felt from the in-going nip towards the suction roll. Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a side-elevational view of a transfer apparatus according to one embodiment of the present invention for transferring a tail of a web from a press roll to a dryer of a dryer section; Figure 2 is an enlarged side-elevational view of the rotatable suction roll and dryer shown in Figure 1; and Figure 3 is a side-elevational view of a further embodiment of the present invention including a deflector shield. Similar reference characters refer to similar parts throughout the various embodiments of the present invention. With reference to Fig. 1 of the drawings, a transfer apparatus generally designated 10C includes a lead-in roll 22C which is disposed adjacent to and spaced relative to a press roll 12C for leading a tail TC of a web WC from the press roll 12C towards a dryer 14C of a dryer section generally designated 16C. A dryer felt 20C extends around the lead-in roll 22C and from the lead-in roll 22C to the dryer 14C such that the tail TC of the web WC is supported by the felt 20C from the lead-in roll 22C to the dryer 14C. The felt 20C and the dryer 14C define therebetween a positive air pressure in-going nip NC. A rotatable suction roll generally designated 30 is disposed adjacent to and on the opposite side of the felt 20C relative to the in-going nip NC such that in use of the apparatus 10C, the suction roll 30 generates a flow of air as indicated by the arrow 32 from the positive air pressure in-going nip NC through the felt 20C such that when the tail TC of the web WC is being transferred from the press roll 12C towards the dryer 14C, the tendency of the positive air pressure in the vicinity of the in-going nip NC to prevent threading of the tail TC between the felt 20C and the dryer 14C is inhibited. As shown in Figure 1, the dryer felt 20C is disposed between the tail TC of the web WC and the lead-in roll 22C. The suction roll 30 is disposed less than 10.16 cm (4 inches) from the dryer 14C, and in a preferred embodiment of the present invention, as shown in Figure 1, the suction roll 30 is disposed at a distance within the range 2.54 to 5.08 cm (1 to 2 inches) from the dryer 14C. Figure 2 is an enlarged view of the suction roll generally designated 30 and shows the suction roll 30 as including a rotatable perforate shell 34. A stationary hollow shaft 36 is disposed within the shell 34 and is connected to a source of partial vacuum 38. The shaft 36 defines a sector-shaped suction zone 40 which is disposed adjacent to and on the opposite side of the felt 20C relative to the in-going nip NC such that the flow of air 32 flows from the positive air pressure in-going nip NC through the felt 20C into the suction zone 40. Figure 2 shows the felt 20C as wrapping around the perforate shell 34 such that the sector-shaped zone 40 extends towards the dryer 14C a distance 42 within the range 2.54 to 5.08 cm (1 to 2 inches) from a point 44 at which the felt 20C diverges relative to the suction roll 30. The arrangement permits drawing air 32 through the felt 20C from the in-going nip NC while maintaining a space indicated by the arrow 46 between the perforate shell 34 and the dryer 14C to accommodate passage of a wad of paper in the event of the web WC breaking and wrapping around the dryer 14C. As shown in Figure 2, the sector-shaped zone 40 extends away from the dryer 14C a distance as indicated by the arrow 48 within the range 2.54 to 5.08 cm (1 to 2 inches) from a point 50 at which the felt 20C converges with the perforate shell 34. The sector-shaped suction zone 40 maintains a partial vacuum of at least 0.99 kPa (4 inches water column). Figure 3 is a side-elevational view of a further embodiment of the present invention and shows a transfer apparatus generally designated 10D. The apparatus 10D includes a deflector shield 52 which extends between a lead-in roll 22D and a suction roll 30D. A felt 20D is disposed between a tail TD of the web WD and the shield 52. The shield 52 diverges relative to the felt 20D in a direction as indicated by the arrow 54 from the lead-in roll 22D towards the suction roll 30D. Such divergence of the shield 52 generates a flow of air which augments the flow of air as indicated by the arrow 32D which flows from the in-going nip ND towards the suction roll 30D for urging the tail TD of the web WD into close conformity with the felt 20D. The generated air flow also inhibits the build-up of a positive air pressure within a further in-going nip 56 defined between the felt 20D and the suction roll 30D. In operation of the transfer apparatus, as shown in Figures 1 and 2, the tail TC is supported by and beneath the dryer felt 20C. The positive air pressure generated within the in-going nip NC due to the pumping effect between the felt 20C and the dryer 14C is reduced by the suction roll 30 which draws a flow of air 32 from the in-going nip NC through the felt 20C towards the suction roll 30. The perforate shell 34 of the suction roll 30 cooperates with the felt 20C, as shown in Figure 5, so that the suction roll 30 is disposed at a distance 46 from the dryer 14C. The distance 46 is relatively small so that the suction within the zone 40 effectively reduces the air pressure within the in-going nip NC. However, in the event of the threaded web WC breaking and becoming enwrapped around the dryer 14C, the distance 46 permits several layers of the web WC to be enwrapped in order to allow time for stopping the rotation of the dryer 14C so that damage to the dryer 14C and the suction roll 30 is prevented. In the embodiment shown in Figure 3, the shield 52 diverges relative to the dryer felt 20D so that a partial vacuum is generated between the shield 52 and the dryer felt 20D. Such partial vacuum augments the flow of air 32D from the positive pressure nip ND and also assists in urging the tail TD into conformity with the dryer felt 20D. Additionally, the shield 52 prevents the build-up of a positive air pressure within a further nip 56 defined between the suction roll 30D and the dryer felt 20D which could otherwise tend to cause detachment of the tail TD from the felt 20D. The present invention provides a transfer apparatus which facilitates threading of a tail of a web into a dryer section and inhibits frictional wear of the dryer felt.

Claims: A transfer apparatus (10C; 10D) for transferring a tail (TC; TD) of a web (WC; WD) from a press roll (12C) to a dryer (14C) of a dryer section (16C), said apparatus (10C; 10D) comprising: a lead-in roll (22C; 22D) disposed adjacent to and spaced relative to the press roll (12C) for leading the tail (TC; TD) of the web (WC; WD) from the press roll (12C) towards the dryer (14C); a dryer felt (20C; 20D) extending around said lead-in roll (22C; 22D) and from said lead-in roll (22C; 22D) to the dryer (14C) such that the tail (TC; TD) of the web (WC; WD) is supported by said felt (20C; 20D) from said lead-in roll (22C; 22D) to the dryer (14C), said felt (20C; 20D) and the dryer (14C) defining therebetween a positive air pressure in-going nip (NC; ND); the tail (TC; TD) of the web (WC; WD) being disposed between said felt (20C; 20D) and the dryer (14C); and a rotatable suction roll (30; 30D) disposed between said lead-in roll (22C; 22D) and said dryer (14C) and on the opposite side of said felt (20C; 20D) relative to said in-going nip (NC; ND); characterized in that said suction roll (30; 30D) is disposed adjacent to said in-going nip (NC; ND) such that in use of said apparatus (10C; 10D), said suction roll (30; 30D) generates a flow of air (32; 32D) from said positive air pressure in-going nip (NC; ND) through said felt (20C; 20D) such that when the tail (TC; TD) of the web (WC; WD) is being transferred from the press roll (12C) towards the dryer (14C), the tendency for said positive air pressure in the vicinity of said in-going nip (NC; ND) to prevent threading of said tail (TC; TD) between said felt (20C; 20D) and the dryer (14C) is inhibited. A transfer apparatus (10C; 10D) as set forth, in claim 1 wherein said suction roll (30; 30D) is disposed less than 10.16 cm (4 inches) from the dryer (14C). A transfer apparatus (10C; 10D) as set forth in claim 2 wherein said suction roll (30; 30D) is disposed at a distance within the range 2.54 to 5.08 cm (1 to 2 inches) from the dryer (14C). A transfer apparatus (10C; 10D) as set forth in any one of the preceding claims wherein said suction roll (30; 30D) further includes: a rotatable perforate shell (34); a stationary hollow center shaft (36) disposed within said shell (34) and connected to a source of partial vacuum (38); said center shaft (36) defining a sector-shaped suction zone (40) disposed adjacent to said in-going nip (NC; ND) and on the opposite side of said felt relative to said in-going nip (NC; ND) such that said flow of air (32; 32D) flows from said positive air pressure in-going nip (NC; ND) through said felt (20C; 20D) into said suction zone (40). A transfer apparatus as set forth in claim 4 wherein said felt (20C; 20D) wraps around said perforate shell (34) such that said sector-shaped zone (40) extends towards the dryer (14C) a distance (42) within the range 2.54 to 5.08 cm (1 to 2 inches) from a point (44) at which said felt (20C; 20D) diverges relative to said suction roll (30; 30D) for drawing air (32; 32D) through said felt (20C; 20D) from said in-going nip (NC; ND) while maintaining a space (46) between said perforate shell (34) and the dryer (14C) to accommodate passage of a wad of paper therethrough in the event of the web (WC; WD) wrapping the dryer (14C). A transfer apparatus (10C; 10D) as set forth in claim 4 or 5 wherein said sector-shaped zone (40) extends away from the dryer (14C) a distance within the range 2.54 to 5.08 cm (1 to 2 inches) from a point (50) at which said felt (20C; 20D) converges with said perforate shell (34). A transfer apparatus (10C; 10D) as set forth in any one of claims 4 to 6 wherein said sector-shaped suction zone (40) maintains a partial vacuum of at least 0.99 kPa (4 inches water column). A transfer apparatus (10D) as set forth in any one of the preceding claims and further including: a deflector shield (52) extending between said lead-in roll (22D) and said suction roll (30D), said felt (20D) being disposed between the tail (TD) of the web (WD) and said shield (52), said shield (52) diverging relative to said felt (20D) in a direction (54) from said lead-in roll (22D) towards said suction roll (30D) for augmenting said flow of air (32D) for urging the tail (TD) of the web (WD) into close conformity with said felt (20D) and for inhibiting the build-up of a positive air pressure in the vicinity of a further in-going nip (56) defined between said felt (20D) and said suction roll (30D). A method of transferring a tail (TC; TD) of a web (WC; WD) from a press roll (12C) to a dryer (14C) of a dryer section (16C), said method comprising the steps of: leading a tail (TC; TD) of the web (WC; WD) from the press roll (12C) around a lead-in roll (22C; 22D) such that the tail (TC; TD) of the web (WC; WD) is supported by a felt (20C; 20D) extending around the lead-in roll (22C; 22D) and from the lead-in roll (22C; 22D) to the dryer (14C) of the dryer section (16C), the tail (TC; TD) of the web (WC; WD) being disposed between said felt (20C; 20D) and said dryer (14C); and drawing air from a positive pressure in-going nip (NC; ND) defined between the felt (20C; 20D) and the dryer (14C) such that the flow of air (32; 32D) flows from the in-going nip (NC; ND) through the felt (20C; 20D); characterized by the steps of: guiding said felt (20C; 20D) and said tail (TC; TD) of the web (WC; WD) around a suction roll (30; 30D) which is disposed between said lead-in roll (22C; 22D) and said dryer (14C) adjacent to said in-going nip (NC; ND) and on the opposite side of the felt (20C; 20D) relative to the in-going nip (NC; ND); and applying a partial vacuum (38) to said suction roll (30; 30D) so as to generate said flow of air (32; 32D) flowing from said in-going nip (NC; ND) through the felt (20C; 20D) towards said suction roll (30; 30D) such that any tendency for the positive air pressure in the vicinity of the in-going nip (NC; ND) to prevent threading of the tail (TC; TD) between the felt (20C; 20D) and the dryer (14C) is inhibited.

Inventors: WEDEL GREGORY LYNN, WEDEL, GREGORY LYNN
Applicants: BELOIT CORP, BELOIT CORPORATION
Application year: 1990
Main classification: D21G9
IPC codes: D21G9, D21F7, D21F9, D21F3