HYDRID FORMER FOR A PAPER MACHINE

Abstract: Hybrid former for a paper machine, which said former comprises a lower-wire (10) loop, which forms a single-wire dewatering zone (10a), in which water is removed from the web (W) being formed by means of dewatering members placed inside the wire loop through the lower wire (10), and an upper-wire unit (50), which includes an upper-wire loop (20), which forms a twin-wire second dewatering zone after the first dewatering zone together with the run of the lower wire (10). The former comprises a hollow-faced (21′) first forming roll (21) fitted inside the upper-wire loop (20), at (A) which said forming roll the said second, twin-wire dewatering zone begins, which said zone is curved upwards within a certain sector (a) of this forming roll (21). After the forming roll (21) a forming shoe (14) fitted inside the lower-wire loop (10) guides the second dewatering zone, which said forming shoe (14) is provided with a curved deck (14a) guiding the lower-wire loop (10). On the twin-wire dewatering zone between the first forming roll (21) and the forming shoe (14) deflector units (100,110) are fitted both inside the lower-wire loop (10) and inside the upper-wire loop (20), by means of which said deflector units sufficiently strong impulses improving the formation are produced, which act upon the web (W) that is being formed from both sides.

Description: The invention concerns a hybrid former for a paper machine, which said former comprises a lower-wire loop, which is jointly operative with the head box of the paper machine and which forms the first single-wire, preferably substantially horizontal dewatering zone, in which water is removed from the web being formed by means of dewatering members placed inside the wire loop through the lower wire, and upper-wire unit, which includes an upper-wire loop guided by guide and web-forming rolls, which said upper-wire loop forms a twin-wire second dewatering zone after the first dewatering zone together with the run of the lower wire, and which said former comprises a hollow-faced first forming roll fitted inside the upper-wire loop, at which said forming roll the said second, twin-wire dewatering zone begins, which said zone is curved upwards within a certain sector of this forming roll, as well as, after the said forming roll, a forming shoe fitted inside the lower-wire loop and guiding the said second dewatering zone, which said forming shoe is provided with a curved deck guiding the lower-wire loop, whose centre or centres of curvature are at the side of the lower-wire loop. It is known in prior art that the dewatering of a web that is being formed on the fourdrinier former of a fourdrinier paper machine takes place exclusively downwards, whereby fines and fillers are removed from the web from the side of the wire owing to the washing effect of either stationary dewatering members, e.g. foils, or revolving table rolls. This is why a paper web produced by a fourdrinier machine is always anisotropic in respect of the properties of its two sides so that the upper face of the web is smoother and contains a larger amount of fines and fillers than the face that was placed against the wire, which thus has a lower content of fines and fillers and in which, more­ over, a so-called wire marking can be seen. Out of the above reasons, so-called twin-wire formers have been developed, in which the forming of the wire takes place for a significant part between two wires, so that the two-sidedness of the web can be eliminated at least partly. Paper produced by means of such machines is also considered better, in particular in respect of the printing qualities, than paper produced by means of fourdrinier machines. In such prior-art twin-wire formers in which no stationary dewatering members are used the formation is usually poor, for by means of revolving dewatering members it is impossible to produce such pulsation of the dewatering pressure as is ideal for improving the formation. A further drawback has been that these prior-art formers have not included the possibility to control the proportion of the quantities of dewatering taking place through the upper wire and through the lower wire. In several cases operators of paper machines have expressed the wish that such possibility of control should be provided. In twin-wire formers of paper machines, in a way known in prior art, different types of so-called forming shoes are used as stationary dewatering elements, which said shoes are most commonly composed of several ribs transverse to the direction of running of the wire. In addition to the dewatering effect, these ribs also produce pulsation in the partly formed web by-passing them between two wires, by the effect of which said pulsation the fibres in the web are displaced relative each other so that the fibre agglomerations or flocks present in the web are decomposed to some extent. In such forming shoes the guide or glide face placed against the wire is curved, and its structure is usually the same over the entire length of the shoe. It has also been possible to notice that such a forming shoe operates optimally only within quite a limited speed range of the paper machine and, as a rule, with a certain specific paper quality produced only. With twin-wire formers, a considerable pro­ portion of the dewatering takes place within the area of the forming shoe. Thus, the forming shoe has con­ siderable potential possibilities of affecting both the dewatering capacity and the formation. In prior art, it has, however, not been realized how to make use of these possibilities, except to a limited extent. Moreover, it should be noticed that the forming shoe acts as an element controlling the joint run of the wires, thereby for its part affecting the stability of the runs of the wires. In respect of the prior art related to the present invention, reference is made to the applicant's Finnish Patent Application No. 771364 (filed 28 April, 1977), wherein a method for the manufacture of multi-­ layer board and a web forming unit are described, wherein on the twin-wire part such a forming shoe is used in which the length of the open and closed guide face is arranged adjustable by means of filler ribs, by means of which the slot face on the forming shoe can be converted to a completely solid guide face. The said forming shoe is intended expressly for the manufacture of multi-layer board. Reference is also made to the applicant's Finnish Patent Applications 820742 (corresponds to US Pat. 4,614,566) and 821531, of which in the latter one a forming-shoe construction is described which consists of two or more rib face components of different curve radii, whose length proportions relative each other are adjustable. In recent years, such modernizations of exist­ ing fourdrinier machines have become common in which onto the fourdrinier wire part, jointly operative with it, most commonly one upper-wire unit has been placed, within whose area the dewatering can also be made to take place upwards. What is aimed at hereby is both to increase the dewatering capacity and to improve the retention. Such wire parts are called hybrid formers. The wire parts of entirely new paper machines can also be designed as of hybrid type right from the beginning. As a rule, an increased dewatering capacity permits an increased running speed of a paper machine, or at least, if the running speed remains unchanged, it permits a lowering of the consistency of the pulp fed out of the head box, which has in itself favourable effects. In some cases, by means of the upper-wire units mentioned above, old slow newsprint machines have been modernized to board machines without increasing the running speed of the machine. It is a particular object of the present inven­ tion to provide such a dewatering arrangement applicable in hybrid formers by means of which an improved formation of the web is obtained. Another particular object is, by means of the said dewatering arrangement, to control the dewatering process so that by its means it is pos­ sible to affect the distribution of fillers and fines in the web. One particular object of the invention is to provide such a dewatering arrangement applicable in hybrid formers by means of which, within the twin-wire dewatering zone, an improved support and stability of running are obtained for the wires. What is aimed at hereby is to improve the formation and to reduce streaks in the web, which are caused by folding owing to unstable running of the wires. It is a particular object of the present in­ vention to provide such a dewatering member and arrange­ ment to be used in the twin-wire part of the hybrid former by whose means the wire part of the paper machine can be adjusted so as to operate optimally in respect of both its dewatering capacity and the web formation at differ­ ent running speeds of the paper machine and when differ­ ent paper qualities are manufactured. In respect of the theory of dewatering taking place in the twin-wire curved forming zone, reference is made to the following papers: Papper och Trä 1972, No. 4, p. 137-146, Jouni Koskimies, Jorma Perkinen, Heikki Puolakka, Eero Schulz, Björn Wahlström, "A Drainage Model for the Forming Zone of a Two-wire Former" and Pulp and Paper Magazine of Canada , Vol. 74, No.2/February 1973, pp. 72-77, E.G. Hauptmann and J. Mardon, "The Hydrodynamics of Curved Wire Formers". The dewatering arrangement in accordance with the invention is mainly characterized in that on the twin-wire dewatering zone between the said first forming roll and the said forming shoe, whose run is substan­ tially straight and upwardly inclined, deflector units are fitted both inside the lower-wire loop and inside the upper-wire loop, by means of which said deflector units sufficiently strong impulses improving the forma­ tion are produced, which are preferably adjustable and which act upon the web that is being formed from both sides. In the following, the advantages provided by the invention will be dealt with in detail. Owing to the deflector dewatering member and arrangement, a better formation is obtained for the web than by means of a conventional forming shoe. Dewater­ ing adjustable in respect of its quantity and proportions is achieved by means of adjustment of the ribs included in the deflector part of the dewatering member. By means of choice the adjustability of the types and numbers of deflector ribs, it is possible to control the dewatering capacity and even the direction. The above makes it possible that in the single-wire first dewatering zone of a hybrid former the dewatering pro­ cess can be controlled so as to make it slower and, at the same time, more gentle so that a dewatering propor­ tion of appropriate magnitude is still left over to take place in the twin-wire second dewatering zone, where the ultimate formation of the web is achieved. The deflector arrangement in accordance with the invention is placed ahead of the forming-shoe part proper, where adjustable suction is preferably used. In the following, the invention will be de­ scribed in detail with reference to an exemplifying em­ bodiment of the invention shown in the figures in the drawing, whereat the invention is in no way strictly con­ fined to the details of the said embodiment. Figure 1 is a schematical side view of a hybrid former, which has been accomplished in the modernization of an existing fourdrinier wire part and in which the dewatering arrangement in accordance with the invention has been applied. Figure 2 shows a second exemplifying embodiment of the invention in the way corresponding to Fig. 1 but more schematically. Figure 3 is an overall view of the main parts and the location of the dewatering arrangement in accord­ ance with the invention in the twin-wire second dewater­ ing zone of the hybrid former shown in Fig. 1. Figure 4 is a more detailed view of the deflec­ tor part of the web formation and dewatering arrangement shown in Fig. 3. As is shown in Figures 1 and 2, the fourdrinier wire part of a fourdrinier paper machine has been pro­ vided with an upper-wire unit 50, and thereby converted to a hybrid former. The wire plane of the original fourdrinier wire part is denoted with reference T-T. The hybrid former includes the frame 95 of the old wire part, the dry suction boxes 16, the wire suction roll 17 and the drive roll 18, as well as the guide rolls 19 guiding the lower run of the wire 10, all of which were included in the original wire part. When the present invention is applied to hybrid formers in accordance with the figures, a lower deflector unit 100 is fitted in accordance with the present in­ vention on a frame part supported from outside the wire part or on the old frame part 95. The upper-wire unit 50 includes the frame part 45 shown in Fig. 1, to which the different parts, also the upper deflector unit 110, are attached. The running of the upper-wire loop 20 is guided, starting from the beginning of the twin-wire section, by a preferably hollow-faced 21′ first forming roll 21, after it by the dewatering elements 100 and 110 in accordance with the invention and by the first leading roll 22 placed inside the loop 20 of the upper wire, and in the area or at the proximity of the said roll 22 the run of the twin-wire section joins the original plane T-T of the lower wire 10. The twin-wire dewatering zone ends before the drive roll 23 of the upper wire 20. The upper guide rolls of the upper wire 20 are denoted with reference numeral 24. The rolls 22, 23 and 24 are provided with doctors 31. The roll 21 is also provided with cleaning means (not shown) and water collecting means in themselves known. The hybrid former obtained as a result of the modernization is, before its twin-wire section, provided with a single-wire first dewatering zone 10a, which is formed by the original fourdrinier wire and in which the dewatering takes place preferably by means of the dewatering members included in the original fourdrinier wire part, such as forming board and foils (not shown). In the first dewatering zone 10a the dewatering takes place downwards through the lower wire 10, however, preferably relatively gently, so that possibilities for adequate retention are retained and that an adequate proportion is left over for dewatering taking place up­ wards in view of good formation. After the line of departure C from the forming members 100,110,14,15, there is a downwardly inclined straight joint run of the wires 10 and 20 down to the roll 22, on which the joint run of the wires 10 and 20 is directed slightly upwards, finally joining the ori­ ginal plane T-T of the lower wire 10. The web W is detached from the lower wire 10 on the downwardly inclined run between the rolls 17 and 18 by the effect of the suction zone 40 of the pick-up roll 40, being transferred onto the pick-up fabric 41, which transfers the web W further into the press section (not shown). In the following, the dissimilar features of construction in Figures 1 and 2 will be described. As is shown in Fig. 1, after the deflector units 100 and 110 there follows a forming shoe 14 provided with a ribbed deck 14a, within whose area the joint run of the wires 10 and 20 passes all the time upwards with a relatively large curve radius R, which is of an order of R = 2.5 to 5 m. Further, according to Fig. 1, after the curved ribbed deck 14a of the forming shoe 24, a very short straight run of the wires 10,20 follows, after which there is a forming roll 15, on whose sector b the joint run of the wires 10 and 20 is turned downwards. After that there is the said smooth-faced roll 22 placed in­ side the loop of the wire 20, within whose sector c the joint run of the wires is turned and joins the plane T-T of the lower wire 10. Fig. 1 shows a water removing trough in which the front edge 30 of its bottom plane is placed at the proximity of the sector b of the roll 15. The water removing trough 36 is attached to the frame 45 by means of horizontal shafts 37, and it can be pivoted by means of a screw transmission 37 by the inter­ mediate of rods 38. By means of the water removing trough 36, the waters drained through the upper wire 20 are passed to the side of the paper machine. The water level in the trough 36 is denoted with S. The hybrid former shown in Fig. 2 differs from the above in respect of the twin-wire dewatering zone following after the deflector units 100 and 110. According to Fig. 2, after the deflector units 100 and 110 the run of the wires 10,20 is substantially straight, and within the area of the said deflectors the run is curved, being guided by a curved ribbed deck 14a on the forming shoe 14 connected to a suction source 13, e.g. a suction leg, and becomes a downwardly inclined run. The said downwardly inclined run is so steep or so long that the twin-wire dewatering zone extends on the sector c of the roll 22 by the height difference H₁ below the plane T-T. By means of this arrangement, space is allowed for the particular dewatering trough 28 shown in Fig. 2, which said trough includes walls 26 and 27 fitted at the proximity of the downwardly inclined run of the wires 10 and 20, between which said walls the water drained through the upper wire 20 is cast by the effect of dynamic energy in the direction of the arrow F and is removed because of this and owing to the differ­ ence in height without a necessity to use any particular suction devices, such as AUTO-SLICE (TM) devices known in prior art. This makes the construction simpler and less expensive. According to Fig. 2, on the sector c of the roll 22 the joint run of the wires 10,20 is turned upwards and becomes a gently upwardly inclined run, whereinafter a guide roll 16a follows, on whose sector d the twin-wire 10,20 forming zone joins the plane T-T of the lower wire 10 and on which sector, at the area of the line B, the upper wire 20 departs from the web W, which follows along with the lower wire 10. As an essential constituent the combination of the invention includes the deflector units 100 and 110, which guide the joint run of the wires 10 and 20 upwards from the sector a of the forming roll 21 up to the inlet edge of the ribbed deck 14a of the forming shoe 14. Figures 3 and 4 are more detailed views mainly of the exemplifying embodiment shown in Fig. 1, and, according to Figures 3 and 4, inside the loop of the lower wire 20 there is a deflector unit 100, which includes subsequent deflectors 101, 102 and 103 with a mutual spacing K₁, of which the first deflector 101 is placed close to the sector a of the forming roll 21 (at the distance K₀) and the last one 103 near the first rib 14a₁ of the forming shoe 14 (Fig. 4). Correspondingly inside the loop of the upper wire there is a deflector unit 110, which includes two subsequent deflectors 111 and 112, whose plane front faces are placed against the inner face of the upper wire 20. The lower deflector unit 100 is preferably stationary, but its deflectors 101, 102 and 103 may also be arranged displaceable in guides 105 or equivalent mainly in the direction of running of the wires 10 and 20. The upper deflector unit 110 is arranged adjust­ able either as a whole or separately in the direction of the arrows A₁, i.e. in a direction perpendicular to the plane of the wires 10 and 20, so that the front faces of the deflectors 111 and 112 guide the run of the wires together with the deflectors 101 and 102 in the unit 100 in such a way that a straight or with very low wave height meandering joint run is obtained for the wires 10,20, by means of which run strong impulses are produced in the web W at both of its sides. By the effect of these impulses the formation of the web W is improved. By adjusting the position of the upper deflectors 111 and 112 in the direction A₁ it is possible to adjust the magnitude of the said impulses to an optimal level in consideration of the quality of paper to be manufactured, of the running speed of the machine, and of other circumstances. In stead of adjusting the position of the whole upper deflector unit 110, it is possible to attach the deflectors 111 and 112 to a frame part which is arranged adjustable in the direction of the arrows A₁by means of guides 113,114 in connection with the frame part of the deflector unit 110. In this way, if necessary, the first and second upper de­ flector 111 and 112 can be adjusted independently from each other. In some applications, it is also possible to arrange the lower deflectors 101,102 and/or 103 adjustable in respect of their position in a direction perpendicular to the plane of the wires 10 and 20. The mutual spacing of the upper deflectors 111 and 112 is denoted with K₁. Correspondingly, the mutual spacing of the lower deflectors 101,102 and 103 is denoted with K₂. In the invention K₀ ≈ K₁ ≈ K₂ = 150... 300 mm, preferably K₀ ≈ K₁ ≈ K₂ = 200...250 mm. The length of the front face of the upper de­ flectors 111,112 is denoted with L₁, and correspondingly the corresponding length of the front face of the lower deflectors 101,102,103 is denoted with L₂. In the in­ vention, as a rule, L₁ ≈ L₂ = 10...40 mm, preferably L₁ ≈ L₂ = 20...30 mm. The blade angle or deflector angle of the upper deflectors 111,112 is denoted with a₁. The said angle a₁ = 15°...40°, preferably a₁ = 20°...25°. In a corresponding way, the deflector angle of the lower de­ flectors 101,102,103 is denoted with a₂. Generally speaking, it can be ascertained that it is advantageous that a₁ < a₂, and a₂ = 30°...60°, preferably a₂ = 40°...45°. The angles a₁ of different deflectors 111 and 112 may be different from each other. In a corres­ ponding way, the angles a₂ of different deflectors 101, 102,103 may be to some extent different from each other. The locations of the deflectors are preferably such that the blade edges of the deflectors 111 and 112 placed inside the upper-wire loop 20 are placed halfway between the deflectors 101,102,103 placed inside the lower-wire loop 10. The planes of the front faces of the deflectors are substantially in the same plane as the tangent plane that contacts the face of the forming roll 21, on one hand, and the first rib 14a₁ of the forming shoe 14, on the other hand. The front faces of the deflectors may also be placed slightly apart from the inner faces of the wires 10 and 20 in view of avoiding wear of the wires. The deflector ribs are preferably made of a ceramic material or of any other, corresponding wear-resistant material. In the following, the results of comparisons made in trial runs with the applicant's test paper machine will be given. In the following table, on the first line the discharge opening (mm) of the head box is given, on the second line the Beta formation with a former geometry in accordance with Fig. 1 without the deflector units 100 and 110, and on the third line the corresponding Beta formation figures when using de­ flectors fitted and dimensioned in accordance with Fig. 4. In the following the patent claims will be given, whereat the various details of the invention may show variation within the scope of the inventive idea defined in the said claims and differ from the details described above for the sake of example only.

Claims: 1. Hybrid former for a paper machine, said former comprising of lower-wire (10) loop, which is jointly operative with the head box of the paper machine and forms a first single-wire, preferably substantially horizontal dewatering zone (10a), in which water is removed through the lower wire (10) from the web (W) being formed by means of dewatering members placed inside the said wire loop, and an top-wire unit (50), which includes an upper-­ wire loop (20) guided by guide and web-forming rolls (21,22,23,24), said upper-­ wire loop forming after the first dewatering zone a second twin-wire dewatering zone together with the run of the lower wire (10), and which said former comprises a hollow-faced (21′) first forming roll (21) fitted inside the upper-­ wire loop (20), at a location (A) where said second, twin-wire dewatering zone begins, which zone is curved upwards within a certain sector α of this forming roll (21), and further, after the said forming roll (21), a forming shoe (14) fitted inside the lower-wire loop (10) which shoe guides the said second dewatering zone, and is provided with a curved deck (14a) guiding the lower-wire loop (10), whose centre or centres of curvature are at the side of the lower-wire loop (10), characterized in that between the said first forming roll (21) and the said forming show (14) on the twin-wire dewatering zone, whose run is substantially straight and upwardly inclined, deflector units (100,110) are fitted both inside the lower-wire loop (10) and inside the upper-wire loop (20), by means of which said deflector units impulses are produced which act from both sides upon the web being formed and which are preferably adjustable and sufficiently strong to improve the sheet formation. 2. Former as claimed in claim 1, characterized in that each deflector unit (100,110) includes at least two deflector ribs (101,102,103,111,112), whose planar faces contact against the inner surfaces of the wires (10,20) and are placed substantially in the joint tangent plane that is imagined passing between the forming roll (21) preceding the deflector units (100,110) and the first forming rib (14a₁) in the rib deck (14a) of the forming shoe (14). 3. Former as claimed in claim 1 or 2, characterized in that the position of the deflector ribs (101,102,103,111,112) in both or one of the deflector units (100,110) is adjustable at least in a direction (A) perpendicular to the plane of the wires (10,20) at the place of the deflectors for controlling the magnitude of the impulses directed at the web (W) in accordance with the quality of the paper to be manufactured, with the running speed of the machine, and with other, comparable parameters. 4. Former as claimed in claim 3, characterized in that the lower deflector unit (100) is fixed and that the position of the upper deflector unit (110) or one or preferably all of its deflectors (111,112) is adjustable, preferably in a direction (A₁) perpendicular to the direction of the plane of the wires (10,20). 5. Former as claimed in any of the claims 1 to 4, char­ acterized in that in the deflector unit (100) placed inside the lower-wire loop (10) there are three subsequent deflector ribs (101,102,103), of which the last one is placed at the proximity of the first deck rib (14a₁) of the forming shoe (14), and that in the deflector unit (110) placed inside the upper-wire loop (20) there are two deflector ribs (111), which are placed in the spaces between the deflector ribs (101,102,103) of the lower deflector unit, preferably at the middle of the said spaces (Fig. 4). 6. Former as claimed in any of the claims 1 to 5, char­ acterized in that the distance (K₀) between the first lower deflector (101) and the point where the wires (10,20) separate from the said forming roll (21) is substantially equal to the mutual distance (K₂) between the first (101), second (102) and a possible third deflector (103). 7. Former as claimed in any of the claims 1 to 6, char­ acterized in that the deflector angle a₁ of the deflector ribs (111,112) of the upper deflector unit (110) is a₁ = 15°...40°,preferably a₁ = 20°...25°, and/or that the deflector angle a₂ of the deflector ribs (101,102,103) of the said lower deflector unit (100) is a₂ = 30°...60°, preferably a₂ = 40°...45°. 8. Former as claimed in any of the claims 1 to 7, char­ acterized in that the face lengths of the deflectors in the said upper and lower deflector units (100,110) are L₁ ≈ L₂ = 10mm...40mm, preferably L₁ ≈ L₂ = 20mm...30mm, and/or that the mutual distances between the said deflectors are K₁ ≈ K₂ = 150...300mm, preferably K₁ ≈ K₂ = 200...250mm. 9. Former as claimed in any of the claims 1 to 8, char­ acterized in that the curved rib deck (14a) of the said forming shoe (14) is followed by a forming roll (15) placed inside the lower-wire loop (10), so that within a certain sector (b) of said roll the twin-wire zone is curved downwards, and that said preferably smooth-faced forming roll (15) is followed by a downwardly inclined joint run of the wires (10,20), which is curved upwards within a certain sector (c) of a forming or guide roll (22) and joins the plane (T-T) of the single-wire initial portion (10a) of the lower wire (10) (Fig. 1). 10. Former as claimed in any of the claims 1 to 8, char­ acterized in that within the area of the rib deck (14a) of the said forming shoe (14), which is preferably connected to a suction source (13), the joint run of the wires (10,20) is curved downwards and runs onto a forming or guide roll (22) placed inside the upper-wire loop (20), the lowest point of the said roll (22) being placed preferably below (H₁) the lever (T-T) determined by the single-wire initial portion (10a), and that after the said forming or guide roll (22) is followed by an upwardly inclined run, which goes on up to a guide roll (16a) placed inside the lower-wire loop (10), the twin-­ wire forming zone ending preferably within the area (B) of the said roll (16a) (Fig. 2).

Inventors: KOIVURANTA, MAURI, ODELL, MICHAEL
Applicants: VALMET PAPER MACHINERY INC.
Application year: 1988
Main classification: D21F9
IPC codes: D21F1, D21F9