Grouping of cylinders in the drying section of a paper machine

Abstract: The invention concerns a grouping of cylinders in the drying section of a paper machine, in which drying section the paper web (W) and the wire (H) are carried meandering from a heated, preferably steam-heated, drying cylinder (K) onto a leading cylinder (V) and from the leading cylinder (V) further onto the next heated drying cylinder (K). A drying group (R) consists of a number of subsequent groupings of cylinders, whereby, in a grouping of cylinders, the drying cylinders (K n-2 ,K n-1 ,K n ) and the leading cylinders (V n-1 , V n ) are placed, in relation to one another, substantially at three different height levels, so that the drying cylinders (K n-2 , K n ) with larger diameter are placed at the height level (Y₁) and the drying cylinder (K n-1 ) that has a diameter smaller than said larger diameter is placed at the height level (Y₂). In the grouping of cylinders the leading cylinders (V n-1 , V n ) are placed at the third height level (Y₃).

Description: The invention concerns a grouping of the cylinders in the drying section of a paper machine, according to the preamble of claim 1. In the prior-art constructions of drying sections in paper machines, see WO-A-90 12 150 on which the preamble of claim 1 is based, the drying section consists of drying groups. Each drying group comprises heated drying cylinders and cold leading cylinders placed in a level different from the level of the drying cylinders. Being supported by the wire, the paper web is passed meandering from a drying cylinder onto a leading cylinder and further from the leading cylinder onto the next drying cylinder. The drying cylinders are placed in two levels in relation to one another, those levels being different from the level of the leading cylinders. In such a prior-art construction of drying sections, the overall length of the drying section becomes remarkably long. On the other hand, the overall length of the drying section affects the requirement of the building area of the paper mill. If it is possible to reduce the length of the drying section, it is also possible to lower the building cost required by the paper machine in the same proportion. Thus, the object of the invention is to provide a drying section of a novel type for a paper machine, which is considerably shorter than a prior-art drying section with an equivalent drying capacity and with an equal number of cylinders. The object of the invention has been achieved by the features of the characterizing clause of claim 1. As a result of the novel grouping, the overall length required by the drying section can be reduced considerably. However, the drying section in accordance with the invention has a drying capacity equal to that of a prior-art drying section with the same number of cylinders. Thus, according to the invention, the drying section has been formed so that it comprises heated, in particular steam-heated, drying cylinders of two sizes. The drying cylinders of larger diameter are fitted to be placed at a height level of their own, and, in a corresponding way, the drying cylinders of smaller diameter are fitted to be placed at a height level of their own. Further, the drying section comprises cold leading cylinders, which are placed at two different height levels, i.e. at a height level Y 3 and at a height level Y 2 ', the latter height level being substantially the same as that of the drying cylinders of smaller diameter. The paper web and the wire are passed meandering from a drying cylinder of larger diameter onto a leading cylinder and from the leading cylinder onto a drying cylinder of smaller diameter. From the drying cylinder of smaller diameter the paper web and the wire are passed onto a second leading cylinder and from the leading cylinder onto a second heated drying cylinder of larger diameter. By means of the above grouping of cylinders and choice of diameters of drying cylinders, it is possible to form, for example, a drying section whose overall length is, compared with a prior-art 71-cylinder Sym-Run drying section, 18 metres shorter. The invention will be described in the following with reference to some preferred embodiments of the invention illustrated in the figures in the accompanying drawings, the invention being, yet, not supposed to be confined to said embodiments alone. Figure 1 shows a prior-art drying section. Figure 2 shows a drying section in accordance with the invention. Figure 3 is a more detailed illustration of the grouping of the cylinders in a drying section in accordance with the invention. As is shown in Fig. 1, a prior-art drying section consists of groups R 1 ,R 2 ,...R n of drying cylinders. Each group R 1 ,R 2 ,R 3 ,R 4 ,...R n of drying cylinders comprises hot, preferably steam-heated drying cylinders of larger diameter and smaller cold, so-called leading cylinders placed at a level different from the level of the drying cylinders. In each group R 1 ,R 2 ,..., the paper web is passed, being supported by the wire H, from a drying cylinder K onto a leading cylinder V placed at a different level and further from the leading cylinder V back to the upper level onto a heated drying cylinder placed at said level. The leading cylinders are preferably perforated Uno-Vac cylinders, into which an internal negative pressure is introduced and which negative pressure is allowed to act upon the entire space in the interior of the drying cylinder, whereby the web is kept in contact with the wire also in the web draws in which the web W is not supported by a wire. Fig. 1 shows a construction of a drying section that comprises seven groups of drying cylinders, of which the second group from the end is an inverted group, in which the steam-heated drying cylinders K are placed at a lower level and the cold leading cylinders V are placed at a higher level above them. Fig. 2 shows an improvement over the prior art illustrated in Fig. 1. In the construction, it has been possible to reduce the length of the drying section by forming the drying groups by means of a novel grouping of the drying cylinders and leading cylinders. In the solution shown in Fig. 2, there are six drying groups R 1 ...R 6 , the second group R 5 from the end being a so-called inverted group, in which the steam-heated drying cylinders K are placed at the lowest levels and the leading cylinders V at a higher level above them. The groups R 1 ...R 4 and R 6 are provided with a grouping of the heated drying cylinders K and of the leading cylinders V in accordance with the invention. The whole drying section comprises 28 steam-heated drying cylinders K and 29 cold cylinders, i.e. leading cylinders V. In the way shown in Fig. 2, the heated drying cylinders K in a drying group R are placed in such a way in relation to one another that a drying cylinder K of smaller diameter is placed at a height level Y 2 , which is a height level different from the height level Y 1 of the drying cylinders K of larger diameter. The leading cylinders V are placed at the height level Y 2 ' and at the height level Y 3 . The paper web W is passed, e.g. in the drying group R 1 , from the leading cylinder V 1 placed at the height level Y 2 ' onto the drying cylinder K 2 placed at the height level Y 1 and from the drying cylinder K 2 onto the leading cylinder V 2 placed at the height level Y 3 , and from said leading cylinder onto the heated drying cylinder K 3 of smaller diameter placed at the height level Y 2 . From the heating cylinder K 3 the web R is passed onto the leading cylinder V 3 placed at the height level Y 3 and from the leading cylinder V 3 onto the drying cylinder K 4 placed at the height level Y 1 . From the drying cylinder K 4 the web R is again passed onto the leading cylinder V 4 placed at the height level Y 2 '. In a corresponding way, the wire H 1 is passed so that in connection with the heated drying cylinders K 2 and K 4 the paper web W runs between the wire H 1 and the face of the drying cylinder K 2 and K 4 , and in connection with the leading cylinders V 2 and V 3 the web W runs outermost. Correspondingly, in connection with the drying cylinder K 3 with smaller diameter the paper web W runs between the drying cylinder K 3 and the wire H 1 . Thus, in the groups R 1 ,R 2 ,R 3 ,R 4 and in the group R 6 the hot drying cylinders K and the leading cylinders V are placed at four different height levels Y 1 ,Y 2 ,Y 2 ',Y 3 so that the hot drying cylinders K are placed at two different levels Y 1 ,Y 2 and the leading cylinders V at the level Y 2 ' and at the level Y 3 . The height levels Y 2 and Y 2 ' are levels substantially equal to one another. The level Y 2 ' is placed slightly higher than the level Y 2 . The diameter dimensions of the leading cylinders V placed at the levels Y 2 ' and Y 3 are just slightly different from one another. The leading cylinders V at the level Y 2 ' have a slightly larger diameter than the leading cylinders V at the level Y 3 . The diameters of both of the leading cylinders V placed at the levels Y 3 and Y 2 ' are slightly smaller than the diameters of the heated drying cylinders K placed at the height level Y 2 . The diameter of the drying cylinder K placed at the middle height position Y 2 is smaller than the diameter of the drying cylinders K placed at the first height level Y 1 . In this way, between the drying cylinders K and the leading cylinders V, a novel grouping has been provided which results in considerable economies of space in the machine direction. The drying capacity is good and corresponds to that of a prior-art drying section of equal number of cylinders and larger length. Fig. 3 is a more detailed illustration of the grouping in accordance with the invention between the heated drying cylinders and the cold cylinders, i.e. the leading rolls. In the way shown in Fig. 3, each drying group R 1 ,R 2 ... consists of cylinder groupings in which the heated drying cylinders are placed at two height levels, the levels Y 1 and Y 2 . The leading cylinders are placed at the height level Y 2 ' and at the height level Y 3 . Moreover, the diameter of the heated drying cylinder placed at the middle height level Y 2 is smaller than the diameter of the drying cylinder placed at the level Y 1 . Together with the wire H, the paper web W is passed from the leading cylinder V n-2 of the height level Y 2 ' onto the drying cylinder K n-2 , of the level Y 1 . From the drying cylinder K n-2 , the web W is passed onto the leading cylinder V n-1 , and from the leading cylinder V n-1 further, with the wire H, onto the middle heated drying cylinder K n-1 . From the heated drying cylinder K n-1 the paper web W and the wire H are passed onto the second leading cylinder V n of the level Y 3 . From the leading cylinder V n the paper web W is passed onto the second heated drying cylinder K n of larger diameter, placed at the height level Y 1 . From the drying cylinder K n the web W is passed onto the leading cylinder V n+1 of the height level Y 2 '. In a corresponding way, the wire H is passed from one cylinder onto the other. The paper web W runs in contact with the faces of the drying cylinders on the heated drying cylinders K. On the leading cylinders V the paper web W runs outermost, and the wire H is placed in contact with the cylinder V face. The leading cylinders V n-1 , and V n are placed symmetrically at the same distance from the vertical plane X drawn through the centre point of the heated drying cylinder K n-1 , of smaller diameter. The heated drying cylinders K n-2 ,K n of larger diameter are also placed symmetrically at equal distances from the vertical plane. In a corresponding way, the leading cylinders V n-2 ,V n+1 of the height level Y 2 ' are placed symmetrically to the centre plane X and at equal distances from same.

Claims: Grouping of cylinders in the drying section of a paper machine, in which drying section the paper-web (W) and the wire (H) are carried meandering from a heated, preferably steam-heated, drying cylinder (K) onto a leading cylinder (V) and from this leading cylinder (V) onto the next heated drying cylinder (K), and in which construction of drying section the drying section consists of a number of drying groups (R 1 , R 2 , R 3 ...). a drying group (R) consisting of a number of subsequent groupings of cylinders, whereby, in a grouping of cylinders, the drying cylinders (K n-2 , K n-1 , K n ) and the leading cylinders (V n-1 , V n ) are placed, in relation to one another, substantially at three different height levels, characterized in that said drying cylinders in the drying group (R) have different diameters, two of them being larger than the third, that the drying cylinders (K n-2 , K n ) with larger diameter are placed at the first height level (Y 1 ) and the drying cylinder (K n-1 ) with the smaller diameter is placed at the second, middle height level (Y 2 ), while the leading cylinders (V n-1 , V n ) are placed at the third height level (Y 3 ), whereby the paper web (W) and the wire (H) pass said drying and leading cylinders in the following order: the first drying cylinder (K n-2 ) of larger diameter, a first leading cylinder (V n-1 ), the drying cylinder (K n-1 ) of the smaller diameter, a second leading cylinder (V n ) and the second drying cylinder (K n ) of larger diameter. Grouping of cylinders in the drying section of a paper machine as claimed in claim 1, characterized in that the paper web (W) is passed onto the first drying cylinder (K n-2 ) of larger diameter from a third leading cylinder (V n-2 ), which is placed substantially at the same height level (Y 2 ') as the drying cylinder (K n-1 ) of smaller diameter, and that, in the grouping of cylinders, the paper web is passed from the second drying cylinder (K n ) of larger diameter onto a fourth leading cylinder (V n+1 ), which is placed substantially at the same height level (Y 2 ') as the drying cylinder (K n-1 ) of smaller diameter. Grouping of cylinders in the drying section of a paper machine as claimed in claim 1 or 2, characterized in that, in the grouping, the leading cylinders (V n-1 ,V n ) are placed symmetrically in relation to the vertical plane (X) drawn through the centre point of the drying cylinder (K n-1 ) of smaller diameter at equal distances from the vertical plane (X) and that, in the grouping of cylinders, the heated drying cylinders (K n-2 ,K n ) of larger diameter are also placed symmetrically in relation to the vertical plane (X). Grouping of cylinders in the drying section of a paper machine as claimed in any of the preceding claims, characterized in that, in the grouping of cylinders, the heated drying cylinders (K n-2 ,K n ) of larger diameter are placed at the highest height level, the drying cylinder (K n-1 ) of smaller diameter is placed at the middle height level (Y 2 ), and the leading cylinders (V n-1 , V n ) are placed at the lowest height level (Y 3 ).

Inventors: TOERMAENEN AIMO, TOERMAENEN, AIMO, Törmänen, Aimo
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1992
Main classification: D21F5
IPC codes: D21F5