Patentamt JEuropaischesEuropean Patent Office © Publication number: 0 027 621 Office europeen des brevets /\1 © EUROPEAN PATENT APPLICATION © Application number: 80106192.0 © Int. CI.3: D 21 G 1/00 © Date of filing: 10.10.80 © Priority: 15.10.79 Fl 793201 ©Applicant. Valmet Oy Punanotkonkatu 2 SF-00130 Helsinki 13IFI) (j3) Date of publication of application: 29.04.81 Bulletin 8117 © Inventor: Kankaanpaa, Matti, M.Eng. Kaskenkaatajantie 12 (84) Designated Contracting States: SF-02100 Espoo 10(FI) AT DE FR GB IT SE © Representative: Tiedtke, Harm, Dipl.-lng. et al, Patentanwaltsburo Tiedtke-Buhling-Kinne- Grupe-Pellmann Bavariaring 4 D-8000Munchen2(DE) (© Paper calendering procedure and calender applying same. Method and apparatus for calendering paper webs orthe like wherein a plurality of hard calendering rolls (15-18) are situated to constitute a roll stack and wherein a plurality of soft calender rolls (11-14) are situated in nip defining relationship with respective ones of the hard rolls whereby a plurality of corresponding hard (S1-S3) and soft or supercalender nips (N1-N4) are defined The apparatus is adapted to be directly associated with a paper machine and force apparatus (36, 37, 41) are provided in conjunction with the apparatus for sup- porting the hard and soft calender rolls so that the hard nips (S1-S3) are closed and the supercalendering nips (N1-N4) are open during threading of the apparatus while the hard nips are opened and the supercalendering nips are closed afterthe web is threaded in order to perform continuous supercalen- dering of the paper web. The invention present concerns a paper calendering pro- cedure wherein is employed a plurality of calendering rolls and a plurality of soft rolls disposed to define soft super-calender nips together with the said hard rolls. Furthermore, the invention concerns a paper calender in- tended for carrying out the procedure of the invention and intended to be immediately connected to a paper or card- board machine and to operate as a so-called machine super- calender, and which comprises a plurality of hard calender rolls disposed upon each other to constitute a roll stack, and a plurality of soft rolls disposable to define soft super-calender nips together with said hard rolls. The paper coming out from the drying section of a paper machine is not sellable as such as a rule: it requires a finishing treatment. One step in the finishing is the calendering of the paper, by which an influence is exerted in the first place on the smoothness and gloss of the paper and on the compactness of the paper. Calendering is accomplished oy conducting the continuous paper web through the press gaps, or nips, between calender rolls acting against each other, and further onward. In accordance with the conventional techniques, the calendering takes place with a so-called machine calender immediately connected with the paper machine. Likewise conventionally, this treatment may, if necessary, be supplemented by a super-calendering process in a separate so-called super-calender. The rolls which are employed in machines intended for paper calendering may be either "hard" or "soft" rolls. In this disclosure of the invention, hard rolls are under- stood to be rolls of which the material is chill-cast metal or steel and which have a surface that has been ground smooth. Soft rolls, again, are in the following understood to be rolls with a surface of a resilient, elastic, non-metallic material. Most usually, the soft rolls are so-called filled rolls, of which the elastic material consists of paper courses overlayed around the axis perpendicularly thereto and which have been power- fully compressed to form a coherent, compact roll covering. In a machine calender all rolls are hard rolls, whereas a super-calender contains, on the side of hard rolls, also soft rolls in the same calender stack. Super- calenders of conventional design and which are known in themselves in the art have in the roll stack mainly alternatingly hard and soft rolls. The number of soft rolls is substantially the same as that of hard rolls. In this disclosure of invention, the designation "soft nip" shall be used referring to the line of contact in the calender between a soft roll and a hard roll working thereagainst. Similarly "hard nip" refers to a line of contact which is defined in the calender- between two hard rolls. The term "nip" properly refers to the line of contact between rolls, but in a wider sense it means that point on a roll, or on rolls, where a nip can be established. In this disclosure the expression "to open a nip" will mean the separation of rolls which are in nip contact with each other and "to close a nip" signifies that rolls which are separate are brought into mutual nip contact. The terms "machine calendering" and "machine burnishing" refer, in this disclosure of invention, only to a web treatment taking place between hard calender nips, as a result of which the web is compacted and its surface is smoothed and acquires the so-called "machine gloss". Similarly, "super-calendering" or "super-burnishing" refers to a treatment between soft nips, as a result of which the web attains a gloss considerably superior to the "machine gloss". However, in this connection "super- gloss" does not denote any specific grade of gloss: it merely indicates generally that the gloss has been achieved by super-calendering between soft nips. Thus, the grade of "super-gloss" may vary, depending e.g. on the number of soft nips used in super-calendering, or on the nip pressure. Machine calendering may be carried out, depending on the paper brand and on the requirements thereon imposed, even with a calender having only one nip and therefore constituted by one pair of rolls. Most usually, however, a machine calender comprises six to eight rolls, which thus constitute five to seven nips. It is usually endeavoured in super-calendering, to obtain equal gloss on both sides of the web. Therefore there must be at least two soft nips and, in addition, so that each side of the web will in turn face against the surface of a hard roll, which is considered more than the surface of a soft roll to act towards the generation of gloss. Two soft nips are not in all cases able to endow the paper with such "super-gloss" which would be substantially superior to machine gloss. Therefore the number of soft nip pairs must be more than one, and actual separate super- calenders have in fact up to ten pairs of nips. With a view to boosting production in paper manufacturing, it has been found necessary to try to accomplish a calendering unit wherein are combined the functions of machine calender and of super-calender. Accordingly, in the same applicant's Finnish patent application No. 761764 a so-called machine super-calender intended to be connected to a paper machine has been disclosed. This calender consists of a roll stack composed of conventio- nal hard rolls and of substantially equal number of soft rolls which have been disposed outside the roll stack to define soft nips against the hard rolls. It is possible with the aid of this combination of pre- viously known machine calender and super-calender, to carry out the super-calendering of the web immediately after the paper machine, without any intermediate steps. But it has been found that the calendering result it- self, i.e., the super-gloss which is obtained on the paper by such calender treatment, is not uniform but instead spotty, in other words, that areas with higher gloss occur locally in the web. It has also been found that the web has a tendency to blacken. This is partly due to the circumstances that the hard nips are un- necessarily hard and inelastic. The object of the present invention is to provide a super-calender for connection to a paper machine and the operation of which does not cause the above- mentioned defects of the paper, and wherein the "bagging" due to distension of the paper, occurring between certain nips, can be prevented. It is furthermore an object of the invention: to pro- vide a calender in which the web may, to the purpose of commencing its treatment, be passed through the calender with ease and without trouble at a high speed, equally as in standard machine calenders. In order to attain the above-mentioned aims, and others which will become apparent later on, the procedure of the invention is mainly characterized in that both the said hard rolls and the soft rolls are mutually so dis- placed that when the web is being pulled through, the hard nips between hard rolls are closed and the super- calender nips are opened, and that for performing continuous super-calendering, said hard nips are opened and the super-calender nips are closed. A calender applying the procedure of the invention is mainly characterized in that both the hard rolls and the soft rolls have been disposed to be supported by such support means provided with force means that when the web is being conducted through, the nips between hard rolls are closable and the super-calender nips openable and that when the said means are used towards calendering the said hard nips are openable and the super-calender nips are closable. As taught by the invention, super-calendering in connection with the paper machine takes place by con- ducting the web through four consecutive soft nips, the first two nips providing rolls with resilient surface against one and the same side of the paper and the next two, against the other, opposite surface of the paper without any treatment of the web in hard nips between the soft nips.