METHOD FOR CLEANING A CENTER ROLL OF A PRINTING PRESS

Abstract: Procedure for cleaning the middle cylinder of a press, in which procedure wash fluid (2) is applied to the surface of the middle cylinder (1) to be cleaned and the middle cylinder is rotated while at the same time limiting the speed of the paper running around it so as to produce a speed difference between the circumferential velocity of the middle cylinder and the running velocity of the paper, producing abrasion between the paper and the surface of the middle cylinder to remove dirt from it. The motion of the paper (3) is prevented during cleaning by pressing it against the middle cylinder (1).

Description: METHOD FOR CLEANING A CENTER ROLL OF A PRINTING PRESS The present invention relates to a procedure for cleaning the middle cylinder of a press. On a press, the imprint is transferred from a rubber cylinder to paper by pressing the paper between the rubber cylinder and a hard-surfaced middle cylin¬ der. Often the imprint is printed onto the paper web in two stages in such a way that the first side of the paper web is printed while the web is being passed around the middle cylinder of one printing unit and the second side when the web is being passed around the middle cylinder of another printing unit. When the second side of the paper is being printed, its first side already printed is pressed against the middle cylinder. During printing, printing ink and paper fibre are transferred from the already printed paper surface to the surface of the middle cylinder until print quality begins to deteriorate. For this reason, printing has to be interrupted at certain intervals to allow the middle cylinder to be cleaned. In many presses, the paper runs around the middle cylinder in such a way that the middle cylinder is not sufficiently exposed to enable it to be cleaned with current methods without removing the paper. At present, to wash the middle cylinder, the press is stopped and the paper web is cut to expose the middle cylinder. The cylinder is washed by manu¬ ally rubbing its surface with a sponge wetted in wash fluid. After the washing, the paper web is again in- stalled into the machine. The main problem with the current washing method is the production time consumed by manual washing of the cylinder and reinstallation of the paper web. To eliminate the problems referred to, de- vices like those presented in specifications US 4781116 and US 5080015 have been used. In these, the running speed of the press, i.e. the rotational speed of the cylinders, is reduced during the cleaning. They have the drawback that a mere speed difference between the cylinder and paper web and the paper's own weight are not sufficient to achieve effective cleaning. The object of the invention is to eliminate the drawbacks mentioned above. A specific object of the invention is to present a new procedure for clean¬ ing the middle cylinder which is simpler and more ef- fective than current methods. As for the features characteristic of the in¬ vention, reference is made to the claims. In the procedure of the invention, wash fluid is applied to the surface of the middle cylinder to be cleaned and the middle cylinder is rotated while at the same time limiting the movement of the paper web running around it with respect to the movement of the middle cylinder so that a speed difference is produced between the circumferential velocity of the middle cylinder and the running speed of the paper, causing the paper to abrade the surface of the middle cylinder and remove the dirt from it. According to the inven¬ tion, the motion of the paper is completely stopped by pressing it against the middle cylinder. As the sur- face is simultaneously under the influence of wash fluid, the abrasion by the paper effectively removes dirt from the surface of the middle cylinder. In this way, the dirt adheres to the paper, which carries it away from the press. The cleaning is generally per- formed by disconnecting the unit containing the middle cylinder to be cleaned from the press so that the mid¬ dle cylinder can be rotated alone and apart from the rest of the press. The wash fluid used may be any one of the wash fluids generally known in the industry which dis¬ solve printing ink and contain no water, causing prac¬ tically no deterioration of the fibrous structure of the paper. The wash fluid can be applied directly onto the surface of the middle cylinder, especially when the latter is sufficiently exposed. In most cases, however, the middle cylinder is almost completely surrounded by paper and in this case, according to a preferable embodiment of the in¬ vention, the wash fluid can be applied to the outer surface of the paper, e.g. onto the outer surface of the paper around the middle cylinder, in which case the wash fluid soaks through the paper and wets the surface of the middle cylinder. It is also possible to apply the wash fluid to a suitable area on the inner surface of the paper. The ram used to stop the paper movement dur- ing cleaning can preferably be one made of elastic ma¬ terial, such as rubber or polyurethane plastic. The ram may consist of a squeegee, spatula, doctor knife, cylinder, roller or an equivalent instrument. The action stopping the paper movement can also be performed at some other point by gripping the paper or by suitably pressing it. However, this action should be so effected that it is applied relatively evenly across the whole width of the paper so as to avoid tearing the paper. When the paper is pressed against the middle cylinder with a suitable elastic ram, the pressing force of the latter increases the mechanical abrasion between the paper and the surface of the middle cylin¬ der, thereby improving the cleaning result. When this is done, impurities often gather as a heap on the mid¬ dle cylinder surface under the ram, but they are car¬ ried away with the paper or detached from the surface of the middle cylinder. It is also possible that a heap or lump of impurities large enough to cause shredding of the pa¬ per web may accumulate in front of the squeegee or doctor knife during cleaning. This can be avoided in a preferred embodiment which uses at least two doctor knives. In this case, at least one of the squeegees is pressing the paper web against the middle cylinder during cleaning. However, they are alternately disen- gaged from contact with the middle cylinder and paper web so that if a lump of impurities has been accumu¬ lated, it can move away with the paper web before growing too large and damaging the paper web. The procedure of the invention has signifi- cant advantages over known technology. The washing is done quickly and in a simple manner without manual washing operations. Moreover, as there is no need to cut the paper during washing, the washing operation can be carried out very quickly. Therefore, the proce- dure has a considerable effect on the impression in general, because the middle cylinder can be cleaned mo e often than before. At present, the middle cylin¬ der is generally only cleaned upon detection of clear deterioration of impression. In the following, the invention is described by referring to the attached drawing, which illus¬ trates the implementation of the procedure of the in¬ vention in a diagrammatic form. The drawing presents a diagram representing a printing unit comprising a middle cylinder 1 and four rubber cylinders 7 around it. The paper 3 runs around the middle cylinder 1, passing between the middle cyl¬ inder and each one of the rubber cylinders. The print is transferred from the rubber cylinders to the outer surface of the paper between the middle cylinder and the rubber cylinders, i.e. in the nip 8. Placed near the middle cylinder 1 on the out¬ side of the paper 3 is a spraying device 9 and an elongated doctor knife 6 made of an elastic material, mounted in the same direction with the axis of the middle cylinder. The spraying device may consist of a tube extending across the width of the paper and pro- vided with jet holes at suitable distances, through which a wash fluid is sprayed onto the paper. It is also possible to use only one jet which is moved transversely relative to the paper web. In the sim- plest application, the wash fluid can also be sprayed manually onto the paper at the beginning of the clean¬ ing operation. According to the invention, the middle cylin¬ der 1 is cleaned as follows. The press is stopped, but the paper 3 is not cut. The printing unit is discon¬ nected from the rest of the press so that its middle cylinder can be rotated independently. By means of the spraying device 9, wash fluid 2 is applied to the outer surface 4 of the paper 3 substantially across the whole width of the paper. The wash fluid soaks through the paper and thus wets the surface of the middle cylinder as well. After this, the middle cylinder 1 is rotated slowly and at the same time a pressure is applied with the elastic doctor knife 6 on the outer surface 4 of the paper 3, pressing it against the surface of the middle cylinder so as to prevent paper movement, i.e. so that the paper remains stationary. This results in a speed difference between the circumferential veloc- ity of the middle cylinder and the stationary paper web, producing mechanical abrasion between the paper and the middle cylinder. In this way, the dissolving wash fluid and the abrading paper remove any ink and fibre material from the surface of the middle cylin- der. The dirt sticks to the paper, which conveys it away from the press when the paper movement is re¬ leased. Once the desired washing effect has been achieved, i.e. when the surface has been cleaned suf- ficiently, the doctor knife 6 is disengaged from con¬ tact with the paper and middle cylinder, whereupon the press is immediately ready to continue production. In the above, the invention has been de¬ scribed by way of example by referring to the attached drawing, but different embodiments of the invention are possible within the scope of the inventive idea defined by the claims.

Claims: CLAIMS 1. Procedure for cleaning the middle cylinder of a press, in which procedure wash fluid (2) is ap¬ plied to the surface of the middle cylinder (1) to be cleaned and the middle cylinder is rotated while at the same time limiting the speed of the paper running around it so as to produce a speed difference between the circumferential velocity of the middle cylinder and the running velocity of the paper, producing abra- sion between the paper and the surface of the middle cylinder to remove dirt from it, characterized in that the motion of the paper (3) is prevented during clean¬ ing by pressing it against the middle cylinder (1). 2. Procedure as defined in claim 1, charac- terized in that the pressure is applied by means of an elastic doctor knife (6) or roller. 3. Procedure as defined in claim 1, charac¬ terized in that the wash fluid (2) is applied to the outer surface (4) of the paper (3). 4. Procedure as defined in claim 1, charac¬ terized in that the wash fluid (2) is applied to the inner surface (5) of the paper (3). 5. Procedure as defined in claim 1, charac¬ terized in that the wash fluid (2) is applied to the surface of the middle cylinder (1). 6. Procedure as defined in claim 2, charac¬ terized in that two or more doctor knives (6) or roll¬ ers are used, and that these are pressed against the paper and middle cylinder simultaneously and alter- nately so as to prevent the accumulation of a heap or lump of impurities in front of the doctor knife.

Inventors: HAEMAELAEINEN KLAUS, HASSINEN ARI PEKKA, PAUNONEN RISTO, HAEMAELAEINEN, KLAUS, HASSINEN, ARI, PEKKA, PAUNONEN, RISTO
Applicants: GRAFISYSTEMS OY, HAEMAELAEINEN KLAUS, HASSINEN ARI PEKKA, PAUNONEN RISTO, HAEMAELAEINEN, KLAUS, HASSINEN, ARI, PEKKA, PAUNONEN, RISTO
Application year: 1996
Main classification: B41F35
IPC codes: B41F35