Method for manufacturing a metal belt used in a paper/board or finishing machine

The present invention relates to a method for manufacturing a metal belt used in a paper/board or finishing machine.

An endless steel belt is used, for example, in a metal belt calendar and a CondeBelt band dryer. Currently employed metal belts comprise metal bands manufactured by traditional metallurgical melting techniques and processed further by various hot and cold working methods. A typical raw stock for the band is a web of stainless steel, from which are cut webs of required length and width, which are welded together to form an endless metal belt. After welding, the seams are ground, which is a relatively difficult and slow procedure in the case of an endless metal belt.

The aim of the present invention is to provide an improved metal belt manufacturing method for facilitating and expediting metal belt manufacture, especially as concerns the grinding treatment following welding.

To achieve this aim, the method according to the invention for manufacturing a metal belt is characterised in that in the method, the seams are welded from the outside against a fixed backing by a welding method selected from a group comprising TIG-, MIG/MAG-, laser, FSW-(friction stir welding) and laser-hybrid-welding, and that the grinding of the metal belt to final thickness is carried out essentially only on the outer surface. The fixed backing is preferably of non-weldable material. It is also conceivable that a thin protective non-weldable sheet metal be located between the metal belt and the fixed backing to prevent fusion between the metal belt and fixed backing.

In operation, metal belts are subjected to both a fatigue load and corrosion stress. Because of these factors, the belts must be replaced from time to

time due to evident corrosion fatigue. The belts are further subjected to powerful abrasive forces, which is why the material thereof should have sufficient strength and surface hardness. In the event that the hardness is not adequate, the belt may develop scratches which may lead to the formation of a fatigue crack. If such a crack appears at the guide roll, where the belt is bent, the edges of the crack will tend to turn outwards, whereupon repair welding, for example as TIG- or MIG/MAG-welding supported against the guide roll is not possible as such, because the edges of the crack are not in contact with the guide roll. An object of the present invention is, therefore, to provide a relatively simple method for repairing a crack in a metal belt.

This method according to the invention for repairing a crack formed in a metal belt is characterised in that in the method, the crack is tack welded by means of a one-sided spot welding method in such a way that the welding electrode presses the edges of the crack tightly against the guide roll, while an electric current passing between the electrode and the belt melts the surface of the belt, whereupon the edges of the crack are welded together and, after the tack welding, the actual repair welding is carried out against the guide roll by means of a welding method selected from a group comprising TIG-, MIG/MAG-, laser, FSW- and laser-hybrid-welding.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which:

Figures Ia-Ic show schematically some arrangements of metal belt blanks used for manufacturing a metal belt.

Figures 2 and 2A show schematically a method according to the invention for repairing a crack formed in the metal belt.

Figure Ia illustrates schematically a metal belt 102 comprised of metal belt blanks 10a, the length of which corresponds to the final width of the metal belt 102. The metal belt blanks 10a are placed side by side and welded to one another to form welded seams 11a between them, which extend essentially perpendicularly to the longitudinal direction of the metal belt. Figure Ib shows the formation of the metal belt 102 of metal belt blanks 10b corresponding essentially to the final length of the metal belt, wherein the seam lib between the blanks becomes essentially parallel with the longitudinal direction of the metal belt. The seam between the abutting longitudinal ends of each metal belt blank 10b may be essentially perpendicular to the longitudinal direction of the metal belt, the ends of adjacent metal belt blanks 10b being positioned essentially in alignment in the lateral direction of the metal belt 102, thus forming an essentially perpendicular transverse seam 12. Figure Ib also shows an alternative embodiment, wherein the abutting ends of the metal belt blanks 10b are cut into a diagonal position with respect to the longitudinal direction of the blank and adjacent blanks 10b are positioned in such a way with respect to one another that an essentially continuous seam extending diagonally across the metal belt 102 is formed, the seam being indicated with broken line in Figure Ib, with reference numeral 12a. Figure Ic shows yet another alternative embodiment, wherein the metal belt blanks 10c are positioned side by side diagonally to the longitudinal direction of the final metal belt 102, whereby the seams lie between them also extend diagonally to the longitudinal direction of the belt 102. The longitudinal ends of the blanks 10c are cut diagonally to correspond essentially to the longitudinal edge of the final belt 102. Various combinations of the above-described belt manufacturing methods are also feasible, for example arranging several metal belt blanks shorter than the metal belt's final length in succession for a length equalling the final belt length, and side by side in a number necessitated by the final width of the belt. It is also conceivable to manufacture a metal belt having a width exceeding its final width, in which case it can be narrowed, for example, by trimming or grinding to its final width after welding the band.

Each welded seam is formed by TIG-, MIG/MAG-, laser, FSW- or laser- hybrid-welding from the outside against a fixed backing, whereby the inner surface will be essentially smooth and level also at the seams, and grinding of the inner surface may essentially be omitted or only minor localised grinding may be carried out. The grinding of the metal belt to final thickness is carried out essentially only on the outer surface, for example in a roll grinding machine as stone grinding against a high-tolerance backing roll.

Figure 2 shows the travelling of the metal belt 1 around a guide roll 2 and in Figure 2a is shown schematically, on an enlarged scale, the method according to the invention for repairing a crack 3 formed in the metal belt 1. The edges 3a, 3b of the crack are bent outwards due to the tensions formed in the belt as the belt bends while on the guide roll 2. In Figure 2, the edges 3a, 3b of the crack are shown in an exaggerated size for illustrative purposes. In the method according to the invention, the crack can be repaired on the guide roll 2 by using a spot welding electrode 4 which presses the edges of the crack tightly against the surface of the guide roll. By then conducting an electric current between the electrode and the belt, the surface of the belt heats up to a molten or almost molten state and the edges of the crack are welded together at the electrode. This is repeated at different points over the length of the crack to provide the desired tack welding between the edges of the crack and, after the tack welding, the actual repair welding is carried out, for example by means of the TIG- or MIG/MAG-method against the guide roll. Between the metal belt and the guide roll is preferably located a thin protective sheet metal covering the area of the crack, the said sheet metal being non-weldable, thus preventing the metal belt and guide roll from welding together during welding. The protective sheet metal may be, for example, copper, aluminium, titanium or their various alloys. As a welding method may also be used, for example laser, FSW- or laser-hybrid-welding.