WO2019140470A1

WO2019140470A1 - Method for the manufacture of an endless belt

Info

Publication number: WO2019140470A1
Application number: PCT/AT2019/060008
Authority: WO
Inventors: Karl Morgenbesser
Original assignee: Berndorf Band Gmbh
Priority date: 2018-01-17
Filing date: 2019-01-10
Publication date: 2019-07-25
Also published as: AT16422U1; JP3221052U

Abstract

The invention relates to a method for the manufacture of an endless belt (1), which has at least one weld seam (7, 9), wherein the weld seam (7, 9) preferably runs at least one time helically around the endless belt (1) and/or the weld seam (7, 9) is inclined relative to a longitudinal di¬ rection of the endless belt (1) and/or the width of the endless belt (1) is greater than 2 m, pref¬ erably greater than 4 m. In this connection, at least one material (12) that reduces the thermal conductivity of the weld seam (7, 9) is introduced into the weld seam (9), or the thermal conductivity is increased at least in a region (14) of the endless belt (1) immediately adjoining the weld seam (7, 9) by modification of a material composition in and/or of a microstructure of the endless belt (1) in this region (22). The invention also relates to an endless belt (1).

Description

METHOD FOR THE MANUFACTURE OF AN ENDLESS BELT

The invention relates to a method for the manufacture of an endless belt according to the pre amble of claim 1. Furthermore, the invention relates to an endless belt. Beyond this, the in vention has an apparatus for film casting as subject matter.

Endless belts of steel have a broad range of application. Depending on area of application, the condition of the belt must also be developed. In this connection, the surface texture, the thick ness and the length of the sheet metal are of special importance, as are also the condition and arrangement of the weld seam.

Such belts are known, for example, from AT283194B, EP1812191B 1, AT500488B 1, WO2013/177604A1 or EP1154290B 1. In the last publication, it is mentioned that, because of the weld seam, which leaves an imprint, steel belts are not suitable for the manufacture of films, and therefore casting drums should be used.

Conveyor ovens for baked goods are known, wherein the baked goods are disposed on an endless belt that is hundreds of meters long and are guided on the belt through the conveyor oven. In this situation, the speed of the belt is relatively low and, for the surface texture, it is merely necessary that the ability of the baked goods to adhere to the steel surface be only slight. The surface of the weld seam on the working area, i.e. that area on which the portions of baked goods are applied, merely has to lie in the working plane and have the same rough ness as the working area.

Particularly high demands are placed on the endless belts of a belt press, especially double belt press, when transparent plastic foils, for example, are to be produced, since these must be optically blank. Weld seams are inhomogeneity sites, which leave behind undesired impres sions in the manufactured foils or films.

In order to obtain belts with particularly large widths, two or even more belts are joined by means of longitudinal weld seams. These longitudinal weld seams cause thickness differ ences, albeit only most minute, in the belts, and so no straight generatrix exists in rolled-up long material webs that were produced with the belts, but instead, depending on structure of the weld seams, either thickness maxima or thickness minima exist at these sites, whereby a tensioning of the material web occurs in the form of a product that can no longer be aligned in planar manner.

If the material webs are cut into individual pieces, which are stacked one upon the other, then skewed layers, which may lead to disturbances in the production, are also formed in the stack. In order to distribute these thickness deviations along the width of the material web, it is known to form the endless belt by only a partial belt, wherein only one longitudinal weld seam is present, which is disposed in a manner inclined relative to the longitudinal direction of the belt. In such a steel belt, it is disadvantageous that a tension, which is to be attributed to the different length of the weld seam compared with the partial belt, exists between the weld seam and the partial belt. Thereby the useful life of the endless belt is shortened.

During the manufacture of films, especially triacetate films, which are used for the production of LCD display screens, for example, endless belts are used on which such films are applied. The manufacture of larger display screens also necessitates the use of broader endless belts. It is also of advantage to use broader belts for the purpose of the productivity increase during the manufacture of film material. Since the belt widths of the raw belts used for the manufac ture of endless belts are usually approximately 2 m, two or more raw belts are welded to one another along their longitudinal edges for achievement of greater belt widths. For manufactur ing-related reasons, the weld seams differ from the rest of the belt body in terms of their struc tural composition. Consequently, different thermal conductivities also result for the weld seams and the rest of the belt body of the endless belt, wherein it has been found that the ther mal conductivity of the weld seams is higher than the thermal conductivity of the rest of the endless belt.

During the manufacture of films, it is customary to cast the starting product onto an endless belt, to dry it partly and to strip it from the endless belt once again. For drying of the film, at least one inner side of the endless belt opposite a product side carrying the film is heated, for example by means of hot air and/or by means of at least one heated deflecting roll. On the ba sis of the increased thermal conductivities of the weld seams in comparison with the rest of the endless belt, faster drying of the film takes place in the region of the weld seams, which has the consequence of an increase of the surface tension in the faster-drying regions of the film. This in turn causes a migration of film particles in the direction of the weld seams and the formation of local thickenings of the film in the region of the weld seams. However, this has the disadvantage that the weld seams are visible as an imprint in the finished product. Such imprints are undesired, however, and they reduce the quality of the film to the point of unusability in the case of optical films.

For weld seams that are inclined relative to the longitudinal direction of the endless belt (which therefore run helically around the endless belt), such imprints are particularly strongly marked in the film. They therefore lead to particularly large quality losses. Moreover, obliquely oriented imprints in a display screen (in contrast to horizontally or vertically ori ented imprints) have a much greater noticeability.

It is therefore one task of the invention to overcome the above-mentioned disadvantage and to manufacture a high-quality film.

This task is accomplished according to the invention with a method of the type mentioned in the introduction, to the effect that at least one material that reduces the thermal conductivity of the weld seam is introduced into the weld seam, or that the thermal conductivity is in creased at least in a region of the endless belt immediately adjoining the weld seam by modi fication of a material composition in and/or of a microstructure of the endless belt in this re gion. The modification of the material composition may take place, for example, by removal and/or addition of material, while the microstructure of the endless belt can be modified, for example by forming, especially thermal and/or mechanical forming.

The approach according to the invention makes it possible to reduce the differences in the thermal conductivities of a weld seam and of the adjoining regions of the endless belt (which is a metal belt) or to minimize differences in the heat flows through the weld seam and the re gions of the endless belt adjoining it.

For the manufacture of foils for PVOH applications, the preferred total width of the endless belt is between 4.5 and 6 m. For the manufacture of foils for TAC applications, the preferred total width of the endless belt is between 2.3 and 2.5 m.

The thickness of the endless belt is preferably between 0.9 and 2 mm.

The typical length of an endless belt according to the invention (circumferential length in the closed state) is preferably 50 m - 150 m.

Preferably, the endless belt is constructed from only one partial belt, which is narrower than the endless belt, and the endless belt preferably has only one weld seam. The manufacture of the endless belt from a single partial belt, which then runs helically along the endless belt, has the advantage that, on the one hand, the endless belt is made from the same partial belt and therefore no dimensional or material deviations develop between belt portions, and that, on the other hand, the inhomogeneities caused by the weld sites are distributed more uniformly over the width of the endless belt. By virtue of the feature according to the invention, the ef fect of these inhomogeneities (imprints in the film) can be largely neutralized.

A preferred helically oriented weld seam is illustrated by way of example in AT283194B. The weld seam here runs at least one time around the endless belt. According to the present Appli cation, however, "runs helically around the endless belt" also includes the possibility that the helical weld seam runs around only part of the endless belt.

According to an advantageous variant of the invention, it may be provided that the material introduced into the weld seam is a constituent of an alloy of a base material of a belt body of the endless belt.

Alternatively, however, it is also possible that the material introduced into the weld seam is not a constituent of an alloy of a base material of a belt body of the endless belt.

A particularly good reduction of the thermal conductivity can be achieved by selecting the material introduced into the weld seam from the group Cr, Ni, Co.

According to a variant of the invention, which permits a particularly good equalization of the heat flows through the weld seam and regions adjoining it, it may be provided that a depres sion of the belt surface relative to the weld seam is produced on the endless belt in the region immediately adjoining the weld seam, wherein the depression is filled with a material that has a higher thermal conductivity than the weld seam. For this purpose, the depression may be formed by mechanical or chemical or electrochemical removal of material or even be a result of the welding process.

It has proved particularly advantageous when the material is applied by means of a galvanic method, especially by means of tampon plating.

A further very efficient method for reduction of the difference of the heat flows through the weld seam and a region adjoining it can be achieved by forming the region adjoining the weld seam by application of further weld seams, wherein directly adjacent weld seams overlap one another at least partly.

It has proved to be particularly favorable when a penetration depth of the further weld seams into the base material of the endless belt decreases with increasing distance of the further weld seams from the at least one weld seam.

According to an advantageous further development of the invention, it may be provided that the thickness of the at least one weld seam is reduced in the direction of a thickness of the endless belt by removal of material and a depression produced by the removal is filled with a material that has a lower thermal conductivity than the weld seam. This variant of the inven tion makes it possible to be able to adjust the heat flow in a region of the weld seam very well, since this can be varied according to the type of material used. As an example, thermally poorly conductive plastics may be used as the materials.

A preferred embodiment is characterized in that the weld seam includes an angle of 1° to 25°, especially of 6° to 9°, with the longitudinal direction of the endless belt. Thereby a uniform distribution of the inhomogeneity sites caused by the weld seam is assured over the width of the product to be produced and the advantage further exists that the total length of the weld seam can be kept small. A preferred embodiment is characterized in that the ratio between the thermal conductivity of the belt body of the endless belt formed by a partial belt at the belt surface in the middle re gion of the partial belt, and the thermal conductivity at the belt surface in the middle region of the weld seam is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1.

A preferred embodiment is characterized in that the ratio between the thermal conductivity of the belt body of the endless belt formed by a partial belt at the belt surface in the middle re gion of the partial belt, and the thermal conductivity of the weld seam at the belt surface in the middle region of the weld seam at an angle greater than 5° is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1.

The production of the weld seam/seams during the manufacture of the endless belt according to the invention may take place, for example, with the aid of the welding apparatus and method disclosed in AT516447A1 (including the clamping jig disclosed therein).

For all exemplary embodiments mentioned in the foregoing, the endless belt can be preferably subsequently machined, for example polished, especially high-gloss polished after production of the weld seam/seams.

The task is also accomplished by an endless belt that is a metal belt according to claim 14.

The advantages of the individual embodiments described with regard to the method are also valid logically for the embodiments of the endless belt.

A particularly preferred endless belt of steel, which if necessary is constructed from only one partial belt that is narrower than the endless belt and possibly has only one weld seam, which preferably runs at least one time helically around the belt and/or is inclined relative to a longi tudinal direction of the belt, and the partial belt has compressive residual stresses on a surface layer, consists substantially in the fact that an inner surface layer, relative to the endless belt, has the compressive residual stresses and the weld seam, relative to a middle plane, has sub stantially identical spacings between the inner surface and an outer surface and thus is struc tured substantially symmetrically. In such belts, it is known that the outer surface, i.e. the working area, has compressive residual stresses in order, for example, to reduce the abrasion or else to lessen the stress corrosion cracking. If an inner surface layer has compressive resid ual stresses, then the useful life can surprisingly be prolonged. This is all the more remarkable because of the fact that the inner side of the belt is compressed during deflection, i.e. without having been provided with compressive stresses. A symmetric structure of the weld seam means that the length difference between weld seam and the adjoining regions of the partial belt can be kept substantially smaller and thereby the useful life of the belt can be additionally prolonged.

If the steel of the partial belt is precipitation-hardened, the advantages of a precipitation-hard ened belt may be utilized, wherein the weld seam as such does not have to be precipitation- hardened, wherewith the length difference between partial belt and weld seam can be kept smaller.

If only one, preferably an inner surface layer of the partial belt has compressive residual stresses, smaller forces are opposed to the elastic elongation during the deflection of the belt, whereby likewise the useful life of the belt can be prolonged.

If the inner surface layer of the partial belt that adjoins the weld seam is machined down, notch sites that contribute to premature destruction of the belt can be avoided.

If the width of the weld seam amounts to 1.0 to 1.5 times the thickness of the partial belt, a prevention of the transverse contraction and thereby a reinforcement of the tensile strength of such a weld seam are achieved during tensile loading.

If the partial belt has a thickness of 0.3 mm to 3.5 mm, especially of 0.8 mm to 1.2 mm, a belt is obtained that has a particularly small thickness, wherewith no substantial impairment of the useful life takes place during deflection even with rolls of, for example, 590 mm.

One aspect of the invention also relates to a metal belt, especially a stainless steel belt, which defines an outer area as well as an inner area, wherein at one of the areas at least several measuring fields for determination of the content of nonmetallic inclusions are defined, espe cially on the basis of DIN EN 10247, July 2007, and so respectively a complete raster map ping of all measuring fields is possible at a magnification of 200:1. In a preferred embodiment, the endless belt comprises an outer surface as well as an inner sur face, on one or both of which several measuring fields, each of 625 mm², each contain 0 to 25 nonmetallic inclusions between 2 pm and smaller than 5 pm, 0 to 6 nonmetallic inclusions be tween 5 pm and smaller than 10 pm and 0 to 4 nonmetallic inclusions between 10 pm and smaller than 15 pm. Thereby a metal belt having a very high purity and associated therewith a very high surface quality is created.

The advantage resulting due to the above embodiment lies in the fact that, with this small number of inclusions, a very high surface quality of the metal belt with an approximately con sistent and uniform metallic surface is created, which is therefore most suitable for the use of the metal belt as a carrier belt (process belt) for the casting of foil material. In the present Ap plication, the terms "carrier belt" and "process belt" are used synonymously, since not only does the belt carry the film or the foil but also the film or the foil on the belt passes through a process that is influenced or assisted by the belt. Thus, in particular, the belt may be heated from the underside and thus be used for heat transfer to the film or the foil.

Furthermore, however, it is even also possible to achieve a substantially better surface quality in a subsequent polishing process, since the size and number of the nonmetallic inclusions is reduced to an acceptable minimum and thus surface flaws are almost avoided. Thus a defect- free pattern of the metal surface is transferred onto the foil material to be manufactured. In this connection, it is possible to manufacture, among other options, a polymer film, which subsequently may be used as an optical film or in LCD display screens. Due to this high pu rity and undisturbed surface quality of the metal belt, it is possible, in conjunction with the use of the metal belt as support or bracing means, to further improve the quality of the foil material to be manufactured substantially during the manufacture of the same. Thus the pat terns of the inclusions transferred from the surface of the metal belt to the foil material can be kept very small, so that a high-quality product can be manufactured therewith.

A preferred embodiment of the endless belt is characterized by 0 to 3 inclusions between 15 pm and smaller than 20 pm per measuring field and/or by 0 to 3 inclusions between 20 pm and smaller than 25 pm per measuring field. Thereby the number of inclusions with larger area or volume may likewise be kept very small and therefore the surface of the metal belt on the whole is able to have only a very small num ber of defect areas. Thereby damage due to broken-out inclusions in the course of a polishing process may also be almost avoided since, as seen in terms of area or volume, these represent only a very small proportion of the total surface of the metal belt.

Preferably, at least the outer surface of the endless belt has a structureless mirror polish with a surface roughness Ra of < 0.02 pm or Rz of < 0.1 pm. Thereby, with regard to the product to be manufactured, an appropriate material for formation of the metal belt can be exactly matched to it. This is the case in particular for the surface quality to be achieved during the polishing process.

Preferably, the metallic material from which the endless belt or the partial belt/belts is/are formed is selected from the group of XlOCrNil8-8, X5CrNil8-l0, X5CrNiMol7-l2-2, X3CrNiMol3-4, CrNiCuTil5-7, Ck 67, Ti-II, XlNiCrMoCu25-20-5. Thereby it is ensured that a uniform material quality is consistently available over the entire width of the metal belt. Therewith the permissible tolerances in the material quality are also not mixed with one an other during the manufacture of the primary product or primary material. Thus consistently uniform and equal material grades for the bracing means are supplied for the product to be manufactured, for which the metal belt is used as support or carrier material.

The task is also accomplished by an apparatus for the manufacture of a film, especially a tri acetylcellulose (TAC) film, a polyvinyl alcohol (PVOH) film, a polyimide (PI) film or an acrylic film, characterized in that the apparatus is provided with an endless belt according to the invention.

The task is likewise accomplished by the use of an endless belt according to the invention for the manufacture of a film, especially a triacetylcellulose (TAC) film, a polyvinyl alcohol (PVOH) film, a polyimide (PI) film or an acrylic film.

As an example of the foil material, a polymer film can be manufactured as a wide film. The base material is applied, especially cast, onto the surface of the endless belt, and then high- quality optical films or foils are formed from it. One possible material is cellulose triacetate (CTA), also known as triacetate or TAC film, which is a plastic that is obtained from cellulose in a reaction with acetic acid. In the process, the CTA polymer, which is mixed with a solvent such as dichloromethane, for example, can be applied in a continuous process onto the surface of the metal belt and then passed together with the endless belt through a drying oven. In the process, the solvent evaporates and, upon attainment of a sufficient strength, the dried film can be stripped from the metal belt. This CTA foil material may be used for the manufacture of LCD display screens, among other purposes. This CTA film is applied as a two-sided pro tective foil onto the polarizers. This is usually done in a lamination process.

For better understanding of the invention, it will be explained in more detail on the basis of the following figures.

Therein, respectively in greatly simplified schematic diagrams:

Fig. 1 shows a perspective diagram of an endless belt according to the invention;

Fig. 2 shows a section through a first variant of an endless belt according to the inven tion;

Fig. 3 shows a section through a second variant of an endless belt according to the in vention;

Fig. 4 shows a section through a third variant of an endless belt according to the inven tion;

Fig. 5 shows a section through a fourth variant of an endless belt according to the inven tion;

Fig. 6 shows an apparatus according to the invention;

Fig. 7 shows a variant of an endless belt according to the invention;

Fig. 8 shows a detail of an endless belt having helically running weld seam; Fig. 9 shows a cross section through the endless belt in the region of a weld seam; and

Fig. 10 shows a variant of a weld-seam structure.

By way of introduction, it is pointed out that like parts in the differently described embodi ments are denoted with like reference symbols or like structural part designations, wherein the disclosures contained in the entire description can be carried over logically to like parts with like reference symbols or like structural-part designations. The position indications chosen in the description, such as top, bottom, side, etc., for example, are also relative to the figure be ing directly described as well as illustrated, and these position indications are to be logically transferred to the new position upon a position change.

All statements about value ranges in the description of the subject matter are to be understood to the effect that they jointly comprise any desired and all sub-ranges therefrom, e.g. the state ment 1 to 10 is to be understood to the effect that all sub-ranges, starting from the lower limit 1 and the upper limit 10 are jointly comprised, i.e. all sub-ranges begin with a lower range of 1 or greater and end at an upper limit of 10 or smaller, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

An endless belt 1, especially an endless steel belt, which has a total width 2 transverse to its longitudinal extent, is shown in schematically simplified form in Fig. 1. The width of this endless belt 1 is greater than 2 m, preferably greater than 4 m.

In order to achieve the desired total width 2, the endless belt 1 is formed preferably from sev eral partial belts 3, 4 disposed next to one another in the direction of its longitudinal extent. These partial belts 3, 4 are welded to one another at longitudinal side edges. This takes place by a weld seam 9 illustrated in simplified manner and designated as longitudinal weld seam. The partial belts 3, 4 are formed from prefabricated sheet- metal portions, wherein, prior to the welding, the longitudinal side edges are subjected to a suitable preparation method depending on the chosen welding process.

Furthermore, for the manufacture of the endless belt 1, it may be joined at axial ends 5, 6 turned toward one another by means of a weld seam 7 designated as transverse weld seam. In the process, the two partial belts 3, 4 are usually welded to one another in their longitudinal extent first of all and then the transverse weld seam 7 is formed. In the exemplary embodi ment shown here, the transverse weld seam 7 is disposed in a manner running at a predeter mined angle relative to outer longitudinal side edges 8, 10 of the endless belt 1. It would also be possible, however, to choose a perpendicular alignment of the weld seam 7 relative to the longitudinal side edges 8, 10.

In dependence on the belt thickness of the endless belt 1 and of the material used for it, the ra dius of the deflection of the endless belt 1 is to be matched correspondingly to it. In the pro cess, a spacing 11 between deflecting rolls spaced apart from one another is established in the case of a linearly oriented belt travel of the endless belt 1. If further deflections of the endless belt 1 are provided, the spacing 11 is shortened accordingly.

The two partial belts 3, 4 may be designed with approximately equal width. Considered as a whole, the total width 2 of the endless belt 1 is given by the belt widths of the partial belts 3,

4. For joining of the partial belts 3, 4, the longitudinal side edges to be joined to one another are disposed abutting one another at their axial ends and in this position are welded to one an other. As an example, the welding may be accomplished with or without shield gas, by means of laser welding, TIG welding, plasma welding, MIG/MAG welding, ultrasonic welding or friction stir welding.

Fig. 7 shows a variant of an endless belt according to the invention. Here, the endless belt 1 has at least one weld seam 9, which runs helically around the endless belt 1 and is inclined relative to a longitudinal direction of the endless belt 1. A preferred helically oriented weld seam is also illustrated by way of example in AT283194B. The weld seam here runs at least one time around the endless belt. The method steps and features of the endless belt described in the following are equally applicable to endless belts according to Fig. 1 as they are also to endless belts according to Fig. 7 or according to AT283194B.

According to Fig. 2, a material 12 that reduces the thermal conductivity of the weld seam 9 can be introduced into a weld pool during the production of the weld seam 9. The material 12 introduced into the weld pool may be a constituent of an alloy of a base mate rial of a belt body 13 of the endless belt 1. Alternatively to this, however, a material 12 may also be chosen that is not a constituent of the base material of the belt body 13. Examples listed in the following for possible materials for the belt body 13 relate to the stand ard designations according to EN 10027 Sheet 1 and Sheet 2. Here, the materials Xl0CrNil8- 8 with the material number 1.4310, X5CrNil8-l0 with the material number 1.4301,

X5CrNiMol7-l2-2 with the material number 1.4401, X3CrNiMol3-4 with the material num ber 1.4313, CrNiCuTil5-7 or similar materials, Ck67 with the material number 1.1231, and Ti-II with the material number 3.7035, XlNiCrMoCu25-20-5 can be cited as examples. The material Ck 67 is also designated by a protected factory designation "Ti 994-Ti-grade2".

Concerning the materials described in detail in the following for the belt body 13, these are formed with the individual alloying elements for the respective material. In Table 1, these val- ues are given in per cent by weight, unless a different unit is indicated.

Table 1:

For example, if the material X5CrNil8-l0 (1.4301) or the material X5CrNiMol7-l2-2 (1.4401) is used for the belt body 13, the thermal conductivity of the weld seam 9 can be re duced by addition, in the weld pool, of Cr or Ni, which are already contained in the alloy of the base material of the belt body 13. For this purpose, preferably sufficient Cr or Ni is ad mixed in the weld pool that the content of Cr or Ni in the weld seam 9 is at least between 5% and 20% higher than in the base material of the belt body 13. According to the above exam ples, if Cr is admixed as material 12 in the weld seam 9, the Cr content of the weld seam 9 may lie above 18% and below 24%, for example, depending on base material used.

By admixture of Co into the weld pool, the thermal conductivity of the weld seam 9 in the above examples can be reduced by an element not contained in the alloy of the base material of the belt body 13. The quantity of Co that is admixed in the weld seam 9 in this case is pref erably designed such that the content of Co in the weld seam is between 5% and 20%.

Due to the admixture in the material 12, the thermal conductivity of the weld seam 9 can be adapted to the thermal conductivity of a region of the belt body 13 adjoining the weld seam 9.

According to Fig. 2, the thermal conductivity in the region 14 of the endless belt 1 directly ad joining the weld seam 9 can be increased by modification of a material composition in this re gion. Thus a depression 15 of the belt surface relative to the weld seam 9 can be created on the endless belt 1 in the region 14 directly adjoining the weld seam 9. This may be done, for example, by removal of material in the region 14. The depression 15 may be filled with a ma terial 16 that has a higher thermal conductivity than the weld seam 9. In this way, the thermal conductivity of the region 14 can be increased and thus made to approach the thermal conduc tivity of the weld seam 9. As an example, Cu may be used as the material 16. For application of the material 16, it is possible to use a galvanic method, for example tampon plating.

As illustrated in Fig. 4, the region 14 adjoining the weld seam 9 can be formed by application of further weld seams 17, 18, 19. For this purpose, the further weld seams 17, 18, 19 are ap plied over and next to the weld seam 9, wherein the directly adjacent weld seams 17, 18, 19 overlap at least partly. Since the weld seams 17, 18, 19 have a higher thermal conductivity than the base material of the belt body 13, the thermal conductivity in the region 14 is in creased by the arrangement of the additional weld seams 17, 18, 19, to the effect that a differ ence between the thermal conductivity of the region 14 and the thermal conductivity of the weld seam 9 is decreased.

According to Fig. 5, a thickness of the at least one weld seam 9, viewed in the direction of a thickness of the belt body 13 of the endless belt 1, can be reduced by removal of material. A depression 21 formed by the material removal may be filled with a material 20 that has a lower thermal conductivity than the weld seam 9. As an example, a plastic, especially Teflon, may be used as the material 20.

For all exemplary embodiments mentioned in the foregoing, the endless belt 1 can be subse quently machined, for example polished, especially high-gloss polished after production of the weld seam/seams 7, 9. The weld seams 7, 9 themselves may also be subsequently ma chined, for example ground and/or polished. A thickness adaptation of the endless belt 1 may also be performed, so that it has substantially a constant thickness over its entire circumferen tial length.

It is preferred when the ratio between the thermal conductivity of the belt body 13 of the end less belt 1 formed by a partial belt 31 at the belt surface in the middle region of the partial belt 31, and the thermal conductivity of the weld seam 9 at the belt surface in the middle region of the weld seam 9 is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1. This is particularly preferred for an angle a (angle of inclination of the helically running weld seam 9 relative to the longitudinal extent a of the endless belt) larger than 5°. In one exemplary configuration, the endless belt 1 has a width 2 of 2,200 mm and is com posed of a revolving partial belt 31 having a width b₂ of 1,400 mm. The partial belt 31, illus trated as narrower in Fig. 8, is joined via only one revolving weld seam 9. It is also possible for several partial belts to be welded to one another. The weld seam 9 includes an angle a of 6.1° with the longitudinal direction a of the endless belt 1.

The detail illustrated in Fig. 9 shows, in cross section, a weld seam 9 together with the adjoin ing regions of the partial belt 31. At the outer surface 33, the weld seam 9 has a width b₃ of 3.3 mm, which represents a 1.15 times multiple relative to the thickness di of 2.9 mm of the partial belt 31. An imaginary middle plane 34 is illustrated as a dashed line symmetrically be tween the outer surface 33 and the inner surface 32. Relative to this middle plane 34, the weld seam 9 is substantially symmetrically structured; possibly notch sites, such as are formed dur ing welding, are present. Both the outer surface layer and the inner surface layer may be ma chined down. The inner surface layer may have, for example, compressive residual stresses in the range of 400 MPa. The weld seam according to Fig. 9 may be produced electrically using a tungsten electrode and inert gas (TIG).

The cross section illustrated in Fig. 10 corresponds to that of Fig. 9 and differs only by the weld seam 9, produced with an Nd:YAG laser, which is rectangular in cross section.

Example 1:

Partial belt portions having a width of 800 mm and a thickness of 0.8 mm were welded by TIG welding using a voltage of 10 V, amperage of 29 A and helium as the inert gas. The width of the weld seam was 2.1 mm. The weld was V-shaped. The sheet metal was then de flected by 180° in a test system over a roll having a radius of 590 mm. Cracks appeared in the region of the weld seam only after 2 times 10⁶ cycles.

Example 2:

Partial belt portions having a width of 1,211 mm and a thickness of 0.8 mm, which portions represent parts of a partial belt, were welded by TIG welding using a voltage of 8.7 V, amper age of 16 A and helium as the inert gas. The width of the weld seam was 1.05 mm. The weld was double-V-shaped. In addition, one side was shot peened, so that compressive residual stresses of 400 MPa could be developed. The sheet metal was then deflected by 180° in a test system over a roll having a radius of 590 mm, with the shot-peened face in contact with the roll. Cracks appeared in the region of the weld seam only after 2.8 times 10⁷ cycles.

Example 3: The production of the weld seam/seams takes place with the aid of the welding apparatus and method disclosed in AT516447A1 (including the clamping jig disclosed therein).

For completeness, it should be pointed out that each of the exemplary embodiments men tioned above and illustrated in Figs. 1 to 10 may be combined with any other or several of these exemplary embodiments. For example, the weld seam 9 illustrated in Fig. 1 and Fig. 7 may also be combined additionally with the application of further weld seams 17, 18, 19 or with the introduction of an additional material 20 illustrated in Fig. 5. The combination of the illustrated and described method is of advantage in terms of a particularly exact influencing of the thermal conductivity in the weld seam 9 and/or in the region 14.

According to Fig. 6, an apparatus 22 according to the invention has a casting region 24 for the manufacture of a film 23 or of a foil. This film 23 may be a solvent-based film, such as, for example, so-called TAC films, PVOH films, etc. Examples of solvents that may be used are dichloromethane (methylene chloride) in the case of TAC films or water in the case of PVOH films.

The casting region 24, which in the prior art is also known as "casting chamber", may be inte grated, for example, with a lining of sheet metal. Furthermore, an endless belt 1 and at least one casting apparatus 25 are disposed in the casting region 24 for application of a material 26 onto the endless belt 1. The endless belt 1 revolves between two rolls 29 and 30. One of these rolls 29, 30 may be driven and be used as the driving roll for the endless belt 1.

The application of the material 26 onto the endless belt 1 may take place by casting, for exam ple by means of curtain coating, extruding, spraying, etc. The cast material 26 forms, on the endless belt 1, a film- like layer, and passes on the endless belt 1 through a process that leads to an at least partial drying and/or curing of the material 26. For stripping of the (partly) dried film 23 from the endless belt 1, it is possible to provide a stripping apparatus 27, for example in the form of a roll. In order to achieve a high production speed, the film 23 is usually stripped from the belt in an as yet incompletely dried, "moist" state. For solvent-based films, the term "moist" relates to the solvent fraction still contained in the film 23. In a completely dried film, for example, the solvent fraction would be zero.

For partial drying of the material 26 or of the film 23, it is possible to provide heating apparat uses 28, which heat an inner side of the endless belt 1 opposite the material 26 or the product side carrying the film 23. The heating apparatuses 28 may comprise, for example, nozzle boxes, through which hot air is expelled in the direction of the inner side of the endless belt 1.

In addition to the heating apparatuses 28, one or both of the rolls 29, 30 may be heated.

By virtue of the use of the endless belt 1 according to the invention, the visibility of weld seams of the endless belt 1 in the film 23 can be avoided very well.

Finally, it must be pointed out as a matter of form, for better understanding of the structure of the endless belt, this or its components have sometimes been illustrated not to scale and/or magnified and/or reduced.

Preferred manufacturing variants and materials for the endless belt are described in the fol lowing. During the manufacture of the endless belt 1, which is a metal belt, the usual proce dure is to cast, in a casting process, the metal provided for the purpose as a metal block, which is then formed, especially rolled, to the corresponding sheet metal in a rolling process. In de pendence on the width of the system available for sheet-metal rolling, the maximum width of the sheet metal that can be manufactured therewith is also defined or limited. With currently known and standard rolling systems for such high-quality sheet metal, it is possible to manu facture a sheet-metal width of approximately 2000 mm.

Alternatively to the arrangement of two partial belts alongside one another as shown in Fig. 1, it is also possible to supplement a broader middle belt portion with two side belt portions, as is described, for example, in WO2013/177604A1. Depending on belt length to be manufac tured, is also possible to weld more than two partial belts to one another. Depending on intended use of the endless belt 1, this or the partial belts from which it is con structed may be formed from the most diverse stainless steel materials, carbon steels or tita nium, and this is possible in different grades. The metal belts may be used as process or con veyor belts.

Examples listed in the following for materials for the belt body relate to the standard designa tions according to EN 10027 Sheet 1 and Sheet 2. Here, the materials XlOCrNil8-8 with the material number 1.4310, X5CrNil8-l0 with the material number 1.4301, X5CrNiMol7-l2-2 with the material number 1.4401, X3CrNiMol3-4 with the material number 1.4313,

CrNiCuTil5-7 or similar materials, Ck67 with the material number 1.1231, and Ti-II with the material number 3.7035, XlNiCrMoCu25-20-5 can be cited as examples. The material Ck 67 is also designated by a protected factory designation "Ti 994-Ti-grade2".

For the different materials mentioned in the foregoing and in Table 1, consideration is also to be given to the micro structural constitution. Concerning the grain size, especially the grain- size number (grain-size index) according to the standard ASTM E 112-84, the number "G" should be > (greater than / equal to) 9.0. This grain-size number (grain-size index) is to be de termined according to the "Lineal Intercept Procedure" according to Sections 11.6, 11.6.1 and 11.6.2 of the standard, under compliance with all other relevant requirements, with an accu racy of at least ½ ASTM number. The microstructural condition is completely austenitic with out delta ferrite in the cold-rolled starting material of the metal belt 1. Transformation marten site is permissible only to such a small extent that, during cold rolling to strength level 1 ac cording to the following Table 2, the permissible magnetic permeability is not exceeded. The surface subsequently polished to high gloss is not permitted to exhibit any orange-peel-like structure or cell structure.

The magnetic permeability of the belt rolled to the strength levels indicated in Table 2 is measured according to ASTM A-342. Thus, for example, strength level 1 is applicable for the material X5CrNil8-l0 (1.4301):

Relative permeability pr < 1.15 at an excitation of 200 oersted (Oe). This value, reported in oersted (Oe), may be expressed in SI units of A/m (ampere / m) by means of the following formula.

1 Oe = 1000 / (4 * p)

Table 2:

Starting from their condition as primary material, up to the finished metal belt 1, the individ ual sheets of metal may be subjected to different and if necessary multiple quality tests. One of the many tests is the "Micrographic examination of the non-metallic inclusion content of steels using standard pictures", which is performed on the basis of the standard DIN EN

10247, July 2007 edition. In a modification of this standard, an even finer test or test proce dure is carried out, which differs from the foregoing in the points listed in the following.

According to Section 4.1.4 as well as 6.3 concerning the measuring field, the standard pro- vides that the measuring field should have a size of at least 200 mm². In contrast to this, the measuring field is increased to an extent of 625 mm², wherein, in view of the high purity of the materials used, a complete raster mapping is carried out with this area extent and in the process the observed inclusions are counted completely. This area extent of 625 mm² may be achieved, for example, by a square with a side length of 25 mm. In this connection, the re- spective measuring field or measuring fields are always aligned parallel to the rolled surface or sheet-metal surface, wherein multiple arrangements of the measuring fields distributed over the entire surface of the belt are also used. The sheets of metal to be tested in this way have a wall thickness between 1.0 and 3.0 mm, preferably between 1.5 mm and 2.0 mm. Since the entire endless belt 1 or the partial belts forming the endless belt 1 respectively form separate structural parts that belong together, the individual measuring fields are to be dis posed in distributed manner on their surface. A magnification of 200X is to be used for the evaluation, and this is not permitted to be changed during the evaluation process. This is de- fined in the standard EN 10247, in Section 7.1 "Magnification". The evaluation and complete raster mapping of the measuring field described in the foregoing are carried out independently of the magnification factor. Due to the high quality requirements, all found inclusions per measuring field are divided into different size classes. For this purpose, the following class divisions are chosen: 2 pm to smaller than 5 pm, 5 pm to smaller than 10 pm, 10 pm to smaller than 15 pm, 15 pm to smaller than 20 pm, 20 pm to smaller than 25 pm. An example of a count of inclusions on a sheet-metal slab is reproduced in the following, wherein the measuring field has an extent of 625 mm² and the material X5CrNil8-l0 (1.4301) is used as the material for formation of the metal belt 1.

On the basis of this overview, it can be seen that only a larger number of inclusions were found in the first size class between 2 mhi and smaller than 5 mhi.

Thus a number of inclusions in this first size class from 2 mhi to smaller than 5 mhi lies be- tween a lower limit of zero inclusions to 15 inclusions and an upper limit of 25 inclusions. In the second, next size class between 5 pm and smaller than 10 pm, the number of the nonmet- allic inclusions is much smaller, wherein the lower limit here lies at zero inclusions and the upper limit at 6 inclusions. In the third size class between 10 pm and smaller than 15 pm, the number of the inclusions lies between a lower limit of zero inclusions and an upper limit of 4 inclusions. In the further, fourth size class between 15 mih and smaller than 20 mih as well as the further, fifth size class between 20 mih and smaller than 25 mih, the lower limit lies at zero inclusions and the upper limit at 3 inclusions respectively.

From the determined inclusion numbers of the respective different measurement points 1 to 6, different mean value or average values are obtained per size class, lying at 19.16 inclusions in the first size class between 2 pm and smaller than 5 pm, at 2.33 inclusions in the second size class (5 pm to smaller than 10 pm), at one inclusion in the third size class (10 pm to smaller than 15 pm), at 0.16 inclusions in the fourth size class (15 pm to smaller than 20 pm), and fi nally at 0.33 inclusions in the fifth size class (20 pm to smaller than 25 pm).

Since a very high surface quality is required in many applications for such endless belts 1, the material should be suitable for application of a structureless mirror polish with a surface roughness Ra (arithmetical mean roughness) or Rz (ten-point mean roughness): Ra < 0.02 pm; Rz < 0.1 pm. This is the case not only in the region of the surfaces of the endless belt 1 but also in the region of the joints between the individual partial belts. For larger belts, the area extent may even amount to several 100 m².

The prerequisite for this is a very high degree purity of the primary material (low phosphorus, sulfur and aluminum content), a very dense material without pores as well as the absence of hard phases, such as may be caused by stabilizing elements or hardness-increasing elements (e.g. titanium, cobalt, tantalum, nitrogen).

A further quality criterion may also be the final thickness or bulk of the endless belt 1. For this purpose a large number of measurements is necessary, in order to obtain a measured re sult that is informative here over the entire belt surface. In the process, a predetermined spac ing in transverse direction from the longitudinal side edges of the metal belt 1 is maintained for this measurement over its longitudinal extent. As an example, this spacing may amount to between 5 mm and 15 mm. Several measurements are likewise performed in longitudinal ex tent of the metal belt 1. In this way, a grid of measurement points distributed over the surface is achieved.

If the total width 2 of the endless belt 1 is given in cm, at least half of the value of the total width 2 in cm is to be chosen as the number of measurement points in transverse direction, es pecially in perpendicular direction relative to the longitudinal side edges. For example, if the total width is 200 cm, the thickness is to be measured at a number of at least 100 measure ment points in transverse direction. The broader the metal belt is, the larger is the number of measurement points that can be chosen transverse to the longitudinal extent. This number of measurement points may also correspond to the total width 2 in cm or else to an even larger number. In this connection, it is preferred to choose a transverse distance between the individ ual measurement points that is equal from one to another, and so the measurement points are uniformly distributed over the measurement width.

Thus the deviations from the average thickness of the endless belt 1 should amount, for exam ple, to between ± 5% in a marginal region of the endless belt 1 and to between ± 5% in a mid dle region of the endless belt 1. Thus a high accuracy is also achieved in regard to waviness as well as flatness of the endless belt 1.

As already mentioned in the introduction, very strict requirements are to be placed on the sur face quality as well as purity of the material of the endless belt 1. By virtue of the small inclu sions in the material, this leads to an almost consistent, uniform surface quality, whereby the foil material manufactured on it has an equally high quality.

List of reference symbols

Endless belt 31 Partial belt

Total width 32 Inner surface

Partial belt 33 Outer surface

Partial belt 34 Middle plane

Axial end

Weld seam

Longitudinal side edge

Weld seam

Longitudinal side edge

Spacing from axial end

Material

Belt body

Region

Depression

Material

Weld seam

Material

Depression

Apparatus

Film

Casting region

Casting apparatus

Material

Stripping apparatus

Heating apparatus

Roll

Claims

C l a i m s

1. Method for the manufacture of an endless belt (1), which has at least one weld seam (7, 9), wherein the weld seam (7, 9) preferably runs at least one time helically around the end less belt (1) and/or the weld seam (7, 9) is inclined relative to a longitudinal direction of the endless belt (1) and/or the width (2) of the endless belt (1) is greater than 2 m, preferably greater than 2.5 m, particularly preferably greater than 4 m, characterized in that at least one material (12) that reduces the thermal conductivity of the weld seam (7, 9) is introduced into the weld seam (9), or in that the thermal conductivity is increased at least in a region (14) of the endless belt (1) immediately adjoining the weld seam (7, 9) by modification of a material composition in and/or of a micro structure of the endless belt (1) in this region (22).

2. Method according to claim 1, characterized in that the endless belt is constructed from only one partial belt (31), which is narrower than the endless belt (1), and in that the endless belt (1) preferably has only one weld seam (9).

3. Method according to claim 1 or 2, characterized in that the material (12) introduced into the weld seam (7, 9) is a constituent of an alloy of a base material of a belt body (13) of the endless belt (1).

4. Method according to claim 1 or 2, characterized in that the material (12) introduced into the weld seam (9) is not a constituent of an alloy of a base material of a belt body (13) of the endless belt (1).

5. Method according to one of claims 1 to 4, characterized in that the material (12) intro duced into the weld seam (9) is selected from the group Cr, Ni, Co.

6. Method according to one of claims 1 to 5, characterized in that a depression (15) of a belt surface relative to the weld seam (9) is produced on the endless belt (1) in the region (14) immediately adjoining the weld seam (9), wherein the depression (15) is filled with a material (16) that has a higher thermal conductivity than the weld seam (9).

7. Method according to claim 6, characterized in that the material (16) is applied by means of a galvanic method, especially by means of tampon plating.

8. Method according to one of claims 1 to 7, characterized in that the region (14) adjoin ing the weld seam (9) is formed by application of further weld seams (17, 18, 19), wherein di rectly adjacent weld seams (17, 18, 19) overlap one another at least partly.

9. Method according to claim 8, characterized in that a penetration depth of the further weld seams (17, 18, 19) into the base material of the belt body (13) of the endless belt (1) de creases with increasing distance of the further weld seams (17, 18, 19) from the at least one weld seam (9).

10. Method according to one of claims 1 to 9, characterized in that a thickness of the at least one weld seam (9), viewed in the direction of a thickness of the belt body (13) of the endless belt (1), is reduced by removal of material, and a depression (21) produced by the re moval is filled with a material (20) that has a lower thermal conductivity than the weld seam

(9).

11. Method according to one of the preceding claims, characterized in that the weld seam (9) includes an angle (a) of 1° to 25°, especially of 6° to 9°, with the longitudinal direction (a) of the endless belt (1).

12. Method according to one of the preceding claims, characterized in that the ratio be tween

the thermal conductivity of the endless belt (1) formed by at least one partial belt (3, 4, 31) at the belt surface in the middle region of the partial belt (3, 4, 31) of a belt body (13), and the thermal conductivity of the weld seam (7, 9) at the belt surface in the middle region of the weld seam (7, 9)

is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1.

13. Method according to claim 11 or 12, characterized in that the ratio between the thermal conductivity of the endless belt (1) formed by at least one partial belt (3, 4, 31) at the belt surface in the middle region of the partial belt (3, 4, 31) of a belt body (13), and the thermal conductivity of the weld seam (7, 9) at the belt surface in the middle region of the weld seam (7, 9)

at an angle (a) greater than 5° is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1.

14. Endless belt (1), which is composed of at least one partial belt (3, 4, 31), which is nar rower than the endless belt (1) and which has at least one weld seam (7, 9), wherein the weld seam (7, 9) preferably runs at least one time helically around the endless belt (1) and/or the weld seam (7, 9) is inclined relative to a longitudinal direction of the endless belt (1) and/or the width (2) of the endless belt (1) is greater than 2 m, preferably greater than 2.5 m, particu larly preferably greater than 4 m, characterized in that at least one material (12) that reduces the thermal conductivity of the weld seam (7, 9) is introduced into the weld seam (9), or in that the thermal conductivity is increased at least in a region (14) of the endless belt (1) imme diately adjoining the weld seam (7, 9) by modification of a material composition in and/or of a microstructure of the endless belt (1) in this region (22).

15. Endless belt (1), especially according to claim 14, which is constructed from at least one partial belt (3, 4, 31), which is narrower than the endless belt (1), and which has at least one weld seam (7, 9), characterized in that the endless belt (1) is manufactured according to a method according to one of claims 1 to 13.

16. Endless belt according to claim 14 or 15, characterized in that the endless belt (1) is constructed from only one partial belt (31), which is narrower than the endless belt (1), and in that the endless belt (1) preferably has only one weld seam (9).

17. Endless belt according to one of claims 14 to 16, characterized in that the weld seam (9) includes an angle (a) of 1° to 25°, especially of 6° to 9°, with the longitudinal direction (a) of the endless belt (1).

18. Endless belt according to one of claims 14 to 17, characterized in that the ratio be tween

is at most 1.5, preferably at most 1.3, particularly preferably at most 1.1.

19. Endless belt according to claim 17 or 18, characterized in that the ratio between the thermal conductivity of the endless belt (1) formed by at least one partial belt (3, 4, 31) at the belt surface in the middle region of the partial belt (3, 4, 31) of a belt body (13), and the thermal conductivity of the weld seam (7, 9) at the belt surface in the middle region of the weld seam (7, 9)

20. Endless belt according to one of claims 14 to 19, characterized in that a partial belt (3, 4, 31) has compressive residual stresses on a surface layer (32, 33), wherein an inner surface layer (32), relative to the endless belt (1), has compressive residual stresses and the weld seam (7, 9), relative to a middle plane (34), has substantially identical spacings between the inner surface (32) and an outer surface (33) and thus is structured substantially symmetrically.

21. Endless belt according to one of claims 14 to 20, characterized in that the steel of the at least one partial belt (3, 4, 31) is precipitation-hardened.

22. Endless belt according to one of claims 14 to 21, characterized in that only one surface layer of the endless belt (1), preferably the inner surface layer (32), has compressive residual stresses.

23. Endless belt according to one of claims 14 to 22, characterized in that a region of the inner surface layer (32) of the partial belt (31) that adjoins the weld seam (7, 9) is machined down.

24. Endless belt according to one of claims 14 to 23, characterized in that the width (b₃) of the weld seam (7, 9) amounts to a 1.0 to 1.5 times multiple of a thickness (di) of the partial belt (31).

25. Endless belt (1) according to one of claims 14 to 24, characterized in that the partial belt (31) has a thickness (di) of 0.3 mm to 3.5 mm, especially of 0.8 mm to 1.2 mm.

26. Endless belt according to one of claims 14 to 25, comprising an outer surface (33) as well as an inner surface (32), on one or both of which several measuring fields, each of 625 mm², each contain 0 to 25 nonmetallic inclusions between 2 pm and smaller than 5 pm, 0 to 6 nonmetallic inclusions between 5 pm and smaller than 10 pm and 0 to 4 nonmetallic inclu sions between 10 pm and smaller than 15 pm.

27. Endless belt according to claim 26, characterized by 0 to 3 inclusions between 15 pm and smaller than 20 pm per measuring field and/or characterized by 0 to 3 inclusions between 20 pm and smaller than 25 pm per measuring field.

28. Endless belt (1) according to one of the preceding claims, characterized in that at least the outer surface (33) of the endless belt (1) has a structureless mirror polish with a surface roughness Ra of < 0.02 pm or Rz of < 0.1 pm.

29. Apparatus (22) for the manufacture of a film (23), especially a triacetylcellulose (TAC) film, a polyvinyl alcohol (PVOH) film, a polyimide (PI) film or an acrylic film, char acterized in that the apparatus (22) is provided with an endless belt (1) according to one of claims 14 to 28.

30. ETse of an endless belt (1) according to one of claims 14 to 28 for the manufacture of a film (23), especially a triacetylcellulose (TAC) film, a polyvinyl alcohol (PVOH) film, a poly imide (PI) film or an acrylic film.