WO2007082994A1

WO2007082994A1 - Method for manufacturing a metal belt for use in a paper/board machine or in a finishing machine

Info

Publication number: WO2007082994A1
Application number: PCT/FI2007/050009
Authority: WO
Inventors: Tony Lehto; Reijo PIETIKÄINEN; Mika Viljanmaa; Mikko Mononen; Mika Korhonen
Original assignee: Metso Paper, Inc.
Priority date: 2006-01-20
Filing date: 2007-01-10
Publication date: 2007-07-26
Also published as: JP2009523680A; CN101365841A; FI20065037A0; FI117982B; EP1977038A1

Abstract

The invention relates to a method for manufacturing a metal belt (102) for use in a paper/board machine or in a finishing machine. The method comprises producing a metal belt by placing side by side and/or in succession several metal belt blanks (10a; 10b; 10c) narrower than a final width of the metal belt in a number necessitated by the belt (102) of a desired width and length, and welding joints therebetween by friction welding, the joint developing a composition substantially similar to the basic material.

Description

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

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

Endless steel belt is used e.g. in a metal belt calender and in 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 is formed an appropriate endless band by welding. The subsequent description only discusses main aspects of the manufacturing principle for such bands, as that is considered obvious for a person skilled in the art. In traditional production, the manufacturing process of a band is set in motion by melting scrap metal and/or dressed ore, as well as necessary alloying elements, for example in an arc furnace. This is followed by decarburization of the melt in a converter for a desired carbon content. After decarburization, the steel is alloyed as desired before a ladle process. Then, the melt is cast for an ingot which is conveyed directly to hot rolling, the ingot being subjected therein to a number of rolling processes at high temperature for reducing its thickness while of course increasing its width and length. Hot rolling is completed by having the rolled band reeled up and delivered to cold rolling. In a cold rolling mill, the steel band is first heated for tempering the internal make-up and etched for scouring the band surface. This is followed by starting the actual cold rolling, in which the steel band is reduced in a cold state to its final thickness. If necessary, the band is heated between rolling processes, if the degree of rolling is particularly high. Finally, the band can still be finished off by grinding, heating and etching. In addition, it can still further be subjected to gentle finish-rolling for smoothing the surface and improving its flatness. This can be followed by cutting the band for webs of required length and width, the butts of which are welded together for producing an endless metal belt, typically by either TIG-welding or laser. The width of rolling mills restricts the width of blank material to 1500 mm or 2000 mm, depending on a blank material, so the belt used for paper machine widths shall inevitably include a multitude of welded joints. In operation, metal belts are subjected to both 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 a 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. The mechanical properties of a weld joint fall typically about 20% short of those of the basic material, which may lead to the emergence of the joints as a result of wearing or grinding. A scratchy or otherwise uneven belt is quick to wear down e.g. the packings of a band dryer and causes further problems e.g. in terms of cleanliness.

An objective of the present invention is to provide a method which enables improving the properties of a prior art belt.

In order to accomplish this objective, a method of the invention is characterized in that the method comprises producing a metal belt by placing side by side and/or in succession several metal belt blanks narrower than a final width of the metal belt in a number necessitated by the belt of a desired width and length, and welding joints therebetween by friction welding, the joint developing a composition substantially similar to the basic material.

The metal belt blanks can be made e.g. to a length equal to a final width of the belt and placed substantially orthogonally relative to the belt's longitudinal direction, whereby all weld joints are respectively substantially orthogonal relative to the belt's longitudinal direction. The metal belt blanks can also be made to a length equal to a final length of the belt and a number of those can be placed side by side to match a final width of the belt, whereby weld joints between the belt blanks extend substantially in the belt's longitudinal direction. The ends of metal belt blanks equal to the belts' final length can be cut for an angular position other than rectangular, whereby a weld joint between the ends is respectively in an angular position relative to the belt's longitudinal direction. In this case, the adjacent belt blanks are preferably disposed in such a way that the butt joints thereof become a substantially continuous joint extending diagonally across the belt. The metal belt blanks can also be designed as side-by-side disposable blanks with a length that exceeds a final width of the belt, the lengthwise joints of said blanks extending diagonally relative to the final belt's longitudinal direction. It is also conceivable that the belt be initially made to a width exceeding the final width, followed by cutting/grinding the same to its final width.

In friction stir welding technique (FSW) makes use of a wear-resistant rotary tool, which works its way into a groove between pieces to be joined and, as a result of friction, develops heat in the pieces to be joined. Consequently, the pieces soften without melting and the soft material works its way from ahead of the rotary tool to the back of it and develops a weld joint thereat. The weld joint has a composition which is similar to that of the basic material. The joint can be provided with mechanical properties substantially equal to those of the basic material by means of a suitable heat treatment, thus avoiding the emergence of joints as a result of wear or grinding. Welding is performed against an anvil, whereby the bottom side of a joint is established exactly flush with the basic material and the belt only needs grinding over its outer surface. Neither does FSW-welding cause thermal distortion, thus resulting in dimensionally precise belts.

In a metal belt calender, for example, the steel belt circle has its inside in a direct contact with guide rolls supporting it. The belt circle can have its outside in a direct contact with a thermo roll, for example in a web break incident with no paper web between the contact surfaces. Test runs have revealed strong scratching and wearing of the belt's inside surface. When in contact with a thermo roll, the belt's outside surface has also been discovered to sustain wearing and scratching. In a rolling contact of the belt, the contact between a belt and a belt pulley develops a so-called holding and slipping zone (Contact Mechanics, K.L.Johnson, 1985). Upstream of the contact, the belt proceeds directly to the holding zone, but downstream of the contact there is established a slipping zone.

Two conditions can be distinguished.

1. Belt cooling in a roll contact (e.g. a cooling roll)

When establishing a contact, the belt has a tensile stress σ_v. The belt proceeds directly into a holding zone. Upon cooling, the belt develops a tensile stress increment (σ_heat) resulting from thermal stress, because shrinkage and slippage of the belt within the holding zone is denied as a result of friction. As tensile stress increases, a normal pressure applied by the belt shows also a respective localized increase. As the belt proceeds into a slipping zone on the downstream side, the discharge of thermal stress occurs by way of slippage. Hence, the tension induced in the belt within the holding zone resumes a level of the tensile stress σ_v, while at the same time the belt becomes shorter because of thermal contraction.

In this case, the discharge of tensile stress takes place as a slippage counter to the running direction (the belt slides with respect to the roll in a direction opposite to the running direction). Accordingly, the speed of a belt coming out of a contact is slightly lower than that of a belt about to establish a contact.

2. Belt heating in a roll contact (e.g. a heating guide roll)

The belt makes a contact at a tensile stress σ_v and, as above, proceeds directly into a holding zone. Upon heating, the belt develops compressive thermal stress with a lessening effect on tensile stress. In the event that the temperature change is quite significant, the tensile stress over the holding zone falls to zero (strainless condition) or even crosses over to compression. This may result in the buckling of a belt, i.e. the belt rises off a roll.

As the belt proceeds to a slipping zone, the belt tension resumes a level consistent with the tensile stress σ_v. Equalization occurs by way of slippage, the slippage taking place this time in the running direction. The outgoing belt also has a speed which is slightly higher than the incoming speed.

Being a solid, thick-shelled body, the roll has its temperature variations limited to its surface, whereby the roll does not sustain circumferential thermal deformations. On the other hand the belt, being made of a thin material, heats/cools throughout and thermal deformations are more intense. The difference between thermal expansions translates into slippage.

One objective of the invention is also to provide a solution, by means of which the belt of an apparatus using the metal belt of a paper/board machine or a finishing machine develops neither thermal stresses nor thermal deformations, and which enables scratching of the belt to be reduced or eliminated. In order to accomplish this objective, the metal belt of a metal belt calender, or another fibrous web processing apparatus provided with a metal belt, is manufactured from a material with a very low thermal expansion coefficient, preferably 2 x 10^'6 or less. The optimum condition is reached if the thermal expansion coefficient can be brought to zero. In this case, the belt heating and cooling conditions do not develop thermal strains, nor thermal deformations. The slippage caused by such factors is absent and thus the belt receives no scratching. One solution that fulfils the above condition is to manufacture the belt from high- nickel Invar®-steel, having a thermal expansion coefficient of about 1 x 10^'6, which is less than 1/10 of ordinary steel's value. Thermal strains, and thus the slippage, are 1/10 of the corresponding values in an ordinary belt. The selected belt material can be any other metal composition or alloy that meets the above conditions, e.g. Incotel® or some other high-nickel steel, or stainless steel. The belt is required to have a fairly high thermal conductivity (not less than 5-10 W/mK) as well as a reasonable specific heat capacity for making it functional as a heat transfer medium. In addition, the belt is required to have a competent strength, workability, weldability, as well as corrosion and fatigue resistance.

The price of a belt material is not a highly critical factor as long as supreme advantages are gained. For example, the price of a raw material which is 3-5 times higher is tolerable as long as manufacturing is made easier and more convenient and, above all, as long as the durability (belt replacement interval) of a belt can be multiplied.

Major savings can be obtained in production when no grinding is needed for the belt and, most importantly, if the replacement frequency (production breaks) can be brought down to half.

The benefits of Invar®-steel are e.g.

- thermal expansion is not more than 1/10 of that of ordinary steel, providing a significant reduction in scratching

- corrosion fatigue (fretting) properties are outstanding,

- workability is good - weldability is good, welding does not produce thermal strains or distortion - thermal conductivity is adequate, although slightly lower than in ordinary steel grades.

One option is to manufacture a belt entirely or partially powder metallurgically. By virtue of powder technology, the belt material shall be more homogeneous, more compact, as well as neater than before, and its microstructure will also be more finely divided, whereby its wear and corrosion resistance properties will be substantially better than those of belts manufactured by traditional methods. Consequently, the interval between belt replacements can be clearly longer than with traditional belts, thus reducing also production disturbances and belt replacement costs. By using components made by powder technology, the maintenance-free interval may extend 3-8 times longer with respect to the use of traditional components. Another advantage is that powder technology also enables the preparation of such material compositions which are difficult or practically even impossible to produce by traditional methods. Powder metallurgy provides a possibility of manufacturing such belts in stainless steel, which have a corrosion resistance within the same range as titanium and so-called supersteel alloys of high nickel, yet have a much more attractive price than the latter, thus providing a possibility of manufacturing such belts in stainless steel, which have a corrosion resistance within the same range as titanium and so-called supersteel alloys of high nickel, yet have a much more attractive price than the latter.

A few embodiments for a metal belt of the invention will now be described in reference to the accompanying drawings, in which:

Figs. Ia-Ic show schematically a few arrangements of metal belt blanks used for manufacturing a metal belt.

Hg. 2 shows schematically one embodiment for a metal belt calender, and

Hg. 3 shows a metal belt calender, which is provided with a web feeding device.

Hg. Ia illustrates schematically a metal belt 102, which is composed of metal belt blanks 10a with a length equal to a final width of the metal belt 102. The metal belt blanks 10a are set side by side and welded to each other by friction welding, thus creating therebetween weld joints 11a which extend substantially orthogonally relative to the metal belt's longitudinal direction. Hg. Ib illustrates the making of a metal belt 102 from metal belt blanks 10b substantially consistent with a final length of the metal belt, whereby a joint lib between the blanks becomes substantially parallel to the belt's longitudinal direction. A joint between the abutting longitudinal ends of each metal belt 10b can be substantially orthogonal to the metal belt's longitudinal direction, the butts of adjacent metal belt blanks 10b being set essentially in alignment with each other in a lateral direction of the metal belt 102 for a substantially orthogonal cross-joint 12. Hg. Ib shows also an alternative embodiment, wherein the abutting ends of the metal belt blanks 10b are cut for position diagonal relative to the blank's longitudinal direction and adjacent blanks 10b are disposed relative to each other so as to form a substantially continuous joint, extending diagonally across the metal belt 102 and indicated with dashed lines in fig. Ib by reference numeral 12a. Hg. Ic shows still another alternative embodiment, wherein metal belt blanks 10c are set side by side in a position diagonal relative to a longitudinal direction of a final metal belt 102, whereby joints lie therebetween extend in a likewise diagonal position relative to a longitudinal direction of the belt 102. The longitudinal ends of the blanks 10c are cut diagonally to substantially coincide with a lengthwise edge of the final belt 102. Various combinations of the above-described belt manufacturing methods are also feasible, e.g. arranging several metal belt blanks shorter than the metal belt's final length in succession for a length equal to the final belt length, and side by side in a number necessitated by a final width of the belt. It is also conceivable that a metal belt be manufactured for a width exceeding its final width, in which case it can be narrowed e.g. by trimming or grinding to its final width after welding the belt.

When using a conventional metal belt, for example a belt of stainless steel, the metal belt calender develops a temperature difference between the metal belt and a thermo roll, which leads to wearing of the belt.

In order to avoid a temperature difference between the metal belt and a roll, it is possible to use e.g. a heating hood solution as shown in fig. 1. In fig. 1, a metal belt 102 circles around heated guide rolls 103. A thermo roll is designated by reference numeral 104. The heating hood consists of a heater 100 mounted on one side of the belt 102 and a mirror 101 mounted on the other side. Optionally, a heater can be mounted on each side of the belt. The mirror and the heater can also be disposed in reversed order with respect to fig. 1, i.e. the mirror can be outside the belt circle and the heater inside the same. The heater may operate e.g. on hot oil, gas, electricity, water, steam or induction. In fig. 1, reference numeral 107 is used to schematically depict a heat source, e.g. a hot oil system, for conducting heat to the heater 100. In order to maintain a convection of the belt 102 as low as possible, a gap existing between the belt and the hood 100, 101 must be made as small as possible. Shown in fig. 1 is also an optional extra heater 105, which enables controlling the belt temperature within a contact zone between the belt 102 and the guide roll 103.

Hg. 2 shows schematically a web feeding device 110, which is appropriate for use in connection with a metal belt calender and which uses the calender's metal belt 102 for assistance. The belt 102 runs around guide rolls 103 and establishes, together with a thermo roll 104 functioning as a counter element, a treatment zone PN therebetween for passing a presently treated web therethrough. The belt 102 is preferably manufactured according to the invention with the belt's joints welded by friction welding. A web W travels in a normal circle along with the metal belt around the guide rolls 103, counter-clockwise in the example of fig. 2, and then through the treatment zone PN and around the thermo roll 104 to further processing. When one and the same calender is used for treating the web on both sides, a web Wi can be conveyed along a route indicated by dashed lines in fig. 2 directly into the treatment zone PN between the metal belt and the thermo roll for treating one side of the web, in which case the calender requires two web feeding devices 110. After the treatment zone PN, the web Wi is conveyed around a guide roll 108b to further processing.

The web feeding device 110 is adapted to travel along a guideway 112, designed e.g. as a C-bar, in keeping with the metal belt circle 102. The device is provided with an actuator, which presses the web W against the metal belt 102 and which starts moving along with the belt either as a result of friction or by means of a drive motor, the web feeding device 110 proceeding along the guideway and taking up the force of the actuator. The actuator may function e.g. pneumatically, in which case it is an ordinary compressed air cylinder. Air supply can be provided by using e.g. a ball lock assembly familiar from suction tables or by some other air lock system used in cylinders without piston rods. The actuator may also electrically operated, the load adjusting itself by a spring relative to the position and the electric power being transmitted by carbon blocks. The drive motor runs the device up to a desired speed. The device is designed as lightweight as possible for ensuring a good initial acceleration. The initial acceleration can be accomplished e.g. by means of a pneumatic cylinder 111 or by using a tensioned spring.

Claims

1. A method for manufacturing a metal belt (102) for use in a paper/board machine or in a finishing machine, characterized in that the method comprises producing a metal belt by placing side by side and/or in succession several metal belt blanks (10a; 10b; 10c) narrower than a final width of the metal belt in a number necessitated by the belt (102) of a desired width and length, and welding joints therebetween by friction welding, the joint developing a composition substantially similar to the basic material.

2. A method as set forth in claim 1, characterized in that the metal belt (102) is subjected to a heat treatment for essentially eliminating stress differences between the joints and the basic material.

3. A method as set forth in claim 1 or 2, characterized in that the metal belt blanks (10a) are made to a length substantially equal to a final width of the belt (102) and placed substantially orthogonally relative to the belt's longitudinal direction, whereby weld joints (Ha) between adjacent blanks are respectively substantially orthogonal relative to the belt's longitudinal direction.

4. A method as set forth in claim 1 or 2, characterized in that the metal belt blanks (10b) are made to a length substantially equal to a final length of the belt (102), and a number of those are placed side by side to match a final width of the belt, whereby weld joints (lib) between adjacent blanks extend substantially in the belt's longitudinal direction.

5. A method as set forth in claim 1 or 2, characterized in that the metal belt blanks (10c) are made to a length exceeding a final width of the belt (102) and placed side by side in a position diagonal relative to the belt's longitudinal direction, whereby weld joints (lie) between the blanks are in a position respectively diagonal relative to the belt's longitudinal direction.

6. A method as set forth in any of the preceding claims, characterized in that the belt material has been selected from the group, including high-nickel steel, e.g. Invar® or Inconel®, stainless steel or powdered metal.