EP0474625A2 - Method of dressing in particular endless bands - Google Patents

Abstract

Method of straightening metallic bands, in particular endless metallic bands, for production equipment or the like, e.g. band presses and double band presses, the areas to be straightened being determined and subjected to forces via a device, a relative motion being performed between the band and the device exerting the force, and the forces acting on the surface of the band in the form of a multiplicity of pulses and causing compressive internal stresses in the surface acted upon. <IMAGE>

Description

The invention relates to a method for straightening, in particular endless, metallic strips for production plants, for. B. belt presses, double belt presses.

Metals have the properties that they deform plastoelastically under the action of force. This property is used for the most diverse shaping processes. A widely used process is the so-called deep drawing, in which a sheet is quickly deformed by a stamp into a mold. Another shape is that, for example, the force is not applied mechanically, but by a detonation, and the sheet is pressed into a shape arranged below it.

Another method is that, for. B. a piece of pipe is stretched by the action of a hydraulic fluid in a form so that an expansion of the cross section is carried out at predetermined locations.

Another shaping method, which is described, for example, in DE-29 06 509 A1 and DE-32 13 896 A1, consists in shaping areas of a sheet to be deformed by shot peening, with residual compressive stresses being applied to the surface of the sheet to be deformed and the sheet bulges against the direction of shot peening. Such methods can be used to free-form sheet metal and are particularly suitable for deforming difficult-to-shape materials, such as titanium.

In the case of objects that must have a particularly high level of precision, the precision during production is not sufficient, but a straightening must take place. This straightening is not only for rod-shaped products, such as drill collars for the petroleum industry, but also for flat structures, such as those used in endless belts in double belt presses with an isochoric system. In the case of metallic objects, if they are subject to a plastically elastic shaping, stresses are introduced, particularly in the case of cold shaping. These tensions can be removed by a longer heat treatment, after which the objects can be straightened. However, the mechanical properties then do not correspond to the desired property level, so that a metallurgical aftertreatment, such as hardening and tempering, has to be carried out, which again causes deformations. These deformations must then be aligned mechanically by applying forces. In spite of the high level of automation, as described, for example, in DE-24 52 435, this straightening work requires a particularly high level of experience. A step-by-step determination of the deformation with subsequent step-by-step application of forces requires a significant simplification, but it must be taken into account in all straightening work of plastoelastic material that plastic and elastic deformation occurs when the forces are applied. During the application of force, only the sum of the plastic and elastic deformation can be measured, the plastic deformation only being able to be determined when the force decreases and then again having to be determined whether the desired plastic deformation has occurred. This plasto-elastic behavior applies particularly to materials that are not high Have ductility, such as steel alloys, also stainless steel, high-strength alloys and. the like

The straightening of sheets, in particular endless strips, which are said to have a high level of accuracy, is extremely difficult, since the application of force in one area introduces additional stresses into the sheet, so that straightening in one area may result in deformation in another Area occurs. A high precision of sheet metal strips is desired in particular in the case of the band presses, in particular double band presses, since products with a high uniform thickness are produced in these plates. Different thicknesses of the products not only result in higher material consumption, but in many cases lead to the product being unusable. An example of this is the production of door films.

Also in the course of the production process, e.g. B. in the production of chipboard, laminates, deformations occur in the belts of belt presses, which are due to different mechanical and thermal loads on the belts with respect to the center and side area. The side regions are elongated, causing the surface to curve in the transverse direction. It is now known in production plants that such curved sheets are turned, whereby the tension of the rolls, in particular the end rolls, of a belt system exerts forces on the belt, which leads to the straightening of the belt by continuous application of force.

The present invention aims to provide a method for straightening, in particular endless, to create metallic strips for production plants or the like, which requires a targeted application of force with the least elastic deformation, a straightening of the sheet without complex abutments below it, and the tensile forces, especially in the surface layers, are kept as low as possible.

The inventive method for straightening, in particular endless, metallic strips for production plants or the like., For. B. belt presses, double belt presses, the areas to be straightened are determined and these are subjected to forces via a device, a relative movement being carried out between the belt and the force-exerting device, consists essentially in the fact that the forces are in the form of a large number of Attack pulses, in particular at least 1 to 10 pulses per mm², on the surface and cause residual compressive stresses in the exposed surface. Due to the known relative movement between the band to be straightened and the device exerting the forces, the force exerted in the longitudinal direction can be carried out in a particularly simple manner, particularly with uniform warping of the bands. Due to the fact that the forces act on the surface of the strip in the form of a large number of impulses, the elastic deformation can be kept particularly low during straightening, the internal compressive stresses applied in the surface layer being able to achieve a balance of forces within the sheet and at the same time the advantage What is achieved is that, for example, the corrosion behavior, in particular the stress corrosion cracking behavior, is significantly improved. Contrary to the usual procedure, when Internal compressive stresses over a large number of pulses cause the sheet to deform against the direction of the force.

Are the impulses on the surface via a fluid flow with solid, in particular round, particles, e.g. B. glass or steel balls, for example with a diameter of 200 microns to 400 microns, a conventional method can be used, the so-called shot peening being present with a gas stream, whereas additional treatments of the surface, for example in the case of a liquid stream or a vaporous medium of the sheet are possible. Such a fluid flow can be made particularly variable simply by changing the outlet opening in its impact surface, as a result of which an adaptation to the size of the sheet and to the deformations that usually occur can be carried out particularly easily.

If the impulses are applied to the surface via silent electrical discharges, another method known in the art for introducing residual compressive stresses is used, this method being particularly advantageous for small changes in the surface with higher melting alloys. The size of the pulse can be kept variable both via the current strength and via the voltage and, if appropriate, via the design of the electrode.

If the impulses on the surface mechanically, e.g. B. applied by a hammer actuated by a hammer mechanism, there is only a slight thermal load on the surface, and at the same time no solid particles which subsequently have to be collected, are conditional, so that a particularly dust-free and particle-free process is given which is particularly suitable for use in extreme conditions, for example in dust-free rooms or the like.

If the solid particles, if necessary with the fluid, are sucked off the surface, especially during exposure, shot peening can also be carried out even in rooms with increased cleanliness requirements, with the pulses also being controlled in the interaction between the pressure of the fluid, which Particles are transported and the suction pressure is enabled.

If the particles are suctioned off essentially in a ring around the point where the particles are applied, then an exact positioning of the particles on the surface is possible, whereby the reflected particles, which are simultaneously deflected by the fluid, get around the beam in a particularly simple and effective manner can be.

If the number of pulses is controlled by the dwell time of the device over the areas of the belt to be straightened, the parameters of the device for exerting the pulses can be kept constant and it is only necessary for either the device or the belt in the speed of the relative movement to change each other.

If the endless belt in a production plant, e.g. B. belt press, the circulation speed and the belt tension corresponds to the operating conditions during the production of products with the production system, so either an alignment of the belts Take place under production conditions, or what is also of particular importance, the straightening of the belts can be carried out during the normal production process, so that no downtimes, as are caused, for example, when turning the endless belts, are caused.

If the device for applying impulses, in particular after one or more complete passes (runs), is moved transversely to the direction of rotation, the substantially uniform deformation in a longitudinal direction is particularly easily taken into account when straightening the strip, so that a continuous tension compensation, as it is particularly advantageous for straightening work, is simple and reliable to carry out.

If the application of impulses is carried out, starting at the edge areas of the belt, the areas of greatest deformation in a belt, as they exist after production use, are first aligned, so that a tension compensation is carried out from the outside to the inside.

If the endless belt is returned to the production area, e.g. B. the shaping of webs, impulses, so there is the least disruption during production, while no constructive changes to the press, z. B. double belt press, like other inlet or outlet area, is required.

The invention is explained in more detail below with reference to the drawings.

• Fig. 1 eine schematische Längsansicht einer Doppelbandpresse mit Kugelstrahlanlage,
• Fig. 2 eine Queransicht der Vorrichtung gemäß Fig. 1,
• Fig. 3 eine Halterung tür den Strahlkopf der Vorrichtung gemäß Fig. 1 und
• Fig. 4a gemäß Linie IV - IV von Fig. 1 das Band vor dem Richten bzw.
• Fig. 4b gemäß Linie IV - IV von Fig. 1 das Band nach dem Richten.

Show it:

• 1 is a schematic longitudinal view of a double belt press with shot peening system,
• 2 is a transverse view of the device of FIG. 1,
• Fig. 3 is a holder door the jet head of the device of FIG. 1 and
• 4a along line IV - IV of Fig. 1, the tape before straightening or
• Fig. 4b along line IV - IV of Fig. 1, the tape after straightening.

The double belt press for the production of chipboard according to FIGS. 1 and 2 has a machine bed 1, in which an upper endless belt 2 by the deflecting rollers 6 and 6 'and a lower endless belt 3 by the deflecting rollers 7 and 7' tensioned and are kept in circulation in the same sense. The band has a width of 2.5 m and a length of 45 m. The circulating speed is 6.0 m / min. The tensile stress exerted on the strips is 10 N / mm². The strips are made of a stainless steel alloy with the following composition:

1 and 2, both the upper band 2 and the lower band 3 are supported by rollers 25 in the production position and by rollers 26 in the return position. Shot peening systems 4 and 5 are arranged in the area of the return. On the underside of the double belt press, a bearing 10 is arranged on L-shaped supports 23 in the machine tunnel 8 of the foundation 9, to which a linear unit 11 is attached. This carries a carrier 12, on which two jet heads 13 are arranged so that they can be swiveled and moved transversely to the longitudinal direction of the double belt press. As can clearly be seen, the lower shot blasting system is arranged in the direct connection to the deflection roller 7. The upper shot peening system 4 is further away from the deflection roller 6 and is arranged between two rollers 26. The blasting head 13 is fastened to the linear unit 15 via the receptacle 16, which in turn is connected to the machine bed 1 via C-shaped supports 14. The jet head above the upper band 2 has the same mobility as that of the lower band. As can be seen particularly clearly in FIG. 2, the jet heads 13 are supplied with the solid particles and also with the carrier gas via supply lines 21 from the jet device 18. Glass spheres with a diameter of 300 μm serve as solid particles, and the glass spheres are thrown against the surface of the steel strip by the fluid at a speed of 150 m / sec. The impact area of the jet on the belts, which is circular, has a diameter of 12 mm, and the jet head is designed as a suction jet head and has an annular suction, through which suction is carried out with a negative pressure relative to the atmospheric pressure of 0.1 bar, in line 21 a corresponding suction line with a larger volume than that of the supply line is provided. The transverse movement of the jet heads can be carried out by servomotors 24.

3, in which the blasting system 5 for the lower belt 3 is shown. A C-shaped carrier 19 is attached to the carrier 20 and supports the linear unit 11. The carriage 22 has a carrier 12 which supports the jet head 13, which is height-adjustable both in direction a and laterally adjustable in direction b. The jet head is also rotatably and pivotably arranged. The movement of the jet head transversely to the longitudinal extent of the belt is carried out with the servo motor 24.

In the direction of movement of the belt in front of the blasting head, a ruler with a cross-section is arranged, with which the deviation from the linearity is determined. The linearity can be determined both mechanically and optically, e.g. B. about interference, depending on what accuracy is required for the measurement.

In Fig. 4a a band 3 is shown in cross section, which is already strongly deformed and no longer comes to rest on the rollers in the central region.

In the band shown in FIG. 4b, a curvature has been carried out in the opposite direction in order to achieve a longer service life of the band up to the permissible countercurve.

Through shot peening, residual compressive stresses are introduced in the surface areas, which curvature of the Condition the tape in the opposite direction to the beam direction.

A tape with the length, width, chemical composition and circulation speed as well as a thickness of 1.2 mm and a maximum deformation without tensile load of the tape in the middle of it of 1,050 mm against a straight cross-section with parabolic deformation, was used under the conditions already mentioned as follows the straightening process. The individual paths of exposure to the particles during shot peening were arranged side by side.

In the first straightening process, web in addition to web with 10 pulses per mm², u. between the entire width of the belt.

In a second pass, which only extended to the inside of the two edge areas up to 600 mm, web was also laid next to web, with 10 pulses per mm².

In the third pass, web was also placed next to web, with only an edge area of 400 mm being subjected to 10 pulses per mm 2 and

in a fourth pass, only an edge area of 250 mm was applied with 10 pulses per mm².

A flat alignment of the endless belt could be achieved by the residual compressive stresses introduced into the surface in this way.

Straightening of other flat surfaces by blasting, whereby the anomaly spots are not necessarily elongated, but can also be circular, is also possible by applying residual compressive stresses.

The procedure according to the invention is particularly suitable for materials which tend to build up residual compressive stresses by cold forming, such as steel alloys, duralumin alloys and the like. Like. Although shot peening is a particularly simple and well-established method, the impulses can also be carried out, for example, by pneumatically or mechanically operated hammers, the mass of the hammer, the speed and the size of the impact surface being decisive for the impulse.

If the impulses are not caused mechanically but, for example, by silent electrical discharges, the size of the impulses can be determined by selecting the voltage and current strength and the size of the electrode tip.

Claims (11)

Process for straightening, in particular endless, metallic strips for production plants or the like, for. B. belt presses, double belt presses, the areas to be straightened are determined and these are subjected to forces via a device, a relative movement being carried out between the belt and the force-exerting device, characterized in that the forces are in the form of a large number of Attack pulses, in particular at least 1 to 10 pulses per mm² on the surface of the belt and cause residual compressive stresses in the exposed surface. A method according to claim 1, characterized in that the pulses on the surface via a fluid stream with solid, in particular round, particles, for. B. glass or steel balls with a diameter of 200 microns to 300 microns, are applied. A method according to claim 1 or 2, characterized in that the pulses are applied to the surface via silent electrical discharges. Method according to one of claims 1, 2 or 3, characterized in that the pulses on the surface mechanically, for. B. applied by a hammer operated by a hammer. A method according to claim 2, characterized in that the solid particles, if appropriate with the fluid, are suctioned off the surface, in particular during the application. A method according to claim 2 or 5, characterized in that the particles are suctioned off in a substantially annular manner around the point to which the particles are applied. Method according to one of claims 1 to 6, characterized in that the number of pulses is controlled via the dwell time of the device over the areas to be straightened. Method according to one of claims 1 to 7, characterized in that the endless belt in production plants, for. B. belt presses is moved, the rotational speed and the belt tension corresponds to the operating conditions during the production of products with the production plant. Method according to one of claims 1 to 8, characterized in that the device for applying impulses, in particular after one or more full runs (runs) of the belt, is moved transversely to the direction of rotation. Method according to one of claims 1 to 9, characterized in that the application of pulses is carried out starting at the edge regions of the belt. Method according to one of claims 1 to 10, characterized in that the endless belt during the return to the production area, for. B. the shaping of webs, impinged with pulses.

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