EP3848131A1

EP3848131A1 - Process for straightening of metal plates and apparatus for carrying out this straightening process

Info

Publication number: EP3848131A1
Application number: EP21150266.1A
Authority: EP
Inventors: Fabio BADIN
Original assignee: Badin Block Srl
Current assignee: Badin Block Srl
Priority date: 2020-01-10
Filing date: 2021-01-05
Publication date: 2021-07-14
Anticipated expiration: 2041-01-05
Also published as: EP3848131C0; EP3848131B1; IT202000000307A1

Abstract

A process and apparatus (50) for straightening metal plates (30) by means of a flat support bench (40) provided with clamping means configured to hold the plate (30) in close contact with the flat bench (40) but free to expand, upon heating, and to contract, upon cooling, forcing the crystal lattice of the plate (30) to recompose in a flat position.

Description

This invention relates to a process and related apparatus for straightening metal elements, such as metal plates or sheets of varying thickness by means of localised heating and cooling of the sheet itself.
By heating the sheet, a change in the crystalline structure and a redistribution of stresses is obtained; these lead to a straightening of the sheet during subsequent cooling.
It is well known that the sheets obtained from the cutting of a metal strip maintain the curvature that they assume following the rolling up of the strip on the corresponding coil. The curvature of metal sheets causes significant problems in the processing and assembly operations thereof. In fact, a sheet that has not been straightened can cause a malfunction in the moulding operations due to incorrect insertion of the sheet inside the mould or difficulty in ejecting the piece and scraps. In extreme cases, the curvature of the sheet can even entail loss of the final piece.
These drawbacks obviously produce production stoppages and cause increased maintenance costs and delays in delivery times.
It is also known that the curvature or non-flatness of the metal sheets can also derive from the original state of the raw material, or from deformations and stresses induced by thermal cutting and metal processing to which the sheets are usually subjected.
Therefore, the flatness of the material becomes particularly important in order to obtain a high-quality final product that does not require subsequent processing and a consequent increase in production costs.
Generally, several processes and different types of equipment are used for straightening metal sheets until they are flat.
A first straightening process, mainly used for thin sheets, involves the use of manually controlled presses that exert pressure on the convexity of the sheet and cause it to yield in the opposite direction until a basically flat sheet is obtained.
Presses that combine mechanical action and heating of the sheet are also known in order to decrease the yield stress of the material and save on the energy to be exerted by the press, as described in the European patent application EP 3 566 807 A1 , for example.
A second process involves the use of machines equipped with several straightening rollers or cylinders that act on the upper and lower sides of the metal sheet. The action of the cylinders subjects the sheet to alternating plastic deformation until it becomes flat.
The quantity of cylinders and the relative diameters are chosen according to the thickness of the metal sheet and the degree of straightening that needs to be obtained. Thus, multi-cylinder machines require a significant outlay and frequent adjustment, replacement, and maintenance operations for the cylinders.
In addition, this process involves complex equipment and high operating costs due to the very high power required for processing thick sheets or high-tensile steel sheets. For example, Italian patent N. 1082823 describes a cylinder machine for straightening metal laminates.
Another known process involves the use of flame straightening by means of which the metal sheet is subjected to localised heating and subsequent cooling, as, for example, described in " The Golden Rules of Flame Straightening" by Volkmar Schuler, Australian Welding, 1 October 2015, pp. 26-27, XP055700967. It is well known that, contrary to the action of the mechanical press that elongates the metal sheet, heating by flame initially produces an expansion of the piece with a consequent weakening of the compression zone and, in the subsequent cooling step, a shrinkage of the heated zone. Thus, heating and subsequent cooling of the convexities/bumpiness of a sheet makes it possible to obtain an acceptable flatness of the latter. However, this process must be carried out by experienced operators who are able to apply the right amount of heat at precise points on the metal sheet to be straightened.
Flame straightening benches are also known. These are mainly used for straightening thin plates intended for the mass production of railway cars.
In this case, the sheet is placed on a resting surface and clamped by means of clamping tools that prevent the expansion thereof. A drilled metal template is placed over the sheet to be straightened and clamps it in place during the heating process, which is carried out at the template holes.
The size of the drilled template, its thickness, and the distances between the holes depend on the component material and the thickness of the piece to be straightened. It is essential, therefore, that these operations are carried out by specialised and very experienced operators.
Flame straightening with drilled templates only works if the area of the sheet to be straightened is supported on its back by a stable resting surface. In the construction of railway cars wherein the sheets of the passenger compartment cells or of the outer covering of the car are predominantly composed of aluminium, the strikers consist of magnetic plates that strongly attract the drilled plates, through the aluminium sheet, by forcing the component into the desired plane. Pricking is done through the holes in the drilled template. This process has the drawback of preventing the sheet from shrinking during the cooling step and generates induced stresses that manifest themselves in the deformation of the sheet as soon as it is freed from the clamping tools.
In addition, several types of drilled plates must be prepared with characteristics suitable for the characteristics of the material to be straightened. Therefore, known flame straightening processes have the main limitation of requiring the preparation of numerous types of drilled plates, which are economically viable only in mass production. Finally, the known flame straightening processes require highly skilled personnel and numerous manual operations in order to carry them out.
The main purposes of the process and apparatus according to the invention are to overcome these limitations and to make the straightening process faster and more functional.
These and other purposes are achieved with a straightening process and a related apparatus according to the independent claims at the end of this description. Other aspects and examples are defined in the dependent claims.
The purposes and characteristics of the process and apparatus will be apparent from the following description with reference to the attached schematic drawings in which:

Figure 1 represents a perspective view of a metal sheet to be straightened using the process and apparatus described herein;
Figures 2A, 2B, and 3 schematically illustrate and in longitudinal section respective operating positions of an apparatus for straightening a metal sheet of the type illustrated in Figure 1;
Figure 4 schematically illustrates and in longitudinal section a side view of the straightening apparatus;
Figures 5 and 6 schematically illustrate and in orthogonal section with respect to Figure 4, respective side views of the straightening apparatus.

The process comprises, for example, the following steps:

the metal sheet (or plate) to be straightened 30 is rested on a flat support bench 40 provided with clamping means configured to hold the sheet 30 in close contact with the bench 40 but free to expand, parallel to the sheet 30, upon heating, and to contract, upon cooling, forcing the crystal lattice to recompose in a flatter position compared to the known processes;
scanning means 45 identify sheet 30 irregularities and transmit the coordinates thereof to an electronic control and command device;
heating means 47 that can be moved over the entire surface of the support bench 40 are activated by said electronic control and command device to heat the sheet 30 irregularities until it is straightened;
the sheet 30 can be cooled by means of cooling means 49 which can also be moved over the entire surface of the support bench 40 and can be activated by the electronic control and command device. Said cooling means 49 may consist of nozzles that supply a cooling fluid. The cooling means 49 are optional. In fact, the apparatus may be configured so that the sheet 30 may be cooled by means of free air cooling. This means that cooling takes place without the use of dedicated means but simply because the sheet 30 is crossed by free air.
finally, the straightened sheet 30 may be separated from the support bench 40 as soon as the electronic control and command device deactivates the clamping means that are holding the sheet 30 in close contact with the support bench 40.

The scanning means 45 may be moved over the entire surface of the support bench 40 in order to analyse all the defects in the plate 30. Alternatively, the scanning means 45 may consist of, for example, two or more 3D cameras attached to a structure of the apparatus that reproduce a topography of the plate 30 by working in triangulation.
The clamping means may consist of any means capable of maintaining the plate or sheet 30 in close contact with the flat support bench 40 during the step for heating and/or cooling the sheet 30 irregularities.
According to one embodiment, the clamping means configured to hold sheet 30 in close contact with the bench 40 are mechanical, and the upper surface of the support bench 40 is coated with a layer 42 of sliding material that is configured to resist high temperatures.
According to another embodiment, the clamping means configured to hold the sheet 30 in close contact with the bench 40 are electromagnetic and the upper surface of the support bench 40 is coated with a layer 42 of sliding and anti-friction material that, in addition to being configured to resist high temperatures, does not hinder the attraction force exerted by said electromagnetic clamping means.
According to an additional embodiment, the clamping means may comprise both mechanical and electromagnetic means.
It should be noted that in all three of these embodiments, the presence of the layer 42 of sliding and anti-friction material capable of resisting high temperatures serves to ensure greater freedom for the plate 30 to expand, upon heating, and to contract, upon cooling, while still remaining in close contact with the flat bench 40.
In this way, it is possible to obtain automated apparatus to perform the processing described above.
By way of non-limiting example, one embodiment of the straightening apparatus 50 is described below.
With particular reference to Figures 4, 5, and 6, the apparatus 50 comprises an external frame 44, with a parallelepiped shape, that houses a flat bench 40 for supporting the sheet 30 to be straightened.
According to one example, the support bench 40 may be connected to mechanical clamping means configured to hold the sheet 30 in close contact with the flat bench 40 but free to expand, upon heating, and to contract, upon cooling. For example, the mechanical clamping means may be compression rollers.
According to another example, electromagnetic means may be connected to the support bench 40. In particular, a single electromagnet 41 or multiple individual electromagnets 41, which exert their attraction force on the sheet 30, may be connected. The electromagnet force may be homogenously exerted, from a single electromagnet 41 that extends across the whole surface of the support bench 40. Alternatively, several electromagnets 41 may be connected to the support bench 40 and the electromagnetic attraction force developed by each single electromagnet 41 may be adjusted so as to perform a differentiated action on the surface portion of the sheet 30 placed near the individual electromagnet 41. It should be noted that, when electromagnet clamping means are used, the upper surface of the support bench 40 is covered with a layer 42 of sliding and anti-friction material configured to resist high temperatures and permeable to the attraction force exerted by the electromagnets 41 (such as, for example: bronze, graphite, lubricated steel). It should be noted, however, that although such an anti-friction layer does not prevent the electromagnetic force from acting on the plate 30, the layer 42 may nevertheless partially reduce the original maximum force generated by the electromagnet 41.
A scanning device 45 (Figures 5 and 6) may be slidably moved above the entire surface of the support bench 40 to enable the identification and location of sheet 30 irregularities. Alternatively, the scanning device 45 is fixed to the apparatus and may consist of a pair of 3D video cameras (not shown in the figure).
The scanning device 45 transmits the coordinates of the irregularities detected on the sheet 30 to an electronic control and command device, of a known type that is not shown.
One or more heating torches, or one or more electric heating devices, of a known type, are slidably connected both horizontally and vertically to a crossbar 48 that can also be moved above the entire surface of the support bench 40 to heat the sheet 30 irregularities.
In a known way, a cooling device 49 may be connected to each torch or electrical heating device (Fig. 3) configured to emit a cooling fluid over the surface of the sheet 30.
Based on the readings of the scanning device 45, and on the basis of predetermined algorithms, the electronic control and command device makes the heating means 47 perform the most suitable movements and heating/cooling cycles for straightening the sheet 30.
The metal sheet 30 to be straightened is placed on the support bench 40 (Fig. 2A) and activation of the mechanical clamping means, according to one embodiment, or of the electromagnets 41, according to another embodiment, brings the lower surface of the sheet 30 into close contact with the layer of anti-friction material 42 of the support bench 40 and into a basically horizontal position (Fig. 2B). It is clear that the dimensions of the support bench may be such as to enable the simultaneous straightening of several sheets 30.
Thus, the sheet 30 is subjected to a heating step of a known type, for example by flame or electrically (Fig. 2B), carried out using appropriate heating means 47, for example flame heating torches or electric heating devices, and to a subsequent cooling step (Fig. 3) that may occur, also in a known manner, either in free air or by supplying fluids (air, gas, or liquid) via nozzles 49 that accelerate the cooling process.
It should be noted that, during heating and/or subsequent cooling, the sheet 30 is always kept in a horizontal position and in close contact with the support bench 40 but can expand and contract freely thanks to the layer of anti-friction material 42.
At the end of the cooling step, the clamping means (for example, the mechanical means or the electromagnets 41) are deactivated and the straightened sheet 30 can be separated from the support bench 40 and conducted for subsequent processing.
The process and related apparatus described herein significantly improve the degree of straightening of the sheet 30 since they avoid the induced stresses that occur in sheets straightened using known straightening processes and equipment.
In the above example, the sheet 30 is a single sheet and has a rectangular shape. However, it is clear that the process and apparatus 50 would be equally advantageous if there were more than one sheet 30 and they had shapes other than rectangular ones.
From what has been described, it is clear that the invention achieves the main purpose of providing a manufacturing process and a related apparatus 40 which make it possible to straighten the sheet 30 in a simple and practical way and without requiring the employment of highly specialised personnel and avoiding the arrangement of an impractical and expensive assortment of drilling templates.
It is well understood that several modifications can be made to the process and to the apparatus according to the invention without, however, exiting the scope of what is described and claimed below with reference to the attached drawings and, therefore, from the protection domain of this industrial property right.

Claims

Process for straightening metal plates (30) previously placed on a flat support plane (40) and subjected to heating and subsequent cooling until the metal plate (30) is recrystallized in a flat position, comprising the following steps:
(a) placing at least one metal plate to be straightened (30) on a flat support bench (40) provided with clamping means to hold the plate (30) in close contact with the flat bench (40) but free to expand parallel to the plate, upon heating, and to contract, upon cooling, forcing the crystal lattice of the plate (30) to recompose in a flat position;

(b) inspecting the surface of the plate (3) using scanning means (45) in order to identify irregularities of the plate (30) and to transmit the coordinates of said irregularities to an electronic control and command device;

(c) heating and/or cooling the irregularities identified on the surface of the plate (30) until said plate (30) is straightened, wherein the heating occurs using heating means (47) that can be moved over the entire surface of the bench (40) and can be activated by said electronic control and command device; and

(d) separating the straightened plate (30) from the support bench (40) following the deactivation of the clamping means by the electronic control and command device,
characterised in that
the plate (30) is held in close contact with the flat support bench (40), being free to expand, upon heating, and to contract, upon cooling, thanks to a layer (42) of sliding and anti-friction material configured to resist high temperatures, which covers the upper surface of the flat bench (40).
The process according to claim 1, wherein the clamping means consist of electromagnetic means (41) and/or mechanical means.
The process according to claim 2, wherein, if the clamping means consist of electromagnetic means (41), the layer (42) of sliding and anti-friction material is furthermore permeable to the electromagnetic attraction force.
The process according to one of claims 2 to 3, wherein the clamping means consist of multiple electromagnets (41) and the electromagnetic attraction force developed by each individual electromagnet (41) can be adjusted so as to perform a differentiated action on the portion of the plate (30) located at the individual electromagnet (41).
The process according to one of the preceding claims, wherein heating occurs via a flame heating or an electrical heating process, and wherein cooling occurs via the supply of a cooling fluid or by means of free air cooling.
Apparatus (50) for straightening metal plates (30) subjected to heating and subsequent cooling until the metal plate (30) is recrystallized in a flat position, comprising: an external frame (44) housing a flat bench (40) for supporting the plate (30) to be straightened; clamping means to hold the plate (30) in close contact with the flat bench (40); scanning means (45) for identifying the plate (30) irregularities and for transmitting the coordinates of the irregularities to an electronic control and command device; heating means (47) that can be moved across the entire surface of the bench (40) and can be activated by said electronic control and command device for heating the plate (30) irregularities until the plate is straightened,
characterised in that
the upper surface of the flat bench (40) is coated with a layer (42) of sliding and anti-friction material configured to resist high temperatures.
The apparatus (50) according to claim 6, wherein the clamping means consist of electromagnetic means (41) and/or mechanical means.
The apparatus (50) according to claim 7, wherein, if the clamping means consist of electromagnetic means (41), the layer (42) of sliding and anti-friction material is furthermore permeable to the electromagnetic attraction force.
The apparatus (50) according to one of claims 7 to 8, wherein said clamping means consist of at least one electromagnet (41) joined to the flat support bench (40).
The apparatus (50) according to one of claims 7 to 9, wherein said clamping means consist of multiple electromagnets (41) and the electromagnetic attraction force developed by each individual electromagnet (41) can be adjusted so as to perform a differentiated action on the portion of plate (30) located near the individual electromagnet (41).
The apparatus (50) according to one of claims 6 to 10, wherein said scanning means (45) are configured to slidably move above the entire surface of the flat support bench (40) or are fixed on a structure of the apparatus (50) for identifying irregularities in the flatness of the plate (30) and to transmit their coordinates to an electronic control and command device.
The apparatus (50) according to one of claims 6 to 11, wherein said heating means (47) consist of at least one flame heating torch or at least one electric heating device and are slidably connected, both horizontally and vertically, to a crossbar (48) that can also be moved above the entire surface of the support bench (40) and is configured to be activated by the control and command device to heat the plate (30) irregularities.
The apparatus (50) according to one of claims 6 to 12, wherein said heating means (47) consist of multiple flame heating torches or multiple electric heating devices.
The apparatus (50) according to one of claims 6 to 13, additionally comprising cooling means (49) that can be moved over the entire surface of the bench (40) and can be activated by the electronic control and command device to cool the plate (30) irregularities or being configured to cool the plate (30) by free air.
The apparatus (50) according to claim 14, wherein the cooling means (49) consist of one or more nozzles joined to the heating means (47) and configured to supply a cooling fluid across the plate (30) surface.