EP4039381A1

EP4039381A1 - Method for reducing the thickness of a strip of metal by hot-roll-forming and system for roll-forming a strip of metal by hot-roll-forming

Info

Publication number: EP4039381A1
Application number: EP21155547.9A
Authority: EP
Inventors: Ali Mashi; Khaled Alhajeri
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-02-05
Filing date: 2021-02-05
Publication date: 2022-08-10

Abstract

The present invention relates to a method for reducing the thickness of a strip of metal 121 by hot-roll-forming, wherein the strip of metal 123 comprises a first thickness of 2.0mm up to 5.0mm prior to the process and the strip of metal 123 with the first thickness is processed to a strip of metal 125 with a second thickness of 0.6mm to 2.5mm by at least one pair of rollers 103, wherein the second thickness is smaller than the first thickness, comprising the following steps:- heating the strip of metal 123 with the first thickness to a temperature above a recrystallization temperature of the metal, thus a pre-heated strip of metal 123 with the first thickness is present,- introducing the pre-heated strip 123 of metal with the first thickness into the pair of rollers 107, whereas the pair of rollers 107 is adjusted to a distance to reduce the first thickness to the second thickness by roll-forming,- processing the pre-heated strip of metal 123 with the first thickness through the pair of rollers 107, thus the strip of metal 125 with the second thickness is formed,thus, the thickness of a strip of metal 121 is reduced. The invention further relates to a system for roll-forming a strip of metal 121 by hot-roll-forming.

Description

The present invention relates to and concerns a method for reducing the thickness of a strip of metal by hot-roll-forming. The invention also relates to a system for roll-forming a strip of metal by hot-roll-forming set up to perform an according method.
For reducing the thickness of a strip of metal by hot-roll-forming, multiple methods and systems are known. Those methods are used to form a strip of metal or a piece of sheet metal, comprising a desired thickness.
However, those methods are limited to producing strips of metal with a thickness down to about 1.0 mm, whereas thinner thicknesses have to be produced by a so-called cold-rolling-process. In comparison to a hot-rolling-process, such a cold-rolling-process leads to a better surface quality of the so produced metal strip, but also creates the need for higher processing forces, heat treatments and more effort to produce this strip of metal or sheet metal.
The object of the present invention is to improve the known state of the art.
This objective is solved by a method for reducing the thickness of a strip of metal by hot-roll-forming, wherein the strip of metal comprises a first thickness of 2.0 mm up to 5.0 mm prior to the process and the strip of metal with the first thickness is processed to a strip of metal with second thickness of 0.6 mm to 2.5 mm by at least one pair of rollers, wherein the second thickness is smaller than the first thickness, comprising the following steps:

heating the strip of metal with the first thickness to a temperature above a recrystallization temperature of the metal, thus a pre-heated strip of metal with the first thickness is present,
introducing the pre-heated strip of metal with the first thickness into the pair of rollers, whereas the pair of rollers is adjusted to a distance to reduce the first thickness to the second thickness by roll-forming,
processing the pre-heated strip of metal with the first thickness through the pair of rollers, thus the strip of metal with the second thickness is formed,

Especially by performing a hot-roll-forming of a strip of metal with a thickness of 2.0 mm up to 5.0 mm to form a strip of metal with a second thickness of 0.6 mm to 2.5 mm, usual drawbacks of a hot-roll-forming-process can surprisingly be overcome. The pre-heated strip of metal in that way can be roll-formed to a significantly thinner thickness of 0.6 mm to 2.5 mm without the drawbacks of a known process of roll-forming the same strip from a greater thickness.
As utilized in accordance to the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:
"Reducing the thickness" of a strip of metal indicates any process suitable for transferring a strip of metal or a piece of sheet metal to a lower thickness during that process of reducing. For example, the reduction of thickness is performed by pushing or pulling the strip of metal or a piece of sheet metal through a pair of rollers or multiple pairs of rollers.
A process of "hot-roll-forming" relates to a process in which mentioned strip of metal is formed and/or reduced in thickness by means of rollers or multiple rollers, which is especially done in "hot" condition. This "hot" condition, in respect to applicable material science, describes, that the process is performed with the strip of metal being at a temperature which is above or well above recrystallization temperature of that very metal.
A "thickness" determines a measurement of that metal strip in one direction, this direction usually being measured between the forming rolls or multiple stages of forming rolls. Such a thickness does not have to be the same for all the strip of metal or the whole piece of sheet metal which is processed, it can also be determined as an average thickness or a representative thickness of this very strip of metal or piece of sheet metal.
A "pair of rollers" describes any kind of or any set of rotating and in general round-shaped solid bodies, which by their opposing position are enabled to process the strip of metal or any piece of sheet metal in between of them. Those rollers, for example, can be drums or solid metal rollers or any other embodiment in cylindrical or in general cylindrical shape. Those rollers usually are made from a metal or steel or a ceramic material, which is harder than the metal to be processed.
"Heating" the strip of metal describes any raise in temperature of that strip of metal to prepare this strip of metal or the respective piece of sheet metal to be processed above its recrystallization temperature. Such a heating can be performed by electrical or chemical means, for example, heating the strip of metal with an oven or other suitable means. Also, such a heating can be done by using process heat from any prior process, for example, by introducing the strip of metal in a pre-heated stage from any prior process.
A "recrystallization temperature" describes a temperature for any given metal or any given metal compound or alloy, above which its deformed grains are replaced by a new set of defect-free grains that nucleate and grow until the original grains have been partly or entirely consumed. Recrystallization is usually accompanied by a reduction in strength and hardness of a material and a simultaneous increase in the ductility. This recrystallization temperature is related to the very type, kind and/or mixture of metal, for example, defined by the specific alloy of a specific metal which is used.
"Introducing" the so pre-heated strip of metal into the air of rollers describes the process of feeding and/or pulling and pushing the strip of metal towards or into the pair of rollers in a way that ensures the pair of rollers to catch the strip of metal safely to be processed through this pair of rollers.
"Processing" the pre-heated strip of metal through the pair of rollers describes any process that performs the wanted goal, namely to reduce the thickness of the strip of metal by compressing said strip of metal along a thickness axis, in a way that its thickness is reduced by the established force or forces from the rollers towards that strip of metal.
In a preferred embodiment, the first thickness is between 2.5 mm and 4.5 mm and/or the second thickness is between 1.0 mm and 2.0 mm, in particular between 1.2 mm and 1.8 mm.
By these thicknesses, the process forces needed to perform the process are comparably low. This way, the process can be performed in a way that the second thickness is established for the strip of metal with a high surface quality and specifically low flaws in the material.
In another embodiment of the invention, the first thickness is reduced to the second thickness by a multi-step process, wherein the strip of metal is introduced into and processed by multiple pairs of rollers consecutively.
This way, the method can be performed in comparably small-sized machine or device, as the strip of metal is passed through different pairs of rollers to perform different steps of a reduction of its thickness.
To enable a stable and safe process, the multiple pairs of rollers are each adjusted to decreasing distances, thus the multi-step process is realized by each pair of rollers with decreasing distances reducing the thickness of the metal strip in consecutive steps.
In a preferred embodiment of the invention, the multi-step process is performed by a reversing or partly reversing process, wherein the strip of metal is moved back and forth through one pair of rollers or multiple pairs of rollers consecutively.
As a result, such a multi-step process can be performed in a single pair of rollers, whereas this pair of rollers can be set to decreasing distances with every consecutive step of reducing the thickness of a processed strip of metal or piece of sheet-metal.
To enable a safe and stable process and to reduce deflections of the system used to perform the method, the pair of rollers or pairs of rollers are presented as tandem mills or Steckel-mills.
A "tandem mill" describes any system of multi roller mill-stages, wherein such a tandem mill can also comprise multiple stages of rollers, whereas the process is done in one path in multiple steps of thickness. Those tandem mills can comprise from two up to 18 pairs of rollers.
A "Steckel-mill", also known as a reversible finishing mill, is similar to a reversing roller mill, except two coilers are used to feed the material to the mill. Such a coiler is on the entrance side and another coiler on the exit side. The coilers pull the material through the mill, therefore the process is more similar to drawing than rolling. The material can be fed back and forth through the mill until the desired thickness is reached, much like a reversing roller mill.
In another embodiment of the invention, the strip of metal is de-coiled prior to introducing the metal strip into the pair of rollers or the airs of rollers.
This way, the strip of metal can be stored in a relatively small space prior to the process and can be de-coiled in the very moment of introducing into the pair of rollers and, by that, introducing into the process.
To enable a clean and stable process, furthermore, the strip of metal can be cleaned prior to introducing the metal strip into the pair of rollers or pairs of rollers. This cleaning can be done by mechanically cleaning with, e.g., brushing and/or using high pressure water and/or sand blasting or by using acid, similar to the pickling line in a cold rolling process.
In a further embodiment of the invention, the strip of metal is re-coiled prior to processing and/or the strip of metal with a reduced thickness is re-coiled after processing in the pair of rollers for pairs of rollers in a re-coiling device.
This way, the overall process can be performed in a relatively small area or relatively small space, thus can be performed economically.
To ensure a stable and safe heating of the material, the heating of the strip of metal is performed by induction, wherein electromagnetic fields are induced in the metal and/or by gas, wherein gas is burned to heat the metal with a flame directly or by heating an oven and/or a heating device for the metal.
In yet another embodiment of the invention, the strip of metal is cooled after its processing in the pair of rollers or pairs of rollers, especially by water cooling and/or air cooling. This embodiment, in all possible combinations, is especially used for controlling the microstructure and mechanical properties of the strip of metal.
By cooling the strip of metal after being processed in the pair of rollers, in particular a preparation for re-coiling this strip of metal after the process can be performed.
In a further aspect, the objective can be solved by a system for roll-forming a strip of metal by hot-roll-forming comprising at least one pair of rollers for processing the strip of metal comprising a first thickness to a strip of metal with a second thickness, set up to perform a method according to one or more of the embodiments described above.
Such a system can successfully be used to produce a strip of metal with a thickness of < 2.5 mm as described above in a hot-rolling-process, whereas the quality of the produced strip of metal can be comparable to a cold-rolling-process.
To perform a multi-step process with such a system, the system comprises multiple rollers or multiple pairs of rollers, whereas the multiple rollers or multiple pairs of rollers are set up for processing the strip of metal comprising a first thickness to the strip of metal comprising a second thickness in consecutive steps.
In another embodiment, the system comprises a heating device, whereas the heating device is located in proximity to the strip of metal for heating the strip of metal.
With a heating device, especially located in proximity to the strip of metal, the strip of metal can easily be heated to be prepared for the hot-roll-forming-process.
In an embodiment, the system comprises a cooling device, especially a water-cooling device, whereas the cooling device is located in proximity to the strip of metal for cooling the strip of metal.
A "heating device" can be any device or system to heat up the strip of metal. For example, such a heating device comprises a torch, a flame, an electric heating system and/or an inductive heating system. For example, such a heating device is an oven, an electromagnetic coil or comprises an electromagnetic resistor to convert electrical energy into heat.
A "cooling device" can be any device which is suitable for cooling a strip of metal or for introducing a cold environment in proximity to the strip of metal. For example, such a cooling device comprises a system for water spray, a heat converter or any other suitable device.
Further aspects of the present invention will be apparent from the figures and from the description of particular embodiments as

Fig. 1: shows a schematic picture of a hotrolling-process with a rolling mill,
Fig. 2: shows an overall schematic view of the rolling process with a de-coiling device and a re-coiling device,
Fig. 3: shows another roll-forming-process with an additional cooling device, and
Fig. 4: shows a schematic diagram of different steps of a roll-forming-process.

A roll-forming-process 101 is performed in a rolling mill 107, comprising a roller 103 and a roller 105. The roll-forming-process 101 is performed as a so-called hot-roll-forming-process, wherein the temperature of a roll-formed metal strip 121 is above the recrystallization temperature of that very metal. In the presented example, this temperature is well above 800 °C, as the metal is a steel. The metal strip 121 comprises an initial part 123, which is roll-formed into a compressed part 125. The initial part 123 comprises a primary thickness 151, which is reduced to a secondary thickness 153 of the compressed part 125 in the process.
In the described example, the primary thickness 151 is 3.5mm, the secondary thickness is 1.5mm.
A roll-forming-process 201 takes advantage of the rolling mill 107. A metal strip 211 is presented on a primary roll 203, which is pre-heated. A shield 205 prevents an operator touching the metal strip or any other moving parts. The metal strip 211 is rolled around a shaft 207 to form the primary roll 203.
The metal 211 is then fed around guiding rollers 221 which lead the metal strip 211 to support rollers 251. The so presented first part 213 of the metal strip 211 is then fed into the roller mill 107. In the roller mill 107, the metal 211 is reduced in its thickness according to the process prior presented.
A second part 215 of the metal strip 211 is a result of the roll-forming-process performed in the roller mill 107. The second part 215 comprises a lower thickness than the first part 213 according to the example presented above.
The second part 215 of the metal strip 211 is fed onto support rollers 261 and around guiding rollers 223 onto a secondary roll 233. The secondary roll 233 is protected by a shield 235 to prevent an operator from injury or from interfering with the secondary roll 233. The secondary roll 233 is built around a shaft 237 which can actively be driven to pull the metal strip 211 through the roller mill 107. Thus, a metal strip 241 with a reduced thickness is drawn onto the secondary roll 233. As an example, the process is shown to be performed along a direction 271.
In between the first primary roll 203 and the secondary roll 233, the metal strip 211, respectively metal strip 241, can be drawn back and forth in between those two rolls. In each step of consecutively moving the metal strip back and forth, a distance of the roller 103 to the roller 105 within the rolling mill 107 can be reduced, thus the thickness of the metal strip is reduced step by step.
Another roll-forming-process 301 is shown and described as follows:
A metal strip 321 is pre-heated in an oven 303. The oven 303 comprises means to coil and de-coil the metal strip 321 according to the example above. The metal strip 321 is then fed onto a support 305 whereas a primary strip 321 is fed into a reversing roller mill 307 and thereby passively cooled to a suitable processing temperature. The reversing roller mill 307 works according to the above-mentioned example. After reducing the thickness of the metal strip, a secondary strip 325 with a lower thickness than the primary strip 323 is fed onto a support 309 and then into an oven 311. The thickness of the primary strip 323 in this case is 4.0mm, the secondary strip 325 comprises a thickness of 1.8mm.
The oven 311 also comprises means to coil and re-coil the metal strip, this way the metal strip 321 can be moved back and forth through the reversing roller mill 307 by the oven 303 and the oven 311. This way, the thickness of the metal strip 321 can be reduced step by step.
When reaching a desired thickness of the metal strip 321, the secondary strip 325 with this exact thickness can be fed through the oven 311 without re-coiling, thus feeding the metal strip 321 onto a support 313 with a cool waterspray 314 to cool the metal strip. After cooling the metal strip, it is fed onto a coiling device 315, in which the metal strip is re-coiled for further processing or transportation.
A schematic flow of a process 401 for hot-roll-forming a strip of metal is described as follows:
First, heating 403 of the metal strip is performed. Then, introducing 405 of the metal strip into a hot-roll-forming-process takes places. Finally, processing 407 a hot-roll-forming-process is performed, thus a strip of metal with a reduced thickness is presented.

Reference numerals

101: roll-forming-process
103: roller
105: roller
107: rolling mill
121: metal strip
123: initial part
125: compressed part
151: primary thickness
153: secondary thickness
201: roll-forming-process
203: primary roll
205: shield
207: shaft
211: metal strip
213: first part
215: second part
221: guiding rollers
223: guiding rollers
233: secondary roll
235: shield
237: shaft
241: metal strip
251: support rollers
261: support rollers
271: direction
301: roll-forming-process
303: oven
305: support
307: reversing roller mill
309: support
311: oven
313: support
314: waterspray
315: coiling device
321: metal strip
323: primary strip
325: secondary strip
401: process
403: heating
405: introducing
407: processing

Claims

Method for reducing the thickness (151) of a strip of metal (121) by hot-roll-forming (101), wherein the strip of metal (121) comprises a first thickness (151) of 2.0mm up to 5.0mm prior to the process and the strip of metal (123) with the first thickness (151) is processed to a strip of metal (125) with a second thickness (153) of 0.6 mm to 2.5mm by at least one pair of rollers (107), wherein the second thickness (153) is smaller than the first thickness (151), comprising the following steps:
- heating (203, 303) the strip of metal (123) with the first thickness (151) to a temperature above a recrystallization temperature of the metal, thus a pre-heated strip of metal (123) with the first thickness (151) is present,

- introducing the pre-heated strip of metal (123) with the first thickness (151) into the pair of rollers (107), whereas the pair of rollers (107) is adjusted to a distance to reduce the first thickness (151) to the second thickness (153) by roll-forming,

- processing (271) the pre-heated strip of metal (123) with the first thickness (151) through the pair of rollers (107), thus the strip of metal (125) with the second thickness (153) is formed,
thus, the thickness of a strip of metal is reduced.
Method according to claim 1, wherein the first thickness (151) is between 2.5mm and 4.5mm and/or the second thickness (153) is between 1.0mm and 2.0mm, in particular between 1.2mm and 1.8mm.
Method according to claim 1 or 2, wherein the first thickness (151) is reduced to the second thickness (153) by a multi-step process (201, 301), wherein the strip of metal (121, 211) is introduced into and processed by multiple pairs of rollers consecutively.
Method according to claim 3, wherein the multiple pairs of rollers are each adjusted to decreasing distances, thus the multi-step process is realized by each pair of rollers with decreasing distances reducing the thickness of the strip of metal (121) in consecutive steps.
Method according to claim 3 or 4, wherein the multi-step process is performed by a reversing or partly reversing process, wherein the strip of metal (121, 211, 321)) is moved back and forth through one pair of rollers or multiple pairs of rollers consecutively.
Method according to one or more of the previous claims, wherein the pair of rollers (107) or pairs of rollers are presented as tandem mills or Steckel-mills.
Method according to one or more of the previous claims, wherein the strip of metal (121, 211, 321) is de-coiled prior to introducing the metal strip into the pair of rollers (107) or pairs of rollers.
Method according to one or more of the previous claims, wherein the strip of metal (121, 211, 321) is cleaned prior to introducing the strip of metal (121, 211, 321) into the pair of rollers (107) or pairs of rollers, especially by brushing, water pressure, sand blasting or by using acid.
Method according to one or more of the previous claims, wherein the strip of metal (121, 211, 321) is re-coiled prior to processing and/or the strip of metal (125, 215, 325) with the reduced thickness (153) is re-coiled after processing in the pair of rollers (107) or pairs of rollers in a re-coiling device (311, 315).
Method according to one or more of the previous claims, wherein the heating of the strip of metal is performed by induction, wherein electromagnetic fields are induced in the metal and/or by gas, wherein gas is burned to heat the metal with a flame directly or by heating an oven and/or a heating device for the metal.
Method according to one or more of the previous claims, wherein the strip of metal (121, 211, 321) is cooled after its processing in the pair of rollers (107) or pairs of rollers, especially by water cooling (314).
System for roll-forming a strip of metal by hot-roll-forming, comprising at least one pair of rollers (103, 105) for processing a strip of metal (121, 123) comprising a first thickness (151) to a strip of metal (125) with a second thickness (153), set up to perform a method according to one or more of the claims 1 through 11.
System according to claim 12, comprising multiple rollers or multiple pairs of rollers, whereas the multiple rollers or multiple pairs of rollers are set up for processing the strip of metal (123) comprising a first thickness (151) to the strip of metal (125) comprising a second thickness (153) in consecutive steps.
System according to claim 12 or 13, comprising a heating device (303), whereas the heating device (303) is located in proximity to the strip of metal (321) for heating the strip of metal (321).
System according to one of the claims 12 through 14, comprising a cooling device (314), especially a water-cooling device (314), whereas the cooling device is located in proximity to the strip of metal (321) for cooling the strip of metal (321).