The present invention relates to an equipment for cooling down a continuously moving metallic strip. This invention is particularly suited for the cooling of steel sheets, during metallurgical processes.
In a hot steel strip cooling process, cooling the strip with a cooling roll is a known process. Such cooling rolls can be used at various step of the process, e.g.: downstream a furnace or a coating bath. The strip is majorly cooled down due to the thermal conduction between the cooled cooling roll and the strip. However, the efficiency of such a technique is greatly impacted by the flatness of the strip and the surface contact between the roll and the strip. The strip flatness is worsened when there is a contact unevenness between the roll and the strip along the strip width due to uneven cooling rates.
Patent JPH04346628 relates to an apparatus, a roll, for cooling down a strip. Magnets are provided inside a roll body continuously or at suitable intervals. Over the magnets, there is one cooling tube wrapped helicoidally around the magnets, the cooling system. The outer shell of the roll is preferably coated with Al2O3/ZrO2.
Patent JP59-217446 relates to an apparatus, a roll, for cooling or heating a metallic strip. The inside of the roll holds a heat carrier, the cooling system, while magnets are disposed in the outer shell of the roll.
However, by using the above equipment, the strip is not sufficiently in contact with to the roll in order to overcome the potential flatness defects of the strip and thus its flatness is worsened during the cooling and the quality of the strip is consequently degraded. Moreover, the cooling system does not permit to sufficiently and homogeneously cool the strip leading to temperature variations along the strip width, especially between the edges and the center of the strip. Furthermore, due to the arrangement of the different parts of the cooling roll, the heat transfer coefficient is not optimal.
Consequently, there is a need to find a way to reduce or suppress the contact unevenness between the roll and the strip in order to improve the contact homogeneity and thus the cooling homogeneity along the strip width. There is also a need to improve the efficiency of the cooling system.
It is an object of the present invention to provide a roll permitting to cool down a strip more homogeneously in its width direction without deteriorating the flatness of said strip.
The present invention provides a cooling roll (1) comprising an axle (2) and a sleeve (3), said sleeve having a length and a diameter comprising, from the inside to the outside:
an inner cylinder (4),
a plurality of magnets (5) on the periphery of said inner cylinder disposed along at least a portion of the inner cylinder length, each magnet being defined by a width, a height and a length,
a cooling system (6) surrounding at least a portion of said plurality of magnets (5),
said cooling system and said plurality of magnets being separated by a gap (7) defined by a height, the gap height being the smallest distance between a magnet (5) and the cooling system above (6),
said magnets (5) having a width such that the following formula is satisfied:
gap height×1.1≤magnet width≤gap height×8.6.
The present invention also provides a method for cooling a continuously moving metallic strip, in an installation as described, comprising the steps of attracting magnetically a portion of said strip (15) to at least one cooling roll (1) and putting said strip (15) in contact with the at least one cooling roll (1).
Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention.
To illustrate the invention, various embodiments and trials of non-limiting examples will be described, particularly with reference to the following figures:
As illustrated in
an inner cylinder 4,
a plurality of magnets 5 on the periphery of said inner cylinder disposed along at least a portion of the inner cylinder length, each magnet being defined by a width, a height and a length,
a cooling system 6 surrounding at least a portion of said plurality of magnets 5,
said cooling system and said plurality of magnets being separated by a gap 7 defined by a height, the gap height being the smallest distance between a magnet 5 and the cooling system above 6,
said magnets 5 having a width such that the following formula is satisfied:
gap height×1.1≤magnet width≤gap height×8.6.
In the prior art, it seems that it is not possible to sufficiently attract the strip to the roll in order to overcome the flatness defects and obtain a homogeneous contact. This results in an even more uneven flatness and so a downgrade of the strip quality. Moreover, the arrangement of the cooling system does not permit to perform a sufficient and homogeneous cooling, failing to achieve the desired microstructure and properties.
On the contrary, with the equipment according to the present invention, it is possible to strongly and sufficiently attract the strip, overcoming the existing flatness defects. Thus, the strip is cooled down without engendering flatness defects or uneven properties. Moreover, the arrangement of the cooling system renders possible the production of a homogeneous cooling along the strip width.
Advantageously, said gap height satisfies the following formula:
gap height×1.4≤magnet width≤gap height×6.0.
It seems that respecting this formula allows to have at minimum 70% of the maximal attractive force.
Advantageously, said gap height satisfies the following formula:
gap height×1.6≤magnet width≤gap height×5.0.
It seems that respecting this formula allows to have at minimum 80% of the maximal attractive force.
Advantageously, said plurality of magnets is disposed along the whole inner cylinder length. Such an arrangement enhances the homogeneity of the cooling.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
Advantageously, said magnets are permanent magnets. The use of permanent magnets permits to create a magnetic field without requiring wires or current, easing the management of the cooling roll. Moreover, it seems that the permanent magnets create a stronger magnetic field compared to electro-magnets. Furthermore, electro-magnets while in use generate an inductive current heating the roll and the coolant which seems to lower the cooling efficiency. Said magnets can be made of a Neodymium based alloy, NdFeB for example.
Advantageously, as illustrated in
Advantageously, as illustrated in
Advantageously, as illustrated in
Advantageously, as illustrated in
Advantageously, said cooling system surrounds said plurality of magnets. Such an arrangement enhances the homogeneity and performance of the cooling.
Advantageously, as illustrated in
As illustrated in
Such a method combined with the equipment previously described permits to strongly and sufficiently attract the passing strip overcoming the existing flatness defects. Thus, the passing strip is cooled down without engendering flatness defects or uneven properties.
Advantageously, at least three cooling rolls are being used and said strip is in contact with the at least three cooling rolls at the same time. Such a use of several rolls enables a good cooling along the strip.
Advantageously, said strip in contact with the cooling roll has a speed comprised between 0.3 m.s−1 and 20 m.s−1. It seems that because the heat transfer coefficient is increased, the strip needs less time contact on the roll to achieve the desired temperature hence the possibility to work with higher roll speed rotation.
The following description will concern two uses of the invention in different installations for the cooling of a strip using cooling rolls. But, the present invention is applicable to every process where a metallic strip is cooled e.g. in the finishing, galvanisation, packaging or annealing lines.
As represented
As represented
Experimental Results
In order to assess the benefits of this invention and show that it reduces or at least it does not increase the temperature difference along the strip width, several results are showed and explained.
The experimental results have been obtained using the following roll and strip:
Roll dimensions and characteristics:
The inner cylinder is 1400 mm long and has a diameter of 800 mm made of carbon steel.
The magnets are composed of Nd2Fe14B and disposed parallel to the roll rotation axis having a height of 30 mm and a width of 30 mm, separated by gaps of 2 mm disposed around and on the inner cylinder
The cooling system is made of stainless steel. The cooling channels are disposed parallel to the axis of the roll. Moreover, the coolant is flowed in the cooling channels from their lateral sides. Injections of the coolant in said cooling channels are done at the opposite side of consecutive cooling channels permitting to have opposite coolant flow directions in adjacent cooling channels.
The gap height between the magnetic layer and the cooling system is of 10 mm.
The strip speed can be varied from 0.3 to 20 m.s−1.
The strip is 1090 mm wide and made of steel.
In order to verify that the temperature is more homogeneous after than before the cooling roll, the temperature difference between the temperature extremums along the strip width is compared before and after its cooling by the cooling roll.
If the difference between the hottest and the coldest point along the strip width is of 20° C. before the cooling roll and is of 10° C. after the cooling roll then the temperature gap difference is of 10° C. If the difference between the hottest and the coldest point along the strip width is of 20° C. before the roll and is of 30° C. after the roll then the temperature gap difference is of −10° C.
This means that the obtained temperature gap difference is superior to 0 then the temperature homogeneity along the strip width has been increased. Moreover, higher is the temperature gap difference value, better is the temperature homogeneity improvement.
It is clear from the reading of the graph, in
In order to verify the improvement of the temperature homogeneity along the strip width, the roll temperature profiles along different width 11′ has been measured, as it can be seen in
In order to assess the ratio between the gap height and the magnet width, the attraction force generated by the magnets on the outer surface of the roll is determined in function of this ratio.
From this graph, plotted in
gap height×1.1≤magnet width≤gap height×8.6, corresponding to approximately 50% of the maximum attraction force.
Number | Date | Country | Kind |
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PCT/IB2018/056831 | Sep 2018 | WO | international |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2019/057256 | 8/28/2019 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2020/049418 | 3/12/2020 | WO | A |
Number | Name | Date | Kind |
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4993478 | George, II | Feb 1991 | A |
5665177 | Fukuno et al. | Sep 1997 | A |
5728036 | Kagan et al. | Mar 1998 | A |
20100219567 | Imanari | Sep 2010 | A1 |
Number | Date | Country |
---|---|---|
S59217446 | Dec 1984 | JP |
S6199634 | May 1986 | JP |
S639577 | Mar 1988 | JP |
04346628 | Dec 1992 | JP |
H04346628 | Dec 1992 | JP |
H05269549 | Oct 1993 | JP |
H0741978 | Feb 1995 | JP |
H1017184 | Jan 1998 | JP |
2175587 | Nov 2001 | RU |
427062 | May 1974 | SU |
688523 | Sep 1979 | SU |
WO2013028925 | Feb 2013 | WO |
Entry |
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Machine Translation of JP-04346628-A (Year: 1992). |
International Search Report of PCT/IB2019/057256, dated Nov. 25, 2019. |
Number | Date | Country | |
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20210332455 A1 | Oct 2021 | US |