MAGNETIC COOLING ROLLER

Abstract

The invention relates to a cooling roller comprising a shaft and a sleeve, said sleeve having a length and a diameter and structured as follows: an inner cylinder, a plurality of magnets arranged along at least a portion of the length of the inner cylinder, each magnet being defined by a width, a height and a length, a cooling system surrounding at least a portion of said plurality of magnets, said cooling system and said plurality of magnets being separated by a space defined by a height, the height of the space being the smallest distance between a magnet and the cooling system above, said magnets having a width such that the following formula is satisfied: height of space x 1.1 = width of magnet = height of space x 8.6.

Description

MAGNETIC COOLING ROLLER The present invention relates to equipment for cooling a continuously moving metal strip. This invention is particularly suitable for cooling steel sheets during metallurgical processes. In a hot steel strip cooling process, cooling the strip with a cooling roller is a common method. Such cooling rollers can be used at various stages of the process, for example, after a furnace or coating bath. The strip cools primarily through thermal conduction between the cooling roller and the strip. However, the effectiveness of this technique is significantly affected by the strip's flatness and the surface contact between the roller and the strip. Strip flatness deteriorates when there is uneven contact between the roller and the strip across the strip's width due to uneven cooling rates. Patent JPH04346628 relates to an apparatus, a roller, for cooling a belt. Within the roller body, magnets are provided continuously or at suitable intervals. Above the magnets is a cooling tube helically wrapped around them, i.e., the cooling system. The outer layer of the roller is preferably coated with Al2Os / ZrO2. Patent JP59-217446 relates to an apparatus, a roller, for cooling or heating a metal strip. The interior of the roller contains a heat transfer medium, the cooling system, although the magnets are arranged on the outer layer of the roller. However, when using the equipment described above, the belt does not maintain sufficient contact with the roller to overcome any potential flatness defects. Consequently, its flatness worsens during cooling, and the belt's quality degrades. Furthermore, the cooling system does not provide sufficient and uniform cooling, resulting in temperature variations across the belt's width, particularly between the edges and the center. Additionally, the arrangement of the cooling roller's components results in a suboptimal heat transfer coefficient. Therefore, there is a need to find a way to reduce or eliminate the uneven contact between the roller and the belt to improve contact uniformity and, consequently, cooling uniformity across the width of the belt. There is also a need to improve the efficiency of the cooling system. The purpose of this invention is to provide a roller that allows a strip to be cooled more homogeneously in its width direction without deteriorating the flatness of the strip. This is achieved by providing equipment according to claim 1. The equipment may also comprise any feature according to claims 2 to 10. This is also achieved by providing methods according to claims 11 to 14. Other features and advantages of the invention will become evident from the following detailed description of the invention. To illustrate the invention, several embodiments and non-limiting example trials will be described, / / ^ζηη / ίζηζ / Β / γι particularly with reference to the following figures: Figure 1 is a cross-sectional view of one type of roller showing a possible arrangement of the different elements. Figure 2 shows one form of a function where it passes through a support medium, i.e., an axis. Figure 3 shows a preferred magnet length compared to the band width. Figure 4 shows the poles of a magnet. Figure 5 shows a preferred orientation of the cooling flows through the cooling channels. Figure 6 shows a possible arrangement of the support media, cooling systems, and means for connecting them. Figure 7 shows a second possible arrangement of the support media, cooling systems, and means for connecting them. Figure 8 shows a possible position of the belt on the cooling roller. Figure 9 shows a possible use of the cooling roller after a coating process. Figure 10 shows a second possible use of the cooling roller in a finishing process. Figure 11 comprises a graph showing the evolution of the temperature discrepancy across the bandwidth. Figure 12 shows the roller surface temperature along its width and a preferred belt position in view of the roller length. Figure 13 shows the influence of the relationship between the width of the magnet and the height of the space between the magnets and the cooling system. As illustrated in Figure 1, the invention relates to a cooling roller 1 comprising a shaft 2 and a sleeve 3, said sleeve having a length and a diameter and is structured from the inside out as follows: - an inner cylinder 4, - a plurality of magnets 5 on the periphery of said inner cylinder arranged along at least a part of the length of the inner cylinder, 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 are separated by a space 7 defined by a height, the height of the space being the smallest distance between a magnet 5 and the aforementioned cooling system 6, - These 5 magnets have a width such that the following formula is fulfilled: space height x 1.1 < magnet width < space height x 8.6. In the prior art, it appears that it is not possible to sufficiently draw the web onto the roller to overcome flatness defects and achieve homogeneous contact. This results in even more uneven flatness and, consequently, a degradation of web quality. Furthermore, the arrangement of the cooling system does not allow for sufficient and homogeneous cooling, thus failing to achieve the desired microstructure and properties. Conversely, with the equipment according to the present invention, it is possible to draw the belt in strongly and sufficiently, overcoming any existing flatness defects. Thus, the belt is cooled without generating flatness defects or irregular properties. Furthermore, the arrangement of the cooling system makes it possible to produce homogeneous cooling across the width of the belt. Advantageously, this space height satisfies the following formula: space height x 1.4 < magnet width < space height x 6.0. It appears that respecting this formula allows for at least 70% of the maximum attraction force. Advantageously, this space height satisfies the following formula: space height x 1.6 < magnet width < space height x 5.0. It appears that respecting this formula allows for at least 80% of the maximum attraction force. Advantageously, this plurality of magnets is arranged along the entire length of the inner cylinder. This arrangement improves the uniformity of the cooling. As illustrated in Figure 1, the magnets are preferably attached to the inner cylinder 4, around its periphery. As illustrated in Figure 2, the inner cylinder 4 preferably comprises means for supporting, rotating, and transporting the cooling roller, preferably positioned on both side faces 8. Such means may be a shaft 2 inserted within holes 9 centered on the axis of rotation of the cylinder 10 on both side faces 8. The cylindrical hole 9 may extend from one side face to the other so that the shaft 2 passes through the cylinder. As illustrated in Figure 3, the magnets 5 are preferably arranged parallel to the axis of rotation of roller 10. Even more preferably, each magnet length 11 is greater than the belt width 12. Such an arrangement appears to increase the uniformity of the belt's attraction to the cooling roller. As illustrated in Figure 4, the north pole is oriented towards the cooling system 6, while the south pole is oriented towards the inner cylinder 4. The height of the magnet can be defined as the distance between the north face 5N and the south face 5S. Advantageously, these magnets are permanent magnets. The use of permanent magnets allows for the creation of a magnetic field without the need for wires or current, simplifying the operation of the cooling roller. Furthermore, permanent magnets appear to create a stronger magnetic field compared to electromagnets. Additionally, electromagnets, while in use, generate an inductive current that heats the roller and the coolant, which seems to decrease cooling efficiency. These magnets can be made of a neodymium-based alloy, such as NdFeB. Advantageously, as illustrated in Figure 5, said cooling system 6 is made of a metallic layer comprising at least two cooling channels 12 through which a coolant can flow. Preferably, said cooling system has a hollow cylindrical shape. y / frznn / Lznz / E / Yi Multiple cooling channels are preferable because the coolant can be easily and frequently renewed, resulting in a lower coolant temperature compared to a single compartment. Cooling system 6 is preferably a casing containing the coolant. Ideally, the cooling system covers at least the entire width of the through-band being cooled, and even more. This allows for greater uniformity of cooling across the entire width. Advantageously, as illustrated in Figure 5, these cooling channels 12 are arranged parallel to the axis of rotation of roller 10. Apparently, this positioning of the cooling channels allows the cooling length of a channel to be shortened so that the coolant temperature at the end of the channel is lower than if the cooling channel were sinuous. This improves coolant efficiency. Advantageously, as illustrated in Figures 6 and 7, the cooling system 6 comprises means for injecting a coolant 13 into said cooling channels 12. Preferably, the means for injecting a coolant 13 are connected to at least one roller support means 2, where the coolant can flow from a system for continuously cooling the coolant (not shown) to the cooling channels 12 by means of at least one support means 2 and the means 13 for injecting a coolant. The cooling system 6 also comprises recovery means 14 for returning the coolant from the cooling channel 12 to a system for continuously cooling the coolant. Consequently, the coolant preferably flows in a closed circuit. Advantageously, as illustrated in Figures 6 and 7, the means 13 for injecting a refrigerant are arranged alternately on either side of the cooling channels 12. As illustrated in Figure 8, the cooling channels 12 are connected alternately to an injection means 13 or a recovery means 14. This alternation improves the uniformity of cooling because the direction of the cooling flow in adjacent channels is opposite. Advantageously, this cooling system surrounds the plurality of magnets. This arrangement improves the uniformity and efficiency of the cooling. Advantageously, as illustrated in Figure 5, the coolant in these cooling channels flows in the opposite direction in adjacent cooling channels. This cooling method allows for more homogeneous cooling across the width of the strip. As illustrated in Figure 8, the invention also relates to a method for cooling a continuously moving belt 15 in an installation according to the invention, comprising the steps of magnetically attracting a portion of said belt to at least one cooling roller 1 and placing said belt 15 in contact with at least one cooling roller 1. This method, combined with the equipment described above, allows the through-belt to be drawn in strongly and sufficiently, overcoming any existing flatness defects. Therefore, the through-belt is cooled without generating flatness defects or irregular properties. Advantageously, at least three cooling rollers are used, and the belt is in contact with at least three cooling rollers simultaneously. This use of multiple rollers allows for good cooling along the entire length of the belt. Advantageously, the belt in contact with the cooling roller has a speed between 0.3 and 20 m.s'1. It appears that because the heat transfer coefficient is increased, the belt needs less contact time with the roller to reach the desired temperature, therefore allowing for a higher roller rotation speed. The following description will refer to two uses of the invention in different installations for cooling a strip using cooling rollers. However, the present invention is applicable to all processes in which a metal strip is cooled, for example, in finishing, galvanizing, packaging, or annealing lines. As shown in Figure 9, in a coating line, at least one cooling roller 1 can be positioned downstream of a coating bath (not shown) and coolers 16 blowing air on either side of the belt 15'. Several cooling rollers 1 can be used depending on the belt speed, the inlet and target belt temperatures, Te and Tt respectively, and the roller surface temperature. In this case, the belt is cooled from an inlet temperature of approximately 250 °C to a target temperature of approximately 100 °C as it exits the last cooling roller. As illustrated in Figure 9, the rollers can be offset slightly toward the side where the belt makes contact with them to maximize the contact area between the rollers and the belt. As shown in Figure 10, in a finishing line, at least one cooling roller 1 may be used after a slow cooling zone 17, where the web 15 is cooled by contact with ambient air, and a fast cooling zone 18, where coolers 16' blow air on either side of the web. Typically, the web enters the slow cooling zone 19 at a temperature of approximately 800 °C and then, depending on the grade, the inlet temperature, Te, is between 400 and 700 °C just before contacting the first cooling roller, and the target temperature, Tt, is approximately 100 °C. Experimental results In order to evaluate the benefits of this invention and show that it reduces or at least does not increase the temperature difference across the bandwidth, several results are shown and explained. The experimental results were obtained using the following roller and belt: Roller dimensions and characteristics: - The inner cylinder has a length of 1400 mm and a diameter of 800 mm, made of carbon steel. - The manes are composed of NdsFeuB and arranged parallel to the rotation axis of the roller with a height of 30 mm and a width of 30 mm, separated by 2 mm spaces arranged around and on the inner cylinder. The cooling system is made of stainless steel. The cooling channels are arranged parallel to the roller axis. Coolant flows into the cooling channels from their sides. Coolant is injected into these channels from opposite sides of consecutive channels, resulting in opposite coolant flow directions in adjacent channels. - The height of the space between the magnetic layer and the cooling system is 10 mm. - The speed of the belt can vary from 0.3 to 20 m.s'1. The band is 1090 mm wide and is made of steel. Example 1 To verify that the temperature is more homogeneous after than before passing through the cooling roller, the temperature difference between the temperature extremes along the width of the belt before and after cooling by the cooling roller is compared. If the difference between the hottest and coldest points across the width of the belt is 20°C before passing the cooling roller and 10°C after the cooling roller, then the temperature difference is 10°C. If the difference between the hottest and coldest points across the width of the belt is 20°C before passing the roller and 30°C after the roller, then the temperature difference is -10°C. This means that the temperature interval difference obtained is greater than 0, indicating increased temperature homogeneity across the bandwidth. Furthermore, the greater the temperature interval difference, the greater the improvement in temperature homogeneity. From the graph in Figure 11, it is clear that temperature homogeneity across the bandwidth is improved after cooling. The vertical axis represents the temperature difference values, all above 0, and the vast majority above 40 °C. Therefore, the temperature difference between the hottest and coldest points across the bandwidth has been reduced by at least 40 °C in the vast majority of cases. This result is a clear improvement compared to prior art results. Example 2 To verify the improved temperature uniformity across the width of the belt, the roller's temperature profiles were measured along different widths 11', as shown in Figure 12. The temperature is uniform along the section in contact with the belt width 12'. Consequently, the belt cools uniformly in the width direction, so that the edge and center of the belt width are at the same temperature. This result clearly demonstrates the expected results of this invention and an improvement compared to the prior art. Example 3 To evaluate the relationship between the height of the space and the width of the magnet, the attraction force generated by the magnets on the outer surface of the roller is determined based on this ratio. From this graph, plotted in figure 13, it is clear that the optimal interval is for a proportion that is governed by this equation: i / frznn / Lznz / E / Yii space height x 1.1 < magnet width < space height x 8.6, corresponding to approximately 50% of the maximum attraction force.

Claims

1. A cooling roller (1) comprising a shaft (2) and a sleeve (3), said sleeve having a length and a diameter comprising, from the inside out: - an inner cylinder (4), - a plurality of magnets (5) on the periphery of said inner cylinder arranged along at least a part of the length of the inner cylinder, each magnet being defined by a width, a height and a length, - a cooling system (6) surrounding at least a part of said plurality of magnets (5), - said cooling system and said plurality of magnets being separated by a space (7) defined by a height, the height of the space being the smallest distance between a magnet (5) and the cooling system (6) above, - said magnets (5) having a width such that the following formula is satisfied: space height x 1.1 < magnet width < space height x 8.

6.

2. The equipment according to claim 1, wherein said magnets (5) are permanent magnets.

3. The equipment according to any of claims 1 or 2, wherein said cooling system (6) is made of a metal part comprising at least two cooling channels (12) through which a coolant can flow.

4. The equipment according to claim 3, wherein said cooling channels (12) are arranged parallel to the height of the cooling roller.

5. The equipment according to claim 3, wherein the cooling system (6) comprises means (13) for injecting a coolant into said cooling channels (12).

6. The equipment according to claim 5, wherein said means (13) for injecting a coolant are arranged alternately on both sides of the cooling channels (12).

7. The equipment according to any of claims 1 to 6, wherein said magnet width satisfies the following formula: space height x 1.4 < magnet width < space height x 6.

0.

8. The equipment according to claim 7, wherein said magnet width meets the following formula: space height x 1.6 < magnet width < space height x 5.

0.

9. The equipment according to any of claims 1 to 8, wherein said plurality of magnets is arranged along the entire length of the inner cylinder.

10. The equipment according to any of claims 1 to 9, wherein said cooling system (6) surrounds said plurality of magnets (5).

11. A method for cooling a continuously moving metal strip in an installation according to claims 1 to 8, comprising the steps of magnetically attracting a portion of said strip (15) to at least one cooling roller (1) and bringing said strip (15) into contact with at least one cooling roller (1).

12. The method according to claim 11, wherein at least three cooling rollers (1) are used and said belt (15j) is in contact with at least three cooling rollers (1) at the same time.

13. The method according to any of claims 11 to 12, wherein said belt in contact with the cooling roller has a speed of between 0.3 and 20 ms-1.

14. The method according to any of claims 11 to 13, wherein such a cooling system (6) is made of a metal part comprising at least two cooling channels (12) through which a coolant can flow, the coolant flowing in said cooling channels (12) in opposite directions in adjacent cooling channels (12).