A hot dip coating device with stabilizing means and a method of coating using a hot dip coating device

Abstract

A hot dip coating device 19 for providing a metal coating on a metal strip 2, comprising, a second container 22 comprising a second liquid metal bath 18 of a second metal coating material in use; a snout 50 for guiding the metal strip 2 into the second liquid metal bath 18 comprising a lower opening 39 immersed in the second liquid metal bath 18 wherein the hot dip coating device 19 further comprises at least two stabilisers 100 on each side of the metal strip such that the at least two stabilisers form a first container 220 within the second container 22. The first container 220 comprises a first liquid metal bath 180 of a first metal coating material in use. The lower opening 39 of the snout encloses the upper portion 100a of the pair of stabilisers.

Description

Field of the invention

[0001] The present invention relates to a hot dip coating device for providing a metal coating on a metal strip. In a further aspect the present invention relates to a method of coating using a hot dip coating device.Background of the invention

[0002] Hot dip coating is a well-known process for protecting a steel product against corrosion. An example of a hot dip coating device is a hot dip galvanizing device. A hot dip coating device is used to provide a metal coating such as zinc or aluminum on a moving metal strip. The hot dip coating device typically comprises a container for a liquid metal bath that contains the coating material in use. The coating layer can be a single layer or multiple layers that are coated on the metal strip in a single process or in multiple processes. The coating material can be a first coating layer or an intermediate coating layer prior to a final coating layer or a final coating layer. For some applications the coating material may consist almost entirely of zinc (>99%) known as GI coatings or almost entirely of aluminium (>99%). For other applications, the use of zinc coatings or aluminium coatings alloyed with other metals such as magnesium or silicon is used, which is advantageous owing to their improved corrosion resisting performance and improved pressing performance. In the context of the present invention, the metal strip is also called a metal sheet.

[0003] To guide the metal strip from a previous furnace into the hot dip coating device, several rolls can be present in the furnace. The last roll or rolls to guide the metal strip into the hot dip coating device is known as a hot bridle. A snout is a duct that is placed between the hot bridle and the metal bath surface, as part of a hot dip coating device. Typically at least one supporting roll is also provided in the liquid metal bath to influence the shape of the metal sheet in its width direction. This supporting roll may be provided between the sink roll and the surface level of the liquid bath at the side of the gas knife. Generally, the snout is one of the last pieces of a furnace that guides a steel strip into a liquid metal bath in the hot dip coating device. The snout is typically rectangular in cross section, but it is also possible for a snout to have a different cross section other than being rectangular. The lower part of the snout has an opening that is immersed in the liquid metal bath, during its use. The metal strip or the metal sheet passes through this opening into the liquid metal bath. The snout shields the annealed steel strip from an open atmosphere, which is necessary to avoid oxidation and to maintain the strip temperature. The atmosphere in the snout is generally dry and this dry atmosphere is known to lead to metal evaporation. For a hot dip coating device such as a hot dip galvanizing device, this dry atmosphere leads to zinc evaporation. The zinc evaporation results in condensation of zinc against the snout walls which, in turn, leads to formation of zinc dust against the walls that can fall on to the steel strip or on to the zinc bath surface which leads to coating defects. The evaporation of zinc is limited by moistening the atmosphere inside the snout directly above the liquid zinc surface. This creates an oxide layer that limits the zinc evaporation.

[0004] It is known that in a continuous galvanizing line, the molten zinc bath is mostly saturated with iron, which dissolves from the steel strip that is continuously passed through the bath. The molten zinc bath may also contain unwanted particles such as oxide particles that are formed when oxygen in the surrounding air oxidises the liquid metal. Such oxide particles typically stay in the top layer of the liquid metal. Further, at the operating temperature of the liquid metal bath, dissolution of iron from the steel strip into the metal bath can occur that forms intermetallic particles. These intermetallic particles as well as the oxide particles are known as dross. Dross present on the surface of the liquid metal bath or that rises to the surface if present underneath the surface is known as surface dross or floating dross or top dross. Since the lower part of the snout is immersed in the liquid metal bath, the liquid metal bath that is present within the snout also contains dross such as surface dross. If not properly controlled, the surface dross within the snout will be collected by the moving metal strip, which will have detrimental effects on the final products that are manufactured from the steel strips. For example, small dross particles may be incorporated in the coated alloy layer and affect the appearance of the coated steel parts. This is particularly disadvantageous for steel strips, from which exterior automotive parts are shaped by pressing. The included particles may cause inhomogeneous deformation resulting in surface defects and irregularities such as tiny projections and bulges, even when present at the non-exposed side of the automotive parts. The unevenness in the surface of the steel parts results in undesired reflections that affect the appearance in an unacceptable way. Surface defects are also related to a different dynamic wetting process when the steel strip moves into the zinc bath in the snout of a hot dip coating device. A vibration of the moving metal strip will make wetting more difficult and has an effect on the entrainment of surface debris or surface dross. Since the metallic coating is applied after the hot dip coating step, the applied coating should fulfil requirements such as that the metal layer has to be without any dross or debris. This is important not only to be able to subject the coated steel strip to forming operations but also for the appearance of the final steel product formed from the coated steel strip. The moving metal strip in this context is also called a metal strip.

[0005] The surface debris or surface dross that floats on the metal bath surface in the snout is similar to a floating fleece. The surface dross has a mechanical strength. By getting exposed to mechanical disturbance the surface dross get loose and will be picked up by the moving metal strip. Typically these mechanical disturbances are enhanced by vibrations or instability of the moving metal strip perpendicular to the travel direction of the moving metal strip. If the strip is unstable in the snout due to its vibrations that are typically perpendicular to the travel direction of the steel strip, then the surface dross will be detached from the floating fleece. The detached surface dross will be easily picked up by the moving metal strip, which will contaminate a subsequent coating process. Also, a stable strip will lead to less generation of free zinc surface that can evaporate or oxidise, thus reducing the formation of further oxidic dross.

[0006] In addition to this, for some applications it is beneficial to coat the steel strip with an inhibition layer or a reaction layer before coating with the coating material from the liquid metal bath. A dual bath system comprising two baths may be used for coating a reaction layer followed by a metallic coating layer, in a single process step. Such processes having dual baths also require reduction in vibrations of the moving metal strip within the snout for reducing the mechanical disturbances. This will eventually reduce coating contamination and defects in the coated metal strip and will lead to a homogenous coating. Prior art documents describe methods to remove surface dross from the liquid metal bath within the snout. However, it is also required that the surface dross present within the snout, especially the surface dross that is present close to the moving strip entering the bath or baths, does not have any exposure to mechanical disturbance. If there is exposure to mechanical disturbance, it can lead to a breakup of the dross fleece near the moving strip and will result in a subsequent dross pickup by the moving strip.Objectives of the invention

[0007] It is therefore an object of the invention to reduce the vibration of the moving metal strip before entering a liquid metal bath within a snout.

[0008] It is also an object of the invention to avoid picking up of any surface dross by a moving metal strip within a snout in a commercial galvanizing section.

[0009] It is also an object of the invention to improve the wettability of a steel strip in a hot dip coating device.

[0010] It is also an object of the invention to reduce the vibration of the moving metal strip before entering a dual liquid metal bath system.Description of the invention

[0011] One or more of these objectives are reached with a hot dip coating device for providing a metal coating on a moving metal strip according to the attached claims. In the first aspect, there is described a hot dip coating device for providing a metal coating on a moving metal strip. The hot dip coating device comprises a second container holding a second liquid metal bath of a second metal coating material in use. The hot dip coating device further comprises a snout for guiding the metal strip into the second liquid metal bath comprising a lower opening immersed in the second liquid metal bath. The hot dip coating device further comprises at least two stabilisers on each side of the metal strip such that the at least two stabilisers form a first container within the second container. The first container holds a first liquid metal bath of a first metal coating material in use. The lower opening of the snout encloses the upper portion of the pair of stabilisers. The second container holds a second liquid metal bath of a second metal coating material that can be coated on the moving metal strip or the metal sheet. The at least two stabilisers can be a pair of stabilisers that are positioned on both sides of the moving metal strip in such a way that on usage, the pair of stabilisers form a first container within the second container. The first container holds a first liquid metal bath of a first metal coating material that can be coated on the moving metal strip. The lower opening of the snout encloses the upper portion of the at least two stabilisers so that the first container is only partially immersed in the second container. The moving metal strip passes from the snout directly into the first container where a first metal coating material is applied on the metal strip before it enters the second container. On entering the second container a second coating material is coated on the metal strip, which is already coated with the first coating material. The lower opening of the snout is immersed in the second liquid metal bath. The moving metal strip passes from the snout into the second liquid metal bath through the first liquid metal bath. The immersed portion of the snout encloses the first liquid metal bath within it and also encloses a part of the second liquid metal bath. The at least two stabilisers are placed as opposing stabilisers on both sides of the metal strip so that they rely on the pressure built up by the flow induced by the moving metal strip. As the molten metal such as zinc has a much higher density than air, the pressure that is build up in the molten metal bath or the zinc bath dampens the vibrations effectively and flattens the strip thereby reducing strip vibration. This reduced or dampened vibrations of the moving steel strip perpendicular to the strip travel direction, prevents picking up of surface dross from within the snout. Typically a sink roll is provided in the second container below the surface level of the second liquid metal bath in use to guide the metal strip out of the liquid metal bath. The at least two stabilisers are placed in between the snout and a sink roll of the hot dip coating device.

[0012] US patent application US2019 / 0032188A1 discloses hydrodynamic stabilisation of a travelling metal strip after exiting the liquid metal bath of a hot dip coating device. These stabilisers are mainly used for increasing the drying process of the coated metal after hot dip coating. US patent application US2010 / 0140985 A1 discloses at least one supporting roll that is in the form of a stabilizer roll and / or a correcting roll within the metal bath between the sink roll in the bath and the gas knife above the bath. It also discloses at least one supporting roll that is positioned above surface level of the liquid bath at the location before the metal sheet enters the liquid metal bath to maintain a desired shape of the metal sheet. None of the prior art documents disclose any solution to stabilise a moving strip within the snout before it enters a liquid metal bath. European patent application EP2954087B1 discloses a dual metal bath system for a hot dip coating device. The dual bath system is used for coating a metallic product first by a metallic alloy layer followed by a metallic surface layer, in one process step where the metallic alloy layer and the metallic surface layer have different chemical compositions. However, EP2954087B1 is silent on how a moving strip can be stabilised within the snout so that its vibrations perpendicular to its travelling direction can be reduced. The present invention differs from the disclosures of EP2954087B1; as the present invention discloses a dual metal bath system where the moving metal strip is also stabilised within the snout.

[0013] The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example of such a layer is Fe 2 Al 5 barrier layer. The first metal coating material can be coated for a thickness that is less than 10 µm, preferably less than 8 µm, more preferably less than 6 µm, even more preferably less than 4 µm. In some embodiments, the first metal coating material can be coated for a thickness that is less than 3 µm, preferably less than 2 µm. As the first coating layer typically acts as an inhibition layer or a reaction layer, lower thicknesses are preferred.

[0014] In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The coating can be also applied in a continuous process by passing the sheet steel through a molten bath with a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally 5-15 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon (AlSi) coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating (including the Fe 2 Al 5 barrier layer) preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % Magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0015] When the first liquid metal bath and the second liquid metal bath comprises metal coating materials of different chemical composition, then there will be a transition region between the first metal coating material and the second metal coating material. This continuous transition region is typically less than 2 µm, preferably less than 1.5 µm and more preferably less than 1 µm. The metal strip is continuously transferred from the first liquid metal bath to the second liquid metal bath so that the metal coating is performed in a single surface coating process. The subsequently coated second metal coating material comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. In another embodiment, the second metal coating material in use comprises a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy, an aluminium silicon magnesium alloy. In another embodiment, the second metal coating material can also contain zinc - aluminium or zinc - aluminium - magnesium alloys but with for example having a higher content of aluminium. When coated, the second metal coating material has a thickness that is higher than 3 µm, preferably higher than 5 µm and more preferably higher than 6 µm. In some embodiments, the second liquid metal bath that is used to coat a second metal coating material on the moving metal strip can be a molten bath having a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally 5-15 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0016] The hot dip coating device further comprises at least two stabilisers on each side of the metal strip such that the at least two stabilisers form the first container within the second container. The lower opening of the snout encloses the upper portion of the pair of stabilisers or the upper portion of the first container. Typically the lower portion of the snout is tapered and it is immersed in the liquid metal bath during its use. For some applications, the opening at the lower portion of the snout may have a circular or rectangular cross section. From the snout, the moving metal strip enters the first liquid metal bath in the first container formed by the at least two stabilisers. The lower portion of the at least two stabilisers forms an opening through which the moving steel strip is transferred from the first metal bath to the second metal bath. However, if the opening at the lower portion of the at least two stabilisers is very narrow, the moving steel strip has less space for its travel. Moreover, if the moving metal strip vibrates perpendicular to its travel direction within this narrow opening then the metal strip can hit the walls of the at least two stabilisers. Hence, there needs to be enough room for the moving metal strip to avoid hitting to the walls of the at least two stabilisers. In one embodiment of the present invention, the lower portion 100b of the at least two stabilisers forms an opening, wherein the distance between the stabilisers is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm. This reduced distance between the opening reduces the risk of hitting the walls of the at least two stabilisers by the moving metal strip.

[0017] In one embodiment of the present invention the at least two stabilisers are pads. The pads are made of a non-corrosive material in order to withstand any corrosion from the compositions of both the first metal bath and the second metal bath. Preferably the at least two stabilisers are stainless steel pads or tungsten pads. The pads are rigid structures. The thickness of the pads are typically in the range of 5-10 mm. In another embodiment of the present invention the at least two stabilisers are foils. Preferably the at least two stabilisers are stainless steel foils or tungsten foils. The foils are also made of a non-corrosive material in order to withstand any corrosion from the compositions of both the first metal bath and the second metal bath. The thickness of the foils can be typically in the range of 0.01 mm to 2 mm. The thickness of the foils can be preferably in the range of 0.03 mm to 1 mm or even preferably in the range of 0.05 mm to 0.5 mm. The foils are comparatively more flexible than pads. Also, the thickness of the foils is less than the thickness of the pads.

[0018] The surface bath level of the first liquid metal bath and the surface bath level of the second liquid metal bath need not be in the same level. In one embodiment of the present invention the upper portion of the at least two stabilisers is above the surface bath level of the liquid metal bath. This ensures that the first liquid metal bath and the second liquid metal bath will not mix excessively.

[0019] Prior art documents describe electromagnetic stabilisers that are used for reducing vibrations of a steel strip after exiting the liquid metal bath of a hot dip coating device. Typically an electromagnetic stabilizer consists of an electromagnet, an eddy-current type displacement sensor, a control unit, and a power unit. In such an arrangement, the electromagnet of the electromagnetic stabilizer is placed near the surface of the steel strip. Vibration are detected by the sensor, which activates the magnet to keep the steel strip flat and vibration-free. Electromagnets with dynamically controlled power amplifiers are used to correct and stabilise position and to limit strip vibrations. In this manner a majority of frequencies are damped to a level that is close to a noise spectrum. In a further aspect the present invention relates to a hot dip coating device for providing a metal coating on a metal strip where a pair of electromagnetic stabilisers are placed within the snout, above the first liquid metal bath and the second liquid metal bath. The hot dip coating device comprises a first container holding the first liquid metal bath of a first metal coating material in use and a second container holding the second liquid metal bath of a second metal coating material in use; wherein the first container is within the second container. The hot dip coating device further comprises a snout for guiding the metal strip into the second liquid metal bath through the first liquid metal bath wherein the snout comprises a lower opening that is immersed in the first liquid metal bath. The hot dip coating device also comprises at least two electromagnetic stabilisers provided within the snout, on each side of the metal strip; wherein the at least two electromagnetic stabilisers are above the first liquid metal bath and the second liquid metal bath. In this way the at least two electromagnetic stabilisers are not in fluidic contact with the first liquid metal bath and the second liquid metal bath. As described earlier, if the opening at the lower portion of the first container is very narrow, then the moving metal strip has less space for its travel. Further, if the moving metal strip vibrates perpendicular to its travel direction then it can hit the walls of the first container. Hence, there need to be enough room for the moving metal strip to avoid hitting to the walls of the first container. In one embodiment of the present invention the distance between the walls of the opening in the first container is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm. This substantially reduces the risk of the moving metal strip hitting the walls of the first container.

[0020] For industrial applications, it is often required that the at least two stabilisers stabilise the moving metal strip continuously during the continuous process of hot dip coating. On a commercial scale in the steel industry, for example for a hot dip galvanizing line, a single galvanizing bath is continuously operated for time periods of some weeks up to several months, before any shut down occurs in view of a necessary maintenance and replacement. In practice such a galvanizing line is used to produce galvanized steel strips of different qualities in consecutive runs. In particular a switch from producing steel strips that meet less stringent quality requirements to steel strips for high demanding end purposes is complicated and critical. After such a switch of production, if the freshly produced steel strip does not meet the required higher standards, it will likely be rejected. Hence, there is also a requirement for a continuous stabilisation of the moving metal strip before that entering the liquid metal bath so that it will not affect the quality of steel production if switch of production occurs. If the stabiliser is not able to continuously stabilise the moving metal strip, the moving metal strip will easily pick up surface dross. For other applications it may also needed to occasionally remove the stabilisers for various purposes such as maintenance, cleaning or for replacement. In one embodiment of the invention, the at least two stabilisers or the at least two electromagnetic stabilisers are removably mounted within the snout to accommodate replacement and / or maintenance.

[0021] The moving metal strip or the metal sheet enters from the snout into the first liquid metal bath. As described previously, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip. The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example for this is Fe 2 Al 5 barrier layer. The first metal coating material can be coated for a thickness that is less than 10 µm, preferably less than 8 µm, more preferably less than 6 µm, even more preferably less than 4 µm. In some embodiments, the first metal coating material can be coated for a thickness that is less than 3 µm, preferably less than 2 µm. When the first liquid metal bath and the second liquid metal bath comprises metal coating materials of different chemical composition, then there will be a continuous transition region between the first metal coating material and the second metal coating material. The continuous transition region is less than 2 µm, preferably less than 1.5 µm and more preferably less than 1 µm. The metal strip is continuously transferred from the first liquid metal bath to the second liquid metal bath so that the metal coating can be done in a single surface coating process.

[0022] In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. In another embodiment of the present invention the first liquid metal bath of the first metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or wherein the first liquid metal bath of the first metal coating material is from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy. The coating can be also a hot-dip galvanized coating applied in a continuous process by passing the steel sheet through a molten bath with a zinc content of at least 99%. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99% and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13% by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0023] The subsequently coated second metal coating material comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The second liquid metal bath of the second metal coating material in use may also comprise a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy, an aluminium silicon magnesium alloy. In one embodiment of the present invention the second liquid metal bath of the second metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy or wherein the second liquid metal bath of the second coating material is from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy. When coated, the second metal coating material has a thickness that is higher than 3 µm, preferably higher than 5 µm and more preferably higher than 6 µm. The second metal coating can be also a hot-dip galvanized coating applied in a continuous process by passing the steel sheet through a molten bath with a zinc content of at least 99%. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99% and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13% by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 %. aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0024] Any moving part present within the snout will create extra flows in the bath or attract zinc dust that is present in the snout wall. Rotating parts are additionally costly as they have to be regularly maintained. Often the bearings of the moving parts has to be occasionally replaced. In one embodiment of the present invention the at least two stabilisers are arranged such that a fixed facing surface of each of the stabilizer is placed on each side of the metal strip. This reduces the presence of moving parts present within the snout. The pads or the foils or the electromagnetic stabilisers have a fixed facing surface that is placed on each side of the metal strip. In another embodiment of the present invention, the at least two stabilisers are placed between hot bridle and the sink roll.

[0025] In another aspect, the present invention relates to a method of coating a metal strip using a hot dip coating device as described above. The method comprises passing the metal strip through the at least two stabilisers for stabilising the metal strip; coating the metal strip with a first metal coating material from a first container of the hot dip coating device; and coating the metal strip with a second metal coating material from a second container of the hot dip coating device. The moving metal strip is passed through the at least two stabilisers as described above. The at least two stabilisers can be a foil or a pad or an electromagnetic stabiliser that is placed within the snout. When the at least two stabilisers are pads or foils, they are formed as the first metal bath itself. The moving metal strip is coated with a first metal coating material from a first container of the hot dip coating device and then coated with a second metal coating material from a second container of the hot dip coating device. The second metal coating material is coated subsequent to the coating of the first metal coating material. The first liquid metal bath of the first metal coating material in use, or the second liquid metal bath of the second metal coating material in use, comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy an aluminium silicon magnesium alloy. Similarly, the second liquid metal bath of the second metal coating material in use, comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or wherein the second liquid metal bath of the second metal coating material in use is a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy an aluminium silicon magnesium alloy. In one embodiment of the present invention the first liquid metal bath of the first metal coating material or the second liquid metal bath of the second material coating material is a liquid bath of a the zinc alloy coating comprising 3 - 4.0% Mg and.3 - 6.0% Al; optionally at most.% of one or more additional elements; unavoidable impurities; the remainder being zinc. In an even further embodiment of the present invention, the first liquid metal bath of the first metal coating material is a liquid bath of an aluminium-silicon coating comprising 8 to 11 % of silicon. The hot dip coating device as described above or the method of coating a metal strip using a hot dip coating device as described above comprises the first liquid metal bath of the first metal coating material or the second liquid metal bath of the second material coating material having a liquid bath of a zinc alloy coating comprising 0.3 - 4.0% Mg and 0.3 - 6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example for this is Fe 2 Al 5 barrier layer. In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The coating can be also a hot-dip galvanized coating applied in a continuous process by passing the sheet steel through a molten bath with a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating (including the Fe 2 Al 5 barrier layer) preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0-2.0 % magnesium and 1.0-3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment the zinc alloy coating comprises at most 1.6% Mg and between 1.6 and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.Brief description of the drawings

[0026] The invention is further explained by the following figures. FIG. 1 shows a schematic representation of a hot dip coating device. FIG. 2 shows a schematic representation of an embodiment of a hot dip coating device with at least two pads. FIG. 3 shows a schematical view of the at least two pads of FIG. 2. FIG. 4 shows a schematic representation of another embodiment of a hot dip coating device with a at least two foils. FIG. 5 shows a schematical view of the at least two foils of FIG. 4. FIG. 6 shows a schematic representation of an even further embodiment of a hot dip coating device with a pair of electromagnetic stabilisers. Detailed description of the drawings

[0027] Coated steel strips are used for manufacturing parts for example in the automotive industry, where the applied coating is required to fulfil requirements like the metal layer should not be with any dross as that can contaminate a subsequently applied coating. The present invention embodiments reduce the chance of any contamination in a coating by stabilising the moving steel strip before entering the liquid metal bath by reducing the chances that the surface dross that is present within the snout to adhere on the moving metal strip. The present invention embodiments also provides the possibility of applying an additional coating such as a barrier layer to the metal strip before applying the metal coating.

[0028] FIG. 1 shows a schematic representation of a hot dip coating device comprising a snout 50. The steel strip 2 is passed from an annealing section through the introduction point 31 into the hot dip coating device 19 using hot bridles 16. The hot dip coating device 19 comprises a liquid metal bath 18 having a surface bath level 20. An ingot 15 is placed in the a liquid metal bath 18. The hot dip coating device 19 may also comprise supporting rolls 33, 34 for acquiring a desired shape of the metal sheet. The hot dip coating device 19 also comprises sink rolls 28 to pass the steel strip 2 out of the liquid metal bath 18 into the air knives 14. Air knives 14 are used for adjusting the coating amount of molten metal of the steel sheet.

[0029] FIG. 2 shows a schematic representation of an embodiment of a hot dip coating device 19 with at least two stabilisers 100 placed within the snout 50. The at least two stabilisers 100 are a pair of pads having its fixed facing surface placed on each side of the moving metal strip 2. The pads are rigid structures and are made of non-corrosive material. The pads are made of stainless steel. The steel strip 2 is passed from a previous annealing section into a second container 22 comprising a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the direction of travelling of the steel strip 2. An ingot 15 is placed in the liquid metal bath 18. The pads are placed as opposing stabilisers on both sides of the moving metal strip 2 so that they rely on the pressure built up by the flow induced by the moving metal strip 2. As the molten zinc has a much higher density than air, the pressure that is build up in the molten zinc bath 18 dampens the vibrations of the metal strip 2 effectively and flattens the metal strip 2. This reduces the strip vibration thereby reduces the possibilities of picking up of any surface dross that is floating in the liquid metal bath within the snout 50. The snout 50 has a lower opening 39 that is immersed in the second liquid metal bath 18 that has a surface bath level 20. The pair of pads 100 are placed on either side of the moving metal strip 2 such that the pair of pads 100 form a first container 220. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The first container 220 is formed inside the second container 22.

[0030] FIG. 3 shows a schematic zoomed in view of the pads 100 forming the first container 220. The liquid level of the first container 220 can be at a different level compared to the liquid level of the second container 22. The pads 100 have a upper portion 100a and a lower portion 100b. The upper portion 100a of the pads is kept above the bath level 20 of the second container 22 and the lower portion 100b of the pads is kept below the bath level 20 of the second container 22. The lower opening 39 of the snout 50 encloses the upper portion 100a of the pads 100. The lower portion 100b of the pads opens into the second liquid metal bath 18 of the second container 22. The lower portion 100b of the pads forms an opening that is in the range of 20 mm to 80mm through which the metal strip 2 can enter from the first container 220 to the second container 22. The hot dip coating device 19 of Fig. 2 also comprises at least a sink roll 28 to pass the steel strip 2 out of the liquid metal bath 18 into the air knives 14. Air knives 14 are used for adjusting the coating amount of molten metal such as molten zinc of the steel strip.

[0031] FIG. 4 shows a schematic representation of another embodiment of a hot dip coating device 19 with a pair of stabilisers 110 within the snout 50 where the moving steel strip 2 is passed from a previous annealing section into a second container 22 comprising a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the travelling direction of the steel strip 2. An ingot 15 is placed in the a liquid metal bath 18 that has a surface bath level 20. The at least two stabilisers 110 are a pair of foils having its fixed facing surface placed on each side of the moving metal strip 2. The foils 110 are placed as opposing stabilisers on both sides of the moving metal strip 2 so that they rely on the pressure built up by the flow induced by the moving metal strip 2. As the molten zinc has a much higher density than air, the pressure that is build up in the molten zinc bath 18 dampens the vibrations of the metal strip 2 effectively and flattens the metal strip 2. This reduces the strip vibration thereby reduces the possibilities of picking up of any surface dross that is floating in the liquid metal bath within the snout 50. The snout 50 has a lower opening 39 that is immersed in the second liquid metal bath 18. The pair of foils are placed on either side of the moving metal strip 2 such that the pair of foils 110 form a first container 220. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The foils 110 are flexible structures and are made of noncorrosive material such as stainless steel. The first container 220 is formed inside the second container 22.

[0032] FIG. 5 shows a schematic zoomed in view of the pair of foils 110 forming a first container 220. The liquid level of the first container 220 is different compared to the liquid level of the second container 22. The foils 110 have an upper portion 110a and a lower portion 110b. The upper portion 110a is placed above the surface bath level 20 of the second container 22. The lower portion 110b of the foils 110 is placed below the bath level 20 of the second container 22. The lower opening 39 of the snout 50 encloses the upper portion 110a of the foils 110. The lower portion 110b of the foils 110 opens to the second liquid metal bath 18 of the second container 22. The lower portion 110b of the foils forms an opening that is in the range of 20 mm to 80 mm. The moving metal strip 2 passes through the lower portion 110b of the pair of foils into the liquid metal bath 18. The hot dip coating device 19 also comprises at least a sink roll 28 to guide the moving steel strip 2 upwards and out of the liquid metal bath 18 into the air knives 14, which are used for adjusting the coating amount of the molten zinc.

[0033] FIG. 6 shows a schematic representation of a further embodiment of a hot dip coating device 19 with a pair of electromagnetic stabilisers 120 placed within the snout 50 where the moving steel strip 2 is passed from a previous annealing section into a second container 22. The second container 22 comprises a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the travelling direction of the moving steel strip 2. The pair of electromagnetic stabilisers 100 are placed above both the first container 220 and the second container 22. An ingot 15 is placed in the a liquid metal bath 18 of the second container 22 that has a surface bath level 20. The hot dip coating device 19 comprises a first container 220 wherein the first container is formed inside the second container 22. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The snout 50 has a lower opening 39 that is immersed in the first container 220. The lower portion of the first container 220 has an opening 220b that is in the range of 20 mm to 80mm. The hot dip coating device 19 also comprises at least a sink roll 28 to guide the moving steel strip 2 upwards and out of the liquid metal bath 18 into the air knives 14, which are used for adjusting the coating amount of the molten zinc.

[0034] Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the hot dip coating device of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

Examples

Embodiment Construction

[0027]Coated steel strips are used for manufacturing parts for example in the automotive industry, where the applied coating is required to fulfil requirements like the metal layer should not be with any dross as that can contaminate a subsequently applied coating. The present invention embodiments reduce the chance of any contamination in a coating by stabilising the moving steel strip before entering the liquid metal bath by reducing the chances that the surface dross that is present within the snout to adhere on the moving metal strip. The present invention embodiments also provides the possibility of applying an additional coating such as a barrier layer to the metal strip before applying the metal coating.

[0028]FIG. 1 shows a schematic representation of a hot dip coating device comprising a snout 50. The steel strip 2 is passed from an annealing section through the introduction point 31 into the hot dip coating device 19 using hot bridles 16. The hot dip coating device 19 compr...

Field of the invention

[0001] The present invention relates to a hot dip coating device for providing a metal coating on a metal strip. In a further aspect the present invention relates to a method of coating using a hot dip coating device.Background of the invention

[0002] Hot dip coating is a well-known process for protecting a steel product against corrosion. An example of a hot dip coating device is a hot dip galvanizing device. A hot dip coating device is used to provide a metal coating such as zinc or aluminum on a moving metal strip. The hot dip coating device typically comprises a container for a liquid metal bath that contains the coating material in use. The coating layer can be a single layer or multiple layers that are coated on the metal strip in a single process or in multiple processes. The coating material can be a first coating layer or an intermediate coating layer prior to a final coating layer or a final coating layer. For some applications the coating material may consist almost entirely of zinc (>99%) known as GI coatings or almost entirely of aluminium (>99%). For other applications, the use of zinc coatings or aluminium coatings alloyed with other metals such as magnesium or silicon is used, which is advantageous owing to their improved corrosion resisting performance and improved pressing performance. In the context of the present invention, the metal strip is also called a metal sheet.

[0003] To guide the metal strip from a previous furnace into the hot dip coating device, several rolls can be present in the furnace. The last roll or rolls to guide the metal strip into the hot dip coating device is known as a hot bridle. A snout is a duct that is placed between the hot bridle and the metal bath surface, as part of a hot dip coating device. Typically at least one supporting roll is also provided in the liquid metal bath to influence the shape of the metal sheet in its width direction. This supporting roll may be provided between the sink roll and the surface level of the liquid bath at the side of the gas knife. Generally, the snout is one of the last pieces of a furnace that guides a steel strip into a liquid metal bath in the hot dip coating device. The snout is typically rectangular in cross section, but it is also possible for a snout to have a different cross section other than being rectangular. The lower part of the snout has an opening that is immersed in the liquid metal bath, during its use. The metal strip or the metal sheet passes through this opening into the liquid metal bath. The snout shields the annealed steel strip from an open atmosphere, which is necessary to avoid oxidation and to maintain the strip temperature. The atmosphere in the snout is generally dry and this dry atmosphere is known to lead to metal evaporation. For a hot dip coating device such as a hot dip galvanizing device, this dry atmosphere leads to zinc evaporation. The zinc evaporation results in condensation of zinc against the snout walls which, in turn, leads to formation of zinc dust against the walls that can fall on to the steel strip or on to the zinc bath surface which leads to coating defects. The evaporation of zinc is limited by moistening the atmosphere inside the snout directly above the liquid zinc surface. This creates an oxide layer that limits the zinc evaporation.

[0004] It is known that in a continuous galvanizing line, the molten zinc bath is mostly saturated with iron, which dissolves from the steel strip that is continuously passed through the bath. The molten zinc bath may also contain unwanted particles such as oxide particles that are formed when oxygen in the surrounding air oxidises the liquid metal. Such oxide particles typically stay in the top layer of the liquid metal. Further, at the operating temperature of the liquid metal bath, dissolution of iron from the steel strip into the metal bath can occur that forms intermetallic particles. These intermetallic particles as well as the oxide particles are known as dross. Dross present on the surface of the liquid metal bath or that rises to the surface if present underneath the surface is known as surface dross or floating dross or top dross. Since the lower part of the snout is immersed in the liquid metal bath, the liquid metal bath that is present within the snout also contains dross such as surface dross. If not properly controlled, the surface dross within the snout will be collected by the moving metal strip, which will have detrimental effects on the final products that are manufactured from the steel strips. For example, small dross particles may be incorporated in the coated alloy layer and affect the appearance of the coated steel parts. This is particularly disadvantageous for steel strips, from which exterior automotive parts are shaped by pressing. The included particles may cause inhomogeneous deformation resulting in surface defects and irregularities such as tiny projections and bulges, even when present at the non-exposed side of the automotive parts. The unevenness in the surface of the steel parts results in undesired reflections that affect the appearance in an unacceptable way. Surface defects are also related to a different dynamic wetting process when the steel strip moves into the zinc bath in the snout of a hot dip coating device. A vibration of the moving metal strip will make wetting more difficult and has an effect on the entrainment of surface debris or surface dross. Since the metallic coating is applied after the hot dip coating step, the applied coating should fulfil requirements such as that the metal layer has to be without any dross or debris. This is important not only to be able to subject the coated steel strip to forming operations but also for the appearance of the final steel product formed from the coated steel strip. The moving metal strip in this context is also called a metal strip.

[0005] The surface debris or surface dross that floats on the metal bath surface in the snout is similar to a floating fleece. The surface dross has a mechanical strength. By getting exposed to mechanical disturbance the surface dross get loose and will be picked up by the moving metal strip. Typically these mechanical disturbances are enhanced by vibrations or instability of the moving metal strip perpendicular to the travel direction of the moving metal strip. If the strip is unstable in the snout due to its vibrations that are typically perpendicular to the travel direction of the steel strip, then the surface dross will be detached from the floating fleece. The detached surface dross will be easily picked up by the moving metal strip, which will contaminate a subsequent coating process. Also, a stable strip will lead to less generation of free zinc surface that can evaporate or oxidise, thus reducing the formation of further oxidic dross.

[0006] In addition to this, for some applications it is beneficial to coat the steel strip with an inhibition layer or a reaction layer before coating with the coating material from the liquid metal bath. A dual bath system comprising two baths may be used for coating a reaction layer followed by a metallic coating layer, in a single process step. Such processes having dual baths also require reduction in vibrations of the moving metal strip within the snout for reducing the mechanical disturbances. This will eventually reduce coating contamination and defects in the coated metal strip and will lead to a homogenous coating. Prior art documents describe methods to remove surface dross from the liquid metal bath within the snout. However, it is also required that the surface dross present within the snout, especially the surface dross that is present close to the moving strip entering the bath or baths, does not have any exposure to mechanical disturbance. If there is exposure to mechanical disturbance, it can lead to a breakup of the dross fleece near the moving strip and will result in a subsequent dross pickup by the moving strip.Objectives of the invention

[0007] It is therefore an object of the invention to reduce the vibration of the moving metal strip before entering a liquid metal bath within a snout.

[0008] It is also an object of the invention to avoid picking up of any surface dross by a moving metal strip within a snout in a commercial galvanizing section.

[0009] It is also an object of the invention to improve the wettability of a steel strip in a hot dip coating device.

[0010] It is also an object of the invention to reduce the vibration of the moving metal strip before entering a dual liquid metal bath system.Description of the invention

[0011] One or more of these objectives are reached with a hot dip coating device for providing a metal coating on a moving metal strip according to the attached claims. In the first aspect, there is described a hot dip coating device for providing a metal coating on a moving metal strip. The hot dip coating device comprises a second container holding a second liquid metal bath of a second metal coating material in use. The hot dip coating device further comprises a snout for guiding the metal strip into the second liquid metal bath comprising a lower opening immersed in the second liquid metal bath. The hot dip coating device further comprises at least two stabilisers on each side of the metal strip such that the at least two stabilisers form a first container within the second container. The first container holds a first liquid metal bath of a first metal coating material in use. The lower opening of the snout encloses the upper portion of the pair of stabilisers. The second container holds a second liquid metal bath of a second metal coating material that can be coated on the moving metal strip or the metal sheet. The at least two stabilisers can be a pair of stabilisers that are positioned on both sides of the moving metal strip in such a way that on usage, the pair of stabilisers form a first container within the second container. The first container holds a first liquid metal bath of a first metal coating material that can be coated on the moving metal strip. The lower opening of the snout encloses the upper portion of the at least two stabilisers so that the first container is only partially immersed in the second container. The moving metal strip passes from the snout directly into the first container where a first metal coating material is applied on the metal strip before it enters the second container. On entering the second container a second coating material is coated on the metal strip, which is already coated with the first coating material. The lower opening of the snout is immersed in the second liquid metal bath. The moving metal strip passes from the snout into the second liquid metal bath through the first liquid metal bath. The immersed portion of the snout encloses the first liquid metal bath within it and also encloses a part of the second liquid metal bath. The at least two stabilisers are placed as opposing stabilisers on both sides of the metal strip so that they rely on the pressure built up by the flow induced by the moving metal strip. As the molten metal such as zinc has a much higher density than air, the pressure that is build up in the molten metal bath or the zinc bath dampens the vibrations effectively and flattens the strip thereby reducing strip vibration. This reduced or dampened vibrations of the moving steel strip perpendicular to the strip travel direction, prevents picking up of surface dross from within the snout. Typically a sink roll is provided in the second container below the surface level of the second liquid metal bath in use to guide the metal strip out of the liquid metal bath. The at least two stabilisers are placed in between the snout and a sink roll of the hot dip coating device.

[0012] US patent application US2019 / 0032188A1 discloses hydrodynamic stabilisation of a travelling metal strip after exiting the liquid metal bath of a hot dip coating device. These stabilisers are mainly used for increasing the drying process of the coated metal after hot dip coating. US patent application US2010 / 0140985 A1 discloses at least one supporting roll that is in the form of a stabilizer roll and / or a correcting roll within the metal bath between the sink roll in the bath and the gas knife above the bath. It also discloses at least one supporting roll that is positioned above surface level of the liquid bath at the location before the metal sheet enters the liquid metal bath to maintain a desired shape of the metal sheet. None of the prior art documents disclose any solution to stabilise a moving strip within the snout before it enters a liquid metal bath. European patent application EP2954087B1 discloses a dual metal bath system for a hot dip coating device. The dual bath system is used for coating a metallic product first by a metallic alloy layer followed by a metallic surface layer, in one process step where the metallic alloy layer and the metallic surface layer have different chemical compositions. However, EP2954087B1 is silent on how a moving strip can be stabilised within the snout so that its vibrations perpendicular to its travelling direction can be reduced. The present invention differs from the disclosures of EP2954087B1; as the present invention discloses a dual metal bath system where the moving metal strip is also stabilised within the snout.

[0013] The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example of such a layer is Fe 2 Al 5 barrier layer. The first metal coating material can be coated for a thickness that is less than 10 µm, preferably less than 8 µm, more preferably less than 6 µm, even more preferably less than 4 µm. In some embodiments, the first metal coating material can be coated for a thickness that is less than 3 µm, preferably less than 2 µm. As the first coating layer typically acts as an inhibition layer or a reaction layer, lower thicknesses are preferred.

[0014] In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The coating can be also applied in a continuous process by passing the sheet steel through a molten bath with a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally 5-15 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon (AlSi) coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating (including the Fe 2 Al 5 barrier layer) preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % Magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0015] When the first liquid metal bath and the second liquid metal bath comprises metal coating materials of different chemical composition, then there will be a transition region between the first metal coating material and the second metal coating material. This continuous transition region is typically less than 2 µm, preferably less than 1.5 µm and more preferably less than 1 µm. The metal strip is continuously transferred from the first liquid metal bath to the second liquid metal bath so that the metal coating is performed in a single surface coating process. The subsequently coated second metal coating material comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. In another embodiment, the second metal coating material in use comprises a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy, an aluminium silicon magnesium alloy. In another embodiment, the second metal coating material can also contain zinc - aluminium or zinc - aluminium - magnesium alloys but with for example having a higher content of aluminium. When coated, the second metal coating material has a thickness that is higher than 3 µm, preferably higher than 5 µm and more preferably higher than 6 µm. In some embodiments, the second liquid metal bath that is used to coat a second metal coating material on the moving metal strip can be a molten bath having a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally 5-15 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0016] The hot dip coating device further comprises at least two stabilisers on each side of the metal strip such that the at least two stabilisers form the first container within the second container. The lower opening of the snout encloses the upper portion of the pair of stabilisers or the upper portion of the first container. Typically the lower portion of the snout is tapered and it is immersed in the liquid metal bath during its use. For some applications, the opening at the lower portion of the snout may have a circular or rectangular cross section. From the snout, the moving metal strip enters the first liquid metal bath in the first container formed by the at least two stabilisers. The lower portion of the at least two stabilisers forms an opening through which the moving steel strip is transferred from the first metal bath to the second metal bath. However, if the opening at the lower portion of the at least two stabilisers is very narrow, the moving steel strip has less space for its travel. Moreover, if the moving metal strip vibrates perpendicular to its travel direction within this narrow opening then the metal strip can hit the walls of the at least two stabilisers. Hence, there needs to be enough room for the moving metal strip to avoid hitting to the walls of the at least two stabilisers. In one embodiment of the present invention, the lower portion 100b of the at least two stabilisers forms an opening, wherein the distance between the stabilisers is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm. This reduced distance between the opening reduces the risk of hitting the walls of the at least two stabilisers by the moving metal strip.

[0017] In one embodiment of the present invention the at least two stabilisers are pads. The pads are made of a non-corrosive material in order to withstand any corrosion from the compositions of both the first metal bath and the second metal bath. Preferably the at least two stabilisers are stainless steel pads or tungsten pads. The pads are rigid structures. The thickness of the pads are typically in the range of 5-10 mm. In another embodiment of the present invention the at least two stabilisers are foils. Preferably the at least two stabilisers are stainless steel foils or tungsten foils. The foils are also made of a non-corrosive material in order to withstand any corrosion from the compositions of both the first metal bath and the second metal bath. The thickness of the foils can be typically in the range of 0.01 mm to 2 mm. The thickness of the foils can be preferably in the range of 0.03 mm to 1 mm or even preferably in the range of 0.05 mm to 0.5 mm. The foils are comparatively more flexible than pads. Also, the thickness of the foils is less than the thickness of the pads.

[0018] The surface bath level of the first liquid metal bath and the surface bath level of the second liquid metal bath need not be in the same level. In one embodiment of the present invention the upper portion of the at least two stabilisers is above the surface bath level of the liquid metal bath. This ensures that the first liquid metal bath and the second liquid metal bath will not mix excessively.

[0019] Prior art documents describe electromagnetic stabilisers that are used for reducing vibrations of a steel strip after exiting the liquid metal bath of a hot dip coating device. Typically an electromagnetic stabilizer consists of an electromagnet, an eddy-current type displacement sensor, a control unit, and a power unit. In such an arrangement, the electromagnet of the electromagnetic stabilizer is placed near the surface of the steel strip. Vibration are detected by the sensor, which activates the magnet to keep the steel strip flat and vibration-free. Electromagnets with dynamically controlled power amplifiers are used to correct and stabilise position and to limit strip vibrations. In this manner a majority of frequencies are damped to a level that is close to a noise spectrum. In a further aspect the present invention relates to a hot dip coating device for providing a metal coating on a metal strip where a pair of electromagnetic stabilisers are placed within the snout, above the first liquid metal bath and the second liquid metal bath. The hot dip coating device comprises a first container holding the first liquid metal bath of a first metal coating material in use and a second container holding the second liquid metal bath of a second metal coating material in use; wherein the first container is within the second container. The hot dip coating device further comprises a snout for guiding the metal strip into the second liquid metal bath through the first liquid metal bath wherein the snout comprises a lower opening that is immersed in the first liquid metal bath. The hot dip coating device also comprises at least two electromagnetic stabilisers provided within the snout, on each side of the metal strip; wherein the at least two electromagnetic stabilisers are above the first liquid metal bath and the second liquid metal bath. In this way the at least two electromagnetic stabilisers are not in fluidic contact with the first liquid metal bath and the second liquid metal bath. As described earlier, if the opening at the lower portion of the first container is very narrow, then the moving metal strip has less space for its travel. Further, if the moving metal strip vibrates perpendicular to its travel direction then it can hit the walls of the first container. Hence, there need to be enough room for the moving metal strip to avoid hitting to the walls of the first container. In one embodiment of the present invention the distance between the walls of the opening in the first container is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm. This substantially reduces the risk of the moving metal strip hitting the walls of the first container.

[0020] For industrial applications, it is often required that the at least two stabilisers stabilise the moving metal strip continuously during the continuous process of hot dip coating. On a commercial scale in the steel industry, for example for a hot dip galvanizing line, a single galvanizing bath is continuously operated for time periods of some weeks up to several months, before any shut down occurs in view of a necessary maintenance and replacement. In practice such a galvanizing line is used to produce galvanized steel strips of different qualities in consecutive runs. In particular a switch from producing steel strips that meet less stringent quality requirements to steel strips for high demanding end purposes is complicated and critical. After such a switch of production, if the freshly produced steel strip does not meet the required higher standards, it will likely be rejected. Hence, there is also a requirement for a continuous stabilisation of the moving metal strip before that entering the liquid metal bath so that it will not affect the quality of steel production if switch of production occurs. If the stabiliser is not able to continuously stabilise the moving metal strip, the moving metal strip will easily pick up surface dross. For other applications it may also needed to occasionally remove the stabilisers for various purposes such as maintenance, cleaning or for replacement. In one embodiment of the invention, the at least two stabilisers or the at least two electromagnetic stabilisers are removably mounted within the snout to accommodate replacement and / or maintenance.

[0021] The moving metal strip or the metal sheet enters from the snout into the first liquid metal bath. As described previously, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip. The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example for this is Fe 2 Al 5 barrier layer. The first metal coating material can be coated for a thickness that is less than 10 µm, preferably less than 8 µm, more preferably less than 6 µm, even more preferably less than 4 µm. In some embodiments, the first metal coating material can be coated for a thickness that is less than 3 µm, preferably less than 2 µm. When the first liquid metal bath and the second liquid metal bath comprises metal coating materials of different chemical composition, then there will be a continuous transition region between the first metal coating material and the second metal coating material. The continuous transition region is less than 2 µm, preferably less than 1.5 µm and more preferably less than 1 µm. The metal strip is continuously transferred from the first liquid metal bath to the second liquid metal bath so that the metal coating can be done in a single surface coating process.

[0022] In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. In another embodiment of the present invention the first liquid metal bath of the first metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or wherein the first liquid metal bath of the first metal coating material is from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy. The coating can be also a hot-dip galvanized coating applied in a continuous process by passing the steel sheet through a molten bath with a zinc content of at least 99%. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99% and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13% by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0023] The subsequently coated second metal coating material comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The second liquid metal bath of the second metal coating material in use may also comprise a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy, an aluminium silicon magnesium alloy. In one embodiment of the present invention the second liquid metal bath of the second metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy or wherein the second liquid metal bath of the second coating material is from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy. When coated, the second metal coating material has a thickness that is higher than 3 µm, preferably higher than 5 µm and more preferably higher than 6 µm. The second metal coating can be also a hot-dip galvanized coating applied in a continuous process by passing the steel sheet through a molten bath with a zinc content of at least 99%. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99% and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13% by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0 - 2.0 % magnesium and 1.0 - 3.0 %. aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment, the zinc alloy coating comprises at most 1.6% Mg and between 1.6% and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.

[0024] Any moving part present within the snout will create extra flows in the bath or attract zinc dust that is present in the snout wall. Rotating parts are additionally costly as they have to be regularly maintained. Often the bearings of the moving parts has to be occasionally replaced. In one embodiment of the present invention the at least two stabilisers are arranged such that a fixed facing surface of each of the stabilizer is placed on each side of the metal strip. This reduces the presence of moving parts present within the snout. The pads or the foils or the electromagnetic stabilisers have a fixed facing surface that is placed on each side of the metal strip. In another embodiment of the present invention, the at least two stabilisers are placed between hot bridle and the sink roll.

[0025] In another aspect, the present invention relates to a method of coating a metal strip using a hot dip coating device as described above. The method comprises passing the metal strip through the at least two stabilisers for stabilising the metal strip; coating the metal strip with a first metal coating material from a first container of the hot dip coating device; and coating the metal strip with a second metal coating material from a second container of the hot dip coating device. The moving metal strip is passed through the at least two stabilisers as described above. The at least two stabilisers can be a foil or a pad or an electromagnetic stabiliser that is placed within the snout. When the at least two stabilisers are pads or foils, they are formed as the first metal bath itself. The moving metal strip is coated with a first metal coating material from a first container of the hot dip coating device and then coated with a second metal coating material from a second container of the hot dip coating device. The second metal coating material is coated subsequent to the coating of the first metal coating material. The first liquid metal bath of the first metal coating material in use, or the second liquid metal bath of the second metal coating material in use, comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy an aluminium silicon magnesium alloy. Similarly, the second liquid metal bath of the second metal coating material in use, comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy, or wherein the second liquid metal bath of the second metal coating material in use is a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy an aluminium silicon magnesium alloy. In one embodiment of the present invention the first liquid metal bath of the first metal coating material or the second liquid metal bath of the second material coating material is a liquid bath of a the zinc alloy coating comprising 3 - 4.0% Mg and.3 - 6.0% Al; optionally at most.% of one or more additional elements; unavoidable impurities; the remainder being zinc. In an even further embodiment of the present invention, the first liquid metal bath of the first metal coating material is a liquid bath of an aluminium-silicon coating comprising 8 to 11 % of silicon. The hot dip coating device as described above or the method of coating a metal strip using a hot dip coating device as described above comprises the first liquid metal bath of the first metal coating material or the second liquid metal bath of the second material coating material having a liquid bath of a zinc alloy coating comprising 0.3 - 4.0% Mg and 0.3 - 6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. The first liquid metal bath and the second liquid metal bath of the present invention embodiments may contain different metal coating materials having different chemical compositions. They may also comprise metal coating materials having same composition. The first metal provides a coating that mainly acts as an inhibition layer or a reaction layer with the metal strip surface. An example for this is Fe 2 Al 5 barrier layer. In some embodiments, the first liquid metal bath is used to coat a first metal coating material on the moving metal strip, which can be a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy. The coating can be also a hot-dip galvanized coating applied in a continuous process by passing the sheet steel through a molten bath with a zinc content of at least 99 %. The coating can be zinc-iron alloy coating that is generated by immersing the prepared strip in a molten bath containing a zinc content of at least 99 % and a subsequent annealing as a result of which iron diffuses into the zinc layer. The resulting zinc-iron coating has an iron content of normally to 13 % by mass and is referred to as a galvannealed coating. The coating can be also be a high aluminium coating comprising 0.3-0.8% Al. The coating can also be an aluminium-silicon coating by passing the prepared strip through a molten aluminium bath with a silicon content of 8 to 11 %. The coating can also be a zinc-magnesium coating by passing the prepared strip through a molten zinc bath alloyed with magnesium and aluminium. The zinc alloy coating (including the Fe 2 Al 5 barrier layer) preferably comprises 0.3-4.0% Mg and 0.3-6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc. More Preferably the alloying element contents in the coating shall be 1.0-2.0 % magnesium and 1.0-3.0 % aluminium, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc. In an even more preferred embodiment the zinc alloy coating comprises at most 1.6% Mg and between 1.6 and 2.5% Al, optionally at most 0.2% of one or more additional elements, unavoidable impurities and the remainder being zinc.Brief description of the drawings

[0026] The invention is further explained by the following figures. FIG. 1 shows a schematic representation of a hot dip coating device. FIG. 2 shows a schematic representation of an embodiment of a hot dip coating device with at least two pads. FIG. 3 shows a schematical view of the at least two pads of FIG. 2. FIG. 4 shows a schematic representation of another embodiment of a hot dip coating device with a at least two foils. FIG. 5 shows a schematical view of the at least two foils of FIG. 4. FIG. 6 shows a schematic representation of an even further embodiment of a hot dip coating device with a pair of electromagnetic stabilisers. Detailed description of the drawings

[0027] Coated steel strips are used for manufacturing parts for example in the automotive industry, where the applied coating is required to fulfil requirements like the metal layer should not be with any dross as that can contaminate a subsequently applied coating. The present invention embodiments reduce the chance of any contamination in a coating by stabilising the moving steel strip before entering the liquid metal bath by reducing the chances that the surface dross that is present within the snout to adhere on the moving metal strip. The present invention embodiments also provides the possibility of applying an additional coating such as a barrier layer to the metal strip before applying the metal coating.

[0028] FIG. 1 shows a schematic representation of a hot dip coating device comprising a snout 50. The steel strip 2 is passed from an annealing section through the introduction point 31 into the hot dip coating device 19 using hot bridles 16. The hot dip coating device 19 comprises a liquid metal bath 18 having a surface bath level 20. An ingot 15 is placed in the a liquid metal bath 18. The hot dip coating device 19 may also comprise supporting rolls 33, 34 for acquiring a desired shape of the metal sheet. The hot dip coating device 19 also comprises sink rolls 28 to pass the steel strip 2 out of the liquid metal bath 18 into the air knives 14. Air knives 14 are used for adjusting the coating amount of molten metal of the steel sheet.

[0029] FIG. 2 shows a schematic representation of an embodiment of a hot dip coating device 19 with at least two stabilisers 100 placed within the snout 50. The at least two stabilisers 100 are a pair of pads having its fixed facing surface placed on each side of the moving metal strip 2. The pads are rigid structures and are made of non-corrosive material. The pads are made of stainless steel. The steel strip 2 is passed from a previous annealing section into a second container 22 comprising a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the direction of travelling of the steel strip 2. An ingot 15 is placed in the liquid metal bath 18. The pads are placed as opposing stabilisers on both sides of the moving metal strip 2 so that they rely on the pressure built up by the flow induced by the moving metal strip 2. As the molten zinc has a much higher density than air, the pressure that is build up in the molten zinc bath 18 dampens the vibrations of the metal strip 2 effectively and flattens the metal strip 2. This reduces the strip vibration thereby reduces the possibilities of picking up of any surface dross that is floating in the liquid metal bath within the snout 50. The snout 50 has a lower opening 39 that is immersed in the second liquid metal bath 18 that has a surface bath level 20. The pair of pads 100 are placed on either side of the moving metal strip 2 such that the pair of pads 100 form a first container 220. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The first container 220 is formed inside the second container 22.

[0030] FIG. 3 shows a schematic zoomed in view of the pads 100 forming the first container 220. The liquid level of the first container 220 can be at a different level compared to the liquid level of the second container 22. The pads 100 have a upper portion 100a and a lower portion 100b. The upper portion 100a of the pads is kept above the bath level 20 of the second container 22 and the lower portion 100b of the pads is kept below the bath level 20 of the second container 22. The lower opening 39 of the snout 50 encloses the upper portion 100a of the pads 100. The lower portion 100b of the pads opens into the second liquid metal bath 18 of the second container 22. The lower portion 100b of the pads forms an opening that is in the range of 20 mm to 80mm through which the metal strip 2 can enter from the first container 220 to the second container 22. The hot dip coating device 19 of Fig. 2 also comprises at least a sink roll 28 to pass the steel strip 2 out of the liquid metal bath 18 into the air knives 14. Air knives 14 are used for adjusting the coating amount of molten metal such as molten zinc of the steel strip.

[0031] FIG. 4 shows a schematic representation of another embodiment of a hot dip coating device 19 with a pair of stabilisers 110 within the snout 50 where the moving steel strip 2 is passed from a previous annealing section into a second container 22 comprising a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the travelling direction of the steel strip 2. An ingot 15 is placed in the a liquid metal bath 18 that has a surface bath level 20. The at least two stabilisers 110 are a pair of foils having its fixed facing surface placed on each side of the moving metal strip 2. The foils 110 are placed as opposing stabilisers on both sides of the moving metal strip 2 so that they rely on the pressure built up by the flow induced by the moving metal strip 2. As the molten zinc has a much higher density than air, the pressure that is build up in the molten zinc bath 18 dampens the vibrations of the metal strip 2 effectively and flattens the metal strip 2. This reduces the strip vibration thereby reduces the possibilities of picking up of any surface dross that is floating in the liquid metal bath within the snout 50. The snout 50 has a lower opening 39 that is immersed in the second liquid metal bath 18. The pair of foils are placed on either side of the moving metal strip 2 such that the pair of foils 110 form a first container 220. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The foils 110 are flexible structures and are made of noncorrosive material such as stainless steel. The first container 220 is formed inside the second container 22.

[0032] FIG. 5 shows a schematic zoomed in view of the pair of foils 110 forming a first container 220. The liquid level of the first container 220 is different compared to the liquid level of the second container 22. The foils 110 have an upper portion 110a and a lower portion 110b. The upper portion 110a is placed above the surface bath level 20 of the second container 22. The lower portion 110b of the foils 110 is placed below the bath level 20 of the second container 22. The lower opening 39 of the snout 50 encloses the upper portion 110a of the foils 110. The lower portion 110b of the foils 110 opens to the second liquid metal bath 18 of the second container 22. The lower portion 110b of the foils forms an opening that is in the range of 20 mm to 80 mm. The moving metal strip 2 passes through the lower portion 110b of the pair of foils into the liquid metal bath 18. The hot dip coating device 19 also comprises at least a sink roll 28 to guide the moving steel strip 2 upwards and out of the liquid metal bath 18 into the air knives 14, which are used for adjusting the coating amount of the molten zinc.

[0033] FIG. 6 shows a schematic representation of a further embodiment of a hot dip coating device 19 with a pair of electromagnetic stabilisers 120 placed within the snout 50 where the moving steel strip 2 is passed from a previous annealing section into a second container 22. The second container 22 comprises a second liquid metal bath 18 of a second metal coating material in use. The arrow denotes the travelling direction of the moving steel strip 2. The pair of electromagnetic stabilisers 100 are placed above both the first container 220 and the second container 22. An ingot 15 is placed in the a liquid metal bath 18 of the second container 22 that has a surface bath level 20. The hot dip coating device 19 comprises a first container 220 wherein the first container is formed inside the second container 22. The first container 220 has a first liquid metal bath 180 of a first metal coating material in use. The snout 50 has a lower opening 39 that is immersed in the first container 220. The lower portion of the first container 220 has an opening 220b that is in the range of 20 mm to 80mm. The hot dip coating device 19 also comprises at least a sink roll 28 to guide the moving steel strip 2 upwards and out of the liquid metal bath 18 into the air knives 14, which are used for adjusting the coating amount of the molten zinc.

[0034] Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the hot dip coating device of the invention, the invention is not restricted to these particular embodiments which can be varied in many ways without departing from the invention. The discussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to these exemplary embodiments. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using these exemplary embodiments.

Examples

Embodiment Construction

[0027]Coated steel strips are used for manufacturing parts for example in the automotive industry, where the applied coating is required to fulfil requirements like the metal layer should not be with any dross as that can contaminate a subsequently applied coating. The present invention embodiments reduce the chance of any contamination in a coating by stabilising the moving steel strip before entering the liquid metal bath by reducing the chances that the surface dross that is present within the snout to adhere on the moving metal strip. The present invention embodiments also provides the possibility of applying an additional coating such as a barrier layer to the metal strip before applying the metal coating.

[0028]FIG. 1 shows a schematic representation of a hot dip coating device comprising a snout 50. The steel strip 2 is passed from an annealing section through the introduction point 31 into the hot dip coating device 19 using hot bridles 16. The hot dip coating device 19 compr...

Claims

1. A hot dip coating device (19) for providing a metal coating on a metal strip (2), comprising: - a second container (22) holding a second liquid metal bath (18) of a second metal coating material in use; - a snout (50) for guiding the metal strip (2) into the second liquid metal bath (18) in use, the snout comprising a lower opening (39) immersed in the second liquid metal bath (18) in use; characterized in that the hot dip coating device (19) further comprises at least two stabilisers (100, 110), at least one on each side of the metal strip (2), such that the at least two stabilisers (100, 110) form a first container (220) within the second container (22); wherein the first container (220) holds a first liquid metal bath (180) of a first metal coating material in use; and wherein the lower opening (39) of the snout (50) encloses the upper portion (100a) of the at least two stabilisers (100, 110).

2. The hot dip coating device (19) according to claim 1, wherein the lower portion (100b) of the at least two stabilisers (100, 110) forms an opening, and wherein the distance between the stabilisers at the opening is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm.

3. The hot dip coating device according to claims 1-2, wherein the at least two stabilisers (100) are pads.

4. The hot dip coating device according to claims 1-2, wherein the at least two stabilisers (110) are foils.

5. The hot dip coating device (19) according to any one of the preceding claims, wherein the upper portion (100a, 110a) of the at least two stabilisers (100, 110) is above the surface bath level (20) of the second liquid metal bath (18).

6. A hot dip coating device (19) for providing a metal coating on a metal strip (2), comprising: - a first container (220) holding a first liquid metal bath (180) of a first metal coating material in use; - a second container (22) holding a second liquid metal bath (18) of a second metal coating material in use; wherein the first container (220) comprising an opening (220b) is placed within the second container (22); - a snout (50) for guiding the metal strip (2) into the second liquid metal bath (18) through the first liquid metal bath (180) in use, wherein the snout (50) comprises a lower opening (39) that is immersed in the first liquid metal bath (18) in use; wherein the hot dip coating device (19) further comprises at least two electromagnetic stabilisers (120) provided within the snout (50), at least one on each side of the metal strip (2); wherein the at least two electromagnetic stabilisers (120) are above the first liquid metal bath (180) and the second liquid metal bath (18) in use.

7. The hot dip coating device (19) according to claim 6, wherein the distance between the stabilisers at the opening (220b) of the first container (220), is in a range of 20 mm to 80mm, preferably in a range of 30 mm to 70mm, more preferably in a range of 40 mm to 60 mm.

8. The hot dip coating device (19) according to any one of the previous claims, wherein the at least two stabilisers (100, 110) or the at least two electromagnetic stabilisers (120) are removably mounted within the snout (50) to accommodate replacement and / or maintenance.

9. The hot dip coating device (19) according to any one of the previous claims, wherein the second liquid metal bath (18) of the second metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy; or from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy.

10. The hot dip coating device according to any one of the previous claims, wherein the first liquid metal bath (180) of the first metal coating material is from a list of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy; or from a list of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy.

11. The hot dip coating device (19) according to any one of the previous claims, wherein the at least two stabilisers (100, 110, 120) are arranged such that a fixed facing surface of each of the stabilizers is placed on each side of the metal strip (2).

12. The hot dip coating device (19) according to any one of the previous claims, wherein the at least two stabilisers (100, 110, 120) are placed between a hot bridle (16) and a sink roll (28).

13. A method of coating a metal strip (2) using a hot dip coating device (19) according to any one of the claims 1 - 12, comprising: - passing the metal strip (2) through the at least two stabilisers (100, 110, 120) for stabilising the metal strip (100); - coating the metal strip (2) with a first metal coating material from a first container (220) of the hot dip coating device (19); and - coating the metal strip (2) with a second metal coating material from a second container (22) of the hot dip coating device (19).

14. The method of coating a metal strip (2) using a hot dip coating device (19) according to claim 13, wherein the first liquid metal bath (180) of the first metal coating material in use, or the second liquid metal bath (18) of the second metal coating material in use, comprises a liquid bath of zinc or zinc alloy, preferably a zinc aluminium alloy, zinc magnesium alloy or zinc aluminium magnesium alloy; or a liquid bath of aluminium or aluminium alloy, preferably an aluminium silicon alloy or an aluminium silicon magnesium alloy.

15. The hot dip coating device (19) according to any one of the claims 1-12 or the method of coating a metal strip (2) using a hot dip coating device (19) according to any one of the claims 13-14; wherein the first liquid metal bath (180) of the first metal coating material or the second liquid metal bath (18) of the second metal coating material is a liquid bath of a zinc alloy coating comprising 0.3 - 4.0% Mg and 0.3 - 6.0% Al; optionally at most 0.2% of one or more additional elements; unavoidable impurities; the remainder being zinc.

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