Equipment for continuous hot-dip coating of a metal strip, and method the replace the snout part

Abstract

A hot dip coating equipment able to coat a steel strip (1) running along a given path, comprising an annealing furnace (2), a snout (3), a snout tip (5) able to be partly immersed in a molten metal tank (6), wherein a tight and deformable gap compensator (4) is fitted between the snout (3) and the snout tip (5).

Description

[0001] Equipment for continuous hot-dip coating of a metal strip, and method the replace the snout part

[0002] The present invention relates to the equipment for the continuous hot- dip coating of a metal strip, in particular a steel strip.

[0003] In many industrial applications steel sheets are coated with a protective coating layer against corrosion. This type of sheet metal is used in a variety of industries to manufacture all kinds of parts, and in particular exposed parts with good appearance.

[0004] To obtain this type of sheet, continuous dip coating installations are used, in which a steel strip is immersed in a bath of molten metal. The molten metal is not limited. For example, it can be based on zinc or on aluminium. It may contain other chemical elements, iron coming from the dissolution of the steel strip, unavoidable impurities and possible additives such as lead, antimony.

[0005] In the recent years, aluminium, magnesium and even silicon are added to the zinc-based bath of molten metal to increase the corrosion performance of the coated steel sheets. The bath temperature depends on the nature of the metal: in the case of zinc-based baths, the bath temperature is set from 450 to 490°C.

[0006] The corrosion resistance of parts coated in this way is ensured by the coating, the thickness of which is usually achieved by gas wiping.

[0007] Before the steel strip passes through the molten metal bath, it first runs through an annealing furnace under a reducing atmosphere, in order to recrystallize after the significant work-hardening associated with the cold rolling operation, and to prepare its surface chemical state in order to promote the chemical reactions required for the quenching operation itself. The steel strip is heated to around 650 to 900°C, depending on the grade, for the time required for recrystallization and surface preparation. It is then cooled to a temperature close to that of the molten metal bath, using heat exchangers.

[0008] After passing through the annealing furnace, the steel strip runs through a duct, also called a "snout", under a protective atmosphere with respect to the steel, and is immersed in the molten metal bath. The lower part of the snout is immersed in the metal bath to form a liquid seal with the surface of the bath. The steel strip runs through said snout directly from the annealing furnace atmosphere into the molten metal.

[0009] At the point where the steel strip enters the bath, the strip crosses the surface of the molten metal bath. Some particles can float on the bath surface and stick to the metallic strip passing through the bath which can lead to surface defects. Consequently, systems have been developed to avoid the adhesion of such particles on the strip surface by collecting the particles near the strip. For example, an overflow consists of a compartment placed in the lengthening of the snout. Such a system permits to create a natural flow that traps the floating particles.

[0010] In case two or more different metallic coatings are performed on the same equipment, the tank containing the molten metal bath must be removed and replaced by another tank with another molten metal bath of another composition. The snout immersed in the metal bath must also be replaced to avoid contamination of the bath with undesirable chemical elements. When the equipment is run by campaigns, each campaign corresponding to a specific coating, the operation of changing the snout is consuming several shifts up to one day of production.

[0011] When the snout is immersed into the bath, the highest part of the snout remains in contact with the ambient air, a induces the thermal gradient in normal function when production is running.

[0012] When the snout is removed from the bath, it cools down by convection in contact with the ambient air, and the thermal gradient is exerted the other way around. This leads to thermo-mechanical constraints and thus deformation of the snout and the overflow. After several cycles of immersion and removal from the molten bath, the geometry of the snout is impaired. The repeated deformations can lead to an anticipated failure the snout.

[0013] Furthermore, when the snout is not straight enough, the strip running through can encounter the inner snout walls, which is detrimental for the production process. The aim of the present invention is to provide an equipment that increases the lifetime of the snout. It also aims at providing a method to replace the snout without losing productivity.

[0014] This is achieved by an equipment comprising an annealing furnace, a snout, a snout tip able to be partly immersed in a molten metal tank, wherein a gap compensator is fitted between the snout and the snout tip.

[0015] The invention is illustrated with the following figures, they are not limiting: Figure 1 shows an equipment according to the invention when production is running. Figure 2 shows a cross-section of a gap compensator according to the invention. Figure 3 shows when the front and rear platforms are placed around the path of the steel strip after removal of the molten metal tank.

[0016] Figures 4 shows when the platform provided with the fastening device is moved back.

[0017] Figure 5. a) shows a fastening set in cross section.

[0018] Figure 5.b) shows a fastening set attaching the snout tip to the snout.

[0019] Figure 5.c) shows a fastening set attaching the snout tip to the fastening device.

[0020] The figures are labelled with the following references:

[0021] 1 : steel strip

[0022] 2: annealing furnace

[0023] 3: snout

[0024] 31 : snout arm

[0025] 4: gap compensator

[0026] 41 : gap compensator outer bellows

[0027] 42: gap compensator inner sleeve

[0028] 43: gap compensator flange to be mounted on the snout 3

[0029] 45: gap compensator flange to be mounted on the snout tip 5

[0030] 5: snout tip

[0031] 6: molten metal tank

[0032] 7: rear platform

[0033] 71 : wheels 8: front platform

[0034] 81 : rail

[0035] 9: fastening device

[0036] 10: fastening set

[0037] 101 : shaft

[0038] 103: piece connected to the snout arm

[0039] 109: piece connected to the fastening device

[0040] The gap compensator 4 according to the invention is tight and deformable. It ensures the tightness of the atmosphere in the snout.

[0041] According to the invention, the snout tip 5 being immersed in the molten metal bath is connected to the rest of the snout 3 by the gap compensator 4. Said gap compensator allows the snout tip 5 to deform by thermal dilatation. This reduces the usual thermal constraints in the part and increases its lifetime.

[0042] The gap compensator is usually of square cross-section.

[0043] Preferably, the gap compensator 3 is made of two shells: an outer expandable bellows 41 and an inner sliding sleeve 42. The expandable bellows ensures the tightness, and the inner sleeve allows deformations while being able to withstand the forces exerted on the snout-tip.

[0044] Preferably, the gap compensator 4 is provided with one flange 43 to be mounted on the snout 3, and one another flange 45 to be mounted on the snout tip 5. The assembly of the gap compensator with the snout 3 and the snout tip 5 must be tight. The assembly can be realized by any mean. For example, it is performed by a flat sealing gasket and a series of bolts and nuts.

[0045] Preferably, the gap compensator is fitted with a tie-rod 46 that can be attached between the two flanges 43, 45 to lock the compensator.

[0046] Optionally, the snout tip 4 can comprise an overflow.

[0047] Preferably, the equipment is provided with a rear and a front platform that can be placed around the path of the steel strip after removal of the molten metal tank. One of both platforms is provided with a fastening device 9 to attach the snout tip, said device being adjustable in the vertical direction. Optionally, the platforms are provided with barriers to prevent operators from falling.

[0048] In a preferred embodiment, the platform 8, which is provided with the fastening device 9, is supported by wheels 81 rolling on rails 71 fitted on the other platform. This embodiment permits to easily move the snout tip that must be replaced. It also ensures a repeatable positioning of the snout tip on the snout.

[0049] Preferably, the vertical position of the fastening device is adjustable with a hand crack.

[0050] Preferably, the snout 3 is provided with arms 31 and the snout tip 5 is equipped with at least one fastening set 10 able to be attached either to the arms 31 of the snout or to the or to the fastening device 9, each set comprising:

[0051] - One shaft 101 mounted on the snout tip 5,

[0052] - One piece 103 connected to the arm 31 of the snout 3 and comprising a cylindrical groove with a shape complementary to that of the shaft 101 ,

[0053] - One piece 109 connected to the fastening device 9 and comprising a cylindrical groove with a shape complementary to that of the shaft 101 ,

[0054] - Two clamping flanges 104 able to be tightened on the pieces 103 and 109.

[0055] The clamping flanges 104 can be tightened by any means. For example, they are tightened by screws.

[0056] When the shaft 101 is clamped on the piece 103, the snout tip is attached to the snout thanks to the snout arms, as shown on figure 5.b). In this configuration, the assembly of the gap compensator 4 with the snout 3 and the snout tip 5 can be realized in an effective manner, as the operators can walk around the snout on the platforms. They can stand while working on the bolt and nuts of said assembly.

[0057] When the shaft 101 is clamped on the piece 109, the snout tip is attached to the fastening device 9, as shown on figure 5.c). In this configuration, the snout tip can be easily removed from the equipment. The aim of the present invention is also to provide a method to replace the snout without losing productivity.

[0058] This is achieved by the method of claims 11 to 13.

[0059] The platforms can be moved by any mean. For example, they are moved by a travelling crane, a bridge crane, a lift or a fork-lift truck.

[0060] Thanks to the method of claims 11 to 13, the snout tip 5 can be attached to the fastening device 9 and mounted on the snout 3, whatever the snout deformation due to thermal dilatation. The contact by mean of the shafts 101 for positioning the gap compensator 4 on the snout 3 allows a tight assembly even with a deformed snout tip 5.

[0061] The inventors have found that the method according to the invention allows reducing the time necessary to replace the snout tip from one day to a few hours.

Claims

CLAIMS1. A hot dip coating equipment able to coat a steel strip (1 ) running along a given path, comprising an annealing furnace (2), a snout (3) and a snout tip (5) able to be partly immersed in a molten metal tank (6), wherein a gap compensator (4) is fitted between the snout (3) and the snout tip (5).

2. An equipment according to claim 1 , wherein the gap compensator (4) is made of two shells: an outer expandable bellows (41 ) and an inner sliding sleeve (42).

3. An equipment according to claim 2, wherein the outer bellows (41 ) and the inner sleeve (42) of the gap compensator (4) are made of steel.

4. An equipment according to claims 2 or 3, wherein the gap compensator (4) is provided with one flange (43) to be mounted on the snout (3), and one another flange (45) to be mounted on the snout tip (5).

5. An equipment according to claim 4, wherein the gap compensator (4) is fitted with a tie-rod (46) that can be attached between the two flanges (43, 45) to lock the gap compensator.

6. An equipment according to anyone of claims 1 to 5, wherein a rear (7) and a front platform (8) can be placed around the path of the steel strip after removal of the molten metal tank (6), and wherein one of both platforms (7, 8) is provided with a fastening device (9) to attach the snout tip (5), said device being adjustable in the vertical direction.

7. An equipment according to claim 6 wherein the fastening device (9) to attach the snout tip is equipped with a hand crack to adjust its vertical position.

8. An equipment according to claims 6 or 7, wherein the snout (3) is provided with arms (31 ) and the snout tip (5) is equipped with at least one fastening set (10) able be attached either to the arms (31 ) of the snout or to the fastening device (9), each set comprising:- One shaft (101 ) mounted on the snout tip (5),- One piece (103) connected to the arm (31 ) of the snout (3) and comprising a cylindrical groove with a shape complementary to that of the shaft (101 ),- One piece (109) connected to the fastening device (9) and comprising a cylindrical groove with a shape complementary to that of the shaft (101 ),- Two flanges (104) able to be tightened on the pieces (103) and (109) to clamp the shaft (101 ).

9. An equipment according to anyone of claims 6 to 8, wherein the platform (8), which is provided with the fastening device (9), is supported by wheels (81 ) rolling on rails (71 ) fitted on the other platform.

10. A method to replace a snout tip (5) of an equipment according to claim anyone of claims 3 to 9, said method comprising the following steps:A. Removing the liquid metal tank (6) from the snout region,B. Placing the rear (7) and front platforms (8) around the path of the strip (1 ),C. Attaching the snout tip (5) to the device (9) and releasing the gap compensator (4) from the snout (3),D. Removing the gap compensator (4) and the snout tip (5) by moving back the platform (8) provided with the device (9),E. Replacing the gap compensator (4) and the snout tip (5) by another on the device (9),F. Placing the platform provided with the device (9) around the path of the steel strip (1 ),G. Adjusting the height of the gap compensator (4) and the snout tip (5) to meet the snout (3),H. Attaching the replaced gap compensator (4) and snout tip (5) to the snout (3) and releasing the snout tip (5) from the device (9),I. Moving away the rear (7) and front platforms (8).J. Placing the liquid metal tank in the snout region so that the snout tip is partly immersed in the liquid metal.

11. The method according to claim 11 , wherein the step C), comprises the following sub-steps:- Locking the gap compensator (4) by mean of the tie-rod (46)- Clamping the shafts (101 ) on the pieces (109) connected to the fastening device (9),- Releasing the assembly of the gap compensator (4) with the snout (3) by untightening the flange (43) from said snout (3)- Releasing the shafts from the piece (103) connected to the snout arm (31 ).

12. The method according to claims 10 or 11 , wherein the step H), comprises the following sub-steps:- Clamping the shafts (101 ) on the pieces (103) connected to the snout arms (31 ).- Performing the assembly of the gap compensator (4) with the snout (3) by tightening the flange (43) to said snout (3)- Releasing the shafts (101 ) from the piece (109) connected to the fastening device (9),- Unlocking the gap compensator (4) by releasing the tie-rod (46).

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