EP2454392B1

EP2454392B1 - Apparatus for metal coating a continuous metal product

Info

Publication number: EP2454392B1
Application number: EP10716866.8A
Authority: EP
Inventors: Andrea Guadagnini; Edoardo Guadagnini
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2009-02-09
Filing date: 2010-02-09
Publication date: 2013-11-06
Anticipated expiration: 2030-02-09
Also published as: WO2010089666A1; ITPI20090011A1; ES2444540T3; IT1395468B1; EP2454392A1

Description

Field of the invention

The present invention relates to a metallurgy process and it relates, in particular, to an improved method for coating a continuous metal product.
The present method relates, for example, to a continuous hot-dip galvanizing process of semi-finished products such as metal strips and/or wires, normally wound in coils.
Furthermore, the invention relates also to a structure that carries out this method.

Background of the invention

Many coating processes exist of products, for example of steel or iron, with a metal layer.
In particular, in a continuous coating processes a continuous product, for example metal strip or wire, is hot-dipped continuously in a bath of molten metal. The coating metals useful to this end are those that have a melting temperature low enough to avoid thermal modifications of the products to coat.
One of the most common coating processes is hot-dip galvanizing, with which a coating layer of zinc is topped to the metal strip or wire for protecting it from corrosion. Among the many types of processes continuous hot dipping is known, which allows treating continuously and quickly a large amount of material.
The zinc coating is carried out by dipping the wire or metal strip in a bath of molten zinc that is kept at a temperature between 440-490°C by means of electric induction systems or by combustion of natural gas. The control of temperature of the bath is essential, since a too high temperature would cause an increase of the oxidation of the surface of the molten bath and then an increase of the floating dross thickness, whereas a too low bath temperature would cause an increase the viscosity of the molten metal that hampers the formation of a thin coating layer.
The hot dipped metal strip (or the wire) leaves the bath with a certain amount of molten zinc on the surface. To obtain the exact required thickness, the metal strip is caused to pass through a plurality of air jets oriented towards its surface, by means of blade blowers located above the bath and shifted with respect to each other. This way, the excess of zinc is removed by blowing air or nitrogen and the system is usually adjusted by a thickness sensor of the coating metal. Since the rate of liquid excess "squeezing" that is operated by the blade blowers depends sensibly on the distance run by the metal strip after exiting the molten bath, the level of the molten bath has to be kept strictly fixed.
to achieve this goal, according to the prior art, automatic complex systems exist, which drop slowly zinc ingots into the bath responsive to the hourly consumption of molten zinc, associated with a system of sensors for controlling the zinc level. Without these systems, at each introduction of a whole ingot in the bath, an oscillation would occur of the zinc level that would cause unhomogeneity in the coating.
In other cases, for limiting the increase of the level caused by the addition of an ingot, very large galvanizing tanks are made having high capacity. This way, the level growth that is caused by the introduction of an ingot remains within acceptable limits. This solution, however, induces to increase costs since the amount of molten metal into the tank is much more than necessary, and consequently high is the energy for heating the metal and the subsequent heat dispersion through the liquid surface of the metal.
The contact of the air blades with the molten zinc, and also the contact of the air with the liquid surface of the zinc, furthermore, causes an increase of formation of dross, or "scum", which floats on the molten bath. Even if a certain thickness of floating dross protects the molten bath from the contact with the air, thus limiting the heat dispersion and protecting from oxidation the molten metal located underneath, an excess of floating dross is detrimental to the process.
In particular if the dross that floats close to the outlet zone of the product to coat would adhere to the surface of the product, it would be not eliminable, giving rise to a production reject. On the other hand, with an optimum amount of floating dross, the outlet zone of the product to coat would be free from the risk of dross adhesion, since the emersion movement of the continuous product from the molten bath creates a vortical flow that keeps the floating dross away from the outlet zone. This vortical flow can be increased by heaters of the zinc bath that are located under the outlet zone.
However, an excess of floating dross forms a floating dross head that tends to eliminate the dross-free space about the outlet zone, since said vortical flow cannot remove any more the floating dross from the outlet zone.
In the known plants, therefore, an operator is required to eliminate continuously the floating dross surplus by means of and a T rake, which causes the dross to slide parallel to the surface of the bath, and a net, in order to keep a minimum level of floating dross. This step involves safety concerns, since it is very dangerous for the operator, who must operate close to the bath of molten metal. In addition, a manual operation cannot reach an ideal level of floating dross that would optimize the coating process and would ensure an energy saving and of molten metal.
Another method, which is described in JP60141854A , provides a duct immersed in the hot-dip galvanizing tank with an end exiting at a height above the molten zinc surface of the hot-dip galvanizing tank. By forcing the molten zinc in the duct it exits from the duct end and falls into the hot-dip galvanizing tank. This solution generates however a high waste of molten metal since the fall increases the oxidation of the metal owing to contact with the oxygen. In addition, to allow the movement of the metal strip product at the bottom of the duct it is necessary to provide an sealed passage to allow the molten metal to create a surface current that frees the zone of the fall.
Another device, as described in JP10140309 , comprises a storage reservoir for collecting floating dross associated with a hot-dip galvanizing tank capable of separating the floating dross generated by the molten metal. The device comprises a means for conveying the molten metal from the hot-dip galvanizing tank to the reservoir.
In particular, the reservoir provides a plurality of walls that are shifted from each other in order to make a labyrinth that causes separation of the floating dross, as well as of a dross accumulated at the bottom of the molten metal. However, the area and the size of the storage reservoir are so high that much power is consumed for keeping steady the temperature of the bath of molten metal.

Summary of the invention

it is therefore a feature of the invention to provide an apparatus for coating continuous metal products that allows to eliminate the floating dross surplus of the molten bath.
It is also a feature of the invention to provide an apparatus for coating continuous metal products that control and keep a fixed level of the molten bath, in order to optimize the coating process.
It is another feature of the invention to provide an apparatus for coating continuous metal products that is simple and cost effective.
It is still a feature of the invention to provide an apparatus for coating continuous metal products for reducing the capacity of the existing tanks, even if maintaining a fixed level of the molten bath.
These and other objects are achieved by an apparatus for metal coating a continuous metal product, in particular a metal strip or a wire, comprises:

a galvanizing tank adapted to contain a molten metal bath to coat said continuous metal product with a metal layer, said molten metal bath reaching in said tank a determined fill level and on said molten metal bath a floating dross layer is formed;
means for moving said continuous metal product between an inlet zone, in which said continuous metal product enters said molten bath, a hot-dipped path of the metal product in said molten bath, and an outlet zone at which said metal product exits from said molten bath coated by said metal layer;
means for removing said floating dross from said molten metal bath;

This way, the floating dross, and, in particular, the floating dross surplus, which accumulates on the surface layer of the molten metal bath flows down into the exit channel with part of the molten metal, whereas advantageously in the bath a layer remains of floating dross adapted to protect the molten metal from the oxygen and to limit heat dispersion. In other words, the floating dross, near the outlet zone of the continuous metal product, is withdrawn from exit zone of the product from the molten bath that creates a vortical flow that frees the outlet zone of the metal strip or wire, such that the floating dross cannot reach a level for which it sticks to the product at the outlet of the molten metal bath and does not cause rejects of production. This way, the exit channel allows keeping the level of the metal bath fixed, avoiding expensive controls and monitoring operations of the level to obtain a valid final product, as instead necessary with the prior art.
Owing to the invention, in fact, the upper edge of the channel has a function of "weir" or "overflow level", maintaining always that level in a fixed way.
In particular said exit channel is arranged peripherally along said galvanizing tank such that said closed bottom and said upper edge are in said galvanizing tank. This way, the exit channel creates a gutter channel in the galvanizing tank that works as "overflow level" and gathers the floating dross surplus present on the surface of the molten bath along with a certain amount of molten metal.
Preferably, said exit channel has an upper edge having two heights, a lower height at said outlet zone that defines the filling level and lets to remove locally the floating dross present on the molten metal, and a higher height in all the other extension of the exit channel in the galvanizing tank in order to leave a protection of the molten metal zinc by means of the floating dross cover. This way, the bath in the outlet zone of the metal strip is free of the floating dross in order, as above described, not to cause the floating dross to stick on the metal product, whereas the resting zone of the molten bath keeps a floating dross layer to protect from heat dispersion.
A collection basin is provided associated with said exit channel in which said floating dross and part of the molten metal is collected. In particular the collection basin is arranged adjacent to the galvanizing tank and separated from it, so that the exit channel delivers in the collection basin said part of floating dross and the amount of that has flown down the channel, and the floating dross cannot return to the tank. It should be noted that in the past galvanizing tanks were smaller than the modern tanks. The trend is to increase their volume for keeping as steady as possible the level of the molten bath. With the present invention it is possible to return to smaller tanks with high energy saving and many tons missing of molten zinc.
Alternatively, said collection basin is arranged within said galvanizing tank in order to allow a heat exchange from said galvanizing tank towards said collection basin. This way, the temperature of the molten zinc in the collection basin remains substantially equal to the temperature of the zinc present in the galvanizing tank. Such a solution allows, furthermore, to avoid changes on the galvanizing tank and to minimize the masonry work that is necessary to the installation. Furthermore, the technical time for executing the change is reduced with savings on the costs of installation. This solution is obviously possible if the size of the galvanizing tank permits it.
Preferably, said closed bottom of said exit channel is sloped with respect to the level of said molten bath for causing said floating dross and part of the molten metal to flow quickly towards said collection basin.
In particular the exit channel and the collection basin act as molten metal reservoirs, allowing to add a whole ingot into the tank without need to check the fill level. In fact, only the level in the channel and the collection basin grows. The collection basin acts as storage reservoir for the molten metal, such that it is possible to add different ingots at a time, saving manual work and simplifying the loading system the ingots.
Preferably, the collection basin is located under the conveying passageway, or "snout" of the metal strip, in order to exploit that space and leave free other places in the tank.
The floating dross is removed from said collection basin through lifting means that convey the floating dross to a disposal site. This way, the floating dross that reaches the collection basin with part of the molten metal is withdrawn through a mechanical device overcoming the safety problems in case this step is effected manually. In particular the a conveyor belt is provided, for example a grid-shaped belt, is dipped in the collection basin and exits from it in a sloped direction, conveying away the floating dross and leaving the molten metal free to fall again into the collection basin.
Alternatively, said floating dross is removed superficially from said collection basin by a basket lifting means, comprising a basket integral to an arm, said arm rotatably connected about an axis, in particular said arm is arranged below said level of said molten metal and an rotate from a dipped position to an emptying position running through a draining position, wherein
in said dipped position said basket is dipped into said molten metal;
in said draining position said basket is arranged above said fill level such that the dross is drained from the molten metal in said basket;
said emptying position reached after a programmable time, said basket slowing down quickly at said emptying position such that said arm is beaten suddenly against an abutment portion and causes said dross to fall down from said basket into a disposal site.
Preferably, said disposal site comprises an ingot mould that reciprocates between a loading position in which said dross is collected, to a discharge position, where the disposed dross is collected.
In particular the amount of molten metal present in said collection basin is recirculated into said galvanizing tank by a pump that intakes the molten metal at the closed bottom of said collection basin. This way, the amount of molten metal that unavoidably drops in the exit channel is not wasted but used again for feeding the molten metal bath. Preferably, the pump comprises a piston and a cylinder, which has two lateral apertures, a lower and an upper aperture. The piston has a diameter slightly less than the cylinder, in order to allow a calibrated leakage. When lifting the piston a part of the molten metal that has entered the cylinder through the lower aperture when the piston was at the lower end stop is lifted and exits through the upper side aperture. This way, rotating elements are avoided in the molten metal. Alternatively, the pump can comprise an impeller immersed in the collection basin and that delivers directly the molten metal into the tank.
An adjusting means is advantageously provided for adjusting the reciprocation pace of the piston responsive to the thickness of floating dross that has to be left to float on the molten metal of the tank.
In particular said exit channel is mounted on said galvanizing tank by a connection portion. This way, the exit channel can be arranged on an existing galvanizing tank as retrofit. Alternatively, said exit channel is made in phase of construction directly in said tank. Preferably, the channel is U-shaped, with an upper edge that works as weir, and the other edge, opposite to the channel, which protrudes upwards with an L-shaped portion, which can touch the edge of the tank, and then connected to it by means of suitable fixing means, for example screw connections.
In particular an adjustment means is provided associated with said exit channel, adapted to adjust the height of said upper edge and then of said fill level.
These adjustment means can be for example selected from the group comprised of:

thickening laminas put between the connection portion and the edge of the tank;
a coupling that is slidable and lockable between the connection portion and the channel;
screw lifting systems between the connection portion and the tank;
upper edge that works as movable upper edge portion for sliding with respect to the channel;
a housing in which a wedge fixed joint engages.

Advantageously, between the connection portion and the upper edge stiffening elements can be provided, for example brackets, tie rods, stiffening ribs.

Brief description of the drawings

The invention will be made clearer with the following description of its exemplary embodiments, exemplifying but not limitative, with reference to the attached drawings wherein:

figure 1 shows an elevational side view of a structure for coating continuous metal products, according to the invention;
figure 2 shows a top plan view of Fig. 1, in which the flow is shown of the floating dross and of the molten metal towards the collection basin;
figures 3 and 4 show respectively in an elevational side view and top plan view an exemplary embodiment of the structure that provides different means for removing the floating dross;
figures 5 and 6 show instead the structure of Fig. 3 and 4 with the collection basin located out of the galvanizing tank;
figures 7 and 8 show respectively a cross sectional view of the shape of the exit channel that is made within the galvanizing tank filled with molten metal;
figure 9 and the relative enlarged view of Fig. 10 show the adjustment in height of the exit channel, according to the invention;
figure 11 and the exemplary embodiment of Fig. 11' show a perspective view of the exit channel of Fig. 9, in which are shown respectively the stiffening ribs of the channel or the support elements;
figure 12 and the relative enlarged view of Fig. 13 show the exit channel with the upper edge portion having double height in order to optimize the process of production of the metal strip;
figure 14 shows a zinc exit channel that can also be made at the edge of the tank;
figures from 15 to 19 show an exemplary embodiment where the zinc exit channel is separated from the edge of the tank for being connected to a container immersed in the tank.
figures from 20 to 25 show an exemplary embodiment where the feeding operation of the zinc ingots is carried out laterally to the tank with a walking beam system;
figures from 26 to 27 show an exemplary embodiment of the system for collecting the floating dross from a collection point to a storage and disposal zone.

Description of preferred exemplary embodiments

With reference to Figs. 1 and 2 an apparatus is shown for metal coating a continuous metal product, in particular a metal strip 15 or a wire (not shown). The structure comprises a galvanizing tank 10 containing a molten metal bath 11, for example zinc, suitable to coat the metal strip 15 with a metal layer in order to obtain a zinc topped metal strip 15' and then a calibrated metal strip 15". In particular strip 15 leaves the molten bath 11 along with a certain amount of metal liquid on the surface, indicated in Fig. 1 with 15'; to obtain the exact thickness required, the web 15' passes through a plurality of air jets slightly shifted from each other and oriented towards the metal strip, in the form of air blade blowers 29 arranged above the surface of the bath 17; this way, the excess of metal is removed from the metal strip by blowing air or nitrogen, obtaining the final metal strip 15".
The contact of the air blades 29 with the molten metal, and also the contact of the oxygen with the liquid surface of the zinc, causes the production of floating dross 12, or "scum", which floats on the molten bath 11. In particular the molten metal bath 11 achieves into the tank 10 a determined fill level 17 given by the combination between the molten metal and the floating dross layer 12. Even if the layer 12 represents a protection barrier for the bath, since it minimizes heat dispersion and keeps an insulation of molten metal 11 located underneath, which in turn would oxidize at the contact with oxygen causing a waste of molten metal, an excess of floating dross 12 leads to other problems described below.
As known, the continuous movement of the metal product 15, made by a mechanism 25, brings the product between an inlet zone 26 where the metal product enters in the molten bath 11, a hot-dipping zone 27, where the product crosses the galvanizing tank 10, dipping in the molten bath 11, and an outlet zone 28, where the metal product 15 exits from the molten metal bath coated by metal topping 15'.
In other words, floating dross 12, near the outlet zone 28 of the continuous metal product 15, keeps at a distance from exit zone of the product in the molten bath 11 owing to a vortical flow that is caused in the outlet zone 28 by the exiting metal strip or wire, such that floating dross 12 cannot reach a level for which it sticks to the product that would cause rejects of production.
In particular the metal strip 15 in hot-dipping zone 27 passes through a transport roller 13 and a respective counter-roller 14 in order to come out substantially in a vertical position. The metal strip or the wire then passes through, as above said, through the concentrated air blade blows 29 that control the thickness of the coating calibrating the amount of metal that is deposited on the outer surface of the continuous metal product 15".
The structure, according to the invention, comprises an exit channel 16 associated with galvanizing tank 10 and arranged peripherally along the latter. In particular the channel 16, as better shown in Fig. 3 and 4, has a closed bottom 37 and an upper edge 38, the closed bottom 37 arranged below the fill level 17 of the tank 10, whereas upper edge 38 substantially at the level of the fill level 17, such that floating dross 12 flows down exit channel 16. In other words, exit channel 16 works as a gutter channel in galvanizing tank 10 that gathers floating dross 12 surplus present on the surface of the molten bath along with a certain amount of molten metal in order to work as overflow. This way, floating dross 12 surplus flows down into exit channel 16 whereas advantageously in the bath a layer remains of floating dross 12 that protects as above described the molten metal from the oxygen and limits heat dispersion. Furthermore, the fixed position of upper edge 38 ensures that molten metal bath level 17 the remains fixed, avoiding expensive controls and monitoring operations of the level to obtain a valid product, as instead necessary with the prior art. Owing to the invention, in fact, upper edge 38 of channel 16 has a function of "weir" or "overflow level", maintaining always fixed level 17.
A collection basin is provided 40 associated with exit channel 16 in which floating dross 12 accumulates along with part of the molten metal which has flown down into channel 16. In particular collection basin 40 is arranged adjacent to galvanizing tank 10 such that suitably conformed exit channel 16 delivers in it the dross surplus and the molten metal amount that has flown down the channel. Furthermore, as shown in Fig. 2, collection basin 40 is located under the conveying passageway 20of the metal strip 15, or "snout", in order not to hamper other places in the tank. In Fig. 2 also the flow of floating dross 12 towards collection basin 40 is indicated.
In particular it is preferable to provide an outflow channel 16 with a certain slope that allows the liquid stream, very dense, and the floating dross to outflow by gravity. This way, alternative mechanical systems are avoided that would bring to additional costs.
Furthermore, exit channel 16 and collection basin 40 act as molten metal reservoirs, allowing to add a whole ingot into the tank without the need to check the fill level. In fact, only the level in channel 16 and collection basin 40 can grow. By providing a sufficient storage reservoir, it is possible in particular to add different ingots at a time, saving manual work and simplifying the loading system of the ingots.
A step of automatic removal of dross 12 from collection basin 40 is provided that delivers it to a disposal site 35. In particular once dross 12, joined to molten metal 11, has reached collection basin 40, it is removed from collection basin 40 by a lifting mechanism, visible in Fig. 1, which conveys floating dross 12 to a disposal site, for example an ingot mould or a bin 35. This way, the automatic device overcomes the safety problems when this step is effected manually. In particular conveyor 31, for example a grid belt, is dipped partially in collection basin 40 and exits from it in a sloped direction, conveying away floating dross 12 and leaving the molten metal free to drop back into collection basin 11. The path of conveyor 31 has then a plane portion 32 that allows floating dross 12 to be discharged precisely in bins 35 arranged below. As shown in Fig. 2, conveyor 31 is moved by motor 90 arranged at plane portion 32. Always advantageously the disposal site is shown through a plurality of ingot moulds 35 that are shuttled between a loading position in which they receive the dross, to a discharge position, where the disposed dross is collected.
A further mechanism of removing floating dross 12, is shown in Figs. 3 and 4 and described correspondingly.
On the other hand, the amount of molten metal 11 present in collection basin 40 is recirculated into galvanizing tank 10 by a pump 45 that intakes the molten metal at the bottom 11 so that it is not wasted but used again for feeding the molten metal bath of tank 10.
Always advantageously a step is provided of controlling the molten metal recirculation flow 11 from collection basin 40 to galvanizing tank 10. This way, the control of the recirculation flow, in fact, in association to exit channel 16 and collection basin 40 allows to control the thickness of floating dross 12 that must remain on the surface of the bath.
In particular, pump 45 comprises a piston 46 and a cylinder 47, which has two lateral apertures, a lower lateral aperture 48 and an upper lateral aperture 49. Piston 46 has a diameter slightly less than cylinder 47, in order to allow a calibrated leakage. When lifting piston 46, a part of molten metal 11, which has entered cylinder 47 through lower lateral aperture 48 when the piston is at the bottom dead centre, is raised and exits through the upper lateral aperture 49 connected to a duct 41 pours it into galvanizing tank 10. This way, rotating elements in the molten metal are avoided. Alternatively, in a way not shown, the pump can comprise an impeller immersed in collection basin 40 that delivers directly molten metal 11 into the tank.
To pump 45 furthermore, an adjustment means is associated for adjusting the reciprocation pace of piston 46 responsive to the thickness of floating dross 12 that has to be left to float on the molten metal of the tank.
Figures 3 and 4 show an exemplary embodiment of the structure, according to the invention, where collection basin 40' is arranged dipped in galvanizing tank 10 so that the temperature of the molten zinc in the collection basin remains substantially fixed and in line with the temperature of the zinc present the tank. In fact, a heat exchange occurs between the molten metal and the walls of basin 40', in order to make uniform the temperature and transfer the heat of galvanizing tank. This way, other heating devices are not necessary for keeping the molten metal at the desired temperature. Furthermore, changes on galvanizing tank 10 are not required and masonry work is minimum. Still advantageously, the technical time for executing the change are reduced and allow to save on the costs of installation. This solution is obviously possible if the size of galvanizing tank 10 permits it.
In the representation of Fig. 5 and 6, as also in Figs. 3 and 4, floating dross 12 is removed superficially by collection basin 40 by a basket device 91 integral to an arm 92 pivotally connected about an axis 92'. In particular basket 91 that normally is dipped in the molten zinc of collection basin 40, rotates from a dipped starting position 97 to a draining position 98 (visible in Fig. 5), substantially above the level of the molten metal, it waits for a determined time in order to drain the molten metal associated with floating dross 12. Then, basket 91 moves up to an emptying position 99 where, after a determined time, ends its stroke with a sudden beat that causes arm 92 to stop against a shoulder portion, to shake the "scum" off from basket 91 into bin 35. In particular arm 92 is moved by a motor 95 and the movement of basket 91 is protected by a shielding body 93.
Furthermore, the structure of Fig. 5, 6, 7 and 8 may have exit channel 16 with an upper edge 38 with two heights, a lower height portion 16' in the outlet zone 28 of continuous metal product 15, in order to control the level of the zinc and a higher height 16", extending along galvanizing tank 10, in order to leave a thickness of floating dross 12 to protect the molten zinc. In particular the zone covered by the dross is preferably that of inlet zone 26 of the product and the zone below the conveying passageway 20. This way, the bath in the outlet zone 28 of the metal strip is free of the floating dross in order, as above described, not to cause the floating dross to stick on the metal product, whereas the resting zone of the molten bath keeps the floating dross to protect from of heat dispersion.
Figures 7 and 8 show instead the exemplary embodiment of the structure of Fig. 5 and 6 with collection basin 40 located out of galvanizing tank 10. As specified the tanks of the past galvanizing lines were smaller than the modern galvanizing lines, which are larger for keeping more easily the fixed level of the bath. The system described allows then to go back to tanks more compact fro saving energy and reducing the tons of zinc in fusion.
Figures 9 and 10 show a cross sectional view of the shape of the exit channel 16, according to the invention mounted on galvanizing tank 10 by a connection portion 60 that is blocked, for example, through a plurality of screws 70 suitably spaced. This way, exit channel 16 can be arranged on an existing galvanizing tank as retrofit. Preferably, the channel is U-shaped, with upper edge 38 that works as weir, and the other edge 38', opposite to the channel, which protrudes upwards and forms L connection portion 60, which can touch the edge of the tank suitably distant by means of portions 65, and then connected to it by means of suitable fixing means, for example screw connections.
Always as shown in Figs. 9 and 10, upper edge 38 can be made with different height, indicated respectively with H1 and H2, in order to adapt to the process and to the features of the molten metal present in the galvanizing tank 10, optimizing the thickness of floating dross 12 present in the molten bath. Alternatively, to this solution, as shown in Fig. 11 and 12, an exit channel 16 can be made adjustable in height for adjusting the height of upper edge 38 of the channel and then the fill level 17 of the molten bath. In particular, adjusting the height of upper edge 38 is obtained by raising the whole channel 16 through a plurality of thickness elements 67, shown in detail in Fig. 10, arranged above a head 69 of the edge of tank 10 and locked by screws 70. In this case, associated with screws 70, guiding elements are provided 71 adapted to keep aligned exit channel 16.
Alternatively, between the adjustment means, not shown, for example a coupling can be provided that is slidable and lockable between the connection portion and the channel, screw lifting systems can be provided between the connection portion and the tank, or a upper edge can be provided that is movable for sliding with respect to the channel.
Another adjustment system, shown in Figs. 3 and 5, provides instead a plurality of wedge portions 19 that engage a respective housing 19' integral to the connection portion of the exit channel 16. This way an operator 100 can adjust the height and align exit channel 16;
Figure 11 shows, perspectively, exit channel 16 of Fig. 9, in which stiffening ribs 75 are provided adapted to confer a better structural stiffness, whereas Fig. 11' shows the reinforcement of the channel made by means of suitably distant bracket elements 76.
Figure 12 and the relative enlarged view of Fig. 13 show, in a diagrammatical view, galvanizing tank 10 with exit channel 16 that has a double height. In particular as above described, this allows keeping a predetermined level of floating dross 12 in the zone under conveying passageway 20 that leads strip 15 into the bath, in order to minimize the energy consumption, whereas it allows to eliminate the floating dross at the outlet zone 28 of the strip. This is possible owing to a different height of upper edge 38 that works as weir for the molten metal flowing down. In fact, as shown in Fig. 13, the height changes from a height H3 to a height H4 whose difference is Δ. Value of delta can be adjusted responsive to the kind of plant and of tank and is comprised between a few mm to several centimeters.
With reference to Fig. 14, exit channel 16 can also be made on the edge of the tank.
With reference to Figs. from 15 to 19, exit channel 16 can be detached from the edge tank and cantilevered with respect to a collection basin immersed in the tank.
In particular the exit channel may be U-Shaped and have side branches 16a that run parallel to the edge of the tank and that have a portion 16d with an upper edge where the molten metal flows into them, laterally to the outlet zone of the metal strip from the bath of molten zinc. A central branch 16b reaches in 16c collection basin 40 that is immersed in the tank. Collection basin 40 has two compartments that communicate in depth with each other, and precisely a compartment 40b where the floating dross and the molten zinc enter from an inlet port 40c, coincident to the outlet of the channel 16c, and a compartment 40a where a pump is immersed that recirculates the molten zinc into tank 10.
Collection basin 40 is kept immersed by the weight of the liquid zinc in it contained, which however reaches a level that is lower than the level surface in the tank, and by beams 170 anchored to a basement plate laterally to the tank.
A heater 300 is provided in a tank zone that is left free laterally outside collection basin 40. This way, the heat of the heater keeps hot also the zinc present in collection basin 40.
The ingots can be then dipped into the tank at this point close to heater 300
With reference to Figs. from 20 to 25, in an exemplary embodiment, the feeding step of zinc ingots is carried out laterally to the tank with a walking beam system 160.
More precisely, walking beam 160 is arranged orthogonally to the tank edge above heater 300. The walking beam is mounted on a carriage 161, which is movable on wheels 162 that run on rails 163, and carries out a reciprocation and stroke predetermined by means of an actuator not shown. Arms 164 raise walking beam 160 in order to lift packs of ingots 200 that are arranged on saddle supports to B C D, in order to load at each stroke a stack of ingots on a lift 155 in position E.
The latter is suspended by a frame150 on uprights 151, and is lowered by an actuator 152, in order to dip the ingots in front of the heater 300 in the bath of molten zinc under the liquid surface 17 in a zone 10a of the tank 10.
The loading operation of zinc ingots by walking beam 160 can be easily carried out by a loading means 180, and saddle supports A,B C D can be loaded all at the same time, giving to the walking beam a high autonomy.
Owing to the presence of collection basin 40, furthermore, packs 200 can be also very large, since collection basin 40 and the overflow level system that is assured by the presence of upper edge portion of channel 16 maintains in any case zinc level 17 fixed.
The floating dross 12 can be easily picked up from compartment 40b of collection basin 40 by the system of Figs. 26 and 27 through basket 95. It provides an arm 103 that rotates on hinges 101 up to beating the basket 95 against an abutment of ingot mould 108 where the dross is gathered. Ingot mould slides on rails 109 and can a large amount of dross so that it has to be emptied after many hours requiring very limited intervention by operators.
A chute guide 105 that is heated by resistance 105a and a protection body 107 that is mounted on uprights 102 avoid that the droplets of zinc solidify.
The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

An apparatus for metal coating a continuous metal product (15), in particular a metal strip or a wire, said apparatus comprising:
- a galvanizing tank (10) for containing a molten metal bath (11) suitable to coat said continuous metal product (15) with a metal layer, said molten metal bath (11) reaching in said tank (10) a determined fill level (17) and on said molten metal bath a floating dross layer (12) is formed;

- means for moving said continuous metal product between an inlet zone (26) at which said continuous metal product enters said molten bath (11), a hot-dipped path of the metal product in said molten bath, and an outlet zone (28) at which said metal product exits from said molten bath coated by said metal layer;

- means for removing said floating dross (12) from said molten metal bath, wherein said means for removing said floating dross comprises at least one exit channel (16) associated with said galvanizing tank (10), said exit channel having a closed bottom (37) and an upper edge (38), said closed bottom (37) being arranged below said fill level (17) and said upper edge (38) defining said fill level, such that at least one part of said floating dross (12) flows down into said exit channel (16) in order to be easily collected;

- a collection basin (40), associated with said exit channel (16) in which said floating dross and part of the molten metal is collected,
characterized in that there is provided lifting means to pick up the floating dross (12) from said collection basin (40), said lifting means being selected from the group comprised of:

- lifting means that convey said floating dross towards a disposal site (35);

- a basket lifting means comprising a basket (91) integral to an arm (92), said arm (92) rotatably connected about an axis (92').
The apparatus according to claim 1, wherein said collection basin (40) is arranged according to a position selected from the group comprised of:
- adjacent to said galvanizing tank (10) so that the exit channel (16) delivers in it in said collection basin (40) said part of floating dross and said amount of molten metal that has flown down into said exit channel, and the floating dross cannot return to the tank;

- in said galvanizing tank (10) in order to allow an heat exchange from said galvanizing tank towards said collection basin (40).
The apparatus according to claim 1, wherein said exit channel (16) is arranged peripherally along said galvanizing tank (10) such that said closed bottom (37) and said upper edge (38) are in said galvanizing tank (10), in particular said exit channel has an upper edge having:
- a lower height at said outlet zone (28) and lets to remove locally the floating dross present on the molten metal and

- a higher height at said inlet zone (26) of said galvanizing tank in order to keep an insulation of the molten metal by means of the floating dross.
The apparatus according to claim 1, wherein, when basket lifting means is provided, said arm (92) is arranged below the level of said molten metal and rotates from a dipped position (97) to an emptying position (99) running through a draining position (98), wherein:
- in said dipped position (97) said basket (91) is dipped into said molten metal;

- in said draining position (98) said basket (91) is arranged above said fill level (17) such that the dross is drained from the molten metal in said basket;
said emptying position (99) being reached after a programmable time, said basket (91) being adapted to slow down quickly at said emptying position (99) such that said arm (92) is beaten suddenly against an abutment portion and causes said dross to fall down from said basket (91) into a disposal site.
The apparatus according to claim 1, wherein an adjustment means is provided associated with said exit channel (16), adapted to adjust the height of said upper edge (38) and, then, of said fill level (17).
The apparatus according to claim 1, where said exit channel (16) can be free from the edge tank and is cantilever connected to a container immersed in the tank.
The apparatus according to claim 6, wherein the exit channel is U-shaped and has side branches (16a) that run parallel to the edge of the tank and have a portion (16d) with an upper edge that act as a weir, at the sides of the outlet zone of the metal strip from the bath of molten zinc, in particular the central branch (16b) converges (16c) into a collection basin (40) immersed in the tank, in particular collection basin (40) has two compartments communicating in depth with each other, a compartment (40b) where the floating dross and the molten zinc enter by an inlet port (40c), coincident to the exit of the channel (10c), and a compartment (40a) where a pump is immersed that recirculates the molten zinc back into the tank (10).
The apparatus according to claim 6, wherein the collection basin (40) is kept immersed by the weight of the liquid zinc, which achieves a level that is lower than the tank, and by beams (170) connected to a basement plate at the side of the tank.
The apparatus according to claim 6, wherein a heater (300) is provided into the tank zone left free by collection basin (40), such that the heat of the heater keeps hot also the zinc present in collection basin (40).
The apparatus according to claim 9, wherein ingots can be then dipped into the tank in a point close to the heater (300).
The apparatus according to claim 1, wherein the feeding of zinc ingots is carried out laterally to the tank by a walking beam system (160).
The apparatus according to claim 11, wherein walking beam (160) is arranged orthogonally to the tank above the heater (300) and is mounted on a carriage (161) on wheels (162) that run on rails (163) with predetermined reciprocation and stroke by means of an actuator and arms (164) raise walking beam (160) in order to lift packs of ingots (20) arranged on saddle supports (A, B, C, D), loading at each stroke a pack on a lift (155) in an end position (E).
The apparatus according to claim 11, wherein a frame (150) is provided on uprights (151), and is lowered by an actuator (152), in order to dip the ingots in front of the heater (300) in the bath of molten zinc under the liquid surface (17) in a zone (10a) of the tank (10).
The apparatus according to claim 11, wherein a loading means (180) of the walking beam (160) is provided that is adapted to load the ingots on saddle supports (A, B, C, D) all at a same time obtaining a high autonomy.