FR2568895A1 - DEVICE AND METHOD FOR HOT METALIZING BY IMMERSION - Google Patents

Abstract

IN A HOT METALLIZATION DEVICE 1 BY IMMERSION OF A FERROUS METAL PART, FOR EXAMPLE IN THE FORM OF A TAPE 12, THE DEPTH T OF A CONTAINER OR CRUCIBLE 2 IS EQUAL TO OR GREATER THAN DIAMETER D OF THIS CRUCIBLE . A GROUP 5 OF INDUCTION COILS, LOCATED ON SIDE WALL 4 OF CRUCER 2 TO HEAT BY INDUCTION THE CONTENT 9 OF THIS CRUCIBLE, INCLUDES SEVERAL PARTIAL COILS 6, 7, 8 AGENCY OVERLAPPED AND CAN BE INDIVIDUALLY CONNECTED TO A SOURCE ENERGY.

Description

1. 2568895

  HOT METALLIZING DEVICE AND METHOD

BY IMMERSION

  The present invention relates to a metal device

  hot dipping by immersion, intended for the metallization of a piece of ferrous metal continuously scrolling and being for example in the form of a ribbon, and provided with a container for receiving a bath of molten liquid coating metal , wherein said piece of ferrous metal is immersed from top to bottom after having possibly undergone a preliminary treatment such as cleaning and preheating, to then be again extracted from this bath; as well as a group of coils

  induction, respectively arranged in or on the pa (s)

  side kings of said container in order to induction heat the contents of this container. The invention further relates to a method of hot metallization by immersion of a part.

  continuously scrolling metal, using such a device.

  A device of the aforementioned type is known from patent DE-C-2 363 222. This known device is distinguished by

  the peculiarity consisting in that the depth of the reci-

  pient is smaller than the diameter of the latter. These di-

  mensions of the container must respectively allow or promote good mixing of the molten metal bath enclosed by this container, so as to avoid an accumulation of deposits on the bottom of said container. It is well known that in

  devices of the type in question, the group of

  duction not only inductively heats the material

  molten stream, but, in addition, permanent mixing of the metal bath as a result of the currents induced in the metal

molten liquid.

  When, for example, a steel strip of zinc or aluminum alloys and of zinc is coated, what is called hardened zinc is formed in the molten metal bath enclosed by the containers.

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  of hot metallization devices by immersion. This hardened zinc consists of a bond of iron, zinc, aluminum and silicon, and it accumulates at the bottom of the container. In the case of the known container, this accumulation must be avoided by the special ratings given to this container. This, however, implies that the hardened zinc, present in virtually all areas inside the molten metal bath as a result of intensive mixing, also adheres to the steel strip to be metallized. This results in the appearance of pustules at the

  surface of metallic metallic tape. This pus-

  tules means a lower quality of the coated material, because

  an extremely smooth surface is desirable.

  However, it has been found that, in order to obtain good product quality, it is not impossible to eliminate at intervals

  regular hardened zinc deposits from the molten metal bath.

  However, a purification of this bath to eliminate the crusts

  hard metal takes a considerable amount of time, which is

  due to notable declines in production. The frequency of the necessary cleaning interventions increases strongly

  when the containers are shallow.

  The subject of the invention is a device of the aforementioned type, improved so that it prevents the quality of the metallized ferrous part from being adversely affected by zinc.

  hardened forming over time in the container, and that an eli-

  mination of this hardened zinc from the metal bath or only

  necessary at relatively long time intervals.

  Based on a device of the aforementioned type, this object is achieved by the fact that the depth of the container is equal to or greater than the diameter of this container; and by the fact that the group of induction coils comprises several partial coils which are arranged in superposition and can be connected independently of each other to a power source. Thus, unlike the device known from the patent

  DE-C-2 363 222, the device according to the invention

  is distinguished by the following characteristics: 1) the depth of the container is at least equal to the diameter of

3 C56 895

  this one; and 2) the coil is in the form of several partial coils which are superposed in the axial direction of this coil, said individual partial coils being able to be subjected independently to each other to the action

of an alternating current.

  Thanks to these measures, the moving metal part

  is, when it continuously crosses the metal bath in fu-

  sion, separated by a considerable distance from the bottom of the container, even in the deepest region. During the operation of the device, that is to say during metallization, only

  the upper partial coils are conveniently snapped

  chées; in this way, the molten metal bath is certainly subjected to sufficient induction heating and there is sufficient mixing of this metal bath in the upper region of the container, but the movement of the molten liquid metal towards the lower region of said container becomes

  weaker and weaker, so that hardened zinc deposits if-

  killed in the lower region of the container remain in

  this region and are not driven upward by the arm-

  intensive sage of the entire molten bath, as is the case in the prior art. Therefore, the bath

  molten metal enclosed by the upper region of the container

  pient is free to the greatest extent possible from

  hardened zinc so that no part or, in any case, only a very small part of these hardened zinc particles reaches the steel strip to be metallized. he

  this results in high product quality.

  If, after a longer operating period, it has

  formed in the lower region of the container an amount re-

  laterally large deposits of hardened zinc such as removal

  nation of these deposits is impractical, the partial coil

  occupying the lowest position can also be fed

  alternating current so that in the vicinity of the

  bottom of the containers the action of the power becomes respecti-

  sufficient or amplified to remove zinc

  hardened from said container. In addition to the aforementioned advantages, the installation

4 - 2; 48895

  lation of several partial coils also offers the pos-

  sibility of optimally adjusting the heating power in

  depending on the working conditions considered.

  In a very simple embodiment, two partial coils are, for example, arranged on the external face of the peripheral wall of the container, the upper partial coil possibly having a greater height than that of the lower partial coil. However, in a preferred design of the invention, provision is made to arrange in superposition three partial coils of equal height and which can therefore be identical in design. Depending on the depth with which the ferrous tape to be coated is

  immersed in the molten metal bath, as well as

  intensity of the power induced by a partial coil in the metal bath, the two upper partial coils or possibly only the upper partial coil are connected to the energy source, while none

  current is only supplied to the lowest partial coil.

  This lowest partial coil is then engaged only when it is necessary to remove the hardened zinc deposits.

that have accumulated.

  In summary, during hot metallization by im-

  mersion, the partial coil occupying the lower position

  remains permanently disconnected from the energy source.

  First of all only the two upper partial coils,

  then only the partial coil occupying the posi-

  the highest are respectively connected to the energy source. It has proved particularly convenient to choose the ratio between the depth of the container and the diameter of this

  container equal to 1: 1 ... 1: 0.5, preferably 1: 0.8 ... 1: 0.7.

  In this case, together with the presence of three partial coils of equal heights, it is possible to achieve high product quality despite the relatively arranged

simple.

  The invention will now be described in more detail by way of non-limiting example, with reference to the drawing

2568895

  annexed in which the single figure is a longitudinal section

  schematic of a hot metallization device by im-

  mersion with a crucible to receive a metal bath in

  melting, as well as a warming oven.

  The device for hot metallization by immersion il-

  glossy in the figure contains a crucible 2 substantially cylin-

  drique, consisting of a refractory material and comprising a bottom 3 and a side wall 4 of circular section. In the drawing, the internal diameter of the crucible 2 is designated by D, the depth (and therefore the height) of this crucible being identified

  by T. In the example illustrated, the T / D ratio between the pro-

  foundry and the diameter of the container is approximately 1: 0.78.

  A group 5 of induction coils, having a cylindrical shape, is placed on the external face of the side wall

  4. In this case, this group 5 is made up of three coils

  nes partial 6, 7 and 8 which are of identical embodiments, are arranged in superposition in the axial direction of the container and the aforementioned group, and each time have points

  separate connection 6 ', 6'; 7 ', 7' and 8 ', 8', respectively

  vement. These partial coils 6, 7 and 8 can be connected to an energy source independently of each other, so that an alternating voltage is applied to them. In a well known manner, when the coils are subjected to the action of an alternating voltage, there is an induction heating of the internal space of the crucible containing, in this case, a bath 9 of molten zinc. The electric currents induced in this metal bath 9 cause the mixing of the

molten liquid metal. -

  In the drawing, a layer 10 of hardened zinc deposit is

  illustrated by dashes near the bottom 3 of the crucible 2.

  This hardened zinc consists of a bond of iron, zinc, aluminum

nium and silicon.

  The level 11 of the bath 9 of molten zinc rises to a small distance below the upper edge of the

side wall 4.

  In the example considered, the device is used to metallize a steel strip 12 which is first of all immersed in the bath 9 6 Ä56S895 of molten zinc as illustrated, in the direction of the arrow, passing over return rollers 13 and 14 and facing a stabilization roller 15, then again leaves this bath of molten zinc; on leaving the bath 9, the steel strip is coated with zinc on its surface. The stabilization roller 15 makes it possible to convey the metallic strip without any lashing out of the molten bath. Return roller 14

  is inside this bath 9.

  The return roller 13 is housed in a reheating oven.

  line 16 that the steel strip 12 traverses before being immersed in the bath 9 of molten zinc. Optionally, the steel strip can be cleaned beforehand. At the outlet of the oven 16, there is connected a supply muzzle 17 which extends to below the level 11 of the bath, in order to prevent oxygen from entering the upper face of this bath, between the oven 16 and said bath 9. The device 1 described above operates in the following way: by means of return rollers 13 and 14, the steel strip 12 is continuously pulled through the bath 9 of zinc in fusion. A traction device is not provided for this purpose, not shown in detail. Concurrently, alternating current is supplied to the two partial coils 6 and 7 of group 5 from an energy source not shown, so that the bath 9 of molten zinc enclosed by the container 2 is heated and stirred; more precisely, this heating occurs first of all in the upper and central regions of the container. Likewise, the above-mentioned mixing of

  molten liquid zinc only occurs in these regions above

  central and central, while barely a

  of molten liquid metal enclosed by the lower region

  bottom of the container which is approximately surrounded by the lower partial coil 8. Thus, deposits of hardened zinc can accumulate in the vicinity of the bottom of the container 2 without being drawn upwards by too strong stirring.

  of the whole bath of molten zinc, nor that they adhere to the ru-

  ban steel by forming pustules.

  When, after a longer operating period, the

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  layer 10 of hardened zinc deposit increases very strongly at the bottom of the container, the central partial coil 7 of the illustrated embodiment can also be triggered, so that heating and stirring of the molten bath are no longer ensured except by the upper partial coil 6. If, after a longer operating life, the deposits of hardened zinc formed have to be removed, the bottom region

  of the container is subjected to the action of a power by initiation

  of the lower partial coil 8, which causes ascending vortices to be printed with zinc deposits

hardened as a result of heavy brewing.

  In a variant of the embodiment described above, it is also possible to provide only two partial coils. Four or more partial coils can also be used to obtain a more differentiated action on the

contents of container.

  It goes without saying that many modifications can be made to the device and to the method described and shown, e

  without departing from the scope of the invention.

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Claims (5)

  1. A device for hot metallization by immersion, intended for the metallization of a piece of ferrous metal continuously traveling and being for example in the form of a ribbon, and provided with a container or crucible for receiving a bath of molten liquid coating metal, in which said ferrous metal part is immersed from top to bottom after possibly having undergone a preliminary treatment such as cleaning and preheating, to then be again extracted from   this bath; as well as a group of induction coils, respec-   placed in or on the side wall (s) of said   container in order to heat the contents of the latter by induction   deny, device characterized in that the depth (T) of the container (2) is equal to or greater than the diameter (D) of this container; and by the fact that the group (5) of induction coils comprises several partial coils (6, 7, 8)   arranged in superposition and capable of being connected to a source   this energy independently of each other.   2. Device according to claim 1, characterized in that it comprises three partial coils (6, 7, 8) of equal heights.   3. Device according to one of claims 1 and 2, charac-   terified by the fact that the ratio (T / D) between the depth of the container and the diameter of this container is 1: 1 ... 1: 0.5, preferably 1: 0.8 ... 1: 0.7.   4. Method of hot metallization by immersion of a part in a continuously moving ferrous metal, using the   device according to any one of claims 1 to 3,   process characterized in that, during the metallization -   hot immersion, the partial coil (8) occupying the lower position remains permanently disconnected from the energy source.   5. Method according to claim 4, using a dis-   positive comprising three partial coils (6, 7, 8), process characterized in that first of all only the two upper partial coils (6, 7), and then only the   partial coil (6) occupying the highest position are   pectively connected to the energy source.