RU2374363C2 - Upgrade electrodeposit of metallic strip - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: invention relates to electrolytic metallurgy field. Method of high-speed electrotinning of metallic strip includes plating in electrolytic cell of tinned coating on strip by means of anodic dissolution in electrolyte of directed to strip tin anodes in the form of anode bins with tin fractions and sedimentation of anode-dissolved tin on strip operating as cathode, herewith tin is fed into anode bin in the form of fractions, part of tin anodes are masked using regulated end cover-ups which are located and directed depending on width of strip and/or distribution of thickness of tinned coating, herewith plating of tinned coating is implemented at movement of strip downwards and upwards. ^ EFFECT: minimisation of harmful, heavy, inappropriate work, increasing of evenness of tinned coating by thickness and reduction of wastes flows for regeneration. ^ 8 cl, 10 dwg, 2 ex

Description

This invention relates to a method for high-speed electrotinning of a metal strip, in which the strip is coated by anodic dissolution of tin anodes facing the strip in an electrolytic solution.

This method is known from practice and is described in detail, for example, in the reference book “The Making, Shaping and Treating of Steel”, 10 ^th ed., Pp.1146-1153, which describes a typical industrial a tinning process called FERROSTAN, which is considered incorporated herein by reference.

As is known, see also Figs. 36-5 of the referenced manual, in this known method, the anode bars need to be moved and the positions of the anode bars set regularly, which is time-consuming because the mass of the anode bars is typically 50 kg, which is potentially dangerous from the point of view of fumes , strong acids and high electric currents and worsens the uniformity of the thickness of the tin coating along the width of the strip.

When the anode bars are used up to the set minimum thickness, they are removed from the electroplating unit and processed during remelting to new cast anodes.

Since the optimal location of the anodes is important for stable and uniform coating, the position of the anodes must be constantly adjusted.

The goal is to minimize the relatively harmful, hard and uncomfortable work with and above or near the details of electroplating plants used in electrolytic tinning processes.

In addition, the goal is to propose a highly stable electroplating process that can be sufficiently controlled to minimize disturbances caused by feeding, (inadequate) regulation and removal of the anode parts.

At least some of these and other objectives and additional advantages are achieved in the method according to the aspects of the present invention claimed in the 1st and subsequent claims.

In this regard, the term “facing the strip” is intended to mean that at least a portion of the anode tin is “visible” from at least a portion of the strip.

In the method of the present invention, the problem of adjusting the position of the anodes to minimize tin edges when changing the path of the strip and / or the width of the strip can be avoided. Adjustments can, for example, be conveniently performed using controlled masking (“plugs”) of the anode part. In this context, the term "masking" means the location of some object between the anode and cathode in order to prevent the coating "in the shadow of this object", if we consider the anode as a light source.

Due to the fact that the anode substance, namely tin, is fed in the form of a fraction and loaded into baskets, the tin bars described above are no longer used, and therefore there is no need to regulate them. The need to feed heavy anode bars is eliminated. Instead, the anode substance is supplied in the form of easily manipulated anode beads. The present invention also avoids the removal of spent anode material since the shot can be completely consumed.

It should be noted that for the purpose of this application, the term "fraction" will mean balls, ovals, briquettes, granules and the like.

In a preferred embodiment, a portion of the anode is masked according to claim 2. Preferably, masking agents possess the features of claim 3. Surprisingly, by simply masking, for example, the edge sections of the anode using a mechanical device that acts as an adjustable shutter or curtain, it is possible to easily and optimally control tinning also on the edge sections of the strip.

In one embodiment, the fraction is brought into electrical contact by means of a current collector (current collector) made of a material with low electrical resistance, providing good electrical contact with the tin fraction and being electrochemically inert in the electrolyte. Suitable materials for the current collector include Ti and Zr.

In one aspect, an automated feed system is provided for adding pewter to the anode basket.

The present invention will now be explained using examples in the form of a description of aspects of a conventional method as a comparative example and aspects of the present invention.

In the drawings:

Figure 1 shows a cross section of a traditional tinning cell and various elements used in such a tinning cell;

FIG. 2 shows an example screen shot of a process control device displaying coating thicknesses at various positions along a strip width in a conventional tinning processing line;

Figure 3 shows a top view of the anode bridge forming part of a traditional tinning cell;

Figure 4 schematically shows the movement of the anode bars along the anode bridge in a traditional tinning method;

5 schematically shows the removal or addition of anode bars in a traditional tinning process;

6 schematically shows the location and appearance of the anode basket intended for use in the method of the present invention;

Fig. 7 schematically but in more detail shows an anode basket for use in the method of the present invention;

Fig. 8 is a graph generally showing i / i _avg as a function of D ES;

Fig. 9 schematically shows a shutter placed as a mask in front of an anode basket for use in the method of the present invention.

COMPARATIVE EXAMPLE: CONSUMABLE ANODES SYSTEM

A typical soluble anode system is illustrated in FIG. As shown in FIG. 1, tin is supplied in the form of a tin anode 1, which has an anode slot 2 and an anode recess 3. Each of the row of tin anodes 1 is supported by an anode bridge 4 in the upper part near its anode recess 3 and in the lower part by the anode box 5 The insulated plate 6 separates two tin sections in one electrolytic cell. Power is supplied to the strip through a conductive roller 7. Near the bottom of the electrolytic cell, the strip is guided by a guide roller 8. The pressure roller 9 is also shown. The anode bridge 4 has an isolated location 10 for receiving a fresh tin anode 1. The tin anodes 1 are connected to the anode bridge by means of a contact insert 14 .

During the operation of the soluble anode system, three different procedures can be distinguished.

Procedure 1 - Anode Arrangement

During the tinning process, the anodes should be positioned properly to obtain a uniform thickness of the tin coating over the entire width of the strip. Figure 2 gives an example of the thickness of the tin coating along the width of the strip in a situation where the anodes were not placed properly.

To prevent the situation described above, the anodes should be positioned as can be seen in Figure 3, which is a top view of the anode bridge.

Depending on the width of the strip 11, the thickness of the tin coating and the speed of the processing line, the optimal positions of the anodes are given by the parameters AG. The following are the optimal parameters in one specific example for a production line speed of 400 m · min ^-1 , a strip width of 732 mm and a tin coating thickness of 2.8 g · m ^-2 on each side of the strip.

- A = 95 mm (at the height of the anode bridge) and 85 mm (at the height of the anode box)

- B = 60 mm (at the height of the anode bridge) and 50 mm (at the height of the anode box)

- C = 13 mm

- D = 14 mm (anodes are located at an equal distance)

- E = 76 mm (fixed anode width); only 8 anodes

- F = 50 mm

- G = 15 mm

Using these predetermined parameters, uniform tin coating thickness across the strip width can be achieved. Parameter C is of particular importance since this position leads to the well-known “tin edge” phenomenon, also known as the “dog bone” effect.

Moreover, the anode is located closer to the strip below to compensate for ohmic losses in the anode and strip, which would otherwise cause undesirable differences in current density along the height of the strip. Therefore, the parameters A and B are less at the bottom of the anode than at the top.

In a system of soluble anodes, the arrangement (placement at a certain distance) of the anodes is a regularly repeated operation after replacing the consumed anodes (see procedure 2), after changing the bandwidth and after switching to differential coating (see procedure 3). The anodes are manually placed by placing an insulated hook in the anode gap.

In connection with the arrangement of the anodes, at least three important disadvantages of the soluble anode system can be identified. The first disadvantage is the occurrence of deviations in the thickness of the tin coating along the width of the strip, for example, in the form of tin edges; external anodes may be too close to the edge of the strip (parameter C), or the anodes may be unequally distant (parameter D) or unevenly used along the length of the strip due to improper arrangement of the anodes. The second disadvantage is the complexity of the regulatory work, and the third disadvantage is that the regulation is dangerous in terms of exposure to the electrolyte, vapors, and the presence of electrical parts of the installation.

Procedure 2 - Removing Spent Anodes

The thickness of the consumed anodes is regularly monitored by a thickness gauge. When the thickness of the anode at the previously described optimal location of the anodes (see procedure 1) becomes less than 15 mm, this anode is disconnected from the anode bridge and placed in the nearest isolated location, see Figure 4, where the arrows show how the anodes “move” along anode bridge. On the other hand, a new anode is placed on an isolated location and transferred to the anode bridge. After each replacement, the anodes must be rearranged again (see procedure 1). 4, a fresh tin anode is designated N, and a spent anode is designated W.

In the process of tinning, the anodes dissolve, which leads to a change in the distance between the anode and the strip. This is the reason for the uneven thickness of the tin coating across the width of the strip. In practice, this is compensated by placing the anode bridge and strip at a certain small angle (see procedure 1, parameters A and B).

The disadvantages of the soluble anode system due to the replacement of the anodes mainly relate to the arrangement of the anodes (see procedure 1). An additional disadvantage is that the anodes are not constantly located in accordance with the optimal location of the anodes during the replacement of the anodes. This causes variations in the thickness of the tin coating across the width of the strip.

Procedure 3 - Switching to a Different Bandwidth or Differential Coating

After changing the bandwidth, parameter C in FIG. 3 no longer has an optimal value. Moreover, after the transition to differential coverage, i.e. to a lower-mass coating on one side of the strip, tin edge buildup becomes more noticeable on the low-mass side. In practice, both of these situations are compensated by the removal (or addition) and / or rearrangement of the anodes on the anode bridge.

In this regard, refer to FIG. 5, showing the removal or addition of anodes after switching to a different bandwidth or to differential coatings.

If the strip width is changed, for example, from 732 to 580 mm, in the previously described optimal arrangement of anodes (see procedure 1), two anodes should be disconnected from the anode bridge (see Figure 5). After removing the anodes, the remaining anodes must be moved again (see procedure 1).

If a differential coating of 2.8 / 5.6 g · m ^{-2 is used} , in the previously described optimal arrangement of anodes (see procedure 1), one anode should be added to the anode bridge facing the side of the strip with a high coating weight. After addition, the anodes should be rearranged again (see procedure 1). With a sharper difference in the coating mass, the most distant anodes should also be shifted more inward (parameter C in FIG. 3) with respect to the edge of the strip.

DISADVANTAGES OF THE PRIOR ART AND ADVANTAGES OF THE PRESENT INVENTION

The disadvantages of the soluble anode system due to the transition to a different bandwidth or differential coating mainly relate to the arrangement of the anodes (see procedure 1). An additional disadvantage is that the anodes are not positioned according to the optimal location of the anodes (see procedure 1) during the removal or addition of the anodes. This leads to deviations in the thickness of the tin coating along the width of the strip.

To overcome these drawbacks of the soluble anodes (SA) noted in the comparative example, dimensionally stable anodes (DSA) are sometimes used. This system is less time consuming and leads to smaller deviations in the thickness of the tin coating along the strip width. The main disadvantage of DSA is that it requires an external dissolution reactor to make up the tin content in the electrolyte.

According to the present invention, the advantages of SA- and DSA systems are combined here in a system that is completely new for high-speed strip electroplating, and this new system is hereinafter referred to as the DSSA system (with dimension-stable soluble anodes, from the English. "Dimension stable soluble anode ").

According to the method according to the invention, more uniform tin coatings can be applied, and it is even less labor-intensive, implies fewer hazards and is cost effective. The tin supply may be less, and in this case, in comparison with the DSA system, a separate dissolution reactor is not required. Less personnel are required to manipulate the anodes. In addition, when using tin as the anode in the form of the fraction contained in the anode basket of the present invention, the voltage on the electrolytic cell can be reduced. This is probably due to an increase in the anode surface. It will be clear that this also opens the way to an increase in production rates and thus a potentially higher yield in the case of the electrowinning production line under consideration.

The present invention will now be described in more detail by describing one example of the present invention.

EXAMPLE OF THE PRESENT INVENTION

In the example of the present invention, the details of the electroplating installation and process fluids, as well as the parameters were traditional, except when it is mentioned separately.

According to one aspect of the present invention, instead of individual tin bars, referring to FIGS. 1 and 6, anode baskets 12 are attached to the anode rod 4 through the contact insert 14. Contact inserts 14 made of copper in the experiments of this example can be coated on them surface in contact with the anode basket 12, a noble metal such as Au or Pt. In this embodiment, the contact inserts 14 were coated with Pt, which worked very well.

The anode baskets 12 of FIG. 6 are filled with tin shot (2-20 mm, preferably 5-9 mm in diameter). To replenish the anode substance, the tin fraction is fed regularly, which can be done with a fully working electroplating line. The anode baskets 12, in the experiments according to this example, made of titanium, are designed and arranged so that the anode is closer to the strip below to compensate for ohmic losses in the anode and strip, which would otherwise cause undesirable differences in current density in height stripes. For part of the production according to this example, the anode basket was closed with an anode bag to prevent small particles of tin from entering the electrolyte. Under normal operating conditions, the anode bags may need to be replaced 1-2 times a year. On the other hand, it turned out that for the other part of the production according to this example, where the anode bags were not used, this did not cause the problem of the ingress of small particles of tin into the electrolyte.

By supplying the DSSA system with an edge (edge) mask 13, see FIG. 7, tin buildup at the edges can even be reduced (“dog bone” effect). The design of these edge masks and the system for moving them are designed in such a way that they can be controlled from a safe distance from the plating process line, which eliminates time-consuming and possibly dangerous work.

With such a cathode / anode geometry, where the strip width is 1020 mm and the anode width exactly matches the strip and also is 1020 mm, when the strip width is subsequently changed from 1020 to 940 mm, the normalized current density, defined as i _avg , where i denotes the local current density, ai _avg denotes the average current density (for example, in A / m ² ), and therefore, the degree of tin buildup at the edges of the strip reaches an unacceptable level, see the upper curve in Fig. 8.

In Fig. 8, the horizontal axis shows D ES representing the distance in mm from the edge of the strip, the lower curve shows the i / i _avg from D ES for the strip and anode 1020 mm wide, and the upper curve shows i / i _avg after the strip width was changed to 940 mm with the anode configuration remaining the same as in the case of a strip 1020 mm wide.

To overcome this problem of tin buildup, a shutter is placed as a mask in front of the anode basket at the edge of a strip of smaller width. Figure 9 is a schematic representation of this situation. In Fig. 9, the vertical axis (Y-axis) is a plane passing through the center of the strip and perpendicular to the strip surface Y = 0 corresponds to the cross section of the front side of the strip and Y = 50 corresponds to the cross section of the front side of the anode, and the values on the Y axis correspond to distance from the cathode, abbreviated D AC. The horizontal axis (X-axis) corresponds to the distance from the center of the strip, D CS. The gray area in the range X = (450; 700) and Y = (10; 15) corresponds to the cross-section of the shutter, designated as M.

If in Fig. 9 the position of the shutter is changed from X = 470 mm (which corresponds to 0 mm of overlap with a strip having a width of 940 mm) to 440, 425 and 410 mm (which corresponds to overlap with a strip of 30, 45 and 60 mm, respectively), then the current density at the edge of the strip decreases, see Figure 10. 10, the upper curve corresponds to an overlap of 0 mm, the next curve below is 30 mm, the next curve below is 45 mm, and the lower curve is 60 mm.

In practice, an optimal distribution of the tin layer thickness can be detected by overlapping a mask and anode of about 45 mm.

It will be clear that the present invention represents a significant improvement by which the features and operation of existing electrotherapy lines can be significantly improved by providing a method that can be easily controlled, which is less time consuming, eliminates hazards and reduces waste streams (regeneration).

As an example, an automated feeding system can be designed so that the amount of tin fraction in the anode basket is maintained at a sufficient level to ensure a stable flow of tin ions into the electrolytic solution. An automated feed system may include a tin shot tank, conveyors to enable the tin shot to move from the tank to the anode basket, such as a conveyor belt or trough, means for measuring the tin shot level in the anode basket, and shutoff means, such as a valve or damper allowing tin shots to move from the tank to the anode basket by means of transportation if the means for measuring the tin shot level in the anode Rzine discovered a decrease in the level of tin fraction in the anode basket below a certain threshold value, as well as controls for the operation of the above funds.

Claims (8)

1. A method of high-speed electrotinning of a metal strip, comprising applying a tin coating to the strip in an electrolytic cell by anodic dissolution of tin anodes facing the strip in the form of anode baskets with tin shot and depositing the anode-dissolved tin on the strip serving as the cathode, wherein tin is fed into the anode basket in the form of a fraction, a part of the tin anodes is masked using adjustable edge masking tools, which are positioned and guided depending on the width of the strip and / or and distribution of the thickness of the tin coating, while applying the tin coating is carried out when the strip moves up and down. 2. The method according to claim 1, wherein the masking means include a shutter or a shutter. 3. The method according to claim 1 or 2, in which the tin fraction is brought into electrical contact by means of a current collector made of a material with low electrical resistance, which provides good electrical contact with the tin fraction and is electrochemically inert in the electrolyte. 4. The method according to claim 3, in which the anode basket is a current collector. 5. The method according to claim 3, in which the supply of tin fraction to the anode basket is automated. 6. The method according to claim 1, wherein the supply of tin fraction to the anode basket is automated. 7. The method according to claim 2, in which the supply of tin fraction to the anode basket is automated. 8. The method according to claim 3, in which the anode basket is a current collector and the supply of tin fraction to the anode basket is automated.

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