DESCRIPTION METHOD OF ELECTRIC TINNING
TECHNICAL FIELD [0001]
The present invention relates to a method of electric tinning using an insoluble electrode.
The present application is based on Japanese Patent Application No. 2004-228957, filed August 5, 2004, and Japanese Patent Application No. 2005-009569 filed January 17, 2005, the contents of which are incorporated herein by reference.
BACKGROUND ART [0002]
In a method of electric tinning using an insoluble electrode, since an anode is not dissolved compared to a method of electric tinning using a soluble electrode, a space between a strip of a cathode and the anode can be kept constant. Therefore, the method has an advantage of having a constant plating deposit and a uniform plating quality. Moreover, from the aspect of equipment operation, the method of electric tinning using an insoluble electrode has an advantage in that, since replacement of plating electrodes is less frequent, the number of workers for the replacement can be reduced. [0003]
In this method of electric tinning using an insoluble electrode, oxygen is blown into a metal tin dissolution tank filled with metal tin particles, while tin (Sn) is being dissolved therein, and thereby SnO is formed on the surface of the tin (Sn) particles. That

is, a reaction of the following equation (1) is obtained.
Sn+l/2O2- SnO (1)
H+ in the plating liquid reacts with SnO formed by this reaction, and Sn2+ is formed. That is, a reaction of the following equation (2) is obtained.
SnO+2H+ - Sn2++H20 (2)
At this time, if the amount of dissolved oxygen is excessive, SnO obtained by the reaction of the above equation (1) reacts with oxygen and thus becomes SnO2. That is, a reaction of the following equation (3) occurs.
SnO+l/2O2 - SnO2 (3)
Since this SnO2 is insoluble, it becomes sludge in the plating liquid. [0004]
If sludge is formed in the plating liquid due to tin ion Sn2+ oxidization, problems such as a decrease in the efficiency of tin ion formation, and clogging of the liquid supply pipe are caused. In order to avoid such problems, it is necessary to frequently collect and remove the sludge.
Moreover, if sludge is discharged into a plating tank and adhered onto the surface of an electroplating sheet, there is also a problem of impairing its aesthetic appearance. As to a method of inhibiting such sludge formation due to tin ion Sn2+ oxidization, it can be considered to decrease the concentration of oxygen dissolved in the plating liquid to be supplied into the metal tin dissolution tank. However, since metal tin is dissolved utilizing the reactions described in the above equations (1) and (2), in order to dissolve and supply a necessary amount of tin ion Sn2+, it is necessary to supply oxygen of an amount corresponding to this, and there is a limit to the method of decreasing the concentration of oxygen dissolved in the plating liquid. [0005]

3 For example, in the following Patent Document 1, in order to inhibit sludge
formed in a plating liquid due to oxidation of tin ion Sn2+, there is disclosed a method of forcedly agitating metal tin particles by means of machinery, and thereby increasing the dissolution rate of tin, so as to reduce the sludge formation. Moreover, in the following Patent Document 2, there is disclosed a method of supplying an electroplating liquid having a concentration of dissolved oxygen of 300 ppm or less, to metal tin particles in a metal tin dissolution tank that have been communicated through a plating liquid circulation tank to an electroplating tank equipped with insoluble anodes. [0006]
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H03-180493
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H04-131399
DISCLOSURE OF INVENTION [Problems to be Solved by the Invention] [0007]
The method disclosed in Patent Document 1 is a method of forcedly agitating metal tin particles by means of machinery, and thereby increasing the dissolution rate of tin, so as to reduce the sludge formation. However, it is not a method of reducing the sludge formation by adjusting the circulation amount of a plating liquid according to tin ion consumption. Moreover, in the method disclosed in Patent Document 2, if thick Sn plating is performed, there is a problem in that the target Sn plating can not be always obtained by a plating liquid having a concentration of dissolved oxygen of 300 ppm or less. [0008]

FIG. 7Ato 7D show examples of variations in tin ion consumption scheduled rates,
tin ion formation rates, tin ion concentrations, and tin sludge formation rates over time in a conventional method of electric tinning. Since the tin ion formation rate is determined corresponding to the actual tin ion concentration, for example as shown in FIG. 7B, there is a time lag due to following after changing the amount of oxygen to be blown and supplied into the metal tin dissolution tank until the tin ion concentration in the plating tank becomes stable. Therefore, for example as shown in FIG. 7C, the tin ion concentration may exceed the control target upper or lower critical values. For example, in the case where a thin-coating material is changed into a thick-coating material, the amount of tin ions supplied may be insufficient. In this case, an operator can put a large amount of oxygen for a short time to increase the circulation amount of the plating liquid so as to maintain the tin ion concentration. However, a large amount of sludge is formed at the same time. [0009]
Moreover, in a method in which an operator estimates the tin ion consumption to adjust the amount of oxygen to be blown and the circulation amount of the plating liquid, since setting can not be delicately changed, the adjustment is performed to supply excessive oxygen so that the amount of oxygen to be blown has some extra, and thus the sludge formation is prone to be increased.
The present invention takes the above problems into consideration with an object of providing a method of electric tinning which enables minimizing tin sludge formation while keeping the tin ion concentration in a plating tank within a control range.
[Means for Solving the Problem] [0010]

In order to solve the above problems, the present invention employs the following
means. That is,
(1) A method of electric tinning is employed in which metal tin is dissolved while
a plating liquid with oxygen dissolved therein is circulated between a metal tin dissolution
tank and a plating liquid circulation tank, and electroplating is performed using an
insoluble electrode while the plating liquid is circulated between the plating liquid
circulation tank and an electroplating tank, including: a first step of obtaining variation in
tin ion consumption scheduled rates over time from a sheet passing schedule when the
amount of oxygen to be blown is adjusted to control tin ion formation rates; a second step
of segmenting the tin ion formation rates per predetermined time based on the variation in
tin ion consumption scheduled rates over time, and setting the tin ion formation rates
obtained by averaging per each segment as the average variation over time; and a third step
of adjusting the amount of oxygen to be blown so that the tin ion concentration according
to the average variation over time is the tin ion formation rate not exceeding the control
target upper and lower critical values in each of the segments.
[0011]
(2) In the second step, when the tin ion formation rates are segmented per
predetermined time, segmentation may be performed by each time in which these tin ion
formation rates are prone to be increased, and the tin ion formation rates may be averaged
for each of these segments.
(3) In the second step, when the tin ion formation rates are segmented per
predetermined time, segmentation may be performed so that the tin ion concentration does
not exceed control target upper and lower critical values, and the tin ion formation rates
may be averaged for each of these segments.

(4) In the second step, when the tin ion formation rates are segmented per
predetermined time, segmentation may be performed by each time in which the averaged
tin ion formation rates are increased, and the averaged tin ion formation rates may be
averaged for each of these segments.
(5) In the second step, when the tin ion formation rates are segmented per
predetermined time, segmentation may be performed so that the tin ion concentration does
not exceed control target upper and lower critical values, and the averaged tin ion
formation rates may be averaged for each of these segments.
[0013]
(6) If there is a difference between scheduled tin ion formation and actual tin ion
formation in a segment per predetermined time, the tin ion formation rate averaged for
each of the segments may be corrected in the segment.
(7) The correction of the tin ion formation rate may be obtained by the following
equation:
tin ion formation rate correction = {(scheduled tin ion formation - actual tin ion formation) before correction in each segment}/ remaining time after correction in each time-basis segment. [Effects of the Invention] [0014]
According to the method of electric tinning of the present invention, since the tin ion formation rate can be made closer to the average tin ion consumption scheduled rate, while the tin ion concentration does not exceed the control target upper and lower critical values, the tin sludge can be reduced. Due to this reduction of tin sludge, a reduction in the tin basic unit becomes possible. Moreover, due to the reduction of adherence of tin sludge

onto the plating equipment, maintenance operation can be reduced. The concern that the
tin sludge is discharged into a plating tank and is adhered onto the surface of an electroplating sheet, impairing the aesthetic appearance, can also be decreased, and such excellent effects can be demonstrated.
BRIEF DESCRIPTION OF THE DRAWINGS [0015]
FIG. 1 is an overall schematic diagram of an apparatus to which a method of electric tinning according to a first embodiment of the present invention is applied.
FIG. 2A shows variation in control elements over time in the method of electric tinning, showing variation in tin ion consumption scheduled rates over time.
FIG. 2B shows variation in control elements over time in the method of electric tinning, showing variation in tin ion formation rates over time.
FIG. 2C shows variation in control elements over time in the method of electric tinning, showing variation in tin ion concentrations over time.
FIG. 2D shows variation in control elements over time in the method of electric tinning, showing variation in tin sludge formation rates over time.
FIG. 3 A shows variation in control elements over time in the method of electric tinning according to a second embodiment of the present invention, showing variation in tin ion consumption scheduled rates over time.
FIG. 3B shows variation in control elements over time in the method of electric tinning, showing variation in tin ion formation rates over time.
FIG. 3C shows variation in control elements over time in the method of electric tinning, showing variation in tin ion concentrations over time.
FIG. 3D shows variation in control elements over time in the method of electric

tinning, showing variation in tin sludge formation rates over time.
FIG. 4A shows a case where there is a difference between scheduled tin ion formation and actual tin ion formation in the middle of a certain segment over time, showing variation in tin ion consumption rates over time.
FIG. 4B shows a case of having the difference, showing variation in tin ion formation rates over time.
FIG. 4C shows a case of having the difference, showing variation in tin ion consumption rates over time.
FIG. 4D shows a case of having the difference, showing variation in tin ion formation rates over time.
FIG. 5 A shows a case where, if there is a difference between scheduled tin ion formation and actual tin ion formation in the middle of a certain segment over time similarly to the case of FIG. 4A to 4D, correction is performed only by means of next coil treatment, showing variation in tin ion formation rates over time.
FIG. 5B shows the case where correction is performed only by means of next coil treatment, showing variation in tin ion concentrations over time.
FIG. 5C shows the case where correction is performed only by means of next coil treatment, showing variation in tin sludge formation rates over time.
FIG. 6A shows variation in control elements over time in the method of electric tinning according to a third embodiment of the present invention, showing variation in tin ion formation rates over time.
FIG. 6B shows variation in control elements over time in the method of electric tinning, showing variation in tin ion concentrations over time.
FIG. 6C shows variation in control elements over time in the method of electric tinning, showing variation in tin sludge formation rates over time.

FIG. 7A shows variation in control elements over time in a conventional method
of electric tinning, showing variation in tin ion consumption scheduled rates over time.
FIG. 7B shows variation in control elements over time in the conventional method of electric tinning, showing variation in tin ion formation rates over time.
FIG. 7C shows variation in control elements over time in the conventional method of electric tinning, showing variation in tin ion concentrations over time.
FIG. 7D shows variation in control elements over time in the conventional method of electric tinning, showing variation in tin sludge formation rates over time.
[Brief Description of the Reference Symbols] [0016]
1 Metal tin dissolution tank
2 Metal tin supply unit
3 Metal tin particles
4 Plating liquid circulation tank
5 Electroplating tank
6 Pump
7 Open/close valve
8 Plating liquid circulation pipe
9 Insoluble electrode

10 Strip
11 Pipe
12 Tin ion concentration meter
13 Oxygen supply source

BEST MODE FOR CARRYING OUT THE INVENTION
Hereunder is a description of a first embodiment of a method of electric tinning of the present invention, with reference to the drawings.
As shown in the overall schematic diagram of FIG. 1, an electric tinning apparatus to which the method of electric tinning of the present embodiment is applied comprises a metal tin dissolution tank 1, a metal tin supply unit 2, metal tin particles 3, a plating liquid circulation tank 4, an electroplating tank 5, pumps 6, open/close valves 7, plating liquid circulation pipes 8, insoluble electrodes 9, a strip 10, a pipe 11, a tin ion concentration meter 12, an oxygen supply source 13, and a controller (not shown and described later).
As shown in the drawing, in the metal tin dissolution tank 1, metal tin particles 3 supplied from the metal tin supply unit 2 through the open/close valve 7 are dissolved while a plating liquid into which oxygen is blown from the oxygen blowing pipe 11 is being circulated between the plating liquid circulation tank 4 and the metal tin dissolution tank 1. Moreover, the apparatus is designed such that electric tinning is performed onto the strip 10 using the insoluble electrodes 9 while the plating liquid is being circulated between the electroplating tank 5 and the plating liquid circulation tank 4. Furthermore, between the plating liquid circulation tank 4 and the electroplating tank 5, and between the plating liquid circulation tank 4 and the metal tin dissolution tank 1, are respectively connected plating liquid circulation pipes 8 through which the plating liquid is circulated. Among these plating liquid circulation pipes 8, the plating liquid circulation pipe 8 which supplies the plating liquid from the plating liquid circulation tank 4 to the metal tin dissolution tank 1, is furnished with the pump 6 and the open/close valve 7. On the other hand, the plating liquid circulation pipe 8 which supplies the plating liquid from the plating liquid circulation tank 4 to the electroplating tank 5, is furnished with the pump 6.

Between plating liquid circulation tank 4 and the metal tin dissolution tank 1, and between the plating liquid circulation tank 4 and the electroplating tank 5, is formed two circulation routes having a route through which the plating liquid on one side supplied from the plating liquid circulation tank 4 returns through the metal tin dissolution tank 1 to the plating liquid circulation tank 4, and a route through which the plating liquid on the other side supplied from the plating liquid circulation tank 4 returns through the electroplating tank 5 to the plating liquid circulation tank 4.
Between the oxygen supply source 13 and the plating liquid circulation pipe 8 which supplies the plating liquid from the plating liquid circulation tank 4 to the metal tin dissolution tank 1, is connected by the oxygen blowing pipe 11. Moreover, when the plating liquid is supplied from the plating liquid circulation tank 4 to the metal tin dissolution tank 1, the plating liquid is supplied with oxygen gas from the oxygen supply source 13 through the oxygen blowing pipe 11.
The tin ion concentration in the electroplating tank 5 that is decreased as electric tinning is performed onto the strip 10 using the insoluble electrodes 9, is supplemented by the plating liquid replenished from the plating liquid circulation tank 4. Reference symbol 12 denotes a tin ion concentration meter for measuring the tin ion concentration in the plating liquid circulation tank 4. [0019]
In the electric tinning apparatus having the structure described above, it is necessary to appropriately control the tin ion concentration. From operational experience up to now, the present applicants have found that there are relations such as the following equations (4) and (5) between the tin sludge formation rate and the tin ion formation rate.
(tin sludge formation rate) /x (amount of oxygen to be blown )2 (4)

(tin ion formation rate) /x (amount of oxygen to be blown) (5)
Thus, the following equation (6) is obtained from the above equations (4) and (5). (tin sludge formation rate) oc (tin ion formation rate )2 (6)
Consequently, it is understood that, in order to inhibit the tin sludge formation at the time of tin ion formation, as shown in the following equation (7), the average tin ion consumption scheduled rate during the tin ion consumption, may be set as the tin ion formation rate. [0020]
y = (x+Xl)2+(x+X2)2+(x+x3)2+... = nx2+Zxi2 (7) Here tin ion formation rate : x+x;
average tin ion consumption scheduled rate : x
sludge formation rate : y
However, the tin ion concentration is closely related to the quality of glossiness of a plated product. Generally, the tin ion concentration is necessarily kept within a constant narrow range. [0021]
Assuming that the average tin ion consumption scheduled rate during the tin ion consumption is the tin ion formation rate, the tin ion concentration in the plating liquid is continuously increased as the plating progresses at the time of thin-plating, and the tin ion concentration in the plating liquid is decreased as the plating progresses at the time of thick-plating. In either case, there is a possibility of defective glossiness. Accordingly, in the present embodiment, using the controller which controls the tin ion formation, (a) a

sheet passing schedule is received from a process computer (not shown) so as to calculate
tin ion consumption scheduled rates, (b) based on this tin ion consumption scheduled rate, the sheet passing schedule is segmented into each predetermined time, (c) the tin ion formation rates are averaged per each segment, and (d) according to the term (time) within the averaged control target value, the tin ion concentration in the plating liquid circulation tank 4 is controlled. The "sheet passing schedule" in the present invention means data containing a lot order of the sheet passing schedule and; (i) lot No., (ii) sheet passing weight (ton), (iii) sheet passing speed (ton/hour), (iv) sheet width (mm), (v) sheet thickness (mm), and (vi) amount of plating (g/m2) per lot. [0022]
FIG. 2A to 2D show respective variation in control elements over time in the method of electric tinning of the present embodiment, wherein FIG. 2 A shows variation in tin ion consumption scheduled rates over time, FIG. 2B shows variation in tin ion formation rates over time, FIG. 2C shows variation in tin ion concentrations over time, and FIG. 2D shows variation in tin sludge formation rates over time. As shown in these drawings, the term of which the tin ion consumption scheduled rate is to be averaged, is determined, and the tin ion formation rate (variation over time) is determined, by the following procedures of (1) to (5). [0023]
(1) Using the controller which controls the tin ion formation, the sheet passing
schedule is received from the process computer so as to calculate tin ion consumption
scheduled rates to produce FIG. 2A.
(2) The tin ion formation rates are averaged per each term (terms a, p, and y
shown in FIG. 2A) during which it is estimated that the tin ion formation rate is increased,
so as to calculate variation in tin ion formation rates over time to produce a graph

corresponding to FIG. 2B.
(3) The variation in tin ion concentrations over time is calculated from the current
tin ion concentration, the variation in tin ion consumption scheduled rates over time shown
in FIG. 2A, and the variation in tin ion formation rates over time shown in FIG. 2B, to
produce FIG. 2C.
(4) The steps (2) and (3) are repeated until the tin ion concentration in at least one
of the respective terms (term a, p, and y) exceeds the control target upper and lower critical
values.
(5) The variation in tin ion formation rates over time for a case where the tin ion
concentration did not exceed the control target upper and lower critical values in any one
of the respective terms (term a, p, and y) in step (4) is set as a planned value of variation in
tin ion formation rates over time (FIG. 2B).
[0024]
By the above procedure, the tin ion formation rates can be leveled without the tin ion concentration exceeding the control target upper and lower critical values, and the tin sludge formation rate can be suppressed. This is well understood by comparing FIG. 2D and FIG. 7D. For example, even for the same tin ion consumption scheduled rate, although the tin sludge formation (that is, tin sludge formation rate y x time t) of the conventional technique is 100, it is decreased to 79.5 in the present embodiment. [0025]
Subsequently, hereunder is a description of a second embodiment of the method of electric tinning of the present invention, with reference to FIG. 3 A to 3D. In the following description, points differing from the first embodiment are mainly described, and the rest is regarded as the same as that of the first embodiment and the description thereof is omitted.

FIG. 3 A to 3D show respective variations in control elements over time in the
method of electric tinning of the present embodiment, wherein FIG. 3 A shows variation in tin ion consumption scheduled rates over time, FIG. 3B shows variation in tin ion formation rates over time, FIG. 3C shows variation in tin ion concentrations over time, and FIG. 3D shows variation in tin sludge formation rates over time.
As shown in these drawings, the term of which the tin ion consumption scheduled rate is to be averaged, is determined, and the tin ion formation rate (variation over time) is determined, by repeating the following procedures of (1) to (5). [0026]
(1) Using the controller which controls the tin ion formation, the sheet passing
schedule is received from the process computer so as to calculate the tin ion consumption
scheduled rates to produce FIG. 3A.
(2) The tin ion formation rates of two consecutive terms are averaged, so as to
calculate variation in tin ion concentrations over time.
(3) The variation in tin ion concentrations over time is calculated from the current
tin ion concentration, the variation in tin ion consumption scheduled rates over time, and
the variation in tin ion formation rates over time.
(4) Steps (2) and (3) are repeated until the tin ion concentration in the term to be
averaged exceeds the control target upper and lower critical values.
(5) The variation in tin ion formation rates over time of a case where the tin ion
concentration did not exceed the control target upper and lower critical values in the
respective terms (term a and p shown in FIG. 3 A) in step (4) is set as a planned value of
variation in tin ion formation rates over time (FIG. 3B).
[0027]
By the above procedure, the tin ion formation rates can be leveled without the tin

ion concentration exceeding the control target upper and lower critical values, and the tin
sludge formation rate can be suppressed. This is well understood by comparing FIG. 2D and FIG. 7D. For example, even for the same tin ion consumption scheduled rate, although the tin sludge formation (that is, tin sludge formation rate y x time t) of the conventional technique is 100, it is decreased to 80 in the present embodiment. [0028]
In the case where there is a difference between the scheduled tin ion formation and the actual tin ion formation in the middle of a certain segment (certain term) in the time-based direction (on the time axis), the controller which controls the tin ion formation is used so as to calculate the difference and perform correction, by the following procedures of (1) to (3).
(1) At each time when one coil treatment per each segment (each term) in the
time-based direction is completed, the difference between the scheduled tin ion formation
(= tin ion formation rate x scheduled time) and the actual tin ion formation (= tin ion
formation rate x actual time) is calculated.
(2) If there is a difference between the scheduled tin ion formation and the actual
tin ion formation, the difference is divided by the remaining time in the present segment,
which is then set as the tin ion formation correction.
(3) The averaged tin ion formation that was previously scheduled, is added with
the tin ion formation correction, which is then set as the tin ion formation averaged after
correction.
[0029]
FIG. 4A to 4D show the case where there is a difference between the scheduled tin ion formation and the actual tin ion formation in the middle of a certain segment (term) in the time-based direction, showing an example where the treatment time for the first coil in

the certain segment (term) is affected by decrease in line speed, line halt, or the like, and is
doubled. That is, FIG. 4A shows variation in tin ion consumption rates over time, FIG. 4B shows variation in tin ion formation rates over time, FIG. 4C shows variation in tin ion consumption rates over time, and FIG. 4D shows variation in tin ion formation rates over time.
As understood by comparing FIG. 4B and FIG. 4D, the actual tin ion formation at the time of completion of one coil treatment in a segment is greater than the scheduled tin ion formation. [0030]
FIG. 5 A to 5C show a comparative example of the case where, if there is a difference between scheduled tin ion formation and actual tin ion formation in the middle of a certain segment (term) in the time-based direction similarly to the case of FIG. 4Ato 4D, correction is performed only by means of next coil treatment. That is, they show the case where the difference between FIG. 4C showing the scheduled tin ion formation and FIG. 4D showing the actual tin ion formation at the time of completion of one coil treatment in a certain segment, is corrected only by means of next coil treatment. FIG 5 A shows variation in tin ion formation rates over time, FIG. 5B shows variation in tin ion concentrations over time, and FIG. 5C shows variation in tin sludge formation rates over time.
If correction is performed only by means of next coil treatment in order to correspond to the case of having a difference between scheduled tin ion formation and actual tin ion formation in the middle of a certain segment (term) in the time-based direction, then, as shown in FIG. 5C, it is understood that the sludge formation is great. [0031]
FIGS. 6A to 6C show variation in respective control elements over time in the

method of electric tinning according to a third embodiment of the present invention,
showing the case where, if there is a difference between FIG. 4C showing the scheduled tin ion formation and FIG. 4D showing the actual tin ion formation at the time of completion of one coil treatment in a certain segment, the difference is evenly corrected within the remaining time in the segment. Specifically, FIG. 6A shows variation in tin ion formation rates over time, FIG. 6B shows variation in tin ion concentrations over time, and FIG. 6D shows variation in tin sludge formation rates over time.
If correction is evenly performed within the remaining time in the segment such as with the present embodiment, then as understood by comparing FIG. 5C and FIG. 6C, although the tin sludge formation (tin sludge formation rate y x time) of the comparative example where correction is performed only by means of next coil treatment is 27, the tin sludge formation (tin sludge formation rate y x time) is decreased to 22.5 in the present embodiment where correction is evenly performed within the remaining time in the segment.
As described above, according to the present embodiment, if there is a difference between scheduled tin ion formation and actual tin ion formation in the middle of a time-basis segment, tin sludge can be reduced by evenly correcting the tin ion formation within the remaining time in the segment. [0032]
As described above, according to the present embodiment, since the tin ion formation rate can be made closer to the average consumption scheduled rates within the time for consuming tin ion, while the tin ion concentration does not exceed the control target upper and lower critical values, the tin sludge can be reduced. Due to this reduction of tin sludge, a reduction in the tin basic unit becomes possible. Moreover, since adherence of tin sludge onto the electric tinning apparatus can be reduced, the time and

19 effort for maintenance can be reduced. Furthermore, concern that this sludge is discharged
into a plating tank (such as the electroplating tank 5) and is adhered onto the surface of an electroplating sheet (such as the strip 10), impairing the aesthetic appearance, can also be decreased.
INDUSTRIAL APPLICABILITY
According to the method of electric tinning of the present invention, since the tin ion formation rate can be made closer to the average consumption scheduled rates within the time for consuming tin ion, while the tin ion concentration does not exceed the control target upper and lower critical values, the tin sludge can be reduced. Due to this reduction of tin sludge, a reduction in the tin basic unit becomes possible. Moreover, since adherence of tin sludge onto the electric tinning apparatus can be reduced, the time and effort for maintenance can be reduced. Furthermore, concern that this sludge is discharged into a plating tank and is adhered onto the surface of an electroplating sheet, impairing the aesthetic appearance, can also be decreased.

WE CLAIM;
1. A method of electric tinning which treats coil wherein metal tin is dissolved while
a plating liquid with oxygen dissolved therein is circulated between a metal tin
dissolution tank and a plating liquid circulation tank, and electroplating is performed
using an insoluble electrode while said plating liquid is circulated between said plating
liquid circulation tank and an electroplating tank, characterized in that the method
comprising:
a first step of obtaining variation in tin ion consumption scheduled rates over time from a sheet passing schedule when said amount of oxygen to be blown is adjusted to control tin ion formation rates;
a second step of segmenting said tin ion formation rates per predetermined time based on said variation in tin ion consumption scheduled rates over time, and setting the tin ion formation rates obtained by averaging per each segment as the average variation over time; and
a third step of adjusting said amount of oxygen to be blown so that said tin ion concentration according to said average variation over time of said tin ion formation rate becomes the tin ion formation rate not exceeding the control target upper and lower critical values in each of said segments.
2. The method of electric tinning as claimed in claim 1, wherein, in said second step, when said tin ion formation rates are segmented per predetermined time, segmentation is performed by each time in which these tin ion formation rates are prone to be increased, and the tin ion formation rates are averaged for each of these segments.
3. The method of electric tinning as claimed in claim 1, wherein, in said second step, when said tin ion formation rates are segmented per predetermined time, segmentation is performed so that said tin ion concentration does not exceed control
target upper and lower critical values, and the tin ion formation rates are averaged for each of these segments.
4. The method of electric tinning as claimed in claim 1, wherein, in said second step, when said tin ion formation rates are segmented per predetermined time, segmentation is performed by each time in which said averaged tin ion formation rates are increased, and the averaged tin ion formation rates are averaged for each of these segments.
5. The method of electric tinning as claimed in claim 1, wherein, in said second step, when said tin ion formation rates are segmented per predetermined time, segmentation is performed so that said tin ion concentration does not exceed control target upper and lower critical values, and the averaged tin ion formation rates are averaged for each of these segments.
6. The method of electric tinning as claimed in claim 1, wherein, if there is a
difference between scheduled tin ion formation and actual tin ion formation in a segment
per predetermined time, said tin ion formation rate averaged for each of said segments are
corrected in the segment.
7. The method of electric tinning as claimed in claim 6, wherein correction of said tin ion formation rate is obtained by the following equation: tin ion formation rate correction = {(scheduled tin ion formation - actual tin ion formation) before correction in each segment} / remaining time after correction in each time-basis segpaent.