Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-10-20
2003-07-08
Valentine, Donald R. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S232000, C204S275100
Reexamination Certificate
active
06589399
ABSTRACT:
TECHNICAL FIELD
This invention relates to an electrolytic apparatus with a liquid throttle unit that establishes non-contacting sealing between a strip and a liquid electrolyte during electrolytic plating, of the surface of a metal strip, with tin, zinc, chromium or other metal or during pickling or other surface treatment.
BACKGROUND TECHNOLOGY
Numerous methods and apparatuses have been proposed for electrolytic plating of the surface of a metal strip with tin, zinc, chromium or other metals. Recently, particular demand has arisen for high-efficiency, high-speed plating equipment that offers high performance in excess of 500 m/min. For such high-speed plating, however, a specific requirement must be met, because, in the vertical type plating apparatus, the strip passes vertically and the running strip penetrates a portion of the cell body at its bottom end, while in the horizontal type plating apparatus the strip passes horizontally and the running strip laterally penetrates a center portion of the cell body. In order to conduct the plating (including pickling and other treatments) while continuously moving the metal strip to be plated, it is therefore necessary to seal the penetrated portion so as to prevent leakage of the treatment liquid. This is because the constant running state of the strip results in the plating treatment liquid also being leaked as an entrained flow along the running strip surface.
Specifically, as shown in
FIG. 1
, the amount of plating treatment liquid leakage owing to entrained flow is proportional to strip running speed. It was found that at a strip running speed of around 200 m/min, the amount of plating treatment liquid leakage (loss) rises to 20% or more of the fed treatment liquid, at a strip running speed of about 500 m/min, it reaches 80% or higher, and at 1000 m/min, the maximum strip running speed currently conceivable, the amount of leakage reaches nearly 100%. With such increasing leakage, the amount of treatment liquid fed must be increased to continue operation with the plating treatment cell kept constantly full.
Sealing methods for preventing treatment liquid leakage include one, such as taught by JP-A-(unexamined published Japanese patent application)5-331695, in which a pair of damrolls are installed one on either side of the strip pass line to be rotatable in contact with the strip surface, the opposite axial ends of the damrolls are sealed by seal rings from the outside, and seal plates are installed for sealing by contact with the peripheral surfaces of the damrolls. This method, which is an improvement on the well-known rotating seal system, enables the sealing capability with respect to the strip surface to be increased substantially in proportion to the squeezing force between the damrolls.
FIG. 12
illustrates a vertical type electrolytic apparatus disclosed by JP-A-5-171495. As shown, liquid electrolyte
103
is fed between a strip
100
and electrodes
101
,
102
to impart an agitation effect between the strip and the electrodes. In addition, liquid seal devices
104
a
and
104
b
equipped with seal rolls
105
a,
105
b
are installed at the lowermost portion of the vertical type electrolytic apparatus for preventing runoff of the liquid electrolyte
103
, thereby obtaining a high current density while maintaining the level of the liquid electrolyte.
As shown in
FIG. 13
, a vertical type electrolytic apparatus disclosed in JP-A-60-56092 (U.S. Pat. No. 5,236,566) imparts an agitation effect between a strip
115
and a liquid electrolyte
110
by using liquid feed nozzles
113
and
114
to feed liquid electrolyte into spaces between electrodes
1
.
11
and electrodes
112
immersed in the liquid electrolyte
110
.
In the method of squeezing the strip with damrolls, however, the strip surface tends to be easily scratched. One reason for this is that the squeezing force of the rolls on the strip has to be maintained high in order to secure sealing pressure. Another is that contact scratches are produced between the strip and the roll surfaces owing to mismatching between the strip running speed and the circumferential speed of the rolls. What happens most often, however, is that sludge carried in from the exterior and, particularly in the electrolytic cell, foreign matter such as electrolytic deposits, get into the treatment liquid and lodge between the strip surface and the damrolls to become sources of scratching. This lowers production yield, degrades quality, makes more frequent roll inspection and exchange necessary, and leads to a decline in production line operating rate. In a case where the strip passes between the seal rolls while running in a meandering state, moreover, if the strip should snake in the manner of weaving in the axial direction of the rolls, then, since the strip is squeezed between the rolls, the portions of the strip strongly squeezed by the rolls pass with no freedom in the thrust direction, thereby producing wrinkles in the strip. This, in conjunction with the aforesaid biting of foreign matter, further markedly degrades quality.
In the aforesaid vertical type electrolytic apparatus, achievement of electrolytic plating at high current density during high-speed strip streaming of the strip requires efficient feeding of metallic ions to the plating surface and rapid removal the large quantity of gas produced by the high-current-density electrolysis from between the electrodes. The problems posed by these needs have not yet been solved. The vertical type electrolytic apparatus disclosed by JP-A-5-171495 (
FIG. 12
) still has the following problems:
1) Since the liquid electrolyte
103
is retained solely by electrode units formed by the electrodes
101
and
102
and, furthermore, prevention of liquid electrolyte runout is conducted by the pair of seal rolls
105
a,
105
b,
the loads on the liquid seal devices
104
a,
104
b
are excessive, making liquid retention difficult during high-speed strip streaming.
2) Scratching owing to slipping between the strip
100
and the seal rolls
105
a,
105
b
is liable to occur during high-speed strip streaming and scratching is also produced by foreign matter pressed onto the strip after lodging between the strip and seal rolls.
3) Since the seal rolls themselves experience damage and wear that degrades their liquid seal performance and leads to increased liquid electrolyte leakage, the flow rate required at the electrodes for plating becomes hard to secure and defective plating therefore arises owing to uneven liquid electrolyte flow.
On the other hand, the vertical type electrolytic apparatus disclosed by JP-A-60-56092 (
FIG. 13
) conducts plating with the electrodes
111
and
112
immersed in the liquid electrolyte
110
and can adequately handle currently used strip running speeds. However, if the strip running speed should be raised to a high level without implementing some measure such as installation of a liquid throttle device or the like, the loss owing to the entrained flow caused by movement of the strip
115
will, as shown in
FIG. 1
, increase with increasing running speed of the strip, namely, will accelerate up to and reach substantially 100% at around 500 m/min. Even if the strip running speed is further increased to around 1000 m/min, the loss by entrained flow will remain saturated. When this phenomenon occurs, the flow rate between the strip
115
and the electrodes
111
,
112
becomes hard to secure and plating defects such as burnt deposits occur.
DISCLOSURE OF THE INVENTION
The present invention was made to overcome the foregoing problems. One of its objects is to provide a method for prevention of plating treatment liquid leakage and utmost avoidance of strip surface scratching and wrinkling. Another of its objects is to provide an electrolytic apparatus with a strip non-contacting liquid throttle unit that can facilitate inter-electrode liquid retention during high-speed strip streaming, prevent clinging of the strip to the electrodes, and enhance plated product quality and plating operation efficiency.
A first aspect of the pre
Sanada Masaharu
Shimamura Michihiro
Kenyon & Kenyon
Nippon Steel Corporation
Valentine Donald R.
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