Information
-
Patent Grant
-
6325913
-
Patent Number
6,325,913
-
Date Filed
Monday, August 23, 199925 years ago
-
Date Issued
Tuesday, December 4, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Valentine; Donald R.
- Smith-Hicks; Erica
Agents
- Mattingly, Stanger & Malur, P.C.
-
CPC
-
US Classifications
Field of Search
US
- 204 242
- 204 206
- 204 208
- 204 2302
- 204 269
-
International Classifications
- C25D1700
- C25B900
- C25B1500
- C25F106
-
Abstract
This invention relates to an improved apparatus and method for electrolytic descaling of steel strips. The apparatus comprises electrodes integrated with nozzles having jet openings for dispensing electrolyte onto the surface of the steel strips. By jetting the electrolyte to the steel strip in the air and applying a voltage to the electrode, the scale on the surface of the steel strip is removed. This jetting of electrolyte reduces the size requirement of the electrolyte tank storing the electrolyte because the required quantity of electrolyte decreases. The present invention does not require immersion of the electrodes in the electrolyte and thus avoids the problem of short-circuiting that occurs with submerged electrodes. This results in a significant improvement in electric power efficiency. By individually adjusting the jet pressure of the electrolyte jets, the waving and the flexure of the steel strip is prevented and the electrodes can be arranged close to the steel strip to reduce required electric power. With the reduction in short circuit currents, many electrodes can be provided and the speed of the descaling can be increased as a result of the increase in electric current to the steel strip.
Description
The present invention relates to a steel strip descaling apparatus and a steel strip manufacturing apparatus using the descaling apparatus.
BACKGROUND OF THE INVENTION
A technique that removes an oxide (scale) formed on the surface of steel strips by electrolyzing scale in solutions such as a neutral salt, a nitrate and a sulfate is known.
The Japanese patent Laid-open No. 3-56699 describes pumping an electrolyte to a steel strip submerged in the electrolyte from the hole of an electrolyte in order to prevent the steel strip from waving.
The Japanese patent Laid-open No.8-100299 describes spraying an electrolyte to a steel strip in the air in order to apply an electric current.
SUMMARY
However, in the art of No. 3-56699, because electrolyte and an electric conductor do not contact each other directly, a large quantity of electrolyte is necessary. The apparatus is large because of a large electrolyte bath. As the electrodes are also located in the electrolyte, a third disadvantage of this prior art technique is that short circuits occur among the electrodes through the electrolyte.
In the art of No.8-100299, because whirls occur between an electrode and the steel strip, electric current provided to the steel strip from the electrodes is small and the electric current is variable. Therefore the steel strip is not descaled rapidly and uniformly because of the variable electric current. We can not produce a steel strip which has uniformly beautiful surfaces with this art.
The present invention relates to a steel strip descaling apparatus and a steel strip manufacturing apparatus.
The purpose of the present invention is to provide the steel strip descaling apparatus and the steel strip manufacturing apparatus which improve the electric power efficiency, processing speed and miniaturization.
To achieve the above purpose, a feature of the present invention is that electrodes have jet openings which jet the electrolyte to the steel strip, that is to say, the electrode is integrated with the nozzle which jets an electrolyte.
With these electrodes, by jetting the electrolyte to the steel strip in the air and applying a voltage to the electrode, the scale (oxide coating or layer) on the surface of the steel strip is removed.
According to a feature of the present invention, it is possible to reduce the size of an electrolyte tank storing the electrolyte, because the quantity of an electrolyte decreases by jetting the electrolyte in the air. Therefore, the descaling apparatus is miniaturized.
In contrast to the conventional art wherein the steel to be treated is submerged in the electrolyte, the present invention's use of jetting means for jetting the electrolyte onto the steel strip obviates immersion of the steel strip and the occurrence of short-circuit electric current between the electrodes, thus improving electric power efficiency.
Because the electrolyte jetted from the jet opening contacts an conductor applied the voltage, we can supply large electric current to the steel strip through the jetted electrolyte.
Therefore, the electric current density of the steel strip is large and the steel strip is descaled rapidly.
Providing many electrodes improves the speed of the descaling because the electric current density in the steel strip increases.
Another feature of the present invention is that the descaling apparatus further has force adjustment of the jetted electrolyte.
By adjusting the force of the jetted electrolyte, the waving and the flexure of the steel strip is prevented, and we can arrange the electrodes close to the steel strip.
Because the electrodes are moved closer to the steel strip, a voltage drop between the electrodes and the steel strip becomes lower, and the electric power for the descaling can be decreased.
By using the above-mentioned descaling apparatus, the steel strip manufacturing apparatus attains an improvement in electric power efficiency and the processing speed, and the manufacturing apparatus becomes small.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
shows the stainless steel strip manufacturing apparatus of the first example.
FIG. 2
shows neutral salt solution electrolysis part of
FIG. 1
in greater detail.
FIG.
3
A and
FIG. 3B
shows the electrode in detail and in plan view, respectively.
FIGS. 4A
to
4
D show normal steel strip manufacturing apparatus of the second example.
FIG.
5
A and
FIG. 5B
show another example of electrode in detail and in sectional view, respectively.
FIG. 6
shows an example of power supply systems and jet adjusting systems.
FIG. 7
shows an example of electrodes arrangement in plan view.
EMBODIMENTS
EXAMPLE 1
The stainless steel strip manufacturing apparatus according to the first embodiment of the present invention is explained with respect to FIG.
1
.
The steel strip
1
unwound from the pay off reel
2
is rolled by the cold rolling mill
3
and is annealed in the annealing hearth
4
for the heat characteristic improvement of the ductility and the like. At this time, a scale that is a thin oxide film such as a chrome oxide, an iron oxide and so on, is formed on the surface of the steel strip
1
and causes a quality declination.
The rolled steel strip
1
passes through the cooling hearth
5
and passes through the neutral salt solution electrolysis part
6
that is the first electrolysis part. In the neutral salt solution electrolysis part
6
, with the neutral salt solution
20
(shown in
FIG. 2
) as a sulfate sodium solution, chrome oxide is eliminated.
Next, the steel strip
1
passes through the alkali solution electrolysis part
8
that is the middle electrolysis cell via washing tank
7
. Next, the steel strip
1
passes through the nitrate solution electrolysis part
10
via washing tank
9
. In the alkali solution electrolysis part
8
, with a sodium hydroxide solution, a very small quantity of oxide such as a copper oxide niobium oxide is eliminated. In the nitrate solution electrolysis part
10
, with a nitrate solution, an iron oxide is eliminated. It is possible to substitute the nitric acid and hydrofluoric acid for the nitrate solution. In accordance with the kind of stainless steel, the processing is possible to perform without the alkali solution electrolysis part
8
and washing tank
9
. The processing temperature and the density of the electrolyte solution are the same as the conventional processing.
Finally, the steel strip
1
is wound to the reel
14
via the washing tank
11
, the drier
12
and the skin pass roller
13
.
The neutral salt solution electrolysis part
6
is explained in detail, in
FIG. 2
as representative of the parts
6
,
8
,
10
that are structurally identical with respect to the detail shown in the disclosure.
The neutral salt solution electrolysis part
6
comprises an electrolyte tank
21
storing the neutral salt solution
20
, a pump
22
that pressurizes the neutral salt solution
20
, anodes
23
and cathodes
24
that also serve as a nozzle, and power
25
connected to the anodes
23
and the cathodes
24
. The anodes
23
are arranged in the upstream region relative to the movement direction of the steel strip
1
, and the cathodes
24
are arranged in the downstream region, on both sides of the steel strip
1
. In the respective regions, the electrodes of both sides are the same polarity.
The anodes
23
and the cathodes
24
have jet openings
26
that jet neutral salt solution
20
to the steel strip
1
. That is, the anodes
23
and the cathodes
24
are integrating with the nozzles that jet the neutral salt solution
20
. The neutral salt solution
20
in the electrolyte tank
21
is pressurized by the pump
22
and is jetted on both sides of steel strip
1
from the jet openings
26
of the anodes
23
and the cathodes
24
. Thereby both sides of steel strip
1
are covered by a film of the neutral salt solution
20
. The excessive neutral salt solution
20
returns to the electrolyte tank
21
.
In the example 1, by descaling the steel strip
1
without immersing in the neutral salt solution
20
, the quantity of the neutral salt solution
20
is small.
Therefore, as the size of the electrolyte tank is reduced, it is possible to miniaturize the descaling apparatus.
FIG. 3A
shows the anode
23
of
FIG. 1
in detail.
The anode
23
has a pressure adjustment valve
27
that adjusts a jet pressure, a liquid receiver
28
storing the neutral salt solution
20
supplied from the pump
22
through the pressure adjustment valve
27
, and an electrical conductor
29
connected with the power supply
25
. The liquid receiver
28
and the conductor
29
are separated by an electric insulating material
30
so that the anode
23
is insulated from the electrolyte tank
21
. The jet opening
26
is long in the direction of according to the width of the steel strip
1
, as shown in FIG.
3
B.
The neutral salt solution
20
drawn from the electrolyte tank
21
by the pump
22
is stored under adjusted pressure for a while in the liquid receiver
28
and is jetted from the jet opening
26
to the steel strip
1
. With the pressure adjustment valve
27
, we can adjust the jet pressure of the neutral salt solution
20
to the steel strip
1
individually for each electrode.
In this example, we adjust the pressure of the electrolyte independently to the both sides of the steel strip
1
properly in order to prevent the flexure of the steel strip
1
. Because the steel strip
1
does not have flexure, we can arrange the anodes
23
and the cathodes
24
close to the steel strip
1
. Since the distance between the electrodes (the anodes
23
and the cathodes
24
) and the steel strip
1
thereby became short, the voltage drop in the distance became small, and the voltage applied to the electrodes became lowered. Therefore, the total electric power for the electrolysis is reduced.
We have brought the anodes
23
and the cathodes
24
as close as 1 cm to the steel strip
1
in practice. The distance is {fraction (1/10)} or less as compared with the conventional electrolysis submerging steel strip. As a result, the electrolytic efficiency improves 65-95% or more compared with the prior art. Therefore, we reduce the voltage from 20V to 7V or less to obtain the same electric current density of 20 A/cm
2
as the prior art.
Next, a flow of the electric current in the neutral salt solution electrolysis part
6
is explained with respect to FIG.
2
.
The power supply
25
applies a voltage between the anodes
23
and the cathodes
24
. On the one hand the surface of steel strip
1
between the cathodes
24
becomes negatively charged, on the other hand the surface between the anodes
23
becomes positively charged. The electric current of power supply
25
flows to the negative charged part of the steel strip
1
through the jet stream
31
(
FIG. 3A
) from the anode
23
and the neutral salt solution film
32
that covers the surface of the steel strip
1
. Next, through the inside of steel strip
1
, the electric current flows to the positive charged part between the cathodes
24
, and then, through the neutral salt solution film
32
and the jet streams
31
of the cathodes, the electric current returns to the power supply
25
through suitable wiring to provide a closed series circuit independent of the bath.
In the conventional electrolysis, because the anodes
23
and the cathodes
24
were arranged immersed in the neutral salt solution
20
the short-circuit current flowed between the anodes
23
and the cathodes
24
through the bath of the neutral salt solution
20
to result in a lot of loss of the electric current. Compared with the conventional electrolysis, however, in this invention the short-circuit current between the anodes
23
and the cathodes
24
decreases very much, since the route of short-circuit current is limited to only the film
32
, and the electric power efficiency improves.
The positive charged part of the steel strip
1
between the cathodes
24
locally becomes an anode
33
(FIG.
2
), and on the anode
33
chrome oxide in the oxide film ionizes according to the chemical reaction (1) and dissolves in the neutral salt solution
20
.
Cr
2
O
3
+4H
2
O→Cr
2
O
7
2−+
8H
+
+6E (1)
The oxide chrome ions dissolved in the neutral salt solution
20
fall in the electrolyte tank
21
and the chrome oxide is eliminated from the surface of the steel strip
1
.
On the surface of steel strip
1
between the anodes
23
, chrome oxide separates out according to the adverse chemical reaction to the reaction (1). The arrangement of the anodes
23
to the upper stream side and the cathodes
24
to the downstream side respectively, prevents from separating out again by the reduction similar to the conventional electrolysis.
As there are a lot of anodes
23
and cathodes
24
, the electric current to the steel strip
1
is large. Therefore, a lot of anodes
23
and cathodes
24
increase the electric current density in the steel strip
1
and thereby improve the descaling speed. In this example, since we increased the number of cathodes
24
in order to improve the descaling speed, the anode
33
provided the electric current density enough to properly descale.
Because the neutral salt solution
20
contacts conductor
29
immediately surrounding in jet opening
26
, we supply the large electric current to the steel strip
1
constantly through the jetstreams
31
of the salt solution
20
without interruption. Therefore, as the electric current density of the steel strip
1
is large, we can descale rapidly and uniformly.
Likewise with the neutral salt solution electrolytic part
6
, in the alkali solution electrolysis part
8
and the nitrate solution electrolytic part
10
, descaling is performed by jetting the electrolyte and electrolysis with the anodes
23
and the cathodes
24
.
Table 1 shows the total electrolyte quantity, the total electric energy and the maximum line speed of the example 1, compared with the conventional electrolysis submerging steel strip.
TABLE 1
|
|
Conventional
Present Invention
|
|
|
total electrolyte
1
0.3
|
quantity (neutral salt +
|
nitrate)
|
total electric energy
1
0.4
|
maxinlum line speed
1
1.5
|
|
The total electrolyte quantity is about 30% and the total electric energy is 40% or less of the conventional electrolysis. The maximum line speed improves 50% in comparison with conventional electrolysis. Jetting has an effect of peeling off the scale and contributes to the improvement of the line speed.
EXAMPLE 2
The steel strip manufacturing apparatus according to the second example of the present invention is explained with respect to
FIG. 4A
to
FIG. 4D
, wherein steel strip is an annealed normal steel with mainly Fe
2
O
3
and Fe
3
O
4
formed on the surface.
In
FIG. 4A
, the steel strips wound on the inlet coil cars
40
and
41
are duet joined together by a welder
42
and fed out continuously.
Next, the steel strip
43
passes to the mechanical scale breaker
45
via the loop car
44
. In the mechanical scale breaker
45
, breakages are formed to the scale of the steel strip
43
, and then the broken scales are rubbed off with the mechanical brush
46
.
After these processings, the steel strip
43
passes through the descaling apparatus
47
in
FIG. 4B
, which has the structural details of
FIG. 2
,
3
A and
3
B. The descaling apparatus
47
has a hydrochloride electrolysis part
48
using hydrochloric acid
49
as an electrolyte. In hydrochloride electrolysis part
48
, the cathodes
24
are arranged in a first upstream half, and the anodes
23
are arranged in the latter downstream half.
The chemical reactions in the hydrochloride electrolysis cell part
48
are the following; (on the cathodes)
Fe
2
O
3
+6H
+
+2E→2Fe
2
+
+3H
2
O (2)
Fe
3
O
4
+8H
+
+2E→2Fe
2
+
+4H
2
O (3)
(on the anodes )
Fe→Fe
2
+
+2E (4)
The hydrochloride density is 180 G/L, which is the same as the conventional electrolysis, and the temperature is 85° C.
According to the chemical reactions (2) and (3) on the cathode
24
, the scale dissolves and is removed from the steel strip
1
. According to the chemical reaction (4) on the anode
23
, the foundation (normal steel) dissolves, and as a result the scale exfoliates from steel strip
43
. While the electric current density has a preferred value according to by a steel kind such as a normal steel and a stainless steel, or a size of the steel, it is preferred to control the electric current density in the range of the 1-20 A/cm
2
generally.
The steel strip
43
passes through the mill stand
51
via the centering apparatus
50
in FIG.
4
C. The steel strip
43
is cold-rolled by the HC mill of No. 1-4, and it is manufactured to thin plate. In
FIG. 4D
, the thin plate steel strip
43
passes through the rotary type scrap chopper
52
and the oiler
53
and is wound on the outlet coil car
54
.
According to the example 2, jetting the hydrochloric acid
49
in the air reduces the quantity of the hydrochloric acid
49
, to miniaturize the hydrochloride electrolytic part
48
and thereby to miniaturize the manufacturing apparatus similar to the example 1.
According to the example 1 and 2, by adjusting the jet pressure of the electrolyte to both sides of the steel strip
1
,
43
, the waving and the flexure of the steel strip
1
,
43
are prevented, and so it is possible to arrange the anodes
23
and the cathodes
24
close to the steel strip
1
,
43
. Therefore, as the voltage drop between the electrodes and the steel strip
43
becomes lower, the electric power for the descaling decreases similar for bath to the examples 1 and 2.
According to the example 2, compared with the conventional electrolysis, since the short-circuit current between the anodes
23
and the cathodes
24
decreases very much, the electric power efficiency improves similar to the example 1.
According to the example 2, because the electrode is integrated with the nozzle that jets the hydrochloric acid
49
, supply of the large electric current to the steel strip
43
through the jetted electrolyte, similar to the example 1.
Therefore, as the electric current density of the steel strip
43
is large, the descaling rapidly similar to the example 1. Providing many electrodes improves the descaling speed more because the electric current to the steel strip
43
increases similar to the example 1.
Another example of the electrodes
23
,
24
is explained with respect to
FIG. 5. A
conductor
29
is placed at a electrolytic passage way
34
, and an electric insulating material
30
covers an end of the electrodes
23
,
24
. As
FIG. 5B
show, the electric insulating material
30
surrounds the conductor
29
, which surrounds the electrolytic passage way
34
. The electric insulating material
30
prevent a discharge between the electrodes and the steel strip when the electrodes
23
,
24
contact the steel strip and we can protect the steel strip against damage by the discharge.
Other examples of jet force adjustment by electrolyte pressure adjustments are explained with respect to
FIG. 6
, which shows an arrangement of them on one side of the steel strip.
Each electrode
23
(or
24
) connects a pressure adjustment element
35
and every pressure adjustment element is connected to a controller
36
which controls the respective pressures. Each electrode
23
(or
24
) is also connected to a power supply
25
and a controller
37
controls the power for each power supply, respectively.
Thereby we can control a jet pressure of the electrolyte, voltage and polarity applied to the conductor
29
according to a kind of steel or electrolyte and control an extent of descaling. Because a descaling reaction advances more at a downstream region, altering a distribution of electrodes
23
,
24
in
FIG. 7
is suitable to coordinate the descaling.
Claims
- 1. A steel strip descaling apparatus for descaling a steel strip passing through the apparatus in a longitudinal direction with an electrolyte, comprising:an electrolyte tank for storing a solution; a pump that pressurizes and circulates the solution; a plurality of electrodes each with an electrolyte jet opening, wherein the electrolyte jet opening passes the solution that has been pressurized by said pump from said electrolyte tank to both surfaces of said steel strip in jet streams, said electrodes being arranged close to said steel strip, and said electrodes including anodes in an upstream region with respect to the direction of movement of the steel strip and cathodes in a downstream region with respect to the upstream region; and a power supply connected to said anodes and said cathodes to make an electrical circuit between said cathodes and said anodes through the jet streams, wherein an electric current flows along each surface of said steel strip with one part of a surface of said steel strip that is opposite to said cathodes being negatively charged and another part of said surface of said steel strip opposite to said anodes being positively charged.
- 2. A descaling apparatus according to claim 1, further including:said electrodes having an electrical conductor that contacts the electrolyte jetted through said electrolyte jet opening in order to directly apply voltage of said electrode to the jet stream of electrolyte wherein the voltage is applied to the steel strip through the jet stream.
- 3. A descaling apparatus according to claim 2, further comprising a controller that controls the pressure of the electrolyte jetted through said jet openings.
- 4. A descaling apparatus according to claim 3, further comprising a valve for adjusting the pressure of the electrolytes jetted through the jet openings of the electrodes.
- 5. A descaling apparatus according to claim 4, further comprising a controller for controlling said valve that is adjusted to maintain a distance between said electrodes and said steel strip constant.
- 6. A descaling apparatus according to claim 1, further including a voltage controller that controls a voltage applied to said electrode and a polarity of said voltage.
- 7. A descaling apparatus according to claim 1, further comprising a plurality of rollers to hold the steel strip above a level of the stored solution in the electrolyte tank.
- 8. A steel strip manufacturing apparatus comprising the descaling apparatus of claim 1.
- 9. A steel strip descaling apparatus for descaling a steel strip passing through the apparatus in a longitudinal direction with an electrolyte, comprising:an electrolyte tank for storing an electrolyte solution in a bath; means for suspending said steel strip so that said steel strip is not immersed in said electrolyte bath; a pump that pressurizes and circulates the electrolyte solution; a plurality of electrodes each with an electrolyte jet opening; means for jetting the electrolyte that has been pressurized by said pump through said electrodes to pass the solution from said electrolyte tank to both surfaces of said steel strip in jet streams; said electrodes being arranged close to said steel strip, and said electrodes including anodes in an upstream region with respect to the direction of movement of the steel strip and cathodes in a downstream region with respect to the upstream region; and means supplying power to said anodes and said cathodes and said steel strip to make an electrical circuit between said cathodes and said anodes through the jet streams, wherein an electric current flows along each surface of said steel strip with one part of a surface of said steel strip that is opposite to said cathodes being negatively charged and another part of said surface of said steel strip opposite to said anodes being positively charged.
- 10. A descaling apparatus according to claim 9, further including means for adjusting the pressure of the electrolyte solution that is jetted through said electrolyte jet openings.
- 11. A steel strip descaling method for descaling a steel strip passing in a longitudinal direction with an electrolyte, comprising the steps of:storing an electrolyte solution in an electrolyte tank; positioning a plurality of electrodes, each with a jet opening, close to both surfaces of said steel strip; pressurizing and circulating the solution to pass the solution through the jet openings of said plurality of electrodes in jet streams onto both surfaces of said steel strip, applying an electric potential to said electrodes as anodes in an upstream region with respect to the direction of movement of the steel strip and as cathodes in a downstream region with respect to the upstream region; and electrically connecting said anodes and said cathodes to make an electrical circuit through the jet streams, wherein an electric current flows along each surface of said steel strip with one part of a surface of said steel strip that is opposite to said cathodes being negatively charged and another part of said surface of said steel strip opposite to said anodes being positively charged.
- 12. A descaling apparatus according to claim 1, further including:adjusting the pressure of the electrolyte solution that is jetted through said electrolyte jet openings.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-237231 |
Aug 1998 |
JP |
|
US Referenced Citations (1)
Number |
Name |
Date |
Kind |
4374719 |
Blakewell et al. |
Feb 1983 |
|
Foreign Referenced Citations (6)
Number |
Date |
Country |
086 115 |
Aug 1983 |
EP |
0086115 A1 |
Aug 1983 |
EP |
870 854 |
Oct 1998 |
EP |
0870854 A1 |
Oct 1998 |
EP |
3-56699 |
Mar 1991 |
JP |
8-100299 |
Apr 1996 |
JP |