Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates to a method and an ap~aratus
for continuous electrolytic descaling of a steel wire by non-
contact current flow, and more particularly, to a method and an
apparatus for efficiently effecting the electrolytic descaling of
a steel wire to provide steel wire of good quality using a current
density usually used in the prior art without formation of gases on
the electrode surfaces and without significant loss of electrode
material.
The inventors of the present invention have invented an
apparatus for continuous electrolytic descaling of a steel wire by
non-contact current flow and filed Japanese Patent Application
No. 31901/1977 which was irst disclosed to the public on October
11, 1978 as Laid-Open Specification No. 116232/1978 and which
corresponds to Japanese Patent Publication No. 14160/1980 which
was published on April 14, 1982.
According to the disclosure made in the above mentioned
application, (1) an aqueous solution of alkali metal chloride,
such as sodium chloride (NaCl), potassium chloride (KCl),
lithium chloride (LiCl) etc., or (2) an aqueous solution of
alkali metal sulfate, such as sodium sulfate (Na2SO4),
potassium sulfate (K2SO4) etc. is used as an electrolyte.
In addition, the temperature of an electrolyte is adjusted
to between room temperature and a temperature lower than
100C and the electrolyte is recycled at a rate of more than
0.1 m/sec. Thel electrode material may be titanium, zirconium,
tantalum, carbon, stainless steel, etc. Particularly,
graphite is suitable for a non-contact current flow method in
which an aqueous solution of sodium chloride or potassium
chloride is used as an electrolyte and lead is suitable in
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using an aqueous solution of sodium sulfate or potassium
sulfate as an electrolyte in view of their corrosion
resistance and economy. The electrodes may be in the form
of plate or tube.
However, in a method for electrolytic desclaing
of a steel wire, such as referred`to in the above mentioned
application, the current density has been limited to lower
than 50 A/dm2 (500 mA/cm2). This is because at a current
density of higher than 50 A~dm2 a remarkable consumption
loss of the electrode is inevitable.
In case of an electrolyte comprised of an aqueous
solution of alkali metal chloride, chlorine gas formed
during operation is converted to hypochlorous acid (HC10)
in accordance with the following equation:
C12 + H2O - ~ HC10 ~HCl ........ (1)
The resulting corrosive hypochlorous acid accelerates the
consumption of a graphite electrode. ~;
In case of an electrolyte comprised of an a~ueous
solution of alkali metal sulfate, the lead electrode is
easily dissolved into the electrolyte in accordance with
the following equation:
Pb ~ Pb2~ ~ 2e- .... (2)
The term "non-contact current flow" used herein
is to be understood as meaning that current flows through
the steel wire being processed without any direct contact
with either electric power source or electrodes.
The object of the present invention is to provide a
method for electrolytic desclaing of a steel wire eliminating
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these disadvantages of the prior art.
Another object of the present invention is to provide
a method of preventing the formation of chlorine gas and
dissolution of electrode material to make it possible to
raise the current density to higher than 50 A/dm2.
Still another object of the present invention is to
provide an efficient method for electrolytic descaling of a
steel wire by raising the current density without significant
loss of electrode material.
Further, an object of the present invention is to pro-
vide an apparatus for efficiently carrying out the above
mentioned method.
The inventors of the p`resent invention completed this
invention after extensive study and experiments with the aim
in mind of achieving these objects.
The inventors found that the presence of ferrous ions
(Fe2+) in an electrolyte composed of an aqueous alkali metal
salt successfully eliminates these prior art disadvantages
even under operations using a current density higher than
50 A/dm .
Thus, the present invention is characterized by
incorporating ferrous ions in an electrolyte as an inhibitor
to the consumption of electrode. The ferrous ion may be
derived from ferrous chloride or sulfate.
According to one embodiment of the invention, therefore,
in the case in which the electrolyte is comprised of an aqueous
Solution of an alkali metal chloride and graphite electrodes
are used, ferrous chloride is added to the electroly-te and
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the electrolytic descaling of a steel wire is carried out
in the presence of ferrous ions by the non-contact current
flow method.
According to another embodiment of the invention,
in which the electrolyte is comprised of an aqueous solution
of an alkali metal sulfate and lead electrodes are used,
ferrous sulfate is added to the electrolyte and the electro-
lytic descaling of a steel wire is carried out in the presence
of ferrous ions by the non-contact current flow method.
Thus, the consumption of graphite electrodes and dis-
solution of lead electrodes are prevented successfully, making
it possible to carry out electrolytic descaling at a current
density higher than 50 A/dm2 by the non-contact current flow
method, since the present invention employs ferrous ions as
an inhibitor of corrosion and dissolution of electrode material.
However, instead of formation of chlorine gas and dissolution
of lead electrode, a large amount of sludge is formed in the
present invention resulting from desca]ing of wire. It is
~ necessary to provide in the system oE the present invention
a means of removing sludge.
Therefore, the present invention is also characterized
by an apparatus for electrolytic descaling of a steel wire,
in which an electrolyte circulating system is provided
including a means of removing sludge and a means of adjusting
the concentration of ferrous ions in the electrolyte.
In summary, according to the present invention due to
the presence of ferrous~ions in the electrolyte and the removal
of sludge from the electrolyte circulating system~ electrolytic
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descaling proceeds successfully and continuously at a high
current density to give the wire surface a bright finish.
The mechanism of preventing loss of electrode by the
addition of ferrous ions to the electrolyte can be explained
as follows.
In case of a graphite electrode and an electrolyte of
aqueous sodium chloride, anodic reactions take place in the
absence of ferrous ions as follows:
2H2O ~ 2 + 4H + 4e .... (3)
2Cl ~ C12 + 2e .............. (4)
The chlorine gas thus ormed attacks the electrode causing
weight loss of the electrode as hereinbefore mentioned. On
the contrary, in the presence of ferrous ions, the following
reaction takes place instead of reactions (3) and (4) to
suppress the formation of corrosive chlorine gas.
Fe2+ Fe + e .. (5)
In case of a lead electrode and an electrolyte of an
aqueous solution of sodium sulfate, anodic xeactions take
place in the absence of ferrous ions as follows.
2 2 + 4H + 4e ............. (6)
Pb ~ pb2 + 2e ................ (7)
When ferrous ions are present in the electrolyte,
in this case, too, reaction (5) in the above predominates
over the reactions (6) and (7) to prevent dissolution of lead
electrode.
The ferrous ions which have been oxidized in accordance
with equation (5) are then precipitated as sludge in the
electrolyte.
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It is to be noted that in addition to hydrogen
- formation iron sometimes deposits on cathodic portions of
oper~
the wire surface when opcratcd at a high current density in
accordance with the following equation:
Fe2+ + 2e~ ~ Fe .... (8)
Because of this iron deposition, the wire surface turns
black and this lowers the product value remarkably. There-
fore, the addition of ferric ions to an electrolyte is
desirable, though not always necessary, only at the beginning
of the operation at a hlgh current density, since in the
presence of ferric ions the following reaction takes place
instead of reaction (8) in the above.
Fe3~ ~ e~ ~ Fe .... (9)
Thus, in a preferred embodiment of the present
invention method, a small amount of ferric ions is added to
an electrolyte containing ferrous ions so as to prevent the
deposition of iron on cathodic portions of the wire surface.
The concentration of ferrous ions in the electrolyte
composed of an aqueous solution of an alkali metal salt, as
hereinafter described in more detail, is more than 0.2% by
weight on the basis of ferrous chloride or sulfate, preferably
more than 1.0%. When the ferrous chloirde or sulfate is
added in an amount of more than 0.2% by weight to the elec-
trolyte, the consumption loss of a graphite electrode is
reduced to at least one half compared with the case in which
it is not added. When it is added in an amount of more than
1.0% by weight, no significant consumption loss of the graphite
electrode is found. The ferrous chloride or sulfate may be
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added to the electrolyte until it is saturated. That is,
the upper point of the concentration of ferrous ions is
the solubility thereof.
Ferric chloride or sulfate may also be added in an
amount of more than 0.1% by weight of the electrolyte.
As hereinbefore mentioned, since, according to the
present invention, the formation of sludge during operation
is inevitable, a larger amount of sludge is formed compared
with the method which does not use ferrous ions. Thus, it
is necessary to remove the sludge from the electrolyte during
operation so as not only to maintain the effectiveness of
the electrolyte for a longer period of time, but also to make
it effective to wash the descaled wire after descaling. Thus,
it is desirable to provide a means of removing sludge and of
supplying ferrous ions during operation in an apparatus of
the present invention.
The present invention will be further described in
conjunction with the drawings in which:
Fig. l is a diagrammatical view showing paxtly in
section the apparatus of the present invention for electro-
lytically descaling a steel wire by a non-contact current
flow method;
Fig. 2 is a graph showing the consumption loss of a
graphi-te electrode with respect to the concentration of ferrous
chloride in an electrolyte comprised of an aqueous solution
of sodium chloride; and
Fig. 3 is a graph showing the consumption loss of a
lead electrode with respect to the concentration of ferrous
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sulfate in an electrolyte comprised of an aqueous solution
of sodium sulfate.
~ ow referring to Fig. 1 an apparatus for continuous
electrolytic descaling of a steel wire 1 is shown, which
comprises, essentially, a direct power source 2, a plurality
of electrodes 3 ~only one pair of electrodes is shown), a
series of electrolytic cells 4 (only one cell 4 is s~own),
guide rollers 5, and an electrolytic solution circulating
system 6. The electrolytic circulating system 6 comprises a
sludge removing means and a means of adjusting the ferrous ion
concentration in the electrolyte. Details including pumps,
valves and so on are eliminated for the purpose of clarifica-
tlon.
A pair of the electrodes 3 consists of an anodic
electrode 31 connected to the anode (+) of the direct cur-
rent power source 2 and a cathodic electrode 32 connected to
the cathode (-) of the direct current power source 2. The
electrode may be either the tube type as shown or the plate
type . The plate type electrodes may consists either of -two
plate electrodes opposed either vertically or horizontally
with spacers of insulating material therebetween or may
consist of four plate electrodes assembled into a tube having
a square or rectangular section.
The method of the present invention is applied to a
steel wire 1 - 40 mm in diameter, which, prior to the introduc-
tion into the electrolyte containing ferrous ions, is
repeatedly bent and stretched by 1 - 20% in elongation wi-th
a roll-bender (not shown). Thereafter, the wire having been
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subjected to roll-bending is supplied to a series of
electrolytic cells 4 provided with a means of removing
sludge and a means of adjusting the electrolyte in accordance
with the present invention. The electrolyte which is useful
for a non-contact current flow method is: (1) 1 - 30% aqueous
solution of alkali metal chloride (e.g. NaCl, KCl, etc.)
containing ferrous chloride in an amount of from 0.2% by
weight to the solubility thereof, and if necessary, in
addition thereto ferric chloride in an amount of from 0.1% by
weight to the solubility thereof, or (2) 1 - 30% aqueous
solution of alkali metal sulfate (e.g. Na2SO4, K2SO~, etc.)
containing ferrous sulfate in an amount of from 0.2% by weight
to the solubility thereof, and if necessary in addition
thereto ferric sulfate (Fe2(SO4)3) in an amount of from 0.1%
by weight to the solubility thereof.
The current density supplied during operation of
descaling is desirably from 5 A/dm to 500 A/dm . At a
current density lower than 5 A/dm2, the rate of electrolytic
descaling is so small that too long a time is required to
finish the descaling. Therefore, such a low current density
is not suitable for high speed descaling. At a current density
- higher than 500 A/dm2, the desirable effect due to the presence
of ferrous ions in the electrolyte seems to be off-set, result-
ing in such disadvantages as mentioned hereinbefore with
respect to the prior art.
The electrode is made of graphite in case of an
electrolyte comprised of an aqueous solution of alkali metal
chloride and is made of lead in case of an electrolyte
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comprised of an aqueous solution of alkali metal sulfate.
The electrolytic descaling is carried out in the
presence of ferrous ions in accordance with the present
invention. Fig. 1 shows only one electrolytic cell, but
usually steel wire is passed through four or more elec-
trolytic cells in series.
Since the present invention utilizes intentional
addition of ferrous ions to an electrolyte, a large amount
of ferrous and ferric chloride or sulfate is precipitated
as sludge within the cell. Therefore, it is necessary to
remove the sludge comprised of these sulfatesand chlorides
from the electroly-te. In addition, when ferrous ions are
consumed in the process of electrolytic descaling of the
present invention, it is also necessary to add ferrous ions
to the electrolyte so as to maintain the ferrous ion con-
centration on a predetermined level.
As hereinbefore mentioned, the apparatus of the
present invention comprises the electrolyte solution circulat-
ing system 6 including a sludge removing means and the
electrolyte adjusting means. The sludge removing means may
include a solid-liquid separator 7, such as a super decanter
- using centrifugal force separation, a filter provided with
filter cloth, a thickner utilizing settling separation etc.
A stream of an electrolyte is passed to the solid-liquid
separator 7 via lines 8 and 9, in which sludge is separated
from the electrolyte and discharged through the line 10, as
shown by an arrow. The electrolyte after removal of the
sludge is passed to a tank 11 via line 12, where its pH is
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adjusted by the addition of HC1 or H2SO~ and if necessary
alkali metal ehloride or sulfate and ferrous chloride or
sulfate are added to the electrolyte through the line 13
as shown by an arrow.
The recovered sludge, after neutrali~ation with eaustie
soda and water, is disposed of.
The eleetrolyte, after adjustment of i-ts pH and
concentration of electrolytic components and ferrous ions, is
recycled to the electrolytic cell 4 via lines 14 and 15. The
circulating rate of the electrolyte is above 0.1 m/sec so
that the electrolytie aetivity of the eleetrolyte at the
steel wire surfaee and the eoneentration of ferrous ions are
maintained at predetermined levels, i.e. as the same as of
the bulk solution.
As hereinbefore mentioned, only one eleetrolytie
eell 4 is shown in Fig. 1, though usually four or more cells
are used in series. Therefore, the electrolytic circulation
system 6 shown in Fig. 1 may also be provided in each of
them, or only one such system may be provided. In the latter
case, the lines 8 and 9 collect the eleetrolyte d1scharged
from all the cells and the lines 14 and 15 distribute the
regènerated eleetrolyte to each of them.
Example 1
An aqueous 10% sodium chloride solution containing
varied amounts of ferrous chloride was used to carry out the
electrolytic descaling of a steel wire using a pair of
electrolytic cells shown in Fig. 1. The anodic eurrent
density was 40 A/dm and the temperature of the eleetrolyte
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1 was 40C. The results are summarized in Fig. 2.
The consumptioll loss of graphite anode was determined
in terms of decrease in thickness (mm) per year. The relation
between the concentration of ferrous ions designated in terms
of the concentration of ferrous chloride and the consumption
of the graphite electrode is shown in Fig. 2. ~s is apparent
from Fig. 2, the loss of the electrode is reduced to one half
that experienced when ferrous chloride was not added to the
electrolyte at the concentration level of 0.2~ by wei~ht of
ferrous chloride.
Example 2
In this example, Example 1 was repeated except that
an electrolyte was comprised of an aqueous 10% sodium sulfate
solution containing varied amounts of ferrous sulfate. The
electrode was made of lead.
The results are summarized in Fi~. 3, which shows the
relation between the concentration of ferrous ions designated
in terms of the concentration of ferrous sulfate and the
consumption of the lead electrode. The consumption of the
electrode was determined in terms of decrease in thickness
(mm) per year. As is apparent from Fig. 3 r at the concen-
tration level of 0.2% by weight of ferrous sulfate the
electrode loss is reduced to one half that experienced when
ferrous sulfate was not added to the electrolyte.
Example 3
In this example, it was determined that the concentra-
tions of ferrous and ferric ions have an influence on the forma-
tion of chlorine gas. In this example,~xample 1 was repeated
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except that descaling conditions ~eY~{f~3~ in Table 1
were used. The descaling conditions and results are
summarized in Table 1.
As is apparent from the data shown in Table 1, the
addi-tion of 0.2% FeC12 to an electrolyte comprised of a
10% aqueous solution of sodium chloride reduced the formation
of chlorine gas one half that formed in the case in which
ferrous chloride was not added. When ferrous chloride was
added in an amount of more than 1.0%, chlorine gas was not
found at all. Thus, according to the present invention it is
possible to carry out efficient descaling of steel wire.
As the current density increases above 40 A/dm2, the
rate of descaling also increasesO It is to be no-ted, on the
other hand, that at a higher current density, the addition of
a small amount of ferric chloride is desirable in order that
the deposition of iron according to the equation: Fe2+ + 2e
---? Fe ~ successfully prevented in cathodic portions of
the steel wire being treated.
Example 4
In this example, Example 3 was repeated except that
ferrous sulfate was added to an electrolyte comprised of
- an aqueous solution of sodium sulfate. The dissolution of
lead electrode is accompanied by the generation of oxygen gas.
Therefore, in this example, the consumption of the electrode
is presumed to be approximately in accordance with the volume
of oxygen generated during operation. The descaling conditions
and results are summarized in Table 2.
As is apparent from the data shown in Table 2, the
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addition of ferrous sulfate in an amount of more than 0.2~
reduced the consumption of the electrode designated in terms
of thickness (mm) per year to at least one half that
experienced when no ferrous sulfate was added. By the
addition thereof in an amount of more than 1%, -the consumption
of the electrode can be substantially prevented.
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Table 1
Descaling of Steel Wire in an Elec-trolyte
NaCl + FeC12 Circulating at 40C
Time of 1)
polarity of 3
Steel Electrolyte Current steel wire~ de- 2) C12 )
wire ~ FeC13 dens ty scaling forma- Remarks
_
0 0 40 10 - 10 ~ X tive
0 0 80 6 - 6 O XX
0 0 120 4 - 4 O XX
. . . _ _ _ ___
0.3 0 40 10 - 10 ~ /~ this
A inven-tion
0.5 0 40 10 - 10 ~ /~
h ¦ 10 1. 0 O 40 10 - 10 O O
5.0 0 40 10 - 10 O O
~ ~ 10 10.0 0 40 10 - 10 O O
~ , 10 29 1 0 40 10 - 10 O O
satura-ted)
h¦ 10 5.9 0.5 30 6 - 6 O O
~I 10 5.0 1.0 120 4 - 4 O O
I ~ 1 3 5.0 0 40 10 - 10 ~ O
5.0 0 40 10 - 10 O O
5.0 1.0 500 1 - 1 O O
. . . . .
5.0 1.0 600 . 1 - 1 _ XX compara
0 0 120 4 - 4 O _ XXX
hI 1 0 O O 240 3 - 3 O XXX
0 0 0 300 25 - 25 O XXX
~, 10 5.0 0 40 10 - 10 ~ O~ this
: ~ invention
5.0 0.5 806.5 - 6.5 O O
3 10 5.0 0.5 1204.5 - 4.5 O O '.
5.0 1.0 240 3 - 3 O I O
5.0 1.0 300 2.5 - 2.5 O ~ O
Note:
1) Descaling time was varied by changing the feed
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1 rate of the steel wire. Cathode--Anode 10 - 10 means that the
steel wire resides within the tube graphite cathodic elec-trode,
the length of which is 1000 mm, for 10 seconds and within the
anodic electrode, the length of which is 1000 mm, for 10 seconds.
2) 0: good surface finish, ~ : slightly
inferior surface finish
3) 0: none, ~: relatively small,
X: marked, XX: vigorous, XXX: extreme excess
.
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Table 2
Descaling of Steel Wire in an Electrolyte
of Na2SO4 + FeSO4 Circulating at 40C
I Time ofl) I
Steel (% by weight) Current of steel)~DeiScal forma- Remark
wire Na2SO4lFesO4TlFe2(so4)3 ~ Cathode-~ t~on
O O 40 10 - 10 ~ X tCimvPara~
0 0 80 6 - 6 O XX
0 _ 120 4 - 4 O XXX
O.2 0. 40 10 - 10 ~ ~ this
h lnvention
~ 10 0.~ 0 40 10 - 10
s 10 1.0 0 40 10 - 10 O O
3 10 5.0 0 40 10 - 10 O O
10.0 0 40 10 - 10 O O
l22 0 40 10 - 10 O O
(saturated) .
10 5.0 0.5 50 7 - 7 O O
10 5.0 1.0120 5 - 5 O O
5 5.0 0 40 10 - 10 X O
15 5.0 0 40 10 - 10 O O
10 5.0 1.050 _ 1 - 1 O O _
_ ¦ 5.0 ¦ 1.0¦ 550 1 - 1 O X compara-
0 0 120 4 - 4 O XXX
0 0 240 3 - 3 O XXX
0 0 300 2.5 - 2.5 O XXX
,1 a) . _ _
3 ~ 15 5.0 1.0¦ 1205.5 - 5.5 O O this
5.0 1.0¦ 200 4 - 4 O O invention
5.0 1.01 300 3 - 3 O O
Note: 1), 2) and 3) are the same as in Table 1.
