Cleaning composition for electrocleaning cold-rolled steel

A cleaning composition for electrolytically cleaning cold-rolled steelwork includes sodium or potassium hydroxide, sodium or potassium orthosilicate and a combination of non-ionic surface-active agents; said non-ionic surface active agent includes a major amount of lauryl polyethylene glycol ether with 10 moles of average ethylene oxide, and a minor amount of nonyl phenyl polyethylene glycol ether with 1 mole of average ethylene oxide. By virtue of adding two non-ionic surface active agents in such an amount ratio, an excellent defoaming and cleaning effect can be obtained. Inclusion of hexamethylenetetramine in the cleaning composition can inhibit the deposition of ferric oxide and silicone oxide during electrocleaning which normally gives rise to the problem of light fault.

BACKGROUND OF THE INVENTION 
The present invention relates to a cleaning composition for 
electrocleaning, and particularly to a cleaning composition for 
electrolytically cleaning cold-rolled steel with high current density. 
If it is intended that a thinner steel coil be manufactured, the steel work 
can be subjected to the treatment of cold-rolling. In doing this, a roll 
coolant must be added for dissipating the heat generated by mechanical 
rolling on the surface of the steel work. Therefore, subsequent to the 
cold rolling operation, roll coolant which primarily includes animal oil 
or mineral oil together with other soils, such as iron smut, will be left 
on the surface of the cold-rolled steel. Before the cold-rolled steel work 
is subjected to annealing treatment, such soils should be thoroughly 
removed from the surface. Otherwise the residual oil smudge will be 
cracked into carbon residue or a lower carbon compound which is 
deleterious to the quality of the surface of the resultant steel plate, 
and this problem manifests itself in a poor finishing job, e.g. poor 
adherence in electroplating. 
Due to its property of saponifying fats and oils to make water-soluble 
soaps, its capabilities of attacking organics and splitting esters, sodium 
or potassium hydroxide has been used as the most important alkali for 
metal cleaning. Particularly, its highest conductivity renders it an 
indispensible component in electrolytic cleaning composition. 
It has been also described that when compounded with surfactants, silicates 
are the best emulsifying and deflocculating agents of all the alkali. Also 
their excellent buffer function in high basicity make them necessary for 
long-life electrocleaning compositions. On the other hand, silicates can 
be a possible source of trouble in subsequent plating operations and thus 
are suggested not to be included in the cleaning compositions for some 
metal cleaning processes. Sodium orthosilicate has been reported as one 
silicate which is widely used in steel cleaners. 
Chelating agents have acquired an important role in conventional cleaning 
formulations in the case that little or no phosphate should be included. 
The most widely used chelating agents in metal cleaners are sodium 
gluconate, trisodium nitrilotriacetate and EDTA. These compounds can 
soften water and tie up many metal ions so as to enhance the cleaning 
effect of the cleaners. 
Evidently, decreasing surface and interfacial tension will help in washing 
out the oil from the surface. However, specific selection of surfactants 
is important in electrolytic cleaning. Though nonionic surfactants have 
been used in combination with anionics in soak and spray cleaners, they 
have not been positively disclosed or suggested to be used in 
electrocleaners. Only the anionic type of surfactants has been disclosed 
for the purpose of electrocleaning. Finally, it is particularly desired in 
high-current-density electrocleaning to select a combination of 
surfactants which have good defoaming properties, because in 
electrocleaning with high current density, an enormous amount of hydrogen 
and oxygen evolves giving rise to voluminous foams which adversely cause 
current loss and affect the efficiency of the electrolysis. 
It is known that hexamethylenetetramine can be used as a pickling inhibitor 
in hydrochloric and sulfuric acid. However, to the knowledge of the 
inventors, no literature has disclosed hexamethylenetetramine used in a 
formulation for electrolytic cleaning. 
In view of the fact that conditions needed for conducting a electrolytic 
cleaning of a rolled metal sheet with high current density are very 
unique, to figure out a suitable cleaning formulation which can perform 
optimal cleaning function involves an enormous amount of experiments in 
light of the general teachings as discussed above. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a cleaning composition which 
can perform optimal electrocleaning action on a cold-rolled steel sheet. 
It is another object of this invention to provide a cleaning composition 
for electrolytic cleaning with high density current without much 
consumption of defoaming agent. 
It is a further object of this invention to provide an electrocleaning 
composition which will alleviate the problem of the tendency to adhere of 
two opposed surfaces on two adjacent segments of a coil of steel sheet. 
It is still another object of this invention to provide an electrocleaning 
composition which can inhibit the occurrence of overvoltage as to reduce 
the consumption of electricity. 
In accordance with the present invention, a cleaning composition for 
electrolytically cleaning cold-rolled steelwork comprises sodium or 
potassium hydroxide, a silicate and a non-ionic surface-active agent, in 
which said non-ionic surface active agent includes a major amount of 
lauryl polyethylene glycol ether with 10 moles of average ethylene oxide, 
and a minor amount of nonyl phenyl polyethylene glycol ether with 1 mole 
of average ethylene oxide. By virtue of adding two non-ionic surface 
active agents in such an amount ratio, excellent defoaming property can be 
obtained and the need of defoaming agent is greatly decreased. Preferably 
said silicate is sodium orthosilicate. Most preferably, said cleaning 
composition contains from about 20 to about 60 percent by weight of sodium 
hydroxide, from about 20 to about 60 percent by weight of sodium 
orthosilicate and from about 0.1 to about 20 percent by weight of nonionic 
surface active agent. The inclusion of sodium orthosilicate in the 
cleaning composition can not only increase the usable life of the cleaning 
solution, but also causes the formation of a thin layer of silicon dioxide 
which can effectively protect the surface of the cleaned steel sheet from 
scratching and sticking during the annealing procedure. (Such problems are 
encountered quite often with the use of the conventional electrocleaning 
composition.) 
In accordance with another aspect of this invention, from about 1 to about 
20 percent by weight of hexamethylenetetramine is added so as to inhibit 
the phenomenon of overvoltage which develops during the procedure of 
electrolytic cleaning. 
In accordance with a further aspect of this invention, from about 1 to 
about 20 percent by weight of a chelating agent can be added. Said 
chelating agent is selected from a group consisting of sodium gluconate, 
trisodium nitrilotriacetate and the mixtures thereof. Due to the 
incorporation of the chelating agent, calcium and magnesium as well as 
other heavy metal ion will be sequestered and prohibited from contacting 
sodium orthosilicate and the stearates resulted from saponification. 
Therefore the formation of insoluble scum which affects the conductivity 
of the electrocleaning solution and contaminates the surface of the steel 
sheet will substantially be eliminated.

The following exemplary embodiments are provided for illustration of the 
present invention and should not be construed as limiting the scope of 
this invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
150 kg sodium hydroxide, 200 kg sodium orthosilicate, 100 kg sodium 
gluconate, 100 kg trisodium nitrilotriacetate, 100 kg Lauryl polyethylene 
glycol ether having a formula of C.sub.12 H.sub.25 --O--(CH.sub.2 CH.sub.2 
O).sub.10 --H and 10 kg nonyl phenyl polyethylene glycol ether having a 
formula of C.sub.9 H.sub.19 --C.sub.6 H.sub.4 --O--(CH.sub.2 CH.sub.2 
O)--H and 10 kg hexamine are mixed to form a basic cleaning composition 
and pumped into a circulation tank. About 21,663 kg water is added to the 
basic cleaning composition to make up 3% by weight of the basic 
electrocleaning solution. The basic electrocleaning solution is used to 
wash the conveyed cold-rolled steel at the stage of brush scrubbing and 
then is sprayed into a high-current-density electrolytic cleaning tank for 
the processing of electrocleaning. In the electrocleaning the cold-rolled 
steel to be washed is made the cathode, while the inert anode is made of 
steel. Due to the evolution of copious gas at the surface of the 
cold-rolled steel, the mechanical action of the gas helps in dislodging 
the soil and simultaneously bring up fresh solution to the surface. No 
deposition on the steel anode appears even after a period of time; it is 
believed that this effect is due to the inclusion of hexamine. As a 
consequence, no light fault caused by overvoltage occurs when utilizing 
the electrocleaning solution according to this invention as opposed to a 
electrocleaning solution without hexamine. The advantage of the addition 
of hexamine in the electrocleaning solution will be illustrated hereafter. 
It is to be noted that adding lauryl polyethylene glycol ether having a 
formula of C.sub.12 H.sub.25 --O--(CH.sub.2 CH.sub.2 O).sub.10 --H and 
nonyl phenyl polyethylene glycol ether having a formula of C.sub.9 
H.sub.19 --C.sub.6 H.sub.4 --O--(CH.sub.2 CH.sub.2 O)--H as surface-active 
agents in such a proportion attains an excellent defoaming effect which 
desirably decreases the consumption of defoaming agents. The effectiveness 
of the combination of these two surface-active agents will be illustrated 
hereafter. 
The used electrocleaning solution is collected and flow back to the 
recirculation tank. The consumed amount of electrocleaning solution should 
be frequently supplemented before it is recirculated for the next use. 
Subsequently, the cold-rolled steel plate is subject to be rinsed twice 
with hot water in the hot rinse tank and then dried. The cleanliness of 
the surface of the resultant steel plate is assessed by the water break 
test as very satisfactory. 
In practice, it has been found that only 0.367 kg of the basic 
electrocleaning composition accompanied by 0.018 kg defoaming agent is 
needed for producing 1 ton of steel plate. At the same time, light fault 
on the anode develops rather slowly, so the average operation time can 
last for 172 hours. In view of the slow development of anodic overvoltage, 
consumption of electricity can be desirably reduced. Furthermore, the 
sufficient amount of silicon dioxide left on the surface can efficiently 
alleviate the sticking problem of the surface of the steelwork. 
To show the excellent defoaming effect provided by a combination of a minor 
amount of nonyl phenyl polyethylene glycol ether with 1 mole of average 
ethylene oxide and a major amount of lauryl polyethylene glycol ether with 
10 moles of average ethylene oxide, two electrocleaning solutions, i.e. 
CTY410 and CTY412 are prepared for testing the defoaming effect. CTY412 is 
prepared by repeating the same procedure as for the preparation of the 
above-mentioned basic electrocleaning solution except that no hexamine is 
included and balanced water is added to make up 3% by weight of 
electrocleaning solution. CTY410 is prepared by repeating the same 
procedure for the preparation of CTY412 except that nonyl phenyl 
polyethylene glycol ether with 1 mole of average ethylene oxide is not 
included and the balanced water is added to make up 3% by weight of 
electrocleaning solution. In other words, adding about 0.01% by weight of 
nonyl phenol polyethylene glycol ether with 1 mole of average ethylene 
oxide to CTY410 will form electrocleaning solution CTY412. The test of the 
defoaming effect is conducted for CTY412 and CTY410 according to ASTM 
D1173 method. The height of foam in the respective solution varying with 
time is listed in Table I. 
TABLE I 
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CTY410 CTY412 CTY410* 
CTY412* 
height height height height 
time of foam of foam of foam 
of foam 
(min) (cm) (cm) (cm) (cm) 
______________________________________ 
0 3.5 1.2 12.0 3.5 
0.5 2.0 1.0 9.0 1.5 
1.0 1.5 0.8 2.0 1.2 
1.5 1.2 0.7 1.0 1.0 
2.0 1.0 0.7 0.8 0.8 
3.0 0.7 0.3 0.7 0.7 
4.0 0.5 0.1 0.5 0.5 
5.0 0.5 0.1 0.5 0.3 
______________________________________ 
*To the electrocleaning solutions CTY410 and CTY412 are respectively adde 
0.5% by volume of rolling oil which comprises about 45% by weight of 
animal oil, such as tallow oil or lard oil, and 45% by weight of mineral 
oil as well as a slight amount of emulsifying agents and other additives. 
The rolling oil is left on the surface of coldrolled steel after the 
coldrolling treatment. 
It can be noted from the lower height of the foam in testing CTY412 that 
inclusion of a slight amount of nonyl phenol polyethylene glycol with 1 
mole of average ethylene oxide mole number greatly enhances the defoaming 
effect. To demonstrate the excellent capability of hexamine of inhibiting 
overvoltage on the inert steel electrode, nine sample solutions as listed 
in Table II are prepared. For simulating used electrocleaning solution 
which has been used for three days in electrocleaning the cold-rolled 
sheet as mentioned above, 70 ppm concentration of ferric ion is added to 
CTY412 to act as a control solution. The test results are tabulated in 
Table II. 
TABLE II 
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Voltage 
deposition 
Sample Added Fe Electrolysis 
change on anode 
No. conc. (ppm) 
time (volt) surface 
______________________________________ 
control 
70 2 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
1 70 .sup. 2 hrs 
12.fwdarw.12 
No 
2 70 .sup. 2 hrs 
12.fwdarw.12 
No 
3 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
4 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
5 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
6 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
7 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
8 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
9 70 &lt;5 min 12.fwdarw.20 
Fe.sub.2 O.sub.3 + SiO.sub.2 
______________________________________ 
NOTE: 
1. Sample 1 is prepared by adding 0.1% by weight of hexamine to CTY412. 
2. Sample 2 is prepared by adding 0.2% by weight of hexamine to CTY412 
3. Sample 3 is prepared by adding 0.2% by weight of triethylamine to 
CTY412. 
4. Sample 4 is prepared by adding 0.2% by weight of diphenylamine to 
CTY412. 
5. Sample 5 is prepared by adding 0.2% by weight of cyclohexylamine to 
CTY412. 
6. Sample 6 is prepared by adding 0.2% by weight of npropylamine to 
CTY412. 
7. Sample 7 is prepared by adding 0.2% by weight of 2butyn-1,4-diol to 
CTY412. 
8. Sample 8 is prepared by adding 0.2% by weight of 
2mercaptobenzothiazole. 
9. Sample 9 is prepared by adding 0.2% by weight of 1,2,3benzothiazole. 
It can be seen that inclusion of hexamethylenetetramine can inhibit to a 
surprising extent the deposition of ferric oxide and silicone oxide on the 
surface of the anode, which is believed to cause overvoltage during 
electrocleaning. Though some other pickling inhibitors, such as 
2-butyn-1,4-diol and cyclohexylamine as shown in Table II have been 
utilized for this purpose, no desirable effect can be obtained, as with 
hexamethylenetetramine. The mechanism of inhibition of deposition by using 
hexamethylenetetramine is not very clear to us. It is believed that 
probably its high molecular weight and electron donor capability to the 
steel surface accounts for its excellent inhibition of deposition. In 
addition, hexamethylenetetramine is not easily oxidized.