Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
1999-07-29
2001-11-06
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S469000, C427S193000, C427S199000, C427S284000
Reexamination Certificate
active
06312764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The invention relates to a treatment process limiting the overoxidation of steel, such as for example the sides of a coiled, hot-rolled sheet strip delivered from a strip mill.
2. Discussion of the Background
In iron-and-steel plants, cooling, prior to pickling, of strips of steel sheet prepared in the form of coils, requires substantial stocking areas. Cooling time in ambient air for a single coil is on the order of 70 hours. This time may be even longer in the event that the coils are superposed. In some plants, the coils are immersed in pools to accelerate their cooling. The advantages of this technique are to reduce the stocking area, the stocking time in particular between the strip mill and pickling, and the duration of pickling, the thickness of the scale forming on the steel strips being, less at the sides.
The scale formed at the time of hot rolling in the strip mill, between 800° C. and 700° C., consists of3 oxides which each have their own rate of growth.
Hematite, Fe
2
O
3
, in contact with the atmosphere, is the most oxidized compound. For a scale of 10, &mgr;m in thickness, formed at 700° C., the thickness of the hematite film is on the order of 0.01 &mgr;m.
FeO, in contact with the steel, is the least oxidized compound. For a scale of 10 &mgr;m in thickness, the thickness of the FeO film formed is on the order of 7.26 &mgr;m.
Between these two oxides, there is formed a compound of the spinel type, formed by the two preceding oxides. The thickness of this spinel, for a scale thickness of 10 &mgr;m, is about 0.63 &mgr;m.
The thickness of the scale formed on the hot-rolled steels depends on the dwell time on the cooling table, therefore on the coiling speed, on the rolling temperature and on the coiling temperature.
In the course of cooling in coil, at the sides, the oxygen present between the consecutive turns allows the continuation of oxidation, while this is checked rapidly at the center of the coil.
The center of the coil cools very slowly. The cooling speed is a function, in particular, of the mass of said coil. The decomposition of FeO sheltered from the air is practically complete; it is transformed into Fe
3
O
4
+Fe eutectoid.
The sides undergo an overoxidation according to the coiling temperature and the coil mass. This overoxidation occurs through the formation of a film of hematite the removal time for which determines the duration of pickling.
As the speed of cooling of the sides is more rapid, the decomposition of FeO into eutectoid is not complete, and the presence of magnetite is observed.
To promote adherence of the scale at the sides, it is necessary to avoid overoxidation and to approach the structure of the oxide forming the scale at the center of the coiled strip.
Cooling in a pool makes it possible to obtain this result but with the drawback on the one hand, of being burdensome and, on the other, of altering the mechanical characteristics of the steel which constitutes the strips.
OBJECT OF THE INVENTION
One object of the invention is to avoid the formation of a film of hematite on the sides of a hot-rolled steel sheet strip, without altering the mechanical characteristics of the steel, which is a risk in the technique of cooling in a pool. Other objects apply this technology to steel in general.
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the invention is a treatment process limiting the overoxidation of the sides of coiled, hot-rolled sheet strips including those delivered from a strip mill, characterized in that a powder which becomes solidified and ensures the air-tightness of the space contained between the turns of the coil, is sprayed onto the lateral portions of the coil, called edges.
Other characteristics of the invention are:
a vitrifiable powder is sprayed onto the coil edges, fusing at the time of its contact with the steel coil delivered from hot rolling, the sheet strip undergoing cooling at a temperature below the coiling temperature, the cooling of the strip ensuring the solidification of an impervious enamel on the surface of the coil edges,
the vitrifiable powder is mixed with a compound endowing said compound with an electrostatic behavior and preventing adsorption of water,
the vitrifiable powder forming the enamel is a glass the composition (percentages by weight) comprising, consisting essentially of, or consisting of the following:
10%<Fe
2
O
3
<50%
10%<Na
2
B
4
O
7
<80%
0%<P
2
O
5
<10%
5%<SiO
2
<50%
0%<TiO
2
<15%
5%<Na
2
CO
3
<20%
5%<K
2
CO
3
<20%
0%<CaCO
3
<10%,
the vitrifiable powder forming the enamel preferably is a glass the composition of which comprises, consists of, or consists essentially of:
Fe
2
O
3
30%
Na
2
B
4
O
7
15%
P
2
O
5
3%
SiO
2
15%
TiO
2
9%
Na
2
CO
3
11%
K
2
CO
3
15%
CaCO
3
2%.
The invention also includes a glass in the form of a powder and its use to ensure the air-tightness of the space contained between the turns of a coil of a hot-rolled steel sheet delivered from a strip mill, a powder which fuses at a temperature below the coiling temperature and becomes solidified on cooling of the coil, to ensure air-tightness of the space contained between the turns of said coil.
Other characteristics of the invention include:
the powder is vitrifiable, fusing at the time of its contact with the steel coil delivered from hot rolling, the cooling of the strip ensuring the solidification of a continuous impervious enamel on the surface of the coil edges,
it has the composition of a glass comprising, consisting of, or consisting essentially of:
10%<Fe
2
O
3
<50%
10%<Na
2
B
4
O
7
<80%
0%<P
2
O
5
<10%
5%<SiO
2
<50%
0%<TiO
2
<15%
5%<Na
2
CO
3
<20%
5%<K
2
CO
3
<20%
0%<CaCO
3
<10%,
it preferably has the composition of a glass comprising, consisting of, or consisting essentially of:
Fe
2
O
3
30%
Na
2
B
4
O
7
15%
P
2
O
5
3%
SiO
2
15%
TiO
2
9%
Na
2
CO
3
11%
K
2
CO
3
15%
CaCO
3
2%
the powder is mixed with a compound endowing said powder with an electrostatic behavior and preventing adsorption of water.
The following description and the sole FIGURE presented, all given by way of non-limitative example, will make the invention clearly understood.
REFERENCES:
patent: 2786782 (1957-03-01), Zimmerman et al.
patent: 3671278 (1972-06-01), Borowski
patent: 3759240 (1973-09-01), Borowski
patent: 3765205 (1973-10-01), Schaumburg
patent: 3836380 (1974-09-01), Kramer
patent: 3930062 (1975-12-01), Nedeljkovic
patent: 4221824 (1980-09-01), Leonard et al.
patent: 4469798 (1984-09-01), Nishino et al.
patent: 5512521 (1996-04-01), Fu et al.
patent: 0 736 334 (1996-10-01), None
patent: 2 083 650 (1971-12-01), None
patent: 2 140 709 (1984-12-01), None
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Parker Fred J.
Sollac
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