Field of Invention:
This invention relates in general to a controlled cooling process, which is
applicable to number of applications in hot rolled steel products such as wire
rod cooling, Run-Out-Table cooling and cooling of rebars, strips, plates etc. In
particular the invention relates to a process of improved uniformity in surface
temperature of steel products during cooling by water from high
temperatures.
Background and Prior Art:
Cooling of steel products is very important stage in the manufacturing of such
products. Cooling must be controlled to ensure that the end product meets
the standards of metallurgical and mechanical properties and the desired
surface finish. The cooling process must also ensure that it is cost effective
and poses least threat to the environment.
In describing the prior art, the following documents have been referred to:
Referred Patents:
1. Centre de recherches metallurgiques-centrum voor research in de
metallurgie, 1978, "Process for improving the quality of steel section",
GB1522972.

2. Kudou, I., Takahashi, H., Shimada, K., and Taniguchi, H., 1982, "Uniform
quencher for bar steel material", JP57016130.
3. Conklin, M.T. and Mowry, C.F., 1984, "Cooling heated metal surfaces",
US4476687.
4. IKenaga, A., 1994, "Apparatus for quenching metal wire", JP6073460.
5. Nakahara, M., 1995, "Device for directly quenching flat steel", JP7088529.
6. Tomono, K., Yasuzawa, N., Nishino, J., 1996, "Direct quenching of rolled
wire rod", JP8176681.
7. Takada, Y., Hidaka, S., Ito, T., 2003, Method and Device for cooling metal
material, JP2003181519.
8. Zhang, K., 2004, "Water-soluble quenching medium", CN1465722.
Reference
1. Dupont, 2001, "Dupon™ ZonylR FSH Flurosurfactant" (Information on
technical data).
Spray cooling is known in the art, which is typically used for controlled
cooling of hot surfaces, such as rebars and wirerods and strips having
temperatures in the range of 1000°C to 400°C.

A process for improving the quality of a steel section having at least one flat
face is disclosed in GB1522972 in GB1522972 (Centre de recherches
metallurgiques-centrum voor research in de metallurgre, 1978), where only
the outer layer of flat face is subjected to surface quenching by means of
cooling fluid, which comprises of water or an aqueous suspension or solution
of one or more mineral salts and/or surfactants, in the form of mist (a
suspension of liquid in gas) and may be projected at surpersonic speed. The
disadvantage with mist cooling is that surfactants can form foam, which is not
good heat transfer medium. This can result into loss in heat transfer
coefficient if foam comes in direct contact with the hot surface to be cooled.
To uniformly cool the whole circumference of a bar steel material, a method
is disclosed in JP57016130 (Kudou, et al., 1982), which uses deviating the
jetting direction of a quenching liquid from nozzle in directions opposite to
each other at fixed angle to axis of inner tube of quenching tubes alternately
arranged in the running direction of the bar steel material. For quenching
tubes, position, number and jetting directions are optimized through advance
detection of eccentricity width of the bar steel material. This is biggest
disadvantage in processing, which also limits highest accuracy for uniform
cooling.
A method is disclosed in US4476687 (Conklin and Mowry, 1984), which uses
comparatively low flow rates for rapidly cooling of heated surfaces by water
having one or more of nonionic surfactants sprayed without foam to cool
faster than conventionally used water systems. However, it has disadvantage
in terms of the cooling efficiency not being quantified with respect to the
improvement in cooling time or cooling rate over that of water system.
Further disadvantage of this cooling process is the total time it takes

for cooling of a plate or sheet from 1100°C to 80°C, which is of the order of
few minutes. The other disadvantage of the invention disclosed in US4476687
is the limiting range of surfactant additive(s) cloud point from 68°F - 212°F,
beyond which the cooling efficiency goes down drastically.
To obtain evenness of quenching, JP6073460 (Ikenaga, 1994) discloses
cooling with water-soluble quenching liquid in the ideal form, which provides
suitable cooling during transformation at uniform temperature, which leads to
quenched steel wire having no strain and good straightness in the metal wire.
The majour disadvantage in this approach is that large quantity of this liquid
is required to be stored in the tank in which the cylindrical ejection nozzle is
arranged. Additionally, this is aimed for quenching of metal wires, which are
small sized and hence have less heat to be removed.
A method to cool uniformly all the circumference of flat steel is disclosed in
JP7088529 (Nakahara, 1995), which has group of cooling nozzles forming
water flim zones to cover all the circumference of the circumferential surface
and into multistages by installing cooling zones onto plural places. The
disadvantage however is with the groupings of cooling nozzles that lessens
but not eliminate the water flim zone interferences.
Direct quenching method for cooling of hot-rolled ring shape wire rod is
disclosed in JP8176681 (Tomono, et al.1996,), which injects a foam fluid
generated from an aqueous solution containing a surfactant or/and a water-
soluble polymer at a speed of 0.1 to 50 m/s. The concentration of water was
2 to 80% and the steel is cooled below martensite intiation temperature
before quenching. The disadvantages of this method are of using high
concentration of aqueous surfactant solution and foam generation.

A method and device capable of artificially and easily controlling quenching
points in the cooling process is disclosed in JP2O03181519 (Takada, et al.,
2003). Surface wettability is temporarily improved by irradiating the surface
of steel plate with plasma for a period of 60 seconds before water is sprayed.
This reduces contact angle and shortens cooling time. The disadvantage is of
having additional device for irradiating plasma and 60 seconds of uncooled
steel surface travel length, which reduces the productivity.
CN1465722 (Zhang, 2004) discloses invention, which relates to a water-
soluble quenching medium having surfactant. The disadvantage is that
surfactant is not the component of this quenching medium. It has with
surfactant, polyether high-molecular mixture, inorganic salt, sterilizing agent,
inorganic alkali and water.
The disclosed method is suited for controlled cooling of wirerods, rebars,
strips and plates of steel. This cooling method uses nonionic surfactant
DuPont™ Zonyl® FSH for improving uniformity in temperature by reducing
temperature fluctuation during water cooling of steel. The nonionic
surfactant DuPont™ Zonyl® FSH is injected in the water stream and the
resulting aqueous surfactant solution is sprayed through nozzles. This cooling
method of the present invention has advantage over that disclosed in
US4476687 with respect to the cloud point of the surfactant additive(s); while
a single nonionic surfactant or combinations of these surfactants should have
could point in the range of 68°F - 212°F as per the invention disclosed in
US4476687, the nonionic surfactant DuPont™ Zonyl® FSH used in the
present invention has no cloud point in the temperature range of 68°F- 212°F
(DuPont, 2001).

Objects of the invention:
An object of this invention, is to propose a cooling process for improving
uniformity in temperature during water cooling of steel for applications such
as wire rod and rebar cooling, Run-Out-Table cooling and continuous casting
of steel strip.
Yet another object of this invention is to propose a cooling process that
employs spray cooling using pressure sprays.
Still another object of this invention, is to propose a cooling process that
provides cooling for cooling of steel in the temperature range of interest from
950°C to 840°C.
A further object of this invention is to propose a cooling process, which uses
Rf CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) y, a chemical commonly
known in trade as DuPont™ Zonyl® FSH as an additive to water.
A still further object of this invention, is to propose a cooling process, which
uses surfactant additive(s) having no cloud point in the range of 68°F -
212°F.
Brief description of accompany ing drawings :-
Fig1- Shows schematic diagram of experimental facility of injection system of
the invention.
Fig2-(a-c)- Show temperature time variation and water switching on and off
conditions for water(fig2a) & with surfactant solution at low concentration
(fig2b), at high concentration (fig-2C).

Fig3(a-d)- Show photographs of wire rod surface (fig3a) which are cooled by
water (fig 3b), low surfactant concentration (fig 3c) & with high surfactant
concentration (fig 3d).
Fig 4 (a-c)- Show SEM photographs of microstructure of wire rod surface,
cooled by water (fig4a), low surfactant concentration solution (Fig-4b) & high
surfactant concentration solution (fig-4c).
Description of the invention:
According to this invention there is provided a method of controlled cooling
process for cooling of steel wherein the process comprises of spray cooling ie,
applying water under pressure & adding pure Rf CH2CH2O (CH2CH2O)x H,
where Rf = F(CF2CF2) y surfactant (nonionic) as an additive to water, leading
to predetermined concentration & the steel products being in the respective
temperature range of interest.
A nonionic fluorosurfactant having structure as RfCH2CH2O(CH2CH2O)xH,
where Rf = F(CF2CF2)y. The above chemical is commonly known in the trade
as DuPont™Zony®FSH(DuPont,2001). It gives exceptionally low surface
tension in its aqueous solutions, the values of which are of the order of 17 to
22 dyn/cm for the surfactant concentration range of 0.1 to 0.001% and
provides better wetting and spreading characteristics. Even at very low
concentrations, it delivers much improved wetting power. Additionally, the
surfactant concentration is small, which changes only the surface tension of
water and the other properties of water remain same . Moreover, Rf
CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) yM is nonhazardous,
nonflammable thus making it an appropriate choice as safe and economically
useful additive.

Aqueous solutions having volumetric concentrations in the range of 0.01% to
0.4% of Rf CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) y have been
investigated for cooling wire rod of 5.5 mm diameter from temperature in the
range of 950 to 930°C to temperature in the range of 840 to 880°C. The
rolling speed was 55 m/s and the water flow rate to water box was in the
range of 1500 to 1800 Ipm under the pressure of 4 bars. Rf CH2CH2O
(CH2CH2O)x H, where Rf = F(CF2CF2) y was injected from a closed vessel
fabricated for applying air pressure at 6 bars to the pure surfactant liquid.
This differential pressure is maintained for injecting surfactant liquid in water
stream. The injection point was at the downstream of pump and upstream of
the water box with around 10 meters of mixing length provided for mixing
the injected surfactant with the water stream before exiting out of the
nozzles in the water box in the form of spray to cool the wire rod surface.
The inventing will now be described with accompanying drawings which
depict an exemplary embodiment of invention.
However, there can be other embodiment, all of which are deemed covered
by the description.
Fig.l is the schematic diagram of experimental facility showing the injection
system for the Rf CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) y in water
stream for cooling of 5.5 mm wire rod. The facility was first calibrated with
water. The surfactant is allowed to drain with water and is not recirculated.
Fig. 2 (a-c) presents charts showing temperature-time variations and water
switching on and off conditions for experimental water flow (Fig. 2a) and
aqueous surfactant solution flows with concentrations ranging from low
(Fig.2b) to high (Fig.2c). The temperature fluctuations are
reduced/smoothened out significantly with low surfactant concentration and

are eliminated at high surfactant concentration. The surfactant Rf CH2CH2O
(CH2CH2O)x H, where Rf = F(CF2CF2) y provides better wetting and
spreading characteristics. Improved wetting reduces contact angle such that
water spreads better on the hot steel surface. The reduction or smoothening
of temperature fluctuations are due to this improvement in wetting
characteristics of water. With higher Rf CH2CH2O (CH2CH2O)x H, where Rf =
F(CF2CF2) y concentration, there is further improvement to the point of
elimination. This leads to improved uniformity in steel surface temperature
during cooling of water.
Fig. 3 (a-d) shows photographs of wire rod surfaces (Fig. 3a), which are
cooled by water (Fig. 3b), low surfactant concentration solution (Fig. 3c) and
high surfactant concentration solution (Fig. 3d). The surfaces show drastic
difference with respect to surface finish for wire rod cooled using aqueous
surfactant Rf CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) y solutions.
The uniformity in temperature is correlated directly. The smoothest surface
corresponds to elimination of temperature fluctuations.
Fig. 4 (a-c) shows the SEM photographs of microstructure of wire rod
surfaces cooled by water (Fig. 4a), low surfactant concentration solution (Fig.
4b) and high surfactant concentration solution (Fig. 4c). The microstructures
show improvement & difference between the coolants used.

We claim:-
1. A method of improving uniformity in surface temperature of steel products
during water cooling of steel, comprising the steps;
-mixing by injecting a non-ionic surfactant Rf CH2CH2O (CH2CH2O)x H,
where Rf = F(CF2CF2) y in pure form as an additive in water for better
wetting & spreading characteristics, wherein said additive in its aqueous
solution is provided in a predetermined concentration for controlled cooling
by reducing temperature fluctuation in surface of steel products,
-applying said water mixed with the additive, under pressure for spray
cooling of hot rolled steel products.
2. The method as claimed in claim 1, wherein said nonionic surfactant in
aqueous solution has a volumetric concentration of 0.01% - 0.4%.
3. The method as claimed in claims 1 and 2, wherein said nonionic surfactant
has no cloud point in the temperature range of 68°F - 212°F.
4. The method as claimed in claim 1, wherein said temperature fluctuating in
surface of steel products in substantially reduced at low surfactant
concentration and eliminated at high surfactant concentration.
5. A method as claimed in claim 1 & 2, wherein One of the said temperature
range of interest is 950°C - 840°C.

A method of improving uniformity in surface temperature of steel products during water cooling of steel, comprising the steps;
-mixing by injecting a non-ionic surfactant Rf CH2CH2O (CH2CH2O)x H, where Rf = F(CF2CF2) y in pure form as an additive in water for better
wetting & spreading characteristics wherein said additive in its aqueous solution is provided in a predetermined concentration for reducing
temperature fluctuation in surface of steel products, -applying said water mixed with the additive, under pressure for spray cooling of hot rolled steel products.