WO2010092586A1

WO2010092586A1 - A process and apparatus for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill

Info

Publication number: WO2010092586A1
Application number: PCT/IN2009/000242
Authority: WO
Inventors: Deb Roy; Jayabrata Bhaduri; Sumitesh Das; Debashish Bhattacharjee
Original assignee: Tata Steel Limited
Priority date: 2009-02-16
Filing date: 2009-04-20
Publication date: 2010-08-19
Also published as: EP2247395A1; EP2247395A4

Abstract

This invention relates to an apparatus for application of coolants to achieve higher cooling rates in water boxes of a wire rod mill producing wire rods in a batch production scheme, the apparatus comprising; a mixing unit (7) capable of accommodating and maintaining industrial grade water at a temperature between 20 °C to 3O °C, a predetermined lot-size of nanoparticles including dispersants at a volumetric ratio of at least 0.1% being mixed with the industrial grade water filled in the mixing unit (7); a reservoir (6) constituting an inert tank capable of accommodating nanofluid when pumped in from the mixing unit (7), and having a capacity of at least 900 % more than that of the mixing unit (7); a pumping unit (5) for supplying the nanofluid at a predetermined pressure and flow from the reservoir (6) to at least one water box unit (4), at least one wire rod (1) exiting a last of a plurality of rollers (2) at a temperature around 900 to 95O °C being caused to push inside the at least one water box (4) at a speed between 0.4 to 0.8 m/sec in which the at least one wire rod (1) getting cooled to a temperature about 775 to 781 °C.

Description

TITLE

A process and apparatus for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill.

FIELD OF INVENTION

This invention relates to a process and an apparatus for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill.

BACKGROUND OF INVENTION

Process plants such as wire rod mills are expected to periodically produce new steel grades to meet the market demand. One of the methods of achieving this upgradation of the wire rod mill is to enable the mill to cool the products at higher cooling rates in the water boxes provided to the wire rod mill.

In an industrial wire rod mills, the steel billets of dimensions 120~130 mm square are heated up to 1000~1200°C in an inert atmosphere reheating furnace. The heated billets pass through a series of rollers that change the cross section of the billet to produce a square or round product. When the product is round in geometry and the diameter is below 5.5 mm, it is termed as a wire. Once the wire comes out of the last roller, the wire temperature is around 900~950°C. In metallurgical terms, for low carbon steels, this phase of steel is termed 'austenite'. Austenitic steels are characterized as being soft and ductile. However, the application of the product i.e. wire demands certain stringent properties e.g. toughness, high yield strength etc. To achieve this, the read hot wire must be cooled in a controlled manner so that the desired hard phases can come out during the cooling process.

Different phases of steel have distinct strength levels. These phases can be developed by heating steel to 1000⁰C and cooling to room temperatures. The cooling is defined in terms of cooling rates. Cooling is achieved in wire rod mills producing steel rods by using water in water boxes. For a fixed layout and process conditions the cooling rates remaining fixed. Any change in the cooling rate is done by either changing the process conditions, or modification of the plant (wire rod mill) itself.

The different degrees of cooling required by the product calls for variable and often high cooling rates. Cooling in a wire rod mill takes place by passing the red hot wire through a closed compartment called the "water box'. Often in typical industrial mills, 2~6 water boxes are provided.

Each water box is fed through a water line at a certain pressure and flow rate. Water boxes can be switched on and off to monitor and control the cooling rates. For a given water box and a fixed flow, the heat transfer capacity is more of less fixed.

However, there are at least three known approaches which are capable to increase the cooling rate for example, (a) Increase the number of water boxes, (b) Increase the flow rates and pressures (c) Decrease the water temperatures at the inlet to the water box. Increase the number of water boxes is restricted due to the system space and cost. The additional disadvantages of the known approaches can be summarized as under : Increasing the flow rate affects the wire stability due to the geometrical dimensions of 5.5 mm. Decreasing the water temperature calls for an additional investment of a chilled water line.

To the best of knowledge of the inventors, this is the first disclosure of its kind.

OBJECTS OF INVENTION

It is therefore an object of the invention to provide a process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill.

Another object of the invention is to provide a process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill which is implemented in a batch production scheme of wire rods in a by-pass circuit of the water boxes.

A still another object of the invention is to provide a process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill, which adapts nanopartides and surfactants as coolant in controlled volume. A further object of the invention is to provide an apparatus for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill.

SUMMARY OF THE INVENTION

Accordingly, in one aspect of the invention, there is provided an apparatus for application of coolants to achieve higher cooling rates in water boxes of a wire rod mill producing wire rods in a batch production, the apparatus comprising; a mixing unit capable of accommodating and maintaining industrial grade water at a temperature between 20°c to 30°c, a predetermined lot-size of nanoparticles including dispersants at a volumetric ratio of at least 0.1% being mixed with the industrial grade water filled in the mixing unit; a reservoir constituting an inert tank capable of accommodating nanofluid when pumped in from the mixing unit and having a capacity of at least 500 % to 900% more than that of the mixing unit; a pumping unit for supplying the nanofluid at a predetermined pressure and flow from the reservoir to at least one water box unit, at least one wire rod exiting a last of a plurality of rollers at a temperature around 900 to 95O⁰C being caused to push inside the at least one water box at a speed between 0.4 to 0.8 m/sec in which the at least one wire rod getting cooled to a temperature about 775 to 781⁰C.

In a second aspect of the invention, there is provided a process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill, comprising the steps of; filling-up a mixing unit at least upto 20% of its capacity with industrial grade water maintained at ambient temperature; selecting a lot- size of nanoparticles including dispersants and mixing with the industrial grade water in the mixing unit preferably at a volumetric ratio of 0.1%; pumping in the nanaofiuid from the mixing unit to a reservoir; pushing - out at least one wire- rod from an exit-roller into at least one waterbox at a speed of 0.4 to 0.8 m/sec, the wire rod at the entry level into the water box having a temperature of about 900 to 950°c; and delivering the nanofluid using a pump-unit from the reservoir to the at least one water box causing a fast cooling down of the wire rod upto 775 to 781⁰C.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE

Hg. 1 - shows a schematic diagram of an apparatus for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill according to the invention.

DETAIL DESCRIPTION OF THE INVENTION

As shown in Fig - 1, the apparatus of the invention comprises :

(a) A nanocoolant reservoir (6), (b) A nanocoolant preparation unit (7),

(c) A nanocoolant pumping unit (5)

The nanocoolant preparation unit (7) constitutes a high speed shear mixer that enables a fast dispersion of nano-sized particles so as to ensure stability in the long term. Nano-sized particles in the range of 30~80 nanometers are used that are metallic in nature. Particle stability is also ensured by the use of dispersants in equal volumetric proportions. In this apparatus, a dispersant sodium hexa meta phosphate is used and maintained at a pH of 7.5~9. Further details of this component is disclosed in the applicant's Indian patent application. No. filed on 16.02.2009.

The nanocoolant reservoir (6) is an inert tank capable of holding a quantity of (5000~9000 litres) of stable coolant. For a preferred embodiment of the invention the nano - coolant reservoir (6) is having a volumetric capacity of 20000 liters. This volume is capable of cooling at least three wires (1) of diameter 5.5 mm exiting at 900⁰C from a least roller (2) of a plurality of rollers

(2)-

The pumping unit (5) is configured to pump the nano-coolant at a desired pressure and flow.

A pyrometer (8) is used to sense the wire (1) before coiling. The apparatus of the present invention is enabled to compare the stored temperature data by the pyrometer (8) using water (Tw) with the temperature data recorded by the pyrometer (8) using nano-coolant (Tc). This difference (Tc-Tw) gives the efficiency of the apparatus of the invention.

The inventive process for achieving higher cooling rates in a wire rod mill comprises the steps of :

a) Industrial grade water is filled up in a mixing unit (7) to a capacity of 200 liters. The mixing unit (7) is such that this can accommodate upto 1000 litres at once.

b) Temperature of the industrial grade water is maintained between 20-30⁰C i.e. ambient conditions. No pre-processing of the industrial grade water is done.

c) Nanoparticles are measured by a measuring unit (not shown) in lot sizes of 250 gms along with dispersants in lot sizes of 250 gms.

d) The quantity of the nanoparticles is decided on the basis of a predetermined operating rule of 1 gram in 1 litre of industrial grade water. This is a volumetric ratio of 0.1%.

e) The lot sizes of the nanoparticles vary depending on the wire rod (1) type being cooled. f) The mixing is done using the high speed shear mixing unit (7).

g) The mixing is completed in 1 minute after the nanoparticles and dispersants are added to the system.

h) A pump is used to fill up a reservoir (6). This reservoir (6) now having the nanofluid.

i) The wire rod (1) is pushed from the roller (2) such that it achieves a speed of 0.4~0.8 m/sec in the water box (4). The wire rod (1) is at a temperature of 900~950oC at the entry point into the water unit (4).

j) A pumping unit (5) is switched on. This pump unit (5) sends the nanofluid into the water box unit (4).

/

k) The wire rod (1) is cooled in the water box unit (4) by the nanofluid

I) The wire rod (1) exits the water box unit (4) and the temperature is measured by a pyrometer (8).

m) The wire rod (1) temperature is lowered to 775~781°C using the nanofluid. For comparison purposes, when only industrial grade water is used, the wire rod temperature is lowered to 870~890°C. All other parameters remaining constant. This means that using the nanofluid, higher cooling rates of the order of 100~120°c can be achieved.

Claims

WE CLAIM

1. An apparatus for application of coolants to achieve higher cooling rates in water boxes of a wire rod mill producing wire rods in a batch production scheme, the apparatus comprising :

- a mixing unit (7) capable of accommodating and maintaining industrial grade water at a temperature between 20°c to 30°c, a predetermined lot-size of nanoparticles including dispersants at a volumetric ratio of at least 0.1% being mixed with the industrial grade water filled in the mixing unit (7);

- a reservoir (6) constituting an inert tank capable of accommodating nanofluid when pumped in from the mixing unit (7), and having a capacity of at least 900% more than that of the mixing unit (7);

- a pumping unit (5) for supplying the nanofluid at a predetermined pressure and flow from the reservoir (6) to at least one water box unit (4), at least one wire rod (1) exiting a last of a plurality of rollers (2) at a temperature around 900 to 95O⁰C being caused to push inside the at least one water box (4) at a speed between 0.4 to 0.8 m/sec in which the at least one wire rod (1) getting cooled to a temperature about 775 to 781⁰C.

2. The apparatus as claimed in claim 1, comprising a pyrometer (8) to sense the temperature of the wire-rod (1) before and after cooling.

3. The apparatus as claimed in claim 1 or 2, wherein the mixing unit (7) is provided with a high speed shear mixture.

4. A process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill, comprising the steps of :

- filling-up a mixing unit (7) at least upto 20% of its capacity with industrial grade water maintained at ambient temperature;

- selecting a lot-size of nanoparticles including dispersants and mixing with the industrial grade water in the mixing unit (7) preferably at a volumetric ratio of 0.1%;

- pumping in the nanaofluid from the mixing unit (7) to a reservoir (6);

- pushing - out at least one wire-rod (1) from an exit-roller (2) into at least one waterbox (4) at a speed of 0.4 to 0.8 m/sec, the wire rod (1) at the entry point of the water box (4) having a temperature of about 900 to 950°c; and - delivering the nanofluid using a pump-unit (5) from the reservoir (6) to the at least one water box (4) causing a fast cooling down of the wire rod (1) upto 775 to 781⁰C.

5. The process as claimed in claim 4, wherein the size of the nanoparticles can be selected in the range of 30-80 nanometers, and wherein the nanaoparticles are metallic in nature.

6. The process as claimed in claim 4 or 5, wherein the dispersants and the nanoparticles are used in equal volumetric proportions.

7. The process as claimed in claims 4 to 6, wherein the dispersant constitutes sodium hexa meta phosphate maintained at a pH of 7.5 to 9.

8. An apparatus for application of coolants to achieve higher cooling rates in water boxes of a wire rod mill producing wire rods in a batch production as substantially described herein with reference to the accompanying drawings.

9. A process for application of coolants to achieve higher cooling rates in the water boxes of a wire rod mill, as substantially described herein with reference to the accompanying drawings.