METHOD AND EQUIPMENT FOR CONTROLLED PATENTING OF STEEL WIRE

Abstract

A method of continuous controlled cooling of a plurality of heated steel wires having a diameter larger than 2.8 mm and having an austenite microstructure and of transformation to a pearlite microstructure of the steel wires. The method comprises the steps of: a) Providing a first coolant bath comprising a first coolant liquid. The first coolant liquid comprises water and a stabilizing additive. b) Guiding the plurality of previously heated steel wires parallel to each other along individual paths through the first coolant liquid contained in the first coolant bath; and directing impinging liquid immersed inside the first coolant bath towards each of the steel wires over a certain length L. The impinging liquid decreases the thickness of or destabilizes the steam film around each of the plurality of steel wires, resulting in an increase of the speed of cooling over said length L. The intensity of the impinging liquids is individually set and/or controlled for each individual steel wire or for subsets of the plurality of steel wires. c) Guiding the plurality of steel wires parallel to each other through air for further cooling.

Description

TECHNICAL FIELD

The invention relates to methods and equipment for patenting of steel wires in which coolant baths comprising water as coolant liquid are used.

BACKGROUND ART

Patenting of steel wires involves conversion of the steel wire in a furnace or via other heating means into austenite; and cooling the austenite steel wires in a controlled way to a pearlite structure. Preferably, the obtained pearlite structure is a fine pearlite structure, also called sorbite. Preferably, the pearlite structure is uniform over the cross section of the steel wire. It is preferred that the pearlite structure is free from bainite or martensite. The pearlite structure allows drawing of the steel wires to finer diameters.

Traditionally, the cooling step in patenting of steel wires is performed in a molten lead bath, which allows isothermal transformation of the austenite in fine pearlite. Because of environmental and health issues, lead patenting is more and more replaced by alternative cooling techniques; of which the use of water based coolant baths is one example.

EP0524689A1 discloses a process of patenting at least one steel wire with diameter less than 2.8 mm. The cooling is alternatingly done by film boiling in water during one or more water cooling periods and in air during one or more air cooling periods. A water cooling period immediately follows an air cooling period and vice versa. The speed of cooling in water is high, while the speed of cooling in air is much lower. The high speed of cooling in water poses a serious risk for wires with a diameter less than 2.8 mm. Cooling in air in between cooling in water sections is performed in order to slow down the cooling of the steel wires. The number of the water cooling periods, the number of the air cooling periods and the length of each water cooling period are so chosen so as to avoid the formation of martensite or bainite.

WO2014/118089A1 entitled “Forced water cooling of thick steel wires” discloses a forced cooling process on straight steel wires having a diameter larger than 5 mm. An impinging liquid immersed inside a coolant bath is directed to the steel wire to accelerate the cooling speed of the heated steel wire. This “forced” cooling zone in the coolant bath is followed by a cooling zone in which an undisturbed (this means without impinging liquid on the boiling film around the wire) boiling film cools the wires further.

DISCLOSURE OF INVENTION

The first aspect of the invention is a method of continuous controlled cooling of a plurality of heated steel wires having an austenite microstructure and of transformation to a pearlite microstructure of the steel wires. The plurality of steel wires comprises—and preferably consists out of—steel wires having a diameter larger than 2.8 mm. The method comprises the steps of

a) providing a first coolant bath. The first coolant bath comprises a first coolant liquid. The first coolant liquid comprises water and a stabilizing additive. Preferably, the first coolant liquid in the first coolant bath has a temperature of more than 80° C.;

b) guiding the plurality of previously heated steel wires parallel to each other along individual paths through the first coolant liquid contained in the first coolant bath; and directing impinging liquid immersed inside the first coolant bath towards each of the steel wires over a certain length L. The impinging liquid decreases the thickness of or destabilizes the steam film around each of the plurality of steel wires, resulting in an increase of the speed of cooling over said length L. The intensity of the impinging liquids is individually set and/or controlled for each individual steel wire or for subsets of the plurality of steel wires;

c) guiding the plurality of steel wires parallel to each other through air for further cooling.

The required parameters for the cooling in patenting processes depend on the diameter of the steel wire and on the steel alloy. When cooling using a lead bath, the parameters are less critical, as the transformation from austenite to pearlite occurs isothermal, thanks to the properties of the lead bath. When using water based cooling media, this is no longer the case. Therefore, parameter setting becomes much more critical in order to obtain proper transformation to fine pearlite when treating at the same time steel wires of different diameter and/or different steel alloy. It is a benefit of the invention that steel wires of different diameter and/or of different steel alloys can be patented at the same time; each to an optimum microstructure. It is a further benefit that the microstructure of each of the steel wires is more constant over the length of the wire.

In the method, the steel wires can comprise a plurality of subsets, parallel to each other. Each subset of wires can consist of wires of specific diameter and specific alloy. By setting and/or controlling the intensity of the impinging liquids for each subset of the plurality of steel wires; the steel wires in each subset can be optimally patented.

It is even possible to set and control the intensity of the impinging liquids for each individual steel wire. Such embodiments allow high flexibility of the method in that more steel wires of different diameter and/or alloy can be patented at the same time. In addition, each steel wire—even steel wires of the same diameter and same alloy—can be optimally patented taking differences in wire positions in the equipment and in previous process steps (e.g. in the heating furnace, in pickling . . . ) into account.

The stabilizing additive is provided to increase the stability of the vapor/steam film around the steel wires. The stabilizing additive may comprise surface active agents such as soap, stabilizing polymers such as polyvinyl pyrrolidone, polyvinyl alcohol and/or polymer quenchants such as alkalipolyacrylates or sodium polyacrylate. The additives are used to increase the thickness and stability of the vapor film around the steel wire.

Preferably, the impinging liquid has the same composition as the coolant liquid of the first coolant bath.

Preferably, the impinging liquid is taken from the first coolant bath. More preferably, the impinging liquids are continuously recirculated and controlled by pumps and a flow rate control system.

Preferably, the diameter of each of the steel wires is between 2.8 mm and 20 mm.

As an example, the impinging liquids can be provided via nozzle openings in a plate provided horizontally and below the steel wires in the first coolant bath.

Preferably, the method comprises—after cooling the plurality of steel wire in the first coolant bath by means of the impinging liquid—the additional step of guiding the plurality of steel wires along individual paths parallel to each other through a second coolant bath. The second coolant bath comprises a second coolant liquid. The second coolant liquid comprises water and a stabilizing additive. Preferably, no turbulence is present in the second coolant bath. Preferably, the steam film created in the second coolant bath around each of the steel wires is undisturbed.

Preferably, the temperature of the first coolant liquid in the first coolant bath is substantially the same as the temperature of the second coolant liquid in the second coolant bath.

Preferably, the composition of the first coolant liquid is the same as the composition of the second coolant liquid.

Preferably, in the second coolant bath laminar flow of the second coolant liquid is present. The second coolant liquid can e.g. be refreshed via an overflow and supply of new second coolant liquid via a laminar flow. More preferably, the second coolant liquid is continuously recirculated.

In a preferred embodiment, an air gap is provided between the first coolant bath and the second coolant bath, such that the plurality of steel wires is cooled by air in between the first coolant bath and the second coolant bath.

In a preferred embodiment, the first coolant bath and the second coolant bath are the same bath. It is meant that the steel wires do not run through an air gap between the first coolant bath and the second coolant bath, but are continuously submerged in coolant liquid when moving from the first coolant bath into the second coolant bath, which is the same bath.

Preferably, the intensity of the impinging liquid is individually set and/or controlled for each individual steel wire of for subsets of the plurality of steel wires by means of setting and/or controlling the flow rate of the liquid flows creating the impinging liquids. This can e.g. be implemented by controlling the flow rate of the pump or pumps creating the liquid flows for the impinging liquids; or by controlling or setting one or a plurality of valves or orifices.

More preferably, one or a plurality of sensors are provided. Control of the intensity of the impinging liquids for each individual steel wire or for subsets of the plurality of steel wires is provided by means of a measurement by the one or the plurality of sensors for or at each individual steel wire; or for or at subsets of the plurality of steel wires. Setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids is performed using the measured signals and a controller.

Even more preferably, the sensor or sensors comprise or consist out of pressure sensors. The pressure sensors are provided for measurement of the liquid pressure at the nozzles creating the impinging liquids; and the sensor measurements are used for setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids. As an alternative—or in addition to—pressures sensors, the sensor or sensors comprise or consist out of flow sensors. The flow sensors are provided for measurement of the flow at the nozzles creating the impinging liquids; and the sensor measurements are used for setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids.

Preferably, one or a plurality of magnetic sensors are provided to measure the magnetic response of one or of subsets of the steel wires; and to provide feedback to adapt in a closed loop control the impinging liquids in the first coolant bath.

Preferably, the first coolant bath is provided with partitioning walls separating the steel wires or the subsets of steel wires in the first coolant bath along the full length of the steel wires along which the steam film around the steel wires is affected by the impinging liquids. This way impinging liquid onto a first steel wire do not affect the steam film around a second steel wire. This way, the setting or control on the impinging liquids is more effective, as no effect on the cooling of the steel wires is derived from the impinging liquids of neighboring steel wires or neighboring subsets of wires. As an example, the impinging liquids can be provided via nozzle openings in a plate provided horizontally and below the steel wires in the first coolant bath; and the partitioning walls are provided vertically; and positioned onto the plate; and preferably attached onto the plate.

Preferably, the impinging liquid is immersed below each steel wire itself along each individual path; or the impinging liquid is immersed partially below some of the plurality of steel wires along their individual paths.

Preferably, the length of the individual paths of each of the steel wires through the first coolant batch and/or through the second coolant bath is adjustable.

Preferably, the speed of the steel wires through the continuous process is individually adjustable in order to optimize the transformation of each of the steel wires in function of their diameter and/or alloy composition.

Preferably, the length through which each of the steel wires runs through the first coolant bath is the same.

Preferably, the steam film created in the second coolant bath around each of the steel wires is undisturbed.

When a second coolant bath is provided, preferably the steel wires are guided out of the second coolant bath and further cooled to room temperature in air.

A second aspect of the invention is equipment for performing the method of the first aspect of the invention. The equipment comprises

• • a first coolant bath for comprising a first coolant liquid,
  • means for guiding the plurality of previously heated steel wires parallel to each other along individual paths through the coolant liquid contained in the first coolant bath,
  • impinging liquid generator(s) immersed inside the first coolant bath(s), wherein the impinging liquid generator(s) are adapted to direct impinging liquid towards the steel wires over a certain length L;
  • means for individually setting or controlling the intensity of the impinging liquids for each individual steel wire or for subsets of the plurality of steel wires; and
  • means for guiding the plurality of steel wires parallel to each other through air for further cooling.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIG. 1 illustrates an example of the invention.

FIG. 2 shows a cross section along line II-II of FIG. 1.

MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates an example of a preferred method and equipment according to the present invention. FIG. 2 shows a cross section along line II-II of FIG. 1. The cooling length with impinging liquid in the first coolant bath (CB1) is fixed. The first coolant bath comprises a first coolant liquid. The first coolant liquid comprises water and a stabilizing additive. The first coolant liquid in the first coolant bath has a temperature of more than 80° C. A short air gap (AG) has been added to separate the first coolant bath (CB1) and the second coolant bath (CB2). The second coolant bath (CB2) is adjustable in length. The second coolant bath comprises a second coolant liquid; which has in this example the same composition and the same temperature as the first coolant liquid. No turbulence is present in the second coolant bath; the steam film created in the second coolant bath around each of the steel wires is undisturbed. Laminar flow of coolant liquid is present in the second coolant baths, ensuring refreshment of coolant liquid in the second coolant baths. The first coolant bath is provided with partitioning walls separating the first coolant bath in different “lanes”; each subset of steel wires is treated in a separate lane (or even one single steel wire per lane). Preferably, as shown in FIG. 1, in the first coolant baths, the impinging liquid generators and the air gaps along each individual path have a fixed length and the length of the second coolant baths is adjustable for each of the subsets of steel wires. A plurality of steel wires is patented at the same time, parallel to each other. The intensity of the impinging liquids in the first coolant bath is individually set and controlled in each lane, thus for each subset of steel wires.

As shown in FIG. 2—which shows a cross section along line II-II of FIG. 1—, steel wires 10 are led out of a furnace 12 having a temperature T of about 1000° C. The wire running speed can be adjusted according to the diameter of the wire, e.g. about 20 m/min. The first coolant bath 14 of an overflow-type is situated immediately downstream the furnace 12; the steel wire is led between partitioning walls in the first coolant bath. A plurality of jets 16 from the holes 20 of a perforated plate 22 immersed inside the first coolant bath are forming an impinging liquid, whose flow rate is set and controlled by a circulation pump and control system 18 outside the first coolant bath. The cooling rate is adjusted by tuning the coolant flow by means of the pressure in front of the jets, via control of the pumps providing the liquid flow for the impinging jets. To this end, pressure sensors can be used at the perforated plate to measure the coolant liquid pressure; the measurement signal can be used in a closed feedback control system towards the pump generating the liquid flow for that subset of steel wires. The flow rate can be set individually for each subset of steel wires. The flow rate of the jets for forced cooling and the length of air gap region are so chosen as to avoid the formation of martensite or bainite. The partitioning walls can be provided vertically; and positioned onto the perforated plate and attached onto the plate to avoid that impinging jets acting on one subset of wires in a lane affect the boiling film present on steel wires in another lane, meaning in another subset of steel wires. The impinging liquid under pressure from the holes 20 is jetting towards the steel wire 10. As illustrated in FIG. 2, the first length L₁ is the distance from the exit of furnace 12 to the impinging liquid. The second length L₂ indicates the length used for forced coolant cooling process—forced coolant cooling length—in the first coolant bath. The steel wire 10 is then led out of the first coolant bath and subjected to an air gap region with a length L₄ as indicated in FIG. 2. Thereafter, the steel wire 10 is guided into a second coolant bath 17 to further cool down. The immersion length of the steel wire 10 in the second coolant bath 17 is indicated as L₅. The length L₅ can be variable depending on the diameter and the desired tensile strength of the steel wire 10. After the second coolant bath, the steel wires are guided through air to be further cooled.

Claims

1-15. (canceled)

16. A method of continuous controlled cooling of a plurality of heated steel wires having an austenite microstructure and of transformation to a pearlite microstructure of the steel wires, wherein the plurality of steel wires comprises steel wires having a diameter larger than 2.8 mm; the method comprises the steps of:a) providing a first coolant bath, wherein the first coolant bath comprises a first coolant liquid, wherein the first coolant liquid comprises water and a stabilizing additive,b) guiding the plurality of previously heated steel wires parallel to each other along individual paths through the first coolant liquid contained in the first coolant bath,and directing impinging liquid immersed inside the first coolant bath towards each of the steel wires over a certain length L; wherein the impinging liquid decreases the thickness of or destabilizes the steam film around each of the plurality of steel wires, thereby increasing the speed of cooling over said length L;wherein the intensity of the impinging liquids is individually set and/or controlled for each individual steel wire or for subsets of the plurality of steel wires;c) guiding the plurality of steel wires parallel to each other through air for further cooling.

17. Method as in claim 16, comprising after cooling the plurality of steel wire in the first coolant bath by means of the impinging liquid—the additional step of guiding the plurality of steel wires along individual paths parallel to each other through a second coolant bath; wherein the second coolant bath comprises a second coolant liquid, wherein the second coolant liquid comprises water and a stabilizing additive.

18. Method as in claim 17, wherein an air gap is provided between the first coolant bath and the second coolant bath, such that the plurality of steel wires is cooled by air in between the first coolant bath and the second coolant bath.

19. Method as in claim 17, wherein the first coolant bath and the second coolant bath are the same bath.

20. Method as in claim 16, wherein the intensity of the impinging liquid is individually set and/or controlled for each individual steel wire of for subsets of the plurality of steel wires, by means of setting and/or controlling the flow rate of the liquid flows creating the impinging liquids.

21. Method as in claim 20, wherein one or a plurality of sensors are provided,wherein control of the intensity of the impinging liquids for each individual steel wire or for subsets of the plurality of steel wires is provided by means of a measurement by the one or the plurality of sensors for or at each individual steel wire; or for or at subsets of the plurality of steel wires;and setting of or feedback control to the flow rate of the liquid flows creating the impinging liquids using the measured signals and a controller.

22. Method as in claim 21, wherein the sensor or sensors comprise pressure sensors or flow sensors,and wherein the pressure sensors are provided for measurement of the liquid pressure at the nozzles creating the impinging liquids, or wherein the flow sensors are provided for measurement of the flow at the nozzles creating the impinging liquids;and wherein the sensor measurements are used for setting of or feedback control of the flow rate of the liquid flows creating the impinging liquids.

23. Method as in claim 16, wherein one or a plurality of magnetic sensors are provided to measure the magnetic response of one or of subsets of the steel wires; and to provide feedback to adapt in a closed loop control the impinging liquids in the first coolant bath.

24. Method as in claim 16, wherein the first coolant bath is provided with partitioning walls separating the steel wires or the subsets of steel wires in the first coolant bath along the full length of the steel wires along which the steam film around the steel wires is affected by the impinging liquids.

25. Method as in claim 16, wherein the impinging liquid is immersed below each steel wire itself along each individual path; or wherein the impinging liquid is immersed partially below some of the plurality of steel wires along their individual paths.

26. Method as in claim 16, wherein the length of the individual paths of each of the steel wires through the first coolant bath and/or through the second coolant bath is adjustable.

27. Method as in claim 16, wherein the speed of the steel wires through the continuous process is individually adjustable in order to optimize the transformation of each of the steel wires in function of their diameter and/or alloy composition.

28. Method as in claim 17, wherein the steam film created in the second coolant bath around each of the steel wires is undisturbed.

29. Method as in claim 16, wherein the length through which each of the steel wires runs through the first coolant bath is the same.

30. Equipment for performing the method as in claim 16, comprising a first coolant bath for comprising a first coolant liquid,means for guiding the plurality of previously heated steel wires parallel to each other along individual paths through the coolant liquid contained in the first coolant bath,impinging liquid generator(s) immersed inside the first coolant bath(s), wherein the impinging liquid generator(s) are adapted to direct impinging liquid towards the steel wires over a certain length L;means for individually setting or controlling the intensity of the impinging liquids for each individual steel wire or for subsets of the plurality of steel wires;means for guiding the plurality of steel wires parallel to each other through air for further cooling.