CA1124555A - Rolling of steel strip - Google Patents
Rolling of steel stripInfo
- Publication number
- CA1124555A CA1124555A CA308,793A CA308793A CA1124555A CA 1124555 A CA1124555 A CA 1124555A CA 308793 A CA308793 A CA 308793A CA 1124555 A CA1124555 A CA 1124555A
- Authority
- CA
- Canada
- Prior art keywords
- mill
- strip
- slab
- train
- partially reduced
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Metal Rolling (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a continuous or semi-continuous strip-mill for the hot rolling of steel slab into strip, comprising: a. a roughing mill for partial reduction of the steel slab, b. an in-line roller hearth tunnel furnace with heated walls into which the partially-reduced slab is passed and in which it remains in a flat and uncoiled form, and c. a multi-stand finishing mill-train adapted to reduce the partially reduced slab to produce strip of the required thickness.
The present invention provides a continuous or semi-continuous strip-mill for the hot rolling of steel slab into strip, comprising: a. a roughing mill for partial reduction of the steel slab, b. an in-line roller hearth tunnel furnace with heated walls into which the partially-reduced slab is passed and in which it remains in a flat and uncoiled form, and c. a multi-stand finishing mill-train adapted to reduce the partially reduced slab to produce strip of the required thickness.
Description
, This invention relates to the rolling of s~teel strip, and more particularly to the hot rolling of steel ~labs into strip~ ~
~ here is a technological problem in desi~ning a wide hot strip mill which is capable of economic operation at medium tonnage rates oX less than about -one million tons per annum.
In its pre~ent form th~ conventio~al continuous hot strip mill requires the use of 5 or 6 roughing stands followed by a 6 or 7-stand finishing train to achieve the o~erall reductio~ in thickness from a slab, usuall~ in the range of 200 to 250 mm thickness, down .to hot-rolled coil of gauge 2 mm to ~ mm, A mil~ of this type is characterised by high capital cost and a hi~h intrinsic rolling capacity. An ~nnual tonnage output of about 3 million tonnes of hot rolled coil, for example, would be typlcal for a modern rully conti~uous mill of about 1O5 metre wid~h. An alternative mill configuration is available in the form of the semi-oontinuous mill, comprising a reversing roughing mill (usually maki~lg 5 pa~ses) followed by a . continuous multi-stand finishing trai~O m e semi-continuous mill is of shorter len~th and lower capital ..l.
co~t than the fully continuous type ~ut i.t is ~-till a high tonnage-capacity unit. '~he requirement of a high coil waight for the finished product tends to increase the overall length of the miIl and necessitates the use _ 1 _ ., ' ' ~
' s~
of higher rolllng speeds to avoid excessive temperature loss of the steel in its passa~e through -the mill. The temperature of the steèl at the las-t finishing stand, and the problem of tail-end temperature loss, are among the most critical factors determining the operating speed of the mill.
It is an object of the present invention to provide a strip mill of more compact length tnan has hitherto been available and which is capable of rolling at lower speecls than are conven-tionally used at present, and to allow economic production of wide (wider than about 2/3 metre) hot-rolled coil at a rate of some half a million to one million tons per annum.
The underlying concept upon which this invention is based is the introduction of an intermediate in-line thermal shield between the roughing mill and the finishing -train of a hot strip mill. It will be understood that by a thermal shield is meant either an arrangement by which heat loss from the partially reduced slab is prevented, e.g. an insulated tunnel, or an arrangement fQr re-heating the partially-reduced slab, e.g.
a furnace. I'his thermal shield serves the purpose of preventing further heat loss from the slab after completion of rolling through the roughing mill and during the time when the slab is being fed into the finishing train. This enables lower rolling speeds ~ -2-and lower driving power to be employed in the finishing train.
It also enables the temperature of the steel to be controlled accurately a-t en~ry to the finishing train and a substantially uniform temperature to be maintained along the length of the strip at each finishing stand A Eurther advantage of this means of temperature control is that it enables a constant entry speed to be maintained at the finishing train.
Thus in one aspect the present invention provides a continuous or semi-continuous strip-mill for the hot rolling of steel sla~ into strip, comprising: a. a roughing mill for partial reduction of the steel slab, b. an in-line roller hearth tunnel furnace with heated walls into which the partially reduced slab is passed and in which it remains in a flat and uncoiled form, and c. a multi-stand finishing mill-train adapted to reduce the partially reduced slab to produce strip of the required thickness.
The furnace may be suitably heated either by a multi-zone gas- or oil-fired burner system, or alternatively by means of electric resistance heating elements~
Provision may optionally be made for induction heating the partially-reduced slab, preferably at least ~ -3-~245~1 at -the outle-t end of the thermal shield.
- Preferably an inert or non-oxidizing atmosphere is maintained within the thermal shield -to prevent secondary scale formation.
Preferably the temperature of the partially-reduced s~ab leaving the thermal shield is adjusted to a precise figure from 1000 to 1100C. This is to provide a temperature of the strip leaving the last finishing stand of from 850 to 900C.
The finishing mill train of the rolling mill preferably comprises a plurali-ty of closely-spaced rolling mill stands.
(suitably from 4 to 6).
Pre~erably the finishing train is operated at constant entry speed by virtue of the fact that the slab temperature is controlled independently by t~e thermal shield.
One stand of the finishing mill train (described as the reference stand) is driven at constant speed, preferably by an alternating current synchronous motor.
Preferably at least one stand of the finishing mill train is operated with a pre-determined Fixed reduction irrespective of the finished gauge of the strip being rolled.
Thus, because the strip leaves the thermal shield at a substan-tially constant temperature along its whole length, it is possible to operate at least one stand of the finishing mill train, preferably the first stand, at a relatively large constant reduction. This would not be possible if the temperature of the strip were allowed to drop siynlficantly below that at which it leaves the roughing mill, or if the temperature o~ the strip varied significantly from end to end. This results in a more uniformed product than has been possible hitherto.
In another aspect the invention provides a method of hot rolling steel slab into strip comprising partially reducing the slab in a roughing mill, passing the partially reduced slab ~2~ 5 into a thermal furnace as aforesaid and maintaining the temper-ature of the slab within the furnace at between lOOOdegrees C
and 1100 degrees C and passing the slab to a finishing mill train at a constant entry speed.
The invention will ~e further described, by way of example only, with reference to the accompanying drawing, which is a schematic view of a rolling mill according to the invention.
The dimens'ions, temperatures and speed given in the following description are by way of example only.
Steel slabs, typically of 200 mm thickness, 1 to 1.5 metres width and about 10 metres length are initially heated to about 1200C in a slab-heating furnace 1 of known design.
They are then passed through a roughi'ng mill 2which comprises a de-scaling unit 3 and reversing rougher 4 of conventional de-sign. The slab thi'ckness is reduced to about 36 mm by means of five passes through the reversing rougher 4. The slab then enters a gas-fired tunnel furnace 5 which constitutes a thermal shield, with a temperature ranging from 1075C at the front end of the'slab to 1040C at the rear end. In the absence o:E this thermal shield the slab temperature would fall at a rate of about 2C per second due to thermal radiation. The inner surface of the thermal shleld is ma'inta'in'ed at about 1100C.
The exit temperature of the slab as it leaves the tunnel fur-nace 5 prior to entering ~Z4~
a ~inishing train 6 is unifor~ly within the range 1075C to 1080C over its whDle length. The slab then enters the finishing train comprising si~ :
consecutive rolling mill stands 6a, 6b~ 6c, 6d, 6e and 6f, the fi.rst of which operates at constant speed and with a fixed reduction ratio. In the first sta~d 6a the thickness of the slab is reduced from ~6 mm to about 18 mm a~d this is ~urther reduced duri~g passa6e throu~h the other five stands to a minimum value of about 2 mm. ~he linear speed of the slab entering the finishing train 6 is about 0.4 ~etres per second and leaving the finishing train is about 8 metres/second~
~he strip leaving the fi~ishing train is cooled by water sprays in the ncrmal way as it passes alon~ a run-out table in order to reach the downcoiler at the correct temperature for coiling. Because o~
the relatively slow speed of the finishing train, ho~ever, the run-out table length is signi~icantly shorter than would be necessary in the case of a conventional strip mill.
'
~ here is a technological problem in desi~ning a wide hot strip mill which is capable of economic operation at medium tonnage rates oX less than about -one million tons per annum.
In its pre~ent form th~ conventio~al continuous hot strip mill requires the use of 5 or 6 roughing stands followed by a 6 or 7-stand finishing train to achieve the o~erall reductio~ in thickness from a slab, usuall~ in the range of 200 to 250 mm thickness, down .to hot-rolled coil of gauge 2 mm to ~ mm, A mil~ of this type is characterised by high capital cost and a hi~h intrinsic rolling capacity. An ~nnual tonnage output of about 3 million tonnes of hot rolled coil, for example, would be typlcal for a modern rully conti~uous mill of about 1O5 metre wid~h. An alternative mill configuration is available in the form of the semi-oontinuous mill, comprising a reversing roughing mill (usually maki~lg 5 pa~ses) followed by a . continuous multi-stand finishing trai~O m e semi-continuous mill is of shorter len~th and lower capital ..l.
co~t than the fully continuous type ~ut i.t is ~-till a high tonnage-capacity unit. '~he requirement of a high coil waight for the finished product tends to increase the overall length of the miIl and necessitates the use _ 1 _ ., ' ' ~
' s~
of higher rolllng speeds to avoid excessive temperature loss of the steel in its passa~e through -the mill. The temperature of the steèl at the las-t finishing stand, and the problem of tail-end temperature loss, are among the most critical factors determining the operating speed of the mill.
It is an object of the present invention to provide a strip mill of more compact length tnan has hitherto been available and which is capable of rolling at lower speecls than are conven-tionally used at present, and to allow economic production of wide (wider than about 2/3 metre) hot-rolled coil at a rate of some half a million to one million tons per annum.
The underlying concept upon which this invention is based is the introduction of an intermediate in-line thermal shield between the roughing mill and the finishing -train of a hot strip mill. It will be understood that by a thermal shield is meant either an arrangement by which heat loss from the partially reduced slab is prevented, e.g. an insulated tunnel, or an arrangement fQr re-heating the partially-reduced slab, e.g.
a furnace. I'his thermal shield serves the purpose of preventing further heat loss from the slab after completion of rolling through the roughing mill and during the time when the slab is being fed into the finishing train. This enables lower rolling speeds ~ -2-and lower driving power to be employed in the finishing train.
It also enables the temperature of the steel to be controlled accurately a-t en~ry to the finishing train and a substantially uniform temperature to be maintained along the length of the strip at each finishing stand A Eurther advantage of this means of temperature control is that it enables a constant entry speed to be maintained at the finishing train.
Thus in one aspect the present invention provides a continuous or semi-continuous strip-mill for the hot rolling of steel sla~ into strip, comprising: a. a roughing mill for partial reduction of the steel slab, b. an in-line roller hearth tunnel furnace with heated walls into which the partially reduced slab is passed and in which it remains in a flat and uncoiled form, and c. a multi-stand finishing mill-train adapted to reduce the partially reduced slab to produce strip of the required thickness.
The furnace may be suitably heated either by a multi-zone gas- or oil-fired burner system, or alternatively by means of electric resistance heating elements~
Provision may optionally be made for induction heating the partially-reduced slab, preferably at least ~ -3-~245~1 at -the outle-t end of the thermal shield.
- Preferably an inert or non-oxidizing atmosphere is maintained within the thermal shield -to prevent secondary scale formation.
Preferably the temperature of the partially-reduced s~ab leaving the thermal shield is adjusted to a precise figure from 1000 to 1100C. This is to provide a temperature of the strip leaving the last finishing stand of from 850 to 900C.
The finishing mill train of the rolling mill preferably comprises a plurali-ty of closely-spaced rolling mill stands.
(suitably from 4 to 6).
Pre~erably the finishing train is operated at constant entry speed by virtue of the fact that the slab temperature is controlled independently by t~e thermal shield.
One stand of the finishing mill train (described as the reference stand) is driven at constant speed, preferably by an alternating current synchronous motor.
Preferably at least one stand of the finishing mill train is operated with a pre-determined Fixed reduction irrespective of the finished gauge of the strip being rolled.
Thus, because the strip leaves the thermal shield at a substan-tially constant temperature along its whole length, it is possible to operate at least one stand of the finishing mill train, preferably the first stand, at a relatively large constant reduction. This would not be possible if the temperature of the strip were allowed to drop siynlficantly below that at which it leaves the roughing mill, or if the temperature o~ the strip varied significantly from end to end. This results in a more uniformed product than has been possible hitherto.
In another aspect the invention provides a method of hot rolling steel slab into strip comprising partially reducing the slab in a roughing mill, passing the partially reduced slab ~2~ 5 into a thermal furnace as aforesaid and maintaining the temper-ature of the slab within the furnace at between lOOOdegrees C
and 1100 degrees C and passing the slab to a finishing mill train at a constant entry speed.
The invention will ~e further described, by way of example only, with reference to the accompanying drawing, which is a schematic view of a rolling mill according to the invention.
The dimens'ions, temperatures and speed given in the following description are by way of example only.
Steel slabs, typically of 200 mm thickness, 1 to 1.5 metres width and about 10 metres length are initially heated to about 1200C in a slab-heating furnace 1 of known design.
They are then passed through a roughi'ng mill 2which comprises a de-scaling unit 3 and reversing rougher 4 of conventional de-sign. The slab thi'ckness is reduced to about 36 mm by means of five passes through the reversing rougher 4. The slab then enters a gas-fired tunnel furnace 5 which constitutes a thermal shield, with a temperature ranging from 1075C at the front end of the'slab to 1040C at the rear end. In the absence o:E this thermal shield the slab temperature would fall at a rate of about 2C per second due to thermal radiation. The inner surface of the thermal shleld is ma'inta'in'ed at about 1100C.
The exit temperature of the slab as it leaves the tunnel fur-nace 5 prior to entering ~Z4~
a ~inishing train 6 is unifor~ly within the range 1075C to 1080C over its whDle length. The slab then enters the finishing train comprising si~ :
consecutive rolling mill stands 6a, 6b~ 6c, 6d, 6e and 6f, the fi.rst of which operates at constant speed and with a fixed reduction ratio. In the first sta~d 6a the thickness of the slab is reduced from ~6 mm to about 18 mm a~d this is ~urther reduced duri~g passa6e throu~h the other five stands to a minimum value of about 2 mm. ~he linear speed of the slab entering the finishing train 6 is about 0.4 ~etres per second and leaving the finishing train is about 8 metres/second~
~he strip leaving the fi~ishing train is cooled by water sprays in the ncrmal way as it passes alon~ a run-out table in order to reach the downcoiler at the correct temperature for coiling. Because o~
the relatively slow speed of the finishing train, ho~ever, the run-out table length is signi~icantly shorter than would be necessary in the case of a conventional strip mill.
'
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a continuous or semi-continuous strip mill for hot rolling of steel slab into strip comprising a roughing mill for partial reduction of the steel slab and a multi-strand fini-shing mill train adapted to reduce the partially reduced slab to produce strip of the required thickness, the improvement in which an in-line roller hearth tunnel furnace with heated walls is located on the mill axis between the roughing mill and the fini-shing mill train, adapted to receive the partially reduced slab directly from the roughing mill and pass it directly to the fini-shing mill train, whereby the partially reduced slab on pasaage in the finishing mill train leaves the furnace at substantially constant temperature along its whole length, which temperature is not significantly less than that at which the partially reduced slab leaves the roughing mill, said strip mill being a medium tonnage strip mill.
2. A strip-mill as claimed in claim 1 in which the tunnel furnace walls are heated by electrical resistance heating.
3. A strip-mill as claimed in claim 1 in which the tunnel furnace walls are heated by burning gas or oil.
4. A strip-mill as claimed in claim 1, 2 or 3, in which an inert or non-oxidising atmosphere is maintained within the tunnel furnace.
5. A strip-mill as claimed in claim 1, 2 or 3, in which one stand of the finishing mill train is driven at a constant speed, and with a predetermined fixed reduction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA308,793A CA1124555A (en) | 1978-08-04 | 1978-08-04 | Rolling of steel strip |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA308,793A CA1124555A (en) | 1978-08-04 | 1978-08-04 | Rolling of steel strip |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1124555A true CA1124555A (en) | 1982-06-01 |
Family
ID=4112067
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA308,793A Expired CA1124555A (en) | 1978-08-04 | 1978-08-04 | Rolling of steel strip |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1124555A (en) |
-
1978
- 1978-08-04 CA CA308,793A patent/CA1124555A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |