GB2175228A

GB2175228A - Hot rolling slabs

Info

Publication number: GB2175228A
Application number: GB08611729A
Authority: GB
Inventors: Ewan Christian Hewitt; David Robert Howard; Thomas Hope; John Clifford Dobson; Kenneth Thomas Lawson
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1985-05-14
Filing date: 1986-05-14
Publication date: 1986-11-26
Also published as: GB2175228B; GB2175229A; GB2175229B; GB8611729D0; GB8512225D0; GB8611730D0

Abstract

In a method of increasing the width of a metal slab, the slab 9 is hot rolled between a pair of rolls 1,3 having enlarged portions 5,7 which produce a longitudinally extending groove in each face of the slab, the rolls are then axially shifted and the slab re-rolled so as to widen each groove and, thereafter, the slab is hot rolled to reduce it to substantially uniform thickness. <IMAGE>

Description

SPECIFICATION The rolling of metal workpieces The invention relates to the hot rol li ng of metal work- pieces, particularly metal slabs.

It has recently become advantageous to continuously cast metal slabs in a continuous casting machine. As the width of the slab is dependent upon thewidthofthe mould used inthecontinuouscasting machine, itis usual to limit the number of predetermined widths which are produced in the machine, otherwise a large number of moulds are required and there is considerable down-time required for chang- ing moulds.

In addition tothe down-time,there is a loss in yield and output involved in changing moulds. All interme diate widths have then to be obtained by rolling to size in the hot strip mill and this is normally done by rolling on the edges ofthe slab to reduce its width bya vertical edger mill. However, such a mill is an expensive mill and the amount of width reduction it can achieve is very limited.

It is known that, if a pairofgrooves are rolled in the opposite faces of a slab, the width of the slab is increased and, if the slab is then rolled to uniform thickness between parallel cylindrical rolls,theslabis spread further.

Aspread oftypically 150 mm in a metal slab 1000 mm wide can be achieved by incorporating a single groove in each of its opposite faces. To maximisethe amount of spread, it is necessary to carefully select the width of the grooves. It has been found that, for a steel slab, the width of the groove formed in each of its opposite faces should be about 55% of the width of the slab before it is spread. Satisfactory amounts of spread, however, can be achieved with the ratio ofthe groovetothe unspread width ofthe slab, ranging from 45%to75% and useful amounts of spread can be achieved even when the ratio is extended beyond these limits.

It will be appreciated, therefore, that, in order to be able to obtain spread slabs of a wide range of widths, it is necessary to be able to increase the width of the grooves.

According to the present invention, a method of increasing the width of a metal slab comprises the steps of passing the slabwhile hot between a pair of rolls which act upon opposite faces of the slab to produce a longitudinally extending groove in each face; axially shifting the rolls and passing the slab again between the rolls to widen each groove; and thereafter hot rolling the slab to reduce the slabto substantially uniform thickness.

By providing for axial displacement ofthe rolls, the grooves can be widened and only one roll set is re quired to produce grooves ofvarious widths. lfthe rolls were not displaceable axially, itwould be neces- saryto provide at least two roll stands with different sized rolls in order to widen the grooves.

A preferred embodiment of the invention resides in passing the hot slab between a pair of rolls to produce a longitudinally extending groove in each face, the two grooves being non-aligned with each other but conveniently at equal distances on opposite sides of the slab centre line, and then axially shifting the rolls in opposite directions so that, afterthe second pass, the grooves are widened and are aligned with each other conveniently symmetrical about the centre line of the slab. To presenttransverse distortion, an attempt is made to keep all parts of the slab across its width in contact with the rolls in order to supportthe slab as much as possible across its full width.

In orderthatthe invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawing which shows schematically the profile of the slab and the rolls in accordancewith oneembodimentof the invention.

A pairof rolling mill rolls 1,3 each comprise a cylindrical portion having an enlarged portion 5, 7, respectively, extending along part of its axial length.

The enlarged portion is, say, 450 mm in axial length and has tapered lateral walls8.

To provide a first pair of longitudinally extending grooves in opposite faces of a slab 9, the two rolls are arranged with the enlarged portions offset on opposite sides ofthe mill centre line 11. The two rolls are spaced apart such that, as the hot slab is passed between them, the rolls and slab touch along the entire width of the slab and the offset grooves 13 (ABCD) are formed. The rolls are then displaced axially with respect to the mill housing in which they are supported, but in oppositedirections,sothattheen- larged portions are still offset symmetrically about the centre line but they have each moved across the centre iineto the opposite side from their original position.The first and second positions of each of the enlarged portions overlap to some extent and the hot slab is passed for a second time between the rolls, thus widening the grooves to produce aligned grooves 15 (ABGF) symmetrical about the centre line.

Each pass between the rolls brings about spreading ofthe slab.

The slab is then rolled between a pair of cylindrical rolls which reduce the slab to substantially uniform thickness and further spreading is achieved.

The edges of the slab of reduced thickness and increased width can be 'squared up' and the slab width modified slightly, if necessary, by use of vertical edger rolls.

Ingoing guidesfortheworkpiece must be positioned fairly close to the edges ofthe slab and guiding must continue close up to the mill rolls. Outgoing guides need not be so close to the mill rolls, but they must be kept reasonably close and parallel to the sides ofthe slab over a length of about halfor more of the slab length.

An alternative method for guiding the slab utilises pinch rolls before and/or after the spreading mill.

Conventional side guides would first of all align the slab on the pass-line. The slab would then be gripped by a heavy pinch roll and fed forward into the mill.

Another pinch roll on the exit side of the mill would also grip the slab and hold it in alignmentwhilstthe tail end is being rolled.

1. A method of increasing the width of a metal

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION The rolling of metal workpieces The invention relates to the hot rol li ng of metal work- pieces, particularly metal slabs. It has recently become advantageous to continuously cast metal slabs in a continuous casting machine. As the width of the slab is dependent upon thewidthofthe mould used inthecontinuouscasting machine, itis usual to limit the number of predetermined widths which are produced in the machine, otherwise a large number of moulds are required and there is considerable down-time required for chang- ing moulds. In addition tothe down-time,there is a loss in yield and output involved in changing moulds. All interme diate widths have then to be obtained by rolling to size in the hot strip mill and this is normally done by rolling on the edges ofthe slab to reduce its width bya vertical edger mill. However, such a mill is an expensive mill and the amount of width reduction it can achieve is very limited. It is known that, if a pairofgrooves are rolled in the opposite faces of a slab, the width of the slab is increased and, if the slab is then rolled to uniform thickness between parallel cylindrical rolls,theslabis spread further. Aspread oftypically 150 mm in a metal slab 1000 mm wide can be achieved by incorporating a single groove in each of its opposite faces. To maximisethe amount of spread, it is necessary to carefully select the width of the grooves. It has been found that, for a steel slab, the width of the groove formed in each of its opposite faces should be about 55% of the width of the slab before it is spread. Satisfactory amounts of spread, however, can be achieved with the ratio ofthe groovetothe unspread width ofthe slab, ranging from 45%to75% and useful amounts of spread can be achieved even when the ratio is extended beyond these limits. It will be appreciated, therefore, that, in order to be able to obtain spread slabs of a wide range of widths, it is necessary to be able to increase the width of the grooves. According to the present invention, a method of increasing the width of a metal slab comprises the steps of passing the slabwhile hot between a pair of rolls which act upon opposite faces of the slab to produce a longitudinally extending groove in each face; axially shifting the rolls and passing the slab again between the rolls to widen each groove; and thereafter hot rolling the slab to reduce the slabto substantially uniform thickness. By providing for axial displacement ofthe rolls, the grooves can be widened and only one roll set is re quired to produce grooves ofvarious widths. lfthe rolls were not displaceable axially, itwould be neces- saryto provide at least two roll stands with different sized rolls in order to widen the grooves. A preferred embodiment of the invention resides in passing the hot slab between a pair of rolls to produce a longitudinally extending groove in each face, the two grooves being non-aligned with each other but conveniently at equal distances on opposite sides of the slab centre line, and then axially shifting the rolls in opposite directions so that, afterthe second pass, the grooves are widened and are aligned with each other conveniently symmetrical about the centre line of the slab. To presenttransverse distortion, an attempt is made to keep all parts of the slab across its width in contact with the rolls in order to supportthe slab as much as possible across its full width. In orderthatthe invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawing which shows schematically the profile of the slab and the rolls in accordancewith oneembodimentof the invention. A pairof rolling mill rolls 1,3 each comprise a cylindrical portion having an enlarged portion 5, 7, respectively, extending along part of its axial length. The enlarged portion is, say, 450 mm in axial length and has tapered lateral walls8. To provide a first pair of longitudinally extending grooves in opposite faces of a slab 9, the two rolls are arranged with the enlarged portions offset on opposite sides ofthe mill centre line 11. The two rolls are spaced apart such that, as the hot slab is passed between them, the rolls and slab touch along the entire width of the slab and the offset grooves 13 (ABCD) are formed. The rolls are then displaced axially with respect to the mill housing in which they are supported, but in oppositedirections,sothattheen- larged portions are still offset symmetrically about the centre line but they have each moved across the centre iineto the opposite side from their original position.The first and second positions of each of the enlarged portions overlap to some extent and the hot slab is passed for a second time between the rolls, thus widening the grooves to produce aligned grooves 15 (ABGF) symmetrical about the centre line. Each pass between the rolls brings about spreading ofthe slab. The slab is then rolled between a pair of cylindrical rolls which reduce the slab to substantially uniform thickness and further spreading is achieved. The edges of the slab of reduced thickness and increased width can be 'squared up' and the slab width modified slightly, if necessary, by use of vertical edger rolls. Ingoing guidesfortheworkpiece must be positioned fairly close to the edges ofthe slab and guiding must continue close up to the mill rolls. Outgoing guides need not be so close to the mill rolls, but they must be kept reasonably close and parallel to the sides ofthe slab over a length of about halfor more of the slab length. An alternative method for guiding the slab utilises pinch rolls before and/or after the spreading mill. Conventional side guides would first of all align the slab on the pass-line. The slab would then be gripped by a heavy pinch roll and fed forward into the mill. Another pinch roll on the exit side of the mill would also grip the slab and hold it in alignmentwhilstthe tail end is being rolled. CLAIMS

1. A method of increasing the width of a metal slab comprising the steps of passing the slab while hot between a pair of rolls which act upon opposite facesoftheslabto producea longitudinallyextend- ing groove in each face; axially shifting the rolls and passing the slab again between the rolls to widen each groove; and thereafter hot rolling the slab to reduce the slab to substantially uniform thickness.

2. A method of increasing the width of a metal slab as claimed in claim 1, in which the grooves formed during the first pass are non-aligned with each other, the rolls are shifted in opposite directions so that, after the second pass, the widened g rooves are aligned with each other.

3. A method of increasing the width of a metal slab as claimed in claim 2, in which the grooves formed during the first pass are at equal distances from, and on opposite sides of, the slab centre line and, afterthe second pass, the widened grooves are symmetrical aboutthe centre line ofthe slab.

4. A method of increasing the width of a metal slab substantially as hereinbefore described with reference to the accompanying drawing.