GB2098114A

GB2098114A - Adjusting the mould dimension during continuous casting

Info

Publication number: GB2098114A
Application number: GB8213341A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1981-05-08
Filing date: 1982-05-07
Publication date: 1982-11-17
Also published as: FR2505215A1; FR2505215B1; JPS57187144A; DE3118986C1; GB2098114B; BE893092A

Abstract

The risk of billet quality deterioration is reduced in a method in which at least two sides of the mould are adjusted inwardly during casting from a position at which the largest dimensions of the mould are defined. The speed of billet withdrawal is maintained at at least that which applies for the format with the largest cross-section, and the inclination of the adjustable sides is proportioned to the slab width such that the percentage value of the taper remains unchanged. Any adjustment is carried out at a constant speed.

Description

SPECIFICATION The adjustment of mould walls during casting The invention relates to the adjustment of the mould walls of continuous casting moulds during the casting process, to produce billets of differing crosssectional dimensions. The invention has particular application to the casting of slab shapes.

It is known that the productivity of a continuous casting installation can be increased, and that the operational costs can be reduced, by adopting the sequence casting technique. In this technique, several smelts come to casting without the casting process being interrupted.

With flat products, the charge regulation requires frequent alterations in dimensions of the billet slabs for application on belt conveyors. Even with a medium-term charge planning and regulation, a restriction of the charge lots for a specific dimension is to be expected. With high weights of charge, therefore, an alteration of the billet shape during the casting of a smelt may become necessary.

In particular, however, to increase the sequence sizes, the billet width must be able to be altered during the casting.

Adjustment of the billet width is possible according to various methods; for example by displacement of the narrow sides of the mould, both inwards (reduction of the billet width) and outwards (increase of the billet width). At the same time the speed of withdrawal of the billet is distinctly reduced because of the danger of rupture. In some cases, even a brief stoppage of the billet i > necessary.

Along with production losses through slower casting or stoppage of billet, such irregularities in the casting cycle can entail appreciable losses in quality of the billets produced. The internal quality is impaired through the increasing billet shell bulging when the billet is at a starldstill, and through rising extraction forces on restdrting; and the surface quality is impaired through overcooling in contact with rolls, or the deteriorated distribution of spray water with the necessary reduction in quantity. In addition, the backin rolls can distort, when the billet is at a standstill, under the thermal load.

The invention seeks to mitigate the disadvantages described above, without suffering losses in production and quality during the adjustment of the mould.

To this end, the invention provides a method of altering the billet dimension by adjustment of at least two side walls of a mould during casting, the side walls initially defining the largest dimensions of the mould, wherein the speed of billet withdrawal is maintained at at least that which applies for the format with the largest cross-section; wherein the inclination of said at least two sides is proportioned to the slab width such that the percentage value of the taper remains unchanged; and wherein the adjustment of the side wall of the mould is carried out continuously, and at a constant speed. Said constant speed is typically in the range 5 to 50 mm/min.

The level of melt in the bath is preferably maintained substantially constant during the casting process. Further, the speed of billet withdrawal is adapted to the volume flow of the smelt.

Investigations have shown that the heat which is carried away, and hence the billet shell formation can show marked differences on the adjustment of the narrow sides of a casting mould. The drawing shows the variation with time of the heat-flux density during an adjustment inwards and outwards.

It can be seen that on adjustment outwards, the heat which is carried away distinctly decreases, and in fact beyond the value which is produced from the alteration in pouring rate alone. The contact conditions between the mould wall and billet shell are worse than in the normal casting cycle. The shell growth is slow, the shell temperature rises and the risk of rupture increases, as does the likelihood that discontinuance of casting will become necessary.

In contrast to the above, the heat-flux density and hence the shell growth on adjustment inwards remains substantialy unchanged. The values obtained depend solely on the rate of pouring and other casting conditions, such as lubrication, for example. With this method of operation, in contrast to methods and applications to date, casting can take place at unchanged rate of pouring during the adjustment. Because the quantity and distribution of spray water, and also the melting-on speed of the casting powder, bulging and roll load may thus remain the same, the quality need not be impaired.

For example, let a slab 200 mm thick and 1800 mm wide be cast. The rate of pouring is 1.2 m/min. Let the next required dimension be 1700 mm. Both narrow sides are displaced inwards at a speed of 20 mm/min. With the rate of pouring remaining the same, the duration of adjustment amounts to 2.5 min, and the region of adjustment 3.0 m billet length.

The transition region can be made full use of for further processing. As a consequence, the cleaning epxenditure is reduced and output is improved.

1. A method of altering the billet dimension by adjustment of at least two side walls of a mould during casting, the side walls initially defining the largest dimensions of the mould, wherein the speed of billet withdrawal is maintained at at least that which applies for the format with the largest crosssection; wherein the inclination of said at least two sides is proportioned to the slab width such that the percentage value of the taper remains unchanged; and wherein the adjustment of the side wall of the mould is carried out continuously, and at a constant speed.

2. A method according to Claim 1 wherein said constant speed is in the range 5 to 50 mm/min.

3. A method according to Claim 1 or Claim 2 wherein the charge lots are integrated into the casting sequence of smelts such that billets with large widths are cast first, and subsequently billets with gradually decreasing widths are cast.

4. A method according to any preceding Claim wherein the input of molten metal is controlled to maintain constant the height of the bath level in the mould.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION The adjustment of mould walls during casting The invention relates to the adjustment of the mould walls of continuous casting moulds during the casting process, to produce billets of differing crosssectional dimensions. The invention has particular application to the casting of slab shapes. It is known that the productivity of a continuous casting installation can be increased, and that the operational costs can be reduced, by adopting the sequence casting technique. In this technique, several smelts come to casting without the casting process being interrupted. With flat products, the charge regulation requires frequent alterations in dimensions of the billet slabs for application on belt conveyors. Even with a medium-term charge planning and regulation, a restriction of the charge lots for a specific dimension is to be expected. With high weights of charge, therefore, an alteration of the billet shape during the casting of a smelt may become necessary. In particular, however, to increase the sequence sizes, the billet width must be able to be altered during the casting. Adjustment of the billet width is possible according to various methods; for example by displacement of the narrow sides of the mould, both inwards (reduction of the billet width) and outwards (increase of the billet width). At the same time the speed of withdrawal of the billet is distinctly reduced because of the danger of rupture. In some cases, even a brief stoppage of the billet i > necessary. Along with production losses through slower casting or stoppage of billet, such irregularities in the casting cycle can entail appreciable losses in quality of the billets produced. The internal quality is impaired through the increasing billet shell bulging when the billet is at a starldstill, and through rising extraction forces on restdrting; and the surface quality is impaired through overcooling in contact with rolls, or the deteriorated distribution of spray water with the necessary reduction in quantity. In addition, the backin rolls can distort, when the billet is at a standstill, under the thermal load. The invention seeks to mitigate the disadvantages described above, without suffering losses in production and quality during the adjustment of the mould. To this end, the invention provides a method of altering the billet dimension by adjustment of at least two side walls of a mould during casting, the side walls initially defining the largest dimensions of the mould, wherein the speed of billet withdrawal is maintained at at least that which applies for the format with the largest cross-section; wherein the inclination of said at least two sides is proportioned to the slab width such that the percentage value of the taper remains unchanged; and wherein the adjustment of the side wall of the mould is carried out continuously, and at a constant speed. Said constant speed is typically in the range 5 to 50 mm/min. The level of melt in the bath is preferably maintained substantially constant during the casting process. Further, the speed of billet withdrawal is adapted to the volume flow of the smelt. Investigations have shown that the heat which is carried away, and hence the billet shell formation can show marked differences on the adjustment of the narrow sides of a casting mould. The drawing shows the variation with time of the heat-flux density during an adjustment inwards and outwards. It can be seen that on adjustment outwards, the heat which is carried away distinctly decreases, and in fact beyond the value which is produced from the alteration in pouring rate alone. The contact conditions between the mould wall and billet shell are worse than in the normal casting cycle. The shell growth is slow, the shell temperature rises and the risk of rupture increases, as does the likelihood that discontinuance of casting will become necessary. In contrast to the above, the heat-flux density and hence the shell growth on adjustment inwards remains substantialy unchanged. The values obtained depend solely on the rate of pouring and other casting conditions, such as lubrication, for example. With this method of operation, in contrast to methods and applications to date, casting can take place at unchanged rate of pouring during the adjustment. Because the quantity and distribution of spray water, and also the melting-on speed of the casting powder, bulging and roll load may thus remain the same, the quality need not be impaired. For example, let a slab 200 mm thick and 1800 mm wide be cast. The rate of pouring is 1.2 m/min. Let the next required dimension be 1700 mm. Both narrow sides are displaced inwards at a speed of 20 mm/min. With the rate of pouring remaining the same, the duration of adjustment amounts to 2.5 min, and the region of adjustment 3.0 m billet length. The transition region can be made full use of for further processing. As a consequence, the cleaning epxenditure is reduced and output is improved. CLAIMS

5. A method according to Claim 4 wherein the speed of billet withdrawal is adapted to the volume flow of the smelt.

6. A method of altering billet dimensions by adjustment of at least two side walls of a mould during casting, according to Claim 1 and substantially as herein described.

7. Application of the method according to Claims 1 and 3 to sequence casting of smelts.