GB2050888A

GB2050888A - Method of monitoring the continuous casting of metals

Info

Publication number: GB2050888A
Application number: GB8016443A
Authority: GB
Original assignee: Centre de Recherches Metallurgiques CRM ASBL
Current assignee: Centre de Recherches Metallurgiques CRM ASBL
Priority date: 1979-05-17
Filing date: 1980-05-19
Publication date: 1981-01-14
Also published as: BE876340A; JPS55156657A; FR2456580A1; DE3018820A1; LU82456A1

Abstract

A method of monitoring the continuous casting of metals, in particular of steel, in which, during a continuous metal casting operation, a secondary cooling operation is carried out on a cast strand and this secondary cooling is regulated so as to maintain a predetermined thermal profile along the zone being subjected to the cooling, wherein the surface temperature of the strand at the straightening point is calculated on the basis of the thermal profile selected and the dwell time of the metal in the ingot mould, if the casting speed has to be modified for any reason the probable new surface temperature of the strand at the straightening point is ascertained from a preliminary calculation, this latter temperature is compared with the predetermined values and a new thermal profile providing the temperature required at the straightening point is determined by calculation, and the secondary cooling is adjusted to obtain the thermal profile modified in this way.

Description

SPECIFICATION Method of monitoring the continuous casting of metals The present invention relates to a method of monitoring the continuous casting of metals, in particular of steel.

The principle of monitoring the continuous casting of metals, in particular of steel, comprises, after the determination of a casting speed to be observed, regulating water flow rates to be used in each of secondary cooling zones of a strand, in such a way as to follow a predetermined thermal profile for the cooling of the strand, when the strand is displaced at a chosen casting speed.

Such a regulation of the water flow rate in the various cooling zones is very difficult to carry out, in particular when variations in the strand extraction speed take place during casting. Such variations are inevitable and intrinsic both to the nature of the method itself and to various customary operating stoppages.

These speed variations are due, for example, to the stages of starting or stopping of casting, the casting of several ladles in a continuous sequence, and replacements of ladles or baskets, and to operational malfunctions such as, for example, nozzle blockages. There may therefore be quite large speed variations due to the above-mentioned causes.

In order to take into account these speed variations it is necessary to modify, in a suitable way, the flow rates of the water provided at the various secondary cooling zones, in such a way that the predetermined thermal profile is still observed.

Various methods have already been proposed for this purpose, but, in the majority of cases, the point at which the strand is straightened is not sprayed by cooling water and consequently the surface temperature of the strand is at variance with the casting speed at this point.

This is a considerable drawback and it has been noted that various external and internal defects could occur when the strand was subjected to certain deformations such as, for example, bending or straightening in an unsuitable temperature range.

It is an object of the present invention to provide a method by means of which it is possible to remedy these drawbacks.

The present invention provides a method of monitoring the continuous casting of a metal, in which, during a continuous metal casting operation, a secondary cooling operation is carried out on a cast strand, and the secondary cooling is regulated so as to maintain a predetermined thermal profile along the zone being subjected to the cooling, wherein: the surface temperature of the strand at the straightening point is calculated, on the basis of the thermal profile selected and the dwell time of the metal in the ingot mould; if the casting speed has to be modified for any reason, the probable new surface temperature of the strand at the straightening point is ascertained from a preliminary calculation, all other casting parameters remaining unchanged; the said latter temperature is compared with the predetermined values and new thermal profile providing the temperature required at the straightening point is determined by calculation; and the secondary cooling is adjusted to obtain the thus modified thermal profile.

Thus the method of the present invention in which, during a continuous metal casting operation, in particular a steel casting operation, a secondary cooling operation is carried out on the cast strand, this secondary cooling being regulated so as to maintain a predetermined thermal profile along the zone being subjected to the cooling, is essentially characterized in that:: - the surface temperature of the strand at the straightening point is calculated on the basis of the selected thermal profile and the dwell time of the metal in the ingot mould, i.e. the casting speed, - if the casting speed has to be modified for any reason, the probable new surface temperature of the strand at the straightening point is ascertained from a preliminary calculation, all other casting parameters remaining unchanged, - this latter temperature is compared with the predetermined values and a new thermal profile providing the temperature required at the straightening point is determined by calculation, - the rates of flow of the secondary cooling are adjusted to obtain the thermal profile modified in this way.

In practice, the secondary cooling is firstly adjusted to obtain this new profile, and if the adjustment limits of the water flow rates are reached in doing this, it is proposed to modify the casting speed and a further calculation is carried out to determine the water flow rates to be used for the new casting conditions.

The desired theoretical temperature is in fact replaced by an acceptable range of temperatures between a maximum and a minimum predetermined value.

The invention will be further described with reference to the following illustrative Example.

Example In an operation for casting blooms having a section of 200mm x 1 500mm, carried out on a continuous casting machine of the "curve" type having a radius of 1 2m, the normal casting speed is 1 .2m/min.; the adjustment selected for the water flow rates used for the so-called secondary cooling is selected such that the bloom has a predetermined thermal profile over its length, this thermal profile being designated by C1. In the case of the casting machine in question, there are 9 spray zones indicated respectively by Z1, Z2,...Z9.

It is supposed that as a result of a malfunction it is necessary at a time T to reduce the casting speed from v, (1.2m/min.) to v2(0.8m/min.) and to maintain it at this value.

In the known case in which the secondary water flow rates are adjusted in accordance with the value C1, the results shown in Figure 1 of the accompanying drawings are obtained. This represents, as a function of time, the variations of the rates of flow carried out in two zones (Z8 and Zg) and the variation of surface temperature in the middle of the bloom at the straightening point (i.e. the point at which the bloom is provided with its rectilinear shape).

It is noted that the prolonged speed decrease causes a considerable cooling (from t1 to t2) of the bloom at the straightening point This may cause, in certain cases, the formation of surface cracks.

Figure 2 of the accompanying drawings shows how this drawback may be prevented by the method of the present invention. During the reduction in the casting speed, the value ofthe thermal profile of the bloom is modified from C1 to C2,....Cn, from temporary successive calculations. These new profiles control different water flow rates in the secondary spray zones, which enables the temperature at the straightening point to be maintained at all times within the desired range of 950 to 10000C.

Claims

1. A method of monitoring the continuous casting of a metal, in which, during a continuous metal casting operation, a secondary cooling operation is carried out on a cast strand, and the secondary cooling is regulated so asto maintain a predetermined thermal profile along the zone being sub jected to the cooling, wherein : the surface temperature of the strand at the straightening point is calculated, on the basis of the thermal profile selected and the dwell time of the metal in the ingot mould; if the casting speed has to be modified for any reason, the probable new surface temperature of the strand at the straightening point is ascertained from a preliminary calculation, all other casting parameters remaining unchanged; the said latter temperature is compared with the predetermined values and a new thermal profile providing the temperature required at the straightening point is determined by calculation; and the secondary cooling is adjusted to obtain the thus modified thermal profile.

2. A method as claimed in Claim 1, wherein the metal being cast is steel.

3. A method according to Claim 1, of monitoring the continuous casting of a metal, substantially as herein described in the foregoing Example.