Method to determine the crater end location of a cast metal product

Abstract

A method to determine the crater end location of a cast metal product during its casting, the crater end location being the location at which the cast metal product becomes fully solidified. A continuous casting method and a continuous casting machine are also provided.

Claims

1. A method to determine a crater end location of a cast metal product during casting, the crater end location being the location at which the cast metal product becomes fully solidified, the method comprising the steps of: casting molten metal in a continuous casting machine including a plurality of upper and lower segment frames bearing rolls, the upper and lower segment frames being located respectively above and below the cast metal product; estimating a location P.sub.est within the continuous casting machine where the metal product becomes fully solidified; at least measuring a bending of the nearest upper segment frame of the estimated location P.sub.es, wherein the bending is measured at least on two ends of the nearest upper segment frame; and calculating a location P.sub.mes of the crater end based on the measured bending.

2. The method as recited in claim 1 wherein the estimating of the location P.sub.est is performed with a model.

3. A method of casting a metal product at a casting speed S, the method comprising monitoring the casting speed S according to the crater end location as determined by the method as recited in claim 1.

4. The method of casting as recited in claim 3 wherein the casting speed S is monitored so as to minimize a distance between the crater end location and an output end of the continuous casting machine.

5. The method of casting as recited in claim 3 further comprising applying a dynamic soft reduction to the metal product and the casting speed is monitored so that the dynamic soft reduction is applied to the metal product before the crater end position is reached.

6. The method as recited in claim 1, wherein the bending is measured at a plurality of locations, and wherein the location P.sub.mes calculated as between two locations of the plurality of locations having a biggest bending variation in respective signals.

7. The method recited in claim 1, wherein the bending is measured at locations on the nearest segment frame which are between vertical support beams.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the invention will appear at the reading of the following description.

(2) In order to illustrate the invention, trials have been performed and will be described by way of non-limitative examples, notably in reference to figures which represent:

(3) FIG. 1 illustrates a casting machine, or caster

(4) FIG. 2 illustrates a segment of a caster

(5) FIG. 3 is a set of three curves representing the casting speed and the bending measurement performed by two bending measurement means

(6) FIG. 4 illustrates results which may be obtained by using a method according to the invention

DETAILED DESCRIPTION

(7) FIG. 2 describes a segment 5 of a continuous caster to cast a metal product 1. The metal product 1 goes between an upper 2A and a lower 2B segment frame, each segment frame 2A, 2B bearing rolls 3. Each roll 3 is connected to the segment frames 2A, 2B through a roll shock 4 and a bearing 6 which makes the junction between the roll shock 4 and the roll 3. Upper and lower segment frames 2A, 2B are connected to each other by beams 7. In a method according to the invention for each new product cast, for example for each new steel grade and/or each time the casting speed is changed, the location P.sub.est of the crater end, i.e. the point at which the cast product becomes fully solidified, is estimated. This estimation may be done for example by using Abaqus, statistic or physical models. The bending of the nearest upper segment frame 2A of this estimated location is then measured. This measurement may be done by a strain gauge, an extensometer or any other appropriate bending measurement means 8. The bending measurement means 8 may be placed on the external surface of the upper segment frame 2A as illustrated in FIG. 2. It may be glued or welded to the segment frame. In a preferred embodiment the bending measurement is performed at the entry and the exit of the segment frame 2A, the entry being the side where the strand first goes between the rolls and the exit being the opposite side where the strand leaves the segment. When the estimated location of the crater end is between two segments, the bending measurement is performed on both segments. When the range of cast product or the casting speed variation is broad, measurement means are installed on several upper segment frames so as to be able to measure bending in all configurations without necessity to add or displace measurement means for each new casting campaign. The principle of this measurement is based on the fact that when the product state changes, from a mushy to a solid state, the load applied by the metal product on the segment's rolls change due to the reduction or the increase of the ferrostatic pressure. This explains why prior art methods were focused on measurements at the roll level, but the inventors discovered that this load variation is transmitted to the segment frame and in sufficient proportion to be measured by an appropriate sensor. As a matter of illustration, a segment frame is made of a volume of 1 m.sup.3 of pig iron.

(8) Once the bending is measured it is possible to calculate the location P.sub.mes of the crater end based on said bending. When only one bending measurement is performed the measured signal can be compared with a predefined value of bending in a mushy state, if the measured bending is below said value it means that the load applied to the segment frame is lower than expected in a mushy state and so that the metal product is already solidified. The crater end is thus located before the bending measurement means location. If the measured bending is above or equal to the predefined value it means the crater end is located after said measurement mean. Depending on the difference between the bending measured value and the predefined value it is possible to calculate the distance between the position of the sensor and the crater end location.

(9) When several bending measurement means are used it is possible to compare the bending measured by each one, the crater end being located between the two positions of the measurement sensors having the biggest bending variations in their respective signals. This is illustrated in FIG. 3. In this example, the signals of two bending measurement means which are extensometers are represented in function of the casting speed. These two extensometers were installed on an upper segment frame, respectively at the entry and at the exit of said segment. Looking at the signal in the dotted frame, for the given casting speed, the extensometer 1 sees a mushy product, bending is high, while the extensometer 2 sees a solid product, bending is low. The crater end location is consequently between the positions of those two bending measurement means.

(10) By multiplying the casting speed variations and calculation of the crater end location with a method and processor 100 (shown schematically in FIG. 3 receiving signals from the two extensometers 1, 2) according to the invention it is possible to accurately determine for a given grade and a given thickness of the solidified slab what is the maximum casting speed allowed to have the crater end and so the full solidification of slab within the caster. This is illustrated in FIG. 4.

(11) FIG. 4 represents the crater end location determined with a method according to the invention in function of the casting speed. In practice, the method according to the invention was performed several times for a given casting speed and then said casting speed was increased, crater end position determined, and so on until the crater end location almost reaches the output end of the casting machine so as to avoid any damage. The dotted line is the maximum length of the caster, i.e. the output end 15, and length zero being the tundish exit. As can be seen on the graph, for this given metal product the maximum speed allowable to have the crater end within the caster is of 1.60 m/s. Knowing this maximum speed allows to increase the productivity of the caster.

(12) Using a method according to the invention it is possible to accurately and robustly detect the crater end location. Indeed, the measurement being performed on the upper segment frame, the measurement means are positioned on said frames and may perform the measurement as long as they work and there is no need to wait for a caster stop and part replacement to replace a defective sensor.