METHOD OF CONTINUOUS CASTING METAL STRIP

Abstract: When casting metal strip in a twin-roll caster, start-up apparatus is used which permits the rotation of the rolls (1, 3) to commence before molten metal enters the roll bite (5). The apparatus comprises a leaderstrip (7) which is placed between the rolls (1, 3) and is held when rotation commences. The leaderstrip (7) is released after molten metal is added to the bite (5) and is driven through the roll gap leading a cast metal strip with it.

Description: METHOD OF CONTINUOUS CASTING METAL STRIP This invention relates to a method of casting metal strip in a twin-roll caster and to start-up apparatus for use with the twin-roll caster. The casting of metal strip in a twin-roll caster is known and essentially the method consists of introducing molten metal into the roll bite on the ingoing side of a pair of cooled rotating rolls. The molten metal solidifies in contact with each of the rolls to form a skin and the two metal skins come together and as they pass through the roll gap they are compressed to form strip. When a twin roll caster is to be started, the gap between the two εpaced apart rolls has to be filled to prevent molten metal from passing straight through the gap between the rolls. Usually a leaderstrip is placed between the rolls to substantially close off the gap. If the molten metal is introduced into the bite before the rolls are rotated, the rolls will start under high loading conditions requiring high torque from the drive motors, and before the rolls start to rotate, the hot metal in contact with the stationary rolls can cause overheating of the parts of the rolls with which it comes in contact. On the other hand, if the rolls are rotated before the molten metal is introduced into the bite, the leaderstrip is driven through the roll gap as soon as the rolls commence to rotate and the leaderstrip may be driven out of the roll gap before a satisfactory bond is made between the solidified metal and the leaderstrip. An object of the present invention is to overcome these difficulties. According to a first aspect of the present invention in a method of casting metal strip an elongate leaderstrip is positioned between the rolls of a twin-roll caster to substantially close the gap therebetween with an end portion of the strip positioned in the bite between the rolls on the ingoing side of the caster rolls; rotation of the rolls is commenced in the direction which would drive the leaderstrip through the gap to the outlet side of the caster but the strip is held against the action of the rolls with the end portion in the bite on the ingoing side of the caster rolls; molten metal is then introduced into the bite on the ingoing side of the caster rolls and the end portion of the leaderstrip bonds with solidified metal and the leaderstrip is released and is driven by the rolls through the gap leading the cast metal strip with it. By this method the rolls are started and at least partially brought up to speed without having the molten metal in contact with them. The leaderstrip is held in position when rotation commences and it is held against the action of the rolls, with the rolls slipping against the leaderstrip, until the leaderstrip is released. Conveniently, the means retaining the leaderstrip in position is one or more thin links which melts when it comes into contact with the molten metal thereby allowing the leaderstrip to be driven through the gap between the rolls. According to a second aspect of the invention start-up apparatus of a twin-roll strip caster comprises an elongate leaderstrip having an end portion configured to assist bonding of the end portion with solidifying molten metal, a holding device for holding the leaderstrip in the gaf between a pair of rotating rolls of the twin roll strip caster with said end portion positioned in the bite between the rolls on the ingoing side of the caster rolls, and said holding device including release means by which the leaderstrip is released from the holding device. In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawing which is a diagrammatic perspective view of a twin roll caster having start-up apparatus in accordance with the present invention. A twin-roll caster comprises two rotatable rolls 1,3 arranged with their longitudinal axes horizontal and spaced apart to define a gap between them. End dams (not shown) bear against the end of the rolls. The rolls are cooled by means not shown. The rolls are rotated in the directions indicated by the arrows by drive means. In use, molten metal, such as steel, is poured into the roll bite 5 on the ingoing side of the caster rolls. Molten metal, solidifies in contact with the cooled peripheries of the rolls to form skins and as they pass through the roll gap they are compressed to form strip. In order to commence casting, a leaderstrip 7 of approximately the same width as the strip to be cast is placed in the roll gap and the head end 9 of the leaderstrip is positioned in the bite 5 on the ingoing side of the caster rolls. To assist bonding of the metal with the head end, it is configured such as the head end is tapered to a reduced width and holes 11 are in the head end. To one side of the roll 1 there is a fixed support plate 13 and a wire 15 passes through a hole in the plate and is connected at one end to a stop member 17 and at the other to a tension spring 19. The spring draws the stop member into engagement with the plate 13. One or more fusible links 21 are connected between the stop member and the head end 9 of the leaderstrip. The rolls 1 and 3 are driven in their normal direction of rotation prior to molten metal being poured into the bite 5. The rolls attempt to drive the leaderstrip out of the roll gap but are prevented from doing so by the tension in the wire 15 and the links 21. The rolls skid against the leaderstrip and the head-end 9 of the leaderstrip remains in the bite 5. When molten metal is poured into the bite 5 some of it solidifies in bonding relation with the head end of the leaderstrip. The solidifying metal fills the holes 11 and connects to the tapered shoulder of the strip. As bonding is achieved, the leaderstrip is driven through the bite stretching the tension spring and as the level of molten metal in the bite 5 rises it comes into contact with the links 21 and causes them to melt. This releases the leaderstrip from the stop member 17 and the leaderstrip continues to be driven by the rolls out of the roll gap. The solidified metal which has bonded to the head of the strip is drawn with the leaderstrip through the roll gap where it is compressed to the dimension of the roll gap to form strip. Molten metal which has already begun to solidify continues to be drawn from the roll bite and through the roll gap where it is compressed into metal strip. Eventually the leaderstrip is cut-off from the cast strip. In an alternative arrangement, the head end 9 of the strip is held in the bite 5 by some form of anchored clamp mounted on a tension spring. A predetermined interval of time after molten metal has been introduced into the bite, the, clamp is released to allow the leaderstrip to be driven out of the caster. As a result of the present invention the rolls can be rotated prior to the molten metal being poured into the roll bite so enabling a lower start-up torque to be required and a reliable bond between the head end of the leaderstrip and the solidified metal is assured.

Claims: Claims : 1. A method of casting a metal strip in which an elongate leaderstrip is positioned between the rolls of a twin-roll caster to substantially close the gap therebetween with an end portion of the strip positioned in the bite between the rolls on the ingoing side of the caster rolls; rotation of the rolls is commenced in the direction which would drive the leaderstrip through the gap to the outlet side of the caster but the leaderstrip is held against the action of the rolls with the end portion in the bite on th ingoing side of the caster rolls; molten metal is then introduced into the bite on the ingoing side of the caster rolls and the end portion of th leaderstrip bonds with solidified metal and the leaderstrip is released and is driven by the rolls through the gap leading the cast metal strip with it. 2. A method as claimed in claim 1 in which the leaderstrip is held in position with the end portion in the bite by means which melts and hence releases the leaderstrip when it comes into contact with the molten metal. 3. A method as claimed in claim 1 in which the leaderstrip is held in position with the end portion in the bite until a predetermined time interval after the molten metal is introduced into the bite and then the leaderstrip is released. 4. Start-up apparatus of a twin-roll strip caster comprising an elongate leaderstrip having an end portion configured to assist bonding of the end portion with solidifying molten metal; a holding device for holding the leaderstrip in the gap between a pair of rotating rolls of the twin roll strip caster with said end portion positioned in the bite between the rolls on the ingoing side of the caster rolls, and said holding device including release means by which the leaderstrip is released from the holding device. 5. Start-up apparatus as claimed in claim 4 in which said holding device comprises a spring-loaded elongate tension strip and at least one fusible link, which serves as the release means, connected between the end portion of the leaderstrip and the tension strip. 6. Start-up apparatus as claimed in claim 4 in which the release means comprises a clamp which grips the end of the leaderstrip and which is caused to release the leaderstrip a predetermined interval of time after molten metal is introduced into the bite.

Inventors: JEONG SEONG IN, PERRY ROBERT MAIDENS, WINDER EDWARD ALEXANDER, YOON JONG CHIL, JEONG, SEONG, IN, PERRY, ROBERT, MAIDENS, WINDER, EDWARD, ALEXANDER, YOON, JONG, CHIL
Applicants: DAVY DISTINGTON LTD, JEONG SEONG IN, PERRY ROBERT MAIDENS, WINDER EDWARD ALEXANDER, YOON JONG CHIL, DAVY DISTINGTON LIMITED, JEONG, SEONG, IN, PERRY, ROBERT, MAIDENS, WINDER, EDWARD, ALEXANDER, YOON, JONG, CHIL
Application year: 1996
Main classification: B22D11
IPC codes: B22D11