Patent GB-1402640-A (GB)
Title: Withdrawing a continuous casting
IPC: B22D11/128
Filed: 1972-06-30
Abstract: 1402640 Continuous casting; rolling SCHLOEMANNAG 30 June 1972 [3 July 1971] 30879/72 Headings B3F and B3M [Also in Division B8] The pressure applied by each pair of rolls of a withdrawing or a withdrawing and straightening apparatus (e.g. the former having six sections each with three pairs of rolls) when the casting thickness falls below a prescribed thickness or a thin dummy bar is fed or withdrawn, is only that required for producing the necessary traction, but when that thickness is exceeded the pressure is raised to reduce the casting to the prescribed thickness. It may be desirable to reduce the thickness of the strand progressively between consecutive pairs of rolls or consecutive roll sections. In an arrangement for carrying out the process, piston-and-cylinder units 5, shown in Fig. 2, as applied to yoked rolls but applicable to single rolls, Fig. 1 (not shown), may draw upper driving rolls towards lower idling or driven rolls whose bearings are fixed in position, there being stops 6 on the piston-rods coacting with replaceable abutment pieces 7 which limit the minimum roll gap, determined by the units 5, to the prescribed casting thickness. To obtain a smaller roll gap for driving a dummy bar or undersized strand, thrustor cylinders 10 may be mounted on pistons 12 fixed on the piston-rods of units 5 to draw, with less force, the upper rolls down. A thrustor cylinder, of a roll contacting a thin dummy bar, because the friction is less than that of contact with the casting 1, may be capable of developing greater pressure than the others until the pressure is reduced by a monitor when the (large) dummy head approaches or passes. Instead of cylinders 10, stacks of Belleville washers on the rods may provide the thrust. Instead of a pair of units 5 being applied to the end of a single roll, Fig. 1 (not shown), it may be applied to a pivot 24, Fig. 2, of a tiltable yoke 25 extending across the cast strand and holding three idling reaction rolls 21, there being a lower set of an idling, fixed-bearing roll 22 and two driven rolls 23 mounted on titltable chocks 26. As well as or instead of the units 5 acting on the yoke, each end of a driven roll 23 is raised by a piston 31 of a differential ram 27 until the piston contacts an abutment 32 and the roll 23 is raised to a prescribed strand surface plane 35. If the strand thickness falls, a smaller thrust raises an auxiliary buffer piston 34 to lift the roll 23 beyond the plane 35 to supply sufficient traction. Instead of the differential ram, a spring-loaded thrustor may be used as a support. The driven rolls 23 and the reaction rolls 21 may be supported by the units 5 and thrustors 10 or by the rams 27. In another modification of the arrangement, Fig. 4 (not shown), there are only two rolls mounted in a tiltable yoke drawn downwards, by units 5 and thrustors 10. To prevent a roll, which is lowered because of a narrowing of the strand, from squeezing the strand, there is a pair of piston-and-cylinder units (48) to each roll, in opposition to the pull of the units 5. A detector (49) associated with each pair of units (48) monitors the position of the associated roll and the signals from the detectors are automatically compared with one another and each with a signal representing the prescribed thickness. When one roll is in a position outside that corresponding to that thickness, the units (48) associated with the other roll oppose the yoke pressure to reduce the pressure of that roll to that required for withdrawal although the first roll will apply a strand-reducing pressure. In another arrangement, without units 5 with stops and thrustors 10, a pair of cylinder-andpiston units 53, Fig. 5, connected to the bearings of one of a pair of rolls 51, 52 (one is driven), adjusts the roll spacing. The bottom roll 52 may be supported like a roll 23 in Fig. 2. At least one position-reporting device 54 at one end of that one roll 51 generates a signal corresponding to the actual thickness of the strand where the roll contacts the strand. A unit 56 compares the signal with a reference related to the desired thickness and the difference is applied as a controlling signal, to a servo-unit 58 for controlling the fluid of the units 53 so that the rolls apply the required contact pressure according to the actual strand thickness and to signals 59 of other parameters, such as strand width if the plant is adjustable for different cross-sections. For feeding-in the dummy bar, a signal 57 for its thickness is provided. Instead of measuring the strand thickness at the rolls, it may be measured by monitors located upstream of the controlled rolls.