CURVED-TYPE

CONTINUOUS

CASTING

MACHINES

Continuous steel casting machines with curved molds are modern, highly efficient units which are easy to operate and produce high-quality slabs of carbon, low-alloy, and other steel grades with minimum capital investment. The machine being described has been developed by the designers and production engineers of the famous Urals Heavy Engineering Plant who took full account of the latest advances in continuous casting technology. The new and original solutions used in designing mechanisms and units of this machine were thoroughly tested for several years in a specially constructed prototype plant intended for 150 x 600 mm-cross section slabs and, where necessary, were altered. In Soviet machines built on the "curved" principle, as well as on the machines of other types, the principle of truly ~ontinuous casting, i.e., the casting of a series of heats of the some grade steel without a break in the process, was realized for the first time. In contrast to the radial continuous steel casting machines which were developed mainly in order to reduce the height and cost of the machine, the curved-mold machines, incorporating the above advantages of the radial design, are made primarily to increase the productivity. This has been achieved by creating favorable conditions for a stable prolonged casting using the "heat on heat" method and also by raising the speed of slab withdrawal. The former problem was successfully solved by Soviet engineers, who designed the device for replacing the intermediate ladies with damaged lining without interruption of the casting process. This device has proved very successful in vertical continuous casting machines of the Novo-Lipetsk Metallurgical Plant. After modification, each of the machines of this plant has been able to produce dozens of heats in a p r o c e s w h i c h can operate without a break for several days. The capacity of the converters used here is 100 tons. The continuous casting machines of the curved-mold type are characterized by a high casting speed made possible by the fact that, after an ingot with a liquid core has been straightened, its crystallization continues on a horizontal section of any length. To produce high-quality slabs, the Uralmashzavod developed a special curve whicl~ prorides optimum conditions of deformation of the slab in its two-phase state. Some

Design

of the

Features

Curved-Mold

Intermediate Ladle.

of the

Continuous

Casting

Machines

Type The d ~ i g n provides a good view of the mold and a stable feed of the liquid metal.

The intermediate ladle can be placed onto a lifting and revolving table or on a trolley of special design. This enables the elimination of crane operations involved in the removal of the ladle and makes it easier to attend to the mold and to intermediate ladle tundishes. Mold. In designing the machine the fact was taken into account that in high-speed casting,the slab leaving the curved mold has a thinner crust and so provision was made for the prevention of its damage. The molds used in new machines ensure an intense and uniform cooling of the slab on the entire length of the mold. The design of the mold provides a free access to water feed and discharge collectors, for a rapid replacement of molds, and for a considerable reduction in the cooling water consumption. The feed of liquid metal from the intermediate ladies into molds can be effected in two different ways: with an open or a dosed jet. Translated from Metallurg, No. 2, pp. 25-26, February, 1974. 9 1974 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission o[ the publisher. A copy of this article is available [rom the publisher for $15.00.

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The mold reciprocating mechanism enables a stepless variation of the reciprocation amplitude during the casting and during the adjustment of the machine. The system permits the optimization of the mold reciprocation process. Walking Beams. For reliable guiding of the slab which has left the mold, walking beams of special design are provided which move the slab along a circular arc through the secondary cooling zone without applying additional stresses to the crust. These beams represent a main feature of this type of casting machines. The beams improve the slab quality and create favorable conditions for an increased casting rate. The design of the working surfaces of the slab withdrawing device excludes the possibility of open jet cooling of the metal. The system of water circulation in the mold and in the walking beams has reduced the water consumption to 1/3 to 1/2 of the initial vaIue. This "dry" secondary cooling has made it possible to obtain slabs of perfect geometrical shape and has ensured a high uniformity of the process without emission of steam. The secondary cooling rolls straighten the slab at strain rates below the extreme permissible values due to the use as the technological axis of the machine of a special curve plotted by the designers of the Urals Heavy Engineering PLant and tested in service. This made possible an eiongation of the secondary cooling zone to any length without increasing the machine height. The dummy bar is of a blown-up design requiring no heavy devices for its separation, whichhas made possible the feed of the dummy bar into the mold from the top, reducing sharply th e preparation time of the machine for c a g ing. The dimensions of the dummy bar head are identical to those of the actual slab; the dummy bar must be replaced by another if the section is changed but the body of the bar can be used, within certain limits, with other cross sections. The dummy bar body consists of several hinged links which can be moved apart to increase the bar thickness. The device for separating and lifting the dummy bar provides a perfect separation of the bar head from the slab and for lifting the trolley and dummy bar from ahorizontal to a vertical position. An auxiliary crane can lift it from this position and carry it into a special pocket on the casting platform or lower it directly into the mold. The sealing device provides an inert gas shield to protect the meniscus of metal in the mold and its jet leaving the intermediate ladle. The gas is supplied under pressure. This device enables a high quality of the slab surface to be obtained, particularly in the case of special steels. Advantages Casting

of the

Use o f C u r v e d - M o l d

Continuous

Machines

These advantages are: 1.5-2 times higher output than that of other similar machines achieved by the use of a more efficient casting method "heat into heat" and an almost double slab withdrawal speed; high quality of slabs due to the use of molds of special design, special walking beams, and an efficient cooling zone as well as the use of molds with a special copper plate and shortening of the working-in period; reduction of gas and nonmetallic inclusions in slabs, which is achieved, as it has been shown in special investigations, by a definite position of the metal level in the mold in relation to its reciprocation curve; automatic control of the inert gas pressure in the mold volume; reliable and efficient operation of the upper secondary cooling zone designed as walking beams embracing the slab from both its broad sides; high-quality operation of the lower part of the secondary cooling system designed as a roll section forming the curved and horizontal parts of the technological axis; reduced amount of metal needed for the manufacture of special dummy bars; a slab withdrawal force equal to the force applied in vertical and radial machines and often smaller;

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lower specific pressures than those observed in other machines during the withdrawal of molds. Compared with other types of machines this results in a reduced possibility of the crust being torn off; wider range of sIab sizes; and c o m p l e t e automation and m e c h a n i z a t i o n of the continuous casting process, A c u r v e d - m o l d continuous casting m a c h i n e for slabs with a cross section of 280 x 1800 m m has been in o p e r a tion since 1968 at the N i z h n i i - T a g i l ' M e t a l l u r g i c a l Combine. Its t e c h n i c a l specification is as follows: No. of stands - 1; ladle c a p a c i t y - 160 tons; m a c h i n e o u t p u t - 800,000 t o n / y e a r ; radius of curvature of the mold - ? m; working platform height above the horizontal slab - 7.8 m; length of the secondary cooling zone - 21,5 m; slab withdrawal speed, according to the mechanisms used - 0,2-2.0 m / m i n . The casting takes p l a c e at a rate equal to the withdrawal speed of the slab which is twice the speed achieved with other machines of the same type; this is a c c o m p a n i e d by an i m p r o v e m e n t in the quality of slabs and a reduction in cost. A c o m p l e t e specification and the supply conditions of these machines can be obtained from the sole export agents: V / O Machinoexport, USSR, Moscow, 117380.

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