TECHNOLOGICAL DEVELOPMENTS FOR HIGH SPEED CASTING OF SENSITIVE STEEL GRADES ROBERT HEARD* and N. KAELL Paul Wurth Inc., Stealth Tech Center, 333 Technology Drive, Canonsburg, PA, 15317-9581, USA (Received 1 October 1999 ; in revised form 1 October 1999 ; accepted 1 October 1999) AbstractÐSeveral years ago, in response to the trends in continuous casting technology, Paul Wurth undertook a program to develop and improve casting technology for high quality billet and bloom pro- duction. The goal of the program was to simplify the casting machine and design the equipment to be able to produce high quality billets at higher casting speeds. The approach was three-fold: ®rst, design a new oscillation system with more control and ¯exibility; second, improve the spray conditions to sup- port the higher casting speeds; and third, implement longer mold designs. # 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved. Re sume ÐIl y a plusieurs aneeÂes, en reÂsponse aux tendances de la technologie de couleÂe continue, Paul Wurth a entrepris un programme de deÂveloppement et d'ameÂlioration de la technologie de couleÂe pour la production de haute qualite de billette et de lingot. Le but du programme eÂtait de simpli®er l'appareil de couleÂe et de concevoir de l'eÂquipement permettant de produire des billettes de haute qualite aÁ de plus grandes vitesses de couleÂe. L'approache comprenait trois parties; premieÁrement, concevoir un nou- veau systeÁme d'oscillation avec plus de controÃle et de felxibiliteÂ, deuxieÁmement, ameÂliorer les conditions d'aspersion a®n de supporter les plus grandes vitesses de couleÂe et, troiseÁmement, fabriquer des moules plus longs. # 2000 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved. DEVELOPMENT OF VIBROMOLD In the oscillating system used for continuous casting, stroke length and oscillation frequency are often varied with the casting speed in order to optimize the surface quality of the cast product. The negative strip ratio, which is thought to be of importance in the stability of casting, is a value determined by these three variables. As casting speeds are increased on existing oscillation systems, often limits to either oscillation rate or stroke length are reached and compromises must be made to the negative strip ratio. Negative strip ratio can be calculated according to the half cycle or full cycle. In this work, the negative strip ratio (NSR) is calculated according to the formula: NSR  2 t n t  100 t=oscillation period and t n =negative strip time, where t n is the negative strip time as de®ned by t n  1 pf cos  V c pfs  f=oscillation frequency (Hz), s=stroke length (mm), V c =casting speed (mm/s). The relationship between stroke length, oscillation frequency, and casting speed at constant negative strip ratio is shown in Fig. 1. To maintain a constant negative strip ratio as casting speeds are increased, either stroke length or oscillation frequency must be changed. In the design of electromechanical casting systems common to billet casting systems, it is usual to operate with a ®xed oscillation stroke, and to vary the oscillation rate with casting speed. Changes can be made in stroke length, however, not during the casting operation. As a result, in order to achieve a constant negative strip ratio, oscillation frequency is the only variable that may be changed to maintain a constant negative strip ratio. Changes to the oscillation frequency can be made as casting speed increases, however, only up to the limits imposed by the design of the electromechanical oscillation system. This upper limit may reduce the ¯exibility of the caster in cases of multiple section casting, or at times when casting conditions are undesirable (sticking or rhomboidity occurring). It would be bene®cial to be able to independently vary both of these parameters while casting. To be able to accomplish this, hydraulic oscillation can be a useful tool. Taking into account increased casting speeds will require higher oscillation rates, an evaluation of the complete oscillation system for billet and bloom casters was Canadian Metallurgical Quarterly, Vol. 38, No. 5, pp. 331±335, 1999 # 2000 Canadian Institute of Mining and Metallurgy Printed in Great Britain. All rights reserved 0008-4433/00 $20.00+0.00 PII: S0008-4433(99)00032-4 *Author to whom correspondence should be addressed. Tel.: +1- 724-873-7200; fax: +1-724-873-7299. 331