A protective coating for stopper plugs

Abstract

The progressive method of stopperless steelcasting, i.e., with slide gates, is being used on an increasing scale but the bulk of the steel is still cast from ladles equipped with stoppers and plugs. An analysis of the relevant data at the Zaporozhstal Plant showed that one of the causes of unsatisfactory steelcasting lies in the welding of the plug to the nozzle socket by a solidified layer of metal, as a result of which the plug breaks away when the stopper is opened. The welding effect can be reduced by the application of a protective coating on the plug or on the plug and nozzle. The protective coatings proposed hitherto* [1][2][3] are not used to a significant extent in the industry because they are not efficient enough.In a joint project with the Zaporozhstal, the Zaporozhe Industrial Institute has developed the composition of a protective coating, tests with which showed that it ensures that the stopper functions normally.In the development work tests were carried out with fillers in the form of silver graphite, foundry graphite, titanium slag, ferrotitaninm concentrate, chrome--magnesite powder, and kyanite--sillimanite SB type paste, and with binders in the form of a solution of spent sulfite lye (s. s. I. ), aluminophosphate compositions, heat-resistant lacquers KO-075 and KO-087, and carbamide resin, The steel and slag resistance of the coating was increased by adding boron nitride to its composition.The best results were obtained with a coating which contained 98% SB type kyanite--sillimanite pastej of density 1.80-1.85 g/cm 3 and 2% boron nitride.The dried coating was smooth and hard. Its cohesion with the material was characterized by a tensile strength of 2.4 kgf/cm 2 and a shear strength of 4.6 kgf/cm 2. The thermal-shock resistance of the coating was assessed in terms of the weight loss of specimens dried at II0-150~The thermal-shock conditions were: heating of the specimen to 1500~ for 15 min followed by rapid cooling in air to room temperature. The weight loss after one thermal shock was 2.23%. The wetting angle of molten steel on the coating was 142 ~ .Preliminary industrial tests in the open-hearth division of the Zaporozhstal ~ Plant confirmed that a coating of such a composition is better than any other investigated type but it has a serious fault, i.e., the mix for the coating rapidly separates into layers. *U.S. A. Patent No. 3472432 (1969); U. S. A. Patent No. 3549124 (1970). $ The kyanite--sillimanite paste consisted of 83% kyanite--sillimanite concentrate, 2.5% s. s. 1., 1.5% bentonite, 0.5% technical soap, the remainder water. *Density o--~he molasses 1.74-1.7'~ g/c 9 *In the nurg~ator after 7h; in the denominator. atter z4n. ' __ Zaporozhe Industrial Institute.