Consumable lance

#This invention relates to elongated tubular devices which are immersed into molten liquid metal. It relates specifically to the construction of consumable lance devices used to introduce oxygen or other gases into molten steel.

#In metallurgical operations using continuous casting machines it has become necessary to tap the heats "hot" from the furnaces to insure sufficient temperature at delivery to the caster. Missed caster sequences require either (a) diverting pours into ingots, with the consequence of lower quality steel and higher production costs, (b) providing a ladle reheat furnace for raising the temperature of the liquid steel in the ladle or (c) blowing oxygen into the liquid steel through an oxygen lance to raise the temperature of the liquid steel to the required casting temperature. Heretofore, it has been the practice to use either water-cooled nonconsumable lances or refractory covered consumable lances during such oxygen blowing reheating operations.

#Consumable lances in the past have used several designs. The first design injects oxygen into the molten steel bath through a centrally located longitudinal tubular steel member encased within a protective refractory covering.

#FIG. 1 is a cross-sectional view of a prior art lance illustrating the erosion encountered at the lance tip when ferrous tubular members are used as oxygen passageways.

#FIG. 2 is a similar cross-sectional view of a prior art lance illustrating the erosion encountered at the lance tip when spirally wound tubular members are used as oxygen passageways.

#FIG. 3 is an elevational view in cross-section of the preferred embodiment of this invention.

#Before describing the unique design of the consumable reheating lance of this invention, it will be helpful to review the problems of the prior art.

#Referring to FIG. 1 of the drawings, a consumable reheating lance tip 10 is seen to comprise one or more elongated tubular steel members 11 encased within a protective refractory covering 12. The tubular steel members 11 are connected to an oxygen source, not shown, and provide passageways through which oxygen 13 is injected into the molten steel bath. During actual use in reheating operations, it was discovered that the reaction between the oxygen 13 and the tubular steel members 11 in combination with the high temperatures of the reheating operation caused excessive concave erosion 14 at the lance tip resulting in lance consumption at a rate of from 5.5 inches/min. to 15.4 inches/min. It was also discovered that "straight through lances", as shown in FIG. 1, performed satisfactorily when reheating low carbon grades of steel (below about 0.50% C), but produced heavy splash when higher carbon steels were reheated.

#In an effort to overcome the problem of heavy splash produced during the reheating of high carbon steels (above about 0.50% C) a second design, as described in U.S. Pat. No. 3,645,520, was tried. This second design, illustrated in FIG. 2, comprises a consumable lance tip 10a having one or more spiral tubular members 11a encased within a protective refractory covering 12a. The angle of the spiral tubular members 11a is controlled so that as the lance is consumed the oxygen 13a will be injected into the molten steel at a predetermined selected angle. U.S. Pat. No. 3,645,520 teaches that a gas injection angle of 15.degree. to 90.degree. from the vertical will produce a minimal splashing effect. However, it has been discovered that as the gas is injected into the molten bath at the above selected angles, it causes uneven erosion of the protective refractory covering, as shown at 14a in FIG. 2. This erosion exposes the tubular members 11a a to the molten bath and causes up line burn through 15 of the tubular members 11a thereby intensifying the erosion of the protective covering. Such lances have been consumed at a rate of about 9.4 inches/min.