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Introduction to the Sub‑Gun Machine
The secondary lance is equipped with four types of probes: a temperature‑measuring probe, a temperature‑and‑carbon‑determination probe, a temperature‑and‑oxygen‑determination probe, and a molten steel‑level probe.
A secondary lance refers to an additional metal‑penetrating probe, similar to the oxygen lance used for blowing oxygen into the converter, which can be raised and lowered and inserted directly into the molten bath. The tip of the secondary lance is fitted with various probes capable of measuring parameters such as temperature and chemical composition during the smelting process; the data collected are then transmitted via computer to the converter’s main control room. The lifting and lowering of the secondary lance, the loading and unloading of probes, the transmission of measurement data, and the replenishment of the probe magazine are all managed by computer, enabling mechanization and automation. To improve the accuracy of endpoint control in converter steelmaking, it is essential to continuously monitor key variables—such as molten steel temperature and composition—during the blowing process and to refine these measurements using advanced dynamic control models, thereby ensuring precise attainment of the target endpoint. However, because the converter operates in a semi‑enclosed environment, obtaining reliable information from the molten bath during continuous blowing poses significant challenges. As the level of automation in converter steelmaking continues to rise, the use of a secondary lance to probe the molten bath has become the primary means of acquiring real‑time data on changes within the bath throughout the refining process.
Advances in the level of converter steelmaking technology and in automation have largely been driven by secondary lance technology, which is closely integrated with well‑established metallurgical modeling. The converter smelting process is a highly complex physicochemical operation. Factors influencing product quality include raw material conditions, target compositions and temperatures of the molten steel at tapping, fundamental theoretical calculations, accumulated production experience, and the pace of production. The current technological trend in converter steelmaking is to combine “real‑time monitoring of molten steel conditions” with “advanced, flexible model‑based control.” Such model‑based control stems from the integration of sound scientific theory and practical plant experience, while the primary methods for monitoring molten steel are secondary lance technology and off‑gas analysis. Off‑gas analysis systems infer the state of the molten steel inside the furnace by measuring the composition of the furnace gases; however, beyond the need for further refinement of its theoretical underpinnings, this approach is complicated by numerous extraneous factors affecting furnace gas composition that are unrelated to the molten steel itself. Consequently, very few plants rely solely on off‑gas analysis. In contrast, secondary lance technology employs a probe inserted directly into the molten steel to provide on‑site measurements, offering unquestionably higher accuracy than off‑gas analysis. Today, secondary lance technology remains the principal method used in converter steelmaking.
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