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New furnace Precautions for Sintering Underlayment

(1) During the initial stage of sintering, the furnace lining temperature should be raised at a rate no faster than 100°C per hour until it reaches 1050°C. This slow heating rate facilitates the gradual release of moisture from the lining materials. Once the furnace lining temperature reaches 1050°C, it should be held at this temperature for 3 to 5 hours to promote the stable phase transformation of quartz crystals. If the furnace lining is heated too rapidly during sintering, it will trigger an abrupt phase transition in the quartz material, leading to excessive internal stresses that may cause cracking and surface spalling during subsequent use of the lining. Such rapid phase transitions significantly reduce the service life and operational safety of the furnace lining.

(2) At Lining of the furnace After the temperature reaches 1050℃, fully load the furnace and then raise the temperature at a rate of 100℃ per hour, strictly following the furnace lining sintering procedure. The general principle is to “slowly raise the temperature during the low-temperature stage and maintain this stage for a relatively long duration.” During the sintering process, the furnace must be fully loaded, and additional charge materials should be continuously added during the melting and heating phase to ensure uniform temperature distribution throughout the furnace lining. The maximum sintering temperature for silica-based acidic furnace lining materials is 1650℃. Typically, a normal sintering temperature of 1620℃ is sufficient. The specific maximum sintering temperature should be determined based on the required pouring temperature—generally about 50℃ higher than the usual highest molten iron temperature. Once this temperature is reached, maintain it for 2 to 3 hours before tapping the molten iron; this completes the entire furnace lining sintering process.

During the later-stage high-temperature sintering process, it is crucial to ensure that the sintering temperature is continuously monitored. The furnace lining should develop, from inside to outside, three distinct layers: a sintered layer accounting for one-third of the total thickness, a transition layer, and a loose layer. This layered structure not only provides the furnace lining with a certain resistance to high-temperature erosion but also ensures good strength and toughness. A well-sintered furnace lining will have a smooth, erosion-resistant glaze layer on its inner surface, typically colored gray. If the lining appears white and glassy, resembling glazed porcelain, it may indicate that the sintering temperature has been excessively high; this situation warrants close attention.

(3) The number of furnace campaigns for electric furnaces from different manufacturers and for electric furnaces of different tonnages can only serve as reference figures. The actual number of campaigns used should be determined through continuous refinement and summarization by the operators. Based on experience in the casting industry, the lining thickness must not fall below 10 centimeters; if it does, the furnace must be relined. The lifespan of the furnace lining is influenced by numerous external factors, such as improper lining construction methods, use of incorrect lining materials, excessively short cold-start-up times, inadequate daily maintenance, and irregular charging patterns that cause impact damage to the lining.

In short, the lifespan of a furnace lining largely depends on whether operators follow the correct procedures for using electric furnaces. Operators must never take any chances when it comes to furnace bodies that may harbor hidden risks. At the root of all serious and catastrophic furnace failures, the primary factor is invariably human subjectivity and carelessness.