The acidic working lining of a medium-frequency induction furnace is essentially a "particle packing - low-melting bonding phase - high-temperature sintered shell" system: high-purity quartz aggregate forms the skeleton, and the boron-based binder forms a low-melting glassy phase during heating, filling pores and allowing the lining to gain strength before molten metal is charged. Too much boric acid/boron oxide lowers effective refractoriness and increases leakage risk; too little results in a thin sintered shell and insufficient mechanical stress resistance.

The first life lever is grading. Coarse particles resist slag and erosion but are harder to compact; fine particles and powders fill voids, increase contact area and density, and make phase change and sintering more uniform. In practice, the main strategy is "coarse skeleton + fine filling," using grading to trade for strength, density, and slag resistance stability.

The second lever is the binder window. For cast-iron high-temperature conditions, literature suggests boric acid addition around 1.2% - 1.8% (with constraints on B2O3 content, moisture, and particle size). The logic is to form a continuous sintered shell while avoiding excessive low-melting phase that softens the system and increases penetration paths.

The third lever is dry-out and sintering execution. The goal after ramming is not simply "dry it and run," but to remove water, control phase change, and build a dense ceramicized inner surface. A common approach is low power and slow ramp, with power switching and soaking in mid-to-high temperature ranges to control cracks and shell quality.

In practice, turning these three items into a "repeatable process card" makes a clear difference: grading table, boric acid target and fluctuation range, layer thickness and compaction, and staged heating and soaking points. Xinhui locks the grading and binder target values into the batch card by furnace type; on site, you just execute "layering - equal thickness - continuous compaction - staged dry-out," and furnace life variation converges faster.