Abstract: In order to improve the long-term stable operation ability of the reverse flotation system in Yuanjiacun Iron Mine of Lanxian Mining Co.，Ltd.，Taiyuan Iron and Steel (Group)，in view of the 160 m3 Dorr ultra-large inflatable flotation machine，when the air supply is interrupted or the air pressure is insuf⁃ ficient，the negative pressure effect of the hollow shaft causes the slurry to be counter-suctioned into the bearing chamber，which in turn causes problems such as bearing burning loss，low equipment operation rate and substandard metal recovery rate，the comprehensive control technology of anti-backdraft ore with the synergistic effect of mechanical isolation and intelligent interlocking is studied. The research results show that the physical real-time isolation of pulp reverse flow is realized by adding air pressure driven rub⁃ ber check valve inside the hollow shaft of flotation machine，and the intelligent interlocking control system of air volume is constructed based on Siemens PLC，which realizes the self-diagnosis of air pressure and in⁃ terlocking protection during the full start-stop and operation of the equipment.After the industrial applica⁃ tion，the equipment failure caused by slurry reverse attraction is completely eliminated，the operation rate of flotation machine is increased from 78.8% to more than 95.0%，the total consumption of spare parts is significantly reduced，the recovery rate of hematite metal is increased from 74.70% to more than 80.0%， and the grade of tailings is reduced to less than 19.5%.This technology provides a key technical support for the stable operation of the ultra-large flotation machine in the micro-fine hematite magnetite mixed refrac⁃ tory anionic reverse flotation process，and has a wide range of application value.

Key words: ultra-large flotation machine, anti-backdraft ore, hollow shaft, check valve, PLC inter? lock, bearing protection