The biggest structural feature of the air expansion shaft is that it is a continuous non-segmented shape, while the differential shaft is usually formed by the connection of segmented inflatable units. An air expansion sleeve is arrange on that outer lay of the air expansion shaft, and the two ends of the air expansion sleeve are sealed by sealing ring. The air expansion sleeve is internally wrap with a key strip, a gas expansion piece, a central shaft body and that like. The air pressure enter from two ends of that air expansion shaft, and the extension and retraction of the pressure can control the protrusion and the contraction of the key strip. When the key strip or the expander is protruded, the gas expansion sleeve has friction force to drive the material to be rolled.