Measurements and theoretical predictions of head/tape spacing over a flat-head

Experimental measurements and theoretical calculations of the head/tape spacing are presented for the self-acting subambient foil bearing phenomenon at the interface of a flexible tape and a flat surface (e.g., tape-head). The air entrained at the flat-head/tape interface forms a subambient pressure layer which creates suction on the tape to pull it down to contact the head. The head/tape spacing for flat-heads is measured with a commercially available, two-wavelength, digital interferometer by using transparent tape and Al2O3-TiC flat-heads. Measurements for a large array of tape speed, tension, wrap-angle values, and head-lengths are presented. The interferometric spacing measurements show that, in general, the tape contacts the flat-head in the central region of the head and forms displacement-bumps adjacent to the edges of the head in the upstream and downstream corners. Experiments also show that the length of the displacement-bump affects whether a central contact region will form. The length of the displacement-bump is proportional to tape tension and wrap angle and inversely proportional to tape speed. The experimental results compare favorably to results of a mathematical model of the flat-head/tape interface.