The effect of head cleaning agents on the wear mechanisms of video heads

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Abstract
Wear mechanisms occurring at the video head were examined for a Mn-Zn ferrite single-crystal head in sliding contact with iron oxide formulation video tape. Of particular interest was the effect on wear due to the inclusion of a head cleaning agent (HCA) in the tape formulation. Wear tests were performed in situ using specially formulated iron oxide video tape samples containing a range of levels of two types of HCA: Al2O3 and Cr2O3. Head performance was monitored by measuring the degradation of the RF signal during wear, and wear to the head was measured using Knoop diamond indentation. The resulting wear surfaces were examined using optical and scanning electron microscopy. The tape was examined in cross section using transmission electron microscopy. Results showed that the dominant mechanism of wear was abrasive, characterized by the ploughing of isolated asperities on the tape surface through the ferrite head, and damage to the head gap by three-body abrasion. Evidence is presented which suggests that the isolated asperities are a result of poor dispersion of tape particles. The addition of an HCA to the tape formulation reduced the abrasion damage. Wear increased with increasing HCA content, but the total signal degradation did not vary significantly with HCA level for either HCA. Substantial differences in wear were observed between the two types of HCA, and evidence is presented which suggests that the differences are a product of the relative quality of dispersion of the two HCA materials.