The measurement of abrasiveness of magnetic tape

Magnetic tapes differ substantially in abrasiveness and consequent effect on head life. Logically, the consumer has expressed a need for a means to evaluate this property. In response to this demand, a number of articles and suggested test methods have appeared. The natural tendency of these offerings has been toward tests that are attractively economical of tape, time, and equipment. Such tests often involve the use of wear mechanics and geometries that are quite alien to practical tape usage. The purpose of this paper is to present evidence that efforts toward economy can be unexpectedly costly in terms of test validity. Using a test format that identifies closely with customer usage patterns, effects are shown for parameters controlled, perhaps involuntarily, by the consumer. These include contact pressure, tape speed, metal surface, and relative humidity. The effect of relative humidity, alone, is very profound. There is also a surprising degree of interaction between the relative humidity level and the type of metal being worn. The behavior of pole-piece metals is diametrically opposite to that of other structural and shielding components of a head, such as copper and aluminum, in this regard. The results of these parameter studies have been used to determine limitations that must be placed upon any valid field test for abrasiveness. These limitations appear to prohibit any field test which is very economical of tape and time. However, one possible field test design is proposed, within the limitations imposed by this study, which is relatively modest in equipment requirement and will give results in which one can justifiably have confidence.