Wear mechanisms of metal-evaporated magnetic tapes in helical scan videotape recorders

The wear processes of metal-evaporated magnetic tapes by rotary heads in videotape recorders were investigated by continuous microscopic observations of the rubbing surfaces of magnetic tapes and rotating heads using stroboscopes. It was found that the magnetic layers of the metal-evaporated tapes were worn out by two different wear mechanisms, depending on the contact pressure between the tapes and rotary heads. Under higher contact pressure, the frictional force between the tape and the rotary head increased with an increasing number of head traces, and the magnetic layer was partly peeled by the rotary head as soon as the frictional force exceeded a critical value. Under lower contact pressure, the magnetic layer of the tape was worn gradually in a mild wear process and eventually a part of it fractured because of decreasing mechanical strength with a decrease in its thickness. In each case, the large metal particles from the fractured magnetic layer transferred onto the rotary head, and in turn provided a higher frictional force to the magnetic layer of the tape and initiated a severe wear process