Wear of Permalloy Magnetic Heads against Striped Motion-Picture Film
F. J. Kolb, R. S. Perry
A simplified abrasion tester has been developed to study the action of a head against the magnetic stripe on motion-picture film, and to investigate the factors affecting head life. In a study using only permalloy dummy heads, the data over the range of variables normally encountered in motion-picture work can be correlated by the equation — $$(dA/dL)=k_{f}k_{h}P^{1.1}M^{1.0}V^{-0.3}$$ — where A = loss of metal per unit width of the head, L = length of stripe run against the head, and kf and kh are abrasiveness factors characteristic of the film and head respectively. P, M and V are the pressure of the head against the stripe, the contact or chord length of the head and the film velocity respectively. Head pressure can be chosen within limits by the systems designer; it is found advantageous to work at low levels. Accordingly, the control of the stripe presentation to the head and the uniformity of that presentation is preferably controlled by means other than head pressure, such as by film-path constraints. This work is being extended into a study of other polepiece alloys and into very high-speed magnetic transfer.