A magnetic disc cartridge includes a casing formed of upper and lower shell
halves mated together, a disc-like recording medium supported for rotation
in the casing and a liner fixed to each of the inner surfaces of the upper
and lower shell halves by ultrasonic welding by use of an ultrasonic
welding horn. The liner has an outer contour defined by an outer
peripheral edge, a central opening defined by an inner peripheral edge,
and a slit-like cutaway portion defined by a pair of linear edges
extending between the outer peripheral edge and the inner peripheral edge.
The ultrasonic welding horn is provided with a welding pattern in the form
of a protrusion pattern formed on a welding face thereof over the entire
welding area in which the ultrasonic welding horn is brought into contact
with the liner, and the liner is welded to the inner surface of the shell
half over the entire area of the liner along the welding pattern.
