DISK-SHAPED GLASS SUBSTRATE, MAGNETIC-DISK GLASS SUBSTRATE, METHOD FOR MANUFACTURING MAGNETIC-DISK GLASS SUBSTRATE, AND MAGNETIC DISK

摘要

A disk-shaped glass substrate for a magnetic-disk glass substrate includes an outer circumference having a roundness of 1.3 μm or less. A first reference circle is obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference. A second reference circle is obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline. A ratio of the second peak count value defined by the number of peaks of the second outline that project outward in a radial direction from the second reference circle to the first peak count value defined by the number of peaks of the first outline that project outward in a radial direction from the first reference circle is 0.2 or less.

主权项

1. A disk-shaped glass substrate comprising:
a pair of main surfaces, the disk-shaped glass substrate being to be made into a magnetic-disk glass substrate, an outer circumference of the disk-shaped glass substrate having a roundness of 1.3 μm or less, a first reference circle being obtained with a least squares method from a first outline corresponding to a shape of a lap around the outer circumference of the disk-shaped glass substrate, and the number of peaks of the first outline that project outward in a radial direction from the first reference circle being defined as a first peak count value, a second reference circle being obtained with a least squares method from a second outline obtained by performing low-pass filtering using a period in which the number of peaks per lap is 150 as a cut-off value on the first outline, and the number of peaks of the second outline that project outward in a radial direction from the second reference circle being defined as a second peak count value, and a ratio of the second peak count value to the first peak count value being 0.2 or less.