Texturizing
The disc surface speed and the D/Y ratio fix the ceiling. Running near it is what turns a texturizing machine into a broken-filament generator.
— m/min
Yarn speed at which twist stability breaks down
Solid-cylinder diameter ignores filament packing, so the twist figure is a geometric reference for comparing settings rather than an absolute measurement. Decision-support only: confirm against the machine builder's disc rating.
False Twist Texturizing Surge Speed Calculator — free, with the formula and a worked example, at Textile School.