| 摘要 |
In a screw vacuum pump having a pair of screw rotors, when one of a plurality of curves constituting the cross-sectional shape, perpendicular to the axis, of helical teeth is formed from an epitrochoid curve, the gap between the helical teeth of the two screw rotors becomes wider on the rotation center side thereof and narrower toward the outer peripheral side thereof. When the gap between the tooth surfaces of the two helical teeth 22a, 22b is set to zero, a first curve is drawn in such a way that the radial coordinates (Xt, Yt) of an epitrochoid curve formed by points on a second arc of the paired other screw rotor are corrected on the basis of the coordinates and a correction angle (α) calculated according to the following formula (formula 1), and then the respective corrected coordinates (X = Xtcosα - Ytsinα, Y = Xtsinα + Ytcosα) are connected to each other. |
