Abstract: A pair of dry-sealed screw rotors for compressors which includes rotor tooth profiles in which an inter-tooth gap at a profile point on male and female rotor of a normal temperature is determined by an amount of interference due to thermal expansion caused during the operation of the compressors and an amount of minimum safety clearance necessary for the operation. The inter-tooth gap is further determined by a total thickness of seal coatings applied to the peripheral surfaces of the rotors at a profile point at which the thus determined gap is smaller than the total thickness of seal coatings. With the thus shaped rotor teeth, a most preferable seal line is achieved so as to produce an improved compression efficiency.

Abstract: A screw rotor mechanism which includes a female rotor F having tooth crests each being formed by a leading side arc g2-a2 overlying a tooth tip circle Cf thereof and a following side are a2-b2 having its center at a point 07 on a pitch circle Pf thereof, and a male rotor M having tooth tips each being formed by an arc c1-d1 having its center at an interaxial line passing through axes Of,Om of the female and male rotors F,M. The male rotor M also has tooth bottoms being complementary to tooth female tooth crests or tips and forms no seal grooves thereon. The thus shaped rotors are adapted to be machined with a high efficiency by a gear hobbing machine.