Abstract: (1) Polyester fiber which consists substantially of polyethylene terephthalate, the fiber being characterized by strength of least 7.0 g/d, initial Young's modulus of at least 85 g/d, elongation of less that 20%, degree of crystallization X.rho. of at least 45% and the ratio of birefringence (.DELTA.n) and the degree of crystallization X.rho. from 0.38 to 0.45.(2) Method of making polyester fiber, characterized as follows: Polyethylene terephthalate is melt spun then passed through the heated cylinder which is installed directly under the spinning die; cooled and solidified; the oil agent is imparted and the yarn is taken-up at the speed of over 2000 m/min; this is drawn to a ratio of 1.5-2.3 in at least 2-drawing stages in continuation; then heat treated; the surface temperature of the drawing rollers at the final drawing stage is kept at 220.degree.-250.degree. C.; a non-contact type heating plate heated to a surface temperature of 250.degree.-500.degree. C.

Abstract: A continuous spin-draw process of making dimensionally stable polyester fiber having high strength and low shrinkage by melt spinning polyethylene terephthalate and drawing comprising multiple drawing stages of at least two stages where the spun yarn is passed from the takeup roller to a first pair of drawing rollers, then to a final pair of drawing rollers, then to a pair of relaxation rollers and then to yarn take up means; the surface temperature of said final pair of drawing rollers being maintained at 10.degree. to 60.degree. C. lower than the melting point of the drawn fiber; a non-contct type heated plate whose surface temperture is heated to 250.degree. to 500.degree. C. is positioned 20 to 100 mm separated from the yarn, thereby heating the yarn to obtain the relaxation heat treatment; and applying a commingling treatment to the drawn fiber by installing a commingling treatment apparatus between the final pair of drawing rollers and the pair of relaxation rollers.

Abstract: Polyester fiber which is characterized as follows:the fiber is made of polyethylene terephthalate or of polyester in which this is the main component. The fiber has the following combination of property characteristics:(a) an intrinsic viscosity of 0.70 to 1.05 dl/g(b) a tenacity of at least 8.0 g/d(c) an elongation at break of 17% or less,(d) an amorphous chain size of 60-70 A,(e) a density at least 1.395 g/cm.sup.3,(f) a dry heat shrinkage of 3.5% or less,(g) a heat resistance of at least 80%.