Extrusion method and extruder used for obtaining phenolic resin pipe

An extrusion method for preparing a phenolic resin pipe with an extruder comprising a screw, a cylinder, a die comprising an inlet and an outlet and defining a flow path, and a mandrel, the mandrel being inserted into a through-hole formed in the screw along the screw axis and protruding into the die along the screw axis so as to be able to more forward and backward and being fitted to the screw so as to be able to freely rotate independently from the screw or the mandrel being firmly fitted to the front end of the screw so as to be able to rotate synchronously with the screw, the die satisfying the following formulas

• R.sub.1 /R.sub.2 =0.25.about.1.0
• S.sub.1 /S.sub.2 =0.1.about.2.5
• where R.sub.1 is an outside diameter of the die flow path at the die outlet, S.sub.1 is a cross-sectional area of the die flow path at the die outlet, R.sub.2 is an outside diameter of the die flow path at the die inlet, and S.sub.2 is a cross-sectional area of the die flow path at the die inlet, wherein the die further comprises a uniform flow path portion having the same cross section as the die outlet and a length of 1D to 300D where D is the inside diameter of the die, said uniform flow path portion being spaced from the die inlet and wherein an outer periphery of the die flow path is inclined from the die inlet to the uniform flow path portion with the inclination not greater than 35.degree. with respect to the axis of the screw, which method comprises shaping and extruding a phenolic resin material whereby the material after extrusion is cured so as to be able to retain its shape, by controlling the temperature of a heating zone of the cylinder communicating with the die inlet.