Patent EP-0373294-A2 (EP)
Inventor: SHIMADA SHUSAKU FUKUVI CHEMICA
IPC: B29D1/00
Filed: 1989-08-11
Abstract: The present invention relates to a method for producing an FRP screw-like fastening element. The screw to be produced has a thread portion and a head the cross section of which is larger than that of the thread portion. The method includes the following steps of a primary molding process and secondary molding process. The primary molding process includes the following steps of: (a) preparing a rod material including an elongated matrix formed of a plastic material (6) and a plurality of elongated parallel fiber elements (2) embedded within the matrix along the length of the matrix, the fiber elements having melting points substantially higher than the softening point of the matrix; (b) placing the prepared rod material of the screw into a molding chamber, the molding chamber including an internal surface of a semi-circular cross section, the internal surface having a small diameter portion and a large cross section portion communicating concentrically to the small diameter portion, the material being placed in the molding chamber in such a manner that the longitudinal axis of the rod material is generally aligned with the axis of the internal surface of the molding chamber; (c) heating the placed rod material to a temperature not less than the softening point of the matrix; (d) pressing the heated material perpendicularly to the axis thereof by a ram which has a plane surface facing to the internal surface of the molding chamber, thereby forming a half round bar from the material, the half round bar being generally in the form of half a round bar cut at a   plane including a center axis thereof, the half bar having an end portion and an other portion, the end portion being of a radius larger than the radius of the other portion; (e) cooling the half round bar to a temperature lower than the softening point of the matrix; and (f) taking the cooled rod material out of the molding chamber. The secondary molding process includes the following steps of: (g) joining the half round bar to another half round bar which is processed similarly to the half round bar to form a generally fully cylindrical material, the fully cylindrical material having a head portion of a larger cross section constituted by the end portion; (h) placing the fully cylindrical material within a cylindrical molding wall in such a manner that the longitudinal axis of the rod material is generally aligned with the axis of the molding wall, the molding wall including a large cross section portion for receiving the head portion, and a small diameter having an internal thread formed thereon to receive the portion except for the head portion of the fully cylindrical material; (i) heating the placed fully cylindrical material to a temperature not less than the softening point of the matrix; (j) inserting a stick member (48) into the heated fully cylindrical material along the longitudinal axis of the fully cylindrical material so as to laterally expand the full cylindrical material and to bring the peripheral face of the full cylindrical material into contact with the entire molding wall, thereby forming an external thread on the peripheral face of the fully cylindrical material; (k) cooling the thread-formed fully cylindrical material to a temperature   lower than the softening point of the matrix; and (l) taking the cooled fully cylindrical material out of the molding wall.