Method for producing FRP screw-like fastening elements

A method of producing a fiber-reinforced plastic screw having a thread portion and a head portion wherein the cross section of the head portion is larger than that of the thread portion, the method comprising the steps of:

• a first molding process sequence including:
• (a) preparing a rod material including an elongated matrix comprising a thermoplastic resin material and a plurality of elongated parallel fiber elements embedded within the matrix material along the length of the matrix, the fiber elements having melting points substantially higher than the softening point of the matrix material;
• (b) placing the prepared rod material into a mold chamber, the mold 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 rod material being placed in the mold 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 mold chamber;
• (c) heating the placed rod material to a temperature equal to or greater than the softening point of the matrix material;
• (d) pressing the heated material perpendicularly to the axis thereof by a ram which has a plane surface facing said internal surface of said mold chamber, thereby forming a half round bar from the material, the half round bar being generally in a form of half a round bar cut at a plane including a center axis thereof, the half round bar having a first end portion and a second portion, the first end portion being of a radius larger than the radius of the second portion;
• (e) cooling the half round bar to a temperature lower than the softening point of the matrix material;
• and
• (f) taking the cooled half round bar out of said mold chamber;
• and
• a second molding process sequence including:
• (g) joining the half round bar to another half round bar which is processed similarly to said half round bar to form a generally fully cylindrical material, the fully cylindrical material having a head portion of a larger cross section consisting of said first end portion;
• (h) placing the fully cylindrical material within a cylindrical mold wall in such a manner that the longitudinal axis of the fully cylindrical material is generally aligned with the axis of the mold wall, the mold wall including a large cross section portion for receiving said head portion and small diameter portion having an internal thread formed thereon to receive the second portion;
• (i) heating the placed fully cylindrical material to a temperature equal to or greater than the softening point of the matrix material;
• (j) inserting a stick member into the heated fully cylindrical material along the longitudinal axis of the fully cylindrical material so as to laterally expand the fully cylindrical material and to bring the peripheral face of the fully cylindrical material into contact with the entire mold 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 material;
• and
• (l) taking the cooled fully cylindrical material out of the mold wall.

A method of producing a fiber-reinforced plastic rivet, the rivet to be produced having a shank portion and a head portion, wherein the cross section of the head portion is larger than that of the shank portion, the method comprising the steps of:

• (a) a preparing a rod material including an elongated matrix formed of a plastic material and a plurality of elongated parallel fiber elements embedded within the matrix along the length of the matrix material, the fiber elements having melting points substantially higher than the softening point of the matrix;
• (b) placing the prepared rod material of the rivet into a mold chamber, the mold 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 mold 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 mold chamber;
• (c) heating the placed rod material to a temperature equal to or greater than the softening point of the matrix material;
• (d) pressing the heated rod material perpendicularly to the axis thereof by a ram which has a plane surface facing said internal surface of said mold 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 a first end portion and a second portion, the first end portion being of a radius larger than the radius of the second portion;
• (e) cooling the half round bar to a temperature lower than the softening point of the matrix;
• (f) taking the cooled rod material out of the mold chamber;
• and
• (g) joining the half round bar to another half round bar formed in the same manner as said first-mentioned half round bar to form a generally fully cylindrical material, the fully cylindrical material having a head portion of a larger cross section consisting of said first end portion.

A method of producing a fiber-reinforced plastic screw, the method comprising the steps of:

• (a) preparing a rod material including an elongated matrix formed of a plastic material and a plurality of elongated parallel fiber elements embedded within the matrix material along the length of the matrix, the fiber elements having melting points substantially higher than the softening point of the matrix material;
• (b) placing the prepared rod material within a cylindrical mold wall in such a manner that the longitudinal axis of the rod material is generally aligned with the axis of the mold wall, the mold wall defining a generally cylindrical first mold chamber and having an internal thread formed thereon, said cylindrical mold wall being formed in a mold, the mold having a inner peripheral wall and an end wall which define a second mold chamber in direct communication with the first mold chamber, for molding a head portion of the screw, the peripheral wall continuously extending from one of the opposite ends of the mold wall, the end wall defining an end of the second mold chamber and tapering off toward the first mold chamber, the apex of the end wall being located on the axis of the first mold chamber and wherein the pressing step comprises pressing the rod material toward the second mold chamber so that the softened rod material laterally expands and is injected, under the guidance of the tapered end wall, into the second mold chamber, whereby the thread-formed rod material has a head portion formed by the second mold chamber, the head portion having a hollow section formed therein by the end wall;
• (c) heating the placed rod material to a temperature equal to or greater than the softening point of the matrix material;
• (d) axially pressing the heated rod material so as to laterally expand the rod material and to bring the peripheral face of the rod material into contact with the entire mold wall, whereby an external thread is formed on the peripheral face of the rod material;
• (e) cooling the thread-formed rod material to a temperature lower than the softening point of the matrix material;
• and
• (f) taking the cooled rod material out of the mold wall.

A method of producing a fiber-reinforced plastic screw, the method comprising the steps of:

• (a) preparing a rod material including an elongated matrix formed of a plastic material and a plurality of elongated parallel fiber elements embedded within the matrix material along the length of the matrix, the fiber elements having melting points substantially higher than the softening point of the matrix material;
• (b) placing the prepared rod material into a mold chamber, the mold chamber including an internal surface of a generally semi-circular cross section, the internal surface having an internal thread formed thereon, the rod material being placed in the mold 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 mold chamber;
• (c) heating the placed rod material to a temperature equal to or greater than the softening point of the matrix material;
• (d) pressing the heated material perpendicularly to the axis thereof by a ram which has a plane surface said internal surface of said mold 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 eternal thread on the peripheral face thereof;
• (e) cooling the thread-formed half round bar to a temperature lower than the softening point of the matrix material;
• (f) taking the cooled half round bar out of the mold chamber;
• and
• (g) joining the half round bar to another half round bar which is formed in the same manner as said first-mentioned half round bar to form a generally fully cylindrical material, and with the fully cylindrical material having an external thread thereon.