A method for producing a non-bolt joint structure, the non-bolt structure comprising:
- a fluid conduit having a receiving opening section, an inner circumference of the receiving opening section including an engaging means;
- a polyethylene pipe having an insertion opening section, the insertion opening section being configured to be inserted into the receiving opening section, wherein the polyethylene pipe and the fluid conduit are configured to be connected without using bolts;
- a packing ring inserted between the receiving opening section and the insertion opening section to seal between the receiving opening section and the insertion opening section;
- and
- a tubular metallic inner core fit into an inner circumference of the insertion opening section of the polyethylene pipe;
- wherein the engaging means is configured to prevent the polyethylene pipe from disengaging from the receiving opening section by engaging with an outer circumferential surface of an engaged portion of the polyethylene pipe;
- wherein the inner core includes a bulge portion that is in a plastically deformed state, a cross-sectional shape of the bulge portion along an axis of the inner core being curved to bulge in an outward radial direction toward the fluid conduit from the axis of the inner core;
- wherein the polyethylene pipe is in a deformed state so as to include a bulge portion, the bulge portion of the polyethylene pipe being formed as a result of the bulge portion of the inner core and having an inner circumferential surface that is in close contact with an outer circumferential surface of the bulge portion of the inner core, a cross-sectional shape of the bulge portion of the polyethylene pipe along the axis being curved to bulge in the outward radial direction,
- wherein the bulge portion of the inner core includes a first tapered portion, a diameter of the first tapered portion gradually expanding as the first tapered portion extends into the fluid conduit in a longitudinal direction from an opening in the receiving opening section;
- and
- wherein the engaged portion is formed on the outer circumferential surface of the bulge portion of the polyethylene pipe by the bulge portion of the polyethylene pipe bulged in the outward radial direction, a diameter of the engaged portion gradually expanding as the engaged portion extends into the conduit in the longitudinal direction from the opening, and the polyethylene pipe is prevented from disengaging from the fluid conduit by the engaging means engaging with the outer circumferential surface of the engaged portion;
- the method comprising:
- a first insertion step of inserting the inner core into the inner circumference of the insertion opening section of the polyethylene pipe, an outer diameter of the inner core being uniform and an inner diameter of the insertion opening section being uniform,
- a second insertion step of inserting the polyethylene pipe having the uniform inner diameter into the receiving opening section of the fluid conduit, which the packing ring is attached to, with the inner core having the uniform outer diameter being inserted into the polyethylene pipe,
- a diameter expansion step of carrying out a diameter expansion that expands the diameter of the inner core in the outward radial direction by applying a force to the inner core from an inside of the inner core in the outward radial direction with respect to the axis of the inner core as well as carrying out a plastic deformation of the inner core, the diameter expansion step being carried out after the second insertion step, whereby a work hardening phenomenon in which the inner core is plastically deformed and is never restored to its original shape occurs,
- wherein as a result of the expansion of the inner core and the plastic deformation of the inner core, the diameter of the polyethylene pipe is expanded in the outward radial direction by the inner core pushing the inner circumference of the polyethylene pipe in the outward radial direction, whereby the bulge portion is formed in the polyethylene pipe,
- wherein a diameter of the bulge portion of the polyethylene pipe is expanded until the engaged portion of the polyethylene pipe abuts on the engaging means of the receiving opening section,
- wherein by the bulge portion being formed in the polyethylene pipe, the engaged portion of the bulge portion of the polyethylene pipe is engageable with the engaging means, whereby a function preventing the polyethylene pipe from disengaging from the fluid conduit is fulfilled as well as the packing ring being compressingly deformed to be in close contact with the outer circumferential surface of the polyethylene pipe.