Patent ID: 11958454
Assignee: SANOH INDUSTRIAL CO., LTD.
Field: Mechanical elements (Mechanical engineering)
Classification: CPC B  F | IPC B  F

Claim 6:
7. A tube fitting that is fitted to an outer periphery of a metal tube having, at an end portion thereof, a ring-shaped portion projecting outward in a tube radial direction, and which is, by being fastened to a mating member in a state in which the tube fitting is in contact with the ring-shaped portion, capable of connecting the tube to the mating member, the tube fitting comprising:
a threaded portion in which are formed male threads that mate with female threads provided at the mating member;
a head portion that is provided at one end side of the threaded portion and to which a tightening torque is input during fastening;
a contact portion that is provided at another end side of the threaded portion and is for contacting the ring-shaped portion and simultaneously pressing the ring-shaped portion against the mating member, during fastening to the mating member;
a zinc-based plated layer that is provided at the threaded portion, the head portion, and the contact portion; and
a resin coating layer that is positioned at an outermost surface at an outer side of the zinc-based plated layer and includes a polyethylene-based substance, a lubricant, and solid particles,
wherein:
a through hole extends through the threaded portion, the head portion, and the contact portion, in a direction parallel to an advancing direction of the male threads during fastening,
the male threads of the threaded portion have an outer diameter of 9.53 to 14.0 mm,
the head portion includes a first plane facing an opposite direction from the advancing direction and a second plane orthogonal to the first plane,
the contact portion includes a contact surface capable of contacting the ring-shaped portion and has an inner diameter of 4.98 to 8.44 mm,
in a case of, counting from a head portion side, the number of threads configuring the male threads in a cross-section that includes a center line extending in the same direction as the through hole and is orthogonal to the second plane of the head portion, a first thread is defined as the first thread, a second thread is defined as the second thread, a third thread is defined as the third thread, and a fourth thread is defined as the fourth thread,
a first area set in the first plane of the head portion, a second area set in the second plane of the head portion, a third area set on a trailing flank of the third thread, a fourth area set on a trailing flank of the fourth thread, and a fifth area set on the contact surface of the contact portion are defined in the cross-section, and
a value obtained by (X1+X2+X3+X4+X5+T1+T2+T3+T4)/9 is defined as a fitting average plating thickness t in μm in a case in which X1, X2, X3, X4, and X5 denote five calculated values obtained by calculating, for each of the first area to the fifth area, the arithmetic mean of a thickness of the zinc-based plated layer measured at seven points forming a line in one direction at 10 μm intervals in each of the first area to the fifth area and T1, T2, T3, and T4 denote four measured values obtained by measuring the thickness of the zinc-based plated layer at each of a root between the second thread and the third thread, a crest of the third thread, a root between the third thread and the fourth thread, and a crest of the fourth thread in the cross-section, and
in a case in which a testing member corresponding to the mating member and a testing tube with a same outer diameter as the tube and having a testing ringlike portion corresponding to the ring-shaped portion are prepared and a fastening test including a fastening operation for fastening the tube fitting to the testing member with a tightening torque in a range of 12.0 to 22.0 Nm in a state in which the tube fitting is in contact with the testing ringlike portion and a disconnect operation for loosening the tube fitting after the fastening operation to disconnect the testing tube is repeated n times (where 1<n<6), a maximum axial force occurring in a first fastening test is defined as an initial axial force F1 in kN, a maximum axial force occurring in an n-th fastening test is defined as an n-th axial force Fn in kN, and a value obtained by −(Fn−F1)/(n−1) is defined as an axial force decrease rate α [kN/test round],
a range of the fitting average plating thickness t is set so that 10.0<F1<14.0 and 0<α<1.75 are true.