Joint for spiral pipe and connecting method

#1. Field of the Invention

#The present invention relates to a joint which is mounted on the end portion of a spiral pipe used for protection of a communication cable or a conductor cable or a spiral pipe used for transport of fluid, and is used to connect the spiral pipe to another spiral pipe or to the box body of a manhole. The present invention also relates a method of connecting a joint to a spiral pipe with an outer periphery of a pipe wall thereof formed in an uneven spiral shape.

#2. Description of the Related Art

#FIG. 1 is a side surface half section view of a joint according to a first embodiment of the invention, showing a state thereof in which it is mounted on a spiral pipe;

#FIG. 2 is a side surface half section view of a nipple employed in the first embodiment;

#FIG. 3 is a back view of the nipple;

#Now, description will be given below of a preferred embodiment of a joint according to the invention with reference to the accompanying drawings. FIG. 1 is a side surface half section view of a joint according to a first embodiment of the invention, showing a state thereof in which it is mounted on a spiral pipe. FIGS. 2 to 5 are a side surface half section view of a nipple employed in the first embodiment, a back view thereof, a front view thereof and a perspective view thereof, respectively. Also, FIGS. 6 and 7 are respectively aside surface half section view of a caulking ring employed in the first embodiment and a front view thereof. Further, FIGS. 8 and 9 are respectively a side view of a pressure contact member employed in the first embodiment and a front view thereof.

#In FIG. 1, a joint according to the present invention includes a nipple 1, a caulking ring 2 and a pressure contact member 3. The nipple 1 includes a flange portion 12, an inserting portion 11, and a small-diameter stepped portion 13. The invention is structured in the above-mentioned manner and, in enforcing the invention, the nipple 1, as in the nipple of the related art, may be made of a pipe member, which is formed of carbon steel (SS). The basic shape of the nipple 1 is generally the same as the nipple of the related art. The outside diameter of the inserting portion 11, which is the characteristic of the invention, may be set to the standards of a spiral pipe to be connected by the joint. The outer peripheral surface of the nipple 1 is formed in a flat cylindrical surface and, in the position of the cylindrical surface that is near to the flange portion 12, there is formed the small-diameter stepped portion 13. The step level difference of the small-diameter stepped portion 13 is set so as to obtain a fixing force, which can stand a tensile force applied to the spiral pipe to thereby prevent the spiral pipe against removal. And, therefore, the invention can be used almost regardless of the nominal diameter of the spiral pipe to be connected by the invention and, generally, when the invention is used for a spiral pipe having a nominal diameter in the range of 120 mm to 300 mm, the step level difference of the small-diameter stepped portion 13 may be set of the order of 1 to 2 mm. And, the outer periphery of the end face of the stepped portion where the small-diameter stepped portion 13 is in transit to the large-diameter portion of the inserting portion 11, preferably, may be chamfered. The reason for this is to be able to prevent the inner wall of the spiral pipe from being broken on the present end face. Also, from the viewpoint of prevention of the pipe body P against damage and removal, most preferably, the winding portion of the pipe body P to be wound by the pressure contact member 3 may be the outer peripheral portion of the portion of the pipe body P that exists above the inserting portion 11 and near to the small-diameter stepped portion 13, that is, the pressure contact member 3 is wound on a portion of the outer peripheral surface of the pipe body P near to a portion inside of which the small-diameter stepped portion 13 is disposed.

#The caulking ring 2 is a metal pipe which is formed of the same material as the nipple 1, while the inside diameter of the caulking ring 2 is set according to the standards of a spiral pipe to be connected by the joint, that is, almost equal to or slightly larger than the maximum outside diameter of the spiral pipe. The thickness of the caulking ring 2, preferably, may be set equal to or slightly smaller than the thickness of the nipple 1. Next, in the case of the flexible string-shaped pressure contact member 3 to be fitted into the spiral groove formed in the outer peripheral surface of the pipe body P, the section of the pressure contact member 3 may have any shape, for example, a circular shape, an elliptical shape, a rectangular shape, or a trapezoidal shape. Preferably, however, the section may have a shape of such a dimensional width that it can be embedded into the section of the spiral groove or may have a shape of such a dimensional width slightly larger than the width of the spiral groove section, while the longitudinal dimension of the section of the pressure contact member 3 may be set equal to or larger than the depth of the spiral groove. For the pressure contact member 3, actually, there can be used a ready-made member such as a V belt: that is, the pressure contact member 3 is readily available simply by cutting the V belt to a desired length.