GB984340A - Joint and method of making the same - Google Patents

Abstract

984,340. Pipe and rod joints. KOBE Inc. Dec. 16, 1963, No. 49536/63. Heading F2G. [Also in Division B3] A forced fit tapered spigot and socket joint has the axial length of the faces in contact so related to the coefficient of friction of the surfaces and the engagement pressure produced by a high hoop tension stress in the socket and a high compression stress in the spigot that a joint strength at least nearly equal to the yield strength of the body portion of the spigot or socket is attained. The axial length of the tapered surfaces in pressural contact are between 0À5 and 6À0 of the outside diameter of the body portion of the spigot or socket and preferably at least equal to L but not more than 3L in the equation wherein one member of the joint is a critical member limiting the strength of the joint; where K 1 is the ratio of the tensile yield stress of the body portion of one member to the hoop yield stress of the critical member; K 2 is the ratio of the cross-sectional area of the body portion of one member to the cross-sectional area of the criticial member at the axial midpoint of the interface between the tapered surfaces; f is the effective coefficient of friction between the surfaces; a is the included taper angle of the surfaces; d is the interface diameter of the critical member at the axial midpoint of the interface between the tapered surfaces; and 9 is zero when the spigot is the critical member and equal to 4A 1 /K 2 when the socket is the critical member where A 1 is the crosssectional area of the body portion of one member. The joint may comprise two tubes connected by an internal or external sleeve, two rods connected by an external sleeve or two tubes with the ends belled to form a spigot and a socket. The thickness of the tapered portions may be constant or may decrease towards the open end of the tube. The friction between the tubes may be increased by inserting keying agents embedding themselves in the contacting surfaces, by roughening the surfaces or by having wide, shallow tapered threads on the contacting surfaces. The included taper angle should be between 0 degrees 30 minutes and 18 degrees. The tension and compression forces are preferably produced by injecting fluid under high pressure between the contacting surfaces to force them apart, further inserting the spigot info the socket and releasing the fluid pressure. However, the spigot may be injected into the socket with a sufficiently high force to cause the required tension and compression stresses, preferably with a lubricant between the contacting faces.