Lockring tube joint

A tube joint comprising:

• first and second tubes each having walls and having about the same wall thickness, said tubes having end portions and the end portion of said first tube lying telescoped closely within the end portion of said second tube, said tube end portions having compressed and uncompressed parts;
• a lockring having a front section, a center section, and a rear section, said front section having an internal taper with a location of smallest inside diameter which is less than the outside diameter of the end portion of said second tube at the uncompressed part thereof, and said center section having a cylindrical internal surface of an inside diameter equal to the inside diameter of said front section location of smallest inside diameter;
• said rear section having a push surface for receiving push forces, and said center section having a length at least three times its wall thickness to facilitate its deflection away from and against the outside of said second tube;
• said lockring lying around the compressed part of said end portion of said second tube, with said center section compressing said second tube, the wall thickness of said center section being about the same as the wall thickness of each of said tubes at said end portions, and the modulus of elasticity of said ring and tubes being about the same.

A method for joining a pair of tubes comprising:

• inserting an end portion of a first tube into an end portion of a second tube, wherein the outside diameter of said end portion of said first tube is about the same as the inside diameter of said end portion of said second tube;
• placing a lockring which has an internally tapered front section whose minimum internal diameter is less than the outside diameter of said second tube end portion, a cylindrical center section of smaller internal diameter than the outside diameter of said second tube end portion, and a rear section forming a rearwardly-facing push surface, over said first tube with said front section closest to said second tube;
• moving said lockring forwardly including moving said tapered front section forwardly over said second tube end portion to reduce the diameter of said second tube end portion and the first tube end portion lying therewithin and to apply a rearward force to said lockring front section, including pushing said push surface forwardly to move said lockring forwardly, and elastically deflecting said center section radially outwardly under the forces on said front and rear sections to avoid high friction between said center section and said second tube end portion;
• and
• ceasing to move said ring forwardly including ceasing to apply a force to said push surface, and allowing said center section to undeflect and press radially inwardly on said second tube end portion.

Apparatus for joining the ends of a pair of interfitting tubes wherein the end portion of a first tube lies within the end portion of said second tube, and wherein said end portion of said second tube has a predetermined outside diameter comprising:

• a lockring having front, center and rear sections, said front section having an internal surface which is tapered in a forward radially-outward direction and which has a location of predetermined minimum diameter, said minimum diameter being less than said predetermined outside diameter of said second tube end portion, said center section having a cylindrical internal surface of said predetermined minimum diameter, and said rear section forming a rearwardly-facing push surface, said center section having a smaller outside diameter than said forward section at the location of said minimum diameter and having a length of more than three times its wall thickness, the length of said center section being great enough that said center section bows outwardly far enough to avoid high frictional contact with said second tube end portion when said lockring is pushed over said second tube end portion by a force applied to said push surface;
• said first and second tubes each being constructed of material having a predetermined modulus of elasticity, said tubes each having substantially a predetermined wall thickness, and said lockring is constructed of material of about the same modulus of elasticity as said tube material but of over twice the yield strength, and said center section of said lockring has about the same thickness as said wall thickness of said tubes.