Thermal treated reinforcing bar splice and method

Abstract

A reinforcing bar has a controlled heating on its threaded end (or other engagement portion for engaging a coupler), which extends beyond the threads, and provides improved mechanical properties at the end. The heating may be a controlled heating that case hardens the threaded end, including heating of an unthreaded portion beyond the threaded portion. The heating may be done in multiple steps, for example with a heating/hardening, follow by cooling, a reheating for tempering, and a recooling. The bar end may be threaded into a coupler or splice, with the heated end extending axially beyond (outside of) the coupler. Regions of the reinforcing bar beyond the heated end may be untreated, and therefore weaker than the thermally-treated bar end. The resulting coupling or splice may therefore be able to achieve bar break (failure at a location in the bulk of the bar, away from the coupler).

What is claimed is: 
     
         1 . A method of preparing a reinforcing bar, the method comprising:
 preparing an engagement portion of the reinforcing bar for mechanically engagement with a coupler to be mechanically coupled to the engagement portion;   subsequent to the preparing, heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating; and   subsequent to the heating, cooling the heated end.   
     
     
         2 . The method of  claim 1 , wherein the heating includes induction heating the heated end, using a heater that surrounds at least part of the heated end. 
     
     
         3 . The method of  claim 1 , wherein the heating includes case hardening of the heated end, such that an outer part of the heated end is harder than an internal core of the heated end, which remains ductile. 
     
     
         4 . The method of  claim 1 , wherein the heating makes the heated end stronger than the bulk of the reinforcing bar. 
     
     
         5 . The method of  claim 1 , wherein the heating includes heating such that the heated end has an axial length of between 1.5 and 2.5 times a diameter of the engagement portion. 
     
     
         6 . The method of  claim 1 , wherein the cooling includes cooling the heated end using a liquid. 
     
     
         7 . The method of  claim 1 , further comprising, subsequent to the cooling, reheating at least part of the heated end. 
     
     
         8 . The method of  claim 7 , wherein the reheating is tempering of the at least part of the heated bar end. 
     
     
         9 . The method of  claim 7 , wherein the reheating is performed at a lower heating level then the heating. 
     
     
         10 . The method of  claim 7 , wherein reheating is accomplished using a heater that is also used in the heating. 
     
     
         11 . The method of  claim 10 , wherein the reinforcing bar is moved relative to the heater during the reheating. 
     
     
         12 . The method of  claim 7 , further comprising, after the reheating, recooling the heated bar end. 
     
     
         13 . The method of  claim 1 , wherein the preparing includes forming threads on the engagement portion. 
     
     
         14 . The method of  claim 13 , wherein the forming threads includes taper threading to form tapered threads. 
     
     
         15 . The method of  claim 13 ,
 wherein the method is part of a method of making a reinforcing bar splice that includes threading the threads into an internally-threaded sleeve; and   wherein, after the threading is completed, the heated end extends outside of the sleeve.   
     
     
         16 . The method of  claim 1 ,
 wherein the method is part of a method of making a reinforcing bar splice that includes mechanically coupling the engagement portion with a coupler; and   wherein, after the threading is completed, the heated end extends outside of the coupler.   
     
     
         17 . A reinforcing bar splice comprises:
 a reinforcing bar with an engagement portion; and   a sleeve that mechanically engages the engagement portion to hold the engagement portion within the sleeve;   wherein a strengthened end of the reinforcing bar is stronger than a bulk of the reinforcing bar beyond the strengthened end, with the strengthened end extending outside of the sleeve; and   wherein the strengthened end includes a thermally-treated section that includes the engagement portion.   
     
     
         18 . The reinforcing bar splice of  claim 17 , wherein the engagement portion is a threaded portion that engages internal threads of the sleeve. 
     
     
         19 . The reinforcing bar splice of  claim 17 , wherein part of the strengthened end is a cold-worked section that is not part of the thermally-treated section. 
     
     
         20 . A method of preparing a reinforcing bar, the method comprising:
 preparing an engagement portion of the reinforcing bar for mechanically engaging another object; and   substantially axisymmetrically heating a heated end of the reinforcing bar, wherein the heated end extends beyond the engagement portion, and wherein a bulk of the reinforcing bar beyond the heated end is left unheated by the heating.