Status of Rebar Mechanical Connection Technology in China

Rebar Mechanical Connection Technology in China was developed in the late 1980s, with the development and application of cold stamping rebar coupler (also called cold extrusion sleeve), the Rebar Mechanical Connection Technology has developed rapidly in recent years: Taper Thread Technology, Upset Forging & Thread Cutting Technology, and Rib-peeling & Parallel Thread Rolling Technology etc., which have played a significant role in promoting the development of China's construction industry.

The above-mentioned Rebar Mechanical Connection Technologies have some advantages, but also have some disadvantages.

For example, the Cold Stamping/Extrusion Technology adopts a high pressure pump as the power source, through an extruder to press the coupler, and then splice coupler and rebar by occurring plastic deformation on coupler. But the machine is very heavy, so Labor Intensity is big, and also it will pollute the environment if leak oil when could not make good maintenance. What is more, the connection speed is not as fast as the speed of Thread Connection Technology.

The Taper Thread Technology adopts Taper Thread Cutting Machine to process tapered thread on rebar end, and then connect tapered thread coupler and rebar. Workers must exert certain tightening torque to ensure the connection quality when splice coupler and rebar. If workers are negligent, the rebar will be very easy to slip out of coupler when rebar is forced. The diameter of Bottom Thread is smaller than the Base Circle Diameter of rebar, so the joint strength will be weakened, and affect joint performance. Although taper thread connection has good centering, but has strict requirement for rebar, the rebar can’t be bent or have horseshoe-shaped incision, otherwise the thread will not be complete, which will be very dangerous for the construction. Therefore, the site should be managed strictly.

For Upset Forging & Thread Cutting Technology, it firstly cuts horseshoe-shaped rebar end, and then adopts Upset Forging Machine to forge rebar end, then adopts Thread Cutting Machine to process parallel thread, finally connect coupler and rebar. This technology has complicated procedure, and microstructure of rebar end changes after upsetting. Also without tempering treatment, it will happen stress concentration, and reduce ductility, so it is unfavorable to improve the joint force.

Rib-peeling & Parallel Thread Rolling Technology adopts Thread Rolling Machine to roll thread on rebar end, and then connect parallel thread coupler and rebar. Because the thread is rolled by cold treatment, the strength of thread and steel has been increased, also make up the adverse affection that the joint strength is weakened due to the smaller diameter of Bottom Thread than the Base Circle Diameter of rebar, and realize equal strength connection. The advantage of this technology is with less procedure, high connection strength, and easy to operate etc. But the rolling tolerance of rebar is big, so it is difficult to control the thread quality, also the threading roller is forced in poor conditions, so has low working life.  

Source: http://www.cabr.com.cn/DepInfo/jxh/guoneiluowen.htm                                Edit: OCEPO