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Connecting Technology of Thick Straight Thread Reinforcement Bar in Pier

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Connecting Technology of Thick Straight Thread Reinforcement Bar in Pier

Abstract: The steel bar and other strong straight thread connection technology is a new generation of steel bar mechanical connection technology that has been successfully developed recently in my country. It uses a cold heading machine to upset the end of the steel bar, and then uses a special machine tool to thread the upsetting section. The internally threaded connecting sleeve connects the two steel bars. This technology combines the advantages of sleeve extrusion connection and taper thread connection, and has the advantages of high joint strength, stable quality, convenient construction, fast connection speed, wide application range, and good comprehensive economic benefits.

   Construction Technology

The strong straight thread connection technology of steel bars is a new generation of mechanical connection technology for steel bars recently developed in my country. It uses a cold heading machine to upset the end of the steel bar, and then uses a special machine tool to thread the upsetting section. The connecting sleeve connects the two steel bars. This technology combines the advantages of sleeve extrusion connection and taper thread connection, and has the advantages of high joint strength, stable quality, convenient construction, fast connection speed, wide application range, and good comprehensive economic benefits. It avoids the weakening of the cross-sectional area of the tapered thread due to threading, thereby ensuring that the joint can fully exert the strength of the base material—that is, the strong technical effect of steel bars; at the same time, this technology overcomes the shortcomings of poor quality and reliability of the tapered thread joint.

1. Construction preparation

(1) Material requirements

 The steel should have a factory certificate and a mechanical performance inspection report, and the results should meet the current specifications and design requirements. The connecting sleeve should have a factory certificate, and the sleeve and lock nut should be made of high-quality carbon steel or low-alloy structural steel. The tensile value should be greater than 1.2 times the standard value of the tensile bearing capacity of the connected steel bars. The diameter and type of the connected steel bars should be marked on the surface of the sleeve. Anti-rust and anti-fouling work should be done during transportation and storage.

(2) Turn over

According to the design drawings and the height of the project, adjust the length of the cut steel bars in time to determine the length of the cutting material, so as to avoid the joints being too concentrated and affecting the operation, and install the joints in the section with less stress.

2. Construction process

(1) Process principle

The upsetting straight thread process is to use the cold heading machine to upset the end of the steel bar, and then use the threading machine to process the straight thread on the upsetting section of the end of the steel bar, and then use the connecting sleeve to butt the two steel bars. Due to the cold heading of the end of the steel bar, not only the section is enlarged; but also the strength is improved. In addition, after the straight thread is processed at the end of the steel bar, the minimum diameter of the bottom of the thread should not be less than the diameter of the base metal of the steel bar. Therefore, the joint can be as strong as the parent metal of the reinforcement.

(2) Process flow

The process flow of equal straight thread steel bar connection is: steel bar blanking→hydraulic upsetting→processing thread→installing sleeve→processing thread→hydraulic upsetting→rebar U-turn→installing plastic protective sleeve→marking→on-site installation.

(3) Cutting and blanking

The ends of the steel bars used for processing must be straightened, and the section of the cut is required to be perpendicular to the axis of the steel bars. Because of this, only the grinding wheel cutting machine is used to cut the material, and the length is cut according to the length of the batching.

(4) Hydraulic upsetting

The upsetting machine for steel bar upsetting can automatically realize centering, clamping, upsetting and other processes. The time required for each upsetting is about 30~40s, and each shift is about 500~600 upsetting. The upsetting operation is very simple. The weight of the upsetting machine is only 380kg, which is convenient to be transported to the site for processing. Before formal processing, the appropriate upsetting pressure should be determined through experiments according to the diameter of the steel bar, the performance of the hydraulic press, and the shape effect after upsetting. During the operation, care should be taken to ensure that the angle between the upsetting head and the axis of the steel bar shall not exceed 4°. After the steel bar is upset, it should be carefully checked. If any transverse cracks perpendicular to the axis of the steel bar are found, they should be cut off in time and re-upset, but the original upsetting steel bar is not allowed to be upset again. The dimensions of the upsetting head should meet the requirements of the corresponding national specifications.

(5) Thread processing

The upsetting steel bars that pass the inspection are threaded one by one on the special threading machine, and matched with the matching sleeves one by one for inspection. Those that pass the inspection will enter the next process, and all qualified threads will be cut off. In order to ensure that the thread is damaged or manipulated during installation and transportation, it should be protected with a sleeve or plastic cap in time.

(6) Steel connection

  The connecting sleeve is prefabricated in the factory according to the design specifications and precision, and then packed into a box for use. Use the connecting sleeve to butt the steel bar on site, and tighten it with a common wrench. Attention should be paid to the degree of tightening during operation. Generally speaking, a steel bar joint can be considered to be tightened if no more than one complete thread is exposed.

3. Manufacturing process requirements

(1) When cutting steel bars, the end face of the incision should be perpendicular to the axis of the steel bar, without horseshoe shape or deflection, and the end should be straightened before cutting.

(2) The upsetting head must not have transverse surface cracks perpendicular to the axis of the steel bar.

(3) The diameter d1 of the base circle of the upsetting head should be greater than the outer diameter of the thread of the thread head, the length L should be greater than 1/2 the length of the sleeve, and the slope of the transition section should be ≤1:3.

(4) The unqualified upsetting head should be cut off and re-upset, and the upsetting head should not be subjected to secondary upsetting.