English
In high-rise buildings, bridges, subways, and other projects, the connection of large-diameter rebars (≥ Φ16) is of utmost importance — it must be both strong and efficient. Today, we’ll walk you through the upset straight thread connection process from principles to practical operation, and key pitfalls to avoid — all in one complete guide!
I. First Understand: Why Can This Process Be “Stronger Than the Base Metal”?
The core logic lies in just two steps, solving the problem of traditional cut threads that “weaken the rebar”:
Cold Upsetting Strengthening
Use hydraulic equipment to compress the rebar end, causing plastic deformation of the metal. The cross-sectional area increases by 10%–20% (for example, a Φ25 rebar becomes about Φ30 after upsetting), pre-compensating for the material loss from subsequent threading.
Straight Thread Engagement
High-precision straight threads are processed on the upset end, and then an internally threaded coupler is used to tightly connect two rebars, forming a rigid connection, with final strength ≥ the rebar itself.
II. Full Practical Workflow: 6 Steps, Each with “Critical Red Lines”
1. Rebar Pre-treatment: Flat End Face for Smooth Follow-up
Operation:
Cut the rebar using a grinding wheel saw or cutting machine (gas cutting is prohibited, as it causes embrittlement). Then remove rust, oil, and burrs.
Key Reminder:
End-face perpendicularity deviation ≤ 1°. If not, it must be ground flat.
2. Cold Upsetting: Pressure and Time Are Critical
Operation:
Insert the rebar into the upsetting machine mold. Adjust pressure according to rebar grade/diameter (e.g., HRB400 Φ25 ≈ 60–80 MPa). Hold pressure for 3–5 seconds, then release.
Key Reminder:
After upsetting, diameter must reach 1.2–1.4× original diameter, and the surface must be free of cracks and dents.
3. Straight Thread Processing: Precision Determines Quality
Operation:
Use a thread rolling machine (chipless) or threading machine (requires chip removal).
Key Reminder:
Use “Go Gauge + No-Go Gauge” for inspection:
Go gauge must fully screw in
No-go gauge penetration ≤ 3 threads
(Non-conforming parts must be scrapped.)
4. Coupler Preparation: Avoid “Three-No Products”
Operation:
Select matching couplers (usually made of No.45 steel). Check factory certificate and test report.
Key Reminder:
Internal threads must be undamaged, end faces flat, and markings clear (rebar diameter, manufacturer).
5. Rebar Connection: Don’t Skip the Torque Wrench!
Operation:
Screw the coupler onto one rebar until it contacts the step
Align and screw in the second rebar; switch to a torque wrench when hand-tightening stops
Tighten to the specified torque (e.g., HRB400 Φ25 ≥ 300 N·m), then mark both ends to prevent loosening
Key Reminder:
Exposed threads ≤ 2 pitches. Never rely on feel with a regular wrench.
6. Quality Inspection: 3 Mandatory Checks
Appearance Check:
Inspect exposed threads, fit, and ensure no looseness or misalignment
Torque Check:
Re-tighten 10% of joints — torque must meet the requirement
Mechanical Test:
Every 500 joints = 1 batch; sample 3 for tensile testing
Tensile strength ≥ standard value of base rebar
(If failed: double sampling; if still failed, reject entire batch)
III. Pros & Cons: Choose What Fits Best
✅ Core Advantages
High Efficiency:
Each joint takes only 1–3 minutes — much faster than welding
High Strength:
Tensile strength ≥ base rebar, suitable for seismic Grade I structures
Environmental Adaptability:
Usable in -40°C to 60°C, humid or high-altitude conditions
Stable Quality:
Equipment-controlled parameters reduce human error, with pass rates > 99%
⚠️ Limitations
High Equipment Cost:
Requires upsetting machine, thread rolling machine, torque wrench — suitable for large-scale projects
Rebar Condition Requirements:
Bent or heavily corroded ends must be corrected/cleaned first
Not Economical for Small Diameters:
For Φ14 and below, tying or electroslag pressure welding is more cost-effective
IV. Where Should It Be Used? (Applicable Scenarios)
According to Technical Specification for Mechanical Splicing of Rebars (JGJ107), priority use in:
Rebar Diameter:
Φ16–Φ50 (HRB400/500, HRBF400/500 hot-rolled ribbed rebars)
Structure Types:
Frame columns, beams, shear walls, bridge caps, pile foundations
(especially in dynamic load/high-stress areas)
Non-Rotatable Rebar Situations:
Rebar cage splicing, confined spaces (underground structures, dense reinforcement zones)
→ Use extended or reverse-thread couplers
Environment:
Normal concrete, seismic structures, low temperature (above -40°C), low-corrosion underground works
