Common problems of upsetting straight thread connection

 

Deviation of steel bar upsetting diameter

The diameter of steel bar after upsetting shall be the nominal diameter of steel bar + 2mm, with a tolerance of ± 0.5mm.

 

Larger upsetting diameter will increase the possibility of brittle fracture of reinforcement, increase the difficulty of thread cutting and reduce the tool life;
If the upsetting diameter is too small, the thread profile will not be full and the thread tooth tip will be bald.

 

Insufficient upsetting length of reinforcement

The upsetting length of reinforcement is the effective length of upsetting section, which shall not be less than the thread processing length, otherwise the tooth profile within the effective thread length will be incomplete.

 

The appearance of upsetting head is unqualified

There is obvious bending at the rear end of steel bar upsetting, or there is a transverse crack perpendicular to the steel bar axis.

 

Deviation of nominal size of screw head

The processed steel wire head shall be tested with a special thread ring gauge. The ring gauge shall be divided into two ends. The wire head with qualified size can be smoothly screwed into the through end of the ring gauge, and 0 ~ 3 buckles can be exposed by hand; The end stop shall be screwed in by hand for no more than 3 buckles. If the screw head is too large, it will not be able to screw into the sleeve smoothly. If the screw head is too small, the fit gap between the screw head and the sleeve will increase.

 

Effective thread length deviation of screw head

The effective length of the screw head shall be consistent with the effective length of the sleeve thread, with a tolerance of 0 ~ + 2p.
(1) The length is too long, which will lead to more exposed threads after the screw head is tightened, and the joint is easy to break at the exposed thread when being pulled.
(2) If the length of the screw head is too short, the fitting length with the sleeve cannot be reached, and the joint strength will be affected.

 

The appearance of thread head profile is unqualified

The steel wire head shall meet the accuracy requirements of grade 6F. Within the effective length of the thread, the cumulative number of bare teeth or broken buckle shall be greater than 2 turns. The tooth profile has low finish and rough tooth profile.

Insufficient joint connection

The screw head cannot be screwed into the sleeve completely, resulting in insufficient thread matching length and affecting the connection strength.