Seamless pipe cold drawing rate measurement and control

Seamless pipe cold drawing rate measurement and control

1) Cold drawing stress control situation:

Steel bars of grades II, III, IV and No. 5, which are used as prestressed reinforcement after cold drawing, should be controlled by cold drawing stress. However, after the inspection of steel bars after cold drawing, the maximum cold drawing rate exceeds the specified value in the specification, and the mechanical energy test needs to be carried out again.

2) Cold drawing rate measurement and control requirements:

When cold drawing of steel bars is controlled by cold drawing rate, the control value should be determined through experiments. Test measurement requirements: no less than 4 samples in the same furnace and the same batch. Each test piece shall be measured according to the cold tensile stress specified in the specification. The actual cold drawing rate of this batch of steel bars. If the strength of the steel bar is high, the average cold drawing rate is less than 1%, and the cold drawing rate should still be controlled at 1% when cold drawing the steel bar.

3) Cold drawing control of different batches:

For steel bars that are mixed in batches and cannot be distinguished, the cold drawing cannot be controlled by the cold drawing rate, and the cold drawing rate and control stress of each steel bar must meet the requirements of the specification.

4) Cold drawing speed control:

In order to fully deform the steel bar, the cold drawing speed must be properly controlled. Generally, 0.5-1.0 is appropriate; at the same time, after the cold drawing reaches the specified stress and cold drawing rate, stop drawing for 2-3 minutes, then loosen the steel bar and end the cold drawing, so that the steel bar has enough time to deform.

5) Cold drawing control method:

When cold drawing, only control the cold drawing rate or cold drawing stress, which is called single control; when cold drawing applies both cold drawing rate and cold drawing stress, it is called double control. Single control, simple and convenient construction. But for steel bars with uneven material, it is impossible to test one by one; it is impossible to test one by one, which is labor-intensive, and some steel bars of the same kind have different cold-drawing rates, so the quality of cold-drawing cannot be guaranteed. The dual control method can avoid the above problems. During cold drawing, if the control stress has reached the cold drawing rate and does not exceed the allowable value, it can be considered qualified; however, if the cold drawing rate has reached but the cold drawing stress has not reached the control stress, the strength of the steel bar should be reduced. For prestressed reinforcement, a dual control method must be used.