Forming control of cold-drawn seamless pipe

Forming control method of cold drawn seamless tubing

1) The situation of cold drawing stress control:

For steel bars of grades II, III, and IV and steel bars of No. 5 steel, after cold drawing, they are used as prestressed steel bars, and cold drawing stress control should be used. However, after the steel bar is cold-drawn, it is checked that the maximum cold-drawing rate has exceeded the specified value, and the mechanical energy test must be carried out again.

2) Control requirements for determination of cold drawing rate:

When the cold drawing rate is used to control the cold drawing of steel bars, the control value should be determined by experiments. Requirements for test determination: There should be no less than 4 test pieces in the same furnace and the same batch. Each test piece should measure the corresponding cold drawing rate according to the cold drawing stress specified in the specification, and take the average value of the test piece as the actual cold drawing rate of the batch of steel bars in the furnace. If the strength of the steel bar is high and the average cold drawing rate is lower than 1%, the cold drawing rate of 1% should still be controlled when the steel bar is cold drawn.

3) Cold drawing control of different heat batches:

For steel bars that are mixed and cannot be distinguished from batches, the cold drawing rate cannot be used to control the cold drawing, and multiple connected steel bars must be cold drawn, and the cold drawing rate and control stress of each bar must comply with the specifications.

4) Cold drawing speed control:

To fully deform the steel bar, it is necessary to properly control the cold drawing speed. Generally, 0.5-1.0 is appropriate; at the same time, it is required that after the cold drawing reaches the specified stress and cold drawing rate, stop the drawing for 2-3 minutes, then relax the steel bar and end the cold drawing to give the steel bar sufficient deformation time.

5) Cold drawing control method:

When cold drawing, only cold drawing rate or cold drawing stress control is called single control; cold drawing rate and cold drawing stress are applied at the same time during cold drawing, which is called double control. Using single control, the construction is simple and convenient. But for steel bars with uneven materials, it is impossible to test one by one; the test is laborious and material-intensive, it is impossible to do this, and some of the same steel bars have different cold drawing rates, and the cold drawing quality cannot be guaranteed. The dual control method can avoid the above problems. When 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, this kind of steel bar should be used with reduced strength. The double control method must be adopted for prestressed steel bars.

Cold-drawn seamless pipe is a product that has appeared in recent years, mainly because the inner hole and outer wall have strict tolerances and roughness. Compared with seamless pipes, cold-drawn (rolled) finished products have high precision, good surface quality, superior performance of steel pipes, and denser metals.

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