Cold-rolled flat steel is a finished steel, which is a type of section steel. Because the section is rectangular, it is a simple section steel. The cold-rolled flat steel production workers use the flat steel finishing machine to pre-level and level the thickness direction of the cold flat steel wool with two sets of leveling wheels arranged up and down staggered; a pair of oppositely arranged finishing wheels are used. Squeeze in the width direction, so that the width is compressed to achieve the expected parameters, and the amount of compression is adjustable. The entire production process requires two cold rolling processes to complete.
1. Start cold rolling
Take a steel bar and apply tensile stress to it by cold rolling, and the steel bar will deform. As the tensile stress increases, the tensile stress within the steel bar increases gradually. When the tensile stress generated inside the steel bar exceeds the yield point A of the steel bar and reaches C, the cold rolling is stopped and the load is removed. At this time, it can be seen that the steel bar has undergone plastic deformation. During the unloading process, there is a change in the stress-strain diagram, and the straight line O1C is slower than the straight line OA.
2. The second cold rolling
The tensile stress is re-applied, and the steel bar is stretched to failure, and the stress-strain diagram has a new change. The new yield point is near point C, which is significantly higher than the original yield point A. This change shows that the plasticity of the steel bar has changed, the plasticity is small, the hardness is large, and the strength of the steel bar is improved. This phenomenon is called deformation hardening. After the above two processes, the cold-rolled steel bar is produced.
Control of cold rolling stress:
For grades II, III, IV and No. 5 steel bars, after cold rolling, those used as prestressed steel bars should be controlled by cold rolling stress. However, after inspection of the steel bar after cold rolling, the cold rolling rate exceeds the specified value of the specification, and another mechanical energy test is required.
Cold rolling rate measurement and control requirements:
When the cold rolling of steel bars is controlled by the cold rolling rate, the control value shall be determined by experiments. Requirements for the test and measurement: 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 rolling rate according to the cold rolling stress specified in the specification, and take the average value of the test pieces as the furnace. The actual cold rolling rate of the batch of steel bars. If the strength of the steel bar is high, and the average cold rolling rate is lower than 1%, the cold rolling rate of 1% should still be controlled during the cold rolling of the steel bar.
Cold rolling speed control: In order to fully deform the steel bar, it is necessary to properly control the cold rolling speed, generally 0.5--1.0 is appropriate. At the same time, it is required that after the cold rolling reaches the specified stress and cold rolling rate, immediately stop pulling for 2-3, and then relax the steel bar and end the cold rolling, so as to give the steel bar sufficient time to deform.
Cold rolled flat steel can be used as a material for making iron hoops, tools and machine parts. Used as building frame structure and escalator. Flat steel is divided into two types according to its shape: flat steel with flat springs and flat steel with double grooves on one side. Hot-rolled spring flat steel is mainly used in the manufacture of mechanical leaf springs for automobiles, tractors, and railway transportation.
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