What is Cold Drawing of Steel? Cold drawing is to forcibly stretch the steel bar under normal temperature conditions to exceed the tensile stress of the original steel yield point strength, so that the steel bar produces plastic deformation to improve the strength of the steel yield point and save steel for the purpose.
What is Cold Drawing of Steel
Cold drawing produces cold tensile strengthening effect: the tensile stress exceeds the yield strength of the steel after unloading. The yield strength of the steel will be increased to the unloading stress level.
Cold drawing effect: the yield strength of steel can be increased by 20% ~ 30% after cold support. And it has the effect of removing rust and straightening. But the plasticity of steel decreases after cold support. And the strength yield ratio of the steel bar is reduced. Because the design strength of mild steel is equal to the yield strength, cold drawing improves the design strength. But the compressive strength of steel bar does not change after cold drawing, so this production step reduces the strength yield ratio of steel bar. At the same time, it also reduces the plastic deformation performance of steel bars.
Cold-Draw Equipment
Electric winch: The traction force of the general electric hoist is 29 ~ 49kN, the drum diameter is 350 ~ 450mm. And the drum speed is 6 ~ 8r/min.
Block and return block: The number and tonnage of the doors of the cold pulley block are generally 3 ~ 8 doors and 150 ~ 500kW. The number of doors and tonnage of the return block, when the cold pull and the return use the same hoist, with the reverse and reverse rotation of the drum to achieve the return, the number of doors and the cold pull block are the same. When the special hoist is used to achieve the return journey. It is generally used 2 ~ 3 doors, 30 ~ 50kN.
Cold Drawing Fixture
The cold drawing fixture is a tool for clamping steel bars, which requires strong clamping force, safe and reliable, durable and easy to operate. Commonly used clips have:
(1) Wedge fixture. The fixture is made of high quality carbon steel, which is suitable for cold drawing steel bar with diameter below 14mm.
(2) Eccentric fixture. Made of high quality carbon steel, it is suitable for cold drawing I class disk round bar.
(3) Slot fixture. There is no fixed form and specifications, depending on the site conditions. It is suitable for cold drawing steel bar with screw or upsetting head at both ends. In addition, there are crescent fixture and conical tooth plate clamp and other forms.
When cold drawing, only the cold drawing rate or cold drawing stress control is called single control, and when cold drawing, the cold drawing rate and cold drawing stress are applied simultaneously, which is called double control. Using single control, the construction is simple and convenient. However, for steel bars with uneven materials, it is impossible to test root by root (root by root test, labor and material costs, it is impossible to do so. And some of the same steel bar cold drawing rate is not the same) cold drawing quality is not guaranteed. Dual control method can avoid the above problems.
When cold drawing, if the control stress has been reached and the cold drawing rate has not exceeded the allowable value, it can be considered qualified. However, if the cold tensile rate has been reached, and the cold tensile stress has not reached the control stress, the steel bar should be used to reduce the strength. Dual control method must be adopted for prestressed reinforcement.
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