Drawing concept: to save steel, steel for the purpose of improving the yield strength, with more than the yield strength and less than the ultimate strength tensile stress tensile steel, the plastic deformation of the practice thatdrawing.

In 1 the first cold effect:

A reinforced applied tensile stress of the steel bar cold drawn, deformation will occur (and stress -- strain diagram).With the increase of steel tensile stress, tensile stress increases. When the steel internal stresses exceed the yield point of the reinforcement with A, to C, to stop cold, remove the load. This time we can see, steel has plastic deformation, in the unloading process, stress -- strain map to have a change, linear O1C slower than line OA.

2 second cold effect:

Re applied tensile stress, the reinforcing bar tension to failure, changes in stress -- strain diagram appears new,near the yield point of the new points in the C, significantly higher than the original yield point A. This change shows that, changes of plastic steel, plastic small, high hardness, the strength of the reinforcing bar is improved, thisphenomenon is called "deformation hardening".

After more than two times of cold drawn steel (rebar) completed.

Cold drawing control on different situations:

1) cold stress control:

For the reinforced II, III, IV grade steel and 5 steel, in the cold, for prestressed reinforced use, must use cold stress control. But after cold drawing steel after inspection, the maximum tension rate exceeds the standard value (Table 3-- 1), and then to the mechanical experiment.

2) drawing rate measurement control requirements:

Control drawing to cold pull rate, control values to be determined by the test. Requirements: the same test furnace by the same batch of specimen, not less than 4, each specimen by the rules and regulations of cold stress determination corresponding cold pull rate, and take the average of the specimen as the actual drawing the furnacethe reinforcement ratio. If the strength of steel, cold high, average rate of less than 1%, in the cold drawn steel, are still on the 1% cold pull rate control.

3) cold drawing control different heats:

For hybrid, confuse reinforced, batch of cold drawn, cannot use cold pull rate control, but also to drawing a plurality of connection, each cold pull rate and the control stress must conform to the rules and regulations (3 -- 1).

4) cold drawing speed control:

To make steel fully deformation, we should properly control the cold drawing speed, generally 0.5 -- 1 is appropriate.At the same time, cold drawn to the specified shall force and cold draw ratio, then pulled up the 2 -- 3, and then relax the steel, cold drawn steel end, to give sufficient deformation time.

5) cold drawing control method:

Cold drawn only when tension rate or cold stress control called the single control, during cold drawn and cold stress at the same time application, called the dual control. Using a single control, simple and convenient construction. But for the reinforced material is not uniform, not by the root test (one test, labour and material consuming, not possible to do so, some with a reinforced cold pull rate are not the same) drawing quality can not be guaranteed. Double control method can avoid these problems. Cold, to control the stress has been reached, cold pull rate did not exceed the allowable value, can be considered qualified. However, if the tension rate has been reached, and cold stress is not up to the control stress, this kind of steel to reduce the intensity of use. For prestressed must adopt the double control method.