In the production process of steel rolling, the processing of metal by a rolling mill follows three basic laws. Today we will introduce to you.
1. Volume Invariance Law
We know that the law of constant mass exists objectively in nature, mass = density × volume.
Therefore, it can be seen that in the process of pressure processing, as long as the density of the metal does not change, its volume will not change before and after deformation.
During hot rolling of steel, there is little change in volume before and after processing due to air bubbles, shrinkage or looseness in the slab.
Therefore, in the theoretical research and engineering of metal press working, it is generally believed that the volume of metal is constant before and after deformation.
During cold rolling, the density of the metal is reduced by approximately 0.1% to 0.2%. Obviously, these volume changes are negligible.
2. The law of least resistance
The law of least resistance is a general principle of mechanics.
In the theory of metal plastic deformation, it can be used to analyze the flow law of particles, and can also be used to qualitatively analyze the flow direction of metal particles.
According to Gubkin, when the particles of the deformable body may move in different directions, each particle moves in the direction of least resistance. Because the circumference of a circle is the shortest for the same cross-sectional area, the law of least resistance is also known as the law of least circumference.
Golovin's claim is that there is friction between the contact surface of the tool and the metal.
If the properties of the metal body are uniform and the friction coefficients of the contacting surfaces are exactly the same, the work done by the customer's frictional resistance as the particles flow to the free surface is proportional to the distance of the particle from the contacting surface.
Therefore, the closer to the free boundary, the lower the resistance, and the metal particles must flow in this direction, that is, in the direction of the shortest line of the cross-section.
3 Explanation of the coexistence of elastic-plastic deformation
Metals are made up of polycrystals, with the atoms in each grain oriented differently. Under the action of external force, some grains are in the orientation favorable for deformation, and some are in the orientation unfavorable for deformation.
Therefore, atoms in some grains can move to a new equilibrium position, while atoms in other grains can only move to a distance less than 1/2 the distance between atoms. Therefore, at a certain moment of macroscopic deformation, some atoms must be in an unstable state in the process of moving from one stable position to another.
Once unloaded, these unstable atoms will return to their original stability. Up position, which manifests as a small amount of elastic recovery.
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