The laminating (rolling) process

The laminating process

Lamination means a process applied to alloys metal, plastics and other materials, consistent in subjecting the material to the constriction action by a machine called a rolling mill, made up of two conjugated cylinders [fig.1] rotating in the opposite direction with the same peripheral speed, so that the material is forced to assume a section corresponding to the free light that remains among the cylinders themselves.

Execution of a flat rolling between cylinders with a predefined light and an example of lamination
Fig.1 Execution of a flat rolling between cylinders with a predefined light and an example of lamination

Through lamination, the material is subjected to a progressive process elongation and a reduction in cross-section between cylinders of the rolling mill, which are flat or suitably shaped [fig.2]. It should be noted that, unlike what happens in processing drawing and extrusion, in lamination the mass of material occupying the central area of ​​the starting blank moves more slowly than the peripheral one. Lamination is a widely used procedure for producing building and industrial elements.

Examples of flat and shaped cylinders; in the figure the succession of "passes" for the production of a profile.
Fig.2 Examples of flat and shaped cylinders; in the figure the succession of “passes” for the production of a profile.

Lamination of steel

Steel rolling can be hot or cold. Hot rolling is the most widespread system. The steel, before being passed to the rolling mill, is heated to a temperature of 1100 ÷ 1300 °C, in order to increase its plasticity and therefore workability, and it comes out before the temperature has dropped below 800 °C. Cold rolling causes a hardening of the material due to the deformation and the crushing of the crystalline grains, due to the mechanical action of the rollers. Once the lamination has been completed, the material is annealed, to bring it back to its initial characteristics. Cold rolling produces products with better mechanical characteristics and greater dimensional accuracy.

Lamination of metal alloys

The rolling of metal alloys makes it possible to produce sheets, strips, rods, rods for reinforced concrete and profiles [fig. 2] of various sections. Lamination is carried out continuously and produces finished elements, ready for subsequent operations (molding, drawing, etc.).

The rolling of metal alloys can be performed cold: in this case slight deformations due to work hardening of the material may occur, but surfaces that are well finished and free from oxidation are obtained. In order to avoid anomalous internal deformations and tensions, it can be carried out hot, at higher temperatures, the lower the pressure which one wants to subject the material being processed. The surface quality of the laminates depends on the accuracy of the individual operations: if it is insufficient, defects such as embedding, folding, wrinkles or scratches may appear.

Particular uses of lamination

Lamination can also be used for very special purposes, such as the plating of a metal with a more precious one; in this case the strong pressure exerted by the cylinders makes “Anchoring” the sheets of the two different materials together through the interpenetration of superficial microasperities.

Work hardening
Increased mechanical properties, sometimes accompanied by a decrease in toughness, obtained with a cold plastic processing.

Wire rod
Iron rod or steel that serves as a basis for further processing.

Roll mill cylinders
The rollers of the rolling mill are made of steel or cast iron and their surface must have a very high hardness and a great resistance to wear.