Rolling of long products - Rolls, sizing, defects

The surface condition of the cylinders plays an important role because it partly guarantees the quality of the products. Furthermore, fluting, which requires complex internal transformations of the product, must be carried out properly and requires the skills of the roller and calibrator.

During rolling, the cross-section of the product is gradually reduced by passing through several successive grooves (passes) until the desired finished product is obtained. These grooves are machined into the cylinders mounted in the cages.

At the entrance to each pass, tools ensure that the product is positioned correctly in relation to the grooves machined on the cylinders. The product is also guided at the exit.

The sequence of grooves used to transition from the initial bloom to the finished product is called "calibration" or "rolling descent." The definition of this calibration is the key point in the rolling of long products.

To ensure the quality of the finished product, it is important that the surface condition of the cylinders and tools is controlled, that the rolling descent is well designed, and that the cage settings are regularly adjusted, particularly in relation to tool wear.

Various types of defects (surface, geometry, etc.) can be observed on products coming out of the rolling mill. They are caused either by incorrect adjustment of the mill or by pre-existing defects in the semi-finished products (blooms or ingots). It is important to understand these defects in order to prevent them from occurring, as they are very often unacceptable.

Surface defects observed on rolled products appear during rolling, or result from either incorrect mill settings or pre-existing defects in the semi-finished products (blooms or ingots). To prevent these defects from being transferred to the finishing mill, the semi-finished products can be inspected and repaired if necessary (usually by grinding or cutting away the defective parts).

This article specifies the stresses experienced by cylinders and tools. It then presents the different grooves and finally describes the defects found on products and how to remedy them.

To supplement this article, other aspects of long product rolling are discussed in:

• [M 7 900]  Rolling of long products. Definitions and parameters;