Continuous layout rolling mill

In addition to rolling one pass in sequence for each rolling mill, the principle of equal metal flow rate per second per unit time for each rolling mill in the continuous rolling relationship must also be maintained. Due to the continuous arrangement of rolling mills, it is easy to achieve mechanization and automation of the rolling process. Higher rolling speeds can be used, resulting in significant production capacity. The continuous arrangement of rolling mills is the direction of development for various types of rolling mills.

Comparison between horizontal rolling mill and continuous rolling mill:

Horizontal rolling mills, especially rough rolling mills, require multiple passes of rolling, with slow rolling speed and long rolling rhythm. However, due to the small cross-section of the billet, rapid temperature drop of the rolled piece, and large temperature difference between the head and tail, it is necessary to choose a rapid extension pass system as much as possible to minimize the number of rolling passes when given the billet size and finished product specifications. For example, elliptical square and hexagonal square hole types.

The automation level of the horizontal rolling mill is low, and the feeding and flipping of steel in the rolling mill require manual or mechanized operation of auxiliary equipment before and after the rolling mill. Therefore, there are high requirements for biting conditions, clamping force of the pass on the rolled piece, and stability of the rolled piece in the pass. It is necessary to choose the hexagonal square, rhombic square and other pass systems as much as possible.

The continuous bar rolling mill has a large cross-section of the billet and a small spacing between stands. Single pass rolling, temperature drop of the rolled piece, and temperature difference between the head and tail are no longer the main factors affecting steel rolling production and product quality; On the contrary, during high-speed rolling (v ≥ 10m/s), the heat converted from deformation work dominates the temperature change during rolling, resulting in a temperature rise in the rolled piece. Temperature control rolling with intermediate water cooling as the main means and low-temperature rolling with the purpose of energy conservation and consumption reduction are relatively prominent. Therefore, the requirement to minimize rolling passes is far less urgent than that of a horizontal rolling mill.

The continuous bar and wire rolling mill takes improving the operating rate and output of the rolling mill, ensuring the internal and external quality of the billet and the dimensional accuracy of the finished product, and reducing roller consumption and cost as the main means to enhance product market competitiveness. Therefore, it is required to select a pass system with gentle deformation, stable production, and uniform wear of the pass, which are typical features of an elliptical circular pass system.

The range of product specifications for continuous bar and wire rolling mills is wide. In order to use shared and adjusted passes as much as possible, especially for the production of larger specifications from the first few stands of the finishing mill or even the finished products from the middle mill group, it is required to have round holes in front, which correspondingly expands the scope of use of the elliptical circular pass system.

Continuous bar rolling mills have widely used micro tension and loop control technologies. The micro tension control system of the coarse and medium rolling units not only requires relative stability of the cross-section of the rolled pieces in each pass, but also requires relative stability of the working diameter of the rolls, that is, uniform wear of the pass, in order to shorten the adaptive process of the rolling mill and reduce the adjustment frequency of the micro tension control system; In terms of loop control, the setting and operating conditions of the loop are closely related to the shape and size of the rolled piece cross-section. Obviously, compared to other equiaxed rolled pieces with the same cross-sectional area, circular and elliptical rolled pieces have smaller moments of inertia and are easier to assemble. Moreover, their cross-sectional areas are curved, which can reduce the impact of bending of the rolled piece and contact between the looper roller and the rolled piece on the surface quality of the rolled piece during the assembly process. This is more advantageous for alloy steel bars that are sensitive to cracks and use temperature controlled rolling, which is also an important reason for choosing the elliptical circular pass system.

Comparing the advantages and disadvantages of various rolling mill layout forms, this design adopts a fully continuous layout rolling mill.