Principles of rolling mill selection
The main basis for the selection of the rolling mill is the steel grade, product variety and specification, the size of the production scale and the product production process determined by the workshop.
When choosing a rolling mill, generally pay attention to the following principles:
1) Under the premise of concealing the product plan, make the rolling mill composition reasonable and compact;
2) High production efficiency and equipment utilization factor;
3) Guarantee to obtain products of good quality, taking into account the possibility of producing new products;
4) Conducive to the realization of mechanization and automation of rolling mills, and help to improve the working conditions of workers;
5) The structure of the rolling mill is advanced and reasonable, easy to manufacture, simple to operate and easy to maintain;
6) The replacement of spare parts is easy, and it is conducive to the standardization of spare parts;
7) Have good comprehensive technical and economic indicators.
For wire and bar mills, steel pipe mills, and steel plate mills, in addition to a certain strength, sufficient stiffness is also required to ensure the correct geometry and precise dimensions of these rolled products. Therefore, in addition to following the above general principles when selecting a rolling mill, the structural type, main technical parameters and their layout of the rolling mill should be determined according to the production characteristics and specific requirements of different products based on the process requirements of the product.
Comparison of Mill Arrangement Options
1.open train mill
open train mill , especially roughing mills, require multiple passes, slow rolling speeds and long rolling rhythms. However, the section of the billet is small, the temperature drop of the rolled piece is fast, and the temperature difference between the head and the tail is large. When the size of the billet and the specification of the finished product are given, in order to minimize the number of rolling passes, it is necessary to use a rapid extension pass system as much as possible. Such as ellipse-square, hexagonal-square hole type. For a rolling mill arranged in a row, the rotating speed of the rolls in the same row is the same, and the rolling speed does not increase with the increase of the length of the rolling stock, so the output is small, the labor productivity of the rolling mill is low, and the quality of the rolled products is also poor, and it is difficult to achieve automatic control. Abroad has been eliminated. This is an important disadvantage of rolling mills arranged in tandem.
2.In-line arrangement of rolling mills
Using the tracking rolling method, each rolling mill only rolls one pass, and each rolling mill has different rolling speeds, which can increase the rolling speed with the increase of the length of the rolling stock, so it has higher productivity. Each rolling mill only rolls one pass, the roll L/D=1.5～2.5, the stand mostly adopts closed type, high rigidity, high product precision, no continuous rolling, each stand does not affect each other, and it is easy to adjust.
However, the length of the rolling stock increases with the increase of the number of passes. The distance between the stands also increases with the length of the rolling stock. Therefore, the rolling mills arranged in parallel have a longer workshop, which leads to an increase in the floor space and investment of the workshop, so it is only suitable for the production of steel with larger cross-sectional dimensions, or for rough rolling mills in other layouts.
3.rolling mill in continuous arrangement
In addition to rolling one step in sequence for each frame, the principle of equal flow of metal per second per unit time of each frame of the continuous rolling relationship must also be maintained. The mechanization and automation of the rolling process is easy to achieve due to the continuous arrangement of the rolling mill. Higher rolling speeds can be used, resulting in great productivity. Continuously arranged rolling mills are the development direction of various types of rolling mills.
Comparison of open train mill and Continuous Mills:
Tandem rolling mills, especially roughing mills, require multiple passes, slow rolling speeds and long rolling rhythms. However, the section of the billet is small, the temperature drop of the rolled piece is fast, and the temperature difference between the head and the tail is large. When the size of the billet and the specification of the finished product are given, in order to minimize the number of rolling passes, it is necessary to use a rapid extension pass system as much as possible. Such as ellipse-square, hexagonal-square hole type.
The automation degree of the tandem rolling mill is low, and the feeding and turning of the rolling mill need to be done manually or mechanized with auxiliary equipment before and after the rolling mill. Therefore, the requirements for the bite conditions, the clamping force of the pass to the rolling piece, and the stability of the rolling piece in the pass are high, and the pass system such as hexagonal-square and diamond-square should be selected as much as possible.
The billet section of the continuous bar rolling mill is large and the stand spacing is small. On the contrary, during high-speed rolling (v≥10m/s), the heat transformed by deformation work dominates the rolling temperature change, and the temperature of the rolled piece rises. The temperature-controlled rolling with intermediate water cooling as the main method and the low-temperature rolling with the purpose of energy saving and consumption reduction are relatively prominent. Therefore, the requirement to reduce the number of rolling passes as much as possible is far less urgent than that of the tandem rolling mill.
Continuous bar and wire rolling mills take improving mill operation rate and output, ensuring internal and external quality of billets and finished product dimensional accuracy, and reducing roll consumption and costs as the main means to enhance product market competitiveness. Therefore, the selected pass system is required to have soft deformation, stable production and uniform pass wear, which are the typical characteristics of the elliptical-circular pass system.
Continuous bar and wire rod mills have a wide range of product specifications, and try to use common pass and adjustment pass. Especially in the production of larger specifications, the finished products can be produced from the first few stands of the finishing mill or even from the middle mill, so the round holes are required to be placed in front, which also correspondingly expands the application range of the oval-round pass system.
Micro tension and looper control techniques have been widely used in continuous bar mills. The micro-tension control system of the roughing and intermediate rolling mills requires not only a relatively stable section of each pass, but also a relatively stable working diameter of the rolls. That is to say, the wear of the pass is required to be uniform, thereby shortening the self-adaptation process of the rolling mill and reducing the adjustment frequency of the micro-tension control system. As far as looper control is concerned, the setting of the looper and its working conditions are closely related to the shape and size of the section of the rolling stock. Obviously, compared with other equiaxed rolling pieces of the same cross-sectional area, the circular and elliptical rolling pieces have a smaller moment of inertia and are easier to complete sets, and the perimeter of their cross-sections is arc-shaped. It can reduce the influence of the bending of the rolling piece and the contact between the looper roll and the rolling piece on the surface quality of the rolling piece during the complete set process. This is more beneficial to alloy steel bars that are sensitive to cracks and temperature-controlled rolling, and these are also important reasons for choosing the elliptical-round pass system.
Comparing the advantages and disadvantages of each rolling mill arrangement, this design adopts a fully continuous arrangement of rolling mills.
4.Determination of the number of rolling mill stands
For a continuous rolling mill with only one pass per stand, it is relatively easy to determine the number of stands. Because the number of stands is generally not less than the number of rolling passes, the number of stands can be determined as long as the rolling passes are known.
The number of rolling passes and stands can be determined by the following formula:
Select the number of racks as 18.
In the production of large-sized products, the number of passes (empty passes) can be thrown away, reducing the number of rolling passes.
To sum up, the cantilever mill for thick and short stress line rolling, short stress line rolling mill for medium and finishing rolling can be used, and the whole line is fully continuous. The specific specifications are shown in Table
rolling stand | layout | Mill structure |
1#~6# | Alternate horizontal/vertical arrangement | Cantilever Mill |
7#~12~ | Alternate horizontal/vertical arrangement | Chuck-type stand, four-tie rod mechanism short stress line rolling mill |
13#~18# | Horizontal/vertical alternate arrangement (14#, 16#, 18# racks are horizontal/vertical convertible racks). | Chuck-type stand, four-tie rod mechanism short stress line rolling mill |
Rolling is divided into three parts: rough, medium and finishing. A rolling mill with alternating horizontal and vertical rolls is adopted, so that the rolling stock can be twisted in the rolling mill, which can improve the bite and reduce the occurrence of accidents.
The structure of the rolling mill is mainly distinguished by the number, configuration and size of the rolls, which are as follows:
(1) Two-roll mill
(2) Three-roll mill
(3) Four-high rolling mill and multi-stand continuous rolling
(4) Multi-roll mill
(5) Composite multi-roll mill
(6) Universal rolling mill
According to the requirements of this design, due to the full continuous rolling production, all the rolling mills are arranged alternately with two-high rolling mills, which can improve the bite and reduce the occurrence of accidents.
