The improvement of the dimensional accuracy of rolled products will produce huge economic benefits. Plate and strip is mainly used for punching various parts, so it requires high thickness accuracy and flat shape to improve the life of the die and the accuracy of the stamping parts. In addition to the high requirements for the thickness and shape accuracy of the plate and strip, the surface roughness of the steel plate also has special requirements due to the deep processing of the plate and strip. High-precision rods, wires, profiles and tubes can reduce the amount of workpiece cutting. Therefore, the high precision ratio of rolled products is one of the important trends in the development of rolling technology.
China has done a lot of research and development work in high-precision rolling technology. On the one hand, it has digested and studied the imported high-precision rolling technology. On this basis, combined with the actual situation of our country, it has developed some basic theories and practical advanced technologies and equipment to improve the accuracy of products, some of which have reached or exceeded the advanced level of foreign countries. But in general, due to the backward level of technology and equipment of China's iron and steel enterprises, the gap between high-precision rolling technology and foreign developed countries is still large, and more than 90% of China's existing rolling mills are still not up to the advanced level of foreign countries. Therefore, it is urgent for the development of China's iron and steel industry to improve the high precision ratio of our products. The biggest advantage of high-precision rolling is to save steel, which can improve the utilization rate of steel by 1 ~ 5%.
Section 1
hot rolled strip technology
The traditional tropical mill with its variety of specifications, high quality advantages, still occupy the automotive, home appliances, coating, high quality welded pipe and other high quality requirements of the sheet market, its new technology is mainly:
(1) The direct hot loading (DHCR) and direct rolling (HDR) of continuous casting billets realize the continuity between the two processes, with a series of advantages such as energy saving, investment saving and shortening the delivery time, and the effect is remarkable;
(2) online width adjustment, the use of heavy vertical rollers, fixed width press to achieve large side pressure, heavy vertical rollers per pass width under the amount of pressure is generally 150mm, fixed width press per pass width under the amount of pressure up to 350mm or more;
(3) Automatic width control (AWC), the width accuracy can reach less than 5mm;
(4) Hydraulic automatic thickness control (AGC), the thickness accuracy of the full length of the strip has reached ± 30μm;
(5) shape control, developed HC, CVC, PC and many other models and shape instrument, can realize the closed-loop control of shape;
(6) controlled rolling and controlled cooling, so that the steel has the required microstructure and better mechanical properties;
(7) Coil plate box and heat preservation cover to reduce the temperature drop and reduce the temperature difference between the head and tail of the strip;
(8) full hydraulic coiler, roll, hydraulic expansion and contraction using step control, multi-stage drum expansion and contraction;
(9) endless rolling, the strip after rough rolling is welded on the middle roller, and the whole endless continuous rolling is realized in the finishing mill.
Section II
Cold-rolled strip and coating technology
Cold rolled strip and its coating products are widely used in construction, automobile, household appliances, transportation and other industries, especially the coating plate still maintains a strong growth momentum. Its technological development is mainly manifested in:
(1) The combination of pickling and cold rolling can increase the yield by 1 ~ 3%, increase the hourly output by 30 ~ 50%, reduce the intermediate warehouse by 5000~10000 m2, reduce the consumption of rolls by 40 ~ 50%, and reduce the production cost and construction investment;
(2) continuous annealing, its product quality is high, good plate shape, smooth surface, uniform performance, can improve the yield of 1 ~ 3%, steel diversification, energy saving more than 20%, the production cycle is shortened from 10 days to less than 1 day, the equipment occupies a small area;
(3) All-hydrogen bell-type annealing, which is "times more efficient than traditional bell-type furnaces, has good deep-drawing properties and smooth surface, and is especially suitable for producing cold-rolled coils with small batches and many varieties;
(4) The shape control technology has developed greatly, with the widespread use of hydraulic bending rolls, process lubrication and cooling, and closed-loop control, and the development of a number of new rolling mills that can effectively control the shape of the plate;
(5) Hot-dip galvanized, hot-dip galvanized aluminum and zinc-iron alloy, electro-galvanized, electro-galvanized nickel, fingerprint-resistant plate, organic coating plate, damping plate, electroplating tin, low nickel tin plating, electroplating chromium, hot-dip lead, hot-dip lead tin and other coating production technology has made great progress.
Section III
section steel rolling mill technology
Since the 1980 s, the development of steel production equipment has been relatively slow compared to strip mills. Although the mill structure has been greatly improved, such as the development of cantilever CL mill, short stress line high stiffness HS mill, short stress line universal mill, but there is no completely new type of steel mill, rolling speed increase is not big. The new development of steel production equipment mainly lies in:
(1) Direct hot loading of continuous casting billets;
(2) the application of near net shape continuous casting billet;
(3) The development of flexible rolling equipment, has been put into production a variety of flexible rolling capacity of the new type of steel mill unit, the development of H-beam free size rolling, extended pass non-hole rolling, multi-roll universal pass rolling and other flexible rolling new technology;
(4) The popularization and application of split rolling technology, widely used split roller and split wheel equipment, has the advantages of increasing production, reducing passes, reducing energy consumption and roll consumption;
(5) Tight tolerance precision rolling equipment, its product tolerance range can be controlled in the international general standard 1/4~1/10, the use of small roll diameter, short roll body and single-hole type roll, high stiffness, compact rolling mill, flat and vertical alternating arrangement of 2~3 pass, small reduction, which is the basic characteristics of precision rolling equipment;
(6) the application of low temperature rolling, temperature control rolling and on-line heat treatment, comprehensive energy saving up to 20%, and greatly improve the performance of steel;
(7) Modern finishing equipment, finishing equipment to achieve continuous, automated, such as stepping rack cooling bed, continuous cutting length (CCL) unit, cantilever structure of single straightening equipment;
(8) equipment condition diagnosis technology, monitoring equipment operation status, timely maintenance.
Section IV
wire rod rolling mill technology
In the mid -1960 s, Morgan 450 the development and application of non-twisted finishing mill and loose coil control cooling device, which enabled the rolling speed of wire rod mill to exceed 40 m/s. At present, the highest design speed is 140 m/s, the guaranteed value is 115 m/s, and the dimensional accuracy of the product can reach +/-0.1mm. Among them, the new technical equipment mainly includes:
(1) The high-pressure sizing mill (IRSM) is used as a pre-finishing mill, consisting of 3 stands, and its reduction rate ranges from 6 to 25%;
(2) Double-module high-speed finishing mill (TMB), with a total of 12 stands, this transverse double-module finishing mill can greatly save time for changing stands, its utilization coefficient can reach more than 90%, and the product has high precision and good surface quality;
(3)V-shaped micro-mill, using Morgan's sixth generation V-shaped finishing roll box structure to form a micro-modular mill, can expand the range of product specifications, improve capacity, its compact structure, easy roll change, high utilization rate;
(4) The reducing and sizing mill (RSM) can be moved out and in from the rolling line separately. After being arranged in the non-torsion finishing mill unit, the final rolling speed is increased, the productivity is increased by more than 15%, the utilization rate of the mill is increased by 5-10%, the product precision is high, the tolerance is 0.1mm, the ellipticity is 0.1, and the free size rolling is realized, and the free sizing range is 0.3mm, the metallurgical performance can also be improved by water cooling in front of the machine;
(5) Rolling profile measuring instrument and hot online diameter measurement and eddy current flaw detection;
(6) Rotary high-speed cutting head (tail) flying shear;
(7) Tilt laying machine and coil collection system equipped with coil distributor;
(8) Controlled rolling and controlled cooling devices are becoming more and more perfect.
Section V
Seamless tube rolling technology
Seamless steel pipe is developing in the direction of high alloying, high precision and high quality. The development of its production equipment and technology is mainly manifested in:(1) The popularization and application of continuous casting tube billet, whose diameter range is Φ80~560mm, and its internal quality and dimensional tolerance are better than those of rolled tube billet. Basically, it can be rolled directly without grinding. The metal yield can be increased by 10 ~ 15% and energy saving by 40 ~ 50%, the cost of tube blank is reduced by 20 ~ 25%;
(2) The conical roller perforator adopts large feeding angle and rolling angle perforation, which improves the perforation efficiency and the expansion ratio can reach 1.4~2;
(3) Restricted (semi-restricted) mandrel pipe rolling mill has become the mainstream of seamless pipe production equipment and is suitable for the requirements of high output and large batch. Its product diameter is up to Φ426mm, length is 50m, single machine output is up to 80~1 million t/a, outer diameter tolerance is up to 0.2~0.4, wall thickness deviation is 3.0~6.5, inner wall is smooth, tool consumption is low, and steel pipe cooling is low, the reheating furnace before sizing can be canceled. The newly developed three-roll adjustable limited mandrel pipe mill (PQF) can roll high-strength and thinner steel pipes, and the head and tail can be pre-pressed to reduce pipe end thickening;
(4) The reducing machine adopts an online wall thickness detector to automatically control the wall thickness distribution in the length direction of the steel pipe;
(5) On-line heat treatment (quenching and regularization) has been widely used in production;
(6) On-line detection means and finishing equipment continue to improve.
Section VI
Key points of hot rolling mill operation
When the hot rolling mill is running, the starting speed must be controlled well, because it has a very important influence on the high efficiency of the whole rolling mill. What I don't want to see is that the starting speed of the hot rolling mill is slow when it is running accurately, which not only affects the work efficiency, but also causes the force between the blank or rolled piece and the roll to fail to reach a good state.
The slow start-up speed of the hot rolling mill indicates that it has obvious shortcomings in performance. If the speed of the machine is not effectively improved, then the production efficiency of the blank or rolled piece will become lower and lower. If the rapid overload start is not possible, the rolling speed of the larger billet will be too slow.
In order to reduce the occurrence of similar phenomena, before the hot rolling mill starts to run, it should first check its motor power, rolling speed, product specifications, pass technology, etc., to ensure that the amount of blank reproduction will not exceed the bearing capacity of the equipment, otherwise it will cause the equipment to start slower.
Secondly, it is necessary to check the bearings of the hot rolling mill to observe whether the lubrication is good. If the lubrication is not enough, the pneumatic speed of the hot rolling mill will slow down, causing a series of adverse consequences. If there are no problems in these two aspects, the hot rolling mill can basically start normally.
In addition to the slow start-up speed of the hot rolling mill, the finished products it produces sometimes have deviations. There are many reasons for this consequence. Even the size of the products rolled by the same hot rolling mill will be uneven. However, it also shows that either the roll gap is unreasonable or the pass process is incorrect.
In order to reduce the deviation of the product size of the hot rolling mill, it is necessary to strictly abide by the product rolling process, especially the on-line adjustment of the bar is required to be carried out according to the standard, and the negative deviation rolling is within the scope of the internal control standard.
Section VII
Parameters setting of rolling mill speed, over-steel rate, roll diameter, etc.
Whether it is for cold rolling mill or hot rolling mill, the speed and over-steel rate are important technical indicators of equipment, which seriously affect the rolling pass and consumption index of rolling mill products. However, when these two parameters are kept constant, the motion state of the rolling mill roll is stable, so the rolling pass and consumption mentioned above depend on the size of the blank.
At present, the rolling speed of the rolling mill is mostly one or two kinds of small-size wire rod final rolling speed selected below the guaranteed rolling speed, mainly the production efficiency of the rolling mill and the accuracy of the rolling mill products, etc. What are the factors related to these two aspects?
If the roll diameter of the rolling mill configuration is too large, it will cause a large number of impacts and a large roll working surface to reduce productivity. However, the roll diameter is too small, there will be the same consequences, because the impact force is too large and the wear seriously affects productivity.
The rolling speed range allowed by the rolling mill includes the maximum speed of the motor, the speed when the roller is the minimum diameter and the motor is the basic speed, and the speed when the roller is the maximum diameter. These speeds should be controlled within a reasonable range to reduce the negative impact on the rolling mill.
Because the rolling speed is too fast, the rolling piece will be easily deformed due to the number of impacts. In order to ensure the rolling speed, it is necessary to leave the rolling speed with the allowance of looper adjustment when the roll diameter is the minimum. The roll diameter of the rolling mill needs to be adjusted according to the rolling piece, rolling speed, and product specifications, and the product accuracy obtained on this basis will be more uniform.
This is the speed of the mill, the rate of steel and roll diameter configuration need to consider the factors, but the ultimate goal is to be able to normal and stable rolling mill quality products.