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Development history of thin slab continuous casting and rolling technology in China
From the technical characteristics and industrial application, the development process of thin slab continuous casting and rolling in China can be divided into four stages.
The first stage: 1984-1999, the introduction period.
From 1975 to 1985, the Ministry of Science and Technology determined the technical research work of thin slab continuous casting and rolling, and opened the development process of thin slab continuous casting in China.
Guangzhou Zhujiang Steel CSP and put into use the first domestic production line; Zhujiang Steel, Baotou Steel, Handan Iron and Steel introduced the SMS technology in Germany, was in the process of rapid development of steel industry, steel demand to a large number of cases under Thin slab continuous casting and rolling can play a certain role.
The second stage: from 2002 to 2008, nine thin slab continuous casting and rolling projects were constructed, including 26 continuous casting machines, with a single line output of 3 million tons.
The third stage: After 2008, the period of stable development. During this period, the basic configuration of thin slab continuous casting and rolling was basically determined, and the main equipment was basically stable. Among them, China carried out related research on high-quality special steel and silicon steel, and realized industrialization to a certain extent.
The fourth stage: the current research and application of the ESP production line and ESP technology for endless rolling.Rizhao Steel Holding Group Co., Ltd., the first company to introduce the Prius special metallurgy Technology Co., Ltd. ESP endless casting and rolling strip steel production lines of the company, the first single ESP market and delivered to users in May 2015, its ESP Headless rolling production line, design steel grades including low carbon steel, medium carbon steel, IF steel, HSLA, DP dual phase steel, the specifications of some products are as follows:
The traditional strip hot strip rolling mill is produced by rolling a single intermediate billet. Therefore, it is inevitable to pass through the belt, accelerate the rolling, reduce the rolling, throw the steel, and the tail. After a series of processes, the resulting dimensional tolerances and mechanical properties are difficult to resolve within the original process framework. The new technology of hot rolling with endless rolling is an important technological breakthrough to solve these problems.
Currently, there are two types of tropical endless rolling technology:
First, in the conventional hot rolling line, the high-temperature intermediate strip after rough rolling is rapidly connected between the rough rolling and the finishing rolling in a few seconds, and the endless rolling is realized in the finishing rolling process;
The second is the headless continuous casting and rolling technology (ESP technology). ESP technology can be regarded as the most representative cutting-edge technology in the headless rolling produced by the continuous development and upgrading of thin slab continuous casting and rolling technology.
Next, explain the process without a head casting and rolling technology (ESP technology).
Preparation before pouring a continuous casting machine
The intermediate tank that has been repaired and dried in the drying station is transported by crane to the intermediate tanker on the pouring platform, and then the intermediate tank is baked to 1100 Â° C by the baking station on the platform, and the immersion nozzle is baked to about 1250 Â° C. .
Turn on the crystallizer cooling water, secondary cold water, compressed air, equipment cooling water, hydraulic pressure, lubrication and other systems to make it in a normal state.
The spindle rod is sent to a suitable position in the crystallizer, and the spindle head is stoppered in the crystallizer, and the scrap scrap for cooling is filled.
2 caster casting operation
The molten steel entering the intermediate tank through the ladle is opened when the liquid level reaches a certain height, and the molten steel is injected into the crystallizer through the immersion nozzle.
When the molten steel rises to the specified drawing position in the crystallizer, the "casting" button on the operating box is activated, and the segment driving roller starts the drawing at a predetermined starting speed. At the same time, the crystallizer vibrating device, the two cold spray water, and the second cold room exhaust steam fan are simultaneously started.
The slab which has solidified into a solid shell with a liquid core in the crystallizer is pulled away from the lower mouth of the crystallizer by the spindle, and moves downward through the foot roll, the curved section and the curved section. At this time, the cooling water and the compressed air are atomized. The cooling water is sprayed directly onto the slab for cooling. The curved slab is straightened into the straightening section and then enters the horizontal section.
After the slab is out of the horizontal section and the roughing mill, the slab is separated from the spindle by shearing shearing, and the spindle is quickly sent to the spindle storage device. The continuous casting slab separated from the spindle is sent to the rolling mill at the rear.
3 continuous rolling
Headless rolling mode
Large reduction rolling the slab after rolling to a thickness of 8mm -20mm the headless intermediate blank. The headless intermediate blank is transported to the induction heating furnace via a roller belt with a heat shield which heats the headless intermediate blank to a desired temperature of about 1200 Â° C in an efficient, accurate, dynamic online and flexible manner. A pinch roller descaling box is arranged after the induction heating furnace. After the descaling, the headless intermediate billet enters the finishing mill and is rolled into a strip of the target thickness. The strip is cooled by the output roller and laminar to obtain the desired microstructure. At the end of the output roller, before the coiler, the high-speed flying shears wind the endless strip and then take it up on the underground coiler.
Semi-headless rolling mode
Thickness in excess of 1 mm for hot strip, with the rotation or pendulum shears shears silk gauze will be segmented intermediate material produced according to the size of a single coil, whereby ESP line into the semi-endless rolling mode. The split intermediate blank will accelerate forward to slightly open the head of the next intermediate blank. The intermediate billet which is divided into single-roll specifications is heated, descaled and put into the finishing mill to be rolled into the finished product specification, and then cooled by laminar flow to obtain a strip with uniform microstructure and good machinability. Finally, the underground coiler is rolled into a steel coil.
Other endless rolling technologies that are currently popular
1. Headless rolling technology on conventional hot rolling line
In the conventional hot rolling line, the rough stripped intermediate strip is quickly connected between the rough rolling and the finishing rolling in a few seconds, and the endless rolling is performed in the finishing rolling mill, and the laminar cooling is performed. The flying shear after the wire is wound into a hot coil by a coiler.
2.JFE and Nippon Steel Tropical Headless Rolling Technology
In 1996, Japan JFE Corporation Chiba Plant successfully developed induction welding as the intermediate strip connection method after rough rolling. This method requires rapid heating of the strip joint zone to form a hot melt zone to achieve butt weld connection. After the production of the endless rolling production line, it has achieved remarkable results in improving the production efficiency and finished product rate of the hot-rolled strip and the thickness of the plate-shaped plate, reducing the roll consumption, and expanding the thin and wide specification varieties, and has produced significant impact in the international metallurgical industry. influences.
3. Pohang Steel Tropical Headless Rolling TechnologyIn early 2007, South Korea's Posco and Mitsubishi-Hitachi jointly developed a headless rolling technology for the successful hot rolling of intermediate strips, which is the use of cutting head flying shears to complete the instantaneous solid connection of the strip.
For the development direction of thin slab continuous casting and rolling
First, the characteristics of the thin slab continuous casting and rolling process itself are utilized to achieve continuous production.
Studies have shown that for single billet rolling, as the thickness is reduced, the accident rate of production increases abruptly, but there is no such problem with headless rolling. Especially for extremely thin and wide specifications, there is almost no way to produce a traditional process.
However, if thin slab continuous casting and rolling is used, the continuously cast billet is originally a complete billet, so thin slab continuous casting and rolling has unique conditions for continuous production. This is why ESP technology is widely used around the world.
Therefore, in the future, the development of thin slab continuous casting and rolling should be continuous production, that is, endless rolling. Of course, there are many process configurations and technologies for achieving endless rolling, and how to achieve better implementation is still under discussion.
The second is to give full play to the characteristics of thin slab continuous casting and rolling, and develop competitive products.
The rapid solidification of thin slab continuous casting and rolling makes the product less segregation and more uniform as-cast structure. This advantage is very beneficial for the production of special steel products with more complex components.
At present, China has developed a series of products in high-quality special steel, high-strength steel, silicon steel and thin gauge products, and has entered the market. However, there is still a lot of work to be done in the future, such as high-grade silicon steel.
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