The production process of hot rolled strip steel mainly controls the process of billet preparation, heating, descaling, rough rolling, head cutting, finishing, cooling, coiling and finishing.
Hot-rolled strip billets are generally continuous cast slabs or primary rolled slabs, chemical composition, dimensional tolerances, curvature and end shapes should meet the requirements, for cold loaded billets should be checked, for hot loaded billets should provide defect-free billets, i.e. the surface should not have defects visible to the naked eye, there should be no internal shrinkage, loosening and segregation, etc.
Heating mainly controls the heating temperature, time, speed and temperature regime (including preheating section, heating section and even heating section temperature). Prevent overheating, over-burning, oxidation, decarburisation or sticking of the steel. It is preferable to use a step-heating furnace, which is beneficial for the surface quality.
The devices for descaling are flat roll descaling machines, vertical roll descaling machines and high-pressure water descaling boxes. It is widely used to remove the iron oxide skin by rolling the edges with vertical rolls and then using high pressure water (10-15 MPa).
The role of rough rolling is to compress and extend the billet to provide the finishing roll with a billet of the required size and plate shape. The rough rolling process should be controlled by setting the amount and speed of each pass of pressing down, increasing the output temperature of the rough rolling unit as much as possible, and ensuring the thickness and width of the rough rolling billet. In order to shorten the distance between stands, the last two stands of the roughing mill set are arranged in a continuous manner.
Cutting head is to remove the head and tail of the rough rolling billet, to facilitate the finishing mill bite and winding machine rolled.
Finishing rolling is according to the rolling regulations for each rack under the amount of pressure, rolling temperature, speed for rolling. It is generally controlled by equal second flow or constant tension mode. Hydraulic or electric AGC is used to control the thickness, and the temperature control of the rolling process includes final rolling temperature and head and tail temperature difference control. In order to control the sheet shape, roll profiles and pre-bending roll devices are used to ensure the transverse thickness difference of the strip.
The steel strip temperature is 900 to 950°C after finishing rolling and must be cooled to 600 to 650°C within a few seconds before it can be rolled. Laminar cooling and water curtain cooling are generally used. Laminar flow cooling is the use of low water pressure and large amount of water cooling, according to the strip thickness and the final rolling temperature automatically adjust the amount of water. Water curtain cooling of the strip is uniform, fast and high cooling capacity.
In order to ensure that the organisation and properties of the hot-rolled strip meet the requirements, the rolled steel must be rolled at a lower temperature and a higher speed, the rolled temperature is generally in the 500 ~ 650 ℃. Coiling temperature is too high, coarse grain.
Post time: Aug-11-2022