Detailed Explanation Of The Working Principle Of Hot Rolling Mills

Hot rolling mills are core equipment used in the metallurgical industry for processing metal materials. They process metal billets into the required shapes and sizes through high-temperature rolling. Its working principle combines materials science, thermodynamics and mechanical engineering, and it is an indispensable key technology in modern steel industry. The following is a detailed analysis of the working principle of the hot rolling mill.
I. Definition and process characteristics of Hot rolling ‌
Hot Rolling refers to the rolling process carried out above the recrystallization temperature of metals. Steel billets are usually rolled after being heated to 1100-1300℃ (the specific temperature depends on the material). At this point, the metal is in an austenitic state, with high plasticity and low deformation resistance, which is convenient for processing large deformations through rolls. The main characteristics of the hot rolling process include:
Machining at high temperature ‌ : eliminate internal defects in material, improve uniformity;
Large reduction ‌ : Significantly change material thickness in a single roll;
Coarse-grained structure ‌ : The microstructure of the material needs to be controlled by cooling after rolling.
2. The working process of hot rolling mill ‌
The complete technological process of the hot rolling mill can be divided into the following five stages:
1. Heat the blank ‌
Metal billets (such as continuous casting slabs and square billets) are uniformly heated to the target temperature through a step-by-step or push-steel heating furnace. Heating furnaces usually use gas or electricity for heating to ensure that the internal structure of the metal is fully austenitized (the temperature uniformity error needs to be controlled within ±20℃).
2. Rough rolling stage ‌
The heated billets enter the roughing mill (usually composed of multiple roughing mills), and through repeated rolling, the thick billets are thinned to an intermediate thickness (for example, rolling a 200mm thick slab to 30-50mm). Roughing mills are mostly two-high or four-high reversible rolling mills, which can gradually compress materials through multiple passes of rolling.
3. Finishing rolling stage ‌
The intermediate billet enters the finishing mill group (usually 6 to 7 four-high or six-high mills arranged in series), and is further thinned to the target thickness (for example, 1 to 20mm) through continuous rolling in multiple stands. The precision rolling stage has extremely high requirements for dimensional accuracy and surface quality.
4. Cooling and winding ‌
After rolling, the steel strip enters the laminar flow cooling device and is cooled at a controllable rate to below 600℃ (the specific temperature depends on the steel type), and then is coiled into a steel coil by the coiler. The cooling rate directly affects the mechanical properties of the material (such as strength and toughness).
Cooling mode ‌ :
Ordinary carbon steel: Rapid cooling (mainly water cooling);
Alloy steel: Staged slow cooling (to avoid internal stress cracking).
5. Post-processing ‌
After hot-rolling, steel coils need to go through processes such as shearing and inspection. Some products also need to be pickled to remove the residual oxide layer, and finally become hot-rolled plate (coil) products.
Iii. Core components of the hot rolling mill ‌
Roll system ‌ : The combination of work roll and support roll to withstand rolling force, material mostly high chromium cast iron or high speed steel;
Main drive system ‌ : The high power motor drives the roll to rotate, with torque up to several million Newton-meters;
Hydraulic AGC system ‌ (automatic thickness control) : real-time adjustment of roll gap, precision up to micron level;
Temperature measurement and detection device ‌ : infrared thermometer, laser thickness gauge, etc. ensure closed-loop control of process parameters.
The hot rolling mill achieves efficient processing of metal materials through the combination of high-temperature plastic deformation and precise control. Its technological innovation not only promotes the progress of the metallurgical industry, but also provides high-performance raw material support for downstream manufacturing industries. In the future, with the deep integration of intelligent technologies, the hot rolling process will further enhance efficiency and quality, facilitating industrial upgrading.