A rolling mill is a metalworking machine that applies pressure through rotating rolls to plastically deform metal stock and produce the required dimensions and cross-sectional shape. A complete rolling mill generally consists of a rolling stand, main drive system, auxiliary production equipment, and supporting utility systems. The specific configuration varies according to the rolled product, production process, and level of automation.
Rolling stand
The rolling stand is the main mechanical assembly of a rolling mill. It supports the rolls, withstands rolling loads, and performs the rolling operation. Its main components include rolls, roll bearings, housings, soleplates, roll adjustment mechanisms, top roll balancing devices, and roll changing equipment. Depending on the mill type, work tables and rolling guides may also be installed.
Rolls
Rolls are the main working components that apply pressure to the metal and cause plastic deformation. During rolling, the rotating rolls draw the metal stock into the roll gap and reduce its thickness or change its cross-sectional shape.
Depending on the mill structure and rolling process, rolls can be arranged in different configurations, including two-high, four-high, and multi-roll arrangements. Each roll has a specific function. Work rolls make direct contact with the material, while backup rolls support the work rolls and carry or transfer rolling loads.
Roll bearings
Roll bearings are installed between the roll necks and roll chocks. They support the rolls and maintain their correct positions within the mill stand.
During rolling, the bearings carry heavy loads that can vary considerably. They therefore need sufficient load capacity, stiffness, and operating accuracy. Friction losses, lubrication conditions, and ease of roll replacement must also be considered during bearing selection.
Roll bearings are generally classified as rolling bearings and plain bearings. Oil-film bearings are a type of plain bearing.
Rolling bearings: These bearings transmit loads through rolling elements. They offer relatively low friction, good rotational accuracy, and convenient maintenance. Common types include cylindrical roller bearings and tapered roller bearings. The bearing structure is selected according to roll dimensions, load, and operating conditions.
Semi-dry friction plain bearings: Traditional designs include Bakelite bearings, bronze bushings, and nylon-lined bearings. They carry loads through sliding contact between the bearing surface and roll journal. They are still used in some conventional section mills and blooming mills.
Oil-film bearings: These bearings support the roll journal through a lubricating oil film. They are available in hydrodynamic, hydrostatic, and hybrid hydrodynamic-hydrostatic designs. They provide high load capacity and are widely used in backup rolls of strip rolling mills and other heavy-duty rolling applications.
Bearing selection depends on the mill load, rotational speed, and accuracy requirements. Rolling bearings can also be used for backup rolls in certain mill configurations, so their application should not be restricted to work rolls.
Mill housing
The mill housing, also called the mill stand or housing frame, supports the roll chocks, roll adjustment mechanisms, and related components. During rolling, forces pass from the rolls through the bearings and adjustment mechanisms to the housing. The housing must have sufficient strength and stiffness to limit deformation under load and maintain rolling accuracy.
Mill housings are generally classified into closed and open types.
Closed housings use an integrated frame structure with high overall rigidity and load capacity. They are commonly used in blooming mills and strip mills where rolling forces are relatively high.
Open housings usually consist of a housing body and a removable top section. Their structure makes roll replacement easier, so they are commonly used in cross-country section rolling mills.
Some mills also use housingless mill stands to meet specific installation and operating requirements.
Soleplates
Soleplates, also called baseplates or foundation plates, are installed on the equipment foundation to support and secure the mill housing.
They carry the weight of the rolling stand and the overturning moment generated during rolling. They also maintain the required installation position and elevation of the housing. Soleplate installation accuracy affects the positioning and operating stability of the entire rolling stand.
Roll adjustment mechanisms
Roll adjustment mechanisms change the distance between the upper and lower rolls, known as the roll gap. This adjustment controls the thickness or cross-sectional dimensions of the rolled material. The upper roll adjustment mechanism is commonly referred to as the screwdown.
According to the drive method, screwdown systems are generally divided into manual, electric, and hydraulic types.
Manual screwdowns have a relatively simple structure. They are mainly used in small rolling mills and some section mills.
Electric screwdown systems generally consist of a motor, reducer, brake, screwdown screw, screwdown nut, position indicator, spherical support blocks, and rolling force measuring instruments. The motor drives the screw through the reduction mechanism to change the position of the upper roll. Compared with hydraulic screwdown systems, traditional electric mechanisms have greater inertia in their moving components, which limits adjustment response speed and control accuracy.
Hydraulic screwdown systems use hydraulic cylinders to adjust roll position. They offer fast response and relatively high adjustment accuracy, making them widely used in modern strip cold rolling and hot rolling mills. Hydraulic screwdown systems are often integrated with AGC (Automatic Gauge Control). Based on measurement data collected during rolling, the system adjusts the roll gap to control strip thickness deviation.
Top roll balancing device
The top roll balancing device counterbalances the weight of the upper roll and related components. It can also raise the upper roll and hold it in the required position.
This device helps reduce changes in the roll gap and limits impact when the rolled material enters or leaves the roll gap. Common designs include spring-type, counterweight-type, and hydraulic balancing devices.
Spring-type devices are used in some section mills. Counterweight-type devices are commonly found in blooming mills where the rolls have a relatively large vertical travel. Hydraulic balancing devices are frequently used in four-high strip mills.
Roll changing equipment
Rolls wear during operation and need to be replaced or adjusted at regular intervals. Roll changing equipment removes worn rolls from the mill stand and installs replacement rolls to reduce equipment downtime.
Common roll changing methods include C-hook, sleeve-type, trolley-type, and complete stand replacement systems.
C-hook and sleeve-type systems generally require cranes to assist with lifting and removing the rolls. Trolley-type systems use dedicated roll changing trolleys to support and transport rolls. They are suitable for larger rolling mills and make mechanical and automated roll changing easier.
Complete stand replacement involves exchanging the entire operating stand with a spare stand. This method usually requires two sets of mill stands.
The choice of roll changing method depends on the mill structure, roll dimensions, and production line configuration. Quick roll changing equipment can reduce downtime, but the actual replacement cycle varies with the mill and its roll changing arrangement.
The rolling stand may also be equipped with work tables and rolling guides. Work tables support and transfer the rolled material, while guides installed at the roll entry and exit direct the material into and out of the roll gap, reducing misalignment and rolling problems.
Main drive system
The main drive system supplies power to the rolls and transmits torque from the motor to the rolling stand. Its main components include the electric motor, reducer, pinion stand, and connecting shafts.
The motor provides the power required for rolling. Depending on the mill specifications and operating requirements, AC or DC drive systems can be used.
The reducer adjusts the motor output speed and torque to meet roll operating requirements. The pinion stand distributes the transmitted torque to two or more rolls.
Connecting shafts generally use universal spindles or other suitable coupling structures. They connect the drive equipment to the roll ends, transmit torque, and accommodate positional changes that occur during equipment operation and adjustment.
For non-standard connecting components, locating parts, and other machined components used in main drive systems, we provide custom machining based on customer drawings. This service supports different equipment installation and assembly requirements.
Auxiliary production equipment
Auxiliary production equipment handles material preparation before rolling, transportation and processing during production, and subsequent operations such as shearing, cooling, straightening, and inspection. The equipment configuration depends on the rolling process, product specifications, and production line layout.
Common equipment includes:
Raw material preparation equipment: Used for material inspection, cutting, and surface preparation before rolling.
Heating equipment: Used in hot rolling lines to heat metal billets to the required rolling temperature. Various types of furnaces are used depending on the production process.
Turning and transfer equipment: Used to change the position and orientation of billets or rolled material and transport them between rolling passes.
Shearing equipment: Used to remove the head, tail, or edge scrap of rolled material, or to cut products to specified lengths. Common types include billet shears, plate shears, and flying shears.
Straightening equipment: Used to correct bending, waviness, and other shape defects that develop during rolling and cooling. Common types include roller straighteners and press straighteners.
Cooling equipment: Used to control the cooling process after rolling. The equipment type depends on the material and process requirements.
Inspection equipment: Used to check product dimensions, surface quality, and internal defects. Some production lines also use automated online inspection systems.
Heat treatment equipment: Used to process rolled metal according to the required material properties and product specifications.
Pickling equipment: Used primarily to remove oxide scale from metal surfaces. It is commonly found in steel processing lines that require pickling.
Coiling and uncoiling equipment: Used to wind, unwind, and transfer strip materials, supporting continuous rolling operations.
Roller tables, cooling beds, transfer cars, cranes, and transfer machines are also important parts of the production line. They transport, hold, and transfer rolled material between different processing stages.
Supporting utility systems
In addition to the main rolling equipment and auxiliary production machinery, a rolling mill requires supporting utility systems for operation, maintenance, and environmental management.
These systems generally include:
Power supply and distribution system: Supplies electricity to mill motors, variable-frequency drives, control systems, and other electrical equipment.
Lubrication system: Supplies lubricant to roll bearings, gearboxes, and other moving components to reduce friction and wear.
Hydraulic system: Provides hydraulic power for screwdown mechanisms, roll balancing devices, roll bending systems, and other hydraulic actuators.
Water supply and drainage system: Supplies water for rolling and equipment cooling and handles wastewater generated during production.
Compressed air system: Provides compressed air for pneumatic actuators, control components, and other air-operated equipment.
Descaling system: Removes oxide scale generated during rolling or adhering to the metal surface.
Roll shop equipment: Mainly includes roll lathes and grinding machines used to restore roll surfaces and dimensions through machining and grinding.
Maintenance equipment: Includes machinery and tools for mechanical and electrical inspection, maintenance, and fault repair.
Recovery and environmental protection equipment: Collects and treats waste oil, wastewater, spent acid solutions, and other production waste. These systems also help control environmental pollution during manufacturing.
These utility systems operate alongside the main mill and auxiliary production equipment. Their configuration depends on the production process, mill capacity, and site conditions.
Custom precision machining for industrial equipment
Rolling mills contain numerous drive components, mounting structures, and other mechanical parts. Different equipment designs have their own dimensional, assembly, and machining requirements.
Our precision machining services also cover components used in industries beyond rolling mills. Hansheng Automation provides drawing-based custom machining for non-standard parts used in tobacco and packaging machinery, filling equipment, yacht systems, and remote-controlled racing cars. Customers can submit their design drawings for the production of precision mechanical components according to their specified requirements.
